Polypropylene resin composition for injection molding and injection molded article

Abstract

To provide an injection-molded body excellent in hinge characteristics and low-temperature impact resistance, and a polypropylene-based resin composition for injection molding suitable for producing the same.SOLUTION: The polypropylene-based resin composition for injection molding contains: a polypropylene-based resin (component A) containing a continuous phase comprising a propylene-ethylene copolymer and a rubber phase comprising an ethylene-α-olefin copolymer; and optionally another ethylene-α-olefin copolymer (component B) and a nucleating agent (component C). The content ratio of the component A is 90-100 mass%. The MFR of the composition is 0.1 g / 10 min or more and less than 10 g / 10 min. Each of the copolymers constituting the component A satisfies predetermined physical properties.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene resin composition for injection molding and an injection molded article. [Background technology]

[0002] Polypropylene has an excellent balance of physical properties such as impact resistance, rigidity, transparency, chemical resistance, and heat resistance, and is therefore used as a resin material for containers, etc. For example, Patent Document 1 discloses a polypropylene composition suitable for molding food containers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-157084 Summary of the Invention [Problem to be solved by the invention]

[0004] Some food containers and lidded cases have hinges. The hinges are required to have high resistance to repeated bending (hinge characteristics). The polypropylene composition of Patent Document 1 is suitable for molding food containers with excellent transparency and flexibility, but there is a need to improve its hinge characteristics. In addition, high low-temperature impact resistance is also required for storage in refrigerators and freezers.

[0005] The present invention provides an injection-molded article having excellent hinge properties and low-temperature impact resistance, and a polypropylene-based resin composition for injection molding suitable for producing the same. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A polypropylene-based resin composition containing a polypropylene-based resin (A) including a continuous phase made of a propylene-ethylene copolymer optionally containing a propylene homopolymer and a rubber phase made of an ethylene-α-olefin copolymer, wherein the polypropylene-based resin composition has an MFR of 0.1 g / 10 min or more and less than 10 g / 10 min at a temperature of 230°C and a load of 2.16 kg, the content of the polypropylene-based resin (A) being 90 to 100 mass% based on the total mass of the polypropylene-based resin composition, the xylene-soluble portion of the polypropylene-based resin (A) having an intrinsic viscosity of 0.8 to 1.5 dl / g in tetrahydronaphthalene at 135°C, and the polypropylene-based resin (A) having an MFR of 0.1 g / 10 min or more and less than 10 g / 10 min at a temperature of 230°C and a load of 2.16 kg, a MFR under a load of 2.16 kg of 0.1 g / 10 min or more and less than 10 g / 10 min, the propylene-ethylene copolymer optionally containing a propylene homopolymer has an ethylene-derived unit content of 0.1 to 10 mass % relative to the total mass of the propylene-ethylene copolymer optionally containing a propylene homopolymer, the α-olefin has 3 to 10 carbon atoms, the ethylene-derived unit content of the ethylene-α-olefin copolymer is 70 to 85 mass % relative to the total mass of the ethylene-α-olefin copolymer, and the content of the ethylene-α-olefin copolymer relative to the mass of the polypropylene-based resin (A) is 10 to 50 mass %. [2] The polypropylene-based resin composition for injection molding according to [1], wherein the propylene-ethylene copolymer optionally containing the propylene homopolymer has an MFR of 0.1 g / 10 min or more and less than 10 g / 10 min at a temperature of 230°C and a load of 2.16 kg. [3] The polypropylene-based resin composition for injection molding according to [1] or [2], further comprising an ethylene-α-olefin copolymer (B) in addition to the ethylene-α-olefin copolymer constituting the polypropylene-based resin (A), wherein the ethylene-α-olefin copolymer (B) has a MFR of 0.1 g / 10 min or more and 40 g / 10 min or less at a temperature of 190°C and a load of 2.16 kg, and the content of the ethylene-α-olefin copolymer (B) relative to the total mass of the polypropylene-based resin composition is 10 mass% or less. [4] The polypropylene-based resin composition for injection molding according to [1] or [2], further comprising a nucleating agent (C), wherein the content of the nucleating agent (C) relative to the total mass of the polypropylene-based resin composition is 0.5 mass% or less. [5] The polypropylene-based resin composition for injection molding according to any one of [1] to [4], wherein the propylene-ethylene copolymer optionally containing the propylene homopolymer and the ethylene-α-olefin copolymer are mixed by polymerization, and the polypropylene-based resin is a polymerization mixture produced using a catalyst containing the following components (a) to (c): (a) A solid catalyst containing magnesium, titanium, a halogen, and an electron donor compound. (a) Organoaluminum compounds (c) Organosilicon compounds that are external electron donor compounds [6] The polypropylene resin composition for injection molding according to [5], wherein the electron donor compound is a phthalate compound or a succinate compound. [7] An injection-molded article obtained by injection molding the polypropylene resin composition for injection molding according to any one of [1] to [6]. [8] The injection-molded article according to [7], wherein the injection molding is an injection molding other than injection blow molding. [Effects of the Invention]

[0007] The polypropylene resin composition for injection molding of the present invention has high fluidity, so that it is unlikely to cause insufficient filling of a mold during injection molding, even in a mold having a complex shape such as a hinge portion, etc. The injection-molded article obtained by injection molding has excellent hinge properties and low-temperature impact resistance. [Brief explanation of the drawings]

[0008] [Figure 1] This is the appearance of the hinged box produced in the example when it is open. [Figure 2] This is a cross-sectional photograph of the hinge part of a hinged box before bending. [Figure 3] This is a cross-sectional photograph of the hinged box after bending the hinge part. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Polypropylene-based resin composition> The polypropylene-based resin composition for injection molding (hereinafter abbreviated as "polypropylene-based resin composition") according to a first embodiment of the present invention contains a polypropylene-based resin (A) (hereinafter also referred to as component (A)) which includes a continuous phase made of a propylene-ethylene copolymer optionally containing a propylene homopolymer, and a rubber phase made of an ethylene-α-olefin copolymer. The polypropylene resin composition may further contain an ethylene-α-olefin copolymer (B) in addition to the ethylene-α-olefin copolymer constituting the polypropylene resin (A). The polypropylene resin composition may further contain a nucleating agent (C).

[0010] The polypropylene resin composition has an MFR at a temperature of 230°C under a load of 2.16 kg of 0.1 g / 10 min or more and less than 10 g / 10 min, with the lower limit being preferably 0.3 g / 10 min or more, more preferably 0.5 g / 10 min or more, and even more preferably 1.0 g / 10 min or more, and the upper limit being preferably 8.0 g / 10 min or less, more preferably 7.0 g / 10 min or less, even more preferably 5.0 g / 10 min or less, and particularly preferably 4.0 g / 10 min or less. Here, the MFR is a value measured by the measurement method described below. When the content is at least the lower limit of the above range, the injection moldability is improved. When the content is less than or equal to the upper limit of the above range, the hinge characteristics and low-temperature impact resistance of the injection-molded article can be further improved.

[0011] The content of the polypropylene resin (A) is 90 to 100 mass %, preferably 92 to 99 mass %, based on the total mass of the polypropylene resin composition. When the content is at least as large as the lower limit of the above range, the hinge characteristics and rigidity of the injection-molded article can be further improved.

[0012] [Polypropylene resin (A)] The polypropylene resin (A) contained in the polypropylene resin composition of the present invention is one embodiment of impact-resistant polypropylene polymers defined in JIS K6921-1, and is composed of two or more phases including a continuous phase (hereinafter also referred to as "component (1)") made of a propylene-ethylene copolymer optionally containing a propylene homopolymer, and a rubber phase (hereinafter also referred to as "component (2)") made of an ethylene-α-olefin copolymer present as a dispersed phase in the continuous phase. The polypropylene-based resin (A) may be a mixed resin (polymerization mixture) in which component (1) and component (2) are mixed during polymerization, or may be a mixed resin in which component (1) and component (2) obtained separately are mixed by melt-kneading. However, for the following reasons, it is preferable that the polypropylene-based resin (A) is a mixed resin in which component (1) and component (2) are mixed during polymerization (polymerization mixture). In the polymerization mixture, component (1) and component (2) can be mixed at the submicron level. Therefore, polypropylene resin compositions based on the polymerization mixture exhibit an excellent balance of mechanical properties, such as rigidity and low-temperature impact resistance, as well as good hinge properties. On the other hand, if a similar homogeneous mixture is achieved by simply melt-kneading separately obtained components (1) and (2) to obtain an excellent balance of mechanical properties, this generally results in high production costs due to the need for additional processes such as storage, keeping, transporting, measuring, mixing, and melt-kneading, and is also undesirable from the standpoint of energy costs. However, as described below, when a specific ethylene-α-olefin copolymer is included as component (B) in a specific ratio, it is possible to suppress production costs and energy costs while exhibiting an excellent balance of mechanical properties such as rigidity and low-temperature impact resistance, as well as good hinge characteristics. The reason why the polymerized mixture and the mechanical mixture may show different physical properties is presumably due to differences in the dispersion state of component (2) in component (1). However, there is currently no known practical means for analyzing the dispersion state at the molecular level, including the state of the interface between component (2) and component (1). The method for producing the polypropylene resin (A) will be described in detail later.

[0013] The intrinsic viscosity (hereinafter also referred to as "XSIV") of the xylene soluble matter of the polypropylene resin (A) is 0.8 to 1.5 dl / g, preferably 0.9 to 1.4 dl / g, more preferably 1.0 to 1.3 dl / g, and even more preferably 1.0 to 1.2 dl / g. When the polypropylene content is at least as high as the lower limit of the above range, it can be easily produced as polypropylene. When the content is equal to or less than the upper limit of the above range, the hinge characteristics of the injection-molded article can be further improved. Here, XSIV is a value measured in tetrahydronaphthalene at 135°C. The xylene solubles are obtained by dissolving a polypropylene resin sample in o-xylene at 135°C, cooling it to 25°C, filtering the cooled solution using filter paper, and evaporating the filtrate to dryness.

[0014] The MFR of component (1) constituting polypropylene resin (A) at a temperature of 230°C and a load of 2.16 kg is preferably 0.1 g / 10 min or more as a lower limit, more preferably 0.5 g / 10 min or more, and even more preferably 1.0 g / 10 min or more. The upper limit is preferably less than 10 g / 10 min, more preferably 8.0 g / 10 min or less, even more preferably 7.0 g / 10 min or less, particularly preferably 5.0 g / 10 min or less, and most preferably 4.0 g / 10 min or less. The MFR is a value measured by the measurement method described below. When the content is at least as high as the lower limit of the above range, injection molding can be easily carried out. When the content is less than or equal to the upper limit of the above range, the hinge properties of the injection-molded article can be further improved.

[0015] The content of ethylene-derived units (hereinafter also referred to as "C2a") in component (1) constituting polypropylene resin (A) is 0.1 to 10% by mass relative to the total mass of component (1), with the lower limit being preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more. The upper limit is preferably 7.0% by mass or less, more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, and particularly preferably 4.0% by mass or less. When the content is at least as large as the lower limit of the above range, the hinge properties of the injection-molded article can be further improved. When the content is equal to or less than the upper limit of the above range, the rigidity of the injection-molded article can be further increased. C2a is 13 It is measured by C-NMR.

[0016] The ethylene-α-olefin copolymer constituting the polypropylene-based resin (A) is a copolymer having ethylene-derived units and α-olefin-derived units. The α-olefin has 3 to 10 carbon atoms, preferably 3 to 6 carbon atoms, more preferably 3 or 4 carbon atoms, and even more preferably 4 carbon atoms.

[0017] The content of ethylene-derived units (hereinafter also referred to as "C2b") in the ethylene-α-olefin copolymer constituting the polypropylene resin (A) is 70 to 85% by mass, preferably 72% by mass or more and more preferably 75% by mass or more, based on the total mass of the ethylene-α-olefin copolymer, and preferably 83% by mass or less and more preferably 80% by mass or less as the upper limit. When the content is at least as large as the lower limit of the above range, the hinge properties of the injection-molded article can be further improved. When the content is equal to or less than the upper limit of the above range, the low-temperature impact resistance of the injection-molded article can be further improved. C2b is 13 It is measured by C-NMR.

[0018] The content of the ethylene-α-olefin copolymer relative to the total mass of the polypropylene resin (A) is 10 to 50% by mass, with the lower limit being preferably 12% by mass or more, and more preferably 15% by mass or more, and the upper limit being preferably 48% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. When the content is at least as high as the lower limit of the above range, the low-temperature impact resistance of the injection-molded article can be further improved. When the content is equal to or less than the upper limit of the above range, the risk of clogging of flow paths in production equipment due to deterioration of powder flowability during production of the polypropylene-based resin (A) can be reduced, thereby enabling stable continuous production of the polypropylene-based resin (A).Furthermore, the rigidity of the injection-molded article can be increased.

[0019] The MFR of the polypropylene resin (A) at a temperature of 230°C and a load of 2.16 kg is 0.1 g / 10 min or more but less than 10 g / 10 min, with the lower limit being preferably 0.3 g / 10 min or more, more preferably 0.5 g / 10 min or more, and even more preferably 1.0 g / 10 min or more. The upper limit is preferably 8.0 g / 10 min or less, more preferably 7.0 g / 10 min or less, even more preferably 5.0 g / 10 min or less, and particularly preferably 4.0 g / 10 min or less. Here, the MFR is a value measured using the measurement method described below. When the content is at least the lower limit of the above range, the injection moldability is improved. When the content is less than or equal to the upper limit of the above range, the low-temperature impact resistance of the injection-molded article can be further improved.

[0020] [Ethylene-α-olefin copolymer (B)] The ethylene-α-olefin copolymer (B), which is an optional component that may be added separately from the polypropylene resin (A), is a copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene. Specific examples of the ethylene-α-olefin copolymer (B) include ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-pentene copolymer, ethylene-hexene copolymer, and ethylene-octene copolymer. Among these, ethylene-butene copolymers and ethylene-octene copolymers are preferred in consideration of the ease of procurement as raw materials, economic efficiency, etc., in addition to the effect of improving low-temperature impact resistance.

[0021] The MFR of the ethylene-α-olefin copolymer (B) is 0.1 to 40 g / 10 min at 190°C under a load of 2.16 kg. The lower limit is preferably 0.5 g / 10 min or more, more preferably 0.8 g / 10 min or more. The upper limit is preferably 30 g / 10 min or less, more preferably 20 g / 10 min or less, even more preferably 10 g / 10 min or less, and most preferably 5 g / 10 min or less. When the content is at least as large as the lower limit of the above range, the flowability of the polypropylene resin composition is improved. When the content is equal to or less than the upper limit of the above range, the occurrence of blocking in the polypropylene resin composition can be suppressed, the continuous production of the composition can be improved, and the low-temperature impact resistance of the injection-molded article can be improved.

[0022] The content of the ethylene-α-olefin copolymer (B) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass, based on the total mass of the polypropylene resin composition. When the content is equal to or less than the upper limit of the above range, the rigidity of the injection molded article can be increased.

[0023] [Nucleating agent (C)] Nucleating agent (C), also known as a crystal nucleating agent or nucleating agent, is an additive used to reduce the size of the crystalline components in the resin to increase transparency and further increase the amount of crystalline components to improve rigidity. Examples of crystal nucleating agents include organic nucleating agents such as nonitol-based nucleating agents, sorbitol-based nucleating agents, phosphate ester-based nucleating agents, triaminobenzene derivative-based nucleating agents, metal carboxylate-based nucleating agents, xylitol-based nucleating agents, and rosin-based nucleating agents. Because it accelerates the cooling and solidification of molten resins, it can be used to shorten the cycle time during the injection molding process, in addition to imparting transparency and rigidity. The crystal nucleating agent is not particularly limited, and any commonly used agent in the field may be used. However, it is preferred to select from organic crystal nucleating agents such as phosphate ester nucleating agents, nonitol nucleating agents, sorbitol nucleating agents, triaminobenzene derivative nucleating agents, metal carboxylate nucleating agents, xylitol nucleating agents, or rosin nucleating agents, with phosphate ester nucleating agents being particularly preferred. Examples of phosphate ester nucleating agents include aromatic phosphate ester nucleating agents such as sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, aluminum 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, and lithium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate. Examples of nonitol-based nucleating agents include 1,2,3-trideoxy-4,6:5,7-bis-[(4-propylphenyl)methylene]-nonitol. Examples of sorbitol-based nucleating agents include 1,3:2,4-bis-o-(3,4-dimethylbenzylidene)-D-sorbitol. Examples of triaminobenzene derivative-based nucleating agents include 1,3,5-tris(2,2-dimethylpropanamido)benzene. Examples of metal carboxylate-based nucleating agents include sodium adipate, potassium adipate, aluminum adipate, sodium sebacate, potassium sebacate, aluminum sebacate, sodium benzoate, aluminum benzoate, aluminum di-para-t-butylbenzoate, titanium di-para-t-butylbenzoate, chromium di-para-t-butylbenzoate, and aluminum hydroxy-di-t-butylbenzoate. Examples of xylitol-based nucleating agents include bis-1,3:2,4-(5',6',7',8'-tetrahydro-2-naphthaldehyde benzylidene)1-allylxylitol and bis-1,3:2,4-(3',4'-dimethylbenzylidene)1-propylxylitol. Rosin-based nucleating agents are rosin acid metal salt compounds or rosin acid partial metal salt compounds obtained by reacting rosin acids such as pimaric acid, sandaracopimaric acid, palustric acid, isopimaric acid, abietic acid, dehydroabietic acid, neoabietic acid, dihydropimaric acid, dihydroabietic acid, and tetrahydroabietic acid with metals such as calcium and magnesium, such as rosin acid partial calcium salts. Crystal nucleating agents may be used alone or in combination. Among these, phosphate ester-based nucleating agents and triaminobenzene derivative-based nucleating agents are preferred. When a nucleating agent and other components described below are added, the polypropylene-based resin composition of the present invention can be obtained by stirring the polymer obtained by polymerization, the nucleating agent, and other additives using a Henschel mixer, Brabender, or the like, and then melt-blending them at 180°C to 280°C using an extruder. The nucleating agent and other additives may be added using a connected extruder after the polymerization, residual monomer removal, and drying processes. Furthermore, in the present invention, a so-called masterbatch, in which a high concentration of nucleating agent is melt-kneaded with polypropylene, may be mixed with the polypropylene-based resin composition during injection molding. In this case, the carrier contained in the masterbatch corresponds to the other components described below.

[0024] The content of the nucleating agent (C) is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0% by mass, relative to the total mass of the polypropylene resin composition. If the content exceeds the upper limit of the above range, the improvement in rigidity of the injection-molded article will reach a plateau, which is not preferable from the viewpoint of economy.

[0025] [Other ingredients] The polypropylene resin composition of the present invention may contain, as optional components, synthetic resins or synthetic rubbers other than the polypropylene resin (A) and the ethylene-α-olefin copolymer (B), inorganic fillers, and additives other than the nucleating agent (C), within the scope of not impairing the effects of the present invention. The polypropylene resin composition of the present invention may contain only one kind of synthetic resin or synthetic rubber other than the polypropylene resin (A) and the ethylene-α-olefin copolymer (B), or may contain two or more kinds of synthetic resins or synthetic rubbers. The content may be a known amount. Examples of inorganic fillers that may be contained in the polypropylene resin composition of the present invention, from the viewpoint of substance, include natural silicic acid or silicates such as talc, kaolinite, clay, pylophyllite, selinite, wollastonite, and mica; synthetic silicic acid or silicates such as hydrous calcium silicate, hydrous aluminum silicate, hydrous silicic acid, and anhydrous silicic acid; carbonates such as precipitated calcium carbonate, heavy calcium carbonate, and magnesium carbonate; hydroxides such as aluminum hydroxide and magnesium hydroxide; and oxides such as zinc oxide and magnesium oxide. In terms of shape, examples of suitable inorganic fillers include powdered fillers such as synthetic silicic acid or silicate salts, such as hydrous calcium silicate, hydrous aluminum silicate, hydrous silicic acid, and anhydrous silicic acid; plate-like fillers such as talc, kaolinite, clay, and mica; whisker-like fillers such as basic magnesium sulfate whiskers, calcium titanate whiskers, aluminum borate whiskers, sepiolite, PMF (Processed Mineral Filler), xonotlite, potassium titanate, and ellestadite; balloon-like fillers such as glass balloons and fly ash balloons; and fibrous fillers such as glass fiber. These inorganic fillers may be used alone or in combination. Surface treatment of the inorganic fillers may be performed as necessary to improve their dispersibility. The inorganic fillers used in the present invention are not limited, but plate-like inorganic fillers are preferred in terms of enhancing the rigidity and low-temperature impact resistance of the injection-molded body. As the plate-like inorganic filler, known materials such as talc, kaolinite, clay, and mica can be used. However, considering the affinity with polypropylene-based resins, ease of procurement as a raw material, and economic efficiency, talc and mica are preferred, and talc is more preferred. The volume-average particle diameter of the plate-like inorganic filler is preferably 1 to 10 μm, more preferably 2 to 7 μm. The volume-average particle diameter can be measured as the 50% diameter in the cumulative volume fraction by laser diffraction (based on JIS R1629). The polypropylene-based resin composition of the present invention may contain only one type of inorganic filler, or two or more types.The content may be a known amount, but from the viewpoint of not deteriorating appearance properties such as transparency and gloss in addition to the hinge properties which are the effects of the present invention, the content is preferably 0.5 mass% or less, and more preferably 0 mass%, relative to the total mass of the polypropylene-based resin composition. Examples of additives other than the nucleating agent (C) that may be contained in the polypropylene resin composition of the present invention include antioxidants, neutralizing agents, weathering agents, pigments (organic or inorganic), internal lubricants, external lubricants, antiblocking agents, antistatic agents, chlorine absorbers, heat stabilizers, light stabilizers, UV absorbers, slip agents, antifogging agents, flame retardants, dispersants, copper inhibitors, plasticizers, foaming agents, bubble inhibitors, crosslinking agents, peroxides, and oil extenders. The polypropylene resin composition of the present invention may contain only one additive other than the nucleating agent (C), or two or more additives. The content may be a known amount.

[0026] <Method of producing polypropylene resin composition> A method for producing the polypropylene-based resin composition of the first embodiment includes mixing a polypropylene-based resin (A), an optional ethylene-α-olefin copolymer (B), and an optional nucleating agent (C), followed by melt-kneading. Examples of the mixing method include dry blending using a mixer such as a Henschel mixer, a tumbler, or a ribbon mixer. Examples of the melt-kneading method include a method of mixing while melting using a mixer such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader, a roll mill, etc. The melting temperature in the melt-kneading is preferably 160 to 350° C., more preferably 170 to 260° C. After melt-kneading, the mixture may be further pelletized.

[0027] [Method for producing polypropylene resin (A)] The polypropylene resin (A) may be obtained by mixing the component (1) and the component (2) during polymerization, or by mixing the component (1) and the component (2) that have been produced separately by melt-kneading. The polypropylene resin (A) is preferably a polymerization mixture in which components (1) and (2) are mixed during polymerization. From the viewpoint of further improving the hinge properties of the injection-molded article, it is preferable that component (1) is substantially free of propylene homopolymer and consists solely of a propylene-ethylene copolymer. For example, the content of propylene homopolymer relative to the total mass of component (1) is preferably 0.5 mass% or less.

[0028] A multi-stage polymerization method is typically used as a method for producing the polymerization mixture. For example, a polymerization apparatus having three polymerization reactors is provided with a first-stage polymerization reactor in which propylene monomer and, if necessary, ethylene monomer are polymerized, and the resulting propylene polymer (homopolymer) or propylene-ethylene copolymer is supplied to a second-stage polymerization reactor, where propylene monomer and ethylene monomer are further polymerized, and the resulting component (1) is supplied to a third-stage polymerization reactor, and ethylene monomer and an α-olefin monomer are polymerized in the third-stage polymerization reactor, thereby obtaining a polymerization mixture in which the components (1) and (2) are mixed during polymerization. The polymerization conditions may be the same as known polymerization conditions. For example, the first and second polymerization conditions may be slurry polymerization, in which propylene is in a liquid phase and has high monomer density and productivity. The third polymerization condition may be gas phase polymerization. In addition, when producing a propylene-ethylene copolymer that does not contain a propylene homopolymer as component (1), a three-stage polymerization reactor is not required, and the copolymer can be produced using, for example, a two-stage polymerization reactor consisting of a slurry polymerization method and a gas-phase polymerization method. The polymerization temperature is preferably 50 to 90° C., more preferably 60 to 90° C., and even more preferably 70 to 90° C. When the polymerization temperature is at least the lower limit of the above range, the productivity is better. When the polymerization is carried out in a liquid phase, the polymerization pressure is preferably 25 to 60 bar (2.5 to 6.0 MPa). The polymerization of the monomers is usually carried out using a catalyst, and hydrogen may be added during the polymerization, if necessary, to adjust the molecular weight. Before the polymerization in the first-stage polymerization reactor, propylene may be prepolymerized to form polymer chains on the solid catalyst component, which will serve as a foothold for the subsequent main polymerization. The prepolymerization is usually carried out at a temperature of 40° C. or lower, preferably 30° C. or lower, and more preferably 20° C. or lower.

[0029] As the catalyst, a known olefin polymerization catalyst can be used, a stereospecific Ziegler-Natta catalyst is preferred, and a catalyst containing the following components (A), (B), and (C) (hereinafter also referred to as "catalyst (X)") is particularly preferred. (a) A solid catalyst containing magnesium, titanium, a halogen, and an electron donor compound. (a) Organoaluminum compounds. (c) Organosilicon compounds that are external electron donor compounds.

[0030] When catalyst (X) is used, a production method including a step of polymerizing ethylene monomer and α-olefin monomer in the presence of the propylene-ethylene copolymer to obtain polypropylene-based resin (A) is preferred. By using catalyst (X), polypropylene-based resin (A) having physical properties within the above ranges can be easily obtained.

[0031] Component (A) is prepared, for example, using a titanium compound, a magnesium compound and an electron donor compound. The titanium compound used in component (A) has the general formula: Ti(OR) g X 4-g A tetravalent titanium compound represented by the formula (R is a hydrocarbon group, X is a halogen, 0≦g≦4) is preferred. Examples of the hydrocarbon group include methyl, ethyl, propyl, and butyl, and examples of the halogen include Cl and Br. More specific examples of titanium compounds include titanium tetrahalides such as TiCl, TiBr, and TiI; Ti(OCH)Cl, Ti(OCH)Cl, and Ti(O n-C4H9)Cl3, Ti(OC2H5)Br3, Ti(O-isoC4H9)Br3; alkoxytitanium trihalides such as Ti(OCH3)2Cl2, Ti(OC2H5)2Cl2, Ti(O n -C4H9)2Cl2, alkoxytitanium dihalides such as Ti(OC2H5)2Br2; Ti(OCH3)3Cl, Ti(OC2H5)3Cl, Ti(O n -C4H9)3Cl, Ti(OC2H5)3Br, etc.; monohalogenated trialkoxy titanium compounds such as Ti(OCH3)4, Ti(OC2H5)4, Ti(O n and tetraalkoxytitanium such as —C4H9)4. These titanium compounds may be used alone or in combination of two or more. Among the above titanium compounds, preferred are halogen-containing titanium compounds, more preferred are titanium tetrahalides, and particularly preferred is titanium tetrachloride (TiCl4).

[0032] Examples of magnesium compounds used in component (A) include magnesium compounds having a magnesium-carbon bond or a magnesium-hydrogen bond, such as dimethyl magnesium, diethyl magnesium, dipropyl magnesium, dibutyl magnesium, diamyl magnesium, dihexyl magnesium, didecyl magnesium, ethyl magnesium chloride, propyl magnesium chloride, butyl magnesium chloride, hexyl magnesium chloride, amyl magnesium chloride, butylethoxy magnesium, ethylbutyl magnesium, butyl magnesium hydride, etc. These magnesium compounds can also be used in the form of complex compounds with, for example, organoaluminum, etc., and may be in either liquid or solid form. Further preferred magnesium compounds include magnesium halides such as magnesium chloride, magnesium bromide, magnesium iodide, and magnesium fluoride; alkoxymagnesium halides such as methoxymagnesium chloride, ethoxymagnesium chloride, isopropoxymagnesium chloride, butoxymagnesium chloride, and octoxymagnesium chloride; allyloxymagnesium halides such as phenoxymagnesium chloride and methylphenoxymagnesium chloride; alkoxymagnesiums such as ethoxymagnesium, isopropoxymagnesium, butoxymagnesium, n-octoxymagnesium, and 2-ethylhexoxymagnesium; dialkoxymagnesiums such as dimethoxymagnesium, diethoxymagnesium, dipropoxymagnesium, dibutoxymagnesium, and ethoxymethoxymagnesium; and allyloxymagnesiums such as ethoxypropoxymagnesium, butoxyethoxymagnesium, phenoxymagnesium, and dimethylphenoxymagnesium. These magnesium compounds may be used alone or in combination of two or more.

[0033] The electron donor compound used in component (A) preferably contains a phthalate-based compound (Pht) or a succinate-based compound (Suc), and more preferably contains a phthalate-based compound. Examples of phthalate compounds include monoethyl phthalate, dimethyl phthalate, methyl ethyl phthalate, monoisobutyl phthalate, mono-n-butyl phthalate, diethyl phthalate, ethyl isobutyl phthalate, ethyl-n-butyl phthalate, di-n-propyl phthalate, diisopropyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, di-n-heptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, dineopentyl phthalate, didecyl phthalate, benzyl butyl phthalate, diphenyl phthalate, etc. Among these, diisobutyl phthalate is particularly preferred. The molecular weight and stereoregularity distributions of propylene polymers obtained using the electron donor compound (component (A)) in catalyst (X) vary, and these differences affect the crystallization behavior and, consequently, the physical properties of the molded product. However, the details of this relationship remain unclear. To clarify this, it is necessary to analyze both the molecular weight distribution and the stereoregularity distribution as molecular structures. However, the crystallization process is complicated by the interactions between components with different molecular weights and stereoregularities, making it even more difficult to interpret the effects of the molecular weight and stereoregularity distributions on crystallization behavior. Furthermore, because actual injection molding is performed at very high speeds and in a fluid state, it is difficult to grasp the phenomenon, even with advanced analytical techniques. Therefore, it is virtually impossible to numerically characterize the differences in crystallization behavior due to the molecular weight and stereoregularity distributions in polypropylene resin compositions obtained using catalysts containing specific electron donor compounds.

[0034] The succinate compound may be an ester of succinic acid or an ester of a substituted succinic acid having a substituent such as an alkyl group at position 1 or 2 of succinic acid. Specific examples include diethyl succinate, dibutyl succinate, diethyl methyl succinate, diethyl diisopropyl succinate, and diallyl ethyl succinate. Specific examples of particularly preferred succinate compounds include diethyl-2,3-bis(trimethylsilyl)succinate, diethyl-2,2-sec-butyl-3-methylsuccinate, diethyl-2-(3,3,3-trifluoropropyl)-3-methylsuccinate, diethyl-2,3-bis(2-ethylbutyl)succinate, diethyl-2,3-diethyl-2-isopropylsuccinate, diethyl-2,3-diisopropyl-2-methylsuccinate, diethyl-2,3-dicyclohexyl-2-methylsuccinate, and diethyl-2, 3-Dibenzylsuccinate, diethyl-2,3-diisopropylsuccinate, diethyl-2,3-bis(cyclohexylmethyl)succinate, diethyl-2,3-di-t-butylsuccinate, diethyl-2,3-diisobutylsuccinate, diethyl-2,3-dineopentylsuccinate, diethyl-2,3-diisopentylsuccinate, diethyl-2,3-(1-trifluoromethylethyl)succinate, diethyl-2,3-tetradecylsuccinate, diethyl-2,3-fluorenylsuccinate, diethyl-2-iso Propyl-3-isobutylsuccinate, diethyl-2-tert-butyl-3-isopropylsuccinate, diethyl-2-isopropyl-3-cyclohexylsuccinate, diethyl-2-isopentyl-3-cyclohexylsuccinate, diethyl-2-tetradecyl-3-cyclohexylmethylsuccinate, diethyl-2-cyclohexyl-3-cyclopentylsuccinate, diethyl-2,2,3,3-tetramethylsuccinate, diethyl-2,2,3,3-tetraethylsuccinate, diethyl-2,2,3,3-tetradecylsuccinate diisobutyl-2,3-diethyl-2,3-diisopropylsuccinate, diisobutyl-2,3-bis(trimethylsilyl)succinate, diisobutyl-2,2-sec-butyl-3-methylsuccinate, diisobutyl-2-(3,3,3-trifluoropropyl)-3-methylsuccinate, diisobutyl-2,3-bis(2-ethylbutyl)succinate, diisobutyl-2,3-diethyl-2-isopropylsuccinate, diisobutyl-2,3-diisopropyl-2-methylsuccinate, diisobutyl-2,3-Dicyclohexyl-2-methylsuccinate, diisobutyl-2,3-dibenzylsuccinate, diisobutyl-2,3-diisopropylsuccinate, diisobutyl-2,3-bis(cyclohexylmethyl)succinate, diisobutyl-2,3-di-t-butylsuccinate, diisobutyl-2,3-diisobutylsuccinate, diisobutyl-2,3-dineopentylsuccinate, diisobutyl-2,3-diisopentylsuccinate, diisobutyl-2,3-(1-trifluoromethylethyl)succinate, diisobutyl-2,3 -n-propyl succinate, diisobutyl-2,3-tetradecyl succinate, diisobutyl-2,3-fluorenyl succinate, diisobutyl-2-isopropyl-3-isobutyl succinate, diisobutyl-2-tert-butyl-3-isopropyl succinate, diisobutyl-2-isopropyl-3-cyclohexyl succinate, diisobutyl-2-isopentyl-3-cyclohexyl succinate, diisobutyl-2-n-propyl-3-(cyclohexylmethyl) succinate, diisobutyl-2-tetradecyl-3-cyclohexyl succinate Diisobutyl-2,2,3,3-tetramethylsuccinate, diisobutyl-2,2,3,3-tetraethylsuccinate, diisobutyl-2,2,3,3-tetrapropylsuccinate, diisobutyl-2,3-diethyl-2,3-diisopropylsuccinate, diisobutyl-2-cyclohexyl-3-cyclopentylsuccinate, dineopentyl-2,3-bis(trimethylsilyl)succinate, dineopentyl-2,2-sec-butyl-3-methylsuccinate, dineopentyl-2-(3,3,3 -trifluoropropyl)-3-methylsuccinate, dineopentyl-2,3-bis(2-ethylbutyl)succinate, dineopentyl-2,3-diethyl-2-isopropylsuccinate, dineopentyl-2,3-diisopropyl-2-methylsuccinate, dineopentyl-2,3-dicyclohexyl-2-methylsuccinate, dineopentyl-2,3-dibenzylsuccinate, dineopentyl-2,3-diisopropylsuccinate, dineopentyl-2,3-bis(cyclohexylmethyl)succinate, dineopentyl-2,3-Di-t-butylsuccinate, dineopentyl-2,3-diisobutylsuccinate, dineopentyl-2,3-dineopentylsuccinate, dineopentyl-2,3-diisopentylsuccinate, dineopentyl-2,3-(1-trifluoromethylethyl)succinate, dineopentyl-2,3-dineopentylsuccinate, dineopentyl-2,3-diisopentylsuccinate, dineopentyl-2,3-tetradecylsuccinate, dineopentyl-2,3-fluorenylsuccinate, dineopentyl-2-isopropyl-3-isobutylsuccinate, dineopentyl-2-tert-butyl-3-iso Examples of the dimethyl siloxane include dimethyl siloxane, ...

[0035] Examples of the electron donor compound in the solid catalyst other than the phthalate-based compound and the succinate-based compound include diether-based compounds.

[0036] Examples of diether compounds include 2-(2-ethylhexyl)-1,3-dimethoxypropane, 2-isopropyl-1,3-dimethoxypropane, 2-butyl-1,3-dimethoxypropane, 2-sec-butyl-1,3-dimethoxypropane, 2-cyclohexyl-1,3-dimethoxypropane, 2-phenyl-1,3-dimethoxypropane, 2-tert-butyl-1,3-dimethoxypropane, 2-cumyl-1,3-dimethoxypropane, 2-(2-phenylethyl)-1,3-dimethoxypropane, and 2-(2-cyclohexylethyl) -1,3-dimethoxypropane, 2-(p-chlorophenyl)-1,3-dimethoxypropane, 2-(diphenylmethyl)-1,3-dimethoxypropane, 2-(1-naphthyl)-1,3-dimethoxypropane, 2-(p-fluorophenyl)-1,3-dimethoxypropane, 2-(1-decahydronaphthyl)-1,3-dimethoxypropane, 2-(p-tert-butylphenyl)-1,3-dimethoxypropane, 2,2-dicyclohexyl-1,3-dimethoxypropane, 2,2-diethyl-1,3-dimethoxypropane, 2,2-dipropyl- 1,3-Dimethoxypropane, 2,2-Dibutyl-1,3-dimethoxypropane, 2,2-Diethyl-1,3-diethoxypropane, 2,2-Dicyclopentyl-1,3-dimethoxypropane, 2,2-Dipropyl-1,3-diethoxypropane, 2,2-Dibutyl-1,3-diethoxypropane, 2-Methyl-2-ethyl-1,3-dimethoxypropane, 2-Methyl-2-propyl-1,3-dimethoxypropane, 2-Propyl-2-pentyl-1,3-diethoxypropane, 2-Methyl-2-benzyl-1,3-dimethoxypropane, 2-Methyl -2-phenyl-1,3-dimethoxypropane, 2-methyl-2-cyclohexyl-1,3-dimethoxypropane, 2-methyl-2-methylcyclohexyl-1,3-dimethoxypropane, 2,2-bis(p-chlorophenyl)-1,3-dimethoxypropane, 2,2-bis(2-phenylethyl)-1,3-dimethoxypropane, 2,2-bis(2-cyclohexylethyl)-1,3-dimethoxypropane, 2-methyl-2-isobutyl-1,3-dimethoxypropane, 2-methyl-2-(2-ethylhexyl)-1,3-dimethoxypropane, 2,2-bis(2-ethylhexyl)-1,3-dimethoxypropane, 2,2-bis(p-methylphenyl)-1,3-dimethoxypropane, 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2,2-diphenyl-1,3-dimethoxypropane, 2,2-dibenzyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-diethoxypropane Examples of 1,3-diethers include 2,2-diisobutyl-1,3-dibutoxypropane, 2-isobutyl-2-isopropyl-1,3-dimethoxypropane, 2,2-di-sec-butyl-1,3-dimethoxypropane, 2,2-di-tert-butyl-1,3-dimethoxypropane, 2,2-dineopentyl-1,3-dimethoxypropane, 2-isopropyl-2-isopentyl-1,3-dimethoxypropane, 2-phenyl-2-benzyl-1,3-dimethoxypropane, and 2-cyclohexyl-2-cyclohexylmethyl-1,3-dimethoxypropane. Further specific examples of the 1,3-diether compounds include the following: 1,1-Bis(methoxymethyl)-cyclopentadiene;1,1-Bis(methoxymethyl)-2,3,4,5-tetramethylcyclopentadiene;1,1-Bis(methoxymethyl)-2,3,4,5-tetraphenylcyclopentadiene; 1,1-bis(methoxymethyl)-2,3,4,5-tetrafluorocyclopentadiene; 1,1-Bis(methoxymethyl)-3,4-dicyclopentylcyclopentadiene; 1,1-Bis(methoxymethyl)indene; 1,1-Bis(methoxymethyl)-2,3-dimethylindene;1,1-Bis(methoxymethyl)-4,5,6,7-tetrahydroindene;1,1-Bis(methoxymethyl)-2,3,6,7-tetrafluoroindene;1,1-Bis(methoxymethyl)-4,7-dimethylindene;1,1-Bis(methoxymethyl)-3,6-dimethylindene;1,1-Bis(methoxymethyl)-4-phenylindene;1,1-Bis(methoxymethyl)-4-phenyl-2-methylindene;1,1-Bis(methoxymethyl)-4-cyclohexylindene;1,1-Bis(methoxymethyl)-7-(3,3,3-trifluoropropyl)indene; 1,1-Bis(methoxymethyl)-7-trimethylsilyl indene;1,1-Bis(methoxymethyl)-7-trifluoromethyl indene;1,1-Bis(methoxymethyl)-4,7-dimethyl-4,5,6,7-tetrahydroindene; 1,1-Bis(methoxymethyl)-7-methylindene;1,1-Bis(methoxymethyl)-7-cyclopentylindene;1,1-Bis(methoxymethyl)-7-isopropylindene;1,1-Bis(methoxymethyl)-7-cyclohexylindene;1,1-Bis(methoxymethyl)-7-tert-butylindene;1,1-Bis(methoxymethyl)-7-tert-butyl-2-methylindene;1,1-Bis(methoxymethyl)-7-phenylindene;1,1-Bis(methoxymethyl)-2-phenylindene;1,1-Bis(methoxymethyl)-1H-benzindene;1,1-Bis(methoxymethyl)-1H-2-methylbenzindene;9,9-Bis(methoxymethyl)fluorene; 9,9-bis(methoxymethyl)-2,3,6,7-tetramethylfluorene;9,9-bis(methoxymethyl)-2,3,4,5,6,7-hexafluorofluorene; 9,9-Bis(methoxymethyl)-2,3-benzofluorene;9,9-Bis(methoxymethyl)-2,3,6,7-dibenzofluorene;9,9-Bis(methoxymethyl)-2,7-diisopropylfluorene;9,9-Bis(methoxymethyl)-1,8-dichlorofluorene;9,9-Bis(methoxymethyl)-2,7-dicyclopentylfluorene;9,9-Bis(methoxymethyl)-1,8-difluorofluorene;9,9-Bis(methoxymethyl)-1,2,3,4-tetrahydrofluorene;9,9-Bis(methoxymethyl)-1,2,3,4,5,6,7,8-octahydrofluorene; 9,9-bis(methoxymethyl)-4-tert-butylfluorene.

[0037] Examples of halogen atoms constituting component (A) include fluorine, chlorine, bromine, iodine, and mixtures thereof, with chlorine being particularly preferred.

[0038] Examples of the organoaluminum compound of component (a) include trialkylaluminums such as triethylaluminum and tributylaluminum, trialkenylaluminums such as triisoprenylaluminum, dialkylaluminum alkoxides such as diethylaluminum ethoxide and dibutylaluminum butoxide, alkylaluminum sesquialkoxides such as ethylaluminum sesquiethoxide and butylaluminum sesquibutoxide, R 1 2.5 Al(OR 2 ) 0.5 (R 1 ,R 2are hydrocarbon groups which may be different or the same. Examples of the alkylaluminum include partially alkoxylated alkylaluminums having an average composition represented by the formula (I), dialkylaluminum halides such as diethylaluminum chloride, dibutylaluminum chloride, and diethylaluminum bromide, alkylaluminum sesquihalides such as ethylaluminum sesquichloride, butylaluminum sesquichloride, and ethylaluminum sesquibromide, partially halogenated alkylaluminums such as alkylaluminum dihalides such as ethylaluminum dichloride, propylaluminum dichloride, and butylaluminum dibromide, partially hydrogenated alkylaluminums such as dialkylaluminum hydrides such as diethylaluminum hydride and dibutylaluminum hydride, and alkylaluminum dihydrides such as ethylaluminum dihydride and propylaluminum dihydride, and partially alkoxylated and halogenated alkylaluminums such as ethylaluminum ethoxychloride, butylaluminum butoxychloride, and ethylaluminum ethoxybromide. One type of the component (A) may be used alone, or two or more types may be used in combination.

[0039] As the external electron donor compound of component (c), an organosilicon compound is used. Preferred organosilicon compounds include, for example, trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, t-butylmethyldimethoxysilane, t-butylmethyldiethoxysilane, t-amylmethyldiethoxysilane, diphenyldimethoxysilane, phenylmethyldimethoxysilane, diphenyldiethoxysilane, bis-o-tolyldimethoxysilane, bis-m-tolyldimethoxysilane, bis-p-tolyldimethoxysilane, bis-p-tolyldiethoxysilane, bisethylphenyldimethoxysilane, dicyclopentyldimethoxysilane, dicyclohexyldimethoxysilane, cyclohexylmethyldimethoxysilane, cyclohexylmethyldiethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, n-propyltriethoxysilane, decyltrimethoxysilane, methyltrimethoxysilane, n-propyltriethoxysilane, decyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxy ... Methoxysilane, decyltriethoxysilane, phenyltrimethoxysilane, γ-chloropropyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, t-butyltriethoxysilane, thexyltrimethoxysilane, n-butyltriethoxysilane, iso-butyltriethoxysilane, phenyltriethoxysilane, γ-aminopropyltriethoxysilane, chlortriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, 2-norbornanetrimethoxysilane, 2-norbornanetriethoxysilane, 2-norbornanemethyldimethoxysilane, ethyl silicate, butyl silicate, trimethylphenoxysilane, methyltriallyloxysilane, vinyltris(β-methoxyethoxysilane), vinyltriacetoxysilane, dimethyltetraethoxydisiloxane, methyl(3,3,3-trifluoro-n-propyl)dimethoxysilane, cyclohexylethyldimethoxysilane, cyclopentyl-t-butoxydimethoxysilane, diisobutyldimethoxysilane, isobutylisopropyldimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, t-butylethyldimethoxysilane, t-butylpropyldimethoxysilane, t-butyl-t-butoxydimethoxysilane, isobutyltrimethoxysilane, cyclohexylisobutyldimethoxysilane, di-sec-butyldimethoxysilane, isobutylmethyldimethoxysilane, bis(decahydroisoquinolin-2-yl)dimethoxysilane, diethyl Examples of the silane include methylaminotriethoxysilane, dicyclopentyl-bis(ethylamino)silane, tetraethoxysilane, tetramethoxysilane, isobutyltriethoxysilane, t-butyltrimethoxysilane, i-butyltrimethoxysilane, i-butylsec-butyldimethoxysilane, ethyl(perhydroisoquinolin-2-yl)dimethoxysilane, tri(isopropenyloxy)phenylsilane, i-butyl-i-propyldimethoxysilane, cyclohexyl-i-butyldimethoxysilane, cyclopentyl-i-butyldimethoxysilane, cyclopentylisopropyldimethoxysilane, phenyltriethoxysilane, and p-tolylmethyldimethoxysilane. Among these, ethyltriethoxysilane, n-propyltriethoxysilane, n-propyltrimethoxysilane, t-butyltriethoxysilane, t-butylmethyldimethoxysilane, t-butylmethyldiethoxysilane, t-butylethyldimethoxysilane, t-butylpropyldimethoxysilane, t-butylt-butoxydimethoxysilane, t-butyltrimethoxysilane, i-butyltrimethoxysilane, isobutylmethyldimethoxysilane, i-butylsec-butyldimethoxysilane, ethyl(perhydroisoquinolin-2-yl)dimethoxysilane, bis(decahydroisoquinolin-2-yl)dimethoxysilane, tri(isopropenyloxy)phenylsilane, thexyltrimethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, vinyltributoxysilane, diphenyldimethoxysilane, diisopropyldimethoxysilane, diisobutyldimethoxysilane silane, i-butyl i-propyl dimethoxysilane, cyclopentyl t-butoxy dimethoxysilane, dicyclopentyl dimethoxysilane, cyclohexyl methyl dimethoxysilane, cyclohexyl i-butyl dimethoxysilane, cyclopentyl i-butyl dimethoxysilane, cyclopentyl isopropyl dimethoxysilane, di-sec-butyl dimethoxysilane, diethylamino triethoxysilane, tetraethoxysilane, tetramethoxysilane, isobutyl triethoxysilane, phenyl methyl dimethoxysilane, phenyl triethoxysilane, bis p-tolyl dimethoxysilane, p-tolyl methyl dimethoxysilane, dicyclohexyl dimethoxysilane, cyclohexyl ethyl dimethoxysilane, 2-norbornane triethoxysilane, 2-norbornane methyl dimethoxysilane, diphenyl diethoxysilane, methyl (3,3,3-trifluoro-n-propyl) dimethoxysilane, ethyl silicate, and the like are preferred. The above component (c) may be used alone or in combination of two or more.

[0040] Organosilicon compounds play an important role in adjusting the amount of xylene-insoluble matter in propylene-ethylene copolymers, thereby controlling their rigidity. With other catalyst components remaining constant, the amount of xylene-insoluble matter depends on the type and amount of organosilicon compound and the polymerization temperature. However, even with appropriate organosilicon compounds, the amount of organosilicon compound drops significantly below a certain level, except for diether catalysts. Therefore, when the polymerization temperature is 75°C, the lower limit of the molar ratio of organosilicon compound to organoaluminum compound (organosilicon compound / organoaluminum compound) is preferably 0.015, more preferably 0.018. The upper limit of this ratio is preferably 0.30, more preferably 0.20, and even more preferably 0.10. When a phthalate compound is used as the electron donor compound, increasing the polymerization temperature increases the amount of xylene-insoluble matter, thereby lowering the lower and upper limits of the preferred molar ratio of the organosilicon compound to the organoaluminum compound (organosilicon compound / organoaluminum). Specifically, when polymerizing at 80°C using a phthalate compound, the lower limit of the molar ratio is preferably 0.010, more preferably 0.015, and even more preferably 0.018. The upper limit of the molar ratio is preferably 0.20, more preferably 0.14, and even more preferably 0.08.

[0041] As the catalyst (X), a catalyst in which component (A) is a trialkylaluminum such as triethylaluminum or triisobutylaluminum, and component (C) is an organosilicon compound such as dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane or diisopropyldimethoxysilane is preferred.

[0042] The method for obtaining the polymerization mixture by the multistage polymerization method is not limited to the above method, and the propylene-ethylene copolymer may be polymerized in a plurality of polymerization reactors, or the ethylene-α-olefin copolymer may be polymerized in a plurality of polymerization reactors. The polymerization mixture may be obtained using a polymerization vessel having a gradient of monomer concentration or polymerization conditions. For example, such a polymerization vessel may have at least two polymerization zones joined together, and the monomers may be polymerized by gas phase polymerization. Specifically, in the presence of a catalyst, a monomer is supplied to a polymerization zone consisting of a riser pipe and polymerized therein, and another monomer is supplied to a downcomer pipe connected to the riser pipe and polymerized therein. The monomer is then circulated between the riser pipe and the downcomer pipe, and the polymerization product is recovered. This method includes a means for completely or partially preventing the gas mixture present in the riser pipe from entering the downcomer pipe. Furthermore, a gas and / or liquid mixture having a composition different from that of the gas mixture present in the riser pipe is introduced into the downcomer pipe. For example, the method described in JP-A-2002-520426 can be used for this polymerization method.

[0043] (Method for producing ethylene-α-olefin copolymer (B)) The ethylene-α-olefin copolymer (B) can be produced by a known method using a metallocene catalyst or a half-metallocene catalyst during polymerization (for example, the method described in International Publication WO2006 / 102155). During the polymerization, a known molecular weight regulator such as a chain transfer agent (for example, hydrogen or diethyl zinc) may be used.

[0044] <Injection molded body> A second aspect of the present invention is an injection-molded article obtained by injection molding the polypropylene-based resin composition for injection molding of the first aspect. The polypropylene resin composition of the first embodiment has excellent flowability and is therefore ideal as a resin composition for injection molding, and can give injection-molded articles with a thickness of, for example, 0.5 to 3 mm. Specific examples of injection-molded articles include molded articles having hinge portions such as caps, containers and lids for packaging food, beverages, batteries, etc., as well as miscellaneous goods, daily necessities, home appliance parts, electrical and electronic parts, automobile parts, housing materials, toy parts, furniture parts, building materials, packaging materials, industrial materials, logistics materials, agricultural materials, etc.

[0045] Although the type of injection molding used to produce the injection-molded article of this embodiment is not particularly limited, from the viewpoint of obtaining an injection-molded article having a hinge portion with excellent hinge characteristics, an injection molding method other than injection blow molding, in which a gas is blown in to form a hollow portion (gas-assisted injection molding, i.e., a method for obtaining a molded article without a hinge portion), is preferred. Specifically, an injection molding method using a general injection molding machine and mold, including low-pressure molding, injection compression molding, or two-color molding, is preferred.

[0046] The temperature of the molten resin used in injection molding is preferably 150 to 350°C, more preferably 170 to 250°C. Temperatures above 350°C can cause deterioration of the resin composition and molding defects, while temperatures below 170°C can reduce fluidity, resulting in poor appearance and molding defects due to insufficient filling of the mold. The mold temperature is preferably in the range of 10 to 60°C. A mold temperature above 60°C can produce molded articles with excellent surface finish and rigidity, but the molding cycle is lengthened, resulting in reduced productivity. Conversely, setting the mold temperature below 10°C can result in significant warping and shrinkage, making it difficult to obtain satisfactory molded articles. Conversely, setting the mold temperature below 10°C can also lead to significant warping and shrinkage, making it difficult to obtain satisfactory molded articles, and can also lead to condensation on the mold, which can accelerate mold corrosion. This is also unsuitable from the perspective of the energy costs associated with cooling.

[0047] The tensile modulus of the injection molded article of this embodiment is preferably 300 MPa or more, more preferably 350 MPa or more, and even more preferably 400 MPa or more. The higher the tensile modulus, the more rigid the molded article can be said to be.

[0048] The dart impact strength at −20° C. of the injection molded article of this embodiment is preferably 10 J or more, more preferably 12 J or more, and even more preferably 20 J or more. The higher the value of the dart impact strength at low temperature, the more excellent the low-temperature impact resistance of the molded article.

[0049] The crack area ratio of the injection molded article of this embodiment is preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, particularly preferably 9% or less, and most preferably 8% or less. The lower the crack occupied area ratio, the more excellent the hinge characteristics (flexural durability) of the molded article at the hinge portion. Here, the crack occupied area ratio is a value measured by the method described below. [Example]

[0050] Examples and comparative examples are shown below, but the present invention is not limited to the following examples.

[0051] <Preparation of Copolymer 1> A solid catalyst in which TiCl4 and diisobutyl phthalate as an internal donor were supported on MgCl2 was prepared by the method described in Example 5 of EP 728769. Next, the solid catalyst was contacted with triethylaluminum (TEAL) as an organoaluminum compound and dicyclopentyldimethoxysilane (DCPMS) as an external electron donor compound at a mass ratio of 20% by mass of TEAL to the solid catalyst and a mass ratio of 10% by mass of TEAL / DCPMS (equivalent to a molar ratio of 0.05 between the organosilicon compound and the organoaluminum). The resulting catalyst system was suspended in liquid propylene and kept at 20° C. for 5 minutes to carry out prepolymerization. The resulting prepolymer was introduced into the first reactor of a two-stage polymerization reactor in series, where propylene (C3) and ethylene (C2) were fed to produce a propylene-ethylene copolymer in the liquid phase. The resulting prepolymer was then introduced into the second reactor, where ethylene and butene-1 (C4) were fed to produce an ethylene-butene-1 copolymer. During the polymerization, temperature and pressure were controlled, and hydrogen (H2) was used as a molecular weight regulator. The polymerization temperature, ethylene concentration, and hydrogen concentration in the first reactor were 80°C, 0.84 mol%, and 0.09 mol%, respectively, while the polymerization temperature, H2 / C2, and C4 / (C2+C4) were 80°C, 0.27 mol%, and 0.48 mol%, respectively, in the second reactor. The residence time distribution between the first and second reactors was adjusted so that the amount of copolymer component was 18% by mass, and powdery polymer 1 (copolymer 1) was obtained. The obtained copolymer 1 is a polymer mixture of component (1), a propylene-ethylene copolymer constituting the continuous phase, and component (2), an ethylene-butene-1 copolymer constituting the rubber phase, and is the aforementioned polypropylene-based resin (A). Note that component (1) obtained here does not contain propylene homopolymer. For copolymer 1, the MFR of component (1), the ethylene-derived unit content of component (1), the mass ratio component (2) / [component (1) + component (2)], the ethylene-derived unit content of component (2), the XSIV of component (1) + component (2), and the MFR of component (1) + component (2) are shown in Table 1. Here, component (1) is a propylene-ethylene copolymer, component (2) is an ethylene-butene-1 copolymer, and component (1) + component (2) is a polypropylene-based resin (A) (also referred to as component (A)). In Table 1, catalyst (X) containing a phthalate compound as the electron donor compound used in component (A) is represented as "Pht."

[0052] <Preparation of Copolymer 2> Copolymer 2 was obtained in the same manner as Copolymer 1, except that the hydrogen concentration in the first reactor was adjusted to 0.02 mol % and the residence time distribution in the first and second reactors was adjusted so that the content of component (2) in component (A) was 45 mass %. The above-mentioned various physical property values of the obtained copolymer 2 are shown in Table 1.

[0053] <Preparation of Copolymer 3> Copolymer 3 was obtained in the same manner as in Copolymer 1, except that the molar ratio of C4 / (C2+C4) in the second reactor was changed to 0.43. The above-mentioned various physical property values of the obtained copolymer 3 are shown in Table 1.

[0054] <Preparation of Copolymer 4> Copolymer 4 was obtained in the same manner as in Copolymer 1, except that the molar ratio of C4 / (C2+C4) in the second reactor was changed to 0.80. The above-mentioned various physical property values of the obtained copolymer 4 are shown in Table 1.

[0055] <Preparation of Copolymer 5> Copolymer 5 was obtained in the same manner as in Copolymer 1, except that the molar ratio of C4 / (C2+C4) in the second reactor was changed to 0.27. The above-mentioned various physical property values of the obtained copolymer 5 are shown in Table 1.

[0056] <Preparation of Copolymer 6> Copolymer 6 was obtained in the same manner as Copolymer 1, except that the hydrogen concentration in the first reactor was changed to 0.16 mol % and the H2 / C2 molar ratio in the second reactor was changed to 0.11. The above-mentioned various physical property values of the obtained copolymer 6 are shown in Table 1.

[0057] <Preparation of Copolymer 7> Copolymer 7 was obtained in the same manner as Copolymer 1, except that the hydrogen concentration in the first-stage reactor was changed to 1.50 mol %. The above-mentioned various physical property values of the obtained copolymer 7 are shown in Table 1.

[0058] <Preparation of Copolymer 8> Copolymer 8 was obtained in the same manner as Copolymer 1, except that the hydrogen concentration in the first-stage reactor was changed to 0.01 mol %. The above-mentioned various physical property values of the obtained copolymer 8 are shown in Table 1.

[0059] <Preparation of Copolymer 9> Copolymer 9 was obtained in the same manner as Copolymer 1, except that the ethylene concentration and hydrogen concentration in the first reactor were changed to 0.80 mol% and 0.06 mol%, respectively, C3 was used instead of C4 in the second reactor, and the H2 / C2 and C3 / (C2+C3) molar ratios were 0.66 and 0.89, respectively. The above-mentioned various physical property values of the obtained copolymer 9 are shown in Table 1.

[0060] <Preparation of Copolymer 10> A solid catalyst having TiCl4 and diethyl-2,3-(diisopropyl)succinate as an internal donor supported on MgCl2 was prepared according to Example 1 of International Application WO2009 / 050045, except that the temperature was increased to 110°C instead of 100°C during the initial temperature increase. The solid catalyst was then contacted with TEAL as an organoaluminum compound and DCPMS as an external electron donor compound at a mass ratio of 20 for TEAL to the solid catalyst and a mass ratio of 10 for TEAL / DCPMS at 12°C for 24 minutes. The resulting catalyst system was suspended in liquid propylene and kept at 20° C. for 5 minutes to carry out prepolymerization. The obtained prepolymer was introduced into the first-stage polymerization reactor of a polymerization apparatus equipped with two-stage polymerization reactors connected in series, and copolymer 10 was obtained in the same manner as copolymer 9, except that the ethylene concentration and hydrogen concentration in the first-stage reactor were changed to 0.71 mol % and 0.14 mol %, respectively, and the H2 / C2 and C3 / (C2+C3) molar ratios in the second-stage reactor were changed to 0.50 and 0.71, respectively. The above-mentioned various physical property values of the obtained copolymer 10 are shown in Table 1. In Table 1, catalyst (X) containing a succinate compound as the electron donor compound used in component (A) is represented as "Suc."

[0061] <Preparation of Copolymer 11> A solid catalyst in which TiCl4 and diisobutyl phthalate as an internal donor were supported on MgCl2 was prepared by the method described in Example 1 of EP 674991. Then, the solid catalyst was contacted with TEAL as an organoaluminum compound and DCPMS as an external electron donor compound at a mass ratio of 11 to the solid catalyst and a mass ratio of TEAL / DCPMS of 10 at -5°C for 5 minutes. The resulting catalyst system was suspended in liquid propylene and kept at 20° C. for 5 minutes to carry out prepolymerization. The resulting prepolymer was introduced into a polymerization reactor, and propylene and ethylene were fed to produce propylene-ethylene copolymer (copolymer 11) in the liquid phase of propylene. The polymerization temperature, ethylene concentration, and hydrogen concentration were 75°C, 0.48 mol%, and 0.05 mol%, respectively. The MFR and ethylene-derived unit content of the obtained copolymer 11 are shown in Table 1.

[0062] [Table 1]

[0063] The measurement results in Table 1 were measured by the following measurement method.

[0064] <MFR of ingredient (1)> To a 5 g sample of component (1) polymerized in the first-stage reactor, 0.05 g of H-BHT manufactured by Honshu Chemical Industry Co., Ltd. was added, and the mixture was homogenized using a dry bland. Then, measurements were carried out at a temperature of 230°C and a load of 2.16 kg in accordance with JIS K6921-2.

[0065] <Total ethylene content of component (A) and ethylene-derived unit content of component (1)> Each copolymer sample dissolved in a mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene was analyzed by a Bruker AVANCE III HD400 ( 13 C resonance frequency 100MHz) under the conditions of measurement temperature 120℃, flip angle 45 degrees, pulse interval 7 seconds, sample rotation speed 20Hz, and cumulative number 5000. 13 C-NMR spectra were obtained and measured. The content of ethylene-derived units in component (1) in component (A) was measured by collecting a sample from the polymerized product in the first reactor.

[0066] <Content of ethylene-derived units in component (2)> The content of ethylene-derived units in the component (2) was calculated using the following formula. Ethylene-derived unit content of component (2) (unit: mass%) = [Total ethylene content of component (A)] - the content of ethylene-derived units in component (1) × the content ratio of component (1) in component (A) / (content of component (2) in component (A) / 100)

[0067] <Component (1) + Component (2) XSIV> The xylene soluble fraction of the copolymer was obtained by the following method, and the intrinsic viscosity (XSIV) of the xylene soluble fraction was measured. 2.5 g of each copolymer sample was placed in a flask containing 250 mL of o-xylene (solvent). Using a hot plate and reflux hood, the mixture was stirred for 30 minutes at 135°C while purging with nitrogen to completely dissolve the copolymer. The mixture was then cooled to 25°C for 1 hour. The resulting solution was filtered using filter paper. 100 mL of the filtrate was transferred to an aluminum cup or similar container and evaporated to dryness at 140°C while purging with nitrogen. The mixture was then left to stand at room temperature for 30 minutes to obtain the xylene-soluble fraction. The intrinsic viscosity was measured in tetrahydronaphthalene at 135° C. using an automatic capillary viscosity measuring device (SS-780-H1, manufactured by Shibayama Scientific Instruments Co., Ltd.).

[0068] <MFR of ingredient (1) + ingredient (2)> To a 5 g sample of the copolymer, 0.05 g of H-BHT manufactured by Honshu Chemical Industry Co., Ltd. was added, and after homogenization with a dry bland, the sample was measured at a temperature of 230° C. and a load of 2.16 kg according to JIS K6921-2.

[0069] [Examples and Comparative Examples] Components (A) to (C) were blended according to the composition shown in Table 2. For a total of 100 parts by mass of components (A) to (C), 0.2 parts by mass of BASF B225 as an antioxidant and 0.05 parts by mass of calcium stearate (manufactured by Dannan Chemical Industry Co., Ltd.) as a neutralizer were added. Furthermore, for Example 7, 0.3 parts by mass of Neotalc UNI05 (manufactured by Neolite Industries Co., Ltd.) was added. The mixture was then stirred and mixed for 1 minute using a Henschel mixer. The resulting mixture was melt-kneaded and extruded at a cylinder temperature of 200°C using a co-rotating twin-screw extruder TEX-30α (manufactured by JSW Corporation). The strands were cooled in water and then cut using a pelletizer to obtain pellets of the polypropylene resin composition. The physical properties of the polypropylene resin compositions thus produced and the injection-molded articles obtained using them were evaluated. The results are shown in Table 2.

[0070] [Table 2]

[0071] The components in Table 2 are as follows: Component (A) is a copolymer of Table 1. Component (B) is the following ethylene-α-olefin copolymer: B-1: Mitsui Chemicals, Inc., Tafmer A-1085S, ethylene-butene copolymer, MFR (temperature 190°C, load 2.16 kg) = 1.2 g / 10 min B-2: Dow Chemical Company, Engage 8100, ethylene-octene copolymer, MFR (temperature 190°C, load 2.16 kg) = 1.0 g / 10 min Component (C) is a nucleating agent as described below. C-1: ADEKA Corporation, ADK STAB NA71 (phosphate ester nucleating agent) The other components are the following additives. Inorganic filler: Neotalc UNI05 manufactured by Neolite Kosan Co., Ltd., talc with a volume average particle size measured by laser diffraction method of 5 μm Antioxidant: BASF B225 Neutralizer: Calcium stearate, manufactured by Tannan Chemical Industry Co., Ltd.

[0072] The measurement results and evaluation results in Table 2 are values measured and evaluated by the following methods.

[0073] <Liquidity MFR> Measurements were made in accordance with JIS K7210-1, and for polypropylene resin compositions, measurements were made at a temperature of 230°C and a load of 2.16 kg in accordance with JIS K6921-2. Measurements were made at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K6922-2 for ethylene-α-olefin copolymers.

[0074] <Rigidity Tensile modulus> According to JIS K6921-2, a polypropylene resin composition was injection-molded into a multipurpose test piece (Type A1) specified in JIS K7139 using an injection molding machine (FANUC ROBOSHOT S2000i manufactured by FANUC Corporation) under the following conditions: molten resin temperature 200°C, mold temperature 40°C, average injection speed 200 mm / s, dwell time 40 seconds, and total cycle time 60 seconds. According to JIS K7161-2, a precision universal testing machine (Autograph AG-X 10kN manufactured by Shimadzu Corporation) was used to measure the tensile modulus at a temperature of 23°C, relative humidity of 50%, and a test speed of 1 mm / min.

[0075] <Low temperature impact resistance, surface impact strength [-20℃]> Using an injection molding machine (FANUC ROBOSHOT α100C manufactured by FANUC Corporation), a 130mm x 130mm x 2.0mm flat plate was produced from the polypropylene resin composition under the following conditions: molten resin temperature 230 ° C, mold temperature 40 ° C, average injection speed 35 mm / s, dwell time 10 seconds, total cycle time 45 seconds. Using a Shimadzu Corporation Hydroshot HITS-P10, a test specimen was placed on a support with a hole with an inner diameter of 40 mm φ in a tank adjusted to -20 ° C, and fixed using a sample holder with an inner diameter of 76 mm φ. The test specimen was then struck at an impact speed of 1 m / s with a striker with a diameter of 12.7 mm φ and a hemispherical striking surface. The puncture energy (J) was determined according to JIS K7211-2. The average puncture energy of each of the four test specimens was taken as the surface impact strength.

[0076] <Hinge characteristics: Crack area ratio> Using an injection molding machine (FANUC ROBOSHOT α100C manufactured by FANUC Corporation), a polypropylene resin composition was injection molded into a hinged box (72 mm long, 0.82 mm wide, and 0.52 mm thick) measuring 92 mm long, 125 mm wide, 41 mm high, and 2 mm thick, under the following conditions: melt temperature 250°C, mold temperature 40°C, average injection speed 35 mm / s, dwell time 10 seconds, and total cycle time 33 seconds. After conditioning at 23°C for more than 48 hours after molding, a bending test was performed 100 times at a rate of once per second, with each cycle consisting of folding the hinge 180° and returning it to the original 0° position (see Figures 1 to 3). After applying liquid paraffin to the front and back surfaces of the hinge portion, the center of the hinge portion was observed under a microscope under the following conditions. Equipment: OLYMPUS microscope BX-50 Magnification: 40x Mode: Darkfield By applying liquid paraffin, the wrinkles on the surface that occurred during the bending test were hidden, making it possible to observe only the cracks related to the hinge characteristics. Using a CCD camera and QImaging's image analysis software Q-Capture Pro, the RGB image was converted to grayscale, and the proportion of cracks in the hinge area (crack occupation area ratio) was calculated.

[0077] <Moldability> The moldability was evaluated in injection molding of a hinged box. "1": Injection molding can be performed without any problems in all shots (the molded body is fully filled up to the end). "2": Not all shots can be injection molded, but most can be. "3": Injection molding cannot be performed with many shots (the shots are short and the molded body is not filled to the end).

[0078] The injection-molded articles of the Examples, which used polypropylene-based resin compositions having the prescribed physical properties, were superior in low-temperature impact resistance and hinge properties, and also had good moldability, compared to the Comparative Examples. Examples 6, 7, 9, and 10 are reference examples.

[0079] The injection-molded article of Comparative Example 1, which used Copolymer 4, in which the content of ethylene-derived units in the ethylene-butene-1 copolymer in the polypropylene-based resin (A) was lower than the specified range, had poor hinge properties. The injection-molded article of Comparative Example 2, which used Copolymer 5 in which the content of ethylene-derived units in the ethylene-butene-1 copolymer in the polypropylene-based resin (A) was higher than the specified range, had poor low-temperature impact resistance. The injection-molded article of Comparative Example 3, which used Copolymer 6 in which the XSIV of component (1)+component (2) in the polypropylene-based resin (A) was outside the specified range, had poor hinge properties. The injection-molded article of Comparative Example 4, which used Copolymer 7 in which the MFR of component (1) and the MFR of component (1) + component (2) in the polypropylene-based resin (A) were outside the specified range, had poor hinge properties. The injection-molded article of Comparative Example 5, which used Copolymer 11 in which component (2) / [component (1)+component (2)] was outside the specified range, had poor low-temperature impact resistance.

Claims

1. A polypropylene-based resin composition containing a polypropylene-based resin (A) including a continuous phase made of a propylene-ethylene copolymer optionally containing a propylene homopolymer and a rubber phase made of an ethylene-α-olefin copolymer, the polypropylene resin composition has an MFR of 0.1 g / 10 min or more and less than 5.0 g / 10 min at a temperature of 230°C and a load of 2.16 kg; the content of the polypropylene-based resin (A) is 90 to 100% by mass relative to the total mass of the polypropylene-based resin composition, the xylene-soluble portion of the polypropylene-based resin (A) has an intrinsic viscosity of 0.8 to 1.5 dl / g in tetrahydronaphthalene at 135°C; the polypropylene-based resin (A) has an MFR of 0.1 g / 10 min or more and less than 10 g / 10 min at a temperature of 230°C and a load of 2.16 kg; the content of ethylene-derived units in the propylene-ethylene copolymer optionally containing the propylene homopolymer is 0.1 to 10% by mass based on the total mass of the propylene-ethylene copolymer optionally containing the propylene homopolymer, the α-olefin has 4 carbon atoms, the ethylene-derived unit content in the ethylene-α-olefin copolymer is 70 to 85 mass% based on the total mass of the ethylene-α-olefin copolymer, and the content of the ethylene-α-olefin copolymer relative to the mass of the polypropylene-based resin (A) is 10 to 50 mass%, The polypropylene resin composition does not contain a nucleating agent or an inorganic filler. A polypropylene resin composition for injection molding.

2. 2. The polypropylene-based resin composition for injection molding according to claim 1, wherein the propylene-ethylene copolymer optionally containing the propylene homopolymer has an MFR of 0.1 g / 10 min or more and less than 10 g / 10 min at a temperature of 230°C and a load of 2.16 kg.

3. In addition to the ethylene-α-olefin copolymer constituting the polypropylene-based resin (A), an ethylene-α-olefin copolymer (B) is further contained, the ethylene / α-olefin copolymer (B) has an MFR of 0.1 g / 10 min or more and 40 g / 10 min or less at a temperature of 190°C and a load of 2.16 kg; 3. The polypropylene resin composition for injection molding according to claim 1, wherein the content of the ethylene-α-olefin copolymer (B) relative to the total mass of the polypropylene resin composition is 10 mass% or less.

4. The polypropylene-based resin composition for injection molding according to any one of claims 1 to 3, wherein the propylene-ethylene copolymer optionally containing the propylene homopolymer and the ethylene-α-olefin copolymer are mixed by polymerization, and the polypropylene-based resin is a polymerization mixture produced using a catalyst containing the following components (A) to (C): (A) A solid catalyst containing magnesium, titanium, a halogen, and an electron donor compound. (a) Organoaluminum compounds (c) Organosilicon compounds that are external electron donor compounds

5. 5. The polypropylene resin composition for injection molding according to claim 4, wherein the electron donor compound is a phthalate compound or a succinate compound.

6. An injection-molded article obtained by injection molding the polypropylene-based resin composition for injection molding according to any one of claims 1 to 5.

7. 7. The injection molded article according to claim 6, wherein the injection molding is an injection molding other than injection blow molding.

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