JP7405099B2 - Method for manufacturing biaxially oriented polypropylene film - Google Patents

Description

The present invention relates to a method for producing a biaxially oriented polypropylene film having excellent rigidity and heat resistance. Specifically, the present invention relates to a method for producing a biaxially oriented polypropylene film that can be suitably used for packaging bags because it easily maintains the shape of the bag when it is made into a packaging bag and has fewer wrinkles in the sealed portion when heat-sealed.

Biaxially oriented polypropylene films are used for packaging and industrial purposes because they are moisture-proof and have the necessary rigidity and heat resistance. In recent years, as the applications for which they are used have expanded, higher performance has been required, and in particular, improvements in rigidity are expected. Furthermore, due to environmental considerations, it is also required to maintain strength even when the film is reduced in volume (thinner film thickness), and to this end, it is essential to significantly improve rigidity. It is known that improving the catalyst and process technology during polymerization of polypropylene resin can improve the crystallinity and melting point of the polypropylene resin as a means of improving rigidity, but despite these improvements, Until now, there has been no biaxially oriented polypropylene film with sufficient stiffness.

In the manufacturing process of biaxially oriented polypropylene film, after stretching in the width direction, the first stage of heat treatment is performed while relaxing the film at a temperature below the temperature during width direction stretching, and the second stage is heat treated at the temperature of the first stage to the width direction stretching temperature. (for example, refer to Reference Document 1), and a method to further stretch in the longitudinal direction after stretching in the width direction (for example, refer to Reference Document 2) have been proposed. However, although the film described in Patent Document 2 has excellent rigidity, wrinkles tend to occur in the sealed portion after heat sealing, and the film has poor heat resistance. Further, the orientation of the film described in Patent Document 1 is low, and the rigidity is not sufficient.

WO2016/182003 International Publication Japanese Patent Application Publication No. 2013-177645

An object of the present invention is to solve the above-mentioned problems. That is, the present invention relates to a biaxially oriented polypropylene film that has excellent film rigidity, and further relates to a biaxially oriented polypropylene film that has excellent film rigidity and heat resistance at temperatures as high as 150°C. Specifically, it is an object of the present invention to provide a method for producing a biaxially oriented polypropylene film that easily maintains the bag shape when used as a packaging bag and that has fewer wrinkles in and around the sealed portion when heat-sealed.

As a result of intensive studies by the present inventors to achieve this objective, the following manufacturing method has been used to produce a biaxially oriented polypropylene film with excellent film rigidity, and further with excellent film rigidity and heat resistance at temperatures as high as 150°C. It has been found that biaxially oriented polypropylene films can be obtained.
That is, the present invention comprises a step of extruding a polypropylene resin composition containing a polypropylene resin having a mesopentad fraction of 97.0% or more to obtain an unstretched sheet, a step of stretching the unstretched sheet in the longitudinal direction, and a longitudinally stretched film. A preheating step of heating to a preheating temperature in the range of Tm to Tm + 25°C, a step of stretching the preheated longitudinally stretched film in the width direction at a temperature of Tm - 10°C or higher and below the preheating temperature, preheating at Tm - 10°C or higher. A biaxially oriented polypropylene film comprising, in order, a step of stretching in the width direction at a temperature below Tm-70°C and a temperature of Tm-5°C or less, which is lower than the temperature of the step of stretching in the width direction at a temperature equal to or lower than that temperature, and a heat treatment step. This is a manufacturing method.

In this case, the step of stretching in the width direction at a temperature lower than the above-mentioned step of stretching in the width direction at a temperature of Tm-10°C or higher and lower than the preheating temperature, and at a temperature of Tm-70°C or higher and Tm-5°C or lower. During the heat treatment step, the width is lower than the temperature of the step of stretching in the width direction at a temperature of Tm-10°C or higher and lower than the preheating temperature, and at a temperature of Tm-70°C or higher and Tm-5°C or lower. It is preferable to include a step of lowering the temperature to a temperature lower than that of the step of stretching in the direction and lower than Tm-80°C to Tm-15°C.

Further, in this case, it is preferable that 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.

Furthermore, in this case, it is preferable that the polypropylene resin constituting the biaxially oriented polypropylene film has a melt flow rate of 4.0 g/10 minutes or more.

Furthermore, in this case, it is preferable that the amount of components having a molecular weight of 100,000 or less in the polypropylene resin constituting the biaxially oriented polypropylene film is 35% by mass or more.

By applying the method for producing a biaxially oriented polypropylene film of the present invention, the biaxially oriented polypropylene film can be suitably used for packaging bags because it has high rigidity and easily maintains the bag shape when made into a packaging bag. can be obtained. Furthermore, it has high rigidity and excellent heat resistance at temperatures as high as 150°C, so it is easy to maintain the shape of the bag when used as a packaging bag, and there are few wrinkles in the sealed area when heat-sealed, so it is suitable for use in packaging bags. A biaxially oriented polypropylene film can be obtained.
In addition, the biaxially oriented polypropylene film has excellent rigidity, and can maintain its strength even when the thickness of the film is reduced, and can also be suitably used for applications that require higher rigidity.

Hereinafter, the method for producing a biaxially oriented polypropylene film of the present invention will be explained in more detail.

The biaxially oriented polypropylene film obtained by the present invention is made of a polypropylene resin composition containing polypropylene resin as a main component. The term "main component" means that the proportion of the polypropylene resin in the polypropylene resin composition is 90% by mass or more, more preferably 93% by mass or more, still more preferably 95% by mass or more, particularly preferably is 97% by mass or more.

(Polypropylene resin)
As the polypropylene resin used in the present invention, a polypropylene homopolymer or a copolymer with ethylene and/or an α-olefin having 4 or more carbon atoms can be used. A propylene homopolymer that does not substantially contain ethylene and/or an α-olefin having 4 or more carbon atoms is preferable, and even when it contains ethylene and/or an α-olefin component having 4 or more carbon atoms, ethylene and/or The amount of the α-olefin component having 4 or more carbon atoms is preferably 1 mol % or less. The upper limit of the component amount is more preferably 0.5 mol%, still more preferably 0.3 mol%, and particularly preferably 0.1 mol%. Within the above range, crystallinity tends to improve. Examples of the α-olefin component having 4 or more carbon atoms constituting such a copolymer include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, and 4-methylpene. Examples include thene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. As the polypropylene resin, two or more different polypropylene homopolymers, a copolymer with ethylene and/or an α-olefin having 4 or more carbon atoms, or a mixture thereof can be used.

(stereoregularity)
The mesopentad fraction ([mmmm]%), which is an index of stereoregularity of the polypropylene resin used in the present invention, is preferably within the range of 97.0 to 99.9%, and 97.5 to 99.7%. %, even more preferably 98.0 to 99.5%, particularly preferably 98.5 to 99.3%.
When it is 97.0% or more, the crystallinity of the polypropylene resin increases, the melting point, crystallinity, and crystal orientation of the crystal in the film improve, and rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, it is easy to reduce costs in terms of polypropylene production, and it becomes difficult to break during film formation. More preferably, it is 99.5% or less. The mesopentad fraction is measured by nuclear magnetic resonance method (so-called NMR method).
In order to keep the mesopentad fraction of the polypropylene resin within the above range, it is necessary to wash the obtained polypropylene resin powder with a solvent such as n-heptane, select a catalyst and/or co-catalyst, and adjust the polypropylene resin composition. A method in which components are selected appropriately is preferably employed.

(melting temperature)
The lower limit of the melting temperature (Tm) measured by DSC of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is preferably 160°C, more preferably 161°C, and even more preferably 162°C. , even more preferably 163°C. When Tm is 160°C or higher, rigidity and heat resistance at high temperatures can be easily obtained.
The upper limit of Tm is preferably 170°C, more preferably 169°C, still more preferably 168°C, even more preferably 167°C, particularly preferably 166°C. When Tm is 170° C. or less, it is easy to suppress cost increases in polypropylene production, and it becomes difficult to break during film formation. By blending a crystal nucleating agent into the above-mentioned polypropylene resin, the melting temperature can be further increased.
Tm is 1 to 10 mg of sample packed in an aluminum pan, set in a differential scanning calorimeter (DSC), melted at 230°C for 5 minutes in a nitrogen atmosphere, and heated to 30°C at a scanning speed of -10°C/min. This is the main peak temperature of the endothermic peak associated with melting, which is observed when the temperature is lowered, held for 5 minutes, and then raised at a scanning rate of 10° C./min.

(crystallization temperature)
The lower limit of the crystallization temperature (Tc) measured by DSC of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is 105°C, preferably 108°C, and more preferably 110°C. When Tc is 105° C. or higher, crystallization tends to proceed during the width direction stretching and subsequent cooling process, and rigidity and heat resistance at high temperatures can be easily obtained.
The upper limit of Tc is preferably 135°C, more preferably 133°C, even more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. It is. If Tc is 135° C. or less, it will be difficult to increase the cost in terms of polypropylene production, and it will be difficult to break during film formation.
Tc is observed when 1 to 10 mg of a sample is packed in an aluminum pan, set in a DSC, melted at 230°C for 5 minutes under a nitrogen atmosphere, and lowered to 30°C at a scanning speed of -10°C/min. This is the main peak temperature of the exothermic peak.
By blending a crystal nucleating agent with the above-mentioned polypropylene resin, the crystallization temperature can be further increased.

(melt flow rate)
The melt flow rate (MFR) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is 4.0 when measured according to condition M (230°C, 2.16 kgf) of JIS K7210 (1995). ~30 g/10 minutes is preferred, 4.5 ~ 25 g/10 minutes is more preferred, 4.8 ~ 22 g/10 minutes is even more preferred, and 5.0 ~ 20 g/10 minutes is preferred. Particularly preferred, and most preferred is 6.0 to 20 g/10 minutes.
When the melt flow rate (MFR) of the polypropylene resin is 4.0 g/10 minutes or more, it is easy to obtain a biaxially oriented polypropylene film with low heat shrinkage.
Moreover, when the melt flow rate (MFR) of the polypropylene resin is 30 g/10 minutes or less, it is easy to maintain the film formability of the film.

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 minutes, more preferably 5.5 g/10 minutes. More preferably, it is 6.0 g/10 minutes, particularly preferably 6.3 g/10 minutes, and most preferably 6.5 g/10 minutes.
If the melt flow rate (MFR) of the polypropylene resin is 5.0 g/10 minutes or more, the amount of low molecular weight components of the polypropylene resin constituting the film will increase, so the widthwise stretching step in the film forming process described later will be difficult. By adopting this method, the oriented crystallization of the polypropylene resin is further promoted, and the degree of crystallinity in the film is more likely to increase. It is easier to improve your sexuality.
In order to keep the melt flow rate (MFR) of the polypropylene resin within the above range, a method of controlling the average molecular weight and molecular weight distribution of the polypropylene resin is preferably adopted.

That is, the lower limit of the amount of components having a molecular weight of 100,000 or less in the GPC integration curve of the polypropylene resin constituting the film of the present invention is preferably 35% by mass, more preferably 38% by mass, and even more preferably 40% by mass. It is particularly preferably 41% by weight, most preferably 42% by weight.
The upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components having a molecular weight of 100,000 or less in the GPC integration curve is 65% by mass or less, the film strength is unlikely to decrease.
At this time, if high molecular weight components and long chain branched components with long relaxation times are included, it becomes easier to adjust the amount of components with a molecular weight of 100,000 or less contained in the polypropylene resin without significantly changing the overall viscosity. It is easy to improve film formability without significantly affecting heat shrinkage and heat shrinkage.

(molecular weight distribution)
In the polypropylene resin used in the present invention, the lower limit of mass average molecular weight (Mw)/number average molecular weight (Mn), which is an index of the breadth of molecular weight distribution, is preferably 3.5, more preferably 4.0. , more preferably 4.5, particularly preferably 5.0. The upper limit of Mw/Mn is preferably 30, more preferably 25, still more preferably 23, particularly preferably 21, and most preferably 20.
Mw/Mn can be obtained using gel permeation chromatography (GPC). When Mw/Mn is within the above range, it is easy to increase the amount of components having a molecular weight of 100,000 or less.

The molecular weight distribution of polypropylene resin can be determined by polymerizing components with different molecular weights in multiple stages in a series of plants, by blending components with different molecular weights off-line in a kneader, or by blending catalysts with different performances. It can be adjusted by using a catalyst that can realize a desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC has a single peak in a GPC chart with the logarithm (logM) of the molecular weight (M) on the horizontal axis and the differential distribution value (weight fraction per logM) on the vertical axis. The molecular weight distribution may be gentle or may have multiple peaks or shoulders.

(Method for forming biaxially oriented polypropylene film)
The method for producing a biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made of a polypropylene resin composition containing the above-mentioned polypropylene resin as a main component and biaxially stretching it. Biaxial stretching can be achieved by simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential tenter biaxial stretching. It is preferable to employ an axial stretching method. In particular, it is preferable to stretch in the longitudinal direction and then in the width direction, but a method in which the film is stretched in the width direction and then in the longitudinal direction may also be used.

Next, a method for producing a biaxially oriented polypropylene film of the present invention will be described below, but the method is not necessarily limited thereto. Note that the biaxially oriented polypropylene film obtained by the present invention may have a layer having another function laminated on at least one side. The layers may be laminated on one side or both sides. In that case, the above-mentioned polypropylene resin composition may be used as the resin composition for the other layer or the center layer. Moreover, it may be different from the above-mentioned polypropylene resin composition. The number of layers to be laminated on one side may be one, two, three or more layers, but from the viewpoint of manufacturing, one or two layers is preferable. As a method of lamination, coextrusion using a feed block method or a multi-manifold method, for example, is preferable. In particular, for the purpose of improving the processability of the biaxially oriented polypropylene film, a resin layer having heat-sealing properties can be laminated within a range that does not deteriorate the properties. Further, in order to impart printability, corona treatment can be applied to one or both sides.

In the following, a case will be described in which a tenter sequential biaxial stretching method is adopted as an example of a single layer.
First, a resin composition containing a polypropylene resin is heated and melted using a single-screw or twin-screw extruder, extruded into a sheet from a T-die, and ground on a cooling roll to be cooled and solidified. For the purpose of promoting solidification, it is preferable to further cool the sheet cooled with a cooling roll by immersing it in a water tank or the like.

Next, the sheet is stretched in the longitudinal direction by two pairs of heated stretching rolls by increasing the number of revolutions of the rear stretching roll to obtain a uniaxially stretched film.

Subsequently, after preheating the uniaxially stretched film, it is stretched in the width direction at a specific temperature while gripping the ends of the film using a tenter-type stretching machine to obtain a biaxially stretched film. This width direction stretching step will be described in detail later.

After the width direction stretching step is completed, the biaxially stretched film is heat-treated at a specific temperature to obtain a biaxially oriented film. In the heat treatment step, the film may be relaxed in the width direction.

The biaxially oriented polypropylene film thus obtained can be subjected to, for example, a corona discharge treatment on at least one side, if necessary, and then wound up with a winder to obtain a film roll.

Each process will be explained in detail below.
(Extrusion process)
First, a polypropylene resin composition containing polypropylene resin as a main component is heated and melted in a range of 200°C to 300°C using a single-screw or twin-screw extruder, and the sheet-shaped molten polypropylene resin composition that comes out from a T-die is extruded. , and cooled and solidified by contacting with a metal cooling roll. It is preferable that the obtained unstretched sheet is further placed in a water tank.
The temperature of the cooling roll or the cooling roll and the water bath is preferably in the range of 10°C to Tc. If you want to increase the transparency of the film, solidify by cooling with a cooling roll at a temperature in the range of 10 to 50°C. is preferable. When the cooling temperature is 50°C or lower, the transparency of the unstretched sheet tends to increase, and the cooling temperature is preferably 40°C or lower, more preferably 30°C or lower. In order to increase the degree of crystal orientation after sequential biaxial stretching, it may be preferable to set the cooling temperature to 40°C or higher, but as mentioned above, a propylene homopolymer with a mesopendat fraction of 97.0% or higher is used. In this case, it is preferable to set the cooling temperature to 40° C. or lower in order to facilitate the stretching in the next step and to reduce thickness unevenness, and it is more preferable to set the cooling temperature to 30° C. or lower.
The thickness of the unstretched sheet is preferably 3,500 μm or less in terms of cooling efficiency, more preferably 3,000 μm or less, and can be adjusted as appropriate depending on the film thickness after successive biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition, the lip width of the T-die, etc.

(Longitudinal stretching process)
The lower limit of the longitudinal stretching ratio is preferably 3 times, more preferably 3.5 times, particularly preferably 3.8 times. Within the above range, strength can be easily increased and film thickness unevenness can be reduced. The upper limit of the longitudinal stretching ratio is preferably 8 times, more preferably 7.5 times, particularly preferably 7 times. Within the above range, it is easy to stretch in the width direction in the width direction stretching step, and productivity is improved.
The lower limit of the longitudinal stretching temperature is preferably Tm-40°C, more preferably Tm-37°C, and even more preferably Tm-35°C. Within the above range, subsequent stretching in the width direction becomes easy and thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, and still more preferably Tm-12°C. Within the above range, the thermal shrinkage rate can be easily reduced, and the quality is less likely to be degraded due to difficulty in stretching by being passed through a stretching roll or increased surface roughness.
Note that the longitudinal direction stretching may be performed in multiple stages of two or more stages using three or more pairs of stretching rolls.

(Preheating process)
Before the width direction stretching step, it is necessary to heat the uniaxially stretched film after longitudinal direction stretching in the range of Tm to Tm+25°C to soften the polypropylene resin composition. When the temperature is higher than Tm, softening progresses and stretching in the width direction becomes easier. By controlling the temperature to be Tm+25° C. or lower, orientation during lateral stretching progresses, making it easier to develop rigidity. More preferably Tm+2 to Tm+22°C, particularly preferably Tm+3 to Tm+20°C. Here, the maximum temperature in the preheating step is defined as the preheating temperature.

(Width direction stretching process)
In the width direction stretching step after the preheating step, a preferred method is as follows.

In the width direction stretching step, a section (early section) is provided in which the film is stretched at a temperature of Tm-10° C. or higher and lower than the preheating temperature. At this time, the start of the first period may be at the time when the preheating temperature is reached, or at the time when the temperature is lowered after reaching the preheating temperature to reach a temperature lower than the preheating temperature.
The lower limit of the temperature in the first section in the width direction stretching step is preferably Tm-9°C, more preferably Tm-8°C, and still more preferably Tm-7°C. When the stretching temperature in the first period is within this range, stretching unevenness is less likely to occur.
Following the first section, there is provided a section (second half section) in which the stretching is performed at a temperature lower than the first section and at a temperature of Tm-70°C or higher and Tm-5°C or lower.
The upper limit of the stretching temperature in the latter period is preferably Tm-8°C, more preferably Tm-10°C. When the stretching temperature in the latter period is within this range, rigidity is likely to be developed.
The lower limit of the stretching temperature in the latter period is preferably Tm-65°C, more preferably Tm-60°C, and even more preferably Tm-55°C. When the stretching temperature in the latter period is within this range, film formation is likely to be stable.
Immediately after the end of the latter period, that is, the final stretch ratio in the width direction is reached, the film can be cooled. The cooling temperature at this time is preferably below the temperature in the latter period, and between Tm - 80°C and Tm - 15°C, and preferably between Tm - 80°C and Tm - 20°C. The temperature is more preferably Tm-80°C or higher and Tm-30°C or lower, and particularly preferably Tm-70°C or higher and Tm-40°C or lower.
The temperature in the early period and the temperature in the latter period can be lowered gradually, stepwise or in one step, or each may be constant. Gradually lowering the temperature makes it difficult for the film to break and also makes it easier to reduce variations in film thickness. Further, it is preferable because it is easy to reduce the heat shrinkage rate and there is little whitening of the film.
In the width direction stretching step, the temperature can be gradually lowered from the temperature at the end of the early section to the temperature at the start of the latter section, but it can also be lowered stepwise or in one step.

The lower limit of the stretching ratio at the end of the first section of the width direction stretching step is preferably 4 times, more preferably 5 times, still more preferably 6 times, particularly preferably 6.5 times. The upper limit of the stretching ratio at the end of the first period is preferably 15 times, more preferably 14 times, and even more preferably 13 times.

The lower limit of the final width direction stretching ratio in the width direction stretching step is preferably 5 times, more preferably 6 times, still more preferably 7 times, particularly preferably 8 times. If it is 5 times or more, the rigidity can be easily increased and film thickness unevenness can be easily reduced.
The upper limit of the width direction stretching ratio is preferably 20 times, more preferably 17 times, and still more preferably 15 times. When it is 20 times or less, it is easy to reduce the heat shrinkage rate and it is difficult to break during stretching.

In this way, by using a highly crystalline polypropylene resin with high stereoregularity and a high melting point, and by adopting the above-mentioned width direction stretching process, the molecules of the polypropylene resin can be stretched without extremely increasing the stretching ratio. are highly aligned in the main orientation direction (which corresponds to the width direction in the width direction stretching process mentioned above), so crystals with very strong crystal orientation and high melting point in the resulting biaxially oriented film are likely to be generated. .
In addition, the orientation of the amorphous part between the crystals increases in the main orientation direction (in the width direction stretching process described above, the width direction corresponds to the direction), and since there are many crystals with high melting points around the amorphous part, the crystal At temperatures lower than the melting point, the elongated polypropylene molecules in the amorphous part are difficult to relax and tend to maintain their tense state. Therefore, the entire biaxially oriented film can maintain high rigidity even at high temperatures.
What should also be noted is that by employing such a width direction stretching step, the heat shrinkage rate at a high temperature of 150° C. is also likely to decrease. The reason for this is that since there are many crystals with high melting points around the amorphous part, the elongated polypropylene resin molecules in the amorphous part are difficult to relax at temperatures lower than the melting point of the crystals, and moreover, the molecules are less entangled with each other. be.

It is also worth noting that by increasing the low molecular weight component of the polypropylene resin, the degree of crystallinity of the film increases more easily, and the entanglement of the polypropylene resin molecular chains in the amorphous part is reduced, reducing heat shrinkage stress. By weakening it, it is possible to further reduce the heat shrinkage rate. This can be said to be revolutionary considering that conventionally, if either strength or heat shrinkage rate improved, the other property tended to decrease.

(Heat treatment process)
The biaxially stretched film can be heat-treated to further reduce the heat shrinkage rate, if necessary.
The upper limit of the heat treatment temperature is preferably Tm+10°C, more preferably Tm+7°C. By keeping the temperature below Tm+10°C, rigidity is easily developed, the roughness of the film surface does not become too large, and the film does not easily whiten.
The lower limit of the heat treatment temperature is preferably Tm-10°C, more preferably Tm-7°C. If it is less than Tm-10°C, the heat shrinkage rate may become high.
By adopting the above-mentioned width direction stretching process, the highly oriented crystals generated in the stretching process are difficult to melt even if heat treatment is performed at a temperature between Tm-10°C and Tm+10, which reduces the rigidity of the resulting film. It is possible to further reduce the heat shrinkage rate without decreasing it.
In order to adjust the heat shrinkage rate, the film may be relaxed (relaxed) in the width direction during heat treatment. The upper limit of the relaxation rate is preferably 10%. Within the above range, the film strength is less likely to decrease and film thickness fluctuations are more likely to be reduced. More preferably, it is 8%, still more preferably 7%, even more preferably 3%, particularly preferably 2%, and most preferably 0%.

(Film thickness)
The thickness of the biaxially oriented polypropylene film obtained by the present invention is set according to each application, but in order to obtain the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, and Preferably it is 4 μm, particularly preferably 8 μm and most preferably 10 μm. When 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, even more preferably 60 μm, particularly preferably 50 μm, and most preferably 40 μm. When the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion process is unlikely to become low.
The biaxially oriented polypropylene film obtained by the present invention is usually formed into a roll having a width of about 2,000 to 12,000 mm and a length of about 1,000 to 50,000 m, and then wound into a film roll. Furthermore, it is slit according to each purpose and provided as a slit roll with a width of 300 to 2000 mm and a length of about 500 to 5000 m. With the biaxially oriented polypropylene film of the present invention, it is possible to obtain a longer film roll.

(Thickness uniformity)
The lower limit of the thickness uniformity of the biaxially oriented polypropylene film obtained by the present invention is preferably 0%, more preferably 0.1%, still more preferably 0.5%, and particularly preferably 1%. be. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, still more preferably 15%, particularly preferably 12%, and most preferably 10%. Within the above range, defects are less likely to occur during post-processing such as coating and printing, making it easy to use in applications that require precision.
The measurement method was as follows. A test piece of 40 mm in the width direction was cut out from a steady region where the film physical properties were stable in the length direction of the film, and a test piece of 40 mm in the width direction was cut out using a film feeding device manufactured by Micron Keiki Co., Ltd. (product number: A90172 was used) and a film manufactured by Anritsu Corporation. Using a continuous thickness measuring device (product name: K-313A wide-range high-sensitivity electronic micrometer), the film thickness was continuously measured over 20,000 mm, and the thickness uniformity was calculated from the following formula.
Thickness uniformity (%) = [(maximum thickness - minimum thickness) / average thickness] x 100

(Film characteristics)
The biaxially oriented polypropylene film obtained by the present invention is characterized by the following properties. Here, the "longitudinal direction" in the biaxially oriented polypropylene film obtained by the present invention is a direction corresponding to the flow direction in the film manufacturing process, and the "width direction" is a direction corresponding to the flow direction in the film manufacturing process. The directions are perpendicular to each other. For polypropylene films whose flow direction during the film manufacturing process is unknown, wide-angle X-rays are incident perpendicularly to the film surface, and the scattering peak originating from the (110) plane of the α-type crystal is scanned in the circumferential direction. The direction in which the diffraction intensity of the obtained diffraction intensity distribution is the largest is defined as the "longitudinal direction", and the direction orthogonal thereto is defined as the "width direction".

(Young's modulus at 23℃)
The lower limit of Young's modulus in the longitudinal direction at 23° C. of the biaxially oriented polypropylene film obtained by the present invention is preferably 2.0 GPa, more preferably 2.1 GPa, and still more preferably 2.2 GPa, Particularly preferred is 2.3 GPa, and most preferred is 2.4 GPa. When the pressure is 2.0 GPa or more, the rigidity is high, so the bag shape is easily maintained when used as a packaging bag, and the film is less likely to be deformed during processing such as printing. The upper limit of Young's modulus in the longitudinal direction is preferably 4.0 GPa, more preferably 3.8 GPa, even more preferably 3.7 GPa, particularly preferably 3.6 GPa, and most preferably 3.5 GPa. It is. When the pressure is 4.0 GPa or less, practical manufacturing is easy, and the balance between longitudinal and widthwise properties is likely to be improved.

The lower limit of Young's modulus in the width direction at 23° C. of the biaxially oriented polypropylene film obtained by the present invention is preferably 6.0 GPa, more preferably 6.3 GPa, still more preferably 6.5 GPa, Particularly preferred is 6.7 GPa. When the pressure is 6.0 GPa or more, the rigidity is high, so that the bag shape is easily maintained when used as a packaging bag, and the film is less likely to be deformed during processing such as printing. The upper limit of the Young's modulus in the width direction is preferably 15 GPa, more preferably 13 GPa, and even more preferably 12 GPa. When the pressure is 15 GPa or less, practical manufacturing is easy and the balance between longitudinal and widthwise properties is likely to be improved.
Young's modulus can be controlled within the range by adjusting the stretching ratio, relaxation rate, or adjusting the temperature during film formation.

(150℃ heat shrinkage rate)
The upper limit of the longitudinal heat shrinkage rate at 150°C of the biaxially oriented polypropylene film obtained by the present invention is preferably 10%, more preferably 8.0%, particularly preferably 7.0%. be. The upper limit of the heat shrinkage rate in the width direction at 150° C. is preferably 30%, more preferably 25%, particularly preferably 20%. When the heat shrinkage rate in the longitudinal direction is 10% or less and the heat shrinkage rate in the width direction is 30% or less, wrinkles are less likely to occur during heat sealing, especially when the heat shrinkage rate in the longitudinal direction at 150°C is 8.0%. % or less, and a heat shrinkage rate in the width direction at 150° C. of 20% or less is preferable because distortion when fusing the chuck portion to the opening portion is small. In order to reduce the heat shrinkage rate at 150°C, it is necessary to adjust the stretching ratio, film forming temperature, and relaxation rate, and to adjust the molecular weight when measuring the gel permeation chromatography (GPC) integration curve of the polypropylene resin that makes up the film. It is effective to set the lower limit of the amount of components below 100,000 to 35% by mass.

The biaxially oriented polypropylene film obtained by the present invention preferably has the following properties and structure.

(Young's modulus at 80℃)
The lower limit of Young's modulus in the longitudinal direction at 80° C. of the biaxially oriented polypropylene film obtained by the present invention is preferably 0.5 GPa, more preferably 0.7 GPa. When the pressure is 0.5 GPa or more, printing pitch deviation is less likely to occur when high temperature printing ink is transferred. The upper limit of Young's modulus in the longitudinal direction at 80° C. is preferably 3.0 GPa, more preferably 2.5 GPa. Practical manufacturing is easy at 3.0 GPa or higher.
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 still more preferably 3.0 GPa. At 2.5 GPa or more, printing pitch deviations are less likely to occur when high temperature printing ink is transferred. 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 still more preferably 4.5 GPa. Practical manufacturing is easy when the pressure is 5.0 GPa or less.
Young's modulus at 80° C. can be controlled within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(Stress at 5% elongation at 23°C)
The lower limit of the stress (F5) at 5% elongation in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is 40 MPa, preferably 42 MPa, more preferably 43 MPa, and even more preferably 44 MPa. The pressure is particularly preferably 45 MPa. When the pressure is 40 MPa or more, the rigidity is high, so that the bag shape is easily maintained when used as a packaging bag, and the film is less likely to be deformed during processing such as printing. The upper limit of F5 in the longitudinal direction is preferably 70 MPa, more preferably 65 MPa, even more preferably 62 MPa, particularly preferably 61 MPa, and most preferably 60 MPa. When the pressure is 70 MPa or less, practical manufacturing is easy and the longitudinal and width balance is likely to be improved.
The lower limit of F5 in the width direction at 23° C. of the biaxially oriented polypropylene film of the present invention is 160 MPa, preferably 165 MPa, more preferably 168 MPa, and even more preferably 170 MPa. When the pressure is 160 MPa or more, the rigidity is high, so that the bag shape is easily maintained when used as a packaging bag, and the film is less likely to be deformed during processing such as printing. The upper limit of F5 in the width direction is preferably 250 MPa, more preferably 245 MPa, and even more preferably 240 MPa. When the pressure is 250 MPa or less, practical manufacturing is easy and the vertical and width balance is likely to be improved.
F5 can be controlled within the range by adjusting the stretching ratio, relaxation rate, or adjusting the temperature during film formation.
(Stress at 5% elongation at 80°C)
The lower limit of the stress (F5) at 5% elongation in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 80°C is 15 MPa, preferably 17 MPa, more preferably 19 MPa, and even more preferably 20 MPa. be. When the pressure is 15 MPa or more, the rigidity is high, so that the bag shape when used as a packaging bag is easily maintained, and the film is less likely to be deformed during processing such as printing. The upper limit of F5 at 80°C in the longitudinal direction is preferably 40 MPa, more preferably 35 MPa, even more preferably 30 MPa, particularly preferably 25 MPa. When the pressure is 40 MPa or less, practical manufacturing is easy and the vertical and width balance is easy to improve.
The lower limit of F5 in the width direction at 80°C of the biaxially oriented polypropylene film of the present invention is 75 MPa, preferably 80 MPa, more preferably 85 MPa, still more preferably 90 MPa, particularly preferably 95 MPa. . When the pressure is 75 MPa or more, the rigidity is high, so that the bag shape when used as a packaging bag is easily maintained, and the film is less likely to be deformed during processing such as printing. The upper limit of F5 at 80°C in the width direction is preferably 150 MPa, more preferably 140 MPa, and even more preferably 130 MPa. When the pressure is 140 MPa or less, practical manufacturing is easy and the vertical and width balance is likely to be improved.
80°C F5 can be kept within the range by adjusting the stretching ratio and relaxation rate, or adjusting the temperature during film formation.

(120℃ heat shrinkage rate)
The upper limit of the longitudinal heat shrinkage rate at 120°C of the biaxially oriented polypropylene film obtained by the present invention is preferably 2.0%, more preferably 1.7%, and even more preferably 1.5%. %. When it is 2.0% or less, printing pitch deviations are less likely to occur when printing ink is transferred. The upper limit of the heat shrinkage rate in the width direction at 120° C. is preferably 5.0%, more preferably 4.5%, and still more preferably 4.0%. When it is 5.0% or less, wrinkles are less likely to occur during heat sealing.
If the longitudinal heat shrinkage rate at 120°C is smaller than the widthwise heat shrinkage rate at 120°C, printing pitch deviations will be less likely to occur when printing ink is transferred. The heat shrinkage rate at 120°C and the balance between the heat shrinkage rate in the longitudinal direction and the width direction can be kept within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(TMA heating elongation)
The upper limit of the maximum elongation of the biaxially oriented polypropylene film obtained by the present invention at 150°C or less in the longitudinal direction measured by a thermomechanical analyzer (TMA) is preferably 1.5 mm, more preferably 1.45 mm. It is more preferably 1.4 mm, particularly preferably 1.35 mm, and most preferably 1.3 mm. Within the above range, deformation during heating processing with a roll or printing may be small, and processability may be improved. The lower limit of the maximum elongation in the longitudinal direction at 150°C or less is preferably 0.5 mm, more preferably 0.6 mm, still more preferably 0.7 mm, particularly preferably 0.75 mm, and most preferably Preferably it is 0.8 mm. Within the above range, practical production may become easier.
The upper limit of the maximum elongation in the width direction at 150°C or less is preferably 0.1 mm, more preferably 0.09 mm, still more preferably 0.08 mm, particularly preferably 0.075 mm, and most preferably Preferably it is 0.07 mm. The lower limit of the maximum elongation in the width direction at 150°C or less is preferably 0.005 mm, more preferably 0.01 mm, still more preferably 0.015 mm, particularly preferably 0.018 mm, and most preferably Preferably it is 0.2 mm. Within the above range, deformation may be small and the appearance may be improved.

(Refractive index)
The lower limit of the longitudinal refractive index (Nx) of the biaxially oriented polypropylene film obtained by the present invention is preferably 1.4950, more preferably 1.4970, and still more preferably 1.4980. When it is 1.4950 or more, it is easy to increase the rigidity of the film. The upper limit of the refractive index (Nx) in the longitudinal direction is preferably 1.5100, more preferably 1.5070, and still more preferably 1.5050. When it is 1.5100 or less, the film tends to have an excellent balance of properties in the longitudinal direction and the width direction.

The lower limit of the refractive index (Ny) in the width direction of the biaxially oriented polypropylene film obtained by the present invention is preferably 1.5230, more preferably 1.5235, and even more preferably 1.5240 or more. When it is 1.5230 or more, it is easy to increase the rigidity of the film. 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. When it is 1.5280 or less, the film tends to have an excellent balance of properties in the longitudinal direction and the width direction.

The lower limit of the refractive index (Nz) in the thickness direction of the biaxially oriented polypropylene film obtained by the present invention is preferably 1.4960, more preferably 14965, and even more preferably 1.4970. When it is 1.4960 or more, it is easy to increase the rigidity of the film. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and still more preferably 1.5010. When it is 1.5020 or less, the heat resistance of the film can be easily improved.
The refractive index can be adjusted within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(△Ny)
The lower limit of ΔNy of the biaxially oriented polypropylene film obtained by the present invention is preferably 0.0220, more preferably 0.0225, still more preferably 0.0228, particularly preferably 0.0230. . If it is 0.0220 or more, the rigidity of the film tends to be high. As a practical value, the upper limit of ΔNy is preferably 0.0270, more preferably 0.0265, still more preferably 0.0262, and particularly preferably 0.0260. When it is 0.0270 or less, thickness unevenness tends to be good. ΔNy can be controlled within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature of the film.
△Ny is calculated using the following formula, with the refractive index along the longitudinal direction, width direction, and thickness direction of the film being Nx, Ny, and Nz, respectively. It means the degree of orientation in a direction.
△Ny=Ny-[(Nx+Nz)/2]

(planar orientation coefficient)
The lower limit of the planar orientation coefficient (ΔP) of the biaxially oriented polypropylene film obtained by the present invention is preferably 0.0135, more preferably 0.0138, and still more preferably 0.0140. When it is 0.0135 or more, the balance in the plane direction of the film is good and the thickness unevenness is also good. The upper limit of the planar orientation coefficient (ΔP) is preferably 0.0155 as a practical value, more preferably 0.0152, and even more preferably 0.0150. When it is 0.0155 or less, heat resistance at high temperatures tends to be excellent. The plane orientation coefficient (ΔP) can be controlled within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.
In addition, the planar orientation coefficient (ΔP) was calculated using the following formula: [(Nx+Ny)/2]-Nz.

(Haze)
The lower limit of the haze of the biaxially oriented polypropylene film obtained by the present invention is preferably 0.1% as a practical value, more preferably 0.2%, still more preferably 0.3%, Particularly preferred is 0.4%. If it is 0.1% or more, it is easy to manufacture. The upper limit of haze is preferably 5.0%, more preferably 4.5%, even more preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. %. When it is 5.0% or less, it is easy to use in applications that require transparency. Haze can be controlled by adjusting the cooling roll (CR) temperature, the width direction stretching temperature, the tenter preheating temperature before width direction stretching, the width direction stretching temperature, or the heat setting temperature, or the amount of a component with a molecular weight of 100,000 or less of the polypropylene resin. However, it may become larger by adding an anti-blocking agent or applying a sealing layer.

(Half width of diffraction peak derived from oriented crystals)
In the azimuth angle dependence of the scattering peak of the (110) plane of the polypropylene α-type crystal of the biaxially oriented polypropylene film obtained by the present invention, which is obtained by wide-angle X-ray measurement incident perpendicularly to the film surface, The upper limit of the half width (Wh) of the diffraction peak derived from oriented crystals is preferably 27°, more preferably 26°, still more preferably 25°, particularly preferably 24°, and most preferably is 23°.
The lower limit of Wh is preferably 13°, more preferably 14°, and even more preferably 15°. When the half width (Wh) is 27° or less, it is easy to increase the rigidity of the film.

(X-ray orientation degree)
The lower limit of the degree of X-ray orientation calculated by the following formula from Wh of the biaxially oriented polypropylene film obtained by the present invention is preferably 0.85, more preferably 0.855, and still more preferably 0.861. It is. Rigidity can be easily increased by setting it to 0.85 or more.
X-ray orientation degree = (180-Wh)/180
The upper limit of the degree of X-ray orientation is preferably 0.928, more preferably 0.922, and still more preferably 0.917. By setting it to 0.928 or less, film formation is likely to be stable.

(Practical properties of film)
Practical properties of the biaxially oriented polypropylene film obtained by the present invention will be explained.
(Tensile breaking strength)
The lower limit of the longitudinal tensile strength of the biaxially oriented polypropylene film obtained by the present invention is preferably 90 MPa, more preferably 95 MPa, and even more preferably 100 MPa. When the pressure is 90 MPa or more, printing pitch deviations are less likely to occur when printing ink is transferred, and the durability of the packaging bag is also likely to be excellent. As a practical value, the upper limit of the tensile strength at break in the longitudinal direction is preferably 200 MPa, more preferably 190 MPa, and still more preferably 180 MPa. If the pressure is 200 MPa or less, breakage of the film and breakage of the packaging bag will be less likely.
The lower limit of the tensile strength at break in the width direction of the biaxially oriented polypropylene film obtained by the present invention is preferably 320 MPa, more preferably 340 MPa, and still more preferably 350 MPa. When the pressure is 320 MPa or more, printing pitch deviations are less likely to occur when printing ink is transferred, and the durability of the packaging bag is also likely to be excellent. As a practical value, the upper limit of the tensile strength at break in the width direction is preferably 500 MPa, more preferably 480 MPa, and still more preferably 470 MPa. When the pressure is 500 MPa or less, breakage of the film and breakage of the packaging bag are likely to be reduced.
The tensile strength at break can be controlled within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(Tensile elongation at break)
The lower limit of the tensile elongation at break in the longitudinal direction of the biaxially oriented polypropylene film obtained by the present invention is preferably 50%, more preferably 55%, and even more preferably 60%. When it is 50% or more, breakage of the film and breakage of the packaging bag are likely to be reduced. As a practical value, the upper limit of the tensile elongation at break in the longitudinal direction is preferably 230%, more preferably 220%, and still more preferably 210%. When it is 230% or less, printing pitch deviation is less likely to occur when printing ink is transferred, and the durability of the packaging bag is also likely to be excellent.
The lower limit of the tensile elongation at break in the width direction of the biaxially oriented polypropylene film obtained by the present invention is preferably 10%, more preferably 15%, and even more preferably 17%. If it is 10% or more, breakage of the film and breakage of the packaging bag tend to decrease. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and still more preferably 50%. When it is 60% or less, printing pitch deviations are less likely to occur when printing ink is transferred, and the durability of the packaging bag is also likely to be excellent.
The tensile elongation at break can be controlled within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(bending resistance)
The lower limit of the bending resistance in the longitudinal direction at 23° C. of the biaxially oriented polypropylene film obtained by the present invention is preferably 0.3 mN·cm, more preferably 0.33 mN·cm, and still more preferably 0.3 mN·cm. It is 35 mN·cm. When it is 0.3 mN·cm or more, it is possible to make the film thinner, and it is suitable for applications that require rigidity. The lower limit of the bending resistance in the width direction is preferably 0.5 mN·cm, more preferably 0.55 mN·cm, and still more preferably 0.6 mN·cm. When it is 0.5 mN·cm or more, it is possible to make the film thinner, and it is suitable for applications that require rigidity.

(loop stiffness stress)
The lower limit of the longitudinal loop stiffness stress S (mN) at 23°C of the biaxially oriented polypropylene film of the present invention is preferably 0.00020×t, where t (μm) is the thickness of the biaxially oriented polypropylene film. ³ , more preferably 0.00025× ^t3 , still more preferably 0.00030× ^t3 , particularly preferably 0.00035× ^t3 . When it is 0.00020×t ³ or more, the shape of the package can be easily maintained.
The upper limit of the longitudinal loop stiffness stress S (mN) at 23 °C is preferably 0.00080 x ^t3 , more preferably 0.00075 x ^t3 , even more preferably 0.00072 x t3. ³ , particularly preferably 0.00070× ^t3 . When it is 0.00080×t ³ or less, it is practically easy to manufacture.
The lower limit of the loop stiffness stress S (mN) in the width direction at 23°C of the biaxially oriented polypropylene film of the present invention is preferably 0.0010×t, where t (μm) is the thickness of the biaxially oriented polypropylene film. ³ , more preferably 0.0011×t ³ , even more preferably 0.0012×t ³ , particularly preferably 0.0013×t ³ . When it is 0.0010×t ³ or more, the shape of the package can be easily maintained.
The upper limit of the loop stiffness stress S (mN) in the width direction at 23° C. is preferably 0.0020× ^t3 , more preferably 0.0019× ^t3 , and even more preferably 0.0018×t3. ³ , particularly preferably 0.0017× ^t3 . When it is 0.0020×t ³ or less, it is practically easy to manufacture.

Loop stiffness stress is an index representing the stiffness of a film, but it also depends on the thickness of the film. The measurement method is as follows. Two strips each measuring 110 mm x 25.4 mm were cut out with the longitudinal direction of the film as the long axis (loop direction) or the width direction of the film as the long axis (loop direction). One side of the film is held in a clip and one side of the film becomes the inner surface of the loop, and the other side is the measuring loop, and the long axis of the strip is in the longitudinal and width directions of the film. Created. A measuring loop with the long axis of the strip in the longitudinal direction of the film was set in the chuck part of the Loop Stiffness Tester DA manufactured by Toyo Seiki Co., Ltd. with the width direction perpendicular, the clip was removed, and the chuck interval was 50 mm. The loop stiffness stress was measured with an indentation depth of 15 mm and a compression speed of 3.3 mm/sec.
The loop stiffness stress and thickness were measured five times with one side of the film being the inner surface of the loop, and then five times with the other side being the inner surface of the loop. Using the data from a total of 10 times, plot the cube of the thickness (μm) of each test piece on the horizontal axis and the loop stiffness stress (mN) on the vertical axis, and approximate it with a straight line with an intercept of 0. The slope a was determined. The slope a means a film-specific characteristic value that determines rigidity and is not dependent on thickness. The slope a was taken as the evaluation value of waist feeling. A measurement loop in which the long axis of the strip was in the width direction of the film was similarly measured.

(Wrinkles during heat sealing)
To form a bag for packaging food, the bag is filled with contents and heated to melt and fuse the film to seal it. In addition, the same process is often performed when making bags while filling them with food. Usually, a sealant film made of polyethylene, polypropylene, etc. is laminated on a base film, and the surfaces of the sealant films are fused together. The heating method is to apply pressure with a heating plate from the base film side to press and seal the film, and the seal width is often about 10 mm. Since the base film is also heated at this time, the contraction at that time causes wrinkles. The fewer wrinkles the better for the durability of the bag, and the fewer wrinkles the better to increase purchasing motivation. The sealing temperature may be about 120° C., but in order to increase the bag manufacturing speed, a higher sealing temperature is required, and even in that case, it is preferable that the shrinkage is small. When fusing a zipper to the opening of a bag, sealing at an even higher temperature is required.

(Print pitch deviation)
The basic structure of a packaging film is often a laminated film of a printed base film and a sealant film. Bag making machines are used to manufacture bags, including three-sided bags, standing bags, gusset bags, etc., and a variety of bag making machines are used. The printing pitch shift is thought to occur because the base material of the film expands and contracts as tension and heat are applied to the film during the printing process. Eliminating defective products due to printing pitch deviations is important from the point of view of effective use of resources, and is also important for increasing purchasing motivation.

(Film processing)
The biaxially oriented polypropylene film obtained by the present invention can be printed by letterpress printing, planographic printing, intaglio printing, stencil printing, or transfer printing, depending on the purpose.
In addition, unstretched sheets, uniaxially oriented films, and biaxially oriented films made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester are laminated together as a sealant film to impart heat-sealing properties. It can also be used as a laminate. If you want to further improve gas barrier properties and heat resistance, use unstretched sheets made of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, or polyvinyl alcohol, uniaxially oriented films, or biaxially oriented polypropylene films. and a sealant film as an intermediate layer. For bonding the sealant film, an adhesive applied by a dry lamination method or a hot melt lamination method can be used.
To improve gas barrier properties, aluminum or an inorganic oxide can be vapor-deposited on the biaxially oriented polypropylene film, intermediate layer film, or sealant film. Vacuum deposition, sputtering, and ion plating methods can be employed as the deposition method, but it is particularly preferable to vacuum deposit silica, alumina, or a mixture thereof.

The biaxially oriented polypropylene film obtained by the present invention includes antifogging agents such as fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines and amides of higher fatty acids. By controlling the amount of the agent present in the film in the range of 0.2 to 5% by mass, the film is suitable for packaging perishable products made of plants that require high freshness, such as vegetables, fruits, and flowers. be able to.
In addition, various additives may be added to improve quality such as slipperiness and antistatic properties, as long as they do not impair the effects of the present invention. For example, lubricants such as wax and metal soap, plastic It is also possible to add additives, processing aids, heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers, and the like.

(Industrial applicability)
Since the biaxially oriented polypropylene film obtained by the present invention has the above-mentioned excellent properties not found in the past, it can be preferably used for packaging bags, and the thickness of the film can be made thinner than before. be. Furthermore, rigidity is required for applications that are used at high temperatures, such as insulating films for capacitors and motors, back sheets for solar cells, barrier films of inorganic oxides, base films for transparent conductive films such as ITO, and for separate films. It is also suitable for applications such as In addition, high-temperature coating and printing processes can be performed using coating agents, inks, laminating adhesives, etc. that were previously difficult to use, which is expected to improve production efficiency.

Hereinafter, the present invention will be explained in detail with reference to Examples. In addition, the characteristics were measured and evaluated by the following method.
(1) Melt flow rate Melt flow rate (MFR) was measured at a temperature of 230° C. and a load of 2.16 kgf in accordance with JIS K 7210.

(2) Mesopentad fraction The mesopentad fraction ([mmmm]%) of the polypropylene resin was measured using ¹³ C-NMR. The mesopentad fraction was calculated according to the method described by Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). ¹³ C-NMR measurement was carried out at 110°C by dissolving 200 mg of the sample in an 8:2 mixture of o-dichlorobenzene and heavy benzene at 135°C using AVANCE 500 manufactured by BRUKER.

(3) Number average molecular weight, weight average molecular weight, amount of components with a molecular weight of 100,000 or less, and molecular weight distribution of polypropylene resin Using gel permeation chromatography (GPC), the molecular weight was determined as a PP equivalent molecular weight based on monodisperse polystyrene. When the baseline was not clear, the baseline was set in the range up to the lowest position on the high molecular weight side of the elution peak on the high molecular weight side that was closest to the elution peak of the standard substance.
The GPC measurement conditions are as follows.
Equipment: HLC-8321PC/HT (manufactured by Tosoh Corporation)
Detector: RI
Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%)
Column: TSKgelguardcolumnHHR(30)HT (7.5mmI.D. x 7.5cm) x 1 + TSKgelGMHHR-H(20)HT (7.8mmI.D. x 30cm) x 3 Flow rate: 1.0mL/min
Injection volume: 0.3mL
Measurement temperature: 140℃
The number average molecular weight (Mn) and the mass average molecular weight (Mw) are each defined by the following formula by the number of molecules (N _i ) of the molecular weight (M _i ) at each elution position of the GPC curve obtained through the molecular weight calibration curve. Ru.
Number average molecular weight: Mn=Σ(N _i・M _i )/ΣN _i
Mass average molecular weight: Mw=Σ(N _i・M _i ² )/Σ(N _i・M _i )
Here, the molecular weight distribution can be obtained by Mw/Mn.
Furthermore, the proportion of components with a molecular weight of 100,000 or less was determined from the integral curve of the molecular weight distribution obtained by GPC.

(4) Crystallization temperature (Tc), melting temperature (Tm)
Heat measurements were performed in a nitrogen atmosphere using a Q1000 differential scanning calorimeter manufactured by TA Instruments. Approximately 5 mg was cut out from a polypropylene resin pellet and sealed in an aluminum pan for measurement. After raising the temperature to 230°C and holding it for 5 minutes, it was cooled to 30°C at a rate of -10°C/min, and the exothermic peak temperature was taken as the crystallization temperature (Tc). The heat of crystallization (ΔHc) was determined by setting a baseline so that the area of the exothermic peak was smoothly connected from the start of the peak to the end of the peak. The temperature was maintained at 30°C for 5 minutes, and the temperature was increased to 230°C at a rate of 10°C/min, and the main endothermic peak temperature was taken as the melting temperature (Tm).

(5) Film Thickness The thickness of the film was measured using Militron 1202D manufactured by Seiko EM.

(6) Haze Measured using NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. at 23° C. according to JIS K7105.

(7) Tensile test The tensile strength of the film in the longitudinal direction and width direction was measured at 23° C. in accordance with JIS K 7127. The sample was cut out from the film to a size of 15 mm x 200 mm, the chuck width was 100 mm, and the sample was set in a tensile tester (Instron 5965 dual column tabletop tester manufactured by Instron Japan Company Limited). A tensile test was conducted at a tensile speed of 200 mm/min. From the obtained strain-stress curve, the Young's modulus was determined from the slope of the straight line portion at the initial stage of elongation, and the stress at 5% elongation (F5) was determined. The tensile strength at break and the tensile elongation at break were the strength and elongation at the time the sample broke, respectively.
The Young's modulus and F5 at 80°C were determined by performing the measurement in a constant temperature bath at 80°C. In addition, the measurement was performed by setting the chuck in a constant temperature bath previously set at 80° C., and holding it there for 1 minute until the sample was measured.

(8) Heat shrinkage rate Measured according to JIS Z 1712 by the following method. The film was cut to a width of 20 mm and a length of 200 mm in the longitudinal direction and the width direction, respectively, and was hung in a hot air oven at 120° C. or 150° C. and heated for 5 minutes. The length after heating was measured, and the heat shrinkage rate was calculated as the ratio of the shrunk length to the original length.
(9) TMA heating elongation The heating elongation was performed by TMA measurement, and the TMA measurement was performed using a thermomechanical analyzer TMA-60 manufactured by Shimadzu Corporation. Samples were prepared by cutting strips of 20 mm in length in the longitudinal direction and 4 mm in the width direction from the film. The distance between the chucks was set to 10 mm, the measurement load was 40 g, the temperature was raised from 30°C to 180°C at a rate of 20°C/min, the maximum elongation in the temperature range up to 150°C was measured, and it was defined as TMA heating elongation. .

(10) Refractive index, ΔNy, plane orientation coefficient Measured at a wavelength of 589.3 nm and a temperature of 23° C. using an Abbe refractometer manufactured by Atago Co., Ltd. The refractive index along the longitudinal direction and the width direction of the film was set as Nx and Ny, respectively, and the refractive index in the thickness direction was set as Nz. ΔNy was determined using Ny−[(Nx+Nz)/2] using Nx, Ny, and Nz. In addition, the planar orientation coefficient (ΔP) was calculated using the following formula: [(Nx+Ny)/2]-Nz.

(11) X-ray half-width, degree of orientation Measured by transmission method using an X-ray diffraction device (RINT2500 manufactured by Rigaku Co., Ltd.). X-rays with a wavelength of 1.5418 Å were used, and a scintillation counter was used as a detector. A sample was prepared by stacking the films to a thickness of 500 μm. Place the sample stage at the diffraction peak position (diffraction angle 2θ = 14.1°) of the (110) plane of the α-type crystal of polypropylene resin, and rotate the sample 360° around the film thickness direction to detect the (110) plane. The azimuthal dependence of the diffraction intensity was obtained. From this azimuthal angle dependence, the half-width Wh of the diffraction peak originating from the oriented crystals in the width direction of the film was determined.
In addition, the degree of X-ray orientation was calculated using the following formula using Wh.
X-ray orientation degree = (180-Wh)/180

(12) Bending resistance and amount of droop It was determined according to the JIS L 1096B method (slide method) using the following procedure. A test piece of 20 mm x 150 mm was prepared, and after making sure that the top surface of the testing machine body and the moving table were aligned, the test piece was placed on the testing machine stand so as to protrude 50 mm, and a weight was installed. Then, the sample stage was lowered by gently turning the handle, and the amount of droop (δ) at the time when the free end of the sample separated from the sample stage was measured. Using this drooping amount δ, film thickness, test piece size, and film density of 0.91 g/cm ³ , bending resistance (Br) was determined from the following formula.
Br= ^WL4 /8δ
Br: Bending resistance (mN・cm)
W: Gravity per unit area of test piece (mN/cm ² )
L: Length of test piece (cm)
δ: Drooping amount (cm)

(13) Loop stiffness stress, stiffness feeling A strip-shaped test piece of 110 mm x 25.4 mm, where the longitudinal direction of the film is the long axis (loop direction) of the strip, or the width direction of the film is the long axis (loop direction) of the strip. I cut out 10 pieces of each. One side of the film is held in a clip and one side of the film becomes the inner surface of the loop, and the other side is the measuring loop, and the long axis of the strip is in the longitudinal and width directions of the film. Created. Set a measuring loop with the long axis of the strip in the longitudinal direction of the film in the chuck part of the Loop Stiffness Tester DA manufactured by Toyo Seiki Seisakusho Co., Ltd. with the width direction perpendicular, remove the clip, and check the chuck interval. Loop stiffness stress was measured at an indentation depth of 50 mm, an indentation depth of 15 mm, and a compression speed of 3.3 mm/sec.
The loop stiffness stress and thickness were measured five times with one side of the film being the inner surface of the loop, and then five times with the other side being the inner surface of the loop. Using the data from a total of 10 times, plot the cube of the thickness (μm) of each test piece on the horizontal axis and the loop stiffness stress (mN) on the vertical axis, and approximate it with a straight line with an intercept of 0. The slope a was determined. The slope a was taken as the evaluation value of waist feeling. A measurement loop in which the long axis of the strip was in the width direction of the film was similarly measured.

(Example 1)
As the polypropylene resin, propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., Sumitomo Noblen FLX80E4) with MFR = 7.5 g / 10 minutes, Tc = 116.2 ° C., Tm = 162.5 ° C. was used. . It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then put into a water tank at 20°C as it was. After that, it was stretched 4.5 times in the longitudinal direction with two pairs of rolls at 145°C, then both ends were sandwiched with clips, and introduced into a hot air oven. The film was stretched 6 times at 100° C., and then stretched 1.36 times at 145° C. as a second stage, thereby stretching a total of 8.2 times. Immediately after stretching in the width direction, the film was cooled at 100°C while being held in a clip, and then heat-set at 163°C. The thickness of the film thus obtained was 18.7 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage at high temperatures was obtained.

(Example 2)
As a polypropylene resin, 80 parts by weight of PP-1, MFR = 11 g/10 min, [mmmm] = 98.8%, Tc = 116.5°C, Tm = 161.5°C, a propylene homopolymer PP- 2 (manufactured by Sumitomo Chemical Co., Ltd., EL80F5) and 20 parts by weight were used. The procedure was the same as in Example 1 except that the stretching temperature in the longitudinal direction was 142°C, the first stage stretching temperature in the width direction was 162°C, and the heat setting temperature was 165°C. The thickness of the obtained film was 21.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage rate at high temperatures was obtained.

(Example 3)
The same procedure as in Example 2 was carried out except that 3% relaxation was applied during heat setting. The thickness of the obtained film was 21.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage rate at high temperatures was obtained.

(Example 4)
The same procedure as in Example 2 was carried out except that the stretching temperature in the longitudinal direction was 145°C and the cooling temperature immediately after stretching in the width direction was 140°C. The thickness of the obtained film was 18.9 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity was obtained.

(Example 5)
After stretching in the width direction, the same procedure as in Example 2 was carried out, except that heat setting was performed at 165°C while being held in a clip without cooling. The thickness of the obtained film was 19.5 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage rate at high temperatures was obtained.

(Example 6)
The same procedure as in Example 2 was carried out except that the second stage stretching temperature in the width direction was 155°C. The thickness of the film thus obtained was 20.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage rate at high temperatures was obtained.

(Example 7)
The same procedure as in Example 2 was carried out except that the stretching ratio in the longitudinal direction was 4.8 times. The thickness of the obtained film was 19.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage rate at high temperatures was obtained.

(Example 8)
In the width direction stretching, the same procedure as in Example 2 was carried out, except that the first stage stretching ratio was 6.6 times, the second stage stretching ratio was 1.5 times, and the stretching was 9.9 times in total. . The thickness of the obtained film was 20.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As for the physical properties, as shown in Table 3, a film with high rigidity and low heat shrinkage rate at high temperatures was obtained.

(Comparative example 1)
Using PP-1 as the polypropylene resin, it was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then put into a water tank at 20°C as it was. Thereafter, longitudinal stretching was performed 4.5 times at 143°C, and 8.2 times stretching was performed using a tenter at a preheating temperature of 170°C and a stretching temperature of 158°C during width direction stretching, followed by heat setting at 168°C. I did it. The thickness of the obtained film was 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. As shown in Table 3, its physical properties were low in rigidity.

(Comparative example 2)
Comparative Example 1 was carried out in the same manner as in Comparative Example 1, except that 80 parts by weight of PP-1 and 20 parts by weight of PP-2 were used as the polypropylene resin. The thickness of the obtained 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. As shown in Table 3, its physical properties were low in rigidity.

(Comparative example 3)
As the polypropylene resin, PP-3 (manufactured by Nippon Polypro Co., Ltd., FL203D) having MFR = 3 g/10 minutes, Tc = 117.2°C, and Tm = 160.6°C was used. It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then put into a water tank at 20°C as it was. After that, it was stretched 4.5 times in the longitudinal direction at 135°C, and in the width direction stretching with a tenter, the preheating temperature was 166°C, the temperature in the first stage of stretching was 155°C, the temperature in the second stage was 139°C, and the cooling temperature. was set at 95°C, and the heat setting temperature was set at 158°C. The thickness of the obtained film 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. As for its physical properties, as shown in Table 3, it had a high thermal shrinkage rate at high temperatures.

(Comparative example 4)
As the polypropylene resin, PP-4 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) with MFR = 2.7 g/10 minutes, Tc = 114.7°C, and Tm = 163.0°C was used. It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then put into a water tank at 20°C as it was. After that, the film was stretched 5.8 times in the longitudinal direction at 130°C, then heated in a tenter at a preheating temperature of 167°C, then stretched 8.6 times in the width direction at a stretching temperature of 161°C, and then , heat setting was performed at 130° C. while applying 10% relaxation, and then a second heat setting was performed at 140° C. The thickness of the obtained film was 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 for its physical properties, as shown in Table 3, it had a high thermal shrinkage rate at high temperatures.

(Reference example)
PP-4 was used as a polypropylene raw material. It was extruded into a sheet from a T-die at 250°C, brought into contact with a cooling roll at 20°C, and then put into a water tank at 20°C as it was. After that, it was stretched 4.5 times in the longitudinal direction at 145°C, and in the widthwise stretching with a tenter, the preheating temperature was 170°C, the temperature in the first stage of stretching was 160°C, the temperature in the second stage of stretching was 145°C, and the temperature was cooled. The temperature was 100°C and the heat setting temperature was 163°C. The thickness of the obtained film 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. As for its physical properties, as shown in Table 3, it had a high thermal shrinkage rate at high temperatures.

Claims (4)

Extrusion step of obtaining an unstretched sheet by extruding a polypropylene resin composition containing a polypropylene resin having a melt flow rate (MFR) of 4.0 g/10 minutes or more and a mesopentad fraction of 97.0% or more, below 40°C A step of cooling and solidifying the unstretched sheet at a temperature of A first section widthwise stretching step in which the longitudinally stretched film is stretched in the width direction at a temperature of Tm -10° C. or higher and below the preheating temperature, followed by a first section widthwise stretching step in which stretching is performed in the width direction; The latter stage is lower than the temperature of the step of stretching in the width direction at a temperature of Tm-10°C or higher and lower than the preheating temperature, and a temperature of Tm-70°C or higher and Tm-5°C or lower. A method for producing a biaxially oriented polypropylene film, comprising, in order, a later section width direction stretching step in which stretching is performed in the width direction, and a heat treatment step in which heat treatment is performed at a temperature between Tm-10°C and Tm+10. 2. The method according to claim 1, further comprising a step between the later section widthwise stretching step and the heat treatment step, at a temperature lower than the temperature of the latter section widthwise stretching step and from Tm-80°C to Tm-15°C or lower. A method for producing a biaxially oriented polypropylene film as described. The method for producing a 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. The method for producing a biaxially oriented polypropylene film according to any one of claims 1 to 3 , wherein the amount of components having a molecular weight of 100,000 or less in the polypropylene resin constituting the biaxially oriented polypropylene film is 35% by mass or more.