JP2003170555A - Biaxially stretched multilayer polypropylene film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched multilayer polypropylene film having excellent heat sealing strength and laminating strength, and an excellent thickness accuracy. <P>SOLUTION: The biaxially stretched multilayer polypropylene film comprises (C) a propylene.α-olefin copolymer layer laminated on at least one side surface of a base layer obtained from a propylene polymer composition of (A), a propylene homopolymer, and (B) a propylene.α-olefin copolymer having a biaxially stretched α-olefin content of a range of 0.2 to 1.8 mol%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched multi-layer polypropylene film which has excellent heat-sealing strength and laminating strength and is excellent in thickness accuracy.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene films (hereinafter sometimes referred to as OPP films) have been used in a wide range of fields including packaging materials by taking advantage of their excellent transparency, mechanical strength, moisture resistance and rigidity. There is. However, the OPP film has a drawback that a single layer has a high heat-sealable temperature and a proper heat-seal temperature range is narrow. Therefore, in order to improve the heat-sealing property of the OPP film, a biaxially stretched composite film in which a low melting point propylene / ethylene copolymer layer is laminated on one side or both sides of the OPP film (Japanese Patent Publication No. 49-14343), is specified. Of the ternary random copolymer layer as a heat seal layer (Japanese Patent Publication No. 8-5174), a specific propylene / 1-butene random copolymer and a crystalline propylene / α-olefin random copolymer A polypropylene composite film in which the composition is laminated (Japanese Patent Publication No. 61-42626), and the like,
Many methods of laminating a resin having a melting point lower than that of polypropylene have been proposed and widely used.

However, since the composite film obtained by such a method is a composite film, the heat-sealing property is often a problem depending on the application, and improvement of the heat-sealing property is always desired.

[0004]

Therefore, the present invention has conducted various studies for the purpose of improving the heat-sealing property of a biaxially oriented multilayer polypropylene film. As a result, propylene homopolymer and propylene
By using a propylene polymer composition composed of an ethylene random copolymer, the thickness accuracy of the biaxially stretched film is improved, and as a result, heat seal strength and laminate strength can be obtained. did it.

[0005]

[Means for Solving the Problems]

SUMMARY OF THE INVENTION The present invention provides a propylene homopolymer (A) and a propylene / α-olefin copolymer having a biaxially stretched α-olefin content of 0.1 to 1.8 mol%. Provided is a biaxially oriented multilayer polypropylene film comprising a propylene / α-olefin copolymer (C) layer laminated on at least one surface of a base layer obtainable from the propylene polymer composition with (B). It is a thing.

In the present invention, the propylene polymer composition comprises propylene homopolymer (A) 95 to 10% by weight and propylene / α-olefin copolymer (B) 5 to 90.
The present invention provides a biaxially stretched multi-layer polypropylene film which is a composition consisting of 10 wt%.

The present invention also provides a propylene homopolymer (A) and a propylene / α-olefin copolymer having a biaxially stretched α-olefin content of 0.1 to 1.8 mol%. A propylene / α-olefin copolymer (C) layer is laminated on one side of a base layer obtainable from a propylene polymer composition with (B), and a propylene-based polymer (D) layer on the other side. The present invention provides a biaxially stretched multi-layer polypropylene film in which is laminated.

Further, in the present invention, the propylene / α-olefin copolymer (C) layer and the propylene-based polymer (D) layer laminated on both surface layers of the base layer are biaxially containing an antiblocking agent. An oriented multilayer polypropylene film is provided.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Propylene Homopolymer (A) The propylene homopolymer (A) according to the present invention comprises a propylene homopolymer and is usually MFR (melt flow rate; ASTM D-1238, load 2160 g,
The temperature (230 ° C.) is usually in the range of 0.5 to 10 g / 10 minutes, preferably 2 to 5 g / 10 minutes.

Propylene / α-olefin copolymer
(B) The propylene / α-olefin copolymer (B) according to the present invention contains propylene having an α-olefin content of 0.4 to 2.2 mol%, preferably 0.6 to 1.8 mol%. Is a random copolymer of. When the content of α-olefin is less than 0.4 mol%, the stretchability during biaxial stretching is not improved, while when it exceeds 2.2 mol%, the resulting biaxially stretched film is inferior in rigidity. . Examples of the α-olefin include ethylene, 1-butene, 1-hexene, 4-methyl / 1-pentene, 1-octene and the like. Of these, ethylene is preferred. Moreover, MFR (melt flow rate; ASTM D-1238 load 2160)
g, temperature 230 ° C.) is not particularly limited as long as it can be a biaxially stretched film, but is usually 0.5 to 10 g /
It is in the range of 10 minutes, preferably 2 to 5 g / 10 minutes.

Propylene / α-olefin copolymer
(C) The propylene / α-olefin copolymer (C) according to the present invention is preferably a random copolymer with propylene having a melting point of 80 to 155 ° C, more preferably 90 to 145 ° C. If the melting point exceeds 155 ° C,
There is a possibility that the low-temperature heat-sealing property and laminate strength of the obtained biaxially stretched film may not be improved, while if it is less than 80 ° C, stickiness may occur in the biaxially stretched film obtained,
Blocking tends to occur easily. The propylene / α-olefin copolymer (C) usually has an α-olefin content of 1 to 40 mol%, preferably 2 to 3
It is in the range of 5 mol%. When the content of α-olefin is within such a range, a biaxially stretched multilayer polypropylene film having an excellent balance of low temperature heat sealability, laminate strength, blocking resistance and the like can be obtained. Examples of the α-olefin copolymerized with propylene include ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. Specific copolymers include propylene / ethylene random copolymer, propylene / ethylene / 1-butene random copolymer, propylene / 1.
-Butene random copolymer and the like. These copolymers may be used alone or in combination of two or more.

The propylene / α-olefin copolymer (C) according to the present invention includes a heat resistance stabilizer, a weather resistance stabilizer, an ultraviolet absorber, a lubricant, a slip agent, a nucleating agent, an antiblocking agent,
Various additives usually used for polyolefins such as antistatic agents, antifogging agents, pigments, dyes, inorganic or organic fillers may be added within a range not impairing the object of the present invention.

Among them, the anti-blocking agent is 0.01 to
By adding 3.0% by weight, preferably 0.05 to 1.0% by weight, it is possible to obtain a biaxially stretched multilayer polypropylene film having excellent transparency and antiblocking property. 0.01% by weight of antiblocking agent
If less than 3.0, the resulting biaxially stretched multilayer polypropylene film is not sufficiently effective in preventing blocking, while 3.0
When the content is more than 10% by weight, the transparency of the obtained biaxially oriented multilayer polypropylene film tends to be poor. As such an anti-blocking agent, various publicly known ones, for example, silica, talc, mica, inorganic compound particles such as metal oxides obtained by firing zeolite or further metal alkoxide, polymethyl methacrylate, melamine formalin resin, Organic compound particles such as melamine urea resin and polyester resin can be used. Among these, silica and polymethylmethacrylate are particularly preferable in terms of antiblocking property and transparency.

Propylene-Based Polymer (D) The propylene-based polymer (D) according to the present invention is a polymer mainly composed of propylene, which is generally manufactured and sold under the name of polypropylene, and usually has a density of 0.890. ~ 0.9
30 g / cm ³ , MFR (ASTM D1238 load 2160 g, temperature 230 ° C.) 0.5 to 60 g / 10
Min, preferably 0.5 to 10 g / 10 min, more preferably 2 to 5 g / 10 min of propylene homopolymer or other small amount, for example, 5 mol% or less of α-olefin, such as ethylene, butene, It is a random or block copolymer with hexene-1 and the like. Among these, a homopolymer of propylene or a random copolymer of 2 mol% or less, which is a polymer having a high isotacticity, is obtained, and the biaxially stretched film surface is excellent in scratch resistance, which is preferable. Further, the propylene polymer (D) according to the present invention
May be the above-mentioned propylene homopolymer (A) and propylene / α-olefin copolymer (B), or may be a composition thereof.

Like the propylene / α-olefin copolymer (C), various additives are added to the propylene-based polymer (D) according to the present invention within a range that does not impair the object of the present invention. Similarly, 0.01 to 3.0% by weight, preferably 0.05 to 1.
By adding 0% by weight, a biaxially oriented multilayer polypropylene film having excellent transparency and antiblocking properties can be obtained.

Production Method of Polymer Propylene homopolymer (A), propylene / α-olefin copolymer (B), propylene / α- relating to the present invention
The olefin copolymer (C) and the propylene-based polymer (D) are prepared by various known methods, for example, a catalyst typically formed from a solid titanium catalyst component and an organometallic compound catalyst component, or both components and an electron. It can be produced using a catalyst formed from a donor.

As the solid titanium catalyst component, titanium trichloride or a titanium trichloride composition produced by various methods,
Alternatively, a carrier-supported titanium catalyst component having a specific surface area of preferably 100 m 2 / g or more, which contains magnesium, halogen, an electron donor, preferably an aromatic carboxylic acid ester or an alkyl group-containing ether and titanium as essential components, can be mentioned. In particular, a polymer produced by using the latter catalyst component with a carrier is suitable.

The organoaluminum compound catalyst component is preferably an organoaluminum compound, specifically, trialkylaluminum, dialkylaluminum halide,
Examples thereof include alkyl aluminum sesquihalide and alkyl aluminum dihalide. Among these compounds, a suitable organometallic compound catalyst component varies depending on the type of the titanium catalyst component used.

The electron donor is an organic compound containing nitrogen, phosphorus, sulfur, oxygen, silicon, boron and the like, and preferable specific examples thereof include organic esters and organic ethers having these elements. .

Regarding the method for producing a polymer using a catalyst component with a carrier, for example, JP-A-50-108385 and JP-A-50-
No. 126590, JP-A-51-20297, JP-A-51-28189, JP-A-52-151691 and the like.

The propylene homopolymer and propylene / α-olefin copolymer having a high Iso according to the present invention can also be produced by using a single site catalyst. The single-site catalyst is a catalyst having a uniform active site (single site), and examples thereof include a metallocene catalyst (so-called Kaminsky catalyst) and a Brookhart catalyst. For example, a metallocene catalyst is a catalyst composed of a metallocene-based transition metal compound and at least one compound selected from the group consisting of an organoaluminum compound and a compound that reacts with the metallocene-based transition metal compound to form an ion pair, and an inorganic substance It may be supported on.

The metallocene-based transition metal compound is, for example, JP-A-5-209014 and JP-A-6-10.
0579, JP-A-1-301704, JP-A3-1
Examples thereof include the compounds described in JP-A No. 93796, JP-A No. 5-148284 and the like.

Examples of the organic aluminum compound include alkylaluminum, chain or cyclic aluminoxane, and the like. The chain or cyclic aluminoxane is produced by contacting alkylaluminum and water. For example, it can be obtained by adding alkylaluminum at the time of polymerization and then adding water, or by reacting water of crystallization of a complex salt or adsorbed water of an organic or inorganic compound with alkylaluminum.

The compound which reacts with the metallocene-based transition metal compound to form an ion pair is, for example, JP-A-1-50.
Examples thereof include compounds described in 1950, JP-A-3-207704 and the like. Examples of the inorganic material supporting the single-site catalyst include silica gel, zeolite, diatomaceous earth and the like.

Polymerization methods include bulk polymerization, solution polymerization,
Examples include suspension polymerization and gas phase polymerization. These polymerizations may be a batch method or a continuous method. The polymerization conditions are usually a polymerization temperature of −100 to + 250 ° C., a polymerization time of 5 minutes to 10 hours, and a reaction pressure of atmospheric pressure to 300 Kg / cm ² (gauge pressure).

Propylene Polymer Composition The propylene polymer composition according to the present invention is a composition obtainable from a propylene homopolymer (A) and a propylene / α-olefin copolymer (B). The content is 0.1 to 1.8 mol%, preferably 0.1 to 1.
It is in the range of 5 mol%, preferably 95 to 10% by weight of the propylene homopolymer (A), and more preferably 90 to 2%.
0% by weight, the propylene / α-olefin copolymer (B) is 5 to 90% by weight, and more preferably 10 to 80% by weight. If the α-olefin content is less than 0.1 mol% and further the propylene / α-olefin copolymer (B) is less than 5% by weight, the effect of improving the stretching temperature range in obtaining a biaxially stretched film may be small. Therefore, it may not be possible to obtain a biaxially stretched film having excellent thin and thin precision. As a result, the lamination strength with the propylene / α-olefin copolymer (C) layer is not improved, and the heat seal strength of the obtained film is also improved. It may not be improved. On the other hand, when the α-olefin content exceeds 1.8 mol%, the content is further 90%.
If the content exceeds the weight%, the rigidity, mechanical strength, etc. of the obtained biaxially stretched film may decrease.

The propylene polymer composition according to the present invention can be obtained by mixing the propylene homopolymer (A) and the propylene / α-olefin copolymer (B) by various known methods. For example, propylene homopolymer (A) and propylene / α-olefin copolymer (B) are previously prepared.
And the propylene homopolymer (A) or the propylene / α-olefin copolymer (B). After the polymerization, the propylene / α-olefin copolymer (B) or the propylene homopolymer (A) may be subsequently polymerized.

The propylene homopolymer (A), propylene / α-olefin copolymer (B) or propylene polymer composition of the present invention may be used either individually or in any of the following manners.
The heat stabilizer, the weather stabilizer, the ultraviolet absorber, the lubricant, the slip agent, the nucleating agent, the antistatic agent, the antifogging agent, the pigment, the dye, the various additives used in the ordinary polyolefin such as the inorganic or organic filler, etc. You may add in the range which does not impair the purpose of.

Biaxially Stretched Multilayer Polypropylene Film The biaxially stretched multilayer polypropylene film of the present invention comprises the propylene / α-olefin copolymer (C) on at least one side of the base layer obtained from the biaxially stretched propylene polymer. Layers are laminated. In addition, the biaxially stretched multilayer polypropylene film of the present invention has a layer comprising the propylene / α-olefin copolymer (C) on one side of the base layer obtained from the biaxially stretched propylene polymer and the other side. A biaxially stretched multilayer polypropylene film in which a layer comprising the propylene-based polymer (D) is laminated on the propylene.α, which is preferably a coating layer.
A biaxially oriented multilayer polypropylene film comprising an olefin copolymer (C) and the propylene polymer (D) each containing an antiblocking agent. The thickness of the biaxially stretched multi-layer polypropylene film having such a configuration is variously determined depending on the application and is not particularly limited, but usually the propylene polymer composition layer has a thickness of 7 to 100 μm.
m, preferably 10 to 50 μm, propylene / α
The olefin copolymer (C) layer is in the range of 0.5 to 15 μm, preferably 1 to 10 μm, and the propylene-based polymer (D) layer is in the range of 0.5 to 15 μm, preferably 1 to 10 μm.

The biaxially oriented multilayer polypropylene film of the present invention comprises a propylene homopolymer (A) and propylene / α.
-Propylene polymer composition obtainable from olefin copolymer (B), propylene / α-olefin copolymer (C) and, if necessary, propylene polymer (D) by coextrusion molding The multilayer sheet can be obtained by a known biaxially stretched film production method such as a simultaneous biaxially stretched method or a sequential biaxially stretched method. The conditions for biaxial stretching are known OPP.
Film production conditions, for example, in the sequential biaxial stretching method, the longitudinal stretching temperature is 125 ° C to 145 ° C, and the stretching ratio is 4.5 to 6
The transverse stretching temperature, the transverse stretching temperature is 165 to 190 ° C., and the stretching ratio is 9 to 11 times.

In the propylene polymer composition according to the present invention, the temperature range of transverse stretching can be widened to 7 ° C. as compared with the conventional method in the method for producing a biaxially stretched film, and the transverse stretching operation becomes easy. Thickness accuracy of the obtained biaxially stretched film, for example, thickness variation (2σ) with respect to the reference thickness of the OPP film can be reduced by 20 to 50% with respect to the biaxially stretched film obtained from the propylene polymer (A) alone. As a result, the laminate strength and heat seal strength of the obtained biaxially oriented multilayer polypropylene film are improved.

The biaxially stretched multilayer polypropylene film of the present invention may be subjected to surface treatment such as corona treatment or flame treatment on one side or both sides, if necessary. In addition, the biaxially stretched multilayer polypropylene film of the present invention may further have a low-temperature heat-sealing property depending on its use, in order to impart low-temperature heat-sealing property, high-pressure low-density polyethylene, linear low-density polyethylene, crystalline or low-crystalline ethylene and carbon number 3 A low-melting polymer such as a random copolymer of 10 to α-olefin or a random copolymer of propylene and ethylene or α-olefin having 4 or more carbon atoms, polybutene, ethylene-vinyl acetate copolymer These compositions may be laminated on the propylene polymer composition layer, the propylene / α-olefin copolymer (C) layer or the propylene polymer (D) layer. Further, in order to impart gas barrier properties, ethylene / vinyl alcohol copolymer, polyamide, polyester, vinylidene chloride-based polymer or the like may be laminated on such a layer by extrusion coating or the like, or a metal or an oxide thereof. , Silica or the like may be vapor-deposited. Of course, the surface of the stretched film may be subjected to anchor treatment with an adhesive such as imine or urethane, or a maleic anhydride-modified polyolefin may be laminated in order to increase the adhesion with other substances.

[0033]

The propylene polymer composition obtained from the propylene homopolymer (A) of the present invention and the propylene / α-olefin copolymer (B) is used as a base layer for producing a biaxially stretched film, The stretchability such as the uniform stretchability and the wide temperature range stretchability at the time of biaxial stretching under high temperature is improved, and the productivity can be more stabilized (the operation rate and the yield rate can be improved). Also,
The biaxially stretched film having the propylene polymer composition of the present invention as a base layer is excellent in thickness accuracy, has high heat seal strength,
There is no stickiness, high rigidity, and excellent transparency.
Any application where the film is used, for example, it can be used for non-food packaging films such as seaweed, rice balls and sushi, rice crackers, candy, food packaging films such as sweet bread, daily sundries, industrial products, etc. Further, it can be particularly preferably used as a film for pillow packaging.

[0034]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

Physical properties and the like in Examples and Comparative Examples were determined by the following evaluation methods. (Evaluation Method) 1) Elastic Modulus: Measured according to JIS K 7127. 2) Film thickness unevenness: The standard deviation of the specified width was measured. 3) Heat-sealing strength: Propylene / α-olefin copolymer composition layers are superposed on each other, and a heat-sealing tester (manufactured by Toyo Seiki Co., Ltd.) is used to set the temperature in the following table,
Heat sealing was performed under the conditions of a heat sealing pressure of 0.1 MPa and 1 second, and a 15 mm width was cut out and a tensile tester (manufactured by Toyo Seiki Co., Ltd.) was used to measure the tensile speed at 300 mm / min.

Example 1 <Base layer: propylene polymer composition layer> 40% by weight of a propylene homopolymer (MFR: 3.0 g / 10 minutes) relative to a propylene / ethylene-random copolymer (ethylene content: 1. 3 mol% MFR: 3.0 g / 10 min) 60
Tetrakis [methylene-3- (3 ', 5'-di-t-butyl-4'hydroxyphenyl) propionate] methane (Japan Product of Ciba-Gaiki Co., Ltd. Product name Irganox 1010) 1000
ppm and calcium stearate (made by NOF Corporation) 10
A propylene polymer composition was prepared in which 00 ppm, stearic acid monoglyceride (manufactured by Riken Vitamin) 6000 ppm as an antistatic agent, and stearyldiethanolamine (manufactured by Toho Chemical Co., Ltd.) 2000 ppm were added. <Heat Seal Layer: Propylene / α-Olefin Copolymer Composition Layer> As a polymer constituting the heat seal layer,
Ethylene content: 4.0 mol%, butene-1 content:
1.1 mol%, melting point 138 ° C, MFR: 7 g / 10 min propylene / ethylene / 1-butene random copolymer:
80% by weight, propylene content: 71.1 mol%, melting point: 110 ° C., MFR: 7.0 g / 10 min propylene / 1-butene random copolymer: 20% by weight, polymethylmethacrylate 0.10% by weight of an anti-blocking agent composed of particles, and tetrakis [methylene-3- (3 ', 5'-di-t-butyl-4'hydroxyphenyl) propionate] methane as a heat-resistant stabilizer (product manufactured by Ciba-Gay-Key Corp., product name Irga Knox 10
10) A propylene / α-olefin copolymer composition containing 1000 ppm and 1000 ppm of calcium stearate (manufactured by NOF CORPORATION) was prepared. <Anti-blocking layer: Propylene-based polymer composition layer>
Melting point 162 as a polymer constituting the anti-blocking layer
C., MFR 2.4 g / 10 min propylene homopolymer, 0.10% by weight of an anti-blocking agent composed of polymethylmethacrylate particles, and tetrakis [methylene-3- (3 ', 5'-di-t -Butyl-4'hydroxyphenyl) propionate] Methane (Product name Irganox 10 manufactured by Ciba-Gaiki Co., Ltd., Japan)
10) A propylene polymer composition containing 1000 ppm and 1000 ppm of calcium stearate (manufactured by NOF CORPORATION) was prepared. <Production of Biaxially Stretched Multilayer Film> The above-mentioned propylene polymer composition, propylene / α-olefin copolymer composition and propylene-based polymer composition are extruded at an extrusion ratio (1/10 /
1) Each was melt-extruded using a screw extruder, shaped using a multi-manifold type T-die, and rapidly cooled on a cooling roll to obtain a multilayer sheet having a thickness of about 1.5 mm. . This sheet was heated to about 125 ° C. and stretched 5 times in the film flow direction (longitudinal direction). The sheet stretched 5 times was heated to 155 ° C. and stretched 10 times in the direction (transverse direction) orthogonal to the flow direction to give a base layer thickness of 25 μm.
A biaxially stretched multilayer polypropylene film having a heat seal layer thickness of 2.5 μm and a blocking prevention layer thickness of 2.5 μm (total thickness: 30 μm) was obtained. The physical properties of the biaxially stretched multilayer polypropylene film were measured by the methods described above. The results are shown in Table 1.

Comparative Example 1 The propylene homopolymer used in Example 1 (MFR: 3.0 g / 10 min) was used alone instead of the propylene polymer composition in place of the base layer polymer used in Example 1. The same procedure as in Example 1 was carried out except that the biaxial stretching was carried out with the thickness of the base layer: 25 μm, the thickness of the heat seal layer: 2.5 μm, and the thickness of the anti-blocking layer: 2.5 μm (total thickness: 30 μm). A multilayer polypropylene film was obtained. The physical properties of the biaxially stretched multilayer polypropylene film were measured by the methods described above. The results are shown in Table 1.

[0038]

[Table 1]

As is clear from the results shown in Table 1, a propylene polymer composition obtained from the propylene homopolymer (A) of the present invention and the propylene / α-olefin copolymer (B) was used as the base layer. It can be seen that the axially stretched multilayer polypropylene film has reduced film thickness unevenness as compared with the biaxially stretched film shown in the comparative example, and also has a higher heat seal strength at the same temperature.

Continued front page    F term (reference) 4F100 AK07A AK25 AK64A AK64B                       AK64C AK66A AK66B AK66C                       AK67B AK67C AL05A BA02                       BA03 BA06 BA07 BA10B                       BA10C CA19 DE01 EC18                       EH20 EH202 EJ38 EJ38A                       EJ382 GB15 JA04B JA04C                       JL04 JL11 JL12 YY00A                 4J002 BB12W BB14X

Claims (10)

[Claims] 1. A propylene homopolymer (A) and a propylene / α-olefin copolymer (B) having a biaxially stretched α-olefin content of 0.1 to 1.8 mol%. A biaxially stretched multi-layer polypropylene film having a propylene / α-olefin copolymer (C) layer laminated on at least one surface of a base layer obtainable from the propylene polymer composition. 2. A propylene homopolymer (A) is 95-10.
The biaxially stretched multilayer polypropylene film according to claim 1, wherein the biaxially stretched multilayer polypropylene film is a propylene polymer composition which can be obtained by containing the propylene / α-olefin copolymer (B) in an amount of 5 to 90% by weight. 3. The propylene / α-olefin copolymer (B) has an α-olefin content of 0.4 to 2.2 mol%.
The biaxially stretched multilayer polypropylene film according to claim 2. 4. The biaxially stretched multilayer polypropylene film according to claim 2, wherein the α-olefin of the propylene / α-olefin copolymer (B) is ethylene and / or 1-butene. 5. The biaxially stretched multilayer polypropylene film according to claim 4, wherein the ethylene content in the propylene polymer composition is 0.1 to 1.5 mol%. 6. The melting point of the propylene / α-olefin copolymer (C) is in the range of 80 to 150 ° C.
The biaxially stretched multi-layer polypropylene film according to. 7. The biaxially stretched multilayer polypropylene film according to claim 1, wherein the propylene / α-olefin copolymer (C) contains an antiblocking agent. 8. The biaxially stretched multilayer polypropylene film according to claim 1, wherein the propylene polymer (D) layer is laminated on the other surface of the base layer obtainable from the propylene polymer composition. 9. The biaxially stretched multilayer polypropylene film according to claim 8, wherein the propylene polymer (D) contains an antiblocking agent. 10. A sheet obtained by coextrusion of a propylene polymer composition layer and a propylene / α-olefin copolymer (C) layer, which can be obtained by biaxially stretching. The biaxially stretched multilayer polypropylene film according to any one of items.