JP7298751B2 - biaxially oriented polypropylene film - Google Patents

Description

The present invention relates to biaxially oriented polypropylene films. Specifically, it relates to a biaxially oriented polypropylene film that is excellent in heat resistance and hand tearability.

BACKGROUND ART Conventionally, stretched polypropylene resin films have been widely used in a wide range of applications, such as packaging of foods and various products, electrical insulation, and surface protection films.
However, the conventional polypropylene film has a high tear strength and is not sufficiently tearable by hand when the bag is opened after being made.

In view of the above circumstances, an object of the present invention is to provide a biaxially oriented polypropylene film having higher heat resistance and hand tearability.

As a result of intensive studies by the present inventors, it was found that even in a biaxially oriented polypropylene film having excellent heat resistance at high temperatures, it is possible to further reduce the tear strength, and the tear strength in a specific direction can be reduced to a predetermined level. and found that the above problems can be solved, and have completed the present invention.

The present invention, which has solved the above problems, provides a biaxially oriented polypropylene film having the following features (a) to (c) and 1) to 4).
(a) It consists of a resin composition containing a polypropylene-based resin as a main component.
(b) Tear strength (N/mm) ≤ (0.014 x film thickness (μm) + 0.35) in the width direction or the longitudinal direction of the film.
(c) The thermal shrinkage rate at 150° C. in the width direction and the machine direction of the film is 7% or less.
(d) The lower limit of the plane orientation coefficient of the film is 0.0125.
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.5 g/10 min or more and 9.0 g/10 min or less.

In this case, it is preferable that the longitudinal tensile modulus in the width direction and longitudinal direction of the film is 2.0 GPa or more, and the tensile modulus in the direction of the large tensile modulus is 4.0 GPa or more. is.

In this case, it is preferable that the impact strength is 0.6J or more.

In this case, it is preferable that the film has a haze value of 5% or less.

The biaxially oriented polypropylene film of the present invention has a low thermal shrinkage at 150° C. and high thermal dimensional stability. Therefore, the film has excellent film workability due to small wrinkles caused by heat and resistance to breakage. In addition, since the tear strength in the lateral direction of the film is small, the film can be easily torn by hand when opening the packaging bag.

(Polypropylene resin composition)
The biaxially oriented polypropylene film of the present invention comprises a resin composition containing the following polypropylene-based resin as a main component. A polypropylene resin refers to a homopolymer of propylene and a copolymer of propylene and ethylene and/or α-olefin. The copolymerization amount of ethylene and/or an α-olefin having 4 or more carbon atoms is preferably 0.5 mol % or less.
At this time, the polypropylene resin composition is preferably a polypropylene resin (A) or a mixture of polypropylene resin (A) and polypropylene resin (B) that satisfies the following conditions. The characteristics of polypropylene resin (A) and polypropylene resin (B) are as follows.
The polypropylene resin (A) is a polypropylene resin that satisfies the following conditions 1) to 4).
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.2 g/10 min or more and 9.0 g/10 min or less.

The polypropylene resin (B) is a polypropylene resin that satisfies the following conditions 1) to 4).
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230°C and 2.16 kgf is 9.2 g/10 min or more.

The mixing ratio of polypropylene resin (A) and polypropylene resin (B) is preferably 85/15 to 65/35 (% by weight) by weight. If the mixing ratio of the polypropylene resin (B) is 15% by weight or more, the orientation of the film in the width direction or the machine direction tends to increase, and the tear strength tends to decrease. When the mixing ratio of the polypropylene resin (B) is 35% by weight or less, problems such as breakage of the film during the stretching process are less likely to occur, making it easier to produce a biaxially oriented film.
Further details are provided below.

(Polypropylene resin (A))
The polypropylene resin (A) contains propylene and ethylene and/or an α-olefin having 4 or more carbon atoms, and 0.5 mol% or less of ethylene and/or an α-olefin having 4 or more carbon atoms with respect to the total olefin monomers. It is preferably a polymer copolymerized so as to be The content of the copolymer component is preferably 0.3 mol % or less, more preferably 0.1 mol % or less, and most preferably a complete homopolypropylene resin containing no copolymer component.
When ethylene and/or α-olefins having 4 or more carbon atoms are copolymerized in excess of 0.5 mol %, the crystallinity and rigidity may be excessively lowered and the tear strength may be increased. A blend of such resins may be used.

The mesopentad fraction ([mmmm]%) measured by 13C-NMR, which is an index of the stereoregularity of the polypropylene resin (A), is preferably 96 to 99.5%. More preferably, it is 97% or more, and still more preferably 98% or more. If the mesopentad ratio of the polypropylene resin (A) is small, the tear strength may be insufficient. 99.5% is a realistic upper limit.

Mw/Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 for the polypropylene resin (A). It is more preferably 3.0 to 5.0, still more preferably 3.2 to 4.5, and particularly preferably 3.3 to 4.0.
The presence of high-molecular-weight components tends to promote the crystallization of low-molecular-weight components. Preferably, the Mw/Mn of resin (A) does not exceed 5.4. If Mw/Mn is too large, the amount of high molecular weight components increases, which tends to increase the tear strength or decrease the tensile elastic modulus (Young's modulus) in the width direction (TD). If the Mw/Mn of the polypropylene resin (A) is less than 3.0, film formation becomes difficult. Mw means the weight average molecular weight and Mn means the number average molecular weight.

The weight average molecular weight (Mw) of polypropylene resin (A) is preferably 180,000 to 500,000. A more preferable lower limit of Mw is 190,000, more preferably 200,000, and a more preferable upper limit of Mw is 320,000, more preferably 300,000, and particularly preferably 250,000.

The number average molecular weight (Mn) of the polypropylene resin (A) is preferably 20,000 to 200,000. A more preferable lower limit of Mn is 30,000, more preferably 40,000, particularly preferably 50,000, and a more preferable upper limit of Mn is 80,000, more preferably 70,000, particularly preferably 60,000. be.

At this time, the melt flow rate (MFR; 230° C., 2.16 kgf) of the polypropylene resin (A) is preferably 6.2 g/10 minutes to 10.0 g/10 minutes.
The lower limit of the MFR of the polypropylene resin (A) is more preferably 6.5 g/10 minutes, even more preferably 7 g/10 minutes, and particularly preferably 7.5 g/10 minutes. The upper limit of the MFR of the polypropylene resin is more preferably 9 g/10 minutes, still more preferably 8.5 g/10 minutes, and particularly preferably 8.2 g/10 minutes.
When the melt flow rate (MFR; 230 ° C., 2.16 kgf) is 6.2 g / 10 minutes or more, the degree of orientation of the film caused by stretching is increased, so the rigidity of the film, especially the tension in the width direction (TD) As the elastic modulus (Young's modulus) increases, the tear strength decreases. Furthermore, thermal shrinkage at high temperatures can also be made smaller. Moreover, when the melt flow rate (MFR; 230° C., 2.16 kgf) is 9.0 g/10 minutes or less, the film can be easily formed without breakage.

When the gel permeation chromatography (GPC) integrated curve of the polypropylene resin (A) is measured, the lower limit of the amount of the component having a molecular weight of 100,000 or less is preferably 35% by mass, more preferably 38% by mass. , more preferably 40% by mass, particularly preferably 41% by mass, and most preferably 42% by mass.
On the other hand, the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% by mass, more preferably 60% by mass, still more preferably 58% by mass, and particularly preferably 56% by mass. and most preferably 55% by mass. Within the above range, stretching is facilitated, thickness unevenness is reduced, stretching temperature and heat setting temperature are easily raised, and tear strength can be suppressed to a lower level.
The molecular weight distribution of the polypropylene resin (A) can be adjusted by polymerizing components with different molecular weights in multiple stages in a series of plants, by blending components with different molecular weights offline in a kneader, or by blending catalysts with different performance. It is possible to adjust the molecular weight distribution by using a catalyst capable of realizing a desired molecular weight distribution.

(Polypropylene resin (B))
The polypropylene resin (B) contains propylene and ethylene and/or an α-olefin having 4 or more carbon atoms, and 0.5 mol% or less of ethylene and/or an α-olefin having 4 or more carbon atoms with respect to the total olefin monomers. It is preferably a polymer copolymerized so as to be The content of the copolymer component is preferably 0.3 mol % or less, more preferably 0.1 mol % or less, and most preferably a complete homopolypropylene resin containing no copolymer component.
If the amount of ethylene and/or α-olefin having 4 or more carbon atoms is 0.5 mol % or less, crystallinity and rigidity may be further improved, and tear strength may be further reduced. Such resins may be used as an improvement over blends.

The mesopentad fraction ([mmmm]%) measured by 13C-NMR, which is an index of the stereoregularity of the polypropylene resin (B), is preferably 96 to 99.5%. More preferably, it is 97% or more, and still more preferably 98% or more. When the polypropylene resin (B) has a high mesopentad ratio, the elastic modulus increases and the tear strength decreases. 99.5% is a realistic upper limit.

Mw/Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 for the polypropylene resin (B). It is more preferably 3.0 to 5.0, still more preferably 3.2 to 4.5, and particularly preferably 3.3 to 4.0.
If the Mw/Mn of the polypropylene resin (B) is less than 5.4, if the Mw/Mn becomes too large, the high molecular weight component will decrease and the tear strength may become smaller. Tensile modulus of elasticity (Young's modulus) tends to increase. If the Mw/Mn of the polypropylene resin (B) is less than 3.0, film formation will be difficult. Mw means weight average molecular weight and Mn means number average molecular weight.

The weight average molecular weight (Mw) of the polypropylene resin (B) is preferably 180,000 to 500,000. A more preferable lower limit of Mw is 190,000, more preferably 200,000, and a more preferable upper limit of Mw is 320,000, more preferably 300,000, and particularly preferably 250,000.

The number average molecular weight (Mn) of the polypropylene resin (B) is preferably 20,000 to 200,000. A more preferable lower limit of Mn is 30,000, more preferably 40,000, and a more preferable upper limit of Mn is 70,000, more preferably 60,000, and particularly preferably 50,000.

At this time, the melt flow rate (MFR; 230° C., 2.16 kgf) of the polypropylene resin (B) is preferably 9.2 g/10 minutes or more.
The lower limit of the MFR of the polypropylene resin (B) is more preferably 9.5 g/10 minutes, still more preferably 10 g/10 minutes, and particularly preferably 11 g/10 minutes. The upper limit of the MFR of the polypropylene resin is more preferably 15 g/10 minutes, still more preferably 13 g/10 minutes, and particularly preferably 12 g/10 minutes.
When the melt flow rate (MFR; 230 ° C., 2.16 kgf) is 9.2 g / 10 minutes or more, the degree of orientation of the film caused by stretching in the width direction (TD) is increased, so the tear strength of the film is increased. can be made smaller. Furthermore, the heat resistance of the film, especially the heat shrinkage coefficient at 150° C. in the width direction (TD) is reduced.

When measuring the gel permeation chromatography (GPC) integration curve of the polypropylene resin (B), the lower limit of the amount of the component having a molecular weight of 100,000 or less is preferably 50% by mass, more preferably 52% by mass, and further Preferably it is 55% by mass.
On the other hand, the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% by mass, more preferably 60% by mass, and still more preferably 58% by mass. Within the above range, stretching is facilitated, thickness unevenness is reduced, stretching temperature and heat setting temperature are easily raised, and tear strength can be suppressed to a lower level.

The mixture of polypropylene resin (A) and polypropylene resin (B) preferably satisfies the following conditions 1) to 4) and is a polypropylene resin.
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.5 g/10 min or more and 9.0 g/10 min or less.

The molecular weight distribution of polypropylene resin (A) and polypropylene resin (B) can be adjusted by polymerizing components with different molecular weights in a series of plants in multiple stages, blending components with different molecular weights offline in a kneader, and achieving different performance. It is possible to adjust the molecular weight by blending and polymerizing the catalysts possessed, or by using a catalyst capable of realizing a desired molecular weight distribution.

The polypropylene resin (A) and polypropylene resin (B) used in the present invention are obtained by polymerizing raw material propylene using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among them, it is preferable to use a Ziegler-Natta catalyst in order to eliminate heterogeneous bonds, and to use a catalyst capable of polymerizing with high stereoregularity.
As a method for polymerizing propylene, known methods may be adopted. For example, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, or xylene, a method of polymerizing in a liquid monomer, a method of polymerizing a gaseous monomer with a catalyst and polymerizing in a gas phase, or a method of polymerizing by combining these.

The resin composition constituting the biaxially oriented polypropylene film may contain additives and other resins in addition to the polypropylene resin. The content of additives and other resins in the resin composition is preferably 20% by weight or less.
Examples of additives include antioxidants, ultraviolet absorbers, nucleating agents, adhesives, antifog agents, flame retardants, inorganic or organic fillers, and the like.
Other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers of propylene and ethylene and/or α-olefins having 4 or more carbon atoms, various elastomers, and the like. These are polymerized sequentially using a multi-stage reactor, blended with polypropylene resin in a Henschel mixer, or prepared in advance using a melt kneader and diluted with polypropylene to a predetermined concentration. Alternatively, the entire amount may be previously melted and kneaded before use.

(Method for producing biaxially oriented polypropylene film)
The biaxially oriented polypropylene film of the present invention is obtained by melt extruding a resin composition containing polypropylene resin as a main component with an extruder to form an unstretched sheet, and stretching and heat-treating the unstretched sheet by a predetermined method. can be obtained by
An unstretched sheet is obtained by using multiple extruders, feed blocks, and multi-manifolds. The melt extrusion temperature is preferably about 200 to 280°C.

The chill roll surface temperature is preferably 25 to 35°C, more preferably 27 to 33°C. Next, the film is stretched in the machine direction (MD) with stretching rolls at 120 to 165° C., and then stretched in the transverse direction (TD). Furthermore, heat fixation is performed while relaxing. The biaxial polypropylene film thus obtained can be subjected, if necessary, to corona discharge, plasma treatment, flame treatment, or the like, and then wound up with a winder to obtain a film roll.

The lower limit of the draw ratio in the machine direction (MD) is preferably 3 times, more preferably 3.5 times, and still more preferably 4.0 times. If it is less than the above, the film thickness may become uneven. The upper limit of the draw ratio in the machine direction (MD) is preferably 7 times, more preferably 6 times. If the above is exceeded, it may become difficult to perform subsequent transverse direction (TD) stretching.
The lower limit of the stretching temperature in the machine direction (MD) is preferably 120°C, more preferably 125°C, still more preferably 130°C. If it is less than the above, the mechanical load may increase, the thickness unevenness may increase, and the surface of the film may become rough. The upper limit of the stretching temperature in the machine direction (MD) is preferably 160°C, more preferably 155°C, and still more preferably 150°C. It may adhere and make it impossible to stretch, or surface roughening may occur.

The lower limit of the draw ratio in the width direction (TD) is preferably 8 times, more preferably 10 times. When it is less than the above, the orientation in the width direction (TD) is less likely to increase in the transverse direction of the film, and the tear strength is less likely to decrease. The upper limit of the draw ratio in the width direction (TD) is preferably 12 times. If the above is exceeded, the heat shrinkage rate may increase, or breakage may occur during stretching. When the polypropylene resin composition constituting the film is a mixture of the polypropylene resin (A) and the polypropylene resin (B), the orientation in the width direction (TD) can be achieved even if the draw ratio in the width direction (TD) is not so large. tend to be large.
The preheating temperature in the width direction (TD) stretching is preferably set 15 to 35° C. higher than the machine direction (MD) stretching temperature in order to quickly raise the film temperature to the vicinity of the stretching temperature. Stretching in the transverse direction (TD) is performed at a temperature higher than that of a conventional biaxially oriented polypropylene film.
The lower limit of the stretching temperature in the width direction (TD) is preferably 155°C, more preferably 157°C, still more preferably 158°C, and particularly preferably 160°C. If it is less than the above, it may be broken without sufficiently softening, or the heat shrinkage rate may increase. The upper limit of the transverse direction (TD) stretching temperature is preferably 170°C, more preferably 168°C, still more preferably 163°C. In order to reduce the heat shrinkage, the temperature is preferably high, but if it exceeds the above, the low molecular weight component melts and recrystallizes, not only lowering the orientation but also surface roughening and whitening of the film.

The stretched film is heat set. Heat setting can be performed at higher temperatures than conventional biaxially oriented polypropylene films. The lower limit of the heat setting temperature is preferably 165°C, more preferably 166°C. If it is less than the above, the heat shrinkage rate may increase. In addition, a long time of treatment is required to reduce the heat shrinkage, which may result in poor productivity. The upper limit of the heat setting temperature is preferably 176°C, more preferably 175°C. If the above is exceeded, the low-molecular-weight components may melt and recrystallize, resulting in surface roughness and whitening of the film.

It is preferable to relax (relieve) at the time of heat setting. The lower limit of the transverse (TD) relaxation rate is preferably 2%, more preferably 3%. If it is less than the above, the heat shrinkage rate may increase. The upper limit of the transverse (TD) relaxation rate is preferably 10%, more preferably 8%. When the above is exceeded, thickness unevenness may become large.

Furthermore, in order to reduce the thermal shrinkage, the film produced by the above process can be wound into a roll and then annealed off-line. The lower limit of the offline annealing temperature is preferably 160°C, more preferably 162°C, and still more preferably 163°C. If it is less than the above, the effect of annealing may not be obtained. The upper limit of the offline annealing temperature is preferably 175°C, more preferably 174°C, still more preferably 173°C. When the above is exceeded, the transparency may be lowered and the thickness unevenness may be increased.

The lower limit of the offline annealing time is preferably 0.1 minutes, more preferably 0.5 minutes, and still more preferably 1 minute. If it is less than the above, the effect of annealing may not be obtained. The upper limit of the offline annealing time is preferably 30 minutes, more preferably 25 minutes, still more preferably 20 minutes. If the above is exceeded, productivity may decrease.

The lower limit of the plane orientation coefficient of the biaxially oriented polypropylene film of the present invention is preferably 0.011, more preferably 0.012, still more preferably 0.013. Within the above range, the heat resistance and rigidity of the film tend to be increased.
The biaxially oriented polypropylene film of the present invention has crystal orientation, the direction and degree of which greatly affect the physical properties of the film. The degree of crystal orientation can be expressed using a plane orientation coefficient as an index, and can be made within the above range by controlling the molecular structure of the polypropylene-based resin and the process and conditions in film production.

(Biaxially oriented polypropylene film)
The thickness of the entire biaxially oriented polypropylene film of the present invention is preferably 9 to 200 μm, more preferably 10 to 150 μm, even more preferably 12 to 100 μm, particularly preferably 12 to 80 μm.

The tear strength (N/mm) of the biaxially oriented polypropylene film of the present invention is in the range of 0.014 x film thickness (μm) + 0.35 or less in the width direction (TD) or the machine direction (MD). is necessary, and if it exceeds 0.014 × film thickness (μm) + 0.35, when the film is torn in each direction, a large resistance to tearing is expected according to each film thickness. The film can be easily cut by hand without It is preferably in the range of 0.014×film thickness (μm)+0.30 or less, more preferably in the range of 0.014×film thickness (μm)+0.28 or less. Within this range, the resistance to tearing is not greater than that of conventional biaxially oriented polypropylene films.
The tear strength (N/mm) of the biaxially oriented polypropylene film of the present invention is preferably in the range of 0.014×film thickness (μm)+0.35 or less, particularly in the width direction (TD).

The tear strength (N/mm) of the biaxially oriented polypropylene film of the present invention is preferably in the range of 4.0 or less in the width direction (TD) or machine direction (MD). More preferably, it is 3.5 or less.

In the biaxially oriented polypropylene film of the present invention, the heat shrinkage in the width direction (TD) at 150° C. is preferably 0.2 to 7.5%, more preferably 0.3 to 7%, and 0 0.4 to 6% is more preferred, and 0.5 to 5% is particularly preferred. If the heat shrinkage ratio is within the above range, the film can be said to be particularly excellent in heat resistance, and for example, wrinkles caused by heat during processing into bags can be reduced. Therefore, it can be used in applications that may be exposed to high temperatures. If the 150° C. heat shrinkage rate is up to about 1.5%, it is possible, for example, by increasing the low molecular weight component and adjusting the stretching conditions and heat setting conditions. It is preferable to

In the biaxially oriented polypropylene film of the present invention, the heat shrinkage rate in the machine direction at 150° C. is preferably 0.2 to 7%, more preferably 0.3 to 6%. If the heat shrinkage ratio is within the above range, the film can be said to have excellent heat resistance, and for example, wrinkles caused by heat during processing into bags can be reduced.
for that reason. It can also be used in applications that may be exposed to high temperatures. If the 150° C. heat shrinkage rate is up to about 1.5%, it is possible, for example, by increasing the low molecular weight component and adjusting the stretching conditions and heat setting conditions. Treatment or the like is preferable.

The lower limit of the impact resistance (room temperature, 25°C) of the biaxially oriented polypropylene film of the present invention is preferably 0.4J, more preferably 0.5J. Within the above range, the film has sufficient toughness and is not broken during handling. The upper limit of the impact resistance is preferably 1.5J, more preferably 1.3J from a practical point of view. Impact resistance tends to decrease, for example, when there are many low molecular weight components, when the overall molecular weight is low, when there are few high molecular weight components, or when the molecular weight of the high molecular weight components is low. These components can be adjusted to be within range.

It is preferable that the tensile modulus of elasticity of the biaxially oriented polypropylene film of the invention is 2.0 GPa or more in the width direction and the machine direction, and 4.0 GPa or more in the direction of the large tensile modulus.

The tensile elastic modulus in the width direction (TD) of the biaxially oriented polypropylene film of the present invention is preferably 4.5 to 8 GPa, more preferably 4.6 to 7.5 GPa, and 4.7 to 7 GPa. is more preferable, and 4.8 to 6.5 GPa is particularly preferable. If the tensile elastic modulus in the lateral direction is within the above range, it is possible to obtain a film that is difficult to break.

The tensile modulus of the biaxially oriented polypropylene film of the present invention in the machine direction (MD) is preferably 1.8 to 4 GPa, more preferably 2.1 to 3.7 GPa, and 2.2 to 3. 0.5 GPa is more preferred, and 2.3 to 3.4 GPa is particularly preferred.

The resistance to folding of the biaxially oriented polypropylene film of the present invention was evaluated by holding the film in a ring shape and compressing it, and evaluating the drag force detected by a load cell (ring crush measurement method). and/or its value in the machine direction (MD) is preferably 120 g or more. The measuring method will be described later.

The haze of the biaxially oriented polypropylene film of the present invention is preferably 5% or less, more preferably 0.2 to 5%, even more preferably 0.3 to 4.5%, and particularly preferably 0.4 to 4%. Within the above range, it may be easy to use in applications where transparency is required. Haze tends to be worsened, for example, when the stretching temperature and heat setting temperature are too high, when the chill roll (CR) temperature is high and the cooling rate of the stretched raw sheet is slow, and when the low molecular weight component is too much, these are adjusted. By doing so, it is possible to make it within the above range. A method for measuring haze will be described later.

The dynamic friction coefficient of the biaxially oriented polypropylene film of the present invention is preferably 0.5 or less, more preferably 0.45 or less, and particularly preferably 0.40 or less. When the coefficient of dynamic friction is 0.5 or less, the film can be smoothly unwound from the roll film, and the printing process is easy. A method for measuring the coefficient of dynamic friction will be described later.

(Surface layer)
The biaxially oriented polypropylene film of the invention may be provided with a separate surface layer, and the polypropylene resin used is a propylene homopolymer or a copolymer of propylene and ethylene and/or an α-olefin having 4 or more carbon atoms. can be used. Examples of α-olefins having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene.
Examples of α-olefins having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. As other copolymer components, maleic acid having polarity may be used.
The total content of ethylene, α-olefins having 4 or more carbon atoms, and other copolymer components is preferably 8.0 mol % or less. Copolymerization in excess of 8.0 mol % may result in whitening of the film, resulting in poor appearance, or tackiness, making film formation difficult.
Two or more of these resins may be mixed and used. When mixed, the individual resins may be copolymerized in excess of 8.0 mol%, but the total amount of ethylene, α-olefins having 4 or more carbon atoms, and other copolymer components in the mixture It is preferably 8.0 mol % or less.

The polypropylene resin used in the surface layer is obtained by polymerizing raw material propylene using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among them, it is preferable to use a Ziegler-Natta catalyst in order to eliminate heterogeneous bonds, and to use a catalyst capable of polymerizing with high stereoregularity.
As a method for polymerizing propylene, known methods may be adopted. For example, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, or xylene, a method of polymerizing in a liquid monomer, a method of polymerizing a gaseous monomer with a catalyst and polymerizing in a gas phase, or a method of polymerizing by combining these.

The surface layer may contain additives and other resins in addition to the polypropylene resin. Examples of additives include antioxidants, ultraviolet absorbers, nucleating agents, adhesives, antifog agents, flame retardants, inorganic or organic fillers, and the like.
Other resins include polypropylene-based resins other than the polypropylene resin used in the present invention, random copolymers of propylene and ethylene and/or α-olefins having 4 or more carbon atoms, various elastomers, and the like. These are polymerized sequentially using a multi-stage reactor, blended with polypropylene resin in a Henschel mixer, or prepared in advance using a melt kneader and diluted with polypropylene to a predetermined concentration. Alternatively, the entire amount may be previously melted and kneaded before use.
It is also a suitable method to incorporate an anti-blocking agent in the surface layer.
The anti-blocking agent is appropriately selected from inorganic anti-blocking agents such as silica, calcium carbonate, kaolin, and zeolite, and organic anti-blocking agents such as acrylic, polymethacrylic, and polystyrene. can do. Among these, it is particularly preferable to use silica.
The average particle size of the antiblocking agent is preferably 1.0-2.0 μm, more preferably 1.0-1.5 μm.
The antiblocking agent is preferably contained in the surface layer in an amount of 0.5% by mass or less. The method of measuring the average particle diameter as used herein is to take a photograph with a scanning electron microscope, measure the Feret diameter in the horizontal direction using an image analyzer, and display the average value.

The wetting tension of the surface of the surface layer is preferably 38 mN/m or more.
When the wet tension is 38 mN/m or more, the adhesion with printing inks and adhesives is improved.
More preferably, the wetting tension is 16 LogΩ or more. Additives such as antistatic agents and surfactants are usually used to increase the wetting tension to 38 mN/m or more. For example, surface treatment such as

The thickness ratio of the surface layer to the biaxially oriented polypropylene film of the present invention is preferably 0.01 to 0.5, more preferably 0.03 to 0.4. is more preferable, and 0.05 to 0.3 is even more preferable. When the surface layer/biaxially oriented polypropylene film ratio exceeds 0.5, the shrinkage tends to increase. The thickness of the biaxially oriented polypropylene film is preferably 50 to 99%, more preferably 60 to 97%, and particularly preferably 70 to 95% of the thickness of the entire film. The rest will be the surface layer or the surface layer and other layers (for example, the C layer). The substantial thickness of the surface layer is preferably 0.5 to 4 μm, more preferably 1 to 3.5 μm, even more preferably 1.5 to 3 μm.
The film may have a two-layer structure having one biaxially oriented polypropylene film and one surface layer, but may have three or more layers. A two-layer structure of biaxially oriented polypropylene film/surface layer is preferred. It may also have a three-layer structure of surface layer/biaxially oriented polypropylene film/surface layer, /biaxially oriented polypropylene film/intermediate layer (C)/surface layer, or a multi-layer structure of more than these.
When there are a plurality of surface layers, the composition may be different as long as each layer satisfies its properties.
When the surface layer is provided, the resin composition for the base layer (for example, a mixture of polypropylene resin (A) and polypropylene resin (B)) and the polypropylene resin for the surface layer are extruded by separate extruders. It can be obtained by forming a laminated unstretched sheet by melt extrusion, stretching the unstretched sheet by a predetermined method, and heat-treating the unstretched sheet.

(Application)
The biaxially oriented polypropylene film of the present invention can be used not only for food packaging such as standing pouches, but also for labels and the like. In the bag-making process, when the bag is made by folding in the direction perpendicular to the flow direction of the machine, the tear strength in the horizontal direction is important because the horizontal direction is the direction of hand tearing. The lower the tear strength, the better the hand tearability of the film.

The present invention will be described in more detail below with reference to examples, but the following examples do not limit the present invention, and are included in the present invention when modified within the scope of the gist of the present invention. Methods for measuring physical properties of films obtained in Examples and Comparative Examples are as follows.

1) Stereoregularity Mesopentad fraction ([mmmm]%) 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 at 110° C. by dissolving 200 mg of a sample in a mixture of o-dichlorobenzene and deuterated benzene at 8:2 (volume ratio) at 135° C. using “AVANCE500” manufactured by BRUKER.

2) Melt flow rate (MFR; g/10 minutes)
It was measured at a temperature of 230° C. and a load of 2.16 kgf according to JIS K7210. As the resin, pellets (powder) were directly weighed and used. After cutting out the necessary amount of the film, a sample cut to about 5 mm square was used.

3) Molecular Weight and Molecular Weight Distribution Molecular weight and molecular weight distribution were determined by monodisperse polystyrene standards using gel permeation chromatography (GPC). Measurement conditions such as columns and solvents used in GPC measurement are as follows.
Solvent: 1,2,4-trichlorobenzene Column: TSKgel GMHHR-H (20) HT x 3
Flow rate: 1.0ml/min
Detector: RI
Measurement temperature: 140°C

The number average molecular weight (Mn), mass average molecular weight (Mw), and molecular weight distribution are determined by the number of molecules (N _{i ) at each elution position of the GPC curve obtained through the molecular weight calibration curve (M i )} . defined by the formula
Number average molecular weight: Mn = Σ (N _i · M _i ) / ΣN _i
Mass average molecular weight: Mw = Σ (Ni · M _i
2)/Σ(N _i ·M _i )
Molecular weight distribution: Mw/Mn
When the baseline was not clear, the baseline was set in the range up to the lowest point of the high-molecular-weight elution peak closest to the elution peak of the standard substance.

4) Thickness The thickness of each layer of the substrate layer (A) and the surface layer (B) was measured by cutting out a cross section of a biaxially oriented laminated polypropylene film solidified with a modified urethane resin with a microtome and observing it with a differential interference microscope. .

5) Thermal shrinkage rate (%)
It was measured by the following method according to JIS Z1712. The film was cut into a width of 20 mm and a length of 200 mm in each of the MD direction and the TD direction, suspended in a hot air oven at 150° C. and heated for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the shrinkage length to the original length.

6) Tensile modulus (Young's modulus (unit: GPa))
The tensile elastic modulus of the film in the MD and TD directions was measured at 23° C. under the following conditions according to JIS K7127.
Measuring equipment: Shimadzu Corporation, Autograph ASS-100NJ
Sample size: width 15mm x length 200mm
Crosshead speed: 200mm/min
Distance between chucks: 100mm
Strain range for elastic modulus measurement: 0.1 to 0.6%

7) Ring crush (g)
Prepare a film sample size of 12.7 mm x 152 mm with a digital ring crush tester (manufactured by Tester Sangyo Co., Ltd.), set the attachment spacer on the sample table according to the thickness of the film sample, and set the MD and TD directions. In each, a film sample is inserted circumferentially. At 23°C, the compression plate was lowered at a speed of 12 mm/min. The maximum load when compressed at 100 mm was taken as the ring crush measurement value.

8) Haze (unit: %)
It was measured according to JIS K7105.

9) Dynamic Friction Coefficient In accordance with JIS K7125, the corona-treated surfaces of the films were superimposed and measured at 23°C.

10) Refractive index and plane orientation coefficient Measured according to JIS K7142-1996 5.1 (method A) using an Abbe refractometer manufactured by Atago. Nx and Ny are the refractive indices along the MD and TD directions, respectively, and Nz is the refractive index in the thickness direction. The plane orientation coefficient (ΔP) was obtained by (Nx+Ny)/2−Nz.

12) Surface resistivity (LogΩ)
According to JIS K6911, after the film was aged at 23° C. for 24 hours, the corona-treated surface of the film was measured.

13) Wetting tension (mN/m)
After aging the film for 24 hours at 23° C. and 50% relative humidity in accordance with JIS K6768-1999, the corona-treated surface of the film was measured by the following procedure.
1) Measurements are performed in a standard laboratory atmosphere (see JIS K7100) at a temperature of 23°C and a relative humidity of 50%.
2) Place the test piece on the substrate of the hand coater (4.1), drop a few drops of the test mixture on the test piece, and immediately pull the wire bar to spread it. If a cotton swab or brush is used to spread the test mixture, spread the liquid quickly over an area of at least 6 ^cm2 . The amount of liquid should be such that it forms a thin layer without pooling. Wetting tension is determined by observing the liquid film of the mixed solution for testing in a bright place and observing the state of the liquid film after 3 seconds. If the applied state is maintained for 3 seconds or more without breaking the liquid film, it means that the liquid is wet. If the wetness is maintained for 3 seconds or more, the mixture proceeds to the next higher surface tension mixture, and conversely, if the liquid film breaks in 3 seconds or less, the mixture proceeds to the next lower surface tension mixture. Repeat this operation and select a mixture that can wet the surface of the test piece accurately in 3 seconds.
3) Use a new swab for each test. Brushes or wire bars should be cleaned with methanol and dried between uses, as residual liquid will change composition and surface tension upon evaporation.
4) The operation of selecting a mixture that can wet the surface of the test piece in 3 seconds is performed at least 3 times. The surface tension of the mixture thus selected is reported as the wetting tension of the film.

14) Tear strength (N/mm)
The average tear strength measured according to the JIS K7128 trouser tear method was taken as the tear strength.

15) Hand tearability of bag product 1) Formation of laminated film with sealant film A continuous dry laminator was used as follows.
The corona surface of the biaxially oriented polypropylene film obtained in Examples and Comparative Examples was gravure-coated with an adhesive so that the dry coating amount was 3.0 g/m ² , and then led to a drying zone at 80°C for 5 seconds. dried with Subsequently, it was laminated with a sealant film between rolls provided downstream (roll pressure: 0.2 MP, roll temperature: 60°C). The obtained laminated film was subjected to aging treatment at 40° C. for 3 days in a wound state.
The adhesive was obtained by mixing 17.9% by mass of the main agent (TM329, manufactured by Toyo-Morton Co., Ltd.), 17.9% by mass of the curing agent (CAT8B, manufactured by Toyo-Morton Co., Ltd.), and 64.2% by mass of ethyl acetate. An ether-based adhesive was used, and a non-stretched polypropylene film (Pylen (registered trademark) CT P1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. was used as the sealant film.
2) Production of Bag Product After folding the laminated film in two in the direction of flow, it was heat-sealed on three sides under the conditions of 120° C., 1 kg, and 1 second to produce a bag product having a width of 200 mm and a length of 200 mm.
3) Evaluation of Tearability by Hand A notch was made in the bag product in the lateral direction, and 10 evaluators evaluated the presence or absence of resistance when tearing the product in the lateral direction by hand. The number of people who answered that they had a sense of resistance was used as an evaluation item. Each was evaluated three times.
0 people ··· ⊚: excellent in hand cutting property.
1 to 5 people .largecircle.: good hand tearability.
6 to 9 people .DELTA.: Poor hand cutting property.
10 people... x: There is no hand cutting property.

(Example 1)
The base material layer contains 79% by weight of the polypropylene homopolymer PP-1 shown in Table 1, 20% by weight of the polypropylene homopolymer PP-2, and an antistatic agent (stearyl diethanolamine stearate (Matsumoto Yushi Co., Ltd. KYM- 4K)) mixed with 1% by weight was used. Furthermore, 3000 ppm of silica particles having an average particle size of 1 μm were added to this mixture.
Using a 60 mm extruder, the raw material resin was melted at 250° C., co-extruded into a sheet from a T-die, cooled and solidified with a cooling roll at 30° C., then extruded at 135° C. in the machine direction (MD) 4. Stretched 5 times. Then, in a tenter, both ends of the film in the width direction are clipped, and after preheating at 175 ° C., the film is stretched 8.2 times in the width direction (TD) at 160 ° C. while relaxing 6.7% in the width direction (TD). , and heat-set at 170°C. The film forming conditions at this time were designated as film forming conditions a, and are shown in Table 2.
One surface side of the obtained biaxially oriented polypropylene film was subjected to corona treatment using a corona treatment machine manufactured by Softal Corona & Plasma GmbH under conditions of an applied current value of 0.75 A, and then subjected to a winder. The biaxially oriented polypropylene film of the present invention was obtained by winding the film. The physical properties of the obtained film are as shown in Table 3.

(Examples 2 and 3)
A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the film thickness was changed as shown in Table 1. The physical properties of the obtained film are as shown in Table 3.

(Example 4)
A 60 mm extruder is used for the mixed raw material used for the base material layer (A), and a 65 mm extruder is used for the mixed raw material used for the surface layer (B). It was co-extruded, cooled and solidified with a cooling roll at 30°C, and then stretched 4.5 times in the machine direction (MD) at 135°C. Then, in a tenter, both ends of the film in the width direction are clipped, and after preheating at 175 ° C., the film is stretched 8.2 times in the width direction (TD) at 160 ° C. while relaxing 6.7% in the width direction (TD). , and heat-set at 170°C. A film was formed under the film forming conditions a shown in Table 2 and wound up with a winder to obtain a biaxially oriented laminated polypropylene film of the present invention in which one base layer (A) and one surface layer (B) were laminated one by one. . The surface side of the surface layer (B) of the obtained biaxially oriented polypropylene film was subjected to corona treatment using a corona treatment machine manufactured by Softal Corona & Plasma GmbH under conditions of an applied current value of 0.75 A. After application, the biaxially oriented polypropylene film of the present invention was taken up by a winder. The physical properties of the obtained film are as shown in Table 3.

(Example 5)
A mixture of 79% by weight of the polypropylene homopolymer PP-1 shown in Table 1 and 20% by weight of the polypropylene homopolymer PP-2 was added to 99% by weight of the polypropylene resin PP-1, and the transverse direction (TD) draw ratio was 10. A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the ratio was changed to 0.0. The physical properties of the obtained film are as shown in Table 3. The film forming conditions at this time were designated as film forming conditions b, and are shown in Table 2.

(Comparative example 1)
A mixture of 79% by weight of the polypropylene homopolymer PP-1 shown in Table 1 and 20% by weight of the polypropylene homopolymer PP-2 was changed to 99% by weight of the polypropylene resin PP-1 shown in Table 1. A biaxially oriented polypropylene film was obtained in the same manner as in Example 1.
The physical properties of the obtained film are as shown in Table 4.

(Comparative example 2)
A mixture of 79% by weight of polypropylene homopolymer PP-1 and 20% by weight of polypropylene homopolymer PP-2 shown in Table 1, 59% by weight of polypropylene homopolymer PP-1 and polypropylene homopolymer PP-2 A biaxially oriented polypropylene film was formed in the same manner as in Example 1, except that the mixture was changed to a 40% by weight mixture, but the film was broken and could not be formed.

(Comparative Example 3)
Example 1 except that the mixture of 79% by weight of polypropylene homopolymer PP-1 and 20% by weight of polypropylene homopolymer PP-2 shown in Table 1 was changed to 99% by weight of polypropylene resin PP-3. A biaxially oriented polypropylene film was obtained in the same manner. The physical properties of the obtained film are as shown in Table 4.

(Comparative Example 4)
A mixture of 79% by weight of polypropylene homopolymer PP-1 and 20% by weight of polypropylene homopolymer PP-2 shown in Table 1 was changed to 99% by weight of polypropylene resin PP-4, and the longitudinal stretching temperature was 125. A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the temperature was changed to 170°C, the width direction stretching preheating temperature to 170°C, the width direction stretching temperature to 158°C, and the heat setting temperature to 165°C. The physical properties of the obtained film are as shown in Table 4. The film-forming conditions at this time were designated as film-forming conditions c, and are shown in Table 2.

(Comparative Examples 5 and 6)
A biaxially oriented polypropylene film was obtained in the same manner as in Comparative Example 3, except that the film thickness was changed as shown in Table 1. The physical properties of the obtained film are as shown in Table 4.

The biaxially oriented polypropylene films obtained in Examples 1 to 5 had low tear strength in the width direction (TD) and low heat shrinkage.
In contrast, the films obtained in Comparative Examples 1 and 3 had high tear strength in the transverse direction (TD).
In Comparative Example 2, film formation was not possible.
The films obtained in Comparative Examples 4, 5, and 6 had high tear strength in the width direction (TD) and high heat shrinkage in the width direction (TD) and machine direction (MD).

The biaxially oriented polypropylene film of the present invention can be used not only for food packaging such as standing pouches, but also for labels and the like. In the bag-making process, when the bag is made by folding in the direction perpendicular to the flow direction of the machine, the tear strength in the horizontal direction is important because the horizontal direction is the direction of hand tearing. The lower the tear strength, the better the hand tearability of the film.

Claims (4)

A biaxially oriented polypropylene film having the following features (a) to (d) and 1) to 4).
(a) It consists of a resin composition containing a polypropylene-based resin as a main component.
(b) Tear strength (N/mm) ≤ (0.014 x film thickness (μm) + 0.35) in the width direction or the longitudinal direction of the film.
(c) The thermal shrinkage rate at 150° C. in the width direction and the machine direction of the film is 7% or less.
(d) The lower limit of the plane orientation coefficient of the film is 0.0125.
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.5 g/10 min or more and 9.0 g/10 min or less. 2. The biaxially oriented polypropylene film according to claim 1, having a tensile modulus of elasticity of 2.0 GPa or more in the width direction and longitudinal direction of the film, and a tensile modulus of elasticity of 4.0 GPa or more in the direction of the large tensile modulus. 3. The biaxially oriented polypropylene film according to claim 1, which has an impact strength of 0.6 J or more. The biaxially oriented polypropylene film according to any one of claims 1 to 3, which has a haze of 5% or less.