Biaxially-oriented polypropylene film

Abstract

Provided is a biaxially-oriented polypropylene film in which the length in the width direction of the film hardly changes even during or at the end of an increase in temperature. This biaxially-oriented polypropylene film is characterized in that, in a dynamic viscoelasticity measurement, when E"(B) represents the minimum value of the loss modulus at 25-75°C and E"(C) represents the maximum value of the loss modulus at 100-160°C, E"(B) / E"(C) is 0.60 or more, the sum of the storage modulus in the longitudinal direction at 23°C and the storage modulus in the longitudinal direction at 140°C is 3.0 GPa or more, and the sum of the storage modulus in the width direction at 23°C and the storage modulus in the width direction at 140°C is 9.2 GPa or more.

Description

Biaxially oriented polypropylene film

[0001] The present invention relates to a biaxially oriented polypropylene film.

[0002] Biaxially oriented polypropylene films have excellent physical properties such as rigidity and heat resistance, and have been used in a wide range of applications, including packaging and industrial use.

[0003] For example, Patent Documents 1 to 3 disclose biaxially oriented polypropylene films that can be used for packaging applications and have various excellent physical properties. Specifically, the film of Patent Document 1 has a low heat shrinkage force and an excellent Young's modulus, the film of Patent Document 2 has a low heat shrinkage rate and an excellent Young's modulus, and the film of Patent Document 3 has a low heat shrinkage force and an excellent stress at 5% elongation.

[0004] International Publication No. 2020 / 196602 International Publication No. 2021 / 070671 International Publication No. 2020 / 137789

[0005] However, the films of Patent Documents 1 to 3 have the problem that when heated, the length of the film in the width direction changes significantly during or after the temperature increase, resulting in a decrease in flatness due to heating. Furthermore, when such films are used to produce bags, there is also the problem that the appearance of the bags deteriorates due to heating during production.

[0006] An object of the present invention is to provide a biaxially oriented polypropylene film whose widthwise length remains almost unchanged both during and after temperature increase.

[0007] That is, the present invention includes the following inventions. [1] A biaxially oriented polypropylene film characterized in that, in dynamic viscoelasticity measurement, where E"(B) is the minimum value of the loss modulus at 25°C to 75°C and E"(C) is the maximum value of the loss modulus at 100°C to 160°C, E"(B) / E"(C) is 0.60 or more, the sum of the longitudinal storage modulus at 23°C and the longitudinal storage modulus at 140°C is 3.0 GPa or more, and the sum of the width direction storage modulus at 23°C and the width direction storage modulus at 140°C is 9.2 GPa or more. [2] In thermomechanical analysis, when the temperature is increased from 30°C to 130°C at a heating rate of 10°C / min, the length in the width direction at 30°C is ０ The maximum value of the width direction length during the temperature rise is X １ , the minimum value of the length in the width direction during the temperature rise is X ２ Then, (X １ -X ０ ) / X ０ The percentage of (X ２ -X ０ ) / X ０ [3] In a thermomechanical analysis, when the temperature is increased from 30°C to 160°C at a heating rate of 10°C / min, the length X in the width direction of the biaxially oriented polypropylene film at 30°C is -0.50% or more. ０ The length in the width direction is 0.9950X ０ [1] or [2] above, wherein the temperature at which the storage modulus is 129°C or higher is 129°C or higher, the storage modulus in the longitudinal direction at 23°C is 2.0 GPa or higher, and the storage modulus in the width direction at 23°C is 8.0 GPa or higher.

[0008] [4] The biaxially oriented polypropylene film according to any one of [1] to [3] above, having a longitudinal storage modulus of 0.5 GPa or more at 120°C and a widthwise storage modulus of 2.1 GPa or more at 120°C. [5] The biaxially oriented polypropylene film according to any one of [1] to [4] above, having a longitudinal heat shrinkage of 2.5% or less at 120°C and a widthwise heat shrinkage of 1.1% or less at 120°C. [6] The biaxially oriented polypropylene film according to any one of [1] to [5] above, having a widthwise stress at 5% elongation of 150 MPa or more at 23°C. [7] The biaxially oriented polypropylene film according to any one of [1] to [6] above, wherein the polypropylene resin composition constituting the biaxially oriented polypropylene film has a mesopentad fraction of 97.0% or more. [8] The biaxially oriented polypropylene film according to any one of [1] to [7] above, wherein the polypropylene resin composition constituting the biaxially oriented polypropylene film has a crystallization temperature of 105°C or more and a melting point of 158°C or more. [9] The biaxially oriented polypropylene film according to any one of [1] to [8], wherein the polypropylene resin composition constituting the biaxially oriented polypropylene film has a melt flow rate of 4.0 g / 10 min or more.

[10] The biaxially oriented polypropylene film according to any one of [1] to [9], wherein the polypropylene resin composition constituting the biaxially oriented polypropylene film has a molecular weight of 100,000 or less of 35% by mass or more.

[0009]

[11] The biaxially oriented polypropylene film according to any one of [1] to

[10] above, wherein in dynamic viscoelasticity measurement, the minimum value of loss modulus at 25°C to 75°C is 0.26 GPa or more.

[12] The biaxially oriented polypropylene film according to any one of [1] to

[11] above, wherein in dynamic viscoelasticity measurement, E"(C) / E"(A) is 0.60 or more, where E"(A) is the maximum value of loss modulus at -25°C to 25°C.

[13] The biaxially oriented polypropylene film according to any one of [1] to

[12] above, wherein the heat shrinkage at 150°C in the longitudinal direction is 4.5% or less and the heat shrinkage at 150°C in the width direction is 9.0% or less.

[0010] The biaxially oriented polypropylene film of the present invention has a storage modulus and a loss modulus in a predetermined temperature range that are both adjusted, so that the length of the film in the width direction hardly changes during and after the temperature rise, and therefore the film maintains its flatness even after heating. Therefore, the biaxially oriented polypropylene film of the present invention is suitable for use in packaging, industrial applications, etc.

[0011] 1 is a diagram showing the relationship between temperature and the length in the film width direction in Example 4, Comparative Example 1, and Comparative Example 8. FIG. 2 is a diagram showing the relationship between temperature and loss modulus in Example 4 and Comparative Example 1. FIG. 3 is a diagram showing the relationship between temperature and storage modulus in Example 4 and Comparative Example 8.

[0012] The biaxially oriented polypropylene film of the present invention comprises a polypropylene resin composition.

[0013] (1-1) Polypropylene Resin Composition The polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention may be a mixture of two or more different polypropylene polymers (polypropylene resins), for example, a mixture of two or more different polypropylene homopolymers, a mixture of two or more different polypropylene copolymers containing an α-olefin other than propylene, or a mixture of one or more polypropylene homopolymers and one or more polypropylene copolymers containing an α-olefin other than propylene.

[0014] The following describes various suitable physical properties of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention. When two or more different polypropylene polymers are used, the physical properties other than the melt flow rate are the mass average values ​​of the physical properties of each polypropylene polymer.

[0015] The melting point (hereinafter sometimes referred to as Tm) of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention is preferably 158 to 170°C, more preferably 159 to 169°C, even more preferably 160 to 168°C, particularly preferably 161 to 167°C, and most preferably 162 to 166°C. When the melting point is 158°C or higher, flatness, rigidity, heat resistance at high temperatures, etc. are likely to be obtained. When the melting point is 170°C or lower, it is easy to suppress cost increases in terms of polypropylene production, and the film is less likely to break during film formation. The melting point of the polypropylene resin composition is the main peak temperature of the endothermic peak accompanying melting, which is observed when 5 mg of the polypropylene resin composition is packed into an aluminum pan, set in a differential scanning calorimeter (DSC), heated from 30°C to 230°C at a heating rate of 20°C / min in a nitrogen atmosphere, and held at 230°C for 5 minutes to melt the polypropylene resin composition, then cooled to 30°C at a heating rate of -10°C / min, held at 30°C for 5 minutes, and then heated at a heating rate of 10°C / min.

[0016] The crystallization temperature (hereinafter sometimes referred to as Tc) of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention is preferably 105 to 135°C, more preferably 108 to 133°C, even more preferably 110 to 132°C, even more preferably 112 to 130°C, particularly preferably 114 to 128°C, and most preferably 116 to 127°C. If the crystallization temperature is 105°C or higher, crystallization is likely to proceed during width direction stretching and the subsequent cooling step, making it easier to obtain rigidity and heat resistance at high temperatures. If the crystallization temperature is 135°C or lower, it is difficult to increase the cost of polypropylene production and the film is less likely to break during film formation. The crystallization temperature of the polypropylene resin composition is the main peak temperature of the exothermic peak observed when 5 mg of the polypropylene resin composition is packed into an aluminum pan, set in a DSC, heated from 30°C to 230°C at a heating rate of 20°C / min in a nitrogen atmosphere, and held at 230°C for 5 minutes to melt the polypropylene resin composition, and then cooled to 30°C at a cooling rate of -10°C / min.

[0017] The melting point and crystallization temperature of the polypropylene resin composition may be increased to fall within the above range by blending a crystal nucleating agent into the polypropylene resin composition.

[0018] The polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention preferably has a mesopentad fraction ([mmmm]%), an index of stereoregularity, of 97.0 to 99.9%, more preferably 97.5 to 99.7%, and even more preferably 98.0 to 99.5%. If it is less than 97.0%, there is a risk that high orientation cannot be achieved during stretching, or that crystallization is inhibited, resulting in deterioration of rigidity and heat resistance. On the other hand, if it is 97.0% or more, the crystallinity of the polypropylene resin composition is enhanced, and the melting point, crystallinity, and crystalline orientation of the crystals in the film are improved, making it easier to achieve flatness, rigidity, heat resistance at high temperatures, and the like. If it is 99.9% or less, it is easier to reduce the cost of polypropylene production and the film is less likely to break during film formation. The mesopentad fraction is measured by nuclear magnetic resonance spectroscopy (NMR spectroscopy). In order to adjust the mesopentad fraction of the polypropylene resin composition to fall within the above range, for example, methods such as washing the obtained polypropylene resin powder with a solvent such as n-heptane, or using an appropriate catalyst and / or co-catalyst may be used.

[0019] The melt flow rate (MFR) of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, as measured in accordance with JIS K 7210 (1995) Condition M (230°C, 2.16 kgf), 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, even more preferably 5.0 to 20 g / 10 min, particularly preferably 6.0 to 20 g / 10 min, and most preferably 7.5 to 15 g / 10 min. When the MFR of the polypropylene resin composition is 4.0 g / 10 min or more, a biaxially oriented polypropylene film with a low heat shrinkage rate is easily obtained. Furthermore, when the MFR of the polypropylene resin composition is 30 g / 10 min or less, the film formability of the film is easily maintained.

[0020] In the GPC cumulative curve of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, the amount of components having a molecular weight of 100,000 or less is preferably 35% by mass or more, more preferably 38 to 65% by mass, even more preferably 40 to 60% by mass, particularly preferably 41 to 55% by mass, and most preferably 42 to 50% by mass. When the amount of components having a molecular weight of 100,000 or less is 35% by mass or more, heat resistance is unlikely to decrease. When the amount of components having a molecular weight of 100,000 or less is 65% by mass or less, film strength is unlikely to decrease. In this case, if a high-molecular-weight component with a long relaxation time or a long-chain branched component is included, it is easy to adjust the amount of components having a molecular weight of 100,000 or less contained in the polypropylene resin composition without significantly changing the overall viscosity, and therefore film formability is likely to be improved without significantly affecting physical properties such as flatness, rigidity, and heat resistance.

[0021] The polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention is primarily composed of polypropylene resin. However, as long as the effects of the present invention are not impaired, additives such as resins other than polypropylene resin, known heat stabilizers, antioxidants, UV absorbers, nucleating agents, adhesives, anti-fogging agents, flame retardants, inorganic or organic fillers, etc. may be added to the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention. However, these additives are preferably added in small amounts. In the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, the amount of resins other than polypropylene resin is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. Furthermore, in the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, the amount of additives other than resin is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. Examples of resins other than polypropylene resin include polyolefin resins other than polypropylene resins and various elastomers. These may be sequentially polymerized using a multi-stage reactor, blended with polypropylene resin using a Henschel mixer, master pellets prepared in advance using a melt kneader may be diluted with polypropylene resin to a predetermined concentration, or the entire amount may be melt kneaded in advance before use.

[0022] (1-2) Polypropylene Resin The biaxially oriented polypropylene film of the present invention is made of a polypropylene resin composition containing a polypropylene resin as a main component. The term "main component" means that the proportion of the 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. When the polypropylene resin composition contains two or more different polypropylene resins, it is preferable that the total content of the polypropylene resins in the polypropylene resin composition be within the above range.

[0023] The polypropylene resin, which is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, may be a polypropylene homopolymer or a polypropylene copolymer containing α-olefins other than propylene. However, it is preferable to use a polypropylene polymer that is substantially free of α-olefins other than propylene. Specifically, a "polypropylene polymer that is substantially free of α-olefins other than propylene" refers to a polypropylene (co)polymer whose structural units are 1 mol% or less of α-olefins other than propylene and 99 mol% or more of propylene. Even when α-olefins other than propylene are contained, the content of α-olefins other than propylene (the total amount of ethylene and α-olefins having 4 or more carbon atoms) is 1 mol% or less, as described above, preferably 0.5 mol% or less, more preferably 0.3 mol% or less, even more preferably 0.1 mol% or less, and particularly preferably 0 mol%. Crystallinity is likely to be improved within the above range. Examples of α-olefin components having 4 or more carbon atoms include 1-butene, 1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. The polypropylene resin, which is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, may be a mixture of two or more different polypropylene polymers, for example, a mixture of two or more different polypropylene homopolymers, a mixture of polypropylene copolymers containing two or more different α-olefins other than propylene, or a mixture of one or more polypropylene homopolymers and one or more polypropylene copolymers containing one or more α-olefins other than propylene. In the case of a mixture of two or more different polypropylene polymers, it is preferable that the total content of the polypropylene polymers in the polypropylene resin composition is within the above range.

[0024] The following describes various suitable physical properties of the polypropylene resin, which is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention. When two or more different polypropylene resins are used, the physical properties other than the melt flow rate are the mass average values ​​of the physical properties of each polypropylene resin.

[0025] The melting point of the polypropylene resin that is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention is preferably 158 to 170°C, more preferably 159 to 169°C, even more preferably 160 to 168°C, particularly preferably 161 to 167°C, and most preferably 162 to 166°C. When the melting point is 158°C or higher, flatness, rigidity, heat resistance at high temperatures, and the like are likely to be obtained. When the melting point is 170°C or lower, it is easy to suppress cost increases in terms of polypropylene production, and the film is less likely to break during film formation. The melting point of the polypropylene resin is the main peak temperature of the endothermic peak accompanying melting, which is observed when 5 mg of polypropylene resin is packed into an aluminum pan, set in a differential scanning calorimeter (DSC), heated from 30°C to 230°C at a heating rate of 20°C / min in a nitrogen atmosphere, and held at 230°C for 5 minutes to melt the polypropylene resin, then cooled to 30°C at a heating rate of -10°C / min, held at 30°C for 5 minutes, and then heated at a heating rate of 10°C / min.

[0026] The crystallization temperature of the polypropylene resin, which is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, is preferably 105 to 135°C, more preferably 108 to 133°C, even more preferably 110 to 132°C, even more preferably 112 to 130°C, particularly preferably 114 to 128°C, and most preferably 116 to 127°C. If the crystallization temperature is 105°C or higher, crystallization is likely to proceed during width direction stretching and the subsequent cooling step, making it easier to obtain rigidity and heat resistance at high temperatures. If the crystallization temperature is 135°C or lower, it is difficult to increase the cost of polypropylene production and the film is less likely to break during film formation. The crystallization temperature of the polypropylene resin is the main peak temperature of the exothermic peak observed when 5 mg of the polypropylene resin is packed into an aluminum pan, set in a DSC, heated from 30°C to 230°C at a heating rate of 20°C / min in a nitrogen atmosphere, and held at 230°C for 5 minutes to melt the polypropylene resin, and then cooled to 30°C at a cooling rate of -10°C / min.

[0027] The melting point and crystallization temperature can be increased by blending a nucleating agent into the polypropylene resin. When a nucleating agent is blended, it is preferable that the melting point and crystallization temperature of the polypropylene resin blended with the nucleating agent be within the above ranges.

[0028] The polypropylene resin, which is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, preferably has a mesopentad fraction ([mmmm]%), an index of stereoregularity, of 97.0 to 99.9%, more preferably 97.5 to 99.7%, and even more preferably 98.0 to 99.5%. If the mesopentad fraction is less than 97.0%, there is a risk that high orientation cannot be achieved during stretching, or that crystallization is inhibited, resulting in deterioration of rigidity and heat resistance. On the other hand, if the mesopentad fraction is 97.0% or more, the crystallinity of the polypropylene resin composition is enhanced, improving the melting point, crystallinity, and crystalline orientation of the crystals in the film, making it easier to achieve flatness, rigidity, heat resistance at high temperatures, and the like. If the mesopentad fraction is 99.9% or less, it is easier to reduce the cost of polypropylene production and make the film less susceptible to breakage during film formation. The mesopentad fraction is measured by nuclear magnetic resonance spectroscopy (NMR spectroscopy). In order to adjust the mesopentad fraction of the polypropylene resin to fall within the above range, for example, methods such as washing the obtained polypropylene resin powder with a solvent such as n-heptane, or using an appropriate catalyst and / or co-catalyst may be used.

[0029] The melt flow rate (MFR) of the polypropylene resin, which is the main component of the polypropylene resin composition constituting the biaxially oriented polypropylene film of the present invention, measured in accordance with JIS K 7210 (1995) Condition M (230°C, 2.16 kgf), 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, even more preferably 5.0 to 20 g / 10 min, particularly preferably 6.0 to 20 g / 10 min, and most preferably 7.5 to 15 g / 10 min. When the MFR of the polypropylene resin is 4.0 g / 10 min or more, a biaxially oriented polypropylene film with a low heat shrinkage rate is easily obtained. Furthermore, when the MFR of the polypropylene resin is 30 g / 10 min or less, the film formability of the film is easily maintained.

[0030] (2) Film-forming method for biaxially oriented polypropylene film The biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made of a polypropylene resin composition containing a polypropylene resin as a main component, and biaxially stretching the sheet. Regarding biaxial stretching, it is preferable to stretch the sheet in the longitudinal direction and then in the width direction, but it may also be stretched in the width direction and then in the longitudinal direction. Examples of biaxial stretching methods include inflation simultaneous biaxial stretching, tenter simultaneous biaxial stretching, tenter sequential biaxial stretching, and tube stretching. From the viewpoint of film-forming stability and thickness uniformity, tenter sequential biaxial stretching is preferred.

[0031] The method for producing a biaxially oriented polypropylene film of the present invention will be described below. Hereinafter, a method for producing a single-layer biaxially oriented polypropylene film using a tenter sequential biaxial stretching method will be described, but the method is not limited to the following production method.

[0032] First, a polypropylene resin composition is heated and melted in a single-screw or twin-screw extruder, extruded through a T-die into a sheet, and then cooled and solidified by contacting it with a cooling roll to obtain an unstretched sheet. Next, this unstretched sheet is stretched in the longitudinal direction between two pairs of heated stretching rolls by increasing the rotation speed of the rear stretching roll to obtain a uniaxially stretched film. Subsequently, the uniaxially stretched film is heated in a preheating step, stretched in the width direction while gripping the film edges in a tenter-type stretching machine, heat-treated, and finally cooled to obtain a biaxially oriented polypropylene film. If necessary, at least one side of the biaxially oriented polypropylene film can be surface-treated, and then wound on a winder to obtain a film roll. Below, the extrusion step, longitudinal stretching step, preheating step, width stretching step, heat-treatment step, and cooling step will be described in this order.

[0033] <Extrusion Process> First, a polypropylene resin composition containing a polypropylene resin as a main component is heated and melted in a range of 200°C to 300°C using a single-screw or twin-screw extruder. The molten polypropylene resin composition is extruded from a T-die into a sheet shape, and then the extruded composition is brought into close contact with a metal cooling roll using a contacting device such as an air knife. The resulting unstretched sheet is then cooled and solidified to obtain an unstretched sheet. The resulting unstretched sheet may then be placed in a water bath. The temperature of the cooling roll, or the cooling roll and water bath, is preferably 10°C or higher and Tc°C or lower. To increase the transparency of the film, cooling and solidification using a cooling roll at 10 to 50°C is preferred. When using a propylene homopolymer with a mesopentad fraction of 97.0% or higher, the cooling temperature is preferably 40°C or lower to facilitate the subsequent stretching step, and more preferably 30°C or lower to reduce thickness unevenness. However, a cooling temperature of 40°C or higher may be preferred to increase the degree of crystalline orientation after sequential biaxial stretching. From the viewpoint of cooling efficiency, the thickness of the unstretched sheet is preferably 3500 μm or less, more preferably 3000 μm or less. The thickness of the unstretched sheet may be appropriately adjusted depending on the thickness of the film after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition, the lip width of the T-die, etc.

[0034] <Longitudinal Stretching Step> The longitudinal stretching temperature is preferably Tm-30 to Tm-7°C, more preferably Tm-27 to Tm-10°C, and even more preferably Tm-25 to Tm-12°C. At Tm-30°C or higher, the subsequent widthwise stretching is facilitated and thickness unevenness is reduced. Furthermore, at Tm-7°C or lower, the heat shrinkage is easily reduced, and there is little risk of the film being difficult to stretch when applied to a stretching roll or of the film becoming rough on the surface, resulting in a decrease in quality. The longitudinal stretching ratio is preferably 3.5 to 8.0 times, more preferably 3.8 to 7.0 times, and even more preferably 4.2 to 6.0 times. At 3.5 times or higher, strength is easily increased and thickness unevenness is easily reduced. At 8.0 times or lower, widthwise stretching is easily performed in the widthwise stretching step, and productivity is easily improved. Although the longitudinal stretching may be performed in two or more stages using three or more pairs of stretching rolls, it is preferable to perform the stretching in one stage using two pairs of stretching rolls. When the stretching is performed in multiple stages, it is preferable that the highest stretching temperature is within the above range.

[0035] <Preheating Step> It is preferable to heat the uniaxially stretched film after longitudinal stretching in the preheating step to sufficiently soften the polypropylene resin composition before the widthwise stretching step. The heating temperature in the preheating step is preferably Tm to Tm + 25°C, more preferably Tm + 2 to Tm + 20°C, and even more preferably Tm + 3 to Tm + 15°C. By setting the heating temperature in the preheating step to the melting point or higher, softening proceeds, making widthwise stretching easier. Furthermore, by setting the heating temperature in the preheating step to Tm + 25°C or lower, orientation proceeds during widthwise stretching, making it easier to develop rigidity. Note that if the preheating step consists of multiple zones, the temperature of the hottest zone among them is taken as the preheating temperature.

[0036] <Width Direction Stretching Step> The width direction stretching temperature is preferably Tm-10°C or higher and lower than the heating temperature in the preheating step. Tm-10°C or higher tends to improve the rigidity of the resulting film. Furthermore, a temperature of Tm-9 to Tm+10°C is more preferable, Tm-7 to Tm+7°C is even more preferable, and Tm-5 to Tm+5°C is particularly preferable. Tm+10°C or lower tends to reduce stretching unevenness. In the width direction stretching step, a width direction stretching step in the above temperature range (hereinafter sometimes referred to as the early stretching step) may be followed by a later stretching step in which stretching is performed at a lower temperature. Providing a later stretching step tends to increase the rigidity of the film. The width direction stretching ratio is preferably 10 to 20 times, more preferably 11 to 17 times, even more preferably 12 to 15 times, and particularly preferably 12.5 to 15 times. A temperature of 10 times or higher tends to increase rigidity and reduce thickness unevenness. Furthermore, when the stretching ratio is 20 times or less, the heat shrinkage rate can be easily reduced and the film is less likely to break during stretching. When a later stretching step is added, it is preferable that the total stretching ratio be in the above range.

[0037] <Heat Treatment Step> Heat treatment is carried out after the width direction stretching step is completed. Specific means for heat treatment include a method of providing a zone with a higher temperature than the stretching zone after the width direction stretching is completed, a method of increasing the zone temperature in the latter half of stretching and passing the film through a zone of the same temperature after the stretching is completed, etc. Heating means include a method of blowing hot air or a method of heating with an infrared heater, but are not particularly limited as long as the method is capable of increasing the temperature of the film from that at the end of the width direction stretching step.

[0038] The heat treatment step is preferably carried out immediately after the width direction stretching step is completed (i.e., immediately after the width direction stretching reaches the final stretch ratio). The temperature in the heat treatment step is preferably higher than that at the end of the width direction stretching step, and specifically, is preferably the width direction stretching temperature + 1°C or more. The heat treatment step is preferably carried out in two stages, an early heat treatment step and a later heat treatment step, and it is preferable that the early heat treatment step is performed at a temperature higher than that at the end of the width direction stretching step, and then the later heat treatment step is performed at a temperature lower than that in the early heat treatment step. The early heat treatment step and the later heat treatment step will be described below.

[0039] (Preliminary Heat Treatment Step) The heating temperature in the initial heat treatment step is preferably Tm to Tm + 20°C, more preferably Tm + 3 to Tm + 18°C, even more preferably Tm + 4 to Tm + 14°C, and particularly preferably Tm + 5 to Tm + 10°C. Heating in the heat treatment step after the stretching step relaxes the molecular chain orientation formed during stretching, making crystallization more likely to occur in the final heat treatment step. Heating at a temperature lower than Tm°C prevents relaxation, leaving the molecular chains highly tense and potentially inhibiting crystallization. On the other hand, heating at a temperature higher than Tm + 20°C promotes melting, relaxing many of the oriented molecular chains and reducing rigidity. The temperature can be gradually increased from the temperature at the end of width direction stretching to the heating temperature, or it can be increased in stages or in a single step. Raising the temperature in stages or in a single step is preferred because it makes it easier to control the molecular chain orientation in the film. In the heat treatment step, the film may or may not be relaxed (relaxed) in the width direction. Specifically, the relaxation rate is preferably 0 to 3%, more preferably 0 to 1%, and even more preferably 0% (no relaxation). Within the above range, the rigidity is less likely to decrease and the film thickness fluctuations tend to be small. If the relaxation rate is higher than 3%, many of the oriented molecular chains are relaxed, so the rigidity is likely to decrease. Note that relaxation is not necessary if a higher rigidity is desired. Furthermore, the film may be slightly expanded to suppress sagging, etc., as long as it does not impair the effects of the present invention.

[0040] (Later Heat Treatment Step) The heating temperature in the later heat treatment step is preferably Tm-70 to Tm°C, more preferably Tm-50 to Tm-1°C, even more preferably Tm-40 to Tm-2°C, and particularly preferably Tm-30 to Tm-3°C. When heat treatment is performed at a temperature higher than Tm°C, crystallization does not proceed and the heat shrinkage rate is less likely to decrease. On the other hand, when heat treatment is performed at a temperature lower than Tm-70°C, lamellar thickening does not proceed and the melting point of the film is less likely to increase. In other words, heat resistance at high temperatures is impaired. In the later heat treatment step, the film may be relaxed in the width direction to adjust the heat shrinkage rate. When relaxed, the relaxation rate is preferably 1 to 8%, more preferably 2 to 6%, and even more preferably 3 to 5%, but relaxation is not necessary. Within the above range, rigidity is less likely to decrease and film thickness variation is likely to be small. However, relaxation is not necessary if greater rigidity is desired.

[0041] During the widthwise stretching process, molecular chains are oriented by stretching, but remain strongly entangled, resulting in an excessively constrained state of the molecular chains. If a heat treatment process is performed in this state, the excessively constrained molecular chains due to entanglement make it difficult to increase the crystallinity, and the lamellae in the crystalline region do not increase in thickness. This leads to the formation of crystalline regions that melt at lower temperatures, resulting in insufficient heat resistance at high temperatures. Therefore, in conventional film-forming processes, in order to eliminate the entanglement of molecular chains after widthwise stretching, the film is relaxed by several percent to several tens of percent during the heat treatment process to promote crystallization. However, relaxation reduces the molecular chain orientation generated during the widthwise stretching process, resulting in a decrease in the rigidity of the film. Therefore, it is difficult to achieve both heat resistance and rigidity in conventional film-forming processes. Furthermore, heat treatment at high temperatures can cause excessive melting, resulting in the whitening of the film. To solve this problem, it is preferable to perform a heat treatment immediately after the widthwise stretching step at a temperature higher than that used for the widthwise stretching step, at a relaxation rate of 3% or less, thereby eliminating the constraint of the molecular chains due to excessive entanglement while maintaining the molecular chain orientation. By performing this heat treatment step, the presence of constrained molecular chains due to entanglement of molecular chains is reduced, which increases the degree of crystallinity and makes it easier to increase the thickness of the lamellae in the crystalline portion, thereby enabling the film to exhibit sufficient heat resistance even at high temperatures.

[0042] Furthermore, increasing the amount of low molecular weight polypropylene components in the polypropylene resin composition constituting the biaxially oriented polypropylene film can reduce the entanglement of molecular chains, thereby weakening the heat shrinkage stress in parts other than the lamellae of the crystalline portion and further reducing the heat shrinkage rate, which is preferable.

[0043] (Cooling step) It is preferable to cool the film immediately after the heat treatment step. The cooling temperature is preferably 10°C or higher and 140°C or lower, more preferably 15°C or higher and 135°C or lower, even more preferably 20°C or higher and 130°C or lower, particularly preferably 20°C or higher and 80°C or lower, and most preferably 20°C or higher and 50°C or lower. By providing the cooling step, the state of molecular orientation in the film can be fixed.

[0044] Although the manufacturing method for the biaxially oriented polypropylene film of the present invention when it is a single layer has been described above, the biaxially oriented polypropylene film of the present invention may have a layer having another function (hereinafter referred to as a functional layer) laminated on at least one side. The functional layer may be laminated on only one side or on both sides. When the functional layer contains a resin, the resin may be the polypropylene resin constituting the biaxially oriented polypropylene film, or a resin other than the polypropylene resin constituting the biaxially oriented polypropylene film. The number of functional layers may be one, two, or three or more per side, but from the viewpoint of ease of manufacturing, one or two layers is preferred. The lamination method is not particularly limited, and, for example, coextrusion using a feed block method or a multi-manifold method is preferred. As long as the effects of the present invention are not impaired, a resin layer having heat sealability can be laminated as a functional layer to improve the processability of the biaxially oriented polypropylene film. In addition, corona treatment can be performed on one or both sides of the film to impart printability.

[0045] The biaxially oriented polypropylene film of the present invention can be wound into a roll to form a film roll having a width of about 2,000 to 12,000 mm and a length of about 1,000 to 50,000 m, making it possible to obtain a long film roll. It can also be slit according to the intended use to form a slit roll having a width of about 300 to 2,000 mm and a length of about 500 to 5,000 m.

[0046] (3) Physical Properties of Biaxially Oriented Polypropylene Film The biaxially oriented polypropylene film of the present invention preferably has the following properties. Here, the "longitudinal direction (MD direction)" of the biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction in the film production process, and the "width direction (TD direction)" refers to the direction perpendicular to the flow direction in the film production process, and the same applies hereinafter. For polypropylene films whose flow direction in the film production process is unknown, wide-angle X-rays are incident perpendicular to the film surface, and scattering peaks derived from the (110) plane of the α-crystals are scanned in the circumferential direction. The direction with the greatest diffraction intensity in the obtained diffraction intensity distribution is defined as the "longitudinal direction," and the direction perpendicular to that is defined as the "width direction."

[0047] <Length in Width Direction> In a thermomechanical analysis, when the temperature was increased from 30° C. to 130° C. at a temperature increase rate of 10° C. / min, the length in the width direction of the biaxially oriented polypropylene film of the present invention at 30° C. was determined as X ０ The maximum value of the width direction length during the temperature rise is X １ , the minimum value of the length in the width direction during the temperature rise is X ２ Then, (X １ -X ０ ) / X ０ The percentage of (X) is preferably 0.20% or less, more preferably 0.19% or less, even more preferably 0.18% or less, particularly preferably 0.17% or less, and most preferably 0.16% or less. When it is 0.20% or less, deformation of the film can be suppressed even after the film is heated at high temperatures during heat processing with a roll, printing, or heat sealing, so that the flatness of the film is less likely to deteriorate and the processability of the film can be improved. Furthermore, high-temperature printing ink is transferred during printing, and printing pitch deviation is less likely to occur during this process. (X) １ -X ０ ) / X ０ The lower limit is not particularly limited, but in view of technical difficulties, it is, for example, 0.01% or more, preferably 0.02% or more. (X ２ -X ０ ) / X ０is preferably -0.50% or more, more preferably -0.45% or more, even more preferably -0.40% or more, particularly preferably -0.35% or more, and most preferably -0.30% or more. When it is -0.50% or more, deformation of the film can be suppressed even after the film is heated at high temperatures during heat processing with a roll, printing, or heat sealing, so that the flatness of the film is less likely to deteriorate and the processability of the film can be improved. (X ２ -X ０ ) / X ０ The larger the content, the better. There is no particular upper limit to the content, but it is, for example, 0.00% or less.

[0048] In a thermomechanical analysis, when the temperature was increased from 30°C to 160°C at a heating rate of 10°C / min, the length in the width direction of the biaxially oriented polypropylene film of the present invention was 0.9950X. ０ The temperature at which the shrinkage becomes equal to or less than 0.9950°C (temperature at 0.5% shrinkage) is preferably 129°C or higher, more preferably 130°C or higher, even more preferably 131°C or higher, particularly preferably 132°C or higher, and most preferably 133°C or higher. ０ The temperature at which the width is 0.9950X or less when the temperature is increased from 30°C to 160°C at a rate of 10°C / min. ０ It refers to the lowest temperature that is below 0.9950X ０ When the temperature at which the temperature becomes equal to or lower than 129°C, deformation of the film can be suppressed even after the film is heated at high temperatures during heat processing with a roll, printing, or heat sealing, so that the flatness of the film is less likely to deteriorate and the processability of the film can be improved. ０ The temperature at which the thickness becomes equal to or less than 0.9950X is preferably higher, and the upper limit is not particularly limited, but is, for example, 160°C or lower, preferably 156°C or lower. When the temperature is 160°C or lower, practical production is easy and transparency is easily maintained. In addition, even when the temperature is increased from 30°C to 160°C, the length in the width direction never becomes equal to or less than 0.9950X. ０ If it is not below this, the temperature at 0.5% shrinkage is determined to exceed 160°C.

[0049] <Loss modulus> The loss modulus was determined by dynamic viscoelasticity measurement. Specifically, the temperature was increased from −60° C. to 160° C. at a rate of 5° C. / min in a nitrogen atmosphere under a measurement load of 10 g and a frequency of 10 Hz, and the loss modulus was measured at each temperature during the temperature increase.

[0050] Hereinafter, five parameters related to the loss modulus will be described: the maximum value E"(A) of the loss modulus between -25°C and 25°C, the minimum value E"(B) of the loss modulus between 25°C and 75°C, the maximum value E"(C) of the loss modulus between 100°C and 160°C, E"(C) / E"(A), and E"(B) / E"(C). In this specification, even when simply referring to "loss modulus," it always refers to the loss modulus in the width direction.

[0051] [Maximum value E"(A) of loss modulus between -25°C and 25°C] Takayanagi Motoo, "Temperature Dispersion of Crystalline Polymers", Polymer, Society of Polymer Science, 1961, Vol. 10, No. 3, pp. 289-295, describes that in polypropylene films, relaxation (main dispersion) due to micro-Brownian motion of the main chain occurs between -25°C and 25°C, and also describes that the loss modulus between -25°C and 25°C increases as the degree of orientation by stretching increases. The present inventors have found that by using highly stereoregular polypropylene and employing the above-mentioned width direction stretching process, it is possible to increase the orientation in the film, i.e., to increase the value of the loss modulus between -25°C and 25°C.

[0052] E"(A) is preferably 0.40 GPa or more, more preferably 0.42 GPa or more, even more preferably 0.44 GPa or more, particularly preferably 0.46 GPa or more, and most preferably 0.48 GPa or more. When E"(A) is 0.40 GPa or more, rigidity tends to be high. There is no particular restriction on the upper limit of E"(A), but a realistic value is, for example, 0.70 GPa or less, and preferably 0.60 GPa or less.

[0053] [Minimum Value E"(B) of Loss Modulus at 25°C to 75°C] Takayanagi Motoo, "Temperature Dispersion of Crystalline Polymers," Polymer, Society of Polymer Science, 1961, Vol. 10, No. 3, pp. 289-295, describes that by increasing the crystallinity in a film, which contributes greatly to heat resistance, and reducing the amount of crystals that melt in a relatively low temperature range above the glass transition temperature of the polypropylene resin (hereinafter referred to as the low temperature range), relaxation due to melting is less likely to occur, and as a result, relaxation of the amorphous portion is also suppressed (even when treated at high temperatures, the mobility of the amorphous portion is reduced, resulting in good heat resistance). The present inventors have found that by using highly stereoregular polypropylene and employing the above-mentioned width direction stretching process, it is possible to reduce the amount of crystals that melt in the low temperature range, and thereby reduce the change in loss modulus from the glass transition temperature to 75°C.

[0054] E"(B) is preferably 0.26 GPa or more, more preferably 0.27 GPa or more, even more preferably 0.28 GPa or more, particularly preferably 0.29 GPa or more, and most preferably 0.30 GPa or more. If E"(B) is 0.26 GPa or more, the heat shrinkage rate is likely to decrease. Furthermore, if E"(B) is 0.26 GPa or more, fewer crystals will melt in the low temperature range, thereby improving flatness. There are no particular restrictions on the upper limit of E"(B), but a realistic value is, for example, 0.60 GPa or less, and preferably 0.50 GPa or less.

[0055] [Maximum value of loss modulus E"(C) at 100°C to 160°C] Takayanagi Motoo, "Temperature Dispersion of Crystalline Polymers," Polymer, Society of Polymer Science, 1961, Vol. 10, No. 3, pp. 289-295, describes that when the loss modulus of a stretched polypropylene film is measured at each temperature while the temperature is increased, a peak due to crystal dispersion appears at 100°C or higher. This crystal dispersion peak is thought to be due to an increase in frictional viscosity between the planes of the crystalline structure, and increases when the film is stretched at an optimum temperature during film formation. An increase in frictional viscosity indicates strong stress transmission within the crystalline phase, and is thought to correlate with increased rigidity. From the above, the present inventors have found that the maximum value of the loss modulus at 100°C or higher can be increased by using highly stereoregular polypropylene and employing the above-mentioned width direction stretching process.

[0056] E"(C) is preferably 0.28 to 0.80 GPa, more preferably 0.29 to 0.75 GPa, even more preferably 0.30 to 0.70 GPa, particularly preferably 0.31 to 0.65 GPa, and most preferably 0.32 to 0.60 GPa. When E"(C) is 0.28 GPa or more, the rigidity is high, so that the shape of the bag when made into a packaging bag is easily maintained, and deformation of the film is less likely to occur during processing such as printing. Furthermore, when E"(C) is 0.80 GPa or less, practical production is easy and tearing in the width direction is less likely.

[0057] E"(C) / E"(A) is preferably 0.60 to 1.30, more preferably 0.62 to 1.20, even more preferably 0.64 to 1.10, particularly preferably 0.66 to 1.00, and most preferably 0.68 to 0.90. When E"(C) / E"(A) is 0.60 or more, the rigidity is high, so that the bag shape when made into a packaging bag is easily maintained, and deformation of the film is less likely to occur during processing such as printing. Furthermore, when E"(C) / E"(A) is 1.30 or less, practical production is easy and tearing in the width direction is less likely.

[0058] E"(B) / E"(C) is 0.60 or more, preferably 0.60 to 1.30, more preferably 0.61 to 1.25, even more preferably 0.62 to 1.20, particularly preferably 0.63 to 1.15, and most preferably 0.64 to 1.10. When E"(B) / E"(C) is 0.60 or more, there is little crystal melting in the low temperature range, making it difficult for relaxation to occur due to melting, which in turn suppresses relaxation of the amorphous portion. As a result, the mobility of the amorphous portion is low even when treated at high temperatures, and flatness and heat resistance can be improved. When E"(B) / E"(C) is 1.30 or less, rigidity is less likely to decrease, and fluctuations in film thickness are likely to be small.

[0059] <Storage Modulus> The storage modulus was determined by dynamic viscoelasticity measurement. Specifically, the temperature was increased from −60° C. to 160° C. at a rate of 5° C. / min under a nitrogen atmosphere with a measurement load of 10 g and a frequency of 10 Hz, and the storage modulus was measured at each temperature during the temperature increase.

[0060] The storage modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 2.0 to 5.0 GPa, more preferably 2.3 to 4.5 GPa, even more preferably 2.5 to 4.3 GPa, particularly preferably 2.8 to 4.2 GPa, and most preferably 3.0 to 4.0 GPa. The storage modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 8.0 to 15.0 GPa, more preferably 8.2 to 14.0 GPa, even more preferably 8.4 to 13.5 GPa, and particularly preferably 8.6 to 13.0 GPa. When the storage moduli in the longitudinal and width directions at 23°C are within the above ranges, the strength of the biaxially oriented polypropylene film is significantly increased, and even if the film is thin, it can maintain its stiffness and strength, which greatly contributes to reducing the volume of the film. Furthermore, the flatness of the film is less likely to deteriorate and the processability of the film can be improved.

[0061] The storage modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 120° C. is preferably 0.5 to 2.5 GPa, more preferably 0.6 to 2.3 GPa, even more preferably 0.7 to 2.1 GPa, and particularly preferably 0.8 to 2.0 GPa. When the storage modulus in the longitudinal direction at 120° C. is within the above range, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when hot printing ink is transferred during printing.

[0062] The storage modulus in the width direction at 120°C of the biaxially oriented polypropylene film of the present invention is preferably 2.1 to 8.0 GPa, more preferably 2.2 to 7.8 GPa, even more preferably 2.3 to 7.6 GPa, and particularly preferably 2.4 to 7.4 GPa. When the storage modulus in the width direction at 120°C is within the above range, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. Furthermore, the flatness of the film is less likely to deteriorate, and the processability of the film can be improved.

[0063] The storage modulus in the longitudinal direction at 140°C of the biaxially oriented polypropylene film of the present invention is preferably 0.3 to 1.5 GPa, more preferably 0.35 to 1.45 GPa, even more preferably 0.4 to 1.4 GPa, and particularly preferably 0.45 to 1.35 GPa. The storage modulus in the width direction at 140°C of the biaxially oriented polypropylene film of the present invention is preferably 1.3 to 5.0 GPa, more preferably 1.35 to 4.6 GPa, even more preferably 1.4 to 4.2 GPa, and particularly preferably 1.45 to 3.8 GPa. When the storage moduli in the longitudinal and width directions at 140°C are within the above ranges, the strength at high temperatures tends to be increased, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. Furthermore, the flatness of the film is less likely to deteriorate, and the processability of the film can be improved.

[0064] The storage modulus in the longitudinal direction at 150°C of the biaxially oriented polypropylene film of the present invention is preferably 0.1 to 1.0 GPa, more preferably 0.15 to 0.9 GPa, even more preferably 0.2 to 0.8 GPa, and particularly preferably 0.25 to 0.7 GPa. The storage modulus in the width direction at 150°C of the biaxially oriented polypropylene film of the present invention is preferably 0.85 to 2.5 GPa, more preferably 0.9 to 2.4 GPa, even more preferably 0.95 to 2.3 GPa, and particularly preferably 1.0 to 2.2 GPa. When the storage moduli in the longitudinal and width directions at 150°C are within the above ranges, the strength at high temperatures tends to be increased, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. Furthermore, the flatness of the film is less likely to deteriorate, and the processability of the film can be improved.

[0065] The sum of the storage modulus in the longitudinal direction at 23°C and the storage modulus in the longitudinal direction at 140°C of the biaxially oriented polypropylene film of the present invention is 3.0 GPa or more, preferably 3.0 to 8.0 GPa, more preferably 3.1 to 7.5 GPa, even more preferably 3.2 to 7.0 GPa, and particularly preferably 3.3 to 6.5 GPa. The sum of the storage modulus in the width direction at 23°C and the storage modulus in the width direction at 140°C of the biaxially oriented polypropylene film of the present invention is 9.2 GPa or more, preferably 9.2 to 19.0 GPa, more preferably 9.2 to 18.0 GPa, even more preferably 9.8 to 17.0 GPa, and particularly preferably 10.0 to 16.0 GPa. When the sum of the longitudinal storage modulus at 23°C and the longitudinal storage modulus at 140°C in the longitudinal and width directions is within the above range, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when hot printing ink is transferred during printing. In addition, the flatness of the film is less likely to deteriorate and the processability of the film can be improved.

[0066] <Thickness> The thickness of the biaxially oriented polypropylene film of the present invention can be appropriately set depending on the application and is not particularly limited, but is preferably 2 to 100 μm, more preferably 3 to 80 μm, even more preferably 4 to 60 μm, particularly preferably 8 to 50 μm, and most preferably 10 to 40 μm. A thickness of 2 μm or more makes it easier to obtain rigidity in the film, and as a result, makes it easier to obtain strength in the film. Furthermore, a thickness of 100 μm or less makes it difficult for the cooling rate of the unstretched sheet to decrease during the extrusion process.

[0067] <Stress at 5% Elongation (F5)> The stress at 5% elongation (F5) in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 40 to 70 MPa, more preferably 42 to 65 MPa, even more preferably 46 to 62 MPa, and particularly preferably 48 to 60 MPa. At 40 MPa or higher, the film has high rigidity, making it easier to maintain the shape of the packaging bag when made into it, and the film is less likely to deform during processing such as printing. At 70 MPa or lower, practical production becomes easier and the balance between the longitudinal and transverse directions tends to improve. The F5 in the longitudinal direction can be adjusted within the above range by adjusting the stretch ratio and relaxation rate, or by adjusting the temperature during film formation.

[0068] The stress at 5% elongation in the width direction (F5) of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 150 to 280 MPa, more preferably 152 to 250 MPa, even more preferably 154 to 230 MPa, particularly preferably 156 to 210 MPa, and most preferably 158 to 200 MPa. At 150 MPa or higher, the film has high rigidity, making it easier to maintain the shape of the packaging bag, and the film is less likely to deform during processing such as printing. At 280 MPa or lower, practical manufacturing is easier and the film is less likely to tear in the width direction. The F5 in the width direction can be adjusted within the above range by adjusting the stretch ratio and relaxation rate, or by adjusting the temperature during film formation.

[0069] <Heat shrinkage rate> The heat shrinkage rate in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 2.5% or less, more preferably 2.0% or less, even more preferably 1.7% or less, and particularly preferably 1.5% or less. If it is 2.5% or less, printing pitch deviation is less likely to occur when transferring printing ink. The lower the heat shrinkage rate in the longitudinal direction at 120°C, the more preferable it is. Although there is no particular restriction on the lower limit, in view of technical difficulties, it is, for example, 0.1% or more, preferably 0.3% or more. The heat shrinkage rate in the longitudinal direction at 120°C can be adjusted to fall within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0070] The heat shrinkage rate in the width direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 1.1% or less, more preferably 1.0% or less, even more preferably 0.7% or less, particularly preferably 0.5% or less, and most preferably 0.3% or less. When it is 1.1% or less, wrinkles are less likely to occur during heat sealing. The lower limit of the heat shrinkage rate in the width direction at 120°C is not particularly limited, but is, for example, -0.2%. The heat shrinkage rate in the width direction at 120°C can be kept within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0071] The heat shrinkage rate in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 10% or less, more preferably 7.0% or less, even more preferably 6.0% or less, particularly preferably 4.5% or less, and most preferably 4.0% or less. If it is 10% or less, printing pitch deviation is less likely to occur when transferring printing ink. A lower heat shrinkage rate in the longitudinal direction at 150°C is preferable, and although there is no particular lower limit, in view of technical difficulties, it is, for example, 0.1% or more, preferably 0.5% or more. The heat shrinkage rate in the longitudinal direction at 150°C can be kept within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0072] The heat shrinkage rate in the width direction of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 20% or less, more preferably 15% or less, even more preferably 12% or less, particularly preferably 10% or less, and most preferably 9.0% or less. If it is 20% or less, wrinkles are less likely to occur during heat sealing. The lower limit of the heat shrinkage rate in the width direction at 150°C is not particularly limited, but is, for example, 0% or more, preferably 1% or more. The heat shrinkage rate in the width direction at 150°C can be kept within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0073] If the heat shrinkage rate in the longitudinal direction at 150°C is 10% or less and the heat shrinkage rate in the width direction is 20% or less, wrinkles are less likely to occur during heat sealing, and it is particularly preferable that the heat shrinkage rate in the longitudinal direction at 150°C is 8.0% or less and the heat shrinkage rate in the width direction at 150°C is 15% or less, because this reduces distortion when a zipper is fused to the opening of the bag when used as a packaging bag. In order to reduce the heat shrinkage rate at 150°C, it is effective to set the amount of components with a molecular weight of 100,000 or less to 35% by mass or more when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin composition constituting the film.

[0074] <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%, 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 or printing, making it suitable for applications requiring precision. The measurement method was as follows. A test piece 40 mm in width was cut from a steady region where the film properties were stable in the length direction of the film. The film thickness was measured continuously over 20,000 mm using a film feeder 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 using the following formula: Thickness uniformity (%) = [(maximum thickness - minimum thickness) / average thickness] x 100

[0075] The biaxially oriented polypropylene film of the present invention exhibits little dimensional change over the entire temperature range from room temperature to 130°C. Therefore, film deformation can be suppressed even after heating at high temperatures, such as during heat processing with a roll, printing, or heat sealing. This prevents the film from losing its flatness and improves its processability. Furthermore, thinner films are possible, contributing to the reduction of packaging material volume. For these reasons, when the biaxially oriented polypropylene film of the present invention is used, the film easily maintains its shape when made into a packaging bag, is less likely to deform during processing such as heat sealing at high temperatures, and is less likely to cause printing pitch deviation during printing, making it suitable for packaging applications. Furthermore, the film is less likely to lose flatness even after being coated with a silicone release agent and heated and dried, making it suitable as a release film for optical applications and other applications requiring high flatness.

[0076] To form a bag for packaging food, the contents are filled into a pre-made bag, and the film is heated to melt and fuse to seal it. This process is often used when making a bag while filling it with food. Typically, a sealant film made of polyethylene resin, polypropylene resin, or the like is laminated onto a base film (the biaxially oriented polypropylene film of the present invention), and the sealant film surfaces are fused together. The heating method involves applying pressure from a heating plate from the base film side to hold down the film and seal it, with a seal width of approximately 10 mm being common. Since the base film is also heated during this process, the resulting expansion and contraction causes wrinkles. Fewer wrinkles are desirable for bag durability and to increase consumer appetite. While the sealing temperature may be around 120°C, a higher temperature is required to increase the bag-making processing speed, and even in this case, minimal expansion and contraction is preferable. Furthermore, if a zipper is fused to the opening of the bag, sealing at an even higher temperature is required.

[0077] (4) Others Printing on the biaxially oriented polypropylene film of the present invention can be carried out by letterpress printing, lithographic printing, intaglio printing, stencil printing, transfer printing, or the like, depending on the application.

[0078] In addition, an unstretched sheet, uniaxially oriented film, or biaxially oriented film made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, or polyester can be laminated as a sealant film to the biaxially oriented polypropylene film of the present invention to form a laminate having heat sealability.

[0079] When gas barrier properties and heat resistance are to be improved, an intermediate layer of aluminum foil, an unstretched sheet, a uniaxially stretched film, or a biaxially stretched film can be provided between the biaxially oriented polypropylene film of the present invention and the sealant film. The raw materials constituting the unstretched sheet, uniaxially stretched film, and biaxially stretched film are not particularly limited, and examples thereof include polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol. Furthermore, an adhesive applied by dry lamination or hot melt lamination can be used to attach the sealant film.

[0080] In order to improve the gas barrier properties, inorganic oxides such as aluminum, silica, and alumina can be vapor-deposited onto the biaxially oriented polypropylene film, the intermediate layer, or the sealant film. Vacuum deposition, sputtering, ion plating, and other known methods can be used as the vapor deposition method.

[0081] The biaxially oriented polypropylene film of the present invention can be made suitable as a packaging material for vegetables, fruits, flowers, and other fresh produce by incorporating an anti-fogging agent such as a fatty acid ester of a polyhydric alcohol, an amine of a higher fatty acid, an amide of a higher fatty acid, or an ethylene oxide adduct of an amine or an amide of a higher fatty acid in an amount ranging from 0.2 to 5 mass%.

[0082] When used as packaging film, it is often made of a laminated film of a printed base film and a sealant film. Examples include three-sided bags, standing bags, and gusset bags, and they can be manufactured using known bag-making machines. It is believed that print pitch deviation occurs because the film base expands and contracts due to the tension and heat applied to the film during the printing process. Eliminating defective products due to print pitch deviation is important in terms of efficient resource utilization and also in increasing purchasing desire.

[0083] This application claims the benefit of priority based on Japanese Patent Applications Nos. 2023-097939, 2023-097940, and 2023-097941, filed on June 14, 2023. The entire contents of the specifications of Japanese Patent Applications Nos. 2023-097939, 2023-097940, and 2023-097941, filed on June 14, 2023, are incorporated herein by reference.

[0084] The present invention will be described in detail below with reference to examples. Of course, the present invention is not limited to these examples. The evaluation methods used in each example and comparative example are as follows. In the following (2) to (4), various physical properties of the polypropylene resin were measured, and for polypropylene resin compositions using two types of polypropylene resins, the mass average of the physical property values ​​of each polypropylene resin was used as the physical property value of the polypropylene resin composition. Meanwhile, in the following (1), for polypropylene resin compositions using two types of polypropylene resins, the melt flow rate of the two polypropylene resins in a blended state was measured.

[0085] (1) Melt Flow Rate The melt flow rate (MFR) was measured in accordance with JIS K7210 at a temperature of 230°C and a load of 2.16 kgf.

[0086] (2) Mesopentad fraction The mesopentad fraction ([mmmm]%) was measured by １３ The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). １３ C-NMR measurement was performed using an AVANCE 500 manufactured by BRUKER, by dissolving 200 mg of a sample in a 8:2 mixture of o-dichlorobenzene and deuterated benzene at 135°C and at 110°C.

[0087] (3) Amount of components with a molecular weight of 100,000 or less: Gel permeation chromatography (GPC) was used to determine the molecular weight in terms of polypropylene using monodisperse polystyrene as the standard. When the baseline was unclear, the baseline was set to the lowest point on the high molecular weight side of the elution peak closest to the elution peak of the standard substance. The GPC measurement conditions were as follows: Apparatus: HLC-8321PC / HT manufactured by Tosoh Corporation 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 + TSK gel GMHHR-H (20) HT (7.8 mm I.D. × 30 cm) × 3 Flow rate: 1.0 mL / min Injection amount: 0.3 mL Measurement temperature: 140°C The mass proportion of components having a molecular weight of 100,000 or less was determined from the integral curve of the molecular weight obtained by GPC.

[0088] (4) Melting point and crystallization temperature Thermal measurements were performed using a Q1000 differential scanning calorimeter manufactured by TA Instruments. Approximately 5 mg was cut out from the pellet, placed in an aluminum pan for measurement, and set in a differential scanning calorimeter. Under a nitrogen atmosphere, the resin was melted by heating from 30 ° C. to 230 ° C. at a heating rate of 20 ° C. / min and holding at 230 ° C. for 5 minutes, and then cooled to 30 ° C. at a heating rate of -10 ° C. / min, held at 30 ° C. for 5 minutes, and then heated to 230 ° C. at a heating rate of 10 ° C. / min. The melting point was the main peak temperature of the endothermic peak associated with melting observed during the second heating. The crystallization temperature was the main peak temperature of the exothermic peak observed when the temperature was lowered from 230 ° C. to 30 ° C.

[0089] (5) Film Thickness The film thickness was measured using a Millitron 1202D manufactured by Seiko EM Corporation.

[0090] (6) Thermomechanical analysis (TMA) measurement (measurement of film width from 30°C to 130°C) A film was cut out so that the width of the film was 40 mm and the length of the film was 4 mm, and the film was set in a thermomechanical analyzer TMA-60 manufactured by Shimadzu Corporation so that the chuck width was 10 mm. The temperature was increased from 30°C to 130°C at a rate of 10°C / min with a measurement load of 0.5 g, and the length X of the sample in the width direction during the temperature increase was continuously measured. The maximum value of the length between the chucks during the temperature increase was determined as X. １ (mm), the minimum value of the length between the chucks during the temperature rise is X ２ (mm), (X １ -10) / 10((X １ -X ０ ) / X ０ ) percentage and (X ２ -10) / 10((X ２ -X ０ ) / X ０ ) and the percentage were calculated.

[0091] (7) Thermomechanical analysis (TMA) measurement (temperature measurement at 0.5% shrinkage) A film was cut so that the width direction of the film was 40 mm and the length direction of the film was 4 mm, and the film was set in a thermomechanical analyzer TMA-60 manufactured by Shimadzu Corporation so that the chuck width was 10 mm. The temperature was increased from 30°C to 160°C at a heating rate of 10°C / min with a measurement load of 0.5 g, and the width direction length of the sample was continuously measured during the temperature increase. From the measurement results, the lowest temperature at which the width direction length of the sample was 9.95 mm or less was determined as the temperature at 0.5% shrinkage.

[0092] (8) Loss modulus by dynamic mechanical analysis (DMA) A film was cut to a width of 40 mm and a length of 4 mm, and set in an RSA-G2 (manufactured by TA Instruments Japan) with a chuck width of 10 mm. The film was heated from -60°C to 160°C at a heating rate of 5°C / min under a nitrogen atmosphere with a measuring load of 10 g and a frequency of 10 Hz, and the loss modulus of the film was measured during the heating in the width direction. A graph was drawn with temperature on the horizontal axis and loss modulus on the vertical axis, and the maximum loss modulus E"(A) from -25°C to 25°C, the minimum loss modulus E"(B) from 25°C to 75°C, and the maximum loss modulus E"(C) at 100°C or higher were calculated. The values ​​of E"(C) / E"(A) and E"(B) / E"(C) were also calculated.

[0093] (9) Storage modulus by dynamic mechanical analysis (DMA) The storage modulus in the longitudinal and transverse directions of the film was measured by the following method. A film was cut so that the measurement direction was 40 mm and the direction perpendicular thereto was 4 mm, and the film was set in an RSA-G2 manufactured by TA Instruments Japan Co., Ltd. so that the chuck width was 10 mm. The temperature was raised from -60 ° C to 160 ° C at a heating rate of 5 ° C / min under a nitrogen atmosphere with a measurement load of 10 g and a frequency of 10 Hz, and the storage modulus was determined at 23 ° C, 120 ° C, 140 ° C, and 150 ° C. From the obtained values, the sum of the storage modulus in the longitudinal direction at 23 ° C and the storage modulus at 140 ° C, and the sum of the storage modulus in the transverse direction at 23 ° C and the storage modulus at 140 ° C, respectively, were calculated.

[0094] (10) Stress at 5% Elongation (F5) The stress at 5% elongation (F5) during a tensile test in the longitudinal and transverse directions of a film was measured at 23°C in accordance with JIS K7127. A film was cut so that the measurement direction was 200 mm and the direction perpendicular thereto was 15 mm, and the film was set in a tensile tester (Instron 5965, a dual-column tabletop tester manufactured by Instron Japan Co., Ltd.) with a chuck width of 100 mm. A tensile test was then carried out at a tensile speed of 200 mm / min. From the obtained strain-stress curve, the stress at 5% elongation was taken as F5.

[0095] (11) Heat Shrinkage Rate The heat shrinkage rates of the film in the longitudinal and transverse directions at 120°C were measured in accordance with JIS Z1712 by the following method. A film was cut so that the measurement direction was 200 mm and the direction perpendicular thereto was 20 mm, and the film was hung in a hot air oven at 120°C and heated for 5 minutes. The length after heating was measured, and the heat shrinkage rate at 120°C was calculated as the ratio of the shrunken length to the original length. The heat shrinkage rate at 150°C was also calculated by the same method as the heat shrinkage rate at 120°C, except that the film was hung in a hot air oven at 150°C.

[0096] (12) Appearance Evaluation of Heat-Sealed Portions An adhesive (TM329 / CAT8B manufactured by Toyo-Morton Co., Ltd.) was applied to the obtained film, and then a 30 μm-thick unstretched polypropylene film (P1128 manufactured by Toyobo Co., Ltd.) was dry-laminated on a metal roll heated to 60°C as a sealant film. The laminate was then aged at 40°C for 3 days to obtain a laminate for evaluation. The sealant films of the laminate were heat-sealed together using a heat sealer to form a 130 mm x 180 mm three-sided sealed bag. The seal bar width was 10 mm and the heat sealing temperature was 150°C at a pressure of 0.2 MPa for 1 second. The appearance of wrinkles in the heat-sealed portions was visually evaluated. A: No wrinkles were observed in the heat-sealed portions in either the width or length direction of the film. B: Wrinkles were observed in the heat-sealed portions in only one of the width or length directions of the film. C: Wrinkles were observed in the heat-sealed portions in both the width and length directions of the film.

[0097] (13) Flatness Evaluation (Flatness after Treatment at 130°C) A sample was cut out from the film so that both the width and length directions were 200 mm, and used as a sample for evaluation. The sample was hung in a hot air oven at 130°C and heated for 5 minutes. After cooling to room temperature, the film was placed on a black mount, and the film surface was observed at a 45-degree angle under a fluorescent lamp. A: No heat wrinkles or large waviness of 5 mm or more were present. B: No heat wrinkles were observed, but large waviness of 5 mm or more was observed. C: Heat wrinkles were observed.

[0098] (Example 1) As the polypropylene resin, MFR 7.5 g / 10 min, [mmmm] 98.9%, melting point 162.5 ° C., crystallization temperature 116.2 ° C., propylene homopolymer PP-1 (Sumitomo Chemical Co., Ltd. Sumitomo Noblen FLX80E4) 80 parts by mass of 40.5% by weight of a molecular weight of 100,000 or less, and MFR 11 g / 10 min, [mmmm] 98.8%, melting point 161.5 ° C., crystallization temperature 116.5 ° C., propylene homopolymer PP-2 (Sumitomo Chemical Co., Ltd., EL80F5) 20 parts by mass of 53.1% by weight of a molecular weight of 100,000 or less was blended and used. It was extruded into a sheet from a T-die at 250 ° C., brought into contact with a 20 ° C. cooling roll, and then placed in a 20 ° C. water bath. The film was then stretched 4.5 times in the longitudinal direction using two pairs of rolls at 142°C. Then, both ends were clamped with clips, introduced into a hot air oven, preheated to 172°C, and then stretched 12.7 times in the width direction at 162°C. Immediately after width-direction stretching, the film was heat-treated at 170°C while still held by the clips without relaxation, and then heat-treated at 140°C to relax the film to a relaxation rate of 3% in the width direction. Finally, it was cooled to room temperature (23°C). The thickness of the resulting film was 20.0 μm. Table 1 shows the film production conditions, and Table 2 shows the film's physical properties. As shown in Table 2, the film of Example 1 exhibited excellent flatness after treatment at 130°C, making it suitable for heat-resistant applications such as release films and casting papers. Furthermore, the three-side sealed bags produced using the film of Example 1 had good heat-sealed appearance and excellent stiffness, resulting in good handleability.

[0099] (Examples 2 to 7) In Examples 2 to 7, the films were produced using the same production method as in Example 1, except that the production conditions were changed to those shown in Table 1. Table 1 shows the film production conditions, and Table 2 shows the physical properties of the films. As shown in Table 2, all of the films of Examples 2 to 7 had excellent flatness after treatment at 130°C, making them suitable for applications requiring heat resistance, such as release films and process paper. Furthermore, all of the three-side sealed bags produced using the films of Examples 2 to 7 had good heat-sealed appearance, and the resulting bags had excellent stiffness, making them easy to handle.

[0100] The biaxially oriented polypropylene films produced in Examples 1 to 7 were used to prepare laminates having the following configurations (1) to (9). Using the laminates (1) to (9), 130 mm x 180 mm three-sided seal type, pillow type, and gusset type packaging bags were produced. Regardless of which biaxially oriented polypropylene film of each Example was used, packaging bags with excellent seal strength and seal appearance were produced. (1) Biaxially oriented PP film layer / printed layer / adhesive layer / linear low-density PE film sealant layer; (2) Biaxially oriented PP film layer / printed layer / adhesive layer / unstretched PP film sealant layer; (3) Biaxially oriented PET film layer / printed layer / adhesive layer / biaxially oriented PP film layer / adhesive layer / unstretched PP film sealant layer; (4) Biaxially oriented PET film layer / printed layer / adhesive layer / biaxially oriented PP film layer / adhesive layer / linear low-density PE film sealant layer. (5) Biaxially oriented PP film layer / anchor coat layer / inorganic thin film layer / inorganic thin film protective layer / printed layer / adhesive layer / linear low-density PE film sealant layer. (6) Linear low-density PE film sealant layer / adhesive layer / biaxially oriented PP film layer / anchor coat layer / inorganic thin film layer / adhesive layer / linear low-density PE film sealant layer. (7) Linear low-density PE film layer / adhesive layer / biaxially oriented PP film layer / anchor coat layer / inorganic thin film layer / adhesive layer / linear low-density PE film layer / low-density PE / paper / low-density PE / linear low-density PE film sealant layer. (8) Biaxially oriented PP film layer / anchor coat layer / inorganic thin film layer / inorganic thin film protective layer / printed layer / adhesive layer / unstretched PP film sealant layer. (9) Biaxially oriented PET film layer / inorganic thin film layer / inorganic thin film protective layer / printed layer / PU adhesive layer / biaxially oriented PP film layer / adhesive layer / easy peel type unstretched PP film sealant layer.

[0101] (Comparative Examples 1 to 5) In Comparative Examples 1 to 5, the films were produced by the same production method as in Example 1, except that the film production conditions were changed to those shown in Table 1. Table 1 shows the film production conditions, and Table 2 shows the film properties. In Comparative Example 1 and Comparative Example 9 described below, the first stage of the heat treatment was performed at 100°C, which means that the first stage of the heat treatment was essentially cooling.

[0102] Comparative Example 6 Comparative Example 6 was produced by the same production method as in Example 1, except that only PP-3 (WF836DG3 manufactured by Sumitomo Chemical Co., Ltd.) having an MFR of 7 g / 10 min, [mmmm] of 95.2%, a melting point of 157.8°C, a crystallization temperature of 111.2°C, an ethylene monomer content of 0.4 mol%, and an amount of components having a molecular weight of 100,000 or less of 39.1 mass% was used as the polypropylene resin, and the film production conditions were changed to those shown in Table 1. Table 1 shows the film production conditions, and Table 2 shows the physical properties of the film.

[0103] (Comparative Example 7) A film was produced by the same production method as in Example 1, except that the production conditions were changed to those shown in Table 1. Immediately after stretching in the width direction, the film was cooled (heat treated) at 120°C while still held by the clips, and then re-stretched to 1.1 times the width direction at 177°C. Table 1 shows the film production conditions, and Table 2 shows the physical properties of the film.

[0104] Comparative Example 8 The procedure was the same as in Example 1, except that the film was introduced into a hot air oven and preheated to 177°C, then stretched 6.8 times in the width direction at 169°C, and immediately after the width direction stretching, it was heat-treated at 170°C while still held by the clips to relax by 16% in the width direction. Table 1 shows the production conditions for the film, and Table 2 shows the physical properties of the film.

[0105] (Comparative Example 9) The film was introduced into a hot air oven and preheated to 170°C, and then stretched 6.0 times in the width direction at 162°C in the first stage, followed by 1.36 times in the second stage at 145°C for a total stretching of 8.16 times. Immediately after the width direction stretching, the film was heat-treated at 100°C while held by the clips without relaxation, and then heat-treated at 165°C without relaxation, in the same manner as in Example 1. Table 1 shows the production conditions for the film, and Table 2 shows the physical properties of the film.

[0106] In Comparative Examples 1 to 9, at least one of E"(B) / E"(C), the sum of the longitudinal storage modulus at 23°C and the longitudinal storage modulus at 140°C, and the sum of the widthwise storage modulus at 23°C and the widthwise storage modulus at 140°C was outside the specified range, and therefore the films of Comparative Examples 1 to 9 all had poor flatness after treatment at 130°C. In Comparative Example 6, the mesopentad fraction of PP-3 was too low, and therefore the flatness was poor. In addition, the three-side sealed bags produced using the films of Comparative Examples 1 to 9 all had poor heat-sealed appearance.

[0107] FIG. 1 is a diagram showing the relationship between the temperature and the length in the width direction of the film in Example 4, Comparative Example 1, and Comparative Example 8, and strictly speaking, it is a graph showing the relationship between the temperature and (X-X ０ ) / X ０ Percentage of (X: film length in the width direction at the temperature, X ０ 2 is a graph showing the relationship between temperature and loss modulus in Example 4 and Comparative Example 1, and FIG. 3 is a graph showing the relationship between temperature and storage modulus in Example 4 and Comparative Example 8.

[0108]

[0109]

Claims

1. A biaxially oriented polypropylene film characterized in that, in dynamic viscoelasticity measurement, E"(B) / E"(C) is 0.60 or more, where E"(B) is the minimum loss modulus at 25°C to 75°C and E"(C) is the maximum loss modulus at 100°C to 160°C, the sum of the longitudinal storage modulus at 23°C and the longitudinal storage modulus at 140°C is 3.0 GPa or more, and the sum of the transverse storage modulus at 23°C and the transverse storage modulus at 140°C is 9.2 GPa or more.

2. In the thermomechanical analysis, when the temperature is increased from 30°C to 130°C at a rate of 10°C / min, the length in the width direction at 30°C is X ０ The maximum value of the width direction length during the temperature rise is X １ The minimum value of the width direction during the temperature rise is X ２ Then, (X １ -X ０ ) / X ０ The percentage of is 0.20% or less, (X ２ -X ０ ) / X ０ The biaxially oriented polypropylene film according to claim 1, wherein the percentage of is -0.50% or more.

3. In a thermomechanical analysis, when the temperature is increased from 30° C. to 160° C. at a rate of 10° C. / min, the length X in the width direction of the biaxially oriented polypropylene film at 30° C. ０ The length in the width direction is 0.9950X ０ The biaxially oriented polypropylene film according to claim 1 or 2, wherein the temperature at which the elastic modulus becomes equal to or lower than 129°C is 1.0 GPa or more, the storage modulus in the longitudinal direction at 23°C is 2.0 GPa or more, and the storage modulus in the transverse direction at 23°C is 8.0 GPa or more.

4. A biaxially oriented polypropylene film according to claim 1 or 2, having a longitudinal storage modulus of 0.5 GPa or more at 120°C and a transverse storage modulus of 2.1 GPa or more at 120°C.

5. A biaxially oriented polypropylene film according to claim 1 or 2, having a thermal shrinkage rate in the longitudinal direction at 120°C of 2.5% or less and a thermal shrinkage rate in the transverse direction at 120°C of 1.1% or less.

6. A biaxially oriented polypropylene film according to claim 1 or 2, having a stress at 5% elongation in the width direction at 23°C of 150 MPa or more.

7. A biaxially oriented polypropylene film according to claim 1 or 2, wherein the mesopentad fraction of the polypropylene resin composition constituting said biaxially oriented polypropylene film is 97.0% or more.

8. A biaxially oriented polypropylene film according to claim 1 or 2, wherein the polypropylene resin composition constituting the biaxially oriented polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 158°C or higher.

9. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the polypropylene resin composition constituting said biaxially oriented polypropylene film has a melt flow rate of 4.0 g / 10 min or more.

10. A biaxially oriented polypropylene film as described in claim 1 or 2, in which the amount of components having a molecular weight of 100,000 or less in the polypropylene resin composition constituting the biaxially oriented polypropylene film is 35 mass% or more.

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