Biaxially oriented polypropylene film

Abstract

[Problem] To provide: a biaxially oriented polypropylene film with high rigidity, which maintains the bag shape when easily made into a packaging bag even when the film is thinned, and maintains the same gas barrier properties as before when the film is thinned, and has few wrinkles in the sealing part and its periphery when heat-sealed for making packaging. [Solution] A biaxially oriented polypropylene film that satisfies the following (1) and (2). (1) In the azimuth dependence of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray diffraction, the half-width of the peak of the oriented crystal originating from the width direction is 26° or less. (2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) determined by pulsed NMR based on solid-state echo method is 7% or less.

Description

Technical Field

[0001] This invention relates to a biaxially oriented polypropylene film with excellent rigidity and heat resistance. More specifically, it relates to a biaxially oriented polypropylene film that easily maintains the shape of the bag when made into a packaging bag, and has few wrinkles at the seal during heat sealing, thus making it suitable for use in packaging bags. Background Technology

[0002] Biaxially oriented polypropylene (POP) films possess moisture-proof properties, along with the required rigidity and heat resistance, making them suitable for packaging and industrial applications. In recent years, environmental concerns have led to demands for maintaining strength even with reduced volume (film thickness), making significant improvements in rigidity essential. Techniques for improving rigidity include: improving the crystallinity and melting point of the polypropylene resin through catalysts and process modifications during polymerization; and increasing the stretch ratio in the film-forming process to enhance the film's orientation. However, there is a problem that increasing rigidity simultaneously reduces heat resistance; to date, no biaxially oriented PPO film possesses both sufficient rigidity and heat resistance. Furthermore, improving rigidity to reduce film volume reduces water vapor barrier properties and impairs moisture resistance, potentially leading to food spoilage.

[0003] In the manufacturing process of biaxially oriented polypropylene films, the following methods have been proposed: stretching along the width direction, relaxing the film below the temperature at which it was stretched in the width direction while performing a first-stage heat treatment, and then performing a second-stage heat treatment at the temperature from the first-stage temperature to the width-direction stretching temperature (e.g., Patent Document 1); and stretching along the width direction followed by stretching along the length direction (e.g., Patent Documents 2 and 3). However, while the film described in Patent Document 2 has excellent rigidity, it is prone to wrinkling in the sealing portion after heat sealing, resulting in poor heat resistance. Furthermore, the film described in Patent Document 1 has low orientation and insufficient rigidity. For the film described in Patent Document 3, sequential biaxial stretching and width-direction orientation are followed by further stretching along the length direction. Therefore, the molecular chain arrangement along the length direction is insufficient, resulting in low rigidity in the length direction. Additionally, relaxation along the width direction results in low orientation and insufficient rigidity in the width direction.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. WO2016 / 182003

[0007] Patent Document 2: Japanese Patent Application Publication No. 2013-177645

[0008] Patent Document 3: Japanese Patent Application Publication No. 2001-40111 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] The objective of this invention is to solve the aforementioned problems. Specifically, it relates to a biaxially oriented polypropylene film that balances film rigidity and heat resistance at temperatures up to 150°C. More specifically, it provides a biaxially oriented polypropylene film that exhibits high rigidity, easily maintains the bag shape when made into a packaging bag even when the film is thinned, maintains water vapor barrier properties even when the film is thinned, and has minimal wrinkles at the sealing portion and its periphery when heat-sealed for packaging.

[0011] Solution for solving the problem

[0012] In order to achieve the above objectives, the inventors conducted in-depth research and found that by satisfying (1) and (2) below, a biaxially oriented polypropylene film with excellent rigidity, heat resistance at high temperatures up to 150°C and excellent water vapor barrier properties can be obtained.

[0013] (1) In the azimuth dependence of the (110) plane of polypropylene α-type crystal obtained by wide-angle X-ray diffraction, the half-width of the peak originating from the orientation crystal in the width direction is less than 26°.

[0014] (2) The ratio of (III) when separated into crystalline component (I), constrained amorphous component (II), and unconstrained amorphous component (III) by pulse NMR based on solid-state echo method is less than 7%.

[0015] In this case, it is appropriate to satisfy (3), (4) and (5) below.

[0016] (3) The thermal shrinkage rate at 150℃ is less than 10% in the length direction and less than 30% in the width direction.

[0017] (4) The stress is above 140 MPa when the width is 5% elongated at 23℃.

[0018] (5) The thermal shrinkage rate (%) in the width direction at 150℃ and the stress (MPa) at 5% elongation in the width direction at 23℃ satisfy the following formula.

[0019] Stress (MPa) at 5% elongation in the width direction at 23℃ ≥ 150℃; thermal shrinkage rate in the width direction (%) × 4.0 + 140

[0020] In addition, in this case, it is suitable that the aforementioned biaxially oriented polypropylene film satisfies the following (6) and (7).

[0021] (6) The heat shrinkage rate at 120℃ is less than 2.0% in the length direction and less than 10.0% in the width direction.

[0022] (7) The thermal shrinkage rate (%) in the width direction at 120℃ and the tensile modulus (GPa) in the width direction at 23℃ satisfy the following formula.

[0023] Tensile modulus in the width direction at 23℃ ≥ 120℃; thermal shrinkage rate in the width direction (%) × 0.3 + 7.0

[0024] Furthermore, in this case, it is suitable that the refractive index Ny in the longitudinal direction of the aforementioned biaxially oriented polypropylene film is 1.5250 or more and ΔNy is 0.0240 or more.

[0025] Furthermore, in this case, it is suitable that the haze of the aforementioned biaxially oriented polypropylene film is below 5.0%.

[0026] Furthermore, in this case, it is suitable that the polypropylene resin constituting the aforementioned biaxially oriented polypropylene film has a meso-five-unit component ratio of 97.0% or more.

[0027] Furthermore, in this case, it is suitable that the polypropylene resin constituting the aforementioned biaxially oriented polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 161°C or higher.

[0028] Furthermore, in this case, it is suitable that the melt flow rate of the polypropylene resin constituting the aforementioned biaxially oriented polypropylene film is 4.0 g / 10 min or more.

[0029] Furthermore, in this case, it is suitable that the amount of polypropylene resin with a molecular weight of less than 100,000 constituting the aforementioned biaxially oriented polypropylene film is 35% by mass or more.

[0030] The effects of the invention

[0031] The biaxially oriented polypropylene film of the present invention is characterized by high rigidity, the ability to be thinned into a film, and the maintenance of water vapor barrier properties even when the film is thinned. Furthermore, it exhibits minimal wrinkles in the sealing area and its periphery during heat sealing for packaging. Therefore, it is suitable for use in packaging, industrial applications, and the like. Attached Figure Description

[0032] Figure 1 For the reason 1 A schematic diagram of component separation in the decay curves of spin-spin relaxation time observed by H-pulse NMR.

[0033] Figure 2 A graph comparing the embodiment and the comparative example is provided for the thermal shrinkage rates at F5 and 150°C in the width direction. Detailed Implementation

[0034] The biaxially oriented polypropylene film of the present invention will now be described in detail.

[0035] The biaxially oriented polypropylene film of the present invention is formed from a polypropylene resin composition with polypropylene resin as the main component. It should be noted that "main component" means that the proportion of polypropylene resin in the polypropylene resin composition is 90% by mass or more, more preferably 93% by mass or more, further preferably 95% by mass or more, and particularly preferably 97% by mass or more.

[0036] (Polypropylene resin)

[0037] The polypropylene resin used in this invention can be a polypropylene homopolymer or a copolymer with ethylene and / or an α-olefin having 4 or more carbon atoms. Preferably, it is a propylene homopolymer substantially free of ethylene and / or an α-olefin having 4 or more carbon atoms. If it does contain ethylene and / or an α-olefin having 4 or more carbon atoms, the amount of ethylene and / or the α-olefin having 4 or more carbon atoms is preferably 1 mol% or less, more preferably 0.5 mol% or less, even more preferably 0.3 mol% or less, and particularly preferably 0.1 mol% or less. If it falls within the above range, crystallinity is easily improved. Examples of α-olefins having 4 or more carbon atoms constituting such copolymers include, for example, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene.

[0038] Polypropylene resins can be made from two or more different polypropylene homopolymers, copolymers with ethylene and / or α-olefins having more than four carbon atoms, and mixtures thereof.

[0039] (Structural regularity)

[0040] The percentage of meso-five-unit components (hereinafter sometimes abbreviated as [mmmm]%), which serves as an indicator of the stereoregularity of the polypropylene resin used in this invention, is preferably in the range of 97.0 to 99.9%, more preferably in the range of 97.5 to 99.7%, further preferably in the range of 98.0 to 99.5%, and particularly preferably in the range of 98.5 to 99.3%.

[0041] If the content is 97.0% or higher, the crystallinity of the polypropylene resin is improved, and the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, making it easier to obtain rigidity and heat resistance at high temperatures. If the content is 99.9% or lower, it is easier to control costs in the manufacture of polypropylene, and the film becomes less prone to breakage during film formation. The proportion of the racemic five-unit component is determined by nuclear magnetic resonance (NMR). More preferably, it is 99.5% or lower. The proportion of the racemic five-unit component is determined by nuclear magnetic resonance (NMR).

[0042] To ensure that the meso-pentacomponent composition of the polypropylene resin is within the above-mentioned range, the following methods are preferred: a method for washing the obtained polypropylene resin powder with a solvent such as n-heptane, a method for selecting a suitable catalyst and / or co-catalyst, and a method for selecting the components of the polypropylene resin composition.

[0043] (Meltdown temperature)

[0044] The lower limit of the melting temperature (Tm) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention, as measured by DSC, is preferably 160°C, more preferably 161°C, further preferably 162°C, even more preferably 163°C, and even more preferably 164°C. If Tm is 160°C or higher, rigidity and heat resistance at high temperatures are easily obtained. The upper limit of Tm is preferably 170°C, more preferably 169°C, further preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. If Tm is below 170°C, it is easier to suppress cost increases in the manufacture of polypropylene or to make the film less prone to breakage during film formation. By compounding a crystallizing nucleating agent into the aforementioned polypropylene resin, the melting temperature can also be further increased.

[0045] Tm refers to the main peak temperature of the endothermic peak accompanying melting observed when 1–10 mg of sample is filled into an aluminum disk and installed in a differential scanning calorimeter (DSC), melted at 230 °C for 5 minutes under a nitrogen atmosphere, cooled to 30 °C at a scan rate of -10 °C / min, held for 5 minutes, and then heated up at a scan rate of 10 °C / min.

[0046] (Crystallization temperature)

[0047] The lower limit of the crystallization temperature (Tc) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention, as measured by DSC, is 105°C, preferably 108°C, and more preferably 110°C. If Tc is 105°C or higher, crystallization is easily advanced during the stretching in the width direction and the subsequent cooling process, making it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tc is preferably 135°C, more preferably 133°C, further preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. If Tc is below 135°C, the cost of manufacturing polypropylene is not easily increased, or the film becomes less prone to breakage during film formation. By compounding a crystallizing nucleating agent into the aforementioned polypropylene resin, the crystallization temperature can also be further increased.

[0048] Tc refers to the main peak temperature of the exothermic peak observed when 1–10 mg of sample is filled into an aluminum disk and mounted on a DSC, melted at 230 °C for 5 minutes under a nitrogen atmosphere, and then cooled to 30 °C at a scan rate of -10 °C / min.

[0049] (Mel flow rate)

[0050] When the melt flow rate (MFR) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is measured according to the conditions M (230°C, 2.16 kgf) of JIS K 7210 (1995), it is preferably 4.0 to 30 g / 10 min, more preferably 4.5 to 25 g / 10 min, even more preferably 4.8 to 22 g / 10 min, particularly preferably 5.0 to 20 g / 10 min, and most preferably 6.0 to 20 g / 10 min.

[0051] If the melt flow rate (MFR) of polypropylene resin is above 4.0 g / 10 min, it is easy to obtain biaxially oriented polypropylene films with low heat shrinkage.

[0052] In addition, if the melt flow rate (MFR) of polypropylene resin is below 30 g / 10 min, it is easy to maintain the film-forming properties.

[0053] From the viewpoint of membrane properties, the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the polypropylene resin constituting the membrane is preferably 5.0 g / 10 min, more preferably 5.5 g / 10 min, further preferably 6.0 g / 10 min, particularly preferably 6.3 g / 10 min, and most preferably 6.5 g / 10 min.

[0054] If the melt flow rate (MFR) of polypropylene resin is 5.0 g / 10 min or higher, the amount of low molecular weight components of the polypropylene resin constituting the film increases. Therefore, by using the width stretching process in the film-making process described later, the orientation crystallization of polypropylene resin can be further promoted, and the crystallinity in the film becomes easier to improve. Moreover, the entanglement of polypropylene molecular chains in the amorphous part becomes less, which makes it easier to further improve the heat resistance.

[0055] In order to make the melt flow rate (MFR) of polypropylene resin within the above-mentioned range, it is preferable to use methods such as controlling the average molecular weight and molecular weight distribution of polypropylene resin.

[0056] That is, the lower limit of the amount of the component with a molecular weight of less than 100,000 in the GPC cumulative curve of the polypropylene resin constituting the membrane of the present invention is preferably 35% by mass, more preferably 38% by mass, further preferably 40% by mass, even more preferably 41% by mass, and particularly preferably 42% by mass.

[0057] The upper limit of the amount of components with a molecular weight of less than 100,000 in the GPC cumulative curve is preferably 65% ​​by mass, more preferably 60% by mass, and even more preferably 58% by mass. If the amount of components with a molecular weight of less than 100,000 in the GPC cumulative curve is less than 65% by mass, the film strength is less likely to decrease.

[0058] At this point, if it contains high molecular weight components with long relaxation times or long-chain branched components, it becomes easier to adjust the amount of components with a molecular weight of less than 100,000 in the polypropylene resin without significantly changing the overall viscosity. Therefore, it has little impact on rigidity and heat shrinkage, and it is easy to improve film-forming properties.

[0059] (Molecular weight distribution)

[0060] The lower limit of the mass-average molecular weight (Mw) / number-average molecular weight (Mn) ratio of the polypropylene resin used in this invention, which serves as an indicator of the molecular weight distribution width, is preferably 3.5, more preferably 4, further preferably 4.5, and particularly preferably 5. The upper limit of Mw / Mn is preferably 30, more preferably 25, further preferably 23, particularly preferably 21, and most preferably 20.

[0061] Mw / Mn can be obtained using gel permeation chromatography (GPC). If the Mw / Mn is within the above range, it is easy to increase the amount of components with a molecular weight below 100,000.

[0062] It should be noted that the molecular weight distribution of polypropylene resin can be adjusted by polymerizing components of different molecular weights in multiple stages within a series of devices, blending components of different molecular weights offline in a mixer, blending and polymerizing catalysts with different properties, or using catalysts that can achieve the desired molecular weight distribution. As for the shape of the molecular weight distribution obtained in GPC, a GPC graph with the horizontal axis representing the logarithm of molecular weight (M) (logM) and the vertical axis representing the differential distribution value (weight fraction per unit logM) can show a smooth molecular weight distribution with a single peak, or a molecular weight distribution with multiple peaks and shoulders.

[0063] (Method for preparing biaxially oriented polypropylene films)

[0064] The biaxially oriented polypropylene film of the present invention is preferably obtained as follows: an unstretched sheet is formed from a polypropylene resin composition with the aforementioned polypropylene resin as the main component, and then biaxially stretched. As a method of biaxial stretching, it can be obtained by any of the following methods: simultaneous biaxial stretching via blow-up, simultaneous biaxial stretching via a tenter frame, or sequential biaxial stretching via a tenter frame. From the viewpoint of film stability and thickness uniformity, sequential biaxial stretching via a tenter frame is preferred. Stretching along the length direction followed by stretching along the width direction is particularly preferred; however, stretching along the width direction followed by stretching along the length direction is also acceptable.

[0065] Next, the method for manufacturing the biaxially oriented polypropylene film of the present invention will be described, but it is not necessarily limited thereto. It should be noted that the biaxially oriented polypropylene film of the present invention may have layers with other functions laminated on at least one side. The laminated side may be one side or both sides. In this case, the resin composition of the other layer and the central layer may be the polypropylene resin composition described above. Alternatively, it may be different from the polypropylene resin composition described above.

[0066] The number of layers in a single-sided film can be one, two, or three or more; from a manufacturing point of view, one or two layers are preferred. As for the lamination method, co-extrusion based on a feed head or a multi-manifold method is preferred, for example. In particular, to improve the processability of the biaxially oriented polypropylene film, a heat-sealable resin layer can be laminated without reducing its properties. Furthermore, to impart printability, corona treatment can be applied to one or both sides.

[0067] The following examples illustrate the use of a tenter frame for sequential biaxial stretching in the case of a single-layer structure.

[0068] First, the resin composition containing polypropylene resin is heated and melted in a single-screw or twin-screw extruder, and extruded in sheet form from a T-die, then contacted and cooled on cooling rollers to solidify. For the purpose of promoting curing, it is preferable to immerse the cooled sheet in a water tank or similar solution for further cooling.

[0069] Next, for the sheet, on the two pairs of heated stretching rollers, the rotation speed of the rear stretching roller is increased, thereby stretching the sheet along the length direction to obtain a uniaxial stretched film.

[0070] Next, after preheating the uniaxially stretched film, the film ends are fixed in a tenter frame while it is stretched along the width direction at a specific temperature to obtain a biaxially stretched film. This width-direction stretching process will be described in detail later.

[0071] After the width-direction stretching process is completed, the biaxially stretched film is heat-treated at a specific temperature to obtain a biaxially oriented film. During the heat treatment process, the film can also be relaxed along the width direction.

[0072] The biaxially oriented polypropylene film thus obtained can be wound into rolls by, for example, subjecting at least one side to corona discharge treatment as needed, and then wound up using a winding machine.

[0073] The following is a detailed explanation of each process.

[0074] (Extrusion process)

[0075] First, a polypropylene resin composition, with polypropylene resin as the main component, is heated and melted in a single-screw or twin-screw extruder within a temperature range of 200°C to 300°C. The sheet-like molten polypropylene resin composition exiting from the T-die is extruded, contacted with a metal cooling roller, and cooled and solidified. The resulting unstretched sheet is then preferably placed in a water tank.

[0076] The temperature of the cooling roller, or the cooling roller and the water bath, is preferably in the range of 10°C to Tc. If it is desirable to improve the transparency of the film, it is preferable to perform cooling and curing on a cooling roller with a temperature in the range of 10°C to 50°C. If the cooling temperature is below 50°C, the transparency of the unstretched sheet is easily improved, preferably below 40°C, and more preferably below 30°C. In order to increase the crystal orientation after sequential biaxial stretching, it is sometimes preferable to use a cooling temperature of 40°C or higher. However, as mentioned above, when using a propylene homopolymer with a meso-five-unit component ratio of 97.0% or higher, it is preferable to use a cooling temperature of 40°C or lower to facilitate subsequent stretching processes and to reduce thickness unevenness. It is even more preferable to use a temperature of 30°C or lower.

[0077] When the thickness of the unstretched sheet is set to 3500 μm or less, cooling efficiency is preferred; more preferably, it is set to 3000 μm or less, and can be appropriately adjusted according to the film thickness after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by factors such as the extrusion speed of the polypropylene resin composition and the die lip amplitude of the T-die.

[0078] (Length stretching process)

[0079] The lower limit of the stretch ratio in the length direction is preferably 3.5 times, more preferably 3.8 times, and particularly preferably 4.2 times. If it is within the above range, the strength is easily improved and the film thickness unevenness is reduced.

[0080] The upper limit of the length stretching ratio is preferably 7.0 times, more preferably 6.0 times, and particularly preferably 7 times. If it is within the above range, the width stretching in the width stretching process is easier to perform, and productivity is improved.

[0081] The lower limit of the length-direction stretching temperature is preferably Tm-30℃, more preferably Tm-27℃, and even more preferably Tm-25℃. Within this range, subsequent width-direction stretching becomes easier, and thickness unevenness is reduced. The upper limit of the length-direction stretching temperature is preferably Tm-7℃, more preferably Tm-10℃, and even more preferably Tm-12℃. Within this range, heat shrinkage is easily reduced, and there are fewer instances of stretching becoming difficult due to adhesion to the stretching rollers, or quality degradation due to increased surface roughness.

[0082] It should be noted that for length stretching, more than three pairs of stretching rollers can be used, and stretching can be performed in multiple stages, in two or more stages.

[0083] (Preheating process)

[0084] Before the width-direction stretching process, the uniaxially stretched film in the length direction must be heated within the range of Tm to Tm+25°C to soften the polypropylene resin composition. By setting it above Tm, the softening process is facilitated, making width-direction stretching easier. By setting it below Tm+25°C, the orientation process during transverse stretching is facilitated, making it easier to exhibit rigidity. More preferably, Tm+2 to Tm+20°C, and particularly preferably, Tm+3 to Tm+15°C. Here, the highest temperature in the preheating process is used as the preheating temperature.

[0085] (Width-direction stretching process)

[0086] In the width-direction stretching process following the preheating process, the preferred method is as follows.

[0087] In the width-direction stretching process, stretching is preferably performed at a temperature above Tm-10°C and below the preheating temperature. In this case, the start of width-direction stretching can be at the moment when the preheating temperature is reached, or at the moment when the temperature drops after reaching the preheating temperature and reaches a temperature below the preheating temperature.

[0088] The lower limit of the temperature in the width-direction stretching process is more preferably Tm-9℃, further preferably Tm-7℃, and particularly preferably Tm-5℃. If the width-direction stretching temperature is within this range, the rigidity of the resulting biaxially oriented film can be easily improved.

[0089] The upper limit of the temperature in the width-direction stretching process is preferably Tm+10℃, more preferably Tm+7℃, and particularly preferably Tm+5℃. If the width-direction stretching temperature is within this range, uneven stretching is less likely to occur.

[0090] In the width stretching process, following the width stretching within the aforementioned temperature range, a later stretching process can also be performed at a lower temperature.

[0091] That is, the stretching interval (early stage) can be set at a temperature above Tm-10℃ and below Tm+10℃, or it can be set at a temperature below the early stage, above Tm-70℃ and below Tm-5℃ (late stage). By setting early and late stages, it is easier to improve rigidity.

[0092] The lower limit of the stretching temperature in the later stage is preferably Tm-65℃, more preferably Tm-60℃, and even more preferably Tm-55℃. If the stretching temperature in the later stage is within this range, the film formation is easily stabilized.

[0093] The lower limit of the final width-direction stretching ratio in the width-direction stretching process is preferably 10 times or more, more preferably 11 times or more, and even more preferably 11.5 times or more. If it is 10 times or more, it is easy to improve the rigidity of the film, reduce thickness unevenness, and lower water vapor permeability. The upper limit of the width-direction stretching ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. If it is less than 20 times, it is easy to reduce the heat shrinkage rate and prevent breakage during stretching.

[0094] When the later stretching interval is applied, the total stretching ratio is made to fall within the aforementioned range. In this case, the lower limit of the stretching ratio in the earlier stretching process is preferably 4 times, more preferably 5 times, further preferably 6 times, and particularly preferably 6.5 times. The upper limit of the stretching ratio at the end of the earlier stretching interval is preferably 15 times, more preferably 14 times, and further preferably 13 times.

[0095] Preferably, the film is cooled at the end of the width-direction stretching, i.e., immediately after reaching the final width-direction stretching ratio. The cooling temperature at this time is preferably below the width-direction stretching temperature and above Tm-80°C and below Tm-15°C, more preferably above Tm-80°C and below Tm-20°C, even more preferably above Tm-80°C and below Tm-30°C, and particularly preferably above Tm-70°C and below Tm-40°C. By applying the cooling process, crystallization is induced, and the crystal orientation is fixed. Subsequently, heating to a temperature above melting point can maintain the orientation process, resulting in increased crystal orientation in the film.

[0096] Alternatively, the temperature can be slowly reduced from the end of the stretching process in the width direction to the cooling temperature, or it can be reduced in stages or in one step. If the temperature is reduced in stages or in one step, it is easier to further increase the crystal orientation in the film, so this is preferred.

[0097] Preferably, the membrane is cooled and then stretched again along its width at a high temperature (hereinafter also referred to as width-direction re-stretching). Re-stretching the membrane along its width at a high temperature after cooling easily improves the membrane's crystal orientation, thus easily increasing rigidity and reducing water vapor permeability. The lower limit of the stretching temperature for re-stretching along the width direction is Tm-5℃, preferably Tm℃, more preferably Tm+5℃, further preferably Tm+7℃, and particularly preferably Tm+9℃. If the temperature is above Tm-5℃, rigidity is easily improved, and the thermal shrinkage rate is easily reduced.

[0098] The upper limit of the re-stretching temperature in the width direction is preferably Tm+20℃, more preferably Tm+18℃, and even more preferably Tm+16℃. If it is below Tm+20℃, the rigidity is easily improved.

[0099] The lower limit of the width-direction stretching ratio under high temperature is preferably 1.05 times, more preferably 1.1 times, and even more preferably 1.15 times.

[0100] The upper limit of the width-direction re-stretch ratio at high temperature is preferably 2 times, more preferably 1.7 times, and even more preferably 1.5 times. If the re-stretch ratio is too large, the heat shrinkage rate will be excessively large, or uneven thickness will occur, or the film may sometimes break.

[0101] In other words, it was found that by stretching the material again along the width direction at high temperature, instead of immediately relaxing it at high temperature after stretching along the width direction as before, the thermal shrinkage rate can be reduced, and the rigidity can be further improved.

[0102] That is, in the process of stretching along the width direction again at high temperature, it is preferable to stretch at Tm-5℃ or higher. At Tm-5℃ or higher, the mobility of molecular chains is sufficiently increased, and through stretching, it becomes easier to eliminate the influence of molecular chain entanglement. As a result, the molecular chains are not easily constrained, and therefore, they are less likely to become disordered molecular orientations, and crystallization is also fully carried out.

[0103] After stretching the film along its width at high temperature, the film is cooled to below the temperature at which it can crystallize, thereby obtaining a high-melting-point film with fixed crystal orientation, high crystallinity, and thick plate-like crystals.

[0104] Furthermore, outside the plate-like crystals, the molecular chains with larger strain due to the molecular orientation constrained by the entanglement points are smaller, and even if melting of the crystal begins, the film is less likely to shrink. Consequently, crystallinity improves, and if the plate-like crystals are thick, the melting point tends to be higher, making melting less likely to occur below the melting point. This easily reduces the thermal shrinkage rate.

[0105] As a result, rigidity can be further improved and the thermal shrinkage rate can be reduced.

[0106] In typical film-forming processes (extrusion-longitudinal stretching-width stretching-heat treatment), to eliminate the strain caused by width stretching at temperatures below the melting point, a few percent to tens of percent relaxation is applied during the heat treatment process while exposing the film to high temperatures above the melting point, thereby reducing the thermal shrinkage rate. Relaxation eliminates the constraint of molecular chains, hindering crystallization and contributing to a lower thermal shrinkage rate. However, conversely, the orientation of the molecular chains generated during transverse stretching decreases in the width direction, resulting in reduced rigidity. Therefore, it is difficult to simultaneously achieve low thermal shrinkage and high rigidity. Furthermore, if the temperature is set to extremely high levels, film whitening may occur.

[0107] In conventional film-forming processes (extrusion-longitudinal stretching-width stretching-heat treatment), increasing the temperature of the width stretching step increases the mobility of the molecular chains. During stretching without residual strain, the melting of crystals generated by longitudinal stretching is accelerated, leading to a decrease in crystal orientation. In the method of this invention, width stretching is performed in a single step, ensuring sufficient orientation along the width direction. Cooling then fixes the crystal orientation. Therefore, even after melting, the film possesses sufficient tension. Re-stretching at a high temperature above Tm-5°C maintains sufficient tension, reducing concerns about uneven thickness or film breakage.

[0108] The stretching ratio at high temperatures only needs to be sufficient to loosen the entanglement and alignment of molecular chains, which can be 1.05 times or more. If the stretching ratio is set to less than 2 times, uneven thickness is less likely to occur.

[0109] Thus, by using polypropylene resin with high stereoregularity, high melting point, and high crystallinity, and employing the aforementioned longitudinal stretching process, width stretching process, cooling process, and high-temperature stretching process, the molecules of the polypropylene resin are significantly and highly aligned along the main orientation direction (equivalent to the width direction in the aforementioned width stretching process). Therefore, it becomes easier to generate more crystals with strong crystal orientation and high melting point in the resulting biaxially oriented film.

[0110] Furthermore, by increasing the low molecular weight component of the polypropylene resin, the molecular chain entanglement is reduced, making it easier to further improve the crystallinity of the film and reduce the amount of material outside the lamellar crystals. Additionally, by reducing the thermal shrinkage stress in the areas outside the lamellar crystals, the thermal shrinkage rate can be further reduced.

[0111] In existing technologies, it is difficult to simultaneously enhance crystal orientation and reduce unconstrained amorphous components in the crystal. That is, there is a tendency that if either rigidity or thermal shrinkage can be improved, the other property will be reduced. Considering these factors, the present invention can be said to have a revolutionary effect.

[0112] (Heat treatment process)

[0113] For biaxially stretched films, heat treatment can be performed as needed to further reduce the thermal shrinkage rate. The upper limit of the heat treatment temperature is preferably the aforementioned high-temperature re-stretching temperature, more preferably the high-temperature re-stretching temperature -2°C, and even more preferably the high-temperature re-stretching temperature -3°C. By setting the temperature below the high-temperature re-stretching temperature, the rigidity is less likely to decrease, the surface roughness of the film does not increase excessively, and the film is less prone to whitening. The lower limit of the heat treatment temperature is preferably Tm-3°C, more preferably Tm-2°C, and particularly preferably Tm.

[0114] To adjust the heat shrinkage rate, the film can be relaxed along the width direction during heat treatment. The upper limit of the relaxation rate is preferably 5%, more preferably 3%, and even more preferably 1%. If it is within the above range, the rigidity is less likely to decrease, and the film thickness variation is more likely to be smaller. To further improve the rigidity, heat treatment may not be necessary.

[0115] (Cooling process)

[0116] After stretching in the width direction, and immediately after stretching again in the width direction at a temperature above Tm-5°C, or immediately after a heat treatment process, the film is cooled. The cooling temperature is preferably set to 10°C or higher and 140°C or lower, more preferably 20°C or higher and 120°C or lower, even more preferably 80°C or lower, and particularly preferably 50°C or lower. By incorporating this cooling process, the state of the film can be stabilized.

[0117] (film thickness)

[0118] The thickness of the biaxially oriented polypropylene film of the present invention can be set according to various applications. To obtain film strength, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, further preferably 4 μm, particularly preferably 8 μm, and most preferably 10 μm. If the film thickness is 2 μm or more, it is easy to obtain film rigidity. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, further preferably 60 μm, particularly preferably 50 μm, and most preferably 40 μm. If the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion process is less likely to decrease.

[0119] The biaxially oriented polypropylene film of the present invention is typically rolled into rolls with a width of approximately 2000–12000 mm and a length of approximately 1000–50000 m. Furthermore, it can be slit according to various applications, and supplied in rolls with a width of approximately 300–2000 mm and a length of approximately 500–5000 m. The biaxially oriented polypropylene film of the present invention can yield film rolls of even longer dimensions.

[0120] (Thickness uniformity)

[0121] The lower limit of the thickness uniformity of the biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, further preferably 0.5%, and particularly preferably 1%. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, further preferably 15%, particularly preferably 12%, and most preferably 10%. If it is within the above range, defects are less likely to occur during post-processing such as coating and printing, and it is easy to use for applications requiring precision.

[0122] The measurement method is as follows. A 40 mm wide test piece is cut from a constant region where the membrane properties are stable along the length of the membrane. The membrane thickness is continuously measured over a range of 20,000 mm using a membrane transport device (model: A90172) manufactured by Micron Measuring Instruments Co., Ltd. and a continuous membrane thickness measuring instrument (product name: K-313A wide-range high-sensitivity electronic micrometer) manufactured by Anritsu Co., Ltd. The thickness uniformity is calculated using the following formula.

[0123] Thickness uniformity (%) = [(maximum thickness - minimum thickness) / average thickness] × 100

[0124] (membrane properties)

[0125] The biaxially oriented polypropylene membrane of the present invention is characterized by the following properties. Here, the "length direction" in the biaxially oriented polypropylene membrane of the present invention refers to the direction corresponding to the flow direction in the membrane manufacturing process, and the "width direction" refers to the direction orthogonal to the flow direction in the aforementioned membrane manufacturing process. For polypropylene membranes where the flow direction is unclear in the membrane manufacturing process, wide-angle X-rays are incident in a direction perpendicular to the membrane surface, and the scattering peaks originating from the (110) plane of the α-type crystal are scanned in a circumferential direction. The direction with the highest diffraction intensity of the obtained diffraction intensity distribution is taken as the "length direction", and the direction orthogonal to it is taken as the "width direction".

[0126] (Crystal composition determined by pulsed NMR (I), constrained amorphous composition (II), unconstrained amorphous composition (III))

[0127] It is known that, with 1 The decay time constant of the spin-spin relaxation time T2 observed by H-pulse NMR is observed as the sum of two or more decay time constants. For example, according to Polymer Journal, Vol.3, No.4, pp448-462 (1972), in the solid-state echo method of pulse NMR, the decay time constant of the relaxation time of crystalline polymers is resolved by the sum of three components: crystalline composition, mesophase composition, and amorphous composition.

[0128] by 1The spin-spin relaxation time T2 observed by H-pulse NMR decreases in the order of crystalline, mesophase, and amorphous phases. The T2 of the mesophase is faster than that of the amorphous phase, and it is considered to be an amorphous phase with constrained motion. When stretching is performed while loosening the entanglement of molecular chains, a strongly oriented crystalline component (I) is generated, and an amorphous chain component (II) with constrained motion (equivalent to the aforementioned mesophase) is generated near the crystal. On the other hand, when the entanglement is large and the orientation is disordered during stretching, an unconstrained amorphous component (III) (equivalent to the aforementioned amorphous phase) is more likely to be generated in the crystal. The unconstrained amorphous component (III) has high motion and is prone to move in a way that eliminates strain at high temperatures, which is the cause of shrinkage at high temperatures. On the other hand, the constrained amorphous chain (II) is considered to be less prone to shrinkage at high temperatures because its motion is also suppressed at high temperatures.

[0129] The upper limit of the unconstrained amorphous component (III) of the biaxially oriented polypropylene film of the present invention, as determined by pulsed NMR, is 7%, preferably 6%, and more preferably 5%.

[0130] If the amorphous component (III) is 7% or less, wrinkles are less likely to occur during heat sealing, and the strain is smaller when welding the chuck portion at the opening, which is preferable. From the viewpoint of water vapor barrier properties, the amorphous component (III) is further preferred to be 4% or less, and particularly preferred to be 3% or less.

[0131] In order to reduce the unconstrained amorphous component (III), it is particularly effective to increase the area ratio during film formation by sequentially biaxially stretching and then stretching again along the width direction at high temperature.

[0132] In addition, using polypropylene feedstock with a high rate of racemic five-unit components is effective.

[0133] Furthermore, it is effective to set the lower limit of the amount of components with a molecular weight of less than 100,000 when determining the cumulative curve of the polypropylene resin constituting the membrane at 35% by mass.

[0134] Here, a film with an unconstrained amorphous component (III) of less than 7% as determined by pulsed NMR refers to a film with the following characteristics: fewer molecular chains with large strain due to molecular orientation constrained by entanglement points; even if crystal melting begins, the film is not easily shrunk; and wrinkles are not easily generated when heat-sealed at high temperatures.

[0135] When the unconstrained amorphous component (III) obtained by pulse NMR exceeds 7%, there are many molecular chains with large strain in molecular orientation constrained by entanglement points. Therefore, the melting of the crystal begins at the same time as shrinkage, and the film is prone to wrinkling during heat sealing.

[0136] Furthermore, there is no particular limit to the lower limit of the unconstrained amorphous component (III); 0.1% or more is practical, and 0.5% or more is also acceptable. If it is desired to reduce the unconstrained amorphous component (III) to below 0.1%, it is necessary to perform sequential biaxial stretching followed by stretching again along the width direction at high temperature. The tension during stretching accompanied by melting is reduced, sometimes resulting in fracture. In addition, the crystal orientation in the film weakens, and the rigidity sometimes decreases.

[0137] The thermal shrinkage rate (%) in the width direction of the biaxially oriented polypropylene film of the present invention and the stress (MPa) at 5% elongation in the width direction at 23°C satisfy the following formula.

[0138] By satisfying the following formula, higher rigidity and lower thermal shrinkage at high temperatures are achieved. This further improves the ease of maintaining the bag shape during packaging and reduces the likelihood of film deformation during high-temperature heat sealing and other processing, thus further improving packaging quality. Additionally, the ability to further thin the film also facilitates volume reduction in packaging materials.

[0139] Stress (MPa) at 5% elongation in the width direction at 23℃ ≥ 150℃; thermal shrinkage rate in the width direction (%) × 4.0 + 140

[0140] Furthermore, the thermal shrinkage rate (%) in the width direction of the biaxially oriented polypropylene film of the present invention at 150°C and the stress (MPa) at 5% elongation in the width direction at 23°C preferably satisfy the following formula.

[0141] Stress (MPa) at 5% elongation in the width direction at 23℃ ≥ 150℃; thermal shrinkage rate (%) in the width direction at 150℃ × 4.0 + 150

[0142] Furthermore, the thermal shrinkage rate (%) in the width direction of the biaxially oriented polypropylene film of the present invention at 150°C and the stress (MPa) at 5% elongation in the width direction at 23°C more preferably satisfy the following formula.

[0143] Stress (MPa) at 5% elongation in the width direction at 23℃ ≥ 150℃ Thermal shrinkage rate in the width direction (%) × 4.0 + 160

[0144] (Heat shrinkage rate at 150℃)

[0145] The maximum length-direction heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 150°C is 10%, preferably 7.0%, more preferably 6.0%, even more preferably 5.0%, and particularly preferably 4.0% or less. The maximum width-direction heat shrinkage rate at 150°C is 30%, preferably 20%, more preferably 16%, particularly preferably 15% or less, most preferably 12% or less, and especially most preferably 9% or less.

[0146] If the thermal shrinkage rate in the length direction is less than 10% and the thermal shrinkage rate in the width direction is less than 30%, wrinkles are less likely to occur during heat sealing. In particular, if the thermal shrinkage rate in the length direction at 150°C is less than 8.0% and the thermal shrinkage rate in the width direction at 150°C is less than 15%, the strain at the weld head of the opening is small and preferred. To reduce the thermal shrinkage rate at 150°C, it is effective to set the lower limit of the amount of components with a molecular weight of less than 100,000 when measuring the cumulative curve of the polypropylene resin constituting the film by gel permeation chromatography (GPC) to 35% by mass.

[0147] (F5: Stress at 5% elongation at 23°C)

[0148] The lower limit of the width direction F5 of the biaxially oriented polypropylene film of the present invention at 23°C is 140 MPa, preferably 160 MPa, more preferably 180 MPa, further preferably 190 MPa, and most preferably 200 MPa or more. When it is 140 MPa or more, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and the film is less likely to be deformed during printing and other processing.

[0149] The upper limit of F5 in the width direction at 23°C is preferably 300 MPa, more preferably 290 MPa, and even more preferably 280 Pa. If it is below 280 MPa, it is easier to manufacture in practice, or the longitudinal-width balance is easier to optimize.

[0150] The lower limit of the length direction F5 of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 40 MPa, more preferably 42 MPa, further preferably 46 MPa, and particularly preferably 48 MPa. At 40 MPa or higher, the rigidity is high, therefore, it is easy to maintain the shape of the bag when it is made into a packaging bag, and the film is less likely to deform during printing and other processing.

[0151] The upper limit of F5 in the length direction at 23°C is preferably 70 MPa, more preferably 65 MPa, further preferably 62 MPa, and particularly preferably 60 MPa. Below 70 MPa, practical manufacturing becomes easier, or the longitudinal-width balance is easier to optimize.

[0152] F5 can be adjusted within a certain range by changing the stretch ratio, relaxation ratio, or the temperature during film formation.

[0153] The biaxially oriented polypropylene film of the present invention preferably has the following characteristics and structure.

[0154] (Heat shrinkage rate at 120℃)

[0155] The upper limit of the longitudinal heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 2.0%, more preferably 1.5%, further preferably 1.2%, and particularly preferably 1.0%. If it is below 2.0%, it becomes less likely to cause misalignment of printing spacing during transfer printing ink. The upper limit of the transverse heat shrinkage rate at 120°C is 10.0% or less, preferably 5.0%, more preferably 3.5%, and particularly preferably 2.5%. If it is below 10.0%, it is less likely to cause wrinkles during heat sealing. There is no particular limitation on the lower limit of the heat shrinkage rate at 120°C; 0% or more is practical.

[0156] The heat shrinkage rate at 120℃ can be adjusted to a range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0157] The thermal shrinkage rate (%) in the width direction of the biaxially oriented polypropylene film of the present invention at 120°C and the tensile modulus (GPa) in the width direction at 23°C preferably satisfy the following formula.

[0158] By satisfying the following formula, the rigidity is higher and the thermal shrinkage rate at high temperatures is smaller. Therefore, it is less likely to cause misalignment of printing spacing when making packaging bags.

[0159] Tensile modulus in the width direction at 23℃ ≥ 120℃; thermal shrinkage rate in the width direction (%) × 0.3 + 7.0

[0160] Furthermore, the thermal shrinkage rate (%) in the width direction of the biaxially oriented polypropylene film of the present invention at 120°C and the tensile modulus (GPa) in the width direction at 23°C are more preferably satisfied by the following formula.

[0161] Tensile modulus in the width direction at 23℃ ≥ 120℃; thermal shrinkage rate in the width direction (%) × 0.3 + 8.0

[0162] Furthermore, the thermal shrinkage rate (%) in the width direction of the biaxially oriented polypropylene film of the present invention at 120°C and the tensile modulus (GPa) in the width direction at 23°C are preferably satisfied by the following formula.

[0163] Tensile modulus in the width direction at 23℃ ≥ 120℃; thermal shrinkage rate in the width direction (%) × 0.3 + 9.0

[0164] (Tension modulus at 23℃)

[0165] The lower limit of the tensile modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is 2.0 GPa, preferably 2.1 GPa, more preferably 2.2 GPa, further preferably 2.3 GPa, particularly preferably 2.4 GPa, and most preferably 2.6 GPa. At 2.0 GPa or higher, the rigidity is high, therefore, it is easy to maintain the shape of the bag when it is made into a packaging bag, and the film is less likely to deform during printing and other processing. The upper limit of the tensile modulus in the longitudinal direction is preferably 4.0 GPa, more preferably 3.8 GPa, further preferably 3.7 GPa, particularly preferably 3.6 GPa, and most preferably 3.5 GPa. At 4.0 GPa or lower, it is practically easy to manufacture, or the balance of characteristics in the longitudinal and width directions is easy to optimize.

[0166] The lower limit of the tensile modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 6.0 GPa, more preferably 6.5 GPa, more preferably 6.7 GPa, further preferably 7.0 GPa, particularly preferably 8.0 GPa, and most preferably 8.5 GPa. At 6.0 GPa or higher, the rigidity is high, therefore, it is easy to maintain the shape of the bag when it is made into a packaging bag, and the film is less likely to deform during printing and other processing. The upper limit of the tensile modulus in the width direction is preferably 15 GPa, more preferably 13 GPa, and further preferably 12 GPa. If it is below 15 GPa, it is easier to manufacture practically, or the balance of characteristics in the length and width directions is easier to optimize.

[0167] The tensile modulus can be adjusted within a certain range by changing the stretch ratio, relaxation rate, or temperature during film formation.

[0168] (Tensile breaking strength at 23℃)

[0169] The lower limit of the tensile breaking strength in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 90 MPa, more preferably 100 MPa, further preferably 110 MPa, and particularly preferably 115 MPa. If it is 90 MPa or higher, it becomes less likely to cause misalignment of printing spacing during transfer printing ink, and the durability of the packaging bag is also easily improved. The upper limit of the tensile breaking strength in the longitudinal direction, in practical terms, is preferably 200 MPa, more preferably 180 MPa, and further preferably 160 MPa. If it is below 200 MPa, the film breakage and packaging bag breakage are easily reduced.

[0170] The lower limit of the tensile breaking strength in the width direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 400 MPa, more preferably 420 MPa, further preferably 440 MPa, and particularly preferably 450 MPa. If it is 400 MPa or higher, it becomes less likely to cause misalignment of printing spacing during transfer printing ink, and the durability of the packaging bag is also easily improved. The upper limit of the tensile breaking strength in the width direction, based on practical values, is preferably 650 MPa, more preferably 600 MPa, and further preferably 550 MPa. If it is below 650 MPa, the film breakage and packaging bag breakage are easily reduced.

[0171] The tensile breaking strength can be adjusted within a certain range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0172] (Elongation at break under tension at 23℃)

[0173] The lower limit of the elongation at break in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 180%, more preferably 190%, more preferably 200%, and particularly preferably 210% or more. If it is 180% or more, the film breakage and packaging bag breakage are reduced. The upper limit of the elongation at break in the longitudinal direction at 23°C, based on actual values, is preferably 300%, and more preferably 280%.

[0174] The lower limit of the width-direction tensile elongation at break of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 15%, more preferably 20%, and even more preferably 30%. If it is 15% or more, the film breakage and packaging bag tearing are easily reduced. The upper limit of the width-direction tensile elongation at break at 23°C is preferably 60%, more preferably 55%, and even more preferably 50%. If it is 60% or less, it becomes less likely to cause printing spacing misalignment during transfer printing ink, and the durability of the packaging bag is also easily improved.

[0175] The elongation at break can be adjusted within a certain range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0176] (Refractive index)

[0177] The lower limit of the refractive index (Nx) in the longitudinal direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4950, more preferably 1.4970, further preferably 1.4980, particularly preferably 1.4990, and most preferably 1.5000. If it is 1.4950 or higher, the rigidity of the film is easily increased. The upper limit of the refractive index (Nx) in the longitudinal direction is preferably 1.5100, more preferably 1.5070, and further preferably 1.5050. If it is 1.5100 or lower, the balance of the film's characteristics in the longitudinal and width directions is easily excellent.

[0178] The lower limit of the refractive index (Ny) in the width direction of the biaxially oriented polypropylene film of the present invention is 1.5250, preferably 1.5253, more preferably 1.5255, further preferably 1.5260, and particularly preferably 1.5265. If it is 1.5250 or higher, the rigidity of the film is easily increased. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, and further preferably 1.5270. If it is 1.5280 or lower, the balance of the film's characteristics in the length and width directions is easily excellent.

[0179] The lower limit of the refractive index (Nz) in the thickness direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4960, more preferably 1.4965, further preferably 1.4970, particularly preferably 1.4980, and most preferably 1.4990. If it is 1.4960 or higher, the rigidity of the film is easily increased. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and further preferably 1.5010. If it is 1.5020 or lower, the heat resistance of the film is easily improved.

[0180] The refractive index can be adjusted to a range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0181] (△Ny)

[0182] The lower limit of ΔNy for the biaxially oriented polypropylene film of the present invention is 0.0240, preferably 0.0245, more preferably 0.0247, further preferably 0.0250, particularly preferably 0.0255, and most preferably 0.0260. If it is 0.0240 or higher, the rigidity of the film tends to increase. The upper limit of ΔNy, based on actual values, is preferably 0.0280, more preferably 0.0277, further preferably 0.0273, and particularly preferably 0.0270. If it is below 0.0280, thickness unevenness tends to be better. ΔNy can be adjusted to within a certain range by changing the film stretching ratio, stretching temperature, and heat setting temperature.

[0183] △Ny is defined as the refractive indices along the length, width, and thickness directions of the film as Nx, Ny, and Nz, respectively, and is calculated according to the following formula. It refers to the degree of orientation in the width direction among the overall orientation of the length, width, and thickness directions of the film.

[0184] △Ny=Ny-[(Nx+Nz) / 2]

[0185] (Surface orientation coefficient)

[0186] The lower limit of the planar orientation coefficient (ΔP) of the biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and even more preferably 0.0140. If it is 0.0135 or higher, the film exhibits good planar uniformity and thickness unevenness. The upper limit of the planar orientation coefficient (ΔP), based on actual values, is preferably 0.0155, more preferably 0.0152, and even more preferably 0.0150. If it is below 0.0155, the heat resistance at high temperatures is easily excellent. The planar orientation coefficient (ΔP) can be adjusted to a range by changing the stretch ratio, stretching temperature, and heat setting temperature.

[0187] In addition, the orientation coefficient (ΔP) is calculated using the formula ΔP = [(Nx + Ny) / 2] - Nz.

[0188] (Average Refractive Index)

[0189] The lower limit of the average refractive index of the biaxially oriented polypropylene film of the present invention is preferably 1.5080, more preferably 1.5081, further preferably 1.5082, particularly preferably 1.5083, and most preferably 1.5090. The upper limit of the average refractive index, based on actual values, is preferably 1.5150, more preferably 1.5140, further preferably 1.5135, and particularly preferably 1.5130. If it is 1.5080 or higher, wrinkles are less likely to occur during film heat sealing. The average refractive index can be adjusted to a range by changing the film stretching ratio, stretching temperature, and heat setting temperature.

[0190] The average refractive index is calculated by setting the refractive indices along the length, width, and thickness of the film as Nx, Ny, and Nz, respectively, and using the following formula.

[0191] Average refractive index = (Nx + Ny + Nz) / 3

[0192] (Haze)

[0193] The upper limit of haze in the biaxially oriented polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, further preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. If it is below 5.0%, it is easy to use in applications requiring transparency. The lower limit of haze, as a practical value, is preferably 0.1%, more preferably 0.2%, further preferably 0.3%, and particularly preferably 0.4%. If it is above 0.1%, it is easy to manufacture. Haze can be achieved by adjusting the cooling roller (CR) temperature, the width-direction stretching temperature, the preheating temperature before width-direction stretching of the tenter frame, the width-direction stretching temperature, or the heat setting temperature, or the amount of polypropylene resin with a molecular weight of 100,000 or less, but sometimes the haze increases due to the addition of anti-blocking agents or the application of a sealing layer.

[0194] (Half-width of diffraction peaks derived from oriented crystals)

[0195] In the azimuth dependence of the scattering peaks of the (110) plane of the polypropylene α-type crystal obtained in wide-angle X-ray measurements perpendicular to the membrane surface of the biaxially oriented polypropylene membrane of the present invention, the upper limit of the half-width (Wh) of the diffraction peaks originating from the oriented crystals in the width direction is 26°, preferably 25° or less, more preferably 24° or less, particularly preferably 23° or less, most preferably 22.0° or less, and especially most preferably 21.0° or less. If the half-width (Wh) is 26° or less, the rigidity of the membrane is easily improved. In addition, the water vapor transmission rate is easily reduced. The lower limit of Wh is preferably 15°, more preferably 16°, and even more preferably 17°.

[0196] (X-ray orientation)

[0197] The lower limit of the X-ray orientation degree of the biaxially oriented polypropylene film of the present invention, calculated by Wh using the following formula, is preferably 0.856, more preferably 0.861, further preferably 0.867, particularly preferably 0.872, and most preferably 0.878. By setting it to 0.856 or higher, rigidity can be easily improved.

[0198] X-ray orientation degree = (180 - Wh) / 180

[0199] The upper limit of the X-ray orientation degree is preferably 0.917, more preferably 0.911, and even more preferably 0.906. By setting it to below 0.917, the film formation is easier and more stable.

[0200] (Water vapor transmission rate)

[0201] For the water vapor transmission rate of the biaxially oriented polypropylene membrane of the present invention, converted to a thickness of 20 μm, it is preferably set to 5.0 g / m. 2 For doses below d, a more preferred setting is 4.6 g / m³. 2 Below d, a further preferred value is 4.3 g / m 2 Below d. If it is 5.0 g / m 2 For thicknesses below d, the water vapor barrier properties are superior to those of conventional membranes at the same thickness. Therefore, even when thinning, sufficient water vapor barrier properties can be easily obtained.

[0202] (Practical properties of membranes)

[0203] The practical characteristics of the biaxially oriented polypropylene film of the present invention will be described.

[0204] (Rigidity and water vapor barrier properties)

[0205] For packaging materials used in the packaging of food, beverages, etc., in order to protect the contents from various treatments such as circulation, refrigeration, and heat sterilization, in addition to functions such as rigidity and heat resistance, high barrier properties are also required for the purpose of maintaining the quality and quantity of the contents. These properties must be excellent even when the packaging is made into a film.

[0206] (Wrinkles during heat sealing)

[0207] To form bags for packaged food, the bag is filled with contents and heated to melt and fuse the film, thus sealing it. This process is often repeated while filling the bag with food. Typically, a sealant film containing polyethylene, polypropylene, etc., is laminated onto a base film, and the sealant film surfaces are fused together. In heating methods, pressure is applied to the film from the base film side using a heating plate, and the seal width is often around 10mm. During this process, the base film is also heated, and shrinkage causes wrinkles. Fewer wrinkles are better for bag durability and to increase consumer appeal. Sealing temperatures are sometimes around 120°C, but higher sealing temperatures are required to increase bag manufacturing speed; in such cases, low shrinkage is preferred. When the clamps are fused at the bag opening, a high-temperature seal is required.

[0208] (Misaligned printing spacing)

[0209] The basic structure of packaging film typically consists of a laminated film made of a printed substrate film and a sealant film. Bag manufacturing utilizes various bag-making machines, including three-way bags, stand-up pouches, and upright packaging bags. It is believed that the tension and heat applied to the film during the printing process cause the substrate film to elongate and shrink, resulting in misalignment of the printing spacing. Eliminating defects caused by printing spacing misalignment is important for efficient resource utilization and for increasing purchasing power.

[0210] (Membrane processing)

[0211] The printing of the biaxially oriented polypropylene film of the present invention can be carried out according to the application and using letterpress printing / lithographic printing / gravure printing, screen printing, or transfer printing methods.

[0212] Additionally, unstretched sheets, uniaxially stretched films, and biaxially stretched films formed from low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester can be used as sealant films and laminated as heat-sealing laminates. Furthermore, to improve gas barrier properties and heat resistance, unstretched sheets, uniaxially stretched films, and biaxially stretched films formed from aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol can be placed between the biaxially oriented polypropylene film and the sealant film as an interlayer. In the lamination of the sealant film, adhesives applied by dry lamination or hot-melt lamination methods can be used.

[0213] To improve gas barrier properties, aluminum or inorganic oxides can be vapor-deposited onto biaxially oriented polypropylene films, interlayer films, or sealant films. Vacuum deposition methods can include vacuum deposition, sputtering, and ion plating, with vacuum deposition of silicon dioxide, aluminum oxide, or mixtures thereof being particularly preferred.

[0214] In the biaxially oriented polypropylene film of the present invention, the amount of antifogging agents such as fatty acid esters of polyols, amines of higher fatty acids, amides of higher fatty acids, amines of higher fatty acids, and ethylene oxide adducts of amides in the film is in the range of 0.2% to 5% by mass, thereby making it suitable for packaging fresh produce containing vegetables, fruits, flowers, and other plant products that require high freshness.

[0215] In addition, as long as it does not impair the effects of the present invention, various additives for improving properties such as lubricity and antistatic properties can be mixed in, such as lubricants like waxes and metal soaps for improving productivity, plasticizers, processing aids, heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers, etc.

[0216] Example

[0217] The present invention will now be described in detail with reference to embodiments. It should be noted that the characteristics were measured and evaluated using the following methods.

[0218] (1) Melt flow rate

[0219] Melt flow rate (MFR) was measured according to JIS K7210 at a temperature of 230°C and a load of 2.16 kgf.

[0220] (2) Meso-five-unit component ratio

[0221] Determination of the percentage ([mmmm]%) of meso-five-unit components in polypropylene resin 13 The C-NMR was performed. The proportions of the racemic pentagonal components were calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13The C-NMR determination was performed as follows: using an AVANCE 500 instrument manufactured by BRUKER, 200 mg of the sample was dissolved at 135 °C in an 8:2 mixture of o-dichlorobenzene and deuterated benzene, and the determination was performed at 110 °C.

[0222] (3) Number average molecular weight, weight average molecular weight, amount of components with a molecular weight below 100,000, and molecular weight distribution of polypropylene resin.

[0223] Using gel permeation chromatography (GPC), monodisperse polystyrene was used as a reference to calculate the molecular weight of PP. When the baseline was unclear, it was set to the lowest point of the basal region of the high molecular weight side of the elution peak closest to the standard.

[0224] The GPC measurement conditions are as follows.

[0225] Device: HLC-8321PC / HT (manufactured by Tosoh Corporation)

[0226] Detector: RI

[0227] Solvent: 1,2,4-trichlorobenzene + butylated hydroxytoluene (0.05%)

[0228] Column: TSKgelguardcolumnHHR(30)HT(7.5mmI.D.×7.5cm)×1 piece + TSKgelGMHHR-H(20)HT(7.8mmI.D.×30cm)×3 pieces

[0229] Flow rate: 1.0 mL / min

[0230] Injection volume: 0.3 mL

[0231] Measurement temperature: 140℃

[0232] Number-average molecular weight (Mn) and mass-average molecular weight (Mw) are the molecular weights (Mn, Mw ... i The number of molecules (N) i And it is defined by the following formula.

[0233] Number-average molecular weight: Mn=Σ(N i ·M i ) / ΣN i

[0234] Mass-average molecular weight: Mw=Σ(N i ·M i 2 ) / Σ(N i ·M i )

[0235] Here, the molecular weight distribution can be obtained from Mw / Mn.

[0236] In addition, based on the integral curve of the molecular weight distribution obtained by GPC, the proportion of components with a molecular weight of less than 100,000 was determined.

[0237] (4) Crystallization temperature (Tc), melting temperature (Tm)

[0238] Thermal measurements were performed using a TA Instruments Q1000 differential scanning calorimeter under a nitrogen atmosphere. Approximately 5 mg of polypropylene resin granules was cut and sealed into an aluminum measuring dish. The temperature was raised to 230°C, held for 5 minutes, and then cooled to 30°C at a rate of -10°C / min. The exothermic peak temperature was taken as the crystallization temperature (Tc). The heat of crystallization (ΔHc) was calculated by establishing a baseline by smoothly connecting the area of ​​the exothermic peak from its beginning to its end. The temperature was then directly held at 30°C for 5 minutes, raised to 230°C at a rate of 10°C / min, and the temperature of the main endothermic peak was taken as the melting temperature (Tm).

[0239] (5) Film thickness

[0240] The thickness of the membrane was measured using a Millitron 1202D manufactured by Seiko EM.

[0241] (6) Haze

[0242] The test was performed at 23°C using NDH5000 manufactured by Nippon Denshoku Kogyo Co., Ltd., in accordance with JIS K7105.

[0243] (7) Tensile test

[0244] According to JIS K 7127, the tensile strength of the membrane in the longitudinal and transverse directions was determined at 23°C. Samples were cut from the membrane to a size of 15 mm × 200 mm and mounted on a tensile testing machine (Instron 5965, a double-column benchtop testing machine manufactured by Instron Japan Company Limited) with a clamp width of 100 mm. Tensile tests were conducted at a tensile speed of 200 mm / min. Based on the obtained strain-stress curve, the tensile modulus was determined from the slope of the linear portion at the initial elongation. Furthermore, the stress at 5% elongation was taken as F5.

[0245] Tensile breaking strength and tensile breaking elongation are set as the strength and elongation at the moment of sample fracture, respectively.

[0246] (8) Thermal shrinkage rate

[0247] According to JIS Z 1712, the following method is used for determination: Cut the film into 20 mm wide and 200 mm long sections along both the length and width directions, and suspend it in a hot air oven at 120°C or 150°C for 5 minutes. Measure the length after heating, and calculate the heat shrinkage rate as the ratio of the shrunk length to the original length.

[0248] (9) Refractive index, ΔNy, plane orientation coefficient, mean refractive index

[0249] The measurements were performed using an Abbe refractometer manufactured by Atago Co., Ltd., at a wavelength of 589.3 nm and a temperature of 23 °C. The refractive indices along the length and width of the film were designated as Nx and Ny, respectively, and the refractive index along the thickness direction was designated as Nz. ΔNy was calculated using Nx, Ny, and Nz, and then by the formula Ny - [(Nx + Nz) / 2]. The plane orientation coefficient (ΔP) was calculated using the formula [(Nx + Ny) / 2] - Nz. The average refractive index was calculated using the formula (Nx + Ny + Nz) / 3.

[0250] (10) X-ray half-width, X-ray orientation

[0251] The determination was performed using an X-ray diffraction apparatus (SmartLab manufactured by Rigaku Co., Ltd., αβγ accessory included) via transmission method. Wavelength was used. The X-rays were used at a power of 45 kV and 200 mA. A Hypix-3000 hybrid multi-pixel detector was used in 0-dimensional mode. In the parallel beam method, a 2.5° Soler slit, a 10 mm length-limiting slit, and a 1 mm incident slit width were used as the incident slit. Additionally, a 0.228° parallel slit analyzer was used as the light-receiving slit.

[0252] The experiment was conducted with a camera length of 300 mm and an integration amplitude of 2 mm for the detector.

[0253] Samples were prepared by overlapping films to achieve a thickness of 400 μm. A detector was placed at the diffraction peak position (diffraction angle 2θ = 14.1°) on the (110) plane of the α-type crystal of polypropylene resin. The sample was rotated 360° with the film thickness direction as the axis to obtain the azimuth dependence of the diffraction intensity on the (110) plane. Measurements were performed at a step interval of 0.5° and a measurement rate of 60° / min. Based on this azimuth dependence, the half-width Wh of the diffraction peak originating from the oriented crystal in the width direction of the film was determined.

[0254] In addition, using Wh, the X-ray orientation degree is calculated according to the following formula.

[0255] X-ray orientation degree = (180 - Wh) / 180

[0256] (11) Ratio of unconstrained amorphous component (III) determined by pulsed NMR

[0257] Cut the film and fill a glass tube with the cut film (outer diameter 10 mm) until the height is 1 cm. Under the following measuring apparatus and conditions, measure the polypropylene film. 1 The magnetization decay curve is obtained by taking the spin-spin relaxation time T2 of the H nucleus.

[0258] Device: BRUKER Minispec MQ20

[0259] Temperature: 40℃

[0260] Observation frequency: 20MHz

[0261] 90° pulse amplitude: 2.74μs

[0262] Pulse repetition time: 2.0s

[0263] Pulse mode: Solido Echo method

[0264] Total number of times: 128

[0265] Recycle Delay: 4 seconds

[0266] Acquisition Scale: 0.1ms

[0267] The measurements were performed as follows: A glass tube containing a membrane was placed in the apparatus and kept at a constant temperature for 15 minutes. The magnetization decay curve was matched to the fitted curve. The component with the shortest relaxation time was separated using the Gaussian function and the least squares method. The second and third shortest components were separated using the Lorentz function and the least squares method, and their respective ratios were obtained. It should be noted that the shortest component corresponds to the crystalline component (I), and the second and third shortest components correspond to the constrained amorphous component (II) and the unconstrained amorphous component (III), respectively. The fitting and analysis were performed using the software (TD-NMR Analyzer) provided with the aforementioned measuring apparatus.

[0268] The ratio of the unconstrained amorphous component (III) is as follows: the ratio (%) of the amorphous component (III) to the total of the crystalline component (I), the constrained amorphous component (II), and the unconstrained amorphous component (III) obtained by the above method is calculated using the following formula (1).

[0269] The ratio of unconstrained amorphous components (III) = M III / (M I +M II +M III)···(1)

[0270] M I : The amount of crystal component (I)

[0271] M II The amount of the constrained amorphous component (II)

[0272] M III The composition amount of the unconstrained amorphous component (III)

[0273] (12) Water vapor transmission rate

[0274] Water vapor transmission rate was determined according to JIS K7129 B method.

[0275] The water vapor transmission rate was measured using a water vapor transmission rate measuring device (PERMATRAN-W3 / 33, manufactured by MOCON) at 40°C and 90% RH. Since the water vapor transmission rate is inversely proportional to the film thickness, the thickness of each sample was measured and converted to a value at 20 μm.

[0276] (Example 1)

[0277] As a polypropylene resin, 80 parts by weight of propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., Sumitomo Noblen FLX80E4) with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2 °C, Tm = 162.5 °C and 20 parts by weight of propylene homopolymer PP-2 (manufactured by Sumitomo Chemical Co., Ltd., EL80F5) with MFR = 11 g / 10 min, [mmmm] = 98.8%, Tc = 116.5 °C, Tm = 161.5 °C are blended together.

[0278] The film was extruded in sheet form from a T-die at 250°C, contacted with cooling rollers at 20°C, and directly immersed in a water bath at 20°C. It was then stretched 4.5 times its original length using two pairs of rollers at 142°C. The ends were then clamped and fed into a hot air oven for preheating at 170°C. Following this initial stretching, the film was stretched 10 times its original length at 162°C. Immediately after this stretching, it was fixed in the clamps and cooled at 120°C. Then, it was stretched 1.2 times its original length again at 175°C. Finally, it was cooled at room temperature. The resulting film had a thickness of 18.6 μm.

[0279] Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3, resulting in a film with excellent rigidity and low thermal shrinkage at high temperatures. Furthermore, it exhibits excellent water vapor permeability.

[0280] (Example 2)

[0281] The film was stretched 1.2 times along its width at 165°C, otherwise performed in the same manner as in Example 1. The resulting film had a thickness of 18.4 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3, resulting in a film with excellent rigidity and low thermal shrinkage at high temperatures. Furthermore, it exhibits excellent water vapor permeability.

[0282] (Example 3)

[0283] The film was stretched along its length at 147°C, and then stretched 10 times along its width at 165°C as the first stage. After stretching in the width direction, it was fixed in a fixture and cooled at 120°C. Then, it was stretched again at 177°C along its width by 1.2 times. Otherwise, the process was the same as in Example 1. The resulting film had a thickness of 18.9 μm.

[0284] Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3, resulting in a film with high rigidity and low thermal shrinkage at high temperatures. Furthermore, it exhibits excellent water vapor permeability.

[0285] (Example 4)

[0286] The film was then stretched again at 177°C and 1.1 times its original length in the width direction, otherwise performed in the same manner as in Example 3. The resulting film had a thickness of 20.6 μm. The structure of the polypropylene resin is shown in Table 1, and the film-forming conditions are shown in Table 2.

[0287] Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3; it exhibits high rigidity and low thermal shrinkage at high temperatures. Furthermore, it is a membrane with excellent water vapor permeability.

[0288] (Comparative Example 1)

[0289] The film was stretched 12 times at 162°C along its width as the first stage. Immediately after stretching, it was fixed in a fixture and cooled at 100°C. Then, it was heat-set at 170°C while maintaining a constant width. Otherwise, the process was the same as in Example 1. The resulting film had a thickness of 20.8 μm.

[0290] Table 1 shows the structure of polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3. It has excellent water vapor permeability and high rigidity, but poor rigidity at high temperatures.

[0291] (Comparative Example 2)

[0292] The film was stretched 12 times at 162°C along its width as the first stage. Immediately after stretching in the width direction, it was fixed in a fixture without cooling and heat-set at 172°C while maintaining a constant width. Otherwise, the process was the same as in Example 1. The resulting film had a thickness of 23.1 μm.

[0293] Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3; it has poor rigidity. Furthermore, it is a membrane with poor water vapor permeability.

[0294] (Comparative Example 3)

[0295] The film was stretched 12 times at 168°C along its width as the first stage. After stretching in the width direction, it was fixed in a fixture and cooled at 100°C. Then, it was heat-set at 170°C while keeping the width constant. Otherwise, the process was the same as in Example 1. The resulting film had a thickness of 18.7 μm.

[0296] Table 1 shows the structure of polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3; it has a high thermal shrinkage rate at high temperatures and poor rigidity. Furthermore, it is a film with poor water vapor permeability.

[0297] (Comparative Example 4)

[0298] As the polypropylene resin, PP-3 (manufactured by Japan Polypropylene Corporation, FL203D) with MFR = 3 g / 10 min, [mmmm] = 94.8%, Tc = 117.2 °C, and Tm = 160.6 °C was used. The film was extruded in sheet form from a T-die at 250 °C, contacted with a cooling roller at 20 °C, and directly immersed in a water bath at 20 °C. Then, it was stretched 4.5 times along its length at 130 °C. During the width stretching in the tenter frame, the preheating temperature was set to 168 °C, and the first stage of stretching was performed at 155 °C with a stretch of 8.2 times. Immediately after the width stretch, it was fixed in the fixture and cooled at 120 °C. Then, it was stretched again 1.2 times along its width at 170 °C. Finally, it was cooled at room temperature. The resulting film thickness was 18.8 μm.

[0299] Table 1 shows the structure of polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3; it has a high thermal shrinkage rate at high temperatures and poor rigidity. Furthermore, it is a film with poor water vapor permeability.

[0300] (Comparative Example 5)

[0301] As the polypropylene resin, a blend of PP-1 and PP-2 was used in the same manner as in Example 1. The film was obtained under film-forming conditions of heat treatment at 168°C without further stretching in the width direction as shown in Table 2. The thickness of the obtained film was 20.0 μm.

[0302] Table 1 shows the structure of polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3. It has low thermal shrinkage at high temperatures, but also poor rigidity.

[0303] (Comparative Example 6)

[0304] Using PP-4 (manufactured by Japan Polypropylene Corporation, SA4L) as the polypropylene resin with MFR = 5 g / 10 min, [mmmm] = 97.3%, Tc = 116.8 °C, and Tm = 161.6 °C, a film was obtained under the film-forming conditions of heat treatment at 168 °C without further stretching in the width direction as shown in Table 2. The thickness of the obtained film was 20.0 μm.

[0305] Table 1 shows the structure of polypropylene resin, and Table 2 shows the film-forming conditions. Its physical properties are shown in Table 3. It has low thermal shrinkage at high temperatures, but also poor rigidity.

[0306] [Table 1]

[0307] MFR (g / 10 minutes) 7.5 11 3.0 5.0 [mmmm](%) 98.9 98.8 94.8 97.3 Melting temperature Tm (°C) 162.5 161.5 160.6 161.6 Crystallization temperature Tc (°C) 116.2 116.5 117.2 116.8 Heat of crystallization ΔHc (J / g) 104.8 107.8 94.9 106.8 Amount (mass%) of components with a molecular weight below 10,000 4.0 6.9 3.0 5.0 Amount (mass%) of components with a molecular weight below 100,000 40.5 53.1 37.1 47.0

[0308] [Table 2]

[0309]

[0310] [Table 3]

[0311] Thickness (μm) 18.6 18.4 18.9 20.6 20.8 23.1 18.7 18.8 20.0 20.0 Haze (%) 1.2 1.3 0.8 0.8 0.9 1.5 1.1 0.6 1.1 2.5 F5 (width direction) (MPa) 222 263 185 164 189 148 165 168 131 135 F5 (length direction) (MPa) 46 46 49 50 49 47 44 40 44 49 Tensile modulus (width direction) (GPa) 8.1 9.7 7.7 7.3 7.1 5.7 6.8 5.2 5.7 5.0 Tensile modulus (length direction) (GPa) 2.4 2.5 2.8 2.9 2.8 2.3 2.6 2.0 2.6 2.8 Tensile breaking strength (width direction) (MPa) 454 512 446 426 466 399 397 397 344 356 Tensile breaking strength (length direction) (MPa) 101 103 116 120 124 130 107 136 124 134 Elongation at break (width direction) (%) 21 24 34 37 40 30 28 25 44 44 Elongation at break (length direction) (%) 211 216 245 220 239 270 239 231 219 216 Heat shrinkage rate at 120℃ (width direction) (%) 2.7 5.3 0.7 0.5 1.7 0.8 1.0 6.3 1.0 0.5 Heat shrinkage rate at 120℃ (length direction) (%) 0.0 0.0 0.7 0.8 0.3 1.3 0.0 2.8 1.3 1.3 Heat shrinkage rate at 150℃ (width direction) (%) 14.3 21.5 6.8 6.0 19.8 7.7 9.5 32.7 13.2 6.3 Heat shrinkage rate at 150℃ (length direction) (%) 2.7 3.5 3.0 5.0 4.5 3.5 2.7 10.3 4.3 4.0 A: Width-direction thermal shrinkage rate (%) at 150℃ × 4.0 + 140 197 226 167 164 219 171 178 271 193 165 F5 (width direction) (MPa)-A 25 37 17 0 -30 -23 -13 -102 -62 -30 B: Width-direction thermal shrinkage rate at 120℃ (%) × 0.3 + 7.0 7.8 8.6 7.2 7.2 7.5 7.2 7.3 8.9 7.3 7.2 Tensile modulus (width direction) (MPa) - B 0.3 1.1 0.5 0.1 -0.4 -1.5 -0.5 -3.7 -1.6 -2.2 Length direction refractive index N× 1.5018 1.4998 1.5024 1.5023 1.5011 1.5025 1.5035 1.4993 1.5056 1.5073 Broadband refractive index Ny 1.5271 1.5264 1.5259 1.5256 1.5249 1.5259 1.5269 1.5211 1.5245 1.5260 Thickness direction refractive index Nz 1.4997 1.4993 1.4997 1.4997 1.4990 1.5000 1.5012 1.4961 1.5010 1.5023 ΔNy 0.0264 0.0269 0.0248 0.0246 0.0248 0.0246 0.0246 0.0234 0.0212 0.0212 Orientation coefficient ΔP 0.0147 0.0138 0.0145 0.0142 0.0139 0.0142 0.0140 0.0141 0.0141 0.0144 Mean refractive index 1.5095 1.5085 1.5093 1.5092 1.5083 1.5095 1.5105 1.5055 1.5104 1.5118 X-ray half-width (°) 18.1 18.0 20.6 20.4 20.1 21.3 22.0 25.3 28.9 27.0 × Ray Orientation 0.899 0.900 0.884 0.884 0.888 0.882 0.878 0.859 0.839 0.850 Ratio (%) of crystal component (I) 69.0 68.5 68.8 67.2 66.9 67.9 67.4 61.7 66.7 66.7 Ratio (%) of constrained amorphous component (II) 28.9 29.5 26.4 29.1 24.1 23.3 20.7 30.9 21.2 29.6 Ratio (%) of unconstrained amorphous component (III) 2.1 2.0 4.8 3.7 9.0 8.8 11.9 7.4 12.1 3.7 <![CDATA[Water vapor transmission rate (g / m 2 ·d / 20μm)]]> 4.4 4.2 4.9 4.8 4.5 5.5 5.1 6.2 5.4 5.6

[0312] Industrial availability

[0313] The biaxially oriented polypropylene film of the present invention has the aforementioned unprecedented superior properties, and therefore can be preferably used for packaging bags, and the film thickness can be made thinner than ever before.

[0314] Furthermore, it is also suitable for applications requiring high temperatures, such as insulating films for capacitors and motors, backsheets for solar cells, barrier films for inorganic oxides, base films for transparent conductive films like ITO, and rigid applications such as separator films. In addition, by utilizing coating agents, inks, and laminating adhesives that were previously difficult to use, high-temperature coating and printing processes can be achieved, promising increased production efficiency.

[0315] The biaxially oriented polypropylene film of the present invention has high rigidity, can achieve thin film production, and can maintain the same gas barrier properties as before even when the film is made into a thin film. When heat-sealed for packaging, there are fewer wrinkles in the sealing part and its periphery. Therefore, it is suitable for use as packaging film, industrial film, etc.

Claims

1. A biaxially oriented polypropylene film, which satisfies the following (1) and (2). (1) In the azimuth dependence of the (110) plane of polypropylene α-type crystal obtained by wide-angle X-ray diffraction, the half-width of the peak originating from the orientation crystal in the width direction is less than 26°. (2) When separated into crystal composition (I), constrained amorphous composition (II), and unconstrained amorphous composition (III) determined by pulse NMR based on solid echo method, the ratio of unconstrained amorphous composition (III) is less than 7%.

2. The biaxially oriented polypropylene film according to claim 1, wherein, The biaxially oriented polypropylene film satisfies the following (3), (4) and (5). (3) The thermal shrinkage rate at 150℃ is less than 10% in the length direction and less than 30% in the width direction. (4) The stress at 5% elongation in the width direction at 23℃ is above 140MPa. (5) The thermal shrinkage rate (%) in the width direction at 150℃ and the stress (MPa) at 5% elongation in the width direction at 23℃ satisfy the following formula: Stress (MPa) at 5% elongation in the width direction at 23℃ ≥ 150℃ thermal shrinkage rate in the width direction (%) × 4.0 + 140.

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein The biaxially oriented polypropylene film satisfies the following (6) and (7). (6) The heat shrinkage rate at 120℃ is less than 2.0% in the length direction and less than 10.0% in the width direction. (7) The thermal shrinkage rate (%) in the width direction at 120℃ and the tensile modulus (GPa) in the width direction at 23℃ satisfy the following formula: Tensile modulus in the width direction at 23℃ (GPa) ≥ 120℃ thermal shrinkage rate in the width direction (%) × 0.3 + 7.

0.

4. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The biaxially oriented polypropylene film has a refractive index Ny of 1.5250 or higher and a ΔNy of 0.0240 or higher in the width direction. Wherein, ΔNy is defined as the refractive indices along the length, width, and thickness directions of the film, respectively, as Nx, Ny, and Nz, and is calculated according to the following formula. It refers to the degree of orientation in the width direction among the overall orientations of the film's length, width, and thickness directions. △Ny=Ny-[(Nx+Nz) / 2].

5. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The haze of the biaxially oriented polypropylene film is below 5.0%.

6. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The polypropylene resin constituting the biaxially oriented polypropylene film has a meso-five-unit component ratio of 97.0% or higher.

7. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The polypropylene resin constituting the biaxially oriented polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 160°C or higher.

8. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The melt flow rate of the polypropylene resin constituting the biaxially oriented polypropylene film is 4.0 g / 10 min or higher.

9. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The amount of polypropylene resin with a molecular weight of less than 100,000 in the biaxially oriented polypropylene film is 35% by mass or more.

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