TWI813841B - Manufacturing method of biaxially oriented polypropylene film - Google Patents

Abstract

An object of the present invention is to provide a biaxially aligned polypropylene film that has high rigidity, excellent heat resistance at high temperatures up to 150° C., is easy to maintain the bag shape when used as a packaging bag, and is heat-sealed. The sealing part has fewer wrinkles. The invention is a method for manufacturing a biaxially aligned polypropylene film, which includes the following steps in sequence: extruding a polypropylene resin composition containing a polypropylene resin with a meso five-unit component ratio of more than 97.0% to obtain The steps of unstretched sheet; the step of extending the unstretched sheet in the length direction; the preheating step of heating the lengthwise stretched film to a preheating temperature above Tm and below Tm+25°C; extending the preheated lengthwise direction. The step of stretching the film in the width direction at a temperature between Tm-10°C and above and below the preheating temperature; and at a temperature lower than the step of stretching the film in the width direction at a temperature between Tm-10°C and below the preheating temperature, and It is a step of extending in the width direction at a temperature between Tm-70°C and above and Tm-5°C and below; and a heat treatment step.

Description

Manufacturing method of biaxially aligned polypropylene film

The present invention relates to a method for manufacturing a biaxially aligned polypropylene film with excellent rigidity and heat resistance. Specifically, the invention relates to a method for manufacturing a biaxially aligned polypropylene film that is suitable for use in packaging bags because it is easy to maintain the bag shape and has few wrinkles in the sealing portion when heat-sealed. Used for packaging bags.

Biaxially oriented polypropylene films are used in packaging and industrial applications because they are moisture-proof and have the required rigidity and heat resistance. In recent years, as the uses have expanded, higher performance has been sought, and in particular, improvements in rigidity have been expected. Furthermore, out of concern for the environment, it is also necessary to maintain strength even if the volume is reduced (thinner film thickness). However, because of this, it is indispensable to significantly improve the rigidity. As a means to improve rigidity, it is known that improving the catalyst and process technology during polymerization of polypropylene resin will increase the crystallinity and melting point of the polypropylene resin. However, despite such improvements, it still does not have sufficient rigidity so far. biaxially aligned polypropylene film.

It has been proposed that in the manufacturing process of a biaxially aligned polypropylene film, after extending in the width direction, the first stage of heat treatment is performed while relaxing the film at a temperature below the temperature when extending in the width direction, and the first stage of heat treatment is performed in the second stage. A method of performing heat treatment from a segment temperature to a width direction stretching temperature (for example, refer to Patent Document 1, etc.); or a method of extending in the width direction and then further extending in the length direction (for example, refer to Patent Document 2, etc.). However, although the film described in Patent Document 2 has excellent rigidity, it has It is easy to produce wrinkles in the sealing part and has poor heat resistance. In addition, the film described in Patent Document 1 has low orientation and insufficient rigidity.

[Prior technical literature]

[Patent Document]

[Patent Document 1] International Publication No. WO2016/182003.

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

An object of the present invention is to solve the above-mentioned problems. That is, the present invention relates to a biaxially aligned polypropylene film that is excellent in film rigidity, and also relates to a biaxially aligned polypropylene film that is excellent in film rigidity and heat resistance at high temperatures up to 150°C. Specifically, the present invention is to provide a method for manufacturing a biaxially aligned polypropylene film that is easy to maintain the bag shape when used as a packaging bag and has a sealing portion and the surroundings of the sealing portion when heat-sealed. Few wrinkles.

As a result of intensive research to achieve this object, the inventors of the present invention found that by the following manufacturing method, a biaxially aligned polypropylene film with excellent film rigidity can be obtained, and furthermore, the rigidity of the film can be obtained and the film can be used at high temperatures up to 150°C. Biaxially aligned polypropylene film with excellent heat resistance.

That is to say, the present invention is a method for manufacturing a biaxially aligned polypropylene film, which includes the following steps in sequence: extruding a polypropylene resin composition containing a polypropylene resin with a meso five-unit component ratio of more than 97.0%. The step of obtaining an unstretched piece; the step of extending the unstretched piece in the length direction; The preheating step of heating the lengthwise stretched film to a preheating temperature in the range of Tm to Tm+25°C; stretching the preheated lengthwise stretched film in the width direction at a temperature between Tm-10°C and below the preheating temperature. step; at a temperature lower than the aforementioned step of extending in the width direction at a temperature between Tm-10°C and below the preheating temperature, and extending in the width direction at a temperature between Tm-70°C and below Tm-5°C steps; and, heat treatment steps.

In this case, it is more suitable to perform the step of extending in the width direction at a temperature lower than the aforementioned temperature of Tm-10°C or more and below the preheating temperature, and is between Tm-70°C or more and Tm-5°C. Between the following step of stretching in the width direction at a temperature and the aforementioned heat treatment step, the following step is included: setting the temperature lower than the step of stretching in the width direction at a temperature of Tm-10°C or more and below the preheating temperature. The temperature is lower than the temperature of the step of stretching in the width direction at a temperature of Tm-70°C or higher and Tm-5°C or lower, and is Tm-80°C or higher and Tm-15°C or lower.

In this case, it is more suitable 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 more suitable 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 more suitable 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.

By applying the manufacturing method of the biaxially aligned polypropylene film of the present invention, since the rigidity is high, it is easy to maintain the bag shape when used as a packaging bag. Therefore, a biaxially aligned polypropylene film suitable for packaging bags can be obtained. In addition, due to its high rigidity and excellent heat resistance at high temperatures up to 150°C, it is easy to maintain operation. It is in the bag shape when packaging bags, and since the sealing portion has few wrinkles when heat-sealed, a biaxially oriented polypropylene film suitable for use in packaging bags can be obtained.

In addition, the biaxially aligned polypropylene film also has excellent rigidity and can maintain strength even if the thickness of the film is reduced, and can be suitably used for applications requiring higher rigidity.

Hereinafter, the manufacturing method of the biaxially aligned polypropylene film of the present invention will be described in further detail.

The biaxially aligned polypropylene film obtained by the present invention is composed of a polypropylene resin composition containing polypropylene resin as a main component. In addition, the so-called "main component" means that the proportion of the polypropylene resin in the polypropylene resin composition is 90 mass% or more, more preferably 93 mass% or more, still more preferably 95 mass% or more, and particularly preferably It is more than 97% by mass.

[Polypropylene resin]

As the polypropylene resin used in the present invention, polypropylene homopolymers and copolymers of polypropylene, ethylene and/or α-olefin having 4 or more carbon atoms can be used. Preferably, it is a propylene homopolymer that does not substantially contain ethylene and/or α-olefins with 4 or more carbon atoms. Even if it contains ethylene and/or α-olefin components with 4 or more carbon atoms, it is preferably ethylene and /or the content of the α-olefin component having 4 or more carbon atoms is 1 mol% or less. The upper limit of the component amount is more preferably 0.5 mol%, still more preferably 0.3 mol%, and particularly preferably 0.1 mol%. If it is within the above range, the crystallinity will be easily improved. Examples of the α-olefin component having 4 or more carbon atoms constituting the copolymer include 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 can use two or more different polypropylene homopolymers, copolymers of polypropylene and ethylene and/or α-olefins with 4 or more carbon atoms, and mixtures thereof. things.

[Three-dimensional regularity]

The meso pentad ratio ([mmmm]%), which is an index of the stereoregularity of the polypropylene resin used in the present invention, is preferably in the range of 97.0% to 99.9%, more preferably 97.5% to 99.7 %, 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 97.0% or more, the crystallinity of the polypropylene resin will increase, and the melting point, crystallinity, and crystal orientation of the crystals in the film will increase, making it easier to obtain rigidity and heat resistance at high temperatures. If it is 99.9% or less, it will be easier to suppress costs in terms of polypropylene production, and it will be less likely to break during film production. More preferably, it is 99.5% or less. The meso pentad ratio is measured by the nuclear magnetic resonance method (so-called NMR method).

In order to set the meso pentad ratio of the polypropylene resin within the above range, it is preferable to use a method of washing the obtained polypropylene resin powder with a solvent such as n-heptane, or to catalyze it appropriately. And/or the selection of auxiliary catalysts, the method of selecting the components of the polypropylene resin composition, 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 Calorimeter; differential scanning calorimeter) is preferably 160°C, more preferably 161°C. , more preferably 162°C, still more preferably 163°C. If Tm is 160°C or higher, rigidity and high temperature heat resistance can be easily obtained.

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

The so-called Tm is to put 1 mg to 10 mg of sample into an aluminum plate and install it on a differential scanning calorimeter (DSC). It is melted at 230°C for 5 minutes in a nitrogen atmosphere, and then cooled to 30 at a scanning speed of -10°C/min. ℃ The main peak temperature of the endothermic peak accompanying melting was observed when the temperature was raised for 5 minutes at a scanning speed of 10°C/min.

[Crystallization temperature]

The lower limit of the crystallization temperature (Tc) measured by DSC of the above-mentioned polypropylene resin constituting the biaxially aligned polypropylene film of the present invention is 105°C, preferably 108°C, and more preferably 110°C. If Tc is 105° C. or higher, crystallization is likely to progress in the width direction stretching and subsequent cooling steps, and rigidity and high-temperature heat resistance are easily obtained.

The upper limit of Tc is preferably 135°C, more preferably 133°C, further preferably 132°C, still more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. If Tc is 135° C. or less, the cost of polypropylene production is less likely to increase, and the polypropylene is less likely to break during film formation.

The so-called Tc is one of the exothermic peaks observed when a sample of 1 mg to 10 mg is stuffed into an aluminum pan and mounted on 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. Main peak temperature.

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

[Melt flow rate]

The melt flow rate (MFR) of the polypropylene resin constituting the biaxially aligned polypropylene film of the present invention is preferably measured in accordance with the conditions M (230°C, 2.16kgf) of JIS K 7210 (1995). It is 4.0g/10 minutes to 30g/10 minutes, more preferably 4.5g/10 minutes to 25g/10 minutes, further preferably 4.8g/10 minutes to 22g/10 minutes, particularly preferably 5.0g/10 minutes to 20g/10 minutes, optimally 6.0g/10 minutes to 20g/10 minutes.

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.

Furthermore, if the melt flow rate (MFR) of the polypropylene resin is 30 g/10 minutes or less, maintenance will be easy. Film-holding film-forming properties.

From the viewpoint of film properties, it is preferable to set the lower limit of the melt flow rate (MFR) (230°C, 2.16kgf) of the polypropylene resin constituting the film to preferably 5.0g/10 minutes, more preferably 5.5g/ 10 minutes, more preferably 6.0g/10 minutes, particularly preferably 6.3g/10 minutes, most preferably 6.5g/10 minutes.

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 using the width direction stretching in the film forming step described below, This step will further promote the alignment crystallization of the polypropylene resin, and the crystallinity in the film will become easier to increase. In addition, the polypropylene molecular chains in the amorphous part will become less entangled with each other, making it 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 use a method of controlling the average molecular weight and molecular weight distribution of the polypropylene resin.

That is, the lower limit of the amount of components with a molecular weight of 100,000 or less in the GPC (Gel Permeation Chromatography; gel permeation chromatography) accumulation curve of the polypropylene resin constituting the film of the present invention is preferably 35% by mass, more preferably 38% by mass, more preferably 40% by mass, particularly preferably 41% by mass, and most preferably 42% by mass.

The upper limit of the amount of components with a molecular weight of 100,000 or less in the GPC accumulation curve is preferably 65 mass%, more preferably 60 mass%, and still more preferably 58 mass%. If the amount of components with a molecular weight of 100,000 or less in the GPC accumulation curve is 65% by mass or less, the film strength will not easily decrease.

At this time, if a high molecular weight component or a long chain branch component with a long relaxation time is included, it becomes easy to adjust the amount of components with a molecular weight of 100,000 or less contained in the polypropylene resin without greatly changing the overall viscosity, so it is easy to improve the production process. Film properties without affecting rigidity and heat shrinkage.

[The molecular weight distribution]

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

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

In addition, the molecular weight distribution of polypropylene resin can be achieved by polymerizing components with different molecular weights in a multi-stage series of complete equipment, or by blending components with different molecular weights offline using a mixer, or by blending materials with different properties. Use a catalyst to polymerize, or use a catalyst that can achieve the desired molecular weight distribution. As the shape of the molecular weight distribution obtained by GPC, in a GPC chart with the logarithm (logM) of the molecular weight (M) as the horizontal axis and the differential distribution value (weight fraction per logM) as the vertical axis, a single A molecular weight distribution with a gentle peak may also be a molecular weight distribution with multiple peaks and shoulders.

[Film production method of biaxially oriented polypropylene film]

The manufacturing method of the biaxially aligned polypropylene film of the present invention is preferably obtained by producing an unstretched sheet composed of a polypropylene resin composition containing the above-mentioned polypropylene resin as a main component, and biaxially stretching the sheet. As a biaxial stretching method, any of the blowing simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method, and the tenter sequential biaxial stretching method can be obtained. However, film production stability and thickness uniformity are required. The better point of view is to use the stenter sequential biaxial stretching method. In particular, it is preferable to extend in the length direction and then extend in the width direction. However, it may also be a method of extending in the width direction and then extending in the length direction.

Next, the manufacturing method of the biaxially aligned polypropylene film of the present invention will be described below, but it is not necessarily limited to this manufacturing method. In addition, the biaxially aligned polypropylene film obtained by the present invention can also be layered with layers having other functions on at least a single area. Lamination can be done on one side or two sides. session In this case, it suffices that the resin composition of the other layer or the central layer is the above-mentioned polypropylene resin composition. Moreover, it may be a polypropylene resin composition different from the above-mentioned polypropylene resin composition. The number of laminated layers may be 1 layer, 2 layers, or 3 or more layers per side, but from a manufacturing viewpoint, 1 layer or 2 layers is preferred. As a lamination method, for example, co-extrusion by a feed block system or a multi-manifold system is preferred. In particular, for the purpose of improving the processability of the biaxially aligned polypropylene film, a resin layer having heat sealability can be laminated within a range that does not degrade the properties. In addition, in order to provide printability, corona treatment can also be performed on one side or both sides.

The following is an example for a single layer and is stated for the case where the tenter sequential biaxial stretching method is used.

First, a resin composition containing polypropylene resin is heated and melted using a uniaxial or biaxial extruder, and is extruded into a sheet form from a T-die, and is cooled and solidified by contacting a cooling roll. For the purpose of accelerating solidification, it is preferable to further cool the sheet cooled by a cooling roll by immersing it in a water tank or the like.

Then, using two pairs of stretching rollers that heated the sheet, the sheet was stretched in the longitudinal direction by increasing the rotation number of the rear stretching roller, thereby obtaining a uniaxially stretched film.

Next, the uniaxially stretched film is preheated and then stretched in the width direction at a specific temperature while holding the ends of the film using a tenter-type stretching machine to obtain a biaxially stretched film. This step of extending in the width direction 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. In the heat treatment step, the film may be relaxed in the width direction.

The biaxially aligned polypropylene film thus obtained can be obtained by, for example, subjecting at least one side to corona discharge treatment and then winding it with a winding machine to obtain a film roll, if necessary.

Each step is explained in detail below.

[Extrusion step]

First, a polypropylene resin composition with polypropylene resin as the main component is heated and melted using a uniaxial or biaxial extruder in the range of 200°C to 300°C, and a sheet-like product is extruded from a T-shaped die. The polypropylene resin composition is melted and contacted with a metal cooling roller to cool and solidify. The obtained unstretched piece is preferably further 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. When the transparency of the film is to be improved, it is preferred to cool and solidify with a cooling roller having a temperature in the range of 10°C to 50°C. . If the cooling temperature is 50°C or lower, the transparency of the unstretched sheet will be easily improved, and it is preferably 40°C or lower, and further preferably 30°C or lower. In order to increase the degree of crystal orientation after sequential biaxial stretching, it is sometimes preferable to set the cooling temperature to 40°C or higher. However, as mentioned above, use a propylene homogenate with a meso pentad component ratio of 97.0% or higher. In the case of polymers, it is better to set the cooling temperature to 40°C or less to facilitate the next step of stretching and to reduce thickness unevenness, and to set the cooling temperature to 30°C or less is even more preferred.

The thickness of the unstretched sheet is preferably 3,500 μm or less in terms of cooling efficiency, and is further preferably 3,000 μm or less, which can be appropriately adjusted according to the film thickness after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition, the lip width of the T-shaped die, and the like.

[Lengthwise extension steps]

The lower limit of the longitudinal extension ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. If it is within the above range, the strength can be easily improved and film thickness unevenness can be reduced. The upper limit of the longitudinal extension ratio is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. If it is within the above range, the width direction extension in the width direction extension step can be easily performed, and productivity will be improved.

The lower limit of the longitudinal extension temperature is preferably Tm-40°C, more preferably Tm-37°C, and still more preferably Tm-35°C. If it is within the above range, subsequent stretching in the width direction will become easier, and film thickness unevenness will also be reduced. The upper limit of the longitudinal extension temperature is preferably Tm-7°C, more preferably Tm-10°C, and further preferably Tm-12℃. If it is within the above range, the thermal shrinkage ratio can be easily reduced, and it is unlikely to become difficult to stretch due to adhesion to the stretching roller, or the quality will be reduced due to increased surface roughness.

In addition, three or more pairs of stretching rollers may be used for longitudinal stretching, and the stretching may be divided into two or more stages.

[Preheating step]

Before the step of stretching in the width direction, it is necessary to heat the uniaxially stretched film stretched in the length direction in the range of Tm to Tm+25°C to soften the polypropylene resin composition. By setting it to Tm or more, softening progresses and stretching in the width direction becomes easy. By setting the temperature to Tm+25°C or less, the alignment during lateral stretching progresses, making it easier to exhibit rigidity. More preferably, it is Tm+2°C to Tm+22°C, and particularly preferably, it is Tm+3°C to Tm+20°C. Here, the highest temperature in the preheating step is taken as the preheating temperature.

[Width direction extension procedure]

In the width direction stretching step after the preheating step, a preferable method is as follows.

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

The lower limit of the temperature in the previous section in 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, uneven extension will not easily occur.

Following the early stage section, a section (late stage section) extending at a temperature lower than the early stage section and extending from Tm-70°C or more to Tm-5°C or less is provided.

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 in the later period is within this range, it becomes easier to exhibit 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 is Tm-55℃. If the extension temperature in the later period is within this range, film production will be easier to stabilize.

At the end of the later period, that is, when the final stretching ratio in the width direction is reached, the film can be cooled immediately. The cooling temperature at this time is preferably lower than the temperature in the later period and is a temperature between Tm-80°C and Tm-15°C, and more preferably a temperature between Tm-80°C and Tm-20°C. The temperature below is more preferably Tm-80°C or more and Tm-30°C or less, particularly preferably Tm-70°C or more and Tm-40°C or less.

The temperature in the early period and the temperature in the later period can be gradually lowered, can be lowered in stages or in one step, or can be fixed respectively. If the temperature is gradually lowered, the film is less likely to break and the thickness variation of the film is also likely to be reduced. In addition, the thermal shrinkage rate is also easy to reduce, and the whitening of the film is also less, which is preferable.

In the width direction extending step, the temperature at the end of the previous section can be gradually reduced to the temperature at the start of the later section, or the temperature can be reduced in steps or in one step.

The lower limit of the stretching ratio at the end of the early period before the width direction stretching step is preferably 4 times, more preferably 5 times, further preferably 6 times, and particularly preferably 6.5 times. The upper limit of the stretch 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, further preferably 7 times, and particularly preferably 8 times. If it is 5 times or more, the rigidity will be easily improved and film thickness unevenness will be easily reduced.

The upper limit of the width direction extension ratio is preferably 20 times, more preferably 17 times, and still more preferably 15 times. If it is 20 times or less, the thermal shrinkage rate will be reduced easily and it will be less likely to break during elongation.

In this way, by using a polypropylene resin with high stereoregularity and high melting point and high crystallinity, and using the above-mentioned width direction stretching step, the molecules of the polypropylene resin will be highly aligned even if the stretching magnification is not extremely amplified. In the main alignment direction (the width direction extension step described above is corresponding to (in the width direction), the crystal alignment in the biaxially aligned film obtained is very strong, and crystals with high melting points are easily generated.

In addition, since the alignment of the amorphous portion between crystals is also improved in the main alignment direction (the above-mentioned width direction stretching step corresponds to the width direction), there are many crystals with high melting points around the amorphous portion, so it is lower than the crystalline At a temperature above the melting point, the elongated polypropylene molecules in the amorphous part are not easily relaxed, and it is easy to maintain the tense state of the polypropylene molecules. Therefore, the entire biaxial alignment film can maintain high rigidity even at high temperatures.

Furthermore, it is worth noting that by adopting such a width direction stretching step, the thermal shrinkage rate at a high temperature of 150°C is also easily reduced. The reason for this is that 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 resin molecules in the amorphous part are not easy to relax, and the molecules are less entangled with each other. The reason.

Furthermore, it is worth noting that by increasing the low molecular weight component of polypropylene resin, the crystallinity of the film becomes easier to increase, and the polypropylene resin molecular chains in the amorphous part become less entangled with each other, weakening thermal shrinkage. Stress, whereby the thermal shrinkage rate can be further reduced. Taking into account the conventional wisdom that if one of the strength and thermal shrinkage is increased, the properties of the other will decrease, it can be said that the present invention is epoch-making.

[Heat treatment step]

If necessary, the biaxially stretched film can be heat-treated in order to further reduce the thermal shrinkage rate.

The upper limit of the heat treatment temperature is preferably Tm+10°C, more preferably Tm+7°C. By setting it to Tm+10°C or less, rigidity is easily exhibited, the roughness of the film surface does not become too large, and the film is less likely to whiten.

The lower limit of the heat treatment temperature is preferably Tm-10°C, more preferably Tm-7°C. If the temperature is less than Tm-10°C, the thermal shrinkage rate may become high.

By adopting the above width direction stretching step, even at a temperature from Tm-10°C to Tm+10 By performing heat treatment at a high temperature, the highly aligned crystals generated in the stretching step are less likely to melt, and the thermal shrinkage rate can be further reduced without reducing the rigidity of the film obtained.

In order to adjust the heat shrinkage rate, the film can 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 less likely to decrease and the film thickness variation is likely to be smaller. More preferably, it is 8%, still more preferably, 7%, still more preferably, 3%, particularly preferably, 2%, and most preferably, 0%.

[film thickness]

The thickness of the biaxially aligned polypropylene film obtained by the present invention can be set according to various uses. In terms of obtaining the strength of the film, the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, and even more preferably 4 μm. Preferably, it is 8 μm, and most preferably, it is 10 μm. When the film thickness is 2 μm or more, the rigidity of the film can be easily obtained. The upper limit of the film thickness is preferably 100 μm, more preferably 80 μm, further preferably 60 μm, particularly preferably 50 μm, and most preferably 40 μm. If the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion step is less likely to slow down.

The biaxially aligned polypropylene film obtained by the present invention is usually film-formed using a roll with a width of 2000mm to 12000mm and a length of about 1000m to 50000m, and is wound into a film roll shape. In addition, slitting rollers are supplied to suit each application, with a width of 300mm to 2000mm and a length of about 500m to 5000m. The biaxially aligned polypropylene film of the present invention can obtain longer film rolls.

[Thickness Uniformity]

The lower limit of the thickness uniformity of the biaxially aligned polypropylene film obtained by the present invention is preferably 0%, more preferably 0.1%, further preferably 0.5%, and particularly preferably 1%. The upper limit of thickness uniformity is preferably 20%, more preferably 17%, further preferably 15%, particularly preferably 12%, and most preferably 10%. If it is within the above range, defects are less likely to occur during subsequent processing such as coating or printing, and it is easy to use it in applications requiring precision.

The measurement method is as follows. A test piece with a width of 40 mm was cut out in the length direction of the film from a constant zone where the film physical properties are stable, and a film feeding device manufactured by MIKURON Measuring Instruments Co., Ltd. (manufacturing number: A90172) and ANRITSU Co., Ltd. The film thickness connected by the company A continuous measuring instrument (product name: K-313A wide-range high-sensitivity electronic micrometer) continuously measures the film thickness through 20000mm, and calculates the thickness uniformity from the following formula.

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

[Film characteristics]

The biaxially aligned polypropylene film of the present invention is characterized by the following properties. Here, in the biaxially aligned polypropylene film of the present invention, the so-called "longitudinal direction" corresponds to the direction of flow in the film production step, and the so-called "width direction" is orthogonal to the aforementioned film production step. The direction of flow. For a polypropylene film whose flow direction is unknown in the film manufacturing process, wide-angle X-rays are incident on the film surface in the vertical direction, and the scattering peak originating from the (110) plane of the α-type crystal is scanned in the circumferential direction. The obtained diffraction intensity distribution is The direction with the greatest diffraction intensity is regarded as the "longitudinal direction", and the direction orthogonal to the longitudinal direction is regarded as the "width direction".

[Young’s modulus at 23°C]

The lower limit of the Young's modulus of the biaxially aligned polypropylene film obtained by the present invention in the length direction at 23°C is preferably 2.0GPa, more preferably 2.1GPa, further preferably 2.2GPa, particularly preferably 2.3GPa, The best is 2.4GPa. Above 2.0 GPa, due to its high rigidity, it is easy to maintain the bag shape when used as 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 length direction is preferably 4.0 GPa, more preferably 3.8 GPa, further preferably 3.7 GPa, particularly preferably 3.6 GPa, and most preferably 3.5 GPa. When it is below 4.0 GPa, it is easy to actually produce it, and it is easy to improve the balance of the characteristics in the length direction and the width direction.

The lower limit of the Young's modulus of the biaxially aligned polypropylene film obtained by the present invention in the width direction at 23° C. is preferably 6.0 GPa, more preferably 6.3 GPa, further preferably 6.5 GPa, and particularly preferably 6.7 GPa. Above 6.0 GPa, due to its high rigidity, it is easy to maintain the bag shape when used as a packaging bag, and it is less likely to cause deformation of the film during processing such as printing. The upper limit of Young's modulus in the width direction is preferably 15 GPa, more preferably 13 GPa. Furthermore, 12 GPa is more preferable. If it is 15 GPa or less, it will be easy to actually produce it, and it will be easy to improve the balance of the longitudinal direction-width direction characteristics.

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

[Thermal shrinkage rate at 150℃]

The upper limit of the thermal shrinkage rate in the length direction of the biaxially aligned polypropylene film obtained by the present invention at 150° C. is preferably 10%, more preferably 8.0%, and particularly preferably 7.0%. The upper limit of the thermal shrinkage rate in the width direction at 150° C. is preferably 30%, more preferably 25%, and particularly preferably 20%. If the heat shrinkage rate in the length direction is less than 10% and the heat shrinkage rate in the width direction is less than 30%, wrinkles will not easily occur during heat sealing. Especially if the heat shrinkage rate in the length direction at 150°C is less than 8.0%, it will It is preferable that the thermal shrinkage rate in the width direction at 150°C is 20% or less, so that the strain when welding the clip portion at the opening is small. For the thermal shrinkage rate at 150°C, adjust the stretching ratio, film forming temperature, and relaxation rate, or measure the molecular weight of the polypropylene resin constituting the film by gel permeation chromatography (GPC) accumulation curve to 100,000 or less. It is effective to set the lower limit of the amount of the component to 35% by mass.

It would be better if the biaxially aligned polypropylene film obtained by the present invention has the following characteristics and structure.

[80°C Young’s modulus]

The lower limit of the Young's modulus in the longitudinal direction of the biaxially aligned polypropylene film obtained by the present invention at 80° C. is preferably 0.5 GPa, more preferably 0.7 GPa. When it is 0.5 GPa or more, printing pitch deviation becomes less likely to occur when high-temperature printing ink is transferred. The upper limit of the Young's modulus in the longitudinal direction at 80° C. is preferably 3.0 GPa, more preferably 2.5 GPa. 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. When it is above 2.5GPa, it becomes less likely to cause problems when transferring high-temperature printing ink. Printing spacing deviation. 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, and still more preferably 4.5 GPa. If it is 5.0 GPa or less, it will be easy to actually manufacture.

The Young's modulus at 80° C. can be set within the 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) of the biaxially aligned polypropylene film of the present invention at 5% elongation in the length direction at 23°C is 40MPa, preferably 42MPa, more preferably 43MPa, further preferably 44MPa, and particularly preferably 45MPa. . Above 40 MPa, due to high rigidity, it is easy to maintain the bag shape when used as a packaging bag, and 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, further preferably 62MPa, particularly preferably 61MPa, and most preferably 60MPa. Below 70 MPa, it is easy to actually manufacture and it is easy to improve the length-width balance.

The lower limit of F5 in the width direction of the biaxially aligned polypropylene film of the present invention at 23° C. is 160 MPa, preferably 165 MPa, more preferably 168 MPa, and still more preferably 170 MPa. Above 160MPa, due to its high rigidity, it is easy to maintain the bag shape when used as a packaging bag, and is less likely 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 still more preferably 240MPa. If it is 250 MPa or less, it will be easy to actually manufacture and it will be easy to improve the length-width balance.

F5 can be set within the range by adjusting the stretch ratio and relaxation ratio, or adjusting the temperature during film production.

[Stress at 5% elongation at 80°C]

The lower limit of the stress (F5) of the biaxially aligned polypropylene film of the present invention at 5% elongation in the length direction at 80° C. is 15 MPa, preferably 17 MPa, more preferably 19 MPa, and still more preferably 20 MPa. At 15 MPa or above, due to its high rigidity, it is easy to maintain the bag shape when used as 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 length direction is preferably 40MPa, more preferably 35MPa. The optimum is 30MPa, and the particularly optimum is 25MPa. Below 40 MPa, it is easy to actually manufacture and it is easy to improve the length-width balance.

The lower limit of F5 in the width direction of the biaxially aligned polypropylene film of the present invention at 80°C is 75MPa, preferably 80MPa, more preferably 85MPa, further preferably 90MPa, and particularly preferably 95MPa. Above 75MPa, due to its high rigidity, it is easy to maintain the bag shape when used as a packaging bag, and it is less likely to cause film deformation during printing and other processing. The upper limit of F5 at 80° C. in the width direction is preferably 150 MPa, more preferably 140 MPa, and still more preferably 130 MPa. If it is 140 MPa or less, it will be easy to actually manufacture and it will be easy to improve the length-width balance.

F5 at 80°C can be set within the range by adjusting the stretch ratio and relaxation rate, or adjusting the temperature during film production.

[Thermal shrinkage rate at 120℃]

The upper limit of the thermal shrinkage rate of the biaxially aligned polypropylene film obtained by the present invention in the length direction at 120° C. is preferably 2.0%, more preferably 1.7%, and still more preferably 1.5%. If it is 2.0% or less, printing pitch deviation will be less likely to occur when printing ink is transferred. The upper limit of the thermal shrinkage rate in the width direction at 120° C. is preferably 5.0%, more preferably 4.5%, and still more preferably 4.0%. If it is 5.0% or less, wrinkles will not easily occur during heat sealing.

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

[TMA heating elongation]

The upper limit of the maximum elongation of the biaxially aligned polypropylene film obtained by the present invention in the length direction below 150°C as measured by a thermomechanical analyzer (TMA; Thermomechanical Analyzer) is preferably 1.5 mm, more preferably 1.45 mm. , further preferably 1.4mm, particularly preferably 1.35mm, The best is 1.3mm. If it is within the above range, deformation during heating processing of the roller and printing may be small, and workability may be improved. The lower limit of the maximum elongation in the length direction below 150° C. is preferably 0.5 mm, more preferably 0.6 mm, further preferably 0.7 mm, particularly preferably 0.75 mm, most preferably 0.8 mm. If it is within the above range, actual production may become easier.

The upper limit of the maximum elongation in the width direction below 150° C. is preferably 0.1 mm, more preferably 0.09 mm, further preferably 0.08 mm, particularly preferably 0.075 mm, most preferably 0.07 mm. The lower limit of the maximum elongation in the width direction below 150° C. is preferably 0.005 mm, more preferably 0.01 mm, further preferably 0.015 mm, particularly preferably 0.018 mm, most preferably 0.2 mm. If it is within the above range, the deformation may be smaller and the appearance may be improved.

[Refractive index]

The lower limit of the refractive index (Nx) in the longitudinal direction of the biaxially aligned polypropylene film obtained by the present invention is preferably 1.4950, more preferably 1.4970, and still more preferably 1.4980. If it is 1.4950 or more, it is easy to increase the rigidity of a film. The upper limit of the refractive index (Nx) in the longitudinal direction is preferably 1.5100, more preferably 1.5070, and still more preferably 1.5050. If it is 1.5100 or less, it is easy to achieve an excellent balance between the longitudinal direction-width direction characteristics of the film.

The lower limit of the refractive index (Ny) in the width direction of the biaxially aligned polypropylene film obtained by the present invention is preferably 1.5230, more preferably 1.5235, and still more preferably 1.5240 or more. If it is 1.5230 or more, the rigidity of the film will be easily improved. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, and still more preferably 1.5270. If it is 1.5280 or less, it is easy to achieve an excellent balance between the longitudinal direction-width direction characteristics of the film.

The lower limit of the refractive index (Nz) in the thickness direction of the biaxially aligned polypropylene film obtained by the present invention is preferably 1.4960, more preferably 1.4965, and still more preferably 1.4970. If it is above 1.4960, it will be easy To improve the rigidity of the membrane. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and still more preferably 1.5010. If it is 1.5020 or less, the heat resistance of the film will be easily improved.

The refractive index can be set within a range by adjusting the extension magnification, extension temperature, and heat fixing temperature.

[△Ny]

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

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

△Ny=Ny-[(Nx+Nz)/2]

[Plane alignment coefficient]

The lower limit of the plane alignment coefficient (ΔP) of the biaxially aligned polypropylene film obtained by the present invention is preferably 0.0135, more preferably 0.0138, and still more preferably 0.0140. If it is 0.0135 or more, the balance in the plane direction of the film will be good, and thickness unevenness will also be good. As for the actual numerical value, the upper limit of the plane alignment coefficient (ΔP) is preferably 0.0155, more preferably 0.0152, and still more preferably 0.0150. If it is 0.0155 or less, it is easy to achieve excellent heat resistance at high temperatures. The plane alignment coefficient (ΔP) can be set within a range by adjusting the stretching ratio, stretching temperature, and heat fixing temperature.

In addition, the plane alignment coefficient (ΔP) is calculated using (formula) [(Nx+Ny)/2]-Nz.

[Haze]

The lower limit of the haze of the biaxially aligned polypropylene film obtained by the present invention is relatively low in terms of actual values. The optimum is 0.1%, the more preferred is 0.2%, the further preferred is 0.3%, and the particularly preferred is 0.4%. If it is 0.1% or more, it will be easy to manufacture. The upper limit of the haze 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 is easy to use in applications requiring transparency. Although the haze can be adjusted by adjusting the cooling roll (CR) temperature, width direction extension temperature, preheating temperature before width direction extension of the tenter, width direction extension temperature, or heat fixing temperature, or the molecular weight of the polypropylene resin is 100,000 The amounts of the following components are set within the range, but may become larger due to the addition of an anti-blocking agent and the provision of a sealing layer.

[Half-value width of diffraction peak derived from aligned crystals]

In the biaxially aligned polypropylene film obtained by the present invention, the azimuthal dependence of the scattering peak of the (110) plane of the polypropylene α-type crystal obtained by measuring the wide-angle X-ray incident perpendicularly to the film surface originates from the film's The upper limit of the half-maximum width (Wh) of the diffraction peak of the aligned crystal in the width direction is preferably 27°, more preferably 26°, further preferably 25°, particularly preferably 24°, and most preferably 23°.

The lower limit of Wh is preferably 13°, more preferably 14°, and still more preferably 15°. When the half-value width (Wh) is 27° or less, the rigidity of the film can be easily improved.

[X-ray alignment degree]

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

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

The upper limit of the X-ray alignment degree is preferably 0.928, more preferably 0.922, and still more preferably 0.917. By setting it to 0.928 or less, film formation becomes easier to stabilize.

[Practical properties of membrane]

The practical characteristics of the biaxially aligned polypropylene film obtained by the present invention are explained.

[Tensile breaking strength]

The lower limit of the tensile breaking strength in the longitudinal direction of the biaxially aligned polypropylene film obtained by 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 when transferring the printing ink becomes less likely to occur, and the durability of the packaging bag is likely to be excellent. As for the actual numerical value, the upper limit of the tensile breaking strength in the longitudinal direction is preferably 200 MPa, more preferably 190 MPa, and still more preferably 180 MPa. If it is 200 MPa or less, it is easier to reduce film breakage and packaging bag breakage.

The lower limit of the tensile breaking strength in the width direction of the biaxially aligned polypropylene film obtained by the present invention is preferably 320 MPa, more preferably 340 MPa, and still more preferably 350 MPa. If it is 320 MPa or more, printing pitch deviation when transferring printing ink becomes less likely to occur, and the durability of the packaging bag is likely to be excellent. As for the actual numerical value, the upper limit of the tensile breaking strength in the width direction is preferably 500 MPa, more preferably 480 MPa, and still more preferably 470 MPa. If it is 500MPa or less, it is easier to reduce film breakage and packaging bag breakage.

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 longitudinal direction of the biaxially aligned polypropylene film obtained by the present invention is preferably 50%, more preferably 55%, and still more preferably 60%. If it is more than 50%, it is easy to reduce film breakage and packaging bag breakage. The actual upper limit of the tensile elongation at break in the longitudinal direction is preferably 230%, more preferably 220%, and still more preferably 210%. If it is 230% or less, printing pitch deviation when transferring printing ink becomes less likely to occur, and the durability of the packaging bag is likely to be excellent.

The lower limit of the tensile elongation at break in the width direction of the biaxially aligned polypropylene film obtained by the present invention is preferably 10%, more preferably 15%, and still more preferably 17%. If it is 10% or more, it is easy to reduce the film Broken and broken bags of packaging. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and still more preferably 50%. If it is 60% or less, printing pitch deviation when transferring printing ink becomes less likely to occur, and the durability of the packaging bag is likely to be excellent.

The tensile elongation at break can be set within a range by adjusting the extension ratio, extension temperature, and heat fixing temperature.

[Bending stiffness]

The lower limit of the bending stiffness in the length direction of the biaxially aligned polypropylene film obtained by the present invention at 23°C 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 made thinner and the rigidity will be suitable for the required use. 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 made thinner and the rigidity will be suitable for the required use.

[Ring Stiffness Stress]

The lower limit of the ring stiffness stress S (mN) in the length direction of the biaxially aligned polypropylene film of the present invention at 23°C is preferably 0.00020 × t ³ if the thickness of the biaxially aligned polypropylene film is t (μm). , more preferably 0.00025×t ³ , still more preferably 0.00030×t ³ , and 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 ring stiffness stress S (mN) in the length 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, actual production will be easy.

The lower limit of the ring stiffness stress S (mN) in the width direction of the biaxially aligned polypropylene film of the present invention at 23°C is preferably 0.0010 × t ³ if the thickness of the biaxially aligned polypropylene film is t (μm). , more 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 ring stiffness 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, actual production will be easy.

Although the ring stiffness stress is an index indicating the stiffness of the film, the ring stiffness stress also depends on the thickness of the film. The ring stiffness stress is measured as follows. Using the length direction of the film as the long axis of the strip (circular direction) or the width direction of the film as the long axis of the strip (circular direction), cut out two strips of 110 mm x 25.4 mm respectively. Hold these long strips with a clip, and make a measurement ring in which one side of the film becomes the inner surface of the ring, and the opposite side of the film becomes the inner surface of the ring so that the long axis of the long axis becomes the length direction and width direction of the film. Ring for measuring surface. The long axis of the long strip was used as a ring for measuring the length direction of the film, and the width direction was perpendicular to the clamp part of the LOOP STIFFNESS TESTER DA manufactured by Toyo Seiki Co., Ltd., and the clamp was loosened and the clamp interval was set to 50mm, the pushing depth is set to 15mm, and the compression speed is set to 3.3mm/second to measure the ring stiffness stress.

The measurement was performed by measuring the ring stiffness stress and thickness of the ring with one side of the film forming the inner surface of the ring five times, and then measuring the ring stiffness stress and thickness of the ring with the other surface forming the inner surface of the ring five times. Using the data from a total of 10 times, a graph was drawn with the cubic thickness of each test piece (μm) as the horizontal axis and the ring stiffness stress (mN) as the vertical axis, and was approximated by a straight line with an intercept of 0 , find the slope a. The slope a means a characteristic value inherent to the film that does not vary with the thickness that determines the rigidity. Let the slope a be the evaluation value of stiffness. The long axis of the strip serves as a measurement ring in the width direction of the film and is measured in the same manner.

[Wrinkles during heat sealing]

In order to form a bag for packaging food, the finished bag is filled with contents, heated to melt the film, welded and sealed. Moreover, when making a bag while filling food, it is often done similarly. Usually, a sealant film made of polyethylene, polypropylene, etc. is laminated on a base film, and the surfaces of the sealant films are welded to each other. The heating method is to apply pressure from the base film side with a heating plate to press the film to seal, and the sealing The width is often set to about 10mm. At this time, since the base film is also heated, the shrinkage at this time will cause wrinkles. In terms of the durability of the bag, it is better to have fewer wrinkles, and in order to increase purchase intention, it is also better to have fewer wrinkles. Although the sealing temperature may be around 120°C, in order to increase the bag-making processing speed, a higher sealing temperature is required, and it is preferable that the shrinkage is small even in that case. When the clip chain is welded to the opening of the bag, sealing at a higher temperature is required.

[Printing pitch deviation]

As for the structure of the packaging film, in terms of its basic structure, it is often composed of a laminated film of a printed base film and a sealant film. As far as the manufacturing of bags is concerned, bag making machines are used, including three-side sealing bags, stand-up bags, side-clip bags, etc., and various bag making machines are used. The printing pitch deviation is considered to occur because tension or heat is applied to the film during the printing step, causing the base material of the film to expand and contract. It is important to effectively use resources to avoid defective products caused by printing pitch deviation, and it is also important to increase purchase intention.

[Film processing]

The biaxially aligned polypropylene film obtained by the present invention can be printed by letterpress printing, offset printing, gravure printing, screen printing, or transfer printing according to the purpose.

Furthermore, an unstretched sheet, a uniaxially stretched film, or a biaxially stretched film made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, or polyester can also be used as the sealant film. It is used as a laminate with heat sealability imparted to it. To further improve gas barrier properties or heat resistance, unstretched sheets, uniaxially stretched films, or biaxially stretched films made of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, or polyvinyl alcohol can be used. As an intermediate layer between biaxially oriented polypropylene film and sealant film. For the lamination of the sealant film, an adhesive applied by a dry lamination method or a hot melt lamination method can be used.

In terms of improving gas barrier properties, biaxially oriented polypropylene films and interlayer films, or dense The sealant film is vapor-deposited with aluminum or inorganic oxide. As the evaporation method, vacuum evaporation, sputtering, and ion plating can be used, and vacuum evaporation of silicon dioxide, aluminum oxide, or a mixture thereof is particularly preferred.

For the biaxially aligned polypropylene film obtained by the present invention, for example, by combining fatty acid esters of polyols, amines of higher fatty acids, amides of higher fatty acids, amines of higher fatty acids or amide ethylene oxide The amount of anti-fogging agents such as alkyl adducts present in the film is within the range of 0.2% by mass to 5% by mass, making it suitable for packaging fresh products consisting of vegetables, fruits, flowers and other plants that require high freshness. biaxially aligned polypropylene film.

In addition, as long as the effects of the present invention are not impaired, various additives for improving smoothness, antistatic properties, etc. can also be blended. For example, lubricants such as waxes and metallic soaps can be blended to improve productivity. , plasticizers, processing aids or heat stabilizers, antioxidants, antistatic agents, UV absorbers, etc.

[Industrial Availability]

Since the biaxially aligned polypropylene film obtained by the present invention has excellent characteristics not seen in the past as described above, it can be preferably used in packaging bags, and the thickness of the film can also be made thinner than before.

In addition, it is also suitable for use in high-temperature applications such as insulating films for capacitors and motors, backsheets for solar cells, barrier films of inorganic oxides, and base films of transparent conductive films such as ITO (Indium Tin Oxide). , or separation membranes and other applications that require rigidity. In addition, by using coating agents, inks, lamination adhesives, etc. that have been difficult to use in the past, high-temperature coating or printing processing can be used, and production efficiency can be expected to be improved.

[Example]

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

(1) Melt flow rate

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

(2)Meso pentad component ratio

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

(3) Number average molecular weight, weight average molecular weight, component weight with a molecular weight of less than 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 (Polypropylene; polypropylene) 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.

GPC measurement conditions are as follows.

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

Detector: RI (Refractive Index; refractive index)

Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%)

Column: TSKgelguardcolumnHHR(30)HT(7.5mmI.D.×7.5cm)×1 piece+TSKgelGMHHR-H(20)HT(7.8mmI.D.×30cm)×3 pieces

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 based on the number of molecules (N _i ) of the molecular weight (Mi) of each elution position of the GPC curve obtained through the molecular weight calibration curve and are defined by the following formula.

Number average molecular weight: Mn=Σ(N _i ‧M _i )/ΣNi

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

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

Furthermore, from the integral curve of the molecular weight distribution obtained by GPC, the proportion of components with a molecular weight of 100,000 or less is determined.

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

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

(5)Film thickness

The film thickness was measured using Millitron 1202D manufactured by Seiko EM Corporation.

(6)Haze

It was measured in accordance with JIS K 7105 at 23°C using NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd.

(7) Tensile test

The tensile strength of the film in the length direction and width direction was measured at 23°C in accordance with JIS K 7127. The sample was cut out from the film to a size of 15 mm×200 mm, and was installed in a tensile testing machine (Dual Column desktop testing machine Instron 5965 manufactured by Instron Japan Co. Ltd.) with a clamp width of 100 mm. at stretching speed Conduct tensile test at 200mm/min. From the obtained strain-stress curve and the slope of the straight line from the initial stage of elongation, the Young's modulus and the stress at 5% elongation (F5) are calculated. Tensile breaking strength and tensile breaking elongation are respectively the strength and elongation of the sample at the point of rupture.

By measuring in a constant temperature bath at 80°C, the Young's modulus and F5 at 80°C were obtained. In addition, the measurement was performed by installing the jig in a constant temperature bath preset at 80° C. and holding it for 1 minute from the time of installation until the sample was measured.

(8)Thermal shrinkage rate

It is measured by the following method in accordance with JIS Z 1712. Cut the film into length and width directions of 20 mm and 200 mm, respectively, and hang it in a hot air oven at 120°C or 150°C for 5 minutes. The length after heating is measured, and the thermal shrinkage rate is calculated as the ratio of the shrunk length to the original length.

(9) TMA heating elongation

Heating elongation was performed by TMA measurement using a thermomechanical analysis device TMA-60 manufactured by Shimadzu Corporation. A strip with a length of 20 mm in the longitudinal direction and 4 mm in the width direction was cut out from the film to serve as a sample. The distance between the clamps was set to 10 mm, and the maximum elongation in the temperature range up to 150°C was measured with a measurement load of 40g and a temperature rise of 20°C/min from 30°C to 180°C, which was regarded as the TMA heating elongation.

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

An Abbe refractometer manufactured by ATAGO Co., Ltd. was used and measured 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.

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

It measured by the transmission method using an X-ray diffraction device (RINT2500 manufactured by Rigaku Co., Ltd.). 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 and prepared into 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 (110) Azimuth dependence of the diffraction intensity of the surface. From this azimuth angle dependence, the half-value width Wh of the diffraction peak originating from the aligned crystals in the width direction of the film was determined.

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

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

(12) Bending stiffness and sag

Obtain it by following the following procedure in accordance with JIS L 1096B method (sliding method). Make a test piece of 20 mm x 150 mm and align the testing machine body with the top of the moving table. Place the test piece on the testing machine table with a protrusion of 50 mm and set the weight. Then, gently turn the handle to lower the sample table, and measure the hanging amount (δ) of the free end of the sample when it leaves the sample table. Using this sag amount δ, the film thickness, the test piece size, and the film density of 0.91 g/cm ³ , the bending stiffness (Br) was obtained 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 amount (cm)

(13) Ring stiffness stress, stiffness

Using the longitudinal direction of the film as the long axis of the strip (circular direction) or the width direction of the film as the long axis of the strip (circular direction), 10 strip-shaped test pieces of 110 mm×25.4 mm were cut out. These strip-shaped test pieces are clamped with clips, and the other parts of the film are produced so that the long axis of the strip becomes the length direction and width direction of the film. A measuring ring is one in which one side becomes the inner surface of the ring, and the opposite side to this surface becomes the inner surface of the ring. The long axis of the strip is used as a ring for measuring the length direction of the film, and the width direction is perpendicular to the clamp part of the LOOP STIFFNESS TESTER DA manufactured by Toyo Seiki Seisakusho Co., Ltd., and the clamp is loosened and placed at intervals between the clamps. The ring stiffness stress is measured by setting the pushing depth to 15mm, the pushing depth to 50mm, and the compression speed to 3.3mm/second.

The measurement was performed by measuring the ring stiffness stress and thickness of the ring with one side of the film forming the inner surface of the ring five times, and then measuring the ring stiffness stress and thickness of the ring with the other surface forming the inner surface of the ring five times. Using the data from a total of 10 times, a graph was drawn with the cubic thickness of each test piece (μm) as the horizontal axis and the ring stiffness stress (mN) as the vertical axis, and was approximated by a straight line with an intercept of 0 , find the slope a. Let the slope a be the evaluation value of stiffness. The long axis of the strip serves as a measurement ring in the width direction of the film and is measured in the same manner.

[Example 1]

As the polypropylene resin, propylene homopolymer PP-1 (Sumitomo Noblen FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.) with MFR=7.5g/10 minutes, Tc=116.2°C, and Tm=162.5°C was used. The sheet is extruded from a T-die at 250°C, contacted with a cooling roll at 20°C, and directly put into a water tank at 20°C. Then, extend it 4.5 times in the length direction with two pairs of rollers at 145°C, then clamp both ends with clips, guide it to a hot air oven, preheat at 170°C, and extend it 6 times in the width direction at 160°C. The first step is then extended 1.36 times at 145°C as the second step, and a total extension of 8.2 times is performed. After extending in the width direction, it was cooled at 100°C while being held by a clip, and then heat-set at 163°C. The thickness of the film thus obtained was 18.7 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[Example 2]

As a polypropylene resin, 80 parts by weight of PP-1 and 20 parts by weight of MFR=11g/10 are blended. Minute, [mmmm]=98.8%, Tc=116.5°C, Tm=161.5°C propylene homopolymer PP-2 (EL80F5 manufactured by Sumitomo Chemical Co., Ltd.) was used. The process was carried out in the same manner as in Example 1 except that the stretching temperature in the longitudinal direction was 142°C, the stretching temperature in the first step in the width direction was 162°C, and the heat fixing temperature was 165°C. The thickness of the film obtained was 21.3 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[Example 3]

The procedure was carried out in the same manner as in Example 2 except that 3% relaxation was provided during heat fixation. The thickness of the film obtained was 21.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions.

The physical properties of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[Example 4]

The process was carried out in the same manner as in Example 2 except that the stretching temperature in the longitudinal direction was 145°C and the cooling temperature after stretching in the width direction was 140°C. The thickness of the film obtained was 18.9 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties of this film are as shown in Table 3, and a film with high rigidity was obtained.

[Example 5]

The procedure was carried out in the same manner as in Example 2 except that it was not cooled after stretching in the width direction, but was held by the clip and heat-fixed at 165°C. The thickness of the film obtained was 19.5 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[Example 6]

It was the same as Example 2 except that the stretching temperature of the second step in the width direction was 155°C. conduct. 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. The physical properties of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[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 of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[Example 8]

In the width direction stretching, the same procedure as in Example 2 was performed except that the stretching ratio in the first step was set to 6.6 times and the stretching ratio in the second step was set to 1.5 times, resulting in a total stretching of 9.9 times. The thickness of the film obtained was 20.1 μm. Table 1 shows the structure of the polypropylene resin, and Table 2 shows the film forming conditions. The physical properties of this film are as shown in Table 3. A film with high rigidity and low thermal shrinkage at high temperatures was obtained.

[Comparative example 1]

Use PP-1 as polypropylene resin, extrudate it into a sheet form from a T-die at 250°C, make it contact with a cooling roller at 20°C, and put it directly into a water tank at 20°C. After that, 4.5 times of lengthwise extension was performed at 143°C, the preheating temperature during widthwise extension in the tenter was set to 170°C, and the stretching temperature was set to 158°C to extend 8.2 times, and then at 168°C Perform heat fixation. The thickness of the film obtained was 18.6 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. The physical properties of this film, as shown in Table 3, are low rigidity.

[Comparative example 2]

The same procedure as Comparative Example 1 was performed except that 80 parts by weight of PP-1 and 20 parts by weight of PP-2 were blended as the polypropylene resin. The thickness of the film obtained was 20.0 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. The physical properties of the membrane are the same as As shown in Table 3, the system rigidity is low.

[Comparative example 3]

As the polypropylene resin, PP-3 (FL203D, manufactured by Nippon Polypropylene Co., Ltd.) with MFR=3g/10 minutes, Tc=117.2°C, and Tm=160.6°C was used. The sheet is extruded from a T-die at 250°C, contacted with a cooling roll at 20°C, and directly put into a water tank at 20°C. Thereafter, the length direction was extended 4.5 times at 135°C. During the widthwise extension of the tenter, the preheating temperature was set to 166°C, the temperature of the first stretch step was set to 155°C, and the temperature of the second step was set 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. The physical properties of this film, as shown in Table 3, are that the thermal shrinkage rate at high temperatures is high.

[Comparative example 4]

As the polypropylene resin, PP-4 (manufactured by Sumitomo Chemical Co., Ltd., FS2012) with MFR=2.7g/10 minutes, Tc=114.7°C, and Tm=163.0°C was used. The sheet is extruded from a T-die at 250°C, contacted with a cooling roll at 20°C, and directly put into a water tank at 20°C. After that, after stretching 5.8 times in the length direction at 130°C, the film was heated by setting the preheating temperature to 167°C using a tenter, and then stretched 8.6 times in the width direction at a stretching temperature of 161°C. After that, it was relaxed by 10%. One side is heat-set at 130°C, and then the second step is heat-set at 140°C. The thickness of the film obtained was 13.4 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. The physical properties of this film, as shown in Table 3, are that the thermal shrinkage rate at high temperatures is high.

[Reference example]

As the polypropylene raw material, PP-4 is used. The sheet is extruded from a T-die at 250°C, contacted with a cooling roll at 20°C, and directly put into a water tank at 20°C. After that, extend 4.5 times in the length direction at 145°C. While extending in the width direction of the tenter, set the preheating temperature to 170°C and set the temperature of the first stretch Set it to 160°C, set the temperature of the second stretch step to 145°C, set the cooling temperature to 100°C, and set the heat fixing temperature to 163°C. The thickness of the film obtained was 21.2 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the film forming conditions, and Table 3 shows the physical properties. The physical properties of this film, as shown in Table 3, are that the thermal shrinkage rate at high temperatures is high.

Claims (4)

A method for manufacturing a biaxially aligned polypropylene film, which includes the following steps in sequence: making polypropylene resin with a melt flow rate of more than 4.0g/10 minutes and a meso five-unit component rate of more than 97.0%. The extrusion step of extruding the propylene resin composition to obtain an unstretched sheet; the step of cooling and solidifying at a temperature below 40°C; the lengthwise stretching step of extending the unstretched piece in the lengthwise direction; and heating the lengthwise stretched film to Tm Preheating step to a preheating temperature in the range of Tm+25°C; set the preheating interval before stretching the preheated lengthwise stretched film in the width direction at a temperature between Tm-10°C and below the preheating temperature. The step of extending in the width direction of the previous section before extending in the direction; following the step of extending in the width direction of the previous section, set a temperature lower than the step of extending in the width direction at a temperature above Tm-10°C and below the preheating temperature, and is The post-section is extended in the width direction at a temperature above Tm-70°C to below Tm-5°C, and the post-section is extended in the width direction at a temperature between Tm-70°C and below Tm-5°C; and, from Tm-10°C to Tm+10 The heat treatment step of heat treatment at temperature. The manufacturing method of a biaxially aligned polypropylene film as described in Claim 1, wherein between the aforementioned late section width direction stretching step and the aforementioned heat treatment step, the following cooling step is included: setting the temperature to the aforementioned late section width direction stretching step below the temperature, and becomes above Tm-80℃ and below Tm-15℃. The method for manufacturing a biaxially aligned polypropylene film as described in 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 method for producing a 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% by mass or more.