Polypropylene composition for stretched film and stretched film containing same

Abstract

Provided are a polypropylene composition for a stretched film having high thermal resistance and rigidity, and a stretched film containing same.　The polypropylene composition for a stretched film contains a polypropylene selected from the group consisting of a propylene homopolymer and a propylene-ethylene copolymer containing a unit derived from 1.0 wt % or less of ethylene, wherein the polypropylene satisfies the following requirement (1).　(1) The molecular weight distribution Mw / Mn as determined by GPC and the amount γ (wt%) of components having a molecular weight of 1,000,000 or more as determined by GPC satisfy 0.4<(Mw / Mn)·γ<10.

Description

Polypropylene composition for stretched film and stretched film containing the same

[0001] The present invention relates to a polypropylene composition for a stretched film and a stretched film containing the same.

[0002] Stretched polypropylene resin films are widely used for a wide range of applications, including electrical insulation, surface protection, and packaging for various products such as food and industrial components. However, it has been pointed out that conventional stretched polypropylene resin films have poor heat resistance. Stretched polypropylene resin films are significantly inferior in heat resistance to other materials, particularly polyethylene terephthalate films, and have a large heat shrinkage rate of several tens of percent at 150°C. Furthermore, due to their low rigidity, different materials are used depending on the application.

[0003] Various techniques have been proposed for improving the physical properties of biaxially oriented polypropylene films, such as heat resistance and mechanical properties. For example, claim 1 of Patent Document 1 discloses "a propylene polymer having a decalin soluble content of 1.6 wt % or less and a polydispersity index (PI) of at least 5.0" as a propylene polymer having a highly advantageous stiffness-processability balance, particularly for film applications, including biaxially oriented polypropylene film applications.

[0004] Furthermore, claim 1 of Patent Document 2 discloses a biaxially oriented laminated polypropylene film having high heat resistance and rigidity, which "is characterized in that the polypropylene resin constituting the film, which is made of a completely homopolypropylene resin containing no copolymerization component and / or a polypropylene resin copolymerized with ethylene and / or an α-olefin having 4 or more carbon atoms, satisfies the following conditions 1) to 4), and that the lower limit of the plane orientation coefficient of the film is 0.0125, and the tensile modulus of elasticity in the transverse direction of the film is 5.1 GPa or more. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerization monomers other than propylene is 0.1 mol%. 3) The mass average molecular weight (Mw) / number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.5 g / 10 min or more and 9.0 g / 10 min or less."

[0005] JP 2008-540815 A JP 2023-17015 A

[0006] The stretched films obtained from the polypropylene resins of Patent Documents 1 and 2 do not have sufficient heat resistance, and have problems such as being unable to maintain their shape under high-temperature conditions exceeding 150°C, and printed letters, patterns, etc. are easily distorted and wrinkles are easily formed. Furthermore, Patent Documents 1 and 2 do not fully consider the structure, properties, etc. of preferred polypropylene or polypropylene compositions for improving heat resistance. The present invention aims to provide a polypropylene composition that gives a stretched film having high heat resistance and rigidity, and a stretched film containing the same.

[0007] The present inventors have conducted extensive research and found that, by adjusting the relationship between the molecular weight distribution Mw / Mn and the content of high molecular weight components in a specific range for polypropylene, a stretched film having excellent heat resistance and rigidity can be obtained, and have completed the present invention. The present invention relates to the following items [1] to [8].

[0008] [1] A polypropylene composition for a stretched film, comprising a polypropylene selected from the group consisting of a propylene homopolymer and a propylene-ethylene copolymer containing 1.0 wt % or less of units derived from ethylene, wherein the polypropylene satisfies the following requirement (1): (1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (wt %) of components having a molecular weight of 1 million or more measured by GPC satisfy 0.4 < (Mw / Mn)·γ < 10. [2] The polypropylene composition for a stretched film according to [1], wherein the polypropylene satisfies the following requirement (2): (2) The melt flow rate measured in accordance with JIS K7210 at 230°C under a load of 2.16 kg is 3.5 to 20 g / 10 min. [3] The polypropylene composition for a stretched film according to [1] or [2], wherein the polypropylene satisfies the following requirement (3): (3) １３The isotactic mesopentad fraction (mmmm) measured by C-NMR is 95% or more. [4] The polypropylene composition for a stretched film according to any one of [1] to [3], wherein the polypropylene satisfies the following requirement (4): (4) Mw / Mn satisfies 2.0 < Mw / Mn < 5.0. [5] The polypropylene composition for a stretched film according to any one of [1] to [4], wherein the polypropylene satisfies the following requirement (5): (5) γ is less than 5.0% by weight. [6] A stretched film comprising the polypropylene composition for a stretched film according to any one of [1] to [5]. [7] The stretched film according to [6], wherein the heat shrinkage of the stretched film measured in an environment of 150°C for 30 minutes in accordance with JIS K6782 is 0 to 3.5% in the MD direction and 0 to 5.0% in the TD direction. [8] The stretched film according to [6] or [7], wherein the Young's modulus of the stretched film measured in accordance with JIS K7127 is 5.6 GPa or more in the TD direction.

[0009] The polypropylene compositions for stretched films of Aspects 1 to 5 exhibit high heat resistance and rigidity. The stretched films of Aspects 6 to 8 have high heat resistance and rigidity and can maintain their shape even at high temperatures, so they are less likely to wrinkle and printed characters, patterns, etc. do not deform.

[0010] Fig. 1 is a diagram illustrating the baseline and intervals of a chromatogram in GPC measurement. Fig. 2 is a diagram showing an example of a molecular weight distribution curve and an integrated molecular weight distribution curve. Fig. 3 is a diagram showing the molecular weight distribution curve of the polypropylene of Example 1. Fig. 4 is a diagram showing the molecular weight distribution curve of the propylene-based polymer of Comparative Example 2. Fig. 5 is a diagram comparing Fig. 3 and Fig. 4.

[0011] The polypropylene composition for a stretched film of the present invention is a polypropylene composition for a stretched film comprising a polypropylene selected from the group consisting of a propylene homopolymer and a propylene-ethylene copolymer containing 1.0% by weight or less of units derived from ethylene, wherein the polypropylene satisfies the following requirement (1): (1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (wt%) of components having a molecular weight of 1,000,000 or more measured by GPC satisfy 0.4 < (Mw / Mn)·γ < 10. By using the polypropylene composition for a stretched film, a stretched film having high heat resistance and rigidity can be obtained.

[0012] In the present invention, the propylene-based polymer refers to a propylene homopolymer or a propylene-ethylene copolymer containing 1.0% by weight or less of units derived from ethylene. Furthermore, in the present invention, the polypropylene refers to a propylene-based polymer that satisfies the above-mentioned requirement (1).

[0013] [Polypropylene Composition] The polypropylene composition contains a polypropylene selected from the group consisting of a propylene homopolymer and a propylene-ethylene copolymer containing 1.0% by weight or less of units derived from ethylene. In the present invention, the content of units derived from ethylene in the propylene-ethylene copolymer is a value calculated based on the following formula: Content (%) of units derived from ethylene = weight of units derived from ethylene / (weight of units derived from propylene + weight of units derived from ethylene) × 100 The propylene homopolymer and the propylene-ethylene copolymer may each be used alone or in combination of two or more types.

[0014] The polypropylene composition may be in an embodiment containing only one of a propylene homopolymer and a propylene-ethylene copolymer, an embodiment containing both a propylene homopolymer and a propylene-ethylene copolymer, or an embodiment containing a propylene homopolymer and / or a propylene-ethylene copolymer as a main component with other components as secondary components. In the present invention, "containing as a main component" means that the total content of the propylene homopolymer and the propylene-ethylene copolymer in 100% by weight of the polypropylene composition is 50% by weight or more. From the viewpoint of suppressing poor appearance due to secondary components or maintaining film properties such as heat resistance and rigidity, the total content of the propylene homopolymer and the propylene-ethylene copolymer in 100% by weight of the polypropylene composition is preferably 80% by weight or more, more preferably 90% by weight or more. The upper limit of the total content of the propylene homopolymer and the propylene-ethylene copolymer is 100% by weight.

[0015] <Polypropylene> From the viewpoint of the heat resistance and rigidity of the stretched film, the polypropylene is preferably a propylene homopolymer. When the polypropylene is a propylene-ethylene copolymer, the content of units derived from ethylene is 1.0% by weight or less, preferably 0.5% by weight or less, and more preferably 0.3% by weight or less. Within this range, the high rigidity of the stretched film can be maintained.

[0016] The polypropylene may be one obtained by polymerizing other monomers such as α-olefins having 4 or more carbon atoms and non-conjugated dienes, as long as the object of the present invention is not impaired.

[0017] The polypropylene satisfies the following requirement (1): (1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components having a molecular weight of 1 million or more measured by GPC satisfy the relationship 0.4 < (Mw / Mn)·γ < 10. By satisfying the relationship 0.4 < (Mw / Mn)·γ < 10, a stretched film having high rigidity and low heat shrinkage can be obtained. From the viewpoint of obtaining a stretched film having high rigidity and low heat shrinkage, the relationship is preferably (Mw / Mn)·γ < 7, more preferably (Mw / Mn)·γ < 5, and even more preferably (Mw / Mn)·γ < 4. Furthermore, from the viewpoint of formability, such as breakage and uneven elongation during film formation, the relationship is preferably (Mw / Mn)·γ > 0.4, (Mw / Mn)·γ > 0.6, and more preferably (Mw / Mn)·γ ≧ 1.0.

[0018] The Mn, Mw, and γ values ​​defined above are all obtained by gel permeation chromatography (GPC). Details of the measurement method and measurement equipment are as described in the Examples. Here, Mn and Mw are the number-average molecular weight and weight-average molecular weight of polypropylene measured by GPC, and Mw / Mn can be an index of the molecular weight distribution of polypropylene. The Mn, Mw, and Mw / Mn of polypropylene can be easily adjusted by changing the temperature and pressure conditions of propylene polymerization, or, as the most common method, by adding a chain transfer agent such as hydrogen during propylene polymerization. Furthermore, they can be controlled by changing the type of metallocene complex used, or, when two or more complexes are used, by changing the ratio of their amounts. Furthermore, Mn, Mw, and Mw / Mn can also be adjusted by appropriately degrading a higher molecular weight propylene polymer.

[0019] γ is the amount (unit: wt%) of components with a molecular weight of 1 million or more in 100% by weight of polypropylene as determined by GPC measurement. Specifically, γ is the value obtained by subtracting the integral value up to a molecular weight (M) of 1 million (Log(M) = 6.0) from 1 in the integrated molecular weight distribution curve (total amount normalized to 1) obtained by GPC measurement, and multiplying this value by 100. An example of how to determine γ is shown in FIG. 2. γ can be adjusted, for example, by controlling the prepolymerization conditions, the amount of hydrogen during polymerization, etc., in addition to the selection of catalysts, their combinations, and their quantitative ratios. γ can also be adjusted by appropriately degrading a propylene polymer with a higher molecular weight.

[0020] The relationship 0.4 < (Mw / Mn)·γ < 10 can be achieved by narrowing the molecular weight distribution of polypropylene and reducing the amount of high-molecular-weight components with molecular weights of 1 million or more. By satisfying the relationship 0.4 < (Mw / Mn)·γ, film-forming suitability in a biaxial stretching machine is improved, preventing problems during film production and improving quality, such as film thickness accuracy. Furthermore, by satisfying the relationship (Mw / Mn)·γ < 10, the high viscosity due to the fraction of polymer molecules with molecular weights of 1 million or more can be suppressed, while the presence of a large amount of molecules with similar molecular weights makes it possible to suppress entropy-induced heat shrinkage, which is thought to result in the low heat shrinkage of the resulting stretched film.

[0021] The polypropylene preferably satisfies the following requirements (2) to (5).

[0022] (2) The melt flow rate, measured in accordance with JIS K7210 at 230°C under a load of 2.16 kg, is 3.5 to 20 g / 10 min. The melt flow rate (MFR) of the polypropylene, measured in accordance with JIS K7210:1999 at 230°C under a load of 2.16 kg, is preferably 3.5 to 20 g / 10 min, more preferably 5.0 to 18 g / 10 min, and even more preferably 7.0 to 15 g / 10 min. Within the above range, the moldability during film formation is improved. The melt flow rate (MFR) of the polypropylene can be easily adjusted by changing the polymerization temperature and pressure, or, as a general method, by adding a chain transfer agent such as hydrogen during polymerization. The melt flow rate (MFR) can also be adjusted by appropriately degrading a higher molecular weight propylene polymer.

[0023] (3) １３ The isotactic mesopentad fraction (mmmm) measured by C-NMR is 95% or more. １３ The isotactic mesopentad fraction (mmmm) measured by C-NMR is preferably 95% or more, more preferably 96% or more, and even more preferably 97% or more. Furthermore, mmmm can be 95 to 96%. When it is in the above range, the rigidity of the film is good. In this specification, the isotactic mesopentad fraction (mmmm) is a value measured by the following method.

[0024] ( １３ C-NMR measurement method) [Sample preparation and measurement conditions] 200 mg of sample was mixed with o-dichlorobenzene / deuterated bromide benzene (C ６ D ５ The mixture was placed in an NMR sample tube with an inner diameter of 10 mm together with 2.4 mL of a 10% NaOH (Br) = 4 / 1 (volume ratio) and hexamethyldisiloxane, a chemical shift reference substance, and dissolved uniformly in a block heater at 150° C. NMR measurements were performed using a Bruker Biospin AV400 NMR apparatus equipped with a 10 mm φ cryoprobe. １３The C-NMR measurement conditions are a sample temperature of 120°C, a pulse angle of 90°, a pulse interval of 15 seconds, and an accumulation count of 1024, and the measurement is performed using the broadband decoupling method. １３ The C signal was set to 1.98 ppm, and other １３ The chemical shift of the C signal is based on this.

[0025] [Method for calculating isotactic mesopentad fraction (mmmm)] The isotactic mesopentad fraction (mmmm) of five consecutive propylene units is calculated by １３ Measured by C-NMR measurement １３ The integrated intensity of the C signal can be calculated by substituting it into the following formula (1): mmmm (%) = (I ｍｍ -2 x I ｍｒｒｍ ) × 100 / (I ｍｍ +3×I ｍｒｒｍ ) ...Equation (1) where I ｍｍ is attributed to the mm bonding mode of three propylene units. １３ The integrated intensity of the C signal is shown, and the chemical shift is in the range of 23.6 to 21.1 ppm. １３ The integrated intensity of the C signal (hereinafter referred to as "I ２３．６～２１．１ ") is calculated as follows. ｍｒｒｍ The 5-propylene unit sequence is assigned to the mrrm bonding mode. １３ represents the integrated intensity of the C signal, and I １９．９～１９．７ The spectral assignment can be performed with reference to Polymer Journal, Vol. 16, p. 717 (1984), Asakura Publishing, Macromolecules, Vol. 8, p. 687 (1975), and Polymer, Vol. 30, p. 1350 (1989). The chemical shift range shifts slightly depending on the molecular weight of the polymer, but the regions are easy to distinguish.

[0026] (4) Mw / Mn satisfies 2.0 < Mw / Mn < 5.0. The Mw / Mn of polypropylene measured by GPC is preferably 2.0 < Mw / Mn < 5.0, more preferably 2.3 ≦ Mw / Mn ≦ 4.8, and even more preferably 2.6 ≦ Mw / Mn ≦ 4.7. Mw / Mn is an index representing molecular weight distribution, and a smaller value indicates a narrower molecular weight distribution. By reducing and optimizing Mw / Mn, film stretching can be performed uniformly and stably. When Mw / Mn < 5.0, the uniformity of molecular chain length is increased, and the external force applied during stretching is sufficiently transmitted to the material, which tends to improve the rigidity of the molded product. Furthermore, when Mw / Mn > 2.0, moldability is improved, which tends to improve thickness accuracy and surface properties during film production.

[0027] (5) γ is less than 5.0 wt%. The amount γ of components with a molecular weight of 1 million or more as measured by GPC is preferably less than 5.0 wt%, more preferably less than 3.0 wt%, even more preferably less than 2.0 wt%, and particularly preferably less than 1.5 wt%. Furthermore, γ is preferably 0.01 wt% or more, more preferably 0.05 wt% or more, even more preferably more than 0.1 wt%, and particularly preferably 0.4 wt% or more. Within the above range, the stretching tension of the polypropylene is low, and the load on the device during molding can be reduced. Furthermore, when molecular chains are oriented or crystalline structures such as lamellae are rearranged during stretching, uniform and stable molding can be achieved, the rigidity of the film is easily improved, and the higher-order structure makes it less likely to shrink when heated.

[0028] <Method for producing polypropylene> The propylene-based polymer can be obtained by polymerizing propylene or copolymerizing propylene with a small amount of ethylene, preferably using a catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. When the propylene-based polymer obtained in this manner satisfies the above-mentioned requirement (1), this propylene-based polymer can be used as the polypropylene of the present invention.

[0029] An example of a Ziegler-Natta catalyst is a solid component (a) containing magnesium, titanium, a halogen, and an internal electron donor compound selected from phthalate compounds, diether compounds, succinate compounds, etc. In addition to the solid component (a), the Ziegler-Natta catalyst may optionally contain an organoaluminum compound (b) and an external electron donor compound (c). Furthermore, the solid component (a) may be contact-treated with an alkoxysilane or a silane compound having an alkenyl group. Examples of metallocene catalysts include metallocene catalysts comprising a metallocene compound and at least one compound selected from organometallic compounds, organoaluminum oxy compounds, and compounds capable of reacting with the metallocene compound to form an ion pair, and optionally a particulate support. Among these, metallocene catalysts capable of stereoregular polymerization, such as isotactic or syndiotactic structures, are preferred.

[0030] The polymerization method for the propylene polymer may be a known method, and examples thereof include a method of polymerization in an inert solvent such as hexane, heptane, toluene, or xylene; a method of polymerization in a liquid monomer; a method of adding a catalyst to a gaseous monomer and polymerizing in a gas phase; or a method of polymerization using a combination of these. The polymerization of the propylene polymer may be single-stage polymerization carried out in one reactor or multi-stage polymerization carried out in multiple reactors, and in the case of multi-stage polymerization, the polymerization conditions in each reactor may be the same or different. The reactor may be a reactor having a gradient in monomer concentration or polymerization conditions. The molecular weight of the propylene polymer may be adjusted using a chain transfer agent such as hydrogen.

[0031] When the obtained propylene polymer has (Mw / Mn)·γ≧10, the propylene polymer can be degraded with an organic peroxide to adjust Mw / Mn and γ so as to satisfy 0.4 < (Mw / Mn)·γ < 10. In particular, the degradation treatment causes molecular scission in relatively high-molecular-weight components (molecules) constituting the propylene polymer, thereby decreasing γ and satisfying 0.4 < (Mw / Mn)·γ < 10. When the obtained propylene polymer satisfies 0.4 < (Mw / Mn)·γ < 10, the degradation treatment with an organic peroxide is not essential, but may be carried out in order to bring the value of (Mw / Mn)·γ into a more preferred range and further improve the high rigidity and low heat shrinkability of the stretched film. When (Mw / Mn)·γ≦0.4, the propylene polymer as a whole can be adjusted to satisfy 0.4<(Mw / Mn)·γ<10 by blending with a separately produced propylene polymer having a large Mw / Mn or γ and satisfying (Mw / Mn)·γ≧10.

[0032] The propylene polymer before degradation treatment is not particularly limited as long as it is a propylene homopolymer or a propylene-ethylene copolymer containing 1.0% by weight or less of units derived from ethylene, but the Mw / Mn is preferably 5 to 20, more preferably 6 to 15. The melt flow rate (MFR) measured in accordance with JIS K7210:1999 at 230°C under a load of 2.16 kg is preferably 0.1 to 10 g / 10 min, more preferably 0.2 to 5 g / 10 min.

[0033] Examples of organic peroxides include benzoyl peroxide, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 1,1-bis-(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)octane, n-butyl-4,4-bis(t-butylperoxy)valerate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(benzoyl peroxide). Examples of suitable peroxyl groups include 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, 1,3-bis(t-butylperoxyisopropyl)benzene, α,α'-bis(t-butylperoxyisopropyl)benzene, t-butyl hydroperoxide, cumene hydroperoxide, lauroyl peroxide, di-t-butyl diperoxyphthalate, t-butylperoxymaleic acid, t-butylperoxyisopropyl carbonate, and isopropyl percarbonate. These may be used alone or in combination of two or more. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, 1,3-bis(t-butylperoxyisopropyl)benzene, and α,α'-bis(t-butylperoxyisopropyl)benzene are preferred.

[0034] The degradation treatment can be carried out by using 0.005 to 1.0 part by weight of an organic peroxide per 100 parts by weight of the propylene-based polymer and heating and kneading the two at a temperature equal to or higher than the melting temperature of the polymer, for example, 180 to 300°C. Known methods can be used for this, but it is particularly preferable to carry out the treatment in an extruder. Furthermore, to ensure uniform dispersion of the organic peroxide in the propylene-based polymer, the two may be mixed in advance using a mixer such as a Henschel mixer or a ribbon blender before heating and kneading. Furthermore, in order to improve the dispersibility of the organic peroxide, a mixture of the organic peroxide in a suitable medium can also be used.

[0035] The polypropylene thus obtained can be made into pellets, powder, or other forms by known methods.

[0036] <Polypropylene Composition> The polypropylene composition may consist solely of the polypropylene, or may contain the polypropylene and other components. The other components may include additives and polymers other than the polypropylene. Examples of additives include antioxidants, lubricants, antistatic agents, antiblocking agents, UV absorbers, light stabilizers, chlorine absorbers, heat stabilizers, anti-fogging agents, flame retardants, dispersants, copper inhibitors, neutralizing agents, plasticizers, anti-foaming agents, crosslinking agents, peroxides, oil extenders, and pigments.

[0037] Examples of the antioxidant include phenol-based antioxidants and phosphite-based antioxidants. Examples of the phenol-based antioxidant include 2,6-di-t-butyl-p-cresol (BHT), tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (manufactured by BASF Japan Ltd., trade name "IRGANOX (registered trademark) 1010"), and n-octadecyl-3-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate (manufactured by BASF Japan Ltd., trade name "IRGANOX (registered trademark) 1076"). Examples of the phosphite-based antioxidant include bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite and tris(2,4-di-t-butylphenyl)phosphite. Examples of the lubricant include higher fatty acid amides and higher fatty acid esters. Examples of the antistatic agent include glycerin esters of fatty acids having 8 to 22 carbon atoms, sorbitan acid esters, polyethylene glycol esters, etc. Examples of the antiblocking agent include silica, calcium carbonate, talc, etc.

[0038] Examples of the ultraviolet absorber include triazole-based, benzophenone-based, salicylate-based, cyanoacrylate-based, nickel chelate-based, and inorganic fine particle-based compounds. Examples of the triazole-based ultraviolet absorber include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 200; manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) P), 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 340; manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) 399), and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 400). Sumisorb (registered trademark) 320 (manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) 320), 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 350; manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) 328), 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 300; manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) 326). Examples of benzophenone-based ultraviolet absorbers include 2-hydroxy-4-methoxybenzophenone (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 110) and 2-hydroxy-4-n-octoxybenzophenone (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb (registered trademark) 130). Examples of salicylate-based ultraviolet absorbers include 4-t-butylphenyl salicylate (manufactured by Shipro Chemical Co., Ltd., trade name: Seesorb 202). Examples of cyanoacrylate-based ultraviolet absorbers include ethyl (3,3-diphenyl) cyanoacrylate (manufactured by Shipro Chemical Co., Ltd., trade name: Seesorb 501). Examples of nickel chelate-based ultraviolet absorbers include nickel dibutyldithiocarbamate (manufactured by Sumitomo Chemical Co., Ltd., trade name: Antigen (registered trademark) NBC). Examples of inorganic fine particle-based ultraviolet absorbers include TiO２ , ZnO ２ , CeO ２ etc.

[0039] Examples of the light stabilizer include sebacate-type, butane tetracarboxylate-type, succinic acid polyester-type, triazine-type compounds, etc. Examples of the sebacate-type light stabilizer include bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (manufactured by ADEKA Corporation, trade name: Adekastab (registered trademark) LA-77; manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) 770), bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate (manufactured by BASF Japan Ltd., trade name: Tinuvin (registered trademark) 765), and the like. Examples of butane tetracarboxylate type light stabilizers include tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate (manufactured by ADEKA Corporation, trade name: Adeka STAB (registered trademark) LA-57), tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate (manufactured by ADEKA Corporation, trade name: Adeka STAB (registered trademark) LA-52), Examples of the succinic acid polyester light stabilizer include a condensation product of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and tridecyl alcohol (manufactured by ADEKA Corporation, trade name: Adekastab (registered trademark) LA-67), a condensation product of 1,2,3,4-butanetetracarboxylic acid with 1,2,2,6,6-pentamethyl-4-piperidinol and tridecyl alcohol (manufactured by ADEKA Corporation, trade name: Adekastab (registered trademark) LA-62), etc. Examples of the succinic acid polyester light stabilizer include a condensation polymer of succinic acid and 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine, etc.Examples of triazine-type light stabilizers include N,N'-bis(3-aminopropyl)ethylenediamine / 2,4-bis{N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino}-6-chloro-1,3,5-triazine condensate (manufactured by BASF Japan Ltd., trade name: Chimasorb (registered trademark) 199), poly{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)amino}-6-chloro-1,3,5-triazine condensate, poly(6-morpholino-s-triazine-2,4-diyl){(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino} (manufactured by BASF Japan Ltd., trade name: Chimasorb (registered trademark) 944), poly(6-morpholino-s-triazine-2,4-diyl){(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino} (manufactured by BASF Japan Ltd., trade name: Chimasorb (registered trademark) 3346), and the like.

[0040] Examples of other polymers include polypropylene-based resins other than the polypropylene of the present invention, polyethylene, propylene-based or ethylene-based elastomers, etc. Examples of propylene-based or ethylene-based elastomers include ethylene-α-olefin copolymers, binary random copolymers of propylene and an α-olefin having 4 to 12 carbon atoms, and ternary random copolymers of propylene, ethylene, and an α-olefin having 4 to 12 carbon atoms.

[0041] The content of additives in 100% by weight of the polypropylene composition is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less. The content of other polymers in 100% by weight of the polypropylene composition is preferably 49% by weight or less, more preferably 20% by weight or less, and even more preferably 10% by weight or less.

[0042] When the polypropylene composition contains additives or other polymers, the polypropylene composition can be produced by mixing or melt-kneading the polypropylene with the additives or other polymers. Examples of mixing methods include mixing using a Henschel mixer, V-blender, ribbon blender, tumbler blender, or the like. Examples of melt-kneading methods include melt-kneading using a kneader such as a single-screw extruder, multi-screw extruder, kneader, or Banbury mixer. The polypropylene composition thus obtained can be made into pellets, powder, or the like by known methods. The additives may be added during polymerization of the propylene polymer, or may be added simultaneously with or separately from the organic peroxide during degradation of the propylene polymer, or may be added to the polypropylene after degradation. Furthermore, the other polymers are usually added to the polypropylene after degradation. The mixing method is not particularly limited as long as the effects of the present invention are not impaired.

[0043] [Stretched Film] The stretched film contains a polypropylene composition. The content of the polypropylene composition in 100% by weight of the stretched film is preferably 50% by weight or more, more preferably 80% by weight or more. The upper limit of the content of the polypropylene composition in 100% by weight of the stretched film is 100% by weight. The stretched film can be produced by producing an unstretched film of the polypropylene composition using a known melt extrusion film-forming method, and then stretching the film. The stretched film may be a uniaxially stretched film or a biaxially stretched film, and is preferably a biaxially stretched film from the viewpoint of the composition balance in the MD and TD directions. In the case of a biaxially stretched film, either simultaneous biaxial stretching or sequential biaxial stretching may be used.

[0044] The heat shrinkage of the stretched film, measured in accordance with JIS K6782 at 150°C for 30 minutes, is preferably 0 to 3.5% in the MD direction, more preferably 0 to 3.0%. The heat shrinkage is preferably 0 to 5.0% in the TD direction, more preferably 0 to 3.0%, and even more preferably 0 to 1.5%. The heat shrinkage is preferably 0 to 3.5% in the MD direction and 0 to 5.0% in the TD direction, more preferably 0 to 3.0% in the MD direction and 0 to 3.0% in the TD direction, and even more preferably 0 to 3.0% in the MD direction and 0 to 1.5% in the TD direction. Within the above ranges, the film can be used in applications requiring high heat resistance that conventional OPP films could not be used for, and has the advantage of being able to replace PET film, for example.

[0045] The Young's modulus of the stretched film measured in accordance with JIS K7127 is preferably 2 GPa or more in the MD direction, more preferably 2.2 GPa or more, and even more preferably 2.5 GPa or more. The Young's modulus of the stretched film measured in accordance with JIS K7127 is preferably 5.6 GPa or more in the TD direction, more preferably 6.0 GPa or more, and even more preferably 6.5 GPa or more. Within these ranges, the film can be used in applications requiring high heat resistance that could not be achieved with conventional OPP films, and has the advantage of being able to replace PET films, for example.

[0046] In the present invention, the MD direction is the flow direction of the film (sometimes referred to as the length direction or longitudinal direction), and the TD direction is the direction perpendicular to the flow direction and thickness direction of the film (sometimes referred to as the transverse direction or width direction).

[0047] The stretched film may be a single layer containing the polypropylene composition, or a multilayer film in which each layer contains the polypropylene composition. In the case of a multilayer film, the polypropylene compositions constituting each layer may be the same or different. The stretched film may also be a laminate film in which another layer is laminated thereto. In the case of a multilayer film or a laminate film, a single layer film containing the polypropylene composition may be stretched and then formed into a multilayer film or a laminate film, or a multilayer film or a laminate film may be formed and then stretched.

[0048] When the stretched film is a monolayer film, its thickness is preferably 5 to 200 μm, more preferably 10 to 150 μm, even more preferably 12 to 100 μm, and still more preferably 15 to 80 μm.

[0049] When the stretched film is incorporated into a multilayer film or a laminate film in which a stretched film and other layers are laminated, each of the stretched films preferably has a thickness of 5 to 150 μm, more preferably 10 to 100 μm, even more preferably 12 to 80 μm, and even more preferably 15 to 60 μm. When the stretched film is a multilayer film or a laminate film, the total thickness is preferably 5 to 200 μm, more preferably 10 to 150 μm, even more preferably 12 to 120 μm, and even more preferably 15 to 100 μm.

[0050] The method for producing a stretched film is not particularly limited. For example, an unstretched film made from the polypropylene composition can be prepared and stretched uniaxially or biaxially by a known method to obtain a stretched film. The molding temperature when stretching the unstretched film is preferably 140 to 180°C, more preferably 150 to 175°C, and even more preferably 155 to 170°C. The method may also include an MD stretching step in which the unstretched film is stretched in the MD direction by 2 to 10 times, preferably 4 to 7 times, to obtain a uniaxially stretched film using a stretching roll. The method may also include a TD stretching step in which the uniaxially stretched film obtained in the MD stretching step is stretched in the TD direction by 4 to 20 times, preferably 4 to 10 times, using two rows of chucks aligned in the MD direction in a heating furnace to obtain a biaxially stretched film.

[0051] To improve processability, the surface of the stretched film may be subjected to discharge treatment such as corona or plasma treatment, flame treatment, ozone treatment, or the like.

[0052] The stretched film can be used as one layer of a multilayer film or a laminate film. A laminate film is a film in which any layer is laminated on one or both sides of a layer made of a stretched film. Methods for producing a multilayer film or a laminate film include commonly used coextrusion, extrusion lamination, thermal lamination, dry lamination, and inflation, which involves cooling in water or air.

[0053] For example, a laminate film can be constructed by laminating any layer, such as a sealant layer, a gas barrier layer, an adhesive layer, or a printing layer, on a stretched film. Among these, laminating a sealant layer made of an olefin resin on a layer made of a stretched film is preferred, as the resulting laminate film has the advantage of being easily recyclable. Stretched films can be used as various packaging materials. For example, packaging materials formed from the above-mentioned laminated films can be suitably used for packaging any packaging object, such as food, clothing, or miscellaneous goods.

[0054] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. Hereinafter, propylene-based polymers that satisfy the condition 0.4 < (Mw / Mn)·γ < 10 will be referred to as "polypropylene," and those that do not satisfy the condition will be referred to as "propylene-based polymer."

[0055] [Methods for Measuring Physical Properties] Measurements of physical properties and analytical values ​​of each item in the examples were carried out according to the following methods.

[0056] (1) MFR (unit: g / 10 min) Using pellets of polypropylene or propylene-based polymer, MFR was measured under the following conditions in accordance with JIS K7210:1999, Appendix A, Table 1, Condition M: Test temperature: 230°C, Nominal load: 2.16 kg, Die shape: Diameter 2.095 mm, Length 8.000 mm

[0057] (2) GPC Measurement GPC measurement was performed using pellets of polypropylene or propylene-based polymer to determine the number average molecular weight Mn, weight average molecular weight Mw, Mw / Mn, and γ. Details of the measuring equipment are as follows. Apparatus: GPC (ALC / GPC, 150C) manufactured by Waters; Detector: MIRAN, 1A, IR detector (measurement wavelength: 3.42 μm) manufactured by FOXBORO; Column: AD806M / S (3 columns) manufactured by Showa Denko; Mobile phase solvent: o-dichlorobenzene (ODCB); Measurement temperature: 140° C.; Flow rate: 1.0 mL / min; Injection volume: 0.2 mL

[0058] Samples were prepared by preparing a 1 mg / mL solution using polypropylene or propylene-based polymer pellets and ODCB (containing 0.5 mg / mL dibutylhydroxytoluene (BHT)), and dissolving the solution at 140°C for approximately 1 hour. The baseline and interval of the resulting chromatogram were as shown in Figure 1. Conversion of the retention volume obtained by GPC measurement to molecular weight was performed using a calibration curve prepared in advance using standard polystyrenes. The standard polystyrenes used were all the following brands manufactured by Tosoh Corporation. Brands: F380, F288, F128, F80, F40, F20, F10, F4, F1, A5000, A2500, A1000. 0.2 mL of a solution dissolved in ODCB (containing 0.5 mg / mL BHT) was injected so that each was 0.5 mg / mL, and a calibration curve was created. The calibration curve was a cubic equation obtained by approximation using the least squares method. For conversion to molecular weight, a general-purpose calibration curve was used with reference to "Size Exclusion Chromatography" by Sadao Mori (Kyoritsu Shuppan). The viscosity formula used for conversion to molecular weight ([η] = K × M α ) The following values ​​were used: (a) When creating a calibration curve using standard polystyrene PS: K = 1.38 x 10 －４ , α = 0.70 (a) When measuring a sample of polypropylene or propylene-based polymer PP: K = 1.03 × 10 －４ , α=0.78

[0059] γ is a value obtained by subtracting the integral value up to a molecular weight (M) of 1,000,000 (Log(M)=6.0) in an integrated molecular weight distribution curve (total amount normalized to 1) obtained by GPC measurement from 1, and multiplying the result by 100. An example of how to determine γ is shown in FIG. 2.

[0060] (3) １３ Isotactic mesopentad fraction (mmmm) measured by C-NMR Using pellets of polypropylene or propylene-based polymer, the isotactic mesopentad fraction (mmmm) was determined according to the following procedure. １３ C-NMR measurement method) [Sample preparation and measurement conditions] 200 mg of sample was mixed with o-dichlorobenzene / deuterated bromide benzene (C ６ D ５The mixture was placed in an NMR sample tube with an inner diameter of 10 mm together with 2.4 mL of a 10% NaOH (Br) solution (volume ratio: 4 / 1) and hexamethyldisiloxane, a chemical shift reference substance, and dissolved uniformly in a block heater at 150° C. NMR measurements were performed using a Bruker Biospin AV400 NMR apparatus equipped with a 10 mm cryoprobe. １３ The C-NMR measurement conditions were a sample temperature of 120°C, a pulse angle of 90°, a pulse interval of 15 seconds, and an accumulation count of 1024, and the measurement was performed using the broadband decoupling method. １３ The C signal was set to 1.98 ppm, and other １３ The chemical shifts of the C signals were referenced to this.

[0061] [Method for calculating isotactic mesopentad fraction (mmmm)] The isotactic mesopentad fraction (mmmm) of five consecutive propylene units is calculated by １３ Measured by C-NMR measurement １３ The integrated intensity of the C signal was calculated by substituting it into the following formula (1): mmmm (%) = (I ｍｍ -2 x I ｍｒｒｍ ) × 100 / (I ｍｍ +3×I ｍｒｒｍ ) ...Equation (1) where I ｍｍ is attributed to the mm bonding mode of three propylene units. １３ The integrated intensity of the C signal is shown, and the chemical shift is in the range of 23.6 to 21.1 ppm. １３ is the integrated intensity of the C signal, and I ｍｒｒｍ The 5-propylene unit sequence is assigned to the mrrm bonding mode. １３ The integrated intensity of the C signal is shown, and the chemical shift is in the range of 19.9 to 19.7 ppm. １３ C is the integrated intensity of the signal.

[0062] (4) Film Thickness The thickness of the biaxially stretched films of Examples 1 to 5 and Comparative Examples 1 to 5 was measured using ID-SX2 manufactured by Mitutoyo Corporation.

[0063] (5) Glossiness (%) For the biaxially stretched films of Examples 1 to 5 and Comparative Examples 1 to 5, the glossiness of the film was measured at an incident angle of 60° using a GLOSS Meter VG2000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS Z8741:1997.

[0064] (6) Haze (%) The haze of the biaxially stretched films of Examples 1 to 5 and Comparative Examples 1 to 5 was measured in accordance with JIS K7136:2000.

[0065] (7) Young's Modulus (Tensile Elastic Modulus) (MPa) The biaxially stretched films of Examples 1 to 5 and Comparative Examples 1 to 5 were conditioned for 24 hours in an environment of 23°C and 50% RH in accordance with the method described in JIS K7127 (1999) "Plastics - Test methods for tensile properties - Part 3: Test conditions for films and sheets." Then, strip-shaped test specimens 150 mm long and 15 mm wide were cut out in each of the MD and TD directions. The Young's modulus (tensile elastic modulus) of the film in the MD and TD directions was measured using a tensile tester with a chuck distance of 100 mm and a pulling speed of 1 mm / min. A higher Young's modulus indicates better rigidity. The Young's modulus was evaluated according to the following criteria: Excellent: The Young's modulus in the MD direction was 2.5 GPa or more and the Young's modulus in the TD direction was 6.5 GPa or more, indicating that the biaxially stretched film had extremely excellent rigidity. Good: The Young's modulus in the MD direction is 2.2 GPa or more and the Young's modulus in the TD direction is 5.6 GPa or more and less than 6.5 GPa, and the rigidity of the biaxially stretched film is excellent. Poor: The Young's modulus in the TD direction is 5.0 GPa or more and less than 5.6 GPa, and the rigidity of the biaxially stretched film is poor. XX: The Young's modulus in the TD direction is less than 5.0 GPa, and the rigidity of the biaxially stretched film is significantly poor.

[0066] (8) Heat Shrinkage (%) The heat shrinkage of the biaxially stretched films of Examples 1 to 5 and Comparative Examples 1 to 5 was measured in accordance with JIS K6782 using the following method. The films were cut into a width of 20 mm and a length of 200 mm in each of the MD and TD directions and heated for 30 minutes in a hot air oven at 150°C. The length immediately after heating was measured, and the ratio of the shrunken length to the original length was taken as the heat shrinkage. The smaller the value obtained, the lower the heat shrinkage, indicating better heat resistance and dimensional stability during heating. The heat shrinkage was evaluated according to the following criteria: ◎: The heat shrinkage in the MD direction was 0 to 3.0% and the heat shrinkage in the TD direction was 0 to 1.5%, resulting in an extremely excellent heat shrinkage of the biaxially stretched film. ○: The heat shrinkage in the MD direction was 0 to 3.5% and the heat shrinkage in the TD direction was greater than 1.5 to 5.0%, resulting in an excellent heat shrinkage of the biaxially stretched film. ×: The heat shrinkage rate in the MD direction is more than 3.5 to 5.0%, or the heat shrinkage rate in the TD direction is more than 5.0 to 10.0%, and the heat shrinkage rate of the biaxially stretched film is poor. XX: The heat shrinkage rate in the MD direction is more than 5.0% and the shrinkage rate in the TD direction is more than 10.0%, and the heat shrinkage rate of the biaxially stretched film is significantly poor.

[0067] [Resins Used] The various resins used in the Examples and Comparative Examples are listed below. [Polypropylene] A-1: ​​100 parts by weight of Novatec (registered trademark) PP, grade EA9HD (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 0.4 g / 10 min), manufactured by Japan Polypropylene Corporation, was mixed with 0.048 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, using a Henschel mixer. The resulting mixture was melt-extruded using a Technovel KZW-25 twin-screw extruder with a screw diameter of 25 mm, at a screw rotation speed of 300 rpm, and at a kneading temperature of 150°C / 180°C / 230°C / 230°C / 180°C (from below the hopper) to obtain polypropylene pellets. The MFR of the resulting pellets was 10 g / 10 min. A-2: 0.025 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, was added to 100 parts by weight of Novatec (registered trademark) PP, grade FY6H (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 1.8 g / 10 min), manufactured by Japan Polypropylene Corporation, and mixed in a Henschel mixer. Polypropylene pellets were obtained in the same manner as for polypropylene (A-1), except that the resulting mixture was used. The MFR of the resulting pellets was 11.8 g / 10 min. A-3: 0.007 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, was added to 100 parts by weight of Novatec (registered trademark) PP, grade FL1105F (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Japan Polypropylene Corporation, and mixed in a Henschel mixer. Polypropylene pellets were obtained in the same manner as for polypropylene (A-1), except that the resulting mixture was used. The MFR of the resulting pellets was 7.3 g / 10 min.A-4: 0.014 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, was added to 100 parts by weight of Novatec (registered trademark) PP, grade FL1105F (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Japan Polypropylene Corporation, and mixed in a Henschel mixer. Polypropylene pellets were obtained in the same manner as for polypropylene (A-1), except that the resulting mixture was used. The MFR of the resulting pellets was 10.1 g / 10 min. A-5: 0.020 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, was added to 100 parts by weight of Novatec (registered trademark) PP, grade FL1105F (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Japan Polypropylene Corporation, and mixed in a Henschel mixer. Polypropylene pellets were obtained in the same manner as for polypropylene (A-1), except that the resulting mixture was used. The MFR of the resulting pellets was 13.1 g / 10 min.

[0068] [Propylene-based polymers] B-1: Novatec (registered trademark) PP, manufactured by Japan Polypropylene Corporation, grade name SA3D (propylene homopolymer produced by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 11 g / 10 min) B-2: Novatec (registered trademark) PP, manufactured by Japan Polypropylene Corporation, grade name FL1105F (propylene homopolymer produced by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min) B-3: Novatec (registered trademark) PP, grade name FL4 (propylene homopolymer produced by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 4.2 g / 10 min) B-4: Novatec (registered trademark) PP, product name, grade name FL203D (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.0 g / 10 min), manufactured by Japan Polypropylene Corporation. B-5: Novatec (registered trademark) PP, product name, grade name FL1105F (propylene homopolymer produced by a Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Japan Polypropylene Corporation. 0.003 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, was added to 100 parts by weight and mixed using a Henschel mixer. Propylene polymer pellets were obtained in the same manner as for polypropylene (A-1), except that the resulting mixture was used. The MFR of the resulting pellets was 5.2 g / 10 min.

[0069] Example 1 Using a three-layer co-extruder, polypropylene (A-1) was added to each layer, and each layer was melt-extruded at a resin temperature of 240°C, followed by quenching with a cooling roll at 30°C to produce a one-kind, three-layer unstretched film. The unstretched film obtained was then biaxially stretched using a biaxially stretched film molding machine (tenter) manufactured by Mitsubishi Heavy Industries, Ltd., with the roll temperature adjusted to 110°C. The extrusion conditions, stretching conditions, and thickness of the film after biaxial stretching were as follows: Extrusion conditions: Extrusion temperature: 240°C, die width: 300 mm, lip opening: 2.0 mm, chill roll temperature: 30°C, chill roll speed: 3 m / min. Stretching conditions: Stretch roll temperature: 110°C, MD stretch ratio: 5 times, TD stretch ratio: 8 times, take-up speed: 15 m / min, tenter chamber temperature: 165°C in all three zones (preheating, stretching, and heat setting). Film thickness: Total thickness 20 μm. Of these, the thickness of the first layer and the third layer was each 2 μm.

[0070] Example 2 In Example 1, the polypropylene (A-1) was changed to polypropylene (A-2), and a biaxially stretched film of Example 2 was obtained.

[0071] Example 3 In Example 1, the polypropylene (A-1) was changed to polypropylene (A-3), and a biaxially stretched film of Example 3 was obtained.

[0072] Example 4 In Example 1, the polypropylene (A-1) was changed to polypropylene (A-4), thereby obtaining a biaxially stretched film of Example 4.

[0073] Example 5 In Example 1, the polypropylene (A-1) was changed to polypropylene (A-5), thereby obtaining a biaxially stretched film of Example 5.

[0074] Comparative Example 1 In Example 1, the polypropylene (A-1) was changed to a propylene-based polymer (B-1), and a biaxially stretched film of Comparative Example 1 was obtained.

[0075] Comparative Example 2 In Example 1, the polypropylene (A-1) was changed to a propylene-based polymer (B-2), to obtain a biaxially stretched film of Comparative Example 2.

[0076] Comparative Example 3 In Example 1, the polypropylene (A-1) was changed to a propylene-based polymer (B-3), and a biaxially stretched film of Comparative Example 3 was obtained.

[0077] Comparative Example 4 In Example 1, the polypropylene (A-1) was changed to the propylene-based polymer (B-4), and a biaxially stretched film of Comparative Example 4 was obtained.

[0078] Comparative Example 5 In Example 1, the polypropylene (A-1) was changed to the propylene-based polymer (B-5), and a biaxially stretched film of Comparative Example 5 was obtained.

[0079] Table 1 shows the physical properties of the polypropylene and propylene polymers used in the examples and comparative examples, as well as the biaxially stretched films obtained from them.

[0080]

[0081] [Discussion of the Results of Examples and Comparative Examples] Table 1 shows that the biaxially stretched films of Examples 1 to 5, which were formed from polypropylene satisfying 0.4 < (Mw / Mn)·γ < 10, had an extremely high Young's modulus in the TD direction, small heat shrinkage in both the MD and TD directions, and excellent rigidity and heat resistance. On the other hand, the biaxially stretched films of Comparative Examples 1 to 5, which were formed from a propylene-based polymer having an (Mw / Mn)·γ of 10 or more, were inferior in Young's modulus in the TD direction and heat shrinkage in both the MD and TD directions.

[0082] The polypropylene composition can be suitably used as a raw material for stretched films.

Claims

1. A polypropylene composition for use in a stretched film, comprising a polypropylene selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of units derived from ethylene, said polypropylene satisfying the following requirement (1): (1) The molecular weight distribution Mw / Mn as measured by GPC and the amount γ (wt%) of components having a molecular weight of 1,000,000 or more as measured by GPC satisfy 0.4 < (Mw / Mn)·γ < 10.

2. The polypropylene composition for stretched films according to claim 1, wherein the polypropylene satisfies the following requirement (2): (2) The melt flow rate measured in accordance with JIS K7210 at 230°C under a load of 2.16 kg is 3.5 to 20 g / 10 min.

3. The polypropylene composition for stretched films according to claim 1 or 2, wherein the polypropylene satisfies the following requirement (3): (3) １３ The isotactic mesopentad fraction (mmmm) measured by C-NMR is 95% or more.

4. The polypropylene composition for stretched films according to claim 3, wherein the polypropylene satisfies the following requirement (4): (4) Mw / Mn satisfies 2.0 < Mw / Mn < 5.

0.

5. The polypropylene composition for stretched films according to claim 4, wherein the polypropylene satisfies the following requirement (5): (5) γ is less than 5.0% by weight.

6. A stretched film comprising the polypropylene composition for stretched films according to any one of claims 1 to 5.

7. The stretched film according to claim 6, wherein the heat shrinkage of the stretched film measured in an environment of 150°C for 30 minutes in accordance with JIS K6782 is 0 to 3.5% in the MD direction and 0 to 5.0% in the TD direction.

8. The stretched film according to claim 7, wherein the Young's modulus of the stretched film in the TD direction, measured in accordance with JIS K7127, is 5.6 GPa or more.

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