Polypropylene film

Abstract

This invention relates to a polypropylene film, characterized by a tanδ value below 0.25 in the principal alignment direction at 150°C and a Young's modulus above 50 MPa in the orthogonal principal alignment direction at 130°C. This invention provides a polypropylene film with excellent heat resistance, mechanical strength, and overall quality.

Description

[Technical Field]

[0001] This invention relates to a polypropylene film with excellent heat resistance, mechanical strength, and quality, suitable for use as an industrial material film. [Previous Technology]

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

[0003] One of the required characteristics for polypropylene films is heat resistance. For example, when polypropylene films are used as coatings for thermosetting resins, they are exposed to high temperatures after being laminated to the film and undergoing thermosetting. Furthermore, capacitors are used in high-temperature environments within motors. Therefore, the demand for heat resistance has been increasing in recent years for films used in industrial materials and capacitor applications.

[0004] However, compared to polyethylene terephthalate (PET) films, conventional polypropylene films have a lower melting point, resulting in insufficient heat resistance in processes operating at temperatures above 100°C, thus limiting their applications. For example, the melting point of polypropylene films is generally around 160°C. Therefore, in temperature ranges close to the melting point, such as 150°C, the shrinkage force increases, and the mechanical strength also becomes insufficient, making them unsuitable for use in processes intended for high-temperature environments.

[0005] One indicator of heat resistance is heat shrinkage stress. Heat shrinkage stress refers to the stress acting in the shrinkage direction when a film is heated to a specified temperature while maintaining its length. Higher heat shrinkage stress can lead to warping or peeling when the film is bonded to the substrate at the specified temperature. Generally, heat shrinkage stress can be reduced by: mitigating the orientation of amorphous components through high-temperature heat treatment, or using low-molecular-weight polypropylene resin to reduce the high-molecular-weight components. However, while high-temperature heat treatment mitigates amorphous components, it also reduces mechanical strength at high temperatures. Furthermore, low-molecular-weight polypropylene resin has low melt tension when softened by heat; using low-molecular-weight polypropylene resin reduces film-forming properties. Therefore, it is conventionally difficult to maintain both high-temperature mechanical strength and film-forming properties while simultaneously minimizing heat shrinkage stress.

[0006] In the case of polypropylene films with improved heat resistance, for example, patent literature 1 records the following example: using a highly crystalline polypropylene resin and adjusting the preheating roller temperature during longitudinal stretching, thereby reducing the heat shrinkage stress. Furthermore, patent literature 2 and 3 record the following example: the use of polypropylene resin with mainly low molecular weight components to improve the crystallinity, thereby reducing the heat shrinkage rate. Furthermore, the patent literature 4 records the following example: using a polypropylene resin with a low polypropylene composition dissolved in xylene, thereby improving the voltage resistance and reducing the shrinkage stress at high temperatures. [Previous Technical Literature] [Patent Literature]

[0007] 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]

[0008] [Invent the problem to be solved]

[0009] However, in terms of the method described in the aforementioned patent literature 1 and 4, although heat resistance is improved, it is envisaged that in the case of use in the above purposes, there is a subject such as the need to further improve heat resistance. Also, in terms of the method described in the patent literature 2, the Young's modulus at high temperature is low, and the planarity of the film sometimes deteriorates or the film breaks during the handling at high temperature and high tension close to the melting point of the film. Also, the patent literature 3 recorded a high heat shrinkage rate in the main alignment direction of the polypropylene film, and the film will shrink during transportation under high temperature, which is a problem at the point where it is easy to wrinkle. Thus the lesson of the present invention lies in solving the above problem points. Also, the subject matter of the present invention lies in providing a polypropylene thin film of thermal resistance, mechanical strength, and excellent quality. [Means used to solve problems]

[0010] To solve the above topic, the polypropylene film of the present invention comprises the following configuration. Also, the polypropylene film of the present invention is a polypropylene film characterized by having a tanδ of less than 0.25 in the main alignment direction at 150°C and a Young's modulus of more than 50MPa in the orthogonal direction of the main alignment at 130°C. [Effect of the invention]

[0011] The polypropylene film of the present invention is able to be widely adapted for use as a film for industrial materials, a film for surface protection, a film for process use, a release film, and a film for capacitors due to its heat resistance, mechanical strength, and excellent quality. [Implementation Method]

[0013] [Form to implement the invention]

[0014] The polypropylene film of the present invention is a polypropylene film characterized in that the tanδ of the main alignment direction at 150°C is less than 0.25, and the Young's modulus of the main alignment orthogonal direction at 130°C is greater than 50 MPa.

[0015] The term "polypropylene film" refers to a film that, when all components constituting the film are defined as 100% by mass, contains more than 50% by mass and less than 100% by mass of polypropylene resin. When all components constituting the film are defined as 100% by mass, the content of polypropylene resin in the polypropylene film is preferably 70% by mass and less than 100% by mass, more preferably 90% by mass and less than 100% by mass, further preferably 95% by mass and less than 100% by mass, particularly preferably 96% by mass and less than 100% by mass, and most preferably 97% by mass and less than 100% by mass. Furthermore, if multiple components conforming to polypropylene resin are contained, and the combined content of such components exceeds 50% by mass and less than 100% by mass, it is considered to conform to the definition of a polypropylene film. Also, "polypropylene resin" refers to a resin in which propylene units account for more than 50 mol% and less than 100 mol% of all constituent units constituting the resin.

[0016] From the viewpoint of improving heat resistance, it is important that the tanδ of the polypropylene film of the present invention in the main alignment direction at 150°C is 0.25 or less. From the above viewpoint, the tanδ in the main alignment 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, also known as loss tangent, is related to the degree of molecular chain mobility in the film. Generally, as shown in Figure 1, it increases with higher temperatures in the region above 100°C. The inventors have found that the tanδ in the main alignment direction at 150°C is an index related to the degree of molecular chain mobility in the film near 150°C: reducing this value, in other words, suppressing the movement of molecular chains at high temperatures, will suppress the thermal shrinkage stress of the polypropylene film at high temperatures and improve heat resistance. Furthermore, the smaller the tanδ in the main alignment direction at 150°C, the better. The lower limit is not particularly limited, but is essentially around 0.01.

[0017] Here, in this invention, the so-called principal alignment direction refers to the direction that displays the highest value when measuring the Young's modulus in each direction within the film surface, where any direction is defined as 0° and the angles are formed by 0° to 175° in 5° increments. The so-called principal alignment orthogonal direction refers to the direction within the film surface that is orthogonal to the aforementioned principal alignment direction. Furthermore, the Young's modulus can be measured using a tensile testing machine, and the details of the measurement method are shown in the embodiments. 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 as described below, and the principal alignment direction is determined based on the following judgment criteria. That is, for the surface of the thin film, X-rays (CuKα lines) are incident in the vertical direction, and the crystallization peak at 2θ = approximately 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. Furthermore, in this invention, the direction parallel to the direction of film formation of the polypropylene film is called the film formation direction, the long side direction, or the MD direction, and the direction orthogonal to the film formation direction in the film surface is called the width direction or the TD direction.

[0018] When the tanδ in the main alignment direction at 150°C is greater than 0.25, the heat resistance of the polypropylene film will be insufficient. Therefore, if such a polypropylene film is used as a process film or release film, warping or partial peeling of the adhesive may occur at the time point when it is bonded to the substrate and subjected to high temperature, due to the difference in thermal shrinkage stress between the film and the substrate, resulting in quality damage. Furthermore, the tanδ in the main alignment direction at 150°C can be measured using dynamic viscoelasticity, and the details of the measurement method are shown in the examples.

[0019] In order to achieve a tanδ of 0.25 or less in the main alignment direction at 150°C, methods can be used, for example, to define the composition of the polypropylene film within the range described later, and to define the film-forming conditions within the range described later. In particular, a more effective method is to use a highly crystalline resin 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 mitigate shrinkage in the width direction at high temperature after transverse stretching, and to shrink the film in the main alignment direction (e.g., relaxation rate of 12% or more).

[0020] From the viewpoint of improving mechanical strength, the polypropylene film of the present invention has a Young's modulus of 50 MPa or more in the main orthogonal direction 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 main orthogonal direction at 130°C is less than 50 MPa, the mechanical strength will be insufficient. Therefore, when using the polypropylene film as a process film or release film, if high tension is applied in the main orthogonal direction during the high-temperature step of bonding with the substrate, the polypropylene film may deform, resulting in wrinkles or breakage. Furthermore, a higher Young's modulus in the main orthogonal direction at 130°C is preferable, and while its upper limit is not particularly limited, it is substantially around 10,000 MPa. Furthermore, the Young's modulus in the principal alignment orthogonal direction at 130°C can be determined using a tensile testing machine. The details of the determination method are shown in the embodiments, wherein the tensile testing machine is equipped with an oven that can be heated at high temperatures.

[0021] When high-temperature heat treatment is performed to reduce tanδ and the shrinkage of amorphous components is mitigated, the Young's modulus may decrease. Furthermore, to increase the Young's modulus, high stretching ratios are generally used. However, the melt tension of resins with reduced molecular weight components decreases after heating and softening, leading to reduced film stability. Therefore, high stretching ratios may not be possible. Given these circumstances, it is conventionally known that achieving both low tanδ and high Young's modulus at high temperatures is particularly difficult in polypropylene films. However, by using methods such as defining the 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 both low tanδ and high Young's modulus. In particular, a more effective method is to use a highly crystalline resin with a low cold xylene soluble fraction (CXS); or to set the temperature of the casting drum to a low temperature (10°C to 40°C) to uniformly refine the spherulites in the unstretched sheet, and then increase the stretching range during longitudinal stretching. In the longitudinal stretching range, both sides are fully heated by a radiation heater while stretching, thereby reducing tensile stress and uniformly stretching the film longitudinally.

[0022] From a quality perspective, the tanδ of the polypropylene film of the present invention in the main orthogonal direction at 150°C is preferably 0.25 or less, more preferably 0.23 or less, further preferably 0.21 or less, and particularly preferably 0.19 or less. The tanδ in the main orthogonal direction at 150°C is an indicator related to the degree of molecular chain mobility in the film near 150°C; reducing this value improves the heat resistance of the film. When the tanδ in the main orthogonal direction at 150°C is greater than 0.25, during the storage of the polypropylene film in roll form at high temperatures, wrinkles may form on the roll due to shrinkage in the main orthogonal direction, resulting in quality degradation. Furthermore, the lower limit of the tanδ in the main orthogonal direction at 150°C is preferred as small as possible; there is no particular limitation, but it is substantially around 0.01. The tanδ in the main orthogonal direction at 150°C can be measured using the same method as the tanδ in the main orthogonal direction at 150°C.

[0023] In order to achieve a tanδ of 0.25 or less or the preferred range in the main alignment orthogonal direction at 150°C, a method can be used that sets the composition or film-forming conditions of the polypropylene film to the range described below. In particular, it is more effective to use a highly crystalline resin 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 temperature of the casting drum to a low temperature (10°C to 40°C), thereby uniformly refining the spherulites in the unstretched sheet, and then increasing the stretching range during longitudinal stretching, and stretching 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; and after transverse stretching, relaxing the transport tension in the transport flow direction on a high-temperature roller, thereby causing the film to shrink in the main alignment orthogonal direction.

[0024] From a quality point of view, the loss modulus E” of the polypropylene film of the present invention in the principal orthogonal direction at 0°C is preferably 3.5 × 10⁸ Pa or less. More preferably, it is 3.0 × 10⁸ Pa or less, further preferably 2.5 × 10⁸ Pa or less, and particularly preferably 2.0 × 10⁸ Pa or less. The smaller the value of the loss modulus E” in the principal orthogonal direction at 0°C, the better. Its lower limit is not particularly limited, but it is substantially around 0.1 × 10⁸ Pa. Furthermore, the loss modulus E” in the principal orthogonal direction at 0°C can be measured using dynamic viscoelasticity, and the details of the measurement method are shown in the examples.

[0025] The loss modulus E” is related to the degree of molecular chain relaxation in the polypropylene film. When the loss modulus E” in the main alignment orthogonal direction at 0°C is greater than 3.5 × 10⁸ Pa, the degree of amorphous relaxation near 0°C will increase. Therefore, when polypropylene film is rolled up and stored at room temperature or near room temperature, the polypropylene film will shrink in the main alignment orthogonal direction, resulting in wrinkles on the roll and quality loss.

[0026] In order to make the loss modulus E” in the main alignment orthogonal direction at 0°C less than 3.5 × 10⁸ Pa, methods such as setting the composition of the polypropylene film within the range described later and setting the film-forming conditions within the range described later can be used. In particular, it is more effective to use a resin with a high crystallization temperature to reduce the spherulites formed during casting; to set the temperature of the casting drum to a low temperature (10°C to 40°C), thereby uniformly refining the spherulites in the unstretched sheet, and then to increase the stretching range during longitudinal stretching, and to stretch the film longitudinally while fully heating both sides using a radiation heater in the stretching range.

[0027] The polypropylene film of the present invention preferably has a product of Young's modulus in the principal alignment orthogonal direction and film thickness at 130°C of 500 N / m or more, more preferably 700 N / m or more, further preferably 900 N / m or more, and particularly preferably 1100 N / m or more. The product of Young's modulus in the principal alignment orthogonal direction and film thickness at 130°C corresponds to the tension per unit film width generated when the film is stretched in the principal alignment orthogonal direction at 130°C. If this value is less than 500 N / m, defects may occur when exposed to high temperatures during processing steps. For example, when a polypropylene film is used as a release film, if it is bonded to a particularly easily deformable substrate and high tension is applied in the principal alignment orthogonal direction at the time point of the high-temperature step, deterioration of film planarity, substrate deformation, and film breakage may occur. From the above perspective, the upper limit of the product of Young's modulus and film thickness in the principal alignment orthogonal direction at 130℃ is not particularly limited, but it is essentially around 1,000,000 N / m. Furthermore, the thickness of the polypropylene film can be measured using a conventional micro thickness gauge.

[0028] Regarding the method of making the product of Young's modulus and film thickness in the main orthogonal direction at 130°C 500 N / m or more, or in the aforementioned preferred range, methods such as setting the composition of the polypropylene film within the range described later, and setting the film-forming conditions within the range described later, can be used. In particular, it is more effective to use a highly crystalline resin with a low cold xylene soluble portion (CXS); or to set the temperature of the casting drum to a low temperature to uniformly refine the spherulites in the unstretched sheet, and then increase the stretching range during longitudinal stretching, and to stretch the film while fully heating both sides using a radiation heater within the stretching range, thereby reducing tensile stress and uniformly stretching the film longitudinally. Furthermore, the product of Young's modulus and film thickness in the main orthogonal direction at 130°C can also be adjusted by adjusting the thickness.

[0029] 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, and further preferably 4.0 μm. The thickness of the polypropylene film can be adjusted by means of the screw speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, etc., without reducing other physical properties.

[0030] Preferably, the polypropylene film of the present invention satisfies Tc0 (°C) when the crystallization temperature at a cooling rate of 0°C / min is defined as Tc0 (°C) and the melting point of the film is defined as Tm (°C). 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 higher Tc0 indicates easier crystallization. Furthermore, Tm is the melting point of the film; a higher Tm indicates higher heat resistance of the film. The upper limit of the value of Tc0 + Tm is not particularly limited, but is practically around 350.

[0031] By setting the value of Tc0 + Tm 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 state, crystallization proceeds rapidly, making it less likely for large spherulites to form during casting. Therefore, the polypropylene film has a more uniform structure, and fractures during stretching and a reduction in film strength are reduced.

[0032] Tc10 and Tc40 can be determined using a differential scanning calorimeter (DSC) according to the following procedure. Specifically, 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, 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 defined as Tc10. The polypropylene film is then 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 Tc40. Next, as shown in Figure 2, the cooling rate is plotted on the horizontal axis, and the crystallization temperature obtained at each cooling rate is plotted on the vertical axis. A straight line is drawn from Tc40 towards Tc10, and the crystallization temperature at which the cooling rate is extrapolated to 0°C / min is defined as Tc0. Furthermore, when multiple peak temperatures are observable, 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. Moreover, there are no particular restrictions on the DSC system used, as long as it is capable of measurement; any conventional system can be used, specifically, the Seiko Instruments Inc. EXSTAR DSC6220.

[0033] 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 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 include a component with nucleating agent properties, especially branched-chain polypropylene. 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. In particular, a highly crystalline resin with a low cold xylene-soluble fraction (CXS) is preferred.

[0034] From the viewpoint of mitigating quality degradation after exposure to high-temperature environments, the static friction coefficient μs of the polypropylene film of the present invention after heat treatment at 130°C for 10 minutes is preferably 0.80 or less. More preferably, it is 0.70 or less, further preferably 0.60 or less, and particularly preferably 0.50 or less. When polypropylene film is used as a protective film, it may undergo various high-temperature processes. For example, when polypropylene film is used as a release film for thermosetting resins, it may be thermosetting at temperatures above 100°C after being laminated to the thermosetting resin. Compared to polyester films, which are commonly used as process films, polypropylene films generally have lower heat resistance, and when subjected to heat above 100°C, the surface may soften or deform, and the static friction coefficient may increase excessively. Therefore, slip resistance is impaired, and sometimes deflection may occur when winding the film after the heating process.

[0035] Because the μs is below 0.80 after heating at a higher temperature of 130°C, it becomes less prone to wrinkling on the transport roll at the time point of passing through the high temperature step above 100°C, and the winding deviation can be reduced at the time point of winding together with the substrate. The lower limit of the static friction coefficient μs after heat treatment at 130°C for 10 minutes is not particularly limited, but it is actually around 0.10.

[0036] In order to obtain μs of 0.80 or less or the preferred range described above after heat treatment at 130°C for 10 minutes, a method can be used, for example, to define the composition of the polypropylene film within the range described later, and to define the film-forming conditions within the range described later. In particular, a more effective method is to form fine protrusions on the surface by making the polypropylene film into a laminated structure and then making the surface layer into a blended structure containing olefin resins such as poly(4-methylpentene-1) resin. Furthermore, the μs after heating can be measured according to JIS K 7125 (1999).

[0037] The polypropylene film of the present invention preferably has a tensile elongation of 35% or more in the main alignment direction. More preferably, it has a tensile elongation of 40% or more, further preferably, it has a tensile elongation of 45% or more, and most preferably, it has a tensile elongation of 50% or more. Because the tensile elongation in the main alignment direction is 35% or more, the film is less prone to breakage when it is pulled from a roll of pre-wound polypropylene film for use. In cases where tensile elongation and mechanical strength have a trade-off relationship, from the viewpoint of balancing with mechanical strength, the upper limit of the tensile elongation in the main alignment direction is preferably 300% or less, more preferably 200% or less, and further preferably 80% or less. Furthermore, the tensile elongation in the main alignment direction can be evaluated using a tensile testing machine; details of the measurement method are shown in the examples.

[0038] 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 a high 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 while stretching within the stretching range, heat both sides of the film sufficiently using a radiant heater or the like, 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 heat the film using a hot roller when passing through the transverse zone.

[0039] 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. If the maximum height St on both sides of the film exceeds 2.0 μm, when high tension is applied during the step of bonding the polypropylene film to the substrate and subjecting it to high temperature, a portion of the substrate may peel off at the location of the large St, resulting in quality damage. 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.

[0040] 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 temperature of the casting drum to a low temperature to uniformly refine the spherulites in the unstretched sheet, and then increase the stretching range during longitudinal stretching. In the longitudinal stretching range, the film is stretched while both sides are fully heated using a radiation heater, thereby reducing the tensile stress and uniformly stretching the film longitudinally.

[0041] Hereinafter, a suitable polypropylene resin (sometimes referred to as polypropylene resin A) will be described as the component most commonly contained in the polypropylene film of the present invention.

[0042] From the viewpoint of productivity and film properties, polypropylene resin A is preferably a linear polypropylene resin.

[0043] 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 essentially around 1.2. When Mz / Mw is greater than 4.2, when heat is applied to the film, there is a high proportion of high molecular weight components that need to be moderated, and the heat resistance is impaired. In order to achieve the above-mentioned values ​​for the 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 2.0 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 particularly 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 and molecular weight distribution of the polypropylene resin can be used. By reducing the high molecular weight components, the MFR will increase.

[0045] It is preferable that the cold xylene-soluble portion (CXS) of polypropylene resin A is 3.5% by mass or less. By satisfying this condition, the dimensional stability and heat resistance of the obtained polypropylene film will be improved.

[0046] The so-called cold xylene-soluble fraction (CXS) refers to the polypropylene component dissolved in xylene when the sample is completely dissolved in xylene and then precipitated at room temperature. This component is considered difficult to crystallize due to its low stereoregularity and low molecular weight. If this component is abundant and present in large quantities in polypropylene resin A, the thermal dimensional stability of the polypropylene film may be poor. Therefore, from the above perspective, CXS is preferably below 2.0% by mass, and more preferably below 1.5% by mass. Lower CXS is better, but the lower limit is approximately 0.1% by mass. To achieve the above-mentioned preferred range for CXS, methods such as adjusting the polymerization catalyst and process polymerization conditions, improving the catalyst activity at the time of resin acquisition, and washing the obtained resin with solvent or the propylene monomer itself can be used.

[0047] 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 that undergo tempering when heat is applied to the polypropylene film, and the thermal shrinkage stress 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.

[0048] Regarding polypropylene resin A, it may also contain copolymer components based on other unsaturated hydrocarbons without impairing the purpose of the present invention. Examples of monomeric 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%.

[0049] When the total constituent units of polypropylene resin A are defined as 100 mol%, the content of ethylene, which is a copolymer component 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 higher the content of ethylene, the lower the crystallinity, making it easier to improve the transparency when making polypropylene film. However, by suppressing the content of ethylene to 5 mol% or less, the deterioration of thermal shrinkage stress caused by the reduction in strength and heat resistance when making polypropylene film can be mitigated. In addition, the degradation of resin during the extrusion process can also be mitigated, and the formation of fish eyes in the polypropylene film caused by it can also be mitigated.

[0050] The polypropylene resin is a linear polypropylene of type A, preferably satisfying the aforementioned 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.

[0051] 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 during casting can be suppressed by utilizing this nucleating agent effect, thereby improving the heat resistance and mechanical strength of the film.

[0052] From the viewpoint of extrusion stability, the preferred molecular weight ratio (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 preferably 2 g / 10 min. The upper limit of the MFR of branched polypropylene resin is preferably 8 g / 10 min. To achieve the above values ​​for the MFR of branched polypropylene resin, 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 and molecular weight distribution of the polypropylene resin can be used. The MFR increases by decreasing the molecular weight; the more low molecular weight components in the molecular weight distribution, the higher the MFR.

[0053] From the viewpoint of tensile uniformity, the melt tension of branched polypropylene resin is preferably between 3 gf and 40 gf. 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. To achieve the above values ​​of melt tension, methods such as controlling the average molecular weight and molecular weight distribution, and the degree of branching in the polypropylene resin can be used. In particular, when long-chain branches are present, the melt tension can be significantly increased, and optimal values ​​can be achieved by adjusting the molecular chains of the long-chain branches and the degree of branching.

[0054] Branched polypropylene resins are available in various forms, such as Ziegler-Natta catalyst-based or metallocene catalyst-based resins. However, from the perspective of using it in combination with polypropylene resin A, it is better to improve the tensile properties by adding a small amount of Ziegler-Natta catalyst-based branched polypropylene resin with a wide molecular weight distribution.

[0055] 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 polymers (COP), cyclic olefin copolymers (COC), α-olefin elastomers, 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.

[0056] 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 the resin different from polypropylene is added, the transparency of the film may deteriorate, or the heat resistance and rigidity may decrease. Furthermore, if too little is added, the effect of imparting slip properties may be poor.

[0057] 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. Among these, from the viewpoint of antioxidant leaching, it is important to select the type and amount of antioxidant added. That is, for such antioxidants, it is preferable to be a sterically inhibiting phenolic antioxidant, and at least one of them is a high molecular weight type with a molecular weight of 500 or more. In specific examples, various examples can be cited, such as the preferred combination of 2,6-di-tert-butyl-p-cresol (BHT: molecular weight 220.4) with 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 tetramethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 1010: molecular weight 1177.7), etc.

[0058] The total content of these antioxidants is preferably in the range of 0.01 to 1.0 parts by weight relative to 100 parts by weight of polypropylene resin. If there is too little antioxidant, polymer deterioration and film discoloration may occur during the extrusion process, or the long-term heat resistance may be poor. On the other hand, if there is too much antioxidant, the transparency of the polypropylene film may be reduced due to the leaching of these antioxidants. From the above viewpoint, the antioxidant content is more preferably 0.05 to 0.9 parts by weight relative to 100 parts by weight of polypropylene resin, and more preferably 0.1 to 0.8 parts by weight.

[0059] Furthermore, without departing from the purpose, a crystallizing nucleating agent can be added to the polypropylene film of the present invention. Specific examples of crystallizing nucleating agents include: α-crystal nucleating agents (dibenzylsorbitol derivatives, sodium benzoate, phosphate ester metal salts, etc.), β-crystal nucleating agents (potassium 1,2-hydroxystearate, magnesium benzoate, N,N'-dicyclohecyl-2,6-naphthalene dicarboxamide, etc., acetamide compounds, quinacridone compounds, etc.). However, excessive addition of the above-mentioned other types of nucleating agents can cause a decrease in tensile strength or a decrease in transparency and strength due to the formation of voids. Therefore, the amount added is generally 0.5 parts by weight or less relative to 100 parts by weight of total polypropylene 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, which can lead to inorganic particles detaching from the film during the manufacturing process and contaminating the production line or the finished product. Furthermore, if large protrusions are formed due to the high hardness of inorganic particles, they can be embossed onto the resin layer of optical components, sometimes causing quality degradation when used as a protective film or substrate film for high-quality products such as display components. From the above perspective, the polypropylene 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-chain polypropylene resin relative to 100% by mass of total resin content 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 further preferably 70% by mass. The upper limit is more preferably 99% by mass, and further preferably 98% by mass. When the film contains two or more components equivalent to polypropylene resin A, these components are calculated together and considered as the content of polypropylene resin A in the film.

[0062] Furthermore, in the polypropylene film of the present invention, the proportion of branched polypropylene resin in the total film is preferably 0.1% by mass to 30% by mass, more preferably 10% by mass, and even more preferably 5% by mass. When the film contains two or more components equivalent to branched polypropylene resin, these components are calculated together and regarded as the content of branched polypropylene resin in the film.

[0063] The molecular weight distribution Mz / Mw of the polypropylene film of the present invention is preferably below 4.5, more preferably below 4.0, and even more preferably below 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 below 4.5, there are fewer high molecular weight components that are moderated when heat is applied, which can maintain the heat resistance and planarity of the polypropylene film. As for the method of making the molecular weight distribution Mz / Mw of the polypropylene film reach the above value, the following methods are preferred: adjusting the hydrogen concentration during the polymerization of polypropylene resin; or suitable methods for selecting catalysts and / or auxiliary catalysts, adjusting the composition and polymerization amount of each polymerization tank in continuous polymerization, etc.

[0064] In the molecular weight distribution curve determined by gel permeation chromatography, the differential distribution value of the polypropylene film of the present invention when the logarithmic molecular weight Log(M) is 6.5 is preferably 1.0% to 10%. The upper limit is more preferably 8.0% or less, and further preferably 6.0% or less. With a differential distribution value of 1.0% or more when the logarithmic molecular weight Log(M) is 6.5, the high molecular weight components that link the molecules become sufficient during stretching, and the uniformity during stretching is increased. On the other hand, with a differential distribution value of 10% or less when the logarithmic molecular weight Log(M) is 6.5, the molecular chains undergoing tempering do not become excessive when heat is applied to the polypropylene film, and the increase in thermal shrinkage stress is suppressed. 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 polypropylene film constituting the roll can be maintained.

[0065] 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. However, from the viewpoint of satisfying different characteristics such as heat resistance, rigidity, and slip resistance, it is preferable to have a surface layer (I) and a base layer (II). When the polypropylene film is a single layer, it is preferable that the main component of the polypropylene film itself is polypropylene resin. When the polypropylene film is a laminated structure, 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% but less than 100% polypropylene resin when all components constituting the layer are defined as 100% by mass. Furthermore, the determination of whether a layer 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.

[0066] 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".

[0067] 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.

[0068] The polypropylene film of the present invention is preferably biaxially stretched using the above-mentioned resin. The biaxial stretching method can be any of the following: biaxial stretching during blow molding, biaxial stretching during tenter frame operation, or successive biaxial stretching using a roller stretcher and a tenter frame. However, considering the advantages of film stability, thickness uniformity, and control over the high rigidity and dimensional stability of the obtained polypropylene film, the successive biaxial stretching method using a roller stretcher and a tenter frame is preferred.

[0069] Hereinafter, two types of three-layer polypropylene films will be used as examples to illustrate one aspect of the manufacturing method of the polypropylene film of the present invention, but the polypropylene film of the present invention is not limited thereto.

[0070] First, 95 parts by mass of polypropylene resin A and 5 parts by mass of branched chain polypropylene resin are dry-blended and fed to a uniaxial extruder for the base layer (II) (hereinafter sometimes referred to as layer B), and 98 parts by mass of polypropylene resin A and 2 parts by mass of poly4-methylpentene-1 resin are fed to a uniaxial extruder for the surface layer (I) (hereinafter sometimes referred to as layer A). Then, melt extrusion is performed at 200–280°C (more preferably 220–280°C, and even more preferably 240–270°C). After removing foreign matter and modified polymers using a filter located in the middle of the polymer tube, the layers are deposited using a multi-manifold type A / B / A layer composite T-die, sprayed onto a casting drum, and cooled and cured, thereby obtaining an unstretched sheet having an A / B / A layer structure.

[0071] In this case, when the layer thickness ratio is expressed as 1 / X / 1, the layer thickness ratio of layer A / layer B / layer A 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. By making the above range, uniform fine protrusions caused by poly(4-methylpentene-1) resin can be formed on the surface of the film, which can impart slip resistance. 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. When the layer configuration has layer A / layer 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.

[0072] Furthermore, the surface temperature of the casting drum is 10–40°C, preferably 15–30°C, further preferably 15–25°C, and particularly preferably 20–25°C. By setting the temperature of the casting drum within the aforementioned preferred range, the spherulites in the unstretched sheet can be uniformly refined, and the uniformity during stretching can be improved. 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, preferably 15–30°C, further preferably 15–25°C, and particularly preferably 20–25°C. The air velocity is preferably 130-150 m / s. Furthermore, to prevent sheet vibration, the position of the air knife should be adjusted so that the airflow is directed downstream of the film forming process. Moreover, in the case of a two-layer lamination configuration (A layer / B layer), it is preferable to designate the B layer side as the casting drum side.

[0073] The obtained unstretched sheet is introduced into the longitudinal stretching step. In the longitudinal stretching step, the unstretched sheet is preheated by contacting metal rollers that have been kept at 110°C to 150°C (preferably 120°C to 150°C, more preferably 130°C to 150°C), and stretched in the long 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 time, the stretching range during longitudinal stretching 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 is performed by using the circumferential speed difference of two metal rollers, but the film being transported on each metal roller before and after stretching is pressed against the metal rollers by clamping rollers, thereby making the film less likely to slide on the metal rollers. The aforementioned stretching interval refers to the distance between the clamping position of the metal roller before stretching and the clamping position of the metal roller after stretching.

[0074] The temperature (longitudinal stretching temperature) of the rollers with the set circumferential speed difference is preferably 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 set 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 set 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.

[0075] Next, the uniaxially stretched film is guided to the tenter frame by holding both ends in the width direction with clamps and preheated. It is then stretched laterally in the width direction to 8.5 to 14.0 times, preferably 9.0 to 13.0 times, and more preferably 9.5 to 12.0 times. 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 increasing 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) relative to the stretching temperature, it becomes possible to stretch the film uniformly across its width, reduce thickness unevenness, and produce film rolls with good flatness that are less prone to wrinkles. Due to its large necking, uniaxially stretched films have a narrow width, which allows for increased transverse stretching ratios even when using standard tenter frame rail patterns. This method is preferable from the perspective of improving the heat resistance of polypropylene films.

[0076] In the subsequent heat treatment and relaxation steps, while holding both ends in the width direction tightly with clamps, the film is relaxed at a relaxation rate of 12-25% (preferably 14-20%, more preferably 16-20%) in the width direction, and then heat-fixed at a temperature of 165°C or higher and lower than 180°C (preferably 168°C or higher and lower than 180°C, more preferably 170°C or higher and lower than 180°C). Afterwards, while still holding both ends in the width direction tightly with clamps, the film undergoes a cooling step of 80-100°C, is guided to the outside of the tenter frame, and the clamps at both ends in the width direction are released. Next, in the winding step, the film edges are cut, and the polypropylene film is wound into a roll. The heat treatment temperature is set to be at least 5°C higher (preferably 8°C higher, more preferably 10°C higher) than the transverse stretching temperature, thereby mitigating residual stress in the film and reducing heat shrinkage stress.

[0077] Furthermore, from the viewpoint of the heat resistance of the obtained polypropylene film, it is preferable to heat the polypropylene film discharged from the tenter frame as it passes through the cross-section using a hot roller. The temperature of the hot roller is preferably 80–120°C. By setting the temperature of the hot roller to 80°C or higher, the slipperiness between the hot roller and the polypropylene film can be ensured, and the formation of wrinkles and deterioration of flatness in the polypropylene film can be reduced. The heating time using the hot roller 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; from a productivity point of view, it is approximately 2.0 seconds.

[0078] The polypropylene film of the present invention obtained as described above 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, and capacitor film. However, due to its particularly excellent heat resistance, mechanical strength, and quality, it can be better used as a surface protection film, process film, release film, and packaging film.

[0079] Here, the term "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. The term "process film" refers to a film that is attached to a molded body or film to prevent scratches and contamination during manufacturing and processing, and is discarded when used as a final product. The term "release film" refers to a film with high release properties, that is attached to a molded body or film to prevent scratches and contamination during processing or transportation, and has the function of being easily peeled off and discarded when used as a final product. Furthermore, the term "packaging film" refers to a film used for packaging food and various other commodities. [Example]

[0080] Hereinafter, the present invention will be described in detail by way of examples. Furthermore, the characteristics were measured and evaluated by the following methods.

[0081] (1) The film thickness was measured using a micro thickness gauge (manufactured by Anritsu Corporation). A 10 cm square sample of the film was taken, and the thickness was measured at 5 randomly selected points. The average value of the obtained values ​​was defined as the film thickness (μm).

[0082] (2) tanδ (loss tangent) and E” (loss modulus) A rectangular test piece (5 mm wide × 20 mm long) cut from a polypropylene film with the measurement direction as the long side was mounted on the fixture of the device in a gas environment of 23°C and cooled to -100°C. After the heating started, tanδ and E” were measured from -100°C to 180°C. The viscoelastic-temperature curve was plotted by the dynamic viscoelastic method, and tanδ and E” at each temperature were calculated. The test was conducted with n=3 and the average value of the obtained values ​​was defined as tanδ and E” in the measurement direction. Furthermore, the measuring device and conditions are as follows: • Device: Rheogel-E4000 (UBM made) • Geometry: tensile • Spacing between fixtures: 10 mm • Frequency: 10 Hz • Strain: 0.1~0.2% • Temperature range: -100~180°C • Heating rate: 5°C / min • Measurement gas environment: nitrogen.

[0083] (3) A rectangular sample with a length of 150 mm (in the measurement direction) and a width of 10 mm was cut from a polypropylene film to measure the Young's modulus at 130°C. The sample was assembled in a tensile testing machine (ORIENTEC "Tensilon" (registered trademark) UCT-100) with an initial clamping distance of 50 mm, and placed in an oven preheated to 130°C for 1 minute. Then, the tensile speed was set to 300 mm / min and the film tensile test was performed. The Young's modulus was calculated according to the method specified in JIS K7161 (2014). The test was performed 5 times for each sample, and the average value was defined as the Young's modulus of the sample at 130°C.

[0084] (4) Tensile elongation and Young's modulus at room temperature: Rectangular samples with a length of 150 mm (measurement direction) × width of 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. Tensile tests were performed on the film at a tensile speed of 300 mm / min at room temperature. The tensile elongation and Young's modulus were calculated according to the method specified in JIS K7161 (2014). Each sample was tested 5 times, and the average value was defined as the tensile elongation and Young's modulus of the sample. The width direction was set to 0°, and the Young's modulus was measured in each direction forming an angle from 0° to 175° with respect to the width direction at 5° scale intervals. The direction showing the highest value was defined as the principal alignment direction.

[0085] (5) The crystallization temperature Tc0 was obtained by the external interpolation method. Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), 3 mg of polypropylene film was heated from 25°C to 250°C at 20°C / min in a nitrogen atmosphere and held for 5 minutes. Then, it was cooled 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, it was cooled 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 2, the cooling rate was plotted on the horizontal axis, and the crystallization temperature obtained 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 where the cooling rate was extrapolated to 0℃ / min was defined as Tc0. Furthermore, in cases where multiple peak temperatures were observed in the determination of Tc10 or Tc40, the highest peak temperature in the region of 80℃ to 130℃ was used as the crystallization temperature of the polypropylene film. Each sample was measured three times, and the average value was used for evaluation.

[0086] (6) Melting point Tm: A differential scanning calorimeter (EXSTAR DSC6220, Seiko Instruments Co., Ltd.) was used to heat 3 mg of polypropylene film 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 was defined as Tm. The determination was performed three times for each sample, and the average value was used for evaluation.

[0087] (7) Static friction coefficient (μs) in the orthogonal direction of the main alignment after heat treatment at 130°C for 10 minutes: Two polypropylene films, each 6.5 cm wide (main alignment direction) and 12 cm long (orthogonal direction of the main alignment direction), were cut to form test pieces. These were sandwiched in paper and heated in an oven at 130°C for 10 minutes under zero load. After removal, they were cooled at room temperature. Subsequently, the static friction coefficient (μs) in the orthogonal direction of the main alignment of the test pieces was measured using a slip tester from Toyo Seiki Co., Ltd., according to JIS K 7125 (1999), at 25°C and 65%RH. Furthermore, the measurement was performed by aligning the orthogonal directions of the main alignment and then overlapping the films so that different surfaces of the films were in contact with each other. Five identical measurements were performed on a sample, and the average value of the obtained values ​​was determined as the static friction coefficient (μs) of the sample.

[0088] (8) The maximum height (St) measurement was performed using Ryoka Systems Inc.'s "VertScan" (registered trademark) 2.0 R5300GL-Lite-AC. The surface shape was obtained by performing surface correction on the captured image using the accompanying analysis software with a polynomial fourth degree 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 and used as the St of each side. Furthermore, the larger of the St values ​​of the two sides of the film is recorded in the table. • 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.

[0089] (9) Melt tension was measured using an apparatus conforming to JIS K 7199 (1999) under the following conditions. • Apparatus: Capillary chromatography 1BPMD-i (manufactured by Toyo Seiki Co., Ltd.) equipped with a melt tension tester • Temperature: 230°C (using an insulated chamber) • Die: L=8 (mm), D=2.095 (mm) • Extrusion speed: 20 mm / min • Extraction speed: 15.7 m / min • Sample mass: 15-20 g.

[0090] (10) Evaluation of the flatness of the film during heating: A 500 mm wide polypropylene film with a low St value was subjected to corona treatment. An acrylic emulsion adhesive (manufactured by E-TEC, EX243) was applied to the treated surface. The film was then guided to a drying oven at 130°C and transported for 60 seconds with a transport tension of 200 N to remove the solvent from the coating, resulting in an adhesive film with an adhesive layer thickness of 1 μm. Subsequently, the adhesive film was rolled into a 200 m roll to form an adhesive film roll. Next, an adhesive film with a width of 500 mm and a width of only 1 m was rolled out without tension (the state of hanging vertically due to the weight of the film itself). The film width was uniform and the tension was applied at 1 kg / m and 3 kg / m. The flatness defects such as wrinkles or dents were visually checked. The obtained values ​​were used to evaluate the flatness using the following criteria. S: No flatness defects under no tension. A: Areas with poor flatness are visible under no tension, but disappear under a tension of 1 kg / m width. B: Areas with poor flatness are visible under a tension of 1 kg / m width, but disappear under a tension of 3 kg / m width. C: Areas with poor flatness are visible even under a tension of 3 kg / m width.

[0091] (11) Evaluation of warpage when bonding the substrate The adhesive film obtained in (10) above and a 40 μm thick "ZEONOR film" (registered trademark) manufactured by Nippon Zeon Co., Ltd. were cut with a width of 20 cm and a length of 30 cm, and overlapped so that the adhesive layer of the adhesive film was in contact with the "ZEONOR film" (registered trademark), and bonded so that the length direction was aligned, thus obtaining a bonded sample. The bonded sample was heated in an oven at 150°C for 60 seconds and then cooled to room temperature, and the warpage in the width direction of the bonded sample was measured. The warpage was measured by placing the bonded sample on a horizontal plane with the "ZEONOR film" (registered trademark) on the bottom, and measuring the height relative to the horizontal plane at the midpoint of the length side. The same measurement was performed on both length sides, and the average value was set as the warpage of the sample. The evaluation was performed using the following criteria. S: Warpage is less than 1 mm. A: Warpage greater than 1 mm but less than 5 mm. B: Warpage greater than 5 mm but less than 10 mm. C: Warpage greater than 10 mm, or peeling of the polypropylene film from the "ZEONOR film" (registered trademark).

[0092] (12) Differential distribution value and molecular weight distribution Mz / Mw when logarithmic molecular weight Log(M) = 6.5 1,2,4-trichlorobenzene was used as the solvent and stirred at 165°C for 30 minutes to dissolve the polypropylene film. Subsequently, the film was filtered using a 0.5 μm filter, and the molecular weight distribution of the filtrate was determined by gel permeation chromatography. A molecular weight calibration curve was prepared using the following standard samples, and the molecular weight was corrected using this calibration curve to obtain the differential distribution value, weight-average molecular weight Mw, and Z-average molecular weight Mz when the logarithmic molecular weight Log(M) of the sample was 6.5. Furthermore, the measuring apparatus and conditions are as follows. • 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℃ • Injection volume: 0.500 mL • Sample concentration: 0.1 wt% • Standard samples: Tosoh monodisperse polystyrene, Tokyo Chemical Industry Co., Ltd. dibenzyl.

[0093] (13) Cold xylene-soluble fraction (CXS) The raw material is for polypropylene resin. 0.5g is dissolved in 100ml of xylene at 135°C and cooled. After recrystallization in a constant temperature water bath at 20°C for 1 hour, the polypropylene components dissolved in the filtrate are quantitatively determined by liquid chromatography. The amount of polypropylene components dissolved in the filtrate is defined as X (g), and the precision value of 0.5g of the sample is defined as X0 (g), which is calculated from the following formula. Formula: CXS (mass%) = (X / X0) × 100.

[0094] (Polypropylene resin, etc.) Polypropylene resin having the molecular weight distribution Mz / Mw, CXS, MFR, and differential distribution values ​​when Log(M) = 6.5 as shown in Table 1 below was used to manufacture the polypropylene films of the Examples and Comparative Examples. These values ​​were evaluated in the form of resin pellets. Three types of resin were used as polypropylene resin A, and two types of resin were used as other polypropylene resins. Furthermore, regarding branched chain polypropylene resin and resins other than polypropylene, the following were used. In some Examples and some Comparative Examples, those that had been pre-adjusted as follows were used as raw materials for manufacturing polypropylene films.

[0095] <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.

[0096] <Other Polypropylene Resins> Polypropylene Resin 4 (PP4): Made by Prime Polymer Co., Ltd. Polypropylene Resin 5 (PP5): Made by Prime Polymer Co., Ltd.

[0097] <Branched Polypropylene Resins> Branched Polypropylene Resin 1 (Branched PP1): Ziegler-Natta Catalyst-Based Branched Polypropylene Resin (PF-814, manufactured by Basell, melt tension: 15gf, MFR: 3.0g / 10min) Branched Polypropylene Resin 2 (Branched PP2): Metallocene Catalyst-Based Branched Polypropylene Resin (“WAYMAX” (registered trademark) MFX6, manufactured by Japan Polypropylene Corporation, melt tension: 13gf, MFR: 3.0g / 10min).

[0098] [Table 1] type Mz / Mw CXS(%) MFR (g / 10 minutes) 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] <Resins other than polypropylene> 4-Methyl-1-pentene polymer 1: Mitsui Chemicals (stock) MX004.

[0100] <Polypropylene Raw Materials> Polypropylene Raw Material 1: Polypropylene resin 2 and 4-methyl-1-pentene polymer 1 are fed into a biaxial extruder from a metering hopper at a ratio of 90:10 (mass ratio), and melt-blended at 260°C. The molten resin composition is then extruded from the die in bundles and cooled and solidified in a water bath at 25°C before being cut into sheets. Polypropylene Raw Material 2: Polypropylene resin 3 and 4-methyl-1-pentene polymer 1 are fed into a biaxial extruder from a metering hopper at a ratio of 90:10 (mass ratio), and melt-blended at 260°C. The molten resin composition is then extruded from the die in bundles and cooled and solidified in a water bath at 25°C before being cut into sheets.

[0101] (Example 1) Polypropylene resin 2 and polypropylene raw material 1 were dry-blended at a mass ratio of 80:20 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 and then fed to a single-shaft extruder for the base layer (II). Each resin mixture was melt-extruded at 260°C, and after removing foreign matter using a sintered filter with a 20μm retention, it was laminated using a feed block type A / B / A composite T-die to make the surface layer (I) / base layer (II) / surface layer (I) system have a thickness ratio of 1 / 30 / 1, and sprayed onto a casting drum with the surface temperature controlled at 25°C and then pressed into the casting drum through an air knife. Subsequently, compressed air at 20°C, blown at a speed of 140 m / s, is sprayed onto the uncooled drum surface of the sheet on the casting drum to cool and solidify the sheet, resulting in an unstretched sheet. Next, the unstretched sheet is preheated to 140°C using ceramic rollers, and then stretched 5.7 times along its long side by a radiant heater between rollers with a circumferential speed difference of 120°C, to obtain a uniaxially stretched film. The heat source of the radiant heater is fixed at a distance of 90 mm from the sheet surface. The distance between the rollers with the circumferential speed difference (stretching interval) is 320 mm, and the output of the radiant heater is set to 2.8 kW. Next, the obtained uniaxially stretched film is fed into a tenter frame by clamping both ends in the width direction. After preheating at 176°C for 3 seconds, it is stretched 9.8 times in the width direction at 155°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 heating with a hot roller at 115°C for 1.0 second in the crossing zone, it is wound onto a core to obtain a polypropylene film with a thickness of 25 μm. The physical properties and evaluation results of the obtained film are shown in Table 2.

[0102] (Examples 2-5, Comparative Examples 1-5) Except that the composition of each layer and the film-forming conditions were set as 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 raw materials, for the surface layer (I) of Comparative Examples 2 and 5, polypropylene resin 2 and polypropylene raw material 1 were dry-blended at a ratio of 80:20 (mass ratio), similar to the surface layer (I) of Example 1. For the surface layer (I) of Examples 4 and Comparative Examples 4, polypropylene resin 3 and polypropylene raw material 2 were dry-blended at a ratio of 70:30 (mass ratio). For the surface layer (I) and base layer (II) of the other examples, the resin components were dry-blended at the ratios shown in Table 2.

[0103] [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 Comparative Example 5 Surface layer (Ⅰ) PP resin A PP1 (parts by weight) - - - - - - - 95 - - PP2 (parts by weight) 98 - - - - - 98 - - 98 PP3 (parts by weight) - - - 97 - - - - 97 - PP resin PP4 (parts by weight) - 95 - - - - - - - - PP5 (parts by weight) - - - - 100 - - - - - Branched PP resin Branch PP1 (parts by weight) - 5 - - - - - 5 - - Branch PP2 (parts by weight) - - - - - - - - - - 1 part by weight of 4-methyl-1-pentene polymer 2 - - 3 - - 2 - 3 2 Inner layer (II) PP resin A PP1 (parts by weight) 95 - 97 - - - - - - 98 PP2 (parts by weight) - - - 50 95 - - - - - PP3 (parts by weight) - 100 - 50 - - - 30 - - PP resin PP4 (parts by weight) - - - - - - 100 - - - PP5 (parts by weight) - - - - 5 100 - 70 100 - Branched PP resin Branch PP1 (parts by weight) 5 - - - - - - - - 2 Branch PP2 (parts by weight) - - 3 - - - - - - - Film Forming condition Melt extrusion temperature (°C) 260 260 260 260 260 260 260 250 260 260 Layer 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 1 / 10 / 1 1 / 12 / 1 Casting drum temperature (°C) 25 18 38 30 38 30 77 95 30 90 Air temperature (°C) 20 28 38 30 42 45 50 50 50 45 Stretching along the long side Preheating temperature (°C) 140 120 118 135 112 135 142 100 150 153 Tensile temperature (°C) 120 120 123 115 125 135 142 120 150 128 Multiplier (times) 5.7 6.2 4.8 5.2 5.7 4.5 5.1 6.3 3.8 4.9 Tension range (mm) 320 220 260 320 400 220 150 100 220 100 Radiant heater output (kW) 2.8 1.5 2.5 3.2 0.8 2.3 1.5 Unused Unused Unused Width direction stretching Preheating temperature (°C) 176 166 178 175 168 170 169 160 170 180 Tensile temperature (°C) 155 160 170 160 160 180 161 170 180 173 Stretch ratio (times) 9.8 10 8.7 9.4 11.8 8.2 8.8 10.8 9.1 9.4 Heat treatment Heat treatment temperature (°C) 178 169 166 175 167 168 158 170 170 148 Relaxation rate (%) in the width direction 20 20 13 15 13 6.7 11 20 15 11 Cooling temperature (°C) 100 90 80 100 100 50 70 80 80 100 In the Hengdu area heating Temperature (°C) 115 85 Unprocessed 100 92 Unprocessed Unprocessed 90 115 Unprocessed Time (seconds) 1.0 0.4 Unprocessed 0.7 0.5 Unprocessed Unprocessed 3.0 3.0 Unprocessed Thickness (μm) 25 12 20 40 25 20 2.3 25 15 25 Mz / Mw 3.3 4.4 2.9 3.9 3.6 5.8 4.7 5.4 5.6 3.2 Differential distribution value (%) when Log(M) = 6.5 5.3 8.3 2.6 7.1 6.7 15.2 12.4 13.1 14.9 5.1 tanδ in the principal alignment direction at 150℃ 0.19 0.18 0.24 0.22 0.23 0.31 0.28 0.26 0.20 0.26 Young's modulus (MPa) in the principal alignment orthogonal direction at 130℃ 120 70 100 60 60 70 150 100 40 160 tanδ in the principal alignment orthogonal direction at 150℃ 0.15 0.14 0.28 0.24 0.20 0.24 0.21 0.28 0.18 0.27 Loss modulus E'' (Pa) in the principal alignment orthogonal direction at 0℃ 1.8×10 8 1.8×10 8 3.9×10 8 3.3×10 8 2.9×10 8 3.8×10 8 3.0×10 8 4.0×10 8 2.4×10 8 2.8×10 8 Young's modulus × thickness (N / m) in the principal alignment orthogonal direction at 130℃ 3000 840 2000 2400 1500 1400 345 2500 600 4000 Tc0+Tm 292 288 297 278 275 271 275 282 273 281 Static friction coefficient μs after heat treatment at 130℃ for 10 minutes 0.50 0.76 0.84 0.58 1.00 0.90 0.65 0.92 0.64 0.72 Elongation (%) in the principal alignment direction 52 39 63 48 41 51 45 32 58 30 Maximum height St (μm) 0.3 0.2 1.6 0.7 2.2 1.1 1.8 7.2 0.8 2.1 Planarity evaluation S A S B B B C A C A Warp evaluation S S B A B C C C A C

[0104] Furthermore, since Examples 3 and Comparative Example 1 are single-layer structures, they are treated as having no surface layer, and the composition is described in the base layer (II). [Possibility of Industrial Application]

[0105] 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, and capacitor film. However, due to its particularly excellent heat resistance, mechanical strength, and quality, it can be better used as a surface protection film, process film, release film, and capacitor film. [Simplified Explanation of the Diagram]

[0012] Figure 1 is an example of a graph showing the temperature dependence of tanδ of polypropylene film. Figure 2 is an example of a graph showing the crystallization temperature Tc0 of polypropylene film.

Claims

1. A polypropylene film, characterized in that its tanδ coefficient in the principal alignment direction at 150℃ is below 0.25, its Young's modulus in the principal alignment orthogonal direction at 130℃ is above 50 MPa, its molecular weight distribution Mz / Mw coefficient is above 1.5 and below 4.5, and when the crystallization temperature at a cooling rate of 0℃ / min is defined as Tc0 (℃) and the melting point of the film is defined as Tm (℃), Tc0 + Tm ≥ 280; wherein, The crystallization temperature at a cooling rate of 0°C / min was obtained 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.

2. The polypropylene film of claim 1, wherein the tanδ value in the principal orthogonal orientation at 150°C is less than 0.

25.

3. The polypropylene film of claim 1 or 2, wherein the loss modulus E” in the principal alignment orthogonal direction at 0°C is 3.5 × 10⁸ Pa or less.

4. The polypropylene film of claim 1 or 2, wherein the product of Young's modulus and film thickness in the principal orthogonal orientation at 130°C is 500 N / m or more.

5. The polypropylene film of claim 1 or 2, wherein the static friction coefficient μs after heat treatment at 130°C for 10 minutes is less than 0.

80.

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

7. 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.

8. For the polypropylene film of claim 1 or 2, 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 more than 1.0% and less than 10%.

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

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

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

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

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