Biaxially oriented polypropylene film, packaging material and packaging body

Abstract

The present invention provides a biaxially oriented polypropylene film that can suppress thermal shrinkage in the TD direction. [Solution] A biaxially oriented polypropylene film comprising a biaxially oriented film layer containing a propylene polymer, wherein the MFR of the biaxially oriented polypropylene film, measured in accordance with ASTM D1238 at 230°C and a 2.16 kg load, is 6.2 g / 10 min or more and 15.0 g / 10 min or less.

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polypropylene film, packaging material, and packaging body. [Background technology]

[0002] Biaxially oriented polypropylene film offers an excellent balance of properties such as processability, water vapor barrier properties, transparency, mechanical strength, and rigidity, and is used, for example, as packaging film for food packaging.

[0003] Patent Document 1 describes a matte polypropylene laminated stretched film in which a polypropylene resin mat layer (B) having a three-dimensional average surface roughness of 0.15 μm or more is laminated on at least one surface of a polypropylene resin layer (A), characterized in that the thermal shrinkage rate in the MD and TD directions at 150°C is 9% or less, the impact strength is 0.6 J or more, and the haze is 40% or more. Patent Document 1 states that the above polypropylene laminated stretched film can have a low shrinkage rate and high rigidity comparable to PET at 150°C, and thus can be made into a thin film. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-044406 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present invention provides a biaxially oriented polypropylene film that can suppress thermal shrinkage in the TD direction. [Means for solving the problem]

[0006] The inventors have discovered that, in a biaxially oriented polypropylene film comprising a biaxially oriented film layer containing a propylene polymer, thermal shrinkage in the TD direction can be suppressed by setting the MFR of the biaxially oriented polypropylene film within a predetermined range, thereby completing the present invention.

[0007] In other words, the present invention provides the following biaxially oriented polypropylene film, packaging material, and packaging body.

[0008] [1] A biaxially oriented polypropylene film comprising a biaxially oriented film layer containing a propylene polymer, A biaxially oriented polypropylene film having a MFR of 6.2 g / 10 min or more and 15.0 g / 10 min or less, as measured under conditions of 230°C and a 2.16 kg load in accordance with ASTM D1238. [2] The weight-average molecular weight Mw of the biaxially oriented polypropylene film, as measured by gel permeation chromatography (GPC), is 2.80 × 10⁻⁶. 5 The above 3.50 x 10 5 The following is a biaxially oriented polypropylene film as described in [1]. [3] The propylene polymer contained in the biaxially oriented film layer comprises homopolypropylene, as described in [1] or [2], for the biaxially oriented polypropylene film. [4] A biaxially oriented polypropylene film according to any one of [1] to [3], further comprising a surface layer provided on at least one surface of the biaxially oriented film layer. [5] The biaxially oriented polypropylene film according to [4], wherein the surface layer comprises a propylene polymer. [6] The biaxially oriented polypropylene film according to [5], wherein the propylene polymer contained in the surface layer comprises homopolypropylene. [7] The aforementioned surface layer is a first surface layer provided on one surface of the biaxially stretched film layer, a second surface layer provided on the other surface of the biaxially stretched film layer, the biaxially oriented polypropylene film according to any one of [4] to [6], comprising: [8] The number average molecular weight Mn of the biaxially oriented polypropylene film measured by gel permeation chromatography (GPC) is 2.90×10 4 or more and 1.00×10 5 or less, the biaxially oriented polypropylene film according to any one of [1] to [7]. [9] The ratio (Mw / Mn) of the weight average molecular weight Mw to the number average molecular weight Mn of the biaxially oriented polypropylene film, measured by gel permeation chromatography (GPC), is 1.00 or more and 12.0 or less, the biaxially oriented polypropylene film according to any one of [1] to [8].

[10] The propylene-based polymer contained in the biaxially stretched film layer comprises a propylene-based polymer derived from a recycled raw material, the biaxially oriented polypropylene film according to any one of [1] to [9].

[11] The content of the propylene-based polymer derived from the recycled raw material is 15 mass% or more and 100 mass% or less relative to 100 mass% of the biaxially stretched film layer, the biaxially oriented polypropylene film according to

[10] .

[12] The blocking force measured by the following method is 7.9 N or less, the biaxially oriented polypropylene film according to any one of [1] to

[11] . (Method) A corona treatment is performed on the surface of the biaxially oriented polypropylene film. A test piece of 120 mm (TD direction) × 20 mm (MD direction) is cut out from the biaxially oriented polypropylene film. The corona-treated surfaces of the two test pieces are stacked so that the MD direction / TD direction are aligned, a load of 1 kg / (20 mm × 20 mm) is applied thereon, and the assembly is stored at 55°C for 24 hours. Next, in accordance with JIS K 7127:1999, the tensile strength in the TD direction is measured using a tensile tester under the condition of a tensile speed of 5 mm / min. The above measurement is performed 3 times, the average value is calculated, and the obtained value is defined as the blocking force.

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

[12] , wherein the total haze of the biaxially oriented polypropylene film measured in accordance with JIS K 7136:2000 is 1.9% or more and 10.0% or less.

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

[13] , wherein the thermal shrinkage rate in the TD direction when the biaxially oriented polypropylene film is heat-treated at 120°C for 15 minutes is less than 5.5%.

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

[14] , wherein the crystallization enthalpy obtained by differential scanning calorimetry of the biaxially oriented polypropylene film is 89.0 J / g or more and 150.0 J / g or less.

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

[15] , wherein the crystallization temperature obtained by differential scanning calorimetry of the biaxially oriented polypropylene film is 111.0°C or higher and 150.0°C or lower.

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

[16] , which is used for a packaging film.

[18] A packaging material comprising the biaxially oriented polypropylene film according to any one of [1] to

[17] .

[19] The packaging material according to

[18] , and An article inside the packaging material, and A package containing a box. [Effects of the Invention]

[0009] According to the present invention, a biaxially oriented polypropylene film can be provided that can suppress thermal shrinkage in the TD direction. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing an example of the structure of the biaxially oriented polypropylene film of this embodiment. [Figure 2] This is a schematic cross-sectional view showing an example of the structure of the biaxially oriented polypropylene film of this embodiment. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below. In this specification, unless otherwise specified, "A to B" indicating a numerical range means A or greater and B or less. Also, the figures are schematic diagrams and do not correspond to the actual dimensional ratios.

[0012] (Biaxially oriented polypropylene film) The biaxially oriented polypropylene film of this embodiment comprises a biaxially oriented film layer containing a propylene polymer. In this embodiment, the MFR of the biaxially oriented polypropylene film, measured in accordance with ASTM D1238 under conditions of 230°C and a 2.16 kg load, is 6.2 g / 10 min or more and 15.0 g / 10 min or less.

[0013] The inventors have found that, for a biaxially oriented polypropylene film comprising a biaxially oriented film layer containing a propylene polymer, thermal shrinkage in the TD direction can be suppressed by setting the MFR of the biaxially oriented polypropylene film within the above range. Although the mechanism is not entirely clear, the inventors' investigations suggest that by setting the MFR of the biaxially oriented polypropylene film above the above lower limit, the residual stress of the biaxially oriented polypropylene film can be reduced, thereby suppressing thermal shrinkage in the TD direction.

[0014] Moreover, by setting the MFR of the biaxially oriented polypropylene film to the above lower limit value or more, the blocking resistance of the biaxially oriented polypropylene film can be improved.

[0015] The MFR of the biaxially oriented polypropylene film is 6.2 g / 10 min or more and 15.0 g / 10 min or less, preferably 6.3 g / 10 min or more and 14.0 g / 10 min or less, more preferably 6.4 g / 10 min or more and 13.0 g / 10 min or less, still more preferably 6.5 g / 10 min or more and 12.0 g / 10 min or less, and even more preferably 6.6 g / 10 min or more and 11.0 g / 10 min or less. By setting the MFR of the biaxially oriented polypropylene film to the above lower limit value or more, the thermal shrinkage in the TD direction of the biaxially oriented polypropylene film can be further suppressed. In addition, the blocking resistance of the biaxially oriented polypropylene film can be improved.

[0016] The weight average molecular weight Mw of the biaxially oriented polypropylene film measured by gel permeation chromatography (GPC) is preferably 2.80×10 5 or more and 3.50×10 5 or less, more preferably 2.81×10 5 or more and 3.49×10 5 or less, still more preferably 2.82×10 5 or more and 3.48×10 5 or less, even more preferably 2.83×10 5 or more and 3.47×10 5 or less, further preferably 2.84×10 5 or more and 3.46×10 5 or less. By setting the weight average molecular weight Mw to the above upper limit value or less, the thermal shrinkage in the TD direction of the biaxially oriented polypropylene film can be further suppressed. In addition, the blocking resistance of the biaxially oriented polypropylene film can be improved.

[0017] For example, by using a propylene polymer with a low weight-average molecular weight as the propylene polymer contained in the biaxially oriented film layer, or by using a propylene polymer derived from recycled raw materials, the MFR of the biaxially oriented polypropylene film can be increased and the weight-average molecular weight Mw can be decreased.

[0018] The number-average molecular weight (Mn) of biaxially oriented polypropylene film, as measured by gel permeation chromatography (GPC), is 2.90 × 10⁻⁶. 4 The above 1.00 × 10 5 The following is also acceptable: 2.92 × 10 4 The above 9.00 x 10 4 The following is also acceptable: 2.94 × 10 4 The above 8.00 x 10 4 The following is also acceptable: 2.96 × 10 4 The above 7.00 x 10 4 The following is also acceptable: 2.98 × 10 4 The above 6.00 x 10 4 The following may also be true: 3.00 × 10 4 The above 5.00 x 10 4 The following is also acceptable.

[0019] The ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn), measured by gel permeation chromatography (GPC) of a biaxially oriented polypropylene film, may be 1.00 or more and 12.0 or less, 2.00 or more and 11.8 or less, 3.00 or more and 11.6 or less, 4.00 or more and 11.4 or less, 5.00 or more and 11.2 or less, or 5.50 or more and 11.0 or less.

[0020] (Biaxially oriented film layer) The biaxially oriented film layer contains a propylene-based polymer.

[0021] From the viewpoint of improving the balance of thermal dimensional stability, heat resistance, water vapor barrier properties, oxygen barrier properties, mechanical properties, rigidity, bag-making properties, fluidity, and moldability of the biaxially oriented polypropylene film, the content of propylene polymer contained in the biaxially oriented film layer relative to 100% by mass of the biaxially oriented film layer is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, and even more preferably 98% by mass or more and 100% by mass or less.

[0022] From the viewpoint of improving the heat resistance of biaxially oriented polypropylene film, the propylene polymer contained in the biaxially oriented film layer preferably includes homopolypropylene.

[0023] Homopolypropylene includes, for example, at least one selected from the group consisting of propylene homopolymers and propylene copolymers having a content of 2.0 mol% or less of structural units derived from α-olefins other than propylene. The α-olefin other than propylene preferably includes at least one selected from the group consisting of ethylene and α-olefins having 4 to 20 carbon atoms, more preferably includes at least one selected from the group consisting of ethylene and α-olefins having 4 to 6 carbon atoms, even more preferably includes at least one selected from the group consisting of ethylene and 1-butene, and even more preferably includes ethylene.

[0024] The content of constituent units derived from propylene, relative to 100 mol% of the total content of constituent units constituting homopolypropylene, is 98.0 mol% or more, preferably 98.5 mol% or more, more preferably 98.7 mol% or more, even more preferably 99.0 mol% or more, even more preferably 99.5 mol% or more, even more preferably 99.8 mol% or more, and may also be 100.0 mol% or less.

[0025] The content of structural units derived from α-olefins other than propylene, relative to 100 mol% of the total content of structural units constituting homopolypropylene, is 2.0 mol% or less, preferably 1.5 mol% or less, more preferably 1.3 mol% or less, even more preferably 1.0 mol% or less, even more preferably 0.5 mol% or less, even more preferably 0.2 mol% or less, and may also be 0.0 mol% or more.

[0026] From the viewpoint of improving the balance of thermal dimensional stability, heat resistance, water vapor barrier properties, oxygen barrier properties, mechanical properties, rigidity, bag-making properties, fluidity, and moldability of biaxially oriented polypropylene films, the melting point of homopolypropylene is preferably 145°C to 180°C, more preferably 150°C to 175°C, and even more preferably 155°C to 170°C. When two or more types of homopolypropylene are used, the melting point of the homopolypropylene is the peak temperature of the maximum melting peak measured by differential scanning calorimetry.

[0027] The homopolypropylene content per 100% by mass of the biaxially oriented film layer is preferably 5% by mass or more and 100% by mass or less, more preferably 5% by mass or more and 90% by mass or less, even more preferably 10% by mass or more and 85% by mass or less, even more preferably 10% by mass or more and 80% by mass or less, even more preferably 15% by mass or more and 75% by mass or less, and even more preferably 15% by mass or more and 70% by mass or less. By setting the homopolypropylene content per 100% by mass of the biaxially oriented film layer to be above the above lower limit, the heat resistance of the biaxially oriented polypropylene film can be improved.

[0028] The propylene polymer contained in the biaxially oriented film layer preferably includes a propylene polymer derived from recycled raw materials. This reduces the amount of virgin raw materials used during the production of biaxially oriented polypropylene film, thereby reducing the environmental impact.

[0029] Propylene polymers derived from recycled raw materials can be obtained, for example, by recovering used polypropylene film and removing impurities such as ink as needed.

[0030] The content of propylene polymer derived from recycled raw materials per 100% by mass of the biaxially oriented film layer is preferably 15% by mass or more and 100% by mass or less, more preferably 20% by mass or more and 95% by mass or less, even more preferably 25% by mass or more and 90% by mass or less, and even more preferably 30% by mass or more and 85% by mass or less. By setting the content of propylene polymer derived from recycled raw materials per 100% by mass of the biaxially oriented film layer to be above the lower limit, the amount of virgin raw materials used during the manufacture of biaxially oriented polypropylene film can be reduced, thereby reducing the environmental burden. By setting the content of propylene polymer derived from recycled raw materials per 100% by mass of the biaxially oriented film layer to be below the upper limit, the balance of moldability and appearance of the biaxially oriented polypropylene film can be improved.

[0031] From the viewpoint of improving the balance of thermal dimensional stability, moldability, water vapor barrier properties, cost, mechanical properties, transparency, bag-making properties, handling properties, appearance, and lightweight properties of biaxially oriented polypropylene film, the thickness of the biaxially oriented film layer is preferably 5 μm to 100 μm, more preferably 10 μm to 50 μm, even more preferably 12 μm to 40 μm, and even more preferably 15 μm to 30 μm.

[0032] From the viewpoint of improving the balance of thermal dimensional stability, moldability, water vapor barrier properties, cost, mechanical properties, transparency, bag-making properties, handling properties, appearance, and lightweight properties of the biaxially oriented polypropylene film, the ratio of the thickness of the biaxially oriented film layer to the thickness of the biaxially oriented polypropylene film is preferably 50% to 100%, more preferably 60% to 99%, even more preferably 70% to 98%, and even more preferably 80% to 95%.

[0033] The biaxially oriented film layer may, as needed, contain various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, UV absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers, to the extent that they do not impair the purpose of this embodiment.

[0034] (Surface layer) Figure 1 is a schematic cross-sectional view showing an example of the structure of the biaxially oriented polypropylene film of this embodiment. As shown in Figure 1, the biaxially oriented polypropylene film 100 of this embodiment preferably further comprises a surface layer (first surface layer) 103 provided on at least one surface of the biaxially oriented film layer 101. This makes it possible to impart functions such as heat resistance, heat sealability, antistatic properties, blocking resistance, printability, and slip resistance to the biaxially oriented polypropylene film 100.

[0035] From the viewpoint of improving the functions of biaxially oriented polypropylene film, such as heat fusion resistance, heat sealability, antistatic properties, blocking resistance, printability, and slip resistance, the surface layer is preferably provided as the outermost layer of the biaxially oriented polypropylene film.

[0036] From the viewpoint of simplifying the manufacturing process of biaxially oriented polypropylene film, the surface layer is preferably provided so as to be in direct contact with the surface of the biaxially oriented film layer.

[0037] From the viewpoint of improving the functions of biaxially oriented polypropylene film, such as heat fusion resistance, heat sealability, antistatic properties, blocking resistance, printability, and slip resistance, the thickness of the surface layer is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.2 μm or more and 5.0 μm or less, and even more preferably 0.5 μm or more and 3.0 μm or less.

[0038] From the viewpoint of improving the functions of biaxially oriented polypropylene film, such as heat fusion resistance, heat sealability, antistatic properties, blocking resistance, printability, and slip resistance, the ratio of the thickness of the surface layer to the thickness of the biaxially oriented polypropylene film is preferably 1% to 20%, more preferably 2% to 15%, and even more preferably 3% to 10%.

[0039] From the viewpoint of improving the recyclability of biaxially oriented polypropylene film, the surface layer preferably contains a propylene-based polymer.

[0040] From the viewpoint of improving the balance of heat-sealing properties, thermal dimensional stability, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-making properties, fluidity, and moldability of biaxially oriented polypropylene film, the content of propylene polymer contained in the surface layer relative to 100% by mass of the surface layer is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, and even more preferably 98% by mass or more and 100% by mass or less.

[0041] From the viewpoint of improving the balance of heat-sealing properties, thermal dimensional stability, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-making properties, fluidity, and moldability of biaxially oriented polypropylene film, the propylene polymer contained in the surface layer preferably includes homopolypropylene.

[0042] Homopolypropylene includes, for example, at least one selected from the group consisting of propylene homopolymers and propylene copolymers having a content of 2.0 mol% or less of structural units derived from α-olefins other than propylene. The α-olefin other than propylene preferably includes at least one selected from the group consisting of ethylene and α-olefins having 4 to 20 carbon atoms, more preferably includes at least one selected from the group consisting of ethylene and α-olefins having 4 to 6 carbon atoms, even more preferably includes at least one selected from the group consisting of ethylene and 1-butene, and even more preferably includes ethylene.

[0043] The content of constituent units derived from propylene, relative to 100 mol% of the total content of constituent units constituting homopolypropylene, is 98.0 mol% or more, preferably 98.5 mol% or more, more preferably 98.7 mol% or more, even more preferably 99.0 mol% or more, even more preferably 99.5 mol% or more, even more preferably 99.8 mol% or more, and may also be 100.0 mol% or less.

[0044] The content of structural units derived from α-olefins other than propylene, relative to 100 mol% of the total content of structural units constituting homopolypropylene, is 2.0 mol% or less, preferably 1.5 mol% or less, more preferably 1.3 mol% or less, even more preferably 1.0 mol% or less, even more preferably 0.5 mol% or less, even more preferably 0.2 mol% or less, and may also be 0.0 mol% or more.

[0045] From the viewpoint of improving the balance of thermal dimensional stability, heat resistance, water vapor barrier properties, oxygen barrier properties, mechanical properties, rigidity, bag-making properties, fluidity, and moldability of biaxially oriented polypropylene films, the melting point of homopolypropylene is preferably 145°C to 180°C, more preferably 150°C to 175°C, and even more preferably 155°C to 170°C. When two or more types of homopolypropylene are used, the melting point of the homopolypropylene is the peak temperature of the maximum melting peak measured by differential scanning calorimetry.

[0046] From the viewpoint of improving the balance of heat-sealing properties, thermal dimensional stability, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-making properties, fluidity, and moldability of biaxially oriented polypropylene film, the homopolypropylene content per 100% by mass of the surface layer is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less.

[0047] Various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, UV absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the surface layer as needed, to the extent that they do not impair the purpose of this embodiment.

[0048] Surface activation treatments such as corona treatment, flame treatment, plasma treatment, primer coating, and ozone treatment may be performed on the surface of the surface layer.

[0049] Figure 2 is a schematic cross-sectional view showing an example of the structure of the biaxially oriented polypropylene film of this embodiment. As shown in Figure 2, the surface layer preferably includes a first surface layer 103 provided on one surface of the biaxially oriented film layer 101 and a second surface layer 105 provided on the other surface of the biaxially oriented film layer 101. This makes it possible to impart functions such as heat resistance, heat sealability, antistatic properties, blocking resistance, printability, and slip resistance to the biaxially oriented polypropylene film 100.

[0050] From the viewpoint of improving the balance of lamination strength, heat seal strength, and tear resistance of the biaxially oriented polypropylene film, it is preferable that the first surface layer be corona treated.

[0051] Furthermore, preferred embodiments of the first and second surface layers are the same as those described above for the surface layers.

[0052] (Other components of biaxially oriented polypropylene film) From the viewpoint of improving the balance of thermal dimensional stability, moldability, water vapor barrier properties, cost, mechanical properties, transparency, bag-making properties, handling properties, appearance, and lightweight properties of biaxially oriented polypropylene film, the thickness of the biaxially oriented polypropylene film is preferably 5 μm to 100 μm, more preferably 10 μm to 50 μm, even more preferably 12 μm to 40 μm, and even more preferably 15 μm to 30 μm.

[0053] From the viewpoint of improving the thermal dimensional stability of biaxially oriented polypropylene film, the crystallization temperature obtained by differential scanning calorimetry of biaxially oriented polypropylene film is preferably 111.0°C to 150.0°C, more preferably 111.2°C to 140.0°C, even more preferably 111.4°C to 135.0°C, even more preferably 111.6°C to 130.0°C, even more preferably 111.8°C to 125.0°C, and even more preferably 112.0°C to 120.0°C.

[0054] From the viewpoint of improving the thermal dimensional stability of biaxially oriented polypropylene films, the crystallization enthalpy obtained by differential scanning calorimetry of biaxially oriented polypropylene films is preferably 89.0 J / g or more and 150.0 J / g or less, more preferably 89.5 J / g or more and 130.0 J / g or less, even more preferably 90.0 J / g or more and 110.0 J / g or less, and even more preferably 90.5 J / g or more and 100.0 J / g or less.

[0055] The crystallization temperature and crystallization enthalpy obtained by differential scanning calorimetry of a biaxially oriented polypropylene film are obtained by the following method: Differential scanning calorimetry of a biaxially oriented polypropylene film is performed using a differential scanning calorimeter. The first differential scanning calorimetry (1st Run) consists of a heating process where the film is heated from -50°C to 250°C at a heating rate of 10°C / min under a nitrogen atmosphere, and a cooling process where the film is cooled from 250°C to -50°C at a cooling rate of 10°C / min. The second differential scanning calorimetry (2nd Run) consists of a heating process where the film is heated from -50°C to 250°C at a heating rate of 10°C / min. The peak temperature of the maximum exothermic peak in the DSC curve of the cooling process in the 1st Run is defined as the crystallization temperature. The crystallization enthalpy is calculated from the integral value of the exothermic peaks observed in the range of 90°C to 200°C in the DSC curve of the cooling process in the 1st Run.

[0056] The overall haze of a biaxially oriented polypropylene film, measured in accordance with JIS K 7136:2000, is preferably 1.9% to 10.0%, more preferably 2.0% to 8.0%, even more preferably 2.1% to 6.0%, and even more preferably 2.2% to 5.0%. By setting the overall haze of the biaxially oriented polypropylene film to be above the lower limit, the balance between the thermal dimensional stability and tear resistance of the biaxially oriented polypropylene film can be improved. By setting the overall haze of the biaxially oriented polypropylene film to be below the upper limit, the transparency of the biaxially oriented polypropylene film can be improved.

[0057] For example, the overall haze of a biaxially oriented polypropylene film can be adjusted by adjusting the constituent materials, thickness, and stretching ratio of the biaxially oriented film layer, as well as the constituent materials and thickness of the surface layer.

[0058] The blocking force measured by the following method is preferably 7.9 N or less, more preferably 7.7 N or less, even more preferably 7.5 N or less, and even more preferably 7.3 N or less. By keeping the blocking force below the above upper limit, the blocking resistance of the biaxially oriented polypropylene film can be further improved. The blocking force may also be between 1.0 N and 7.9 N, between 2.0 N and 7.7 N, between 3.0 N and 7.5 N, or between 4.0 N and 7.3 N.

[0059] (method) The surface of a biaxially oriented polypropylene film is subjected to corona treatment. A test specimen measuring 120 mm (TD direction) x 20 mm (MD direction) is cut from the biaxially oriented polypropylene film. The corona-treated surfaces of the two test specimens are placed on top of each other so that the MD direction and TD direction are aligned, and a load of 1 kg / (20 mm x 20 mm) is applied from above. The specimens are then stored at 55°C for 24 hours. Next, the tensile strength in the TD direction is measured using a tensile testing machine at a tensile speed of 5 mm / min, in accordance with JIS K 7127:1999. The above measurement is performed three times, and the average value is calculated to determine the blocking force.

[0060] The thermal shrinkage rate in the TD direction when a biaxially oriented polypropylene film is heat-treated at 120°C for 15 minutes is preferably less than 5.5%, more preferably 5.4% or less, and even more preferably 5.3% or less, and may be 0.1% or more, 0.3% or more, or 0.5% or more. The thermal shrinkage rate in the TD direction when a biaxially oriented polypropylene film is heat-treated at 120°C for 15 minutes is also 0.1% or more and less than 5.5%, may be 0.3% or more and 5.4%, or may be 0.5% or more and 5.3%. By setting the thermal shrinkage rate in the TD direction when a biaxially oriented polypropylene film is heat-treated at 120°C for 15 minutes to less than or equal to the above upper limit, the balance between the thermal dimensional stability and tear resistance of the biaxially oriented polypropylene film can be improved.

[0061] (Method for manufacturing biaxially oriented polypropylene film) A biaxially oriented polypropylene film can be obtained, for example, by extruding a propylene-based polymer composition for forming a biaxially oriented film layer, and then biaxially oriented the resulting film using known biaxially oriented film manufacturing methods such as simultaneous biaxial stretching, sequential biaxial stretching, and inflation biaxial stretching. If the biaxially oriented polypropylene film further comprises a surface layer, the biaxially oriented polypropylene film can be obtained, for example, by biaxially stretching a laminated film obtained by multilayer extrusion molding of a propylene-based polymer composition for forming a biaxially oriented film layer and a composition for forming a surface layer.

[0062] The conditions for extrusion molding are not particularly limited, and known conditions can be adopted. As for the molding machine, a T-die extruder, a multi-layer T-die extruder, an inflation molding machine, or a multi-layer inflation molding machine can be used. For the biaxial stretching conditions, for example, known manufacturing conditions for biaxially oriented polypropylene film can be adopted. Specifically, in the sequential biaxial stretching method, for example, the stretching temperature in the MD direction should be in the range of 100°C to 145°C, the stretching ratio in the MD direction should be in the range of 4.5 to 6 times, the stretching temperature in the TD direction should be in the range of 130°C to 190°C, and the stretching ratio in the TD direction should be in the range of 9 to 11 times.

[0063] (Applications of biaxially oriented polypropylene film) The biaxially oriented polypropylene film of this embodiment is preferably used as a packaging film.

[0064] (packaging material) The packaging material of this embodiment includes the biaxially oriented polypropylene film of this embodiment.

[0065] (packaging) The packaging of this embodiment includes the packaging material of this embodiment and the article contained within the packaging material.

[0066] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0067] The present invention will be described in detail below with reference to examples. However, the present invention is not limited in any way to the descriptions in these examples.

[0068] (1) Raw materials The raw materials used in the production of the biaxially oriented polypropylene film are listed below. PP1: Homopolypropylene, Prime Polymers "F113ZA", melting point 157℃ PP2: Homopolypropylene, Prime Polymers "F113A", melting point 159°C PP3: Prime Polymer's "MBR202A", melting point 141℃ PP4: Prime Polymer's "MBR203A" Recycled PP1: Pellets made by removing ink from printed biaxially oriented polypropylene film (RM Tohcello Co., Ltd. "U-1") (pellets containing polypropylene derived from recycled raw materials), melting point 161.4℃, crystallization temperature 114.2℃, crystallization enthalpy 107.1 J / g Recycled PP2: Pellets made by removing ink from printed polypropylene film (pellets containing polypropylene derived from recycled materials), melting point 161.4°C, crystallization temperature 117.4°C, crystallization enthalpy 106.2 J / g

[0069] The melting point, crystallization temperature, and crystallization enthalpy of each raw material were measured by differential scanning calorimetry (DSC). Using a differential scanning calorimeter (TA Instruments "Q200DSC"), two differential scanning calorimetry measurements were performed consecutively: the first (1st Run) consisted of a heating process where the temperature was raised from -50°C to 250°C at a heating rate of 10°C / min, and the second (2nd Run) consisted of a heating process where the temperature was raised from -50°C to 250°C at a heating rate of 10°C / min, under a nitrogen atmosphere. The peak temperature of the maximum exothermic peak in the DSC curve of the cooling process in the 1st Run was defined as the crystallization temperature. The crystallization enthalpy was calculated from the integral value of the exothermic peaks observed in the range between 90°C and 200°C in the DSC curve of the cooling process in the 1st Run. The peak temperature of the maximum endothermic peak in the 2nd Run DSC curve was defined as the melting point.

[0070] (2) Preparation of biaxially oriented polypropylene film (Example 1) A laminated film was obtained by multilayer extrusion molding in the following order: a first surface layer containing PP2: 98.5% by mass and PP3: 1.5% by mass, a film layer containing PP1: 60% by mass and recycled PP1: 40% by mass, and a second surface layer containing PP2: 96.5% by mass, PP3: 2.5% by mass and PP4: 1.0% by mass. The thickness of each layer was designed so that, after biaxial stretching, the film layer thickness was 18 μm, and the thicknesses of the first and second surface layers were 1 μm each. Next, the obtained laminated film was subjected to biaxial stretching, and then the surface of the first surface layer was corona-treated to produce a biaxially oriented polypropylene film.

[0071] The conditions for extrusion molding are as follows. Extrusion molding machine: 60mmφ multilayer T-die extrusion molding machine (screw: L / D=27, manufactured by Screw Seiki Co., Ltd.) Extrusion setting temperature: 230℃~250℃, Processing speed: 20m / min (winding speed)

[0072] The conditions for biaxial stretching are as follows. Preheating temperature in the MD direction (temperature at which the film roll is heated before stretching): 125℃ Stretching temperature in the MD direction (temperature during stretching): 123℃ MD direction heat-fixing temperature (temperature when heat-fixing (annealing) after stretching): 125℃ Preheating temperature in the TD direction (temperature for heating the film roll before stretching): 158℃ Stretching temperature in the TD direction (temperature during stretching): 168°C Heat-fixing temperature in the TD direction (temperature when heat-fixing (annealing) after stretching): 166°C

[0073] (Examples 2-5 and Comparative Example 1) A biaxially oriented polypropylene film was prepared in the same manner as in Example 1, except that the composition of the film layer was changed. The composition of the film layer in each example and comparative example is shown in Table 1.

[0074] (3) Evaluation of biaxially oriented polypropylene film (Measured thickness) The thickness of the biaxially oriented polypropylene film was measured at five points using a micrometer ("Automatic Micrometer" manufactured by Highbridge Manufacturing Co., Ltd.), and the average value was taken as the actual thickness.

[0075] (MFR) The Myofascial Freezing (MFR) of biaxially oriented polypropylene film was measured under conditions of 230°C and a 2.16 kg load, in accordance with ASTM D1238.

[0076] (Gel permeation chromatography (GPC)) Using a GPC instrument (Tosoh Corporation's "HLC-8321GPC / HT"), the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of biaxially oriented polypropylene film were measured by gel permeation chromatography (GPC), with monodisperse polystyrene as the molecular weight standard. The ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) was also calculated. The GPC conditions are shown below. Separation columns: Two TSKgel GNH6-HT (7.5 mm diameter, 300 mm length) and two TSKgel GNH6-HTL (7.5 mm diameter, 300 mm length) were used in series. Column temperature: 140℃ Eluent: o-dichlorobenzene and BHT 0.025% by mass as an antioxidant. Eluent flow rate: 1.0mL / min Detector: Differential refractive index detector Concentration of sample solution: 0.1 w / v% Sample injection volume: 400 μL

[0077] (Differential Scanning Calorimetry (DSC)) Differential scanning calorimetry (DSC) measurements were performed on a biaxially oriented polypropylene film using a differential scanning calorimetry meter (TA Instruments "Q200DSC"). The first differential scanning calorimetry measurement (1st Run) consisted of a heating process (heating from -50°C to 250°C at a heating rate of 10°C / min) and a cooling process (cooling from 250°C to -50°C at a cooling rate of 10°C / min) under a nitrogen atmosphere. The second differential scanning calorimetry measurement (2nd Run) consisted of a heating process (heating from -50°C to 250°C at a heating rate of 10°C / min). The peak temperature of the maximum exothermic peak in the DSC curve of the cooling process in the 1st Run was defined as the crystallization temperature. The crystallization enthalpy was calculated from the integral value of the exothermic peaks observed in the range between 90°C and 200°C in the DSC curve of the cooling process in the 1st Run.

[0078] (Hayes) In accordance with JIS K 7136:2000, the overall haze of biaxially oriented polypropylene film was measured using a haze meter (NDH8000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0079] (Blocking evaluation) A 120mm (TD direction) x 20mm (MD direction) test specimen was cut from a biaxially oriented polypropylene film. The corona-treated surfaces of the two specimens were placed together so that the MD direction and TD direction were aligned, and a load of 1kg / (20mm x 20mm) was applied from above. The specimens were then stored at 55°C for 24 hours. Next, in accordance with JIS K 7127:1999, the tensile strength in the TD direction was measured using a tensile testing machine (A&D Co., Ltd. "5-gang Tensilon RTF-1325") at a tensile speed of 5mm / min. The above measurement was performed three times, and the average value was calculated to determine the blocking force.

[0080] (Thermal contraction coefficient in the TD direction) In accordance with JIS C 2151:2019, the thermal shrinkage rate in the TD direction of a biaxially oriented polypropylene film was measured after heat treatment at 120°C for 15 minutes. A 10cm x 10cm test specimen was cut from the biaxially oriented polypropylene film. The test specimen was then heat-treated at 120°C for 15 minutes. During this time, the test specimen was suspended without any force in a hot air circulating constant temperature bath (ADVANTEC "DRM620DE"). After the test specimen was cooled to room temperature, its length was measured. The length of the test specimen in the TD direction after heat treatment was then measured. 120 Let the measurement be [cm], and the thermal shrinkage rate in the TD direction [%] be 100 × (TD 120 The value was calculated using the formula (-10) / 10. The above measurement was performed three times, and the average value was calculated.

[0081] Table 1 shows the evaluation results for each example and comparative example.

[0082] [Table 1] [Explanation of symbols]

[0083] 100 Biaxially oriented polypropylene film 101 Biaxially oriented film layer 103 Surface layer (first surface layer) 105 2nd surface layer

Claims

1. A biaxially oriented polypropylene film comprising a biaxially oriented film layer containing a propylene polymer, A biaxially oriented polypropylene film having an MFR of 6.2 g / 10 min or more and 15.0 g / 10 min or less, as measured in accordance with ASTM D1238 under conditions of 230°C and a 2.16 kg load.

2. The weight-average molecular weight Mw of the biaxially oriented polypropylene film, as measured by gel permeation chromatography (GPC), is 2.80 × 10⁻⁶. ５ The above 3.50 x 10 ５ The biaxially oriented polypropylene film according to claim 1, which is as follows:

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the propylene polymer contained in the biaxially oriented film layer includes homopolypropylene.

4. The biaxially oriented polypropylene film according to any one of claims 1 to 3, further comprising a surface layer provided on at least one surface of the biaxially oriented film layer.

5. The biaxially oriented polypropylene film according to claim 4, wherein the surface layer contains a propylene polymer.

6. The biaxially oriented polypropylene film according to claim 5, wherein the propylene polymer contained in the surface layer includes homopolypropylene.

7. The aforementioned surface layer is A first surface layer provided on one surface of the biaxially oriented film layer, A second surface layer provided on the other surface of the biaxially oriented film layer, A biaxially oriented polypropylene film according to any one of claims 4 to 6, comprising:

8. The number-average molecular weight Mn of the biaxially oriented polypropylene film, as measured by gel permeation chromatography (GPC), is 2.90 × 10⁻⁶. ４ The above 1.00 x 10 ５ The biaxially oriented polypropylene film according to any one of claims 1 to 7, which is as follows:

9. The biaxially oriented polypropylene film according to any one of claims 1 to 8, wherein the ratio of weight-average molecular weight Mw to number-average molecular weight Mn (Mw / Mn), as measured by gel permeation chromatography (GPC) of the biaxially oriented polypropylene film, is 1.00 or more and 12.0 or less.

10. The biaxially oriented polypropylene film according to any one of claims 1 to 9, wherein the propylene polymer contained in the biaxially oriented film layer includes a propylene polymer derived from recycled raw materials.

11. The biaxially oriented polypropylene film according to claim 10, wherein the content of the propylene polymer derived from the recycled raw material is 15% by mass or more and 100% by mass or less, relative to 100% by mass of the biaxially oriented film layer.

12. A biaxially oriented polypropylene film according to any one of claims 1 to 11, wherein the blocking force measured by the following method is 7.9 N or less. (method) Corona treatment is performed on the surface of the biaxially oriented polypropylene film. A test piece measuring 120 mm (TD direction) x 20 mm (MD direction) is cut from the biaxially oriented polypropylene film. The corona-treated surfaces of the two test pieces are placed on top of each other so that the MD direction and TD direction coincide, and a load of 1 kg / (20 mm x 20 mm) is applied from above, and the pieces are stored at 55°C for 24 hours. Next, the tensile strength in the TD direction is measured using a tensile testing machine in accordance with JIS K 7127:1999, under the condition of a tensile speed of 5 mm / min. The above measurement is performed three times, and the average value is calculated and used as the blocking force.

13. A biaxially oriented polypropylene film according to any one of claims 1 to 12, wherein the overall haze of the biaxially oriented polypropylene film, as measured in accordance with JIS K 7136:2000, is 1.9% or more and 10.0% or less.

14. The biaxially oriented polypropylene film according to any one of claims 1 to 13, wherein the thermal shrinkage rate in the TD direction when the biaxially oriented polypropylene film is heat-treated at 120°C for 15 minutes is less than 5.5%.

15. The biaxially oriented polypropylene film according to any one of claims 1 to 14, wherein the crystallization enthalpy obtained by differential scanning calorimetry of the biaxially oriented polypropylene film is 89.0 J / g or more and 150.0 J / g or less.

16. The biaxially oriented polypropylene film according to any one of claims 1 to 15, wherein the crystallization temperature obtained by differential scanning calorimetry of the biaxially oriented polypropylene film is 111.0°C or higher and 150.0°C or lower.

17. A biaxially oriented polypropylene film according to any one of claims 1 to 16, used for packaging films.

18. A packaging material comprising a biaxially oriented polypropylene film according to any one of claims 1 to 17.

19. The packaging material according to claim 18, The articles inside the aforementioned packaging material, A package containing a box.

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