Biaxially oriented polypropylene film

Abstract

To provide a biaxially oriented polypropylene film which has high rigidity, excellent heat resistance at a high temperature of 150°C, easily maintains the shape of a packaging bag when made into the film, and causes little pitch deviation during printing and wrinkles in the sealed portion when heat-sealed. [Solution] A biaxially oriented polypropylene film that satisfies the following formulas (1) to (4). (1) The thermal shrinkage rate at 150°C is 10% or less in the longitudinal direction and 24% or less in the transverse direction. (2) The tensile elongation at break is 195% or more in the longitudinal direction at 23°C. (3) The refractive index Nx in the longitudinal direction is 1.5050 or less. (4) The refractive index Nz in the thickness direction is 1.5010 or less.

Description

Technical Field

[0001] The present invention relates to a biaxially oriented polypropylene film having excellent rigidity and heat resistance. More specifically, it relates to a biaxially oriented polypropylene film that can be suitably used for packaging bags because it easily retains the bag shape when used as a packaging bag and has few wrinkles in the seal part when heat-sealed.

Background Art

[0002] Biaxially oriented polypropylene films have moisture-proof properties and necessary rigidity and heat resistance, and are thus used in packaging applications and industrial applications. In recent years, as the applications for which they are used have expanded, higher performance has been demanded, and in particular, an improvement in rigidity has been expected. Also, in consideration of the environment, it is required to maintain the strength even when reducing the volume (thinning the film thickness), and for this purpose, it is essential to significantly improve the rigidity. As a means for improving the rigidity, it is known that the crystallinity and melting point of the polypropylene resin are improved by improving the catalyst and process technology during the polymerization of the polypropylene resin. However, despite such improvements, there has not been a biaxially oriented polypropylene film having sufficient rigidity.

[0003] In the manufacturing process of a biaxially oriented polypropylene film, after stretching in the width direction, a first heat treatment is performed while relaxing the film at a temperature below the temperature during width direction stretching, and a heat treatment is performed at the first stage temperature to the width direction stretching temperature in the second stage (see, for example, Patent Document 1, etc.), or a method of further stretching in the longitudinal direction after width direction stretching (see, for example, Patent Document 2, etc.) has been proposed. However, the film described in Patent Document 2 is excellent in rigidity, but wrinkles easily occur in the seal part after heat-sealing and it is inferior in heat resistance. Also, the orientation of the film described in Patent Document 1 is low and the rigidity is not sufficient.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] The object of the present invention is to solve the above-mentioned problems. Specifically, the present invention relates to a biaxially oriented polypropylene film that has excellent rigidity and heat resistance at high temperatures of 150°C, and is less prone to breakage during bag making and other processing. More specifically, the present invention aims to provide a biaxially oriented polypropylene film that easily maintains the shape of a bag when made into a packaging bag, and that exhibits fewer wrinkles in and around the sealed portion when heat-sealed. Means for solving the problem

[0006] As a result of diligent research conducted by the present inventors to achieve the above objective, a biaxially oriented polypropylene film satisfying the following formulas (1) to (4) is provided. (1) The thermal shrinkage rate at 150°C is 10% or less in the longitudinal direction and 24% or less in the width direction. (2) The tensile elongation at break is 195% or more in the longitudinal direction at 23°C. (3) The refractive index Nx in the longitudinal direction is 1.5050 or less. (4) The refractive index Nz in the thickness direction is 1.5010 or less.

[0007] In this case, it is preferable that the heat shrinkage rate of the biaxially oriented polypropylene film at 120°C is 2.0% or less in the longitudinal direction and 5.0% or less in the width direction, and that the heat shrinkage rate at 120°C in the longitudinal direction is smaller than the heat shrinkage rate at 120°C in the width direction.

[0008] Furthermore, in this case, it is preferable that the refractive index Ny in the longitudinal direction of the biaxially oriented polypropylene film is 1.5230 or higher, and that ΔNy is 0.0220 or higher.

[0009] Furthermore, in this case, it is preferable that the haze of the biaxially oriented polypropylene film is 5.0% or less.

[0010] Furthermore, in this case, the mesopentade fraction of the polypropylene resin constituting the biaxially oriented polypropylene film is 97.0% or more. It is preferable to do so.

[0011] Furthermore, in this case, it is preferable that the crystallization temperature of the polypropylene resin constituting the biaxially oriented polypropylene film is 105°C or higher, and the melting point is 160°C or higher.

[0012] Furthermore, in this case, it is preferable that the melt flow rate of the polypropylene resin constituting the biaxially oriented polypropylene film is 4.0 g / 10 min or more.

[0013] Furthermore, in this case, it is preferable that the amount of polypropylene resin components with a molecular weight of 100,000 or less constituting the biaxially oriented polypropylene film is 35% by mass or more.

[0014] Furthermore, in this case, it is preferable that the degree of orientation of the biaxially oriented polypropylene film is 0.85 or higher. [Effects of the Invention]

[0015] The biaxially oriented polypropylene film of the present invention has high rigidity and excellent heat resistance even at high temperatures of 150°C, making it easy to maintain the shape of the bag when used as a packaging bag, and also produces fewer wrinkles at the sealed area when heat-sealed, thus providing a biaxially oriented polypropylene film that can be suitably used as a packaging bag. Furthermore, because the biaxially oriented polypropylene film has excellent rigidity, it can maintain strength even when the film thickness is reduced, and can also be suitably used in applications where even higher rigidity is required. Modes for carrying out the invention

[0016] The biaxially oriented polypropylene film of the present invention will be described in more detail below. The biaxially oriented polypropylene film of the present invention consists of a polypropylene resin composition mainly composed of polypropylene resin. "Main component" means that the proportion of polypropylene resin in the polypropylene resin composition is 90% by mass or more, more preferably 93% by mass or more, even more preferably 95% by mass or more, and particularly preferably 97% by mass or more.

[0017] (Polypropylene resin) The polypropylene resin used in the present invention can be a polypropylene homopolymer or a copolymer of ethylene and / or α-olefins having 4 or more carbon atoms. A propylene homopolymer that is substantially free of ethylene and / or α-olefins having 4 or more carbon atoms is preferred, and even if it contains ethylene and / or α-olefin components, the amount of ethylene and / or α-olefin components is preferably 1 mol% or less. The upper limit of the component amount is more preferably 0.5 mol%, even more preferably 0.3 mol%, and even more preferably 0.1 mol%. Crystallinity tends to improve within the above range. Examples of α-olefin components with four or more carbon atoms that constitute such copolymers include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. Polypropylene resins can be made from two or more different polypropylene homopolymers, copolymers with ethylene and / or α-olefins having 4 or more carbon atoms, or mixtures thereof.

[0018] (stereoregularity) The mesopentad fraction ([mmmm]%), which is an index of the stereoregularity of the polypropylene resin used in the present invention, is preferably in the range of 97.0 to 99.9%, more preferably in the range of 97.5 to 99.7%, still more preferably in the range of 98.0 to 99.5%, and particularly preferably in the range of 98.5 to 99.3%. When it is 97.0% or more, the crystallinity of the polypropylene resin increases, and the melting point, crystallinity, and crystal orientation degree of the crystals in the film improve, and it is easy to obtain rigidity and heat resistance at high temperatures. When it is 99.9% or less, it is easy to suppress the cost in terms of polypropylene production, and it is difficult to break during film formation. More preferably, it is 99.5% or less. The mesopentad fraction is measured by nuclear magnetic resonance method (so-called NMR method). In order to make the mesopentad fraction of the polypropylene resin within the above range, methods such as washing the obtained polypropylene resin powder with a solvent such as n-heptane, appropriately selecting a catalyst and / or a cocatalyst, and appropriately selecting the components of the polypropylene resin composition are preferably adopted.

[0019] (Melting temperature) The lower limit of the melting temperature (Tm) measured by DSC of the above polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is preferably 160 °C, more preferably 161 °C, still more preferably 162 °C, and even more preferably 163 °C. When Tm is 160 °C or higher, it is easy to obtain rigidity and heat resistance at high temperatures. The upper limit of Tm is preferably 170 °C, more preferably 169 °C, still more preferably 168 °C, even more preferably 167 °C, and particularly preferably 166 °C. When Tm is 170 °C or lower, it is easy to suppress the cost increase in terms of polypropylene production, and it is difficult to break during film formation. By blending a crystal nucleating agent with the above polypropylene resin, the melting temperature can also be further increased. Tm is the primary peak temperature of the endothermic peak observed during melting when a 1-10 mg sample is packed into an aluminum pan, placed in a differential scanning calorimeter (DSC), melted at 230°C for 5 minutes under a nitrogen atmosphere, cooled to 30°C at a scanning rate of -10°C / min, held for 5 minutes, and then heated again at a scanning rate of 10°C / min.

[0020] (crystallization temperature) The lower limit of the crystallization temperature (Tc) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention, as measured by DSC, is 105°C, preferably 108°C, and more preferably 110°C. When Tc is 105°C or higher, crystallization proceeds easily during the widthwise stretching and subsequent cooling process, making it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tc is preferably 135°C, more preferably 133°C, even more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. If Tc is 135°C or lower, it is less likely to increase the cost of polypropylene production and less likely to break during film formation. Tc is the primary exothermic peak temperature observed when a 1-10 mg sample is placed in an aluminum pan, set in a DSC, melted at 230°C for 5 minutes under a nitrogen atmosphere, and then cooled to 30°C at a scanning speed of -10°C / min. The crystallization temperature can be further increased by incorporating a nucleating agent into the aforementioned polypropylene resin.

[0021] (Melt flow rate) The melt flow rate (MFR) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is preferably 4.0 to 30 g / 10 min, more preferably 4.5 to 25 g / 10 min, even more preferably 4.8 to 22 g / 10 min, particularly preferably 5.0 to 20 g / 10 min, and most preferably 6.0 to 20 g / 10 min, when measured in accordance with the conditions M (230°C, 2.16 kgf) of JIS K 7210 (1995). When the melt flow rate (MFR) of the polypropylene resin is 4.0 g / 10 min or higher, it is easier to obtain a biaxially oriented polypropylene film with a low thermal shrinkage rate. Furthermore, if the melt flow rate (MFR) of the polypropylene resin is 30 g / 10 min or less, it is easier to maintain the film-forming properties.

[0022] From the viewpoint of film properties, it is preferable to set the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the polypropylene resin constituting the film to preferably 5.0 g / 10 min, more preferably 5.5 g / 10 min, even more preferably 6.0 g / 10 min, particularly preferably 6.3 g / 10 min, and most preferably 6.5 g / 10 min. When the melt flow rate (MFR) of the polypropylene resin is 5.0 g / 10 min or higher, the amount of low molecular weight components in the polypropylene resin constituting the film increases. Therefore, by employing the widthwise stretching process in the film manufacturing process described later, the orientation and crystallization of the polypropylene resin are further promoted, and the degree of crystallinity in the film tends to increase. In addition, the entanglement between polypropylene molecular chains in the amorphous portion is reduced, making it easier to improve heat resistance. In order to keep the melt flow rate (MFR) of the polypropylene resin within the above range, methods such as controlling the average molecular weight and molecular weight distribution of the polypropylene resin are preferably employed.

[0023] In other words, the lower limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve of the polypropylene resin constituting the film of the present invention is preferably 35% by mass, more preferably 38% by mass, even more preferably 40% by mass, particularly preferably 41% by mass, and most preferably 42% by mass. The upper limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is 65% by mass or less, the film strength is less likely to decrease. In this case, including high molecular weight components or long-chain branched components with long relaxation times makes it easier to adjust the amount of components with a molecular weight of 100,000 or less in the polypropylene resin without significantly changing the overall viscosity, thus improving film-forming properties without significantly affecting rigidity or thermal shrinkage.

[0024] (molecular weight distribution) The polypropylene resin used in the present invention has a lower limit of mass-average molecular weight (Mw) / number-average molecular weight (Mn), which is an indicator of the breadth of the molecular weight distribution, preferably 3.5, more preferably 4.0, even more preferably 4.5, and particularly preferably 5.0. The upper limit of Mw / Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20. Mw / Mn can be obtained using gel permeation chromatography (GPC). When Mw / Mn is within the above range, it is easy to increase the amount of components with a molecular weight of 100,000 or less.

[0025] Furthermore, the molecular weight distribution of polypropylene resin can be adjusted by polymerizing components of different molecular weights in a multi-stage process in a series of plants, blending components of different molecular weights offline in a kneader, polymerizing with a blend of catalysts having different properties, or using a catalyst capable of achieving the desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC can be a smooth molecular weight distribution with a single peak in a GPC chart where the horizontal axis is the logarithm of molecular weight (logM) and the vertical axis is the differential distribution value (weight fraction per logM), or it can be a molecular weight distribution with multiple peaks or shoulders.

[0026] (Method for producing biaxially oriented polypropylene film) The biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made from a polypropylene resin composition mainly composed of the polypropylene resin described above, and then biaxially stretching it. The biaxial stretching can be performed by any of the following methods: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential tenter biaxial stretching. However, sequential tenter biaxial stretching is preferred from the viewpoint of film formation stability and thickness uniformity. In particular, it is preferable to stretch in the longitudinal direction first, followed by stretching in the width direction, but a method of stretching in the width direction first, followed by stretching in the longitudinal direction is also acceptable.

[0027] Next, the method for manufacturing the biaxially oriented polypropylene film of the present invention will be described below, but is not necessarily limited thereto. The biaxially oriented polypropylene film of the present invention may have layers having other functions laminated on at least one side. Lamination may be performed on one side or both sides. In that case, the resin composition of the other layer and the central layer may be the polypropylene resin composition described above. Alternatively, it may be different from the polypropylene resin composition described above. The number of layers to be laminated may be one, two, or three or more layers per side, but from a manufacturing viewpoint, one or two layers are preferred. As for the lamination method, for example, co-extrusion by a feed block method or a multi-manifold method is preferred. In particular, in order to improve the processability of the biaxially oriented polypropylene film, a resin layer having heat-sealability can be laminated to the extent that it does not degrade the properties. In addition, corona treatment may be applied to one or both sides to impart printability.

[0028] The following describes an example for a single layer, specifically focusing on the use of the Tenter successive biaxial stretching method. First, a resin composition containing polypropylene resin is heated and melted in a single-screw or twin-screw extruder, extruded into a sheet from a T-die, and cooled and solidified on a cooling roll. To promote solidification, it is preferable to further cool the sheet cooled on the cooling roll by immersing it in a water tank or the like.

[0029] Next, the sheet is stretched longitudinally by increasing the rotation speed of the rear stretching roll using two heated stretching rolls, thereby obtaining a uniaxially oriented film.

[0030] Next, after preheating the uniaxially oriented film, the film is stretched in the width direction at a specific temperature using a tenter-type stretcher while gripping the film edges, thereby obtaining a biaxially oriented film. This width-direction stretching process will be described in detail later.

[0031] After the widthwise stretching process is completed, the biaxially oriented film is heat-treated at a specific temperature to obtain a biaxially oriented film. During the heat treatment process, the film may be relaxed in the widthwise direction.

[0032] The biaxially oriented polypropylene film thus obtained can be subjected to corona discharge treatment on, for example, at least one side, as needed, and then wound up with a winder to obtain a film roll.

[0033] The following sections will explain each step in detail. (Extrusion process) First, a polypropylene resin composition, mainly composed of polypropylene resin, is heated and melted in a single-screw or twin-screw extruder at a temperature in the range of 200°C to 300°C. The sheet-like molten polypropylene resin composition coming out of the T-die is extruded and cooled and solidified in contact with a metal cooling roll. Preferably, the resulting unstretched sheet is then placed in a water tank. The temperature of the cooling roll, or the temperature of the cooling roll and water bath, is preferably in the range of 10°C to Tc. If you want to increase the transparency of the film, it is preferable to cool and solidify it with a cooling roll at a temperature in the range of 10 to 50°C. Lowering the cooling temperature to 50°C or below tends to increase the transparency of the unstretched sheet, so it is preferably 40°C or below, and more preferably 30°C or below. In order to increase the degree of crystal orientation after sequential biaxial stretching, it may be preferable to set the cooling temperature to 40°C or below when using a propylene homopolymer with a mesopentat fraction of 97.0% or more, as described above, in order to facilitate the stretching in the next step and reduce thickness variations, it is preferable to set the cooling temperature to 40°C or below, and more preferably 30°C or below. The thickness of the unstretched sheet is preferably 3500 μm or less for optimal cooling efficiency, and more preferably 3000 μm or less. This can be adjusted as appropriate depending on the film thickness after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition and the lip width of the T-die, etc.

[0034] (Longitudinal stretching process) The lower limit of the longitudinal stretching ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. Within this range, it is easier to increase strength and reduce film thickness unevenness. The upper limit of the longitudinal stretching ratio is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. Within this range, it is easier to perform the widthwise stretching process, and productivity is improved. The lower limit of the longitudinal stretching temperature is preferably Tm-40°C, more preferably Tm-37°C, and even more preferably Tm-35°C. Within this range, the subsequent widthwise stretching is facilitated and thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, and even more preferably Tm-12°C. Within this range, the thermal shrinkage rate is easily reduced, and there is less chance of the material adhering to the stretching roll and becoming difficult to stretch, or of the quality degrading due to increased surface roughness. Furthermore, longitudinal stretching may be performed in two or more stages using three or more stretching rolls.

[0035] (Preheating process) Before the widthwise stretching process, the uniaxially oriented film after longitudinal stretching must be heated to a temperature range of Tm to Tm+25°C to soften the polypropylene resin composition. A temperature above Tm promotes softening, facilitating widthwise stretching. A temperature below Tm+25°C promotes orientation during transverse stretching, making it easier to achieve rigidity. More preferably, the temperature is Tm+2 to Tm+22°C, and particularly preferably Tm+3 to Tm+20°C. Here, the highest temperature reached during the preheating process is defined as the preheating temperature.

[0036] (Width direction stretching process) In the widthwise stretching process after the preheating process, the preferred method is as follows:

[0037] In the widthwise stretching process, it is preferable to stretch at a temperature of Tm -10°C or higher and below the preheating temperature. At this time, the widthwise stretching may start when the preheating temperature is reached, or it may start when the temperature is lowered after reaching the preheating temperature and reaches a temperature lower than the preheating temperature. The lower limit of the temperature in the widthwise stretching process is more preferably Tm-9°C, even more preferably Tm-7°C, and particularly preferably Tm-5°C. When the widthwise stretching temperature is within this range, it is easier to improve the rigidity of the resulting biaxially oriented film. The upper limit of the temperature in the widthwise stretching process is preferably Tm+10°C, more preferably Tm+7°C, and particularly preferably Tm+5°C. When the widthwise stretching temperature is within this range, stretching unevenness is less likely to occur. The film is cooled immediately after the end of stretching in the width direction, that is, when the final stretching ratio in the width direction is reached. The cooling temperature at this time is preferably below the temperature of stretching in the width direction, and is between Tm-80°C and Tm-15°C, more preferably between Tm-80°C and Tm-20°C, even more preferably between Tm-80°C and Tm-30°C, and particularly preferably between Tm-70°C and Tm-40°C. The temperature can be gradually lowered from the end of widthwise stretching to the cooling temperature, but it can also be lowered in steps or in a single step. Lowering the temperature in steps or in a single step makes it easier to increase the crystal orientation within the film. Therefore, it is preferable.

[0038] The lower limit of the final widthwise stretching ratio in the widthwise stretching process is preferably 10 times, more preferably 11 times. A ratio of 10 times or more makes it easier to increase rigidity and reduce film thickness unevenness. The upper limit of the widthwise stretching ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. A ratio of 20 times or less makes it easier to reduce the thermal shrinkage rate and makes it less likely to break during stretching.

[0039] Thus, by using a highly crystalline polypropylene resin with high stereoregularity and a high melting point, and employing the widthwise stretching process described above, the molecules of the polypropylene resin are highly aligned in the principal orientation direction (which corresponds to the widthwise direction in the widthwise stretching process described above). As a result, the resulting biaxially oriented film exhibits strong crystal orientation, and more crystals with high melting points are more easily formed. Furthermore, the orientation of the amorphous regions between crystals increases in the main orientation direction (which corresponds to the width direction in the widthwise stretching process described above), resulting in high rigidity. In addition, because there are many crystals with high melting points around the amorphous regions, the elongated polypropylene molecules in the amorphous regions do not easily relax at temperatures below the melting point of the crystals, and thus maintain their tensioned state. Therefore, the entire biaxially oriented film can maintain high rigidity even at high temperatures. Furthermore, it is noteworthy that by employing this widthwise stretching process, the thermal shrinkage rate at high temperatures of 150°C is also more easily reduced. The reason for this is that there is a strong crystal orientation around the amorphous region, and there are more crystals with high melting points, so the elongated polypropylene resin molecules in the amorphous region do not easily relax at temperatures below the melting point of the crystals. Furthermore, it is noteworthy that although the orientation of the amorphous regions between crystals increases in the main orientation direction (which corresponds to the width direction in the width direction stretching process described above), the tensile elongation at fracture improves because the material is not under extreme tension.

[0040] Furthermore, increasing the low molecular weight components of the polypropylene resin makes it easier to achieve a higher degree of crystallinity in the film, and reduces the entanglement of polypropylene resin molecular chains in the amorphous portion, thereby weakening the thermal shrinkage stress and further reducing the thermal shrinkage rate. This is a groundbreaking development considering that in conventional technology, improving either strength or thermal shrinkage rate tends to decrease the other property.

[0041] (Heat treatment process) The biaxially oriented film can be heat-treated as needed to further reduce its thermal shrinkage. The upper limit of the heat treatment temperature is preferably Tm+10°C, more preferably Tm+7°C, and particularly preferably Tm+5°C. By keeping the temperature below Tm+10℃, rigidity is easily achieved, the film surface roughness does not become too large, and the film is less likely to whiten. The lower limit of the heat treatment temperature is preferably Tm-5℃, more preferably Tm-2℃, and particularly preferably Tm-2℃. If the temperature is below Tm-5℃, the thermal shrinkage rate may increase. By employing the widthwise stretching process described above, even when heat treatment is performed at temperatures between Tm-5°C and Tm+10°C, the highly oriented crystals generated in the stretching process are less likely to melt, and the thermal shrinkage rate can be reduced without decreasing the rigidity of the resulting film. To adjust the thermal shrinkage rate, the film may be relaxed (relaxed) in the widthwise direction during heat treatment, but the upper limit of the relaxation rate is preferably 4%. Within the above range, the film strength is less likely to decrease, and variations in film thickness tend to be small. More preferably, it is 3%, even more preferably 2%, even more preferably 1%, and particularly preferably 0%.

[0042] (Film thickness) The thickness of the biaxially oriented polypropylene film of the present invention is set according to each application, but in order to obtain the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, even more preferably 4 μm, particularly preferably 8 μm, and most preferably 10 μm. When the film thickness is 2 μm or more, it is easier to obtain the rigidity of the film. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, even more preferably 60 μm, particularly preferably 50 μm, and most preferably 40 μm. When the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion process does not tend to decrease. The biaxially oriented polypropylene film of the present invention is typically manufactured as a roll with a width of 2,000 to 12,000 mm and a length of 1,000 to 50,000 m, and then wound into a film roll. Furthermore, it is slit according to various applications and supplied as slit rolls with a width of 300 to 2,000 mm and a length of 500 to 5,000 m. The biaxially oriented polypropylene film of the present invention makes it possible to obtain longer film rolls.

[0043] (Uniformity of thickness) The lower limit of the thickness uniformity of the biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, even more preferably 0.5%, and particularly preferably 1%. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, even more preferably 15%, particularly preferably 12%, and most preferably 10%. Within the above range, defects are less likely to occur during post-processing such as coating and printing, making it easy to use in applications requiring precision. The measurement method was as follows: A 40 mm wide test piece was cut from the steady-state region where the film properties were stable in the length direction of the film. The film thickness was continuously measured over 20,000 mm using a film feeding device manufactured by Micron Measuring Instruments Co., Ltd. (product number: A90172) and a continuous film thickness measuring instrument manufactured by Anritsu Corporation (product name: K-313A wide-range high-sensitivity electronic micrometer), and the thickness uniformity was calculated from the following formula. Thickness uniformity (%) = [(Maximum thickness - Minimum thickness) / Average thickness] × 100

[0044] (Film characteristics) The biaxially oriented polypropylene film of the present invention is characterized by the following properties. Here, the "longitudinal direction" in the biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction in the film manufacturing process, and the "width direction" refers to the direction perpendicular to the flow direction in the film manufacturing process. For polypropylene films in which the flow direction in the film manufacturing process is unknown, wide-angle X-rays are incident perpendicular to the film surface, and the scattering peaks originating from the (110) plane of the α-type crystal are scanned in the circumferential direction. The direction with the largest diffraction intensity in the obtained diffraction intensity distribution is defined as the "longitudinal direction," and the direction perpendicular to it is defined as the "width direction."

[0045] (FHAM of diffraction peaks originating from oriented crystals) In the azimuthal angle dependence of the scattering peak of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray measurement perpendicular to the film surface of the biaxially oriented polypropylene film of the present invention, the upper limit of the full width at half maximum (Wh) of the diffraction peak originating from the orientation crystals in the width direction of the film is preferably 25°, more preferably 24°, more preferably 23°, and particularly preferably 22°. A full width at half maximum (Wh) of 25° or less makes it easier to increase the rigidity of the film. The lower limit of Wh is preferably 16°, more preferably 17°, and even more preferably 18°. To reduce the full width at half maximum (Wh), it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less, when the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film is measured to 35% by mass, and adjust the stretching ratio, stretching temperature, and heat-fixing temperature.

[0046] (Heat shrinkage rate at 150°C) The upper limit of the longitudinal heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 150°C is 10%, preferably 7.0%, more preferably 6.0%, even more preferably 5.0%, and particularly preferably 4.0% or less. The upper limit of the widthwise heat shrinkage rate at 150°C is 24%, preferably 21%, more preferably 18%, and particularly preferably 17% or less. When the thermal shrinkage rate in the longitudinal direction is 10% or less and the thermal shrinkage rate in the width direction is 24% or less, wrinkles are less likely to occur during heat sealing. In particular, when the thermal shrinkage rate in the longitudinal direction at 150°C is 8.0% or less and the thermal shrinkage rate in the width direction at 150°C is 20% or less, distortion is small when the chuck part is fused to the opening, which is preferable. To reduce the thermal shrinkage rate at 150°C, it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less, when the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film is measured, to 35% by mass, and adjust the stretching ratio, stretching temperature, and heat fixing temperature.

[0047] (Tensile elongation at 23°C) The lower limit of the longitudinal tensile elongation at break of the biaxially oriented polypropylene film of the present invention at 23°C is 195%, preferably 200%, more preferably 210%, and particularly preferably 220% or higher. An elongation of 195% or higher tends to reduce film breakage and packaging bag tearing. The upper limit of the longitudinal tensile elongation at break at 23°C is preferably 300%, more preferably 280%, as a practical value.

[0048] The lower limit of the tensile elongation at break in the width direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 25%, more preferably 30%, more preferably 32%, and particularly preferably 35%. If it is 25% or higher, film breakage and packaging bag breakage tend to be less frequent. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and even more preferably 50%. If it is 60% or lower, printing pitch misalignment when transferring printing ink is less likely to occur, and the durability of the packaging bag tends to be excellent. To increase the tensile elongation at break, it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less, when the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film is measured to 35% by mass, and adjust the stretching ratio, stretching temperature, and heat fixing temperature.

[0049] The biaxially oriented polypropylene film of the present invention is preferable if it has the following properties and structure. (Tensile breaking strength at 23°C) The lower limit of the longitudinal tensile breaking strength of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 90 MPa, more preferably 100 MPa, even more preferably 110 MPa, and particularly preferably 120 MPa. A strength of 90 MPa or higher reduces the likelihood of misalignment of the printing pitch when transferring printing ink, and also improves the durability of the packaging bag. The upper limit of the longitudinal tensile breaking strength at 23°C is preferably 200 MPa, more preferably 180 MPa, and even more preferably 160 MPa as a practical value. A strength of 200 MPa or lower tends to reduce film breakage and packaging bag rupture. The lower limit of the tensile breaking strength in the width direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 380 MPa, more preferably 400 MPa, even more preferably 430 MPa, and particularly preferably 450 MPa. A strength of 380 MPa or higher reduces the likelihood of misalignment of the printing pitch when transferring printing ink, and also improves the durability of the packaging bag. The upper limit of the tensile breaking strength in the width direction at 23°C is preferably 550 MPa, more preferably 520 MPa, and even more preferably 500 MPa as a practical value. A strength of 550 MPa or lower tends to reduce film breakage and packaging bag tearing. The tensile breaking strength can be kept within a specified range by adjusting the elongation ratio, elongation temperature, and heat-fixing temperature.

[0050] (Stress at 23°C and 5% elongation) The lower limit of the stress (F5) of the biaxially oriented polypropylene film of the present invention at 23°C with 5% elongation in the longitudinal direction is preferably 40 MPa, more preferably 42 MPa, even more preferably 44 MPa, even more preferably 46 MPa, and particularly preferably 48 MPa. Above 40 MPa, the rigidity is high, making it easier to maintain the shape of the bag when used as a packaging bag, and preventing deformation of the film during processing such as printing. The upper limit of F5 in the longitudinal direction is preferably 70 MPa, more preferably 65 MPa, even more preferably 62 MPa, and particularly preferably 60 MPa. Below 70 MPa, practical manufacturing is easier, and the balance of the vertical width is easier to achieve. The lower limit of F5 in the width direction at 23°C for the biaxially oriented polypropylene film of the present invention is preferably 160 MPa, more preferably 170 MPa, even more preferably 180 MPa, and even more preferably 190 MPa. Above 160 MPa, the rigidity is high, making it easier to maintain the shape of the bag when used as a packaging bag, and preventing deformation of the film during processing such as printing. The upper limit of F5 in the width direction is preferably 250 MPa, more preferably 230 MPa, and even more preferably 220 MPa. Below 250 MPa, practical manufacturing is easier, and the vertical-to-width balance is easier to achieve. F5 can be brought within the range by adjusting the stretching ratio, relaxation rate, and temperature during film formation.

[0051] (Heat shrinkage rate at 120°C) The upper limit of the longitudinal heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 2.0%, more preferably 1.5%, even more preferably 1.2%, and particularly preferably 1.0%. If it is 2.0% or less, misalignment of the printing pitch when transferring printing ink becomes less likely. The upper limit of the widthwise heat shrinkage rate at 120°C is 5.0%, preferably 4.0%, more preferably 3.5%, and particularly preferably 2.5%. If it is 5.0% or less, wrinkles are less likely to occur during heat sealing. If the longitudinal heat shrinkage rate at 120°C is smaller than the widthwise heat shrinkage rate at 120°C, misalignment of the print pitch during ink transfer becomes less likely. The balance between the longitudinal and widthwise heat shrinkage rates at 120°C can be kept within a certain range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature.

[0052] If the longitudinal heat shrinkage rate at 120°C is smaller than the widthwise heat shrinkage rate at 120°C, misalignment of the print pitch during ink transfer becomes less likely. The balance between the longitudinal and widthwise heat shrinkage rates at 120°C can be kept within a certain range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature.

[0053] (Refractive index) The lower limit of the longitudinal refractive index (Nx) of the biaxially oriented polypropylene film of the present invention is preferably 1.4950, more preferably 1.4970, and even more preferably 1.4980. A refractive index of 1.4950 or higher tends to increase the rigidity of the film. The upper limit of the longitudinal refractive index (Nx) is preferably 1.5100, more preferably 1.5070, and even more preferably 1.5050. A refractive index of 1.5100 or lower tends to provide a good balance of longitudinal-width properties of the film.

[0054] The lower limit of the refractive index (Ny) in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 1.5230, preferably 1.5235, and more preferably 1.5240. A refractive index of 1.5230 or higher tends to increase the rigidity of the film. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, and even more preferably 1.5270. A refractive index of 1.5280 or lower tends to provide a good balance of longitudinal-width properties of the film.

[0055] The lower limit of the refractive index (Nz) in the thickness direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4960, more preferably 14965, and even more preferably 1.4970. A refractive index of 1.4960 or higher makes it easier to increase the rigidity of the film. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and even more preferably 1.5010. A refractive index of 1.5020 or lower makes it easier to increase the heat resistance of the film. The refractive index can be kept within a specified range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature.

[0056] (△Ny) The lower limit of △Ny for the biaxially oriented polypropylene film of the present invention is 0.0220, preferably 0.0225, more preferably 0.0228, and even more preferably 0.0230. A value of 0.0220 or higher tends to increase the rigidity of the film. The upper limit of △Ny is preferably 0.0270 as a practical value, more preferably 0.0265, even more preferably 0.0262, and particularly preferably 0.0260. A value of 0.0270 or lower tends to result in good thickness uniformity. △Ny can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature of the film. △Ny is calculated using the following formula, where Nx, Ny, and Nz are the refractive indices along the longitudinal, width, and thickness directions of the film, respectively. It represents the degree of orientation in the width direction within the overall orientation of the film in the longitudinal, width, and thickness directions. △Ny=Ny-[(Nx+Nz) / 2]

[0057] (Coefficient of surface orientation) The lower limit of the plane orientation coefficient (ΔP) of the biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and even more preferably 0.0140. A value of 0.0135 or higher indicates good balance in the plane direction of the film and good thickness uniformity. The upper limit of the plane orientation coefficient (ΔP) is preferably 0.0155, more preferably 0.0152, and even more preferably 0.0150 as a practical value. A value of 0.0155 or lower tends to result in excellent heat resistance at high temperatures. The plane orientation coefficient (ΔP) can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature. The plane orientation coefficient (ΔP) was calculated using the formula [(Nx+Ny) / 2]-Nz.

[0058] (X-ray orientation degree) The lower limit of the X-ray orientation degree calculated from the Wh of the biaxially oriented polypropylene film of the present invention using the following formula is preferably 0.860, more preferably 0.867, and even more preferably 0.872. Setting it to 0.860 or higher makes it easier to increase rigidity. The X-ray orientation degree is calculated as (180-Wh) / 180. The upper limit of the X-ray orientation degree is preferably 0.911, more preferably 0.906, and even more preferably 0.900. Setting it to 0.911 or less helps stabilize film formation.

[0059] (Hayes) The upper limit of the haze of the biaxially oriented polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, even more preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. A haze of 5.0% or less makes it easy to use in applications where transparency is required. The lower limit of the haze is preferably 0.1%, more preferably 0.2%, even more preferably 0.3%, and particularly preferably 0.4% as a practical value. A haze of 0.1% or more makes it easy to manufacture. The haze can be kept within the range by adjusting the cooling roll (CR) temperature, the widthwise stretching temperature, the tenter preheating temperature before widthwise stretching, the widthwise stretching temperature, or the heat setting temperature, or the amount of components with a molecular weight of 100,000 or less in the polypropylene resin, but it may increase with the addition of anti-blocking agents or the application of a sealing layer.

[0060] (Practical characteristics of the film) The practical properties of the biaxially oriented polypropylene film of the invention will be described below.

[0061] (Wrinkles from heat sealing) To form food packaging bags, the contents are filled into pre-made bags, and the film is heated to melt and fuse, creating a seal. This process is often carried out similarly when filling bags while they are being made. Typically, a sealant film made of polyethylene or polypropylene is laminated onto a base film, and these sealant film surfaces are fused together. The heating method involves applying pressure from a heating plate on the base film side to press and seal the film, with a seal width of approximately 10 mm being common. During this process, the base film is also heated, causing shrinkage and resulting wrinkles. Fewer wrinkles are desirable for bag durability and to increase purchasing intent. While the sealing temperature may be around 120°C, higher temperatures are required to increase the bag-making speed, and even then, smaller shrinkage is preferable. When a zipper is fused to the opening of the bag, an even higher sealing temperature is required.

[0062] (Print pitch misalignment) Packaging films typically consist of a laminated film made of a printed base film and a sealant film. Bags are manufactured using bag-making machines, and various types of bags are used, including three-side seal bags, standing bags, and gusseted bags. Print pitch misalignment is thought to occur because the film's base material expands and contracts due to tension and heat applied during the printing process. Eliminating defective products due to print pitch misalignment is important for the efficient use of resources and for increasing consumer purchasing intent.

[0063] (Film processing) The biaxially oriented polypropylene film of the present invention can be printed using letterpress printing, lithographic printing, intaglio printing, stencil printing, or transfer printing methods, depending on the application. Furthermore, unstretched sheets, uniaxially oriented films, and biaxially oriented films made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester can be laminated together as a sealant film to provide heat-sealing properties. To further enhance gas barrier properties and heat resistance, unstretched sheets, uniaxially oriented films, and biaxially oriented films made of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol can be provided as intermediate layers between the biaxially oriented polypropylene film and the sealant film. Adhesives applied by dry lamination or hot-melt lamination can be used to laminate the sealant films. To enhance gas barrier properties, aluminum or inorganic oxides can be deposited onto biaxially oriented polypropylene films, intermediate films, or sealant films. Vacuum deposition, sputtering, and ion plating can be used as deposition methods, but vacuum deposition of silica, aluminum, or mixtures thereof is particularly preferred.

[0064] The biaxially oriented polypropylene film of the present invention can be made suitable for packaging fresh produce such as vegetables, fruits, and flowers, which require high freshness, by adjusting the amount of antifogging agents in the film, such as polyhydric alcohol fatty acid esters, higher fatty acid amines, higher fatty acid amides, and ethylene oxide adducts of higher fatty acid amines and amides, to a range of 0.2 to 5% by mass.

[0065] Furthermore, within limits that do not impair the effects of the present invention, various additives for improving quality such as lubricity and antistatic properties may be incorporated, such as waxes, lubricants such as metal soaps, plasticizers, processing aids, heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers to improve productivity. [Industrial applicability]

[0066] Because the biaxially oriented polypropylene film of the present invention has the above-mentioned superior properties not found in conventional films, it can be preferably used in packaging bags, and it is also possible to make the film thinner than conventional films.

[0067] Furthermore, it is suitable for applications that use high temperatures, such as insulating films for capacitors and motors, backsheets for solar cells, barrier films for inorganic oxides, and base films for transparent conductive films such as ITO, as well as applications that require rigidity, such as separator films. In addition, it enables coating and printing processes at high temperatures using coating agents, inks, and laminating adhesives that were previously difficult to use, which is expected to improve production efficiency. [Examples]

[0068] The present invention will be described in detail below with reference to examples. The characteristics were measured and evaluated by the following methods. (1) Melt flow rate The melt flow rate (MFR) was measured in accordance with JIS K 7210, at a temperature of 230°C and a load of 2.16 kgf.

[0069] (2) Mesopentat fraction The mesopentade fraction ([mmmm]%) of polypropylene resin was measured using 13C-NMR. The mesopentade fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13C-NMR measurements were performed using a BRUKER AVANCE500, with 200 mg of sample being subjected to an 8:1 ratio of o-dichlorobenzene to deuterated benzene. The mixture of two was dissolved at 135°C and then incubated at 110°C.

[0070] (3) The number-average molecular weight, weight-average molecular weight, and amount of components with a molecular weight of 100,000 or less of the polypropylene resin were determined using molecular weight distribution gel permeation chromatography (GPC) and expressed as PP equivalent molecular weight based on monodisperse polystyrene. When the baseline was not clear, the baseline was set within the range from the lowest point of the high molecular weight side of the elution peak closest to the elution peak of the standard substance to the lowest point of the high molecular weight side of the tail. The GPC measurement conditions are as follows: Equipment: HLC-8321PC / HT (manufactured by Tosoh Corporation) Detector: RI Solvent: 1,2,4-Trichlorobenzene + Dibutylhydroxytoluene (0.05%) Columns: TSKgelguardcolumnHHR(30)HT (7.5mm I.D. × 7.5cm) × 1 + TSKgelGMHHR-H(20)HT (7.8mm I.D. × 30cm) × 3 Flow rate: 1.0mL / min Injection volume: 0.3mL Measurement temperature: 140℃ The number-average molecular weight (Mn) and mass-average molecular weight (Mw) are defined by the following equations, based on the number of molecules (Ni) of molecular weight (Mi) at each elution position of the GPC curve obtained via the molecular weight calibration curve. Number average molecular weight: Mn=Σ(N i ·M i ) / ΣN i Mass average molecular weight: Mw=Σ(Ni·M i 2 ) / Σ(N i ·Mi ) Here, the molecular weight distribution can be obtained as Mw / Mn. Furthermore, the proportion of components with a molecular weight of 100,000 or less was determined from the integral curve of the molecular weight distribution obtained by GPC.

[0071] (4) Crystallization temperature (Tc), melting temperature (Tm) Thermal measurements were performed under a nitrogen atmosphere using a Q1000 differential scanning calorimeter manufactured by T.A. Instruments. Approximately 5 mg was cut from a polypropylene resin pellet and sealed in an aluminum pan for measurement. The temperature was raised to 230°C and held for 5 minutes, then cooled to 30°C at a rate of -10°C / min, and the exothermic peak temperature was defined as the crystallization temperature (Tc). The heat of crystallization (ΔHc) was determined by setting a baseline so that the area of ​​the exothermic peak was smoothly connected from the start to the end of the peak. The temperature was then held at 30°C for 5 minutes, and the temperature was raised to 230°C at a rate of 10°C / min, and the main endothermic peak temperature was defined as the melting temperature (Tm).

[0072] (5) Film thickness The film thickness was measured using a Seiko EM Miltron 1202D.

[0073] (6) Hayes Measurements were taken using an NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. at 23°C in accordance with JIS K7105.

[0074] (7) X-ray half-width, degree of orientation Measurements were performed using the transmission method with an X-ray diffractometer (Rigaku RINT2500). X-rays with a wavelength of 1.5418 Å were used, and a scintillation counter was used as the detector. Samples were prepared by stacking films to a thickness of 500 μm. The sample stage was placed at the diffraction peak position (diffraction angle 2θ = 14.1°) of the (110) plane of the α-type crystal of polypropylene resin, and the sample was rotated 360° around the thickness direction of the film to obtain the azimuthal angle dependence of the diffraction intensity of the (110) plane. From this azimuthal angle dependence, the full width at half maximum (FWH) of the diffraction peak originating from the oriented crystals in the width direction of the film was determined. Furthermore, the degree of X-ray orientation was calculated using Wh and the following formula. X-ray orientation degree=(180-Wh) / 180

[0075] (8) Refractive index, ΔNy, surface orientation coefficient Measurements were taken using an Abbe refractometer manufactured by Atago Corporation at a wavelength of 589.3 nm and a temperature of 23°C. The refractive indices along the longitudinal and width directions of the film were denoted as Nx and Ny, respectively, and the refractive index along the thickness direction was denoted as Nz. ΔNy was calculated using Nx, Ny, and Nz with the formula Ny - [(Nx + Nz) / 2]. The surface orientation coefficient (ΔP) was calculated using the formula [(Nx + Ny) / 2] - Nz.

[0076] (9) Tensile test The tensile strength in the longitudinal and widthwise directions of the film was measured at 23°C in accordance with JIS K 7127. Samples were cut from the film to a size of 15 mm x 200 mm, and set in a tensile testing machine (Instron 5965 dual-column benchtop testing machine, manufactured by Instron Japan Company Limited) with a chuck width of 100 mm. Tensile tests were performed at a tensile speed of 200 mm / min. From the obtained strain-stress curve, Young's modulus was determined from the slope of the straight portion in the initial stretching phase, and the stress at 5% stretch (F5) was determined. Tensile breaking strength and tensile breaking elongation were defined as the strength and elongation at the point of fracture, respectively.

[0077] (10) Thermal shrinkage The following method was used to measure the film's properties, in accordance with JIS Z 1712. The film was cut to a length of 20 mm with a width of 20 mm, and then cut in both the longitudinal and width directions. The cut pieces were suspended in a hot air oven at 120°C or 150°C and heated for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the length shrunk to the original length.

[0078] (Example 1) As the polypropylene resin, 80 parts by weight of propylene homopolymer PP-1 (Sumitomo Noblen FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.), with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C, was blended with 20 parts by weight of propylene homopolymer PP-2 (EL80F5, manufactured by Sumitomo Chemical Co., Ltd.), with MFR = 11 g / 10 min, [mmmm] = 98.8%, Tc = 116.5°C, and Tm = 161.5°C. The material was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then immediately placed in a 20°C water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction using two pairs of rolls at 142°C, then clipped at both ends and guided into a hot air oven. After preheating to 170°C, it was stretched 12 times in the width direction at 167°C as the first stage. Immediately after the widthwise stretching, it was cooled at 100°C while still held by the clips, and then heat-treated at 165°C without any relaxation in the width direction. The thickness of the resulting film was 20.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, the resulting film had high rigidity and low thermal shrinkage at high temperatures.

[0079] (Example 2) The procedure was the same as in Example 1, except that the film was stretched in the width direction at 162°C and heat-treated at 170°C. The thickness of the obtained film was 20.8 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, the obtained film had high rigidity and low thermal shrinkage at high temperatures.

[0080] (Example 3) The procedure was the same as in Example 1, except that the film was stretched in the width direction at 162°C. The thickness of the obtained film was 20.7 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, the resulting film had high rigidity and low thermal shrinkage at high temperatures.

[0081] (Example 4) The procedure was the same as in Example 1, except that the film was stretched in the width direction at 162°C and cooled at 140°C. The thickness of the obtained film was 20.6 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. As shown in Table 3, the resulting film had high rigidity and low thermal shrinkage at high temperatures.

[0082] (Comparative Example 1) As the polypropylene resin, PP-1 (Sumitomo Noblen FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.) was used, with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C. It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then immediately placed in a 20°C water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction using two pairs of rolls at 145°C, then both ends were clipped, and it was introduced into a hot air oven. After preheating to 170°C, it was stretched 6 times in the width direction as the first stage at 160°C, and then stretched 1.36 times as the second stage at 145°C, for a total stretch of 8.2 times. Immediately after the width direction stretching, it was cooled at 100°C while still held by the clips, and then heat-set at 163°C. The thickness of the resulting film was 18.7 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. The first stage of the transverse stretching process was designated as the early stage, and the second stage as the later stage. As shown in Table 3, the tensile elongation at break and the thermal shrinkage rate at 150°C were inferior.

[0083] (Comparative Example 2) As the polypropylene resin, a blend of 80 parts by weight of PP-1 and 20 parts by weight of PP-2 (Sumitomo Chemical Co., Ltd., EL80F5), a propylene homopolymer with MFR = 11 g / 10 min, [mmmm] = 98.8%, Tc = 116.5°C, and Tm = 161.5°C, was used. The procedure was the same as in Comparative Example 1, except that the stretching temperature in the longitudinal direction was 142°C, the stretching temperature for the first stage in the width direction was 162°C, and the heat setting temperature was 165°C. The thickness of the obtained film was 21.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0084] (Comparative Example 3) The procedure was the same as in Comparative Example 2, except that a 3% relaxation was applied during heat setting. The thickness of the obtained film was 21.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0085] (Comparative Example 4) The procedure was the same as in Comparative Example 2, except that the stretching temperature in the longitudinal direction was 145°C and the cooling temperature immediately after stretching in the width direction was 140°C. The thickness of the obtained film was 18.9 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0086] (Comparative Example 5) The procedure was the same as in Comparative Example 2, except that after stretching in the width direction, the film was heat-set at 165°C while still held in the clip without cooling. The thickness of the resulting film was 19.5 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties included poor thermal shrinkage at 150°C.

[0087] (Comparative Example 6) The procedure was the same as in Comparative Example 2, except that the second stretching temperature in the width direction was set to 155°C. The thickness of the resulting film was 20.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0088] (Comparative Example 7) The procedure was the same as in Comparative Example 2, except that the longitudinal stretching ratio was set to 4.8 times. The thickness of the obtained film was 19.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0089] (Comparative Example 8) In the widthwise stretching, the stretching ratio for the first stage was set to 6.6 times and the stretching ratio for the second stage to 1.5 times, resulting in a total stretching ratio of 9.9 times. The procedure was the same as in Comparative Example 2. The thickness of the obtained film was 20.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties included low tensile elongation at break and low tensile elongation at break.

[0090] (Comparative Example 9) Using PP-1 as the polypropylene resin, the material was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then immersed in a 20°C water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction at 143°C, and then stretched 8.2 times in the width direction using a tenter with a preheating temperature of 170°C and a stretching temperature of 158°C, followed by heat setting at 168°C. The thickness of the obtained film was 18.6 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film formation conditions, and Table 3 shows its physical properties. As shown in Table 3, its tensile breaking strength and tensile breaking elongation were inferior.

[0091] (Comparative Example 10) The procedure was the same as in Comparative Example 9, except that a blend of 80 parts by weight of PP-1 and 20 parts by weight of PP-2 was used as the polypropylene resin. The thickness of the resulting film was 20.0 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film formation conditions, and Table 3 shows its physical properties. As shown in Table 3, the tensile breaking strength was poor.

[0092] (Comparative Example 11) As the polypropylene resin, PP-3 (manufactured by Nippon Polypropylene Co., Ltd., FL203D) with MFR = 3g / 10 min, [mmmm] = 94.8%, Tc = 117.2℃, and Tm = 160.6℃ was used. It was extruded into a sheet from a T-die at 250℃, brought into contact with a cooling roll at 20℃, and then immediately placed in a 20℃ water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction at 135℃, and in the widthwise stretching on a tenter, the preheating temperature was set to 166℃, and the first stretching stage was performed at 155℃ to a 6x extent. The second stretching stage was performed at 139℃ to a 1.36x extent, for a total stretch of 8.2 times. Immediately after widthwise stretching, it was cooled at 95℃ while still held in a clip, and then heat-treated at 158℃ without widthwise relaxation. The thickness of the obtained film was 19.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film formation conditions, and Table 3 shows its physical properties. As shown in Table 3, the thermal shrinkage rate at 150°C was poor.

[0093] (Comparative Example 12) PP-4 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) with MFR = 2.7 g / 10 min, [mmmm] = 98.7%, Tc = 114.7°C, and Tm = 163.0°C was used as the polypropylene raw material. It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then immediately placed in a 20°C water bath. Subsequently, it was stretched 4.5 times in the longitudinal direction at 145°C, and in the widthwise stretching on a tenter, the preheating temperature was set to 170°C, and the first stretching stage was performed at 160°C to a 6x extension. The second stretching stage was performed at 145°C to a 1.36x extension, for a total stretch of 8.2 times. Immediately after widthwise stretching, it was cooled at 100°C while still held in a clip, and then heat-treated at 163°C without widthwise relaxation. The thickness of the obtained film was 21.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film formation conditions, and Table 3 shows its physical properties. As shown in Table 3, its tensile elongation at break and thermal shrinkage at 150°C are inferior. It was something.

[0094] (Comparative Example 13) PP-4 was used as the polypropylene resin. It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then immediately placed in a 20°C water bath. Subsequently, it was stretched 5.8 times in the longitudinal direction at 130°C, then the film was heated in a tenter with a preheating temperature of 167°C, followed by stretching 8.6 times in the width direction at a stretching temperature of 161°C, and then heat-set at 130°C with 10% relaxation, followed by a second heat-set at 140°C. The thickness of the obtained film was 13.4 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film formation conditions, and Table 3 shows its physical properties. As shown in Table 3, its tensile elongation at break and thermal shrinkage at 150°C were inferior.

[0095] (Comparative Example 14) The procedure was the same as in Example 1, except that the film was stretched eightfold in the width direction at 162°C and cooled at 140°C. The thickness of the obtained film was 19.7 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0096] (Comparative Example 15) The procedure was the same as in Example 1, except that the film was stretched eightfold in the width direction at 162°C. The thickness of the obtained film was 20.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film formation conditions. As shown in Table 3, its physical properties were poor in terms of tensile strength and tensile elongation at break.

[0097] [Table 1]

[0098] [Table 2A]

[0099] [Table 2B]

[0100] Table 3A

[0101] Table 3B

Claims

1. A biaxially oriented polypropylene film that satisfies the following formulas (1) to (7). (1) The thermal shrinkage rate at 150°C is 10% or less in the longitudinal direction and 24% or less in the width direction. (2) The tensile elongation at break is 195% or more in the longitudinal direction at 23°C. (3) The refractive index Nx in the longitudinal direction is 1.5050 or less. (4) The refractive index Nz in the thickness direction is 1.5010 or less. (5) The biaxially oriented polypropylene film has a tensile breaking strength in the width direction of 400 MPa or more at 23°C. (6) The melt flow rate of the polypropylene resin constituting the biaxially oriented polypropylene film is 4.0 g / 10 min or more. (7) The amount of polypropylene resin components with a molecular weight of 100,000 or less that constitute the biaxially oriented polypropylene film is 35% by mass or more.

2. The biaxially oriented polypropylene film according to claim 1, wherein the 120°C heat shrinkage rate of the biaxially oriented polypropylene film is 2.0% or less in the longitudinal direction and 5.0% or less in the width direction, and the 120°C heat shrinkage rate in the longitudinal direction is smaller than the 120°C heat shrinkage rate in the width direction.

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the refractive index Ny in the width direction of the biaxially oriented polypropylene film is 1.5230 or more, and ΔNy is 0.0220 or more.

4. The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the haze of the biaxially oriented polypropylene film is 5.0% or less.

5. The biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein the mesopentad fraction of the polypropylene resin constituting the biaxially oriented polypropylene film is 97.0% or more.

6. The biaxially oriented polypropylene film according to any one of claims 1 to 5, wherein the crystallization temperature of the polypropylene resin constituting the biaxially oriented polypropylene film is 105°C or higher, and the melting point is 160°C or higher.

7. The biaxially oriented polypropylene film according to any one of claims 1 to 6, wherein the degree of orientation of the biaxially oriented polypropylene film is 0.85 or more.

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