Polypropylene-based resin composition and method for producing the same and injection molded body

Abstract

To provide a method for producing a polypropylene-based resin composition capable of obtaining an injection molded body having a small amount of elution component into n-heptane, having excellent balance of rigidity, surface impact strength, moldability, durability (breaking strain) on a mating surface of an in-mold label, appearance, odor and productivity and a method for producing the same and to provide an injection molded body.SOLUTION: There is provided a polypropylene-based resin composition which comprises: a polypropylene-based resin (A) containing a continuous phase composed of a propylene polymer (a1) and a rubber phase composed of a copolymer (a2) of ethylene and an α-olefin having 3 to 10 carbon atoms; an ethylene-α-olefin copolymer (B) of an optional component which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms; and a nucleating agent (C).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene resin composition, a method for producing the same, and an injection-molded article. [Background technology]

[0002] Polypropylene is used in a variety of applications due to its excellent physical properties such as impact resistance, rigidity, transparency, chemical resistance, and heat resistance. Excellent appearance is sometimes required for injection-molded articles of resin compositions containing polypropylene as a main component, and Patent Document 1, for example, discloses a resin composition that can produce injection-molded articles that are excellent in appearance as well as various mechanical properties by adjusting the content of the xylene-insoluble matter (XI) and the Mw / Mn ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-189818 Summary of the Invention [Problem to be solved by the invention]

[0004] Molded articles used as packaging materials, such as containers that come into contact with food, are required to be resistant to leaching of the components of the molded articles into the food. National standards (Ministry of Health, Labour and Welfare Notification No. 370) require that containers (test pieces) primarily made of polypropylene be immersed in n-heptane for an elution test, and that the amount of eluted components be below a specified value. While this specified value varies depending on the temperature of use, meeting the strict standard requires a value of 35 μg / ml or less. Meanwhile, the resin composition disclosed in Patent Document 1 is not expected to necessarily meet the above-mentioned standard.

[0005] The present invention provides a polypropylene resin composition that has a low content of components eluted into n-heptane and that can give an injection-molded article that has an excellent balance of rigidity, dart impact strength, moldability, durability (breaking strain) at the mating surface of an in-mold label, appearance, odor, and productivity; a production method thereof; and an injection-molded article. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A polypropylene resin composition comprising: (A) a polypropylene resin having a continuous phase made of a propylene polymer (a1) and a rubber phase made of a copolymer (a2) of ethylene and an α-olefin having 3 to 10 carbon atoms; (B) an optional ethylene-α-olefin copolymer which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms; and (C) a nucleating agent, the content of the polypropylene-based resin (A) is 90% by mass or more and less than 100% by mass relative to the total mass of the polypropylene-based resin composition, the content of the ethylene-α-olefin copolymer (B) is 0 to 10% by mass based on the total mass of the (A) and the (B), the content of the nucleating agent (C) is 0.02 parts by mass or more and 0.5 parts by mass or less relative to 100 parts by mass of the total mass of the (A) and the (B), the polypropylene resin composition has an MFR of 40 to 120 g / 10 min at a temperature of 230°C and a load of 2.16 kg; The weight average molecular weight M of the propylene polymer (a1) w and number average molecular weight M n Ratio to (M w / M n ) is less than 7, the propylene polymer (a1) has an ethylene-derived unit content of 1.5 mass% or less based on the total mass of the propylene polymer (a1); the content of the copolymer (a2) is 24 to 43 mass% based on the total mass of the polypropylene-based resin (A), the content of ethylene-derived units in the copolymer (a2) is 25 to 60% by mass based on the total mass of the copolymer (a2); the xylene-soluble portion of the polypropylene-based resin (A) has an intrinsic viscosity of 0.5 to 3.0 dl / g in tetrahydronaphthalene at 135°C; The polypropylene resin (A) has an MFR of 40 to 120 g / 10 min at a temperature of 230°C and a load of 2.16 kg. Polypropylene resin composition. [2] The polypropylene-based resin composition according to [1], wherein the propylene polymer (a1) and the copolymer (a2) are mixed by polymerization, and the polypropylene-based resin (A) 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 a phthalate compound as an electron donor compound. (a) Organoaluminum compounds (c) Organosilicon compounds that are external electron donor compounds [3] A method for producing the polypropylene-based resin composition according to [1] or [2], comprising the step of polymerizing an ethylene monomer and an α-olefin monomer having 3 to 10 carbon atoms in the presence of the propylene polymer (a1) using a catalyst containing the following components (a) to (c) to obtain the polypropylene-based resin (A): (A) A solid catalyst containing magnesium, titanium, a halogen, and a phthalate compound as an electron donor compound as essential components. (a) Organoaluminum compounds (c) Organosilicon compounds that are external electron donor compounds [4] An injection-molded article obtained by injection-molding the polypropylene-based resin composition according to [1] or [2]. [5] The injection-molded article according to [4], wherein the thickness of the thinnest part is 1 mm or less. [6] The injection-molded article according to [4] or [5], which is molded into the shape of a container, and the thickness of the side wall of the container is 0.1 to 1 mm. [7] The injection-molded article according to any one of [4] to [6], which is molded into the shape of a container and has an in-mold label on the side wall of the container. [8] The injection-molded article according to any one of [4] to [7], which is used in a low-temperature environment of -10°C or lower. [9] The injection-molded article according to any one of [4] to [8], which is used as a container or packaging material that comes into contact with food. [Effects of the Invention]

[0007] By using the polypropylene resin composition of the present invention, an injection-molded article can be obtained that has excellent food hygiene properties (i.e., low elution of components into n-heptane) and an excellent balance of rigidity, dart impact strength, moldability, durability (breaking strain) at the mating surface of an in-mold label, appearance, odor, and productivity. The polypropylene resin composition of the present invention is also suitable for thin wall injection molding (TWIM). The injection-molded article of the present invention has an excellent balance of the above-mentioned mechanical properties and is therefore particularly suitable for food packaging applications (containers, drink cups, etc.) In addition to food packaging applications, it may also be used for applications such as miscellaneous goods, daily necessities, home appliance parts, electrical and electronic parts, automobile parts, housing materials, toy materials, furniture materials, building materials, packaging materials, industrial materials, logistics materials, agricultural materials, etc. [Brief explanation of the drawings]

[0008] [Figure 1] A container with an in-mold label is placed sideways inside the compression testing machine just before being compressed. [Figure 2] This is the appearance of a container with an in-mold label placed sideways inside a compression testing machine after compression. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Polypropylene-based resin composition> The polypropylene resin composition of the present invention contains a polypropylene resin (A) (hereinafter also referred to as component (A)) including a continuous phase made of a propylene polymer (hereinafter also referred to as component (a1)) and a rubber phase made of a copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms (hereinafter also referred to as component (a2)), and further contains an optional ethylene-α-olefin copolymer (B) (hereinafter also referred to as component (B)), which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms, and a nucleating agent (C) (hereinafter also referred to as component (C)). Component (B) is an optional component, and may or may not be included in the polypropylene resin composition of the present invention.

[0010] The content of the polypropylene-based resin (A) is 90% by mass or more and less than 100% by mass relative to the total mass of the polypropylene-based resin composition, with the lower limit being preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. If the content is equal to or greater than the lower limit of the above range, the above-described effects of the present invention can be sufficiently obtained. If the content is less than the upper limit of the above range, there is room for the inclusion of component (B) or component (C).

[0011] The content of the ethylene-α-olefin copolymer (B) is 0 to 10% by mass relative to the total mass of components (A) and (B), with the upper limit being preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass. When the content is at least as high as the lower limit of the above range, the dart impact strength of the injection-molded article increases. If the content is below the upper limit of the above range, the rigidity of the injection-molded article will increase, whereas if it exceeds 10% by mass, the rigidity will decrease, making handling difficult.

[0012] The content of the nucleating agent (C) is 0.02 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the total mass of the components (A) and (B). When the content is at least as large as the lower limit of the above range, the rigidity of the injection-molded article increases. If the upper limit of the above range is exceeded, the effect of improving the rigidity of the injection molded article will reach a plateau, which is uneconomical.

[0013] The polypropylene resin composition has an MFR of 40 to 120 g / 10 min at a temperature of 230°C and a load of 2.16 kg, with the lower limit being preferably 50 g / 10 min or more, and more preferably 60 g / 10 min or more. The upper limit is preferably 100 g / 10 min or less, and more preferably 85 g / 10 min or less. 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, poor filling into the mold is unlikely to occur even during thin-wall injection molding, and high-cycle (high-speed) molding can also be accommodated. When the temperature 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 sufficiently improved.

[0014] [Polypropylene resin (A)] The polypropylene resin (A) contained in the polypropylene resin composition of the present invention is one embodiment of an impact-resistant polypropylene polymer as defined in JIS K6921-1, and is composed of two or more phases including a continuous phase of a propylene polymer (component (a1)) and a rubber phase of an ethylene-α-olefin copolymer (component (a2)) present as a dispersed phase in the continuous phase. The polypropylene resin (A) may be a mixed resin obtained by mixing components (a1) and (a2) during polymerization, or a mixed resin obtained by melt-kneading separately prepared components (a1) and (a2). A mixture of components (a1) and (a2) during polymerization (polymerization mixture) is preferred, since it provides a resin with an excellent balance of rigidity, low-temperature impact resistance, and tensile properties (hereinafter also referred to as "mechanical property balance") at a lower cost. In the polymerization mixture, component (a1) and component (a2) can be mixed together at the submicron level, and therefore, a polypropylene resin composition based on the polymerization mixture exhibits an excellent balance of mechanical properties. On the other hand, if a similar homogeneous mixture is achieved by simply melt-kneading separately obtained components (a1) and (a2) to obtain an excellent balance of mechanical properties, the production cost will be high due to the need for additional processes such as storage, keeping, transporting, measuring, mixing, melt-kneading, etc. This is also undesirable from the viewpoint of energy costs. The reason why the polymerization mixture and the mechanical mixture may exhibit different physical properties is presumably due to differences in the dispersion state of component (a2) in component (a1), but there is currently no known practical means for analyzing the dispersion state at the molecular level, including the interface state between component (a2) and component (a1). The production method of polypropylene-based resin (A) will be described in detail later.

[0015] The intrinsic viscosity (hereinafter also referred to as "XSIV") of the xylene soluble matter of the polypropylene resin (A) is 0.5 to 3.0 dL / g, with the lower limit being preferably 1.2 dL / g or more, more preferably 1.5 dL / g or more, and the upper limit being preferably 2.4 dL / g or less. If it is equal to or greater than the lower limit of the above range, the low-temperature impact resistance of the injection-molded article will be improved, whereas if it is less than 0.5 dl / g, it will be difficult to produce the polypropylene-based resin composition. 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 is improved, and poor appearance (appearance of bumps) can be suppressed. 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.

[0016] The weight average molecular weight M is an index of the molecular weight distribution of the propylene polymer (component (a1)) that constitutes the polypropylene resin (A). w and number average molecular weight M n Ratio to (M w / M n ) is less than 7. If the thickness is less than the upper limit of the above range, when a container equipped with an in-mold label is formed as an injection molded article, the strength of the mating surface of the in-mold label is improved. The lower limit of the ratio is not particularly limited, and a guideline is, for example, 3 or more. Here, the weight average molecular weight M of the propylene polymer w and number average molecular weight M n is a value measured by gel permeation chromatography (GPC), specifically, a value measured by the method described below.

[0017] The ethylene-derived unit content (hereinafter also referred to as "C2") in the propylene polymer (component (a1)) constituting the polypropylene-based resin (A) is 1.5 mass% or less, preferably 1.2 mass% or less, based on the total mass of the propylene polymer. When C2 is equal to or less than the upper limit, the rigidity of the injection molded article increases. The lower limit of C2 is not particularly limited, and may be 0% by mass. Therefore, the propylene polymer may be a polypropylene homopolymer consisting of only propylene-derived units, or may be a copolymer consisting of 98.5% by mass or more and less than 100% by mass of propylene-derived units and more than 0% by mass and 1.5% by mass or less of ethylene-derived units, but from the viewpoint of increasing the rigidity of the obtained injection-molded article, C2 is preferably 0% by mass. 13 It is measured by C-NMR.

[0018] The ethylene-α-olefin copolymer (component (a2)) constituting the polypropylene-based resin (A) is a copolymer having ethylene-derived units and α-olefin-derived units having 3 to 10 carbon atoms. The content of ethylene-derived units in component (a2) is 25 to 60% by mass, preferably 30% by mass or more as the lower limit, and preferably 50% by mass or less, more preferably 43% by mass or less, based on the total mass of component (a2). 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 is improved. When the content is equal to or less than the upper limit of the above range, the food hygiene of the injection-molded article is improved (the amount of elution into n-heptane can be sufficiently reduced). The content of ethylene-derived units in component (a2) is 13 It is measured by C-NMR.

[0019] The content of the ethylene-α-olefin copolymer (component (a2)) relative to the total mass of the polypropylene resin (A) is 24 to 43 mass%, preferably a lower limit of 27 mass% or more, and preferably an upper limit of 39 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 is improved. When the content is equal to or less than the upper limit of the above range, the risk of blocking flow paths in production equipment due to deterioration of powder fluidity during production of the polypropylene-based resin (A) can be reduced, and the polypropylene-based resin (A) can be produced stably and continuously.

[0020] Examples of the α-olefin constituting the ethylene-α-olefin copolymer (component (a2)) include propylene (1-propene), 1-butene, 1-pentene, 1-hexene, and 1-octene. Specific examples of the component (a2) include ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-pentene copolymers, ethylene-hexene copolymers, and ethylene-octene copolymers. Among these, ethylene-propylene copolymers are preferred in view of improving the productivity of the polypropylene resin (A).

[0021] The polypropylene resin (A) has an MFR of 40 to 120 g / 10 min at a temperature of 230°C under a load of 2.16 kg, with an upper limit of 110 g / 10 min or less, and more preferably 90 g / 10 min or less. The MFR is measured using the method described below. When the MFR is equal to or greater than the lower limit of the range, poor filling into the mold is unlikely to occur even during thin-wall injection molding, and high-cycle (high-speed) molding is also possible. 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 is improved.

[0022] [Ethylene-α-olefin copolymer (B)] The ethylene-α-olefin copolymer (B) is a copolymer of ethylene and an α-olefin having a carbon number of 4 to 10. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, and 1-octene. Specific examples of the ethylene-α-olefin copolymer (B) include ethylene-butene copolymer, ethylene-pentene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, and the like. Among these, ethylene-butene copolymers and ethylene-octene copolymers are preferred in view of ease of procurement as raw materials, economic efficiency, and the like.

[0023] The ethylene-α-olefin copolymer (B) preferably has an MFR of 1.0 to 40 g / 10 min at a temperature of 190° C. and a load of 2.16 kg, where the MFR is a value measured in accordance with JIS K6921-2. When the content is equal to or greater than the lower limit of the range, the flowability of the polypropylene-based resin composition is improved. When the content is equal to or less than the upper limit of the range, the occurrence of blocking in the polypropylene-based resin composition is suppressed, and continuous productivity of the composition can be improved. In addition, the low-temperature impact resistance and tensile properties of the injection-molded article are improved.

[0024] [Nucleating agent (C)] The nucleating agent (C) is also called a crystal nucleating agent. As the nucleating agent (C), known nucleating agents that are conventionally contained in polypropylene-based resin compositions can be used, and a nucleating agent selected from nonitol-based nucleating agents, sorbitol-based nucleating agents, phosphate ester-based nucleating agents, triaminobenzene derivative nucleating agents, metal carboxylate nucleating agents, and xylitol-based nucleating agents is preferred. Talc can also be used as a nucleating agent. From the viewpoint of reducing the odor of injection-molded articles, phosphate ester-based nucleating agents are preferred. Examples of nucleating agents having a nonitol-based structure include 1,2,3-trideoxy-4,6:5,7-bis-[(4-propylphenyl)methylene]-nonitol; examples of nucleating agents having a xylitol-based structure 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; and examples of nucleating agents having a sorbitol-based structure include bis-1,3:2,4-(4'-ethylbenzylidene)1-allylsorbitol, bis-1,3:2,4-(3'-methyl-4'-fluoro-benzylidene)1-propylsorbitol and bis-1,3:2,4-(3',4'-dimethylbenzylidene). 2'-methyl-2'-propenyl sorbitol, bis-1,3,2,4-dibenzylidene 2',3'-dibromopropyl sorbitol, bis-1,3,2,4-dibenzylidene 2'-bromo-3'-hydroxypropyl sorbitol, bis-1,3:2,4-(3'-bromo-4'-ethylbenzylidene)-1-allyl sorbitol, mono 2,4-(3'-bromo-4'-ethylbenzylidene)-1-allyl sorbitol, bis-1,3:2,4-(4'-ethylbenzylidene)1-allyl sorbitol, bis-1,3:2,4-(3',4'-dimethylbenzylidene)1-methyl sorbitol, bis(p-methylbenzylidene)sorbitol, 1,3:2,4-bis-o-(4-methylbenzylidene)-D-sorbitol, and the like. Examples of commercially available nonitol-based nucleating agents include Millad NX8000 (manufactured by Milliken Japan Co., Ltd.), and examples of commercially available sorbitol-based nucleating agents include RiKAFAST R-1 (manufactured by New Japan Chemical Co., Ltd.), Millad 3988 (manufactured by New Japan Chemical Co., Ltd.), Gelall E-200 (manufactured by New Japan Chemical Co., Ltd.), and Gelall MD (manufactured by New Japan Chemical Co., Ltd.). Examples of phosphate ester-based crystal nucleating agents include 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 commercially available phosphate ester-based crystal nucleating agents include Adeka STAB NA-11 (manufactured by ADEKA Corporation), Adeka STAB NA-21 (manufactured by ADEKA Corporation), and Adeka STAB NA-71 (manufactured by ADEKA Corporation). Examples of triaminobenzene derivative crystal nucleating agents include 1,3,5-tris(2,2-dimethylpropanamido)benzene, etc. Examples of commercially available triaminobenzene derivative crystal nucleating agents include IRGACLEAR XT386 (manufactured by BASF Japan Ltd.) and RIGACLEAR PC1 (manufactured by New Japan Chemical Co., Ltd.). Examples of metal carboxylate nucleating agents include calcium 1,2-cyclohexanedicarboxylate, etc. Examples of commercially available metal carboxylate nucleating agents include Hyperform HPN-20E (manufactured by Milliken Japan). These crystal nucleating agents can be used alone or in combination of two or more.

[0025] [Other ingredients] The polypropylene resin composition of the present invention may contain, as optional components, additives other than the polypropylene resin (A), the ethylene-α-olefin copolymer (B), and the nucleating agent (C), as long as the effects of the present invention are not impaired. Examples of the additives include antioxidants, neutralizing agents, nucleating agents other than the nucleating agents described above, weathering agents, pigments (organic or inorganic), internal and 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. These additives may be used alone or in combination of two or more. The content may be a known amount.

[0026] <Method of producing polypropylene-based resin composition> The polypropylene resin composition of the present invention can be produced by mixing the polypropylene resin (A), the optional ethylene-α-olefin copolymer (B), and the 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 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-based resin (A) may be obtained by mixing a propylene polymer (component (a1)) and an ethylene-α-olefin copolymer (component (a2)) during polymerization, or by mixing separately produced components (a1) and (a2) by melt-kneading. The polypropylene resin (A) is preferably a polymerization mixture in which the component (a1) and the component (a2) are mixed during polymerization. Such a polymerization mixture can be obtained by polymerizing ethylene monomer and α-olefin monomer in the presence of component (a1). This method not only increases productivity but also improves the dispersibility of component (a2) in component (a1), thereby improving the balance of mechanical properties of injection-molded articles obtained using the mixture.

[0028] Hereinafter, the case where propylene monomer is used as the α-olefin monomer will be described, but the same production method can be used when other α-olefin monomers are used.

[0029] As a method for producing the polymerization mixture, a multi-stage polymerization method is typically used. For example, in a polymerization apparatus equipped with two polymerization reactors, a propylene monomer and, if necessary, an ethylene monomer are polymerized in a first polymerization reactor to obtain a propylene polymer, and the obtained propylene polymer is supplied to a second polymerization reactor, and at the same time, ethylene monomer and propylene monomer are polymerized in this second polymerization reactor to obtain the polymerization mixture. The polymerization conditions may be the same as known polymerization conditions. For example, the first-stage polymerization conditions may be a slurry polymerization method in which propylene is in a liquid phase and has high monomer density and productivity. The second-stage polymerization conditions may be a gas-phase polymerization method, which generally facilitates the production of a copolymer having high solubility in propylene. 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 and the stereoregularity of the obtained polypropylene are better. The polymerization pressure is preferably 25 to 60 bar (2.5 to 6.0 MPa), more preferably 33 to 45 bar (3.3 to 4.5 MPa), when carried out in a liquid phase, and is preferably 5 to 30 bar (0.5 to 3.0 MPa), more preferably 8 to 30 bar (0.8 to 3.0 MPa), when carried out in a gas phase. Polymerization (polymerization of propylene monomer, polymerization of ethylene monomer and propylene monomer, etc.) is usually carried out using a catalyst. During polymerization, hydrogen may be added, if necessary, to adjust the molecular weight. By adjusting the molecular weight of the propylene polymer or ethylene-propylene copolymer, the MFR of the polypropylene-based resin (A) and, ultimately, the MFR of the polypropylene-based resin composition can be adjusted. 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.

[0030] As the catalyst, a known olefin polymerization catalyst can be used. As the catalyst for polymerizing ethylene monomers and propylene monomers in the presence of the propylene polymer, 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 a phthalate compound as an electron donor compound as essential components. (a) Organoaluminum compounds. (c) Organosilicon compounds that are external electron donor compounds.

[0031] The polypropylene-based resin (A) is preferably produced by a process including a step of polymerizing an ethylene monomer and an α-olefin monomer (e.g., a propylene monomer) in the presence of the propylene polymer using the catalyst (X) to obtain the polypropylene-based resin. By using the catalyst (X), the polypropylene-based resin (A) having the physical properties within the above-mentioned ranges can be easily obtained. The molecular weight and stereoregularity distributions of propylene polymers obtained vary depending on the catalyst used (especially the electron donor compound of component (A)). These differences affect crystallization behavior, but 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 effect of stereoregularity distribution on crystallization behavior. Furthermore, because actual injection molding is performed at extremely 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 identify differences in crystallization behavior due to stereoregularity distribution in polypropylene resin compositions obtained using a specific catalyst. In addition to the type of catalyst mentioned above, molecular weight distribution and stereoregularity distribution can also change due to thermal degradation during melt-kneading and peroxide treatment.

[0032] 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 (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, halogen-containing titanium compounds are preferred, titanium tetrahalides are more preferred, and titanium tetrachloride (TiCl4) is particularly preferred.

[0033] 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.

[0034] The electron donor compound used in component (A) preferably contains a phthalate compound as an essential component. When a catalyst (X) containing a phthalate compound as an electron donor is used, the M of the propylene polymer can be obtained. w / M nA polypropylene resin having a viscosity within the above range can be easily obtained. 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, and diphenyl phthalate. Of these, diisobutyl phthalate is particularly preferred.

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

[0036] 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.

[0037] 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-trifluoromethylindene; 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.

[0038] Examples of halogen atoms constituting component (A) include fluorine, chlorine, bromine, iodine, and mixtures thereof, with chlorine being particularly preferred.

[0039] 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.

[0040] 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.

[0041] The organosilicon compound plays an important role in controlling the amount of xylene insolubles. When other catalyst components are the same, the amount of xylene insolubles depends on the type and amount of organosilicon compound and the polymerization temperature. Even when an appropriate organosilicon compound is used, the amount of organosilicon compound drops significantly when the amount of organosilicon compound 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 compound to organoaluminum compound (organosilicon compound / organoaluminum) 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-based compound is used as the internal electron donor compound, increasing the polymerization temperature increases the amount of xylene-insoluble matter, thereby lowering the upper and lower 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-based 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.

[0042] 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.

[0043] The method for obtaining the polymerization mixture by the multistage polymerization method is not limited to the above method, and the propylene polymer (component (a1)) may be polymerized in a plurality of polymerization reactors, or the ethylene-α-olefin copolymer (component (a2)) 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.

[0044] (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.

[0045] <Injection molded body> The injection-molded article of the present invention can be produced by injection molding the above polypropylene resin composition. Molding is generally performed at a temperature of 150 to 350°C, preferably 170 to 250°C. Molding temperatures exceeding 350°C can lead to deterioration of the resin composition and molding defects, while temperatures below 150°C can result in reduced fluidity, leading to poor appearance and molding defects due to insufficient filling of the mold. Mold temperatures are preferably maintained in the range of 10 to 60°C. Although molded articles with excellent surface finish and rigidity can be obtained at molded articles with a temperature above 60°C, the molding cycle becomes longer and productivity decreases. Conversely, setting a mold temperature below 10°C can result in significant warping and shrinkage, making it difficult to obtain satisfactory molded articles. Furthermore, condensation is more likely to form on the mold, which can accelerate mold corrosion. This is also unsuitable from the perspective of the energy costs associated with cooling.

[0046] The polypropylene resin composition of the present invention is suitable for thin-wall injection molding. For example, it is possible to form an injection-molded article having a thickness of 1 mm or less, preferably 0.7 mm or less, and more preferably 0.5 mm or less at the thinnest part. The lower limit of the thickness of the thin-walled part is approximately 0.1 mm. The thickness of the thin-walled part is measured by observing the cross section of the measurement point using a known means such as a measuring microscope.

[0047] The shape of the injection-molded article of the present invention is not particularly limited, and it is suitable for containers because it has an excellent balance of various mechanical properties and can be made thin. The thickness of the side wall of the container can be, for example, 0.1 to 1 mm, preferably 0.1 to 0.7 mm, and more preferably 0.1 to 0.5 mm. The thickness of the side wall is measured by observing the cross section of the measurement point using a known means such as a measuring microscope.

[0048] When the injection-molded article of the present invention is a container, the side wall of the container may be provided with an in-mold label. An in-mold label may wrap around the side wall (one full circle) and have a joint where the starting edge and the ending edge overlap. Typically, the body of the in-mold label is formed of a resin different from the polypropylene-based resin composition that forms the container body. The thickness of the in-mold label may be, for example, 10 to 100 μm. The thickness of the in-mold label is included in the thickness of the side wall of the container. Letters, pictures, symbols, numbers, or any other figures or designs may be printed on the in-mold label.

[0049] The injection molded article of the present invention has excellent low-temperature impact resistance and can be used in low-temperature environments, for example, at -10°C or below, preferably -20°C or below, and more preferably -30°C or below.

[0050] The injection-molded article of the present invention is formed from a polypropylene-based resin composition that is excellent in food hygiene, and is therefore suitable for use as a container or packaging material that comes into contact with food. The amount of evaporation residue of the injection-molded article made of the polypropylene resin composition as determined by the n-heptane elution test described below is preferably 35 μg / ml or less, more preferably 30 μg / ml or less, and even more preferably 25 μg / ml or less.

[0051] The tensile modulus of elasticity of the injection molded article of the present invention is preferably 900 MPa or more, more preferably 1000 MPa or more. The higher the tensile modulus, the more rigid the injection molded article, which is advantageous for producing an injection molded article having a thin-walled portion.

[0052] When the injection-molded article of the present invention is a container equipped with an in-mold label, the compression distance (breaking strain) measured by the test method described below is preferably 50 mm or more. The longer this compression distance, the more the container can withstand large deformation and is less likely to break. [Example]

[0053] Examples and comparative examples are shown below, but the present invention is not limited to the following examples.

[0054] <Preparation of Copolymer 1> A solid catalyst in which TiCl and diisobutyl phthalate as an internal donor were supported on MgCl was prepared by the method described in lines 46 to 53 of Example 5 of EP 728769. Specifically, the procedure was as follows.

[0055] Microspheroidal MgCl2·2.1C2H5OH was prepared as follows. 48 g of anhydrous MgCl2, 77 g of anhydrous C2H5OH, and 830 mL of kerosene were placed in a 2 L autoclave equipped with a turbine agitator and a suction pipe at room temperature under inert gas. The contents were heated to 120 °C with stirring to form an adduct between MgCl2 and alcohol. This adduct was melted and mixed with the dispersant. The nitrogen pressure inside the autoclave was maintained at 15 atm. The suction pipe of the autoclave was heated to 120 °C externally using a heating jacket. The suction pipe had an inner diameter of 1 mm and a length of 3 m from one end of the heating jacket to the other. The mixture was flowed through this pipe at a velocity of 7 m / sec. At the outlet of the pipe, the dispersion was collected with stirring into a 5 L flask containing 2.5 L of kerosene and externally cooled by a jacket initially maintained at -40 °C. The final temperature of the dispersion was 0 °C. The spherical solid product, which constituted the dispersed phase of the emulsion, was allowed to settle, separated by filtration, washed with heptane, and dried. All operations were carried out under an inert gas atmosphere. MgCl2·3C2H5OH was obtained in the form of solid spherical particles with a maximum diameter of less than 50 μm. The yield was 130 g. The alcohol was removed from the product by gradually increasing the temperature from 50°C to 100°C in a nitrogen stream until the alcohol content per mole of MgCl2 was reduced to 2.1 moles.

[0056] A 500 mL cylindrical glass reactor equipped with a filter barrier was charged with 225 mL of TiCl4 at 0 °C, followed by 10.1 g (54 mmol) of the microspheroidal MgCl2·2.1C2H5OH obtained as described above over a 15-minute period while stirring the contents. The temperature was then raised to 40 °C and 9 mmol of diisobutyl phthalate was added. The temperature was then raised to 100 °C over 1 hour, and stirring was continued for another 2 hours. The TiCl4 was then removed by filtration, and 200 mL of TiCl4 was added while stirring at 120 °C for another 1 hour. Finally, the contents were filtered and washed with n-heptane at 60 °C until the chloride ions completely disappeared from the filtrate. The catalyst component thus obtained contained 3.3 wt% Ti and 8.2 wt% diisobutyl phthalate.

[0057] 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 the molar ratio of organosilicon compound / organoaluminum of 0.05) at 12°C for 24 minutes. The obtained catalyst (X) 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 in series, and propylene was supplied to produce a propylene homopolymer. Subsequently, propylene homopolymer, propylene, and ethylene were supplied to the second-stage polymerization reactor to produce an ethylene-propylene copolymer. During the polymerization, the temperature and pressure were adjusted, and hydrogen was used as a molecular weight modifier. The polymerization temperature and the ratio of reactants were 70°C and 2.32 mol% in the first reactor, respectively, while the polymerization temperature, hydrogen concentration, and the ratio of ethylene to the total of ethylene and propylene were 80°C, 3.62 mol%, and 0.35 mol ratio in the second reactor. The residence time distribution between the first and second reactors was adjusted so that the amount of ethylene-propylene copolymer was 28% by mass. By the above method, the target copolymer 1 was obtained. The obtained copolymer 1 is a polymer mixture of component (a1), a propylene polymer constituting the continuous phase, and component (a2), an ethylene-propylene copolymer constituting the rubber phase, and is the aforementioned polypropylene-based resin (A). For copolymer 1, the molecular weight distribution Mw / Mn of component (a1), the ethylene-derived unit content of component (a1), the mass ratio component (a2) / [component (a1) + component (a2)], the ethylene-derived unit content of component (a2), the XSIV of component (a1) + component (a2), and the MFR of component (a1) + component (a2) are shown in Table 1. In Table 1, catalyst (X) containing a phthalate compound as component (A) is represented as "Pht", and catalyst (X) containing a succinate compound as component (A) is represented as "Suc".

[0058] <Preparation of Copolymer 2-7> We attempted to produce copolymer 2-7, a polymerization mixture of component (a1) and component (a2), using the same production method as for copolymer 1, except that we changed the residence time distribution between the first and second stages so that the mass ratio of component (a2) / [component (a1) + component (a2)] would be the ratio shown in Table 1, and changed the hydrogen concentration in the first stage to the value shown in Table 1 to adjust the MFR of component (a1) + component (a2).For copolymer 2-6, the target copolymer was obtained.For copolymer 7, the mass ratio of component (a2) / [component (a1) + component (a2)] was high (45 mass%), causing the reactor to clog, and the target copolymer could not be obtained. The obtained copolymer was measured in the same manner as for copolymer 1. The measured values ​​(target values ​​in the case of copolymer 7) are shown in Table 1.

[0059] <Preparation of Copolymers 8-9 and 11-12> Copolymers 8-9 and 11-12, which consisted of a polymerization mixture of component (a1) and component (a2), were obtained by the same production method as for copolymer 1, except that the ratio of ethylene to the total of ethylene and propylene in the second reactor was changed to the value shown in Table 1 so that the content of ethylene-derived units in component (a2) would be the ratio shown in Table 1. These copolymers were measured in the same manner as Copolymer 1. The measured values ​​are shown in Table 1.

[0060] <Preparation of Copolymer 10> Copolymer 10, consisting of a polymerization mixture of components (a1) and (a2), was obtained by the same production method as for copolymer 1, except that the hydrogen concentration in the second reactor and the ratio of ethylene to the total of ethylene and propylene were changed to the values ​​shown in Table 1 so that the XSIV of component (a1) + component (a2) and the ethylene-derived unit content of component (a2) would be the values ​​shown in Table 1, and the hydrogen concentration in the first reactor was changed to the value shown in Table 1 to adjust the MFR of component (a1) + component (a2). This copolymer was measured in the same manner as copolymer 1. The measured values ​​are shown in Table 1.

[0061] <Preparation of copolymers 13-18> Copolymers 13-18 were produced using the same production method as for copolymer 1, except that the hydrogen concentration in the second reactor was changed to the value shown in Table 1 so that the XSIV of component (a1) + component (a2) would be the ratio shown in Table 1, and the hydrogen concentration in the first reactor was changed to the value shown in Table 1 to adjust the MFR of component (a1) + component (a2). The copolymers 13-18 were produced using the same production method as for copolymer 1, and the desired copolymers were obtained except for copolymer 15. Copolymer 15 had a small XSIV of component (a1) + component (a2) (0.4), making production difficult, and the desired copolymer could not be obtained. The obtained copolymer was measured in the same manner as for copolymer 1. The measured values ​​(target values ​​in the case of copolymer 15) are shown in Table 1.

[0062] <Preparation of Copolymers 19-23> Copolymers 19-23 consisting of a polymerization mixture of component (a1) and component (a2) were obtained by the same production method as for copolymer 1, except that the hydrogen concentration in the first-stage reactor was changed to the value shown in Table 1 so that the MFR of component (a1) + component (a2) would be the value shown in Table 1. These copolymers were measured in the same manner as Copolymer 1. The measured values ​​are shown in Table 1.

[0063] <Preparation of Copolymers 24 and 25> Copolymers 24 and 25, consisting of a polymerization mixture of component (a1) and component (a2), were obtained by the same production method as for copolymer 1, except that the ethylene concentration in the first-stage reactor was changed so that the content of ethylene-derived units in component (a1) would be the proportion shown in Table 1, and the hydrogen concentration in the first stage was changed to the value shown in Table 1 in order to adjust the MFR of component (a1) + component (a2). These copolymers were measured in the same manner as Copolymer 1. The measured values ​​are shown in Table 1.

[0064] <Preparation of Copolymer 26> According to the preparation method described in the examples of JP-A-2011-500907, a solid catalyst was prepared by the following procedure. In a 500 mL four-necked round-bottom flask purged with nitrogen, 250 mL of TiCl4 was introduced at 0 °C. With stirring, 10.0 g of finely divided MgCl2·1.8C2H5OH (prepared according to the method described in Example 2 of USP-4,399,054, except operating at 3,000 rpm instead of 10,000 rpm) and 9.1 mmol of diethyl-2,3-(diisopropyl)succinate were added. The temperature was raised to 100 °C and maintained for 120 minutes. Next, stirring was stopped, the solid product was allowed to settle, and the supernatant liquid was siphoned off. The following procedure was then repeated twice: 250 mL of fresh TiCl4 was added, the mixture was reacted at 120 °C for 60 minutes, and the supernatant liquid was siphoned off. The solid was washed six times with anhydrous hexane (6 × 100 mL) at 60 °C. The solid catalyst was contacted with TEAL and DCPMS at room temperature for 5 minutes in amounts such that the TEAL to solid catalyst mass ratio was 18 and the TEAL / DCPMS mass ratio was 10. The resulting catalyst system was suspended in liquid propylene and maintained at 20°C for 5 minutes to carry out prepolymerization. The resulting prepolymer was introduced into the liquid-phase polymerization reactor of a polymerization apparatus equipped with a liquid-phase polymerization reactor and a gas-phase polymerization reactor in series. Propylene polymer was produced in the liquid phase of propylene in the first polymerization reactor, and ethylene-propylene copolymer was produced in the gas-phase polymerization reactor in the second polymerization reactor. The polymerization temperature was set to 80°C, and the polymerization pressure and catalyst loading were adjusted. The ethylene and propylene feed rates in the second stage were also adjusted to achieve the desired ethylene-derived unit content of component (a2), resulting in a molar ratio of ethylene to the total ethylene and propylene of 0.27. In addition, hydrogen was used as a molecular weight modifier, and the hydrogen concentration was set to 1.51 mol% in the first stage and 2.69 mol% in the second stage so that the MFR and XSIV of component (a1) + component (a2) would be the desired values. The residence time distribution in the first and second stages was also adjusted so that the mass ratio of component (a2) / [component (a1) + component (a2)] would be the desired amount. The target copolymer 26 was obtained by the above method. The obtained copolymer 26 is a polymer mixture of component (a1), which is a propylene polymer constituting the continuous phase, and component (a2), which is an ethylene-propylene copolymer constituting the rubber phase, and is the aforementioned polypropylene-based resin (A). For copolymer 26, the molecular weight distribution Mw / Mn of component (1), the ethylene-derived unit content of component (1), the mass ratio component (a2) / [component (a1) + component (a2)], the ethylene-derived unit content of component (a2), the XSIV of component (a1) + component (a2), and the MFR of component (a1) + component (a2) are shown in Table 1.

[0065] [Table 1A]

[0066] [Table 1B]

[0067] The measurement results in Table 1 were measured by the following measurement method.

[0068] <Mw / Mn of component (a1)> A 2.5 g sample taken from the component (a1) polymerized in the first-stage reactor was used as a measurement sample, and the number average molecular weight (Mn) and weight average molecular weight (Mw) were measured as follows, and the weight average molecular weight (Mw) was divided by the number average molecular weight (Mn) to determine the molecular weight distribution (Mw / Mn). The Polymer Laboratories PL GPC220 was used as the instrument, and 1,2,4-trichlorobenzene containing an antioxidant was used as the mobile phase. A series of Showa Denko UT-G (1 column), UT-807 (1 column), and UT-806M (2 columns) was used as the column. A differential refractometer was used as the detector. The sample solution was prepared using the same solvent as the mobile phase, with a sample concentration of 1 mg / mL. The sample was dissolved at 150 °C for 2 hours with shaking. 500 μL of the resulting sample solution was injected into the column, and measurements were performed at a flow rate of 1.0 mL / min, a temperature of 145 °C, and a data acquisition interval of 1 second. The column was calibrated using polystyrene standards (Shodex STANDARD, Showa Denko) with molecular weights ranging from 5.8 million to 7.45 million, using a cubic approximation. The Mark-Houwink-Sakurada coefficient for the polystyrene standards was K = 1.21 × 10. -4 , α=0.707, and for polypropylene homopolymer, propylene random copolymer, and polypropylene-based polymer, K=1.37×10 -4 , α=0.75 was used.

[0069] <Total Ethylene Amount in Copolymer and Ethylene-Derived Unit Content in Component (a1)> The copolymer sample dissolved in a mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene was analyzed by a Bruker AVANCEIII HD400 ( 13C 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. Using the spectrum obtained above, the total ethylene content (mass %) of the copolymer sample was determined by the method described in Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 15, 1150-1152 (1982). When component (a1) is used as a sample for measurement, the total ethylene amount (% by mass) obtained by the above method is the ethylene-derived unit content (% by mass) of component (a1).

[0070] <Content of ethylene-derived units in component (a2)> The ethylene-derived unit content (mass%) of component (a2) was determined by calculation in the same manner as for the total ethylene content, except that the integrated intensity T'ββ calculated by the following formula was used instead of the integrated intensity Tββ calculated when measuring the total ethylene content of the copolymer by the method described in the above document. T'ββ=0.98×Sαγ×A / (1-0.98×A) Here, A=Sαγ / (Sαγ+Sαδ), and is calculated from Sαγ and Sαδ described in the above-mentioned document. In a copolymer consisting of components (a1) and (a2), when component (a1) contains ethylene units, the content of ethylene-derived units in component (a2) was calculated by the following formula when the mass ratio component (a2) / [component (a1)+component (a2)] was clear from the polymerization conditions (such as copolymers 24 and 25). Ethylene-derived unit content of component (a2) (unit: mass%)= [Total ethylene content of copolymer - the content of ethylene-derived units in component (a1) × the content ratio of component (a1) in the copolymer] / (content of component (a2) in copolymer)

[0071] <Mass ratio component (a2) / [component (a1) + component (a2)]> It was calculated using the following formula. Component (a2) / [Component (a1)+Component (a2)] (unit: mass %)=Total ethylene content of copolymer / (Content of ethylene-derived units in component (a2) / 100)

[0072] <Component (a1) + Component (a2) 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. A 2.5 g sample of the copolymer was placed in a flask containing 250 mL of o-xylene (solvent). 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 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.).

[0073] <MFR of component (a1) + component (a2)> 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.

[0074] [Examples 1 to 20, Comparative Examples 1 to 12] Components (A) to (C) were blended according to the composition shown in Table 2. 0.2 parts by mass of BASF B225 as an antioxidant and 0.05 parts by mass of calcium stearate (Tannan Chemical Industry Co., Ltd.) as a neutralizer were added to 100 parts by mass of the total amount of components (A) to (C). The mixture was stirred and mixed for 1 minute using a Henschel mixer. The mixture was melt-kneaded and extruded at a cylinder temperature of 200°C using a co-rotating twin-screw extruder TEX-30α (JSW Corporation). The strands were cooled in water and then cut using a pelletizer to obtain pellets of the polypropylene composition. The polypropylene resin compositions thus produced and injection-molded articles obtained using them were evaluated for various physical properties. The results are shown in Table 2.

[0075] [Table 2A]

[0076] [Table 2B]

[0077] The components in Table 2 are as follows: Component (A) is copolymer 1 to 26 in Table 1.

[0078] Component (B) is the following ethylene-α-olefin copolymer: B-1: Dow Chemical Company, Engage 8100, ethylene-octene copolymer, MFR (190°C, load 2.16 kg) = 1.0 g / 10 min

[0079] Component (C) is a nucleating agent as described below. C-1: ADEKA Corporation ADK STAB NA11 (phosphate ester nucleating agent) C-2: Neotalc UNI05 (talc with a volume average particle size of 5 μm measured by laser diffraction method), manufactured by Neolite Kosan Co., Ltd. C-3: Millad 3988 (sorbitol-based nucleating agent) manufactured by Milliken Japan Co., Ltd.

[0080] The other components are the following additives: Antioxidant: BASF B225 Neutralizer: Calcium stearate manufactured by Tannan Chemical Industry Co., Ltd.

[0081] The measurement results and evaluation results in Tables 2A and 2B are values ​​measured and evaluated by the following methods.

[0082] <Liquidity MFR> The MFR of the polypropylene resin composition was measured under conditions of a temperature of 230°C and a load of 2.16 kg in accordance with JIS K6921-2.

[0083] <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.

[0084] <Low temperature impact resistance, surface impact strength> The dent impact strength of the test specimen was measured at −20° C. using a puncture impact tester (Hydroshot HITS-P10 manufactured by Shimadzu Corporation) in accordance with JIS K7211-2. The higher the dent impact strength value, the more excellent the impact resistance.

[0085] <Food hygiene n-heptane elution test evaporation residue> A press sheet measuring 80 mm x 80 mm x 0.5 mm was obtained using a 36-ton press molding machine manufactured by Shoji Corporation under conditions of a hot platen temperature of 230°C, a cooling platen temperature of 30°C, and a pressure of 5 MPa. This press sheet was used as a test specimen and immersed in 250 ml of n-heptane (25°C) for 1 hour. The test specimen was then removed and the resulting n-heptane (test solution) was transferred to an eggplant-shaped flask and concentrated under reduced pressure to several milliliters. The concentrate and the flask were then washed twice with approximately 5 ml of heptane. The resulting solution was then transferred to a heat-resistant glass evaporating dish of known weight, pre-dried at 105°C, and evaporated to dryness in a water bath. The sample was then dried at 105°C for 2 hours, allowed to cool in a desiccator, and weighed to determine the weight difference between the before and after weights of the evaporating dish. The amount of evaporation residue (unit: μg / ml) was calculated. The above test was performed in accordance with the method described in Ministry of Health, Labor and Welfare Notification No. 370. The standard was met when the calculated amount of evaporation residue was 35 μg / ml or less. The smaller the amount, the better.

[0086] <Moldability> The injection moldability was evaluated at a high cycle (cycle time: 10 seconds). Using an injection molding machine (SE230HY, manufactured by Sumitomo Heavy Industries, Ltd.), the polypropylene resin composition was molded into a drink container (a container suitable for holding liquid and serving for consumption) with an outer diameter of 71 mm, a height of 110 mm, and a thickness of 0.5 mm under conditions of a cylinder setting temperature of 250°C, a mold temperature of 15°C, and a cycle time of 10 seconds. To remove the container from the mold, the bottom of the container was ejected at a speed of 100 mm / sec with a 15 mmφ ejector pin. The results were evaluated according to the following criteria. "Good": Molding was completed without any problems. "X": The container has too little rigidity, causing it to buckle under the force of the ejector pin when removed from the mold. Or, the fluidity is too low, resulting in a short shot and making it impossible to mold a perfectly shaped container.

[0087] <Fracture strain of containers with in-mold labels> A container of the same shape was molded in the same manner as above. A rectangular in-mold label film (thickness: 60 μm, material: PP) was loaded into the mold, and an in-mold label (hereinafter referred to as the label) was attached, wrapping around the outer periphery of the container. After molding, the rectangular film wrapped around the side of the container from one short side to the other, and the two short sides were sealed together at the overlapping position. This sealed area was the joining surface (seam) of the label, which was prone to breakage when the container was crushed. As shown in Figures 1 and 2, a Hydroshot (HIPS-P10, manufactured by Shimadzu Corporation) device was used to place the container horizontally on a support table temperature-controlled at 0°C. A striker (a cylindrical push rod with a diameter of 20 mm) was pressed against the label near the center of the side of the container, compressing it at high speed to measure the distance (unit: mm) the striker compressed until fracture occurred along the mating surface of the label. The longer this distance, the more the container with the label could withstand large deformations and was less likely to break. Figure 1 shows the interior of the testing machine at the start of the test, and Figure 2 shows the state after the compressive deformation. The conditions for pressing the striker were as follows: Impact speed: 1m / sec Maximum reach: 80.5mm Number of sampling points: 1200 points Sampling time: 50 μsec Data collection time: 600 msec Number of n: 5

[0088] <Appearance> Using an injection molding machine (α100C, manufactured by FANUC CORPORATION), the polypropylene resin composition was molded into a 130 mm square, 2 mm thick plate at a cylinder temperature of 230°C and a mold temperature of 40°C. Before evaluating the appearance of this plate as a test piece, it was conditioned by storing it in a room at a temperature of 23±2°C and a relative humidity of 50±5% for 48 hours. The test piece was then visually observed and evaluated according to the following criteria. "◯": Good: No poor appearance of the molded product ("gel": granular surface roughness due to aggregation of high-viscosity components in component (a2)) is observed. "x": poor: poor appearance of the molded product ("gel": granular surface roughness due to aggregation of high-viscosity components in component (a2)) is observed.

[0089] <Odor> Containers of the same shape were molded in the same manner as above. Testers smelled the containers and evaluated the odor according to the following criteria. "○": No odor is generated. "△": Odor generation is extremely slight. "X": Odor is generated.

[0090] <Productivity> "Good": The manufacturing process for polypropylene resin was stable and production was possible. "X": The manufacturing process of the polypropylene resin was unstable, making production difficult.

[0091] <Action and effect> The injection-molded articles (drink containers, etc.) of Examples 1 to 20 were made using polypropylene-based resin compositions with specified physical properties, and therefore not only exhibited an excellent balance of rigidity, surface impact strength, moldability, durability (fracture strain) at the mating surface of the in-mold label, appearance, odor, and productivity, but also satisfied the food hygiene requirements for food containers and food packaging applications (evaporation residue in an n-heptane elution test must be below the standard value (here, 35 μg / ml)). To achieve this excellent balance and also to satisfy food hygiene standards, the inventors had to reconsider the formulation of the entire composition. In other words, to reduce the evaporation residue in the n-heptane elution test, it was necessary to limit the ethylene-derived unit content of component (a2) to a certain value or less. However, doing so resulted in problems with poor mechanical properties. For example, the ethylene-derived unit content of component (a2) affects the rubber-like properties of the composition, and if it is too low, impact resistance at low temperatures is likely to deteriorate. Therefore, by carefully adjusting other parameters, such as the XSIV value of component (a1) + component (a2), the inventors were able to achieve a high level of balance between the other mechanical properties and satisfy food hygiene standards, thereby completing the present invention.

[0092] Comparative Example 1 did not contain component (C) and had poor rigidity, which caused problems when the injection-molded article was removed from the mold: due to its low rigidity, it buckled when pushed out of the mold with an ejector pin. In Comparative Example 2, the content of component (B) was high, resulting in poor rigidity, and problems arose when the injection-molded article was removed from the mold: due to the low rigidity, the article buckled when pushed out of the mold with an ejector pin. In Comparative Example 3, the content of component (a2) in component (A) was low, and the dart impact strength was low, raising concerns about use in low-temperature environments. In Comparative Example 4, the content of component (a2) in component (A) was high, making production difficult. In Comparative Example 5, the content of ethylene-derived units in component (a2) was high, and the product did not meet food hygiene standards. In Comparative Example 6, the content of ethylene-derived units in component (a2) was low, and the dart impact strength was low, raising concerns about use in low-temperature environments. In Comparative Example 7, the XSIV of component (a1)+component (a2) was small, and it was difficult to produce component (A). In Comparative Example 8, the XSIV of component (a1) + component (a2) was large, the dart impact strength was low, there was concern about use in low temperature environments, and the appearance of the injection molded article surface was poor. In Comparative Example 9, the fluidity of the component (a1)+component (a2) and the fluidity of the resin composition were low, and the moldability was poor, that is, the problem of short shot occurred. In Comparative Example 10, the fluidity of component (a1)+component (a2) and the fluidity of the resin composition were high, but the dart impact strength was low, raising concerns about use in low-temperature environments. In Comparative Example 11, the content of ethylene-derived units in component (a1) was high, resulting in poor rigidity and causing problems when the injection-molded article was removed from the mold. In Comparative Example 12, the molecular weight distribution of component (a1) is broad, and there are concerns about resistance to compression deformation when an in-mold label is provided.

Claims

1. a polypropylene-based resin (A) comprising a continuous phase made of a propylene polymer (a1) and a rubber phase made of a copolymer (a2) of ethylene and an α-olefin having 3 to 10 carbon atoms; A polypropylene-based resin composition containing an optional ethylene-α-olefin copolymer (B), which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms, and a nucleating agent (C), the content of the polypropylene-based resin (A) is 90% by mass or more and less than 100% by mass relative to the total mass of the polypropylene-based resin composition, the content of the ethylene-α-olefin copolymer (B) is 0 to 10% by mass based on the total mass of the (A) and the (B), the content ratio of the nucleating agent (C) is 0.02 parts by mass or more and 0.5 parts by mass or less relative to 100 parts by mass of the total mass of the (A) and the (B), the polypropylene resin composition has an MFR of 40 to 120 g / 10 min at a temperature of 230°C and a load of 2.16 kg; The weight average molecular weight M of the propylene polymer (a1) ｗ and number average molecular weight M ｎ Ratio to (M ｗ / M ｎ ) is less than 7, the propylene polymer (a1) has an ethylene-derived unit content of 1.5 mass% or less based on the total mass of the propylene polymer (a1), the content of the copolymer (a2) is 24 to 43% by mass based on the total mass of the polypropylene-based resin (A), the content of ethylene-derived units in the copolymer (a2) is 25 to 60% by mass based on the total mass of the copolymer (a2); the xylene-soluble portion of the polypropylene-based resin (A) has an intrinsic viscosity of 0.5 to 3.0 dl / g in tetrahydronaphthalene at 135°C; the polypropylene-based resin (A) has an MFR of 40 to 120 g / 10 min at a temperature of 230°C and a load of 2.16 kg; A polypropylene resin composition having an evaporation residue of 35 μg / ml or less as determined by an n-heptane elution test conducted in accordance with the method described in Ministry of Health, Labor and Welfare Notification No.

370.

2. 2. The polypropylene-based resin composition according to claim 1, wherein the propylene polymer (a1) and the copolymer (a2) are mixed by polymerization, and the polypropylene-based resin (A) 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 a phthalate compound as an electron donor compound. (a) Organoaluminum compounds (c) Organosilicon compounds that are external electron donor compounds

3. 3. A method for producing the polypropylene-based resin composition according to claim 1, comprising the step of polymerizing an ethylene monomer and an α-olefin monomer having 3 to 10 carbon atoms in the presence of the propylene polymer (a1) using a catalyst containing the following components (a) to (c) to obtain the polypropylene-based resin (A): (A) A solid catalyst containing magnesium, titanium, a halogen, and a phthalate compound as an electron donor compound as essential components. (a) Organoaluminum compounds (c) Organosilicon compounds that are external electron donor compounds

4. An injection-molded article obtained by injection molding the polypropylene-based resin composition according to claim 1 or 2.

5. 5. The injection-molded article according to claim 4, wherein the thickness of the thinnest part is 1 mm or less.

6. 6. The injection-molded article according to claim 4, which is molded into the shape of a container, and the thickness of the side wall of the container is 0.1 to 1 mm.

7. 7. The injection-molded article according to claim 4, which is molded into the shape of a container and has an in-mold label on a side wall of the container.

8. The injection molded article according to any one of claims 4 to 7, which is used in a low-temperature environment of -10°C or lower.

9. The injection-molded article according to any one of claims 4 to 8, which is used as a container or packaging material that comes into contact with food.

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