JPWO2018180164A1 - Biaxially oriented polypropylene film - Google Patents

Abstract

To provide a biaxially oriented polypropylene film having higher heat resistance and hand cutting properties. It is a biaxially oriented polypropylene film having the following characteristics (a) to (c). (A) It comprises a resin composition containing a polypropylene resin as a main component. (B) The tear strength (N / mm) in the width direction or longitudinal direction of the film ≦ (0.014 × film thickness (μm)) + 0.35. (C) The heat shrinkage at 150 ° C. is 7% or less.

Description

  The present invention relates to a biaxially oriented polypropylene film. More specifically, the present invention relates to a biaxially oriented polypropylene film having excellent heat resistance and hand cutting properties.

Conventionally, a stretched film of a polypropylene resin has been widely used in a wide range of applications such as packaging of food and various products, electrical insulation, and surface protection film.
However, the conventional polypropylene film has a high tear strength, and the hand-cutting property at the time of opening after forming a bag is not sufficient.

  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 cutting properties.

  The present inventors have conducted intensive studies and as a result, even in a biaxially oriented polypropylene film, even if it has excellent heat resistance at high temperatures, it has become possible to further reduce the tear strength, and to set the tear strength in a specific direction to a predetermined value. Have been found to solve the above-mentioned problem, and have completed the present invention.

The present invention that has solved the above-mentioned problems is a biaxially oriented polypropylene film having the following features (a) to (c).
(A) It comprises a resin composition containing a polypropylene resin as a main component.
(B) The tear strength (N / mm) in the width direction or the longitudinal direction of the film is not more than (0.014 × film thickness (μm) +0.35).
(C) The heat shrinkage at 150 ° C. in the width and length directions of the film is 7% or less.

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

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

  In this case, the haze value of the film is preferably 5% or less.

  The biaxially oriented polypropylene film of the present invention has a small heat shrinkage at 150 ° C. and high thermal dimensional stability. Therefore, the film is excellent in film workability because it has a small heat loss wrinkle and is hard to break. In addition, since the film has a small tear strength in the lateral direction, the film is excellent in hand tearability when the packaging bag is opened.

(Polypropylene resin composition)
The biaxially oriented polypropylene film of the present invention comprises a resin composition containing the following polypropylene resin as a main component. The polypropylene resin refers to a homopolymer of propylene or a copolymer of propylene with ethylene and / or an 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) satisfying the following conditions or a mixture of the polypropylene resin (A) and the polypropylene resin (B). The characteristics of the polypropylene resin (A) and the polypropylene resin (B) are as follows.
The polypropylene resin (A) 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 the comonomer other than propylene is 0.1 mol%.
3) Mass average molecular weight (Mw) / number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The 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) 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 the comonomer other than propylene is 0.1 mol%.
3) Mass average molecular weight (Mw) / number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230 ° C. and 2.16 kgf is 9.2 g / 10 min or more.

The mixing ratio of the polypropylene resin (A) and the polypropylene resin (B) is preferably 85/15 to 65/35 (% by weight) in weight ratio. When the mixing ratio of the polypropylene resin (B) is 15% by weight or more, the orientation in the width direction or the longitudinal direction of the film 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 in the stretching step hardly occur, and it becomes easy to produce a biaxially oriented film.
Further details will be described below.

(Polypropylene resin (A))
The polypropylene resin (A) comprises propylene, 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 based on the entire olefin monomer. It is preferably a polymer copolymerized so that The copolymer component is preferably at most 0.3 mol%, more preferably at most 0.1 mol%, and most preferably a completely homopolypropylene resin containing no copolymer component.
When ethylene and / or an α-olefin having 4 or more carbon atoms are copolymerized in an amount exceeding 0.5 mol%, crystallinity and rigidity are excessively reduced, and the tear strength may be increased. Such resins may be blended and used.

  The mesopentad fraction ([mmmm]%) measured by 13C-NMR, which is an index of the stereoregularity of the polypropylene resin (A), is preferably from 96 to 99.5%. It is more preferably at least 97%, further preferably at least 98%. If the mesopentad ratio of the polypropylene resin (A) is small, the tear strength may be insufficient. 99.5% is a practical upper limit.

Further, Mw / Mn, which is an index of the molecular weight distribution, is preferably from 3.0 to 5.4 for the polypropylene resin (A). It is more preferably from 3.0 to 5.0, further preferably from 3.2 to 4.5, and particularly preferably from 3.3 to 4.0.
When a high molecular weight component is present, the high molecular weight component promotes the crystallization of the low molecular weight component, but the entanglement between the molecules becomes stronger and the tear strength tends to increase even if the crystallinity is high. It is preferable that Mw / Mn of the resin (A) does not exceed 5.4. If Mw / Mn is too large, the high molecular weight component tends to increase, and the tear strength may increase, or the tensile modulus (Young's modulus) in the width direction (TD) tends to decrease. If the Mw / Mn of the polypropylene resin (A) is less than 3.0, it becomes difficult to form a film. Mw means a mass average molecular weight, and Mn means a number average molecular weight.

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

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

The melt flow rate (MFR; 230 ° C., 2.16 kgf) of the polypropylene resin (A) at this time is preferably from 6.2 g / 10 min to 10.0 g / 10 min.
The lower limit of the MFR of the polypropylene resin (A) is more preferably 6.5 g / 10 minutes, further 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, further 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 min or more, the degree of orientation of the film generated by stretching becomes strong, and thus the rigidity of the film, particularly, tensile in the width direction (TD). As the elastic modulus (Young's modulus) increases, the tear strength decreases. Further, the heat shrinkage at a high temperature can be further reduced. When the melt flow rate (MFR; 230 ° C., 2.16 kgf) is 9.0 g / 10 minutes or less, it is easy to form a film without breaking.

When the gel permeation chromatography (GPC) integration 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, and Preferably it is 40% by weight, particularly preferably 41% by weight, most preferably 42% by weight.
On the other hand, the upper limit of the amount of the component having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% by mass, more preferably 60% by mass, further preferably 58% by mass, and particularly preferably 56% by mass. And most preferably 55% by mass. Within the above range, stretching becomes easy, thickness unevenness is reduced, and the stretching temperature and the heat setting temperature are easily increased, so that the tear strength can be further suppressed.
The molecular weight distribution of the polypropylene resin (A) can be determined by polymerizing different molecular weight components in multiple stages in a series of plants, blending different molecular weight components offline with a kneader, or blending catalysts with different performances. The polymerization can be adjusted 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 in an amount of 0.5 mol% or less of ethylene and / or an α-olefin having 4 or more carbon atoms based on the entire olefin monomer. It is preferably a polymer copolymerized so that The copolymer component is preferably at most 0.3 mol%, more preferably at most 0.1 mol%, and most preferably a completely homopolypropylene resin containing no copolymer component.
If the ethylene and / or α-olefin having 4 or more carbon atoms is 0.5 mol% or less, the crystallinity and rigidity are further improved, and the tear strength may be further reduced. Such a resin may be used after being improved from the blend.

  The mesopentad fraction ([mmmm]%) measured by 13C-NMR, which is an index of the stereoregularity of the polypropylene resin (B), is preferably from 96 to 99.5%. It is more preferably at least 97%, further preferably at least 98%. When the meso pentad ratio of the polypropylene of the polypropylene resin (B) is large, the elastic modulus is increased and the tear strength is further reduced. 99.5% is a practical upper limit.

Further, Mw / Mn, which is an index of the molecular weight distribution, is preferably 3.0 to 5.4 for the polypropylene resin (B). It is more preferably from 3.0 to 5.0, further preferably from 3.2 to 4.5, and particularly preferably from 3.3 to 4.0.
If the Mw / Mn of the polypropylene resin (B) is smaller than 5.4, if the Mw / Mn does not become too large, the high molecular weight component will be reduced and the tear strength may be reduced, or the width direction (TD) Tend to have a large tensile modulus (Young's modulus). If the Mw / Mn of the polypropylene resin (B) is less than 3.0, film formation becomes difficult. Mw means mass average molecular weight, and Mn means number average molecular weight.

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

  The number average molecular weight (Mn) of the polypropylene resin (B) is preferably from 20,000 to 200,000. A more preferred lower limit of Mn is 30,000, further preferably 40,000, and a more preferred upper limit of Mn is 70,000, further 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 min, further preferably 10 g / 10 min, and particularly preferably 11 g / 10 min. The upper limit of the MFR of the polypropylene resin is more preferably 15 g / 10 minutes, further 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 min or more, the degree of orientation of the film caused by stretching in the width direction (TD) is increased, so that the tear strength of the film is increased. Can be smaller. Further, the heat resistance of the film, particularly, the heat shrinkage at 150 ° C. in the width direction (TD) decreases.

When a gel permeation chromatography (GPC) integration curve of the polypropylene resin (B) is measured, 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, More preferably, it is 55% by mass.
On the other hand, the upper limit of the amount of the component 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 further preferably 58% by mass. Within the above range, stretching becomes easy, thickness unevenness is reduced, and the stretching temperature and the heat setting temperature are easily increased, so that the tear strength can be further suppressed.

The mixture of the polypropylene resin (A) and the 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 the comonomer other than propylene is 0.1 mol%.
3) Mass average molecular weight (Mw) / number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The 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 the polypropylene resin (A) and the polypropylene resin (B) can be determined by polymerizing different molecular weight components in multiple stages in a series of plants, blending different molecular weight components offline with a kneader, It can be adjusted by blending a catalyst having the same and polymerizing it, or by using a catalyst capable of achieving a desired molecular weight distribution.

The polypropylene resin (A) and the polypropylene resin (B) used in the present invention can be obtained by polymerizing propylene as a raw material 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 and a catalyst capable of polymerization with high stereoregularity in order to eliminate the heterogeneous bond.
As a method for polymerizing propylene, a known method may be employed, 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, or a method in which a gaseous monomer is used as a catalyst. And a method of polymerizing in a gas phase, or a method of polymerizing them in combination.

The resin composition constituting the biaxially oriented polypropylene-based film may contain additives and other resins in addition to the polypropylene-based resin. The content of additives and other resins in the resin composition is preferably 20% by weight or less.
Examples of the additive include an antioxidant, an ultraviolet absorber, a nucleating agent, an adhesive, an antifogging agent, a flame retardant, and an inorganic or organic filler.
Other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers of propylene with ethylene and / or an α-olefin having 4 or more carbon atoms, various elastomers, and the like. These are sequentially polymerized using a multi-stage reactor, blended with a polypropylene resin and a Henschel mixer, or diluted with polypropylene so that a master pellet prepared in advance using a melt kneader has a predetermined concentration. Alternatively, the entire amount may be previously melt-kneaded and used.

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

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

The lower limit of the stretching ratio in the machine direction (MD) is preferably 3 times, more preferably 3.5 times, and further preferably 4.0 times. If it is less than the above, the film thickness may be uneven. The upper limit of the stretching ratio in the machine direction (MD) is preferably 7 times, more preferably 6 times. If the ratio exceeds the above range, the subsequent stretching in the width direction (TD) may be difficult.
The lower limit of the stretching temperature in the machine direction (MD) is preferably 120 ° C, more preferably 125 ° C, and even 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 be roughened. In the machine direction (the upper limit of the MD stretching temperature is preferably 160 ° C., more preferably 155 ° C., and still more preferably 150 ° C. A higher temperature is preferable for lowering the heat shrinkage, but In some cases, the film may stick and cannot be stretched, or may have a rough surface.

The lower limit of the stretching ratio in the width direction (TD) is preferably 8 times, and more preferably 10 times. If it is less than the above, the orientation in the width direction (TD) is less likely to be large in the transverse direction of the film, and the tear strength is not easily reduced. The upper limit of the stretching ratio in the width direction (TD) is preferably 12 times. If the ratio exceeds the above range, the heat shrinkage may increase or the film may be broken 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) is not increased even if the stretching ratio in the width direction (TD) is not so large. It tends to be larger.
The preheating temperature in the width direction (TD) stretching is preferably set to be 15 to 35 ° C. higher than the machine direction (MD) stretching temperature in order to quickly raise the film temperature near the stretching temperature. Stretching in the width direction (TD) is performed at a higher temperature than 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, further preferably 158 ° C, and particularly preferably 160 ° C. If it is less than the above, the material may not be sufficiently softened and may be broken, or the heat shrinkage may increase. The upper limit of the stretching temperature in the width direction (TD) is preferably 170 ° C, more preferably 168 ° C, and even more preferably 163 ° C. To lower the heat shrinkage, the temperature is preferably higher. However, if the temperature exceeds the above range, not only the low molecular components are melted and recrystallized to lower the orientation, but also the surface may be roughened and the film may be whitened.

  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 may increase. Further, a long-time treatment is required to lower the heat shrinkage, which may lower productivity. The upper limit of the heat setting temperature is preferably 176 ° C, more preferably 175 ° C. If the ratio exceeds the above range, the low molecular weight component may be melted and recrystallized, resulting in surface roughness and whitening of the film.

  It is preferable to relax (relax) during heat fixing. The lower limit of the width direction (TD) relaxation rate is preferably 2%, more preferably 3%. If it is less than the above, the heat shrinkage may increase. The upper limit of the width direction (TD) relaxation rate is preferably 10%, and more preferably 8%. If it exceeds the above, thickness unevenness may increase.

  Further, in order to reduce the heat shrinkage, the film produced in the above-mentioned process may be once 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 even 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, and further preferably 173 ° C. If the ratio exceeds the above range, transparency may be reduced or thickness unevenness may be increased.

  The lower limit of the offline annealing time is preferably 0.1 minute, more preferably 0.5 minute, and further preferably 1 minute. If it is less than the above, the effect of annealing may not be obtained. The upper limit of the off-line annealing time is preferably 30 minutes, more preferably 25 minutes, and even more preferably 20 minutes. If it exceeds the above, 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, and still more preferably 0.013. When the content is in the above range, the heat resistance and the rigidity of the film tend to increase.
The biaxially oriented polypropylene film of the present invention has a crystal orientation, and the direction and degree of the orientation have a great influence on the physical properties of the film. The degree of crystal orientation can be expressed using the plane orientation coefficient as an index, and can be controlled 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, further preferably 12 to 100 μm, and particularly preferably 12 to 80 μm.

The tear strength (N / mm) of the biaxially oriented polypropylene film of the present invention may be in the range of 0.014 × film thickness (μm) +0.35 or less in the width direction (TD) or the longitudinal direction (MD). If it exceeds 0.014 × film thickness (μm) +0.35, when tearing the film in each direction, a great resistance is felt to the tearability expected according to each film thickness. The film can be cut easily by hand without the need. It is preferably in the range of 0.014 × film thickness (μm) +0.30 or less, and more preferably in the range of 0.014 × film thickness (μm) +0.28 or less. Within this range, a greater resistance to tearing is not felt as compared with a conventional biaxially oriented polypropylene film.
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 the longitudinal 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%, 0.4 to 6% is more preferable, and 0.5 to 5% is particularly preferable. When the heat shrinkage is in the above range, it can be said that the film is particularly excellent in heat resistance, and for example, it is possible to reduce wrinkles caused by heat during processing into a bag-made product. Therefore, it can be used in applications that may be exposed to high temperatures. If the heat shrinkage at 150 ° C. is up to about 1.5%, for example, it is possible to increase the number of low molecular weight components, adjust stretching conditions and heat setting conditions. Is preferred.

In the biaxially oriented polypropylene film of the present invention, the heat shrinkage in the longitudinal direction at 150 ° C. is preferably from 0.2 to 7%, more preferably from 0.3 to 6%. When the heat shrinkage is in the above range, it can be said that the film is excellent in heat resistance, and for example, it is possible to reduce wrinkles caused by heat during processing into a bag product.
for that reason. It can also be used in applications that may be exposed to high temperatures. If the heat shrinkage at 150 ° C. is up to about 1.5%, for example, it is possible to increase the number of low molecular weight components, adjust stretching conditions and heat setting conditions. It is preferable to carry out the treatment.

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

  It is preferable that the biaxially oriented polypropylene film of the present invention has a tensile modulus of 2.0 GPa or more in the width direction and the longitudinal direction, and a tensile modulus of 4.0 GPa or more in a direction in which the tensile modulus is large.

  The tensile 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. When the tensile modulus in the transverse direction is in the above range, it is possible to make the film hard to break.

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

  The difficulty in breaking the biaxially oriented polypropylene film of the present invention was evaluated by a value obtained by detecting the load with a load cell (ring crush measurement method) by holding the film in a ring shape and compressing the film. 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%, further preferably 0.3 to 4.5%, and particularly preferably 0.4 to 4%. When it is in the above range, it may be easy to use for applications requiring transparency. Haze tends to worsen when, for example, the stretching temperature or heat setting temperature is too high, when the cooling roll (CR) temperature is high, the cooling rate of the stretched raw sheet is slow, or when the low molecular weight component is too large. By doing so, it can be within the above range. The 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 dynamic friction coefficient is 0.5 or less, the film can be smoothly unwound from the roll film, and printing can be easily performed. The method for measuring the dynamic friction coefficient will be described later.

(Surface layer)
The biaxially oriented polypropylene film of the present invention may be provided with a separate surface layer. As the polypropylene resin to be used, a propylene homopolymer or a copolymer of propylene and ethylene and / or an α-olefin having 4 or more carbon atoms is used. Can be used. Examples of the α-olefin having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like.
Examples of the α-olefin having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like. Polar maleic acid or the like may be used as another copolymer component.
The total content of ethylene, α-olefin having 4 or more carbon atoms, and other copolymer components is preferably 8.0 mol% or less. If the copolymerization is more than 8.0 mol%, the film may be whitened and the appearance may be poor, or the film may be difficult to form due to tackiness.
These resins may be used as a mixture of two or more kinds. When mixed, the individual resins may be copolymerized in excess of 8.0 mol%, but ethylene, α-olefins having 4 or more carbon atoms, and other copolymerized components in the mixture in total It is preferably at most 8.0 mol%.

The polypropylene resin used in the surface layer can be obtained by polymerizing propylene as a raw material 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 and a catalyst capable of polymerization with high stereoregularity in order to eliminate the heterogeneous bond.
As a method for polymerizing propylene, a known method may be employed, 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, or a method in which a gaseous monomer is used as a catalyst. And a method of polymerizing in a gas phase, or a method of polymerizing them in combination.

The surface layer may contain additives and other resins in addition to the polypropylene resin. Examples of the additive include an antioxidant, an ultraviolet absorber, a nucleating agent, an adhesive, an antifogging agent, a flame retardant, and an inorganic or organic filler.
Other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers of propylene with ethylene and / or α-olefins having 4 or more carbon atoms, various elastomers, and the like. These are sequentially polymerized using a multi-stage reactor, blended with a polypropylene resin and a Henschel mixer, or diluted with polypropylene so that a master pellet prepared in advance using a melt kneader has a predetermined concentration. Alternatively, the entire amount may be previously melt-kneaded and used.
It is also a preferred method to incorporate an antiblocking agent contained in the surface layer.
As the anti-blocking agent, silica, calcium carbonate, kaolin, zeolite and other inorganic anti-blocking agents and acrylic, polymethacrylic, organic anti-blocking agents such as polystyrene, etc., appropriately selected and used. can do. Among them, it is particularly preferable to use silica.
The average particle diameter of the anti-blocking agent is preferably 1.0 to 2.0 μm, more preferably 1.0 to 1.5 μm.
The content of the antiblocking agent is preferably 0.5% by mass or less in the surface layer. The method for measuring the average particle size here is a method in which a photograph is taken with a scanning electron microscope, the Feret diameter in the horizontal direction is measured using an image analyzer, and the average value is displayed.

It is preferable that the wetting tension on the surface of the surface layer is 38 mN / m or more.
When the wetting tension is 38 mN / m or more, the adhesion to the printing ink or the adhesive is improved.
More preferably, the wetting tension is 16 LogΩ or more. In order to make the wetting tension 38 mN / m or more, it is usual to use additives such as an antistatic agent and a surfactant. However, since there is an effect of lowering the surface specific resistance, corona treatment and flame treatment are used. And the like.

The thickness ratio of the surface layer to the biaxially oriented polypropylene film of the present invention is preferably 0.01 to 0.5, and more preferably 0.03 to 0.4. More preferably, it is even more preferably 0.05 to 0.3. When the ratio of the surface layer / biaxially oriented polypropylene film exceeds 0.5, the shrinkage tends to increase. Further, the thickness of the biaxially oriented polypropylene film relative to the thickness of the entire film is preferably 50 to 99%, more preferably 60 to 97%, and particularly preferably 70 to 95%. The remainder becomes a surface layer or a surface layer and another layer (for example, a C layer). The substantial thickness of the surface layer is preferably 0.5 to 4 μm, more preferably 1 to 3.5 μm, and still 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 a structure of three or more layers. Preferred is a bilayer structure of biaxially oriented polypropylene film / surface layer. Further, it may 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 multilayer structure of more than three layers.
When there are a plurality of surface layers, the composition may be different as long as each layer satisfies the characteristics.
When the surface layer is provided, the resin composition for the base layer (for example, a mixture of the polypropylene resin (A) and the polypropylene resin (B)) and the polypropylene resin for the surface layer are each separately extruded. It can be obtained by melt-extruding to form a laminated unstretched sheet, stretching the unstretched sheet by a predetermined method, and performing heat treatment.

(Application)
The biaxially oriented polypropylene-based film of the present invention can be used not only for food packaging used for standing pouches and the like but also for labels and the like. In the bag making process, when the bag is folded in a direction perpendicular to the machine flow direction to make the bag, the transverse direction is the hand-cutting direction, so the transverse tear strength is important. The lower the tear strength, the better the hand-cutting properties.

  Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention, and include modifications that do not depart from the gist of the present invention. In addition, the measuring method of the film physical property obtained by the Example and the comparative example is as follows.

1) Stereoregularity The mesopentad fraction ([mmmm]%) was measured using 13C-NMR. The mesopentad fraction was calculated according to the method described in “Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973)”. The 13C-NMR measurement was performed at 110 ° C. by dissolving 200 mg of a sample at 135 ° C. in a mixture of o-dichlorobenzene and heavy benzene at 8: 2 (volume ratio) 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 in accordance with JIS K7210. As the resin, pellets (powder) were weighed and used as needed. After cutting out a necessary amount of the film, a sample cut into about 5 mm square was used.

3) Molecular weight and molecular weight distribution The molecular weight and molecular weight distribution were determined based on monodisperse polystyrene using gel permeation chromatography (GPC). The measurement conditions such as the column and the solvent used in the GPC measurement are as follows.
Solvent: 1,2,4-trichlorobenzene Column: TSKgel GMHHR-H (20) HT × 3
Flow rate: 1.0 ml / min
Detector: RI
Measurement temperature: 140 ° C

The number-average molecular weight (Mn), mass-average molecular weight (Mw), and molecular weight distribution are respectively expressed by the number of molecules (N _i ) of the molecular weight (M _i ) at each elution position of the GPC curve obtained through the molecular weight calibration curve. Defined by an expression.
The number average molecular _{weight: Mn = Σ (N i ·} M i) / ΣNi
Mass average molecular weight: Mw = {(N _i · M _i ² ) / Σ (N _i · M _i )
Molecular weight distribution: Mw / Mn
When the base line was not clear, the base line was set in the range from the elution peak closest to the elution peak of the standard substance to the lowest position of the base on the high molecular weight side.

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

5) Heat shrinkage (%)
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, and was suspended in a hot air oven at 150 ° C. and heated for 5 minutes. The length after heating was measured, and the heat shrinkage was determined by the ratio of the contracted length to the original length.

6) Tensile modulus (Young's modulus (unit: GPa))
The tensile modulus in the MD and TD directions of the film was measured at 23 ° C. under the following conditions in accordance with 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 of elastic modulus measurement: 0.1 to 0.6%

7) Ring crush (g)
Using a digital ring crush tester (manufactured by Tester Sangyo Co., Ltd.), prepare a film sample size of 12.7 mm × 152 mm, set the spacer of the attachment on the sample table according to the thickness of the film sample, MD, TD direction In each case, a film sample is inserted along the circumference. At 23 ° C., the compression plate was lowered at a speed of 12 mm / min. The maximum load at the time of compression was defined as the measured value of the ring crash.

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

9) Coefficient of dynamic friction According to JIS K7125, the surfaces of the films subjected to corona treatment were overlapped and measured at 23 ° C.

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

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

13) Wetting tension (mN / m)
According to JIS K6768-1999, the film was aged at 23 ° C. and 50% relative humidity for 24 hours, and the corona-treated surface of the film was measured by the following procedure.
1) The measurement is performed in a standard test room atmosphere (refer to 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 the test mixture is spread using a swab or brush, the liquid should be spread quickly over an area of at least 6 cm2. The amount of liquid should be such that a thin layer is formed without puddles. Judgment of the wetting tension is made by observing the liquid film of the test liquid mixture in a bright place and checking the liquid film state after 3 seconds. It is wet that the state at the time of application is maintained for 3 seconds or more without causing liquid film breakage. If the wetting is maintained for 3 seconds or more, the process proceeds to the next mixture having the next higher surface tension. Conversely, if the liquid film is broken within 3 seconds or less, the process proceeds to the next mixture having the lower surface tension. Repeat this operation to 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 are washed with methanol and dried after each use as residual liquid changes composition and surface tension by evaporation.
4) An operation of selecting a mixed solution that can wet the surface of the test piece in 3 seconds is performed at least three 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 JIS K7128 trouser tear method was taken as the tear strength.

15) Hand-cutting property of bag-made product 1) Preparation of laminated film with sealant film It was carried out as follows using a continuous dry laminating machine.
After the gravure coating of the adhesive on the corona surface of the biaxially oriented polypropylene film obtained in each of the examples and comparative examples was performed so that the applied amount at the time of drying was 3.0 g / m2, the adhesive was guided to a drying zone at 80 ° C. for 5 seconds. Dried. Subsequently, a sealant film was bonded between rolls provided on the downstream side (roll pressure: 0.2 MP, roll temperature: 60 ° C.). The obtained laminated film was subjected to an aging treatment at 40 ° C. for 3 days in a wound state.
The adhesive was obtained by mixing 17.9% by mass of a main agent (TM329, manufactured by Toyo Morton Co., Ltd.), 17.9% by mass of a 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 (Pyrene (registered trademark) CT P1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. was used.
2) Preparation of a bag-formed product After folding the laminate film in the flow direction of the laminate film, it was heat-sealed at 120 ° C., 1 kg, and 1 second for three times to prepare a bag-formed product having a width of 200 mm and a length of 200 mm.
3) Evaluation of hand cutability A notch was formed in the bag-made product in the lateral direction, and ten evaluators evaluated the presence or absence of resistance when the bag was torn by hand in the lateral direction. The number of people who answered that they had resistance was used as an evaluation item. Each was evaluated three times.
0 persons ···· ◎: Excellent hand-cutting property.
1 to 5 persons .largecircle .: Good hand-cutting property.
6 to 9 persons △: Poor hand-cutting property.
X: No hand-cutting property.

(Example 1)
In the base material layer, 79% by weight of a polypropylene homopolymer PP-1 and 20% by weight of a polypropylene homopolymer PP-2 shown in Table 1 and an antistatic agent (stearyl diethanolamine stearate (KYM-Matsumoto Yushi Co., Ltd.) 4K)) was used in an amount of 1% by weight. Further, 3000 ppm of silica particles having an average particle diameter of 1 μm was added to this mixture.
This mixture was melted at 250 ° C. using a 60 mm extruder, co-extruded in a sheet form from a T-die, cooled and solidified by a cooling roll at 30 ° C., and then cooled in a machine direction (MD) at 135 ° C. The film was stretched 5 times. Then, both ends of the film in the width direction are sandwiched by clips in a tenter, and after preheating at 175 ° C., stretched 8.2 times in the width direction (TD) at 160 ° C., and relaxed by 6.7% in the width direction (TD). At 170 ° C. The film forming conditions at this time were defined as film forming conditions a, and are shown in Table 2.
After applying corona treatment to one surface side of the obtained biaxially oriented polypropylene film using a corona treatment machine manufactured by Softal Corona & Plasma GmbH under the conditions of an applied current value of 0.75 A, a winder is used. The biaxially oriented polypropylene film of the present invention was wound up in the above. 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)
Using a 60 mm extruder for the mixed raw material used for the base material layer (A) and a 65 mm extruder for the mixed raw material used for the surface layer (B), each raw material resin is melted at 250 ° C. and formed into a sheet from a T-die. After being co-extruded and solidified by cooling with a cooling roll at 30 ° C., it was stretched 4.5 times in the machine direction (MD) at 135 ° C. Then, both ends of the film in the width direction are sandwiched by clips in a tenter, and after preheating at 175 ° C., stretched 8.2 times in the width direction (TD) at 160 ° C., and relaxed by 6.7% in the width direction (TD). At 170 ° C. The 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 the base material layer (A) and the surface layer (B) were laminated one by one. . Corona treatment was performed on the surface side of the surface layer (B) of the obtained biaxially oriented polypropylene film using a corona treatment machine manufactured by Softal Corona & Plasma GmbH under the conditions of an applied current value of 0.75 A. After the application, the film wound up with a winder was used as the biaxially oriented polypropylene film of the present invention. 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 and 20% by weight of the polypropylene homopolymer PP-2 and 99% by weight of the polypropylene resin PP-1 shown in Table 1 and a transverse (TD) draw ratio of 10% were used. 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 referred to as film forming conditions b and are shown in Table 2.

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

(Comparative Example 3)
Example 1 was repeated except that a mixture of 79% by weight of the polypropylene homopolymer PP-1 and 20% by weight of the polypropylene homopolymer PP-2 and 99% by weight of the polypropylene resin PP-3 shown in Table 1 were used. Similarly, a biaxially oriented polypropylene film was obtained. The physical properties of the obtained film are as shown in Table 4.

(Comparative Example 4)
The mixture of 79% by weight of the polypropylene homopolymer PP-1 and 20% by weight of the polypropylene homopolymer PP-2 shown in Table 1 was changed to 99% by weight of the 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 preheating temperature in the width direction to 170 ° C., the temperature in the width direction 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 referred to 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 a small tear strength in the width direction (TD) and a small heat shrinkage.
On the other hand, the films obtained in Comparative Examples 1 and 3 had a large tear strength in the width direction (TD).
In Comparative Example 2, a film could not be formed.
The films obtained in Comparative Examples 4, 5, and 6 had a large tear strength in the width direction (TD) and a large heat shrinkage in the width direction (TD) and the longitudinal direction (MD).

  The biaxially oriented polypropylene-based film of the present invention can be used not only for food packaging used for standing pouches and the like but also for labels and the like. In the bag making process, when the bag is folded in a direction perpendicular to the machine flow direction to make the bag, the transverse direction is the hand-cutting direction, so the transverse tear strength is important. The lower the tear strength, the better the hand-cutting properties.

Claims (4)

A biaxially oriented polypropylene film having the following features (a) to (c):
(A) It comprises a resin composition containing a polypropylene resin as a main component.
(B) The tear strength (N / mm) in the width direction or longitudinal direction of the film ≦ (0.014 × film thickness (μm) +0.35).
(C) The heat shrinkage at 150 ° C. in the width and length directions of the film is 7% or less.   The biaxially oriented polypropylene film according to claim 1, wherein the tensile modulus in the width direction and the longitudinal direction of the film is 2.0 GPa or more, and the tensile modulus in the direction in which the tensile modulus is large is 4.0 GPa or more.   The biaxially oriented polypropylene film according to claim 1 or 2, having an impact strength of 0.6 J or more.   The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the haze is 5% or less.