Biaxially oriented polypropylene film

Abstract

Provided is a biaxially oriented polypropylene film that is highly rigid, has excellent heat resistance at high temperatures of up to 150°C, easily maintains the bag shape when a bag is made, and has less misregistration during printing, less wrinkles in the seal portion during heat sealing. A biaxially oriented polypropylene film in which, in an azimuthal angle dependence of a (110) plane of an α-type crystal of polypropylene obtained by wide-angle X-ray diffraction measurement, a half-value width of a peak derived from an oriented crystal in the width direction is 27° or less, and a tan δ obtained from a ratio of a loss modulus (E'') to a storage modulus (E') (E'' / E') obtained by dynamic viscoelasticity measurement is 0.2 or more and 0.4 or less in the width direction.

Description

[0001] This application is a divisional application of the application filed on December 19, 2019, with application number 201980086055.X and invention title "Biaxially Oriented Polypropylene Film". Technical Field

[0002] This invention relates to biaxially oriented polypropylene films with excellent rigidity and heat resistance. More specifically, it relates to biaxially oriented polypropylene films that easily maintain the shape of bags when made into packaging bags and have fewer wrinkles at the seal during heat sealing, thus making them suitable for use in packaging bags. Background Technology

[0003] Biaxially oriented polypropylene (POP) films possess moisture resistance, along with the required rigidity and heat resistance, making them suitable for packaging and industrial applications. In recent years, with the expansion of applications, higher performance has been demanded, particularly improvements in rigidity. Furthermore, environmental concerns necessitate maintaining strength even with volume reduction (thinning the film thickness), making significant improvements in rigidity essential. Known methods for improving rigidity include modifying the catalyst and process technology used in the polymerization of polypropylene resin, thereby improving the crystallinity and melting point of the polypropylene resin. Despite these improvements, a biaxially oriented polypropylene film with sufficient rigidity has not yet been achieved.

[0004] In the manufacturing process of biaxially oriented polypropylene films, the following methods have been proposed: stretching along the width direction, then relaxing the film below the temperature at which it was stretched in the width direction while performing a first-stage heat treatment, followed by a second-stage heat treatment at the temperature from the first-stage temperature to the width-direction stretching temperature (see, for example, Reference 1); and stretching along the width direction followed by stretching along the length direction (see, for example, Reference 2). However, while the film described in Patent Document 2 exhibits 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.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. WO2016 / 182003

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-177645 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 exhibiting excellent rigidity and heat resistance at temperatures up to 150°C. More specifically, it provides a biaxially oriented polypropylene film that easily maintains the shape of a bag when made into a packaging bag and exhibits minimal wrinkling at and around the sealing portion during heat sealing.

[0011] In order to achieve the above-mentioned objectives, the inventors conducted in-depth research and found that by producing a biaxially oriented polypropylene film with excellent rigidity and heat resistance at high temperatures up to 150°C, a biaxially oriented polypropylene film with excellent rigidity and heat resistance at high temperatures up to 150°C can be obtained. In the azimuth dependence of the polypropylene α-type crystal (110) plane measured by wide-angle X-ray diffraction, the half-width of the peak originating from the oriented crystal in the width direction is less than 27°, and the tanδ area obtained by the ratio of loss modulus (E”) to storage modulus (E’) (E” / E’) measured by dynamic viscoelasticity is more than 0.2 and less than 0.4 in the width direction.

[0012] In this case, it is suitable that the heat shrinkage rate of the aforementioned biaxially oriented polypropylene film at 120°C is less than 2.0% in the length direction and less than 5.0% in the width direction, and the heat shrinkage rate at 120°C in the length direction is less than the heat shrinkage rate at 120°C in the width direction.

[0013] In addition, in this case, it is suitable that the refractive index Ny in the longitudinal direction of the aforementioned biaxially oriented polypropylene film is 1.5230 or more and ΔNy is 0.0220 or more.

[0014] Furthermore, in this case, it is suitable that the haze of the aforementioned biaxially oriented polypropylene film is 5.0% or less.

[0015] 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.

[0016] 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 160°C or higher.

[0017] 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.

[0018] 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.

[0019] Furthermore, in this case, it is suitable that the orientation degree of the aforementioned biaxially oriented polypropylene film is 0.85 or higher.

[0020] The effects of the invention

[0021] The biaxially oriented polypropylene film of the present invention exhibits high rigidity and excellent heat resistance at temperatures up to 150°C. Therefore, it easily maintains the shape of the bag when manufactured into a packaging bag, and has fewer wrinkles at the sealing portion during heat sealing. This results in a biaxially oriented polypropylene film suitable for use in packaging bags. Furthermore, due to its excellent rigidity, the biaxially oriented polypropylene film maintains its strength even when the film thickness is reduced, making it suitable for applications requiring even higher rigidity. Detailed Implementation

[0022] The biaxially oriented polypropylene film of the present invention will now be described in detail.

[0023] 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.

[0024] (Polypropylene resin)

[0025] The polypropylene resin used in this invention can be a polypropylene homopolymer or a copolymer of polypropylene and / or α-olefins having 4 or more carbon atoms. Preferably, it is a propylene homopolymer substantially free of ethylene and / or α-olefins having 4 or more carbon atoms. If it contains ethylene and / or α-olefins having 4 or more carbon atoms, the amount of ethylene and / or α-olefins having 4 or more carbon atoms is preferably less than 1 mol%. The upper limit of the amount is more preferably 0.5 mol%, further preferably 0.3 mol%, and particularly preferably 0.1 mol%. 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. 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.

[0026] (Structural regularity)

[0027] The percentage of meso-five-unit components ([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%.

[0028] 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. More preferably, it is 99.5% or lower. The proportion of the meso-five-unit components is determined by nuclear magnetic resonance (NMR).

[0029] 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.

[0030] (Melting temperature)

[0031] 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, and even more preferably 163°C. If Tm is 160°C or higher, rigidity and heat resistance at high temperatures are readily obtained.

[0032] 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 control the increase in cost in the manufacture of polypropylene, or to make it 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.

[0033] 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.

[0034] (Crystallization temperature)

[0035] 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 in the width-direction stretching and the subsequent cooling process, and rigidity and heat resistance at high temperatures are easily obtained.

[0036] 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 will not easily increase, or it will become less prone to breakage during film formation.

[0037] 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.

[0038] The crystallization temperature can be further increased by mixing a nucleating agent into the aforementioned polypropylene resin.

[0039] (Mel flow rate)

[0040] 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 K7210 (1995), it is preferably 4.0 to 30 g / 10 min, more preferably 4.5 to 25 g / 10 min, further 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.

[0041] 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.

[0042] 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.

[0043] From the viewpoint of film properties, the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the polypropylene resin constituting the film 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.

[0044] 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 polypropylene resin constituting the film increases. Therefore, by employing 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.

[0045] 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.

[0046] 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 film of the present invention is preferably 35% by mass, more preferably 38% by mass, further preferably 40% by mass, particularly preferably 41% by mass, and most preferably 42% by mass.

[0047] 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.

[0048] 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.

[0049] (Molecular weight distribution)

[0050] 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 4.0, further preferably 4.5, and particularly preferably 5.0. The upper limit of Mw / Mn is preferably 30, more preferably 25, further preferably 23, particularly preferably 21, and most preferably 20.

[0051] 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.

[0052] 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.

[0053] (Method for preparing biaxially oriented polypropylene films)

[0054] 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.

[0055] Next, the manufacturing method of 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 can have layers with other functions laminated on at least one side. The laminated side can be one side or both sides. In this case, the resin composition of the other layer and the central layer can be the polypropylene resin composition described above. Alternatively, it can be different from the polypropylene resin composition described above. The number of laminated layers can be 1, 2, or 3 or more layers per side; from a manufacturing point of view, 1 or 2 layers are preferred. As a lamination method, co-extrusion based on a feed head method or a manifold method is preferred, for example. In particular, for the purpose of improving the processability of the biaxially oriented polypropylene film, a heat-sealable resin layer can be laminated within a range without reducing its properties. In addition, to impart printability, corona treatment can be applied to one side or both sides.

[0056] The following examples illustrate the use of a tenter frame for sequential biaxial stretching in the case of a single-layer structure.

[0057] 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.

[0058] Next, for the sheet, on the heated two pairs of 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.

[0059] 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.

[0060] After the width-direction stretching process, 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.

[0061] The biaxially oriented polypropylene film thus obtained can be wound up by a winding machine after corona discharge treatment on at least one side as needed.

[0062] The following is a detailed explanation of each process.

[0063] (Extrusion process)

[0064] 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.

[0065] 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 desired to improve the transparency of the film, it is preferable to perform cooling curing on a cooling roller at a temperature of 10 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.

[0066] 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.

[0067] (Length stretching process)

[0068] The lower limit of the length-direction stretching ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. Within this range, strength is easily improved, and film thickness unevenness is reduced. The upper limit of the length-direction stretching ratio is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. Within this range, width-direction stretching in the width-direction stretching process is easier to perform, improving productivity.

[0069] The lower limit of the length-direction stretching temperature is preferably Tm-40℃, more preferably Tm-37℃, and even more preferably Tm-35℃. 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.

[0070] It should be noted that for length stretching, more than three pairs of stretching rollers can be used, and the stretching can be performed in two or more stages.

[0071] (Preheating process)

[0072] Before the width-direction stretching process, the uniaxially stretched film after length-direction stretching must be heated in the range of Tm to Tm+25°C to soften the polypropylene resin composition. By setting Tm above, softening is advanced, making width-direction stretching easier. By setting Tm below Tm+25°C, orientation during transverse stretching is advanced, making it easier to exhibit rigidity. More preferably, Tm+2°C to Tm+22°C, and particularly preferably, Tm+3°C to Tm+20°C. Here, the highest temperature in the preheating process is used as the preheating temperature.

[0073] (Width-direction stretching process)

[0074] In the width-direction stretching process following the preheating process, the preferred method is as follows.

[0075] In the width-direction stretching process, the stretching is carried out in a range (early stage range) at a temperature above Tm-10℃ and below the preheating temperature. At this time, the beginning of the early stage range can be the moment when the preheating temperature is reached, or it can be the moment when the temperature drops below the preheating temperature after the preheating temperature is reached.

[0076] The lower limit of the temperature in the initial stage of the width-direction stretching process is preferably Tm-9℃, more preferably Tm-8℃, and even more preferably Tm-7℃. If the stretching temperature in the initial stage is within this range, uneven stretching is less likely to occur.

[0077] Next, the stretching is carried out in the later stage (the initial stage) at a temperature lower than that of the initial stage, and at a temperature above Tm-70℃ and below Tm-5℃.

[0078] The upper limit of the tensile temperature in the later stage is preferably Tm-8℃, more preferably Tm-10℃. If the tensile temperature in the later stage is within this range, the rigidity becomes easier to exhibit.

[0079] 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.

[0080] At the end of the later stage, i.e., just after reaching the final stretch ratio in the width direction, the film can be cooled. The cooling temperature at this time is preferably set below the temperature of the later stage 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.

[0081] The temperatures in both the early and late stages can be gradually reduced, either in stages or continuously. A gradual temperature reduction minimizes film breakage and reduces film thickness variation. It also reduces thermal shrinkage and film whitening, making it a preferred method.

[0082] Alternatively, the temperature at the end of the early stage of the stretching process in the width direction can be slowly reduced to the temperature at the beginning of the later stage, or it can be reduced in stages or in phases.

[0083] The lower limit of the stretching ratio at the end of the initial stage of the width-direction 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 initial stage is preferably 15 times, more preferably 14 times, and further preferably 13 times.

[0084] The lower limit of the final width-direction stretching ratio in the width-direction stretching process is preferably 5 times, more preferably 6 times, further preferably 7 times, and particularly preferably 8 times. If it is 5 times or more, it is easy to improve rigidity and reduce film thickness unevenness.

[0085] The upper limit of the width-direction stretch ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. If it is below 20 times, it is easier to reduce the heat shrinkage rate and make it less prone to breakage during stretching.

[0086] Thus, by using polypropylene resin with high stereoregularity, high melting point, and high crystallinity, and employing the aforementioned width-direction stretching process, even without drastically increasing the stretching ratio, the molecules of the polypropylene resin are highly aligned along the main orientation direction (equivalent to the width direction in the aforementioned width-direction stretching process). Therefore, the resulting biaxially oriented film has a very strong crystal orientation, making it easy to generate crystals with high melting points.

[0087] Furthermore, the orientation of the amorphous portions between the crystals also increases along the main orientation direction (equivalent to the width direction in the aforementioned width-direction stretching process). A large number of high-melting-point crystals exist around the amorphous portions. Therefore, at temperatures below the melting point of the crystals, the elongated polypropylene molecules in the amorphous portions are less likely to relax and easily maintain their taut state. Thus, the biaxially oriented film as a whole can maintain high rigidity even at high temperatures.

[0088] Furthermore, it should be noted that by employing this width-direction stretching process, the heat shrinkage rate at a high temperature of 150°C is also easily reduced. This is because a large number of high-melting-point crystals exist around the amorphous portion; therefore, at temperatures lower than the melting point of the crystals, the elongated polypropylene resin molecules in the amorphous portion are less prone to relaxation, and there is less entanglement between the molecules.

[0089] Furthermore, it is worth noting that increasing the low molecular weight component of polypropylene resin makes it easier to further improve the crystallinity of the film, and reduces the entanglement of the polypropylene resin molecular chains in the amorphous portion, thereby weakening the heat shrinkage stress and thus reducing the heat shrinkage rate. Considering that in the past, improving either strength or heat shrinkage rate tended to result in another property reduction, this can be considered revolutionary.

[0090] (Heat treatment process)

[0091] Biaxially stretched films can be heat-treated as needed to further reduce thermal shrinkage.

[0092] The upper limit of the heat treatment temperature is preferably Tm+10℃, more preferably Tm+7℃. By setting it below Tm+10℃, rigidity is easily manifested, the surface roughness of the film does not increase excessively, and the film is less prone to whitening.

[0093] The lower limit of the heat treatment temperature is preferably Tm-10℃, more preferably Tm-7℃. If it is below Tm-10℃, the heat shrinkage rate may sometimes be high.

[0094] By employing the aforementioned width-direction stretching process, even when heat treatment is performed at temperatures between Tm-10℃ and Tm+10℃, the highly oriented crystals generated during the stretching process are not easily melted, thereby further reducing the thermal shrinkage rate without reducing the rigidity of the resulting film.

[0095] 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 10%. If it is within this range, the film strength is less likely to decrease, and the film thickness variation is more likely to be smaller. More preferably, 8%; further preferably, 7%; even more preferably, 3%; particularly preferably, 2%; and most preferably, 0%.

[0096] (Thin film thickness)

[0097] 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 easier 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.

[0098] 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 slit 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.

[0099] (Thickness uniformity)

[0100] 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.

[0101] The measurement method is as follows. A 40 mm wide test piece is cut from a constant region where the film's physical properties are stable along the length of the film. The film thickness is continuously measured over a range of 20,000 mm using a film conveying device (model: A90172) manufactured by Micron Measuring Instruments Co., Ltd. and a continuous film 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.

[0102] Thickness uniformity (%) = [(maximum thickness - minimum thickness) / average thickness] × 100

[0103] (Thin film characteristics)

[0104] The biaxially oriented polypropylene film of the present invention is characterized by the following properties. Here, the "length direction" in the biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction in the film manufacturing process, and the "width direction" refers to the direction orthogonal to the flow direction in the aforementioned film manufacturing process. For polypropylene films where the flow direction is unclear in the film manufacturing process, wide-angle X-rays are incident in a direction perpendicular to the film 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".

[0105] (Half-width of diffraction peaks derived from oriented crystals)

[0106] 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 film surface of the biaxially oriented polypropylene film of the present invention, the upper limit of the half-width (Wh) of the diffraction peaks originating from the oriented crystal in the width direction of the film is 27°, preferably 26°, more preferably 25°, further preferably 24°, and particularly preferably 23°. If the half-width (Wh) is less than 27°, the rigidity of the film is easily improved. The lower limit of Wh is preferably 13°, more preferably 14°, and further preferably 15°.

[0107] (tanδ area)

[0108] The biaxially oriented polypropylene film of the present invention has a tanδ area obtained by taking the dielectric loss tangent (tanδ) obtained from the ratio of loss modulus (E”) to storage modulus (E’) measured by a dynamic viscoelasticity measuring device (DMA) (E” / E’), preferably 0.35, more preferably 0.32 or less, further preferably 0.3 or less, and particularly preferably 0.29 or less in the length direction. The tanδ area in the length direction is preferably 0.1 or more, more preferably 0.13 or more, further preferably 0.15 or more, and particularly preferably 0.16 or more.

[0109] The tanδ area in the width direction is 0.4 or less, more preferably 0.37, even more preferably 0.35, and particularly preferably 0.33. The tanδ area in the width direction is 0.2 or more, preferably 0.21 or more, more preferably 0.22 or more, and even more preferably 0.23 or more.

[0110] If the tanδ area obtained by DMA measurement is within this range, the strength of the biaxially oriented polypropylene film is significantly increased. Even if the film is thinned, it maintains stiffness and strength. Therefore, it can make a great contribution to the reduction of film volume.

[0111] As mentioned above, it is not easy to set the tanδ area obtained by DMA measurement in the length and width directions to a specific range. This property can be achieved through repeated experiments.

[0112] The biaxially oriented polypropylene film of the present invention has the following characteristics and a better structure.

[0113] (Young's modulus at 23℃)

[0114] The lower limit of the Young's modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 2.0 GPa, more preferably 2.1 GPa, further preferably 2.2 GPa, particularly preferably 2.3 GPa, and most preferably 2.4 GPa. When it is above 2.0 GPa, 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 Young's 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. When it is below 4.0 GPa, it is practically easy to manufacture, or the balance of characteristics in the longitudinal and width directions is easy to optimize.

[0115] The lower limit of the Young's 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 6.3 GPa, further preferably 6.5 GPa, and particularly preferably 6.7 GPa. At 6.0 GPa or higher, the rigidity is high, thus 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 Young's 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 practically easy to manufacture, or the balance of characteristics in the length and width directions is easy to optimize.

[0116] Young's modulus can be adjusted within a certain range by changing the stretching ratio, relaxation rate, or temperature during film formation.

[0117] (Young's modulus at 80℃)

[0118] The lower limit of the Young's modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 80°C is preferably 0.5 GPa, more preferably 0.7 GPa. When it is 0.5 GPa or higher, it becomes less likely to cause misalignment of the printing spacing when transferring printing ink at high temperatures. The upper limit of the Young's modulus in the longitudinal direction at 80°C is preferably 3.0 GPa, more preferably 2.5 GPa. When it is 3.0 GPa or higher, it is practically easy to manufacture.

[0119] The lower limit of Young's modulus in the width direction at 80°C is preferably 2.5 GPa, more preferably 2.8 GPa, and even more preferably 3.0 GPa. At 2.5 GPa or higher, it becomes less likely to cause misalignment of the printing spacing when transferring printing ink at high temperatures. The upper limit of Young's modulus in the width direction at 80°C is preferably 5.0 GPa, more preferably 4.7 GPa, and even more preferably 4.5 GPa. If it is below 5.0 GPa, it is practically easy to manufacture.

[0120] The Young's modulus at 80℃ can be adjusted within a certain range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0121] (Stress at 5% elongation at 23℃)

[0122] The lower limit of the stress (F5) of the biaxially oriented polypropylene film of the present invention at 5% elongation in the length direction at 23°C is 40 MPa, preferably 42 MPa, more preferably 43 MPa, further preferably 44 MPa, and particularly preferably 45 MPa. At 40 MPa or above, the rigidity is high, therefore, it is easy to maintain the bag shape when made into a packaging bag, and the film is less likely to deform during printing and other processing. The upper limit of F5 in the length direction is preferably 70 MPa, more preferably 65 MPa, further preferably 62 MPa, particularly preferably 61 MPa, and most preferably 60 MPa. At 70 MPa or below, it is practically easy to manufacture, or the length-width balance is easy to optimize.

[0123] The lower limit of the width direction F5 of the biaxially oriented polypropylene film of the present invention at 23°C is 160 MPa, preferably 165 MPa, more preferably 168 MPa, and even more preferably 170 MPa. At 160 MPa or higher, the rigidity is high, therefore, it is easy to maintain the bag shape when made into a packaging bag, and the film is less likely to deform during printing and other processing. The upper limit of the width direction F5 is preferably 250 MPa, more preferably 245 MPa, and even more preferably 240 MPa. If it is below 250 MPa, it is practically easy to manufacture, or the length-width balance is easy to optimize.

[0124] F5 can be adjusted within a certain range by changing the stretch ratio, relaxation ratio, or the temperature during film formation.

[0125] (Stress at 5% elongation at 80℃)

[0126] The lower limit of the stress (F5) of the biaxially oriented polypropylene film of the present invention at 5% elongation in the length direction at 80°C is 15 MPa, preferably 17 MPa, more preferably 19 MPa, and even more preferably 20 MPa. At 15 MPa or higher, the rigidity is high, therefore, it is easy to maintain the bag shape when made into a packaging bag, and the film is less prone to deformation during printing and other processing. The upper limit of F5 at 80°C in the length direction is preferably 40 MPa, more preferably 35 MPa, even more preferably 30 MPa, and particularly preferably 25 MPa. At 40 MPa or lower, it is practically easy to manufacture, or the length-width balance is easy to optimize.

[0127] The lower limit of the width direction F5 of the biaxially oriented polypropylene film of the present invention at 80°C is 75 MPa, preferably 80 MPa, more preferably 85 MPa, further preferably 90 MPa, and particularly preferably 95 MPa. At 75 MPa or higher, the rigidity is high, therefore, it is easy to maintain the bag shape when made into a packaging bag, and the film is less likely to deform during printing and other processing. The upper limit of the width direction F5 at 80°C is preferably 150 MPa, more preferably 140 MPa, and further preferably 130 MPa. If it is below 140 MPa, it is practically easy to manufacture, or the length-width balance is easy to optimize.

[0128] The 80℃F5 temperature range can be adjusted by changing the stretch ratio, relaxation rate, or the temperature during film formation.

[0129] (Heat shrinkage rate at 120℃)

[0130] 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 1.7%, and even more preferably 1.5%. If it is below 2.0%, it becomes less likely to cause misalignment of printing spacing when transferring printing ink. The upper limit of the transverse heat shrinkage rate at 120°C is preferably 5.0%, more preferably 4.5%, and even more preferably 4.0%. If it is below 5.0%, it becomes less likely to cause wrinkles during heat sealing.

[0131] If the thermal shrinkage rate in the length direction at 120℃ is less than the thermal shrinkage rate in the width direction at 120℃, it becomes less likely to cause misalignment of the printing spacing during ink transfer. The balance between the thermal shrinkage rate in the length and width directions at 120℃ can be achieved by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

[0132] (Heat shrinkage rate at 150℃)

[0133] The upper limit of the longitudinal heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 10%, more preferably 8.0%, and particularly preferably 7.0%. The upper limit of the transverse heat shrinkage rate at 150°C is preferably 30%, more preferably 25%, and particularly preferably 20%. If the longitudinal heat shrinkage rate is 10% or less and the transverse heat shrinkage rate is 30% or less, wrinkles are less likely to occur during heat sealing. In particular, if the longitudinal heat shrinkage rate at 150°C is 7.0% or less and the transverse heat shrinkage rate at 150°C is 20% or less, the strain at the opening when welding the clamp head is small is preferred. To reduce the heat shrinkage rate at 150°C, adjusting the stretch ratio, film forming temperature, relaxation rate, or setting the lower limit of the amount of components with a molecular weight of 100,000 or less when measuring the cumulative curve of the polypropylene resin constituting the film by gel permeation chromatography (GPC) to 35% by mass is effective.

[0134] (Refractive index)

[0135] 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, and even more preferably 1.4980. 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 even more preferably 1.5050. If it is 1.5100 or lower, the balance of the characteristics in the longitudinal and width directions of the film is easily excellent.

[0136] The lower limit of the refractive index (Ny) in the width direction of the biaxially oriented polypropylene film of the present invention is 1.5230, preferably 1.5235, and more preferably 1.5240. If it is 1.5230 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 even more 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.

[0137] 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, and even more preferably 1.4970. 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 even more preferably 1.5010. If it is 1.5020 or lower, the heat resistance of the film is easily improved.

[0138] The refractive index can be adjusted to a range by changing the stretching ratio, stretching temperature, and heat-fixing temperature.

[0139] (△Ny)

[0140] The lower limit of ΔNy for the biaxially oriented polypropylene film of the present invention is 0.0220, preferably 0.0225, more preferably 0.0228, and even more preferably 0.0230. If it is 0.0220 or higher, the rigidity of the film tends to increase. The upper limit of ΔNy, as a practical value, is preferably 0.0270, more preferably 0.0265, even more preferably 0.0262, and particularly preferably 0.0260. If it is below 0.0270, thickness unevenness tends to be better. ΔNy can be adjusted to a range by changing the film's stretch ratio, stretching temperature, and heat setting temperature.

[0141] △Ny is defined as the refractive indices along the length, width, and thickness directions of the thin 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 thin film in the length, width, and thickness directions.

[0142] △Ny=Ny-[(Nx+Nz) / 2]

[0143] (Surface orientation coefficient)

[0144] The lower limit of the planar orientation factor (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 good thickness uniformity. The upper limit of the planar orientation factor (ΔP) 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 tends to be excellent.

[0145] The face orientation factor (ΔP) can be adjusted within a certain range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0146] In addition, the orientation coefficient (ΔP) is calculated using the formula [(Nx+Ny) / 2]-Nz.

[0147] (X-ray orientation)

[0148] 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 0.85, more preferably 0.855, and even more preferably 0.861. By setting it to 0.85 or higher, rigidity is easily improved.

[0149] X-ray orientation degree = (180 - Wh) / 180

[0150] The upper limit of the X-ray orientation degree is preferably 0.928, more preferably 0.922, and even more preferably 0.917. By setting it to below 0.928, the film formation is easier and more stable.

[0151] (Haze)

[0152] 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 temperature of the cooling roller (CR), 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 the polypropylene resin component 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.

[0153] (Practical properties of thin films)

[0154] The practical properties of the biaxially oriented polypropylene film of the present invention will be described.

[0155] (Tensile breaking strength)

[0156] The lower limit of the tensile breaking strength in the longitudinal direction of the biaxially oriented polypropylene film of the present invention is preferably 90 MPa, more preferably 95 MPa, and even more preferably 100 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 is preferably 200 MPa, more preferably 190 MPa, and even more preferably 180 MPa. If it is below 200 MPa, the breakage of the film and the tearing of the packaging bag are easily reduced.

[0157] The lower limit of the tensile breaking strength in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 320 MPa, more preferably 340 MPa, and even more preferably 350 MPa. If it is 320 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 is preferably 500 MPa, more preferably 480 MPa, and even more preferably 470 MPa. If it is below 500 MPa, the breakage of the film and the tearing of the packaging bag are easily reduced.

[0158] The tensile breaking strength can be adjusted within a certain range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0159] (Elongation at break)

[0160] The lower limit of the elongation at break in the longitudinal direction of the biaxially oriented polypropylene film of the present invention is preferably 50%, more preferably 55%, and even more preferably 60%. If it is 50% or more, the breakage of the film and the tearing of the packaging bag are easily reduced. The upper limit of the elongation at break in the longitudinal direction is preferably 230%, more preferably 220%, and even more preferably 210%. If it is 230% or less, it becomes less likely to cause misalignment of the printing spacing when transferring printing ink, and the durability of the packaging bag is also easily improved.

[0161] The lower limit of the tensile elongation at break in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 10%, more preferably 15%, and even more preferably 17%. If it is 10% or more, the breakage of the film and the tearing of the packaging bag are easily reduced. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and even more preferably 50%. If it is 60% or less, it becomes less likely to cause misalignment of the printing spacing when transferring printing ink, and the durability of the packaging bag is also easily improved.

[0162] The elongation at break can be adjusted within a certain range by changing the stretching ratio, stretching temperature, and heat setting temperature.

[0163] (Stiffness / Softness)

[0164] The lower limit of the stiffness-softness in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 0.3 mN·cm, more preferably 0.33 mN·cm, and even more preferably 0.35 mN·cm. If it is 0.3 mN·cm or higher, thinner film walls can be achieved, or it is suitable for applications requiring rigidity. The lower limit of the stiffness-softness in the width direction is preferably 0.5 mN·cm, more preferably 0.55 mN·cm, and even more preferably 0.6 mN·cm. If it is 0.5 mN·cm or higher, thinner film walls can be achieved, or it is suitable for applications requiring rigidity.

[0165] (loop stiffness stress)

[0166] For the lower limit of the longitudinal ring stiffness stress S (mN) of the biaxially oriented polypropylene film at 23°C of the present invention, when the thickness of the biaxially oriented polypropylene film is set as t (μm), it is preferably 0.00020 × t. 3 More preferably 0.00025×t 3 Further optimization of 0.00030×t 3 0.00035×t is a particularly preferred value. 3 If it is 0.00020×t 3 The above methods make it easier to maintain the shape of the packaging.

[0167] The upper limit of the circumferential stiffness stress S (mN) in the longitudinal direction at 23℃ is preferably 0.00080 × t. 3 More preferably 0.00075×t 3 Further optimization of 0.00072×t 3 0.00070×t is a particularly preferred value. 3 If it is 0.00080×t 3 The following are actually easy to manufacture.

[0168] For the lower limit of the width-direction ring stiffness stress S (mN) of the biaxially oriented polypropylene film at 23°C of the present invention, when the thickness of the biaxially oriented polypropylene film is set as t (μm), it is preferably 0.0010 × t. 3 More preferably 0.0011×t 3 Further optimization of 0.0012×t 3 0.0013×t is a particularly preferred value. 3 If it is 0.0010×t 3 The above methods make it easier to maintain the shape of the packaging.

[0169] The upper limit of the width-direction ring stiffness stress S (mN) at 23℃ is preferably 0.0020 × t. 3 More preferably 0.0019×t 3 Further optimization of 0.0018×t 3 0.0017×t is a particularly preferred value. 3 If it is 0.0020×t 3 The following are actually easy to manufacture.

[0170] While ring stiffness stress is an indicator of the rigidity of a film, it also depends on the film thickness. The measurement method is as follows: Cut two strips of 110mm × 25.4mm each, with the length direction of the film as the long axis (ring direction) or the width direction of the film as the long axis (ring direction). Clamp these strips in a fixture. Prepare a measuring ring with one side of the film as the inner surface of the ring and another with the opposite side as the inner surface of the ring, with the long axis of the strip aligning with the length and width directions of the film. Mount the measuring ring with the long axis of the strip aligned with the length direction of the film onto the clamping head of a ring stiffness tester DA manufactured by Toyo Seiki Co., Ltd., perpendicular to the width direction. Remove the fixture, space the clamping heads 50mm apart, indent to a depth of 15mm, and compress at a speed of 3.3mm / s. Measure the ring stiffness stress.

[0171] The measurements were performed as follows: the ring stiffness stress and thickness of the film, with one side serving as the inner surface of the ring, were measured five times, followed by five measurements on the other side serving as the inner surface of the ring. Using the data from these ten measurements, the thickness (μm) of each test piece was plotted as a cube of its value on the horizontal axis, and the ring stiffness stress (mN) on the vertical axis. The slope 'a' was approximated by a straight line with an intercept of 0. The slope 'a' represents an inherent characteristic value of the film, independent of its thickness and the given stiffness. The slope 'a' was used as an evaluation value for stiffness. The same measurements were performed on the ring used for measuring the width direction of the film, with the major axis of the strip.

[0172] (Wrinkles during heat sealing)

[0173] To form bags for packaged food, the bag is filled with contents and heated to melt and weld 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, causing shrinkage and wrinkles. Fewer wrinkles are preferable 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.

[0174] (Misaligned printing spacing)

[0175] The basic structure of packaging films 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 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.

[0176] (Thin Film Processing)

[0177] 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.

[0178] Alternatively, 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 laminated as sealant films, thus providing heat-sealing properties. 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 films, adhesives applied by dry lamination or hot-melt lamination methods can be used.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] (Industry availability)

[0183] 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.

[0184] 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, and base films for transparent conductive films like ITO, as well as 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.

[0185] Example

[0186] 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.

[0187] (1) Melt flow rate

[0188] Melt flow rate (MFR) was determined according to JIS K 7210 at a temperature of 230°C and a load of 2.16 kgf.

[0189] (2) Meso-five-unit component ratio

[0190] 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). 13 The 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.

[0191] (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.

[0192] 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 high molecular weight side of the dissolution peak closest to the standard.

[0193] The GPC measurement conditions are as follows.

[0194] Device: HLC-8321PC / HT (manufactured by Tosoh Corporation)

[0195] Detector: RI

[0196] Solvent: 1,2,4-trichlorobenzene + butylated hydroxytoluene (0.05%)

[0197] Column: TSKgelguardcolumnHHR(30)HT(7.5mmI.D.×7.5cm)×1 piece + TSKgelGMHHR-H(20)HT(7.8mmI.D.×30cm)×3 pieces

[0198] Flow rate: 1.0 mL / min

[0199] Injection volume: 0.3 mL

[0200] Measurement temperature: 140℃

[0201] 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.

[0202] Number-average molecular weight: Mn=Σ(N i ·M i ) / ΣN i

[0203] Mass-average molecular weight: Mw=Σ(N i ·M i 2 ) / Σ(N i ·M i )

[0204] Here, the molecular weight distribution can be obtained from Mw / Mn.

[0205] 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.

[0206] (4) Crystallization temperature (Tc), melting temperature (Tm)

[0207] 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).

[0208] (5) Film thickness

[0209] The thickness of the film was measured using a Millitron 1202D manufactured by Seiko EM.

[0210] (6) Haze

[0211] The test was performed at 23°C using NDH5000 manufactured by Nippon Denshoku Kogyo Co., Ltd., in accordance with JIS K7105.

[0212] (7) X-ray half-width and orientation

[0213] The measurements were performed using a transmission method with an X-ray diffraction apparatus (Rigaku Co., Ltd., RINT2500). The wavelength was... X-rays were emitted using a scintillation counter. A sample was prepared by overlapping thin films to achieve a thickness of 500 μm. The sample stage was placed at the diffraction peak position (diffraction angle 2θ = 14.1°) on the (110) plane of an α-type polypropylene crystal, with the thickness direction of the film as the axis. The sample was rotated 360° to obtain the azimuth dependence of the diffraction intensity on the (110) plane. Based on this azimuth dependence, the half-width Wh of the diffraction peak originating from the oriented crystal was calculated in the width direction of the film.

[0214] In addition, the X-ray orientation degree is calculated using Wh according to the following formula.

[0215] X-ray orientation degree = (180 - Wh) / 180

[0216] (8) tanδ area

[0217] The dynamic viscoelasticity was measured as follows: Using an RSA-G2 instrument manufactured by TA Instruments Japan, Inc., a 4 mm wide thin film sample was mounted in a 10 mm clamping space. Under a load of 10 g and a nitrogen atmosphere, the temperature was increased from -60 °C to 160 °C at a rate of 5 °C / min, and the dynamic viscoelasticity was measured at a frequency of 10 Hz. The area of ​​the dielectric loss tangent (tanδ) was obtained from the ratio of the loss modulus (E”) to the storage modulus (E’) (loss modulus / storage modulus).

[0218] (9) Refractive index, ΔNy, plane orientation coefficient

[0219] The Abbe refractometer, manufactured by Atago Co., Ltd., was used for measurements at a wavelength of 589.3 nm and a temperature of 23 °C. The refractive indices of the thin film along its length and width directions were designated as Nx and Ny, respectively, and the refractive index along its thickness direction was designated as Nz. ΔNy was calculated using Nx, Ny, and Nz, and by the formula Ny - [(Nx + Nz) / 2]. Furthermore, the planar orientation coefficient (ΔP) was calculated using the formula [(Nx + Ny) / 2] - Nz.

[0220] (10) Tensile test

[0221] According to JIS K 7127, the tensile strength of the film in the length and width directions was determined at 23°C. The sample was cut from the film 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 Young's modulus was determined from the slope of the linear portion at the initial elongation. Additionally, the stress at 5% elongation (F5) was calculated. The tensile strength at break and the elongation at break were set as the strength and elongation at the moment of sample fracture, respectively.

[0222] The Young's modulus and F5 at 80℃ were determined by measuring in a constant temperature bath at 80℃. It should be noted that the measurement was performed as follows: the clamp was installed in the constant temperature bath pre-set to 80℃, the sample was mounted until the measurement was performed, and then held for 1 minute.

[0223] (11) Thermal shrinkage rate

[0224] 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 shrinkage to the original length.

[0225] (12) Stiffness and sag

[0226] The following steps were performed according to the JlS L 1096B method (Slide method): Prepare a 20mm × 150mm test piece. After aligning the main body of the testing machine with the upper surface of the moving stage, place the test piece on the stage of the testing machine with a 50mm protrusion and add weights. Then, gently rotate the handle to lower the test stage and measure the sag (δ) at the moment the free end of the test piece leaves the test stage. Using this sag δ, the film thickness, the test piece size, and the film density of 0.91 g / cm³, the final result is determined. 3 The stiffness (Br) can be calculated using the following formula.

[0227] Br=WL 4 / 8δ

[0228] Br: Stiffness / softness (mN·cm)

[0229] W: Weight per unit area of ​​the test piece (mN / cm²) 2 )

[0230] L: Length of the test piece (cm)

[0231] δ: Sag (cm)

[0232] (13) Ring stiffness stress

[0233] Ten strips, each measuring 110 mm × 25.4 mm, were cut from the film with either the length direction of the strip as its long axis (ring direction) or the width direction of the film as its long axis (ring direction). These strips were clamped in a fixture, and a measuring ring was prepared with one side of the film as the inner surface of the ring and the opposite side as the inner surface of the ring, with the long axis of the strip aligning with the length and width directions of the film. The measuring ring with the long axis of the strip aligned with the length direction of the film was mounted perpendicularly to the width direction in the clamping head of a ring stiffness tester DA manufactured by Toyo Seiki Co., Ltd. The fixture was removed, and the clamping head was spaced 50 mm apart, the indentation depth was 15 mm, and the compression speed was 3.3 mm / s. The ring stiffness stress was measured. The measurements were performed as follows: the ring stiffness stress and thickness of the film with one side as the inner surface of the ring were measured five times, and then the same measurement was performed five times with the other side as the inner surface of the ring. Using data from a total of 10 measurements, the thickness (μm) of each test piece was plotted as a cube power on the horizontal axis, and its ring stiffness stress (mN) was plotted on the vertical axis. The slope 'a' was approximated by a straight line with an intercept of 0. The slope 'a' was used as an evaluation value for stiffness. The ring used for measuring the width direction of the film, with its major axis forming the strip, was also measured in the same manner.

[0234] (Example 1)

[0235] As the polypropylene resin, a propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., Sumitomo Noblen FLX80E4) with an MFR of 7.5 g / 10 min, Tc of 116.2 °C, and Tm of 162.5 °C was used. 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 along the length direction using two pairs of rollers at 145 °C. The ends were then clamped and fed into a hot air oven, preheated to 170 °C, and then stretched 6 times its original length along the width direction as the first stage at 160 °C. Next, it was stretched 1.36 times its original length along the width direction as the second stage at 145 °C, for a total stretch of 8.2 times. Immediately after stretching in the width direction, it was cooled at 100 °C while fixed in the clamps, and then heat-set at 163 °C. The resulting film had a thickness of 18.7 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 high rigidity and low thermal shrinkage at high temperatures.

[0236] (Example 2)

[0237] The polypropylene resin used was a blend of 80 parts by weight of PP-1 and 20 parts by weight of PP-2 (manufactured by Sumitomo Chemical Co., Ltd., EL80F5), a propylene homopolymer with an MFR of 11 g / 10 min, [mmmm] of 98.8%, Tc of 116.5 °C, and Tm of 161.5 °C. The stretching temperature in the length direction was set to 142 °C, the first-stage stretching temperature in the width direction was set to 162 °C, and the heat-setting temperature was set to 165 °C; otherwise, the operation was the same as in Example 1. The resulting film had a thickness of 21.3 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, and a film with high rigidity and low heat shrinkage at high temperatures was obtained.

[0238] (Example 3)

[0239] A 3% relaxation was performed during heat curing, otherwise the procedure was the same as in Example 2. The resulting film had a thickness of 21.1 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, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[0240] (Example 4)

[0241] The stretching temperature in the length direction was 145°C, and the cooling temperature immediately after stretching in the width direction was 140°C. Otherwise, the process was the same as in Example 2. The resulting film had a thickness of 18.9 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, and a film with high rigidity was obtained.

[0242] (Example 5)

[0243] After stretching in the width direction, the film was directly fixed to a fixture without cooling and heat-cured at 165°C. Otherwise, the process was the same as in Example 2. The resulting film had a thickness of 19.5 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 high rigidity and low thermal shrinkage at high temperatures.

[0244] (Example 6)

[0245] The stretching temperature for the second stage in the width direction was set to 155°C, and otherwise performed in the same manner as in Example 2. The resulting film had a thickness of 20.3 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 high rigidity and low thermal shrinkage at high temperatures.

[0246] (Example 7)

[0247] The length-direction stretching ratio was 4.8 times, otherwise the process was the same as in Example 2. The resulting film thickness was 19.1 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, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[0248] (Example 8)

[0249] In the width-direction stretching, the stretching ratio was 6.6 times in the first stage and 1.5 times in the second stage, resulting in a total stretch of 9.9 times. Otherwise, the process was the same as in Example 2. The resulting film had a thickness of 20.1 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, yielding a film with high rigidity and low thermal shrinkage at high temperatures.

[0250] (Comparative Example 1)

[0251] PP-1 was used as the polypropylene resin. It 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. Subsequently, it was stretched 4.5 times its length at 143°C, with a preheating temperature of 170°C and a stretching temperature of 158°C in the width direction of the tenter frame, for a stretch of 8.2 times. It was then heat-fixed at 168°C. The resulting film had a thickness of 18.6 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-forming conditions, and Table 3 shows the physical properties. Its physical properties, as shown in Table 3, exhibit low rigidity.

[0252] (Comparative Example 2)

[0253] The polypropylene resin used was a blend of 80 parts by weight of PP-1 and 20 parts by weight of PP-2, otherwise the process was the same as in Comparative Example 1. The thickness of the resulting film was 20.0 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-forming conditions, and Table 3 shows the physical properties. Its physical properties, as shown in Table 3, exhibit low rigidity.

[0254] (Comparative Example 3)

[0255] As the polypropylene resin, PP-3 (manufactured by Nippon Polypropylene Co., Ltd., FL203D), with an MFR of 3 g / 10 min, Tc of 117.2 °C, and Tm of 160.6 °C, was used. It was extruded as a sheet 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. Subsequently, it was stretched 4.5 times along its length at 135 °C. During the width stretching in a tenter frame, the preheating temperature was 166 °C, the first stretching stage temperature was 155 °C, the second stretching stage temperature was 139 °C, the cooling temperature was 95 °C, and the heat setting temperature was 158 °C. The resulting film thickness was 19.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-forming conditions, and Table 3 shows the physical properties. Its physical properties, as shown in Table 3, exhibit high heat shrinkage at high temperatures.

[0256] (Comparative Example 4)

[0257] As the polypropylene raw material, PP-4 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) with MFR = 2.7 g / 10 min, Tc = 114.7 °C, and Tm = 163.0 °C was used. It was extruded as a sheet 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. Subsequently, it was stretched 4.5 times along its length at 145 °C. During the width stretching in the tenter frame, the preheating temperature was 170 °C, the first stretching stage temperature was 160 °C, the second stretching stage temperature was 145 °C, the cooling temperature was 100 °C, and the heat setting temperature was 163 °C. The resulting film thickness was 21.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-forming conditions, and Table 3 shows the physical properties. Its physical properties, as shown in Table 3, exhibit high heat shrinkage at high temperatures.

[0258] (Comparative Example 5)

[0259] PP-4 was used as the polypropylene resin. 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. Afterward, it was stretched 5.8 times its original length at 130°C, then heated in a tenter frame at a preheating temperature of 167°C. It was then stretched 8.6 times its original length in the width direction at a stretching temperature of 161°C. Following this, it was heat-cured at 130°C with a 10% relaxation, and then heat-cured again at 140°C in a second stage. The resulting film had a thickness of 13.4 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-forming conditions, and Table 3 shows the physical properties. As shown in Table 3, the film exhibits high heat shrinkage at high temperatures.

[0260] [Table 1]

[0261]

[0262] [Table 2]

[0263]

[0264] [Table 3]

[0265]

Claims

1. A biaxially oriented polypropylene film, wherein, in the azimuth dependence of the α-type crystal (110) plane of polypropylene measured by wide-angle X-ray diffraction, the half-width of the peak originating from the oriented crystal in the width direction is 25° or less, and the tanδ area in the width direction obtained by the ratio of loss modulus (E”) to storage modulus (E” / E’) obtained by dynamic viscoelasticity measurement is 0.2 or more and 0.4 or less. The biaxially oriented polypropylene film has a Young's modulus in the width direction of 6.0 GPa or higher at 23°C. in, In biaxially oriented polypropylene films, the "length direction" refers to the direction corresponding to the flow direction in the film manufacturing process, and the "width direction" refers to the direction orthogonal to the flow direction in the film manufacturing process. For polypropylene films where the flow direction in the film manufacturing process is unclear, wide-angle X-rays are incident in a direction perpendicular to the film 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 largest diffraction intensity in the obtained diffraction intensity distribution is taken as the "length direction", and the direction orthogonal to it is taken as the "width direction".

2. The biaxially oriented polypropylene film according to claim 1, wherein, The biaxially oriented polypropylene film has a heat shrinkage rate of less than 2.0% in the length direction and less than 5.0% in the width direction at 120°C, with the length direction heat shrinkage rate at 120°C being less than the width direction heat shrinkage rate at 120°C. The 120℃ heat shrinkage rate is determined according to JIS Z 1712 by the following method: the film is cut into 20mm wide and 200mm long sections along the length and width directions, suspended in a 120℃ hot air oven, heated for 5 minutes, and the length after heating is measured. The heat shrinkage rate is calculated as the ratio of the length that has shrunk relative to the original length.

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The biaxially oriented polypropylene film has a refractive index Ny of 1.5230 or higher and a ΔNy of 0.0220 or higher in the width direction. The ΔNy is calculated using the following formula, with the refractive indices along the length, width, and thickness of the thin film set as Nx, Ny, and Nz, respectively. △Ny=Ny-[(Nx+Nz) / 2] The refractive index was obtained by measuring it using an Abbe refractometer at a wavelength of 589.3 nm and a temperature of 23 °C.

4. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The haze of the biaxially oriented polypropylene film, measured at 23°C according to JIS K7105, is below 5.0%.

5. 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.

6. 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.

7. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The polypropylene resin constituting the biaxially oriented polypropylene film has a melt flow rate of 4.0 g / 10 min or higher, as determined by JIS K 7210 at a temperature of 230°C and a load of 2.16 kgf.

8. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The amount of polypropylene resin constituting the biaxially oriented polypropylene film having a molecular weight of less than 100,000 as determined by gel permeation chromatography is 35% or more by mass.

9. The biaxially oriented polypropylene film according to claim 1 or 2, wherein, The biaxially oriented polypropylene film has an X-ray orientation degree of 0.85 or higher. The X-ray orientation degree is obtained by the following formula: X-ray orientation degree = (180 - Wh) / 180 Wherein, Wh is the half-width of the diffraction peak originating from the oriented crystal in the width direction of the film, in the azimuth dependence of the scattering peak of the polypropylene α-type crystal (110) obtained in wide-angle X-ray measurement perpendicular to the film surface of the biaxially oriented polypropylene film.

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