Polypropylene composition for stretched films and stretched film containing the same

Abstract

The present invention provides a polypropylene composition that provides a stretched film with high heat resistance, and a stretched film containing the same. [Solution] A polypropylene composition for stretched film, comprising polypropylene (A) that satisfies requirements (a1) to (a3) ​​and polypropylene (B) that satisfies requirements (b1) and (b2). (a1) The molecular weight distribution Mw / Mn and the amount γ (weight %) of components with a molecular weight of 1 million or more satisfy 1.0 ≤ (Mw / Mn)·γ < 10. (a2) Selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of ethylene-derived units. (a3) The weight-average molecular weight Mw is between 150,000 and 250,000. (b1) The molecular weight distribution Mw / Mn and the amount γ (weight %) of components with a molecular weight of 1 million or more satisfy 0 ≤ (Mw / Mn)·γ < 1.0. (b2) The weight-average molecular weight Mw is between 10,000 and 40,000.

Description

[Technical Field]

[0001] This invention relates to a polypropylene composition for stretched films and a stretched film containing the same. [Background technology]

[0002] Polypropylene stretched films are widely used for various applications, including electrical insulation, surface protection, and packaging for food products, industrial components, and more. However, conventional polypropylene stretched films have been criticized for their low heat resistance. Compared to other materials, particularly polyethylene terephthalate films, polypropylene stretched films have significantly lower heat resistance, with a high heat shrinkage rate of several tens of percent at 150°C. Furthermore, their low rigidity necessitates the selection of materials based on their intended use.

[0003] Various techniques have been proposed to improve 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 very advantageous stiffness-processability balance, particularly for film applications, encompassing applications for biaxially oriented polypropylene films, as "a propylene polymer having 1.6% by weight or less of decalin soluble content and a polydispersity index (PI) of at least 5.0".

[0004] Furthermore, claim 1 of Patent Document 2 describes a biaxially oriented laminated polypropylene film having high heat resistance and rigidity, characterized in that "the polypropylene resin constituting the film, which consists of a completely homopolypropylene resin that does not contain copolymer components 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), the lower limit of the surface 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 for the amount of copolymer monomers other than propylene is 0.1 mol%. 3) The weight-average molecular weight (Mw) / number-average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) It discloses that 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] Furthermore, Patent Document 3 discloses a branched propylene-based polymer that maintains the melt tension required for molding, has low strain hardening in the low deformation rate range, and a large difference between the strain hardening in the low deformation rate range and the strain hardening in the high deformation rate range, and has a specific melt flow rate (MFR), Mw / Mn ratio, ratio of components with a molecular weight of 1 million or more (W1 million), branch index g', etc.

[0006] On the other hand, a hot melt adhesive composition in which a polypropylene-based wax is blended with a polyolefin resin such as an ethylene-propylene copolymer is known, and it has been shown that coating properties and wettability to an adherend can be imparted by reducing the viscosity of the adhesive (Patent Document 4).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] The stretched films obtained from the polypropylene described in Patent Documents 1 to 3 and the polypropylene composition described in Patent Document 4 do not have sufficient heat resistance. For example, they cannot maintain their shape under high-temperature conditions exceeding 150°C, and printed characters, patterns, etc., deform and wrinkle easily form. Furthermore, Patent Documents 1 to 4 do not adequately consider the structure, properties, etc., of preferred polypropylene or polypropylene composition for improving heat resistance. The present invention aims to provide a polypropylene composition that gives a stretched film with high heat resistance and a stretched film containing the same. [Means for solving the problem]

[0009] The inventors focused on the relationship between the molecular weight distribution Mw / Mn and the content of high molecular weight components in polypropylene and conducted diligent research. As a result, they discovered that by blending two types of polypropylene in which the products of these two ranges are in different ranges, a stretched film with excellent heat resistance can be obtained, thus completing the present invention. The present invention relates to the following [1] to [8].

[0010] [1] A polypropylene composition for stretched film, comprising polypropylene (A) that satisfies the following requirements (a1) to (a3) ​​and polypropylene (B) that satisfies the following requirements (b1) and (b2). (a1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 1.0 ≤ (Mw / Mn)·γ < 10. (a2) Selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of ethylene-derived units. (a3) The weight-average molecular weight Mw is between 150,000 and 250,000. (b1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 0 ≤ (Mw / Mn)·γ < 1.0. (b2) The weight-average molecular weight Mw is between 10,000 and 40,000. [2] The polypropylene composition for stretched film according to [1], wherein the polypropylene (A) satisfies the following requirements (a4) and (a5). (a4) Mw / Mn satisfies 2.0 < Mw / Mn < 5.0. (a5) In accordance with JIS K7210, the melt flow rate measured at 230°C and a load of 2.16 kg was 3.5 to 20 g / 10 min. [3] A polypropylene composition for stretched film according to [1] or [2], wherein polypropylene (A) satisfies the following requirement (a6). (a6) 13 The isotactic mesopentad fraction (mmmm) measured by 13C-NMR is 95% or higher. [4] A polypropylene composition for stretched film according to any one of [1] to [3], wherein polypropylene (A) satisfies requirement (a7) below and polypropylene (B) satisfies requirement (b3) below. (a7) The cold xylene soluble content (CXS) is less than 5.0% by weight. (b3) The cold xylene soluble content (CXS) is 5.0% by weight or more. [5] A polypropylene composition for stretched film according to any one of [1] to [4], wherein polypropylene (A) satisfies the following requirement (a8). (a8) In the molecular weight distribution curve obtained by 3D-GPC, the absolute molecular weight M abs The branching exponent g'(1 million) for 1 million exceeds 0.85. [6] A polypropylene composition for stretched film according to any one of [1] to [5], wherein the proportions of component (A) and component (B) are 85.0 to 99.9% by weight and 0.1 to 15.0% by weight, respectively, based on 100% by weight of the total of component (A) and component (B). A stretched film comprising the polypropylene composition for stretched films described in any one of [7][1] to [6]. [8] The stretched film described in [7], wherein the heat shrinkage rate of the stretched film, measured in accordance with JIS K6782 under conditions of 150°C for 30 minutes, is 0-4.0% in the MD direction and 0-6.0% in the TD direction. [Effects of the Invention]

[0011] The polypropylene compositions for stretched films according to embodiments 1 to 6 exhibit high heat resistance. The stretched films according to embodiments 7 and 8 have high heat resistance and can maintain their shape even at high temperatures, so they are less prone to wrinkles and the characters, patterns, etc. on printed materials do not deform. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 illustrates the baseline and interval of the chromatogram in the GPC measurement. [Figure 2] Figure 2 shows an example of a molecular weight distribution curve and an integrated molecular weight distribution curve. [Figure 3] Figure 3 shows the molecular weight distribution curve of polypropylene (A-1) used in Examples 1 to 6. [Figure 4] Figure 4 shows the molecular weight distribution curve of the propylene polymer (A-7) of Comparative Example 2. [Figure 5] Figure 5 is a comparison of Figure 3 and Figure 4. [Modes for carrying out the invention]

[0013] The polypropylene composition for stretched films of the present invention comprises polypropylene (A) that satisfies the following requirements (a1) to (a3) ​​and polypropylene (B) that satisfies the following requirements (b1) and (b2). (a1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 1.0 ≤ (Mw / Mn)·γ < 10. (a2) Selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of ethylene-derived units. (a3) The weight-average molecular weight Mw is between 150,000 and 250,000. (b1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 0 ≤ (Mw / Mn)·γ < 1.0. (b2) The weight-average molecular weight Mw is between 10,000 and 40,000. By using a polypropylene composition for stretched films, a stretched film with high heat resistance can be obtained.

[0014] In the present invention, a propylene-based polymer means a propylene homopolymer or a propylene-ethylene copolymer containing 1.0% by weight or less of ethylene-derived units. Furthermore, in the present invention, polypropylene (A) means a propylene-based polymer that satisfies the above requirements (a1) and (a3). In the present invention, the percentage of units derived from ethylene in the propylene-ethylene copolymer is a value calculated based on the following formula. Percentage of units derived from ethylene (%) = Weight of units derived from ethylene / (Weight of units derived from propylene + Weight of units derived from ethylene) × 100 Propylene homopolymers and propylene-ethylene copolymers may be used individually or in combination of two or more types.

[0015] [Polypropylene composition] The polypropylene composition contains polypropylene (A) that satisfies the above requirements (a1) to (a3) ​​and polypropylene (B) that satisfies the above requirements (b1) and (b2). The polypropylene composition contains polypropylene (A) and polypropylene (B) as main components. In the present invention, "contained as main components" means that the content ratio of polypropylene (A) and polypropylene (B) in 100% by weight of the polypropylene composition is 50% by weight or more. From the viewpoint of suppressing appearance defects due to auxiliary components or maintaining film properties such as heat resistance and rigidity, the content ratio of polypropylene (A) and polypropylene (B) in 100% by weight of the polypropylene composition is preferably 80% by weight or more, and more preferably 85% by weight or more. The upper limit of the total content ratio of polypropylene (A) and polypropylene (B) is 100% by weight.

[0016] <Polypropylene (A)> Polypropylene (A) satisfies the following requirements (a1) to (a3). By incorporating polypropylene (A), a stretched film with excellent heat resistance can be obtained. Polypropylene (A) may be used alone or in combination of two or more types.

[0017] (a1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 1.0 ≤ (Mw / Mn)·γ < 10. By setting 1.0 ≤ (Mw / Mn)·γ < 10, a stretched film with high rigidity and low heat shrinkage can be obtained. From the viewpoint of obtaining a stretched film with high rigidity and low heat shrinkage, preferably (Mw / Mn)·γ < 7.3, more preferably (Mw / Mn)·γ < 7, even more preferably (Mw / Mn)·γ < 6.0, even more preferably (Mw / Mn)·γ < 5, and particularly preferably (Mw / Mn)·γ < 4. When this value is satisfied, the film appearance will be good. (Mw / Mn)·γ < 7.0, (Mw / Mn)·γ < 5.0, or (Mw / Mn)·γ < 4.0 can also be used. Furthermore, from the viewpoint of moldability, such as breakage and uneven stretching during film formation, (Mw / Mn)·γ ≥ 1.0, preferably (Mw / Mn)·γ ≥ 1.5, and more preferably (Mw / Mn)·γ ≥ 2.0. When these values ​​are met, it becomes easier to stretch the film uniformly.

[0018] The values ​​of Mn, Mw, and γ defined above are all obtained by gel permeation chromatography (GPC). Details of the measurement method and equipment are described in the examples. Here, Mn and Mw are the number-average molecular weight and weight-average molecular weight of polypropylene (A) as measured by GPC, and Mw / Mn can serve as an indicator of the molecular weight distribution of polypropylene (A). The Mn, Mw, and Mw / Mn of polypropylene (A) can be easily adjusted by changing the temperature and pressure conditions of propylene polymerization, or, most commonly, 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, if two or more complexes are used, by changing their ratio. In addition, Mn, Mw, and Mw / Mn can also be adjusted by appropriately reducing the amount of a higher molecular weight propylene polymer.

[0019] γ is the amount (in wt%) of components with a molecular weight of 1 million or more in 100 wt% of polypropylene (A), as measured by GPC. 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 integral molecular weight distribution curve obtained by GPC measurement (total amount normalized to 1), and multiplying the result by 100. An example of how to determine γ is shown in Figure 2. γ can be adjusted by controlling the selection, combination and ratio of catalysts, as well as pre-polymerization conditions, the amount of hydrogen during polymerization, etc. Furthermore, γ can also be adjusted by appropriately reducing the amount of higher molecular weight propylene polymer.

[0020] The condition 1.0 ≤ (Mw / Mn)·γ < 10 can be achieved by narrowing the molecular weight distribution of polypropylene (A) and reducing the amount of high molecular weight components with a molecular weight of 1 million or more. Satisfying 1.0 ≤ (Mw / Mn)·γ improves film-making suitability on a biaxial stretching machine, thus preventing problems during film production and improving quality, such as film thickness accuracy. By satisfying (Mw / Mn)·γ < 10, it is possible to suppress the large viscosity caused by the fraction of polymer molecules with a molecular weight of 1 million or more, while suppressing thermal shrinkage due to entropy due to the presence of a large amount of molecules with a similar molecular weight, resulting in the low thermal shrinkage of the resulting stretched film.

[0021] (a2) Selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of ethylene-derived units. Polypropylene (A) is selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of ethylene-derived units. Polypropylene (A) may consist of only one of propylene homopolymers and propylene-ethylene copolymers, or it may consist of both propylene homopolymers and propylene-ethylene copolymers. The propylene and ethylene constituting polypropylene (A) may be produced from biomass. The propylene and ethylene constituting polypropylene (A) may consist solely of biomass-derived propylene and ethylene, or solely of fossil fuel-derived propylene and ethylene. Alternatively, it may contain both biomass-derived propylene and ethylene and fossil fuel-derived propylene and ethylene.

[0022] From the viewpoint of heat resistance and rigidity of the stretched film, polypropylene (A) is preferably a propylene homopolymer. When polypropylene (A) 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, high rigidity of the stretched film can be maintained.

[0023] Polypropylene (A) may also be obtained by polymerizing other monomers such as α-olefins having 4 or more carbon atoms, or non-conjugated dienes, to the extent that it does not impair the purpose of the present invention.

[0024] (a3) The weight-average molecular weight Mw is between 150,000 and 250,000. By setting the weight-average molecular weight Mw of polypropylene (A) to 150,000 to 250,000, the suitability for film formation in a biaxial stretching machine is improved, thereby preventing problems during film production and improving the quality, such as the thickness accuracy of the film. The weight-average molecular weight Mw is preferably 180,000 to 220,000, and more preferably 190,000 to 200,000.

[0025] Polypropylene (A) is preferably one that satisfies the following requirements (a4) to (a9).

[0026] (a4) Mw / Mn satisfies 2.0 < Mw / Mn < 5.0. For polypropylene (A), the Mw / Mn value 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 the molecular weight distribution, and a smaller value means a narrower molecular weight distribution. By reducing and optimizing Mw / Mn, the stretching of the film can be carried out uniformly and stably. When Mw / Mn < 5.0, the uniformity of the molecular chain length increases, and the external force applied during stretching is sufficiently transmitted to the material, making it easier to improve the rigidity of the molded product. Also, when Mw / Mn > 2.0, the moldability improves, making it easier to improve the thickness accuracy and surface quality during film manufacturing.

[0027] (a5) In accordance with JIS K7210, the melt flow rate measured at 230°C and a load of 2.16 kg was 3.5 to 20 g / 10 min. Polypropylene (A) has a melt flow rate (MFR) measured at 230°C and a 2.16 kg load in accordance with JIS K7210-1:2014, preferably 3.5 to 20 g / 10 min, more preferably 5.0 to 18 g / 10 min, even more preferably 7.0 to 15 g / 10 min, and even more preferably 11 to 13 g / 10 min. Within this range, the moldability when forming the film is good. The melt flow rate (MFR) of polypropylene (A) 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. Furthermore, the melt flow rate (MFR) can also be adjusted by appropriately reducing the amount of higher molecular weight propylene polymer.

[0028] (a6) 13 The isotactic mesopentad fraction (mmmm) measured by 13C-NMR is 95% or higher. Polypropylene (A) is 13The isotactic mesopentad fraction (mmmm) measured by 13C-NMR is preferably 95% or more, more preferably 96% or more, and still more preferably 97% or more. Further, mmmm can be 95 to 96%. When within the above range, the rigidity of the film becomes good. The upper limit of the isotactic mesopentad fraction (mmmm) is preferably 99.5% or less from the viewpoint of maintaining the thickness accuracy of the stretched film. In this specification, the isotactic mesopentad fraction (mmmm) is a value measured by the following method.

[0029] ( 13 13C-NMR measurement method) [Sample preparation and measurement conditions] Put 200 mg of the sample into an NMR sample tube with an inner diameter of 10 mmφ together with 2.4 mL of o-dichlorobenzene / deuterated benzene (C6D5Br) = 4 / 1 (volume ratio) and hexamethyldisiloxane which is a chemical shift reference substance, and dissolve uniformly with a block heater at 150 °C. The NMR measurement is carried out using an AV400 type NMR apparatus manufactured by Bruker BioSpin equipped with a 10 mmφ cryoprobe. 13 The measurement conditions for 13C-NMR are as follows: the sample temperature is 120 °C, the pulse angle is 90°, the pulse interval is 15 seconds, the number of integration times is 1024 times, and the measurement is carried out by the broadband decoupling method. The chemical shift sets the 13C signal of hexamethyldisiloxane at 1.98 ppm, and the chemical shifts of the signals due to other 13C are based on this. 13 C signals are set at 1.98 ppm, and the chemical shifts of the signals due to other 13 C are based on this.

[0030] [Calculation method of isotactic mesopentad fraction (mmmm)] The isotactic mesopentad fraction (mmmm) of a five - consecutive propylene unit can be obtained by substituting the integrated intensity of the 13C signal measured by 13C-NMR into the following formula (1). 13 C-NMR measurement 13 The integrated intensity of the 13C signal can be obtained by substituting it into the following formula (1). mmmm (%) = (I mm - 2×I mrrm) × 100 / (I mm +3 × I mrrm ) ...Equation (1) Here I mm This is attributed to a three-chain propylene unit bond structure of mm. 13 This represents the integrated intensity of the C signal, where the chemical shift is in the range of 23.6 to 21.1 ppm. 13 Integrated intensity of the C signal (hereinafter referred to as "I") 23.6~21.1 It is calculated as follows (written as "). I mrrm This is because a 5-chain of propylene units is attributed to the mrrm binding mode. 13 This represents the integrated intensity of the C signal, and I 19.9~19.7 This is the value shown. Spectra assignment can be done by referring to Polymer Journal, Vol. 16, p. 717 (1984), Asakura Shoten, 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 region can be easily identified.

[0031] (a7) The cold xylene soluble content (CXS) is less than 5.0% by weight. CXS is an indicator of low molecular weight components. The CXS of polypropylene (A) is preferably less than 5.0% by weight, more preferably 0 to 3.0% by weight, and even more preferably 0 to 2.0% by weight. Within this range, the heat resistance and rigidity of the film are good.

[0032] In this specification, CXS is a value measured by the following method. The sample (approximately 5 g) is completely dissolved in 300 ml of p-xylene at 140°C. The mixture is then cooled to 23°C and left at 23°C for 12 hours to precipitate the polymer. After filtering off the precipitated polymer, the p-xylene is evaporated from the filtrate. The polymer remaining after evaporation is dried under reduced pressure at 100°C for 2 hours. The dried polymer is weighed, and the CXS value is obtained as a weight percentage of the sample.

[0033] The CXS of polypropylene (A) can be easily adjusted by changing the type and amount of catalyst used during polymerization.

[0034] (a8) In the molecular weight distribution curve obtained by 3D-GPC, the branching index g'(1 million) for absolute molecular weight Mabs is greater than 0.85. The branching index g' is the intrinsic viscosity [η] of the polymer in question. br The intrinsic viscosity [η] of a linear polymer having the same molecular weight. lin The ratio ([η] br / [η] lin Given by ), if long-chain branched structures are present in the polymer, the branching index g' takes a value less than 1.0. The definition of the branching index g' is described, for example, in "Developments in Polymer Charactarization-4" (JV Dawkins ed. Applied Science Publishers, 1983), and is a well-known indicator to those skilled in the art. The branching index g' can be determined, for example, by using a 3D-GPC equipped with a light scattering meter and a viscometer as detectors, as shown below, to determine the absolute molecular weight M abs It can be obtained as a function of .

[0035] In this invention, 3D-GPC refers to a GPC device in which three detectors are connected. These three detectors are a differential refractometer (RI), a viscometer, and a multi-angle light scattering detector (MALS). As a GPC instrument equipped with a differential refractometer (RI) and a viscometer, for example, the Alliance GPCV2000 from Waters can be used. Furthermore, as a multi-angle light scattering detector (MALS), for example, the DAWN HELEOS II from Wyatt Technology can be used. The detectors are connected in the following order: MALS, RI, and Viscometer.

[0036] Absolute molecular weight obtained from MALS (M absThe mean square radius of inertia (Rg) and the intrinsic viscosity ([η]) obtained from the Viscometer can be calculated using the data processing software ASTRA (version 4.73.04) included with MALS, with reference to the following literature. References: 1.Developments in Polymer Characterization, vol.4. Essex: Applied Science; 1984. Chapter1. 2.Polymer, 45, 6495-6505(2004) 3.Macromolecules, 33, 2424-2436(2000) 4.Macromolecules, 33, 6945-6952(2000)

[0037] The branching index g' is the intrinsic viscosity ([η]) obtained by measuring the sample with the Viscometer described above. br ) and the intrinsic viscosity ([η] obtained by separately measuring the linear polymer. lin ) ratio ([η] br / [η] lin It can be calculated as follows: In this specification, [η] lin The values ​​used are those obtained using a commercially available propylene homopolymer (Novatec® PP grade name: FY6, manufactured by Nippon Polypropylene Co., Ltd.) as the linear polymer. [η] of the linear polymer lin The linear relationship between the logarithm of and the logarithm of molecular weight is known as the Mark-Houwink-Sakurada equation. Therefore, the absolute molecular weight M abs [η] in 1 million lin If data is unavailable, the branching index g'(1 million) can be obtained by appropriately extrapolating to the low molecular weight or high molecular weight side.

[0038] When a long-chain branched structure is introduced into a polymer molecule, its radius of inertia decreases compared to a linear polymer molecule of the same molecular weight. A smaller radius of inertia leads to a smaller intrinsic viscosity, and therefore, as the introduction of a long-chain branched structure increases, the intrinsic viscosity ([η]) of a linear polymer of the same molecular weight decreases. lin The intrinsic viscosity ([η]) of branched polymers relative to ) br ) ratio ([η] br / [η] lin ) becomes smaller. Therefore, polymers with a long-chain branched structure have a branching index g'([η] br / [η] lin When the value becomes less than 1.0, the linear polymer, by definition, has a branching index g' of 1.0.

[0039] The branching index g'(1,000,000) of polypropylene (A) is preferably greater than 0.85, more preferably greater than 0.90, even more preferably greater than 0.95, and particularly preferably greater than 0.99. A branching index g'(1,000,000) within this range is preferable because it suppresses the orientation of molecular chains caused by branching, thereby improving the heat resistance of the polypropylene composition.

[0040] (a9)γ is less than 5.0% by weight. The polypropylene (A) preferably has a component amount γ of 1,000,000 or more molecular weight measured by GPC less than 5.0% by weight, more preferably less than 3.0% by weight, even more preferably less than 2.0% by weight, and particularly preferably less than 1.5% by weight. Furthermore, γ is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, even more preferably more than 0.1% by weight, and particularly preferably 0.4% by weight or more. Within the above range, the stretch tension of polypropylene (A) is low, which can reduce the load on the molding equipment. In addition, when molecular chains are oriented or crystalline structures such as lamellae are rearranged during stretching, it can be molded uniformly and stably, the rigidity of the film is easily improved, and due to its higher-order structure, it can be made less prone to shrinkage when heated.

[0041] <Method for manufacturing polypropylene (A)> The propylene polymer can preferably be obtained by polymerizing propylene or copolymerizing propylene with a small amount of ethylene using a catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. If the propylene polymer obtained in this way satisfies requirement (a1), this propylene polymer can be used as polypropylene (A) of the present invention.

[0042] An example of a Ziegler-Natta catalyst is a solid component (a) containing magnesium, titanium, halogens, and an internal electron donor compound selected from phthalate compounds, diether compounds, and succinate compounds. In addition to the solid component (a), the Ziegler-Natta catalyst may also contain an organoaluminum compound (b) and an external electron donor compound (c) as needed. Furthermore, the solid component (a) may be contacted with an alkoxysilane or a silane compound having an alkenyl group. Examples of metallocene catalysts include metallocene compounds, at least one compound selected from organometallic compounds, organoaluminum oxy compounds, and compounds capable of reacting with metallocene compounds to form ion pairs, and optionally a particulate support. Among these, metallocene catalysts capable of stereoregular polymerization, such as isotactic or syndiotactic structures, are preferred.

[0043] Any known method can be used to polymerize propylene polymers, such as polymerization in an inert solvent like hexane, heptane, toluene, or xylene; polymerization in a liquid monomer; polymerization in the gas phase by adding a catalyst to a gaseous monomer; or polymerization by combining these methods. Polymerization of propylene polymers may be carried out as single-stage polymerization in a single reactor or as multi-stage polymerization in multiple reactors. In the case of multi-stage polymerization, the polymerization conditions in each reactor may be the same or different. The reactors may also have gradients of monomer concentration and polymerization conditions. The molecular weight of the propylene polymer may be adjusted using a chain transfer agent such as hydrogen.

[0044] If the obtained propylene polymer has (Mw / Mn)·γ ≥ 10, the propylene polymer can be deconstituted with an organic peroxide to adjust Mw / Mn and γ so that it satisfies 1.0 ≤ (Mw / Mn)·γ < 10. In particular, the deconstitution treatment causes molecular cleavage in the relatively high molecular weight components (molecules) that make up the propylene polymer, so γ becomes smaller and the condition 1.0 ≤ (Mw / Mn)·γ < 10 can be satisfied. If the obtained propylene polymer satisfies 1.0 ≤ (Mw / Mn)·γ < 10, de-modification treatment with organic peroxides is not essential. However, to bring the value of (Mw / Mn)·γ into a more preferable range and further improve the high rigidity and low thermal shrinkage of the stretched film, the de-modification treatment may be performed.

[0045] The propylene-based polymer before the depolymerization treatment is not particularly restricted as long as it is a propylene homopolymer or a propylene-ethylene copolymer containing 1.0% by weight or less of ethylene-derived units, but the Mw / Mn ratio is preferably 5 to 20, and more preferably 6 to 15. In addition, the melt flow rate (MFR), measured at 230°C and a 2.16 kg load in accordance with JIS K7210-1:2014, is preferably 0.1 to 10 g / 10 min, and more preferably 0.2 to 5 g / 10 min.

[0046] 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 include ylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexine, 1,3-bis(t-butylperoxyisopropyl)benzene, α,α'-bis(t-butylperoxyisopropyl)benzene, t-butyl hydroperoxide, cumene hydroperoxide, lauroyl peroxide, di-t-butyl diperoxyphthalate, t-butyl peroxymaleic acid, t-butylperoxyisopropyl carbonate, isopropyl parkavonate, and the like. These can be used in combination of two or more types, not just one. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexine, 1,3-bis(t-butylperoxyisopropyl)benzene, or α,α'-bis(t-butylperoxyisopropyl)benzene are preferred.

[0047] The depolymerization treatment involves using 0.005 to 1.0 parts by weight of organic peroxide per 100 parts by weight of propylene polymer, and heating and kneading the two at a temperature above the melting point of the polymer, for example, 180 to 300°C. While known methods can be used for this process, it is particularly preferable to perform it in an extruder. Alternatively, to ensure uniform dispersion of the organic peroxide in the propylene polymer, the two materials may be pre-mixed using a mixer such as a Henschel mixer or ribbon blender before heating and kneading. Furthermore, to improve the dispersibility of the organic peroxide, a mixture of the organic peroxide in a suitable medium can also be used.

[0048] The polypropylene (A) obtained in this way can be made into pellets, powder, or other forms by known methods.

[0049] <Polypropylene (B)> Polypropylene (B) satisfies the following requirements (b1) and (b2). Polypropylene (B) is a component that imparts heat resistance to polypropylene compositions for stretched films. By incorporating polypropylene (B), the resulting stretched film has improved heat resistance and can suppress tension during stretching. Polypropylene (B) may be used alone or in combination of two or more types. Polypropylene (B) may be a propylene homopolymer, or a copolymer of propylene and a compound selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms. The content of units derived from propylene in the copolymer is 50% by weight or more, preferably 65% ​​by weight or more, and more preferably 80% by weight or more.

[0050] The propylene, ethylene, and α-olefins having 4 or more carbon atoms that constitute polypropylene (B) may be produced using biomass as a raw material. The propylene, ethylene, and α-olefins having 4 or more carbon atoms that constitute polypropylene (B) may consist only of biomass-derived propylene, ethylene, and α-olefins having 4 or more carbon atoms, or only of fossil fuel-derived propylene, ethylene, and α-olefins having 4 or more carbon atoms. Alternatively, it may contain both biomass-derived propylene, ethylene, and α-olefins having 4 or more carbon atoms and fossil fuel-derived propylene, ethylene, and α-olefins having 4 or more carbon atoms.

[0051] (b1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 0 ≤ (Mw / Mn)·γ < 1.0. By setting 0 ≤ (Mw / Mn)·γ < 1.0, the molecular orientation of the resulting stretched film can be suppressed, and the heat resistance can be improved. Preferably, 0 ≤ (Mw / Mn)·γ < 0.8, more preferably 0 ≤ (Mw / Mn)·γ < 0.5, and even more preferably 0 ≤ (Mw / Mn)·γ < 0.2.

[0052] The values ​​of Mn, Mw, and γ defined above are all obtained by gel permeation chromatography (GPC). Details of the measurement method and equipment are described in the examples. Here, Mn and Mw are the number-average molecular weight and weight-average molecular weight of polypropylene (B) measured by GPC, and Mw / Mn can serve as an indicator of the molecular weight distribution of polypropylene (B). The Mn, Mw, and Mw / Mn of polypropylene (B) can be easily adjusted by changing the temperature and pressure conditions of propylene polymerization, or, most commonly, 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, if two or more complexes are used, by changing their ratio. In addition, Mn, Mw, and Mw / Mn can also be adjusted by appropriately reducing the molecular weight of a higher molecular weight propylene polymer or polypropylene (A). The reduction treatment can be carried out in the same manner as described in <Method for producing polypropylene (A)>.

[0053] γ is the amount (in wt%) of components with a molecular weight of 1 million or more in 100 wt% of polypropylene (B), as measured by GPC. The specific method for determining γ is as described in item (a1) of <Polypropylene (A)>. γ can be adjusted by controlling, for example, the selection, combination, and ratio of catalysts, as well as pre-polymerization conditions and the amount of hydrogen during polymerization. Furthermore, γ can also be adjusted by appropriately reducing the amount of a higher molecular weight propylene polymer or polypropylene (A).

[0054] (b2) The weight-average molecular weight Mw is between 10,000 and 40,000. By setting the weight-average molecular weight Mw of polypropylene (B) to 10,000 to 40,000, the stretchability of the film can be improved and its heat resistance can be enhanced. The weight-average molecular weight Mw is preferably 12,000 to 40,000, and more preferably 13,000 to 40,000.

[0055] Polypropylene (B) is preferably one that satisfies the following requirements (b3) to (b5).

[0056] (b3) The cold xylene soluble content (CXS) is 5.0% by weight or more. The CXS of polypropylene (B) is preferably 5.0% by weight or more, more preferably 7.0 to 30.0% by weight, and even more preferably 9.0 to 25.0% by weight. Within this range, the stretchability of the film is improved and the heat resistance is good. The CXS can be measured by the same method as described in item (a7) of <Polypropylene (A)>. The CXS of polypropylene (B) can be easily adjusted by changing the type and amount of catalyst used during polymerization.

[0057] (b4) Mw / Mn is between 1.5 and 3.0. The polypropylene (B) preferably has an Mw / Mn ratio of 1.5 to 3.0, more preferably 1.7 to 2.6, and even more preferably 1.9 to 2.2, as determined by GPC measurement. By setting the Mw / Mn within the above range, the stretchability of the film can be improved and its heat resistance can be enhanced.

[0058] Polypropylene (B) is commercially available, for example, the Viscol® series manufactured by Sanyo Chemical Industries, Ltd.

[0059] (b5) In the molecular weight distribution curve obtained by 3D-GPC, the branching index g'(1 million) for absolute molecular weight Mabs is greater than 0.85. The branching index g'(1,000,000) of polypropylene (B) is preferably greater than 0.85, more preferably greater than 0.90, even more preferably greater than 0.95, and particularly preferably greater than 0.99. A branching index g'(1,000,000) within the above range is preferable because it suppresses the orientation of molecular chains caused by branching and improves the heat resistance of the polypropylene composition. The measuring device and method for the branching index g'(1 million) are as described above.

[0060] <Percentage of component (A) and component (B)> The proportion of component (A) to 100% by weight of the total of component (A) and component (B) is preferably 85.0 to 99.9% by weight, more preferably 90.0 to 99.5% by weight, and even more preferably 95.0 to 99.0% by weight. Furthermore, the proportion of component (B) to 100% by weight of the total of component (A) and component (B) is preferably 0.1 to 15.0% by weight, more preferably 0.5 to 10.0% by weight, and even more preferably 1.0 to 5.0% by weight. By setting the ratio of component (A) and component (B) within the above range, it is possible to improve the stretchability of the film and enhance its heat resistance without degrading its appearance.

[0061] <Polypropylene composition> The polypropylene composition may also contain other components besides polypropylene (A) and polypropylene (B). Other components include additives and polymers other than polypropylene (A) and polypropylene (B). Additives include antioxidants, lubricants, antistatic agents, antiblocking agents, UV absorbers, light stabilizers, chlorine absorbers, heat stabilizers, antifogging agents, flame retardants, dispersants, copper pollution inhibitors, neutralizing agents, plasticizers, anti-foaming agents, crosslinking agents, peroxides, oil spreaders, pigments, etc.

[0062] Examples of antioxidants include phenolic antioxidants and phosphite antioxidants. Examples of phenolic antioxidants 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, trade name "IRGANOX® 1010"), and n-octadecyl-3-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate (manufactured by BASF Japan, trade name "IRGANOX® 1076"). Examples of phosphite antioxidants include bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite and tris(2,4-di-t-butylphenyl)phosphite. Examples of lubricants include higher fatty acid amides and higher fatty acid esters. Examples of antistatic agents include glycerol esters, sorbitanic acid esters, and polyethylene glycol esters of fatty acids with 8 to 22 carbon atoms. Examples of anti-blocking agents include silica, calcium carbonate, and talc.

[0063] Examples of UV absorbers include triazole-based, benzophenone-based, salicylate-based, cyanoacrylate-based, nickel chelate-based, and inorganic fine particle-based compounds. Examples of triazole-based UV absorbers include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb® 200; manufactured by BASF Japan, trade name: Tinuvin® P), 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb® 340; manufactured by BASF Japan, trade name: Tinuvin® 399), and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumi Examples include Sumisorb® 320 (manufactured by BASF Japan, trade name: Tinuvin® 320), 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb® 350; manufactured by BASF Japan, trade name: Tinuvin® 328), and 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb® 300; manufactured by BASF Japan, trade name: Tinuvin® 326). Examples of benzophenone-based UV absorbers include 2-hydroxy-4-methoxybenzophenone (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb® 110) and 2-hydroxy-4-n-octoxybenzophenone (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumisorb® 130). Examples of salicylate-based UV absorbers include 4-t-butylphenyl salicylate (manufactured by Cipro Chemical Co., Ltd., trade name: Seesorb 202). Examples of cyanoacrylate-based UV absorbers include ethyl (3,3-diphenyl) cyanoacrylate (manufactured by Cipro Chemical Co., Ltd., product name: Seesorb 501). Examples of nickel chelate-based UV absorbers include nickel dibutyldithiocarbamate (manufactured by Sumitomo Chemical Co., Ltd., trade name: Antigen® NBC). Examples of inorganic particulate UV absorbers include TiO2, ZnO2, and CeO2.

[0064] Examples of light stabilizers include compounds such as sebacate, butanetetracarboxylate, succinate polyester, and triazine. Examples of sebacate-type light stabilizers include bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (manufactured by ADEKA Corporation, trade name: Adekastab® LA-77; manufactured by BASF Japan Ltd., trade name: Tinuvin® 770) and bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (manufactured by BASF Japan Ltd., trade name: Tinuvin® 765). Examples of butanetetracarboxylate type light stabilizers include tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (manufactured by ADEKA Corporation, product name: ADEKA Stab® LA-57), tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (manufactured by ADEKA Corporation, product name: ADEKA Stab® LA-52), Examples include a condensate of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and tridecyl alcohol (manufactured by ADEKA Corporation, product name: ADEKA Stab® LA-67), and a condensate of 1,2,3,4-butanetetracarboxylic acid with 1,2,2,6,6-pentamethyl-4-piperidinol and tridecyl alcohol (manufactured by ADEKA Corporation, product name: ADEKA Stab® LA-62). Examples of succinic acid polyester-type light stabilizers include condensation polymers of succinic acid and 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine. 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, trade name: Chimasorb® 199), and poly{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperi Examples include (2,2,6,6-tetramethyl-4-piperidyl)imino hexamethylene (manufactured by BASF Japan, trade name: Chimasorb® 944) and 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, trade name: Chimasorb® 3346).

[0065] Other polymers include polypropylene-based resins other than polypropylene (A) and polypropylene (B) according to the present invention, polyethylene, propylene-based or ethylene-based elastomers, and the like. Examples of propylene-based or ethylene-based elastomers include ethylene-α-olefin copolymers, binary random copolymers of propylene and α-olefins having 4 to 12 carbon atoms, and ternary random copolymers of propylene, ethylene, and α-olefins having 4 to 12 carbon atoms.

[0066] 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.

[0067] When a polypropylene composition contains additives or other polymers, the polypropylene composition can be produced by mixing or melt-kneading polypropylene (A), polypropylene (B), and the additives or other polymers. Mixing methods include using a Henschel mixer, V-blender, ribbon blender, tumbler blender, etc. Methods for melt-mixing include using a single-screw extruder, multi-screw extruder, kneader, or Banbar mixer. The polypropylene composition obtained in this way can be formed into pellets, powder, or other forms by known methods. The additive may be added during the polymerization of the propylene polymer, added to the powder after polymerization, or further granulated. It may also be added simultaneously with or separately from the organic peroxide during the depolymerization treatment of the propylene polymer, or added to the polypropylene (A) after the depolymerization treatment. Other polymers are typically added to the polypropylene (A) after the depolymerization treatment. In any case, the mixing method is not particularly limited as long as it does not impair the effects of the present invention.

[0068] [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, and 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. A stretched film can be produced by first creating an unstretched film from a polypropylene composition using a known melt extrusion method, and then stretching the film. The stretched film may be uniaxially oriented or biaxially oriented, but from the viewpoint of the balance of composition in the MD and TD directions, a biaxially oriented film is preferred. In the case of a biaxially oriented film, either simultaneous biaxial stretching or sequential biaxial stretching may be employed.

[0069] In accordance with JIS K6782, the heat shrinkage rate of the stretched film measured at 150°C for 30 minutes is preferably 0-4.0% in the MD direction and 0-6.0% in the TD direction, more preferably 0-3.7% in the MD direction and 0-5.5% in the TD direction, and even more preferably 0-3.5% in the MD direction and 0-5.0% in the TD direction. Within this range, it becomes possible to use the film in applications requiring high heat resistance, which was not possible with conventional OPP films, and it has the advantage of being usable as a substitute for PET film, for example.

[0070] In this invention, the MD direction is the direction of film flow (sometimes called the length direction or longitudinal direction), and the TD direction is the direction perpendicular to the film flow direction and thickness direction (sometimes called the transverse direction or width direction).

[0071] The stretched film may be a single layer containing a polypropylene composition, or a multilayer film in which each layer contains a polypropylene composition. In the case of a multilayer film, the polypropylene compositions constituting each layer may be the same or different. Furthermore, the stretched film may be a laminated film formed by laminating with other layers. In the case of multilayer films or laminated films, a single-layer film containing a polypropylene composition may be stretched before being made into a multilayer film or laminated film, or the stretching treatment may be performed after the film has been made into a multilayer film or laminated film.

[0072] When the stretched film is a single-layer film, its thickness is preferably 5 to 200 μm, more preferably 10 to 150 μm, even more preferably 12 to 100 μm, and even more preferably 15 to 80 μm. Within this range, the film thickness can be made uniform while obtaining appropriate rigidity.

[0073] When the stretched film is incorporated into a multilayer film in which each of the stretched films contains a polypropylene composition, or into a laminated film in which the stretched film is laminated with other layers, the thickness of each stretched film is preferably 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. In the case of a multilayer film or laminated 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.

[0074] The method for manufacturing the stretched film is not particularly limited. For example, an unstretched film made of 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 include an MD stretching step in which the unstretched film is stretched 2 to 10 times, preferably 4 to 7 times, in the MD direction using a stretching roll to obtain a uniaxially oriented film. Alternatively, the method may include a TD stretching step in which the uniaxially oriented film obtained in the MD stretching step is stretched 4 to 20 times, preferably 4 to 10 times, in the TD direction in a heating furnace using two rows of chucks aligned along the MD direction to obtain a biaxially oriented film.

[0075] To improve processability, the stretched film may be subjected to treatments such as corona or plasma discharge, flame treatment, or ozone treatment on its surface.

[0076] Stretched films can be used as one layer in multilayer films or laminated films. Laminated films are formed by laminating arbitrary layers on one or both sides of a layer made of stretched films. Methods for producing multilayer films or laminated films include commonly used co-extrusion, extrusion lamination, thermal lamination, dry lamination, and inflation lamination, which involves cooling with water or air.

[0077] For example, a laminated film can be constructed by laminating any layer such as a sealant layer, a gas barrier layer, an adhesive layer, or a printed layer onto a stretched film. In particular, it is preferable to laminate a sealant layer made of an olefin resin onto a layer made of a stretched film, and the resulting laminated film has the effect 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 to package any items such as food, clothing, and general merchandise. [Examples]

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Hereinafter, propylene polymers satisfying 1.0 ≤ (Mw / Mn)·γ < 10 will be referred to as "polypropylene (A)", and those satisfying (Mw / Mn)·γ ≥ 10 will be referred to as "propylene polymers".

[0079] [Methods for measuring physical properties] The physical properties and analytical values ​​of each item in the examples were measured and analyzed according to the following methods.

[0080] (1) MFR (unit: g / 10 min) Using pellets of polypropylene (A) or propylene polymer, the MFR was measured under the following conditions in accordance with JIS K7210-1:2014. Test temperature: 230℃ Nominal load: 2.16kg Die shape: Diameter 2.095mm, length 8.000mm

[0081] (2) GPC measurement GPC measurements were performed using powders or pellets of polypropylene (A), propylene polymers, or polypropylene (B) to determine the number-average molecular weight Mn, weight-average molecular weight Mw, Mw / Mn, and γ. Details of the measuring instruments are as follows. Equipment: Waters GPC (ALC / GPC, 150C) Detector: FOXBORO MIRAN, 1A, IR detector (measurement wavelength: 3.42 μm) Columns: Showa Denko AD806M / S (3 pieces) Mobile phase solvent: o-dichlorobenzene (ODCB) Measurement temperature: 140℃ Flow rate: 1.0mL / min Injection volume: 0.2mL

[0082] Sample preparation involved preparing a 1 mg / mL solution using polypropylene (A), propylene polymer, or polypropylene (B) powder or pellets with ODCB (containing 0.5 mg / mL dibutylhydroxytoluene (BHT)), and dissolving it at 140°C for approximately 1 hour. The baseline and intervals of the obtained chromatograms were determined as shown in Figure 1. Furthermore, the conversion from retention capacity obtained by GPC measurement to molecular weight was performed using a calibration curve prepared in advance using standard polystyrene. The standard polystyrene used was the following brand manufactured by Tosoh Corporation. Brands: F380, F288, F128, F80, F40, F20, F10, F4, F1, A5000, A2500, A1000 Calibration curves were created by injecting 0.2 mL of a solution dissolved in ODCB (containing 0.5 mg / mL of BHT) so that each component was at 0.5 mg / mL. The calibration curves were approximated using a cubic equation obtained by the least squares method. For conversion to molecular weight, a general calibration curve was used, referencing "Size Exclusion Chromatography" by Sadao Mori (Kyoritsu Shuppan). The viscosity formula used for conversion to molecular weight is: [η] = K × M α The following values ​​are used. (a) When creating a calibration curve using standard polystyrene PS: K = 1.38 × 10⁻⁴, α = 0.7 (i) When measuring samples of polypropylene or propylene polymers PP:K = 1.03 × 10⁻⁴, α = 0.78

[0083] γ is the value obtained by subtracting the integral value up to a molecular weight (M) of 1,000,000 (Log(M)=6.0) from 1 in the integrated molecular weight distribution curve (normalized to 1) obtained by GPC measurement, and then multiplying the result by 100. An example of how to calculate γ is shown in Figure 2.

[0084] (3) 13 Isotactic mesopentad fraction (mmmm) measured by 1C NMR The isotactic mesopentad fraction (mmmm) was determined using pellets of polypropylene (A) or a propylene-based polymer according to the following procedure. ( 13 (Method for measuring CNMR) [Sample preparation and measurement conditions] 200 mg of the sample was placed in a 10 mm diameter NMR sample tube together with 2.4 mL of o-dichlorobenzene / deuterated bromide benzene (C6D5Br) = 4 / 1 (volume ratio) and hexamethyldisiloxane, the reference substance for chemical shift, and uniformly dissolved using a block heater at 150°C. NMR measurements were performed using a Bruker BioSpin AV400 NMR spectrometer equipped with a 10 mmφ cryoprobe. 13 The 1C-NMR measurement conditions were set to a sample temperature of 120°C, a pulse angle of 90°, a pulse interval of 15 seconds, and a total of 1024 integration cycles. The measurement was performed using the broadband decoupling method. The chemical shift is hexamethyldisiloxane. 13 Set the C signal to 1.98 ppm, and the other 13 The chemical shift of the signal due to C was based on this.

[0085] [Method for calculating isotactic mesopentad fraction (mmmm)] The isotactic mesopentad fraction (mmmm) of a 5-chain propylene unit is: 13 Measured by C-NMR 13 The integral intensity of the C signal was obtained by substituting it into the following equation (1). mmmm(%)=(I mm -2 × I mrrm ) × 100 / (Imm +3 × I mrrm ) ...Equation (1) Here I mm This is attributed to a three-chain propylene unit bond structure of mm. 13 This represents the integrated intensity of the C signal, where the chemical shift is in the range of 23.6 to 21.1 ppm. 13 This is the integrated intensity of the C signal, and I mrrm This is because a 5-chain of propylene units is attributed to the mrrm binding mode. 13 This represents the integrated intensity of the C signal, where the chemical shift is in the range of 19.9–19.7 ppm. 13 This is the integrated intensity of the C signal.

[0086] (4)Cold xylene solubles (CXS) Powder or pellets (approximately 5g) of polypropylene (A), a propylene polymer, or polypropylene (B) were completely dissolved in p-xylene (300ml) at 140°C. The mixture was then cooled to 23°C and left at 23°C for 12 hours to precipitate the polymer. After filtering off the precipitated polymer, p-xylene was evaporated from the filtrate. The polymer remaining after evaporation was dried under reduced pressure at 100°C for 2 hours. The dried polymer was weighed, and the CXS value was obtained as a weight percentage relative to the initially weighed pellet.

[0087] (5) Absolute molecular weight M obtained by 3D-GPC abs The branching exponent g'(1,000,000) at 1,000,000 is 3D-GPC measurements were performed using powder or pellets of polypropylene (A), a propylene-based polymer, or polypropylene (B), and a commercially available propylene homopolymer (Novatec® PP grade name: FY6, manufactured by Nippon Polypropylene Co., Ltd.) as the linear polymer, to determine the absolute molecular weight M abs The branching exponent g'(1,000,000) at 1,000,000 was determined. Details of the measuring instrument are as follows. Equipment: Waters Alliance GPCV2000 Detectors: The differential refractometer (RI) and viscometer (Viscometer) used were those standard equipment on the Alliance GPCV2000. The multi-angle light scattering detector (MALS) used was the DAWN HELEOS II from Wyatt Technology. The detectors were connected in the order of MALS, RI, and Viscometer. Columns: Two Tosoh Corporation GMHHR-H(S)HT columns were connected in series. Mobile phase solvent: 1,2,4-trichlorobenzene (with BASF Japan's antioxidant Irganox® 1076 added at a concentration of 0.5 mg / mL) Temperature of column, sample injection unit, and each detector: 140°C Flow rate: 1.0mL / min Sample concentration: 1 mg / mL Injection volume (sample loop volume): 0.2175 mL

[0088] (6) Film thickness The thickness of the biaxially oriented films of Examples 1-30 and Comparative Examples 1-8 was measured using a Mitutoyo ID-SX2.

[0089] (7) Glossiness (%) For the biaxially oriented films of Examples 1-30 and Comparative Examples 1-8, the glossiness of the films was measured at an incident angle of 60° using a Gloss Meter VG2000 manufactured by Nippon Denshoku Industries, Ltd., in accordance with JIS Z8741:1997.

[0090] (8) Haze (%) The haze of the biaxially oriented films of Examples 1-30 and Comparative Examples 1-8 was measured in accordance with JIS K7136:2000.

[0091] (9) Heat shrinkage rate (%) For the biaxially oriented films of Examples 1-30 and Comparative Examples 1-8, the heat shrinkage rate was measured in accordance with JIS K6782 using the following method. The film was cut to a width of 20 mm and a length of 200 mm in both the MD and TD directions, and heated in a 150°C hot air oven for 30 minutes. The length was measured immediately after heating, and the ratio of the shrunk length to the original length was defined as the heat shrinkage rate. A smaller value indicates a lower heat shrinkage rate, which in turn indicates superior heat resistance and dimensional stability during heating.

[0092] [Resin used] The various resins used in the examples and comparative examples are listed below. [Polypropylene (A)] A-1: 100 parts by weight of Novatec® PP, grade EA9HD (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 0.4 g / 10 min), manufactured by Nippon Polypropylene Co., Ltd., were 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 mixing temperatures of C1 / C2 / C3~C7 / head / die = 150°C / 180°C / 230°C / 230°C / 180°C from the bottom of the hopper to obtain polypropylene pellets. The MFR of the obtained pellets was 10 g / 10 min. A-2: 100 parts by weight of 100 parts by weight of Novatec® PP, grade FY6H (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 1.8 g / 10 min), manufactured by Nippon Polypropylene Co., Ltd., was mixed with 0.023 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, using 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 obtained pellets was 10 g / 10 min. A-3: 100 parts by weight of Novatec® PP, grade FL1105F (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Nippon Polypropylene Co., Ltd., was mixed with 0.007 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, using 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 obtained pellets was 7.0 g / 10 min. A-4: 100 parts by weight of Novatec® PP, grade FL1105F (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Nippon Polypropylene Co., Ltd., was mixed with 0.014 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, using 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 obtained pellets was 10 g / 10 min. A-5: 100 parts by weight of Novatec® PP, grade FL1105F (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Nippon Polypropylene Co., Ltd., was mixed with 0.017 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, using 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 obtained pellets was 12 g / 10 min.

[0093] [Propylene polymer] A-6: Manufactured by Nippon Polypropylene Co., Ltd., product name Novatec® PP, grade name SA3D (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230℃, 2.16kg load) = 11g / 10min) A-7: Manufactured by Nippon Polypropylene Co., Ltd., product name Novatec® PP, grade name FL203D (propylene homopolymer using Ziegler-Natta catalyst, MFR (230℃, 2.16kg load) = 3.0g / 10min) A-8: 100 parts by weight of Novatec® PP, grade FL1105F (propylene homopolymer catalyzed by Ziegler-Natta catalyst, MFR (230°C, 2.16 kg load) = 3.5 g / 10 min), manufactured by Nippon Polypropylene Co., Ltd., was mixed with 0.003 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, an organic peroxide, using 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 obtained pellets was 5.0 g / 10 min.

[0094] Table 1 shows the physical properties of polypropylene (A) and propylene-based polymers.

[0095] [Table 1]

[0096] [Polypropylene (B)] B-1: Manufactured by Sanyo Chemical Industries, Ltd., product name Viscol (registered trademark) 330-P (polypropylene wax, (Mw / Mn)·γ=0, branching index g'(1,000,000)=1.0) B-2: Manufactured by Sanyo Chemical Industries, Ltd., product name Viscol (registered trademark) 440-P (polypropylene wax, (Mw / Mn)·γ=0, branching index g'(1,000,000)=1.0) B-3: Manufactured by Sanyo Chemical Industries, Ltd., product name Viscol (registered trademark) 550-P (polypropylene wax, (Mw / Mn)·γ=0, branching index g'(1,000,000)=1.0)

[0097] The physical properties of polypropylene (B) are shown in Table 2.

[0098] [Table 2]

[0099] Example 1 Using a three-layer co-extruder, a mixture of 99% by weight of polypropylene (A-1) and 1% by weight of polypropylene (B-1) was added to each layer. After melt-extrusion at a resin temperature of 240°C for each layer, the mixture was rapidly cooled with a cooling roll at 30°C to produce three unstretched films of one type. Biaxially oriented films were then obtained from the resulting unstretched films using a Mitsubishi Heavy Industries biaxially oriented film molding machine (Tenter) with the roll temperature adjusted to 110°C. The extrusion conditions, stretching conditions, and the thickness of the film after biaxial stretching are as follows: Extrusion conditions: Extrusion temperature: 240℃, die width: 300mm, lip opening: 2.0mm, cooling roll temperature: 30℃, cooling roll speed: 3m / min Stretching conditions: Stretching roll temperature: 110°C, Stretching ratio in MD direction: 5x, Stretching ratio in TD direction: 8x, Take-up speed: 15m / min, Tenter chamber temperature: 165°C in all three zones: preheating, stretching, and heat setting. The total film thickness is 20 μm. Of this, the thickness of the first and third layers is 2 μm each.

[0100] For Examples 2-30 and Comparative Examples 1-8, biaxially oriented films were prepared using the compositions shown in Tables 3-5 and under the same conditions as in Example 1. The physical properties of the biaxially oriented films obtained in the Examples and Comparative Examples are shown in Tables 3-5.

[0101] [Table 3]

[0102] [Table 4]

[0103] [Table 5]

[0104] [Discussion of the results of the examples and comparative examples] Tables 3-5 show that the biaxially oriented films of Examples 1-30, formed from a mixture containing polypropylene (A) satisfying 1.0 ≤ (Mw / Mn)·γ < 10 and polypropylene (B) satisfying 0 ≤ (Mw / Mn)·γ < 1.0 in predetermined proportions, exhibit low heat shrinkage in both the MD and TD directions and excellent heat resistance. Furthermore, the biaxially oriented films of Examples 1-30 have low haze and high transparency. On the other hand, the biaxially oriented films of Comparative Examples 1 and 2, which are formed from propylene polymers with (Mw / Mn)·γ of 10 or more, and Comparative Examples 3 to 8, which are formed from a mixture containing propylene polymers (A-8) and polypropylene (B) with (Mw / Mn)·γ of 10 or more, exhibited inferior heat shrinkage rates in the MD and TD directions.

[0105] A comparison of Examples 13-30 and Comparative Examples 3-8, which use the same propylene homopolymer (manufactured by Nippon Polypropylene Co., Ltd., trade name Novatec® PP, grade name FL1105F) as the raw material for polypropylene (A), shows that the biaxially oriented films of Examples 19-30, which use polypropylene (A-4) or (A-5) satisfying (Mw / Mn)·γ < 7.3, exhibit significantly superior heat shrinkage and are therefore preferred. In particular, the biaxially oriented films of Examples 25-30, which use polypropylene (A-5) satisfying (Mw / Mn)·γ < 6.0 and having an MFR in the range of 11-13 g / 10 min, have γ and MFR in the most favorable range, and therefore exhibit particularly excellent heat shrinkage. [Industrial applicability]

[0106] Polypropylene compositions can be suitably used as raw materials for stretched films.

Claims

1. A polypropylene composition for stretched films, comprising polypropylene (A) that satisfies the following requirements (a1) to (a3) ​​and polypropylene (B) that satisfies the following requirements (b1) and (b2). (a1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 1.0 ≤ (Mw / Mn)・γ < 10. (a2) Selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers containing 1.0% by weight or less of ethylene-derived units. (a3) The weight-average molecular weight Mw is 150,000 to 250,000. (b1) The molecular weight distribution Mw / Mn measured by GPC and the amount γ (weight %) of components with a molecular weight of 1 million or more measured by GPC satisfy 0 ≤ (Mw / Mn)・γ < 1.

0. (b2) The weight-average molecular weight Mw is between 10,000 and 40,000.

2. The polypropylene composition for stretched film according to claim 1, wherein the polypropylene (A) satisfies the following requirements (a4) and (a5). (a4) Mw / Mn satisfies 2.0 < Mw / Mn < 5.

0. (a5) In accordance with JIS K7210, the melt flow rate measured at 230°C and a load of 2.16 kg is 3.5 to 20 g / 10 min.

3. The polypropylene composition for stretched film according to claim 2, wherein the polypropylene (A) satisfies the following requirement (a6). (a6) １３ The isotactic mesopentad fraction (mmmm) measured by 13C-NMR is 95% or higher.

4. The polypropylene composition for stretched film according to claim 1, wherein polypropylene (A) satisfies the following requirement (a7) and polypropylene (B) satisfies the following requirement (b3). (a7) The cold xylene soluble content (CXS) is less than 5.0% by weight. (b3) The cold xylene soluble content (CXS) is 5.0% by weight or more.

5. The polypropylene composition for stretched film according to claim 1, wherein the polypropylene (A) satisfies the following requirement (a8). (a8) In the molecular weight distribution curve obtained by 3D-GPC, the absolute molecular weight M ａｂｓ The branching index g'(1 million) for 1 million exceeds 0.

85.

6. The polypropylene composition for stretched film according to claim 1, wherein the proportions of component (A) and component (B) to 100% by weight of the total of component (A) and component (B) are 85.0 to 99.9% by weight and 0.1 to 15.0% by weight, respectively.

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

8. The stretched film according to claim 7, wherein the heat shrinkage rate of the stretched film, measured in accordance with JIS K6782 under conditions of 150°C for 30 minutes, is 0 to 4.0% in the MD direction and 0 to 6.0% in the TD direction.

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