TWI711539B - Biaxially stretched laminated polypropylene film - Google Patents

Abstract

The present invention provides a biaxially stretched laminated polypropylene film with high rigidity, excellent heat resistance and excellent antistatic properties. The biaxially stretched laminated polypropylene film of the present invention is a laminated film comprising at least two layers of polypropylene resin composition with different crystallinity, and is characterized in that it is measured by using a differential scanning calorimeter at a heating rate of 20°C/min When the melting endothermic peak area is set to △H, it has: A layer, which is composed of polypropylene resin composition with △H of 78.0J/g or more; and B layer, which is composed of △H less than 82.0J/g and It is composed of a polypropylene resin composition with a ΔH that is 2.0 J/g to 40.0 J/g lower than the ΔH of the aforementioned A layer; the aforementioned B layer is present on at least one of the outermost surfaces.

Description

Biaxially stretched laminated polypropylene film

The invention relates to a biaxially stretched laminated polypropylene film. Specifically, the present invention relates to a biaxially stretched polypropylene film having excellent heat resistance, rigidity, and antistatic properties.

Previously, polypropylene stretched films were widely used in a wide range of applications such as packaging for food or various commodities, electrical insulation, and surface protection films. However, the previous polypropylene film has a shrinkage rate of several tens of% at 150°C. Compared with PET (Polyethylene terephthalate; polyethylene terephthalate) film, it has lower heat resistance and lower rigidity. , So its use is limited.

Various techniques for improving the physical properties of polypropylene films have been proposed. For example, the following technology is known: the use of polypropylene that contains roughly equal amounts of high molecular weight components and low molecular weight components (or less low molecular weight components), wide molecular weight distribution, and less decalin soluble components is used to make films to achieve rigidity and Balance of workability (Patent Document 1). However, in this technology, heat resistance at high temperatures exceeding 150°C is still not sufficient, and polypropylene films with high heat resistance, impact resistance, and transparency are not yet known.

The applicant in this case has made diligent research based on the above-mentioned prior art. As a result, the following situation has been successfully achieved: by using ¹³ C-NMR (Nuclear Magnetic Resonance; nuclear magnetic resonance) as an indicator of the stereoregularity of the polypropylene resin constituting the film Resonance) is a polypropylene polymer with a meso pentad component ratio of 96% or more, and provides a stretched polypropylene film with high rigidity and high heat resistance (Patent Document 2).

[Prior Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Publication No. 2008-540815.

Patent Document 2: Manual No. WO2015/012324.

However, the aforementioned Patent Document 2 has room for improvement in terms of antistatic properties.

In view of the foregoing, the subject of the present invention is to provide a biaxially stretched laminated polypropylene film having high rigidity, excellent heat resistance, and excellent antistatic properties.

The structure of the present invention is as follows.

1. A biaxially stretched laminated polypropylene film, which is a laminated film containing at least two layers of polypropylene resin compositions with different crystallinities, characterized by It is: when the melting endothermic peak area measured by a differential scanning calorimeter at a heating rate of 20°C/min is set to △H, it has: A layer, which is composed of polypropylene resin composition with △H of 78.0J/g or more And the B layer is composed of a polypropylene resin composition with a △H less than 82.0J/g and a △H lower than the △H of the aforementioned A layer by 2.0J/g to 40.0J/g; the aforementioned B The layer system exists on at least one outermost surface side.

2. The biaxially stretched laminated polypropylene film as described in 1 above, wherein the ratio of the total thickness of the B layer to the total thickness of the A layer (the entire B layer/the entire A layer) is 0.01 to 0.5, and the B The total thickness of the layers is 0.5 μm to 4 μm.

3. The biaxially stretched laminated polypropylene film as described in 1 or 2 above, which further has a polypropylene resin with a thickness of 0.01 μm to 1.0 μm and a △H exceeding 76.0 J/g on the outermost surface side of the B layer Other layers formed by the composition.

4. The biaxially stretched laminated polypropylene film described in any one of 1 to 3 above, wherein the MFR (Melt Flow Rate) of the entire film is 2.0 g/10 min to 10.5 g/10 min.

5. The biaxially stretched laminated polypropylene film described in any one of 1 to 4 above, wherein the surface specific resistance (LogΩ) of the entire film is 13.5 or less.

6. The biaxially stretched laminated polypropylene film as described in any one of 1 to 5 above, wherein the dynamic friction coefficient of the entire film is 0.4 or less.

7. The biaxially stretched laminated polypropylene film as described in any one of 1 to 6 above, wherein the heat shrinkage rate at 150°C is lower than MD (Machine Both the Direction (longitudinal) direction and the TD (Transverse Direction; transverse) direction are below 10.0%, the tensile modulus of elasticity in the MD direction is 2.0 GPa or more, and the tensile modulus of elasticity in the TD direction is 3.8 GPa or more.

8. The biaxially stretched laminated polypropylene film as described in any one of 1 to 7 above, wherein the lamination strength in the MD direction after lamination is 1.2N/15mm or more.

The polypropylene film of the present invention has at least two layers of a layer A with high crystallinity and a layer B with low crystallinity, and has a laminated structure in which the layer B is arranged on the outermost surface side, so it is mixed with an antistatic agent in at least one layer It gradually bleeds out on the surface of the low-crystallinity B layer arranged on the outermost surface side. As a result, it is possible to exhibit good antistatic properties while maintaining the excellent heat resistance or rigidity of the A layer with high crystallinity.

The polypropylene film-based biaxially stretched laminated polypropylene film of the present invention contains at least two or more layers of polypropylene resin composition with different crystallinity, and is characterized in that it will use DSC (Differential Scanning Calorimeter; differential scanning Calorimeter) When the melting endothermic peak area (total heat of fusion) measured at a heating rate of 20°C/min is set to △H, it has: A layer, which is composed of a polypropylene resin composition with a △H of 78.0J/g or more constitute; And layer B is composed of a polypropylene resin composition with a △H less than 82.0J/g and a △H lower than the △H of the aforementioned A layer by 2.0J/g to 40.0J/g; and the aforementioned B layer system Exist on at least one of the most surface sides.

Here, the above-mentioned ΔH is a value used as an index of crystallinity. The higher the crystallinity, the greater the energy required to melt the crystal, so the larger the ΔH, the higher the crystallinity. Furthermore, in the present invention, ΔH is determined by measuring the DSC curve at a temperature increase rate of 20°C/min for each raw material used for film production.

First, the ΔH of layer A and layer B, which are the most characteristic of the present invention, will be explained.

Layer A is a layer with high crystallinity that is responsible for heat resistance, rigidity, mechanical strength after lamination, etc., so △H must be 78.0J/g or more, more preferably 80.0J/g or more, and more preferably 81.0J/g Above, it is further 82.0 J/g or more. If the ΔH of the A layer is small, the rigidity such as the tensile modulus of elasticity becomes small, which is not good. In addition, the ΔH of the A layer is preferably 104.0 J/g or less, more preferably 102.0 J/g or less, and still more preferably 100.0 J/g or less. If the ΔH of the A layer is too large, it may require high-temperature and long-term manufacturing, which may actually become difficult in industrial manufacturing.

On the other hand, layer B is a low-crystallinity layer located closer to the outermost surface side than layer A, and performs the following function: of course, the antistatic agent mixed into the low-crystalline layer B (surface layer) is placed on the outermost surface side. The surface of the B layer oozes out, and the antistatic agent mixed in the high crystallinity A layer (core layer) oozes out on the surface of the B layer on the outermost side, giving excellent antistatic properties. Therefore, the △H of layer B It must be less than 82.0J/g and have a △H that is 2.0J/g to 40.0J/g lower than the △H of the A layer. If the ΔH of the B layer is 82.0 J/g or more, the amount of antistatic agent oozes out is reduced, and the antistatic property becomes insufficient. In addition, the lubricity of the film tends to be poor, and there is a possibility that the film cannot be formed stably. Furthermore, the laminate strength described later may decrease. The ΔH of the layer B is preferably 81.0 J/g or less, more preferably 80.0 J/g or less, and particularly preferably less than 78.0 J/g. The lower limit of ΔH of layer B is not particularly limited, but ΔH is preferably 60.0 J/g or more. If ΔH is less than 60.0 J/g, the tensile modulus of elasticity may decrease, the heat shrinkage rate may increase, the transparency may decrease, or it may adhere to the roll.

In addition, the difference between △H of A layer and △H of B layer (△H of A layer-△H of B layer) is 2.0J/g to 40.0J/g. If the difference is less than 2.0 J/g, the effect of the present invention in which a high crystallinity layer and a low crystallinity layer are laminated to achieve the coexistence of the target heat resistance and antistatic property may become insufficient. On the other hand, if the difference is greater than 40.0 J/g, there are problems such as negative heating and whitening of the low crystallinity layer due to heat during stretching. The preferable range of the difference of ΔH is 3.0 J/g to 25 J/g, more preferably 4.0 J/g to 15 J/g.

In the biaxially stretched laminated polypropylene film of the present invention, in order to increase the crystallinity (△H) of the polypropylene resin in the A layer, there are the following methods: reduce the molecular weight of the A layer; reduce the copolymer monomer in the polypropylene resin Body; increase the meso pentad component ratio as an indicator of the stereoregularity of the resin; increase the amount of low molecular weight components with a molecular weight of about 100,000 or less. The reason for the method is that low-molecular-weight components with a molecular weight of less than 100,000 accelerate the formation of The effect of crystallization speed is great. In addition, high-molecular-weight components with a molecular weight of about 1 million or more act as a crystallization nucleating agent to promote the crystallization rate of low-molecular-weight components. Therefore, low-molecular-weight components are mixed with a small amount of high-molecular-weight components to increase the molecular weight distribution ( Mw/Mn) is also an effective method.

On the other hand, in order to reduce the crystallinity (△H) of the polypropylene resin of the B layer, there are the following methods: increase the molecular weight of the B layer; increase the copolymerization component in the polypropylene resin; reduce the meso pentad Composition rate, etc.

The laminated film of the present invention is characterized in that the △H (total heat of fusion) of the A layer, the △H of the B layer and the difference between these △Hs are specified as described above, but the melting endothermic peak temperature in the DSC curve also becomes crystalline A standard of sex. The melting endothermic peak temperature of layer A is preferably 160°C or higher, more preferably 163°C or higher. In addition, it is preferably 176°C or lower, more preferably 173°C or lower, and still more preferably 170°C or lower.

On the other hand, in the case of layer B, the melting endothermic peak temperature is preferably 166°C or less, more preferably 164°C or less. In addition, it is preferably 120°C or higher, more preferably 130°C or higher.

Hereinafter, the A layer and the B layer constituting the laminated film of the present invention will be described in more detail.

(Level A)

The polypropylene resin used in the layer A of the present invention can not only use polypropylene homopolymer, but also polypropylene copolymerized with ethylene and/or α-olefin with a carbon number of 4 or more at 0.5 mol% or less. Such copolymerized polypropylene is also included in the polypropylene-based resin of the present invention (hereinafter sometimes simply referred to as polypropylene). Examples of α-olefins having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. In the case of the A layer, it is preferable to reduce the copolymerized monomers in the polypropylene resin as described above to increase ΔH, so the above-mentioned ethylene or α-olefin with a carbon number of 4 or more, and other copolymerized components are preferably 0.3 Mole% or less, more preferably 0.1 Mole% or less, most preferably completely homopolypropylene (polypropylene homopolymer) without copolymerization components. If more than 0.5 mol% of ethylene and/or α-olefin with a carbon number of 4 or more are copolymerized, ΔH may become small, crystallinity or rigidity may decrease too much, and the heat shrinkage rate at high temperature may increase. In addition, resins satisfying the above conditions (for example, fully homopolypropylene and copolymerized polypropylene) may be blended and used.

The meso pentad fraction ([mmmm]%) measured by ¹³ C-NMR as an indicator of the stereoregularity of the polypropylene constituting the A layer of the present invention is preferably 98% to 99.5%. It is more preferably 98.1% or more, and still more preferably 98.2% or more. If the meso pentad ratio of the polypropylene of the A layer is small, the elastic modulus may decrease and the heat resistance may become insufficient. 99.5% is the actual upper limit.

The mass average molecular weight (Mw) of the polypropylene constituting the A layer of the present invention is preferably 180,000 to 500,000. If it is less than 180,000, the melt viscosity is low, so it is unstable at the time of casting and the film forming properties may deteriorate. If Mw exceeds 500,000, sometimes the extrusion becomes difficult and the film forming performance is poor, so it is not good. In addition, if Mw is high, the amount of low-molecular-weight components with a molecular weight of 100,000 or less in the GPC (Gel Permeation Chromatography) cumulative curve may decrease, and the heat shrinkage rate may increase. A more preferable lower limit of Mw is 190,000, and a more preferable upper limit of Mw is 200,000, and a more preferable upper limit of Mw is 450,000, further preferably 420,000, and particularly preferably 410,000.

Furthermore, in order to easily obtain the required low heat shrinkage rate at high temperature or reduce thickness unevenness, it is preferable to set the content ratio of the above-mentioned low molecular weight component in the A layer to 35% by weight or more, more preferably 38% by weight or more, more preferably 42% by weight or more.

The number average molecular weight (Mn) of the polypropylene constituting the A layer of the present invention is preferably 20,000 to 200,000. If it is less than 20,000, the melt viscosity is low, so it becomes unstable at the time of casting and the film forming properties may deteriorate. If it exceeds 200,000, extrusion may become difficult and film-forming properties may be poor, which is unsatisfactory. In addition, if Mn is high, the thermal shrinkage rate may increase. More preferably, the lower limit of Mn is 30,000, further preferably 40,000, particularly preferably 50,000, and more preferably the upper limit of Mn is 170,000, further preferably 160,000, and particularly preferably 150,000.

In addition, Mw/Mn, which is an index of molecular weight distribution, is preferably 2.8 to 30 for the polypropylene of the A layer. It is more preferably from 3 to 15, further preferably from 3.2 to 10, and particularly preferably from 3.5 to 6.

Here, Mw/Mn can be increased by mixing low-molecular-weight components with a small amount of high-molecular-weight components as described above. That is, the molecular weight is about 100,000 The following low-molecular-weight components have a great effect on accelerating the crystallization rate, but if a high-molecular-weight component with a molecular weight of about 1 million or more is added, it acts as a crystal nucleating agent and promotes the addition of low-molecular-weight components. If low molecular weight components are mixed with a small amount of high molecular weight components, Mw/Mn increases. If there are more low-molecular-weight components, the entanglement of the molecules becomes stronger, and even if the crystallinity is high, the heat shrinkage rate tends to increase. If Mw/Mn becomes too large, the high molecular weight component may increase, and the thermal shrinkage rate may increase, which is undesirable. At this time, Mw/Mn is preferably 8-30, more preferably 8-15. The MFR at this time is preferably 2 g/10 minutes to 6 g/10 minutes.

Furthermore, the molecular weight distribution of polypropylene can be adjusted by the following methods: using a series of plants to polymerize components with different molecular weights in multiple stages; using a mixer to blend components with different molecular weights in an off-line manner ; Or blending with catalysts with different properties for polymerization; or using catalysts that can achieve the desired molecular weight distribution.

The melt flow rate (MFR; 230° C., 2.16 kgf) of the polypropylene of the A layer is preferably 0.5 g/10 min to 20 g/10 min. The lower limit of MFR is more preferably 2 g/10 minutes, further preferably 4 g/10 minutes, particularly preferably 5 g/10 minutes, and most preferably 6 g/10 minutes. The upper limit of the MFR of the polypropylene of the A layer is more preferably 15 g/10 minutes, further preferably 12 g/10 minutes, particularly preferably 10 g/10 minutes, and most preferably 9.5 g/10 minutes. If it is this range, the adhesiveness to the cooling roll is also good, the film forming property is excellent, and the heat shrinkage rate at high temperature can be kept small.

(Level B)

The polypropylene resin used in the layer B of the present invention can not only use polypropylene homopolymer, but also polypropylene copolymerized with ethylene and/or α-olefin with 4 or more carbon atoms. Examples of α-olefins having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. In addition, polar maleic acid or the like can also be used as other copolymerization components. In the case of layer B, the total of ethylene or α-olefin with 4 or more carbon atoms and other copolymerization components (hereinafter sometimes represented by copolymerization components) is preferably 8.0 mol% or less in total, more preferably 6.0 mol% or less . If the copolymerization is performed in excess of 8.0 mol%, the film may whiten, resulting in poor appearance, or adhesiveness may occur and film formation may become difficult. In addition, resins satisfying the above conditions (for example, fully homopolypropylene and copolymerized polypropylene) may be blended and used. In the case of blending, each resin may be copolymerized in excess of 8.0 mol%, and the blend is preferably based on monomer units and monomers other than propylene are 8.0 mol% or less.

In addition, the polypropylene of the layer B of the present invention preferably has an MFR of 0.5 g/10 min to 10 g/10 min. The lower limit of the MFR of the polypropylene of the B layer is more preferably 2 g/10 minutes, and still more preferably 3 g/10 minutes. The upper limit of the MFR of the polypropylene of the B layer is more preferably 8 g/10 minutes, and still more preferably 5.5 g/10 minutes. If it is this range, film forming properties are also good, and the heat shrinkage rate at high temperature can be kept small. In contrast, if the MFR of the polypropylene of the B layer is less than 0.5 g/10 min, when the MFR of the polypropylene of the A layer is large, the viscosity difference between the A layer and the B layer will increase, so it is easy to make the film Produce unevenness (uneven original fabric). If the MFR of layer B exceeds 10g/10 minutes, the adhesion to the cooling roll will change Poor, the air is drawn into the air and the smoothness is poor, and there is a possibility that the defects that the air becomes the starting point will increase.

The meso pentad ratio of polypropylene in layer B is preferably 98.2% or less. More preferably, it is 98.0% or less, and still more preferably 97.8% or less. If the meso pentad ratio of the polypropylene of the B layer is large, the crystallinity becomes too high, it is difficult to cause the antistatic agent to bleed out, and the antistatic property may decrease. In addition, the lubricity and lamination strength also tend to decrease. Furthermore, from the above viewpoint, the meso pentad ratio of the polypropylene of the B layer is not particularly limited, but it is preferably 90% or more in consideration of the appearance of the film or the film forming properties.

The mass average molecular weight (Mw) of the polypropylene constituting the layer B of the present invention is preferably 200,000 to 500,000. If it is less than 200,000, the adhesiveness to the cooling roll may deteriorate, air may be drawn in and smoothness may be poor, and there may be many disadvantages that the air becomes a starting point. If the Mw exceeds 500,000, extrusion may become difficult, and unevenness (unevenness of the original fabric) may easily occur during film formation, which is not preferable. More preferably, the lower limit of Mw is 220,000, and more preferably is 240,000, and the upper limit of Mw is more preferably 450,000, further preferably 420,000, and particularly preferably 410,000.

The number average molecular weight (Mn) of the polypropylene constituting the layer B of the present invention is preferably 50,000 to 200,000. If it is less than 50,000, the melt viscosity will be low, it will be unstable during casting, the adhesion to the cooling roll will be poor, the air will be entrained and the smoothness will be poor, and the air may become a starting point. If it exceeds 200,000, extrusion may become difficult and film-forming properties may be poor, which is unsatisfactory. more The lower limit of Mn is preferably 60,000, and more preferably 70,000, and the upper limit of Mn is more preferably 170,000, further preferably 160,000, and particularly preferably 150,000.

In the B layer, Mw/Mn is preferably 3.5-30, more preferably 3.7-20, and still more preferably 3.7-15.

(Laminated film)

The biaxially stretched laminated polypropylene film of the present invention has the aforementioned A layer and B layer, and is arranged so that the B layer becomes at least one outermost surface side. The so-called "B layer is present on at least one outermost surface side" here means that if viewed from at least one side, the B layer is closer to the A layer. In addition, the so-called "extreme surface side" refers to the relationship between the A layer and the B layer constituting the laminated film. The B layer is located on the outermost surface than the A layer, except that the B layer is arranged on the most surface (top) of the laminated film In addition to the situation, it also includes the spirit of arranging other layers (other than layer A and layer B) on the outermost surface (top) on layer B. That is, the laminated film of the present invention may not only have two layers, but also have a multilayer structure of three or more layers.

Specifically, when the laminated film of the present invention is composed of only the A layer and the B layer as the resin component, it may have a layer A (core layer) and a layer B (surface layer) (that is, the layer A). A film with two two-layer structures with layer B on one side of the layer, or layer B on both sides of layer A (core layer) as two surface layers (that is, layer B on both sides of layer A) Two kinds of three-layer sandwich structure (layer B/layer A/layer B). Or it can be, for example, two kinds of five-layer sandwich The structure (layer B/layer A/layer B/layer A/layer B), etc., can also be a multilayer structure with more layers. Of course, it is not limited to these structures, and there may be various aspects in which the B layer becomes the outermost surface side. For example, aspects such as A layer/A layer/B layer, A layer/B layer/B layer, etc. can be exemplified. Among these structures, the two three-layer structure of B layer/A layer/B layer is preferable. Furthermore, when the laminated film has a plurality of A layers and B layers, each layer may be the same type of resin or different types.

Alternatively, the biaxially stretched laminated polypropylene film of the present invention may further have a polypropylene resin layer other than the A layer and the B layer (for convenience, the layers other than the above are collectively referred to as the C layer). By setting this C layer as the outermost layer, the exudation of the antistatic agent is not substantially hindered, and the heat resistance of the outermost layer can be further ensured. Here, the C layer system ΔH exceeds 76.0 J/g, and it is not classified into any of the above-mentioned A layer and B layer. The C layer can be arranged at any position, and it can be arranged between the A layer and the B layer, closer to the core side than the A layer, and closer to the outermost surface than the B layer. The C layer is preferably arranged on the outermost surface side than the B layer. For example, it may be a three-layer structure of C layer, B layer, and A layer in order from the outermost surface side. Furthermore, the raw materials used in the C layer can appropriately use the raw materials described in the A layer and the B layer. For example, the polypropylene resin composition of the C layer can use the polypropylene resin composition used in the A layer, or a different polypropylene resin composition.

The overall thickness of the film is preferably 9 μm to 200 μm, more preferably 10 μm to 150 μm, further preferably 12 μm to 100 μm, and particularly preferably 12 μm to 80 μm.

The ratio of the thickness of the B layer to the A layer is preferably the entire B layer (in the case of plural B layers, the total thickness of the B layers)/the entire A layer (in the case of plural A layers, the A The total thickness of the layers) is 0.01 to 0.5, more preferably 0.03 to 0.4, and still more preferably 0.05 to 0.3. If the entire B layer/the entire A layer exceeds 0.5, the elastic modulus tends to decrease. In addition, the thickness of the entire A layer relative to the thickness of the entire film is preferably 50% to 99%, more preferably 60% to 97%, and particularly preferably 70% to 95%. The remaining part becomes layer B or layer A and layer C other than layer B.

The substantial thickness of the entire A layer is preferably 5 μm to 50 μm, more preferably 10 μm to 45 μm, and still more preferably 15 μm to 40 μm.

In addition, the substantial thickness of the entire B layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, still more preferably 1 μm or more, still more preferably 1.5 μm or more; preferably 4 μm or less, more preferably 3.5 μm or less It is more preferably 3 μm or less, and still more preferably 2 μm or less.

When the C layer is further present, the thickness of the C layer is preferably 0.01 μm to 1.0 μm, preferably 0.05 μm or more, and more preferably 0.1 μm or more. The thickness of the C layer is preferably thinner than the aforementioned B layer, preferably less than 0.5 μm.

The MFR of the entire film is preferably 2.0 g/10 min to 10.5 g/10 min. If it is less than 2.0 g/10 minutes, the film-forming properties are poor, and the thermal shrinkage rate of the resulting film tends to increase. A more preferable lower limit of MFR is 3.0g/10 minutes. another On the one hand, if it exceeds 10.5 g/10 minutes, the adhesiveness to the cooling roll will decrease, the film formation stability will be poor, or defects such as foreign matter will increase.

The polypropylene used in the present invention can be obtained by polymerizing the raw material propylene using a known catalyst such as Ziegler-Natta catalyst or metallocene catalyst. Among them, Ziegler-Natta catalyst is used in order to eliminate heterogeneous bonding, and it is preferable to use a catalyst that can realize polymerization with high stereoregularity.

As the polymerization method of propylene, any known method may be used, for example, a method of polymerization in an inert solvent such as hexane, heptane, toluene, xylene, etc.; a method of polymerization in a liquid monomer ; A method of adding a catalyst to a gaseous monomer and polymerizing in a gas phase state; or a method of combining these methods to perform polymerization, etc.

The biaxially stretched laminated polypropylene film of the present invention contains an antistatic agent. The content of the antistatic agent contained in the entire film is preferably 0.01% by mass to 3.0% by mass, more preferably 0.05% by mass to 2.8% by mass, and still more preferably 0.10% by mass to 2.5% by mass. The antistatic agent is not particularly limited, and amine-based surfactants or monoglycerides of fatty acids can be cited as preferred antistatic agents.

Specific examples of the amine-based surfactant include: myristyl diethanolamine, palm based diethanolamine, stearyl diethanolamine, oleyl diethanolamine, peanut based diethanolamine, behenyl diethanolamine, more preferably palm based diethanolamine Ethanol Amine, stearyl diethanolamine, and oleyl diethanolamine can also be used in the form of a mixture of two or more selected from these amine-based surfactants.

Specific examples of monoglycerides of fatty acids include: glycerol monolaurate, glycerol monomyristate, glycerol monopalmitate, glycerol monostearate, glycerol monoarachidate, glycerol monobehenate, and more Glycerol monostearate is preferred, and two or more of these monoglycerides may be selected and used as a mixture.

If the antistatic agent is less than 0.01% by mass, it will easily become a film with poor antistatic properties. If it is added more than 3% by mass, the roll may be contaminated during film formation or processing, or the film surface may become sticky, which is not good. Furthermore, if a large amount of antistatic agent is added to layer B during manufacture, the above-mentioned problems are likely to occur. Therefore, it is preferable not to add antistatic agent to the polypropylene resin composition for layer B during manufacture, or to reduce Addition amount, add antistatic agent to layer A within the above amount range. Even in this case, the antistatic agent contained in the A layer can diffuse and move into the B layer, and then ooze out on the surface of the laminated film through the B layer. By setting the △H of the B layer to be less than 82.0J/g, the difference between the △H of the A layer and the △H of the B layer (△H of the HB layer of A layer) is set to 2.0J/g to 40.0J /g, can promote the diffusion, movement and exudation of the antistatic agent to the B layer to obtain sufficient antistatic properties.

Anti-caking agents can also be added to layer B. As an anti-caking agent, it can be selected from inorganic anti-caking agents such as silica, calcium carbonate, kaolin, zeolite and fats Among the organic anti-blocking agents such as tri-fatty acid esters, ethylene bisamide, acrylic, polystyrene, etc., are appropriately selected and used. The anti-caking agent preferably has an average particle size of 0.5 μm to 5.0 μm, more preferably 1.0 μm to 3.0 μm. If the average particle size is less than 0.5μm, a large amount of anti-caking agent is needed to obtain good lubricity, which is not good. On the contrary, if it exceeds 5.0μm, the surface roughness of the film may become too large to satisfy practical characteristics. Therefore it is not good. The anti-blocking agent is preferably set to 0.01% by mass to 0.3% by mass in the B layer. If it is less than 0.01% by mass, the film is not easily lubricated, and if it is added more than 0.3% by mass, the film may be whitened, which is not preferable.

The A layer and/or the B layer of the present invention (the other layer when there are further layers other than these layers) may also contain other additives or other resins. As other additives, for example, antioxidants, ultraviolet absorbers, nucleating agents, adhesives, anti-stagnation agents, flame retardants, inorganic or organic fillers, etc. may be mentioned. Examples of other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers that are copolymers of propylene and ethylene and/or α-olefins with 4 or more carbon atoms, or various elastomers. . These additives or other resins can be polymerized in sequence using a multi-stage reactor, or blended with polypropylene resin using a Henschel mixer, or using polypropylene to make the master batch pellets pre-made with a melt kneader to a predetermined concentration The method is diluted, or all the amounts are melted and kneaded in advance for use.

(Method of manufacturing film)

The biaxially stretched laminated polypropylene film of the present invention can be obtained by using an extruder to combine a polypropylene raw material for layer A (polypropylene resin composition for layer A) and a polypropylene raw material for layer B (for layer B) Polypropylene resin composition) and other layer materials (resin composition for layer C) as necessary are melt-extruded to form an unstretched sheet, and the unstretched sheet is stretched by a predetermined method and heat-treated. The unstretched laminated film is obtained by using multiple extruders or feed blocks and multi-manifolds. The melt-extrusion temperature is preferably about 200°C to 280°C. In order to obtain a laminated film with good appearance without disturbing the layer within this temperature range, it is preferable that the viscosity of the polypropylene raw material for layer A and that for layer B is different. (MFR difference) is set to be 6g/10 minutes or less. If the difference in viscosity is greater than 6 g/10 minutes, the layer is disordered, and the appearance is likely to be poor. It is more preferably 5.5 g/10 minutes or less, and still more preferably 5 g/10 minutes or less.

The surface temperature of the cooling roll is preferably 25°C to 35°C, more preferably 27°C to 33°C. Then, it is preferable to extend the film in the length (MD) direction to preferably 3 times to 8 times (more preferably 3 times to 7 times), and then in the width (TD) direction using a stretching roll at 120°C to 165°C The extension is preferably performed at 155°C to 175°C, more preferably 160°C to 163°C, preferably 4 times to 20 times, more preferably 6 to 12 times.

Furthermore, heat fixing is performed while performing relaxation of preferably 2% to 10% at preferably 165°C to 176°C, more preferably 170°C to 176°C, and still more preferably 172°C to 175°C. For the biaxial extension thus obtained The stretch-laminated polypropylene film is subjected to corona discharge, plasma treatment, flame treatment, etc. as necessary, and then is wound with a coiler to obtain a film roll.

As described above, the lower limit of the MD stretch ratio is preferably 3 times, more preferably 3.5 times. If it is less than the above lower limit, the film thickness may become uneven. The upper limit of the stretching ratio of MD is preferably 8 times, more preferably 7 times. If the upper limit is exceeded, the subsequent TD extension may become difficult. The lower limit of the stretching temperature of MD is preferably 120°C, more preferably 125°C, and still more preferably 130°C. If it is less than the above lower limit, the mechanical load may increase, or the thickness unevenness may increase, or the surface of the film may be rough. The upper limit of the stretching temperature of MD is preferably 165°C, more preferably 160°C, still more preferably 155°C, and still more preferably 150°C. When the temperature is high, it is preferable to reduce the heat shrinkage rate, but sometimes it adheres to the roll and cannot be extended, or causes surface roughness.

The lower limit of the stretching ratio of TD is preferably 4 times, more preferably 5 times, and still more preferably 6 times. If it is less than the above lower limit, the thickness may become uneven. The upper limit of the TD stretching ratio is preferably 20 times, more preferably 17 times, further preferably 15 times, and particularly preferably 12 times. If the upper limit is exceeded, the thermal shrinkage rate may increase, or it may break during stretching. Regarding the preheating temperature during TD stretching, in order to quickly increase the film temperature to near the stretching temperature, it is preferably set to be 5°C to 15°C higher than the stretching temperature. The stretching of TD is performed at a higher temperature than the previous stretched polypropylene film. The lower limit of the extension temperature of TD is preferably 155°C, more preferably 157°C, still more preferably 158°C, and particularly preferably 160°C. If it is less than the above lower limit, it may not be sufficiently softened and broken, or the heat shrinkage rate may change high. The upper limit of the TD extension temperature is preferably 175°C, more preferably 170°C, still more preferably 168°C, and still more preferably 163°C. In order to reduce the thermal shrinkage rate, the temperature is preferably high. However, if the temperature exceeds the above upper limit, not only the low-molecular components are melted and recrystallized to reduce the alignment, but the surface may be roughened or the film may become white.

The stretched film is thermally fixed. The heat fixation can be performed at a higher temperature than the previous stretched polypropylene film. The lower limit of the heat fixing temperature is preferably 165°C, more preferably 166°C. If it is less than the above lower limit, the thermal shrinkage rate may increase. In addition, in order to reduce the thermal shrinkage rate, a long-term treatment is sometimes required, and productivity is poor. The upper limit of the heat fixing temperature is preferably 176°C, more preferably 175°C. If the upper limit is exceeded, low-molecular components may melt or recrystallize, resulting in rough surface or whitening of the film.

It is preferable to perform relaxation during heat fixing. The lower limit of relaxation is preferably 2%, and more preferably 3%. If it is less than the above lower limit, the thermal shrinkage rate may increase. The upper limit of relaxation is preferably 10%, more preferably 8%. If the upper limit is exceeded, uneven thickness may increase.

Furthermore, in order to reduce the thermal shrinkage rate, the film manufactured by the above-mentioned steps may be temporarily wound into a roll shape and then annealed in an off-line manner. The lower limit of the offline annealing temperature is preferably 160°C, more preferably 162°C, and still more preferably 163°C. If it is less than the above lower limit, sometimes the effect of annealing cannot be obtained. The upper limit of the offline annealing temperature is preferably 175°C, more preferably 174°C, and still more preferably 173°C. If the upper limit is exceeded, transparency may decrease or thickness unevenness may increase.

The lower limit of the offline annealing time is preferably 0.1 minute, more preferably 0.5 minute, and still more preferably 1 minute. If it is less than the above lower limit, sometimes the effect of annealing cannot be obtained. The upper limit of the offline annealing time is preferably 30 minutes, more preferably 25 minutes, and still more preferably 20 minutes. If the upper limit is exceeded, productivity may decrease.

(Physical properties of film)

For the biaxially stretched laminated polypropylene film of the present invention, the heat shrinkage rate in the MD direction at 150°C is preferably 0.2% to 10%, more preferably 0.3% to 9%, and still more preferably 0.5% to 8% , Particularly preferably 0.7% to 7%, most preferably 1% to 5%. The heat shrinkage rate in the TD direction at 150°C is also the same. If the heat shrinkage ratio is in the above range, it can be said to be a film excellent in heat resistance, and it can also be used for applications that may be exposed to high temperatures. Furthermore, if the thermal shrinkage rate at 150°C is about 1.5%, it can be achieved by, for example, increasing low molecular weight components, adjusting extension conditions or heat setting conditions, but in order to reduce it to 1.5% or less, it is better to perform annealing off-line. deal with.

For the biaxially stretched laminated polypropylene film of the present invention, the surface intrinsic resistance value is preferably 9.5 (LogΩ) to 13.5 (LogΩ), more preferably 10 (LogΩ) to 13 (LogΩ), and even more preferably 10.5 (LogΩ) ) To 12.5 (LogΩ). If the surface specific resistance value exceeds 13.5 (LogΩ), the antistatic ability may become insufficient.

The haze of the biaxially stretched laminated polypropylene film of the present invention is preferably 0.1% to 6%, more preferably 0.2% to 5%, further preferably 0.3% to 4.5%, particularly preferably 0.4% to 4%, most preferably Preferably, it is 0.4% to 3.5%. If it is in the above range, it may be easily used for applications requiring transparency. For example, when the stretching temperature and heat-fixing temperature are too high, the cooling roll (CR) temperature is high and the cooling rate of the stretched original fabric sheet is slow, and when there are too many low molecular weight components, the haze will deteriorate. The tendency can be set within the above range by adjusting these conditions. The method of measuring haze will be described later.

The lower limit of the surface orientation coefficient of the biaxially stretched laminated polypropylene film of the present invention is preferably 0.013, more preferably 0.014, and still more preferably 0.015. If the value is less than the above range, the heat resistance and rigidity of the film are reduced, the processability is reduced, and the appearance becomes poor, and the effect of the present invention cannot be sufficiently obtained.

The stretched laminated polypropylene film usually has a crystal orientation, and the direction or degree of the crystal orientation has a great influence on the physical properties of the film. The degree of crystal alignment tends to vary depending on the molecular structure of the polypropylene used, or the process or conditions in film manufacturing, and can be set within the above range by adjusting these conditions. The measurement method will be described later.

The tensile modulus of elasticity in the MD direction of the biaxially stretched laminated polypropylene film of the present invention is preferably 2.0 GPa to 4 GPa, more preferably 2.1 GPa to 3.7 GPa, further preferably 2.2 GPa to 3.5 GPa, particularly preferably 2.3 GPa To 3.4GPa, the best is 2.4GPa to 3.3GPa. Stretching elasticity in TD direction The modulus is preferably 3.8GPa to 8GPa, more preferably 4GPa to 7.5GPa, further preferably 4.1GPa to 7GPa, and particularly preferably 4.2GPa to 6.5GPa.

The dynamic friction coefficient of the biaxially stretched laminated polypropylene film of the present invention is preferably 0.2 to 0.4, more preferably 0.22 to 0.38, and still more preferably 0.24 to 0.36. With this, the processability of the film is improved.

The biaxially stretched laminated polypropylene film of the present invention can be used as sealing film, insulating film of capacitors or motors, back sheet of solar cell, barrier film of inorganic oxide, ITO (Indium Tin Oxide; indium tin oxide), etc. Base film (base material layer) used for transparent conductive films. The lamination strength in the MD direction of the laminated film after being laminated with the above film is preferably 1.2N/15mm to 2.5N/15mm, more preferably 1.3N/15mm to 2.3N/15mm, and still more preferably 1.4N/15mm To 2.1N/15mm. The method of measuring lamination strength will be described later.

This application claims the benefit of priority based on Japanese Patent Application No. 2016-064051 filed on March 28, 2016. All the contents of the specification of Japanese Patent Application No. 2016-064051 filed on March 28, 2016 are incorporated into this application for the purpose of reference.

[Example]

Hereinafter, the present invention will be described in further detail with examples, but the following examples do not limit the present invention and are changed within the scope not departing from the spirit of the present invention. More implementation scenarios are included in the present invention. In addition, the methods for measuring the physical properties of the films obtained in the examples and comparative examples are as follows.

1) Three-dimensional regularity

The meso pentad fraction ([mmmm]%) was measured using ¹³ C-NMR. The meso pentad fraction was calculated according to the method described in "Macromolecules" by Zambelli et al., Vol. 6, page 925 (1973)". ¹³ C-NMR measurement system uses "AVANCE500" manufactured by BRUKER Company. Dissolve 200 mg of sample in an 8:2 (volume ratio) mixture of o-dichlorobenzene and deuterated benzene at 135°C. At 110°C get on.

2) Melt flow rate (MFR; g/10 minutes)

According to JIS K7210, the temperature is 230°C and the load is 2.16kgf.

The resin system directly weighs the necessary amount of particles (powder) and uses it.

The film is used to cut out the necessary amount and cut into a sample of about 5mm square.

3) Molecular weight and molecular weight distribution

The molecular weight and molecular weight distribution are determined based on monodisperse polystyrene standards using gel permeation chromatography (GPC). The measurement conditions such as column and solvent used in GPC measurement are as follows.

Solvent: 1,2,4-trichlorobenzene

Column: TSKgel GMH _HR -H(20)HT×3

Flow rate: 1.0ml/min

Detector: RI (Refractive Index; refractive index)

Measuring temperature: 140℃

The number average molecular weight (Mn), the mass average molecular weight (Mw), and the molecular weight distribution are respectively defined by the molecular weight (Ni) of the molecular weight (Mi) at each dissolution position of the GPC curve obtained through the molecular weight calibration curve.

Number average molecular weight: Mn=Σ(Ni．Mi)/ΣNi

Mass average molecular weight: Mw=Σ(Ni．Mi ² )/Σ(Ni．Mi)

Molecular weight distribution: Mw/Mn

When the baseline is not clear, set the baseline from the dissolution peak on the high molecular weight side closest to the dissolution peak of the standard substance to the lowest position under the high molecular weight side.

4) Differential scanning calorimetry (DSC)

A differential scanning calorimeter ("DSC-60" manufactured by Shimadzu Corporation) was used for thermal measurement. Approximately 5 mg of the raw material of the sample film is enclosed in an aluminum pan for measurement. The raw material for layer A and the raw material for layer B were heated from room temperature to 230°C at a rate of 20°C/min, respectively, and kept for 5 minutes. Then the temperature is lowered to room temperature at a rate of 20°C/min, and the temperature is raised from room temperature to 230°C again at a rate of 20°C/min. The melting endothermic peak temperature (°C) and the melting endothermic peak area (△ H(J/g), total heat of fusion). Here, the baseline is set in such a way that the temperature curves before and after melting are smoothly connected from the beginning of the endothermic peak to the end of the peak.

5) Thickness

Regarding the thickness of each layer of the A layer and the B layer, the biaxially stretched laminated polypropylene film was fixed with modified urethane resin, the section of the fixed object was cut out with a microtome, and observed and measured with a differential interference microscope.

6) Heat shrinkage rate at 150℃ (%)

It is measured by the following method based on JIS Z1712. The film was cut into a width of 20 mm and a length of 200 mm in the MD and TD directions, respectively, and hung in a hot air oven at 150°C for heating for 5 minutes. Measure the length after heating, and calculate the heat shrinkage rate based on the ratio of the contracted length to the original length.

7) Tensile modulus (Young's modulus (unit: GPa))

Measure the Young's modulus in the MD and TD directions of the film at 23°C according to JIS K7127. When measuring the Young's modulus, a test piece having a width of 15 mm and a length of 200 mm is used by cutting the film in the MD and TD directions.

8) Surface intrinsic resistance value (LogΩ)

After aging the film at 23°C for 24 hours in accordance with JIS K6911, the corona treatment surface of the film was measured.

9) Haze (unit: %)

It is measured in accordance with JIS K7105.

10) Dynamic friction coefficient

According to JIS K7125, the corona-treated surfaces in the film were superimposed on each other and measured at 23°C.

11) Film density (g/cm ³ )

The density of the film is measured by the density gradient tube method in accordance with JIS K7112.

12) Refractive index, surface alignment coefficient

The measurement was carried out by JIS K7142-1996 5.1 (A method) using an Abbe refractometer manufactured by Atago. Let the refractive index along the MD direction and the TD direction be Nx and Ny, respectively, and let the refractive index in the thickness direction be Nz. The surface orientation coefficient (△P) is calculated as (Nx+Ny)/2-Nz.

13) The appearance of the surface

The appearance of the surface is in the evaluation target area (width 1000mm, length 4000mm), the light is transmitted from one side of the film surface, and the part where the light is blocked by the defect of the film is observed by the camera on the opposite side as a black spot. When measuring the total number of defects with an area exceeding 25 mm ² , the case where the total number of defects is less than 200 is evaluated as ○, and 200 or more is evaluated as ×.

14) Lamination strength in MD direction

The lamination strength is measured by the following procedure.

(a) Laminating with sealing film

Use a continuous dry laminator to produce as follows.

The corona surface of the biaxially stretched laminated polypropylene film obtained in the examples and comparative examples was gravure-coated with the adhesive so that the coating amount became 3.0g/m ² when dried, and then introduced into the drying zone at 80° , 5 seconds for drying. Then, the sealing film was bonded between the rolls provided on the downstream side (roll pressure 0.2MP, roll temperature: 60°C). The resulting laminated film was subjected to an aging treatment at 40°C for 3 days in a rolled state.

Furthermore, the adhesive is a mixture of 17.9% by mass of the main agent (TM329 manufactured by Toyo Morton), 17.9% by mass of hardener (CAT8B manufactured by Toyo Morton), and 64.2% by mass of ethyl acetate. The ether-based adhesive and the sealing film used a non-stretched polypropylene film (Pylen (registered trademark) CT P1128, thickness 30 μm) manufactured by Toyobo Co., Ltd.

(b) Determination of lamination strength

The laminated film obtained above was cut out in a short strip (length 200mm, width 15mm) with long sides in the MD direction, and the laminated film and the sealing film were peeled off using tweezers, and a tensile testing machine (Tensilon, Oriental Made by the company), T-peeling was performed at a tensile speed of 200mm/min under an environment of 23°C, and the peeling strength (N/15mm) at this time was measured. The measurement was performed 3 times, and the average value of the 3 measurements was taken as the lamination strength.

(Example 1)

The polypropylene homopolymer PP-1 shown in Table 1 was used in the A layer, and the polypropylene homopolymer PP-2 shown in Table 1 was used in the B layer. Furthermore, 0.5% by mass of stearyl diethanolamine was blended as an antistatic agent in the layer A material. In addition, In the B layer, 0.15% by mass of silica is used as an anti-caking agent. The A layer uses a 60mm extruder, and the B layer uses a 65mm extruder. It is extruded in a sheet form from a T die at 250°C, cooled and solidified by a cooling roll at 30°C, and then in MD at 135°C The direction extends to 4.5 times. Then, both ends of the film width were clamped in the tenter with clamps, and after preheating at 175°C, it was stretched to 8.2 times in the width direction at 160°C, and heat-fixed at 170°C while relaxing 6.7%. Obtained a biaxially stretched laminated polypropylene film formed by laminating layer A and layer B. The layer B side of the laminated polypropylene film is corona treated and taken up by a coiler. The thickness of the resulting film was 20 μm. Table 1 shows the structure of polypropylene constituting the film, and Table 2 shows the film forming conditions. The physical properties of the obtained film are shown in Table 3.

(Example 2 to Example 10, Comparative Example 1 to Comparative Example 3)

Except having used the polypropylene shown in Table 1 and Table 3, and using the manufacturing conditions shown in Table 2 and Table 3, it carried out similarly to Example 1, and obtained the biaxially stretched laminated polypropylene film. Example 9 and Example 10 are examples of two types of three-layer films in which the feed block is used as the core layer and the layer B is used as the two surface layers. Comparative Example 3 is an example in which the B layer is not laminated. Table 3 shows the physical properties of the film.

[Table 3A]

The biaxially stretched laminated polypropylene film obtained in Example 1 to Example 10 has low heat shrinkage and high Young's modulus (rigidity). Furthermore, the surface specific resistance is small, the antistatic ability is excellent, the dynamic friction coefficient is small, the bag making processability is excellent, and the lamination strength is also high.

In contrast, the film of Comparative Example 1 was manufactured using layer A with ΔH smaller than layer B as the core layer, and the heat-fixing temperature was lower than the preferred temperature, so the Young's modulus became smaller.

The film of Comparative Example 2 uses the B layer with ΔH greater than the A layer for the outermost layer (surface layer), so it is a film with a large surface specific resistance and dynamic friction coefficient.

The film of Comparative Example 3 is an example of a single-layer film with only A layer, the surface specific resistance and dynamic friction coefficient are increased, and the lamination strength is also reduced

The film of Comparative Example 4 is an example in which the ΔH of the B layer is the same as the ΔH of the A layer and the difference of ΔH=0. Therefore, the surface specific resistance is large.

[Industry Availability]

The biaxially stretched laminated polypropylene film system of the present invention has excellent heat resistance and excellent antistatic properties. In addition, the rigidity is also high, so when it is used as a packaging film, it can be thinned, and it can achieve low cost and light weight. In addition, it can be processed at high temperature during coating or printing, so not only can the production efficiency be achieved, but also the previously difficult to use paint or ink, laminating adhesive, etc. can be used. The biaxially stretched laminated polypropylene film of the present invention can also be used for insulating films of capacitors or motors, back sheets of solar cells, and resistance of inorganic oxides. Barrier film, ITO and other transparent conductive film base film, etc.

Claims (8)

A biaxially stretched laminated polypropylene film is a laminated film containing at least two layers of polypropylene resin composition with different crystallinity; the peak area of the melting endothermic heat measured using a differential scanning calorimeter at a heating rate of 20°C/min In the case of △H, it has: A layer, which is composed of polypropylene resin composition with △H of 78.0J/g or more and 100.0J/g or less; and B layer, which is composed of △H of 63.0J/g or more It is composed of a polypropylene resin composition that is less than 82.0 J/g and has a ΔH that is 2.0 J/g to 40.0 J/g lower than the ΔH of the A layer; the B layer is present on at least one outermost surface side. The biaxially stretched laminated polypropylene film described in claim 1, wherein the ratio of the total thickness of the B layer to the total thickness of the A layer (the entire B layer/the entire A layer) is 0.01 to 0.5, and the B layer The total thickness is 0.5μm to 4μm. The biaxially stretched laminated polypropylene film according to claim 1 or 2, wherein the outermost surface side of the B layer further has a polypropylene resin having a thickness of 0.01 μm to 1.0 μm and a △H exceeding 76.0 J/g Other layers formed by the composition. The biaxially stretched laminated polypropylene film according to claim 1 or 2, wherein the melt flow rate of the entire film is 2.0 g/10 min to 10.5 g/10 min. The biaxially stretched laminated polypropylene film described in claim 1 or 2, wherein the surface specific resistance (LogΩ) of the entire film is 13.5 or less. The biaxially stretched laminated polypropylene film described in claim 1 or 2, wherein the dynamic friction coefficient of the entire film is 0.4 or less. For the biaxially stretched laminated polypropylene film described in claim 1 or 2, the heat shrinkage rate at 150°C is 10.0% or less in both the longitudinal and transverse directions, and the tensile modulus of elasticity in the longitudinal direction is 2.0 GPa or more. The modulus of elasticity is 3.8GPa or more. The biaxially stretched laminated polypropylene film described in claim 1 or 2, wherein the longitudinal lamination strength after lamination is 1.2N/15mm or more.