Polypropylene-based resin film

Abstract

To provide a polypropylene-based resin film which is excellent in not only dry adhesion force but also wet adhesion force with respect to a transparent vapor-deposited layer, and can satisfactorily maintain the adhesion force and flatness even after hot water treatment at high temperature and high pressure.SOLUTION: There is provided a polypropylene-based resin film. Therein, based on 100 mass% of total components, an amount of a component having a molecular weight of 1500 or more and 10000 or less is 0.1 mass% or more and 3.5 mass% or less; storage elastic modulus E' at 120°C in a direction perpendicular to a main orientation axis is 0.55 GPa or more and 1.50 GPa or less; and a polar component of surface free energy on at least one surface is 4 mN / m or more and 10 mN / m or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a polypropylene resin film that is particularly suitable for use in packaging applications. [Background technology]

[0002] Polypropylene films are excellent in transparency, mechanical properties, electrical properties, etc., and are therefore used in a variety of applications, such as packaging applications, tape applications, and electrical insulation applications including cable wrapping and capacitors. Among these, in packaging applications, laminated films in which a thin film of aluminum (hereinafter sometimes referred to as "Al") is vapor-deposited onto a polypropylene film are widely used (for example, Patent Document 1).

[0003] Polypropylene films having an Al vapor deposition layer are suitable for applications requiring high water vapor barrier properties or oxygen barrier properties, applications requiring light shielding properties, etc. In recent years, there has been an active movement to design packaging plastic films to be chemically recyclable at the design stage, and in order to improve recyclability, designs in which the vapor deposition layer is made of inorganic oxides such as aluminum oxide (hereinafter sometimes referred to as AlOx) or silicon oxide (hereinafter sometimes abbreviated as SiOx) have also been used (e.g., Patent Documents 2 and 3). When the vapor deposition layer is an inorganic oxide layer, the film has excellent transparency, so that the visibility of the contents is excellent, and in food packaging, there are also advantages such as the application of heat sterilization treatments such as boiling, retort, and high retort, and the ability to heat in a microwave oven. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-105893 A [Patent Document 2] Patent Publication No. 2021-020391 [Patent Document 3] International Publication No. 2022 / 019192 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the polypropylene films of Patent Documents 1 and 2 have a problem that the flatness is significantly deteriorated or the gas barrier property is impaired when the polypropylene films are subjected to a heat sterilization treatment at high temperature and high pressure such as retort or high retort because the heat resistance of the substrate is insufficient. In addition, the laminated polypropylene film of Patent Document 3 is designed to increase the adhesion between the substrate and the AlOx vapor deposition layer (transparent vapor deposition layer) in a dry state (hereinafter, sometimes abbreviated as dry adhesion), but the design to increase the adhesion in a wet state (hereinafter, sometimes abbreviated as wet adhesion) is not fully considered, and there is a problem that the wet adhesion is significantly lower than the dry adhesion. Therefore, there is a concern that peeling may occur between the substrate and the transparent vapor deposition layer such as the AlOx layer, especially when liquid contents are packed or when heat sterilization treatment at high temperature and high pressure such as retort or high retort is performed, so that the application use as a packaging material is limited.

[0006] Therefore, an object of the present invention is to provide a polypropylene-based resin film that has excellent not only dry adhesion to a transparent vapor deposition layer but also wet adhesion, and maintains good adhesion and flatness even after hot water treatment at high temperature and pressure, and can be suitably used, for example, for packaging liquid contents or as a packaging material that is subjected to high-temperature heat sterilization treatment such as retort or high retort. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and have arrived at the following invention. That is, the present invention is a polypropylene-based resin film characterized in that, when all constituent components are taken as 100% by mass, the amount of components having a molecular weight of 1,500 to 10,000 is 0.1% to 3.5% by mass, the storage modulus E' at 120°C in a direction perpendicular to the main orientation axis is 0.55 GPa to 1.50 GPa, and the polar component of the surface free energy on at least one surface is 4 mN / m to 10 mN / m. Effect of the Invention

[0008] The present invention makes it possible to provide a polypropylene-based resin film that has excellent not only dry adhesion to a transparent vapor deposition layer but also wet adhesion, and can maintain good adhesion and flatness even after hot water treatment at high temperature and pressure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The polypropylene-based resin film of the present invention will be described in detail below. The polypropylene-based resin film of the present invention is characterized in that, when the total constituent components are 100% by mass, the amount of components having a molecular weight of 1500 to 10000 is 0.1% to 3.5% by mass, the storage modulus E' at 120°C in the direction perpendicular to the main orientation axis is 0.55 GPa to 1.50 GPa, and the polar component of the surface free energy on at least one surface is 4 mN / m to 10 mN / m. Hereinafter, the polypropylene-based resin may be referred to as "PP".

[0010] A polypropylene-based resin film refers to a sheet-like molded product containing 80% by mass or more and 100% by mass or less of polypropylene-based resin when all constituent components are taken as 100% by mass (when a sheet-like molded product contains multiple types of components equivalent to polypropylene-based resin, if the total amount exceeds 80% by mass, it is considered to be a polypropylene-based resin film.) Specific examples of polypropylene-based resin films include a sheet-like molded product consisting of one layer or multiple layers containing 80% by mass or more and 100% by mass or less of polypropylene-based resin, and a sheet-like molded product consisting of a layer containing more than 80% by mass and 100% by mass or less of polypropylene-based resin and another layer, and the total amount of polypropylene-based resin is 80% by mass or more and 100% by mass or less.

[0011] Moreover, the polypropylene resin refers to a resin in which 70 mol% to 100 mol%, preferably 90 mol% to 100 mol% are propylene units when the total of all the constituent units constituting the resin is taken as 100 mol% (however, when the total of all the constituent units constituting the resin is taken as 100 mol%, those in which the total of the constituent units derived from cyclic olefin monomers exceeds 20 mol%) are excluded. Unless otherwise specified below, other resins can be interpreted in the same way. As the polypropylene resin, so-called bio-PP, part or all of whose constituent units are derived from biomass, and so-called recycled PP produced by chemical recycling or material recycling are also preferably used.

[0012] From the viewpoint of achieving both film-forming properties and adhesion to an adherend having few polar groups, it is important that the amount of components having a molecular weight of 1,500 or more and 10,000 or less is 0.1% by mass or more and 3.5% by mass or less when the total amount of all constituent components is taken as 100% by mass for the polypropylene-based resin film of the present invention.

[0013] By setting the amount of the component having a molecular weight of 1500 to 10000 in the polypropylene resin film to 0.1% by mass or more, the stretchability during film formation of the polypropylene resin film can be improved, and the torque during stretching can be reduced. On the other hand, the component having a molecular weight of 1500 to 10000 is a component having a relatively small molecular weight among polymer compounds such as resins, and if such a component is present in excess, such a component migrates to the surface layer of the polypropylene resin film, and when a layer of a component having a small number of polar groups is laminated on the surface, the interlayer adhesion is reduced. In addition, such a component reduces the crystallinity of the polypropylene resin film, and promotes the bleeding out of additives such as antioxidants and neutralizing agents to the surface, which also reduces the interlayer adhesion. Therefore, by setting the amount of the component having a molecular weight of 1500 to 10000 in the polypropylene resin film to 3.5% by mass or less, it becomes easier to obtain good dry adhesion and wet adhesion, especially when an adherend having few polar groups, such as a transparent vapor deposition layer, is laminated on the surface. From the above viewpoints, the amount of components having a molecular weight of 1,500 or more and 10,000 or less in the polypropylene-based resin film is preferably 3.0% by mass or less, and more preferably 2.7% by mass or less.

[0014] The amount of components having a molecular weight of 1,500 or more and 10,000 or less in the polypropylene resin film can be measured by analyzing a molten sample by gel permeation chromatography (GPC), and the details of the measurement method will be described later.

[0015] In the polypropylene resin film of the present invention, the method for adjusting the amount of components having a molecular weight of 1500 or more and 10000 or less to 0.1% by mass or 3.5% by mass or less or the above-mentioned preferred range is not particularly limited, but examples thereof include a method of using a component (particularly a polypropylene resin as a main component) constituting the polypropylene resin film having a small amount of components having a molecular weight of 1500 or more and 10000 or less, or increasing the ratio of such components. Note that the main component here refers to a component contained in an amount of more than 50% by mass and not more than 100% by mass when the total components of the polypropylene resin film are taken as 100% by mass, and hereinafter the main component can be interpreted in the same way.

[0016] In addition to using the above-mentioned components constituting the polypropylene-based resin film, the production method described below can also be used to suppress the generation of components with molecular weights of 1500 to 10000. Therefore, in order to set the amount of components with molecular weights of 1500 to 10000 to 0.1% by mass to 3.5% by mass or less or the above-mentioned preferred range, it is also effective to use the production method described below, and this is particularly noticeable when the amount of components with molecular weights of 1500 to 10000 as components constituting the polypropylene-based resin film is close to 3.5% by mass.

[0017] Specifically, the surface treatment was performed in an atmosphere of nitrogen gas and / or carbon dioxide gas with a treatment intensity of 30 W min / m 2 Less than or equal to 25 W·min / m 2 Less than or equal to 20 W·min / m 2 and a method of aging the polypropylene-based resin film for 3 days or more at a temperature of 40° C. or higher, more preferably 50° C. or higher, and even more preferably 55° C. or higher after winding the polypropylene-based resin film into a roll. The upper limits of the aging temperature and period are preferably 90° C. and 14 days, respectively, from the viewpoint of preventing the orientation of molecular chains in the polypropylene-based resin film from being excessively relaxed, which would result in a loss of mechanical strength and a deterioration in the wound appearance of the roll.

[0018] In this way, it is effective to use the ingredients and manufacturing methods as described above. These methods can be used in combination as appropriate, but it is not essential to combine all of the methods (this also applies to each item described below unless otherwise specified).

[0019] It is also important that the polypropylene-based resin film of the present invention has a storage modulus E' of 0.55 GPa or more and 1.50 GPa or less in the direction perpendicular to the main orientation axis at 120°C. The storage modulus E' at 120°C is an index showing resistance to high-temperature heat sterilization treatment such as retort and high retort, particularly when used as a packaging material. Conventional packaging films have a low storage modulus E' at 120°C, and although they can maintain flatness and barrier properties in heat sterilization treatments at relatively low temperatures such as boiling treatment (about 90°C) and semi-retort treatment (about 110°C), there is a problem in that it is difficult to maintain these properties when heat sterilization treatments are performed in a higher temperature range.

[0020] By setting the storage modulus E' at 120 ° C. in the direction perpendicular to the main orientation axis to 0.55 GPa or more, the polypropylene-based resin film has a sufficient level of heat resistance, and when used as a packaging material, it is easy to maintain good flatness and appearance even after heat sealing or after heat sterilization treatment in a high-temperature environment such as retort or high retort. From the above viewpoint, the lower limit of the storage modulus E' at 120 ° C. in the direction perpendicular to the main orientation axis is preferably 0.61 GPa, more preferably 0.64 GPa. In addition, by setting the storage modulus E' at 120 ° C. in the direction perpendicular to the main orientation axis to 1.50 GPa or less, the polypropylene-based resin film can have appropriate flexibility and good processability.

[0021] The main orientation axis of a polypropylene-based resin film can be determined by the following procedure. First, a polypropylene-based resin film is prepared and cut into a rectangular sample having a length of 50 mm and a width of 10 mm with an arbitrary direction facing up. <1> Let, <1> The direction in which the long side of the sample faces is defined as 0°. Next, a sample of the same size is placed so that the long side direction is rotated 15° to the right from the 0° direction. <2> Similarly, rotate the rectangular sample by 15° each time and take a sample. <3> ~ <12> Next, each rectangular sample is set in a tensile tester with an initial chuck distance of 20 mm so that the long side direction is the tensile direction, and then a tensile test is performed at a tensile speed of 300 mm / min in an atmosphere of 23°C and 65% RH, and the maximum load until the sample breaks is read. Then, the maximum load is divided by the cross-sectional area (thickness x width (10 mm)) of the sample before the tensile test to calculate the stress at the maximum point strength. The long side direction of the sample where the stress value is maximum is defined as the main orientation axis of the polypropylene resin film, and the direction perpendicular to this in the film plane is defined as the direction perpendicular to the main orientation axis of the polypropylene resin film. The details of the measuring device and method used to identify the main orientation axis will be described later.

[0022] If a sample 50 mm long x 10 mm wide cannot be obtained and the above-mentioned tensile test cannot be performed, measure the crystal orientation of the α crystal (110) plane using wide-angle X-rays as follows, and determine the main orientation axis direction based on the following criteria: Specifically, X-rays (CuKα rays) are irradiated perpendicularly to the film surface, and the crystal peak at 2θ = approximately 14° (α crystal (110) plane) is scanned in the circumferential direction, and the direction with the highest diffraction intensity in the obtained diffraction intensity distribution is determined as the main orientation axis.

[0023] The method of controlling the storage modulus E' at 120°C in the direction perpendicular to the main orientation axis of the polypropylene-based resin film to 0.55 GPa or 1.50 GPa or the above-mentioned preferred range is not particularly limited, but examples thereof include a method of using a homopolypropylene resin having a melting point of 160°C to 168°C (preferably 162°C to 168°C) as the main component of the polypropylene-based resin film, and setting the relaxation rate during transverse stretching in the film-forming process to 6.0% or more, more preferably 7.5% or more, and even more preferably 9.5% or more, and a method of performing an aging treatment at a temperature of 40°C or more, more preferably 50°C or more, and even more preferably 55°C or more for 3 days or more after winding up as a roll. Here, the homopolypropylene resin refers to a polypropylene-based resin in which 99 mol% to 100 mol% of the total structural units constituting the resin are propylene units, when the total structural units constituting the resin are 100 mol%. The upper limits of the stretching temperature during transverse stretching, the relaxation rate, and the temperature and time of aging are 178°C, 20%, 90°C, and 14 days, respectively, from the viewpoint of preventing excessive relaxation of the molecular chain orientation of the polypropylene-based resin film and loss of mechanical strength. The above-mentioned methods can be used in combination as appropriate, but it is not necessary to combine all of the methods.

[0024] In addition, it is important that the polar component of the surface free energy of the polypropylene-based resin film of the present invention is 4.0 mN / m or more and 10.0 mN / m or less on at least one surface. As a result of intensive research, the present inventors have found that it is important to control the "polar component" of the three components of the surface free energy (dispersion component, polar component, hydrogen bond component) within a certain range in order to increase the adhesion to the adherend. By setting the polar component of the surface free energy to 4.0 mN / m or more, the surface of the polypropylene-based resin film is likely to have high adhesion, especially to an adherend that does not have many polar groups such as a transparent deposition layer. From the above viewpoint, the lower limit of the polar component of the surface free energy is preferably 5.0 mN / m. In addition, by setting the polar component of the surface free energy to 10.0 mN / m or less, preferably 8.0 mN / m or less, the affinity between the surface and water can be prevented from becoming excessively high, and as a result, not only the dry adhesion to the transparent deposition layer but also the wet adhesion can be easily increased.

[0025] Here, "at least one surface" means both surfaces or one surface. The polypropylene resin film of the present invention may have a surface free energy polar component of 4.0 mN / m or more and 10.0 mN / m or less on at least one surface, but it is preferable that both surfaces satisfy the above requirements in order to be able to freely select the surface to be vapor-deposited. It is preferable that the requirements stipulated below for at least one surface are similarly satisfied on both surfaces.

[0026] The method of making the polar component of the surface free energy 4.0 mN / m or more and 10.0 mN / m or less or the above-mentioned preferred range is not particularly limited, but for example, a method of making the polypropylene-based resin film have at least one layer X, when the layer X is a layer having a melting point measured by differential scanning calorimetry (DSC) of 152 ° C. or more and less than 162 ° C. and a heat of fusion ΔH of 80 J / g or more and 110 J / g or less, and a method of performing corona discharge treatment with a surface treatment roll kept at a temperature of 40 ° C. or more, more preferably 55 ° C. or more, and even more preferably 70 ° C. or more, in an atmosphere of nitrogen gas and / or carbon dioxide gas when winding up the polypropylene-based resin film in the film-forming process, etc. can be mentioned. In addition, from the viewpoint of preventing deterioration of flatness due to loosening of the polypropylene-based resin film and deterioration of mechanical strength due to excessive relaxation of molecular chain orientation, the upper limit of the corona discharge treatment temperature is 120 ° C. In addition, the above-mentioned methods can be used in combination as appropriate, but it is not necessary to combine all of the methods.

[0027] The polypropylene-based resin film of the present invention preferably has a residual adhesion rate of 93% or more and 99% or less on at least one surface as measured by an acrylic adhesive tape (hereinafter, the "residual adhesion rate measured by an acrylic adhesive tape" may be referred to as the residual adhesion rate). The details of the method for measuring the residual adhesion rate will be described later. A residual adhesion rate of 93% or more means that there is almost no component that hinders the adhesion between the polypropylene-based resin film and the adherend (transparent deposition layer, etc.). Therefore, by adopting such an embodiment, it becomes easy to control the dry adhesion force and wet adhesion force between the polypropylene-based resin film and the transparent deposition layer to a high level. From the above viewpoint, the lower limit of the residual adhesion rate is more preferably 95%, and even more preferably 97%. In addition, the higher the residual adhesion rate, the better, but from the viewpoint of feasibility, the practical upper limit is 99%.

[0028] In order to make the residual adhesion rate on the surface of the polypropylene-based resin film 93% or more or in the above-mentioned preferred range, it is effective to make the surface of the polypropylene-based resin film as free of low molecular weight components that are easily transferred to the adhesive tape as much as possible. Such low molecular weight components mainly include those that are present in the outermost layer of the polypropylene-based resin film from the beginning (the surface layer (B) described below in the case of a multi-layer structure, and the base layer (A) described below in the case of a single-layer structure), those that bleed out from the inside of the polypropylene-based resin film over time, and those that are generated during the surface treatment of the polypropylene-based resin film (they are easily generated when the surface treatment is performed in the presence of oxygen or with excessive treatment intensity).

[0029] Therefore, specific methods for controlling the residual adhesion rate to 93% or more and 99% or less or to the above-mentioned preferred range include, for example, a method of controlling the amount of components having a molecular weight of 1500 or more and 10000 or less to 0.1% by mass or more and 3.5% by mass or less in the outermost layer of the polypropylene-based resin film (the surface layer (B) described below in the case of a multi-layer structure, or the base layer (A) described below in the case of a single-layer structure), a method of controlling the amount of phosphorus-based antioxidant contained in the polypropylene-based resin film to 3000 ppm or less, a method of winding the polypropylene-based resin film at an intensity of 30 W·min / m in a nitrogen gas and / or carbon dioxide gas atmosphere, and a method of winding the polypropylene-based resin film at an intensity of 30 W·min / m 2 Less than or equal to 25 W·min / m 2 Less than or equal to 20 W·min / m 2 or a method in which corona discharge treatment is performed with a surface treatment roll maintained at a temperature of 40° C. or higher, more preferably 55° C. or higher, and even more preferably 70° C. or higher, in an atmosphere of nitrogen gas and / or carbon dioxide gas. The lower limits of the strength and the roll temperature during corona discharge treatment are 8 W min / m, respectively, from the viewpoint of introducing a sufficient amount of polar groups onto the surface of the polypropylene resin film and improving the adhesion to the adherend. 2 , 10°C.

[0030] Among the above, the method of performing corona discharge treatment with a surface treatment roll maintained at a temperature of 40° C. or higher, more preferably 55° C. or higher, and even more preferably 70° C. or higher, is particularly effective in increasing the residual adhesion rate, since it enhances the amorphous mobility of the polypropylene resin during surface treatment and enables efficient introduction of functional groups even with a low treatment intensity that hardly causes molecular chain scission. The above-mentioned methods can be used in combination as appropriate, but it is not essential to combine all of the methods.

[0031] In addition, the polypropylene-based resin film of the present invention preferably has a root-mean-square height Sq of 50 nm or less on at least one surface (hereinafter, the root-mean-square height Sq may be simply referred to as Sq). By setting the Sq of the surface in this range, the unevenness of the surface is reduced, and as a result, even an adherend can be uniformly laminated on a very thin film surface having a film thickness of less than 100 nm, such as a transparent deposition layer, and it becomes easy to improve the adhesion to the adherend. From the above viewpoint, it is preferable that Sq is 35 nm or less on at least one surface, more preferably 28 nm or less. Also, from the viewpoint of imparting appropriate slipperiness to the polypropylene-based resin film, it is preferable that Sq is 10 nm or more on at least one surface. Note that, from the viewpoint of being able to select the surface to be processed by deposition or the like without any restrictions, it is preferable that Sq is 50 nm or less or in the above preferred range on both sides. Sq can be measured by a scanning white light interference microscope, and the measurement method will be described in detail later.

[0032] The method for controlling Sq to 50 nm or less is not particularly limited, but examples thereof include a method in which the melting point measured by differential scanning calorimetry (DSC) on at least one surface is 152°C or more and less than 162°C, a method in which the preheating temperature before stretching in the longitudinal direction during film formation of a polypropylene-based resin film is 140°C or more, more preferably 147°C or more, and a method in which the intensity of surface treatment is 25 W min / m 2 The following methods can be mentioned. The above-mentioned methods can be used in combination as appropriate, but it is not essential to combine all of the methods.

[0033] In addition, the polypropylene resin film of the present invention preferably has at least one layer X, where the layer X is a layer having a melting point of 152°C or more and less than 162°C and a heat of fusion ΔH of 80 J / g or more and 110 J / g or less. By adopting such a configuration, for example, when layer X is present on the surface, molecular chain scission of the polypropylene resin occurring during the treatment of the surface can be minimized, and even after the surface treatment, the amount of components having a molecular weight of 1500 to 10000 in the outermost layer of the polypropylene resin film (surface layer (B) described later in the case of a multi-layer structure, or base layer (A) described later in the case of a single layer structure) can be easily controlled to 0.1% by mass to 3.5% by mass, which makes it easier to increase not only the dry adhesion with the transparent deposition layer but also the wet adhesion. Both the melting point and the heat of fusion ΔH can be measured by differential scanning calorimetry (DSC), and the detailed measurement method will be described later.

[0034] The method for forming a layer having a melting point and heat of fusion measured by differential scanning calorimetry (DSC) that satisfy the above-mentioned preferred ranges is not particularly limited, but examples thereof include a method for forming a layer using a polypropylene resin as a main component having a melting point of 152°C or more and less than 162°C and a heat of fusion ΔH of 80 J / g or more and 110 J / g or less (particularly, it is preferable that the surface layer (B) described later has such an embodiment), a method for increasing the ratio of such a polypropylene resin in the layer, etc. These methods can be used in combination as appropriate, but it is not necessary to combine all of the methods.

[0035] The polypropylene-based resin film of the present invention preferably has a thickness of 7 μm or more and 30 μm or less. By making the thickness 7 μm or more, the polypropylene-based resin film can have sufficient rigidity, and as a result, when various processes such as deposition, coating, printing, and bag making are performed for use as a packaging material, sagging during transportation can be suppressed and it can be made difficult to break due to tension. From the above viewpoint, the lower limit of the thickness is more preferably 10 μm, and even more preferably 12 μm. On the other hand, by making the thickness 30 μm or less, the handleability of the polypropylene-based resin film can be improved and the manufacturing cost per unit area can be reduced. From the above viewpoint, the upper limit of the thickness is more preferably 27 μm, and even more preferably 25 μm. The thickness of the polypropylene-based resin film can be determined by measuring the thickness at any 10 points with a contact micrometer under an atmosphere of 23° C. and 65% RH and calculating the arithmetic average value of all the measured values ​​obtained (the measurement method will be described later in detail).

[0036] The method for making the thickness of the polypropylene-based resin film 7 μm or more and 30 μm or less or the above-mentioned preferred range is not particularly limited, and for example, a method of adjusting the discharge amount of the melt extrusion of the polypropylene-based resin composition during film formation, a method of adjusting the rotation speed of the cast drum when the molten sheet is cooled and solidified, a method of adjusting the lip gap of the die for discharging the molten sheet, a method of adjusting the longitudinal stretch ratio, a method of adjusting the widthwise stretch ratio, etc. can be used. More specifically, the thickness can be reduced by decreasing the discharge amount, increasing the rotation speed of the cast drum, narrowing the lip gap of the die, and increasing the longitudinal and widthwise stretch ratios. Note that these methods can be used in combination as appropriate, but it is not necessary to combine all of the methods.

[0037] The polypropylene-based resin film of the present invention preferably has a polypropylene-based resin content of 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and even more preferably 98% by mass or more. By setting the content in this range, the polypropylene-based resin film can be considered as a material substantially composed of a single material, i.e., a mono-material material, and can be applied to environmentally friendly packaging materials that require suitability for chemical recycling. From the above viewpoint and from the viewpoint of feasibility, the upper limit of the polypropylene-based resin content of the entire polypropylene-based resin film is 100% by mass.

[0038] The layer structure of the polypropylene-based resin film of the present invention may have one or more layers containing 80% by mass or more (100% by mass) of polypropylene-based resin among all the components constituting the layer (hereinafter, such a layer may be referred to as a polypropylene-based resin layer). Hereinafter, in the case of a structure having one polypropylene-based resin layer, the layer is defined as a base layer (A). In addition, in the case of a structure having multiple polypropylene-based resin layers, it is preferable that the base layer (A) accounts for 60% or more of the entire film in terms of thickness ratio.

[0039] In the case where the polypropylene-based resin film of the present invention has a plurality of polypropylene-based resin layers, the layer structure preferably has at least two layers, a base layer (A) and a surface layer (B), and both the base layer (A) and the surface layer (B) are mainly composed of a polypropylene-based resin. Also preferred is an embodiment having the above base layer (A) and surface layer (B), and further having a surface layer (C) on the surface opposite to the surface layer (B), which is mainly composed of a polypropylene-based resin and has a lower polypropylene-based resin content than the surface layer (B).

[0040] Here, "having at least two layers, a base layer (A) and a surface layer (B)" means having a base layer (A) and further having a surface layer (B) on at least one surface. Specific examples of such layer configurations include a two-kind two-layer configuration in which the surface layer (B) is located on one surface of the base layer (A), and a two-kind three-layer configuration in which the surface layer (B) is located on both sides of the base layer (A). In addition, "having a surface layer (C) with a lower polypropylene resin content than the surface layer (B)" refers to an embodiment in which the base layer (A) has surface layers mainly composed of polypropylene resin on both sides, and the polypropylene resin contents (mass % calculated with the entire layer as 100 mass %) of both surface layers are different. In this case, the layer with a relatively higher polypropylene resin content (mass %) is the surface layer (B), and the layer with a lower polypropylene resin content is the surface layer (C).

[0041] The base layer (A) is the layer that occupies the largest thickness proportion in the polypropylene-based resin film of the present invention, and its thickness is preferably 60% or more, and more preferably 70% or more, when the entire polypropylene-based resin film is taken as 100%.

[0042] Examples of commercially available products that can be suitably used as the main component of the base layer (A) include FS2011DG3, a polypropylene resin manufactured by Sumitomo Chemical Co., Ltd., E-200GP and F133A, polypropylene-based resins manufactured by Prime Polymer Co., Ltd., and HA3105, a polypropylene-based resin manufactured by LyondellBasell Industries.

[0043] The components constituting the base layer (A) may be polypropylene-based resins only, or may contain small amounts of other resins. Specific examples of resins other than polypropylene-based resins include cyclic olefin-based resins, α-olefin-based homopolymers and copolymers (including elastomers), petroleum resins, etc. A combination of a plurality of these components may be used. The upper limit of the thickness ratio of the base layer (A) is 100%, and this embodiment is synonymous with the polypropylene-based resin film being a single-layer structure consisting of only the base layer (A).

[0044] In the present invention, the cyclic olefin resin refers to a resin in which the total amount of cyclic olefin monomer-derived structural units is more than 20 mol% and not more than 100 mol%, when the total amount of structural units constituting the resin is 100 mol%. Examples of such resins include resins obtained by polymerizing only cyclic olefin monomers (hereinafter, sometimes referred to as COP), and resins obtained by copolymerizing cyclic olefin monomers and chain olefin monomers (hereinafter, sometimes referred to as COC), and the like, which may be mixed appropriately.

[0045] Examples of the method for producing COP include known methods such as addition polymerization or ring-opening polymerization of cyclic olefin monomers, such as a method of subjecting norbornene, tricyclodecene, tetracyclodecene, and derivatives thereof to ring-opening metathesis polymerization followed by hydrogenation, a method of addition polymerization of norbornene and derivatives thereof, a method of subjecting cyclopentadiene and cyclohexadiene to 1,2-, 1,4-addition polymerization followed by hydrogenation, etc. Among these, from the viewpoints of productivity and moldability, the method of subjecting norbornene, tricyclodecene, tetracyclodecene, and derivatives thereof to ring-opening metathesis polymerization followed by hydrogenation is more preferable.

[0046] In the case of COC, examples of the chain olefin monomers that are preferred for copolymerization include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. Among these, ethylene is particularly preferred from the viewpoints of productivity and cost. In addition, examples of the method for producing a resin obtained by copolymerizing a cyclic olefin monomer and a chain olefin monomer include known methods such as addition polymerization of a cyclic olefin monomer and a chain olefin monomer, such as a method of addition polymerization of norbornene and its derivatives with ethylene. Among these, from the viewpoints of productivity and moldability, it is more preferable to copolymerize norbornene and ethylene.

[0047] In the present invention, the α-olefin homopolymer other than polypropylene resin refers to a polymer having one type of α-olefin other than propylene as a monomer. Examples of the α-olefin include ethylene, 1-butene, 1-hexene, and 4-methylpentene.

[0048] In the present invention, the term "α-olefin copolymer" refers to a copolymer having a polyolefin as the main chain and an α-olefin different from the α-olefin constituting unit of the main chain as a comonomer, and the term "α-olefin elastomer" refers to a copolymer having rubber elasticity among the above-mentioned copolymers. Examples of the α-olefin include ethylene, propylene, 1-butene, 1-hexene, and 4-methyl-pentene. Specific examples of the α-olefin copolymer include ethylene-α-olefin copolymer and propylene-α-olefin copolymer. Specific examples of the α-olefin elastomer include ethylene-α-olefin elastomer and propylene-α-olefin elastomer, but from the viewpoints of productivity and moldability, ethylene-α-olefin elastomer is preferably used.

[0049] In the present invention, the petroleum resin is a petroleum resin that does not have a polar group such as a hydroxyl group, a carboxyl group, a halogen group, a sulfone group, or a modified product thereof, and specifically, is a cyclopentadiene-based resin made from petroleum-based unsaturated hydrocarbons or a resin made from higher olefin-based hydrocarbons as the main raw material.

[0050] In addition, the base layer (A) of the polypropylene-based resin film of the present invention may contain self-recovered raw materials obtained by recovering and reusing parts of the polypropylene-based resin film that are generated during the production process and do not become a product, or laminates having a vapor deposition layer laminated thereon.

[0051] Next, the surface layer (B) will be described. First, it is preferable that the surface layer (B) has a melting point measured by differential scanning calorimetry (DSC) of 152°C or more and less than 162°C, and a heat of fusion ΔH of 80 J / g or more and 110 J / g or less. By adopting such an embodiment, a sufficient amount of amorphous parts is present in the polypropylene resin of the surface layer (B), so that the molecular chain scission of the polypropylene resin occurring during surface treatment such as corona discharge treatment can be minimized. As a result, even in the polypropylene resin film after surface treatment, the amount of components having a molecular weight of 1500 to 10000 in the surface layer (B) can be easily controlled to 0.1% by mass or more and 3.5% by mass or less, and wet adhesion to the transparent vapor deposition layer can be easily increased in addition to dry adhesion.

[0052] In addition, when the total amount of all the constituent components of the surface layer (B) is taken as 100% by mass, the amount of components having a molecular weight of 1500 or more and 10000 or less is preferably 0.1% by mass or more and 3.5% by mass or less. As described above, it is important to control the amount of the components having a molecular weight of 1500 or more and 10000 or less within a certain range in the entire polypropylene-based resin film, but in addition, controlling the amount in the surface layer (B) within a certain range is also effective in improving adhesion.

[0053] By setting the amount of the component having a molecular weight of 1500 to 10000 in the surface layer (B) to 0.1% by mass or more, the action as a stretching aid can be ensured. As a result, the uniform stretchability can be improved during the film formation of the polypropylene-based resin film, and the thickness unevenness of the surface layer (B) can be suppressed. In addition, when the amount of the component having a molecular weight of 1500 to 10000 in the surface layer (B) is set to 3.5% by mass or less, the amount of the component that hinders adhesion to an adherend having few polar groups, such as a transparent deposition layer, is small. As a result, the surface layer (B) is likely to have good not only dry adhesion to such an adherend, but also wet adhesion. From the above viewpoint, the amount of the component having a molecular weight of 1500 to 10000 in the surface layer (B) is preferably 3.0% by mass or less, more preferably 2.7% by mass or less.

[0054] In addition, the surface layer (B) contains inorganic or organic particles such as alumina, silica, crosslinked silicone, and crosslinked polymethyl methacrylate with an average particle size of 200 nm or more, which cause coarse protrusions, in an amount of 1.0 mass% or less, more preferably 0.5 mass% or less, even more preferably 0.3 mass% or less, and particularly preferably 0.2 mass% or less, based on 100 mass% of all components of the surface layer (B). Most preferably, the surface layer (B) does not contain these particles. By adopting such an embodiment, it is possible to suppress the generation of defects that cause deterioration of the barrier property when laminating the transparent vapor deposition layer.

[0055] The polypropylene resin used as the main component of the surface layer (B) preferably satisfies the above-mentioned conditions. Suitable commercially available products include, for example, polypropylene resins E-200GP and F-300SP manufactured by Prime Polymer Co., Ltd., polypropylene resins PC412A and PL500A manufactured by Sun Allomer Co., Ltd., polypropylene resins FL203D manufactured by Japan Polypropylene Co., Ltd., and polypropylene resin FS2011DG3 manufactured by Sumitomo Chemical Co., Ltd.

[0056] The thickness ratio of the surface layer (B) in the polypropylene-based resin film of the present invention is preferably 1% to 40% when the entire polypropylene-based resin film is taken as 100%, from the viewpoint of easily controlling the storage modulus E' at 120°C in the direction perpendicular to the main orientation axis of the polypropylene-based resin film to 0.55 GPa to 1.50 GPa. From the above viewpoint, the upper limit of the thickness ratio of the surface layer (B) is more preferably 25%, and even more preferably 15%. In addition, when the surface layer (B) is present on both sides, the thickness ratio is calculated by adding up the thicknesses of each layer.

[0057] In addition, the polypropylene-based resin film of the present invention is preferably configured to have a base layer (A) and a surface layer (B), and further has a surface layer (C) on the surface opposite to the surface layer (B), the surface layer (C) being mainly composed of a polypropylene-based resin and containing a lower amount of polypropylene-based resin than the surface layer (B). In this case, the surface layer (C) preferably contains a small amount of a thermoplastic resin that is incompatible with the polypropylene-based resin. Hereinafter, the "thermoplastic resin that is incompatible with the polypropylene-based resin" may be simply referred to as an "incompatible resin".

[0058] Generally, in deposition processing and bag making processing, a suitable level of transportability is required for the film, so in the past, a method of imparting slipperiness by forming irregularities on the film surface by adding inorganic or organic particles such as alumina, silica, cross-linked silicone, and cross-linked polymethyl methacrylate with an average particle size of 200 nm or more, or organic lubricants to the film surface (for example, surface layer (B) or surface layer (C)).

[0059] However, the protrusions formed by such particles are hard, and when a laminate (hereinafter sometimes referred to as a vapor-deposited film) in which a vapor-deposited layer is provided on a polypropylene-based resin film is wound up and transported as a rolled product, the protrusions are scraped off the opposing vapor-deposited layer, causing defects such as pinholes and cracks. Therefore, when such particles are used, the barrier properties of the vapor-deposited film are likely to be impaired. In addition, when the polypropylene-based resin film is wound up and transported as a rolled product, the organic particles are likely to be transferred to the opposing surface layer (for example, surface layer (B) when organic particles are added to surface layer (C)), which reduces the adhesive strength between the polypropylene-based resin film and the vapor-deposited layer. When the surface layer (C) contains a small amount of an incompatible resin, it is possible to impart soft surface irregularities to the surface of the surface layer (C) by utilizing its domain structure. Therefore, it is possible to improve both the barrier properties of the vapor-deposited film and the adhesive strength of the vapor-deposited layer without impairing the appropriate slip properties.

[0060] When the surface layer (C) contains the incompatible resin, an excessive increase in the friction coefficient is suppressed, and the processability is improved. Furthermore, by adopting such an embodiment, for example, when a vapor-deposited film having a vapor-deposited layer on the surface layer (B) is wound or unwound, the vapor-deposited layer is rubbed strongly against the opposing surface, and the occurrence of defects such as pinholes and cracks in the vapor-deposited layer can be reduced, and the deterioration of the barrier property can also be reduced.

[0061] As the incompatible resin, for example, polymethylpentene resins and the like can be preferably used. When the surface layer (C) contains a polypropylene resin and an incompatible resin, the size of the α-crystal spherulites of the cast film (unstretched polypropylene resin film) can be made small, or all or part of the polypropylene resin component can be formed as a mesophase, thereby suppressing interfacial peeling between the incompatible resin domain and the polypropylene resin due to stretching. By suppressing interfacial peeling, surface protrusions can be formed without whitening the polypropylene resin film, so that good processing suitability can be obtained while suppressing the occurrence of uneven deposition due to wrinkles in the deposition process and wrinkles during transportation during bag making.

[0062] As such an incompatible resin, for example, the "TPX" (registered trademark) MX series, "TPX" (registered trademark) DX series, and "TPX" (registered trademark) RT series sold by Mitsui Chemicals, Inc. as the "TPX" (registered trademark) series can be preferably used. More specifically, "TPX" (registered trademark) MX002, MX004, DX310, DX845, RT18, RT31, etc. are preferred from the viewpoint of having a relatively high affinity with polypropylene-based resins and being able to reduce the domain size.

[0063] The content of the incompatible resin in the surface layer (C) is preferably more than 0.1% by mass and not more than 10% by mass in the entire layer (100% by mass). When the content of the incompatible resin in the surface layer (C) is 0.1% by mass or more, surface protrusions are efficiently formed on the surface of the surface layer (C), so that the slipperiness of the surface layer (C) is improved, and the occurrence of wrinkles during deposition processing and bag making processing is reduced. On the other hand, when the content of the incompatible resin in the surface layer (C) is 10% by mass or less, excessive domain formation in the surface layer (C) is suppressed, and the decrease in transparency and the decrease in water vapor barrier property due to the excessive occurrence of voids at the interface between the resins during stretching are reduced. From the above viewpoint, the content of the incompatible resin in the surface layer (C) is more preferably more than 0.5% by mass, even more preferably more than 1.5% by mass, and particularly preferably more than 2.5% by mass. In addition, the upper limit of the content of the incompatible resin in the surface layer (C) is more preferably 6.0% by mass, and even more preferably 4.5% by mass.

[0064] In addition, an embodiment in which not only the surface layer (C) but also the above-mentioned surface layer (B) contains an incompatible resin is preferably adopted. By adopting such an embodiment, it is possible to impart fine and soft surface irregularities to the surface of the surface layer (B) by utilizing its domain structure. Therefore, it is possible to impart appropriate slipperiness without containing particles or lubricants, and it becomes easy to control the slipperiness within an appropriate range without impairing the water vapor barrier property or oxygen barrier property of the laminated film after deposition. In this case, it is preferable that the amount of incompatible resin (mass%) in the surface layer (B) does not exceed the amount of incompatible resin (mass%) in the surface layer (C).

[0065] When the surface layer (B) contains an incompatible resin, the content is preferably 0.1% by mass or more and less than 10% by mass, based on 100% by mass of the entire layer, as in the case of the surface layer (C). More preferably, it is 0.5% by mass or more and less than 6.0% by mass, even more preferably 1.5% by mass or more and less than 4.5% by mass, and particularly preferably 2.5% by mass or more and less than 4.5% by mass. However, even when an incompatible resin is added to the surface layer (B), it is preferable to control the amount of components having a molecular weight of 1500 to 10000 contained in the surface layer (B) to 0.1% by mass or more and 3.5% by mass or less, based on 100% by mass of all the constituent components, from the viewpoint of improving adhesion. In addition, examples of commercially available products that can be suitably used as the main component of the surface layer (C) include polypropylene resins E-200GP and F-300SP manufactured by Prime Polymer Co., Ltd., polypropylene resins PC412A and PL500A manufactured by Sun Allomer Co., Ltd., polypropylene resin FL203D manufactured by Japan Polypropylene Corporation, and polypropylene resin FS2011DG3 manufactured by Sumitomo Chemical Co., Ltd.

[0066] In addition, when the polypropylene-based resin film of the present invention has a surface layer (B) and a surface layer (C), it is preferable that the amount of components having a molecular weight of 1500 to 10000 contained in the surface layer (C) is 0.1% by mass to 3.5% by mass when the total components in the surface layer (C) are taken as 100% by mass. By adopting such an embodiment, it is possible to suppress the transfer of unevenness derived from low molecular weight components from the surface layer (C) side to the surface layer (B) side when wound into a film roll and stored for a long period of time. As a result, when a transparent vapor deposition layer is provided on the surface layer (B), the inhibition of adhesion between the polypropylene-based resin film and the transparent vapor deposition layer can be reduced.

[0067] The method for laminating the surface layer (C) is not particularly limited, and examples thereof include a feed block method or a multi-manifold method using melt coextrusion during film formation, as well as extrusion lamination, dry lamination, etc. From the viewpoints of production efficiency and cost, a lamination method using melt coextrusion is preferred.

[0068] The thickness of the surface layer (C) in the polypropylene resin film is not particularly limited, but the lower limit is preferably 0.5%, more preferably 1.0%, relative to the total thickness of the polypropylene resin film (100%), while the upper limit is preferably 35%, more preferably 30%, even more preferably 20%, and particularly preferably 10%.

[0069] Each layer constituting the polypropylene-based resin film of the present invention may contain various additives, such as antioxidants, heat stabilizers, chlorine scavengers, antistatic agents, fillers, viscosity modifiers, color inhibitors, etc., within the scope of the present invention. However, from the viewpoint of preventing deterioration of adhesion with the deposition layer due to bleeding out of the additives, the smaller the amount of these additives, the better. In particular, when antioxidants are added, it is preferable to control the content of phosphorus-based antioxidants to 3000 ppm or less in the polypropylene-based resin film as a whole from the viewpoint of improving adhesion. The content of phosphorus-based antioxidants is more preferably 2700 ppm or less, and even more preferably 2400 ppm or less.

[0070] The polypropylene-based resin film of the present invention has excellent dry adhesion to the transparent vapor deposition layer as well as excellent wet adhesion, and is likely to maintain excellent flatness even after processing steps in which heat and tension are applied, so it can be suitably used as a packaging material. The object to be packaged with the laminate of the present invention is not particularly limited, but examples thereof include items that are easily deteriorated by water vapor, such as food, medicines, cosmetics, and fresh flowers.

[0071] Hereinafter, the method for producing the polypropylene-based resin film of the present invention will be described with reference to specific examples, but the polypropylene-based resin film of the present invention is not limited to the one produced by this method.

[0072] First, a molten polypropylene resin or a polypropylene resin composition is melt-extruded onto a support to form an unstretched polypropylene resin film. Next, this unstretched polypropylene resin film is stretched in the longitudinal direction and then in the transverse direction to sequentially biaxially stretch. Thereafter, the polypropylene resin film of the present invention is produced by subjecting it to a heat treatment and a relaxation treatment. Hereinafter, the method for producing the polypropylene resin film of the present invention will be described in more detail, but the polypropylene resin film of the present invention is not necessarily limited to the one obtained by this method.

[0073] First, when the polypropylene-based resin film is to have a single layer structure, the raw material polypropylene-based resin (or a mixture mainly composed of polypropylene-based resin) is melt-extruded from a single-screw extruder set at an extrusion temperature of 220°C to 280°C, preferably 230°C to 270°C, and passed through a filtration filter to remove foreign matter, etc. Then, the molten resin is molded into a sheet shape and extruded through a slit-shaped die at a temperature of 200°C to 260°C, more preferably 210°C to 245°C.

[0074] On the other hand, when the polypropylene-based resin film has a laminated structure of two or more layers, the polypropylene-based resin (or a mixture mainly composed of polypropylene-based resin) which is the raw material of each layer is melt-extruded from separate single-screw extruders set at an extrusion temperature of 220°C to 280°C, preferably 230°C to 270°C, and passed through a filtration filter to remove foreign matter, and then these molten resins are joined in a feed block or the like so as to have a desired layer structure (for example, in the case of three layers, the unstretched base layer (A) is A, the unstretched surface layer (B) is B, and the unstretched surface layer (C) is C, so that it is B / A / C). Subsequently, the obtained molten laminate is molded into a sheet shape and extruded using a slit-shaped die at a temperature of 200°C to 260°C, more preferably 210°C to 245°C.

[0075] Next, the molten resin sheet extruded from the slit die is cooled and solidified on a casting drum (cooling drum) whose surface temperature is controlled to 10°C to 40°C, to obtain an unstretched polypropylene-based resin film. The molten resin sheet may be adhered to the casting drum by any of the following methods: electrostatic application method, adhesion method using the surface tension of water, air knife method, press roll method, underwater casting method, air chamber method, etc., or a combination of multiple methods. However, the air knife method is preferred because it can improve the flatness of the film and control the surface roughness. In addition, when using the air knife method, it is preferred to appropriately adjust the position of the air knife so that air flows downstream of the film production in order to prevent vibration of the film.

[0076] From the viewpoint of controlling the surface of the polypropylene resin film to be smooth, the surface temperature of the casting drum is preferably 10° C. to 30° C. By setting the temperature within this range, the mesophase fraction of the surface layer portion of the unstretched polypropylene resin film, particularly on the drum surface side (the side on which the deposition layer is formed; in the case where surface layer (B) and surface layer (C) are present, the surface layer (B) side), can be increased, and the unstretched polypropylene film can have a mesophase structure.

[0077] The mesophase is an intermediate phase between crystals and amorphous phases, which is specifically generated when the film is solidified at a very fast cooling rate from a molten state. It is generally known that when polypropylene resin is cooled and solidified, it crystallizes and spherulites grow. When an unstretched polypropylene resin film in which spherulites have been generated is stretched, differences in stretching stress occur inside the spherulites and between the crystals and amorphous between the spherulites, which is thought to cause local stretching spots, leading to thickness spots and structure spots. On the other hand, since the mesophase does not have a spherulite form, it does not cause stretching spots. Therefore, when a mesophase structure is formed, the stretching uniformity is increased, and the thickness of the film can be controlled more uniformly, and the surface roughness can be controlled more uniformly and smaller. In addition, when the unstretched polypropylene resin film does not have a spherulite structure, the temperature when stretching in the longitudinal direction (longitudinal stretching) can be lower than that of an unstretched propylene resin film having spherulites.

[0078] Next, the unstretched polypropylene resin film is biaxially stretched to be biaxially oriented. First, the unstretched polypropylene resin film is preheated by passing it between rolls whose lower limit is preferably 135°C, more preferably 140°C, and even more preferably 147°C, and whose upper limit is preferably 160°C, more preferably 157°C, and even more preferably 154°C. The unstretched polypropylene resin film is then kept in a temperature range whose lower limit is preferably 100°C, more preferably 110°C, even more preferably 132°C, and particularly preferably 142°C, and whose upper limit is preferably 150°C, and is longitudinally stretched at a stretching ratio of 3.8 times to 8.0 times, preferably 4.0 times to 7.0 times, more preferably 4.2 times to 6.0 times, and even more preferably 4.3 times to 5.5 times.

[0079] Subsequently, the stretched polypropylene resin film is passed between rolls whose lower limit is preferably 50°C, more preferably 60°C, and whose upper limit is preferably 90°C, more preferably 80°C, to cool it. Then, the polypropylene resin film is passed between rolls whose lower limit is preferably 70°C, more preferably 80°C, and whose upper limit is preferably 140°C, more preferably 130°C, to use the difference in peripheral speed of the rolls to subject the polypropylene resin film to a heat relaxation treatment whose lower limit is preferably 2.0%, more preferably 3.0%, even more preferably 3.5%, and whose upper limit is preferably 15%, more preferably 13%, even more preferably 12%, and particularly preferably 10%, and then cooled to room temperature to obtain a uniaxially oriented polypropylene resin film. By subjecting the heat relaxation treatment to the ratio as described above, it is possible to efficiently remove only the distortion of some molecular chains whose binding force is weak, while leaving the molecular chains strongly oriented in the longitudinal direction by the longitudinal stretching. As a result, the storage modulus E' of the polypropylene resin film of the present invention at 120° C. in the direction perpendicular to the main orientation axis can be easily controlled to 0.55 GPa or more and 1.50 GPa or less.

[0080] Next, the uniaxially oriented polypropylene resin film is guided to a tenter while holding both ends in the width direction with clips, preheated to a temperature suitable for stretching, and stretched in the width direction (transverse stretching) as it is. The temperature during stretching (width direction stretching temperature) is preferably 155°C to 175°C, more preferably 160°C to 172°C, and even more preferably 165°C to 172°C. The stretching ratio in the width direction is preferably 7.5 times or more and 20 times or less, more preferably 8.5 times or more and 16 times or less, and even more preferably 9.5 times or more and 12 times or less. By setting the stretching ratio in the width direction to 7.5 times or more, it is possible to impart high orientation in the width direction while maintaining a high orientation state in the longitudinal direction, and to increase the in-plane molecular chain tension. As a result, it is possible to improve the heat resistance of the polypropylene resin film. Furthermore, by setting the stretching ratio in the width direction to 20 times or less, it is possible to prevent film breakage during film formation, and to improve the productivity of the polypropylene resin film.

[0081] After the transverse stretching, it is preferable to subject the polypropylene-based resin film to a heat treatment and a relaxation treatment in the width direction. In the present invention, it is preferable to perform a heat treatment while tentatively holding both ends in the width direction with clips of a tenter, and to perform a relaxation treatment in the width direction during the heat treatment. Specifically, it is preferable to perform a heat treatment at 150°C or more and 170°C or less while providing relaxation in the width direction. In the relaxation treatment, from the viewpoint of increasing the structural stability of the polypropylene-based resin film against heat, it is preferable to set the lower limit of the relaxation rate to 6.0%, more preferably 7.5%, and even more preferably 9.5%. Moreover, it is preferable to set the upper limit of the relaxation rate to 20%, more preferably 18%, even more preferably 17%, and particularly preferably 15%.

[0082] By setting the relaxation rate to 6.0% or more under the above heat treatment conditions, the heat resistance of the obtained polypropylene-based resin film can be efficiently improved not only in the width direction but also in the longitudinal direction, and the storage modulus E' at 120°C in the direction perpendicular to the main orientation axis of the polypropylene-based resin film can be easily controlled to 0.55 GPa or more and 1.50 GPa or less. On the other hand, by setting the relaxation rate to 20% or less, the slackness of the film inside the tenter is suppressed, so that the polypropylene-based resin film after film formation is less likely to wrinkle, and further, the deterioration of mechanical properties and unevenness during vapor deposition are also reduced.

[0083] After the heat treatment and relaxation treatment, the polypropylene resin film is cooled to 90°C to 145°C while the widthwise ends are still held taut by the clips, and is then guided to the outside of the tenter, and the clips at the widthwise ends are released. By passing through this cooling process, distortions in the film that could not be completely removed by the heat treatment can be removed, and heat shrinkage in a high-temperature environment can be further suppressed. In this way, a biaxially oriented polypropylene resin film is obtained.

[0084] After the above cooling step, the edges of the biaxially oriented polypropylene resin film on both sides in the width direction are slit in a winder step. Thereafter, it is preferable to perform an in-line surface modification treatment on the surface of the biaxially oriented polypropylene resin film on which the vapor deposition layer is laminated (usually the surface on the side that was in contact with the cast drum (for example, in the case of having surface layer (B) and surface layer (C), the surface layer (B) side) for the purpose of increasing the adhesive force. Examples of in-line surface modification treatment include corona discharge treatment, plasma treatment, ion beam treatment, etc. in the air or in an atmospheric gas of oxygen, nitrogen, hydrogen, argon, carbon dioxide, silane gas, or a mixture thereof. When the gas atmosphere during the surface treatment contains oxygen, molecular chain scission of the polypropylene resin occurs more predominantly than the introduction of polar groups to the outermost layer. As a result, the adhesive force with the adherend may be insufficient, so nitrogen, hydrogen, argon, carbon dioxide, silane gas, or a mixture thereof is preferred among the above gas atmospheres.

[0085] From the viewpoint of reducing the deterioration of the resin due to the surface treatment, it is preferable to perform the surface treatment of the biaxially oriented polypropylene resin film in an environment with a reduced oxygen concentration, specifically, it is preferable to strictly control the oxygen concentration to 500 ppm or less, preferably 300 ppm or less, and more preferably 150 ppm or less. As the atmospheric gas, it is particularly effective to adopt nitrogen gas, carbon dioxide gas, or a mixture of these. When mixing the two, it is preferable to set the ratio of carbon dioxide gas to 20% by volume or more, more preferably 30% by volume or more, so that polar groups can be efficiently introduced even if the surface treatment intensity is reduced, and as a result, the generation of low molecular weight components due to molecular chain scission during the surface treatment is suppressed, and the adhesion strength (dry adhesion strength and wet adhesion strength) between the polypropylene resin film and the deposition layer can be easily increased.

[0086] In addition, the temperature of the rolls for surface treatment in the winder is preferably 40° C. or higher, more preferably 55° C. or higher, and even more preferably 70° C. or higher. The lower limit of the temperature is preferably 120° C. from the viewpoint of preventing deterioration of planarity due to slackening of the polypropylene resin film and excessive relaxation of molecular chain orientation. By setting the temperature in this manner, the efficiency of functional group introduction is greatly improved, and it becomes easy to efficiently impart functional groups while achieving a low-intensity surface treatment that is advantageous for suppressing molecular chain scission as described above.

[0087] After the biaxially oriented polypropylene resin film thus obtained is wound into a roll, it is preferable to perform an aging treatment, and the treatment temperature is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 55°C or higher. The treatment time is preferably 3 days or longer. By performing such an aging treatment, components with extremely small molecular weights are removed by volatilization, and the adhesion between the biaxially oriented polypropylene resin film and the transparent vapor deposition layer is easily increased. In addition, from the viewpoint of preventing the molecular chain orientation of the biaxially oriented polypropylene resin film from being excessively relaxed and causing a deterioration in the rolled appearance, and from the viewpoint of suppressing an increase in production costs and a decrease in operability, the upper limits of the treatment temperature and treatment time are preferably 90°C and 14 days, respectively.

[0088] The polypropylene-based resin film of the present invention thus obtained has excellent not only dry adhesion to a transparent vapor deposition layer but also wet adhesion, and can maintain good adhesion and flatness even after hot water treatment at high temperature and pressure. Therefore, the film can be suitably used, for example, for packaging liquid contents or as a packaging material that undergoes high-temperature heat sterilization treatment such as retort or high retort. EXAMPLES

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the embodiments shown below. Each item was evaluated by the following methods.

[0090] [Methods for measuring characteristic values ​​and evaluating effects] The methods for measuring the characteristic values ​​and the methods for evaluating the effects in the present invention are as follows.

[0091] (1) Amount of components having a molecular weight of 1,500 or more and 10,000 or less in the polypropylene resin film, the surface layer (B), and the surface layer (C) After cutting out a 100 mg sample piece from the polypropylene resin film of the present invention, the sample piece was dissolved by stirring at 165° C. for 30 minutes using 1,2,4-trichlorobenzene as a solvent. The sample was then heated and filtered using a sintered filter with a pore size of 0.5 μm, and the molecular weight distribution of the sample components contained in the filtrate was measured using the following device and conditions. The molecular weight calibration curve was created using the following standard sample. From the obtained molecular weight distribution data, the proportion (mass%) of components with a molecular weight of 1500 to 10,000 was calculated when the total components were taken as 100 mass%. The surface layer (B) and the surface layer (C) were measured in the same manner, except that 100 mg of the sample was obtained by cutting with a microtome. Equipment: Agilent high temperature GPC PL-GPC220 Detector: Agilent refractive index detector (RI detector) Column: Agilent PL1110-6200 (20μm MIXED-A) x 2 ·Flow rate: 1.0mL / min Column temperature: 140℃ ·Injection volume: 0.300mL Sample concentration: 1mg / mL Standard samples: Monodisperse polystyrene manufactured by Tosoh, dibenzyl manufactured by Tokyo Kasei.

[0092] (2) Storage modulus E' at 120°C in the direction perpendicular to the main orientation axis <Method for determining the main orientation axis of polypropylene resin film> First, we will show how to determine the main orientation axis of a polypropylene resin film. Prepare a film, cut it into a rectangle with a length of 50 mm and a width of 10 mm, with the long side in an arbitrary direction, and <1> In this case, the rectangular sample <1> The direction in which the long side of the sample faces was defined as 0°. Next, a sample of the same size was placed so that the long side direction was rotated 15° to the right from the 0° direction. <2> Similarly, the rectangular sample was rotated 15° in the long side direction and the sample was taken. <3> ~ <12> Next, each rectangular sample was set in a tensile tester (Orientec's "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 20 mm so that the long side direction was the tensile direction, and a tensile test was performed at a tensile speed of 300 mm / min in an atmosphere of 23°C and 65% relative humidity, and the maximum load until the sample broke was read. Thereafter, the obtained maximum load value was divided by the cross-sectional area (thickness x width (10 mm)) of the sample before the test to calculate the maximum point strength stress. The same measurement was performed five times for each sample to obtain the average value of the maximum point strength stress, and the long side direction of the sample with the maximum average value was determined as the main orientation axis of the polypropylene resin film, and the direction perpendicular to this in the film plane was determined as the direction perpendicular to the main orientation axis of the polypropylene resin film.

[0093] <Method for measuring storage modulus E' at 120℃> Using the equipment and conditions shown below, a rectangular polypropylene resin film (width (short side) 10 mm x length (long side) 50 mm) cut with the film sample length direction (direction perpendicular to the main orientation axis) as the long side direction was attached to the chuck of the equipment in an atmosphere of 23°C, and measurements were performed by raising the temperature from 23°C to 260°C. A viscoelasticity-temperature curve was drawn using the dynamic viscoelasticity method, and the storage modulus E' (GPa) at 120°C was read. Note that the number of measurement tests was N=5, and the storage modulus E' was calculated by excluding the maximum and minimum values ​​and taking the average of the remaining three values. Equipment: EXSTAR DMS6100 (Seiko Instruments Inc.) Test mode: Tensile mode Chuck distance: 20mm Frequency: 1Hz ·Distortion amplitude: 10.0μm Gain: 1.5 Initial force amplitude: 400mN Temperature range: 23~260℃ Heating rate: 2℃ / min Measurement atmosphere: Nitrogen Measurement thickness: The film thickness was determined by the method described below in (8).

[0094] (3) Polar component of surface free energy of polypropylene resin film First, the polypropylene resin film to be measured was left to stand for 24 hours in an atmosphere with a temperature of 23°C and a relative humidity of 65%. After that, in the same atmosphere, the contact angle of each of four solutions, pure water, ethylene glycol, formamide, and diiodomethane, was measured at five points on the measurement surface using a contact angle meter CA-D type (Kyowa Interface Science Co., Ltd.). The average value of the three measured values ​​excluding the maximum and minimum values ​​of the five measured values ​​was regarded as the contact angle of each solution. Next, using the contact angles of the four types of solutions obtained, the "surface free energy of a solid (γ) is calculated as the dispersion force component (γ S d ), polar force component (γ S p ), and hydrogen bond strength component (γ S h) and the polar component of the surface free energy of the polypropylene-based resin film of the present invention (unit: mN / m) was calculated by the geometric average method based on the extended Fowkes equation (extended Fowkes equation).

[0095] The specific calculation method is shown below. S L When is the tension at the interface between a solid and a liquid, formula (1) holds. The meanings of each symbol are as follows, and known numerical information for four solutions, pure water, ethylene glycol, formamide, and diiodomethane, is shown in Table 1. Formula (1): γ S L =γ S +γ L -2(γ S d ·γ L d ) 1 / 2 -2(γ S p ·γ L p ) 1 / 2 -2(γ S h ·γ L h ) 1 / 2 In addition, the symbols in formula (1) represent the following: Gamma S L : Surface free energy of the resin layer and the known solutions listed in Table 1 Gamma S : Surface free energy of the resin layer Gamma L : Surface free energy of known solutions listed in Table 1 Gamma S d : Dispersion component of the surface free energy of the resin layer Gamma S p : Polar component of the surface free energy of the resin layer Gamma S h : Hydrogen bond component of the surface free energy of the resin layer Gamma L d: Dispersion component of surface free energy of known solutions listed in Table 1 Gamma L p : Polar component of surface free energy of known solutions listed in Table 1 Gamma L h : Hydrogen bonding component of the surface free energy of known solutions listed in Table 1.

[0096] [Table 1]

[0097] (4) Residual adhesion rate measured using acrylic adhesive tape The polypropylene resin film to be measured was cut into a size of 70 mm long x 30 mm wide, and then a No. 31B tape (base material: polyester film, adhesive: acrylic resin, width: 19 mm) manufactured by Nitto Denko was pressed by rolling a 5 kg rubber roller back and forth once, and left to stand for 24 hours under an atmosphere of 23 ° C. and 65% relative humidity. The No. 31B tape was then carefully peeled off, and again a 5 kg rubber roller was rolled back and forth once to attach it to a SUS plate, and the tape was left to stand for 24 hours under an atmosphere of 23 ° C. and 65% relative humidity. Thereafter, the resistance value when the tape was peeled off at a peeling speed of 300 m / min and a peeling angle of 180 ° was measured using a peeling tester manufactured by Kyowa Interface Science, and this value was taken as (F). The peel resistance value was measured by laminating the film to a SUS plate from the beginning instead of the polypropylene resin film of the present invention using the same procedure, and the value was taken as the blank value (F0). These values ​​were applied to the following formula to calculate the residual adhesion rate. Residual adhesion rate (%)=(F) / (F0)×100.

[0098] (5) Root mean square height (Sq) The Sq value of the surface of the polypropylene-based resin film of the present invention was measured using a scanning white light interference microscope VS1540 manufactured by Hitachi High-Tech Science Co., Ltd., which is a three-dimensional non-contact surface shape measuring device. In the analysis, the waviness components of the photographed image were removed using polynomial fourth-order approximation surface correction using the attached analysis software, and then the image was processed using a median (3 x 3) filter, followed by an interpolation process (a process in which pixels for which height data could not be obtained are supplemented with height data calculated from surrounding pixels). The measuring device, software, and measurement conditions were as follows. <Measurement equipment> Scanning white light interference microscope VS1540 (Hitachi High-Tech Science Corporation) <Analysis software> Software: VS-Measure Version 10.0.4.0 Analysis software: VS-Viewer Version 10.0.3.0 <Measurement conditions> Objective lens: 10x 1x telescope tube Zoom lens 1x Wavelength filter 530nm white Measurement mode: Wave Measurement area: 0.561×0.561mm 2 .

[0099] (6) Melting point, heat of fusion A sample was obtained by cutting the layer to be measured from the polypropylene-based resin film of the present invention. Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), a 3 mg sample was heated from 30°C to 260°C at a heating rate of 20°C / min in a nitrogen atmosphere to obtain a curve of the 1st run. Next, after holding at 260°C for 5 minutes, the temperature was lowered to 30°C at a condition of 20°C / min. Furthermore, after holding at 30°C for 5 minutes, the temperature was raised again from 30°C to 260°C at a condition of 20°C / min to obtain a curve of the 2nd run. The melting peak temperature was read from the endothermic curve of the 2nd run, and this was taken as the melting point of the layer. When multiple peak temperatures were observed, the highest temperature was read. The heat of fusion was also read from the endothermic curve of the 2nd run.

[0100] (7) Content of phosphorus-based antioxidant After preparing 200 ± 1 g of the polypropylene-based resin film to be measured and pulverizing it, it was circulated for 6 hours or more in a Soxhlet extractor using a solvent. Then, the phosphorus-based antioxidant to be analyzed was extracted, and after concentration, quantitative analysis was performed by FT-IR / GC-MS.

[0101] (8) Thickness of polypropylene-based resin film Regarding the polypropylene-based resin film of the present invention, the thickness at any 10 locations was measured using a contact-type electronic micrometer (K-312A type) manufactured by Anritsu Corporation in an atmosphere of 23°C and 65% relative humidity. The arithmetic mean value of the thicknesses at those 10 locations was taken as the thickness of the laminate (unit: μm). The accuracy of the thickness obtained by this measurement method (unit: μm) is up to the first decimal place, and when calculating the arithmetic mean, the first decimal place was rounded off.

[0102] (9) Dry adhesion and Wet adhesion of AlOx vapor deposition film <Method of AlOx vapor deposition> A film roll of the polypropylene-based resin film of the present invention was set in a vacuum vapor deposition apparatus equipped with a film running device, and after bringing it to a high vacuum state of 1.00×10 -2 Pa or less, it was run through a cooling metal drum at 20°C, and AlOx was reactively evaporated while introducing oxygen gas to form a vapor deposition layer on the surface-treated surface of the polypropylene-based resin film of the present invention. At that time, it was controlled so that the vapor deposition layer became about 10 nm. After vapor deposition, the inside of the vacuum vapor deposition apparatus was returned to normal pressure, the wound laminated film was rewound, and aged at 40°C for 2 days to obtain a laminate in which a vapor deposition layer of AlOx (aluminum oxide) was laminated on the polypropylene-based resin film.

[0103] <Measurement method of Dry adhesion and Wet adhesion> A polypropylene film (FOR manufactured by Futamura Chemical) having a thickness of 20 μm was laminated on the surface of the laminate on which the AlOx vapor-deposited film was laminated. Specifically, first, DIC Graphics' "Dic Dry" (registered trademark) LX-500 (main agent of adhesive), KW-75 (hardener), and ethyl acetate solvent were mixed at room temperature at a ratio of 10:1:30 (weight ratio) while stirring to prepare an adhesive. Next, the adhesive was applied to the AlOx vapor-deposited surface of the laminate with a wire bar #10 so that the dry thickness was 2 μm, and after drying for 30 seconds in a hot air oven set at 85 ° C, the above-mentioned polypropylene film was laminated. At that time, the lamination pressure was 0.23 MPa, and the conveying speed was 0.5 m / min. After aging this laminate at 40 ° C for 48 hours, a sample was obtained by cutting it to a width of 15 mm, and the peel force was measured using the following device and conditions. The sample was attached to a 1.5 mm thick SUS plate with double-sided tape (Nitto Denko No. 532, tape thickness 0.08 mm) on the deposition substrate side, fixed with an air chuck, and the attached polypropylene film was fixed with the other air chuck and pulled, and the dry adhesion and wet adhesion (measured in a wet state by contacting a cotton swab soaked in water with the measurement site) between the polypropylene resin film of the present invention and the AlOx deposition film were measured. The adhesion was evaluated as excellent or inferior, with ◎, ○, △, and ×, and △ or better was considered to be a pass level, according to the following criteria. (Measurement conditions) Measurement equipment: A&D Co., Ltd. "Tensilon" (registered trademark) universal material testing machine RTG-1210 Load cell: 50N Peel angle: 180° Peeling speed: 50mm / min Measurement atmosphere: temperature 23°C, relative humidity 50%. (Adhesion strength judgement) ◎: 2.0N / 15mm or more ○: 1.3N / 15mm or more, less than 2.0N / 15mm △: 0.7N / 15mm or more, less than 1.3N / 15mm ×:Less than 0.7N / 15mm.

[0104] (10) Film appearance after high retort processing <How to prepare laminate for evaluation> First, a laminate was prepared by laminating an AlOx vapor-deposited film on the polypropylene-based resin film of the present invention by the method described in (9). Next, a 70 μm-thick unstretched polypropylene film ("ZK207" manufactured by Toray Film Processing Co., Ltd.) was laminated on the laminate. Specifically, first, "DicDry" (registered trademark) LX-500 (main agent of adhesive), KO-55 (hardener), and ethyl acetate solvent manufactured by DIC Graphics were mixed at room temperature with stirring at a ratio of 10:1:30 (mass ratio) to prepare an adhesive. Next, the adhesive was applied to the AlOx vapor-deposited surface of the laminate with a wire bar #10 so that the thickness after drying was 2 μm, and the laminate was dried for 30 seconds in a hot air oven set at 85 ° C., and then the unstretched polypropylene film "ZK207" was laminated. The lamination pressure was 0.23 MPa, and the conveying speed was 0.5 m / min.

[0105] <High retort processing method> Two A4-sized sheets were cut out from the laminate produced as described above, and then they were stacked so that the unstretched polypropylene film was on the inside of the bag, and the outer 1 cm part was heat-sealed to make a simple bag. Water was packed as the content. After that, the bag was subjected to hot water treatment at 135℃ for 30 minutes as a high retort treatment, and then removed from the device and slowly cooled to room temperature.

[0106] <How to evaluate film appearance> The appearance of the samples that had been subjected to the high retort treatment was visually inspected and judged as excellent or inferior in appearance according to the following criteria: ◎, ○, △, ×. △ or better was considered to be passable. : Almost no wrinkles were observed. ○: Three or fewer wrinkles were found per A4 size sheet. △: 4 to 9 wrinkles were found per A4 size. ×: 10 or more wrinkles were found per A4 size.

[0107] [Components used in the production of polypropylene films in each Example and Comparative Example] In producing the polypropylene-based resin films of each of the Examples and Comparative Examples, the polypropylene-based resins used were those shown in Table 2. The following resins other than the polypropylene-based resins and masterbatches were used.

[0108] [Table 2]

[0109] In the table, the copolymerization amount is the value when all the structural units constituting the resin are taken as 100 mol %.

[0110] (Master batch for base layer (A) and resin other than polypropylene resin) Petroleum resin 1: "T-REZ" (registered trademark) HA125 (manufactured by ENEOS Corporation, softening point 125°C) AM1: A masterbatch prepared by kneading and extruding A6 (70 parts by mass), petroleum resin 1 (30 parts by mass), and phosphorus-based antioxidant "Irgafos" (registered trademark) 168 (0.1 parts by mass) manufactured by BASF Japan Ltd. in an extruder set at 240°C, and then cooling the strands with water and chipping them.

[0111] (Master batch for surface layer (C) and resin other than polypropylene resin) Polymethylpentene resin 1: "TPX" (registered trademark) manufactured by Mitsui Chemicals, Inc. (RT31, melting point: 235°C, MFR: 21g / 10min (value at temperature 260°C, load 2.16kg)) Polymethylpentene resin 2: "TPX" (registered trademark) manufactured by Mitsui Chemicals, Inc. (DX845, melting point: 232°C, MFR: 9g / 10min (value at temperature 260°C, load 2.16kg)) Particle 1: Silica particles with an average particle size of 2 μm CM1: A masterbatch prepared by kneading and extruding C1 (90 parts by mass), polymethylpentene resin 1 (10 parts by mass), and phosphorus-based antioxidant "Irgafos" (registered trademark) 168 (0.1 parts by mass) manufactured by BASF Japan Ltd. using an extruder set at 260°C, and then cooling the strands with water and chipping them. CM2: A masterbatch prepared by kneading and extruding C3 (90 parts by mass), polymethylpentene resin 2 (10 parts by mass), and phosphorus-based antioxidant "Irgafos" (registered trademark) 168 (0.1 parts by mass) manufactured by BASF Japan Ltd. using an extruder set at 260°C, and then cooling the strands with water and chipping them. CM3: A masterbatch prepared by kneading and extruding C4 (99.5 parts by mass), Particle 1 (0.5 parts by mass), and the phosphorus-based antioxidant "Irgafos" (registered trademark) 168 (0.1 parts by mass) manufactured by BASF Japan Ltd. using an extruder set at 260°C, and then cooling the strands with water and chipping them.

[0112] Example 1 A1 was used as the polypropylene resin raw material for the base layer (A). B1 was used as the raw material for the surface layer (B). Furthermore, a mixture of C1 and CM1 in a mass ratio of 60:40 was used as the raw material for the surface layer (C). The raw materials for each layer were fed to separate single-screw extruders, extruder (A), extruder (B), and extruder (C), respectively, and melt extruded at 260 ° C., and after removing foreign matter with a sintered filter with a cut of 80 μm, the mixture was passed through a pipe set at 250 ° C. Then, the extrusion amount was adjusted using a feed block so that the lamination ratio was 1 / 18 / 1 for a three-layer laminate of b / a / c (unstretched A layer is a, unstretched C layer is c, and unstretched B layer is b), and the molten laminated polymer was extruded from a T-shaped slit die set at 240 ° C. Thereafter, the discharged molten sheet was placed on a casting drum maintained at 20°C, and was cooled and solidified by contacting with an air knife to obtain an unstretched sheet (at this time, the casting drum and the unstretched B layer were in contact with each other). Next, the unstretched sheet was preheated stepwise to 148°C using a group of rolls, and then passed between rolls with a difference in peripheral speed, and stretched at 145°C in the longitudinal direction at a ratio of 4.3 times. Subsequently, the stretched film was passed between rolls maintained at 70°C to cool, and then passed again between rolls maintained at 90°C, and subjected to a 4.0% relaxation treatment in the longitudinal direction using the difference in roll peripheral speed, and then cooled to room temperature to obtain a uniaxially oriented polypropylene resin film. Furthermore, the obtained polypropylene resin uniaxially oriented film was introduced into a tenter, and while holding both ends in the width direction with clips, it was stretched 10.0 times in the width direction at 168°C, and then heat-treated at 163°C while giving 10% relaxation in the width direction. Then, while still holding both ends in the width direction with tension by clips, the film was cooled to 100°C and guided to the outside of the tenter, and the clips on both ends in the width direction of the film were released. Next, the surface of the obtained biaxially oriented polypropylene resin film that came into contact with the casting drum was heated at 18 W·min / m in an atmosphere in which nitrogen gas and carbon dioxide gas were mixed in a volume ratio of 67:33 and oxygen was strictly excluded. 2The corona discharge treatment was performed at a treatment intensity of 1000 ppm. The measured oxygen concentration during the treatment was 110 ppm. The temperature of the surface treatment roll was set to 70°C. The thus obtained biaxially oriented polypropylene resin film having a thickness of 20 μm was then wound into a roll. After the roll was further wound, the film was aged at 55°C for 3 days to obtain a polypropylene resin film. The properties of the obtained polypropylene resin film are shown in Table 3-1.

[0113] (Examples 2 to 4, Comparative Examples 1 to 7) A polypropylene-based resin film was obtained in the same manner as in Example 1, except that the raw materials, film-forming conditions, and surface treatment conditions of the polypropylene-based resin film were changed as shown in Tables 3-1 and 3-2. The properties of the obtained polypropylene-based resin film are shown in Tables 3-1 and 3-2.

[0114] (Example 5, Comparative Example 8) A polypropylene-based resin film was obtained in the same manner as in Example 1, except that one extruder (A) was used to produce a single-layer film having only the base layer (A), and the raw materials, film-forming conditions, and surface treatment conditions were changed as shown in Tables 3-1 and 3-2. Since the film had a single layer structure, the surface that contacted the casting drum was arbitrary. The properties of the obtained polypropylene-based resin film are shown in Tables 3-1 and 3-2.

[0115] [Table 3-1]

[0116] In the table, when only one type of raw material is listed for each layer, it means that the layer is made of only the listed raw material. When the atmospheric gas for the surface treatment is "air," it means that the surrounding gas composition was not adjusted during the surface treatment. The same applies to Table 3-2.

[0117] [Table 3-2] [Industrial Applicability]

[0118] The polypropylene-based resin film of the present invention has excellent not only dry adhesion to a transparent vapor deposition layer but also wet adhesion, and can maintain good adhesion and flatness even after hot water treatment at high temperature and pressure, and can be suitably used, for example, as a food packaging material.

Claims

1. A polypropylene-based resin film characterized in that, when all constituent components are taken as 100 mass%, the amount of components having a molecular weight of 1,500 or more and 10,000 or less is 0.1 mass% or more and 3.5 mass% or less, the storage modulus E' at 120°C in a direction perpendicular to the main orientation axis is 0.55 GPa or more and 1.50 GPa or less, and the polar component of the surface free energy on at least one surface is 4 mN / m or more and 10 mN / m or less.

2. 2. The polypropylene-based resin film according to claim 1, wherein the residual adhesion rate, measured with an acrylic adhesive tape, on at least one surface is 93% or more and 99% or less.

3. The polypropylene-based resin film according to claim 1 or 2, wherein at least one surface of the film has a surface area Sq of 50 nm or less.

4. The polypropylene-based resin film according to any one of claims 1 to 3, wherein the polypropylene-based resin film has at least one layer X, the layer X being a layer having a melting point of 152°C or more and less than 162°C and a heat of fusion ΔH of 80 J / g or more and 110 J / g or less, as measured by differential scanning calorimetry (DSC).

5. The polypropylene-based resin film according to any one of claims 1 to 4, wherein the content of the phosphorus-based antioxidant is 3000 ppm or less.

6. The polypropylene resin film according to any one of claims 1 to 5, having a thickness of 7 µm or more and 30 µm or less.

7. The polypropylene-based resin film according to any one of claims 1 to 6, comprising at least two layers, namely, a base layer (A) and a surface layer (B), wherein both the base layer (A) and the surface layer (B) are mainly composed of a polypropylene-based resin.

8. 8. The polypropylene-based resin film according to claim 7, wherein in the surface layer (B), when all constituent components are taken as 100% by mass, the amount of components having a molecular weight of 1,500 or more and 10,000 or less is 0.1% by mass or more and 3.5% by mass or less.

9. The polypropylene-based resin film according to claim 7 or 8, wherein the base layer (A) has a melting point of 162° C. or higher and 168° C. or lower as measured by differential scanning calorimetry (DSC).

10. The polypropylene-based resin film according to any one of claims 7 to 9, wherein at least one of the surface layers (B) is the layer X.

11. The polypropylene-based resin film according to any one of claims 7 to 10, further comprising a surface layer (C) on a surface opposite to the surface layer (B), the surface layer (C) being mainly composed of a polypropylene-based resin and having a lower content of polypropylene-based resin than the surface layer (B), and wherein, when the total amount of all components in the surface layer (C) is taken as 100% by mass, the amount of components having a molecular weight of 1,500 or more and 10,000 or less contained in the surface layer (C) is 0.1% by mass or more and 3.5% by mass or less.

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