JPH0881588A - Polypropylene resin composition and film made by using it - Google Patents

Abstract

PURPOSE: To obtain a polypropylene resin composition which gives a film free from burn marks and nonuniformity in thickness and improved in impact strength and surface characteristics with improved productivity by mixing a specified polypropylene resin, a silicon dioxide compound, a phenolic antioxidant and a phosphorus antioxidant. CONSTITUTION: This composition is obtained by mixing 100 pts.wt. polypropylene resin having an MI of 1-20g/10min, a pentad fraction fmmmm, determined by the<13> C-NMR spectrometry, of 85.0-95.0mol%, and a polydispersity index (PDI-P) at ω2 /10ω1 of at most 30, wherein ω1 and ω2 respectively are circular frequencies to provide storage elastic moduluses G' of 2×10<3> and 2×10<5> dyne/cm<2> by the melt elastic modulus measurement, 0.05-0.50 pts.wt. surface treated silicon dioxide compound having a di-n-butylamine (DBA) value of at most 400meq/kg, 0.05-0.30 pts.wt. phenolic antioxidant and 0.03-0.20 pts.wt. phosphorus antioxidant. The composition is formed into film by casting at a haul-off speed of at least 50m/min.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polypropylene resin composition and a film using the same. More specifically, in addition to good productivity, there is no burning or uneven film thickness, and a polypropylene-based resin composition that gives a cast film having excellent impact strength and surface characteristics, and a cast using this resin composition as a base material, cast The present invention relates to a film having the above excellent quality obtained by a molding method (T die method).

[0002]

2. Description of the Related Art Unstretched polypropylene films are widely used in the packaging field because of their good transparency, heat resistance, mechanical properties and gloss. This unstretched polypropylene film is usually produced by the cast molding method (T die method), but in recent years, the number of processing manufacturers increasing the take-up speed is increasing in order to improve productivity. Further, in forming the film, as the antioxidant, 2,6-di-t-butyl-p-cresol (BH
T) is most commonly added, but from the viewpoint of safety and hygiene and yellowing, recently, an antioxidant other than BHT has been added. As a substitute for the above-mentioned BHT, a method of using a hindered phenol-based antioxidant and a phosphorus-based antioxidant together is well known, and this antioxidant prescription makes it possible to prevent burning due to a decrease in the molecular weight during molding, and a film. The occurrence of defective phenomena such as uneven thickness is prevented (for example, Japanese Patent Publication No. 56-5417).
On the other hand, as described above, in order to improve productivity, the take-up speed during cast molding has become faster and faster in recent years, resulting in a new problem that the impact strength of the film is lowered due to the orientation. . This problem is remarkable in the case where the base polymer has a wide molecular weight distribution and the combination of a hindered phenol antioxidant and a phosphorus antioxidant is used in combination. Also, narrowing the molecular weight distribution of the base polymer,
If a combination system of the above-mentioned antioxidant is added, the impact strength is improved, but with conventional lubricant and anti-blocking agent formulations, slip properties and anti-blocking properties are deteriorated, and both surface properties and mechanical properties are deteriorated. The problem arises that a film that satisfies the quality cannot be obtained.

[0003]

SUMMARY OF THE INVENTION Under the above circumstances, the present invention is directed to the formation of a film by the cast molding method (T die method), even if the take-up speed is as high as 50 m / min or more. To provide a polypropylene resin composition capable of preventing a defective phenomenon such as thickness unevenness and providing a film excellent in impact strength and surface characteristics, and a film having the above-mentioned excellent quality based on the resin composition. The purpose is to

[0004]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that a polypropylene-based resin having specific properties is added to a specific silicon dioxide compound and a phenol-based antioxidant. It has been found that the object can be achieved by a resin composition prepared by adding a phosphorus antioxidant and a phosphorus antioxidant at a predetermined ratio. The present invention
It was completed based on this knowledge.

That is, according to the present invention, (A) (a) a melt index (MI) of 1 to 20 g / 10 min, and (b) a pentad component obtained by nuclear magnetic resonance spectroscopy ( ¹³ C-NMR) using isotope carbon. Modulus f _mmmm is 85.0 to 95.0 mol% and (c) storage elastic modulus (G ') in melt viscoelasticity measurement
When There was a 2 × 10 ³ dyne / cm ₁ and ² to become such angular frequency ^{ω, 2 × 10 5 dyne /} cm 2 become such angular frequency and omega _2, molecular weight, represented by ω ₂ / 10ω ₁ (B) DBA for 100 parts by weight of a polypropylene resin having a distribution index (PDI-P) of 30 or less.
(Di-n-butylamine) value is 400 meq.
q) / kg or less of silicon dioxide compound 0.05 to 0.50 parts by weight, (C) phenolic antioxidant 0.05 to 0.30 part by weight, and (D) phosphorus antioxidant 0.03 to The present invention provides a polypropylene resin composition containing 0.20 parts by weight. The present invention also provides the above polypropylene-based resin composition for films, and further a film comprising the above polypropylene-based resin composition.

In the polypropylene resin composition of the present invention, the polypropylene resin used as the component (A) should satisfy the following conditions. First, (a)
It is necessary that the melt index (MI) be in the range of 1 to 20 g / 10 minutes. If this MI deviates from the above range, the cast film moldability will deteriorate. From the viewpoint of cast film moldability, the preferred MI is 4.0 to 15.
It is in the range of 0 g / 10 minutes, and particularly preferably in the range of 5.5 to 9.0 g / 10 minutes. The MI is JIS K-72.
It is a value measured according to 10 under the conditions of a temperature of 230 ° C. and a load of 2,160 g.

Next, the pentad fraction f _mmmm determined by nuclear magnetic resonance spectroscopy ( ¹³ C-NMR) with (b) isotope carbon must be in the range of 85.0 to 95.0 mol%. . If the pentad fraction is less than 85.0 mol%,
The rigidity and anti-blocking property of the film are remarkably lowered, the slip property is lowered when it exceeds 95.0 mol%, and the impact resistance is remarkably lowered when the film is formed under a high-speed molding condition of a take-up speed of 100 m / min or more. To do. From the viewpoint of the balance of film rigidity, anti-blocking property, slip property, and impact resistance when molded under high-speed molding conditions, the preferred pendd fraction f _mmmm is in the range of 87.0 to 95.0 mol%. . In addition, this pendad fraction f
_mmmm stands for "Macromolcules
ules) ”, vol. 8, page 687 (1975), and manufactured by JEOL Ltd.
Using M-EX400 type NMR, sample solvent 1,2,4-
Trichlorobenzene / benzene d ₆ (heavy benzene) mixed solvent (volume ratio 9: 1), measurement temperature 130 ° C, number of integrations 4
It is a value obtained by performing ¹³ C-NMR measurement under the conditions of 000 times, pulse angle 45 °, and pulse interval 4 sec (hereinafter referred to as area method). Note that this pentad fraction f
_mmmm is used as a guide, and the ¹³ C-NM obtained in this way is used.
It can be determined from the peak height of the R measurement chart (hereinafter referred to as the peak method). In this case, Pendaddo fraction f _mmmm by peak method corresponding to Pendaddo fraction f _mmmm from 85.0 to 95.0 mol% by the area method is roughly a 91.0 to 97.5 mol%.

Further, (c) the angular frequency at which the storage elastic modulus (G ′) in the melt viscoelasticity measurement is 2 × 10 ³ dyne / cm ² is ω ₁ , 2 × 10 ⁵ dyne / cm ^2. When the angular frequency is ω ₂ , the molecular weight distribution index (PDI-P) represented by ω ₂ / 10ω ₁ needs to be 30 or less. If the PDI-P exceeds 30, the molecular weight distribution will be too wide and the impact resistance of the film will be significantly reduced. PD that is preferable from the viewpoint of impact resistance of the film
IP is 25 or less, more preferably 20 or less. The PDI-P was a cone plate (25 mm
φ, cone angle: 0.10 rad), temperature 1
It is a value obtained by measuring melt viscoelasticity at 75 ° C.

The polypropylene resin as the component (A) may be a propylene homopolymer as long as it satisfies the above conditions (a), (b) and (c). It may be a copolymer with the above olefin. Other olefins used in this copolymer include, for example, ethylene; butene-1; pentene-1; 4
-Methyl-1-pentene; hexene-1; heptene-
1; octene-1, nonene-1, decene-1 and other α-
Mention may be made of olefins. Of these, ethylene is preferred. These other olefins may be used alone or in combination of two or more.

In the resin composition of the present invention, the component (B) has a DBA (di-n-butylamine) value of 400.
A silicon dioxide compound having a meq / kg or less is used.
Although this silicon dioxide compound acts as an anti-blocking agent, the DBA value is an index showing the amount of silanol groups on the surface, and when the value exceeds 400 meq / kg, the effect of improving the slipperiness becomes insufficient, and thus I can't achieve my purpose. To make the slipperiness improving effect better,
The DBA value is preferably 300 meq / kg or less, especially 2
It is preferably 50 meq / kg or less. The DBA value was obtained by baking the sample at 180 ° C. for 2 hours, allowing it to cool in a desiccator, and adding 1 ml of 100 ml of a toluene solution of 0.01N di-n-butylamine (DBA) and stirring with a stirrer. After stirring for 1 hour and standing overnight, 5 ml of the supernatant was taken, water / methanol mixture (weight ratio 1/1) was added, and while measuring the pH with a pH meter, 0.01N (N) hydrochloric acid was added. It is the value obtained by titration with.

The silicon dioxide compound is BET
The specific surface area measured by the method is preferably 150 m ² / g or more. If this specific surface area is less than 150 m ² / g, the antiblocking property may be insufficient. In order to further improve the anti-blocking property, the specific surface area is more preferably 200 m ² / g or more, particularly 200 to 1000 m ² / g, and particularly 250 to 100.
0 m ² / g is preferred. The measurement by this BET method is “Journal of the American Chemical Society (J. Amer. Chem. Soc.)”.
It carried out according to the method described in Volume 60, page 309 (1983). In the present invention, as the silicon dioxide compound, those which are usually surface-treated are used. The surface treatment method is not particularly limited, and a conventionally known method, for example, a method of coating a surface of a silicon dioxide compound with a fatty acid metal salt or wax,
Alternatively, it can be carried out by various methods such as a method in which a silanol group on the surface of the silicon dioxide compound is replaced with an organic substance using a coupling agent such as a silane-based coupling agent, silicone oil or modified silicone oil.

The surface treatment method of the silicon dioxide compound using the above-mentioned silane coupling agent or silicone oil is not particularly limited, and various known methods can be used. For example, the following method can be used. In the case of a silane coupling agent: A solution of a silane coupling agent such as water or an organic solvent is prepared, and a silicon dioxide compound is immersed in this solution, and then the solvent is removed by filtration, compression, centrifugation or the like, and dried. While stirring the silicon dioxide compound using a mixer or a blender, a solution of a silane coupling agent, its water, an organic solvent or the like is sprayed onto this and dried. In the case of silicone oil, etc. After the silicon dioxide compound is immersed in a solution of silicone oil (diluted with toluene, xylene, petroleum ether, isopropyl alcohol, volatile silicone oil, etc.), the solvent is removed and heat baking is performed. The silicon dioxide compound is sprayed with a silicone oil or a solution thereof while stirring with a mixer or a blender, and heat-baked.

The silicone oil and modified silicone oil which can be used for the surface treatment of such a silicon dioxide compound are not particularly limited, but examples of the silicone oil include dimethylpolysiloxane, methylphenylpolysiloxane, methylhydrogenpolysiloxane. , Fluoropolysiloxane, and the like. Modified silicone oils include those having an organic functional group at the side chain of dimethylpolysiloxane, those having an organic functional group at the end of the molecular chain, and those at both the side chain and the end. Some have functional groups, for example, carbinol modified polysiloxane, polyether modified polysiloxane, amino modified polysiloxane, epoxy modified polysiloxane, carboxyl modified polysiloxane, methacryl modified polysiloxane, mercapto modified polysiloxane. Polysiloxane, phenol-modified polysiloxane, alkyl-modified polysiloxane, methylstyryl group-modified polysiloxane, and fluorine-modified polysiloxanes.

On the other hand, the silane coupling agent that can be used for the surface treatment of the silicon dioxide compound is not particularly limited, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, and vinyltrioxide. Acetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane,
Examples thereof include dimethyldimethoxysilane and dimethyldiethoxysilane. In the present invention, the silicon dioxide compound as the component (B) may be used singly or in combination of two or more kinds, and 0.05 parts by weight relative to 100 parts by weight of the polypropylene resin as the component (A). It is compounded at a ratio of 0.50 parts by weight. If the blending amount is less than 0.05 parts by weight, the slip property and anti-blocking property of the film are insufficient, and if the blending amount exceeds 0.50 parts by weight, the effect is not improved relative to the blending amount, which is rather economical. In addition to being disadvantageous, the transparency of the film is deteriorated. From the viewpoints of the slip property of the film, the anti-blocking property, the transparency, the economical efficiency, etc., the preferable compounding amount is in the range of 0.05 to 0.30 part by weight.

In the resin composition of the present invention, a phenolic antioxidant is used as the component (C). There are various phenolic antioxidants,
For example, 2,6-di-t-butyl-4-methylphenol; tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate [Ciba Geigy, Irganox 3114]; 2,2 ' -Methylenebis (4-
Ethyl-6-t-butylphenol); n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate [Ciba-Geigy, Irganox 1076]; 4,4'-thiobis (3 -Methyl-
6-t-butylphenol); tetrakis [methylene-
3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane [Ciba Geigy, Irganox 1010]; 4,4'-butylidene bis (3
-Methyl-6-t-butylphenol); 2,2'-methylenebis (4-methyl-6-t-butylphenol); N, N'-hexamethylenebis (3,5-di-t)
-Butyl-4-hydroxyhydrocinnamide) [manufactured by Ciba-Geigy, Irganox 1098]; triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate]; bis (3 , 5-Di-t-butyl-4-hydroxybenzylphosphonate ethyl) calcium and PE wax mixture (weight ratio 1: 1); pentaerythrityl-tetrakis [3- (3,5-di-t-butyl) -4-hydroxyphenyl) propionate] and the like. Among these, in particular, pentaerythrityl-tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] is preferable from the viewpoint of the effect. Further, these phenolic antioxidants may be used alone or in combination of two or more kinds. In the resin composition of the present invention, the component (C) phenolic antioxidant is blended in a proportion of 0.05 to 0.30 part by weight relative to 100 parts by weight of the component (A) polypropylene resin. It is necessary to. If the blending amount is less than 0.05 part by weight, molding defects such as burning during molding and uneven film thickness may occur, and if it exceeds 0.30 part by weight, it may cause bleeding of the film. Become. From the standpoints of preventing burns during molding, preventing defective molding, and preventing bleeding of the film, the preferred blending amount is 0.0
It is in the range of 5 to 0.20 parts by weight.

In the resin composition of the present invention, a phosphorus-based antioxidant is used as the component (D). There are various phosphorus antioxidants, for example, trimethyl phosphite; tri-n-butyl phosphite;
Tridecyl phosphite; tris (2-ethylhexyl) phosphite; trinonyl phosphite; tricetyl phosphite; dilauryl hydrogen phosphite; tricyclohexyl phosphite; triphenyl phosphite; tribenzyl phosphite; tricresyl phosphite; Tri-p-nonylphenyl phosphite; diphenyldecyl phosphite; tris (dinonylphenyl)
Phosphite; Tris (2,4-di-t-butylphenyl) phosphite; Tris (4-α-methylbenzylphenyl) phosphite; Tris (octylthioethyl)
Phosphite; tris (octylthiopropyl) phosphite; tris (cresylthiopropyl) phosphite; tris (3,5-di-t-butyl-4-hydroxyphenyl) phosphite; tetraphenyldipropylene glycol diphosphite; 4,4′-butylidene bis (3-methyl-6-t-butylphenyl-ditridecyl) phosphite; 1,1,3-tris (2-methyl-)
4-ditridecylphosphite-5-t-butylphenyl) butane; bis (2-chloropropyl) pentaerythritol diphosphite; bisphenylpentaerythritol diphosphite; bisstearyl pentaerythritol diphosphite; trilauryltrithiophosphite Tetrakis (2,4-di-t-butylphenyl)
-4,4'-biphenylene diphosphite etc. are mentioned. Among these, especially tris (2,4-di-t
-Butylphenyl) phosphite is preferable from the viewpoint of the effect. In addition, these phosphorus-based antioxidants may be used alone or in combination of two or more kinds.

In the resin composition of the present invention, the phosphorus antioxidant as the component (D) is 0.03 to 0.2 with respect to 100 parts by weight of the polypropylene resin as the component (A).
It should be blended in a proportion of 0 parts by weight. This blended amount is 0.0
If it is less than 3 parts by weight, molding defects such as burning during molding and unevenness of film thickness may occur, and if it exceeds 0.20 parts by weight, it causes bleeding of the film.
From the standpoints of preventing burns during molding, preventing the occurrence of molding defects, and preventing bleeding of the film, the preferred blending amount is 0.
It is in the range of 03 to 0.15 parts by weight. In the polypropylene-based resin composition of the present invention, in addition to the above components, various addition components, if necessary, within a range not impairing the object of the present invention,
For example, weathering agents, colorants, fillers, other antiblocking agents, lubricants, chlorine scavengers, nucleating agents, antistatic agents, antifogging agents and the like can be added.

The method for preparing the polypropylene resin composition of the present invention is not particularly limited, and a conventionally known method can be used. For example, the component (A), (B)
Component, (C) component, (D) component and various additive components used as needed are mixed by a tumbler blender, a Henschel mixer, etc., and after mixing, further melted using a single-screw extruder or a multi-screw extruder. A method of kneading and granulating, or a method of melt kneading and granulating with a kneader, Banbury mixer or the like can be adopted. The polypropylene resin composition of the present invention thus obtained is particularly suitable for use as a film. The film of the present invention is obtained by molding the polypropylene resin composition by a cast molding method (T die method). The cast molding method is not particularly limited, and a conventionally known method can be adopted. In the present invention, by using the polypropylene resin composition, it is possible to prevent the occurrence of defective phenomena such as burning and film thickness unevenness even when this cast molding is performed at a high take-up speed of 50 m / min or more. It is possible to obtain a film having excellent impact strength and surface characteristics.

[0019]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. The quality of the film was evaluated according to the method described below. (1) Film Impact Film impact was measured using a film impact tester manufactured by Toyo Seiki Seisakusho under the conditions of a capacity of 15 kgf · cm and an impact head of 1/2 inch. The criterion for good film impact is 1,000 kgf · cm / cm or more. (2) Static Friction Coefficient According to ASTM D-1894, a static friction angle measuring device manufactured by Toyo Seiki Seisaku-sho, Ltd. was used to measure the angle θ at which the film started to slide when the inclined plate was tilted, and the value of tan θ was taken as the static friction coefficient. A good standard is 0.2 or less. (3) Rigidity (tensile elastic modulus) Measured by a tensile tester according to JIS K-7127. The measurement conditions are crosshead speed: 500 mm / min,
Measuring direction: Machine direction (MD direction), Load cell: 10
It is kg. (4) Anti-blocking property (blocking strength) A sample obtained by closely contacting two superposed films with a load of 36 g / cm ² at 60 ° C. for 3 hours was used.
The maximum load at the time of shear peeling was evaluated. The test conditions are test speed: 20 mm / min and load cell: 2 kg. (5) Δ [η] The intrinsic viscosity [η] of the pellet and the film was measured using tetralin at 135 ° C. as a solvent, and [η] of the film was subtracted from [η] of the pellet to obtain Δ [η]. . Δ [η]
The smaller the value, the smaller the decrease in the molecular weight during the cast molding process, and the less likely the occurrence of defective phenomena such as burning and uneven film thickness. The standard of Δ [η] is 0.30 deciliter / g or less. (6) Bleed whitening After the film was stored in an oven at 40 ° C for 30 days, the appearance of the film was visually observed and evaluated according to the following criteria. ○: no bleed whitening ×: bleed whitening In addition, the physical properties of polypropylene resin [MI, pendad fraction f _mmmm (area method, peak method), PDI-P] and physical properties of silicon dioxide compound (DBA value, specific surface area) Was measured according to the method described in the text of the specification.

Examples 1 to 4 and Comparative Examples 1 to 8 As polypropylene, A ₁ having the physical properties shown in Table ₁
~ A ₄ was used. Further, as a silicon dioxide compound as an antiblocking agent, B _{1 is} a hydrophobized product of porous synthetic silica (DBA value 105
meq / kg, specific surface area 500 m ² / g) B ₂ : porous synthetic silica (DBA value 800 meq / k)
g, specific surface area 500 m ² / g) was used. And as a phenolic antioxidant, C ₁ : pentaerythrityl-tetrakis [3- (3,5
- di -t- butyl-4-hydroxyphenyl) propionate] C _2: Using 2,6-di -t- butyl -p- cresol.

Further, as a phosphorus-based antioxidant, D ₁ :
Tris (2,4-di-t-butylphenyl) phosphite was used. Polypropylene 100 of the type shown in Table 2
As a chlorine scavenger, 0.05 part by weight of calcium stearate, and as a lubricant, erucic acid amide of 0.10 parts by weight.
In addition to the addition of parts by weight, the types and amounts of antioxidants and synthetic silica as antiblocking agents shown in Table 2 were added, melt-kneaded and pelletized. Next, the obtained pellets were formed into a film by using a 75 mmφ cast molding machine manufactured by Mitsubishi Heavy Industries, Ltd. under the conditions of a processing temperature of 250 ° C., a take-up speed of 150 m / min, and a film thickness of 25 μm. The obtained film was aged for 1 day under the condition of 40 ° C., and the quality thereof was evaluated. The results are shown in Table 3.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

EFFECTS OF THE INVENTION The polypropylene-based resin composition of the present invention, when a film is formed by the cast molding method (T-die method), has a high take-up speed of 50 m / min or more, and is free from burns and uneven film thickness. It is possible to provide a film capable of preventing a defective phenomenon and having excellent impact strength and surface characteristics. Further, the film of the present invention has good productivity and excellent quality as described above, and is suitably used, for example, in the field of packaging food and clothing.

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Claims (7)

[Claims] 1. (A) (a) melt index (M
I) is 1 to 20 g / 10 minutes, and (b) isotope carbon nucleus
Magnetic resonance spectroscopy (¹³Penta determined by C-NMR)
Dead fraction f_mmmmIs 85.0 to 95.0 mol% and (c) melts
Storage elastic modulus (G ′) in viscoelasticity measurement is 2 × 10³dy
ne / cm²The angular frequency such that ₁2 x 10^Five
dyne / cm²The angular frequency such that₂And
Come, ω₂/ 10ω₁Molecular weight distribution index (PDI
-P) is a polypropylene resin having a value of 30 or less, and
(B) DBA (di-n-butyl acetate) based on 100 parts by weight.
Minic acid value of 400 meq / kg or less diacid
Silicon compound, 0.05 to 0.50 parts by weight, (C) pheno
-Based antioxidant 0.05 to 0.30 parts by weight, and (D) phosphorus
Poly-compound containing 0.03 to 0.20 parts by weight of a antioxidant
Propylene resin composition. 2. The silicon dioxide compound as the component (B) is B
The polypropylene resin composition according to claim 1, which has a specific surface area of 150 m ² / g or more as measured by the ET method. 3. The phenolic antioxidant of the component (C) is pentaerythrityl-tetrakis [3- (3,5-
Di-t-butyl-4-hydroxyphenyl) propionate]. The polypropylene resin composition according to claim 1. 4. The polypropylene resin composition according to claim 1, wherein the phosphorus antioxidant as the component (D) is tris (2,4-di-tbutylphenyl) phosphite. 5. The method according to claim 1, which is used for a film.
4. The polypropylene resin composition according to any one of 4 above. 6. A film comprising the polypropylene resin composition according to claim 5. 7. The film according to claim 6, which is formed by a cast molding method (T-die method) at a take-up speed of 50 m / min or more.