Film, method of manufacturing the same, and laminate

Abstract

To provide a film which is made of polypropylene but has sufficient heat resistance and laminating properties, a method of manufacturing the same, and a laminate.SOLUTION: A film includes: a base layer made of a first resin composition containing a polypropylene-based resin; and a laminate layer made of a second resin composition containing the polypropylene-based resin and laminated on the base layer. A plane orientation M calculated by the following method is 0.45 or more and 0.9 or less on a surface BS2 of the base layer opposite the laminate layer, and is -0.3 or more and 0.3 or less on a surface HS2 of the laminate layer opposite the base layer. A calculation method for the plane orientation M: the plane orientation M is calculated from an equation: M=(0.6887ε-0.4395) / (0.4962ε+0.2198), where ε is expressed as ε=(α+β) / (γ+δ) based on the following absorbance peak intensities α, β, γ, and δ measured using polarized ATR-FTIR.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a film, a method for producing the same, and a laminate. [Background technology]

[0002] In recent years, there has been a demand for a sustainable society, and it is becoming increasingly desirable to recycle packaging materials as well. In consideration of this environmental impact, there are hopes for the realization of recyclable packaging materials that can be made by combining films made of a single material, eliminating the need to separate each resin material.

[0003] Polypropylene film, which is flexible and has moderate heat resistance, is widely used as a packaging material in the fields of food, medicine, etc. In addition, depending on the application, another functional layer is often provided on the polypropylene film. For example, a metal-deposited film in which moisture resistance is imparted by vapor-depositing a metal onto the polypropylene film is known (see, for example, Patent Document 1 below). When the packaging material is to be used by heat sealing, a heat-sealing layer is provided on the polypropylene film to impart heat-sealing properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-216537 Summary of the Invention [Problem to be solved by the invention]

[0005] When imparting heat-sealing properties to a polypropylene film, there is a method of laminating a resin film having heat-sealing properties with an adhesive, but from the viewpoint of recyclability and productivity, a method of extrusion laminating a molten polypropylene resin is preferable. However, with a polypropylene film having high heat resistance, it tends to be difficult to obtain sufficient lamination strength with the latter method. It is possible to provide a resin layer with a low melting point on the laminating side of the polypropylene film, but the inventors have found through their studies that this may reduce the heat resistance of the entire film, making it more susceptible to problems such as heat shrinkage and wrinkles.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a polypropylene-based film that has both sufficient heat resistance and sufficient lamination properties, a method for producing the same, and a laminate. [Means for solving the problem]

[0007] One aspect of the present invention relates to the following [1] to [5]. [1] A method for producing a film comprising a base layer made of a first resin composition containing a polypropylene-based resin, and a laminate layer made of a second resin composition containing a polypropylene-based resin laminated on the base layer, the method comprising: Step A: co-extruding the first resin composition and the second resin composition to obtain an unstretched sheet; and Step B: stretching the unstretched sheet to obtain the film, wherein in Step B, the film is stretched so that the planar orientation M, calculated by the following method, is 0.45 or more and 0.9 or less on a surface BS2 of the base layer opposite the laminate layer, and is -0.3 or more and 0.3 or less on a surface HS2 of the laminate layer opposite the base layer. Calculation method for plane orientation M: The surface orientation M is calculated from the formula M = (0.6887ε - 0.4395) / (0.4962ε + 0.2198), using ε represented by ε = (α + β) / (γ + δ), based on the following absorbance peak intensities α, β, γ, δ measured using the polarized ATR-FTIR method. (1) Fix the incident light as S-polarized light, rotate the sample angle by 15 degrees each time, and in the measured spectrum, the absorbance peak intensity at 997 cm The arrangement of the sample where the absorbance peak intensity is the largest is defined as the slow axis arrangement, and the absorbance peak intensity in the slow axis arrangement is denoted as α. (2) With the incident light as S-polarized light, the absorbance peak intensity at 997 cm -1 in the arrangement rotated 90 degrees from the slow axis arrangement is denoted as β (3) With the incident light as P-polarized light, the absorbance peak intensity at 997 cm -1 in the slow axis arrangement is denoted as γ (4) With the incident light as P-polarized light, the absorbance peak intensity at 997 cm -1 in the arrangement rotated 90 degrees from the slow axis arrangement is denoted as δ. [2] The method for producing the film according to [1], wherein when the melting point of the first resin composition is Ml (°C) and the melting point of the second resin composition is M2 (°C), the relationship M2 < Ml is satisfied. [3] A film comprising a base layer made of a first resin composition containing a polypropylene-based resin and a laminate layer made of a second resin composition containing a polypropylene-based resin laminated on the base layer, wherein the surface orientation M calculated by the following method is 0.45 or more and 0.9 or less on the surface BS2 on the side opposite to the laminate layer of the base layer, and -0.3 or more and 0.3 or less on the surface HS2 on the side opposite to the base layer of the laminate layer. Method for calculating the surface orientation M: The surface orientation M is calculated from the formula M = (0.6887ε - 0.4395) / (0.4962ε + 0.2198), using ε represented by ε = (α + β) / (γ + δ), based on the following absorbance peak intensities α, β, γ, δ measured using the polarized ATR-FTIR method. (1) Fix the incident light to S-polarized light, rotate the sample angle by 15 degrees each time, and in the measured spectrum, when the absorbance peak intensity at 997 cm -1 is the largest, the arrangement of the sample is defined as the slow axis arrangement, and the absorbance peak intensity in the slow axis arrangement is denoted as α. (2) Set the incident light as S-polarized light, and denote the absorbance peak intensity at 997 cm -1 in the arrangement rotated 90 degrees from the slow axis arrangement as β. (3) Set the incident light as P-polarized light, and denote the absorbance peak intensity at 997 cm -1 in the slow axis arrangement as γ. (4) Set the incident light as P-polarized light, and denote the absorbance peak intensity at 997 cm -1 in the arrangement rotated 90 degrees from the slow axis arrangement as δ. [4] The film according to [3], wherein when the melting point of the first resin composition is M1 (°C) and the melting point of the second resin composition is M2 (°C), the relationship M2 < M1 is satisfied. [5] A laminate comprising the film according to [3] or [4]. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a film that has both sufficient heat resistance and sufficient laminating property while being a polypropylene-based film, a method for producing the same, and a laminate. [Brief Description of the Drawings]

[0009] [Figure 1] It is a cross-sectional view schematically showing an example of the film of the present embodiment. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each drawing is a schematically shown figure, and the size, shape, etc. of each part are exaggerated as appropriate for easy understanding.

[0011] [Film] The film of this embodiment comprises a substrate layer made of a first resin composition containing a polypropylene-based resin, and a laminate layer made of a second resin composition containing a polypropylene-based resin laminated on the substrate layer.

[0012] In the film of this embodiment, the plane orientation M calculated by the method described below is 0.45 or more and 0.9 or less on the surface BS2 of the base layer opposite the laminate layer, and is −0.3 or more and 0.3 or less on the surface HS2 of the laminate layer opposite the base layer.

[0013] (Calculation method of plane orientation M) The planar orientation M is calculated from the equation M = (0.6887ε - 0.4395) / (0.4962ε + 0.2198), where ε is expressed as ε = (α + β) / (γ + δ), based on the following absorbance peak intensities α, β, γ, and δ measured at 23°C using polarized ATR-FTIR. (1) The incident light was fixed to S-polarized light, and the sample angle was rotated by 15 degrees. In the measured spectrum, -1 The arrangement of the sample in which the absorbance peak intensity is the largest is defined as the slow axis arrangement, and the absorbance peak intensity in the slow axis arrangement is defined as α, (2) When the incident light is S-polarized and rotated 90 degrees from the slow axis arrangement, the 997 cm -1 The absorbance peak intensity is defined as β. (3) The incident light is P-polarized, and the slow axis arrangement is 997 cm -1 The absorbance peak intensity is γ, (4) When the incident light is P-polarized and rotated 90 degrees from the slow axis arrangement, the 997 cm -1 The absorbance peak intensity is defined as δ.

[0014] The film of the present embodiment has the above-described structure, and thus can have both sufficient heat resistance and sufficient lamination properties.

[0015] Incidentally, a conventional method for evaluating orientation is the dichroic ratio method, in which polarized light is incident on a film, the light totally reflected by the film surface is detected to measure the absorption spectrum, and the orientation is evaluated from the ratio of absorbance in the slow axis direction in the film plane to that in the fast axis direction perpendicular to it. However, this conventional method only uses S-polarized light, and the obtained orientation is limited to the slow axis direction in the film plane and the fast axis direction perpendicular to it, so it does not include information about the thickness direction of the film.

[0016] On the other hand, the plane orientation M of the present invention can measure the direction of molecular vibration by irradiating a sample with S-polarized light, which vibrates perpendicular to the incident plane, and P-polarized light, which vibrates parallel to the incident plane.

[0017] Specifically, the film is positioned with its fast axis aligned with the light's propagation direction, and S-polarized light is irradiated onto the film to obtain orientation information related to the slow axis. Irradiating the film with P-polarized light provides orientation information related to the fast axis and the depth direction, i.e., the film's thickness. Next, the sample is rotated 90 degrees and S-polarized light is irradiated onto the film to obtain orientation information related to the fast axis. Irradiating the film with P-polarized light provides orientation information related to the slow axis and the thickness direction. From this orientation information, molecular orientation information can be determined for the slow axis, fast axis, and thickness directions. Furthermore, because it is possible to specifically analyze molecular orientation on the sample surface down to a depth of approximately 1 μm, the infrared light's penetration depth, it is possible to analyze molecular orientation on the sample surface regardless of sample thickness.

[0018] In polypropylene resins, the 997cm -1 The peak at 997 cm is attributed to the hybrid vibration of C-CH3 rocking, C-CH3 stretching, and CH bending, and is a band that absorbs parallel vibrations to the molecular chain, i.e., parallel polarized light. For this reason, in the spectrum measured by fixing the incident light to S-polarized light and rotating the sample angle by 15 degrees, -1It can be seen that the sample orientation where the absorbance peak intensity is greatest is the orientation in which the molecular chains are generally oriented in the film plane direction (hereinafter referred to as the slow axis orientation). The ratio of the absorbance peak intensity α at this time to the absorbance peak intensity β when the orientation is rotated 90 degrees from the slow axis orientation is the dichroic ratio, which indicates the degree of orientation in the plane direction.

[0019] If the polarization of the incident light is P-polarized, the information includes not only the component in the plane direction of the film but also the component in the thickness direction. Therefore, by comparing this with information from S-polarized light, which can measure only the component in the plane direction of the film, it is possible to evaluate the degree of orientation in the thickness direction.

[0020] As a result of various investigations, the range of the plane orientation M on the surface BS2 described above was determined to be the range of the absorbance peak intensity α and the absorbance peak intensity β described above, and the 997 cm -1 The absorbance peak intensity γ of 997 cm in the configuration rotated 90 degrees from the slow axis configuration -1 This is based on the finding that the plane orientation M calculated from the above formula using the absorbance peak intensity δ of the film is correlated with the strength and transparency of the base layer, the lamination properties of the laminate layer, and the heat resistance of the film.

[0021] Fig. 1 is a cross-sectional view schematically showing an example of a film according to the present embodiment. The film 10 shown in Fig. 1 comprises a base layer 30 and a laminate layer 20 laminated in direct contact with the base layer. The base layer 30 is made of a first resin composition containing a polypropylene-based resin, and the laminate layer 20 is made of a second resin composition containing a polypropylene-based resin. The base layer 30 and the laminate layer 20 satisfy the above-mentioned condition for plane orientation M.

[0022] <Base material layer> Examples of polypropylene resins contained in the first resin composition constituting the base layer 30 include polypropylene resins such as homopolypropylene (PP), block polypropylene, and random polypropylene, as well as propylene-α-olefin copolymers. The first resin composition may contain only polypropylene resins as the resin component.

[0023] The first resin composition may contain a single polypropylene resin as the polypropylene resin, or may contain a plurality of polypropylene resins with different melting points, MFRs, and the like.

[0024] The melting point of the polypropylene resin may be 110 to 165°C, which is the melting point of general polypropylene, or may be 130 to 165°C.

[0025] The MFR (melt flow rate) of the polypropylene resin may be 0.01-50, 0.05-20, or 0.1-10.

[0026] The melting point M1 of the first resin composition may be 150°C or higher, 155°C or higher, or 160°C or higher.

[0027] The first resin composition may contain a polypropylene-based resin having a melting point within the above range.

[0028] The first resin composition may contain various additives as long as they do not impair the properties of the present invention. Examples of such additives include antiblocking agents, crosslinking agents, nucleating agents, fillers, reinforcing agents, slip agents, lubricants, plasticizers, antioxidants, heat stabilizers, weathering agents, light stabilizers, UV absorbers, antistatic agents, flame retardants, flame retardant assistants, antifogging agents, pigments, dyes, dispersants, neutralizing agents, natural oils, synthetic oils, waxes, and modifying resins. Two or more of these may be used in combination.

[0029] The stretching ratio in the machine direction (MD) of the base layer 30 may be 2 to 10 times, or 3 to 7 times. The stretching ratio in the cross direction (TD) may be 3 to 15 times, or 5 to 12 times. When the MD and TD of the base layer 30 are within the above ranges, the strength and transparency of the base layer are easily obtained. Furthermore, when the MD and TD of the base layer 30 are within the above ranges, the heat resistance of the film 10 can be improved. Here, heat resistance refers to the property of preventing shrinkage and wrinkles from occurring on the back side of the film when the front side (laminating layer) is laminated.

[0030] The planar orientation M of the base material layer 30, calculated by the above method, may be 0.45 to 0.9, 0.6 to 0.9, or 0.7 to 0.85, on the surface BS2 of the base material layer 30 opposite the laminate layer 20. When the planar orientation M on the surface BS2 of the base material layer 30 is within the above range, the strength and transparency of the base material layer are easily obtained. Furthermore, when the planar orientation on the surface BS2 of the base material layer 30 is within the above range, the heat resistance of the film is easily improved.

[0031] The planar orientation M of the surface BS2 of the base material layer 30 opposite to the laminate layer 20 can be controlled by the stretching temperature, stretch ratio, etc. Increasing the stretching ratio or decreasing the stretching temperature in the stretching step tends to increase the planar orientation M.

[0032] The thickness of the base layer 30 may be 8 μm or more and 80 μm or less, or 10 μm or more and 50 μm or less. When the thickness of the base layer 30 is within the above range, the strength and transparency of the base layer are easily obtained. Furthermore, when the thickness of the base layer 30 is within the above range, the heat resistance of the film can be improved. Here, heat resistance refers to the property that shrinkage and wrinkles are unlikely to occur on the back side of the film when the front side (laminate layer) is laminated.

[0033] <Laminate layer> Examples of the polypropylene-based resin contained in the second resin composition constituting the laminate layer 20 include polypropylene resins such as homopolypropylene (PP), block polypropylene, and random polypropylene, as well as propylene-α-olefin copolymers. The second resin composition may contain only a polypropylene-based resin as a resin component.

[0034] The second resin composition may contain a single polypropylene resin as the polypropylene resin, or may contain a plurality of polypropylene resins with different melting points, MFRs, and the like.

[0035] The melting point M2 of the second resin composition may be 120°C or higher, 130°C or higher, or 135°C or higher. The melting point M2 may be 165°C or lower, 150°C or lower, or 140°C or lower. The melting point M2 may be 120 to 165°C, 130 to 150°C, or 135 to 140°C.

[0036] In the film of the present embodiment, from the viewpoint of lamination properties, the melting point M2 of the second resin composition may be lower than the melting point M1 of the first resin composition. In this case, the difference between M2 and M1 may be 5° C. or more, 10° C. or more, 15° C. or more, 20° C. or more, or 25° C. or more. When the difference in melting points between the laminate layer 20 and the base material layer 30 is within the above range, shrinkage and wrinkling due to heat when extrusion laminating another resin composition can be prevented, for example.

[0037] Various additives may be mixed into the laminate layer 20 as long as they do not impair the properties of the present invention. Examples include antiblocking agents, crosslinking agents, nucleating agents, fillers, reinforcing agents, slip agents, lubricants, plasticizers, antioxidants, heat stabilizers, weathering agents, light stabilizers, UV absorbers, antistatic agents, flame retardants, flame retardant assistants, anti-fogging agents, pigments, dyes, dispersants, neutralizing agents, natural oils, synthetic oils, waxes, modifying resins, etc. Two or more of these may be used in combination.

[0038] The planar orientation M of the laminate layer 20, calculated by the above method, may be −0.3 or more and 0.3 or less, −0.2 or more and 0.2 or less, or −0.1 or more and 0.1 or less, on the surface HS2 of the laminate layer 20 opposite the base layer 30. When the planar orientation M of the surface HS2 of the laminate layer 20 is within the above range, the laminate layer is more likely to have good lamination properties and flexibility.

[0039] The planar orientation M of the surface HS2 of the laminate layer 20 opposite to the base layer 30 can be controlled by the stretching temperature, stretching ratio, etc. Increasing the stretching ratio or the stretching temperature in the stretching step tends to increase the planar orientation M.

[0040] The thickness of the laminate layer 20 may be 1 μm or more and 40 μm or less, or 2 μm or more and 20 μm or less. When the thickness of the laminate layer 20 is within the above range, the strength of the film 10 and the lamination strength during lamination can be improved.

[0041] Other substrates and functional layers may be laminated on the film 10. For example, a heat seal (sealant) layer may be provided on the film surface on the laminate layer 20 side.

[0042] The film of this embodiment can be used as a film for packaging materials.

[0043] <Film manufacturing method> The method for producing the film of this embodiment is a method capable of producing the film of this embodiment described above, and includes step A of co-extruding a first resin composition containing a polypropylene-based resin and a second resin composition containing a polypropylene-based resin to obtain an unstretched sheet, and step B of stretching the unstretched sheet to obtain a film.

[0044] The first resin composition and the second resin composition to be co-extruded in step A can be those mentioned in the description of the film of this embodiment.

[0045] The resin temperature in the co-extrusion molding may be 200 to 300°C, 220 to 280°C, or 240 to 260°C.

[0046] The ratio of the thickness of the layer of the second resin composition (second layer) to the thickness of the layer of the first resin composition (first layer) in the unstretched sheet [second layer / first layer] may be 0.025 to 1, 0.05 to 0.5, or 0.1 to 0.25.

[0047] In step B, the unstretched sheet can be stretched using a known device such as a batch-type stretching machine or a continuous stretching machine.

[0048] The stretching in step B may be uniaxial stretching or biaxial stretching.

[0049] The stretching temperature may be 150°C to 175°C, or may be 155°C to 170°C.

[0050] The stretching temperature may be a temperature equal to or higher than the melting point of the laminate layer 20 and equal to or lower than the melting point of the base layer 30. Stretching within this temperature range tends to decrease the orientation of the laminate layer 20 and increase the orientation of the base layer 30. This allows for both improved strength and heat resistance due to the base layer 30 and lamination properties due to the laminate layer 20. Furthermore, if the stretching temperature is equal to or higher than the melting point of the laminate layer 20, the orientation of the laminate layer 20 is suppressed, making it easier to achieve lamination properties, and the base layer 30 is sufficiently softened, making it easier to prevent breakage of the film. On the other hand, if the stretching temperature is equal to or lower than the melting point of the base layer 30, softening and melting of the entire film is suppressed, making it easier to stretch the unstretched sheet.

[0051] In step B, the stretching ratio in the machine direction (MD) may be 2 to 10 times, or 3 to 7 times. Furthermore, during stretching, the stretching ratio in the transverse direction (TD) may be 3 to 15 times, or 5 to 12 times. When the MD stretching ratio and the TD stretching ratio are within the above ranges, the strength and transparency of the base layer are easily obtained. Furthermore, when the MD and TD of the base layer 30 are within the above ranges, the heat resistance of the film 10 can be improved. Here, heat resistance refers to the property of preventing shrinkage and wrinkles from occurring on the back side of the film when the front side (laminating layer) is laminated.

[0052] In step B, stretching is performed so that the plane orientation M calculated by the above-mentioned method is 0.45 or more and 0.9 or less on the surface BS2 of the base layer opposite the laminate layer, and is -0.3 or more and 0.3 or less on the surface HS2 of the laminate layer opposite the base layer.

[0053] Furthermore, from the viewpoint of improving the lamination property and flexibility of the laminate layer, the film may be stretched so that the planar orientation M calculated by the above method is −0.3 to 0.3, −0.2 to 0.2, or −0.1 to 0.1 on the surface of the laminate layer opposite the base layer. The planar orientation M can be adjusted by changing the stretching temperature, MD stretch ratio, TD stretch ratio, and stretching speed.

[0054] <Laminate> The laminate of this embodiment includes the film of this embodiment.

[0055] As described above, a heat seal (sealant) layer may be laminated on the laminate layer of the film of this embodiment. In this case, the heat seal (sealant) layer may be provided by extrusion laminating a polyolefin resin.

[0056] Examples of polyolefin resins include polyethylene resins and polypropylene resins.

[0057] Examples of polyethylene resins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) which is a copolymer of α-olefin and ethylene, medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0058] The polypropylene-based resin may be the same as that described above. In this embodiment, from the viewpoint of recyclability, the heat-sealable layer may contain a polypropylene-based resin. In this case, from the viewpoint of productivity, the heat-sealable layer may be formed by extrusion laminating a resin composition containing a polypropylene-based resin.

[0059] The laminate of the present embodiment may further include, in addition to the heat seal layer, a printing layer, a protective layer, a light-shielding layer, an adhesive layer, and other functional layers.

[0060] The laminate of this embodiment can be used as a packaging material. [Example]

[0061] Examples prepared by the present inventors will be described in detail below in comparison with comparative examples, but the present invention is not limited to the following examples.

[0062] Example 1 A 1 mm thick multilayer unstretched sheet was produced by coextrusion molding using polypropylene resin F-300SP (Prime Polymer Co., Ltd., melting point 161°C) for the base layer and polypropylene resin F-744NP (Prime Polymer Co., Ltd., melting point 133°C) for the laminate layer. The thickness ratio of each layer in the coextrusion molding was set to 18:2 (base layer:laminate layer), and the resin temperature during extrusion was 250°C. The multilayer unstretched sheet was then biaxially stretched at a stretching ratio of 5x in the MD and 10x in the TD, a stretching speed of 30 mm / sec, and a stretching temperature of 157°C after a preheating time of 3 minutes to obtain a 20 μm thick film.

[0063] Examples 2 to 4 Using Example 1 as the standard conditions, laminated films with different planar orientation M were produced by adjusting the stretching ratio and stretching temperature in the stretching step as follows. Example 2: The magnification in the MD direction was reduced, and the magnification in the TD direction was reduced to adjust the plane orientation M. Example 3: The drawing temperature was lowered to adjust the plane orientation M. Example 4: The planar orientation M was adjusted by decreasing the stretching ratio in the MD direction, decreasing the stretching ratio in the TD direction, and increasing the stretching temperature.

[0064] (Comparative Example 1) Polypropylene resin F-300SP (manufactured by Prime Polymer Co., Ltd., melting point 161°C) was extrusion molded to produce an unstretched sheet with a thickness of 1 mm. The resin temperature during extrusion was 250°C. Subsequently, the unstretched sheet was biaxially stretched under conditions of a stretching ratio of 5 times in the MD direction and 10 times in the TD direction, a stretching speed of 30 mm / sec, a stretching temperature lower than that of Example 1, and a preheating time of 3 minutes, to obtain a film with a thickness of 20 μm.

[0065] (Comparative Examples 2 and 3) Using Example 1 as the standard conditions, laminated films with different planar orientation M were produced by adjusting the stretching ratio and stretching temperature in the stretching step as follows. Comparative Example 2: The drawing temperature was increased to adjust the plane orientation M. Comparative Example 3: The drawing temperature was increased to adjust the plane orientation M.

[0066] [Evaluation of plane orientation M] The following absorbance peak intensities α, β, γ, and δ were measured at 23°C using polarized ATR-FTIR. Using ε, which is expressed as ε = (α + β) / (γ + δ), the planar orientation M was calculated from the formula M = (0.6887ε - 0.4395) / (0.4962ε + 0.2198). (1) The incident light was fixed to S-polarized light, and the sample angle was rotated by 15 degrees. In the measured spectrum, -1The arrangement of the sample in which the absorbance peak intensity is the largest is defined as the slow axis arrangement, and the absorbance peak intensity in the slow axis arrangement is defined as α, (2) When the incident light is S-polarized and rotated 90 degrees from the slow axis arrangement, the 997 cm -1 The absorbance peak intensity is defined as β. (3) The incident light is P-polarized, and the slow axis arrangement is 997 cm -1 The absorbance peak intensity is γ, (4) When the incident light is P-polarized and rotated 90 degrees from the slow axis arrangement, the 997 cm -1 The absorbance peak intensity is defined as δ.

[0067] The polarized ATR prism was made of ZnSe, and measurements were carried out using a single-reflection ATR with a 45-degree incidence angle.

[0068] The plane orientation M was measured for the surface HS2 (first surface) of the laminate layer opposite the base layer and the surface BS2 (second surface) of the base layer opposite the laminate layer. When the film was a monolayer film, the plane orientation M was measured for both main surfaces of the monolayer film.

[0069] [Evaluation of lamination] Polypropylene resin F-744NP (manufactured by Prime Polymer Co., Ltd., melting point 133°C) was extrusion laminated onto the laminate layer of the film produced in the Examples and Comparative Examples (one main surface of the film in Comparative Example 1) to provide a heat seal layer with a thickness of 60 µm, thereby obtaining a laminate. During extrusion lamination, no surface treatments such as corona treatment on the base layer or ozone treatment on the laminate layer were performed, and the discharge temperature and take-up speed were adjusted so that the resin temperature in the laminated portion would be 250°C.

[0070] The laminate obtained above was cut into a 15 mm wide x 100 mm piece, and a cutter was placed from the edge of the film to peel off the interface between the laminate layer (film in Comparative Example 1) and the heat seal layer. A T-peel test was then performed using a tensile tester (model number AGS-500NX) manufactured by Shimadzu Corporation at a pulling rate of 100 mm / min. Cases where the interface between the heat seal layer and the laminate layer could not be peeled off at all and where the average measured strength was 2 N / 15 mm or more were marked "Good," and cases where the average measured strength was less than 2 N / 15 mm were marked "Poor."

[0071] [Heat resistance evaluation] The films produced in the Examples and Comparative Examples were cut into a widthwise length of 20 mm and a lengthwise length of 150 mm, and then hung in a hot air oven at 120°C and heated for 15 minutes. The widthwise and lengthwise lengths after heating were measured, and the ratio of the shrunken length to the length before heating was calculated as the thermal shrinkage rate. Films with a lengthwise shrinkage rate of less than 8% and a widthwise shrinkage rate of less than 6% were evaluated as "Good," while films with a lengthwise shrinkage rate of 8% or more or a widthwise shrinkage rate of 6% or more, or films with a lengthwise shrinkage rate of 8% or more and a widthwise shrinkage rate of 6% or more were evaluated as "Poor."

[0072] [Overall Judgment] If both the lamination property evaluation and the heat resistance evaluation were "○", the overall evaluation was rated as "○", and if at least one of the lamination property evaluation and the heat resistance evaluation was "×", the overall evaluation was rated as "×".

[0073] The film configurations and evaluation results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1. The abbreviations in Table 1 are as follows: PP1: Polypropylene resin F-300SP (Prime Polymer Co., Ltd., melting point 161°C) PP2: Polypropylene resin F-744NP (Prime Polymer Co., Ltd., melting point 133°C)

[0074] [Table 1]

[0075] (Evaluation results) As shown in Table 1, the films of Examples 1 to 4, in which the surface orientation M on the surface HS2 (first surface) of the laminate layer opposite the base layer is -0.30 or more and 0.30 or less, and the surface orientation M on the surface BS2 (second surface) of the base layer opposite the laminate layer is 0.45 or more and 0.9 or less, were confirmed to have an evaluation of "Good" for lamination properties and heat resistance.

[0076] On the other hand, the film of Comparative Example 1 had surface planar orientation M of 0.38 and 0.40, and the lamination properties and heat resistance were evaluated as "×". The film of Comparative Example 2, in which the planar orientation M on the surface BS2 of the base layer opposite the laminate layer was 0.41, was evaluated as "×" in heat resistance, and the film of Comparative Example 3, in which the planar orientation M on the surface HS2 of the laminate layer opposite the base layer was 0.33, was evaluated as "×" in lamination properties. [Explanation of symbols]

[0077] 10...film, 20...laminate layer, 30...base material layer.

Claims

1. A method for producing a film comprising a substrate layer made of a first resin composition containing a polypropylene-based resin, and a laminate layer made of a second resin composition containing a polypropylene-based resin and laminated on the substrate layer, the method comprising: A step A of co-extruding the first resin composition and the second resin composition to obtain an unstretched sheet; and step B of obtaining the film by stretching the unstretched sheet, In the step B, the plane orientation M calculated by the following method is ２ and the surface HS of the laminate layer opposite to the base layer is 0.45 or more and 0.9 or less. ２ The film is stretched so that the stretching ratio is -0.3 or more and 0.3 or less. Calculation method of plane orientation M: The plane orientation M is calculated from the equation M=(0.6887ε−0.4395) / (0.4962ε+0.2198) using ε expressed as ε=(α+β) / (γ+δ) based on the following absorbance peak intensities α, β, γ, and δ measured using polarized ATR-FTIR. (1) The incident light was fixed to S-polarized light, and the sample angle was rotated by 15 degrees. In the measured spectrum, －１ The arrangement of the sample in which the absorbance peak intensity is the largest is defined as the slow axis arrangement, and the absorbance peak intensity in the slow axis arrangement is defined as α, (2) 997 cm when the incident light is S-polarized and rotated 90 degrees from the slow axis arrangement －１ The absorbance peak intensity is defined as β. (3) When the incident light is P-polarized and the slow axis is arranged as described above, the wavelength is 997 cm －１ The absorbance peak intensity is γ, (4) 997 cm when the incident light is P-polarized and rotated 90 degrees from the slow axis arrangement －１ The absorbance peak intensity is defined as δ.

2. The melting point of the first resin composition is M １ (°C), and the melting point of the second resin composition is M ２ (℃), M ２ <M １ The method for producing a film according to claim 1 , wherein the following relationship is satisfied:

3. The laminated sheet has a base layer made of a first resin composition containing a polypropylene-based resin, and a laminate layer made of a second resin composition containing a polypropylene-based resin and laminated on the base layer, The plane orientation M calculated by the following method is the surface BS of the substrate layer opposite to the laminate layer. ２ and the surface HS of the laminate layer opposite to the base layer is 0.45 or more and 0.9 or less. ２ The film has a refractive index of -0.3 or more and 0.3 or less. Calculation method of plane orientation M: The plane orientation M is calculated from the equation M=(0.6887ε−0.4395) / (0.4962ε+0.2198) using ε expressed as ε=(α+β) / (γ+δ) based on the following absorbance peak intensities α, β, γ, and δ measured using polarized ATR-FTIR. (1) The incident light was fixed to S-polarized light, and the sample angle was rotated by 15 degrees. In the measured spectrum, －１ The arrangement of the sample in which the absorbance peak intensity is the largest is defined as the slow axis arrangement, and the absorbance peak intensity in the slow axis arrangement is defined as α, (2) 997 cm when the incident light is S-polarized and rotated 90 degrees from the slow axis arrangement －１ The absorbance peak intensity is defined as β. (3) When the incident light is P-polarized and the slow axis is arranged as described above, the wavelength is 997 cm －１ The absorbance peak intensity is γ, (4) 997 cm when the incident light is P-polarized and rotated 90 degrees from the slow axis arrangement －１ The absorbance peak intensity is defined as δ.

4. The melting point of the first resin composition is M １ (°C), and the melting point of the second resin composition is M ２ (℃), M ２ <M １ The film according to claim 3, which satisfies the relationship:

5. A laminate comprising the film according to claim 3 or 4.

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