Biaxially oriented polypropylene film, and laminate

Abstract

To provide a biaxially oriented polypropylene film capable of obtaining good film making property using a high crystalline polypropylene resin while securing rigidity and antistatic performance in a film using a polymer type anti-static agent, and a laminate.SOLUTION: A biaxially oriented film comprises at least two layers of a substrate layer, and an anti-static layer containing a polymer type anti-static agent, where the substrate layer comprises a high crystallinity resin composition including a polypropylene resin having a mesopentad fraction of 95% or more as a main constituent, the anti-static layer comprises an anti-static resin composition, the anti-static resin composition includes 7 wt.% or more of a polymer-type antistatic agent composed of a copolymer of a hydrophilic polymer and a modified polyolefin, 50-70 wt.% of a polypropylene resin having a mesopentad fraction of less than 95%, and more than 15 wt.%, and less than 40 wt.% of a random copolymer of propylene and α-olefin.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polypropylene film and a laminate using the biaxially stretched polypropylene film, and particularly to a biaxially stretched polypropylene film and a laminate having excellent film-forming properties.

Background Art

[0002] Conventionally, stretched polypropylene films have been widely used in various applications including packaging materials by taking advantage of their excellent transparency, mechanical strength, moisture resistance, rigidity, etc. In recent years, from the perspective of reducing the environmental impact, this type of film tends to reduce the thickness to reduce the amount of resin used. At that time, since the rigidity decreases as the film becomes thinner, it is required to maintain the rigidity while reducing the film thickness. As a method for improving the rigidity in a biaxially stretched polypropylene film, it is conceivable to use a highly crystalline polypropylene resin for the base material layer.

[0003] In biaxially stretched polypropylene films, due to the property of being easily charged, there are problems such as adhesion of dust etc. to the film, electric shock to workers, and scattering of ink during printing. As a method for suppressing the generation of static electricity, in biaxially stretched polypropylene films, adding an antistatic agent for the purpose of imparting antistatic performance etc. can be mentioned.

[0004] Generally, as an antistatic agent for imparting antistatic performance to a film, it is known to use a surfactant, a polymer type antistatic agent, etc. Among these, the surfactant is kneaded into a resin layer such as the base material layer and migrates (bleeds out) to the film surface over time to exhibit antistatic performance. Although the antistatic agent composed of a surfactant is easy to handle, there are cases where it is lost over time due to bleeding out and the antistatic performance cannot be maintained.

[0005] In addition, when a highly crystalline polypropylene resin is used for the base material layer and a surfactant is kneaded into the base material layer, there is also a drawback that the bleeding out of the surfactant to the film surface is hindered and the antistatic performance is difficult to exhibit.

[0006] On the other hand, although a polymer type antistatic agent is a material that is difficult to handle compared to a surfactant, since it has excellent dispersibility in a resin material, it can form a conductive circuit that discharges the charges accumulated on the surface layer by being added to the film surface layer, and it is possible to semi-permanently maintain the antistatic performance without bleeding out.

[0007] As a biaxially stretched film having antistatic performance obtained by adding such a polymer type antistatic agent to the film surface layer, there has been proposed a biaxially stretched polypropylene film having a base material layer made of a propylene homopolymer, 5 to 20% by mass of a block polymer which is a polymer type antistatic agent, 5 to 50% by mass of a propylene-based polymer, and 40 to 90% by mass of a propylene / α-olefin random copolymer (see Patent Document 1).

[0008] In a biaxially stretched polypropylene film having a polymer type antistatic agent on the film surface layer as in Patent Document 1, when a highly crystalline polypropylene resin is used for the base material layer, it is necessary to set a high molding temperature from the viewpoint of film formability. However, in the above-mentioned biaxially stretched polypropylene film, a new problem has been found that the film is likely to stick to the molding roll during molding due to setting a high molding temperature.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been proposed in view of the above points, and provides a biaxially stretched polypropylene film and a laminate that can obtain good film-forming properties while ensuring antistatic performance along with rigidity by using a highly crystalline polypropylene resin in a film using a polymer-type antistatic agent.

Means for Solving the Problems

[0011] That is, a first invention is a biaxially stretched film comprising at least two layers of a base material layer and an antistatic layer containing a polymer-type antistatic agent, wherein the base material layer is made of a highly crystalline resin composition mainly composed of a polypropylene resin having a mesopentad fraction of 95% or more, the antistatic layer is made of an antistatic resin composition, and the antistatic resin composition comprises 7% by weight or more of the polymer-type antistatic agent composed of a copolymer of a hydrophilic polymer and a modified polyolefin, 50 to 70% by weight of a polypropylene resin having a mesopentad fraction of less than 95%, and more than 15% by weight and less than 40% by weight of a propylene / α-olefin random copolymer. It relates to a biaxially stretched polypropylene film.

[0012] A second invention is a biaxially stretched polypropylene film according to the first invention, wherein the biaxially stretched film is stretched by biaxial stretching including longitudinal (MD) stretching with a stretching ratio of 3 to 8 times at a preheating temperature of 105 to 135°C and a stretching temperature of 120 to 135°C, and transverse (TD) stretching with a stretching ratio of 5 to 15 times at a preheating temperature of 175 to 190°C and a stretching temperature of 160 to 170°C.

[0013] A third invention is a biaxially stretched polypropylene film according to the first or second invention, wherein the tensile modulus in the longitudinal (MD) direction of the biaxially stretched polypropylene film measured in accordance with JIS K 7127 (1999) is 2.0 GPa or more, and the tensile modulus in the transverse (TD) direction is 4.0 GPa or more.

[0014] The fourth invention relates to a biaxially stretched polypropylene film in the first or second invention, wherein the haze value of the biaxially stretched polypropylene film measured in accordance with JIS K 7136 (2000) is 10% or less.

[0015] The fifth invention relates to a biaxially stretched polypropylene film in the third invention, wherein the haze value of the biaxially stretched polypropylene film measured in accordance with JIS K 7136 (2000) is 10% or less.

[0016] The sixth invention relates to a biaxially stretched polypropylene film in the first or second invention, wherein the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer.

[0017] The seventh invention relates to a biaxially stretched polypropylene film in the third invention, wherein the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer.

[0018] The eighth invention relates to a biaxially stretched polypropylene film in the fourth invention, wherein the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer.

[0019] The ninth invention relates to a biaxially stretched polypropylene film in the fifth invention, wherein the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer.

[0020] The tenth invention relates to a laminate using the biaxially stretched polypropylene film of the first or second invention, wherein a sealant film is laminated on the biaxially stretched polypropylene film.

[0021] The eleventh invention relates to a laminate using the biaxially stretched polypropylene film of the third invention, wherein a sealant film is laminated on the biaxially stretched polypropylene film.

[0022] The 12th invention relates to a laminate using the biaxially stretched polypropylene film of the 4th invention, which is a laminate formed by laminating a sealant film on the biaxially stretched polypropylene film.

[0023] The 13th invention relates to a laminate using the biaxially stretched polypropylene film of the 5th invention, which is a laminate formed by laminating a sealant film on the biaxially stretched polypropylene film.

[0024] The 14th invention relates to a laminate using the biaxially stretched polypropylene film of the 6th invention, which is a laminate formed by laminating a sealant film on the biaxially stretched polypropylene film.

[0025] The 15th invention relates to a laminate using the biaxially stretched polypropylene film of the 7th invention, which is a laminate formed by laminating a sealant film on the biaxially stretched polypropylene film.

[0026] The 16th invention relates to a laminate using the biaxially stretched polypropylene film of the 8th invention, which is a laminate formed by laminating a sealant film on the biaxially stretched polypropylene film.

[0027] The 17th invention relates to a laminate using the biaxially stretched polypropylene film of the 9th invention, which is a laminate formed by laminating a sealant film on the biaxially stretched polypropylene film.

Advantages of the Invention

[0028] According to the biaxially stretched polypropylene film according to the first invention, it is a biaxially stretched film composed of at least two layers, namely a base material layer and an antistatic layer containing a polymer type antistatic agent. The base material layer is composed of a highly crystalline resin composition mainly composed of a polypropylene resin with a mesopentad fraction of 95% or more. The antistatic layer is composed of an antistatic resin composition. Since the antistatic resin composition contains 7% by weight or more of the polymer type antistatic agent composed of a copolymer of a hydrophilic polymer and a modified polyolefin, 50 to 70% by weight of a polypropylene resin with a mesopentad fraction of less than 95%, and more than 15% by weight and less than 40% by weight of a propylene-α-olefin random copolymer, the film-forming property of the film having antistatic performance along with rigidity is improved.

[0029] According to the biaxially stretched polypropylene film according to the second invention, in the first invention, the biaxially stretched film is stretched by biaxial stretching including longitudinal (MD) stretching with a stretching ratio of 3 to 8 times in the longitudinal direction at a preheating temperature of 105 to 135°C and a stretching temperature of 120 to 135°C, and transverse (TD) stretching with a stretching ratio of 5 to 15 times in the transverse direction at a preheating temperature of 175 to 190°C and a stretching temperature of 160 to 170°C. Therefore, the film-forming property of the film with high rigidity composed of a highly crystalline resin molding for the base material layer can be further improved.

[0030] According to the biaxially stretched polypropylene film according to the third invention, in the first or second invention, the tensile modulus in the longitudinal (MD) direction of the biaxially stretched polypropylene film measured in accordance with JIS K 7127 (1999) is 2.0 GPa or more, and the tensile modulus in the transverse (TD) direction is 4.0 GPa or more. Therefore, it can have good rigidity.

[0031] According to the biaxially stretched polypropylene film according to the fourth invention, in the first or second invention, the haze value of the biaxially stretched polypropylene film measured in accordance with JIS K 7136 (2000) is 10% or less. Therefore, a film with a transparent appearance can be obtained.

[0032] According to the biaxially oriented polypropylene film according to the fifth invention, in the third invention, since the haze value of the biaxially oriented polypropylene film measured in accordance with JIS K 7136 (2000) is 10% or less, a film with a transparent appearance can be obtained.

[0033] According to the biaxially oriented polypropylene film according to the sixth invention, in the first or second invention, since the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer, the occurrence of stretching marks caused by non-uniform stretching can be suppressed.

[0034] According to the biaxially oriented polypropylene film according to the seventh invention, in the third invention, since the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer, the occurrence of stretching marks caused by non-uniform stretching can be suppressed.

[0035] According to the biaxially oriented polypropylene film according to the eighth invention, in the fourth invention, since the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer, the occurrence of stretching marks caused by non-uniform stretching can be suppressed.

[0036] According to the biaxially oriented polypropylene film according to the ninth invention, in the fifth invention, since the base material layer contains 5% by weight or less of a propylene-α-olefin random copolymer, the occurrence of stretching marks caused by non-uniform stretching can be suppressed.

[0037] According to the laminate according to the tenth invention, since a sealant film is laminated on the biaxially oriented polypropylene film of the first or second invention, it can be used as a package for various articles.

[0038] According to the laminate according to the eleventh invention, since a sealant film is laminated on the biaxially oriented polypropylene film of the third invention, it can be used as a package for various articles.

[0039] According to the laminate according to the 12th invention, since a sealant film is laminated on the biaxially stretched polypropylene film of the 4th invention, it can be used as a package for various articles.

[0040] According to the laminate according to the 13th invention, since a sealant film is laminated on the biaxially stretched polypropylene film of the 5th invention, it can be used as a package for various articles.

[0041] According to the laminate according to the 14th invention, since a sealant film is laminated on the biaxially stretched polypropylene film of the 6th invention, it can be used as a package for various articles.

[0042] According to the laminate according to the 15th invention, since a sealant film is laminated on the biaxially stretched polypropylene film of the 7th invention, it can be used as a package for various articles.

[0043] According to the laminate according to the 16th invention, since a sealant film is laminated on the biaxially stretched polypropylene film of the 8th invention, it can be used as a package for various articles.

[0044] According to the laminate according to the 17th invention, since a sealant film is laminated on the biaxially stretched polypropylene film of the 9th invention, it can be used as a package for various articles.

Embodiments for Carrying Out the Invention

[0045] The biaxially stretched polypropylene film according to one embodiment of the present invention is a biaxially stretched film composed of at least two layers including a base material layer and an antistatic layer containing a polymer type antistatic agent. The biaxially stretched polypropylene film of the present invention can be used as a base film of a laminate on which a sealant film is laminated. This laminate is suitably used, for example, as a packaging material for various articles such as foods, daily necessities, and parts.

[0046] The base material layer is formed to have a relatively thicker layer thickness than other layers and serves as the main body of the biaxially stretched film, defining the basic properties of the biaxially stretched film. Therefore, from the perspective of reducing environmental impact in recent years, the base material layer is made of a highly crystalline resin composition mainly composed of a polypropylene resin (highly crystalline polypropylene resin) with a mesopentad fraction of 95% or more, aiming to maintain the rigidity of the entire film while reducing the film thickness. The mesopentad fraction (mmmm) is an index of stereoregularity obtained by high-temperature nuclear magnetic resonance (NMR) measurement. When the mesopentad fraction is large, crystallinity is likely to improve, and a film with excellent rigidity and heat resistance can be obtained. When the mesopentad fraction is small, the rigidity and heat resistance of the film tend to decrease easily.

[0047] The base material layer preferably contains 5% by weight or less of a propylene-α-olefin random copolymer. By the base material layer containing 5% by weight or less of a propylene-α-olefin random copolymer, the stretchability of the film can be improved, and thus the generation of stretching marks caused by non-uniform stretching can be suppressed.

[0048] The antistatic layer corresponds to the surface layer of the biaxially stretched film and is a layer for imparting antistatic performance to the biaxially stretched film. This antistatic layer is made of an antistatic resin composition containing a polymer type antistatic agent.

[0049] The polymer type antistatic agent is an antistatic agent that exhibits antistatic performance by forming a conductive circuit that disperses in the resin material and discharges the charges accumulated on the film surface. Since this polymer type antistatic agent exhibits antistatic performance without migrating (bleeding out) to the film surface, it is possible to semi-permanently maintain the antistatic performance.

[0050] The polymer antistatic agent is composed of a copolymer of a hydrophilic polymer and a modified polyolefin. As the hydrophilic polymer, those generally referred to as polyethers are preferred, and examples include polyether diols, polyether diamines, polyether ester amides, polyether amide imides, polyether urethanes, polyether esters, polyether amides, and modified products thereof. As the modified polyolefin, in an appropriate polyolefin, a carbonyl group, a carboxyl group, an amino group, a hydroxyl group, etc. are introduced as the modifying group, and a polyolefin containing at least one of these at one end is mentioned. Preferably, a carboxyl group-modified polyolefin is mentioned.

[0051] The polymer antistatic agent preferably has a volume resistivity of 1×10 5 ~1×10 11 Ω·cm. The volume resistivity is an index for judging the difficulty of discharging the charges accumulated in the antistatic layer of the film. By setting the volume resistivity to 1×10 5 ~1×10 11 Ω·cm, the film can have good antistatic performance. If the volume resistivity is too large, it may be difficult to discharge the charges accumulated in the antistatic layer of the film, resulting in insufficient antistatic performance of the film.

[0052] In the polymer antistatic agent, the blending amount in the antistatic resin composition is preferably 7% by weight or more. The upper limit of the blending amount of the polymer antistatic agent is not particularly limited, but from the viewpoints of the required antistatic performance and the balance with cost, etc., it is preferably set to about 35% by weight as the upper limit. If the blending amount of the polymer antistatic agent is too small, sufficient antistatic performance may not be obtained.

[0053] In the present invention, in a biaxially stretched polypropylene film having a polymer type antistatic agent with excellent durability of antistatic performance on the film surface (antistatic layer), in order to reduce the volume (make the film thinner) in response to recent demands for reducing environmental impact, as described above, a highly crystalline polypropylene resin is used in the base material layer so as to ensure rigidity that can withstand the volume reduction. When a highly crystalline polypropylene resin is used in the base material layer in this way, since the highly crystalline polypropylene resin has a high melting point, it is necessary to set the forming temperature during film formation higher than before. However, due to film formation at a higher forming temperature than before, a new problem has arisen in that in the conventional resin composition, the film is likely to stick to the forming roll during forming, resulting in a decrease in film formability.

[0054] Therefore, as a result of intensive studies by the inventors, it has been clarified that in the surface layer of a conventional biaxially stretched film, a propylene / α-olefin random copolymer contained for the purpose of improving the dispersibility of the polymer type antistatic agent affects the sticking of the film to the forming roll. Based on this, the inventors have found a means to obtain good film formability corresponding to the high setting of the forming temperature. That is, in the biaxially stretched polypropylene film of the present invention, the antistatic resin composition constituting the antistatic layer contains a polymer type antistatic agent, a polypropylene resin having a mesopentad fraction of less than 95%, and a propylene / α-olefin random copolymer, and the blending amounts are 7% by weight or more of the polymer type antistatic agent, 50 to 70% by weight of the polypropylene resin, and more than 15% by weight and less than 40% by weight of the propylene / α-olefin random copolymer.

[0055] The polypropylene resin contained in the antistatic resin composition is a main component of the antistatic layer, and in particular, it is a polypropylene resin (non-highly crystalline polypropylene resin) having a mesopentad fraction of less than 95%. Since this polypropylene resin is non-highly crystalline (mesopentad fraction of less than 95%), it does not prevent the dispersion of the polymer type antistatic agent. If the mesopentad fraction is too high, the dispersibility of the polymer type antistatic agent may decrease, and sufficient antistatic performance may not be obtained.

[0056] The propylene·α-olefin random copolymer contained in the antistatic resin composition is a component for enhancing the dispersibility of the polymer-type antistatic agent in the antistatic resin composition. The propylene·α-olefin random copolymer is a random copolymer of propylene and an α-olefin (excluding propylene), and examples of the α-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and the like. These copolymers may be used alone or in combination of two or more. Among these propylene·α-olefin random copolymers, propylene·ethylene random copolymer, propylene·ethylene·1-butene random copolymer, and propylene·1-butene random copolymer are preferred, and propylene·ethylene random copolymer is more preferred.

[0057] Since the melting point of the propylene·α-olefin random copolymer is lower than the melting point of the highly crystalline polypropylene resin used for the base material layer, it is desirable to suppress the content in the antistatic layer (antistatic resin composition) in order to avoid melting of the antistatic layer when the molding temperature is set at a high temperature. However, if the content of the propylene·α-olefin random copolymer is suppressed too much, it is considered that the polymer-type antistatic agent cannot be sufficiently dispersed in the antistatic layer and sufficient antistatic performance cannot be obtained.

[0058] Therefore, in the present invention, in a biaxially stretched film using a highly crystalline polypropylene resin for the base material layer, even when the content of the propylene·α-olefin random copolymer in the antistatic resin composition forming the antistatic layer is suppressed, the non-highly crystalline polypropylene resin is 50 to 70% by weight and the propylene·α-olefin random copolymer is more than 15% by weight and less than 40% by weight so that the polymer-type antistatic agent can be dispersed in the antistatic resin composition.

[0059] The balance of the blending ratio between the non-highly crystalline polypropylene resin and the propylene / α-olefin random copolymer enables the compatibility between the film-forming property and the dispersibility of the polymer type antistatic agent by using the non-highly crystalline polypropylene resin, in which the polymer type antistatic agent is relatively easily dispersed, as the main component of the antistatic layer, while suppressing the content of the propylene / α-olefin random copolymer. If the amount of the non-highly crystalline polypropylene resin is too large or the amount of the propylene / α-olefin random copolymer is too small, the dispersibility of the polymer type antistatic agent may decrease, and sufficient antistatic performance may not be obtained. On the other hand, if the amount of the non-highly crystalline polypropylene resin is too small or the amount of the propylene / α-olefin random copolymer is too large, the antistatic layer may melt during film formation, and the film may easily stick to the forming roll. Therefore, by adjusting the blending ratio of the non-highly crystalline polypropylene resin and the propylene / α-olefin random copolymer within the above range, the dispersibility of the polymer type antistatic agent becomes good, excellent antistatic performance can be obtained, and the sticking of the film to the forming roll during formation is suppressed, resulting in good film-forming property.

[0060] The biaxially stretched polypropylene film of the present invention is a film stretched in the biaxial directions of the longitudinal (MD) direction and the transverse (TD) direction of the film. Either sequential biaxial stretching or simultaneous biaxial stretching can be preferably used for the biaxial stretching. In the film formation by biaxial stretching, the orientation of the resin occurs in both the longitudinal (MD) and transverse (TD) directions, and the crystallinity is improved. Therefore, it is possible to improve the thickness accuracy such as thinning and the mechanical properties such as strength, and the mass productivity is also excellent.

[0061] In the biaxially stretched polypropylene film of the present invention, the stretching ratio is about 3 to 8 times in the longitudinal (MD) direction and about 5 to 15 times in the transverse (TD) direction. In particular, since a highly crystalline polypropylene resin is used for the base material layer, it is necessary to set the molding temperature high to soften the highly crystalline polypropylene resin so that it can be molded during film formation, and then perform longitudinal (MD) stretching and transverse (TD) stretching. Specifically, the biaxially stretched film is longitudinally stretched with a longitudinal stretching ratio of 3 to 8 times at a preheating temperature of 105 to 135°C and a stretching temperature of 120 to 135°C, and transversely stretched with a transverse stretching ratio of 5 to 15 times at a preheating temperature of 175 to 190°C and a stretching temperature of 160 to 170°C by biaxial stretching.

[0062] If the preheating temperature for longitudinal (MD) stretching is too low or too high, the longitudinal stretching may not be stable and the transparency of the film may be impaired. Also, if the preheating temperature for transverse (TD) stretching is too low, it may be difficult to soften the base material layer (highly crystalline resin molded product) to enable molding, and the film forming property may be insufficient. If the preheating temperature is too high, the transverse stretching may not be stable and the transparency of the film may be impaired. If the stretching temperature in the longitudinal (MD) direction or the transverse (TD) direction is too low, uniform stretching may not occur and film thickness unevenness may occur. Also, if the stretching temperature in the longitudinal (MD) direction is too high, the adhesion between the sheet and the roll may improve and stretching may become impossible. On the other hand, if the stretching temperature in the transverse (TD) direction is too high, film breakage may occur during stretching. Thus, in the biaxially stretched polypropylene film of the present invention, by setting the molding temperature within the above range, particularly setting the preheating temperature in the transverse (TD) direction, which increases the stretching ratio, to a high temperature, the highly crystalline resin molded product used for the base material layer can be softened, so that the film forming property of a film with high rigidity mainly composed of the highly crystalline resin molded product can be improved.

[0063] In addition, the biaxially stretched polypropylene film of the present invention may have a laminated structure of three or more layers including layers other than the base material layer and the antistatic layer as needed. For example, in the case of a biaxially stretched film having a three-layer structure, it can have a laminated structure including a base material layer, an antistatic layer disposed on one side thereof, and a surface layer disposed on the other side. Further, as a biaxially stretched film of three or more layers, an arbitrary layer such as an intermediate layer may be laminated between the base material layer and the surface layer as needed. In the biaxially stretched polypropylene film of the present invention, a laminated structure of three to five layers is preferable.

[0064] In the biaxially stretched polypropylene film of the present invention, it is preferable that the tensile elastic modulus in the longitudinal (MD) direction of the film is 2.0 GPa or more and the tensile elastic modulus in the transverse (TD) direction of the film is 4.0 GPa or more. The tensile elastic modulus in each direction is an index for judging the film rigidity and is measured in accordance with JIS K 7127 (1999). By setting the tensile elastic modulus in the longitudinal (MD) direction to 2.0 GPa or more and the tensile elastic modulus in the transverse (TD) direction to 4.0 GPa or more, the film can have good rigidity. As the tensile elastic modulus in each direction increases, the film becomes more difficult to deform.

[0065] In the biaxially stretched polypropylene film of the present invention, it is preferable that the haze value of the film is 10% or less. The haze value is an index for judging the cloudiness of the film and is measured in accordance with JIS K 7136 (2000). By setting the haze value to 10% or less, a film with transparency can be obtained, which is suitable for packaging foods and the like. If the haze value increases, the transparency of the film itself may be lost, and the visibility required for packaging foods and the like may be impaired.

[0066] In the biaxially oriented polypropylene film of the present invention, the thickness is appropriately determined according to demands, applications, etc. However, from the viewpoint of volume reduction in response to the demand for environmental load reduction, it is preferably formed to be relatively thin. For example, it is preferably 5 to 70 μm, more preferably 10 to 50 μm. Among these, the thickness of the antistatic layer of the biaxially oriented polypropylene film is preferably 0.3 to 5 μm, more preferably 0.4 to 4 μm, and even more preferably 0.5 to 2 μm. When the antistatic layer is too thin, the amount of the polymer type antistatic agent present may be reduced, resulting in insufficient antistatic performance. When the antistatic layer is too thick, the amount of the polymer type antistatic agent present may be increased, possibly impairing the transparency of the film.

[0067] The biaxially oriented polypropylene film of the present invention can be obtained by a known film forming method such as the T-die method or the inflation method. In particular, it is preferably formed by stretching a sheet shaped by the T-die method. In the formation of a film by the T-die method, it is advantageous in that high thickness accuracy required for the base film of the laminate film can be obtained.

[0068] In the present invention, a laminate film can be provided as a laminate in which the above biaxially oriented polypropylene film is used as a base film and a sealant film is laminated on the biaxially oriented polypropylene film. As the sealant film, an unstretched polypropylene film is preferably used. By forming a sealant layer made of the same polypropylene resin as the biaxially oriented polypropylene film serving as the base film, a single material (monomaterial) can be achieved, facilitating recycling. Furthermore, a package using the laminate film can also be formed. Thus, it is promising as an alternative to existing laminate films and packages, being a film and a package that can be easily recycled.

[0069] In addition, the present invention can also provide a laminated film in which a biaxially stretched polypropylene film used as a base film is appropriately laminated with printing, a gas barrier layer, etc. The printing process is performed on the film surface of the biaxially stretched polypropylene film, and known methods such as screen printing, flexographic printing, offset printing, and gravure printing are used. When printing is performed on the biaxially stretched polypropylene film of the present invention, prior to printing, the film surface is subjected to the above-described surface treatment such as corona discharge treatment to improve the ink affinity and adhesion.

[0070] The gas barrier layer is arranged directly on the surface layer or via an anchor coat layer for the purpose of imparting barrier properties against water vapor, oxygen, etc. When the gas barrier layer is arranged on the biaxially stretched polypropylene film of the present invention, the film surface is pre-treated by corona discharge treatment or the like to improve the wettability and adhesion to the anchor coat layer and the gas barrier layer.

[0071] The anchor coat layer is not particularly limited, and examples include polyurethane-based resins and polyester-based resins. The gas barrier layer is also not particularly limited, and examples include metal thin film layers and inorganic oxide layers. The metal thin film layer is a thin film layer made of a known metal such as aluminum, gold, silver, copper, and chromium, and may be a thin film layer of oxides, sulfides, or nitrides of these metals. Further, the metal thin film layer may be a single layer or a plurality of two or more layers of different or the same kind. The inorganic oxide layer is made of a known inorganic oxide such as aluminum oxide, silicon oxide, magnesium fluoride, and magnesium oxide, and is a thin film layer using one or more inorganic oxides.

Example

[0072] [Production of biaxially stretched polypyropylene film] In the production of biaxially oriented polypropylene films of Prototype Examples 1 to 11 and Comparative Examples 1 and 2, the following materials were kneaded and melted, and were set to be laminated in the order of an antistatic layer, a base layer, and a surface layer. Coextrusion was carried out from a three-layer coextrusion T-die film forming machine set at 240°C, and cooling and solidification were performed with a chill roll at 50°C to obtain a sheet-like material as a raw sheet. Next, the sheet-like material was preheated at a preheating temperature of 120 to 135°C, stretched 5.0 times in the longitudinal (MD) direction at a stretching temperature of 120 to 135°C, then preheated at a preheating temperature of 180 to 190°C, stretched 8.0 times in the transverse (TD) direction at a stretching temperature of 163 to 166°C, and then annealed at 170 to 175°C. Thereafter, corona treatment discharge was applied to the antistatic layer to obtain biaxially oriented polypropylene films of each prototype example. In each prototype example, the blending ratio of the resin was blended so as to be 100% by weight for each of the antistatic layer, the base layer, and the surface layer. The materials used in each layer of Prototype Examples 1 to 11 and Comparative Examples 1 and 2 are shown in Tables 1 to 3 described later. In the films of Prototype Examples 1 to 11 and Comparative Example 2, the thickness was 20 μm, the thicknesses of the antistatic layer and the surface layer were 1 μm, and the thickness of the base layer was 18 μm. In the film of Comparative Example 1, the thickness was 30 μm, the thicknesses of the antistatic layer and the surface layer were 1 μm, and the thickness of the base layer was 28 μm.

[0073] [Materials Used] As materials for each layer, the following polymer type antistatic agent, polypropylene resin, and propylene-α-olefin random copolymer were used. In the polymer type antistatic agent, the volume resistivity is a value measured in an atmosphere of a temperature of 23°C and a humidity of 50%RH in accordance with ASTM D257 (2007). The melt flow rate (MFR) is a value measured at a temperature of 190°C in accordance with JIS K 7210 (2014).

[0074] In each polypropylene resin, the mesopentad fraction (mmmm) was analyzed by performing C-NMR measurement using an FT-NMR apparatus (manufactured by JEOL RESONANCE, Ltd., "JNM-ECA400"). 13 C-NMR measurement was carried out for analysis. 13The 13C-NMR measurement was carried out by adding 0.6 mL of a mixed solution of deuterated orthodichlorobenzene:deuterated benzene = 8:2 (volume ratio) to 120 mg of the sample, heating it to 135 °C for dissolution, and measuring at 135 °C. The mesopentad fraction was calculated by the method described in "Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973)", and the peak assignment was performed based on the revised version of the above literature described in "Macromolecules, Vol. 8, p. 687 (1975)". Observed nucleus: 13 13C (100 MHz) Measurement mode: Single pulse proton broad band decoupling Pulse interval: 5 seconds Pulse width: 45° Shift reference: Solvent-derived signal = 132.39 ppm Number of integrations: 11,000 times

[0075] [Antistatic agent] · AA1: Polymer type antistatic agent: Maleic anhydride modified polypropylene block·poly(ethylene glycol) block copolymer (manufactured by Sanyo Chemical Industries, Ltd.; Perestat VH230), density 1.0 g / cm 3 , melting point 163 °C, volume resistivity 3×10 7 Ω·cm, MFR: 7.0 g / 10 min (190 °C) · AA2: Bleed-out type antistatic agent: Masterbatch of antistatic agent prepared by adjusting the concentration of the antistatic agent to 9% based on a propylene homopolymer (PP1 below).

[0076] [Polypropylene resin] · PP1: Propylene homopolymer (manufactured by Japan Polypropylene Corporation; FL203D), mesopentad fraction (mmmm) 91.0%, melting point 163 °C · PP2: Propylene homopolymer (manufactured by Japan Polypropylene Corporation; FB3M), mesopentad fraction (mmmm) 92.8%, melting point 165 °C · PP3: Propylene homopolymer (manufactured by Japan Polypropylene Corporation; SA3D), mesopentad fraction (mmmm) 93.6%, melting point 163 °C ·PP4: Propylene homopolymer (manufactured by Japan Polypropylene Corporation; FB3EBT), meso-pentad fraction (mmmm) 88.0%, melting point 158 °C ·PP5: Propylene homopolymer (manufactured by Japan Polypropylene Corporation; FL1105F), meso-pentad fraction (mmmm) 96.1%, melting point 166 °C

[0077] [Propylene·α-olefin random copolymer] ·PC1: Propylene·α-olefin random copolymer (manufactured by Japan Polypropylene Corporation; EG6D), melting point 141 °C ·PC2: Propylene·α-olefin random copolymer (manufactured by Mitsui Chemicals, Inc.; PN2060), melting point 162 °C

[0078] [Prototype Example 1] Prototype Example 1 is a biaxially stretched polypropylene film using 7 wt% of AA1, 63 wt% of PP1, 30 wt% of PC1 in the antistatic layer, 95 wt% of PP5, 5 wt% of PC2 in the base layer, and 100 wt% of PP1 in the surface layer.

[0079] [Prototype Example 2] Prototype Example 2 is a biaxially stretched polypropylene film using 9 wt% of AA1, 54 wt% of PP1, 37 wt% of PC1 in the antistatic layer, 95 wt% of PP5, 5 wt% of PC2 in the base layer, and 100 wt% of PP1 in the surface layer.

[0080] [Prototype Example 3] Prototype Example 3 is a biaxially stretched polypropylene film using 10 wt% of AA1, 60 wt% of PP3, 30 wt% of PC1 in the antistatic layer, 95 wt% of PP5, 5 wt% of PC2 in the base layer, and 100 wt% of PP1 in the surface layer.

[0081] [Prototype Example 4] Prototype Example 4 is a biaxially stretched polypropylene film using 12 wt% of AA1, 70 wt% of PP2, 18 wt% of PC1 in the antistatic layer, 95 wt% of PP5, 5 wt% of PC2 in the base layer, and 100 wt% of PP1 in the surface layer used.

[0082] [Prototype Example 5] Prototype Example 5 is a biaxially oriented polypropylene film using 16% by weight of AA1, 60% by weight of PP2, 24% by weight of PC1 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0083] [Prototype Example 6] Prototype Example 6 is a biaxially oriented polypropylene film using 20% by weight of AA1, 50% by weight of PP2, 30% by weight of PC1 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0084] [Prototype Example 7] Prototype Example 7 is a biaxially oriented polypropylene film using 8% by weight of AA1, 80% by weight of PP2, 12% by weight of PC1 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0085] [Prototype Example 8] Prototype Example 8 is a biaxially oriented polypropylene film using 8% by weight of AA1, 20% by weight of PP2, 72% by weight of PC1 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0086] [Prototype Example 9] Prototype Example 9 is a biaxially oriented polypropylene film using 10% by weight of AA1, 60% by weight of PP5, 30% by weight of PC1 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0087] [Prototype Example 10] Prototype Example 10 is a biaxially oriented polypropylene film using 10% by weight of AA1, 30% by weight of PP3, 60% by weight of PP5 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0088] [Prototype Example 11] Prototype Example 11 is a biaxially stretched polypropylene film using 10% by weight of AA1, 90% by weight of PP3 in the antistatic layer, 95% by weight of PP5, 5% by weight of PC2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0089] [Comparative Example 1] Comparative Example 1 is a biaxially stretched polypropylene film using 20% by weight of AA1, 53% by weight of PP4, 27% by weight of PC1 in the antistatic layer, 100% by weight of PP1 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0090] [Comparative Example 2] Comparative Example 2 is a biaxially stretched polypropylene film using 100% by weight of PP1 in the antistatic layer, 87% by weight of PP5, 3% by weight of PC2, 10% by weight of AA2 in the base material layer, and 100% by weight of PP1 in the surface layer.

[0091]

Table 1

[0092]

Table 2

[0093]

Table 3

[0094] For Prototype Examples 1 to 11 and Comparative Examples 1 and 2, the haze value, the surface resistivity of the antistatic layer, and the tensile elastic modulus were measured. In addition, the productivity evaluation and the comprehensive judgment evaluation for each prototype example were conducted. The measurement results and evaluations are shown in Tables 4 to 6 described below.

[0095] [Measurement of Haze Value] The haze value (%) is an index for judging the cloudiness of the film. It was measured in accordance with JIS K 7136 (2000) using a digital turbidimeter (manufactured by Nippon Denshoku Industries Co., Ltd., "NDH-5000"). A haze value of 10% or less was regarded as good.

[0096] [Measurement of surface specific resistivity] The surface specific resistivity (Ω / □) is an index for judging the antistatic performance. If the surface specific resistivity is too high, the antistatic performance is insufficient and electrostatic troubles are likely to occur in the film processing. The surface specific resistivity conforms to JIS K 6911 (2006), and using a high-resistance resistivity meter (manufactured by Nitto Seiko Analytic Co., Ltd., "MCP-HT800"), a 10 cm × 10 cm test piece cut from the biaxially stretched polypropylene film of each prototype example was used, and the antistatic layer was measured in an atmosphere of temperature 23°C and humidity 50%RH. The surface specific resistivity was considered good when it was 1×10 14 Ω / □ or less.

[0097] [Measurement of tensile modulus] The tensile modulus (GPa) is an index for judging the rigidity of the biaxially stretched polypropylene film. When the tensile modulus increases, the film becomes difficult to deform. The tensile modulus conforms to JIS K 7127 (1999), and using a tensile testing machine (manufactured by Orientec Co., Ltd., "RTF-1310"), a 15 mm × 200 mm test piece cut from the biaxially stretched polypropylene film of each prototype example was used, and the film was measured in each direction of the longitudinal (MD) direction and the transverse (TD) direction under the conditions of a chuck distance of 100 mm and a tensile speed of 200 mm / min. The tensile modulus was considered good when the longitudinal (MD) direction was 2.0 GPa or more and the transverse (TD) was 4.0 GPa or more.

[0098] [Evaluation of productivity] For the evaluation of productivity, those in which the film hardly adhered to the forming roll during molding and the film could be stably formed were regarded as good and marked as "〇", and those in which the film adhered to the forming roll during molding and appearance defects occurred were regarded as unacceptable and marked as "×".

[0099] [Evaluation of comprehensive judgment] For the comprehensive judgment evaluation, those with good haze value, surface resistivity, tensile elastic modulus, and productivity among the above were marked as "〇", and those with any of the haze value, surface resistivity, tensile elastic modulus, and productivity being poor were marked as "×".

[0100]

Table 4

[0101]

Table 5

[0102]

Table 6

[0103] [Results and Discussion] As shown in Tables 4 to 6, the comprehensive judgment of Prototype Examples 1 to 6 was "〇", and the comprehensive judgment of Prototype Examples 7 to 11 and Comparative Examples 1 and 2 was "×". Regarding the prototype examples and comparative examples with poor comprehensive judgment, for Prototype Examples 7 and 9, the haze value exceeded 10% and the transparency of the film was insufficient, and the surface resistivity exceeded 1×10 14 Ω / □, and the desired antistatic performance could not be obtained. For Prototype Example 8, the film adhered to the forming roll and appearance defects occurred. For Prototype Examples 10 and 11 and Comparative Example 2, the surface resistivity exceeded 1×10 14 Ω / □, and the desired antistatic performance could not be obtained. For Comparative Example 1, the tensile elastic modulus in the longitudinal (MD) and transverse (TD) directions of the film was insufficient, and the desired film rigidity could not be obtained.

[0104] Comparative Example 1 is an example assuming a conventional biaxially stretched film using a polymer type antistatic agent (AA1). When the base material layer is a non-highly crystalline polypropylene resin (PP1) as in Comparative Example 1, even if it is thicker compared to other prototype examples using a highly crystalline polypropylene resin (PP5) for the base material layer, the tensile elastic modulus in the longitudinal (MD) direction and the transverse (TD) direction of the film is insufficient, and the desired rigidity of the film cannot be obtained. Therefore, when reducing the volume of the film, it was shown that a non-highly crystalline polypropylene resin is not suitable as the resin constituting the base material layer, and a highly crystalline polypropylene resin is preferable.

[0105] Comparative Example 2 is an example in which a bleed-out type antistatic agent (AA2) is used in a biaxially stretched film using a highly crystalline polypropylene resin (PP5) as the constituent resin of the base material layer in response to volume reduction. When a bleed-out type antistatic agent is added to a base material layer composed of a highly crystalline polypropylene resin as in Comparative Example 2, the desired antistatic performance cannot be obtained. This is presumably because the antistatic agent (AA2) in the base material layer is less likely to migrate to the film surface due to the highly crystalline polypropylene resin (PP5), and thus the desired antistatic performance cannot be obtained. From this, it was shown that in a biaxially stretched film with volume reduction using a highly crystalline polypropylene resin, a bleed-out type antistatic agent is not suitable as an antistatic agent, and it is preferable to use a polymer type antistatic agent for the antistatic layer.

[0106] Therefore, in a biaxially stretched film having antistatic performance suitable for volume reduction, it is preferable to use a highly crystalline polypropylene resin as the constituent resin of the base material layer to ensure the rigidity of the film, and to use a polymer type antistatic agent for the antistatic layer to impart antistatic performance. Therefore, from Prototype Examples 1 to 11, the preferable resin formulation of the antistatic layer (antistatic resin composition) of a biaxially stretched film having antistatic performance suitable for volume reduction is examined.

[0107] In Prototype Examples 3, 9 to 11, the blending amount of the polymer type antistatic agent (AA1) in the antistatic layer (antistatic resin composition) is constant, while the blending amounts of the polypropylene resin and the propylene / α-olefin random copolymer are different. Prototype Example 3 is a film in which the antistatic layer contains a non-highly crystalline polypropylene resin (PP3) as a main component and further contains a propylene / α-olefin random copolymer (PC1). Prototype Example 9 is a film in which the main component of the antistatic layer in Prototype Example 3 is replaced with a highly crystalline polypropylene resin (PP5). Prototype Example 10 is a film in which a non-highly crystalline polypropylene resin (PP3) is used instead of the propylene / α-olefin random copolymer (PC1) in Prototype Example 9. Prototype Example 11 is a film in which the main component of the antistatic layer is a non-highly crystalline polypropylene resin (PP3) and does not contain a propylene / α-olefin random copolymer.

[0108] In Prototype Examples 9 and 10 where the main component of the antistatic layer is a highly crystalline polypropylene resin (PP5), the antistatic performance was insufficient in both cases. In particular, in Prototype Example 9, despite containing a propylene / α-olefin random copolymer (PC1) to enhance the dispersibility of the polymer type antistatic agent, sufficient antistatic performance could not be obtained. From these facts, it is considered that when the main component of the antistatic layer is a highly crystalline polypropylene resin, even if a propylene / α-olefin random copolymer is added, the dispersibility of the polymer type antistatic agent decreases and sufficient antistatic performance cannot be obtained.

[0109] On the other hand, in Prototype Examples 3 and 11 where the main component of the antistatic layer is a non-highly crystalline polypropylene resin (PP3), the antistatic performance of Prototype Example 3 containing a propylene / α-olefin random copolymer (PC1) was good, while the antistatic performance of Prototype Example 11 not containing a propylene / α-olefin random copolymer was insufficient. From this, it was shown that as a constituent material of the antistatic layer, it is preferable to contain a non-highly crystalline polypropylene resin and a propylene / α-olefin random copolymer for enhancing the dispersibility of the polymer type antistatic agent.

[0110] Next, as an example of containing a non-highly crystalline polypropylene resin and a propylene / α-olefin random copolymer as the constituent materials of the antistatic layer, specifically, Prototype Examples 4 to 8 using the same constituent materials are compared. The constituent materials of the antistatic layer in Prototype Examples 4 to 8 are a polymer type antistatic agent (AA1), a propylene homopolymer (PP2), and a propylene / α-olefin random copolymer (PC1). As can be understood from Prototype Examples 4 to 8, in Prototype Example 7 where the blending amount of the propylene / α-olefin random copolymer (PC1) is the minimum value (the blending amount of the propylene homopolymer (PP2) is the maximum value), and Prototype Example 8 where the blending amount of the propylene / α-olefin random copolymer (PC1) is the maximum value (the blending amount of the propylene homopolymer (PP2) is the minimum value), the comprehensive judgment is poor, while in Prototype Examples 4 to 6, the comprehensive judgment is good.

[0111] In Prototype Example 7, the antistatic performance was particularly insufficient. This is presumably because there was too little propylene / α-olefin random copolymer to enhance the dispersibility of the polymer type antistatic agent, resulting in insufficient dispersion of the polymer type antistatic agent in the antistatic resin composition and thus insufficient antistatic performance. On the other hand, among Prototype Examples 4 to 6 with good comprehensive judgment, the blending amount of the propylene / α-olefin random copolymer is 18% by weight in Prototype Example 4, which is the minimum value. Since the blending amount of the propylene / α-olefin random copolymer in Prototype Example 7 is 12% by weight, the lower limit of the blending amount of the propylene / α-olefin random copolymer is considered to be about 15% by weight.

[0112] In addition, in Prototype Example 8, a problem occurred in that the film adhered to the forming roll particularly during forming. This is presumably because there was too much propylene-α-olefin random copolymer, resulting in an excessive blending amount of the resin with a low melting point in the antistatic resin composition. During forming, the antistatic layer melted and was likely to adhere to the forming roll. Among Prototype Examples 4 to 6 with good comprehensive evaluations, the blending amount of the propylene-α-olefin random copolymer was up to 30% by weight in Prototype Example 6, which was the highest value. Considering all Prototype Examples 1 to 6 with good comprehensive evaluations, the highest value of the blending amount of the propylene-α-olefin random copolymer was 37% by weight in Prototype Example 2. Therefore, it is considered to be about 40% by weight.

[0113] From the above Prototype Examples 1 to 11, in a biaxially stretched film mainly composed of a highly crystalline polypropylene resin (base material layer), it was shown that the constituent material of the antistatic layer containing a polymer type antistatic agent should mainly be a non-highly crystalline polypropylene resin and contain a propylene-α-olefin random copolymer for enhancing the dispersibility of the polymer type antistatic agent. From Prototype Examples 1 to 6 with good comprehensive evaluations, as the blending amount of each constituent material in the antistatic layer, the polymer type antistatic agent is 7% by weight, the non-highly crystalline polypropylene resin is 50 to 70% by weight, and the propylene-α-olefin random copolymer is about 15 to 40% by weight, more preferably 18 to 37% by weight.

[0114] In addition, in the biaxially stretched film, due to the necessity of setting a high molding temperature because the main component is a highly crystalline polypropylene resin, it has been revealed that when the blending amount of the propylene-α-olefin random copolymer in the antistatic layer is large, the film is likely to stick to the molding roll during molding. Therefore, in the biaxially stretched film, the main component of the antistatic layer is a non-highly crystalline polypropylene resin, and particularly, by setting the blending amount of the non-highly crystalline polypropylene resin to 50 to 70% by weight and suppressing the blending amount of the propylene-α-olefin random copolymer (about 15 to 40% by weight), it becomes possible to avoid the occurrence of sticking of the film to the molding roll while ensuring the dispersibility of the polymer type antistatic agent.

[0115] Thus, by setting the balance of the blending amounts of the non-highly crystalline polypropylene resin and the propylene-α-olefin random copolymer as the constituent materials of the antistatic layer within the above range, even in a film mainly composed of a highly crystalline polypropylene resin (base material layer) that requires molding at a high temperature, it is possible to suppress the sticking of the film to the molding roll and obtain good film-forming properties. Moreover, since the polymer type antistatic agent can be sufficiently dispersed, good antistatic performance can be exhibited.

Industrial Applicability

[0116] The biaxially stretched polypropylene film of the present invention has good film-forming properties for a film having both rigidity and antistatic performance. Furthermore, by forming a laminate in which a sealant film made of an unstretched polypropylene film is laminated on the biaxially stretched polypropylene film of the present invention, a single material (monomaterial) can be achieved and recycling can be facilitated. Furthermore, a package using the laminate can also be produced. Thus, it is promising as an alternative to existing laminates and packages as films and packages that can be easily recycled.

Claims

1. A biaxially oriented film comprising at least two layers, namely a base material layer and an antistatic layer containing a polymer-type antistatic agent, wherein the base material layer is made of a highly crystalline resin composition mainly composed of a polypropylene resin having a mesopentad fraction of 95% or more, the antistatic layer is made of an antistatic resin composition, and the antistatic resin composition contains 7% by weight or more of the polymer-type antistatic agent composed of a copolymer of a hydrophilic polymer and a modified polyolefin, 50 to 70% by weight of a polypropylene resin having a mesopentad fraction of less than 95%, and more than 15% by weight and less than 40% by weight of a propylene / α-olefin random copolymer, and is characterized in that it is a biaxially oriented polypropylene film.

2. The biaxially oriented film according to claim 1, which is stretched by biaxial stretching including longitudinal stretching in the machine direction (MD) with a stretching ratio of 3 to 8 times at a preheating temperature of 105 to 135°C and a stretching temperature of 120 to 135°C, and transverse stretching in the transverse direction (TD) with a stretching ratio of 5 to 15 times at a preheating temperature of 175 to 190°C and a stretching temperature of 160 to 170°C.

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the tensile modulus in the longitudinal direction (MD) of the biaxially oriented polypropylene film measured in accordance with JIS K 7127 (1999) is 2.0 GPa or more, and the tensile modulus in the transverse direction (TD) is 4.0 GPa or more.

4. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the haze value of the biaxially oriented polypropylene film measured in accordance with JIS K 7136 (2000) is 10% or less.

5. The biaxially oriented polypropylene film according to claim 3, wherein the haze value of the biaxially oriented polypropylene film measured in accordance with JIS K 7136 (2000) is 10% or less.

6. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the base material layer contains 5% by weight or less of a propylene / α-olefin random copolymer.

7. The biaxially oriented polypropylene film according to claim 3, wherein the base material layer contains 5% by weight or less of a propylene / α-olefin random copolymer.

8. The biaxially oriented polypropylene film according to claim 4, wherein the base material layer contains 5% by weight or less of a propylene / α-olefin random copolymer.

9. The biaxially oriented polypropylene film according to claim 5, wherein the base material layer contains 5% by weight or less of a propylene / α-olefin random copolymer.

10. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 1 or 2.

11. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 3.

12. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 4.

13. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 5.

14. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 6.

15. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 7.

16. A laminate obtained by laminating a sealant film on the biaxially oriented polypropylene film according to claim 8.

17. A laminate in which a sealant film is laminated on the biaxially stretched polypropylene film according to claim 9.

Images