TWI835964B - Biaxially oriented polypropylene film - Google Patents

Abstract

The object of the present invention is to provide a biaxially oriented polypropylene film that has high rigidity and excellent heat resistance to high temperatures up to 150°C, easily maintains the shape of the bag when it is made into a packaging bag, and is free from spacing deviation during printing or heat sealing. There are few wrinkles in the sealing part. This biaxially aligned polypropylene film is based on the azimuthal dependence of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray diffraction measurement. The half-value width of the peak from the aligned crystals in the width direction is: 27° or less, and the thermal shrinkage at 150°C is 10% or less in the length direction and 30% or less in the width direction.

Description

Biaxially oriented polypropylene film

The present invention relates to a biaxially oriented polypropylene film with excellent rigidity and heat resistance. Specifically, it relates to a biaxially oriented polypropylene film that is easy to maintain the bag shape when made into a packaging bag, and has few wrinkles at the sealing part when heat-sealed, so it can be suitable for packaging bags.

Biaxially oriented polypropylene film can be used for packaging or industrial purposes because it is moisture-proof and has the necessary rigidity and heat resistance. In recent years, as the use of the film has expanded, higher performance is required, especially improved rigidity. In addition, considering the environment, it is necessary to reduce the volume (make the film thinner) while maintaining strength, so the rigidity must be significantly improved. As a means of improving rigidity, it is known to improve the crystallinity or melting point of the polypropylene resin by improving the catalyst or process technology during the polymerization of the polypropylene resin, but despite such improvements, there has never been a biaxially oriented polypropylene film with sufficient rigidity.

The following method has been proposed: in the production process of a biaxially aligned polypropylene film, after stretching in the width direction, the first stage of heat treatment is performed while relaxing the film at a temperature lower than the temperature during the width direction extension, and the second stage is performed in the second stage. A method of heat treatment from a temperature to a stretching temperature in the width direction (for example, refer to Reference 1, etc.); or a method of extending in the width direction and then extending in the length direction (for example, refer to Reference 2, etc.). However, although the film described in Patent Document 2 has excellent rigidity, it is prone to wrinkles in the sealing portion after heat sealing and has poor heat resistance. In addition, the film described in Patent Document 1 has low alignment and insufficient rigidity.

[Prior Art Literature] [Patent Document]

[Patent document 1] International Gazette No. WO2016/182003.

[Patent Document 2] Japanese Patent Publication No. 2013-177645.

The object of the present invention is to solve the above-mentioned problems. That is, a biaxially oriented polypropylene film that is excellent in film rigidity and heat resistance at high temperatures up to 150°C. Specifically, the invention provides a biaxially oriented polypropylene film that easily maintains the shape of the bag when it is made into a packaging bag and has few wrinkles in and around the sealing portion when heat-sealed.

The inventors of the present invention have made great efforts to achieve the above-mentioned purpose and have found that by making a biaxially oriented polypropylene film in which the half-value width of the peak of oriented crystals in the width direction is less than 27° in the azimuthal angle dependence of the (110) plane of polypropylene α-type crystals obtained by wide-angle X-ray diffraction measurement, and the thermal shrinkage rate at 150°C is less than 10% in the length direction and less than 30% in the width direction, a biaxially oriented polypropylene film with excellent film rigidity and heat resistance up to 150°C can be obtained.

In this case, it is preferable that the thermal shrinkage rate of the biaxially aligned polypropylene film at 120°C is 2.0% or less in the length direction and 5.0% or less in the width direction, and the thermal shrinkage rate at 120°C in the length direction is smaller than that in the width direction. Thermal shrinkage rate at 120℃.

In addition, in this case, it is preferred that the refractive index Ny of the aforementioned biaxially oriented polypropylene film in the width direction is greater than 1.5230, and △Ny is greater than 0.0220.

Furthermore, in this case, it is preferred that the haze of the aforementioned biaxially oriented polypropylene film is less than 5.0%.

Furthermore, in this case, it is preferable that the meso pentad component ratio of the polypropylene resin constituting the biaxially aligned polypropylene film is 97.0% or more.

Furthermore, in this case, it is preferable that the polypropylene resin constituting the biaxially aligned polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 160°C or higher.

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

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

Furthermore, in this case, it is preferable that the orientation degree of the biaxially aligned polypropylene film is 0.85 or more.

The biaxially oriented polypropylene film of the present invention has high rigidity and excellent heat resistance to high temperatures up to 150°C, so it is easy to maintain the bag shape when made into a packaging bag, and there are few wrinkles in the sealed part during heat sealing, so a biaxially oriented polypropylene film suitable for packaging bags can be obtained. In addition, since the biaxially oriented polypropylene film has excellent rigidity, it can maintain strength even if the thickness of the film becomes thinner, and can also be appropriately used for applications requiring higher rigidity.

The biaxially oriented polypropylene film of the present invention is further described below in detail.

The biaxially oriented polypropylene film of the present invention is composed of a polypropylene resin composition with a polypropylene resin as the main component. In addition, the so-called "main component" means that the ratio of the polypropylene resin in the polypropylene resin composition is 90 mass% or more, preferably 93 mass% or more, more preferably 95 mass% or more, and particularly preferably 97 mass% or more.

(Polypropylene resin)

The polypropylene resin used in the present invention may be a polypropylene homopolymer or a copolymer of polypropylene and ethylene and/or an α-olefin having more than 4 carbon atoms. Preferably, the polypropylene homopolymer substantially does not contain ethylene and/or an α-olefin having more than 4 carbon atoms. Even if the polypropylene resin contains ethylene and/or an α-olefin having more than 4 carbon atoms, the amount of ethylene and/or an α-olefin having more than 4 carbon atoms is preferably less than 1 mol%. The upper limit of the amount of the component is more preferably 0.5 mol%, more preferably 0.3 mol%, and more preferably 0.1 mol%. If it is within the above range, the crystallinity is easily improved. As the α-olefin component with more than 4 carbon atoms constituting this copolymer, for example, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, etc.

The polypropylene resin may be two or more different polypropylene homopolymers, or a copolymer of polypropylene and ethylene and/or an α-olefin having more than 4 carbon atoms, or a mixture thereof.

(three-dimensional regularity)

The index of stereoregularity of the polypropylene resin used in the present invention is the meso pentad ratio ([mmmm]%), which is preferably in the range of 97.0% to 99.9%, and more preferably 97.5% to 99.7%. within the range, more preferably within the range of 98.0% to 99.5%, particularly preferably within the range of 98.5% to 99.3%.

If it is above 97.0%, the crystallinity of polypropylene resin becomes higher, the melting point, crystallinity and crystal orientation of the film crystal are improved, and it is easy to obtain rigidity and high temperature heat resistance. If it is below 99.9%, it is easy to suppress the cost in terms of polypropylene manufacturing, and it is not easy to break during film making. It is better to be below 99.5%. The meso-pentad fraction is measured by nuclear magnetic resonance method (so-called NMR method).

In order to set the meso pentad component ratio of the polypropylene resin within the above range, the following method can be preferably used: the method of washing the obtained polypropylene resin powder with a solvent such as n-heptane; Or methods for appropriately selecting catalysts and/or cocatalysts, selecting components of polypropylene resin compositions, etc.

(melting temperature)

The lower limit of the melting temperature (Tm) of the above-mentioned polypropylene resin constituting the biaxially aligned polypropylene film of the present invention as measured by DSC (Differential Scanning Calorimeters) is preferably 160°C, more preferably 161°C. , and more preferably 162°C, and still more preferably 163°C.

If Tm is above 160℃, it is easy to obtain rigidity and high temperature heat resistance.

The upper limit of Tm is preferably 170°C, more preferably 169°C, still more preferably 168°C, still more preferably 167°C, and particularly preferably 166°C. If Tm is 170° C. or less, it is easier to suppress an increase in cost in terms of production from polypropylene, and it becomes less likely to break during film formation. By blending a nucleating agent into the aforementioned polypropylene resin, the melting temperature can be further increased.

The so-called Tm refers to putting 1 mg to 10 mg of sample into an aluminum pot and setting it on a differential scanning thermal analyzer (DSC). It is melted at 230°C for 5 minutes in a nitrogen atmosphere and cooled down at a scanning speed of -10°C/min. The main peak temperature of the endothermic peak accompanying melting was observed after reaching 30°C for 5 minutes and then increasing the temperature at a scanning speed of 10°C/min.

(Crystallization temperature)

The lower limit of the crystallization temperature (Tc) of the polypropylene resin constituting the biaxially aligned polypropylene film of the present invention measured by DSC is 105°C, preferably 108°C, and more preferably 110°C. If Tc is above 105°C, crystallization is easy to proceed during the widthwise stretching and the subsequent cooling step, and rigidity and high-temperature heat resistance are easy to obtain.

The upper limit of Tc is preferably 135°C, more preferably 133°C, more preferably 132°C, further preferably 130°C, particularly preferably 128°C, and most preferably 127°C. If Tc is below 135°C, the cost of polypropylene manufacturing is not likely to increase, and it is less likely to break during film making.

The so-called Tc refers to the heat release observed when a sample of 1 mg to 10 mg is put into an aluminum pot and set in a DSC, melted at 230°C for 5 minutes in a nitrogen atmosphere, and cooled to 30°C at a scanning speed of -10°C/min. The main peak temperature of the peak.

By adding a nucleating agent to the aforementioned polypropylene resin, the crystallization temperature can be further increased.

(Melt flow rate)

The melt flow rate (MFR; melt mass-flow rate) of the polypropylene resin constituting the biaxially aligned polypropylene film of the present invention is under the conditions M (230°C, 2.16kgf) is measured, preferably 4.0g/10min to 30g/10min, more preferably 4.5g/10min to 25g/10min, still more preferably 4.8g/10min to 22g/ 10 points, the best range is 5.0g/10 points to 20g/10 points, the best range is 6.0g/10 points to 20g/10 points.

If the melt flow rate (MFR) of the polypropylene resin is 4.0 g/10 minutes or more, a biaxially aligned polypropylene film with low thermal shrinkage can be easily obtained.

In addition, when the melt flow rate (MFR) of the polypropylene resin is 30 g/10 minutes or less, film forming properties of the film can be easily maintained.

From the viewpoint of film properties, the lower limit of the melt flow rate (MFR) (230°C, 2.16kgf) of the polypropylene resin constituting the film is preferably 5.0g/10min, more preferably 5.5g/10min, and The best is 6.0g/10min, the best is 6.3g/10min, and the best is 6.5g/10min.

If the melt flow rate (MFR) of the polypropylene resin is 5.0 g/10 minutes or more, the amount of low molecular weight components of the polypropylene resin constituting the film increases. Therefore, by adopting the width direction stretching step in the film forming step described below, , in addition to promoting the orientation crystallization of polypropylene resin, and making it easier to increase the crystallinity of the film, the polypropylene molecular chains in the amorphous part become less entangled with each other, and it is easier to improve the heat resistance.

In order to set the melt flow rate (MFR) of the polypropylene resin within the above range, it is preferable to adopt a method of controlling the average molecular weight or molecular weight distribution of the polypropylene resin.

That is, the lower limit of the amount of components with a molecular weight of less than 100,000 in the GPC (Gel Permeation Chromatography) integral curve of the polypropylene resin constituting the membrane of the present invention is preferably 35% by mass, more preferably 38% by mass, still more preferably 40% by mass, particularly preferably 41% by mass, and most preferably 42% by mass.

The upper limit of the amount of components with a molecular weight of less than 100,000 in the GPC integral curve is preferably 65% by mass, more preferably 60% by mass, and even more preferably 58% by mass. If the amount of components with a molecular weight of less than 100,000 in the GPC integral curve is less than 65% by mass, the membrane strength is not easily reduced.

At this time, if a high molecular weight component or a long chain branch component with a long relaxation time is contained, the amount of components with a molecular weight of less than 100,000 contained in the polypropylene resin can be easily adjusted without significantly changing the overall viscosity of the polypropylene resin. Therefore, it does not have a significant impact on rigidity or thermal shrinkage and is easy to improve film-forming properties.

(The molecular weight distribution)

For the polypropylene resin used in the present invention, the lower limit of the mass average molecular weight (Mw)/number average molecular weight (Mn), which is an indicator of the breadth of the molecular weight distribution, is preferably 3.5, more preferably 4.0, still more preferably 4.5, and particularly preferably 5.0. The upper limit of Mw/Mn is preferably 30, more preferably 25, still more preferably 23, particularly preferably 21, and most preferably 20.

The Mw/Mn system can be obtained using gel permeation chromatography (GPC). When Mw/Mn is in the above range, the amount of components with a molecular weight of 100,000 or less is likely to increase.

In addition, the molecular weight distribution of polypropylene resin can be adjusted by the following methods: polymerizing components with different molecular weights in multiple stages using a series of equipment; blending components with different molecular weights off-line using a kneader ;Polymerization by blending catalysts with different properties;Using a catalyst that can achieve the desired molecular weight distribution. As for the shape of the molecular weight distribution obtained by GPC, in a GPC chart in which the logarithm (logM) of the molecular weight (M) is taken as the horizontal axis and the differential distribution value (weight fraction in logM) is taken as the vertical axis, it can be a single peak. A gentle molecular weight distribution can also be a molecular weight distribution with multiple peaks or shoulders.

(Film production method of biaxially aligned polypropylene film)

The biaxially oriented polypropylene film of the present invention is preferably obtained by the following method: an unstretched sheet composed of a polypropylene resin composition having the above-mentioned polypropylene resin as the main component is prepared and biaxially stretched. As a method of biaxial stretching, it can be obtained by any one of a blow molding synchronous biaxial stretching method, a tenter synchronous biaxial stretching method, and a tenter stepwise biaxial stretching method, but from the perspective of film making stability and thickness uniformity, it is better to use a tenter stepwise biaxial stretching method. It is particularly preferred to stretch in the width direction after stretching in the length direction, but it can also be a method of stretching in the length direction after stretching in the width direction.

Next, the manufacturing method of the biaxially oriented polypropylene film of the present invention is described below, but it is not limited to this. In addition, the biaxially oriented polypropylene film of the present invention can also have a layer with other functions laminated on at least one side. The lamination can be on one side or on both sides. At this time, the resin composition of the other layer and the other central layer can also adopt the above-mentioned polypropylene resin composition. In addition, it can also be a resin composition different from the above-mentioned polypropylene resin composition.

The number of laminated layers on each single side may be 1 layer, 2 layers, or 3 or more layers, but from a manufacturing point of view, 1 layer or 2 layers is preferred. As a lamination method, co-extrusion by a feed block system or a multi-manifold system is preferred. In particular, when the purpose is to improve the processability of the biaxially aligned polypropylene film, a resin layer having heat sealability can be laminated within a range that does not reduce the characteristics. In addition, in order to impart printability, corona treatment can be applied to one or both sides.

The following describes the case where a tenter frame is used for the step-by-step biaxial stretching method as an example of a single layer.

First, the resin composition containing polypropylene resin is heated and melted by a single-axis or double-axis extruder, and extruded into a sheet through a T-type die, which is then contacted with a cooling roller and cooled to solidify. In order to promote solidification, it is better to immerse the sheet cooled by the cooling roller in a water tank, etc., and then cool it.

Then, the sheet is stretched in the length direction by two pairs of heated stretching rollers, and the rotation number of the rear stretching roller is increased to obtain a uniaxially stretched film.

Then, after preheating the uniaxially stretched film, the ends of the film are held with a tenter-type stretching machine and stretched in the width direction at a specific temperature to obtain a biaxially stretched film. This width direction extending step will be described in detail later.

After the width direction stretching step is completed, the biaxially stretched film is heat treated at a specific temperature to obtain a biaxially aligned film. During the heat treatment step, the film can also be relaxed in the width direction.

The biaxially oriented polypropylene film thus obtained can be wound up by a winder to obtain a film roll, for example, after being subjected to a corona discharge treatment on at least one side as required.

The following is a detailed description of each step.

(Extrusion step)

First, a polypropylene resin composition with polypropylene resin as the main component is heated and melted in a range of 200°C to 300°C by a single-axis or double-axis extruder, and the molten polypropylene resin composition is extruded in a sheet form from a T-die, and is brought into contact with a metal cooling roller and cooled to solidify. The obtained unstretched sheet is preferably then put into a water tank.

The temperature of the cooling roller, or the cooling roller and the water tank, is preferably in the range of 10°C to Tc. If the transparency of the film is to be improved, it is preferable to use a cooling roller with a temperature in the range of 10°C to 50°C for cooling and solidification. . If the cooling temperature is 50°C or lower, the transparency of the unstretched sheet will tend to increase. It is preferably 40°C or lower, and more preferably 30°C or lower. In order to increase the degree of crystal orientation after step-by-step biaxial stretching, it is sometimes preferable to set the cooling temperature to 40°C or higher. In the case of , it is preferable to set the cooling temperature to 40°C or less to facilitate stretching in subsequent steps and to reduce thickness unevenness, and more preferably to set it to 30°C or less.

The thickness of the unstretched sheet is preferably 3500 μm or less in terms of cooling efficiency, and more preferably 3000 μm or less. It can be appropriately adjusted according to the film thickness after gradual biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition and the lip width of the T-die.

(Lengthwise extension step)

The lower limit of the stretching ratio in the length direction is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. If it is within the above range, it is easy to improve the strength and reduce the unevenness of the film thickness. The upper limit of the stretching ratio in the length direction is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. If it is within the above range, the width direction stretching in the width direction stretching step is easy and the productivity is improved.

The lower limit of the longitudinal stretching temperature is preferably Tm-40℃, more preferably Tm-37℃, and more preferably Tm-35℃. If it is within the above range, the subsequent width direction stretching becomes easy and the thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7℃, more preferably Tm-10℃, and more preferably Tm-12℃. If it is within the above range, it is easy to reduce the thermal shrinkage rate, and it is not easy to adhere to the stretching roller and become difficult to stretch, or the surface roughness becomes roughly so that the grade is reduced.

In addition, the longitudinal extension can also be performed using more than 3 pairs of extension rollers, divided into more than 2 stages for extension.

(Preheating step)

Before the width direction stretching step, the uniaxially stretched film stretched in the length direction needs to be heated in the range of Tm to Tm+25°C to soften the polypropylene resin composition. By setting it above Tm, softening proceeds and stretching in the width direction becomes easier. By setting it below Tm+25°C, orientation during transverse stretching proceeds and rigidity becomes easier to show. It is more preferably Tm+2°C to Tm+22°C, and particularly preferably Tm+3°C to Tm+20°C. Here, the highest temperature of the preheating step is regarded as the preheating temperature.

(Width direction extension step)

Among the width direction stretching steps after the preheating step, a preferred method is as follows.

In the width direction stretching step, a section (preliminary section) for stretching at a temperature above Tm-10°C and below the preheating temperature is set. At this time, the beginning of the early period may be a time point when the preheating temperature is reached, or it may be a time point when the temperature is lowered after reaching the preheating temperature and reaches a temperature lower than the preheating temperature.

The lower limit of the temperature in the early period before the width direction stretching step is preferably Tm-9°C, more preferably Tm-8°C, and still more preferably Tm-7°C. If the extension temperature of the previous interval is within this range, it will not easily occur. Uneven extension.

Following the early stage, the temperature is set lower than that of the early stage and the temperature is extended from above Tm-70℃ to below Tm-5℃ (late stage).

The upper limit of the extension temperature in the later period is preferably Tm-8°C, more preferably Tm-10°C. If the extension temperature of the later period is within this range, it becomes easier to express rigidity.

The lower limit of the extension temperature in the later period is preferably Tm-65°C, more preferably Tm-60°C, and still more preferably Tm-55°C. If the extension temperature in the later period is within this range, film formation will be easy and stable.

The film can be cooled immediately after the end of the later period, that is, when the final stretching ratio in the width direction is reached. The cooling temperature at this time is preferably set to a temperature below the temperature in the later period and a temperature between Tm-80°C and above Tm-15°C, and more preferably a temperature between Tm-80°C and below Tm-20°C, and It is more preferable to set it as the temperature from Tm-80 degreeC or more and Tm-30 degreeC or less, and it is especially preferable to set it as the temperature from Tm-70 degreeC or more to Tm-40 degreeC or less.

The temperature in the early interval and the temperature in the later interval may be gradually reduced, or may be reduced in stages or in one stage, or they may each be constant. If the temperature is gradually lowered, the film will be less likely to break and the thickness variation of the film will also be reduced easily. In addition, the thermal shrinkage rate is also easy to reduce, and the whitening of the film is also less, so it is better.

In the widthwise extension step, the temperature can be gradually reduced from the end of the previous interval to the beginning of the later interval, or it can be reduced in stages or in one phase.

The lower limit of the stretching ratio at the end of the early period of the width direction stretching step is preferably 4 times, more preferably 5 times, still more preferably 6 times, and particularly preferably 6.5 times. The upper limit of the extension ratio at the end of the early period is preferably 15 times, more preferably 14 times, and still more preferably 13 times.

The lower limit of the final width direction stretching ratio in the width direction stretching step is preferably 5 times, more preferably 6 times, more preferably 7 times, and most preferably 8 times. If it is 5 times or more, it is easy to improve the rigidity and reduce the unevenness of the film thickness.

The upper limit of the widthwise stretch ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. If it is less than 20 times, the thermal shrinkage rate is likely to be small, and it is not easy to break during stretching.

In this way, by using polypropylene resin with high stereoregularity and high melting point and high crystallinity, and adopting the above-mentioned width direction stretching step, the molecules of the polypropylene resin can be highly aligned in the main alignment direction without extremely increasing the stretching magnification. (In the above-mentioned width direction stretching step, it corresponds to the width direction), so the crystal alignment in the obtained biaxially aligned film is very strong, and crystals with high melting points are easily generated.

In addition, since the orientation of the amorphous part between the crystals is also improved in the main orientation direction (equivalent to the width direction in the above-mentioned width direction extension step), there are many crystals with high melting points around the amorphous part. Therefore, at a temperature lower than the melting point of the crystal, the elongated polypropylene molecules in the amorphous part are not easy to relax and tend to maintain their tension state. Therefore, the biaxial alignment film as a whole can also maintain high rigidity at high temperatures.

In addition, it should be noted that by adopting such a width direction stretching step, the thermal shrinkage rate at a high temperature of 150° C. can be easily reduced. The reason is that there are many crystals with high melting points around the amorphous part, so at temperatures lower than the melting point of the crystals, the elongated polypropylene resin molecules in the amorphous part are not easily relaxed, and the molecules are less entangled with each other.

Further, we should pay attention to the following: by increasing the low molecular weight components of polypropylene resin, it becomes easier to increase the crystallinity of the film, and the molecular chains of polypropylene resin in the amorphous part are less entangled with each other, and by reducing the thermal shrinkage stress, the thermal shrinkage rate can be further reduced. Considering the previous tendency that if one of the strength and thermal shrinkage rate is improved, the other's characteristics will be reduced, this can be regarded as a breakthrough development.

(heat treatment step)

Biaxially stretched film can be heat treated as needed to further reduce thermal shrinkage.

The upper limit of the heat treatment temperature is preferably Tm+10℃, and more preferably Tm+7℃. By setting it below Tm+10℃, it is easy to show rigidity, and the roughness of the film surface will not become too large, and the film will not be easy to whiten.

The lower limit of the heat treatment temperature is preferably Tm-10℃, and more preferably Tm-7℃. If it does not reach Tm-10℃, the thermal shrinkage rate may increase.

By adopting the above-mentioned width direction stretching step, even if the heat treatment is performed at a temperature between Tm-10℃ and Tm+10℃, the highly oriented crystals generated in the stretching step are still not easy to melt, and the thermal shrinkage rate can be further reduced without reducing the rigidity of the obtained film.

When the purpose is to adjust the thermal shrinkage rate, the film can also be relaxed (relaxed) in the width direction during heat treatment. The upper limit of the relaxation rate is preferably 10%. If it is within the above range, the film strength is not easy to decrease and the film thickness change is easy to become small. It is more preferably 8%, more preferably 7%, further preferably 3%, particularly preferably 2%, and the best is 0%.

(film thickness)

The thickness of the biaxially aligned polypropylene film of the present invention is set according to each application. However, in order to obtain the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, more preferably 4 μm, especially 8 μm. Optimum is 10μm. When the film thickness is 2 μm or more, the rigidity of the film is easily obtained. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, still more preferably 60 μm, still more preferably 50 μm, and most preferably 40 μm. When the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion step is less likely to decrease.

The biaxially aligned polypropylene film system of the present invention is usually formed as a roll with a width of 2000 mm to 12000 mm and a length of about 1000 m to 50000 m, and is wound into a film roll shape. It is further slit according to each application and supplied as slitting rollers with a width of 300mm to 2000mm and a length of about 500m to 5000m. The biaxially aligned polypropylene film of the present invention enables longer film rolls.

(Thickness uniformity)

The lower limit of the thickness uniformity of the biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, more preferably 0.5%, and particularly preferably 1%. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, more preferably 15%, particularly preferably 12%, and most preferably 10%. If it is within the above range, it is not easy to produce defects during post-processing such as coating or printing, and it is easy to use for applications requiring precision.

The measurement method is as follows. A test piece of 40 mm in the width direction was cut out from a constant area with stable film physical properties in the length direction of the film, and the film thickness was measured using a film conveying device (product number: A90172) manufactured by MIKURON Measuring Instruments Co., Ltd. and Anritsu Co., Ltd. A continuous measuring device (product name: K-313A wide-range high-sensitivity electronic micrometer) continuously measures the film thickness over 20,000 mm, and calculates the thickness uniformity from the following formula.

Thickness uniformity (%) = [(maximum value of thickness - minimum value of thickness)/average value of thickness] × 100

(membrane properties)

The biaxially aligned polypropylene film system of the present invention is characterized by the following properties. The "length direction" of the biaxially aligned polypropylene film of the present invention here refers to the direction corresponding to the flow direction in the film manufacturing step, and the "width direction" refers to the direction that is perpendicular to the flow direction in the aforementioned film manufacturing step. Turn over the direction. For a polypropylene film with an unknown flow direction in the film manufacturing step, a wide-angle X-ray is incident on the film surface in the vertical direction, and the scattering peak from the (110) plane of the α-type crystal is scanned in the circumferential direction. The diffraction intensity distribution obtained is The direction with the maximum radiation intensity is set as the "length direction", and the direction orthogonal to it is set as the "width direction".

(Half-maximum width of the diffraction peak from aligned crystals)

In the azimuthal dependence of the scattering peak of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray measurement perpendicular to the film surface of the biaxially oriented polypropylene film of the present invention, the upper limit of the half-value width (Wh) of the diffraction peak from the oriented crystal in the width direction of the film is 27°, preferably 26°, more preferably 25°, more preferably 24°, and particularly preferably 23°. If the half-value width (Wh) is 27° or less, the rigidity of the film is easily improved. The lower limit of Wh is preferably 13°, more preferably 14°, and more preferably 15°.

(heat shrinkage rate at 150℃)

The upper limit of the thermal shrinkage rate in the longitudinal direction of the biaxially aligned polypropylene film of the present invention at 150° C. is 10%, preferably 8.0%, and more preferably 7.0%. The upper limit of the thermal shrinkage rate in the width direction at 150°C is 30%, preferably 25%, more preferably 20%. If the heat shrinkage rate in the length direction is 10% or less and the heat shrinkage rate in the width direction is 30% or less, wrinkles will not easily occur during heat sealing, especially if the heat shrinkage rate in the length direction at 150°C is 8.0% or less and 150 The thermal shrinkage rate in the width direction at ℃ is 20% or less, which is preferable because the strain when welding the clip portion to the opening is small. In order to reduce the thermal shrinkage at 150°C, it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less to 35% by mass when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film.

The biaxially oriented polypropylene film of the present invention is better if it has the following characteristics and structures.

(Young’s modulus at 23°C)

The lower limit of the Young's modulus of the biaxially oriented polypropylene film of the present invention in the length direction at 23°C is preferably 2.0 GPa, more preferably 2.1 GPa, more preferably 2.2 GPa, particularly preferably 2.3 GPa, and optimally 2.4 GPa. Above 2.0 GPa, the rigidity is high, so it is easy to maintain the bag shape when making a packaging bag, and it is not easy to cause deformation of the film during processing such as printing. The upper limit of the Young's modulus in the length direction is preferably 4.0 GPa, more preferably 3.8 GPa, more preferably 3.7 GPa, particularly preferably 3.6 GPa, and optimally 3.5 GPa. Below 4.0 GPa, the actual manufacturing is easy, and the balance of the characteristics in the length direction and the width direction is easy to optimize.

The lower limit of the Young's modulus in the width direction at 23° C. of the biaxially aligned polypropylene film of the present invention is preferably 6.0 GPa, more preferably 6.3 GPa, still more preferably 6.5 GPa, particularly preferably 6.7 GPa. Above 6.0 GPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of the Young's modulus in the width direction is preferably 15 GPa, more preferably 13 GPa, and still more preferably 12 GPa. If it is 15 GPa or less, actual manufacturing is easy, and the length direction-width direction The balance of characteristics is easy to optimize.

The Young's modulus can be set within a range by adjusting the stretching ratio or relaxation ratio, or adjusting the temperature during film production.

(Young's modulus at 80℃)

The lower limit of the Young's modulus of the biaxially oriented polypropylene film of the present invention in the longitudinal direction at 80°C is preferably 0.5 GPa, and more preferably 0.7 GPa. When it is above 0.5 GPa, it is not easy to produce printing spacing deviation when transferring high-temperature printing ink. The upper limit of the Young's modulus in the longitudinal direction at 80°C is preferably 3.0 GPa, and more preferably 2.5 GPa. When it is above 3.0 GPa, it is easy to actually manufacture.

The lower limit of the Young's modulus in the width direction at 80° C. is preferably 2.5 GPa, more preferably 2.8 GPa, and still more preferably 3.0 GPa. Above 2.5GPa, printing spacing deviation is less likely to occur when transferring high-temperature printing inks. The upper limit of the Young's modulus in the width direction at 80° C. is preferably 5.0 GPa, more preferably 4.7 GPa, still more preferably 4.5 GPa. If it is 5.0 GPa or less, actual manufacturing will be easy.

The Young's modulus of 80°C can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

(Stress at 5% elongation at 23°C)

The lower limit of the stress (F5) when the biaxially aligned polypropylene film of the present invention is elongated by 5% in the length direction at 23° C. is 40 MPa, preferably 42 MPa, more preferably 43 MPa, still more preferably 44 MPa, and particularly preferably 45 MPa. Above 40 MPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of F5 in the length direction is preferably 70MPa, more preferably 65MPa, still more preferably 62MPa, still more preferably 61MPa, still more preferably 60MPa. Below 70MPa, it is actually easy to manufacture, and the length-width balance is easy to optimize.

The lower limit of F5 in the width direction at 23°C of the biaxially oriented polypropylene film of the present invention is 160MPa, preferably 165MPa, more preferably 168MPa, and even more preferably 170MPa. If it is 160MPa or more, the rigidity is high, so it is easy to maintain the bag shape when making a packaging bag, and it is not easy to cause deformation of the film during processing such as printing. The upper limit of F5 in the width direction is preferably 250MPa, more preferably 245MPa, and even more preferably 240MPa. If it is less than 250MPa, it is easy to actually manufacture and the longitudinal-width balance is easy to optimize.

F5 can be set within the range by adjusting the stretching ratio or relaxation ratio and the temperature during film formation.

(Stress at 5% elongation at 80°C)

The lower limit of the stress (F5) of the biaxially oriented polypropylene film of the present invention when stretched 5% in the longitudinal direction at 80°C is 15MPa, preferably 17MPa, more preferably 19MPa, and more preferably 20MPa. If it is 15MPa or more, the rigidity is high, so it is easy to maintain the bag shape when making a packaging bag, and it is not easy to cause deformation of the film during processing such as printing. The upper limit of F5 at 80°C in the longitudinal direction is preferably 40MPa, more preferably 35MPa, more preferably 30MPa, and particularly preferably 25MPa. If it is less than 40MPa, it is easy to actually manufacture and the length-width balance is easy to optimize.

The lower limit of F5 in the width direction at 80° C. of the biaxially aligned polypropylene film of the present invention is 75 MPa, preferably 80 MPa, more preferably 85 MPa, still more preferably 90 MPa, and particularly preferably 95 MPa. Above 75MPa, the rigidity is high, so it is easy to maintain the shape of the bag when it is made into a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of F5 at 80°C in the width direction is preferably 150MPa, more preferably 140MPa, and still more preferably 130MPa. Below 140MPa, it is actually easy to manufacture, and the length-width balance is easy to optimize.

80℃ F5 can be set within the range by adjusting the stretch ratio or relaxation ratio and the temperature during film formation.

(heat shrinkage rate at 120℃)

The upper limit of the heat shrinkage rate in the length direction at 120°C of the biaxially oriented polypropylene film of the present invention is preferably 2.0%, more preferably 1.7%, and even more preferably 1.5%. If it is below 2.0%, it is not easy to produce printing spacing deviation when transferring printing ink. The upper limit of the heat shrinkage rate in the width direction at 120°C is 5.0%, preferably 4.5%, and even more preferably 4.0%. If it is below 5.0%, it is not easy to produce wrinkles during heat sealing.

If the thermal shrinkage rate in the length direction at 120°C is less than the thermal shrinkage rate in the width direction at 120°C, printing spacing deviation will be less likely to occur when transferring printing ink. The heat shrinkage rate at 120°C and the length-width direction balance of the heat shrinkage rate can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

If the thermal shrinkage rate in the length direction at 120°C is less than the thermal shrinkage rate in the width direction at 120°C, printing spacing deviation will be less likely to occur when transferring printing ink. The heat shrinkage rate at 120°C and the length-width direction balance of the heat shrinkage rate can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

(Refractive Index)

The lower limit of the refractive index (Nx) in the length direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4950, more preferably 1.4970, and even more preferably 1.4980. If it is 1.4950 or more, it is easy to increase the rigidity of the film. The upper limit of the refractive index (Nx) in the length direction is preferably 1.5100, more preferably 1.5070, and even more preferably 1.5050. If it is 1.5100 or less, the balance of the film's characteristics in the length direction and width direction is excellent.

The lower limit of the refractive index (Ny) in the width direction of the biaxially aligned polypropylene film of the present invention is preferably 1.5230, preferably 1.5235, and more preferably 1.5240. If it is 1.5230 or more, the rigidity of the membrane will tend to increase. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, still more preferably 1.5270. If it is 1.5280 or less, the balance of the film's longitudinal direction-width direction characteristics will be excellent.

The lower limit of the refractive index (Nz) in the thickness direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4960, more preferably 1.4965, and even more preferably 1.4970. If it is 1.4960 or more, it is easy to increase the rigidity of the film. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and even more preferably 1.5010. If it is 1.5020 or less, it is easy to improve the heat resistance of the film.

The refractive index can be set within a range by adjusting the stretching ratio, stretching temperature, and thermal fixation temperature.

(△Ny)

The lower limit of ΔNy of the biaxially aligned polypropylene film of the present invention is 0.0220, preferably 0.0225, more preferably 0.0228, and still more preferably 0.0230. If it is 0.0220 or more, the rigidity of the film will tend to become high. The actual upper limit of ΔNy is preferably 0.0270, more preferably 0.0265, still more preferably 0.0262, particularly preferably 0.0260. If it is 0.0270 or less, thickness unevenness will be easily improved. △Ny can be set within a range by adjusting the stretch ratio, stretch temperature, and heat fixing temperature of the film.

△Ny is calculated by the following formula by setting the refractive index along the length direction, width direction, and thickness direction of the film to Nx, Ny, and Nz respectively. It refers to the overall alignment of the film in the length direction, width direction, and thickness direction. The degree of alignment in the width direction.

△Ny=Ny-[(Nx+Nz)/2]

(Surface orientation coefficient)

The lower limit of the plane orientation coefficient (△P) of the biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and even more preferably 0.0140. If it is 0.0135 or more, the balance of the plane direction of the film is good, and the thickness unevenness is also improved. The actual value of the upper limit of the plane orientation coefficient (△P) is preferably 0.0155, more preferably 0.0152, and even more preferably 0.0150. If it is 0.0155 or less, the heat resistance at high temperature is excellent. The plane orientation coefficient (△P) can be set within a range by adjusting the stretching ratio, stretching temperature, and thermal fixing temperature. In addition, the plane orientation coefficient (△P) is calculated using (formula) [(Nx+Ny)/2]-Nz.

(X-ray orientation)

The lower limit of the X-ray alignment degree calculated from Wh of the biaxially aligned polypropylene film of the present invention according to the following formula is preferably 0.85, more preferably 0.855, and still more preferably 0.861. Rigidity can be easily improved by setting it to 0.85 or more.

X-ray orientation = (180-Wh)/180

The upper limit of the X-ray orientation is preferably 0.928, more preferably 0.922, and even more preferably 0.917. By setting it to 0.928 or less, film formation is easy and stable.

(Fog)

The upper limit of the haze of the biaxially aligned polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, further preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. If it is 5.0% or less, it can be easily used for applications requiring transparency. The actual lower limit of the haze is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, particularly preferably 0.4%. If it is 0.1% or more, it will be easy to manufacture. The haze system can be adjusted by adjusting the cooling roll (CR) temperature, width direction extension temperature, tenter preheating temperature before width direction extension, width direction extension temperature, or heat fixing temperature, or the molecular weight of the polypropylene resin is 100,000 If the amount of the following components is within the range, the haze may become larger due to the addition of an anti-adhesion agent or the provision of a sealing layer.

(Practical properties of membrane)

The practical characteristics of the biaxially aligned polypropylene film of the present invention will be described.

(tensile breaking strength)

The lower limit of the tensile breaking strength in the longitudinal direction of the biaxially aligned polypropylene film of the present invention is preferably 90 MPa, more preferably 95 MPa, and still more preferably 100 MPa. If it is 90 MPa or more, printing pitch deviation will not easily occur when transferring printing ink, and the durability of the packaging bag will also be excellent. As an actual upper limit of the tensile breaking strength in the longitudinal direction, 200 MPa is preferable, 190 MPa is more preferable, and 180 MPa is still more preferable. If it is 200 MPa or less, film breakage and packaging bag breakage are likely to be reduced.

The lower limit of the tensile strength in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 320 MPa, more preferably 340 MPa, and more preferably 350 MPa. If it is 320 MPa or more, it is not easy to produce printing spacing deviation when transferring printing ink, and the durability of the packaging bag is also excellent. The actual upper limit of the tensile strength in the width direction is preferably 500 MPa, more preferably 480 MPa, and more preferably 470 MPa. If it is 500 MPa or less, the film rupture or the bag breakage of the packaging bag is easily reduced.

The tensile breaking strength can be set within a range by adjusting the extension ratio, extension temperature, and heat fixing temperature.

(Tensile elongation at break)

The lower limit of the tensile elongation at break in the length direction of the biaxially oriented polypropylene film of the present invention is preferably 50%, more preferably 55%, and even more preferably 60%. If it is above 50%, the film breakage or bag breakage of the packaging bag is easily reduced. The actual upper limit of the tensile elongation at break in the length direction is preferably 230%, more preferably 220%, and even more preferably 210%. If it is below 230%, it is not easy to produce printing spacing deviation when transferring printing ink, and the durability of the packaging bag is also excellent.

The lower limit of the tensile elongation at break in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 10%, more preferably 15%, and even more preferably 17%. If it is above 10%, the film breakage or the bag breakage of the packaging bag is easily reduced. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and even more preferably 50%. If it is below 60%, it is not easy to produce printing spacing deviation when transferring printing ink, and the durability of the packaging bag is also excellent. The tensile elongation at break can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

(Bending stiffness)

The lower limit of the bending stiffness in the longitudinal direction at 23°C of the biaxially aligned polypropylene film of the present invention is preferably 0.3mN‧cm, more preferably 0.33mN‧cm, and still more preferably 0.35mN‧cm. If it is 0.3mN‧cm or more, the film can be thinned and suitable for applications that require rigidity. The lower limit of the bending stiffness in the width direction is preferably 0.5mN‧cm, more preferably 0.55mN‧cm, and still more preferably 0.6mN‧cm. If it is 0.5mN‧cm or more, the film can be thinned and suitable for applications that require rigidity.

(ring stiffness stress)

Regarding the lower limit of the ring stiffness stress S (mN) in the longitudinal direction at 23° C. of the biaxially aligned polypropylene film of the present invention, if the thickness of the biaxially aligned polypropylene film is t (μm), it is preferably 0.00020× t ³ , more preferably 0.00025×t ³ , more preferably 0.00030×t ³ , particularly preferably 0.00035×t ³ . If it is 0.00020×t ³ or more, the shape of the package can be easily maintained.

The upper limit of the hoop rigidity stress S (mN) in the longitudinal direction at 23°C is preferably 0.00080×t ³ , more preferably 0.00075×t ³ , further preferably 0.00072×t ³ , and particularly preferably 0.00070×t ³ . If it is 0.00080×t ³ or less, it is practically easy to manufacture.

Regarding the lower limit of the ring stiffness stress S (mN) in the width direction at 23° C. of the biaxially aligned polypropylene film of the present invention, if the thickness of the biaxially aligned polypropylene film is t (μm), it is preferably 0.0010× t ³ is preferably 0.0011×t ³ , further preferably 0.0012×t ³ , and particularly preferably 0.0013×t ³ . If it is 0.0010×t ³ or more, the shape of the package can be easily maintained.

The upper limit of the hoop rigidity stress S (mN) in the width direction at 23°C is preferably 0.0020×t ³ , more preferably 0.0019×t ³ , further preferably 0.0018×t ³ , and particularly preferably 0.0017×t ³ . If it is 0.0020×t ³ or less, it is practically easy to manufacture.

Hoop stiffness stress is an indicator of the stiffness of the film, which depends on the thickness of the film. The measurement method is as follows. Cut out two strips of 110 mm x 25.4 mm, with the length direction of the film as the long axis of the strip (hoop direction) or with the width direction of the film as the long axis of the strip (hoop direction). Clamp these strips with clamps, and make a measurement ring with one side of the film as the inner surface of the ring, and a measurement ring with the opposite side as the inner surface of the ring, in such a way that the long axis of the strip becomes the length direction of the film or the width direction. The ring used for measuring the film length direction is set with the long axis of the strip as the width direction perpendicular to the clamp part of the ring stiffness tester DA manufactured by Toyo Seiki Co., Ltd., and the clamp is loosened to measure the ring stiffness stress with a clamp interval of 50mm, a pressing depth of 15mm, and a compression speed of 3.3mm/second.

The measurement is to measure the ring stiffness stress and thickness 5 times for one side of the film as the inner surface of the ring, and then measure the ring stiffness stress and thickness 5 times for the other side as the inner surface of the ring. The data of the total of 10 times are plotted with the cube of the thickness (μm) of each test piece as the horizontal axis and the ring stiffness stress (mN) as the vertical axis, and the slope a is approximated with a straight line with an intercept of 0. The slope a represents the inherent characteristic value of the film that is not dependent on the thickness that determines the stiffness. The slope a is set as the evaluation value of stiffness. The measurement ring with the long axis of the strip as the width direction of the film is also measured in the same way.

(Wrinkles during heat sealing)

In order to form a bag for packaging food, the finished bag is filled with contents, and the film is heated to melt and fuse to seal. In addition, when making bags while filling food, the same process is usually performed in the same manner. Usually, a sealant film composed of polyethylene or polypropylene is laminated on a base film, and the surfaces of the sealant films are fused together. The heating method is to apply pressure from the base film side with a heating plate to press the film for sealing. The sealing width is usually set to about 10mm. The base film is also heated at this time, so the shrinkage at this time will cause wrinkles. In terms of durability of the bag, the fewer wrinkles the better, and in order to increase purchase intention, the fewer wrinkles the better. Although the sealing temperature may be around 120°C, in order to increase the bag making processing speed, a higher sealing temperature is required. In this case, it is also preferable to have small shrinkage. When the zipper is fused to the opening of the bag, high-temperature sealing is required.

(Printing spacing deviation)

The basic structure of a packaging film usually consists of a laminated film of a printed base film and a sealant film. Bags are manufactured using bag making machines, including three-sided bags, stand-up bags, side seal bags, etc. Various bag making machines are used. Printing pitch deviation is considered to be caused by expansion and contraction of the base material of the film due to the application of tension or heat to the film during the printing step. Excluding defective products caused by printing pitch deviation is also important in terms of efficient use of resources and in order to increase purchase intention.

(Membrane processing)

The printing of the biaxially oriented polypropylene film of the present invention can be carried out by letterpress printing, lithography, gravure printing, stencil printing, or transfer printing, depending on the application.

In addition, unstretched sheets composed of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester, as well as uniaxially stretched films and biaxially stretched films can be used as sealant films. It can also be used as a laminate that has been given heat sealability. In order to further improve the gas barrier properties or heat resistance, unstretched sheets, uniaxially stretched films, and biaxially stretched films composed of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol can be used as the An intermediate layer is provided between the biaxially oriented polypropylene film and the sealant film. The sealant film can be bonded using an adhesive applied by dry lamination or hot melt lamination.

In order to improve the gas barrier properties, aluminum or inorganic oxide can be evaporated and processed into a biaxially aligned polypropylene film, an interlayer film, or a sealant film. The evaporation method can be vacuum evaporation, sputtering, or ion plating. Vacuum evaporation of silicon dioxide, alumina, or a mixture of these is particularly preferred.

The biaxially oriented polypropylene film of the present invention, for example, allows the presence of antifogging agents such as fatty acid esters of polyols, amines of higher fatty acids, amides of higher fatty acids, ethylene oxide adducts of amines or amides of higher fatty acids in the film to be set in the range of 0.2 mass % to 5 mass %, thereby being suitable for packaging fresh products composed of plants such as vegetables, fruits, and flowers that require high freshness.

In addition, various additives may be blended in order to improve qualities such as sliding properties and antistatic properties within the scope that does not impair the effects of the present invention. For example, lubricants such as waxes and metal soaps, plasticizers, and processing aids may be blended to improve productivity. Or heat stabilizers, antioxidants, antistatic agents, UV absorbers, etc.

[Industrial Availability]

The biaxially aligned polypropylene film system of the present invention has excellent characteristics that have not been seen in the past as mentioned above, so it can be preferably used for packaging bags. In addition, the thickness of the film can be thinner than before.

It is further suitable for the following applications: insulating films for condensers and motors, backsheets for solar cells, barrier films for inorganic oxides, ITO (Indium Tin Oxide; indium tin oxide), etc. The base film of the transparent conductive film is used for high-temperature applications; or the separation film is used for applications requiring rigidity. In addition, it is possible to perform coating or printing processing at high temperatures using coating agents, inks, lamination adhesives, etc. that have been difficult to use in the past, and it is expected that production efficiency will be improved.

[Implementation example]

The present invention will be described in detail below through examples. In addition, the characteristics were measured and evaluated by the following methods.

(1) Melt flow rate

Melt flow rate (MFR) is measured in accordance with JIS K 7210 at a temperature of 230°C and a load of 2.16 kgf.

(2)Meso quintuple component ratio

The meso pentad fraction ([mmmm]%) of polypropylene resin was measured by ¹³ C-NMR. The meso pentad fraction was calculated according to the method described in Macromolecules, Volume 6, Page 925 (1973) by Zambelli et al. ¹³ C-NMR measurement was performed using AVANCE500 manufactured by BRUKER, with 200 mg of the sample dissolved in a mixture of o-dichlorobenzene and heavy benzene in a ratio of 8:2 at 135°C and then at 110°C.

(3) Number average molecular weight, weight average molecular weight, amount of components with molecular weight below 100,000, and molecular weight distribution of polypropylene resin

Gel permeation chromatography (GPC) was used, and the molecular weight was determined in terms of PP, using a monodisperse polystyrene standard. When the baseline is unclear, the range up to the lowest position of the foot of the high molecular weight side of the elution peak closest to the high molecular weight side of the elution peak of the standard substance is set as the baseline.

The GPC measurement conditions are as follows.

Device: HLC-8321PC/HT (manufactured by Tosoh Co., Ltd.)

Detector: RI

Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%) Column: TSK gelguard column HHR (30) HT (7.5mm I.D. × 7.5cm) × 1 column + TSK gel GMHHR-H (20) HT (7.8mm I.D. × 30cm) × 3 columns

Flow: 1.0mL/min

Injection volume: 0.3mL

Measuring temperature: 140℃

The number average molecular weight (Mn) and the mass average molecular weight (Mw) are respectively defined by the following formulas based on the number of molecules (N _i ) of the molecular weight (M _i ) at each elution position of the GPC curve obtained using the molecular weight calibration curve.

Number average molecular weight: Mn=Σ(N _i ‧Mi)/ΣN _i

Mass average molecular weight: Mw=Σ(N _i ‧M _i ² )/Σ(N _i ‧M _i )

Here, the molecular weight distribution can be obtained as Mw/Mn.

In addition, the ratio of components with a molecular weight of less than 100,000 was obtained from the integral curve of the molecular weight distribution obtained by GPC.

(4) Crystallization temperature (Tc), melting temperature (Tm)

Thermal measurement was performed in a nitrogen atmosphere using a Q1000 differential scanning thermal analyzer manufactured by TA Instruments. Approximately 5 mg was cut out from polypropylene resin tablets and sealed in an aluminum pot for measurement. After raising the temperature to 230°C and maintaining it for 5 minutes, it was cooled to 30°C at a rate of -10°C/min. The exothermic peak temperature was defined as the crystallization temperature (Tc). In addition, the heat of crystallization (ΔHc) was set so that the exothermic peaks were smoothly connected from the beginning to the end of the peak, and the area of the exothermic peak was determined by setting a baseline. The temperature was maintained at 30° C. for 5 minutes, and the temperature was raised to 230° C. at 10° C./min. The main peak temperature of the endothermic peak was defined as the melting temperature (Tm).

(5)Film thickness

The thickness of the film was measured using Miritoron 1202D manufactured by SEIKO-EM.

(6) Fog

NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. was used, and it was measured in accordance with JISK7105 at 23°C.

(7) X-ray half value width, alignment degree

It measured by the transmission method using an X-ray diffraction device (RINT2500 manufactured by Rigaku Corporation). X-rays with a wavelength of 1.5418Å are used, and the detector uses a scintillation counter. The films were stacked so as to have a thickness of 500 μm to prepare a sample. Place the sample stage at the diffraction peak position of the (110) plane of the α-type crystal of the polypropylene resin (diffraction angle 2θ = 14.1°), rotate the sample 360° with the thickness direction of the film as the axis, and obtain the (110) plane Azimuth dependence of diffraction intensity. From this azimuth angle dependence, the half-maximum width Wh of the diffraction peak from the aligned crystal in the width direction of the film is determined.

In addition, the X-ray alignment degree was calculated from the following equation using Wh.

X-ray alignment degree=(180-Wh)/180

(8)Refractive index, △Ny, plane alignment coefficient

It was measured using an Abbe refractometer manufactured by ATAGO CO., LTD. at a wavelength of 589.3 nm and a temperature of 23°C. Let the refractive index along the length direction and width direction of the film be Nx and Ny respectively, and let the refractive index in the thickness direction be Nz. △Ny is obtained using Nx, Ny, and Nz, and using (formula) Ny-[(Nx+Nz)/2]. In addition, the plane alignment coefficient (ΔP) is calculated using (formula) [(Nx+Ny)/2]-Nz.

(9) Tensile test

The tensile strength of the film in the length direction and width direction was measured at 23°C according to JIS K 7127. The sample was cut from the film into a size of 15mm×200mm, the clamp width was 100mm, and it was set in a tensile tester (Dual Column desktop tester INSTRON 5965 manufactured by Instron Japan Co. Ltd.). The tensile test was carried out at a tensile speed of 200mm/min. From the obtained strain-stress curve, the Young's modulus and the stress at 5% elongation (F5) were obtained from the slope of the straight line part at the initial elongation. The tensile fracture strength and tensile fracture elongation are the strength and elongation at the time point when the sample fractured, respectively.

By measuring in a constant temperature bath at 80°C, the Young's modulus and F5 at 80°C are obtained. In addition, the measurement is performed as follows: a fixture is set in a constant temperature bath pre-set to 80°C, and the fixture is kept for 1 minute after installation until the sample is measured.

(10)Thermal shrinkage rate

The following method is used to measure the film according to JIS Z 1712. The film is cut into 20 mm wide and 200 mm long pieces in the length direction and width direction of the film, and hung in a hot air oven at 120°C or 150°C and heated for 5 minutes. The length after heating is measured, and the heat shrinkage rate is calculated as the ratio of the shrunk length to the original length.

(11) Bending stiffness and sag

According to the JlS L 1096B method (sliding method), the following flow is used to obtain it. Make a test piece of 20 mm x 150 mm, and then load the test piece with a weight so that it protrudes by 50 mm on the testing machine table so that the testing machine body is aligned with the upper surface of the moving table. Then, gently turn the handle to lower the sample table, and measure the amount of sag (δ) at the time when the free end of the sample leaves the sample table. Using this sagging amount δ, the film thickness, the test piece size, and the film density of 0.91 g/cm ³ , the bending stiffness (Br) was determined by the following equation.

Br = WL ⁴ /8δ

Br: bending stiffness (mN‧cm)

W: Gravity per unit area of the test piece (mN/cm ² )

L: length of test piece (cm)

δ: droop (cm)

(12) Ring stiffness stress, stiffness

The length direction of the film is the long axis of the strip (ring direction), or the width direction of the film is the long axis of the strip (ring direction), and 10 strip-shaped test pieces of 110 mm × 25.4 mm are cut out. These films are clamped in clamps, and a measurement ring with one side of the film as the inner surface of the ring and a measurement ring with the opposite side as the inner surface of the ring are made in such a way that the long axis of the strip becomes the length direction of the film or the width direction of the film. The ring used for measurement is set with the long axis of the strip as the length direction of the film, and the width direction is perpendicular to the clamp part of the ring stiffness tester DA manufactured by Toyo Seiki Seisaku-sho Co., Ltd. The clamp is loosened, and the ring stiffness stress is measured with a clamp interval of 50mm, a pressing depth of 15mm, and a compression speed of 3.3mm/second.

The measurement is to measure the ring stiffness stress and thickness 5 times for one side of the film as the inner surface of the ring, and then measure the ring stiffness stress and thickness 5 times for the other side as the inner surface of the ring. Using the data of the total of 10 times, the cube of the thickness (μm) of each test piece is used as the horizontal axis and the ring stiffness stress (mN) is used as the vertical axis to draw a graph, and the slope a is approximated with a straight line with an intercept of 0. The slope a is set as the evaluation value of stiffness. The measurement ring with the long axis of the strip as the width direction of the film is also measured in the same way.

(Example 1)

As the polypropylene resin, a propylene homopolymer PP-1 (Sumitomo Nobrene FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.) with MFR=7.5g/10min, Tc=116.2℃, and Tm=162.5℃ was used. It was extruded into a sheet at 250℃ by a T-die, contacted with a cooling roller at 20℃, and directly put into a water tank at 20℃. After that, it was stretched 4.5 times in the length direction at 145℃ with two pairs of rollers, and then clamped at both ends and led to a hot air oven. After preheating at 170℃, it was stretched 6 times in the width direction at 160℃ as the first stage, and then stretched 1.36 times at 145℃ as the second stage, thereby stretching a total of 8.2 times. After stretching in the width direction, the film was immediately cooled at 100°C while being held in a clamp, and then heat-fixed at 163°C. The thickness of the film obtained in this way was 18.7μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-making conditions. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Example 2)

As the polypropylene resin, 80 parts by weight of PP-1 and 20 parts by weight of propylene homopolymer PP-2 (EL80F5 manufactured by Sumitomo Chemical Co., Ltd.) with MFR=11g/10min, [mmmm]=98.8%, Tc=116.5℃, Tm=161.5℃ were mixed. The same as Example 1 was used except that the stretching temperature in the length direction was set to 142℃, the stretching temperature in the first section in the width direction was set to 162℃, and the heat fixing temperature was set to 165℃. The thickness of the obtained film was 21.3μm. The structure of the polypropylene resin is shown in Table 1, and the film-making conditions are shown in Table 2. Its physical properties are shown in Table 3, and a film with high rigidity and low heat shrinkage at high temperature was obtained.

(Example 3)

The same procedure as Example 2 was followed except that 3% relaxation was applied during heat fixation. The thickness of the obtained film was 21.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film-making conditions. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Implementation Example 4)

The same method as Example 2 was used except that the stretching temperature in the length direction was set to 145°C and the cooling temperature immediately after the stretching in the width direction was set to 140°C. The thickness of the obtained film was 18.9 μm. The structure of the polypropylene resin is shown in Table 1, and the film-making conditions are shown in Table 2. Its physical properties are shown in Table 3, and a film with high rigidity was obtained.

(Example 5)

The same process as Example 2 was performed except that the film was not cooled after stretching in the width direction and was held in a clamp and heat fixed at 165°C. The thickness of the obtained film was 19.5 μm. Table 1 shows the structure of the polypropylene resin and Table 2 shows the film making conditions. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperature was obtained.

(Example 6)

The process was carried out in the same manner as in Example 2, except that the stretching temperature in the second step in the width direction was 155°C. The thickness of the film thus obtained was 20.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. Its physical properties are shown in Table 3. It has high rigidity and high temperature thermal shrinkage. Low membrane.

(Implementation Example 7)

The procedure was carried out in the same manner as in Example 2 except that the longitudinal stretching ratio was set to 4.8 times. The thickness of the film obtained was 19.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperatures was obtained.

(Example 8)

The same method as Example 2 was used except that the stretching ratio of the first stage was set to 6.6 times, the stretching ratio of the second stage was set to 1.5 times, and the total stretching ratio was set to 9.9 times in the width direction. The thickness of the obtained film was 20.1 μm. The structure of the polypropylene resin is shown in Table 1, and the film-making conditions are shown in Table 2. Its physical properties are shown in Table 3, and a film with high rigidity and low thermal shrinkage at high temperature was obtained.

(Comparison Example 1)

PP-1 was used as the polypropylene resin, which was extruded into a sheet at 250°C by a T-die, contacted with a cooling roller at 20°C, and directly placed in a water tank at 20°C. Afterwards, it was stretched 4.5 times in the length direction at 143°C, the preheating temperature during stretching in the width direction of the tenter was set to 170°C, the stretching temperature was set to 158°C for 8.2 times stretching, and then heat-fixed at 168°C. The thickness of the obtained film was 18.6μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-making conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with low rigidity.

(Comparative example 2)

As the polypropylene resin, the same method as in Comparative Example 1 was used except that 80 parts by weight of PP-1 and 20 parts by weight of PP-2 were mixed. The thickness of the obtained film was 20.0 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film making conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with low rigidity.

(Comparison Example 3)

As the polypropylene resin, use MFR=3g/10 minutes, Tc=117.2℃, Tm=160.6 PP-3 (FL203D manufactured by Polypropylene Corporation of Japan) at ℃. It is extruded from a T-die into a sheet at 250°C, contacted with a cooling roller at 20°C, and directly put into a water tank at 20°C. After that, stretch 4.5 times in the length direction at 135°C. During the stretching in the width direction of the tenter, set the preheating temperature to 166°C, set the temperature of the first stretch section to 155°C, and set the temperature of the second stretch section to 155°C. is 139°C, the cooling temperature is set to 95°C, and the heat fixing temperature is set to 158°C. The thickness of the film obtained was 19.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with a high thermal shrinkage rate at high temperatures.

(Comparison Example 4)

As the polypropylene raw material, PP-4 (FS2012 manufactured by Sumitomo Chemical Co., Ltd.) with MFR=2.7g/10min, Tc=114.7℃, Tm=163.0℃ was used. It was extruded into a sheet at 250℃ by a T-die, contacted with a cooling roller at 20℃, and directly put into a water tank at 20℃. After that, it was stretched 4.5 times at 145℃ in the length direction. During the stretching in the width direction of the tenter, the preheating temperature was set to 170℃, the temperature of the first stretching stage was set to 160℃, the temperature of the second stretching stage was set to 145℃, the cooling temperature was set to 100℃, and the heat fixing temperature was set to 163℃. The thickness of the obtained film was 21.2μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film making conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with high thermal shrinkage rate at high temperature.

(Comparative example 5)

As the polypropylene resin, PP-4 was used. It was extruded into a sheet at 250°C by a T-die, contacted with a cooling roller at 20°C, and directly placed in a water tank at 20°C. After that, it was stretched 5.8 times in the length direction at 130°C, and then the film was heated by setting the preheating temperature at 167°C in the tenter, and then stretched 8.6 times in the width direction at a stretching temperature of 161°C, and then heat-fixed at 130°C while applying a relaxation of 10%, and then heat-fixed in the second stage at 140°C. The thickness of the obtained film was 13.4μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film-making conditions, and Table 3 shows the physical properties. Its physical properties are shown in Table 3, and it is a film with a high thermal shrinkage rate at high temperature.

without.

Claims (7)

A biaxially aligned polypropylene film is composed of a polypropylene resin composition. The polypropylene resin composition contains more than 90 mass% of polypropylene resin, and the meso five-element component rate of the polypropylene resin is 97.0%. Above and below 99.9%, the melt flow rate is above 4.0g/10min and below 30g/10min, based on the azimuth angle dependence of the (110) plane of the polypropylene α-type crystal obtained by wide-angle X-ray diffraction measurement Among them, the half-width of the peak from the aligned crystal in the width direction is 27° or less, the stress at 5% elongation at 80°C is more than 15MPa in the length direction, and the stress at 5% elongation at 80°C is 75MPa in the width direction. Above, and the thermal shrinkage rate at 150°C is 10% or less in the length direction and 30% or less in the width direction. The biaxially oriented polypropylene film as described in claim 1, wherein the 120°C heat shrinkage rate of the biaxially oriented polypropylene film is less than 2.0% in the length direction and less than 5.0% in the width direction, and the 120°C heat shrinkage rate in the length direction is less than the 120°C heat shrinkage rate in the width direction. A biaxially aligned polypropylene film as described in claim 1 or 2, wherein the refractive index Ny in the width direction of the biaxially aligned polypropylene film is greater than 1.5230, and ΔNy is greater than 0.0220. A biaxially oriented polypropylene film as described in claim 1 or 2, wherein the haze of the biaxially oriented polypropylene film is less than 5.0%. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the polypropylene resin constituting the biaxially aligned polypropylene film has a crystallization temperature of 105°C or higher and a melting point of 160°C or higher. The biaxially aligned polypropylene film according to claim 1 or 2, wherein the component amount of the polypropylene resin constituting the biaxially aligned polypropylene film having a molecular weight of 100,000 or less is 35 mass % or more. A biaxially aligned polypropylene film as recited in claim 1 or 2, wherein the degree of alignment of the biaxially aligned polypropylene film is greater than 0.85.