JP6446882B2 - Biaxially stretched polypropylene film - Google Patents

Description

  The present invention relates to a stretched polypropylene film. More specifically, the present invention relates to a biaxially stretched polypropylene film with little bowing during film forming and little physical property difference in the width direction.

  The stretched thermoplastic resin film is used for packaging, industrial use, and other uses, and it is desirable that the same physical property values are used in any part of the film. However, in the normal biaxially stretched film manufacturing process, when transverse stretching and heat setting are continuously performed with the same tenter, the width of the film before entering the tenter is set along the width direction (the film traveling direction ( If a straight line is drawn at right angles to the (MD direction) (TD direction), a concave-shaped deformation remains in the film from the tenter. This phenomenon is called the Boeing phenomenon. As a result, the molecular orientation state is not the same in the central part and the side edge part of the film, and the physical property values in the width direction of the film are uneven. It is considered. In the tenter, the stretching stress in the MD direction generated by the stretching process and the shrinkage stress generated by the heat setting process are less influenced by the gripping means at the center of the film than at the ends of the film that are gripped by the clip. It is considered that a delay is caused by the weakening of the Boeing phenomenon.

  Such a bowing phenomenon tends to cause the angle of the orientation main axis to be different in the width direction of the film. As a result, for example, physical property values such as thermal shrinkage, thermal expansion, wet expansion, and refractive index in the vertical direction differ in the width direction of the film. For this reason, as an example of packaging applications, problems such as printing pitch deviation, generation of spots, curling, and meandering are caused in printing lamination, bag making processes, and the like.

In order to reduce the bowing phenomenon, a manufacturing method has been proposed in which a relaxation step of 20 ° C. to 150 ° C. is interposed between the transverse stretching step and the heat setting step to provide a substantial cooling step (Patent Document 1). ). However, the length of the cooling process is not described at all, and the effect of reducing the bowing phenomenon is completely unknown.
Furthermore, as a technique for reducing or eliminating the bowing phenomenon, a film manufacturing method in which a nip roll group is installed between the transverse stretching process and the heat setting process has been proposed (Patent Document 2). However, this technique is less effective as an improvement measure because the temperature of the intermediate zone in which the nip roll is installed is equal to or higher than the glass transition temperature and the film rigidity at the nip point is low.

  In addition, there has been proposed a process for forcibly advancing only a narrow range near the center by nip roll while gripping both ends of the film after transverse stretching (Patent Document 3). Furthermore, after cooling the film immediately after transverse stretching to below the glass transition temperature, it is heat-set in multiple stages and stretched in the transverse direction at the same time as heat setting (Patent Document 4). In the method for producing a film to be heat-treated, a technique (Patent Document 5) in which a preheating zone having a temperature not lower than the glass transition point and not higher than the heat treatment temperature is provided between the lateral stretching zone and the heat treatment zone only at the side end portion. After cooling the film to a temperature equal to or lower than the transverse stretching temperature, a technique of stretching again in the transverse direction while raising the temperature in multiple stages (Patent Document 6), and a technique of reversing the running direction of the film to perform transverse stretching and heat setting (Patent Document 7) 8) have been proposed. However, these process improvement methods are questionable in process complexity and stability.

Japanese Examined Patent Publication No. 35-11774 Japanese Patent Laid-Open No. 50-73978 Japanese Patent Publication No. 63-24459 Japanese Patent Publication No.62-43856 Japanese Patent Laid-Open No. 62-183327 JP-A-1-165423 Japanese Patent Publication No. 1-2694 Japanese Patent Publication No. 1-26966

  The present invention has been made against the background of such prior art problems. That is, an object of the present invention is to provide a film capable of reducing product loss and reducing costs by producing a biaxially stretched film with less bowing and uniform physical properties in the width direction.

  As a result of intensive studies to achieve the above object, the present inventors have found that bowing can be reduced by controlling the molecular weight distribution, and the present invention has been completed.

That is, the biaxially stretched polypropylene film of the present invention is a biaxially stretched polypropylene film characterized in that the polypropylene resin constituting the film satisfies the following conditions 1) to 3) and the bowing rate is 1% or less. .
1) The range of the melt flow rate (MFR) measured at 230 ° C. and 2.16 kgf is 1 to 20 g / 10 min.
2) The lower limit of the mass average molecular weight (Mw) / number average molecular weight (Mn) is 5.5.
3) The lower limit of z + 1 average molecular weight (Mz + 1) / number average molecular weight (Mn) is 50.

  In this case, the film is preferably stretched at a stretching ratio of 3 to 8 times in the longitudinal direction and at a stretching ratio of 4 to 20 times in the width direction.

  The present invention relates to a biaxially oriented polypropylene film with less bowing. The polypropylene resin constituting the stretched polypropylene film of the present invention has the following characteristics with respect to the melt flow rate and molecular weight distribution.

(Melt flow rate of polypropylene resin)
It is important that the lower limit of the melt flow rate (MFR) measured at 230 ° C. and 2.16 kgf of the entire polypropylene resin constituting the stretched polypropylene film of the present invention is 1 g / 10 minutes. The lower limit of the total MFR is preferably 1.2 g / 10 minutes, more preferably 1.4 g / 10 minutes, still more preferably 1.5 g / 10 minutes, and particularly preferably 1.6 g / 10 minutes. Minutes. Within the above range, the mechanical load is small and stretching is easy. On the other hand, the upper limit of the total MFR is preferably 20 g / 10 minutes, more preferably 17 g / 10 minutes, still more preferably 15 g / 10 minutes, particularly preferably 14 g / 10 minutes, most preferably 13 g / 10 min. When it is within the above range, stretching becomes easy, thickness unevenness is reduced, and the stretching temperature and heat setting temperature are easily increased, resulting in a lower thermal shrinkage rate.

(Component monomer of polypropylene resin)
The polypropylene resin constituting the stretched polypropylene film of the present invention may be a propylene homopolymer obtained only from a propylene monomer or a copolymer with a copolymerization monomer. As the copolymerization monomer species, olefins such as ethylene and butene are preferable.

  The upper limit of the amount of copolymerizable monomers other than propylene in the polypropylene resin is 10 mol%. The upper limit of the amount of copolymerization monomer is preferably 9 mol%, more preferably 8 mol%. When it is in the above range, the crystallinity is improved and the film has the necessary rigidity.

(Molecular weight distribution of polypropylene resin)
One of the characteristics of the stretched polypropylene film of the present invention is the molecular weight distribution state of the polypropylene resin to be constituted.
The polypropylene resin constituting the stretched polypropylene film of the present invention is mainly composed of, for example, a low molecular weight component having a mass average molecular weight (Mw) of about 100,000, and for example, a very molecular weight having a mass average molecular weight (Mw) of about 1,500,000. Contains high molecular weight components. It is considered that the bowing phenomenon can be reduced by increasing the content of the low molecular weight component. On the other hand, a low molecular weight polypropylene resin has a low melt tension when softened by heating and cannot generally be a stretched film. It is considered that the high molecular weight component is allowed to be stretched by the presence of several percent to several tens of percent, thereby achieving the effect of the stretched film of the present invention.

The polypropylene resin constituting the stretched polypropylene film of the present invention is characterized by a wide molecular weight distribution. In general, the breadth of the molecular weight distribution can be represented by, for example, the ratio (Mw / Mn) of the mass average molecular weight (Mw) and the number average molecular weight (Mn) measured using gel permeation chromatography (GPC). .
In the present invention, it is important that the lower limit of Mw / Mn is 5.5. The lower limit of Mw / Mn is preferably 6, more preferably 6.5, still more preferably 7, and particularly preferably 7.2. If it is less than the above, the amount of reduction in bowing is small, and the effects of the present application cannot be obtained. On the other hand, the upper limit of Mw / Mn is preferably 30, more preferably 25, still more preferably 20, particularly preferably 15, and most preferably 13. Exceeding the above may make it difficult to produce realistic resins.

  An average molecular weight that places importance on high molecular weight components is Z + 1 average molecular weight (Mz + 1), and the degree of molecular weight distribution can be expressed more accurately by Mz + 1 / Mn.

  In the present invention, the lower limit of Mz + 1 / Mn is preferably 50. The lower limit of Mz + 1 / Mn is preferably 60, more preferably 70, still more preferably 80, and particularly preferably 90. If it is less than the above, the amount of reduction in bowing is small, and the effects of the present application cannot be obtained. On the other hand, the upper limit of Mz + 1 / Mn is preferably 300, more preferably 200. Exceeding the above may make it difficult to produce a realistic resin.

  The lower limit of the number average molecular weight (Mn) of the entire polypropylene resin constituting the stretched polypropylene film of the present invention is preferably 20000, more preferably 22000, still more preferably 24000, particularly preferably 26000, Preferably it is 27000. Within the above range, there are advantages that stretching is easy, uneven thickness is reduced, stretching temperature and heat setting temperature are easily increased, and thermal shrinkage is decreased. On the other hand, the upper limit of the total Mn is preferably 65000, more preferably 60000, still more preferably 55000, particularly preferably 53000, and most preferably 52000. When the amount is within the above range, the effect of the present application can be easily obtained or the drawing can be easily performed with respect to the reduction amount of bowing.

The lower limit of the mass average molecular weight (Mw) obtained by GPC of the entire polypropylene resin constituting the stretched polypropylene film of the present invention is preferably 250,000, more preferably 260000, still more preferably 270000, and particularly preferably 280000. And most preferably 290000. Within the above range, there are advantages that stretching is easy, uneven thickness is reduced, stretching temperature and heat setting temperature are easily increased, and thermal shrinkage is decreased. On the other hand, the upper limit of the total Mw is preferably 500,000, more preferably 450,000, still more preferably 400,000, particularly preferably 380000, and most preferably 370000. Within the above range, the mechanical load is small and stretching becomes easy.

  The lower limit of Mz + 1 of the entire polypropylene resin constituting the stretched polypropylene film of the present invention is preferably 2500,000, more preferably 3000,000, still more preferably 3300000, particularly preferably 3500000, and most preferably 3700000. . Within the above range, the high molecular weight component is sufficient, and the effects of the present invention are easily obtained. On the other hand, the upper limit of the total Mz + 1 is preferably 40000000, more preferably 35000000, and further preferably 30000000. Within the above range, realistic resin production is easy, stretching is easy, and fish eyes in the film are reduced.

  Moreover, there is also a Z average molecular weight (Mz) as an average molecular weight placing importance on the high molecular weight component, and the lower limit of Mz of the entire polypropylene resin constituting the stretched polypropylene film of the present invention is preferably 1000000, more preferably 1200000. More preferably, it is 1300000, particularly preferably 1400000, and most preferably 1500,000. Within the above range, the high molecular weight component is sufficient, and the effects of the present invention are easily obtained. On the other hand, the upper limit of the overall Mz is preferably 15000000. Within the above range, realistic resin production is easy, stretching is easy, and fish eyes in the film are reduced.

  The lower limit of the peak value (Mp) in the molecular weight distribution curve of the polypropylene resin constituting the stretched polypropylene film of the present invention is preferably 50000, more preferably 60000, still more preferably 70000, and particularly preferably 75000. is there. Within the above range, advantages such as easy stretching, reduced thickness unevenness, easy increase in stretching temperature and heat setting temperature, and lower heat shrinkage rate can be obtained. On the other hand, the upper limit of Mp is preferably 150,000, more preferably 130,000, still more preferably 120,000, and particularly preferably 115,000. If it is within the above range, stretching is also easy.

Since the entanglement of the polymer chain decreases as the molecular weight decreases, it is preferable that the low molecular weight component is large in order to reduce the residual stress.
When the GPC cumulative curve of the entire polypropylene resin constituting the stretched polypropylene film of the present invention 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%. Boeing can be reduced within the above range, the effects of the present application can be easily obtained, and stretching can be facilitated. 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 the heat shrinkage rate can be further reduced.
In addition, molecules having a molecular weight of about 10,000 or less do not contribute to the entanglement between molecular chains, and have a high effect of loosening the entanglement between molecules like a plasticizer, and a specific amount of a component having a molecular weight of 10,000 or less is included. Therefore, it is considered that Boeing can be further reduced.
Therefore, the lower limit of the amount of the component having a molecular weight of 10,000 or less obtained by GPC is preferably 2% by mass, more preferably 2.5% by mass, still more preferably 3% by mass, and particularly preferably 3. 3% by mass, most preferably 3.5% by mass. Within the above range, the effect of the present application in which bowing is reduced can be obtained more easily. On the other hand, the upper limit of the amount of the component having a molecular weight of 10,000 or less is preferably 20% by mass, more preferably 17% by mass, still more preferably 15% by mass, particularly preferably 14% by mass, and most preferably. Is 13% by mass. If it is in the above range, the effect of reducing bowing is great.

  A high molecular weight component and a low molecular weight component suitable for forming a polypropylene resin having such a molecular weight distribution will be described. However, the means for achieving the wide molecular weight distribution of the present invention is not limited to this. Absent.

(High molecular weight component)
The lower limit of the melt flow rate (MFR) measured at 230 ° C. and 2.16 kgf of the high molecular weight component is preferably 0.0001 g / 10 minutes, more preferably 0.0005 g / 10 minutes, and further preferably 0. 0.001 g / 10 min, particularly preferably 0.005 g / 10 min. Within the above range, it is practically easy to produce the resin, and the fish eyes of the film can be reduced.
The upper limit of the MFR measured at 230 ° C. and 2.16 kgf of the high molecular weight component is preferably 0.5 g / 10 minutes, more preferably 0.35 g / 10 minutes, still more preferably 0.3 g / 10 minutes. It is particularly preferably 0.2 g / 10 min, most preferably 0.1 g / 10 min. When the amount is within the above range, the amount of the polymer component necessary for maintaining the entire MFR can be reduced, and the effects of the present application can be more easily obtained.

  The lower limit of Mw of the high molecular weight component is preferably 500,000, more preferably 600,000, still more preferably 700,000, particularly preferably 800,000, and most preferably 1,000,000. When the amount is within the above range, the amount of the polymer component necessary for maintaining the overall MFR can be reduced, and the effects of the present application can be more easily obtained, such as less bowing while maintaining moldability. On the other hand, the upper limit of Mw of the high molecular weight component is preferably 10000000, more preferably 8000000, still more preferably 6000000, and particularly preferably 5000000. Within the above range, it is practically easy to produce the resin, and the fish eyes of the film can be reduced.

  The lower limit of the amount of the high molecular weight component is preferably 2% by mass, more preferably 3% by mass, still more preferably 4% by mass, and particularly preferably 5% by mass in 100% by mass of the polypropylene resin. . Within the above range, it is not necessary to increase the molecular weight of the low molecular weight component in order to maintain the overall MFR, and the effects of the present application such as a low heat shrinkage rate at a high temperature can be more easily obtained. On the other hand, the upper limit of the amount of the high molecular weight component is preferably 30% by mass, more preferably 25% by mass, still more preferably 22% by mass, and particularly preferably 20% by mass in 100% by mass of the polypropylene resin. %. If it is in the above range, the stretchability becomes easy and the thermal shrinkage rate becomes low.

(Low molecular weight component)
The lower limit of the MFR measured at 230 ° C. and 2.16 kgf of the low molecular weight component is preferably 70 g / 10 minutes, more preferably 80 g / 10 minutes, still more preferably 100 g / 10 minutes, particularly preferably 150 g / 10 min, most preferably 200 g / 10 min. Boeing can be easily reduced within the above range. On the other hand, the upper limit of the MFR measured at 230 ° C. and 2.16 kgf of the low molecular weight component is preferably 2000 g / 10 minutes, more preferably 1800 g / 10 minutes, still more preferably 1600 g / 10 minutes. Preferably it is 1500 g / 10 minutes, most preferably 1400 g / 10 minutes. Within the above range, the overall MFR is easily maintained, and the film-forming property is excellent.

  The lower limit of the Mw of the low molecular weight component is preferably 50000, more preferably 53000, still more preferably 55000, particularly preferably 60000, and most preferably 70000. Within the above range, the overall MFR is easily maintained, and the film-forming property is excellent. On the other hand, the upper limit of Mw of the low molecular weight component is preferably 150,000, more preferably 140000, still more preferably 130,000, particularly preferably 120,000, and most preferably 110,000. Within the above range, crystallinity is improved, low molecular weight bleed out is suppressed, and impact resistance is excellent.

  The lower limit of the amount of the low molecular weight component is preferably 40% by mass, more preferably 50% by mass, still more preferably 55% by mass, and particularly preferably 60% by mass in 100% by mass of the polypropylene resin. . Within the above range, the effects of the present application such as a low heat shrinkage at a high temperature exhibited by the low molecular weight component can be obtained more easily. On the other hand, the upper limit of the amount of the low molecular weight component is preferably 98% by mass, more preferably 97% by mass, still more preferably 96% by mass, and particularly preferably 95% by mass in 100% by mass of the polypropylene resin. It is. Within the above range, it is not necessary to increase the molecular weight of the low molecular weight component in order to maintain the overall MFR, and the effects of the present application are more easily obtained.

The high molecular weight component and the low molecular weight component may be a mixture of two or more resins corresponding to each component, and in this case, the preferred range of the amount of each component described above is the total amount of the two or more resins. .
In addition, the polypropylene resin in the present invention may contain a component having a molecular weight other than the above high molecular weight component and low molecular weight component in order to adjust the MFR as the entire polypropylene resin. Further, in order to easily loosen the entanglement of the molecular chains and adjust the stretchability, a polypropylene resin having a molecular weight of the low molecular weight component or less, particularly a molecular weight of about 30,000 or less, and further a molecular weight of about 10,000 or less may be contained. .

  In order to blend the high molecular weight component and the low molecular weight component into a preferable molecular weight distribution state of the polypropylene resin, for example, when the molecular weight of the low molecular weight component is low, the molecular weight of the high molecular weight component is increased. It is preferable to adjust the distribution state by increasing it and to adjust the MFR to be easy to produce as a stretched film.

  In other words, in the present invention, it is possible to produce a film with very little bowing by using the polypropylene resin having the characteristic molecular weight distribution as described above.

(Production method of polypropylene resin)
The polypropylene resin is obtained by polymerizing propylene as a raw material using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. In order to widen the molecular weight distribution, a Ziegler-Natta catalyst or the like is preferable.
As a polymerization method of propylene, a known method may be used, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, xylene, a method of polymerizing in liquid propylene or ethylene, a catalyst in propylene or ethylene as a gas And a method of polymerizing in a gas phase state, or a method of polymerizing these in combination.
There is no particular limitation on the method for achieving a wide molecular weight distribution, and a known method can be used. That is, the high molecular weight component and the low molecular weight component may be polymerized separately and then mixed by an extruder or the like, or may be polymerized in multiple stages in a series of plants having a multistage reactor, and have different polymerization performance. The catalyst may be mixed to achieve a broad molecular weight distribution during polymerization, or may be achieved depending on the performance of the catalyst itself. In particular, a method of polymerizing and blending a high molecular weight component and a low molecular weight component using a plant having a multi-stage reactor is widely used.

The film-forming resin composition is mainly composed of the above polypropylene resin,
If necessary, additives and other resins may be added. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an adhesive, an antifogging agent, a flame retardant, an antiblocking agent, and an inorganic or organic filler. Examples of other resins include polypropylene resins other than the specific polypropylene resin used in the present invention, random copolymers that are copolymers of ethylene and α-olefin, and various elastomers. The addition amount of the additive is preferably 50 parts by mass or less in 100 parts by mass of the resin composition for film molding, and the addition amount of other resins is 80 parts by mass or less in 100 parts by mass of the resin composition for film molding. Preferably there is. These are blended with polypropylene resin and Henschel mixer, etc., or master pellets prepared in advance using a melt kneader are diluted with polypropylene to a predetermined concentration, or the entire amount is melt kneaded in advance. be able to.

The stretching may be sequential biaxial stretching or simultaneous biaxial stretching. In the following, a method for producing a film of sequential biaxial stretching of longitudinal stretching and transverse stretching, which is a particularly preferred example, will be described.
First, a polypropylene resin is heated and melted with a single or twin screw extruder and extruded onto a chill roll to obtain an unstretched sheet. In the case of melt extrusion, for example, it is preferable to extrude into a sheet form from a T die so that the resin temperature is 200 to 280 ° C., and to cool and solidify with a cooling roll having a temperature of 10 to 100 ° C. Next, for example, the film is stretched 3 to 8 times in the longitudinal (MD) direction with a stretching roll of 120 to 165 ° C., and subsequently 155 ° C. to 175 ° C. (more preferably 158 ° C. to 170 ° C.) in the width (TD) direction. It is preferable to stretch 4 to 20 times at temperature. Further, it is preferable to perform heat treatment while allowing relaxation of 1 to 15% at an atmospheric temperature of preferably 165 to 175 ° C (more preferably 166 to 173 ° C). The stretched polypropylene film thus obtained can be subjected, for example, to corona discharge treatment on at least one side, and then a roll sample can be obtained by winding with a winder.

  The lower limit of the draw ratio in the MD direction is preferably 3 times, more preferably 3.5 times. If it is less than the above, film thickness unevenness may occur. On the other hand, the upper limit of the draw ratio in the MD direction is preferably 8 times, more preferably 7 times. If the above is exceeded, it may be difficult to continue stretching in the TD direction.

  The lower limit of the stretching temperature in the MD direction is preferably 110 ° C, more preferably 115 ° C, and further preferably 120 ° C. If it is less than the above, the mechanical load may be increased, the thickness unevenness may be increased, or the film may be roughened. On the other hand, the upper limit of the stretching temperature in the MD direction is preferably higher in terms of heat shrinkage, but it may be difficult to stretch by adhering to the roll, and is preferably 165 ° C, more preferably 160 ° C. More preferably, it is 155 degreeC, Most preferably, it is 150 degreeC.

  The lower limit of the draw ratio in the TD direction is preferably 4 times, more preferably 5 times, and even more preferably 6 times. If it is less than the above, thickness unevenness may occur. On the other hand, the upper limit of the stretching ratio in the TD direction is preferably 20 times, more preferably 17 times, still more preferably 15 times, and particularly preferably 12 times. If it exceeds the above, it may break during stretching.

  In the stretching in the TD direction, preheating is preferably performed, and the preheating temperature is preferably set higher by 10 to 15 ° C. than the stretching temperature in order to quickly raise the film temperature in the vicinity of the stretching temperature.

The lower limit of the stretching temperature in the TD direction is preferably 145 ° C, more preferably 150 ° C, and further preferably 152 ° C. If it is less than the above, it may break without being sufficiently softened, or the thermal shrinkage rate may be increased. On the other hand, the upper limit of the stretching temperature in the TD direction is preferably 175 ° C, more preferably 170 ° C, and more preferably 168 ° C. In order to lower the bowing rate, the temperature is preferably higher, but if it exceeds the above, the low molecular weight component may melt and recrystallize, resulting in surface roughness and whitening of the film.

  The film after stretching is preferably heat-set. The lower limit of the heat setting temperature is preferably 155 ° C, more preferably 157 ° C. If it is less than the above, the thermal shrinkage rate may increase. On the other hand, the upper limit of the heat setting temperature is preferably 175 ° C, more preferably 173 ° C. When the above is exceeded, the low molecular weight component may melt and recrystallize, and the surface roughness and the film may be whitened.

During heat setting, it is preferable to relax. The lower limit of relaxation is preferably 1%, more preferably 2%, and even more preferably 3%. If it is less than the above, the thermal shrinkage rate may increase. On the other hand, the upper limit of relaxation is preferably 15%, more preferably 10%, and even more preferably 8%. When the above is exceeded, the thickness unevenness may increase.
Although the thickness of a film is set according to each use, the minimum of film thickness becomes like this. Preferably it is 2 micrometers, More preferably, it is 3 micrometers, More preferably, it is 4 micrometers. The upper limit of the film thickness is preferably 300 μm, more preferably 200 μm, still more preferably 150 μm, particularly preferably 100 μm, and most preferably 50 μm.

  The stretched polypropylene film thus obtained is usually formed as a roll having a width of about 2000 to 12000 mm and a length of about 1000 to 50000 m, and wound into a roll. Furthermore, it is slit according to each application, and is provided as a slit roll having a width of 300 to 2000 mm and a length of about 500 to 5000 m.

  The stretched polypropylene film of the present invention has excellent properties such as those described above that are not present in the past. Therefore, since there is little difference in physical properties depending on the location in the width direction, a low-cost film can be produced with little product loss.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited by the following examples and the like, and is appropriately within a range that can meet the above and the following purposes. Of course, it is possible to carry out with modifications, and these are all included in the technical scope of the present invention.
In addition, the measuring method of the physical property in a following example and a comparative example is as follows.

(1) Melt flow rate (MFR) (g / 10 min)
Based on JIS-K7210, it measured at the temperature of 230 degreeC.

(2) 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 columns and solvents 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), the mass average molecular weight (Mw), and the Z + 1 average molecular weight (Mz + 1) are determined by the molecular number (Ni) of the molecular weight (Mi) at each elution position of the GPC curve obtained through the molecular weight calibration curve. It is defined by the following formula.
Number average molecular weight: Mn = Σ (Ni · Mi) / ΣNi
Mass average molecular weight: Mw = Σ (Ni · Mi2) / Σ (Ni · Mi)
Z + 1 average molecular weight: Mz + 1 = Σ (Ni · Mi4) / Σ (Ni · Mi3)
Molecular weight distribution: Mw / Mn, Mz + 1 / Mn
The molecular weight at the peak position of the GPC curve was defined as Mp.
When the baseline is not clear, the baseline should be set in a range up to the lowest position on the high molecular weight side of the elution peak closest to the elution peak of the standard substance.
From the obtained GPC curve, two or more components having different molecular weights were subjected to peak separation. The molecular weight distribution of each component is assumed to be a Gaussian function, and Mw / Mn = 4 so as to be the same as the molecular weight distribution of ordinary polypropylene. Each average molecular weight was calculated from the obtained curve of each component.

(3) Stereoregularity The mesopentad fraction ([mmmm]%) and meso average chain length were measured using 13C-NMR. The mesopentad fraction was determined according to the method described in “Zambelli et al., Macromolecules, Vol. 6, 925 (1973)”. (1977) (Academic Press, New York) ".
13C-NMR measurement was performed at 110 ° C. 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.

(4) Boeing rate (unit:%)
A straight line is drawn in the transverse direction on the unstretched raw sheet before the introduction of the tenter, and after being led to the tenter and transversely stretched at a predetermined magnification, the delay in the center of the straight line on the biaxially stretched film coming out of the tenter The length (L) was measured. The ratio with respect to the film width (W) was determined and used as the bowing rate (L / W × 100 [%]).

(5) Thermal shrinkage (unit:%)
It measured based on JIS-Z1712. That is, the stretched film was cut in the MD direction and the TD direction with a length of 20 mm and a length of 200 mm, respectively, suspended in a hot air oven 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) Young's modulus (unit: GPa)
Based on JIS-K7127, the Young's modulus of MD direction and TD direction was measured at 23 degreeC.

(7) Impact resistance (unit: J)
It measured at 23 degreeC using the Toyo Seiki film impact tester.

(8) Thickness unevenness (thickness uniformity) (unit:%)
A square sample having a length of 1 m was cut out from the wound film roll, and divided into 10 parts each in the MD direction and the TD direction, and 100 measurement samples were prepared. The thickness of the substantially central portion of the measurement sample was measured with a contact-type film thickness meter. Then, the average value A of the obtained 100 points of data is obtained, and the difference (absolute value) B between the minimum value and the maximum value is obtained, and the minimum value and the maximum value calculated using the formula of (B / A) × 100. The value obtained by dividing the absolute value of the difference between the values by the average value was defined as the thickness unevenness of the film.

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

(10) Density (Unit: g / cm3)
The density of the film was measured by a density gradient tube method according to JIS-K7112.

Example 1
As a polypropylene resin, a propylene homopolymer having Mw / Mn = 7.7, Mz + 1 / Mn = 140, MFR = 5.0 g / 10 min, and mesopentad fraction [mmmm] = 97.3% (Nippon Polypro Corp.) Manufactured by Novatec (registered trademark) PP “SA4L”: the amount of copolymerization monomer was 0 mol%; hereinafter abbreviated as “PP-1”).
This polypropylene resin was extruded into a sheet form from a T-die at 250 ° C. using a 60 mm extruder, cooled and solidified with a cooling roll at 30 ° C., and then longitudinally (lengthwise) 4.5 times longer at 135 ° C. Stretched, then clipped at both ends, led into a hot air oven, preheated at 170 ° C., then transversely stretched 8.2 times in the width direction (lateral direction) at 160 ° C., then 6.7 in the width direction % Heat treatment at 168 ° C. while relaxing. One side of the film thus obtained was subjected to corona treatment and wound up with a winder to obtain the stretched polypropylene film of the present invention.
The thickness of the obtained film was 20 μm, and the physical properties were as shown in Tables 1 and 2. From the results of the table, it can be seen that this film can produce a film with small bowing while maintaining the general characteristics of the film.

(Example 2)
As a polypropylene resin, a propylene homopolymer having a Mw / Mn = 8.9, Mz + 1 / Mn = 110, MFR = 3.0 g / 10 minutes, and a mesopentad fraction [mmmm] = 97.1% (Samsungthal Co., Ltd.) A stretched polypropylene film was obtained in the same manner as in Example 1 except that the preheating temperature for transverse stretching was 171 ° C., the stretching temperature was 161 ° C., and the heat treatment temperature after transverse stretching was 170 ° C. It was. The thickness of the obtained film was 20 μm, and the physical properties were as shown in Tables 1 and 2.

(Comparative Example 1)
As a polypropylene resin, Mw / Mn = 4, Mz + 1 / Mn = 21, MFR = 2.5 g / 10 min, a polypropylene polymer having a mesopentad fraction [mmmm] = 97.0% (Sumitomo Chemical Co., Ltd. Sumitomo) Nobrene (registered trademark) “FS2011DG3”, ethylene content = 0.6 mol%), transverse stretching temperature was 125 ° C., preheating temperature in longitudinal stretching was 168 ° C., stretching temperature was 155 ° C., and heat treatment temperature was 163 ° C. Except for the above, a stretched polypropylene film for comparison was obtained in the same manner as in Example 1.
The thickness of the obtained film was 20 μm, and the physical properties were as shown in Tables 1 and 2.

  The stretched polypropylene film of the present invention can be widely used for packaging applications and industrial applications, but the cost can be reduced because there are few physical property differences in the width direction.

Claims (2)

A biaxially oriented polypropylene film characterized in that the polypropylene resin constituting the film satisfies the following conditions 1) to 4) and has a bowing rate of 1% or less.
1) The range of the melt flow rate (MFR) measured at 230 ° C. and 2.16 kgf is 1 to 20 g / 10 min.
2) The lower limit of the mass average molecular weight (Mw) / number average molecular weight (Mn) is 5.5 and the upper limit is 13 .
3) The lower limit of z + 1 average molecular weight (Mz + 1) / number average molecular weight (Mn) is 50.
4) The thermal shrinkage in the longitudinal direction at 120 ° C. is 1.9% or less. Polypropylene resin is heated and melted, extruded onto a chill roll to obtain an unstretched sheet, the sheet is stretched 3 to 8 times in the longitudinal direction, then stretched 4 to 20 times in the width direction, and then heat-set at 155 to 175 ° C. The method for producing a biaxially stretched polypropylene film according to claim 1 .