WO2021261313A1 - Production method for biaxially-oriented polypropylene film - Google Patents

Abstract

[Problem] To provide a biaxially-oriented polypropylene film that: has high rigidity; easily maintains a bag shape when used as a packaging bag, even if the film is made thin, while at the same time, being able to maintain gas barrier properties at equivalent thickness to conventional films, even if the film is made thin; and, to make the film into packaging, has few wrinkles in a seal part and the periphery thereof when heat sealed. [Solution] A production method for a biaxially-oriented polypropylene film comprises, in order: a step in which an unstretched sheet is obtained by extruding a polypropylene resin composition containing a polypropylene resin having a mesopentad fraction of at least 97.0%; a step in which the unstretched sheet is stretched in the longitudinal direction; a preheating step in which the longitudinally-stretched film is heated at a preheating temperature of Tm to Tm+25°C; a step in which the preheated, longitudinally-stretched film is stretched by a factor of at least 10 in the width direction at a temperature of Tm–10°C to the preheating temperature; a step in which the film is cooled at the width direction stretching temperature or less when the width direction stretching has finished, and at a temperature of Tm–80°C to Tm–15°C; and a step in which heat fixing is carried out while stretching the film by a factor of 1.03 or more in the width direction at a temperature of Tm–5°C to Tm+20°C.

Description

Manufacturing method of biaxially oriented polypropylene film

The present invention relates to a biaxially oriented polypropylene film having excellent rigidity and heat resistance. More specifically, the present invention relates to a biaxially oriented polypropylene film that can be suitably used for a packaging bag because it is easy to maintain the shape of the bag when it is used as a packaging bag and there are few wrinkles in the sealed portion when heat-sealed.

Biaxially oriented polypropylene film has moisture resistance, and also has the necessary rigidity and heat resistance, so it is used for packaging and industrial applications. In recent years, in consideration of the environment, it has been required to maintain the strength even if the volume is reduced (the film thickness is reduced), and for that purpose, it is indispensable to significantly improve the rigidity. As a means to improve the rigidity, the crystallinity and melting point of the polypropylene resin can be improved by improving the catalyst and process technology during the polymerization of the polypropylene resin, and the draw ratio in the film forming process can be increased to increase the degree of orientation of the film. There was a technology to enhance. However, there is a problem that the heat resistance is lowered at the same time as increasing the rigidity, and there has been no biaxially oriented polypropylene film having sufficient rigidity and heat resistance so far. Further, when the rigidity is improved and the volume of the film is reduced, the water vapor barrier property is lowered and the moisture proof property is impaired, so that there is a problem that the food is deteriorated.

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 lower than the temperature at the time of width direction stretching, and in the second stage, heat treatment is performed at the first stage temperature to the width direction stretching temperature. (For example, see Patent Document 1 and the like), and a method of further stretching in the longitudinal direction after stretching in the width direction (see, for example, Patent Documents 2 and 3 and the like) have been proposed. However, although the film described in Patent Document 2 is excellent in rigidity, wrinkles are likely to occur in the sealed portion after heat sealing, and the heat resistance is inferior. Further, the orientation of the film described in Patent Document 1 is low, and the rigidity is not sufficient. The film described in Patent Document 3 is sequentially biaxially stretched, and the film oriented in the width direction is re-stretched in the longitudinal direction, so that the molecular chains are not sufficiently arranged in the longitudinal direction and the rigidity in the longitudinal direction is low. It was a thing. Further, since the relaxation is performed in the width direction, the orientation in the width direction is low and the rigidity is not sufficient.

WO2016 / 182003 International Bulletin Japanese Unexamined Patent Publication No. 2013-177645 Japanese Unexamined Patent Publication No. 2001-40111

The object of the present invention is to solve the above-mentioned problems. That is, the present invention relates to a biaxially oriented polypropylene film having both the rigidity of the film and the heat resistance at a high temperature of 150 ° C. Specifically, it has high rigidity, and it is easy to maintain the bag shape when it is made into a packaging bag even if the film is thinned, and at the same time, it can maintain the gas barrier property equivalent to the conventional thickness even if the film is thinned, so that it can be made into a package. In addition, it is an object of the present invention to provide a biaxially oriented polypropylene film having less wrinkles in and around the sealed portion when heat-sealed.

As a result of diligent studies to achieve such an object, the present inventors have high rigidity, excellent heat resistance at a high temperature of 150 ° C., easy to maintain the bag shape when used as a packaging bag, and at the time of printing. It has been found that a biaxially oriented polypropylene film having less wrinkles in the sealed portion can be obtained when pitch deviation or heat sealing is performed.
That is, the present invention relates to 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. 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 at a temperature of Tm-10 ° C or higher and lower than the preheating temperature at a magnification of 10 times or more in the width direction. A step of cooling a film at a temperature of Tm-80 ° C or higher and Tm-15 ° C or lower at the end of directional stretching, 1.03 times or more in the width direction at Tm-5 ° C or higher and Tm + 20 ° C or lower. This is a method for producing a biaxially oriented polypropylene film, which comprises a step of heat-fixing while stretching at a magnification of 1.

In this case, it is preferable that the crystallization temperature of the polypropylene resin constituting the biaxially oriented polypropylene film is 105 ° C. or higher and the melting point is 161 ° C. or higher.

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

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

The biaxially oriented polypropylene film of the present invention has high rigidity and can be thinned, and at the same time, it can maintain the same gas barrier property as the conventional thickness even when the film is thinned, and is heat-sealed in order to form a package. It is a biaxially oriented polypropylene film with few wrinkles in and around the sealing part. Therefore, it can be suitably used for packaging, industrial use, and the like.

Hereinafter, the biaxially oriented polypropylene film of the present invention will be described in more detail.
The biaxially oriented polypropylene film of the present invention comprises a polypropylene resin composition containing a 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, still more preferably 95% by mass or more, and 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 is substantially free of ethylene and / or an α-olefin having 4 or more carbon atoms is preferred, and even if 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, more preferably 0.5 mol% or less, still more preferably 0.3 mol% or less, and particularly preferably 0. It is 1 mol or less. 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-methyl. Examples thereof include pentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene and the like.
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.

(Tacticity)
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%, preferably 97.5 to 99.7. It is more preferably in the range of%, further preferably in the range of 98.0 to 99.5%, and particularly preferably in the range of 98.5 to 99.3%.
When it is 97.0% or more, the crystallinity of the polypropylene resin is enhanced, the melting point, crystallinity, and crystallinity of the crystals in the film are improved, and rigidity and heat resistance at high temperature can be easily obtained. When it is 99.9% or less, it is easy to suppress the cost in terms of polypropylene production, and it is difficult to break during film formation. The mesopentad fraction is measured by a nuclear magnetic resonance method (so-called NMR method).
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 keep the mesopentad fraction of the polypropylene resin within 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 co-catalyst, and a polypropylene resin composition A method of appropriately selecting the components is preferably adopted.

(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, still more preferably 162 ° C. , More preferably 163 ° C, even more preferably 164 ° C. When Tm is 160 ° C. or higher, rigidity and heat resistance at high temperature 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., and particularly preferably 166 ° C. When Tm is 170 ° C. or lower, it is easy to suppress an increase in cost in terms of polypropylene production, and it is difficult to break during film formation. By blending the crystal nucleating agent with the polypropylene resin described above, the melting temperature can be further increased.
Tm is a sample of 1 to 10 mg packed in an aluminum pan, set in a differential scanning calorimeter (DSC), melted at 230 ° C for 5 minutes in a nitrogen atmosphere, and up 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 the temperature is raised at a scanning speed 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 is likely to proceed in the stretching in the width direction and the subsequent cooling step, and rigidity and heat resistance at high temperature are easily obtained. The upper limit of Tc is preferably 135 ° C., more preferably 133 ° C., still more preferably 132 ° C., even more preferably 130 ° C., particularly preferably 128 ° C., and most preferably 127 ° C. Is. If the Tc is 135 ° C. or lower, it is difficult to increase the cost in terms of polypropylene production, and it is difficult to break during film formation. By blending the crystal nucleating agent with the polypropylene resin described above, the crystallization temperature can be further raised.
Tc is observed when a sample of 1 to 10 mg is packed in an aluminum pan, set in a DSC, melted at 230 ° C. for 5 minutes under a nitrogen atmosphere, and cooled to 30 ° C. at a scanning speed of -10 ° C./min. This is the main peak temperature of the exothermic peak.

(Melt flow rate)
The melt flow rate (MFR) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is 4 when measured in accordance with the condition M (230 ° C., 2.16 kgf) of JIS K 7210 (1995). .0 g / 10 minutes or more, preferably 30 g / 10 minutes or less, more preferably 4.5 g / 10 minutes or more, 25 g / 10 minutes or less, 4.8 g / 10 minutes or more, 22 g / 10 minutes or less. It is more preferably 5.0 g / 10 minutes or more, particularly preferably 20 g / 10 minutes or less, and most preferably 6.0 g / 10 minutes or more and 20 g / 10 minutes or less.
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 having low heat shrinkage.
Further, when the melt flow rate (MFR) of the polypropylene resin is 30 g / 10 minutes or less, it is easy to maintain the film-forming property of the film.

From the viewpoint of film characteristics, 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. By adopting it, the orientation crystallization of the polypropylene resin is further promoted, the degree of crystallization in the film is more likely to be increased, and the polypropylene molecular chains in the amorphous portion are less entangled with each other, resulting in heat resistance. It is easier to improve sex.
In order to keep the melt flow rate (MFR) of the polypropylene resin within the above range, it is preferable to adopt a method of controlling the average molecular weight and the molecular weight distribution of the polypropylene resin.

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 35% by mass, preferably 38% by mass, and more preferably 40% by mass. It is more preferably 41% by mass, and particularly 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 unlikely to decrease.
At this time, if a high molecular weight component or a long chain branching component having a long relaxation time is included, the amount of the component having a molecular weight of 100,000 or less contained in the polypropylene resin can be easily adjusted without significantly changing the overall viscosity, so that the rigidity is increased. It is easy to improve the film-forming property without significantly affecting the 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, and further. It is preferably 4.5, and particularly preferably 5. 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 in the above range, it is easy to increase the amount of the component having a molecular weight of 100,000 or less.

Regarding the molecular weight distribution of polypropylene resin, components of different molecular weights can be polymerized in a series of plants in multiple stages, components of different molecular weights can be blended offline with a kneader, or catalysts with different performances can be blended and polymerized. It can be adjusted by using a catalyst capable of achieving 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 is the logarithm of the molecular weight (M) (logM) and the vertical axis is the differential distribution value (weight fraction per logM). It may have a gentle molecular weight distribution, or it may have a molecular weight distribution having a plurality of peaks and shoulders.

(Method for forming biaxially oriented polypropylene film)
The biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made of the polypropylene resin composition containing the above-mentioned polypropylene resin as a main component and biaxially stretching the film. As a biaxial stretching method, any of the inflation simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method, and the tenter sequential biaxial stretching method can be obtained, but from the viewpoint of film forming stability and thickness uniformity, the tenter sequential biaxial stretching method can be obtained. 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 stretching in the longitudinal direction may also 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 to this. In the biaxially oriented polypropylene film of the present invention, a layer having another function may be laminated on at least one side thereof. It may be laminated on one side or both sides. At that time, the above-mentioned polypropylene resin composition may be adopted as the resin composition of the other one layer or the central layer. Further, it may be different from the above-mentioned polypropylene resin composition. The number of layers to be laminated may be one layer, two layers, three or more layers per one surface, but one layer or two layers is preferable from the viewpoint of production. As a laminating method, for example, coextrusion 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 within a range that does not deteriorate the characteristics. Further, in order to impart printability, corona treatment may be applied to one side or both sides.

The following describes an example of the case of a single layer when the tenter sequential biaxial stretching method is adopted.
First, the resin composition containing the polypropylene resin is heated and melted by a single-screw or twin-screw extruder, extruded into a sheet from a T-die, and grounded on a cooling roll to be cooled and solidified. 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 or the like.

Then, the sheet is stretched in the longitudinal direction by increasing the rotation speed of the rear stretching rolls with two pairs of stretching rolls in which the sheet is heated to obtain a uniaxially stretched film.

Subsequently, after preheating the uniaxially stretched film, the film is stretched in the width direction at a specific temperature while grasping the end of the film with a tenter type stretcher 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.

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

Each process will be described 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 a sheet-shaped molten polypropylene resin composition discharged from the T-die is extruded. , Contact with a metal cooling roll to cool and solidify. It is preferable to further put the obtained unstretched sheet into 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 if it is desired to increase the transparency of the film, it is cooled and solidified with a cooling roll having 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, preferably 40 ° C. or lower, and 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 described above, a propylene homopolymer having a mesopendat fraction of 97.0% or higher is used. In this case, the cooling temperature is preferably 40 ° C. or lower, which is preferable in terms of facilitating stretching in the next step and reducing 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 sequential 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 3.5 times, more preferably 3.8 times, and particularly preferably 4.2 times. Within the above range, it is easy to increase the strength and the film thickness unevenness is reduced.
The upper limit of the longitudinal stretching ratio is preferably 7.0 times, more preferably 6.0 times, and particularly preferably 7 times. Within the above range, the width direction stretching in the width direction stretching step is easy, and the productivity is improved.
The lower limit of the longitudinal stretching temperature is preferably Tm-30 ° C, more preferably Tm-27 ° C, and even more preferably Tm-25 ° C. Within the above range, the subsequent stretching in the width direction becomes easy and the thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7 ° C, more preferably Tm-10 ° C, and even more preferably Tm-12 ° C. Within the above range, the heat shrinkage rate is likely to be reduced, and it is unlikely that the heat shrinkage will be reduced due to the difficulty in stretching by being attached to the stretching roll or the surface roughness becoming large.
The longitudinal stretching may be performed by using three or more pairs of stretching rolls and stretching in two or more stages.

(Preheating process)
Prior to the widthwise stretching step, it is necessary to heat the uniaxially stretched film after longitudinal stretching in the range of Tm to Tm + 25 ° C. to soften the polypropylene resin composition. When it is set to Tm or more, softening progresses and stretching in the width direction becomes easy. By setting the temperature to Tm + 25 ° C. or lower, the orientation at the time of lateral stretching progresses, and the rigidity is easily developed. It is more preferably Tm + 2 to Tm + 20 ° C, and particularly preferably Tm + 3 to Tm + 15 ° C. Here, the maximum temperature in the preheating process is defined as the preheating temperature.

(Stretching step in the width direction)
In the width direction stretching step after the preheating step, a preferable method is as follows.

In the width direction stretching step, it is preferable to stretch at a temperature of Tm-10 ° C. or higher and a preheating temperature or lower. At this time, the start of stretching in the width direction may be when the preheating temperature is reached, or when the temperature is lowered after reaching the preheating temperature and reaches a temperature lower than the preheating temperature.
The lower limit of the temperature in the width direction stretching step is more preferably Tm-9 ° C, still more preferably Tm-7 ° C, and particularly preferably Tm-5 ° C. When the stretching temperature in the width direction is in this range, it is easy to improve the rigidity of the obtained biaxially oriented film.
The upper limit of the temperature in the width direction stretching step is preferably Tm + 10 ° C, more preferably Tm + 7 ° C, and particularly preferably Tm + 5 ° C. When the stretching temperature in the width direction is in this range, uneven stretching is unlikely to occur.
In the width direction stretching step, a late stretching step of stretching at a lower temperature may be added following the width direction stretching in the above temperature range.
That is, following the section stretched at a temperature of Tm-10 ° C or higher and Tm + 10 ° C or lower (first half section), the section is stretched at a temperature lower than the temperature of the first half section and Tm-70 ° C or higher and Tm-5 ° C or lower. A section (late section) may be provided. It is easier to increase the rigidity by providing the first half section and the second half section.
The lower limit of the stretching temperature in the latter section is preferably Tm-65 ° C, more preferably Tm-60 ° C, and even more preferably Tm-55 ° C. When the stretching temperature in the latter section is in this range, the film formation is likely to be stable.

The lower limit of the final width direction stretching ratio in the width direction stretching step is preferably 9 times, more preferably 10 times. If it is 9 times or more, the rigidity is likely to be increased and the film thickness unevenness is likely to be reduced. The upper limit of the stretch 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 is likely to be reduced, and it is difficult to break during stretching.
When adding a late section, make sure that the total stretch ratio is within the above range. At this time, the lower limit of the draw ratio in the early stretching step is preferably 4 times, more preferably 5 times, still more preferably 6 times, and particularly preferably 6.5 times. The upper limit of the draw ratio at the end of the first half section is preferably 15 times, more preferably 14 times, and further preferably 13 times.

It is preferable to cool the film at the end of widthwise stretching, that is, immediately after reaching the widthwise final stretching ratio. The cooling temperature at this time is preferably not more than the temperature of stretching in the width direction and preferably Tm-80 ° C. or higher and Tm-15 ° C. or lower, and is preferably Tm-80 ° C. or higher and Tm-20 ° C. or lower. It is more preferable to set the temperature to Tm-80 ° C. or higher and Tm-30 ° C. or lower, and it is particularly preferable to set the temperature to Tm-70 ° C. or higher and Tm-35 ° C. or lower. By adding a cooling step, crystallization occurs and the crystal orientation is fixed, and then the orientation history is maintained even if the temperature rises above melting, and as a result, the crystal orientation in the film can be increased. can.
The temperature at the end of stretching in the width direction can be gradually lowered to the temperature at the time of cooling, but it can also be lowered stepwise or in one step. It is preferable to lower the temperature stepwise or stepwise because the crystal orientation in the film tends to be larger.

After cooling the film, it is preferable to perform stretching in the width direction again at a high temperature. The lower limit of the stretching temperature is Tm-5 ° C, preferably Tm, more preferably Tm + 5 ° C, still more preferably Tm + 7 ° C, and particularly preferably Tm + 9 ° C. When the temperature is Tm-5 ° C. or higher, the rigidity is likely to be increased and the heat shrinkage rate is likely to be lowered.
The upper limit of the stretching temperature is preferably Tm + 20 ° C, more preferably Tm + 18 ° C, and even more preferably Tm + 16 ° C. When the temperature is Tm + 20 ° C or lower, the rigidity can be easily increased.
The lower limit of the re-stretching ratio at high temperature is 1.03 times, preferably 1.05 times, and more preferably 1.10 times.
The upper limit of the restretching ratio at high temperature is preferably 2 times, more preferably 1.7 times, still more preferably 1.5 times. If the re-stretching ratio is too large, the heat shrinkage rate may become too large, uneven thickness may occur, or the film may break.

That is, instead of relaxing at a high temperature immediately after stretching in the width direction as in the conventional case, by stretching again in the width direction at a temperature sufficiently higher than the melting point, the rigidity is further improved while lowering the heat shrinkage rate. Found that it is possible.
That is, in the step after the first stretching in the width direction, it is preferable to perform stretching at Tm-5 ° C. or higher. At Tm-5 ° C or higher, the motility of the molecular chain becomes sufficiently high, and it becomes easy to eliminate the influence of the entanglement of the molecular chain by stretching. It is difficult to become, and crystallization progresses sufficiently.
By cooling the film to a temperature below which can be crystallized after stretching in the width direction at a high temperature, a film having a high melting point with a high degree of crystallinity and a thick crystal lamella can be obtained.

Further, even in the portion other than the crystal lamella, the number of molecular chains constrained by the entanglement point is small and the distortion of the molecular orientation is small, so that the film does not easily shrink even when the crystal starts to melt. Further, the degree of crystallinity is improved, and when the crystal lamella is thick, the melting point tends to be high, and below the melting point, melting is unlikely to occur. As a result, the heat shrinkage rate tends to decrease.
As a result, it has become possible to reduce the heat shrinkage rate while further improving the rigidity.

In the normal film-forming process extrusion-longitudinal stretching-width stretching-heat treatment), in order to eliminate the strain caused by the width stretching performed at a temperature lower than the melting point, the film is exposed to a high temperature above the melting point in the heat treatment step. By applying relaxation of several percent to several tens of percent, the heat shrinkage rate was lowered. By relaxing, it is possible to eliminate the difficulty in crystallization due to the restraint of the molecular chain, which contributes to a decrease in the heat shrinkage rate. However, on the contrary, it is difficult to achieve both low thermal shrinkage and high rigidity because the rigidity of the molecular chain generated in the lateral stretching process is lowered due to the decrease in the orientation in the width direction. In addition, there is a problem that the film becomes white when the temperature is too high.
In a normal film forming process (extrusion-longitudinal stretching-width stretching-heat treatment), by raising the temperature of the width stretching step, the motility of the molecular chain is high and stretching is performed so that no strain remains. Since the crystals produced by the longitudinal stretching proceed to melt, the crystal orientation is lowered.
In the method of the present invention, a film having sufficient tension even if the crystal orientation fixed by cooling is melted after being stretched once in the width direction and oriented sufficiently in the width direction is produced at Tm-5 ° C. or higher. Since it is stretched again at a high temperature, there is sufficient tension even when it is stretched again, and there is little concern that thickness unevenness or film breakage will occur.
The draw ratio at a high temperature may be such that the entanglement of the molecular chains can be disentangled and aligned, and may be 1.03 times or more. If the draw ratio is 2 times or less, uneven thickness is unlikely to occur.

As described above, by using the polypropylene resin having high stereoregularity and high crystallinity and adopting the above-mentioned longitudinal stretching step, widthwise stretching step, cooling step, and high temperature stretching step, the molecules of the polypropylene resin are used. Is remarkably highly aligned in the main orientation direction (the width direction is applicable in the above-mentioned width direction stretching step), so that more crystals with strong crystal orientation and high melting point are produced in the obtained biaxially oriented film. It will be easier.

Further, by increasing the low molecular weight component of the polypropylene resin, the entanglement of the molecular chains is reduced, the crystallinity of the film is more likely to be increased, and the portion other than the crystalline lamella is reduced. Further, by weakening the heat shrinkage stress of the portion other than the crystal lamella, the heat shrinkage rate is likely to be further lowered.
It can be said that the present invention has an epoch-making effect in consideration of the fact that in the prior art, if either the rigidity or the heat shrinkage rate is improved, the other property tends to be deteriorated.

(Heat treatment process)
If necessary, the biaxially stretched film can be heat-treated to further reduce the heat shrinkage. The upper limit of the heat treatment temperature is preferably 183 ° C, more preferably 180 ° C, and even more preferably 178 ° C. By setting the temperature to 183 ° C. or lower, the rigidity is less likely to decrease, the roughness of the film surface does not become too large, and the film is less likely to whiten. The lower limit of the heat treatment temperature is preferably Tm-3 ° C, more preferably Tm-2 ° C, and particularly preferably Tm.
The film may be relaxed (relaxed) in the width direction during heat treatment for the purpose of adjusting the heat shrinkage rate, but the upper limit of the relaxation rate is preferably 8%, more preferably 5%, still more preferably 3. %. Within the above range, the rigidity is unlikely to decrease, and the fluctuation in film thickness tends to be small. When increasing the rigidity, it is not necessary to perform heat treatment.

(Cooling process)
After stretching in the width direction, it is preferable to cool the film immediately after stretching again in the width direction at a temperature of Tm-5 ° C. or higher, or immediately after the heat treatment step. The cooling temperature at this time is preferably 10 ° C. or higher and 140 ° C. or lower, more preferably 15 ° C. or higher and 135 ° C. or lower, and 20 ° C. or higher and 130 ° C. or lower. It is more preferable, and it is particularly preferable to set the temperature to 20 ° C. or higher and 125 ° C. or lower. By providing a cooling step, the state of the film can be fixed.

(Film thickness)
The thickness of the biaxially oriented polypropylene film of 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, still more preferably. It is 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 can be easily obtained. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, still 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 decrease.
The biaxially oriented polypropylene film of the present invention is usually formed as a roll having a width of 2000 to 12000 mm and a length of about 1000 to 50,000 m, and is wound into a film roll. Further, it is slit according to each application and is provided as a slit roll having a width of 300 to 2000 mm and a length of about 500 to 5000 m. The biaxially oriented polypropylene film of the present invention can obtain a longer film roll.

(Thickness uniformity)
The lower limit of the thickness uniformity of the biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, still more preferably 0.5%, and particularly preferably 1%. 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, and it is easy to use for applications that require precision.
The measurement method was as follows. A test piece having a width of 40 mm is cut out from a constant region where the film physical characteristics are stable in the length direction of the film, and a film feeder manufactured by Micron Measuring Instruments Co., Ltd. (using the product number: A90172) and a film manufactured by Anritsu Co., Ltd. Using a continuous thickness measuring device (product name: K-313A wide-range high-sensitivity electronic micrometer), the film thickness was continuously measured over 20000 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 of the present invention is characterized by the following characteristics. Here, the "longitudinal direction" in the biaxially oriented polypropylene film of the present invention is a direction corresponding to the flow direction in the film manufacturing process, and the "width direction" is a direction orthogonal to the flow direction in the film manufacturing process. Is. For polypropylene films whose flow direction is unknown in the film manufacturing process, wide-angle X-rays are 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 diffraction intensity of the obtained diffraction intensity distribution is the largest is referred to as the "longitudinal direction", and the direction orthogonal to it is referred to as the "width direction".

It is preferable that the heat shrinkage rate (%) in the width direction at 150 ° C. and the stress during 5% elongation (MPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film of the present invention satisfy the following equations.
By satisfying the following formula, the rigidity is higher and the heat shrinkage rate at high temperature is smaller, so that the ease of maintaining the bag shape when used as a packaging bag is further improved, and heat sealing at high temperature is achieved. Deformation of the film during processing is less likely to occur, and packaging quality is further improved. In addition, the film can be made thinner, which can contribute to the volume reduction of the packaging material.
5% elongation stress (MPa) in the width direction at 23 ° C ≥ heat shrinkage (%) in the width direction at 150 ° C x 4.0 + 140
Further, it is more preferable that the heat shrinkage rate (%) in the width direction at 150 ° C. and the stress at 5% elongation (MPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film of the present invention satisfy the following formulas. ..
5% elongation stress (MPa) in the width direction at 23 ° C ≧ heat shrinkage rate (%) in the width direction at 150 ° C × 4.0 + 150
Further, it is more preferable that the heat shrinkage rate (%) in the width direction at 150 ° C. and the stress at 5% elongation (MPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film of the present invention satisfy the following equations. ..
5% elongation stress (MPa) in the width direction at 23 ° C ≧ heat shrinkage rate (%) in the width direction at 150 ° C × 4.0 + 160

(150 ° C heat shrinkage rate)
The upper limit of the heat shrinkage in the longitudinal direction at 150 ° C. of the biaxially oriented polypropylene film of the present invention is preferably 10%, more preferably 7.0%, still more preferably 6.0%, and particularly. It is preferably 5.0%, and most preferably 4.0% or less. The upper limit of the heat shrinkage rate in the width direction at 150 ° C. is preferably 30%, more preferably 20%, still more preferably 16%, and particularly preferably 15% or less.
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, and in particular, the heat shrinkage rate in the longitudinal direction at 150 ° C. is 8. When the heat shrinkage rate in the width direction at 0% or less and 150 ° C. is 15% or less, the strain when the chuck portion is fused to the open portion is small, which is preferable. In order to reduce the heat shrinkage at 150 ° C, the lower limit of the amount of components with a molecular weight of 100,000 or less when measuring the gel permeation chromatography (GPC) integration curve of the polypropylene resin constituting the film is set to 35% by mass. It is effective to do.

(Stress at 23 ° C 5% elongation)
The lower limit of F5 in the width direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 140 MPa, more preferably 160 MPa, still more preferably 180 MPa, and particularly preferably 190 MPa. At 140 MPa or higher, 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 in the width direction at 23 ° C. is preferably 300 MPa, more preferably 290 MPa, and even more preferably 280 Pa. If it is 280 MPa or less, realistic manufacturing is easy and the vertical width balance is easy to improve.
The lower limit of the stress (F5) of the biaxially oriented polypropylene film of the present invention at 5% elongation in the longitudinal direction at 23 ° C. is preferably 40 Pa, more preferably 42 Pa, still more preferably 46 Pa, and particularly preferably. Is 48 Pa. At 40 MPa or higher, 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 in the longitudinal direction at 23 ° C. is preferably 70 MPa, more preferably 65 MPa, still more preferably 62 MPa, and particularly preferably 60 Pa. At 70 MPa or less, realistic manufacturing is easy and the vertical-width balance is easy to improve.
F5 can be within the range by adjusting the stretching ratio and the relaxing rate, and adjusting the temperature at the time of film formation.

It is better that the biaxially oriented polypropylene film of the present invention has the following characteristics and structure.
(120 ° C. heat shrinkage rate)
The upper limit of the heat shrinkage in the longitudinal direction at 120 ° C. of the biaxially oriented polypropylene film of the present invention is preferably 2.0%, more preferably 1.5%, still more preferably 1.2%. , Particularly preferably 1.0%. When it is 2.0% or less, the printing pitch shift when transferring the printing ink is less likely to occur. The upper limit of the heat shrinkage rate in the width direction at 120 ° C. is 10.0% or less, preferably 5.0%, more preferably 3.5%, and particularly preferably 2.5%. When it is 10.0% or less, wrinkles at the time of heat sealing are less likely to occur.
The heat shrinkage rate at 120 ° C. can be kept within the range by adjusting the stretching ratio, the stretching temperature, and the heat fixing temperature.

It is preferable that the heat shrinkage rate (%) in the width direction at 120 ° C. and the tensile elastic modulus (GPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film of the present invention satisfy the following equations.
By satisfying the following formula, the rigidity is higher and the heat shrinkage rate at high temperature is smaller, so that the printing pitch shift is less likely to occur when the bag is made into a manufacturing bag.
Width tensile modulus at 23 ° C (GPa) ≥ 120 width thermal shrinkage (%) at 120 ° C x 0.1 + 7.0
Further, it is more preferable that the heat shrinkage rate (%) in the width direction at 120 ° C. and the tensile elastic modulus (GPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film of the present invention satisfy the following formulas.
Width modulus of tensile modulus (GPa) at 23 ° C ≥ Heat shrinkage of width at 120 ° C (%) x 0.1 + 8.0
Further, it is more preferable that the heat shrinkage rate (%) in the width direction at 120 ° C. and the tensile elastic modulus (GPa) in the width direction at 23 ° C. of the biaxially oriented polypropylene film of the present invention satisfy the following formulas.
Width modulus of tensile modulus (GPa) at 23 ° C ≥ Heat shrinkage of width at 120 ° C (%) x 0.1 + 9.0

(23 ° C tensile elastic modulus)
The lower limit of the tensile elastic modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 2.0 GPa, more preferably 2.1 GPa, still more preferably 2.2 GPa, and further. It is preferably 2.3 GPa, particularly preferably 2.4 GPa, and most preferably 2.6 GPa. At 2.0 GPa or more, since the rigidity is high, it is easy to maintain the bag shape when it is used as a packaging bag, and the film is less likely to be deformed during processing such as printing. The upper limit of the tensile elastic 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. It is 5 GPa. At 4.0 GPa or less, realistic manufacturing is easy, and the balance of characteristics in the longitudinal direction and the width direction is likely to be improved.
The lower limit of the tensile elastic modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 6.0 GPa, more preferably 6.5 GPa, still more preferably 6.7 GPa, still more preferable. Is 7.0 GPa, particularly preferably 8.0 GPa, and most preferably 8.5 GPa. At 6.0 GPa or higher, 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 the tensile elastic 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, it is easy to manufacture realistically, and it is easy to improve the balance of characteristics in the longitudinal direction and the width direction.
The tensile elastic modulus can be within the range by adjusting the draw ratio and the relaxation rate, or by adjusting the temperature at the time of film formation.

(23 ° C tensile breaking strength)
The lower limit of the tensile breaking strength in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 90 MPa, more preferably 100 MPa, still more preferably 110 MPa, and particularly preferably 115 MPa. If it is 90 MPa or more, the printing pitch shift when transferring the printing ink is less likely to occur, and the durability of the packaging bag is likely to be excellent. The upper limit of the tensile breaking strength in the longitudinal direction is preferably 200 MPa, more preferably 180 MPa, and further preferably 160 MPa as a realistic value. If it is 200 MPa or less, the breakage of the film and the breakage of the packaging bag are likely to decrease.
The lower limit of the tensile breaking strength in the width direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 400 MPa, more preferably 420 MPa, still more preferably 440 MPa, and particularly preferably 450 MPa. If it is 400 MPa or more, the printing pitch shift when transferring the printing ink is less likely to occur, and the durability of the packaging bag is likely to be excellent. The upper limit of the tensile breaking strength in the width direction is preferably 650 MPa, more preferably 600 MPa, and further preferably 550 MPa as a realistic value. If it is 650 MPa or less, the breakage of the film and the breakage of the packaging bag are likely to decrease.
The tensile breaking strength can be set within the range by adjusting the draw ratio, the draw temperature, and the heat fixing temperature.

(23 ° C tensile elongation at break)
The lower limit of the tensile elongation at break in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 180%, more preferably 190%, more preferably 200%, and particularly preferably. It is 210% or more. If it is 180% or more, the breakage of the film and the breakage of the packaging bag are likely to decrease. The upper limit of the tensile elongation at break in the long longitudinal direction at 23 ° C. is preferably 300% as a realistic value, and more preferably 280%.

The lower limit of the tensile elongation at break in the width direction of the biaxially oriented polypropylene film of the present invention at 23 ° C. is preferably 15%, more preferably 20%, more preferably 30%, and 15% or more. Then, the breakage of the film and the breakage of the packaging bag tend to decrease. The upper limit of the tensile elongation at break in the width direction at 23 ° C. is preferably 60%, more preferably 55%, and even more preferably 50%. If it is 60% or less, the printing pitch shift when transferring the printing ink is less likely to occur, and the durability of the packaging bag is likely to be excellent.
The tensile elongation at break can be within the range by adjusting the draw ratio, the draw temperature, and the heat fixing temperature.

(Refractive index)
The lower limit of the refractive index (Nx) in the longitudinal direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4950, more preferably 1.4970, still more preferably 1.4980, and particularly preferably 1.4980. It is 1.4990, most preferably 1.5000. 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 15070, and even more preferably 1.5050. If it is 1.5100 or less, the balance of the characteristics 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 of the present invention is preferably 1.5250, more preferably 1.5253, still more preferably 1.5255, and particularly preferably 1. It is .5260, most preferably 1.5265. If it is 1.5250 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. If it is 1.5280 or less, the balance of the characteristics 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 of the present invention is preferably 1.4960, more preferably 14965, still more preferably 1.4970, and particularly preferably 1. It is 4980, most preferably 1.4990. 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 1.5020, more preferably 1.5015, and even more preferably 1.5010. If it is 1.5020 or less, it is easy to increase the heat resistance of the film.
The refractive index can be set within the range by adjusting the stretching ratio, the stretching temperature, and the heat fixing temperature.

(△ Ny)
The lower limit of ΔNy, which is the degree of orientation of the biaxially oriented polypropylene film of the present invention in the width direction, is preferably 0.0240, more preferably 0.0245, and even more preferably 0.0247. , Particularly preferably 0.0250, most preferably 0.0255, and particularly most preferably 0.0260. If it is 0.0240 or more, the rigidity of the film tends to be high. The upper limit of ΔNy is preferably 0.0280, more preferably 0.0277, still more preferably 0.0273, and particularly preferably 0.0270 as a realistic value. If it is 0.0280 or less, the thickness unevenness tends to be good. ΔNy can be set within the range by adjusting the stretch ratio, the stretch temperature, and the heat fixing temperature of the film.
ΔNy is calculated by the following formula, where the refractive indexes along the longitudinal direction, the width direction, and the thickness direction of the film are Nx, Ny, and Nz, respectively. It means the degree of orientation in the direction.
ΔNy = Ny- [(Nx + Nz) / 2]

(Surface orientation coefficient)
The lower limit of the plane orientation coefficient (ΔP) of the biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and even more preferably 0.0140. 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 even more preferably 0.0150 as a realistic value. If it is 0.0155 or less, the heat resistance at high temperature is likely to be excellent. The plane orientation coefficient (ΔP) can be set within the range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.
The plane orientation coefficient (ΔP) was calculated using (Equation) [(Nx + Ny) / 2] −Nz.

(Average refractive index)
The lower limit of the average refractive index of the biaxially oriented polypropylene film of the present invention is preferably 1.5080, more preferably 1.5081, still more preferably 1.5082, and particularly preferably 1.5083. Yes, most preferably 1.5090. The upper limit of the average refractive index is preferably 1.5150, more preferably 1.5140, still more preferably 1.5135, and particularly preferably 1.5130 as a realistic value. If it is 1.5080 or more, wrinkles are less likely to occur during heat sealing of the film. The average refractive index can be set within the range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature of the film.
The average refractive index is calculated by the following formula, where the refractive indexes along the longitudinal direction, the width direction, and the thickness direction of the film are Nx, Ny, and Nz, respectively.
Average refractive index = (Nx + Ny + Nz) / 3

(Haze)
The upper limit of the haze of the biaxially oriented polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, still more preferably 4.0%, and particularly preferably 3.5%. Yes, most preferably 3.0%. If it is 5.0% or less, it is easy to use in applications where transparency is required. The lower limit of the haze is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, and particularly preferably 0.4% as a practical value. If it is 0.1% or more, it is easy to manufacture. The haze adjusts the cooling roll (CR) temperature, the width stretching temperature, the preheating temperature before stretching in the tenter width direction, the stretching temperature in the width direction, or the heat fixing temperature, or the amount of the component having a polypropylene resin molecular weight of 100,000 or less. However, it may increase due to the addition of a blocking inhibitor or the addition of a seal layer.

(Half width of diffraction peak derived from oriented crystal)
In the azimuth dependence of the scattering peak of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray measurement perpendicularly incident on the film surface of the biaxially oriented polypropylene film of the present invention, the oriented crystal in the width direction of the film. The upper limit of the half-value width (Wh) of the diffraction peak derived from is preferably 21.0 °, more preferably 20.5 ° or less, more preferably 20.0 ° or less, and particularly preferably 19. It is 5 ° or less, and most preferably 19.0 ° or less. When the half width (Wh) is 21.0 ° or less, the rigidity of the film tends to be increased. In addition, it is easy to lower the water vapor transmission rate. The lower limit of Wh is preferably 15 °, more preferably 16 °, and even more preferably 17 °.

(X-ray orientation)
The lower limit of the degree of X-ray orientation calculated from Wh of the biaxially oriented polypropylene film of the present invention by the following formula is preferably 0.883, more preferably 0.886, and even more preferably 0.889. .. It is easy to increase the rigidity by setting it to 0.892 or more.
X-ray orientation = (180-Wh) / 180
The upper limit of the degree of X-ray orientation is preferably 0.917, more preferably 0.911, and even more preferably 0.906. When it is 0.917 or less, the film formation is easy to stabilize.

(Water vapor permeability)
The water vapor transmittance of the biaxially oriented polypropylene film of the present invention ^{is preferably 5.0 g / m 2} · d or less in terms of 20 μm thickness, and more preferably 4.6 g / m ² · d or less. It is more preferably 4.3 g / m ² · d or less. When it is 5.0 g / m ² · d or less, sufficient water vapor barrier property can be obtained even when thinning is performed.

(Practical characteristics of film)
The practical characteristics of the biaxially oriented polypropylene film of the present invention will be described.
(Rigidity and water vapor barrier property)
The packaging materials used for packaging foods and beverages protect the contents from various distributions, storage such as refrigeration, heat sterilization, etc., in addition to the functions such as rigidity and heat resistance, the quality of the contents. High barrier properties are particularly required for the purpose of retaining and retaining the content, and even if the film is thinned, it is required to have excellent these characteristics.

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

(Print pitch shift)
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. A bag making machine is used to manufacture bags, and there are three-way bags, standing bags, gusset bags, etc., and various bag making machines are used. It is considered that the printing pitch shift occurs because the base material of the film expands and contracts because tension and heat are applied to the film during the printing process. Eliminating defective products due to print pitch deviation is important in terms of effective use of resources, and is also important in increasing purchasing motivation.

(Film processing)
The biaxially oriented polypropylene film of the present invention can be printed by letterpress printing, lithographic 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, and biaxially stretched fill are bonded as a sealant film to impart heat-sealing properties. It can also be used as a laminated body. If you want to further improve gas barrier properties and heat resistance, use aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, unstretched sheet made of polyvinyl alcohol, uniaxially stretched film, and biaxially stretched film as biaxially oriented polypropylene film. It can be provided as an intermediate layer between the and the sealant film. An adhesive applied by a dry lamination method or a hot melt lamination method can be used for laminating the sealant film.
In order to enhance the gas barrier property, aluminum or an inorganic oxide can be vapor-deposited on a biaxially oriented polypropylene film, an intermediate layer film, or a sealant film. Vacuum deposition, sputtering, and ion plating can be adopted as the vapor deposition method, but it is particularly preferable to vacuum-deposit silica, allumina, or a mixture thereof.

The biaxially oriented polypropylene film of the present invention contains, for example, antifogging agents such as fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, amines of higher fatty acids and ethylene oxide adducts of amide. By setting the abundance in the film in the range of 0.2 to 5% by mass, it is possible to make it suitable for packaging fresh products made of plants that require high freshness such as vegetables, fruits, and flowers. can.

Further, as long as the effect of the present invention is not impaired, various additives for improving quality such as slipperiness and antistatic property, for example, lubricants such as wax and metal soap for improving productivity, and plasticizers. It is also possible to add agents, processing aids, heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers and the like.

(Industrial applicability)
Since the biaxially oriented polypropylene film of the present invention has excellent properties as described above, it can be preferably used for packaging bags, and the thickness of the film can be made thinner than before.

Furthermore, it is required to be used at high temperatures such as insulating films for capacitors and motors, back sheets for solar cells, barrier films for inorganic oxides, and base films for transparent conductive films such as ITO, and to have rigidity such as separate films. It is also suitable for various applications. In addition, it is possible to coat and print at high temperatures by using coating agents, inks, laminating adhesives, etc., which have been difficult to use in the past, and it is expected that 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 at a temperature of 230 ° C. and a load of 2.16 kgf in accordance with JIS K7210.

(2) Mesopendat 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 in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). ¹³ C-NMR measurement was carried out using AVANCE 500 manufactured by BRUKER, in which 200 mg of a sample was dissolved in an 8: 2 mixture of o-dichlorobenzene and heavy benzene at 135 ° C. and 110 ° C.

(3) Number average molecular weight, weight average molecular weight, component weight of 100,000 or less, and molecular weight distribution of polypropylene resin It was determined as a PP-equivalent molecular weight based on monodisperse polystyrene using gel permeation chromatography (GPC). When the baseline is not clear, it was decided to set the baseline up to the lowest position of the skirt on the high molecular weight side of the high molecular weight side elution peak 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: TSKgelgoldvolume HHR (30) HT (7.5 mm ID x 7.5 cm) x 1 + TSKgelGMHR-H (20) HT ( 7.8 mm I.D. x 30 cm) x 3 Flow rate: 1.0 mL / min
Injection volume: 0.3 mL
Measurement temperature: 140 ° C
The number average molecular weight (Mn), weight average molecular weight (Mw) molecular weight, respectively of the elution position of GPC curve obtained via the molecular weight calibration curve (M _i) number of molecules by (N _i) is defined by the following equation To.
The number average molecular _{weight: Mn = Σ (N i ·} M i) / ΣN i
Weight 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 components 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)
Thermal measurements were performed in a nitrogen atmosphere using a Q1000 differential scanning calorimeter manufactured by TA Instruments. Approximately 5 mg was cut out from the polypropylene resin pellet and sealed in an aluminum pan for measurement. The temperature was raised to 230 ° C. and held for 5 minutes, then cooled to 30 ° C. at a rate of −10 ° C./min, and the exothermic peak temperature was defined as the crystallization temperature (Tc). The amount of heat of crystallization (ΔHc) was determined by setting a baseline so that the area of the exothermic peak could be smoothly connected from the start to the end of the peak. The temperature was kept as it was at 30 ° C. for 5 minutes, the temperature was raised to 230 ° C. at 10 ° C./min, and the main endothermic peak temperature was defined as the melting temperature (Tm).

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

(6) Haze Using NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd., the measurement was carried out at 23 ° C. according to JIS K7105.

(7) Tensile test The tensile strength in the longitudinal direction and the width direction of the film was measured at 23 ° C. according to JIS K7127. The sample was cut out from a film to a size of 15 mm × 200 mm, had a chuck width of 100 mm, and was set in a tensile tester (dual column desktop tester Instron 5965 manufactured by Instron Japan Company Limited). A tensile test was performed at a tensile speed of 200 mm / min. From the obtained strain-stress curve, the tensile elastic modulus was defined from the inclination of the straight line portion at the initial stage of elongation, and the stress at 5% elongation was defined as F5.
The tensile breaking strength and the tensile breaking elongation were taken as the strength and elongation at the time when the sample broke, respectively.

(8) Heat shrinkage rate Measured by the following method according to JISZ1712. The film was cut with a width 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 contracted length to the original length.

(9) Refractive index, ΔNy, plane orientation coefficient, average refractive index 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 indexes along the longitudinal direction and the width direction of the film were Nx and Ny, respectively, and the refractive indexes in the thickness direction were Nz. ΔNy, which is the degree of orientation in the width direction, was determined using (formula) Ny− [(Nx + Nz) / 2] using Nx, Ny, and Nz. The plane orientation coefficient (ΔP) was calculated using (Equation) ΔP = [(Nx + Ny) / 2] −Nz. The average refractive index was calculated using (formula) average refractive index = (Nx + Ny + Nz) / 3.

(10) Half-value width at half maximum and degree of orientation The measurement was performed by a transmission method using an X-ray diffractometer (SmartLab manufactured by Rigaku Co., Ltd., attached to an αβγ attachment). X-rays with a wavelength of 1.5418 Å were used and the X-ray output was 45 kV, 200 mA. As a detector, a hybrid multidimensional pixel detector Hyper-3000 was used in 0-dimensional mode. In the parallel beam method, a solar slit 2.5 °, a length limiting slit 10 mm, and an incident slit width 1 mm were used as slits on the incident side. A parallel slit analyzer 0.228 ° was used as the slit on the light receiving side.
The camera length was 300 mm, and the integration width of the detector was 2 mm.
A sample was prepared by stacking films so as to have a thickness of 400 μm. A detector is placed at the diffraction peak position (diffraction angle 2θ = 14.1 °) on the (110) plane of the α-type crystal of polypropylene resin, and the sample is rotated 360 ° about the thickness direction of the film to rotate the sample on the (110) plane. The azimuth dependence of the diffraction intensity was obtained. The step interval was 0.5 ° and the measurement speed was 60 ° / min. 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 obtained.
Further, using Wh, the degree of X-ray orientation was calculated from the following formula.
X-ray orientation = (180-Wh) / 180

(11) Moisture vapor transmission rate 265 The water vapor transmission rate was measured according to the JIS K7129 B method.
The water vapor transmission rate was measured using a water vapor transmission rate measuring device (PERMATRAN-W3 / 33 MOCON) in an atmosphere of a temperature of 40 ° C. and a humidity of 90% RH. Since the water vapor transmission rate is inversely proportional to the film thickness, the thickness of each sample to be measured was measured and converted into a value at 20 μm.

(Example 1)
As a polypropylene resin, MFR = 7.5 g / 10 minutes, [mmmm] = 98.9%, Tc = 116.2 ° C., Tm = 162.5 ° C., propylene homopolymer PP-1 (Sumitomo Chemical Co., Ltd.) , Sumitomo Noblen FLX80E4) with 80 parts by weight, MFR = 11 g / 10 minutes, [mmmm] = 98.8%, Tc = 116.5 ° C, Tm = 161.5 ° C. Polypropylene homopolymer PP-2 (EL80F5 manufactured by Sumitomo Chemical Co., Ltd.) was used by blending with 20 parts by weight.
It was extruded into a sheet from a T-die at 250 ° C., brought into contact with a cooling roll at 20 ° C., and put into a water tank at 20 ° C. as it was. Then, at 142 ° C, it is stretched 4.5 times in the longitudinal direction with two pairs of rolls, then both ends are clipped, guided into a hot air oven, preheated at 170 ° C, and then 162 ° C as the first step in the width direction. Was stretched 10 times. Immediately after stretching in the width direction, the mixture was cooled at 120 ° C. while being held by a clip, and then re-stretched 1.2 times in the width direction at 175 ° C. Finally, it was cooled at room temperature. The thickness of the film thus obtained was 18.6 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical characteristics of the film are very excellent, and a film having a low heat shrinkage rate at high temperature was obtained. Moreover, it was a film having excellent water vapor transmission rate.

(Example 2)
The procedure was the same as in Example 1 except that the product was re-stretched 1.2 times in the width direction at 165 ° C. The thickness of the obtained film was 18.4 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical characteristics of the film are very excellent, and a film having a low heat shrinkage rate at high temperature was obtained. Moreover, it was a film having excellent water vapor transmission rate.

(Example 3)
Stretched at 147 ° C. in the longitudinal direction, stretched 10 times at 165 ° C. as the first step in the width direction, immediately after stretching in the width direction, cooled at 120 ° C. while being held by a clip, and then cooled at 120 ° C. in the width direction at 177 ° C. It was carried out in the same manner as in Example 1 except that it was re-stretched 1.2 times. 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 shown in Table 3, a film having high rigidity and low heat shrinkage at high temperature was obtained. Moreover, it was a film having excellent water vapor transmission rate.

(Example 4)
The procedure was the same as in Example 3 except that the product was re-stretched 1.1 times in the width direction at 177 ° C. The thickness of the obtained film was 20.6 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical characteristics were high in rigidity and low in heat shrinkage at high temperature. Moreover, it was a film having excellent water vapor transmission rate.

(Comparative Example 1)
As the first step in the width direction, it was stretched 12 times at 162 ° C. Immediately after stretching in the width direction, it was cooled at 100 ° C while being held by a clip, and then heat-fixed at 170 ° C while keeping the width constant. The procedure was the same as in Example 1. The thickness of the obtained film was 20.8 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical characteristics were excellent in water vapor transmission rate and high rigidity, but the heat shrinkage rate was inferior.

(Comparative Example 2)
As the first step in the width direction, it was stretched 12 times at 162 ° C. Immediately after stretching in the width direction, it was not cooled while being held by the clip, and heat was fixed at 172 ° C while keeping the width constant. I did the same. The thickness of the obtained film was 23.1 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, its physical properties were inferior in rigidity. Moreover, the film was inferior in water vapor transmission rate.

(Comparative Example 3)
As the first step in the width direction, it was stretched 12 times at 168 ° C. Immediately after stretching in the width direction, it was cooled at 100 ° C while being held by a clip, and then heat-fixed at 170 ° C with a constant width. The procedure was the same as in Example 1. The thickness of the obtained film was 18.7 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical characteristics were high in heat shrinkage at high temperature and inferior in rigidity. Moreover, the film was inferior in water vapor transmission rate.

(Comparative Example 4)
As the polypropylene resin, PP-3 (manufactured by Japan Polypropylene Corporation, FL203D) having MFR = 3 g / 10 minutes, [mm mm] = 94.8%, Tc = 117.2 ° C., and Tm = 160.6 ° C. is used. board. It was extruded into a sheet from a T-die at 250 ° C., brought into contact with a cooling roll at 20 ° C., and put into a water tank at 20 ° C. as it was. Then, it was stretched 4.5 times in the longitudinal direction at 130 ° C., and in the width direction stretching in the tenter, the preheating temperature was set to 168 ° C., and the first step of stretching was 8.2 times stretching at 155 ° C. Immediately after stretching in the width direction, the mixture was cooled at 120 ° C. while being held by a clip, and then re-stretched 1.2 times in the width direction at 170 ° C. Finally, it was cooled at room temperature. The thickness of the obtained film was 18.8 μm.
Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. As shown in Table 3, the physical characteristics were high in heat shrinkage at high temperature and inferior in rigidity. Moreover, the film was inferior in water vapor transmission rate.

Claims (4)

1. 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 step of stretching the longitudinally stretched film at Tm to Tm + 25 ° C. Preheating step of heating to a range of preheating temperature, step of stretching the preheated longitudinally stretched film at a temperature of Tm-10 ° C or higher and lower than the preheating temperature at a magnification of 10 times or more in the width direction, width direction at the end of widthwise stretching. A step of cooling the film at a stretching temperature of Tm-80 ° C or higher and Tm-15 ° C or lower, while stretching at a magnification of 1.03 times or more in the width direction at Tm-5 ° C or higher and Tm + 20 ° C or lower. A method for producing a biaxially oriented polypropylene film, which comprises a step of heat-fixing in order.
2. The method for producing a biaxially oriented polypropylene film according to claim 1, 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.
3. The method for producing a biaxially oriented polypropylene film according to claim 1 or 2, wherein the melt flow rate of the polypropylene resin constituting the biaxially oriented polypropylene film is 4.0 g / 10 minutes or more.
4. The method for producing a biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the component amount of the polypropylene resin constituting the biaxially oriented polypropylene film having a molecular weight of 100,000 or less is 35% by mass or more.