WO2020137795A1

WO2020137795A1 - Method for manufacturing biaxially oriented polypropylene film

Info

Publication number: WO2020137795A1
Application number: PCT/JP2019/049812
Authority: WO
Inventors: 山田　浩司; 一仁堀之内; 麻洋中野; 今井　徹
Original assignee: 東洋紡株式会社
Priority date: 2018-12-28
Filing date: 2019-12-19
Publication date: 2020-07-02
Also published as: TWI813841B; JP7405099B2; JPWO2020137795A1; TW202031753A

Abstract

Provided is a biaxially oriented polypropylene film which has high rigidity, has excellent heat resistance even at the high temperature of 150˚C, can easily retain a bag shape when used as a packaging bag, and exhibits few wrinkles in seal parts when heat sealing has been performed thereon.　Also provided is a method for manufacturing the biaxially oriented polypropylene film comprising, in the following order: a step in which an unstretched sheet is obtained by extruding a polypropylene resin composition containing a polypropylene resin with a meso pentad fraction of at least 97.0%; a step in which the unstretched sheet is stretched in the length direction thereof; a preheating step in which the length-direction stretched sheet is heated to a preheating temperature of at least Tm and not higher than Tm+25˚C; a step in which the preheated length-direction stretched sheet is stretched in the width direction at a temperature of at least Tm-10˚C and not higher than the preheating temperature; a step in which the sheet is stretched in the width direction at a temperature of at least Tm-70˚C and not higher than Tm-5˚C, and lower than the temperature of the step in which the sheet is stretched in the width direction at a temperature of at least Tm-10˚C and not higher than the preheating temperature; and a heat treatment step.

Description

Method for producing biaxially oriented polypropylene film

The present invention relates to a method for producing a biaxially oriented polypropylene film having excellent rigidity and heat resistance. More specifically, the present invention relates to a method for producing a biaxially oriented polypropylene film, which can be preferably used for a packaging bag because it easily retains the shape of the packaging bag and has few wrinkles at the sealing portion when heat-sealed.

Biaxially oriented polypropylene film is used for packaging and industrial applications because it has moisture resistance and the necessary rigidity and heat resistance. In recent years, as the applications used have expanded, higher performance has been demanded, and improvement in rigidity is particularly expected. Further, in consideration of the environment, it is required to maintain the strength even if the volume is reduced (the film thickness is made thin), but for that purpose, it is essential to remarkably improve the rigidity. As a means of improving rigidity, it is known that the crystallinity and melting point of the polypropylene resin are improved by improving the catalyst and process technology during the polymerization of the polypropylene resin. There was no biaxially oriented polypropylene film with sufficient rigidity up to.

In the manufacturing process of biaxially oriented polypropylene film, after stretching in the width direction, the first stage heat treatment is performed while relaxing the film at a temperature equal to or less than the width direction stretching temperature, and the second stage heat treatment from the first stage temperature to the width direction stretching temperature. (For example, refer to Reference 1, etc.) and a method for further stretching in the longitudinal direction after stretching in the width direction (for example, see Reference 2). However, although the film described in Patent Document 2 is excellent in rigidity, it tends to cause wrinkles in the seal portion after heat sealing, and is inferior in heat resistance. Further, the orientation of the film described in Patent Document 1 is low and the rigidity is not sufficient.

International Publication WO2016/182003 JP, 2013-177645, A

The problem of the present invention is to solve the above-mentioned problems. That is, the present invention relates to a biaxially oriented polypropylene film having excellent film rigidity, and further relates to a biaxially oriented polypropylene film having excellent film rigidity and heat resistance at a high temperature of 150°C. Specifically, it is an object of the present invention to provide a method for producing a biaxially oriented polypropylene film, which easily retains the shape of a packaging bag and has less wrinkles around the seal portion and its periphery when heat sealed.

As a result of intensive investigations by the present inventors to achieve such an object, a biaxially oriented polypropylene film having excellent film rigidity, further excellent film rigidity and heat resistance at a high temperature of 150° C. are obtained by the following production method. It has been found that a biaxially oriented polypropylene film can be obtained.
That is, the present invention provides 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 lower than the preheating temperature, Tm-10°C or higher, preheating Biaxially oriented polypropylene film including a step of stretching in the width direction at a temperature lower than the temperature of the step of stretching in the width direction at a temperature of Tm-70°C or higher and a temperature of Tm-5°C or lower, and a heat treatment step in order. Is a manufacturing method.

In this case, the step of stretching in the width direction at a temperature lower than the temperature of Tm-10° C. and lower than the preheating temperature is lower than the temperature of the step of stretching in the width direction and at a temperature of Tm-70° C. or higher and Tm-5° C. or lower. During the heat treatment step, the temperature is lower than the temperature of the step of stretching in the width direction at a temperature of Tm-10°C or higher and a preheating temperature or lower, and a width of Tm-70°C or higher and Tm-5°C or lower. It is preferable to include a step of controlling the temperature to be not higher than the temperature of the step of stretching in the direction and not higher than Tm-80°C and not higher than 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, the melt flow rate of the polypropylene resin forming the biaxially oriented polypropylene film is preferably 4.0 g/10 minutes or more.

Furthermore, in this case, it is preferable that the content of the component 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, since the rigidity is high, it is easy to maintain the bag shape when formed into a packaging bag, and thus the biaxially oriented polypropylene film can be suitably used for the packaging bag. Can be obtained. Furthermore, it is highly rigid and has excellent heat resistance at temperatures as high as 150°C, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and there are few wrinkles in the sealing part when heat sealed, so it is suitable for use in packaging bags. A biaxially oriented polypropylene film capable of being obtained can be obtained.
In addition, the biaxially oriented polypropylene film has excellent rigidity, can maintain the strength even when the film thickness is reduced, and can be suitably used for applications requiring higher rigidity.

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

The biaxially oriented polypropylene film obtained by the present invention comprises a polypropylene resin composition containing polypropylene resin as a main component. The "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, further 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 which does not substantially contain ethylene and/or α-olefin having 4 or more carbon atoms is preferable. Even when ethylene and/or α-olefin component having 4 or more carbon atoms is contained, ethylene and/or The amount of 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%, further preferably 0.3 mol%, and particularly preferably 0.1 mol%. Within the above range, the 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, 4-methylpen. Examples thereof include ten-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 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, and a mixture thereof can be used.

(Stereoregularity)
The mesopentad fraction ([mmmm]%), which is an index of the stereoregularity of the polypropylene resin used in the present invention, is preferably in the range of 97.0 to 99.9%, and 97.5 to 99.7. % Is more preferable, 98.0 to 99.5% is more preferable, and 98.5 to 99.3% is particularly preferable.
When it is 97.0% or more, the crystallinity of the polypropylene resin is increased, the melting point, crystallinity, and crystal orientation of the crystals in the film are improved, and rigidity and heat resistance at high temperatures are easily obtained. When it is 99.9% or less, the cost is easily suppressed in terms of polypropylene production, and the film is less likely to be broken during film formation. It is more preferably 99.5% or less. The mesopentad fraction is measured by a nuclear magnetic resonance method (so-called NMR method).
In order to bring the mesopentad fraction of the polypropylene resin into the above range, a method of washing the obtained polypropylene resin powder with a solvent such as n-heptane, selection of a catalyst and/or a cocatalyst, and a polypropylene resin composition A method of appropriately selecting components is preferably adopted.

(Melting temperature)
The lower limit of the melting temperature (Tm) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention measured by DSC is preferably 160°C, more preferably 161°C, and further preferably 162°C. , And even more preferably 163°C. When Tm is 160° C. or higher, rigidity and heat resistance at high temperature are easily obtained.
The upper limit of Tm is preferably 170° C., more preferably 169° C., further preferably 168° C., even more preferably 167° C., and particularly preferably 166° C. When the Tm is 170° C. or less, it is easy to suppress the cost increase in the production of polypropylene, and it becomes difficult to break the film during film formation. The melting temperature can be further increased by adding a crystal nucleating agent to the above polypropylene resin.
Tm is 1-10 mg 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 scanned at a speed of -10°C/minute up to 30°C. It is the main peak temperature of the endothermic peak associated with melting observed when the temperature is lowered, the temperature is maintained for 5 minutes, and the temperature is increased at a scanning rate of 10° C./min.

(Crystallization temperature)
The lower limit of the crystallization temperature (Tc) of the above polypropylene resin constituting the biaxially oriented polypropylene film of the present invention measured by DSC is 105°C, preferably 108°C, more preferably 110°C. When Tc is 105° C. or higher, crystallization is likely to proceed in the width direction stretching and the subsequent cooling step, and rigidity and heat resistance at high temperature can be easily obtained.
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., most preferably 127° C. Is. When Tc is 135° C. or less, it is difficult to increase the cost in the production of polypropylene, and it becomes difficult to break the film 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 in a nitrogen atmosphere, and cooled to 30° C. at a scanning speed of −10° C./minute. It is the main peak temperature of the exothermic peak.
The crystallization temperature can be further increased by blending the above-mentioned polypropylene resin with a crystal nucleating agent.

(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 in accordance with JIS K7210 (1995) condition M (230° C., 2.16 kgf). It is preferably -30 g/10 min, more preferably 4.5-25 g/10 min, even more preferably 4.8-22 g/10 min, and 5.0-20 g/10 min. Particularly preferred is 6.0 to 20 g/10 min, and it is most preferred.
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.
When the melt flow rate (MFR) of the polypropylene resin is 30 g/10 minutes or less, the film formability of the film is easily maintained.

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, It is more preferably 6.0 g/10 minutes, particularly preferably 6.3 g/10 minutes, and most preferably 6.5 g/10 minutes.
When 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 increases, so that the width direction stretching step in the film forming step described below is performed. By adopting it, the oriented crystallization of the polypropylene resin is further promoted, and the crystallinity of the film is more easily increased. In addition, the entanglement of the polypropylene molecular chains in the amorphous part is reduced, and the heat resistance is improved. It is easy to improve the sex.
In order to set the melt flow rate (MFR) of the polypropylene resin within the above range, a method of controlling the average molecular weight or the molecular weight distribution of the polypropylene resin is preferably adopted.

That is, the lower limit of the amount of the component 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 further preferably 40% by mass. And particularly preferably 41% by mass, and most preferably 42% by mass.
The upper limit of the amount of the component having a molecular weight of 100,000 or less in the GPC integration curve is preferably 65% by mass, more preferably 60% by mass, and further preferably 58% by mass. When the amount of the component having a molecular weight of 100,000 or less in the GPC integration curve is 65% by mass or less, the film strength is less likely to decrease.
At this time, when a high molecular weight component or a long chain branching component having a long relaxation time is contained, the amount of the component having a molecular weight of 100,000 or less contained in the polypropylene resin can be easily adjusted without largely changing the overall viscosity. It is easy to improve film formability without affecting heat shrinkage.

(Molecular weight distribution)
In the polypropylene resin used in the present invention, the lower limit of the mass average molecular weight (Mw)/number average molecular weight (Mn), which is an index of the breadth of the molecular weight distribution, is preferably 3.5, more preferably 4.0. , More 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.
Mw/Mn can be obtained using gel permeation chromatography (GPC). When Mw/Mn is in the above range, it is easy to increase the amount of the component having a molecular weight of 100,000 or less.

The molecular weight distribution of polypropylene resin is such that components with different molecular weights are polymerized in a series of plants in multiple stages, components with different molecular weights are blended off-line in a kneader, and catalysts with different performance are blended for polymerization. Or by using a catalyst capable of realizing a desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC has a single peak in a GPC chart in which the horizontal axis represents the logarithm of the molecular weight (M) (logM) and the vertical axis represents the differential distribution value (weight fraction per logM). The molecular weight distribution may be gentle or may have a plurality of peaks or shoulders.

(Method for forming biaxially oriented polypropylene film)
The method for producing the biaxially oriented polypropylene film of the present invention is preferably obtained by producing an unstretched sheet made of the polypropylene resin composition containing the above-mentioned polypropylene resin as a main component and biaxially stretching it. The biaxial stretching method may be any of an inflation simultaneous biaxial stretching method, a tenter simultaneous biaxial stretching method, and a tenter sequential biaxial stretching method. However, from the viewpoint of film forming stability and thickness uniformity, the tenter sequential biaxial stretching method is used. It is preferable to adopt the axial stretching method. In particular, it is preferable to stretch in the longitudinal direction and then in the width direction, but a method of stretching in the width direction and then in the longitudinal direction may be used.

Next, the method for producing the biaxially oriented polypropylene film of the present invention will be described below, but the method is not necessarily limited thereto. The biaxially oriented polypropylene film obtained by the present invention may have at least one surface laminated with a layer having another function. One side or both sides may be laminated. In that case, the polypropylene resin composition described above may be adopted as the resin composition of the other layer or the central layer. Further, it may be different from the polypropylene resin composition described above. The number of layers to be laminated may be one layer, two layers, three layers or more per one side, but one layer or two layers are preferable from the viewpoint of production. As a stacking method, for example, co-extrusion by a feed block method or a multi-manifold method is preferable. In particular, for the purpose of improving the processability of the biaxially oriented polypropylene film, a resin layer having a heat-sealing property can be laminated in a range that does not deteriorate the characteristics. Further, corona treatment may be performed on one side or both sides for imparting printability.

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

Next, the uniaxially stretched film is obtained by stretching the sheet in the longitudinal direction by increasing the rotation speed of the rearward stretching roll with two pairs of heated stretching rolls.

Next, after preheating the uniaxially stretched film, the film is stretched in the width direction at a specific temperature while gripping the film end portion with a tenter type stretching machine to obtain a biaxially stretched film. The width direction stretching step will be described in detail later.

After the widthwise stretching process 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.

A film roll can be obtained by subjecting the thus obtained biaxially oriented polypropylene film to corona discharge treatment on at least one side, if necessary, and winding it with a winder.

Each step will be described in detail below.
(Extrusion process)
First, a polypropylene resin composition containing a polypropylene resin as a main component is heated and melted in a range of 200° C. to 300° C. with a single-screw or twin-screw extruder, and a sheet-shaped molten polypropylene resin composition ejected from a T die is extruded. , Contact with a metal cooling roll to cool and solidify. The unstretched sheet thus obtained is preferably placed in a water tank.
The temperature of the cooling roll or the cooling roll and the water tank is preferably in the range of 10° C. to Tc, and when it is desired to increase the transparency of the film, the film is cooled and solidified by the cooling roll in the temperature range of 10 to 50° C. Is preferred. When the cooling temperature is 50°C or lower, the transparency of the unstretched sheet is likely to increase, and the temperature is preferably 40°C or lower, more preferably 30°C or lower. In order to increase the degree of crystal orientation after successive biaxial stretching, it may be preferable to set the cooling temperature to 40° C. or higher, but as described above, a propylene homopolymer having a mesopendat fraction of 97.0% or more is used. In this case, the cooling temperature is preferably 40° C. or lower in order to facilitate the stretching in the next step and reduce thickness unevenness, and more preferably 30° C. or lower.
The thickness of the unstretched sheet is preferably 3500 μm or less, more preferably 3000 μm or less in terms of cooling efficiency, and can be appropriately adjusted according to 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, and the like.

(Longitudinal stretching step)
The lower limit of the longitudinal stretching ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. Within the above range, the strength is easily increased and the film thickness unevenness is reduced. The upper limit of the longitudinal stretching ratio is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. Within the above range, the width direction stretching in the width direction stretching step is facilitated, and the productivity is improved.
The lower limit of the longitudinal stretching temperature is preferably Tm-40°C, more preferably Tm-37°C, even more preferably Tm-35°C. Within the above range, subsequent widthwise stretching is facilitated, and uneven thickness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, and further preferably Tm-12°C. Within the above range, the heat shrinkage rate is likely to be small, it is difficult to stretch the film by putting it on a stretching roll, and the surface roughness is not likely to deteriorate the quality.
The longitudinal stretching may be performed in three or more stages using three or more pairs of stretching rolls.

(Preheating process)
Before the widthwise stretching step, it is necessary to heat the uniaxially stretched film after stretching in the longitudinal direction in the range of Tm to Tm+25° C. to soften the polypropylene resin composition. When it is at least Tm, softening proceeds and stretching in the width direction becomes easy. By setting the temperature to be Tm+25° C. or less, the orientation during transverse stretching proceeds, and rigidity is easily exhibited. The temperature is more preferably Tm+2 to Tm+22° C., and particularly preferably Tm+3 to Tm+20° C. Here, the maximum temperature in the preheating step is the preheating temperature.

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

In the width direction stretching step, a section (first term section) for stretching at a temperature not lower than Tm-10°C and not higher than the preheating temperature is provided. At this time, the start of the previous 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 half section in the width direction stretching step is preferably Tm-9°C, more preferably Tm-8°C, and further preferably Tm-7°C. If the stretching temperature in the previous period is within this range, stretching unevenness is unlikely to occur.
Following the first half section, a section (second half section), which is lower than the temperature of the first half section and stretches at a temperature of Tm-70°C or higher and Tm-5°C or lower, is provided.
The upper limit of the stretching temperature in the latter section is preferably Tm-8°C, more preferably Tm-10°C. If the stretching temperature in the latter section is in this range, rigidity is likely to be exhibited.
The lower limit of the stretching temperature in the latter period is preferably Tm-65°C, more preferably Tm-60°C, and further preferably Tm-55°C. When the stretching temperature in the latter period is within this range, the film formation is likely to be stable.
The film can be cooled at the end of the latter period, that is, immediately after the final stretch ratio in the width direction is reached. At this time, the cooling temperature is preferably not higher than the temperature in the latter period and not lower than Tm-80°C and not higher than Tm-15°C, preferably not lower than Tm-80°C and not higher than Tm-20°C. The temperature is more preferably Tm-80° C. or higher and Tm-30° C. or lower, further preferably Tm-70° C. or higher and Tm-40° C. or lower.
The temperature in the first half section and the temperature in the second half section can be gradually decreased, but can also be decreased stepwise or in one step, and each may be constant. When the temperature is gradually lowered, the film is less likely to be broken and the thickness variation of the film is easily reduced. Further, the heat shrinkage rate is easily reduced, and the whitening of the film is small, which is preferable.
The temperature at the end of the first half section in the width direction stretching process can be gradually decreased from the temperature at the start of the second half section, or can be decreased stepwise or in one step.

The lower limit of the stretch ratio at the end of the first half of the width direction stretching step is preferably 4 times, more preferably 5 times, further preferably 6 times, and particularly preferably 6.5 times. The upper limit of the draw ratio at the end of the previous period is preferably 15 times, more preferably 14 times, and further 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, further preferably 7 times, and particularly preferably 8 times. If it is 5 times or more, the rigidity is likely to be increased and the unevenness of the film thickness is likely to be reduced.
The upper limit of the draw ratio in the width direction is preferably 20 times, more preferably 17 times, and further preferably 15 times. When it is 20 times or less, the heat shrinkage rate tends to be small, and it is difficult to break during stretching.

Thus, by using a polypropylene resin having high stereoregularity and high melting point and high crystallinity, by adopting the above-described width direction stretching step, the molecular weight of the polypropylene resin can be increased without extremely increasing the stretching ratio. Are highly aligned in the main orientation direction (the width direction is applicable in the above-described width direction stretching step), so that the crystal orientation in the obtained biaxially oriented film is very strong and crystals with a high melting point are easily generated. ..
Further, the orientation of the amorphous portion between the crystals also increases in the main orientation direction (the width direction corresponds to the above-described width direction stretching step), and there are many crystals with a high melting point around the amorphous portion. At a temperature lower than the melting point, the stretched polypropylene molecules in the amorphous portion are difficult to relax and the tensioned state is easily maintained. Therefore, the high rigidity of the entire biaxially oriented film can be maintained even at high temperatures.
Further, it should be noted that the heat shrinkage rate at a high temperature of 150° C. is likely to decrease by adopting such a width direction stretching step. The reason is that since there are many crystals with a high melting point around the amorphous part, the expanded polypropylene resin molecules in the amorphous part are difficult to relax at a temperature lower than the melting point of the crystal, and there is little entanglement between the molecules. is there.

Furthermore, it should be noted that by increasing the low molecular weight component of the polypropylene resin, the crystallinity of the film becomes easier to increase, and the entanglement of the polypropylene resin molecular chains in the amorphous part is reduced, which reduces the heat shrinkage stress. It can be mentioned that the heat shrinkage can be further reduced by weakening. Considering that conventionally, if either the strength or the heat shrinkage rate is improved, the property of the other tends to be deteriorated, it can be said to be epoch-making.

(Heat treatment process)
The biaxially stretched film can be heat-treated, if necessary, to further reduce the heat shrinkage rate.
The upper limit of the heat treatment temperature is preferably Tm+10°C, more preferably Tm+7°C. By setting the temperature to be Tm+10° C. or lower, rigidity is easily exhibited, the surface roughness of the film does not become too large, and the film is less likely to be whitened.
The lower limit of the heat treatment temperature is preferably Tm-10°C, more preferably Tm-7°C. If it is lower than Tm-10°C, the heat shrinkage ratio may increase.
By adopting the above-described width-direction stretching step, even if heat treatment is performed at a temperature between Tm-10°C and Tm+10, highly oriented crystals generated in the stretching step are less likely to melt, and the rigidity of the obtained film is improved. The heat shrinkage rate can be further reduced without lowering it.
For the purpose of adjusting the heat shrinkage ratio, 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 strength of the film is unlikely to decrease, and fluctuations in the film thickness tend to be small. It is more preferably 8%, even more preferably 7%, even more preferably 3%, particularly preferably 2%, 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 It is preferably 4 μm, particularly preferably 8 μm, and most preferably 10 μm. When the film thickness is 2 μm or more, the rigidity of the film is easily obtained. 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. When the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion process does not easily decrease.
The biaxially oriented polypropylene film obtained by the present invention is usually formed as a roll having a width of 2000 to 12000 mm and a length of 1000 to 50000 m and wound into a film roll. Further, the slit roll is slit according to each application and provided as a slit roll having a width of 300 to 2000 mm and a length of 500 to 5000 m. The biaxially oriented polypropylene film of the present invention makes it 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%, further preferably 0.5%, and particularly preferably 1%. is there. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, further preferably 15%, particularly preferably 12%, most preferably 10%. 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.
The measuring method was as follows. A test piece of 40 mm in width direction is cut out from a steady region in which the physical properties of the film are stable in the length direction of the film, and a film feeder (manufactured by A90172 is used) manufactured by Micron Measuring Instruments Co., Ltd. and a film manufactured by Anritsu Corporation. Using a continuous thickness measuring instrument (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 value−minimum thickness value)/average thickness value]×100

(Film characteristics)
The biaxially oriented polypropylene film obtained by the present invention is characterized by the following characteristics. 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 the flow direction in the film manufacturing process. It is a direction orthogonal to each other. For a polypropylene film whose flow direction is unknown in the film manufacturing process, a wide-angle X-ray is incident in the direction perpendicular to the film surface, and the scattering peak derived from the (110) plane of the α-type crystal is scanned in the circumferential direction, The direction in which the obtained diffraction intensity distribution has the highest diffraction intensity is the "longitudinal direction", and the direction orthogonal thereto is the "width direction".

(23°C Young's modulus)
The lower limit of the Young's modulus in the longitudinal direction of the biaxially oriented polypropylene film obtained by the present invention at 23° C. is preferably 2.0 GPa, more preferably 2.1 GPa, further preferably 2.2 GPa, Particularly preferred is 2.3 GPa, and most preferred is 2.4 GPa. At 2.0 GPa or more, since the rigidity is high, the bag shape of the packaging bag is easily maintained, and the film is less likely to be deformed during processing such as printing. 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. Is. When it is 4.0 GPa or less, practical production is easy, and the balance of the characteristics in the longitudinal direction and the width direction is easily improved.

The lower limit of the 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, further preferably 6.5 GPa, Particularly preferably, it is 6.7 GPa. At a pressure of 6.0 GPa or more, since the rigidity is high, the bag shape of the packaging bag can be easily maintained, and the film is unlikely 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 further preferably 12 GPa. If it is 15 GPa or less, realistic manufacturing is easy, and the balance of characteristics in the longitudinal direction and the width direction tends to be improved.
The Young's modulus can be adjusted within the range by adjusting the stretching ratio and the relaxation rate, or by adjusting the temperature during film formation.

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

The biaxially oriented polypropylene film obtained by the present invention is better if it has the following characteristics and structure.

(80°C Young's modulus)
The lower limit of the Young's modulus in the longitudinal direction of the biaxially oriented polypropylene film obtained by the present invention at 80°C is preferably 0.5 GPa, more preferably 0.7 GPa. When it is 0.5 GPa or more, a printing pitch shift is less likely to occur when a high-temperature printing ink is transferred. 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 more, practical production is easy.
The lower limit of the Young's modulus in the width direction at 80° C. is preferably 2.5 GPa, more preferably 2.8 GPa, and further preferably 3.0 GPa. When it is 2.5 GPa or more, a printing pitch shift when transferring high-temperature printing ink is less likely to occur. The upper limit of the Young's modulus in the width direction at 80° C. is preferably 5.0 GPa, more preferably 4.7 GPa, and further preferably 4.5 GPa. If it is 5.0 GPa or less, realistic manufacturing is easy.
The Young's modulus at 80° C. can be adjusted within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature.

(Stress at 23°C 5% elongation)
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, further preferably 44 MPa. Yes, and particularly preferably 45 MPa. At 40 MPa or more, since the rigidity is high, the bag shape of the packaging bag can be easily maintained, and the film is unlikely 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, further preferably 62 MPa, particularly preferably 61 MPa, most preferably 60 MPa. When it is 70 MPa or less, realistic manufacturing is easy, and the vertical width balance is likely to be improved.
The lower limit of F5 in the width direction of the biaxially oriented polypropylene film of the present invention at 23° C. is 160 MPa, preferably 165 MPa, more preferably 168 MPa, further preferably 170 MPa. At 160 MPa or more, since the rigidity is high, the bag shape of the packaging bag can be easily maintained, 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, further preferably 240 MPa. If the pressure is 250 MPa or less, realistic manufacturing is easy, and the vertical-width balance is likely to be improved.
F5 can be set within the range by adjusting the stretching ratio and the relaxation rate, and by adjusting the temperature during film formation.
(Stress at 80°C 5% elongation)
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 further preferably 20 MPa. is there. At 15 MPa or more, since the rigidity is high, the bag shape of the packaging bag can be easily maintained, and the film is unlikely 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, further preferably 30 MPa, particularly preferably 25 MPa. If it is 40 MPa or less, realistic production is easy, and the vertical width balance tends to be improved.
The lower limit of F5 in the width direction 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, particularly preferably 95 MPa. .. When the pressure is 75 MPa or more, the rigidity is high, and thus the shape of the packaging bag can be easily maintained, and the film is unlikely 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 further preferably 130 MPa. If the pressure is 140 MPa or less, realistic manufacturing is easy, and the vertical-width balance is likely to be improved.
80° C. F5 can be set within the range by adjusting the stretching ratio and the relaxation rate, and by adjusting the temperature during film formation.

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

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

(Refractive index)
The lower limit of the refractive index (Nx) in the longitudinal direction of the biaxially oriented polypropylene film obtained by the present invention is preferably 1.4950, more preferably 1.4970, and further preferably 1.4980. If 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, further preferably 1.5050. When it is 1.5100 or less, the balance of the properties in the longitudinal direction and the width direction of the film tends to be excellent.

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 further preferably 1.5240 or more. If 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 balance of the properties in the longitudinal direction and the width direction of the film tends to be excellent.

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 further preferably 1.4970. If 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 1.520, more preferably 1.5015, and even more preferably 1.510. When it is 1.5020 or less, the heat resistance of the film is easily increased.
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, and 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. If it is 0.0270 or less, uneven thickness tends to be good. ΔNy can be adjusted within the range by adjusting the stretching ratio, stretching temperature and heat setting temperature of the film.
ΔNy is the refractive index along the longitudinal direction, the width direction, and the thickness direction of the film, and is calculated by the following formula, respectively. The width in the longitudinal direction of the film, the width direction, and the entire thickness direction orientation It means the degree of directional orientation.
ΔNy=Ny−[(Nx+Nz)/2]

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

(Haze)
The lower limit of haze of the biaxially oriented polypropylene film obtained by the present invention is, as a practical value, preferably 0.1%, more preferably 0.2%, further preferably 0.3%, It is particularly preferably 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%, further preferably 4.0%, particularly preferably 3.5%, most preferably 3.0. %. When it is 5.0% or less, it is easy to use in applications where transparency is required. The haze is to adjust the cooling roll (CR) temperature, the width direction stretching temperature, the tenter width direction pre-stretching preheating temperature, the width direction stretching temperature, or the heat setting temperature, or the amount of the component having a molecular weight of polypropylene resin of 100,000 or less. However, it may be increased by the addition of an antiblocking agent or the provision of a seal layer.

(Full width at half maximum of diffraction peak derived from oriented crystal)
The biaxially oriented polypropylene film obtained according to the present invention has an azimuth angle dependence of the scattering peak of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray measurement which is perpendicularly incident on the film surface, in the width direction of the film. The upper limit of the full width at half maximum (Wh) of the diffraction peak derived from the oriented crystal is preferably 27°, more preferably 26°, further preferably 25°, particularly preferably 24°, and most preferably Is 23°.
The lower limit of Wh is preferably 13°, more preferably 14°, and further preferably 15°. When the full width at half maximum (Wh) is 27° or less, it is easy to increase the rigidity of the film.

(X-ray orientation degree)
The lower limit of the X-ray orientation degree calculated from the Wh of the biaxially oriented polypropylene film obtained by the present invention by the following formula is preferably 0.85, more preferably 0.855, and further preferably 0.861. Is. When it is 0.85 or more, the rigidity is easily increased.
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 further preferably 0.917. By setting it to 0.928 or less, the film formation is likely to be stable.

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

(Tensile breaking elongation)
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%, further preferably 60%. When it is 50% or more, the breakage of the film and the breakage of the packaging bag tend to be reduced. The upper limit of the tensile elongation at break in the longitudinal direction is, as a practical value, preferably 230%, more preferably 220%, further preferably 210%. When it is 230% or less, the printing pitch is less likely to shift when the printing ink is transferred, and the durability of the packaging bag is 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%, further preferably 17%. When it is 10% or more, the breakage of the film and the breakage of the packaging bag are likely to be reduced. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, further preferably 50%. When it is 60% or less, the printing pitch is less likely to shift when the printing ink is transferred, and the durability of the packaging bag is likely to be excellent.
The tensile elongation at break can be adjusted within the range by adjusting the stretching ratio, the stretching temperature, and the heat setting temperature.

(Bending)
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 further preferably 0.1. It is 35 mN·cm. When the film thickness is 0.3 mN·cm or more, it is possible to make the film thinner, and it is suitable for applications requiring 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 further preferably 0.6 mN·cm. When it is 0.5 mN·cm or more, the film can be thinned and is suitable for applications requiring rigidity.

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

The loop stiffness stress is an index representing the feeling of stiffness of the film, but it also depends on the thickness of the film. The measuring method is as follows. Two 110 mm×25.4 mm strips were cut out with the longitudinal direction of the film as the long axis of the strip (loop direction) or the width direction of the film as the long axis of the strip (loop direction). For those in which one side of the film is the inner surface of the loop sandwiching these in the clip and the other side is the inner surface of the loop for measurement, the long axis of the strip is the longitudinal direction and width direction of the film It was made. The measuring loop whose long axis is the longitudinal direction of the film is set on the chuck of a loop stiffener tester DA manufactured by Toyo Seiki Co., Ltd. with the width direction vertical, the clip is removed, and the chuck interval is 50 mm. The loop stiffness stress was measured at an indentation depth of 15 mm and a compression speed of 3.3 mm/sec.
For the measurement, the loop stiffness stress and the thickness were measured 5 times, while one side of the film was made to be the inner surface of the loop, and 5 times were also made after the other side was made the inner surface of the loop. Using the data for 10 times in total, the cube of the thickness (μm) of each test piece was plotted on the horizontal axis, and the loop stiffness stress (mN) was plotted on the vertical axis, and approximated by a straight line with intercept 0, The inclination a was determined. The inclination a means a characteristic value peculiar to the film that does not depend on the thickness that determines the rigidity. The inclination a was used as the evaluation value of the waist feeling. The measurement loop in which the long axis of the strip is the width direction of the film was also measured in the same manner.

(Wrinkles during heat sealing)
To form a bag for packaging food, the bag is filled with the contents and heated to melt and fuse the film for sealing. In addition, the same is often done when making bags while filling foods. Usually, a sealant film made of polyethylene, polypropylene or the like is laminated on a substrate film, and the sealant film surfaces are fused. As a heating method, pressure is applied from the side of the base material film with a heating plate to press the film to seal it, and the sealing width is often about 10 mm. At this time, since the base material film is also heated, the shrinkage at that time causes wrinkles. As for the durability of the bag, it is better to have less wrinkles, and it is also better to have less wrinkles in order to increase purchasing will. The sealing temperature may be about 120° C., but a higher sealing temperature is required in order to increase the bag-making processing speed, and even in that case, it is preferable that the shrinkage is small. When fusing the chuck to the open portion of the bag, it is necessary to seal at a higher temperature.

(Print pitch deviation)
As a basic structure of the packaging film, it is often composed of a laminated film of a printed base film and a sealant film. Bag making machines are used to manufacture bags, such as three-sided bags, standing bags, and gusset bags, and various bag making machines are used. Print pitch misalignment is considered to occur because the film base material expands and contracts because tension and heat are applied to the film during the printing process. Eliminating defective products due to printing pitch misalignment is important in terms of effective use of resources, and is also important for increasing purchasing motivation.

(Film processing)
Printing of the biaxially oriented polypropylene film obtained by the present invention can be carried out by letterpress printing, planographic printing, intaglio printing, stencil printing, and transfer printing depending on the application.
In addition, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, unstretched sheet made of polyester, uniaxially stretched film, biaxially stretched film are laminated as a sealant film to provide heat sealability. It can also be used as a laminated body. To further improve gas barrier properties and heat resistance, aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, unstretched sheet made of polyvinyl alcohol, uniaxially stretched film, biaxially stretched film are biaxially oriented polypropylene films. And a sealant film can be provided as an intermediate layer. An adhesive applied by a dry lamination method or a hot melt lamination method can be used for bonding the sealant film.
In order to improve the gas barrier property, aluminum or an inorganic oxide can be vapor-deposited on the biaxially oriented polypropylene film, the intermediate layer film, or the sealant film. As the vapor deposition method, vacuum vapor deposition, sputtering, or ion plating can be adopted, but it is particularly preferable to vacuum vapor deposit silica, alumina, or a mixture thereof.

The biaxially oriented polypropylene film obtained by the present invention includes, for example, 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 higher fatty acid amines and amides. The presence of the agent in the film in the range of 0.2 to 5% by mass makes it suitable for packaging fresh products consisting of vegetables, fruits, flowers and other plants that require high freshness. be able to.
Further, as long as the effect of the present invention is not impaired, various additives for quality improvement such as slipperiness and antistatic property, for example, wax for improving productivity, lubricant such as metal soap, plasticizer It is also possible to add agents, processing aids, heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers and the like.

(Industrial availability)
The biaxially oriented polypropylene film obtained by the present invention has the above-mentioned unprecedented excellent properties, and thus can be preferably used in a packaging bag, and the film thickness can be made thinner than before. is there. Furthermore, applications such as insulating films for capacitors and motors, back sheets for solar cells, barrier films for inorganic oxides, base films for transparent conductive films such as ITO, and high-temperature applications, and rigidity for separate films are required. It is also suitable for various applications. Further, by using a coating agent, an ink, a laminating adhesive, etc., which have been hard to be used conventionally, it becomes possible to coat or print at a high temperature, and it is expected that the production efficiency will be improved.

Hereinafter, the present invention will be described in detail with reference to Examples. The characteristics were measured and evaluated by the following methods.
(1) Melt Flow Rate The melt flow rate (MFR) was measured according to JIS K 7210 at a temperature of 230° C. and a load of 2.16 kgf.

(2) Mesopentad Fraction The mesopentad fraction ([mmmm]%) of polypropylene resin was measured using ¹³ C-NMR. The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, Volume 6, page 925 (1973). ^{The 13} C-NMR measurement was carried out at 110° C. by using AVANCE500 manufactured by BRUKER, 200 mg of the sample was dissolved in a mixture of o-dichlorobenzene and deuterated benzene at 8:2 at 135° C.

(3) Number average molecular weight, weight average molecular weight of polypropylene resin, amount of components having a molecular weight of 100,000 or less, and molecular weight distribution It was determined as a PP-converted molecular weight based on monodisperse polystyrene using gel permeation chromatography (GPC). When the baseline is not clear, it was decided to set the baseline in the range up to the lowest position on the high molecular weight side of the elution peak on the high molecular weight side closest to the elution peak of the standard substance.
The GPC measurement conditions are as follows.
Device: HLC-8321PC/HT (manufactured by Tosoh Corporation)
Detector: RI
Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%)
Column: TSKgelguardcolumnHHR(30)HT (7.5 mmID×7.5 cm)×1 + TSKgelGMHHR-H(20)HT (7.8 mmID×30 cm)×3 Flow rate: 1.0 mL/min
Injection volume: 0.3 mL
Measurement temperature: 140℃
The number average molecular weight (Mn) and the mass average molecular weight (Mw) are respectively defined by the following formulas 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. It
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.
Further, the ratio of the component having a molecular weight of 100,000 or less was obtained from the integral curve of the molecular weight distribution obtained by GPC.

(4) Crystallization temperature (Tc), melting temperature (Tm)
Using a Q1000 differential scanning calorimeter manufactured by TA Instruments Co., Ltd., heat measurement was performed in a nitrogen atmosphere. About 5 mg was cut out from a polypropylene resin pellet and enclosed in an aluminum pan for measurement. After the temperature was raised to 230° C. and kept 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). Further, the heat of crystallization (ΔHc) was determined by setting the 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 as it was at 30° C. for 5 minutes, the temperature was raised to 230° C. at 10° C./minute, and the main endothermic peak temperature was taken as the melting temperature (Tm).

(5) Film Thickness The film thickness was measured using a Millitron 1202D manufactured by Seiko EM.

(6) Haze NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. was used and measured at 23° C. according to JISK7105.

(7) Tensile test According to JIS K 7127, the tensile strength in the longitudinal direction and the width direction of the film was measured at 23°C. The sample was cut out from the film to a size of 15 mm×200 mm, the chuck width was 100 mm, and set in a tensile tester (Dual column tabletop tester Instron 5965 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, Young's modulus was determined from the slope of the straight line portion at the initial stage of elongation, and stress (F5) at 5% elongation was determined. The tensile strength at break and the tensile elongation at break were the strength and the elongation at the time when the sample was broken.
The Young's modulus at 80° C. and F5 were obtained by performing the measurement in a constant temperature bath at 80° C. The measurement was carried out by setting the chuck in a thermostatic chamber set at 80° C. in advance, mounting the sample until measurement, and holding it for 1 minute.

(8) Heat Shrinkage The heat shrinkage was measured by the following method according to JIS Z 1712. The film was cut into a length of 20 mm and a length of 200 mm in the longitudinal direction and the width direction of the film, respectively, and 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 determined by the ratio of the length that was contracted to the original length.
(9) TMA Heat Elongation The heat elongation was measured by TMA measurement, and the TMA measurement was performed by using a thermomechanical analyzer TMA-60 manufactured by Shimadzu Corporation. A strip having a length of 20 mm and a width of 4 mm was cut out from the film to give a sample. The distance between the chucks was set to 10 mm, the temperature was raised from 30° C. to 180° C. at 20° C./min with a measuring load of 40 g, and the maximum amount of elongation in the temperature range up to 150° C. was measured, which was taken as the TMA heating elongation. ..

(10) Refractive Index, ΔNy, Surface Orientation Coefficient Measured with an Abbe refractometer manufactured by Atago Co., Ltd. at a wavelength of 589.3 nm and a temperature of 23° C. The refractive indexes along the longitudinal direction and the width direction of the film were Nx and Ny, respectively, and the refractive index in the thickness direction was Nz. ΔNy was calculated from Nx, Ny, and Nz by using (formula) Ny−[(Nx+Nz)/2]. Further, the plane orientation coefficient (ΔP) was calculated by using the (formula) [(Nx+Ny)/2]−Nz.

(11) X-ray full width at half maximum, orientation degree The measurement was performed by a transmission method using an X-ray diffractometer (RINT2500 manufactured by Rigaku Corporation). A scintillation counter was used as a detector using X-rays having a wavelength of 1.5418Å. Samples were prepared by stacking the films so as to have a thickness of 500 μm. The sample stage was placed at the diffraction peak position (diffraction angle 2θ=14.1°) of the (110) plane of the α-type crystal of polypropylene resin, and the sample was rotated 360° about the thickness direction of the film, and the (110) plane The azimuth dependence of the diffraction intensity was obtained. From this azimuth dependence, the half width Wh of the diffraction peak derived from the oriented crystal in the width direction of the film was determined.
Further, the degree of X-ray orientation was calculated from Wh using Wh.
X-ray orientation degree=(180-Wh)/180

(12) Stiffness and amount of sag According to the JlS L 1096B method (sliding method), the following procedure was used. A test piece of 20 mm×150 mm was prepared, the tester main body and the upper surface of the moving table were aligned with each other, and then the test piece was mounted on the stand of the tester so as to project 50 mm, and a weight was set. Then, the handle was gently turned to lower the sample table, and the amount of sag (δ) when the free end of the sample was separated from the sample table was measured. Using the amount of sag δ, the film thickness, the test piece size, and the film density of 0.91 g/cm ³ , the bending resistance (Br) was calculated from the following formula.
Br=WL ⁴ /8δ
Br: bending resistance (mN·cm)
W: Gravity per unit area of the test piece (mN/cm ² )
L: Length of test piece (cm)
δ: Drooping amount (cm)

(13) Loop stiffness stress, lumbar feeling 110 mm×25.4 mm strip-shaped test piece with the longitudinal direction of the film as the long axis of the strip (loop direction) or the width direction of the film as the long axis of the strip (loop direction). Each of the 10 pieces was cut out. For those in which one side of the film is the inner surface of the loop sandwiching these in the clip and the other side is the inner surface of the loop for measurement, the long axis of the strip is the longitudinal direction and width direction of the film It was made. Set the loop for measurement in which the long axis of the strip is the longitudinal direction of the film in the chuck part of Loop Stiffness Tester DA manufactured by Toyo Seiki Seisakusho Co., Ltd. with the width direction vertical, remove the clips, and set the chuck spacing. The loop stiffness stress was measured at 50 mm, indentation depth of 15 mm and compression speed of 3.3 mm/sec.
For the measurement, the loop stiffness stress and the thickness were measured 5 times, with one side of the film being the inner surface of the loop, and then 5 times were also measured with the other side being the inner surface of the loop. Using the data for 10 times in total, the cube of the thickness (μm) of each test piece was plotted on the horizontal axis and the loop stiffness stress (mN) was plotted on the vertical axis, and approximated by a straight line with intercept 0, The inclination a was determined. The inclination a was used as the evaluation value of the waist feeling. The measurement loop in which the long axis of the strip is the width direction of the film was also measured in the same manner.

(Example 1)
As the polypropylene resin, a propylene homopolymer PP-1 (Sumitomo Noblen FLX80E4 manufactured by Sumitomo Chemical Co., Ltd.) having MFR=7.5 g/10 min, Tc=116.2° C. and Tm=162.5° C. was used. .. It was extruded into a sheet form from a T die at 250° C., brought into contact with a 20° C. cooling roll, and then put into a 20° C. water tank 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 by clips, introduced into a hot air oven, preheated at 170°C, and then 160°C as the first step in the width direction. Was stretched for 6 times, and subsequently, as a second stage, stretching was performed for 1.36 times at 145° C., so that a total of 8.2 times was stretched. Immediately after stretching in the width direction, it was cooled at 100° C. while being held by 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 polypropylene resin, and Table 2 shows film forming conditions. As to the physical properties, as shown in Table 3, a film having high rigidity and low heat shrinkage at high temperature was obtained.

(Example 2)
As polypropylene resin, 80 parts by weight of PP-1, MFR=11 g/10 minutes, [mmmm]=98.8%, Tc=116.5° C., Tm=161.5° C. PP- 20 (part by Sumitomo Chemical Co., Ltd., EL80F5) was blended and used. Example 1 was repeated except that the stretching temperature in the longitudinal direction was 142°C, the stretching temperature in the first step 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 polypropylene resin, and Table 2 shows film forming conditions. As to the physical properties, as shown in Table 3, a film having high rigidity and low heat shrinkage at high temperature 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 polypropylene resin, and Table 2 shows film forming conditions. As to the physical properties, as shown in Table 3, a film having high rigidity and low heat shrinkage at high temperature 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 polypropylene resin, and Table 2 shows film forming conditions. As for the physical properties, as shown in Table 3, a film having high rigidity was obtained.

(Example 5)
After stretching in the width direction, the same procedure as in Example 2 was performed, except that the sample was held in a clip without being cooled and heat-set at 165°C. The thickness of the obtained film was 19.5 μm. Table 1 shows the structure of polypropylene resin, and Table 2 shows film forming conditions. As to the physical properties, as shown in Table 3, a film having high rigidity and low heat shrinkage at high temperature was obtained.

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

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

(Example 8)
The widthwise stretching was performed in the same manner as in Example 2 except that the stretching ratio of the first stage was 6.6 times and the stretching ratio of the second stage was 1.5 times, for a total stretching of 9.9 times. .. The thickness of the obtained film was 20.1 μm. Table 1 shows the structure of polypropylene resin, and Table 2 shows film forming conditions. As to the physical properties, as shown in Table 3, a film having high rigidity and low heat shrinkage at high temperature was obtained.

(Comparative Example 1)
Using PP-1 as a polypropylene resin, it was extruded into a sheet form from a T die at 250° C., brought into contact with a cooling roll at 20° C., and put into a 20° C. water tank as it was. After that, a longitudinal stretching of 4.5 times is performed at 143° C., a preheating temperature of 170° C. and a stretching temperature of 158° C. in the width direction stretching in a tenter are 8.2 times, and then heat setting is performed at 168° C. I went. The thickness of the obtained film was 18.6 μm. Table 1 shows the structure of polypropylene resin, Table 2 shows film forming conditions, and Table 3 shows physical properties. As to the physical properties, as shown in Table 3, the rigidity was low.

(Comparative example 2)
The same procedure as in Comparative Example 1 was carried out except that 80 parts by weight of PP-1 and 20 parts by weight of PP-2 were blended and used as the polypropylene resin. The thickness of the obtained film was 20.0 μm. Table 1 shows the structure of polypropylene resin, Table 2 shows film forming conditions, and Table 3 shows physical properties. As to the physical properties, as shown in Table 3, the rigidity was low.

(Comparative example 3)
As the polypropylene resin, PP-3 (FL203D manufactured by Nippon Polypro Co., Ltd.) having MFR=3 g/10 minutes, Tc=117.2° C. and Tm=160.6° C. was used. It was extruded into a sheet form from a T die at 250° C., brought into contact with a 20° C. cooling roll, and then put into a 20° C. water tank as it was. Then, in the longitudinal direction, it is stretched 4.5 times at 135° C., and in the widthwise stretching with a tenter, the preheating temperature is 166° C., the temperature of the first stage of stretching is 155° C., the temperature of the second stage is 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 polypropylene resin, Table 2 shows film forming conditions, and Table 3 shows physical properties. As for the physical properties, as shown in Table 3, the heat shrinkage at high temperature was high.

(Comparative Example 4)
As the polypropylene resin, PP-4 (FS2012, manufactured by Sumitomo Chemical Co., Ltd.) having MFR=2.7 g/10 minutes, Tc=114.7° C. and Tm=163.0° C. was used. It was extruded into a sheet form from a T die at 250° C., brought into contact with a 20° C. cooling roll, and then put into a 20° C. water tank as it was. Then, after stretching in the longitudinal direction at 130° C. to 5.8 times, the film is heated in a tenter at a preheating temperature of 167° C., and then stretched at a stretching temperature of 161° C. in the width direction by 8.6 times. Then, heat setting was carried out at 130° C. while applying relaxation of 10%, and subsequently, second stage heat setting was carried out at 140° C. The thickness of the obtained film was 13.4 μm. Table 1 shows the structure of polypropylene resin, Table 2 shows film forming conditions, and Table 3 shows physical properties. As for the physical properties, as shown in Table 3, the heat shrinkage at high temperature was high.

(Reference example)
PP-4 was used as a polypropylene raw material. It was extruded into a sheet form from a T die at 250° C., brought into contact with a 20° C. cooling roll, and then put into a 20° C. water tank as it was. Then, it is stretched 4.5 times in the longitudinal direction at 145° C., and in the transverse stretching with a tenter, the preheating temperature is 170° C., the temperature of the first stage of stretching is 160° C., the temperature of the second stage of stretching is 145° C., and cooling is performed. 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 polypropylene resin, Table 2 shows film forming conditions, and Table 3 shows physical properties. As for the physical properties, as shown in Table 3, the heat shrinkage at high temperature was high.

Claims

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 of Tm to Tm+25° C. A preheating step of heating to a preheating temperature in a range, a step of stretching the preheated longitudinally stretched film in the width direction at a temperature of Tm-10°C or higher and a preheating temperature or lower, at a temperature of Tm-10°C or higher and a preheating temperature or lower. A method for producing a biaxially oriented polypropylene film, which comprises a step of stretching in the width direction at a temperature lower than the temperature of the step of stretching in the width direction and a temperature of Tm-70°C or higher and Tm-5°C or lower, and a heat treatment step in that order.
A step of stretching in the width direction at a temperature lower than the step of stretching in the width direction at a temperature of Tm-10° C. or higher and a temperature of preheating or lower, and stretching in the width direction at a temperature of Tm-70° C. or higher and Tm-5° C. or lower; During the process, stretching is performed in the width direction at a temperature lower than the temperature of Tm-10° C. and not higher than the preheating temperature and lower than the temperature of the process of stretching in the width direction and not lower than Tm-70° C. and not higher than Tm-5° C. The method for producing a biaxially oriented polypropylene film according to claim 1, comprising a step of controlling the temperature to be Tm-80°C to Tm-15°C or lower at a temperature not higher than the step temperature.
The method for producing a biaxially oriented polypropylene film according to claim 1 or 2, wherein the polypropylene resin forming 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 polypropylene resin constituting the biaxially oriented polypropylene film has a melt flow rate of 4.0 g/10 minutes or more.
The method for producing a biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein the amount of components having a molecular weight of 100,000 or less of the polypropylene resin constituting the biaxially oriented polypropylene film is 35% by mass or more.