JP2002248719A - Multi-layer biaxially stretched polypropylene film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer biaxially stretched polypropylene film which is excellent in the balance of stretching property, rigidity and anti-static property, and can reduce the using amount for an anti-static agent. SOLUTION: A base layer comprises a polypropylene and an anti-static agent of which the content is within a specified range. In this case, for the polypropylene, the cold xylene soluble content (CXS) is within a specified range, and the melt flow rate is within a specified range. Also, the melting point (Tm) ( deg.C), which is obtained from the melting peak of DSC, and CXS (wt.%) satisfy a specified relationship, and the content of the polypropylene is within a specified range. Then, at least on one surface of such a base layer, a surface layer comprising a polypropylene is laminated for this multi-layer biaxially stretched polypropylene film. In this case, for the polypropylene, the cold xylene soluble content (CXS) is within a specified range, and the melt flow rate is within a specified range. Also, the melting point (Tm) ( deg.C), which is obtained from the melting peak of DSC, and CXS (wt.%) satisfy a specified relationship.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a multilayer biaxially oriented polypropylene film. More specifically, it has a good balance of stretchability, rigidity and antistatic properties,
The present invention relates to a multilayer biaxially oriented polypropylene film capable of reducing the amount of an antistatic agent used.

[0002]

2. Description of the Related Art Biaxially stretched polypropylene films are excellent in optical properties such as transparency and gloss, mechanical properties such as tensile strength and rigidity, and moisture proof properties. Used for a wide range of applications.

[0003] However, the biaxially stretched polypropylene film is easily charged with static electricity, which may cause dust to adhere to the film surface and poor ink deposition during printing. As a method for preventing static electricity of the biaxially stretched polypropylene film, a method of blending an antistatic agent has been conventionally known.

[0004] However, the antistatic agent may cause smoke and roll stains during the formation of the biaxially stretched polypropylene film. Therefore, as a method for preventing smoke and roll stains during film formation, an antistatic agent is contained. There is known a multilayer biaxially oriented polypropylene film in which at least one surface of a polypropylene to be laminated is a polypropylene substantially free of an antistatic agent.

For example, Japanese Patent Application Laid-Open No. 5-104688 discloses that an antistatic agent having a high rigidity and an excellent antistatic effect is contained in an amount of 0.1 to 1.5% by weight and has a density of 0.9070.
g / cm ³ or more of polypropylene as a base layer and a density of 0.
A biaxially stretched composite polypropylene film is described in which polypropylene of less than 9070 g / cm ³ is laminated on one or both sides of the base layer.

[0006] However, the density used for the base layer is 0.1.
9070 g / cm ³ or more polypropylene is generally
The biaxially stretched composite polypropylene film described in JP-A-5-104688 described above has a high melting point and insufficient stretchability, and an improvement in the balance between stretchability, rigidity and antistatic properties has been desired. .

[0007] Japanese Patent Application Laid-Open No. 10-180963 discloses that the evaporation of an antistatic agent causes less contamination of a film forming process and a working environment, and is excellent in antistatic properties and transparency, and has a mesopentad fraction of 92% or more. The mesopentad fraction is 70 to 90% on at least one surface of the base layer polypropylene resin layer.
And a laminated film in which a surface polypropylene resin layer having a melting point of 155 ° C. or more and a crystallization temperature of 100 ° C. or more is laminated.

However, the stretchability of the base layer polypropylene resin having a mesopentad fraction of 92% or more may be insufficient, or the balance between the stretchability and the rigidity may be insufficient, as described in JP-A-10-180963. It has been desired that the laminated film of (1) has an improved balance between stretchability, rigidity and antistatic property.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer biaxially oriented polypropylene film which has an excellent balance between stretchability, rigidity and antistatic properties and can reduce the amount of an antistatic agent used.

[0010]

Means for Solving the Problems In view of such circumstances, the present inventors have conducted intensive studies. As a result, the amount of the cold xylene-soluble component (CXS) is within a specific range, and the melt flow rate is within a predetermined range. The melting point (Tm) (° C.) and CXS (% by weight) determined from the melting peak of DSC satisfy a specific relationship, and the content is within a certain range of polypropylene and the content is within a certain range of antistatic. On at least one side of the base layer made of the agent, the amount of the cold xylene-soluble component (CXS) is in a specific range, the melt flow rate is in a certain range,
Melting point (Tm) (° C) determined from DSC melting peak and C
The present inventors have found that a multilayer biaxially stretched polypropylene film formed by laminating a surface layer made of polypropylene whose XS (% by weight) satisfies a specific relationship can solve the above problems, and have completed the present invention.

That is, according to the present invention, the content of the cold xylene-soluble component (CXS) is less than 1.5 (% by weight), the melt flow rate is 0.5 to 20 (g / 10 minutes),
CXS and melting point (Tm) (° C) obtained from melting peak of C
(Weight%) polypropylene 99.8-98 (weight%) satisfying the following formula (I) 2 (CXS) + 152 ≦ Tm ≦ 2 (CXS) +159 (I) and antistatic agent 0.2-2 ( Wt%) on at least one side of the base layer.
(% By weight) and the melt flow rate is 0.5 to
The melting point (Tm) (° C.) and CXS (% by weight) determined from the melting peak of DSC were 20 (g / 10 minutes), and the following formula (II): 2 (CXS) + 148 ≦ Tm ≦ 2 (CXS) +155 The present invention relates to a multilayer biaxially oriented polypropylene film obtained by laminating a surface layer made of polypropylene satisfying (II). Hereinafter, the present invention will be described in detail.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polypropylene used for the base layer of the present invention includes propylene homopolymer, propylene-based random copolymer, and a mixture of these polymers. The propylene homopolymer is a polymer obtained by polymerizing only propylene, and the propylene-based random copolymer is selected from propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms. And a random copolymer obtained by copolymerizing at least one comonomer.

The α-olefin having 4 to 20 carbon atoms includes, for example, 1-butene, 2-methyl-1-
Propene, 1-pentene, 2-methyl-1-butene, 3
-Methyl-1-butene, 1-hexene, 2-ethyl-1
-Butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1
-Heptene, methyl-1-hexene, dimethyl-1-pentene, ethyl-1-pentene, trimethyl-1-butene, methylethyl-1-butene, 1-octene, methyl-1-pentene, ethyl-1-hexene, Dimethyl-1
-Hexene, propyl-1-heptene, methylethyl-
1-heptene, trimethyl-1-pentene, propyl-
1-pentene, diethyl-1-butene, 1-nonene, 1
-Decene, 1-undecene, 1-dodecene, etc., preferably 1-butene, 1-pentene, 1-hexene, 1-octene, more preferably 1-butene,
1-hexene.

As the propylene random copolymer,
Propylene-ethylene random copolymer, propylene-
α-olefin random copolymer, propylene-ethylene-α-olefin random copolymer, and the like.

Examples of the propylene-α-olefin random copolymer include a propylene-1-butene random copolymer, a propylene-1-hexene random copolymer and the like, and a propylene-ethylene-α-olefin random copolymer. Examples thereof include a propylene-ethylene-1-butene random copolymer and a propylene-ethylene-1-hexene random copolymer. The propylene-based random copolymer is preferably a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, or a propylene-ethylene-1-butene random copolymer.

When the polypropylene used for the base layer of the present invention is a propylene-ethylene random copolymer,
From the viewpoint of balance between stretchability, rigidity and antistatic property,
The ethylene content is preferably 0.1 to 2.5% by weight, more preferably 0.2 to 2% by weight, and still more preferably 0.4 to 1.5% by weight.

When the polypropylene used in the base layer of the present invention is a propylene-α-olefin random copolymer, the content of α-olefin is preferably 0.1 from the viewpoint of balance between stretchability, rigidity and antistatic property. 5-6
%, More preferably 2 to 5% by weight, even more preferably 3.5 to 4.5% by weight.

When the polypropylene used in the base layer of the present invention is a propylene-ethylene-α-olefin random copolymer, the content of ethylene and α-olefin may be reduced from the viewpoint of balance between stretchability, rigidity and antistatic property. The total is preferably from 0.2 to 5% by weight, more preferably from 0.4 to 4% by weight, still more preferably from 0.1 to 4% by weight.
8 to 3% by weight

The amount of the cold xylene-soluble component (CXS) of the polypropylene used for the base layer of the present invention is 1.5 (% by weight).
Less than 1.2, preferably less than 1.2% by weight,
More preferably, it is less than 1.0 (% by weight). When the CXS is 1.5 (% by weight) or more, the rigidity of the obtained multilayer biaxially oriented polypropylene film may be insufficient.

The melt flow rate of the polypropylene used for the base layer of the present invention is 0.5 to 20 (g / 10 minutes), preferably 1 to 10 (g / 10 minutes). If the melt flow rate is less than 0.5 (g / 10 minutes), the fluidity during extrusion may be insufficient, and the melt flow rate may be less than 20 (g / 1).
0 minutes), the stretchability may be insufficient.

The melting point (Tm) (° C.) and CXS (% by weight) determined from the DSC melting peak of the polypropylene used for the base layer of the present invention are represented by the following formula (I): 2 (CXS) + 152 ≦ Tm ≦ 2 (CXS) ) +159 (I), preferably satisfying the following formula (III): 2 (CXS) + 153 ≦ Tm ≦ 2 (CXS) +158 (I−1), and more preferably the following formula (III) IV) 2 (CXS) + 154 ≦ Tm ≦ 2 (CXS) +157 (I-2).

Melting point (Tm) (° C.) and CXS (% by weight)
When Tm <2 (CXS) +152, the obtained multilayer biaxially stretched polypropylene film may have insufficient rigidity, and when Tm> 2 (CXS) +159, the stretchability is insufficient. There may be.

The method for producing the polypropylene used for the base layer of the present invention is not particularly limited, but the method for producing a propylene homopolymer is preferably a method using a metallocene catalyst, and the propylene-based random copolymer is preferably used. As a method for producing the coalescence, a method using a Ziegler-Natta catalyst or a method using a metallocene catalyst is preferable.

The antistatic agent used in the base layer of the present invention comprises:
There is no particular limitation, as long as it is generally used as an antistatic agent for polyolefin films. For example, primary amine salts, tertiary amines, quaternary ammonium compounds, cationic ones such as alkylpyridium salts, sulfated oils, sulfated amide oils, sulfated ester oils, fatty alcohol sulfates, alkyls Anionic compounds such as sulfates, fatty acid ethyl sulfonates, alkyl sulfonates, alkyl benzene sulfonates, phosphates, etc., partial fatty acid esters of polyhydric alcohols, ethylene oxide adducts of fatty alcohols, fatty amines Or ethylene oxide adducts of fatty acid amides, ethylene oxide adducts of alkyl phenols, ethylene oxide adducts of alkyl naphthols, alkyl alcohols, polyethylene glycols, alkyl diethanolamines and fatty acid esters thereof, alkyl diethanol Nonionic ones such as amide, polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ester, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylamine and its fatty acid ester Carboxylic acid derivatives, imidazoline derivatives and the like. These antistatic agents may be used alone or in combination of two or more.

Preferred are nonionic ones such as alkyl alcohols, partial fatty acid esters of polyhydric alcohols, alkyl diethanolamines and fatty acid esters thereof, alkyl diethanolamides, polyoxyethylene alkyl amines and fatty acid esters thereof.

The amount of the antistatic agent used in the base layer of the present invention is from 0.2 to 2% by weight, preferably from 0.5 to 2% by weight.
1.5% by weight. (Accordingly, the amount of the polypropylene used for the base layer of the present invention is 99.8 to 98% by weight.
And preferably 99.5 to 98.5% by weight. ) When the amount of the antistatic agent is less than 0.2% by weight,
If the antistatic property is insufficient, and if it exceeds 2% by weight, smoke and roll contamination may occur during film formation.

The polypropylene used for the surface layer of the present invention includes propylene homopolymer, propylene-based random copolymer, and a mixture thereof. Preferably, it is a propylene-based random copolymer. Examples of the propylene homopolymer and the propylene random copolymer include the propylene homopolymer and the propylene random copolymer used as the polypropylene used in the base layer of the present invention described above.

When the polypropylene used for the surface layer of the present invention is a propylene-ethylene random copolymer,
From the viewpoint of balance between stretchability, rigidity and antistatic property,
The ethylene content is preferably 0.1 to 2.5% by weight, more preferably 0.2 to 2% by weight, and still more preferably 0.4 to 1.5% by weight.

When the polypropylene used for the surface layer of the present invention is a propylene-α-olefin random copolymer, the α-olefin content is preferably 0.1 to 2 from the viewpoint of balance between stretchability, rigidity and antistatic properties. 5-6
%, More preferably 2 to 5% by weight, even more preferably 3.5 to 4.5% by weight.

When the polypropylene used for the surface layer of the present invention is a propylene-ethylene-α-olefin random copolymer, the content of ethylene and α-olefin may be reduced from the viewpoint of balance between stretchability, rigidity and antistatic property. The total is preferably from 0.2 to 5% by weight, more preferably from 0.4 to 4% by weight, still more preferably from 0.1 to 4% by weight.
8 to 3% by weight.

The amount of the cold xylene-soluble component (CXS) of the polypropylene used for the surface layer of the present invention is 2 (% by weight) or more, preferably 2.5 (% by weight) or more. CX
When S is less than 2.0 (% by weight), the obtained multilayer biaxially oriented polypropylene film may have insufficient antistatic properties or may not be able to sufficiently reduce the amount of the antistatic agent used.

The melt flow rate of the polypropylene used for the surface layer of the present invention is 0.5 to 20 (g / 10 minutes), preferably 1 to 10. If the melt flow rate is less than 0.5 (g / 10 minutes), the fluidity during extrusion may be insufficient, and if it exceeds 20 (g / 10 minutes), the stretchability may be insufficient. There is.

The melting point (Tm) (° C.) and CXS (% by weight) determined from the DSC melting peak of the polypropylene used for the surface layer of the present invention are represented by the following formula (II): 2 (CXS) + 148 ≦ Tm ≦ 2 (CXS) ) +155 (II), and preferably satisfy the following formula (II-1) 2 (CXS) + 150 ≦ Tm ≦ 2 (CXS) +154.

When the melting point (Tm) (° C.) and CXS (% by weight) determined from the melting peak of the DSC of the polypropylene used for the surface layer of the present invention are Tm> 2 (CXS) +155, the obtained multilayer biaxial film is obtained. In some cases, the stretched polypropylene film has insufficient antistatic properties, the amount of the antistatic agent used cannot be sufficiently reduced, and Tm <2 (C
XS) +148, the resulting multilayer biaxially oriented polypropylene film may have insufficient rigidity.

The method for producing the polypropylene used for the surface layer of the present invention is not particularly limited, but a method using a Ziegler-Natta catalyst or a method using a metallocene catalyst is preferred.

The surface layer of the present invention may or may not contain an antistatic agent. When the surface layer of the present invention contains an antistatic agent, examples of the antistatic agent include the antistatic agents used in the base layer of the present invention described above. The content of the antistatic agent is preferably smaller than that of the antistatic agent contained in the base layer, from the viewpoints of preventing smoke and roll contamination generated during film formation and reducing the amount of the antistatic agent used.

The method of blending the antistatic agent in the base layer or surface layer used in the present invention is not particularly limited, and the antistatic agent can be uniformly dispersed in the polypropylene used in the base layer or surface layer. Known methods can be used. For example, a method of mixing with a ribbon blender, a Henschel mixer, a tumbler mixer, or the like, and melting and kneading the mixture with an extruder may be used. Further, polypropylene 100 used for the base layer or the surface layer
There is also a method in which a master batch containing about 1 to 100 parts by weight of an antistatic agent is prepared in advance with respect to parts by weight, and the master batch is appropriately blended so that the concentration of the antistatic agent becomes a predetermined concentration. Further, when the antistatic agent is blended, a known antioxidant, neutralizing agent, lubricant, non-dropping agent, antiblocking agent and the like may be appropriately blended as necessary.

The method for forming a multilayer biaxially oriented polypropylene film of the present invention is not particularly limited, and a multilayer method in which a base layer and a surface layer are co-extruded using a common die is usually used.

The method for forming and stretching the multilayer biaxially oriented polypropylene film of the present invention is not particularly limited, and examples thereof include a sequential biaxial stretching method, a simultaneous biaxial stretching method,
Examples include a tubular biaxial stretching method. The sequential biaxial stretching method, simultaneous biaxial stretching method, and tubular biaxial stretching method will be described below.

The polypropylene is melted by an extruder, extruded from a T-die, and cooled and solidified into a sheet by a cooling roll. Next, the obtained sheet is preheated and stretched in a longitudinal direction by a series of heating rolls. Next, both ends of the obtained longitudinally stretched sheet are respectively gripped by two rows of chucks arranged in the flow direction, and the spacing between the two rows of chucks is increased in a heating furnace including a preheating section, a stretching section, and a heat treatment section. Thereby, it is stretched in the lateral direction. Next, if necessary, a corona treatment or the like is performed, and the film is wound up.

The longitudinal stretching temperature in the sequential biaxial stretching method is usually from 100 to 160 ° C., preferably from 110 ° C. to 1 ° C.
It is 50 degreeC, More preferably, it is 120-145 degreeC. The longitudinal stretching ratio is usually 3 to 8 times, preferably 3.
It is 5 to 7.5 times, more preferably 4 to 7 times. The transverse stretching temperature is usually 140 to 180 ° C, preferably 150 to 180 ° C.
To 175 ° C, more preferably 155 to 170 ° C
It is. The transverse stretching ratio is usually 5 to 12 times, preferably 6 to 11 times, and more preferably 7 to 10 times.

Simultaneous biaxial stretching type polypropylene is melted by an extruder, extruded from a T-die, and cooled and solidified into a sheet by a cooling roll. Next, both ends of the obtained sheet are respectively gripped by two rows of chucks arranged in the flow direction, and in a heating furnace including a preheating section, a stretching section, and a heat treatment section, the chuck intervals of the two rows and the individual , The film is stretched simultaneously in the vertical and horizontal directions. Next, if necessary, a corona treatment or the like is performed, and the film is wound up.

In the simultaneous biaxial stretching method, the stretching temperature is usually from 140 to 180 ° C., preferably from 150 to 175 ° C.
° C, more preferably 155 ° C to 170 ° C.
The longitudinal stretch ratio and the transverse stretch ratio are usually 3 to 9 times, preferably 3.5 to 8.5 times, more preferably 4 to 8.5 times.
It is eight times.

Tubular biaxial stretching method Polypropylene is melted by an extruder, extruded from an annular die, and cooled and solidified into a tube in a water tank. The resulting tube is then preheated in a heating furnace or a series of hot rolls, then passed through a low speed nip roll and wound up with a high speed nip roll to stretch in the flow direction. At this time, the tube is expanded in the width direction by expanding the tube by the internal pressure of the air stored between the low-speed nip roll and the high-speed nip roll. Next, the stretched film that has passed through the high-speed nip roll is heat-treated in a heating furnace or a series of hot rolls. Next, a corona treatment or the like is performed as necessary,
Take up.

The stretching temperature in the tubular biaxial stretching method is usually from 120 to 180 ° C., preferably from 130 to 180 ° C.
To 170 ° C, more preferably 140 to 160 ° C. When the ratio of the thickness of the unstretched tube to the thickness of the stretched film is defined as a stretching ratio (unit: times), the stretching ratio is usually 10 to 60 times, preferably 20 to 50 times, and more preferably 30 to 40 times. It is twice.

The melting temperature of polypropylene in the above-mentioned sequential biaxial stretching method, simultaneous biaxial stretching method and tubular biaxial stretching method is usually from 230 to 290 ° C., preferably from 240 to 280 ° C.

The thickness of the multilayer biaxially oriented polypropylene film of the present invention is not particularly limited, but is usually 200 μm or less, preferably 5 to 100 μm, and more preferably 8 to 80 μm.

The thickness of the surface layer of the multilayer biaxially oriented polypropylene film of the present invention is not particularly limited, but from the viewpoint of antistatic properties, reduction of the amount of antistatic agent used or rigidity, it is preferable that the thickness of the base layer be 1 to 50 for thickness
(%).

[0049]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. (1) Production method of pellets Propylene polymer A pellets and antistatic masterbatch pellets used in the base layers of Examples and Comparative Examples,
The method for producing the propylene-based polymer B pellet used for the surface layer is shown below.

(1-1) Propylene Polymer A Pellets As the propylene polymer A, a propylene-1-butene random copolymer produced by a gas phase polymerization method using a Ziegler-Natta catalyst was used. Propylene polymer A
0.1 part by weight of calcium stearate as a stabilizer, 0.15 part by weight of an antioxidant (trade name: Irganox1010, manufactured by Ciba Specialty Chemicals), and 0.15 parts by weight of an antioxidant (trade name: Irganox 168, 0.1 parts by weight (manufactured by Ciba Specialty Chemicals) were mixed with a Henschel mixer, and the mixture was granulated with an extruder and pelletized. Table 1 shows the structural analysis values of the propylene-based polymer A pellets.

(1-2) Propylene Polymer B Pellets As the propylene polymer B, a propylene-ethylene random copolymer produced by a gas phase polymerization method using a Ziegler-Natta catalyst was used. Granulation was performed in the same manner as for the propylene-based polymer A, and pelletized. Table 1 shows the structural analysis values of the propylene-based polymer B pellets.

(1-3) Antistatic Agent Masterbatch Polymerized powder of propylene homopolymer C polymerized by a gas phase polymerization method using a Ziegler-Natta catalyst is granulated in the same manner as propylene-based polymer A, Pelletized.
With respect to 90 parts by weight of pellets of propylene homopolymer C, stearyl diethanolamine as an antistatic agent,
10 parts by weight of a mixture of alkyl diethanolamine monoester and stearyl diethanolamine diester, 0.1 part by weight of calcium stearate as a stabilizer, 0.1 part by weight of an antioxidant (Irganox 1010)
5 parts by weight, and an antioxidant (Irganox 168)
Was mixed with a Henschel mixer, and the mixture was granulated by an extruder and pelletized to obtain an antistatic agent master batch pellet. Table 1 shows the structural analysis values of the propylene-based polymer C pellets.

(2) Method of measuring physical properties Physical properties of each item in Examples and Comparative Examples were measured according to the following methods. (2-1) Melt flow rate (unit: g / 10 min) Measured according to JIS K7210.

(2-2) Comonomer content (unit:% by weight) Ethylene content: Handbook of Polymer Analysis (1985)
In accordance with the method described in “(i) Random copolymer” on page 256, published by Asakura Shoten Co., Ltd., by IR spectroscopy. Butene-1 content: determined from the following equation by IR spectroscopy. Butene-1 content (% by weight) = 1.208 K ′ K ′ = absorbance of 767 cm ⁻¹

(2-3) Amount of cold xylene soluble component (CX
S) (Unit: wt%) After dissolving 10 g of the propylene-based polymer in 1000 ml of boiling xylene, the solution was gradually cooled to 50 ° C, then immersed in ice water, cooled to 20 ° C with stirring, and left at 20 ° C overnight. After that, the precipitated polymer was separated by filtration, xylene was evaporated from the filtrate, and dried under reduced pressure at 60 ° C. to recover a polymer soluble in xylene at 20 ° C., and its weight was measured and determined.

(2-4) Melting point (Tm) (unit: ° C.) Differential scanning calorimeter (DSC-7 manufactured by PerkinElmer)
After heat-treating the pellets at 220 ° C. for 5 minutes, the pellets were cooled to 150 ° C. at a rate of temperature drop of 300 ° C./min, kept at 150 ° C. for 1 minute, and further cooled to 50 ° C. at a rate of 5 ° C./min. , And the melting peak temperature at the time of heating from 50 ° C. to 180 ° C. at a heating rate of 5 ° C./min was determined as the melting point.

(2-5) Antistatic property (unit: second) In a constant temperature and humidity chamber (temperature 23 ° C., humidity 50%), a static honest meter (Static Honestme) was used.
ter, manufactured by Shishido Shokai Co., Ltd.)
After charging an m-size sample piece for 1 minute at an applied voltage of 10 kV, the number of seconds (half-life) until the charged voltage was reduced to half was defined as an antistatic value. The smaller the value, the better the surface conductivity and the better the antistatic property. After measuring the corona discharge treated film in a constant temperature and humidity room for 7 days,
The surface side of the film subjected to the corona discharge treatment was measured three times per sample, and the average value was obtained.

(2-6) Rigidity (unit: MPa) Test pieces each having a width of 20 mm were taken from the longitudinal direction (MD) of the film left for 7 days in a constant temperature and humidity chamber (23 ° C., humidity 50%). Chuck interval 60m by tensile tester
m, an SS curve was taken at a tensile speed of 5 mm / min, and the initial elastic modulus (Young's modulus) was measured.

(2-7) Stretchability (Film Appearance) After completion of the transverse stretching performed by gripping both ends of the sheet after longitudinal stretching with a chuck, the width of the unstretched portion remaining in the chuck portion is measured with a ruler. The value obtained by summing the widths was used as an evaluation value of the stretchability (film appearance) (hereinafter, referred to as a left-to-ear width). The larger the value (the wider the unstretched portion), the worse the film appearance tends to be, indicating that the stretchability is low.

Example 1 (1-a) Preparation of Base Layer Polypropylene Pellets 90 parts by weight of the propylene polymer A pellets obtained in the above (1-1) and the antistatic agent master obtained in the above (1-3) 10 parts by weight of the batch pellets were mixed with a pellet blender to obtain a base layer polypropylene pellet.

(1-b) Preparation of Surface Layer Polypropylene Pellets 100 parts by weight of the propylene polymer B pellets obtained in (1-2) and an anti-blocking agent (trade name: CS-
11 and CS-18, both manufactured by Sumitomo Chemical Co., Ltd.) and 1 part by weight of a master batch pellet of 10% by weight were mixed with a pellet blender to obtain a surface layer polypropylene pellet.

(1-c) Preparation of Cast Sheet The base polypropylene pellets obtained in (1-a) and the surface polypropylene pellets obtained in (1-b) are melt-kneaded by different extruders. , One co-extrusion T at a resin temperature of 260 ° C. and 230 ° C. respectively.
Feeded to die. From the T-die, a resin extruded as a two-layer, three-layer structure of surface layer / base layer / surface layer was rapidly cooled and solidified by a cooling roll at 30 ° C. to obtain a cast sheet having a thickness of 1.0 mm.

(1-d) Stretching and heat treatment The cast sheet obtained in the above (1-c) is subjected to preheating,
The film is stretched 5 times in the machine direction at a stretching temperature of 145 ° C. due to the difference in roll peripheral speed of the longitudinal stretching machine, and subsequently in a heating furnace at a stretching temperature of 162 ° C.
, And heat-treated at 170 ° C. to obtain a multilayer biaxially stretched film having a thickness of 25 μm. Table 2 shows the thickness of the obtained film and the amount of the antistatic agent used.
Further, the width of the film left after the completion of stretching was measured with a ruler to evaluate the stretchability. The results are shown in Table 3.

(1-e) Corona discharge treatment and winding-up One surface of the multilayer biaxially stretched film obtained in the above (1-d) was treated with a corona discharge treatment machine so that the surface wetting tension was 42 dyne / cm. After the treatment, the film was wound by a winder. The obtained multilayer biaxially stretched polypropylene film was allowed to stand for 7 days in a thermo-hygrostat to evaluate rigidity and antistatic properties. The results are shown in Table 3.

Example 2 The extruded amounts of the molten resin of the base layer polypropylene pellets and the molten resin of the surface layer polypropylene pellets in (1-c) of Example 1 to the T-die were changed, and the thicknesses of the base layer and the surface layer are shown in Table 2. Except for having been changed as shown, a multilayer biaxially oriented polypropylene film was obtained in the same manner as in Example 1,
The stretchability, rigidity and antistatic properties were evaluated. The thickness of the film and the amount of the antistatic agent used are shown in Table 2, and the evaluation results of the stretchability, rigidity and antistatic properties are shown in Table 3.

Comparative Example 1 In Example 1 (1-c), the molten resin of the propylene polymer A pellet was extruded from the T-die without using the surface layer.
A multilayer biaxially-stretched polypropylene film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that a single-layer structure consisting of only the base layer was used. Table 2 shows the thickness of the film and the amount of the antistatic agent used,
Table 3 shows the evaluation results of the stretchability, the rigidity, and the antistatic property.

[0067]

[Table 1] Tm (° C) and CXS (% by weight) of propylene polymer A
Is 2 × 0.4 (% by weight) + 152 ≦ 155.3 (° C.) ≦ 2 ×
0.4 (% by weight) +159. Tm (° C) and CX of propylene polymer B
S (% by weight) is 2 × 3.4 (% by weight) + 148 ≦ 158.0 (° C.) ≦ 2 ×
3.4 (% by weight) +155.

[0068]

[Table 2]

[0069]

[Table 3]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 23:00 B29K 23:00 B29L 7:00 B29L 7:00 (72) Inventor Yoichi Obata Chiba 5-1, Anesaki Beach, Ichihara City Sumitomo Chemical Co., Ltd. F-term (reference) 4F100 AK07A AK07B AK07C BA03 BA06 BA10A BA10C BA26 CA22B EH20 EJ38 EJ55 GB15 GB23 JA04A JA04B JA04C JA06A JA06B JA06C JB08JJJJJ08JB08B YY00C 4F210 AA11 AB09 AG01 QC05 QC06 QG01 QG18 4J002 BB121 BB141 BB151 CH052 ED036 EH056 EN006 EN136 EU046 EU116 EV186 EV256 EV266 EW046 FD102 FD106 GF00

Claims (2)

[Claims] 1. The amount of a cold xylene-soluble component (CXS) is 1.5.
(% By weight) and the melt flow rate is 0.5 to
The melting point (Tm) (° C.) and CXS (% by weight) determined from the melting peak of DSC were 20 (g / 10 minutes) and the following formula (I): 2 (CXS) + 152 ≦ Tm ≦ 2 (CXS) +159 The cold xylene soluble component (CXS) is 2 (weight) on at least one surface of a base layer comprising 99.8 to 98 (weight%) of polypropylene satisfying (I) and 0.2 to 2 (weight%) of an antistatic agent. %) Or more, and the melt flow rate is 0.5 to 20
(G / 10 minutes), and the melting point (Tm) (° C.) and CXS (% by weight) determined from the melting peak of DSC are represented by the following formula (I).
I) A multilayer biaxially oriented polypropylene film comprising a laminate of surface layers made of polypropylene that satisfies 2 (CXS) + 148 ≦ Tm ≦ 2 (CXS) +155 (II). 2. The content of the antistatic agent contained in the surface layer is as follows:
The multilayer biaxially oriented polypropylene film according to claim 1, wherein the content of the antistatic agent is less than that of the base layer.