WO2018180164A1

WO2018180164A1 - Biaxially oriented polypropylene film

Info

Publication number: WO2018180164A1
Application number: PCT/JP2018/007729
Authority: WO
Inventors: 理木下; 山田　浩司
Original assignee: 東洋紡株式会社
Priority date: 2017-03-28
Filing date: 2018-03-01
Publication date: 2018-10-04
Also published as: JPWO2018180164A1; JP7298751B2; JP7205462B2; JP2022111158A; TWI781149B; TW201842032A

Abstract

Provided is a biaxially oriented polypropylene film having higher heat resistance and tearability by hand. The biaxially oriented polypropylene-based film has the following features (a) to (c). (a) To comprise a resin composition comprising a polypropylene-based resin as a main component. (b) To satisfy [transverse-direction or machine-direction tear strength (N/mm) of the film]≤[(0.014×(film thickness (μm)))+0.35]. (c) To have a 150°C heat shrinkage of 7% or less.

Description

Biaxially oriented polypropylene film

The present invention relates to a biaxially oriented polypropylene film. In detail, it is related with the biaxially oriented polypropylene film excellent in heat resistance and hand cutting property.

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

In view of the above circumstances, the present invention has been aimed at providing a biaxially oriented polypropylene film having higher heat resistance and hand cutting properties.

As a result of intensive studies, the inventors of the present invention have made it possible to further reduce the tear strength even if the biaxially oriented polypropylene film is excellent in heat resistance at high temperatures, and have a predetermined tear strength in a specific direction. The inventors have found that the above-mentioned problems can be solved and the present invention has been completed.

The present invention that has solved the above problems is a biaxially oriented polypropylene film having the following characteristics (a) to (c).
(A) It consists of the resin composition which has a polypropylene resin as a main component.
(B) Tear strength (N / mm) ≦ (0.014 × film thickness (μm) +0.35) or less in the width direction or longitudinal direction of the film.
(C) The heat shrinkage rate at 150 ° C. in the width direction and the longitudinal direction of the film is 7% or less.

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

In this case, it is preferable that the impact strength is 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 low thermal shrinkage at 150 ° C. and high thermal dimensional stability. Therefore, heat loss wrinkles are small, and since it is hard to break, it is excellent in film processability. In addition, since the tear strength in the lateral direction of the film is small, the film has excellent hand tearability when the packaging bag is opened.

(Polypropylene resin composition)
The biaxially oriented polypropylene film of the present invention is composed of a resin composition containing as a main component the following polypropylene resin. 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 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) 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 copolymerization monomers other than propylene is 0.1 mol%.
3) The 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) 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 copolymerization monomers other than propylene is 0.1 mol%.
3) The 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 (wt%) by weight. 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, for example, a problem that the film is broken in the stretching process hardly occurs, and it becomes easy to produce a biaxially oriented film.
Further details will be described below.

(Polypropylene resin (A))
The polypropylene resin (A) is composed of propylene and ethylene and / or α-olefin having 4 or more carbon atoms, and 0.5 mol% or less of ethylene and / or α-olefin having 4 or more carbon atoms with respect to the entire olefin monomer. It is preferable that the polymer is copolymerized so that The copolymerization component is preferably 0.3 mol% or less, more preferably 0.1 mol% or less, and most preferably a complete homopolypropylene resin containing no copolymerization component.
When ethylene and / or an α-olefin having 4 or more carbon atoms is copolymerized in excess of 0.5 mol%, the crystallinity and rigidity may be excessively lowered, and the tear strength may be increased. You may blend and use such resin.

The mesopentad fraction ([mmmm]%) measured by 13C-NMR, which is an index of stereoregularity of the polypropylene resin (A), is preferably 96 to 99.5%. More preferably, it is 97% or more, and 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.

Further, Mw / Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 in the polypropylene resin (A). More preferably, it is 3.0 to 5.0, still more preferably 3.2 to 4.5, and particularly preferably 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 molecules becomes strong, and even if the crystallinity is high, the tear strength tends to increase. It is preferable that Mw / Mn of the resin (A) does not exceed 5.4. When Mw / Mn becomes too large, the high molecular weight component increases, and the tear strength tends to increase, and the tensile modulus (Young's modulus) in the width direction (TD) tends to decrease. When the Mw / Mn of the polypropylene resin (A) is less than 3.0, film formation becomes difficult. Mw means a mass average molecular weight, and Mn means a number average molecular weight.

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

The number average molecular weight (Mn) of the polypropylene resin (A) is preferably 20,000 to 200,000. The lower limit of Mn is more preferably 30,000, more preferably 40,000, particularly preferably 50,000, and the upper limit of Mn is more preferably 80,000, still more 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 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, so the rigidity of the film, particularly the tensile in the width direction (TD). As the elastic modulus (Young's modulus) increases, the tear strength decreases. Furthermore, the thermal contraction rate at a high temperature can be further reduced. Further, when the melt flow rate (MFR; 230 ° C., 2.16 kgf) is 9.0 g / 10 min 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, Preferably it is 40 mass%, Especially preferably, it is 41 mass%, Most preferably, it is 42 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 integration 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 weight. Within the above range, stretching can be facilitated, thickness spots can be reduced, stretching temperature and heat setting temperature can be easily increased, and tear strength can be further reduced.
The molecular weight distribution of the polypropylene resin (A) is such that components with different molecular weights are polymerized in a series of plants in multiple stages, components with different molecular weights are blended offline using a kneader, or catalysts with different performances are blended. Thus, it is possible to adjust by polymerizing or using a catalyst capable of realizing a desired molecular weight distribution.

(Polypropylene resin (B))
The polypropylene resin (B) is composed of propylene, ethylene and / or α-olefin having 4 or more carbon atoms, and 0.5 mol% or less of ethylene and / or α-olefin having 4 or more carbon atoms with respect to the entire olefin monomer. It is preferable that the polymer is copolymerized so that The copolymerization component is preferably 0.3 mol% or less, more preferably 0.1 mol% or less, and most preferably a complete homopolypropylene resin containing no copolymerization component.
When 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 decreased. Such a resin may be used after being improved from the blend.

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

Further, Mw / Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 in the polypropylene resin (B). More preferably, it is 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 smaller than 5.4, if the Mw / Mn is not increased too much, the high molecular weight component is decreased, and the tear strength may be decreased, or the width direction (TD). The tensile elastic modulus (Young's modulus) of the steel tends to increase. When 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 mass average molecular weight (Mw) of the polypropylene resin (B) is preferably 180,000 to 500,000. The lower limit of Mw is more preferably 190,000, still more preferably 200,000, and the upper limit of more preferable Mw is 320,000, more preferably 300,000, particularly preferably 250,000.

The number average molecular weight (Mn) of the polypropylene resin (B) is preferably 20,000 to 200,000. The lower limit of Mn is more preferably 30,000, still more preferably 40,000, and the upper limit of Mn is more preferably 70,000, still more preferably 60,000, 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 min or more.
The lower limit of the MFR of the polypropylene resin (B) is more preferably 9.5 g / 10 minutes, further 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, 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 generated by stretching in the width direction (TD) becomes strong, so the tear strength of the film is further increased. Can be small. Furthermore, the heat resistance of the film, particularly the thermal shrinkage at 150 ° C. in the width direction (TD) is reduced.

When the 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 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 integration curve is preferably 65% by mass, more preferably 60% by mass, and further preferably 58% by mass. Within the above range, stretching can be facilitated, thickness spots can be reduced, stretching temperature and heat setting temperature can be easily increased, and tear strength can be further reduced.

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 copolymerization monomers other than propylene is 0.1 mol%.
3) The 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) is such that different molecular weight components are polymerized in a series of plants in multiple stages, different molecular weight components are blended offline in a kneader, and different performance is achieved. It is possible to adjust by blending and polymerizing the catalyst having the same or by using a catalyst capable of realizing a desired molecular weight distribution.

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

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 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.
Examples of 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, and various elastomers. These are sequentially polymerized using a multistage reactor, blended with a polypropylene resin and a Henschel mixer, or master pellets prepared in advance using a melt kneader are diluted with polypropylene to a predetermined concentration. Alternatively, the whole amount may be melt kneaded in advance.

(Production method of biaxially oriented polypropylene film)
The biaxially oriented polypropylene film of the present invention is formed by melting and extruding a resin composition containing a 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.
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 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 a stretching roll at 120 to 165 ° C., and then stretched in the width direction (TD) direction. Furthermore, heat fixation is performed while relaxing. The biaxial polypropylene film thus obtained can be subjected to corona discharge, plasma treatment, flame treatment, etc., if necessary, and then wound 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 even more preferably 4.0 times. If it is less than the above, film thickness unevenness may occur. 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 be difficult to carry out stretching in the width direction (TD).
The lower limit of the stretching temperature in the machine direction (MD) is preferably 120 ° C, more preferably 125 ° C, and further preferably 130 ° C. If it is less than the above, the mechanical load may increase, the thickness unevenness may increase, or the film surface may be roughened. Longitudinal direction (the upper limit of the stretching temperature of MD is preferably 160 ° C., more preferably 155 ° C., and further preferably 150 ° C. A higher temperature is preferable for lowering the thermal shrinkage, It may adhere and become unable to stretch, or surface roughness may occur.

The lower limit of the draw ratio in the width direction (TD) is preferably 8 times, more preferably 10 times. If it is less than the above, the orientation in the width direction (TD) is less likely to increase the orientation in the transverse direction of the film, and the tear strength is difficult to decrease. The upper limit of the width direction (TD) stretch ratio is preferably 12 times. If the above is exceeded, the thermal shrinkage rate may be increased or the film may be broken during stretching. When the polypyropylene resin composition constituting the film is a mixture of a polypropylene resin (A) and a polypropylene resin (B), the width direction (TD) orientation is not greatly increased even if the width direction (TD) stretch ratio is not so large. It tends to grow.
The preheating temperature in the width direction (TD) stretching is preferably set to 15 to 35 ° C. higher than the machine direction (MD) stretching temperature in order to quickly raise the film temperature in the vicinity of the stretching temperature. The stretching in the width direction (TD) is performed at a higher temperature than the 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, it may break without being sufficiently softened, or the thermal shrinkage rate may be increased. The upper limit of the width direction (TD) stretching temperature is preferably 170 ° C, more preferably 168 ° C, and further preferably 163 ° C. In order to lower the thermal shrinkage rate, it is preferable that the temperature is higher. However, if the temperature is higher than the above, the low molecular component is melted and recrystallized to lower the orientation, and the surface may be roughened or the film may be whitened.

The stretched film is heat-set. The heat setting can be performed at a higher temperature than the conventional biaxially oriented polypropylene film. The lower limit of the heat setting temperature is preferably 165 ° C, more preferably 166 ° C. If it is less than the above, the thermal shrinkage rate may increase. In addition, a long time treatment is required to lower the heat shrinkage rate, and productivity may be inferior. The upper limit of the heat setting temperature is preferably 176 ° C, more preferably 175 ° C. When the above is exceeded, the low molecular component may melt and recrystallize, and the surface roughness or the film may be whitened.

時には It is preferable to relax when relaxing. The lower limit of the width direction (TD) relaxation rate is preferably 2%, more preferably 3%. If it is less than the above, the thermal shrinkage rate may increase. The upper limit of the width direction (TD) relaxation rate is preferably 10%, more preferably 8%. When the above is exceeded, the thickness unevenness may increase.

Furthermore, in order to reduce the thermal shrinkage rate, the film produced in the above process can be once wound into a roll and then annealed offline. 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. When the above is exceeded, the transparency may decrease, or the thickness unevenness may increase.

The lower limit of the offline annealing time is preferably 0.1 minutes, more preferably 0.5 minutes, and even 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, and further preferably 20 minutes. When the above is exceeded, productivity may be reduced.

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 even more preferably 0.013. Within the above range, the heat resistance and rigidity of the film tend to increase.
The biaxially oriented polypropylene film of the present invention has a crystal orientation, and its direction and degree have a great influence on film properties. The degree of crystal orientation can be expressed by using the plane orientation coefficient as an index, and can be within the above range by controlling the molecular structure of the polypropylene resin and the process and conditions in film production.

(Biaxially oriented polypropylene film)
The total thickness of the 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 is in the range of 0.014 × film thickness (μm) +0.35 or less in the width direction (TD) or the longitudinal direction (MD). Necessary, and if it exceeds 0.014 × film thickness (μm) +0.35, when the film is torn in each direction, a sense of great resistance is felt in the tearability expected according to each film thickness. And can easily cut the film by hand. The range is preferably 0.014 × film thickness (μm) +0.30 or less, more preferably 0.014 × film thickness (μm) +0.28 or less. Within this range, there is no greater sense of resistance to tearing than 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 the longitudinal direction (MD). More preferably, it is 3.5 or less.

In the biaxially oriented polypropylene film of the present invention, the thermal shrinkage in the width direction (TD) at 150 ° C. is preferably 0.2 to 7.5%, more preferably 0.3 to 7%, 4 to 6% is more preferable, and 0.5 to 5% is particularly preferable. If the heat shrinkage ratio is in the above range, it can be said that the film is particularly excellent in heat resistance. For example, heat loss wrinkles during processing into a bag-made product can be reduced. Therefore, it can be used in applications that may be exposed to high temperatures. If the heat shrinkage rate at 150 ° C is up to about 1.5%, for example, it is possible to increase the low molecular weight component, adjust the stretching conditions and heat setting conditions. It is preferable to do so.

In the biaxially oriented polypropylene film of the present invention, the thermal shrinkage in the longitudinal direction at 150 ° C. is preferably 0.2 to 7%, more preferably 0.3 to 6%. If the heat shrinkage rate is in the above range, it can be said that the film has excellent heat resistance. For example, heat loss wrinkles during processing into a bag-made product can be reduced.
for that reason. It can also be used in applications that may be exposed to high temperatures. If the thermal shrinkage at 150 ° C. is up to about 1.5%, for example, it is possible to increase the low molecular weight component, adjust the stretching conditions and the heat setting conditions, but in order to lower it below, anneal offline. It is preferable to perform 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 impact resistance is preferably 1.5 J, more preferably 1.3 J from a practical aspect. For example, impact resistance tends to decrease when the total molecular weight is low when there are many low molecular weight components, when the total molecular weight is low, or when the molecular weight of the high molecular weight components is low. These components can be adjusted to be within the range.

It is preferable that the tensile elastic modulus in the width direction and the longitudinal direction of the biaxially oriented polypropylene film of the invention 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.

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. If the tensile modulus in the transverse direction is in the above range, it is possible to form a film that is difficult 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 More preferably, it is 5 GPa, and 2.3 to 3.4 GPa is particularly preferable.

The difficulty in bending of the biaxially oriented polypropylene film of the present invention was evaluated by the value detected by the load cell (ring crush measurement method) by holding the film in a ring shape and compressing it, and the width direction (TD). 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%, still more preferably 0.3 to 4.5%, and particularly preferably 0.4 to 4%. If it is within the above range, it may be easy to use in applications requiring transparency. For example, when the stretching temperature and heat setting temperature are too high, the haze tends to be worse when the cooling roll (CR) temperature is high and the stretching speed of the stretched raw sheet is slow, or when there are too many low molecular weight components. By doing so, it can be 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 dynamic friction coefficient is 0.5 or less, the film can be smoothly unwound from the roll film, and printing is easy. A method for measuring the dynamic friction coefficient will be described later.

(Surface layer)
The biaxially oriented polypropylene film of the 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. As other copolymer components, polar maleic acid or the like may be used.
The total amount of ethylene, α-olefin having 4 or more carbon atoms, and other copolymerization components is preferably 8.0 mol% or less. If the copolymerization exceeds 8.0 mol%, the film may be whitened to have a poor appearance, or may become sticky and film formation may be difficult.
Moreover, you may use these resin in mixture of 2 or more types. In the case of mixing, each resin may be copolymerized in excess of 8.0 mol%, but ethylene, α-olefin having 4 or more carbon atoms, and other copolymerization components in the mixture are in total. It is preferable that it is 8.0 mol% or less.

The polypropylene resin used in the surface layer is obtained by polymerizing propylene as a raw material using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among these, in order to eliminate the heterogeneous bond, it is preferable to use a Ziegler-Natta catalyst and a catalyst capable of polymerization with high stereoregularity.
As a polymerization method of propylene, a known method may be employed. For example, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, xylene, a method of polymerizing in a liquid monomer, a catalyst for a gas monomer And a method of polymerizing in a gas phase state, or a method of polymerizing these 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.
Examples of 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, and various elastomers. These are sequentially polymerized using a multistage reactor, blended with a polypropylene resin and a Henschel mixer, or master pellets prepared in advance using a melt kneader are diluted with polypropylene to a predetermined concentration. Alternatively, the whole amount may be melt kneaded in advance.
It is also a suitable method to mix an antiblocking agent contained in the surface layer.
As an anti-blocking agent, it can be used by appropriately selecting 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 diameter of the antiblocking agent is preferably 1.0 to 2.0 μm, more preferably 1.0 to 1.5 μm.
The anti-blocking agent is preferably 0.5% by mass or less in the surface layer. The measurement method of the average particle diameter here is a method in which a photograph is taken with a scanning electron microscope, the ferret diameter in the horizontal direction is measured using an image analyzer, and the average value is displayed.

It is preferable that the surface layer has a wetting tension of 38 mN / m or more.
When the wetting tension is 38 mN / m or more, the adhesion to the printing ink and the adhesive is improved.
The wetting tension is more preferably 16 LogΩ or more. In order to increase the wetting tension to 38 mN / m or more, it is usual to use additives such as antistatic agents and surfactants. However, since it has the effect of reducing the surface resistivity, corona treatment, flame treatment And the like, and the like.

The thickness ratio between the surface layer and the biaxially oriented polypropylene film of the present invention is preferably 0.01 to 0.5, and preferably 0.03 to 0.4 for the surface layer / biaxially oriented polypropylene film. More preferably, it is 0.05 to 0.3. When the surface layer / biaxially oriented polypropylene film exceeds 0.5, the shrinkage rate tends to increase. Further, the thickness of the biaxially oriented polypropylene film is preferably from 50 to 99%, more preferably from 60 to 97%, particularly preferably from 70 to 95% with respect to the total film thickness. The remaining portion is a surface layer or a surface layer and other layers (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 even more preferably 1.5 to 3 μm.
Although it may be a two-layer film having one biaxially oriented polypropylene film and one surface layer, it may have a structure of three or more layers. A bilayer structure of biaxially oriented polypropylene film / surface layer is preferred. Further, it may be 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.
In addition, 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 respectively used by different extruders. It can be obtained by melt extruding to form a laminated unstretched sheet, stretching the unstretched sheet by a predetermined method, and heat-treating it.

(Use)
The biaxially oriented polypropylene film of the present invention can be used for labeling as well as food packaging used for standing pouches and the like. In the bag making process, when the bag is folded in the direction perpendicular to the machine flow direction and the bag is made, the transverse direction becomes the hand cutting direction, and thus the lateral tear strength is important. A lower tear strength results in a film with better hand tearability.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and modifications and implementations without departing from the spirit of the present invention are included in 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, 925 (1973)”. The 13C-NMR measurement was performed at 110 ° C. by using “AVANCE 500” manufactured by BRUKER, and dissolving 200 mg of a sample in an 8: 2 (volume ratio) mixture of o-dichlorobenzene and heavy benzene at 135 ° C.

2) Melt flow rate (MFR; g / 10 min)
According to JIS K7210, the temperature was 230 ° C. and the load was 2.16 kgf. The required amount of pellet (powder) was used as the resin. After the required amount of the film was cut out, 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 on the basis of monodisperse polystyrene using gel permeation chromatography (GPC). The measurement conditions such as the column used and the solvent in 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), the mass average molecular weight (Mw), and the molecular weight distribution are respectively represented by the molecular number (N _i ) of the molecular weight (M _i ) at each elution position of the GPC curve obtained through the molecular weight calibration curve. It is defined by an expression.
Number average molecular weight: Mn = Σ (N _i · M _i ) / ΣNi
Mass average molecular weight: Mw = Σ (N _i · 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 from the elution peak closest to the elution peak of the standard substance to the lowest position of the bottom of 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 solidified with a modified urethane resin with a microtome and observing with a differential interference microscope. .

5) Thermal shrinkage (%)
Based on JIS Z1712, it measured by the following method. 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 contraction rate was determined by the ratio of the contracted length to the original length.

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

7) Ring crash (g)
Using a digital ring crush tester (manufactured by Tester Sangyo Co., Ltd.), prepare a film sample size of 12.7 mm x 152 mm, set an attachment spacer on the sample table in accordance with the thickness of the film sample, and MD, TD direction In each, insert a film sample along the circumference. At 23 ° C., the compressed plate is moved down at a speed of 12 mm / min. The maximum load at the time of compression with was used as a ring crush measurement value.

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

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

10) Refractive index and plane orientation coefficient Measured using an Atago Abbe refractometer according to JIS K7142-1996 5.1 (Method A). The refractive indexes 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 resistivity (LogΩ)
In accordance with JIS K6911, the film was aged at 23 ° C. for 24 hours, and then the corona-treated surface of the film was measured.

13) Wetting tension (mN / m)
In accordance with JIS K6768-1999, the film was aged for 24 hours at 23 ° C. and 50% relative humidity, and then the corona-treated surface of the film was measured according to the following procedure.
1) Measurement is performed in a standard test room 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. If the test mixture is spread using a cotton 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 creating a pool. To determine the wetting tension, observe the liquid film of the test mixture in a bright place, and perform the liquid film after 3 seconds. It is wet that it keeps the state when applied for 3 seconds or more without tearing the liquid film. If the wetting is maintained for 3 seconds or more, the process proceeds to the liquid mixture having the next highest surface tension. Conversely, if the liquid film is broken in 3 seconds or less, the process proceeds to the next liquid mixture having the lower surface tension. Repeat this procedure and select a mixture that can wet the surface of the specimen accurately in 3 seconds.
3) Use a new cotton swab for each test. Brushes or wire bars are washed with methanol and dried after each use because residual liquid changes composition and surface tension by evaporation.
4) Perform an operation of selecting a mixed solution that can wet the surface of the test piece in 3 seconds 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 ability of bag-made products 1) Preparation of laminate film with sealant film This was carried out as follows using a continuous dry laminating machine.
The corona surface of the biaxially oriented polypropylene film obtained in Examples and Comparative Examples was gravure coated with an adhesive so that the coating amount upon drying was 3.0 g / m 2, then led to the drying zone at 80 ° C. for 5 seconds. Dried. Subsequently, it was bonded to a sealant film between rolls provided on the downstream side (roll pressure 0.2 MP, roll temperature: 60 ° C.). The obtained laminate film was subjected to an aging treatment at 40 ° C. for 3 days while being wound up.
The adhesive was obtained by mixing 17.9% by mass of a main agent (manufactured by Toyo Morton, TM329), 17.9% by mass of a curing agent (CAT8B, manufactured by Toyo Morton) and 64.2% by mass of ethyl acetate. An ether adhesive was used, and a non-stretched polypropylene film (Pyrene (registered trademark) CTP1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. was used as the sealant film.
2) Production of bag-made product After folding in the flow direction of the laminate film, it was heat-sealed in three directions under the conditions of 120 ° C., 1 kg, and 1 second to produce a bag-made product having a width of 200 mm and a length of 200 mm.
3) Evaluation of hand cutting property A notch was made in the lateral direction of the bag-made product, and the presence or absence of resistance when tearing by hand in the lateral direction was carried out by 10 evaluators. The number of people who answered that there was resistance was used as an evaluation item. Each was evaluated three times.
0: ◎: Excellent hand cutting performance.
1 to 5 people: ○: Good hand cutting.
6 to 9 people △: Inferior to hand cutting.
10 people ······ ×: There is no hand cutting.

Example 1
In the base material layer, 79% by weight of the polypropylene homopolymer PP-1 shown in Table 1 and 20% by weight of the polypropylene homopolymer PP-2 and antistatic agent (stearyl diethanolamine stearate (Matsumoto Yushi Co., Ltd. KYM- 4K)) mixed with 1% by weight was used. 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, the raw resin was coextruded from a T-die into a sheet shape, cooled and solidified with a 30 ° C. cooling roll, and then 4. in the longitudinal direction (MD) at 135 ° C. Stretched 5 times. Next, in the tenter, both ends in the film width direction are sandwiched between clips, preheated 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). And heat-fixed at 170 ° C. The film-forming conditions at this time were set as film-forming conditions a and are shown in Table 2.
After the corona treatment was performed on the surface of one side of the obtained biaxially oriented polypropylene film using a corona treatment machine manufactured by Sophtal Corona & Plasma GmbH under the condition of an applied current value of 0.75 A, a winder The biaxially oriented polypropylene film of the present invention was taken up in Table 3 shows the physical properties of the obtained film.

(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. Table 3 shows the physical properties of the obtained film.

Example 4
The mixed raw material used for the base material layer (A) is a 60 mm extruder, and the mixed raw material used for the surface layer (B) is a 65 mm extruder. After co-extrusion and cooling and solidifying with a 30 ° C. cooling roll, the film was stretched 4.5 times in the longitudinal direction (MD) at 135 ° C. Next, in the tenter, both ends in the film width direction are sandwiched between clips, preheated 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). And heat-fixed at 170 ° C. A biaxially oriented laminated polypropylene film according to the present invention in which the base material layer (A) and the surface layer (B) were laminated one by one was obtained by film formation under the film production condition a shown in Table 2 and winding with a winder. . The surface of the surface layer (B) of the obtained biaxially oriented polypropylene film is subjected to corona treatment using a corona treatment machine manufactured by Sophthal Corona & Plasma GmbH under the condition of applied current value: 0.75A. After the application, the one wound with a winder was used as the biaxially oriented polypropylene film of the present invention. Table 3 shows the physical properties of the obtained film.

(Example 5)
A mixture of 79% by weight of polypropylene homopolymer PP-1 and 20% by weight of polypropylene homopolymer PP-2 shown in Table 1 is 99% by weight of polypropylene resin PP-1 and a transverse direction (TD) draw ratio of 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. Table 3 shows the physical properties of the obtained film. The film forming conditions at this time were set 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)
Table 1 shows a mixture of 79% by weight of polypropylene homopolymer PP-1 and 20% by weight of polypropylene homopolymer PP-2, 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 wt% mixture.

(Comparative Example 3)
Example 1 except that 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-3. 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 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 in the width direction was preheated to 170 ° C, the width direction stretching temperature was changed to 158 ° C, and the heat setting temperature was changed to 165 ° C. The physical properties of the obtained film are as shown in Table 4. The film forming conditions at this time were set 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 rate.
In contrast, the films obtained in Comparative Examples 1 and 3 had a high tear strength in the width direction (TD).
In Comparative Example 2, no film could 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 rate in the width direction (TD) and the machine direction (MD).

The biaxially oriented polypropylene film of the present invention can be used for labeling as well as food packaging used for standing pouches and the like. In the bag making process, when the bag is folded in the direction perpendicular to the machine flow direction and the bag is made, the transverse direction becomes the hand cutting direction, and thus the lateral tear strength is important. A lower tear strength results in a film with better hand tearability.

Claims

A biaxially oriented polypropylene film having the following characteristics (a) to (c).
(A) It consists of the resin composition which has a polypropylene resin as a main component.
(B) Tear strength (N / mm) ≦ (0.014 × film thickness (μm) +0.35) in the width direction or longitudinal direction of the film.
(C) The heat shrinkage rate at 150 ° C. in the width direction and the longitudinal direction of the film is 7% or less.
2. The biaxially oriented polypropylene film according to claim 1, wherein a tensile elastic modulus in a width direction and a longitudinal direction of the film is 2.0 GPa or more and a tensile elastic modulus in a direction in which the tensile elastic 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.