JP7721266B2 - Polypropylene resin composition for injection molding and injection molded article - Google Patents

Description

The present invention relates to a polypropylene resin composition for injection molding and an injection-molded article.

Polypropylene is used as a resin material for containers and other products due to its excellent balance of physical properties such as impact resistance, rigidity, transparency, chemical resistance, and heat resistance. For example, Patent Document 1 discloses a polypropylene composition suitable for molding food containers.

Japanese Patent Application Laid-Open No. 2019-157084

Some food containers and lidded cases have hinges. These 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 for improved hinge characteristics. Furthermore, high low-temperature impact resistance is also required for storage in refrigerators and freezers.

The present invention provides an injection-molded article with excellent hinge properties and low-temperature impact resistance, and a polypropylene-based resin composition for injection molding suitable for producing the article.

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) is 90 to 100 mass% with respect 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, and 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. 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 the 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 the 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 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, 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; (b) an organoaluminum compound; and (c) an organosilicon compound as an external electron donor compound. [6] The polypropylene resin composition for injection molding according to [5], wherein the electron donor compound is a phthalate-based compound or a succinate-based compound.
[7] An injection-molded article obtained by injection molding the polypropylene-based 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.

The polypropylene resin composition for injection molding of the present invention has high fluidity, making it less likely to cause insufficient filling of molds during injection molding, even when used in molds with complex shapes such as hinge sections. The injection-molded articles obtained by injection molding have excellent hinge properties and low-temperature impact resistance.

1 shows the appearance of the hinged box produced in the example in an open state. This is a cross-sectional photograph of the hinged box before bending the hinge portion. This is a cross-sectional photograph of the hinged box after bending the hinge portion.

<Polypropylene 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)) that 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-based resin composition may further contain an ethylene-α-olefin copolymer (B) in addition to the ethylene-α-olefin copolymer constituting the polypropylene-based resin (A). The polypropylene-based resin composition may further contain a nucleating agent (C).

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.

The content of the polypropylene resin (A) is 90 to 100% by mass, preferably 92 to 99% by 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.

[Polypropylene-based resin (A)]
The polypropylene-based resin (A) contained in the polypropylene-based 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 the component (1) and the component (2) are mixed during polymerization, or may be a mixed resin in which the component (1) and the component (2) are obtained separately and mixed by melt-kneading. However, for the following reasons, the polypropylene-based resin (A) is preferably a mixed resin in which the component (1) and the 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, a polypropylene resin composition based on the polymerization mixture exhibits an excellent balance of mechanical properties such as rigidity and low-temperature impact resistance, and also exhibits good hinge properties.
On the other hand, when 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 steps such as storage, keeping, transporting, measuring, mixing, melt-kneading, etc., and is also undesirable from the viewpoint of energy costs. However, when a specific ethylene/α-olefin copolymer is contained as component (B) in a specific ratio as described below, 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 exhibit different physical properties is presumably due to differences in the dispersion state of component (2) in component (1). However, currently, no practical means is known 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.

The intrinsic viscosity (hereinafter also referred to as "XSIV") of the xylene-soluble portion 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 soluble matter is a component 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.

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. Here, 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.

The content of ethylene-derived units (hereinafter also referred to as "C2a") in component (1) constituting polypropylene-based 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 measured by ¹³ C-NMR.

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.

The content of ethylene-derived units (hereinafter also referred to as "C2b") in the ethylene-α-olefin copolymer constituting the polypropylene-based resin (A) is 70 to 85% by mass, preferably 72% by mass or more and more preferably 75% by mass or more, relative to 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 measured by ¹³ C-NMR.

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). Also, the rigidity of the injection-molded article can be increased.

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 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 low-temperature impact resistance of the injection-molded article can be further improved.

[Ethylene-α-olefin copolymer (B)]
The ethylene-α-olefin copolymer (B), which is an optional component that may be added separately from the polypropylene-based 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, and the like, in addition to the effect of improving low-temperature impact resistance.

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.

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.

[Nucleating Agent (C)]
The nucleating agent (C), also called 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 the crystal nucleating agent include organic nucleating agents such as nonitol-based nucleating agents, sorbitol-based nucleating agents, phosphate ester-based nucleating agents, triaminobenzene derivative-based nucleating agents, carboxylic acid metal salt-based nucleating agents, xylitol-based nucleating agents, and rosin-based nucleating agents.
Because it promotes the cooling and solidification of molten resins, it can also 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 art 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, and examples of such rosin acid partial calcium salts include 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 addition of the nucleating agent and other additives may be carried out using a connected extruder after the polymerization, residual monomer removal, and drying steps. Furthermore, in the present invention, a so-called masterbatch, in which a high concentration of the 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.

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.

[Other ingredients]
The polypropylene-based resin composition of the present invention may contain, as optional components, synthetic resins or synthetic rubbers other than the polypropylene-based resin (A) and the ethylene-α-olefin copolymer (B), inorganic fillers, and additives other than the nucleating agent (C), within a range that does not impair 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 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. One or more of these inorganic fillers may be used, or two or more may be used in combination. To improve the dispersibility of these fillers, the inorganic filler may be surface-treated as needed. The inorganic filler used in the present invention is not limited, but plate-like inorganic fillers are preferred from the viewpoint of increasing 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 even 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 one or more inorganic fillers. The content may be a known amount, but from the viewpoint of not impairing appearance properties such as transparency and gloss in addition to the hinge properties that are the effects of the present invention, the content is preferably 0.5% by mass or less, and even more preferably 0% by 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, anti-bubbling agents, 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.

<Method of producing polypropylene resin composition>
[0033] Examples of a method for producing the polypropylene-based resin composition of the first embodiment include a method of mixing the polypropylene-based resin (A), the optional ethylene-α-olefin copolymer (B), and the optional nucleating agent (C), followed by melt-kneading.
The mixing method may be a dry blending method 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 when melt-kneading is preferably 160 to 350° C., more preferably 170 to 260° C. After melt-kneading, the mixture may be further pelletized.

[Method for producing polypropylene resin (A)]
The polypropylene-based 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-based 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% by mass or less.

As a method for producing the polymerization mixture, a multi-stage polymerization method is typically used. For example, in a polymerization apparatus equipped with three polymerization reactors, a propylene monomer and, if necessary, an ethylene monomer are polymerized in the first polymerization reactor, the resulting propylene polymer (homopolymer) or propylene-ethylene copolymer is supplied to a second polymerization reactor, and the propylene monomer and the ethylene monomer are further polymerized, and the resulting component (1) is supplied to a third polymerization reactor, and at the same time, an ethylene monomer and an α-olefin monomer are polymerized in this third polymerization reactor, thereby obtaining a polymerization mixture in which the component (1) and the component (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 a propylene-ethylene copolymer not containing a propylene homopolymer is produced 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 equal to or higher than the lower limit of the above range, the productivity is better.
The polymerization pressure is preferably 25 to 60 bar (2.5 to 6.0 MPa) when carried out in the liquid phase.
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.

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.

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

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) is preferably a tetravalent titanium compound represented by the general formula: Ti(OR) _g X _4-g (R is a hydrocarbon group, X is a halogen, 0≦g≦4).
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 ₄ , TiBr ₄ , and TiI ₄ ; alkoxytitanium trihalides such as Ti(OCH ₃ )Cl ₃ , Ti(OC ₂ H ₅ )Cl ₃ , Ti(O _n -C ₄ H ₉ )Cl ₃ , Ti(OC ₂ H ₅ )Br ₃ , and Ti(O-isoC ₄ H ₉ )Br ₃ ; alkoxytitanium dihalides such as Ti(OCH ₃ ) ₂ Cl ₂ , Ti(OC ₂ H ₅ ) ₂ Cl ₂ , Ti(O _n -C ₄ H ₉ ) ₂ Cl ₂ , and Ti(OC ₂ H ₅ ) ₂ Br ₂ ; and alkoxytitanium dihalides such as Ti(OCH ₃ ) ₃ Cl and Ti(OC _{2 Examples of the titanium} compound include monohalogenated trialkoxytitanium compounds such as Ti( _OCH3 ) _{4 , Ti(OC2H5)4, and Ti(On-C4H9 ) 4 . These titanium compounds may} be used singly or _in combination _{of two} or more.
Among the above titanium compounds, halogen-containing titanium compounds are preferred, titanium tetrahalides are more preferred, and titanium tetrachloride (TiCl ₄ ) is particularly preferred.

The magnesium compounds used in component (A) include magnesium compounds having a magnesium-carbon bond or a magnesium-hydrogen bond, such as dimethylmagnesium, diethylmagnesium, dipropylmagnesium, dibutylmagnesium, diamylmagnesium, dihexylmagnesium, didecylmagnesium, ethylmagnesium chloride, propylmagnesium chloride, butylmagnesium chloride, hexylmagnesium chloride, amylmagnesium chloride, butylethoxymagnesium, ethylbutylmagnesium, and butylmagnesium hydride. These magnesium compounds can also be used in the form of complex compounds with, for example, organoaluminum, and may be in either liquid or solid form. Further suitable 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.

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-normal butyl phthalate, diethyl phthalate, ethyl isobutyl phthalate, ethyl-normal 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 of 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 have not been fully elucidated. 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 because components with different molecular weights and stereoregularities interact with each other, making it even more difficult to interpret the effects of the molecular weight and stereoregularity distributions on the crystallization behavior. Furthermore, because actual injection molding is performed at very high speeds and in a fluid state, it is not easy to grasp the phenomenon, even with advanced analytical techniques. Therefore, it is virtually impossible to numerically identify the differences in crystallization behavior due to the molecular weight and stereoregularity distributions in polypropylene resin compositions obtained using a catalyst containing a specific electron donor compound.

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 the 1st or 2nd position 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, diethyl-2,3-dibenzylsuccinate, diethyl-2,3-diisopropylsuccinate, diethyl-2,3-bis(cyclohexylmethyl)succinate, and 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-isopropyl-3-isobutylsuccinate, diethyl-2-tert-butyl-3-isopropylsuccinate, diethyl-2-isopropyl-3-cyclohexylsuccinate, diethyl-2-isopentyl-3-cyclohexylsuccinate, diethyl-2-tetradecyl-3-cyclohexylmethylsuccinate, diethyl diisobutyl-2-cyclohexyl-3-cyclopentylsuccinate, diethyl-2,2,3,3-tetramethylsuccinate, diethyl-2,2,3,3-tetraethylsuccinate, diethyl-2,2,3,3-tetrapropylsuccinate, diethyl-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 Propyl-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-propylsuccinate, diisobutyl-2,3-tetradecylsuccinate, 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-cyclohexylmethyl succinate, diisobutyl-2,2,3,3-tetramethyl succinate, diisobutyl-2,2,3,3-tetraethyl succinate, diisobutyl-2,2,3,3-tetrapropyl succinate, diisobutyl-2,3-diene dineopentyl-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 dineopentyl-2,3-diisopropylsuccinate, dineopentyl-2,3-bis(cyclohexylmethyl)succinate, dineopentyl-2,3-di-t-butylsuccinate, dineopentyl-2,3-diisobutylsuccinate, dineopentyl-2,3-dineopentyl succinate, dineopentyl-2,3-diisopentyl succinate, dineopentyl-2,3-(1-trifluoromethylethyl)succinate, dineopentyl-2,3-dineopentyl succinate, dineopentyl-2,3-diisopentyl succinate, dineopentyl-2,3-tetradecyl succinate, dineopentyl-2,3-fluorenyl succinate, dineopentyl-2-isopropyl-3-isobutyl Examples of the compound include dineopentyl-2-tert-butyl-3-isopropyl succinate, dineopentyl-2-isopropyl-3-cyclohexyl succinate, dineopentyl-2-isopentyl-3-cyclohexyl succinate, dineopentyl-2-tetradecyl-3-cyclohexylmethyl succinate, dineopentyl-2-n-propyl-3-(cyclohexylmethyl) succinate, dineopentyl-2-cyclohexyl-3-cyclopentyl succinate, dineopentyl-2,2,3,3-tetraethyl succinate, dineopentyl-2,2,3,3-tetrapropyl succinate, and dineopentyl-2,3-diethyl-2,3-diisopropyl succinate. These compounds may be used alone or in combination of two or more.

Examples of electron donor compounds in the solid catalyst other than phthalate compounds and succinate compounds include diether compounds.

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-cuminotyl-1,3-dimethoxypropane, phenyl-1,3-dimethoxypropane, 2-(2-phenylethyl)-1,3-dimethoxypropane, 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-dicyclohexyl 2-propyl-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-isopropyl butyl-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, 2,2-diisobutyl-1,3-dibutoxypropane, 2-isobutyl-2-isopropyl-1,3-dimethoxypropane, 2,2-di-sec 1,3-diethers such as 2-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.

Halogen atoms constituting component (A) include fluorine, chlorine, bromine, iodine, or mixtures thereof, with chlorine being particularly preferred.

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, and R ¹ _2.5 Al(OR ² ) _0.5 (R ¹ , R ² are 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.

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, ethyl triethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, n-propyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, phenyltrimethoxysilane, γ-chloropropyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, t-butyltriethoxysilane, thexyltrimethoxysilane, n-butyltriethoxysilane, isobutyltriethoxysilane, phenyltriethoxysilane, γ-aminopropyltriethoxysilane, chlorotriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, 2-norbornanetrimethoxysilane, 2-norbornanetriethoxysilane, 2-norbornanemethyltriethoxysilane ethyldimethoxysilane, 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-butyl Dimethoxysilane, isobutylmethyldimethoxysilane, bis(decahydroisoquinolin-2-yl)dimethoxysilane, diethylaminotriethoxysilane, 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, p-tolylmethyldimethoxysilane, and the like.
Among these, ethyltriethoxysilane, n-propyltriethoxysilane, n-propyltrimethoxysilane, t-butyltriethoxysilane, t-butylmethyldimethoxysilane, t-butylmethyldiethoxysilane, t-butylethyldimethoxysilane, t-butylpropyldimethoxysilane, t-butyl-t-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 component (c) may be used alone or in combination of two or more.

Organosilicon compounds play an important role in adjusting the amount of xylene insolubles in propylene-ethylene copolymers, and thus controlling their rigidity.When other catalyst components are the same, the amount of xylene insolubles depends on the type and amount of organosilicon compounds and polymerization temperature.Even when using an appropriate organosilicon compound, the amount of organosilicon compounds will decrease significantly when the amount of organosilicon compounds falls below a certain value, except for diether catalysts.Therefore, when the polymerization temperature is 75°C, the lower limit of the molar ratio of organosilicon compounds to organoaluminum compounds (organosilicon compounds/organoaluminum compounds) 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, so the lower and upper limits of the preferred molar ratio of the organosilicon compound to the organoaluminum compound (organosilicon compound/organoaluminum) decrease. Specifically, when a phthalate compound is used to polymerize at 80°C, 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.

Preferred catalyst (X) is one 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.

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, and another monomer is supplied to a downcomer pipe connected to the riser pipe and polymerized, and the polymerization product is recovered while circulating between the riser pipe and the downcomer pipe. 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.

(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 WO 2006/102155).
During the polymerization, a known molecular weight regulator such as a chain transfer agent (for example, hydrogen or diethyl zinc) may be used.

<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 be used to obtain injection-molded articles with a thickness of, for example, 0.5 to 3 mm.
Specific examples of injection-molded articles include molded articles having a hinge portion 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 parts, toy parts, furniture parts, building materials, packaging parts, industrial materials, logistics materials, agricultural materials, etc.

The type of injection molding used to produce the injection-molded article of this embodiment is not particularly limited, but from the perspective of obtaining an injection-molded article with a hinge portion that has excellent hinge characteristics, an injection molding method other than injection blow molding, in which 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, injection molding methods using a general injection molding machine and mold, including low-pressure molding, injection compression molding, or two-color molding, are preferred.

The temperature of the molten resin used in injection molding is preferably 150 to 350°C, and 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 insufficient filling of the mold and resulting in poor appearance and molding defects. It is preferable to keep the mold temperature 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 it also lengthens the molding cycle and reduces productivity. Conversely, setting the mold temperature below 10°C can result in significant warping and shrinkage, making it difficult to obtain satisfactory molded articles. It also promotes condensation on the mold, which can accelerate mold corrosion. It is also unsuitable from the perspective of the energy costs associated with cooling.

The tensile modulus of elasticity 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.

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.

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 occupancy area ratio, the more excellent the hinge characteristics (flexural durability) of the molded article at the hinge portion. Here, the crack occupancy area ratio is a value measured by the method described below.

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

<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. The solid catalyst was then contacted with triethylaluminum (TEAL) as an organoaluminum compound and dicyclopentyldimethoxysilane (DCPMS) as an external electron donor compound at 12°C for 24 minutes, in amounts such that the mass ratio of TEAL to the solid catalyst was 20 and the mass ratio of TEAL/DCPMS was 10 (equivalent to the molar ratio of organosilicon compound/organoaluminum described above of 0.05).
The resulting catalyst system was prepolymerized by keeping it in suspension in liquid propylene at 20° C. for 5 minutes.
The obtained prepolymer was introduced into the first-stage polymerization reactor of a polymerization apparatus equipped with two-stage polymerization reactors arranged in series, and propylene (C3) and ethylene (C2) were fed thereto to produce a propylene-ethylene copolymer in the liquid phase of propylene. Thereafter, the prepolymer was introduced into the second-stage gas-phase polymerization reactor, and ethylene and butene-1 (C4) were fed thereto to produce an ethylene-butene-1 copolymer. During the polymerization, the temperature and pressure were adjusted, and hydrogen (H2) was used as a molecular weight modifier.
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 in the first and second stages was adjusted so that the amount of the copolymer component was 18 mass%, and a powdery polymer 1 (copolymer 1) was obtained.
The obtained copolymer 1 is a polymer mixture of component (1), which is a propylene-ethylene copolymer constituting the continuous phase, and component (2), which is an ethylene-butene-1 copolymer constituting the rubber phase, and is the aforementioned polypropylene-based resin (A). Note that the obtained component (1) 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."

<Preparation of Copolymer 2>
Copolymer 2 was obtained in the same manner as Copolymer 1, except that the hydrogen concentration in the first-stage reactor was adjusted to 0.02 mol % and the residence time distribution in the first and second stages 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.

<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 various physical properties of the copolymer 3 obtained are shown in Table 1.

<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 various physical properties of the copolymer 4 obtained are shown in Table 1.

<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.

<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 various physical properties of the copolymer 6 obtained are shown in Table 1.

<Preparation of Copolymer 7>
Copolymer 7 was obtained in the same manner as Copolymer 1, except that the hydrogen concentration in the first reactor was changed to 1.50 mol %.
The various physical properties of the copolymer 7 obtained are shown in Table 1.

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

<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 molar ratios of H2/C2 and C3/(C2+C3) were 0.66 and 0.89, respectively.
The various physical properties of the copolymer 9 obtained are shown in Table 1.

<Preparation of Copolymer 10>
A solid catalyst in which _TiCl4 and diethyl-2,3-(diisopropyl)succinate as an internal donor were 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 to the solid catalyst and a mass ratio of 10 to the TEAL/DCPMS compound at 12°C for 24 minutes.
The resulting catalyst system was prepolymerized by keeping it in suspension in liquid propylene at 20° C. for 5 minutes.
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 properties of the copolymer 10 thus obtained 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."

<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. 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 11 to the solid catalyst and a mass ratio of 10 to the TEAL/DCPMS at -5°C for 5 minutes.
The resulting catalyst system was prepolymerized by keeping it in suspension in liquid propylene at 20° C. for 5 minutes.
The obtained prepolymer was introduced into a polymerization reactor, and propylene and ethylene were fed thereto to produce a 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 copolymer 11 thus obtained are shown in Table 1.

The measurement results in Table 1 were measured using the following measurement method.

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

<Total Ethylene Amount in Component (A) and Ethylene-Derived Unit Content in Component (1)>
Each sample of the copolymer dissolved in a mixed solvent of 1,2,4-trichlorobenzene/deuterated benzene was subjected to C-NMR spectrum measurement using a Bruker AVANCE III HD400 ( ^C resonance frequency 100 MHz) under the following conditions: measurement temperature ¹²⁰ °C, flip angle 45°, pulse interval 7 seconds, sample rotation speed 20 Hz, and accumulation number 5000.
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.

<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)−Ethylene-derived unit content of component (1)×Content of component (1) in component (A)]
/ (content ratio of component (2) in component (A)/100)

<XSIV of component (1) + component (2)>
The xylene-soluble portion of the copolymer was obtained by the following method, and the intrinsic viscosity (XSIV) of the xylene-soluble portion was measured.
2.5 g of each copolymer sample was placed in a flask containing 250 mL of o-xylene (solvent), and the mixture was stirred for 30 minutes using a hot plate and reflux hood at 135°C while purging with nitrogen to completely dissolve the copolymer, and then cooled to 25°C for 1 hour. The resulting solution was filtered using filter paper. 100 mL of the filtrate was collected and transferred to an aluminum cup or the like, and evaporated to dryness at 140°C while purging with nitrogen, and then allowed 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.).

<MFR of component (1) + component (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 the mixture was homogenized using a dry bland. Measurement was then carried out in accordance with JIS K6921-2 at a temperature of 230° C. and a load of 2.16 kg.

[Examples and Comparative Examples]
Components (A) to (C) were blended according to the composition shown in Table 2. Per 100 parts by mass of the total 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 various 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.

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

The measurement and evaluation results in Table 2 were measured and evaluated using the following methods.

<Liquidity MFR>
The 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, and for ethylene-α-olefin copolymers, measurements were made at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K6922-2.

<Rigidity and tensile modulus>
According to JIS K6921-2, a polypropylene resin composition was injection molded into a multipurpose test piece (Type A1) as defined 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/sec, 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.

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

<Hinge characteristics: Crack area ratio>
Using an injection molding machine (FANUC Corporation FANUC ROBOSHOT α100C), a molten resin temperature of 250 ° C, a mold temperature of 40 ° C, an average injection speed of 35 mm / s, a pressure holding time of 10 seconds, and a total cycle time of 33 seconds, a hinged box (72 mm long, 0.82 mm wide, 0.52 mm thick) measuring 92 mm long x 125 mm wide x 41 mm high and 2 mm thick was injection molded from a polypropylene resin composition. After conditioning at 23 ° C for 48 hours or more after molding, a bending test was performed 100 times at a rate of once per second, with each operation 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: Dark field By applying liquid paraffin, the wrinkles on the surface that occurred during the bending test were hidden, and only the cracks related to the hinge characteristics could be observed. Using a CCD camera and Q-Capture Pro image analysis software from QImaging, the RGB image was converted to grayscale to calculate the percentage of the hinge area occupied by cracks (crack area ratio).

<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 injection molded.
"3": Injection molding is not possible with many shots (short shots occur, and the molded body is not filled to the end).

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.

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 predetermined 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 predetermined range, was inferior in 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 ranges, 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, was inferior in low-temperature impact resistance.

Claims (7)

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. 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. 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. The polypropylene-based resin composition for injection molding according to any one of claims 1 to 3, wherein the propylene-ethylene copolymer optionally containing a 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; (b) An organoaluminum compound; and (c) An organosilicon compound that is an external electron donor compound. 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. 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. The injection molded article according to claim 6 , wherein the injection molding is an injection molding other than injection blow molding.