TW202409115A - Biaxially-oriented polypropylene film - Google Patents

Abstract

Provided is a biaxially-oriented polypropylene film that has high rigidity, excellent heat-resistance at a temperature as high as 150 DEG C, easily maintains a bag shape when used as a packaging bag, undergoes minimal dimensional change during printing, and has few wrinkles in a sealing part when heat sealed. The biaxially-oriented polypropylene film has a full width at half maximum of a peak derived from crystals oriented in the width direction for azimuth dependence of the polypropylene [alpha]-type crystal (110) surface of 27 DEG, as obtained by wide-angle X-ray diffraction measurement , and heat shrinkage at 150 DEG C of not more than 10% in the longitudinal direction and not more than 30% in the width direction.

Description

Biaxially oriented polypropylene film

The present invention relates to a biaxially oriented polypropylene film having excellent rigidity and heat resistance. Specifically, the present invention relates to a biaxially oriented polypropylene film which is easy to maintain the bag shape when made into a packaging bag and has few wrinkles at the sealing part when heat-sealed, so it is suitable for packaging bags.

Biaxially oriented polypropylene films are moisture-proof and have the necessary rigidity and heat resistance, so they can be used for packaging or industrial purposes. In recent years, as their uses have expanded, higher performance, especially increased rigidity, has been required. In addition, considering the environment, it is necessary to reduce the volume (thinner the film thickness) while maintaining strength, and for this purpose, the rigidity must be significantly improved. As a means to improve the rigidity, it is known to improve the crystallinity or melting point of the polypropylene resin by improving the catalyst or process technology during the polymerization of the polypropylene resin. However, despite such improvements, there has not yet been a polypropylene resin with sufficient rigidity. Axis-oriented polypropylene film.

The following method is proposed: in the manufacturing process of a biaxially oriented polypropylene film, after stretching in the width direction, the film is relaxed and heat-treated in the first stage at a temperature below the temperature during the stretching in the width direction, and heat-treated in the second stage from the temperature of the first stage to the stretching temperature in the width direction (for example, refer to reference 1, etc.); or after stretching in the width direction, the film is stretched in the length direction (for example, refer to reference 2, etc.). However, although the film described in patent document 2 has excellent rigidity, it is easy to produce wrinkles in the sealing part after heat sealing, and has poor heat resistance. In addition, the film described in patent document 1 has low orientation and insufficient rigidity. [Prior art document] [Patent document]

[Patent Document 1] International Publication No. WO2016/182003. [Patent Document 2] Japanese Patent Application Publication No. 2013-177645.

[The problem that the invention wants to solve]

The subject of the present invention is to solve the above-mentioned problem. That is, it is about a biaxially oriented polypropylene film with excellent film rigidity and heat resistance up to 150°C. Specifically, it is to provide a biaxially oriented polypropylene film that is easy to maintain the bag shape when made into a packaging bag and has few wrinkles in the sealed part and its surroundings when heat-sealed. [Means for solving the problem]

As a result of the research efforts made by the inventors in order to achieve the above-mentioned purpose, it is found that by making a biaxially oriented polypropylene film in which the half-value width of the peak of oriented crystallization in the width direction is less than 27° in the azimuthal angle dependence of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray diffraction measurement, and the thermal shrinkage rate at 150°C is less than 10% in the length direction and less than 30% in the width direction, a biaxially oriented polypropylene film with excellent film rigidity and heat resistance up to 150°C can be obtained.

In this case, it is preferable that the thermal shrinkage rate of the biaxially aligned polypropylene film at 120°C is 2.0% or less in the length direction and 5.0% or less in the width direction, and the thermal shrinkage rate at 120°C in the length direction is smaller than that in the width direction. Thermal shrinkage rate at 120℃.

In addition, in this case, it is preferable that the refractive index Ny in the width direction of the biaxially aligned polypropylene film is 1.5230 or more, and ΔNy is 0.0220 or more.

Furthermore, in this case, it is preferred that the haze of the biaxially aligned polypropylene film be 5.0% or less.

Furthermore, in this case, it is preferable that the meso pentad component ratio of the polypropylene resin constituting the biaxially aligned polypropylene film is 97.0% or more.

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

Furthermore, in this case, it is preferable that the melt flow rate of the polypropylene resin constituting the biaxially aligned polypropylene film is 4.0 g/10 minutes or more.

Furthermore, in this case, it is preferred that the amount of components having a molecular weight of 100,000 or less of the polypropylene resin constituting the biaxially aligned polypropylene film is 35% by mass or more.

Furthermore, in this case, it is preferable that the orientation degree of the biaxially aligned polypropylene film is 0.85 or more. [Invention effect]

The biaxially oriented polypropylene film of the present invention has high rigidity and excellent heat resistance to high temperatures up to 150°C, so it is easy to maintain the bag shape when made into a packaging bag, and there are few wrinkles at the sealed portion during heat sealing, so a biaxially oriented polypropylene film suitable for packaging bags can be obtained. In addition, since the biaxially oriented polypropylene film has excellent rigidity, it can maintain strength even if the thickness of the film is reduced, and can also be appropriately used for applications requiring higher rigidity.

Hereinafter, the biaxially aligned polypropylene film of the present invention will be described in further detail. The biaxially aligned polypropylene film of the present invention is composed of a polypropylene resin composition with polypropylene resin as the main component. In addition, the so-called "main component" means that the proportion of the polypropylene resin in the polypropylene resin composition is 90 mass% or more, more preferably 93 mass% or more, still more preferably 95 mass% or more, and particularly preferably More than 97% by mass.

(polypropylene resin) The polypropylene resin used in the present invention may be a polypropylene homopolymer or a copolymer of polypropylene, ethylene and/or an α-olefin having 4 or more carbon atoms. Preferably, it is a propylene homopolymer that does not substantially contain ethylene and/or an α-olefin having 4 or more carbon atoms. Even if it contains ethylene and/or an α-olefin component having 4 or more carbon atoms, it is preferably ethylene. and/or the content of the α-olefin component having 4 or more carbon atoms is 1 mol% or less. The upper limit of the component amount is more preferably 0.5 mol%, further preferably 0.3 mol%, further preferably 0.1 mol%. If it is within the above range, crystallinity can be easily improved. Examples of the α-olefin component having 4 or more carbon atoms constituting this copolymer 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, 1-eicosene, etc. As the polypropylene resin, two or more different polypropylene homopolymers, copolymers of polypropylene and ethylene and/or α-olefin having 4 or more carbon atoms, and mixtures thereof can be used.

(three-dimensional regularity) The index of stereoregularity of the polypropylene resin used in the present invention is the meso pentad ratio ([mmmm]%), which is preferably in the range of 97.0% to 99.9%, and more preferably 97.5% to 99.7%. within the range, more preferably within the range of 98.0% to 99.5%, particularly preferably within the range of 98.5% to 99.3%. If it is 97.0% or more, the crystallinity of the polypropylene resin becomes high, and the melting point, crystallinity, and crystal orientation of the film's crystals increase, making it easier to obtain rigidity and high-temperature heat resistance. If it is 99.9% or less, it will be easier to suppress costs in terms of polypropylene production, and it will be less likely to break during film production. More preferably, it is 99.5% or less. The meso pentad ratio is measured by the nuclear magnetic resonance method (so-called NMR method). In order to set the meso pentad component ratio of the polypropylene resin within the above range, the following method can be preferably used: the method of washing the obtained polypropylene resin powder with a solvent such as n-heptane; Or methods for appropriately selecting catalysts and/or cocatalysts, selecting components of polypropylene resin compositions, etc.

(Melting temperature) The lower limit of the melting temperature (Tm) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention measured by DSC (Differential Scanning Calorimeters) is preferably 160°C, more preferably 161°C, further preferably 162°C, and further preferably 163°C. If Tm is 160°C or higher, it is easy to obtain rigidity and high temperature heat resistance. The upper limit of Tm is preferably 170°C, more preferably 169°C, further preferably 168°C, further preferably 167°C, and particularly preferably 166°C. If Tm is 170°C or lower, it is easy to suppress the cost increase from the perspective of polypropylene manufacturing, and it becomes difficult to break during film making. By adding a nucleating agent to the aforementioned polypropylene resin, the melting temperature can be further increased. The so-called Tm refers to the main peak temperature of the endothermic peak accompanying melting observed when 1 mg to 10 mg of a sample is placed in an aluminum pan and set on a differential scanning thermoanalyzer (DSC), melted at 230°C for 5 minutes under a nitrogen atmosphere, cooled to 30°C at a scanning speed of -10°C/min, and then kept for 5 minutes, and then heated at a scanning speed of 10°C/min.

(Crystallization temperature) The lower limit of the crystallization temperature (Tc) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention measured by DSC is 105°C, preferably 108°C, and more preferably 110°C. If Tc is 105°C or higher, crystallization is easily carried out in the width direction stretching and the subsequent cooling step, and rigidity and high temperature heat resistance are easily obtained. The upper limit of Tc is preferably 135°C, more preferably 133°C, more preferably 132°C, further preferably 130°C, particularly preferably 128°C, and most preferably 127°C. If Tc is 135°C or lower, it is not easy to increase the cost from the perspective of polypropylene manufacturing, and it becomes difficult to break during film making. The so-called Tc is the main peak temperature of the exothermic peak observed when 1 mg to 10 mg of sample is placed in an aluminum pan and placed in a DSC, melted at 230°C for 5 minutes under a nitrogen atmosphere, and cooled to 30°C at a scanning speed of -10°C/min. The crystallization temperature can be further increased by adding a nucleating agent to the aforementioned polypropylene resin.

(melt flow rate) The melt flow rate (MFR; melt mass-flow rate) of the polypropylene resin constituting the biaxially aligned polypropylene film of the present invention is measured according to the conditions M (230°C, 2.16kgf) of JIS K 7210 (1995). Among the circumstances, the preferred range is 4.0g/10min to 30g/10min, the more preferred range is 4.5g/10min to 25g/10min, the more preferred range is 4.8g/10min to 22g/10min, and the most preferred range is 5.0g/10min to 20g/10min, the best is 6.0g/10min to 20g/10min. If the melt flow rate (MFR) of the polypropylene resin is 4.0 g/10 minutes or more, a biaxially aligned polypropylene film with low thermal shrinkage can be easily obtained. In addition, when the melt flow rate (MFR) of the polypropylene resin is 30 g/10 minutes or less, film forming properties of the film can be easily maintained.

From the perspective of film properties, the lower limit of the melt flow rate (MFR) (230°C, 2.16kgf) of the polypropylene resin constituting the film is preferably 5.0g/10min, more preferably 5.5g/10min, more preferably 6.0g/10min, particularly preferably 6.3g/10min, and most preferably 6.5g/10min. If the melt flow rate (MFR) of the polypropylene resin is 5.0g/10min or more, the amount of low molecular weight components of the polypropylene resin constituting the film increases. Therefore, by adopting the width direction stretching step in the film forming step described later, in addition to further promoting the orientation crystallization of the polypropylene resin and making it easier to increase the crystallinity of the film, the entanglement of the polypropylene molecular chains in the amorphous part becomes less, and it is easier to improve the heat resistance. In order to set the melt flow rate (MFR) of the polypropylene resin within the above range, it is preferable to adopt a method of controlling the average molecular weight or molecular weight distribution of the polypropylene resin.

That is, the lower limit of the amount of components with a molecular weight of 100,000 or less in the GPC (Gel Permeation Chromatography) integrated curve of the polypropylene resin constituting the film of the present invention is preferably 35 mass %, more preferably 38 % by mass, more preferably 40% by mass, still more 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 integration curve is preferably 65 mass%, more preferably 60 mass%, and still more preferably 58 mass%. If the amount of components with a molecular weight of 100,000 or less in the GPC integral curve is 65% by mass or less, the film strength is less likely to decrease. At this time, if high molecular weight components or long-chain branched components with a long relaxation time are included, the amount of components with a molecular weight of less than 100,000 in the polypropylene resin can be easily adjusted without greatly changing the overall viscosity of the polypropylene resin. It does not have much influence on rigidity or thermal shrinkage and easily improves film forming properties.

(Molecular weight distribution) For the polypropylene resin used in the present invention, the lower limit of the mass average molecular weight (Mw)/number average molecular weight (Mn), which is an index of the breadth of the molecular weight distribution, is preferably 3.5, more preferably 4.0, still more preferably 4.5, and particularly preferably 5.0. The upper limit of Mw/Mn is preferably 30, more preferably 25, still more preferably 23, particularly preferably 21, and most preferably 20. Mw/Mn can be obtained using gel permeation chromatography (GPC). If Mw/Mn is within the above range, the amount of components with a molecular weight of less than 100,000 is likely to increase.

In addition, the molecular weight distribution of polypropylene resin can be adjusted by: polymerizing components of different molecular weights in multiple stages with a series of equipment; blending components of different molecular weights with a kneader off-line; blending with catalysts with different properties for polymerization; using a catalyst that can achieve the desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC, in a GPC chart with the logarithm (logM) of the molecular weight (M) on the horizontal axis and the differential distribution value (weight fraction in logM) on the vertical axis, can be a smooth molecular weight distribution with a single peak, or a molecular weight distribution with multiple peaks or shoulders.

(Film production method of biaxially aligned polypropylene film) The biaxially aligned polypropylene film of the present invention is preferably obtained by producing an unstretched sheet composed of a polypropylene resin composition containing the above-mentioned polypropylene resin as a main component, and biaxially stretching the film. As a biaxial stretching method, it can be obtained by any of the blow molding synchronous biaxial stretching method, the tenter synchronous biaxial stretching method, and the tenter stepwise biaxial stretching method. However, it depends on the film production stability, thickness From the perspective of uniformity, it is better to use the tenter step-by-step biaxial stretching method. In particular, it is preferable to extend in the width direction after extending in the length direction, but it may also be a method of extending in the width direction and then extending in the length direction.

Next, the manufacturing method of the biaxially oriented polypropylene film of the present invention is described below, but it is not limited to this. In addition, the biaxially oriented polypropylene film of the present invention can also have layers with other functions laminated on at least one side. The lamination can be single-sided or double-sided. At this time, the resin composition of the other layer and the other central layer can also adopt the above-mentioned polypropylene resin composition. In addition, it can also be a resin composition different from the above-mentioned polypropylene resin composition. The number of laminated layers can be 1 layer, 2 layers or 3 layers or more on each single side, but from the perspective of manufacturing, it is preferably 1 layer or 2 layers. As a lamination method, it is preferably co-extruded by, for example, a feed block/method or a multi-manifold method. In particular, when the purpose is to improve the processability of biaxially oriented polypropylene film, a resin layer with heat sealability can be laminated within a range that does not reduce the properties. In addition, in order to provide printability, corona treatment can be applied on one or both sides.

The following describes the case where a tenter frame is used for the step-by-step biaxial stretching method as an example of a single layer. First, a resin composition containing polypropylene resin is heated and melted using a single-screw or twin-screw extruder, and is extruded into a sheet through a T-die, and is then contacted with a cooling roller and cooled to solidify. When the purpose is to accelerate solidification, it is preferable to immerse the sheet cooled by a cooling roller in a water tank or the like to further cool it.

Then, the sheet is passed through two pairs of heated stretching rollers, and the rotation number of the rear stretching roller is increased to stretch the sheet in the length direction to obtain a uniaxially stretched film.

Next, after preheating the uniaxially stretched film, the film ends are held by a tenter-type stretching machine and stretched in the width direction at a specific temperature to obtain a biaxially stretched film. The width direction stretching step is described in detail later.

After the width direction stretching step is completed, the biaxially stretched film is heat treated at a specific temperature to obtain a biaxially aligned film. During the heat treatment step, the film can also be relaxed in the width direction.

The biaxially oriented polypropylene film thus obtained can be subjected to a corona discharge treatment on at least one side as required, and then taken up by a take-up machine to obtain a film roll.

The following is a detailed description of each step. (Extrusion step) First, a polypropylene resin composition with polypropylene resin as the main component is heated and melted in a range of 200°C to 300°C by a single-axis or double-axis extruder, and the molten polypropylene resin composition discharged from the T-die is extruded in a sheet form, and is brought into contact with a metal cooling roller and cooled and solidified. The obtained unstretched sheet is preferably further put into a water tank. The temperature of the cooling roller, or the cooling roller and the water tank is preferably in the range of 10°C to Tc. In the case of improving the transparency of the film, it is preferably cooled and solidified with a cooling roller at a temperature in the range of 10°C to 50°C. If the cooling temperature is set below 50°C, the transparency of the unstretched sheet tends to be high, preferably below 40°C, and more preferably below 30°C. In order to increase the crystal orientation after stepwise biaxial stretching, the cooling temperature is sometimes set to above 40°C, but when using a propylene homopolymer with a meso-pentad fraction of 97.0% or more as described above, setting the cooling temperature below 40°C makes it easy to stretch the subsequent steps, and it is also better to reduce thickness unevenness, and it is more preferably set to below 30°C. The thickness of the unstretched sheet is preferably set to 3500μm or less in terms of cooling efficiency, and is more preferably set to 3000μm or less, and can be appropriately adjusted according to the film thickness after stepwise 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.

(Lengthwise stretching step) The lower limit of the lengthwise stretching ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. If it is within the above range, it is easy to improve the strength and reduce the unevenness of the film thickness. The upper limit of the lengthwise stretching ratio is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. If it is within the above range, the widthwise stretching in the widthwise stretching step is easy and the productivity is improved. The lower limit of the lengthwise stretching temperature is preferably Tm-40°C, more preferably Tm-37°C, and even more preferably Tm-35°C. If it is within the above range, the subsequent widthwise stretching becomes easy and the unevenness of the thickness is reduced. The upper limit of the lengthwise stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, and even more preferably Tm-12°C. If it is in the above range, it is easy to reduce the thermal shrinkage rate, and it is less likely to stick to the stretching roller and become difficult to stretch, or the surface roughness becomes large and the quality is reduced. In addition, the longitudinal direction stretching can also use more than 3 pairs of stretching rollers and stretch in multiple stages of more than 2 stages.

(preheating step) Before the width direction stretching step, the uniaxially stretched film after lengthwise stretching needs to be heated in the range of Tm to Tm+25°C to soften the polypropylene resin composition. By setting it to Tm or more, softening proceeds and stretching in the width direction becomes easy. By setting Tm+25°C or less, the alignment during lateral stretching proceeds and rigidity becomes easier to express. More preferably, it is Tm+2°C to Tm+22°C, and even more preferably, it is Tm+3°C to Tm+20°C. Here, the highest temperature in the preheating step is regarded as the preheating temperature.

(Width direction extension step) In the width direction extension step after the preheating step, the best method is as follows.

In the width direction stretching step, a section (early stage section) is set for stretching at a temperature above Tm-10°C and below the preheating temperature. At this time, the start of the early stage section can be the time point when the preheating temperature is reached, or the time point 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 early stage section of the width direction stretching step is preferably Tm-9°C, more preferably Tm-8°C, and more preferably Tm-7°C. If the stretching temperature in the early stage section is within this range, stretching unevenness is less likely to occur. Following the early stage section, a section (latter stage section) is set at a temperature lower than the early stage section and is stretched at a temperature above Tm-70°C and below Tm-5°C. The upper limit of the stretching temperature in the later stage is preferably Tm-8°C, more preferably Tm-10°C. If the stretching temperature in the later stage is within this range, rigidity becomes easy to show. The lower limit of the stretching temperature in the later stage is preferably Tm-65°C, more preferably Tm-60°C, and even more preferably Tm-55°C. If the stretching temperature in the later stage is within this range, film formation is easy and stable. The film can be cooled immediately after the end of the later stage, that is, when the final stretching ratio in the width direction is reached. The cooling temperature at this time is preferably set to a temperature below the temperature of the later period and above Tm-80℃ to below Tm-15℃, more preferably to a temperature above Tm-80℃ to below Tm-20℃, more preferably to a temperature above Tm-80℃ to below Tm-30℃, and particularly preferably to a temperature above Tm-70℃ to below Tm-40℃. The temperature of the early period and the temperature of the later period can be gradually reduced, or can be reduced in stages or in one stage, or can be fixed separately. If the temperature is gradually reduced, the film is not easy to break, and the thickness change of the film is also easy to reduce. In addition, the thermal shrinkage rate is also easy to reduce, and the whitening of the film is less, so it is better. In the widthwise extension step, the temperature can be gradually reduced from the end of the previous interval to the beginning of the later interval, or it can be reduced in stages or in one phase.

The lower limit of the stretching ratio at the end of the early period of the width direction stretching step is preferably 4 times, more preferably 5 times, still more preferably 6 times, and particularly preferably 6.5 times. The upper limit of the extension ratio at the end of the early period is preferably 15 times, more preferably 14 times, and still more preferably 13 times.

The lower limit of the final width direction stretching ratio in the width direction stretching step is preferably 5 times, more preferably 6 times, more preferably 7 times, and particularly preferably 8 times. If it is 5 times or more, it is easy to improve the rigidity and reduce the unevenness of the film thickness. The upper limit of the width direction stretching ratio is preferably 20 times, more preferably 17 times, and more preferably 15 times. If it is less than 20 times, the thermal shrinkage rate is easy to be reduced and it is not easy to break during stretching.

Thus, by using a polypropylene resin with high stereoregularity and high melting point and adopting the above-mentioned width direction stretching step, even if the stretching ratio is not extremely increased, the molecules of the polypropylene resin are highly aligned in the main orientation direction (equivalent to the width direction in the above-mentioned width direction stretching step), so the crystal orientation in the obtained biaxial alignment film is very strong, and it is easy to generate crystals with high melting points. In addition, since the orientation of the amorphous part between the crystals is also improved in the main orientation direction (equivalent to the width direction in the above-mentioned width direction stretching step), there are many crystals with high melting points around the amorphous part, so at a temperature lower than the melting point of the crystal, the polypropylene molecules in the amorphous part that have been stretched are not easy to relax and are easy to maintain their tension state. Therefore, the biaxial alignment film as a whole can maintain high rigidity even at high temperatures. In addition, it should be noted that by adopting this width direction stretching step, the thermal shrinkage rate at a high temperature of 150°C can also be easily reduced. The reason is that there are many crystals with high melting points around the amorphous part, so at a temperature lower than the melting point of the crystals, the polypropylene resin molecules in the amorphous part that have been stretched are not easy to relax, and the molecules are less entangled with each other.

Further, we should pay attention to the following: by increasing the low molecular weight components of polypropylene resin, it becomes easier to increase the crystallinity of the film, and the molecular chains of polypropylene resin in the amorphous part are less entangled with each other, which can further reduce the thermal shrinkage rate by reducing the thermal shrinkage stress. Considering the previous tendency that if one of the strength and thermal shrinkage rate is improved, the other property will be reduced, this can be regarded as a breakthrough development.

(Heat treatment step) The biaxially stretched film can be heat treated as needed to further reduce the thermal shrinkage rate. The upper limit of the heat treatment temperature is preferably Tm+10℃, and more preferably Tm+7℃. By setting it below Tm+10℃, it is easy to show rigidity, and the roughness of the film surface will not become too large, and the film is not easy to whiten. The lower limit of the heat treatment temperature is preferably Tm-10℃, and more preferably Tm-7℃. If it does not reach Tm-10℃, the thermal shrinkage rate may become high. By adopting the above-mentioned width direction stretching step, even if the heat treatment is performed at a temperature between Tm-10℃ and Tm+10℃, the highly oriented crystals generated in the stretching step are still not easy to melt, and the thermal shrinkage rate can be further reduced without reducing the rigidity of the obtained film. When the purpose is to adjust the thermal shrinkage rate, the film can also be relaxed (relaxed) in the width direction during the heat treatment. The upper limit of the relaxation rate is preferably 10%. If it is within the above range, the film strength is not easy to decrease, and the film thickness change is easy to become small. It is more preferably 8%, more preferably 7%, further preferably 3%, particularly preferably 2%, and the best is 0%.

(film thickness) The thickness of the biaxially aligned polypropylene film of the present invention is set according to each application. However, in order to obtain the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, more preferably 4 μm, especially 8 μm. Optimum is 10μm. When the film thickness is 2 μm or more, the rigidity of the film is easily obtained. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, still more preferably 60 μm, still more 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 step is less likely to decrease. The biaxially aligned polypropylene film system of the present invention is usually formed as a roll with a width of 2000 mm to 12000 mm and a length of about 1000 m to 50000 m, and is wound into a film roll shape. It is further slit according to each application and supplied as slitting rollers with a width of 300mm to 2000mm and a length of about 500m to 5000m. The biaxially aligned polypropylene film of the present invention enables longer film rolls.

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

(Film properties) The biaxially oriented polypropylene film of the present invention has the following characteristics. The "length direction" of the biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction of the film manufacturing step, and the "width direction" refers to the direction orthogonal to the flow direction of the aforementioned film manufacturing step. Regarding the polypropylene film whose flow direction in the film manufacturing step is unknown, when wide-angle X-rays are incident on the film surface in the vertical direction, the scattering peak from the (110) plane of the α-type crystal is scanned in the circumferential direction, and the direction with the maximum diffraction intensity of the diffraction intensity distribution is set as the "length direction", and the direction orthogonal to it is set as the "width direction".

(Half-value width of diffraction peak from oriented crystals) In the azimuthal 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 half-value width (Wh) of the diffraction peak from the oriented crystals in the width direction of the film is 27°, preferably 26°, more preferably 25°, more preferably 24°, and particularly preferably 23°. If the half-value width (Wh) is 27° or less, the rigidity of the film is easily improved. The lower limit of Wh is preferably 13°, more preferably 14°, and more preferably 15°.

(heat shrinkage rate at 150℃) The upper limit of the thermal shrinkage rate in the longitudinal direction of the biaxially aligned polypropylene film of the present invention at 150° C. is 10%, preferably 8.0%, and more preferably 7.0%. The upper limit of the thermal shrinkage rate in the width direction at 150°C is 30%, preferably 25%, more preferably 20%. If the heat shrinkage rate in the length direction is 10% or less and the heat shrinkage rate in the width direction is 30% or less, wrinkles will not easily occur during heat sealing, especially if the heat shrinkage rate in the length direction at 150°C is 8.0% or less and 150 It is preferable that the thermal shrinkage rate in the width direction at ℃ is 20% or less because the strain when welding the clip portion to the opening is small. In order to reduce the thermal shrinkage 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 to 35% by mass when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film.

The biaxially oriented polypropylene film of the present invention is better if it has the following characteristics and structures. (23°C Young's modulus) The lower limit of the Young's modulus of the biaxially oriented polypropylene film of the present invention in the longitudinal direction at 23°C is preferably 2.0 GPa, more preferably 2.1 GPa, more preferably 2.2 GPa, particularly preferably 2.3 GPa, and optimally 2.4 GPa. Above 2.0 GPa, the rigidity is high, so it is easy to maintain the bag shape when making a packaging bag, and it is not easy to cause deformation of the film during processing such as printing. The upper limit of the Young's modulus in the longitudinal direction is preferably 4.0 GPa, more preferably 3.8 GPa, more preferably 3.7 GPa, particularly preferably 3.6 GPa, and optimally 3.5 GPa. Below 4.0 GPa, actual manufacturing is easy, and the balance of properties in the length direction-width direction is easy to optimize. The lower limit of the Young's modulus in the width direction at 23°C of the biaxially oriented polypropylene film of the present invention is preferably 6.0 GPa, more preferably 6.3 GPa, more preferably 6.5 GPa, and particularly preferably 6.7 GPa. Above 6.0 GPa, the rigidity is high, so it is easy to maintain the bag shape when making a packaging bag, and it is not easy to cause deformation of the film during processing such as printing. The upper limit of the Young's modulus in the width direction is preferably 15 GPa, more preferably 13 GPa, and more preferably 12 GPa. If it is 15 GPa or less, actual manufacturing is easy, and the balance of properties in the length direction-width direction is easy to optimize. Young's modulus can be set within a range by adjusting the stretch ratio or relaxation ratio, or adjusting the temperature during film formation.

(Young's modulus at 80°C) The lower limit of the Young's modulus in the length direction at 80°C of the biaxially oriented polypropylene film of the present invention is preferably 0.5 GPa, more preferably 0.7 GPa. When it is 0.5 GPa or more, it is not easy to produce printing pitch deviation when transferring high-temperature printing ink. The upper limit of the Young's modulus in the length direction at 80°C is preferably 3.0 GPa, more preferably 2.5 GPa. When it is 3.0 GPa or more, it is easy to actually manufacture. The lower limit of the Young's modulus in the width direction at 80°C is preferably 2.5 GPa, more preferably 2.8 GPa, and even more preferably 3.0 GPa. When it is 2.5 GPa or more, it is not easy to produce printing pitch deviation when transferring high-temperature printing ink. The upper limit of the Young's modulus in the width direction at 80°C is preferably 5.0 GPa, more preferably 4.7 GPa, and even more preferably 4.5 GPa. If it is 5.0 GPa or less, actual manufacturing is easy. The Young's modulus at 80°C can be set within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(Stress at 5% elongation at 23°C) The lower limit of the stress (F5) when the biaxially aligned polypropylene film of the present invention is stretched by 5% in the longitudinal direction at 23° C. is 40 MPa, preferably 42 MPa, more preferably 43 MPa, still more preferably 44 MPa, and particularly preferably 45 MPa. Above 40 MPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of F5 in the length direction is preferably 70MPa, more preferably 65MPa, still more preferably 62MPa, still more preferably 61MPa, still more preferably 60MPa. Below 70MPa, it is actually easy to manufacture, and the length-width balance is easy to optimize. The lower limit of F5 in the width direction at 23° C. of the biaxially aligned polypropylene film of the present invention is 160 MPa, preferably 165 MPa, more preferably 168 MPa, and still more preferably 170 MPa. Above 160 MPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of F5 in the width direction is preferably 250MPa, more preferably 245MPa, and still more preferably 240MPa. If it is 250 MPa or less, manufacturing is actually easy, and the length-width balance is easy to optimize. The F5 system can be set within the range by adjusting the stretch ratio or relaxation rate and adjusting the temperature during film production.

(Stress at 5% elongation at 80°C) The lower limit of the stress (F5) when the biaxially aligned polypropylene film of the present invention is stretched by 5% in the longitudinal direction at 80° C. is 15 MPa, preferably 17 MPa, more preferably 19 MPa, and still more preferably 20 MPa. Above 15 MPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of F5 at 80°C in the length direction is preferably 40MPa, more preferably 35MPa, still more preferably 30MPa, and particularly preferably 25MPa. Below 40MPa, it is actually easy to manufacture, and the length-width balance is easy to optimize. The lower limit of F5 in the width direction at 80° C. of the biaxially aligned polypropylene film of the present invention is 75 MPa, preferably 80 MPa, more preferably 85 MPa, still more preferably 90 MPa, and particularly preferably 95 MPa. Above 75MPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of F5 at 80°C in the width direction is preferably 150MPa, more preferably 140MPa, and still more preferably 130MPa. Below 140MPa, it is actually easy to manufacture, and the length-width balance is easy to optimize. The 80°C F5 system can be set within the range by adjusting the stretch ratio or relaxation rate and adjusting the temperature during film production.

(120°C heat shrinkage rate) The upper limit of the heat shrinkage rate of the biaxially oriented polypropylene film of the present invention in the length direction at 120°C is preferably 2.0%, more preferably 1.7%, and even more preferably 1.5%. If it is 2.0% or less, it is not easy to produce printing spacing deviation when transferring printing ink. The upper limit of the heat shrinkage rate in the width direction at 120°C is 5.0%, preferably 4.5%, and more preferably 4.0%. If it is 5.0% or less, it is not easy to produce wrinkles during heat sealing. If the heat shrinkage rate in the length direction at 120°C is less than the heat shrinkage rate in the width direction at 120°C, it is even less likely to produce printing spacing deviation when transferring printing ink. The heat shrinkage rate at 120°C and the balance of heat shrinkage rate in the length direction and width direction can be set within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

If the thermal shrinkage rate in the length direction at 120°C is less than the thermal shrinkage rate in the width direction at 120°C, printing spacing deviation will be less likely to occur when transferring printing ink. The heat shrinkage rate at 120°C and the length-width direction balance of the heat shrinkage rate can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

(refractive index) The lower limit of the refractive index (Nx) in the longitudinal direction of the biaxially aligned polypropylene film of the present invention is preferably 1.4950, more preferably 1.4970, and still more preferably 1.4980. If it is 1.4950 or more, the rigidity of the membrane will tend to increase. The upper limit of the refractive index (Nx) in the longitudinal direction is preferably 1.5100, more preferably 1.5070, still more preferably 1.5050. If it is 1.5100 or less, the balance of the film's longitudinal direction-width direction characteristics will be excellent.

The lower limit of the refractive index (Ny) in the width direction of the biaxially aligned polypropylene film of the present invention is preferably 1.5230, preferably 1.5235, and more preferably 1.5240. If it is 1.5230 or more, the rigidity of the film is easily increased. 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. If it is 1.5280 or less, the balance of the film's properties in the length direction and width direction is excellent.

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 1.4965, and more preferably 1.4970. If it is 1.4960 or more, it is easy 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 more preferably 1.5010. If it is 1.5020 or less, it is easy to improve the heat resistance of the film. The refractive index can be set within a range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(△Ny) The lower limit of ΔNy of the biaxially aligned polypropylene film of the present invention is 0.0220, preferably 0.0225, more preferably 0.0228, and still more preferably 0.0230. If it is 0.0220 or more, the rigidity of a film will tend to become high. The actual upper limit of ΔNy is preferably 0.0270, more preferably 0.0265, still more preferably 0.0262, particularly preferably 0.0260. If it is 0.0270 or less, thickness unevenness will be easily improved. △Ny can be set within a range by adjusting the stretch ratio, stretch temperature, and heat fixing temperature of the film. △Ny is calculated by the following formula by setting the refractive index along the length direction, width direction, and thickness direction of the film to Nx, Ny, and Nz respectively. It refers to the overall alignment of the film in the length direction, width direction, and thickness direction. The degree of alignment in the width direction. △Ny＝Ny-[(Nx＋Nz)/2]

(Plane alignment coefficient) The lower limit of the plane alignment coefficient (ΔP) of the biaxially aligned polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and still more preferably 0.0140. If it is 0.0135 or more, the balance of the film's surface direction will be good, and thickness unevenness will also be improved. The actual upper limit of the plane alignment coefficient (ΔP) is preferably 0.0155, more preferably 0.0152, and still more preferably 0.0150. If it is 0.0155 or less, the heat resistance at high temperatures will be excellent. The plane alignment coefficient (ΔP) can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature. In addition, the plane alignment coefficient (ΔP) is calculated using (formula) [(Nx+Ny)/2]-Nz.

(X-ray orientation) The lower limit of the X-ray orientation calculated by the following formula for Wh of the biaxially oriented polypropylene film of the present invention is preferably 0.85, more preferably 0.855, and even more preferably 0.861. By setting it to 0.85 or more, the rigidity can be easily improved. X-ray orientation = (180-Wh)/180 The upper limit of the X-ray orientation is preferably 0.928, more preferably 0.922, and even more preferably 0.917. By setting it to 0.928 or less, the film formation is easy and stable.

(Haze) The upper limit of the haze of the biaxially aligned polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, further preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. If it is 5.0% or less, it can be easily used for applications requiring transparency. The actual lower limit of the haze is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, particularly preferably 0.4%. If it is 0.1% or more, it will be easy to manufacture. The haze system can be adjusted by adjusting the cooling roll (CR) temperature, width direction extension temperature, tenter preheating temperature before width direction extension, width direction extension temperature, or heat fixing temperature, or the molecular weight of the polypropylene resin is 100,000 If the amount of the following components is within the range, the haze may become larger due to the addition of an anti-adhesion agent or the provision of a sealing layer.

(Practical properties of the film) The practical properties of the biaxially oriented polypropylene film of the present invention are described. (Tensile strength at break) The lower limit of the tensile strength at break in the longitudinal direction of the biaxially oriented polypropylene film of the present invention is preferably 90 MPa, more preferably 95 MPa, and more preferably 100 MPa. If it is 90 MPa or more, it is not easy to produce printing pitch deviation during transfer printing ink, and the durability of the packaging bag is also excellent. The actual upper limit of the tensile strength at break in the longitudinal direction is preferably 200 MPa, more preferably 190 MPa, and more preferably 180 MPa. If it is 200 MPa or less, the breakage of the film or the breakage of the packaging bag is easily reduced.

The lower limit of the tensile strength in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 320 MPa, more preferably 340 MPa, and more preferably 350 MPa. If it is 320 MPa or more, it is not easy to produce printing spacing deviation when transferring printing ink, and the durability of the packaging bag is also excellent. The actual upper limit of the tensile strength in the width direction is preferably 500 MPa, more preferably 480 MPa, and more preferably 470 MPa. If it is 500 MPa or less, the film rupture or the bag breakage of the packaging bag is easily reduced. The tensile strength can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

(Tensile elongation at break) The lower limit of the tensile elongation at break in the longitudinal direction of the biaxially oriented polypropylene film of the present invention is preferably 50%, more preferably 55%, and even more preferably 60%. If it is 50% or more, the film breakage or bag breakage of the packaging bag is easily reduced. The actual upper limit of the tensile elongation at break in the longitudinal direction is preferably 230%, more preferably 220%, and even more preferably 210%. If it is 230% or less, it is not easy to produce printing spacing deviation when transferring printing ink, and the durability of the packaging bag is also excellent.

The lower limit of the tensile elongation at break in the width direction of the biaxially aligned polypropylene film of the present invention is preferably 10%, more preferably 15%, and still more preferably 17%. If it is 10% or more, film breakage and packaging bag breakage are likely to be reduced. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and still more preferably 50%. If it is 60% or less, printing pitch deviation will not easily occur when transferring printing ink, and the durability of the packaging bag will also be excellent. The tensile elongation at break can be set within a range by adjusting the extension ratio, extension temperature, and heat fixing temperature.

(Bending rigidity) The lower limit of the bending rigidity of the biaxially oriented polypropylene film of the present invention in the length direction at 23°C is preferably 0.3mN·cm, more preferably 0.33mN·cm, and more preferably 0.35mN·cm. If it is 0.3mN·cm or more, the film can be thinned and is suitable for applications requiring rigidity. The lower limit of the bending rigidity in the width direction is preferably 0.5mN·cm, more preferably 0.55mN·cm, and more preferably 0.6mN·cm. If it is 0.5mN·cm or more, the film can be thinned and is suitable for applications requiring rigidity.

(Ring Stiffness Stress) Regarding the lower limit of the ring stiffness stress S (mN) in the longitudinal direction of the biaxially aligned polypropylene film of the present invention at 23° C., if the thickness of the biaxially aligned polypropylene film is t (μm), then 0.00020×t ³ is preferred, 0.00025×t ³ is more preferred, 0.00030×t ³ is still more preferred, and 0.00035×t ³ is particularly preferred. If it is 0.00020×t ³ or more, the shape of the package can be easily maintained. The upper limit of the ring stiffness stress S (mN) in the length direction at 23°C is preferably 0.00080×t ³ , more preferably 0.00075×t ³ , still more preferably 0.00072×t ³ , and particularly preferably 0.00070×t ³ . If it is 0.00080×t ³ or less, manufacturing is actually easy. Regarding the lower limit of the ring stiffness stress S (mN) in the width direction at 23° C. of the biaxially aligned polypropylene film of the present invention, if the thickness of the biaxially aligned polypropylene film is t (μm), it is preferably 0.0010× t ³ is preferably 0.0011×t ³ , further preferably 0.0012×t ³ , and particularly preferably 0.0013×t ³ . If it is 0.0010×t ³ or more, the shape of the package can be easily maintained. The upper limit of the ring stiffness stress S (mN) in the width direction at 23°C is preferably 0.0020×t ³ , more preferably 0.0019×t ³ , further preferably 0.0018×t ³ , and particularly preferably 0.0017×t ³ . If it is 0.0020×t ³ or less, manufacturing is actually easy.

Hoop stiffness stress is an indicator of the stiffness of the film, which depends on the thickness of the film. The measurement method is as follows. Cut out two strips of 110 mm x 25.4 mm, with the length direction of the film as the long axis of the strip (hoop direction), or with the width direction of the film as the long axis of the strip (hoop direction). Clamp these strips with clamps, and make a measurement ring with one side of the film as the inner surface of the ring, and a measurement ring with the opposite side as the inner surface of the ring, in such a way that the long axis of the strip becomes the length direction of the film or the width direction. The ring used for measurement, with the long axis of the strip as the length direction of the film, was set in a state where the width direction was perpendicular to the clamp part of the ring stiffness tester DA manufactured by Toyo Seiki Co., Ltd., and the clamp was loosened. The ring stiffness stress was measured with a clamp interval of 50mm, a pressing depth of 15mm, and a compression speed of 3.3mm/second. The measurement was to measure the ring stiffness stress and thickness 5 times for the measurement ring whose one side of the film became the inner surface of the ring, and then the measurement ring whose other side became the inner surface of the ring was also measured 5 times. Using the data collected 10 times in total, a graph is plotted with the cube of the thickness (μm) of each test piece as the horizontal axis and the hoop stiffness stress (mN) as the vertical axis. The slope a is approximated with a straight line with an intercept of 0 to obtain the slope a. The slope a represents the inherent characteristic value of the film that is not dependent on the thickness that determines the stiffness. The slope a is set as the evaluation value of the stiffness. The measurement ring with the long axis of the strip as the width direction of the film is also measured in the same way.

(Wrinkles during heat sealing) In order to form a bag for packaging food, the finished bag is filled with contents, and the film is heated to melt and fuse to seal. In addition, when making bags while filling food, the same process is usually performed in the same manner. Usually, a sealant film composed of polyethylene or polypropylene is laminated on a base film, and the surfaces of the sealant films are fused together. The heating method is to apply pressure from the base film side with a heating plate to press the film for sealing. The sealing width is usually set to about 10mm. The base film is also heated at this time, so the shrinkage at this time will cause wrinkles. In terms of durability of the bag, the fewer wrinkles the better, and in order to increase purchase intention, the fewer wrinkles the better. Although the sealing temperature may be around 120°C, in order to increase the bag making processing speed, a higher sealing temperature is required. In this case, it is also preferable to have small shrinkage. When the zipper is fused to the opening of the bag, high-temperature sealing is required.

(Printing spacing deviation) The basic structure of a packaging film usually consists of a laminated film of a printed base film and a sealant film. Bags are manufactured using bag making machines, including three-sided bags, stand-up bags, side seal bags, etc. Various bag making machines are used. Printing pitch deviation is considered to be caused by expansion and contraction of the base material of the film due to the application of tension or heat to the film during the printing step. Excluding defective products caused by printing pitch deviation is also important in terms of efficient use of resources and in order to increase purchase intention.

(Film processing) The printing of the biaxially oriented polypropylene film of the present invention can be carried out by relief printing, lithography, gravure printing, stencil printing, or transfer printing, depending on the application. In addition, unstretched sheets composed of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester, as well as uniaxially stretched films and biaxially stretched films can be laminated as sealant films, and can also be used as a laminated body endowed with heat sealability. In order to further improve gas barrier properties or heat resistance, unstretched sheets composed of aluminum foil or polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol, uniaxially stretched films, and biaxially stretched films can be provided as an intermediate layer between the biaxially oriented polypropylene film and the sealant film. The sealant film can be bonded using an adhesive applied by dry lamination or hot melt lamination. In order to improve the gas barrier properties, aluminum or inorganic oxides can be evaporated to a biaxially aligned polypropylene film or an intermediate layer film, or a sealant film. The evaporation method can be vacuum evaporation, sputtering, or ion plating, preferably vacuum evaporation of silicon dioxide, aluminum oxide, or a mixture of these.

The biaxially aligned polypropylene film of the present invention can be used as an anti-fogging agent such as fatty acid esters of polyols, amines of higher fatty acids, amide of higher fatty acids, amines of higher fatty acids or ethylene oxide adducts of amide. The amount present in the film is set in the range of 0.2% by mass to 5% by mass, making it suitable for packaging fresh products composed of vegetables, fruits, flowers and other plants that require high freshness.

In addition, various additives may be blended in order to improve qualities such as sliding properties and antistatic properties within the scope that does not impair the effects of the present invention. For example, lubricants such as waxes and metal soaps, plasticizers, and processing aids may be blended to improve productivity. Or heat stabilizers, antioxidants, antistatic agents, UV absorbers, etc. [Industrial Availability]

The biaxially aligned polypropylene film system of the present invention has excellent characteristics that have not been seen in the past as mentioned above, so it can be preferably used for packaging bags. In addition, the thickness of the film can be thinner than before.

It is further suitable for the following applications: insulating films for condensers and motors, backsheets for solar cells, barrier films for inorganic oxides, and base films for transparent conductive films such as ITO (Indium Tin Oxide). High temperature applications; or applications requiring rigidity such as separation films. In addition, it is possible to perform coating or printing processing at high temperatures using coating agents, inks, lamination adhesives, etc. that have been difficult to use in the past, and it is expected that production efficiency will be improved. [Example]

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

(2) Meso-pentad component ratio The meso-pentad component ratio ([mmmm]%) of the polypropylene resin was measured using ¹³ C-NMR. The meso pentad ratio was calculated based on the method described in Zambelli et al., Macromolecules, Vol. 6, page 925 (1973). ¹³ C-NMR measurement was carried out using AVANCE500 manufactured by BRUKER, and 200 mg of the sample was dissolved in an 8:2 mixture of o-dichlorobenzene and heavy benzene at 135°C, and was performed at 110°C.

(3) The number average molecular weight, weight average molecular weight, amount of components with a molecular weight of less than 100,000, and molecular weight distribution of polypropylene resin were determined by gel permeation chromatography (GPC) using a monodisperse polystyrene standard and PP-converted molecular weight. When the baseline is unclear, the range to the lowest position of the foot of the high molecular weight side of the elution peak closest to the high molecular weight side of the elution peak of the standard substance was set as the baseline. The GPC measurement conditions are as follows. Apparatus: HLC-8321PC/HT (manufactured by Tosoh Co., Ltd.) Detector: RI Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%) Column: TSK gelguard column HHR (30) HT (7.5 mm I.D. × 7.5 cm) × 1 column + TSK gel GMHHR-H (20) HT (7.8 mm I.D. × 30 cm) × 3 columns Flow rate: 1.0 mL/min Injection volume: 0.3 mL Measurement temperature: 140°C The number average molecular weight (Mn) and mass average molecular weight (Mw) are defined by the following formula using the molecular weight (M _i ) and the number of molecules (N _i ) at each elution position of the GPC curve obtained using the molecular weight calibration curve. Number average ^molecular weight: Mn = Σ( _Ni・Mi)/ _ΣNiMass average molecular weight: Mw = Σ( _Ni・_Mi2 )/Σ( _Ni・_Mi ) Here, the molecular weight distribution can be obtained as Mw/Mn. In addition, the ratio of components with a molecular weight of 100,000 or less can be obtained from the integral curve of the molecular weight distribution obtained by GPC.

(4) Crystallization temperature (Tc), melting temperature (Tm) Thermal measurement was performed in a nitrogen atmosphere using a Q1000 differential scanning thermal analyzer manufactured by TA Instruments. Approximately 5 mg was cut out from polypropylene resin tablets and sealed in an aluminum pan for measurement. After raising the temperature to 230°C and maintaining it for 5 minutes, it was cooled to 30°C at a rate of -10°C/min. The exothermic peak temperature was defined as the crystallization temperature (Tc). In addition, the heat of crystallization (ΔHc) was set so that the exothermic peaks were smoothly connected from the beginning to the end of the peak, and the area of the exothermic peak was determined by setting a baseline. The temperature was maintained at 30° C. for 5 minutes, and the temperature was raised to 230° C. at 10° C./min. The main peak temperature of the endothermic peak was defined as the melting temperature (Tm).

(5)Film thickness The thickness of the film was measured using Miritoron 1202D manufactured by SEIKO-EM.

(6)Haze NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. was used, and it was measured in accordance with JISK7105 at 23°C.

(7) X-ray half value width, alignment degree It measured by the transmission method using an X-ray diffraction device (RINT2500 manufactured by Rigaku Corporation). X-rays with a wavelength of 1.5418Å are used, and the detector uses a scintillation counter. The films were stacked so as to have a thickness of 500 μm to prepare a sample. Place the sample stage at the diffraction peak position (diffraction angle 2θ = 14.1°) of the (110) plane of the α-type crystal of polypropylene resin, rotate the sample 360° with the thickness direction of the film as the axis, and obtain the (110) plane Azimuth dependence of diffraction intensity. From this azimuth angle dependence, the half-maximum width Wh of the diffraction peak from the aligned crystal in the width direction of the film is determined. In addition, the X-ray alignment degree was calculated from the following equation using Wh. X-ray alignment degree=(180-Wh)/180

(8)Refractive index, △Ny, plane alignment coefficient It was measured using an Abbe refractometer manufactured by ATAGO CO., LTD. at a wavelength of 589.3 nm and a temperature of 23°C. Let the refractive index along the length direction and width direction of the film be Nx and Ny respectively, and let the refractive index in the thickness direction be Nz. △Ny is obtained using Nx, Ny, and Nz, and using (formula) Ny-[(Nx+Nz)/2]. In addition, the plane alignment coefficient (ΔP) is calculated using (formula) [(Nx+Ny)/2]-Nz.

(9) Tensile test The tensile strength of the film in the longitudinal and width directions was measured at 23°C according to JIS K 7127. The sample was cut from the film into a size of 15 mm × 200 mm, the clamp width was 100 mm, and it was set in a tensile tester (Dual Column desktop tester INSTRON 5965 manufactured by Instron Japan Co. Ltd.). The tensile test was carried out at a tensile speed of 200 mm/min. From the obtained strain-stress curve, the Young's modulus and the stress at 5% elongation (F5) were obtained from the slope of the straight line part at the initial elongation. The tensile fracture strength and tensile fracture elongation are the strength and elongation at the time when the sample fractured, respectively. The Young's modulus and F5 at 80°C were obtained by measuring in a constant temperature bath at 80°C. In addition, the measurement is performed as follows: the fixture is set in a constant temperature bath pre-set to 80°C, and the temperature is kept for 1 minute after installation until the sample is measured.

(10) Thermal shrinkage rate The thermal shrinkage rate is measured according to JIS Z 1712 using the following method. The film is cut into 20 mm wide and 200 mm long pieces in the length direction and width direction of the film, and then hung in a hot air oven at 120°C or 150°C and heated for 5 minutes. The length after heating is measured, and the thermal shrinkage rate is calculated as the ratio of the shrunk length to the original length.

(11) The bending stiffness and sag amount are obtained according to the JIS L 1096B method (sliding method) using the following process. Make a test piece of 20 mm x 150 mm, and then load the test piece with a weight so that it protrudes 50 mm on the testing machine's table so that the testing machine body is aligned with the upper surface of the moving table. Then, gently turn the handle to lower the sample table, and measure the amount of sag (δ) at the time when the free end of the sample leaves the sample table. Using this sagging amount δ, the film thickness, the test piece size, and the film density of 0.91 g/cm ³ , the bending stiffness (Br) was determined by the following equation. Br＝WL ⁴ /8δ Br: Bending stiffness (mN・cm) W: Gravity per unit area of the test piece (mN/cm ² ) L: Length of the test piece (cm) δ: Droop amount (cm)

(12) Ring stiffness stress, stiffness The longitudinal direction of the film is the long axis of the strip (circular direction), or the width direction of the film is the long axis of the strip (circular direction), and ten strip-shaped test pieces of 110 mm×25.4 mm are cut out. These films are held in clamps, and a measuring ring is made with one surface of the film as the inner surface of the ring and its opposite surface as the ring so that the long axis of the strip becomes the length direction of the film or the width direction of the film. Ring for measuring the inner surface of. The long axis of the strip is used as a ring for measuring the length direction of the film, and the width direction is perpendicular to the clamp part of the ring stiffness tester DA manufactured by Toyo Seiki Seisakusho Co., Ltd., loosen the clamp, and place the clamp at intervals The ring stiffness stress was measured by setting the indentation depth to 15mm and the compression speed to 3.3mm/second. The measurement is performed by measuring the ring stiffness stress and thickness five times on a measurement ring with one surface of the film serving as the inner surface of the ring, and then also measuring five times on the measurement ring with the other surface serving as the inner surface of the ring. Using this data from a total of 10 times, plot the thickness (μm) of each test piece to the third power as the horizontal axis and its ring stiffness stress (mN) as the vertical axis, and approximate it with a straight line with an intercept of 0, to find out Get its slope a. The slope a is the evaluation value of stiffness. The long axis of the strip serves as a measurement ring in the width direction of the film and is measured in the same manner.

(Example 1) As the polypropylene resin, a propylene homopolymer PP-1 (Sumitomo Nobrene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd.) with MFR=7.5g/10min, Tc=116.2℃, and Tm=162.5℃ was used. It was extruded into a sheet by a T-die at 250℃, contacted with a cooling roller at 20℃, and directly put into a water tank at 20℃. After that, it was stretched 4.5 times in the length direction at 145℃ with two pairs of rollers, and then clamped at both ends and led to a hot air oven. After preheating at 170℃, it was stretched 6 times in the width direction at 160℃ as the first stage, and then stretched 1.36 times at 145℃ as the second stage, thereby stretching a total of 8.2 times. After stretching in the width direction, the film was immediately cooled at 100°C while being held in a clamp, and then heat-fixed at 163°C. The thickness of the film obtained in this way was 18.7μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-making conditions. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Example 2) As the polypropylene resin, 80 parts by weight of PP-1 and propylene homopolymer PP-2 (Sumitomo Chemical) with MFR = 11 g/10 minutes, [mmmm] = 98.8%, Tc = 116.5°C, and Tm = 161.5°C were used. Co., Ltd., EL80F5) 20 parts by weight. It was the same as Example 1 except that the stretching temperature in the longitudinal direction was 142°C, the stretching temperature in the first step in the width direction was 162°C, and the heat fixing temperature was 165°C. The thickness of the film obtained was 21.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties are as shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Example 3) The procedure was carried out in the same manner as in Example 2 except that 3% relaxation was applied during heat fixation. The thickness of the film obtained was 21.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Example 4) The process was carried out in the same manner as in 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 film obtained was 18.9 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties are shown in Table 3, and a film with high rigidity was obtained.

(Example 5) The same procedure as in Example 2 was performed except that the film was not cooled after stretching in the width direction and was heat-fixed at 165° C. while being held in a clamp. The thickness of the film obtained was 19.5 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Example 6) Except that the stretching temperature of the second section in the width direction is set to 155°C, the same procedure as in Example 2 is performed. The thickness of the film obtained in this way is 20.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-making conditions. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperature is obtained.

(Example 7) Except that the stretching ratio in the longitudinal direction is set to 4.8 times, the same procedure as in Example 2 is performed. The thickness of the obtained film is 19.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-making conditions. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures is obtained.

(Example 8) In the width direction stretching, the same procedure as in Example 2 was performed except that the stretching ratio in the first step was set to 6.6 times and the stretching ratio in the second step was set to 1.5 times, resulting in a total stretching of 9.9 times. The thickness of the film obtained was 20.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Comparative Example 1) PP-1 was used as a polypropylene resin, extruded into a sheet at 250°C by a T-die, contacted with a cooling roller at 20°C, and directly placed in a water tank at 20°C. Afterwards, the sheet was stretched 4.5 times in the length direction at 143°C, the preheating temperature during stretching in the width direction of the tenter was set to 170°C, the stretching temperature was set to 158°C for 8.2 times stretching, and then heat-fixed at 168°C. The thickness of the obtained film was 18.6μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-making conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with low rigidity.

(Comparative example 2) The polypropylene resin was prepared in the same manner as Comparative Example 1 except that 80 parts by weight of PP-1 and 20 parts by weight of PP-2 were used. The thickness of the film obtained was 20.0 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with low rigidity.

(Comparative example 3) As the polypropylene resin, PP-3 (FL203D manufactured by Japan Polypropylene Corporation) with MFR=3g/10 minutes, Tc=117.2°C, and Tm=160.6°C was used. It is extruded from a T-die into a sheet at 250°C, contacted with a cooling roller at 20°C, and directly put into a water tank at 20°C. After that, stretch 4.5 times in the length direction at 135°C. During the stretching in the width direction of the tenter, set the preheating temperature to 166°C, set the temperature of the first stretch to 155°C, and set the temperature of the second stretch to 155°C. is 139°C, the cooling temperature is set to 95°C, and the heat fixing temperature is set to 158°C. The thickness of the film obtained was 19.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with a high thermal shrinkage rate at high temperatures.

(Comparative example 4) As the polypropylene raw material, PP-4 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) with MFR=2.7g/10 minutes, Tc=114.7°C, and Tm=163.0°C was used. It is extruded from a T-die into a sheet at 250°C, contacted with a cooling roller at 20°C, and directly put into a water tank at 20°C. After that, stretch 4.5 times in the length direction at 145°C. During the stretching in the width direction of the tenter, set the preheating temperature to 170°C, set the temperature of the first stretch section to 160°C, and set the temperature of the second stretch section to 160°C. Set to 145°C, cooling temperature to 100°C, and heat fixation temperature to 163°C. The thickness of the film obtained was 21.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with a high thermal shrinkage rate at high temperatures.

(Comparative Example 5) PP-4 was used as a polypropylene resin. It was extruded into a sheet at 250°C by a T-die, contacted with a cooling roller at 20°C, and directly placed in a water tank at 20°C. After that, it was stretched 5.8 times in the length direction at 130°C, and then the film was heated by setting the preheating temperature to 167°C in the tenter, and then stretched 8.6 times in the width direction at a stretching temperature of 161°C, and then heat-fixed at 130°C while applying a relaxation of 10%, and then heat-fixed in the second stage at 140°C. The thickness of the obtained film was 13.4μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-making conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with a high heat shrinkage rate at high temperature.

[Table 1] PP-1 PP-2 PP-3 PP-4 Copolymerization amount of components other than propylene (mol %) 0 0 0 0 MFR(g/10min) 7.5 11 3 2.7 [mmmm](%) 98.9 98.8 94.8 98.7 Tc(℃) 116.2 116.5 117.2 114.7 Tm(℃) 162.5 161.5 160.6 163.0 ΔHc(J/g) 104.8 107.8 94.9 102.4 Amount of components with molecular weight below 10,000 (mass %) 4.0 6.9 3.0 3.5 Amount of components with molecular weight below 100,000 (mass %) 40.5 53.1 37.1 30.0

[Table 2] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Raw material polypropylene resin PP-1 100 80 80 80 80 80 80 80 100 80 PP-2 20 20 20 20 20 20 20 20 PP-3 100 PP-4 100 100 Hybrid polypropylene resin Melt flow rate (g/10 minutes) 7.5 8.5 8.5 8.5 8.5 8.5 8.5 8.5 7.5 8.5 3 2.7 2.7 Amount of ingredients with molecular weight less than 100,000 (mass %) 40.5 43.0 43.0 43.0 43.0 43.0 43.0 43.0 40.5 43.0 37.1 30.0 30.0 Extrusion step Extrusion temperature (℃) 250 250 250 250 250 250 250 250 250 250 250 250 250 Cooling temperature(℃) 20 20 20 20 20 20 20 20 20 20 20 20 20 Lengthwise extension steps lengthwise extension temperature 145 142 142 145 142 142 142 142 143 143 135 145 130 Length direction extension ratio (times) 4.5 4.5 4.5 4.5 4.5 4.5 4.8 4.5 4.5 4.5 4.5 4.5 5.8 warm-up step Preheating temperature (℃) 170 170 170 170 170 170 170 170 170 170 166 170 167 Width direction extension steps Temperature extending in the width direction of the early period (℃) 160 162 162 162 162 162 162 162 158 158 155 160 161 Extension ratio in the width direction of the early stage interval (times) 6 6 6 6 6 6 6 6.6 6 6 6 6 6.2 Later interval width direction extension temperature 145 145 145 145 145 155 145 145 158 158 139 145 161 Post-interval width direction extension magnification (times) 1.36 1.36 1.36 1.36 1.36 1.36 1.36 1.5 1.36 1.36 1.36 1.36 1.39 Final width direction extension ratio 8.2 8.2 8.2 8.2 8.2 8.2 8.2 9.9 8.2 8.2 8.2 8.2 8.6 Temperature immediately after extension in width direction (℃) 100 100 100 140 - 100 100 100 - - 95 100 - Heat treatment steps Heat treatment temperature (℃) 163 165 165 165 165 165 165 165 168 168 158 163 130 Relaxation rate during heat treatment (%) 0 0 3 0 0 0 0 0 0 0 0 0 10 Heat treatment 2 temperature (℃) - - - - - - - - - - - - 140

[table 3] Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Comparison Example 5 Membrane properties Thickness(μm) 18.7 21.3 21.1 18.9 19.5 20.3 19.1 20.1 18.6 20.0 19.2 21.2 13.4 Fog(%) 0.7 2.2 2.0 2.0 2.1 2.1 2.2 2.0 1.0 1.1 0.4 0.4 0.6 23℃F5(width direction) (MPa) 193 180 169 171 183 175 184 188 133 131 158 183 210 23℃F5(length direction) (MPa) 49 44 46 46 46 45 45 46 44 44 39 46 55 80℃F5(width direction) (MPa) 102 89 91 91 100 93 97 100 72 68 65 84 98 80℃F5(length direction) (MPa) twenty one twenty one twenty one 20 twenty one twenty two twenty one twenty one 20 20 13 18 twenty three 23℃ Young's modulus (width direction) (GPa) 7.4 7.1 6.7 6.7 6.9 6.9 7.1 7.3 5.5 5.7 6.1 7.1 7.7 23℃ Young's modulus (length direction) (GPa) 2.7 2.5 2.5 2.6 2.5 2.6 2.5 2.6 2.7 2.6 2.4 2.6 2.9 80℃ Young's modulus (width direction) (GPa) 3.3 3.0 3.0 3.0 3.2 3.0 3.2 3.2 2.2 2.0 2.1 2.9 3.4 80℃ Young's modulus (length direction) (GPa) 0.8 1.0 1.0 0.9 1.0 1.0 0.9 1.0 0.9 0.9 0.6 0.6 0.9 Tensile breaking strength (width direction) (MPa) 450 397 366 396 435 373 379 391 336 344 414 430 476 Tensile breaking strength (length direction) (MPa) 134 106 105 111 114 106 117 113 118 124 163 160 182 Tensile elongation at break (width direction) (%) 27 26 twenty two 32 29 twenty four twenty one twenty two 37 44 29 27 33 Tensile elongation at break (length direction) (%) 178 176 172 179 199 182 173 190 188 219 201 192 160 120℃ thermal shrinkage (width direction) (%) 4.0 3.0 2.2 3.0 3.0 3.3 3.0 2.7 0.7 1.0 9.8 6.5 2.7 120℃ thermal shrinkage (length direction) (%) 1.0 1.0 1.0 0.8 1.0 1.0 1.0 0.8 1.3 1.3 4.0 1.7 1.5 150℃ Thermal Shrinkage (Width Direction) (%) 27.3 22.0 18.2 17.8 24.7 18.3 17.7 17.3 11.7 13.2 57.0 43.0 37.8 150℃ thermal shrinkage (length direction) (%) 7.0 5.0 4.2 5.2 5.3 5.8 3.5 4.3 4.7 4.3 34.0 17.0 13.7 Width direction refractive index Ny 1.5245 1.5254 1.5258 1.5250 1.5261 1.5260 1.5249 1.5259 1.5252 1.5245 1.5187 1.5215 1.5251 Refractive index in length direction Nx 1.5020 1.5028 1.5034 1.5030 1.5020 1.5031 1.5031 1.5020 1.5050 1.5056 1.4991 1.5010 1.4997 Refractive index in thickness direction Nz 1.4985 1.5001 1.5001 1.5000 1.4997 1.5007 1.4998 1.4999 1.5012 1.5010 1.4952 1.4973 1.4980 ΔNy 0.0243 0.0240 0.0240 0.0235 0.0253 0.0241 0.0234 0.0250 0.0221 0.0212 0.0216 0.0224 0.0262 Surface orientation coefficient ΔP 0.0148 0.0140 0.0145 0.0140 0.0144 0.0139 0.0142 0.0141 0.0139 0.0141 0.0137 0.0140 0.0144 X-ray half width (°) 20.6 22.2 23.0 23.8 20.2 23.6 23.6 21.8 28.6 28.9 23.9 24.4 21.2 X-ray orientation 0.89 0.88 0.87 0.87 0.89 0.87 0.87 0.88 0.84 0.84 0.87 0.86 0.88 Bending stiffness (width direction) (mN・cm) 0.60 0.68 0.71 0.70 0.56 0.67 0.60 0.61 0.42 0.50 0.82 0.72 0.36 Bending stiffness (length direction) (mN・cm) 0.34 0.37 0.39 0.39 0.36 0.35 0.33 0.36 0.31 0.34 0.43 0.35 0.24 Ring stiffness stress slope a (width direction) 0.00114 0.00120 0.00117 0.00113 0.00120 0.00117 0.00116 0.00127 0.00112 0.00109 0.00087 0.00087 0.00138 Ring stiffness stress slope a (length direction) 0.00038 0.00048 0.00049 0.00046 0.00044 0.00045 0.00046 0.00046 0.00052 0.00050 0.00035 0.00035 0.00059

without.

Claims (9)

A biaxially aligned polypropylene film, wherein in the azimuthal angle dependence of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray diffraction measurement, the half-value width of the peak from the aligned crystals in the width direction is less than 27°, the lower limit of the stress (F5) when the length direction is elongated by 5% at 23°C is 40MPa, the lower limit of the stress (F5) when the width direction is elongated by 5% at 23°C is 160MPa, and the thermal shrinkage rate at 150°C is less than 10% in the length direction and less than 30% in the width direction. The biaxially oriented polypropylene film as described in claim 1, wherein the 120°C thermal shrinkage of the biaxially oriented polypropylene film is 2.0% or less in the length direction, 5.0% or less in the width direction, and the 120°C heat shrinkage rate in the length direction is 2.0% or less. The shrinkage rate is less than the 120°C thermal shrinkage rate in the width direction. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the refractive index Ny in the width direction of the biaxially aligned polypropylene film is 1.5230 or more, and ΔNy is 0.0220 or more. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the haze of the biaxially aligned polypropylene film is less than 5.0%. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the polypropylene resin constituting the biaxially aligned polypropylene film has a meso five-component component ratio of 97.0% or more. The biaxially aligned polypropylene film as claimed in claim 1 or 2, wherein the polypropylene resin constituting the biaxially aligned polypropylene film has a crystallization temperature of 105° C. or higher and a melting point of 160° C. or higher. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the polypropylene resin constituting the biaxially aligned polypropylene film has a melt flow rate of 4.0 g/10 minutes or more. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the component amount of the polypropylene resin constituting the biaxially aligned polypropylene film having a molecular weight of 100,000 or less is 35 mass % or more. The biaxially aligned polypropylene film as recited in claim 1 or 2, wherein the degree of alignment of the biaxially aligned polypropylene film is greater than 0.85.