JP7487002B2 - Polypropylene resin composition for automobile interior parts, its production method, and molded article for automobile interior parts - Google Patents

Description

The present invention relates to a polypropylene resin composition for automobile interior parts, its manufacturing method, and molded articles for automobile interior parts.

Polypropylene has excellent physical properties such as impact resistance, rigidity, transparency, chemical resistance, and heat resistance, and is therefore used as a resin material for automobile parts, for example, as described in Patent Document 1. In addition, polypropylene-based resin compositions containing 15 to 30 mass % of an inorganic filler in order to obtain high rigidity have also been disclosed (for example, Patent Document 2).
In recent years, with the improvement of injection molding technology, the outer surface of the molded body has become larger and the shape of the molded body has become more complex. For example, in large injection molded bodies such as automobile door trims, ribs are formed on non-design surfaces to increase the strength of the product. Usually, the ribs are designed to be thinner than the thickness of the molded body, so there have been cases where filling failures have occurred, such as the inability to sufficiently fill the grooves for forming the ribs with molten resin. In addition, when the molten resin flows into the cavity, the air present in the cavity may be pushed to the back and accumulate in the grooves for forming the ribs. The accumulated air remains compressed in the grooves or tries to pass through the gap between the molten resin and the inner peripheral surface of the mold, which causes problems with appearance defects such as silver streaks and wrinkles on the surface of the obtained molded body. In order to prevent this problem, it has been proposed to devise a shape of the mold (for example, Patent Document 3).

Japanese Patent Application Laid-Open No. 11-216750 JP 2015-113363 A JP 2012-35586 A

However, when a large amount of inorganic filler, such as 15 to 30% by mass, is blended, there is a drawback in that peeling and whitening between the resin base material and the inorganic filler easily occurs when the surface of the molded body is scratched, and scratches become more noticeable. In addition, when the shape of the mold is devised to prevent appearance defects such as silver streaks and wrinkles, the degree of freedom in mold design is limited, and it may not be possible to obtain a molded body of the desired shape. Regarding appearance defects such as silver streaks and wrinkles, it is possible to correct the appearance defects by touch-up spray painting, etc., but in addition to the high work cost, there is a risk of the worker inhaling the solvent and damaging his health, so there is a practical problem when industrially mass-producing molded bodies. For this reason, a resin composition with reduced occurrence of appearance defects is required. Furthermore, in addition to reducing the occurrence of appearance defects, a resin composition is also required to have high fluidity so as not to cause poor filling into the mold during injection molding, as well as an excellent balance of mechanical properties such as rigidity, low-temperature impact resistance, and tensile properties. In particular, when thinning or foaming injection molded articles, there is a need for the material to be efficiently filled into the flow end and narrow mold cavities, so there is a demand for resin compositions with even better fluidity than before.

The present invention provides a polypropylene resin composition for automobile interior parts, which can produce injection molded articles that have excellent scratch resistance, reduced appearance defects, and an excellent balance of mechanical properties such as rigidity, low-temperature impact resistance, and tensile properties, as well as a method for producing the same and a molded article for automobile interior parts.

The present invention has the following aspects.
[1] A polypropylene-based resin composition comprising a polypropylene-based resin (A) including a continuous phase made of a propylene polymer and a rubber phase made of an ethylene-propylene copolymer, a propylene homopolymer (B), an ethylene-α-olefin copolymer (C) which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms, and optionally an inorganic filler (D), wherein the content of the polypropylene-based resin (A) is 63 to 85 % by mass based on the total mass of the (A) to (D),
The content of the propylene homopolymer (B) is 10 to 20% by mass based on the total mass of the (A) to (D),
The content of the ethylene-α-olefin copolymer (C) is 5 to 15 mass% based on the total mass of the (A) to (D),
In the case where the polypropylene-based resin composition contains an inorganic filler (D), the content of the inorganic filler (D) is 2 mass% or less based on the total mass of the (A) to (D),
The polypropylene resin composition has an MFR of more than 50 to 80 g/10 min at a temperature of 230° C. and a load of 2.16 kg,
The propylene polymer has a xylene insoluble content of 97.5% by mass or more based on the total mass of the propylene polymer;
the ratio (Mw/Mn) of the weight average molecular weight Mw to the number average molecular weight Mn of the propylene polymer is 3 to 10;
The propylene polymer has an ethylene-derived unit content of 0.5% by mass or less based on the total mass of the propylene polymer,
The propylene polymer has a propylene-derived unit content of 99.5% by mass or more,
the content of the ethylene-propylene copolymer is 25 to 35% by mass based on the total mass of the polypropylene-based resin (A);
the ethylene-propylene copolymer has an ethylene-derived unit content of 20 to 40% by mass based on the total mass of the ethylene-propylene copolymer;
The polypropylene-based resin (A) has a xylene-soluble portion having an intrinsic viscosity of 1.5 to 4.0 dl/g in tetrahydronaphthalene at 135° C.;
The polypropylene-based resin (A) has an MFR of 20 to 100 g/10 min at a temperature of 230° C. and a load of 2.16 kg;
The propylene homopolymer (B) has an MFR of 500 to 3,000 g/10 min at a temperature of 230° C. and a load of 2.16 kg;
The polypropylene resin composition for automobile interior parts, wherein the ethylene/α-olefin copolymer (C) has an MFR of 2.0 to 10 g/10 min at a temperature of 190° C. and a load of 2.16 kg.
[2] The polypropylene-based resin composition for automobile interior parts according to [1], wherein the ratio (Mw/Mn) of the weight average molecular weight Mw to the number average molecular weight Mn of the propylene polymer is 4 to 7. [3] The polypropylene-based resin composition for automobile interior parts according to [1] or [2], wherein the propylene polymer and the ethylene-propylene 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 a phthalate-based compound as an electron donor compound; (B) an organoaluminum compound; and (C) an organosilicon compound as an external electron donor compound. [4] A method for producing a polypropylene-based resin composition for automobile interior parts according to any one of [1] to [3], comprising the steps of: polymerizing an ethylene monomer and a propylene monomer in the presence of the propylene polymer using a catalyst containing the following components (A) to (C) to obtain the polypropylene resin:
(a) a solid catalyst containing, as essential components, magnesium, titanium, a halogen, and a phthalate-based compound as an electron donor compound; (b) an organoaluminum compound; and (c) an organosilicon compound as an external electron donor compound. [5] A molded article for automobile interior parts obtained by injection molding the polypropylene-based resin composition for automobile interior parts according to any one of [1] to [3].
[6] The molded article for automobile interior parts according to [5], which is a door trim, a glove box, a column cover, an instrument panel, a package tray, a rear tray, a pillar garnish, or a console box.
[7] The molded article for automobile interior parts according to [6], which is a door trim.

The polypropylene resin composition for automobile interior parts of the present invention has high fluidity and is therefore less likely to cause filling defects during injection molding. The molded articles for automobile interior parts obtained by injection molding have excellent scratch resistance and excellent appearance. Furthermore, even when manufacturing large-area parts such as door trims, which are prone to poor appearance with conventional resin compositions, the resin composition of the present invention can provide injection molded articles with excellent appearance. Furthermore, the obtained injection molded articles have an excellent balance of mechanical properties such as rigidity, low-temperature impact resistance, and tensile properties.

<Polypropylene Resin Composition>
The polypropylene resin composition for automobile interior parts of the present invention (hereinafter, abbreviated as "polypropylene resin composition") contains a polypropylene resin (A) (hereinafter, also referred to as component (A)) containing a continuous phase made of a propylene polymer and a rubber phase made of an ethylene-propylene copolymer, a propylene homopolymer (B) (hereinafter, also referred to as component (B)), and an ethylene-α-olefin copolymer (C) (hereinafter, also referred to as component (C)). It may also contain an inorganic filler (D) (hereinafter, also referred to as component (D)).

The content of the polypropylene resin (A) is 63 to 85 % by mass, preferably 70 to 80% by mass, and more preferably 72 to 78% by mass, based on the total mass of the components (A) to (D).
When the content is at least the lower limit of the above range, the low-temperature impact resistance of the injection-molded article is improved.
When it is equal to or less than the upper limit of the above range, the fluidity of the polypropylene resin composition is increased.

The content of the propylene homopolymer (B) is 10 to 20% by mass, and preferably 12 to 18% by mass, based on the total mass of the components (A) to (D).
When the content is equal to or more than the lower limit of the above range, the fluidity of the polypropylene resin composition is increased.
When the content is equal to or less than the upper limit of the aforementioned range, the low-temperature impact resistance of the injection-molded article is improved.

The content of the ethylene/α-olefin copolymer (C) is 5 to 15% by mass, and preferably 6 to 12% by mass, based on the total mass of the components (A) to (D).
When the content is at least 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 aforementioned range, the rigidity of the injection molded article is increased.

The polypropylene resin composition may contain an inorganic filler (D). The type of the inorganic filler (D) will be described later. The content of the inorganic filler (D) is 2 mass% or less, preferably 0.5 to 1.5 mass%, based on the total mass of the components (A) to (D).
When the content is at least the preferable lower limit of the above range, the rigidity of the injection molded article is increased.
When the content is equal to or less than the upper limit of the above range, the appearance of the injection molded article can be improved, the scratch resistance can be enhanced, and the lightweight nature of the injection molded article can be maintained.

The polypropylene resin composition has an MFR of from 50 to 80 g/10 min at a temperature of 230° C. and a load of 2.16 kg, preferably from 50 to 70 g/10 min, and more preferably from 50 to 65 g/10 min. Here, the MFR is a value measured by the measurement method described later.
If the resin composition is above the lower limit of the aforementioned range, even when a large-area part is manufactured, poor filling of the mold due to insufficient melt fluidity during injection molding will not occur, and the molten resin can reach particularly narrow parts and terminal parts in the mold, making it possible to accommodate thinning and foaming of injection-molded articles.
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.

[Polypropylene resin (A)]
The polypropylene-based resin (A) contained in the polypropylene-based resin composition of the present invention is one embodiment of an impact-resistant polypropylene polymer defined in JIS K6921-1, and is composed of two or more phases including a continuous phase of a propylene polymer and a rubber phase of an ethylene-propylene copolymer present as a dispersed phase in the continuous phase.
The polypropylene resin (A) may be a mixed resin obtained by mixing a propylene polymer and an ethylene-propylene copolymer during polymerization, or a mixed resin obtained by mixing a propylene polymer and an ethylene-propylene copolymer obtained separately by melt kneading. A resin having an excellent balance of rigidity, low-temperature impact resistance, and tensile properties (hereinafter also referred to as "mechanical property balance") at a lower cost is preferably a mixture of a propylene polymer and an ethylene-propylene copolymer during polymerization (polymerization mixture).
In the polymerization mixture, the propylene polymer and the ethylene-propylene copolymer can be mixed at the submicron order, so that a polypropylene resin composition based on the polymerization mixture exhibits an excellent balance of mechanical properties.
On the other hand, when a similar homogeneous mixture is realized and an excellent balance of mechanical properties is obtained by simply melt-kneading a propylene polymer and an ethylene-propylene copolymer obtained separately, the production cost is increased due to the need for separate steps such as storage, keeping, transportation, weighing, mixing, melt-kneading, etc. It is also not preferable from the viewpoint of energy cost.
Incidentally, the reason why the polymerization mixture and the mechanical mixture may show different physical properties is presumably due to differences in the dispersion state of the ethylene-propylene copolymer in the propylene polymer. However, at present, there is no known practical means for analyzing the dispersion state at the molecular level, including the state of the interface between the ethylene-propylene copolymer and the propylene polymer.
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 matter of the polypropylene resin (A) is 1.5 to 4.0 dl/g, preferably 1.5 to 3.5 dl/g, more preferably 2.0 to 3.0 dl/g, and even more preferably 2.2 to 2.6 dl/g.
When the content is at least 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 balance of mechanical properties of the injection molded article can be further improved.
Here, XSIV is a value measured in tetrahydronaphthalene at 135° C. The xylene solubles are a component obtained by dissolving a polypropylene resin sample in o-xylene at 135° C., cooling to 25° C., filtering the cooled solution using filter paper, and evaporating the filtrate to dryness.

The propylene polymer constituting the polypropylene-based resin (A) preferably has an MFR of 100 g/10 min or more at a temperature of 230° C. and a load of 2.16 kg.
When the content is within the above range, the MFR of the polypropylene resin composition can be sufficiently increased. The MFR of the propylene polymer is a value measured by the measuring method described below.

The xylene insoluble matter (hereinafter, also referred to as "XI") of the propylene polymer constituting the polypropylene-based resin (A) is 97.5 mass %, and preferably 98.0 mass %.
When the content is within the above range, the rigidity of the injection molded article can be further increased.
XI is a component obtained by dissolving a propylene polymer sample in o-xylene at 135° C., cooling the solution to 25° C., filtering the cooled solution through filter paper, and collecting the residue on the filter paper. The amount of XI is a value measured by the method described below.

The ratio ( _Mw / _Mn ) of the weight average molecular weight _Mw to the number average molecular weight _Mn of the propylene polymer constituting the polypropylene resin (A) is from 3 to 10, preferably from 4 to 7, and more preferably from 4.5 to 6.5.
When the content is at least the lower limit of the above range, the appearance of the injection molded article can be made good.
When the content is equal to or less than the upper limit of the above range, the tensile properties of the injection molded article can be further improved.
Here, the weight average molecular weight _Mw and number average molecular weight _Mn of the propylene polymer are values measured by gel permeation chromatography (GPC), specifically, values measured by the method described below.

The ethylene-derived unit content (hereinafter also referred to as "C2") in the propylene polymer constituting the polypropylene-based resin (A) is 0.5 mass% or less based on the total mass of the propylene polymer. Therefore, the propylene-derived unit content in the propylene polymer is 99.5 mass% or more. When C2 is equal to or less than the upper limit (i.e., when the propylene-derived unit content is equal to or more than the lower limit), the rigidity of the injection-molded article is increased.
The lower limit of C2 is not particularly limited, and may be 0 mass %.
Therefore, the propylene polymer may be a polypropylene homopolymer consisting only of propylene-derived units, or may be a copolymer consisting of 99.5 mass% or more and less than 100 mass% propylene-derived units and more than 0 mass% and 0.5 mass% or less ethylene-derived units, but from the viewpoint of increasing the rigidity of the obtained injection-molded article, it is preferable that C2 is 0 mass%.
C2 is measured by ¹³ C-NMR spectroscopy.

The ethylene-propylene copolymer constituting the polypropylene-based resin (A) is a copolymer having ethylene-derived units and propylene-derived units.
The content of ethylene-derived units in the ethylene-propylene copolymer constituting the polypropylene-based resin (A) is 20 to 40 mass%, preferably 20 to 35 mass%, and more preferably 25 to 30 mass%, based on the total mass of the ethylene-propylene copolymer.
When the content is at least 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 tensile properties of the injection molded article can be further improved.
The content of ethylene-derived units in the ethylene-propylene copolymer is measured by ¹³ C-NMR spectroscopy.

The content of the ethylene-propylene copolymer relative to the total mass of the polypropylene resin (A) is from 25 to 35 mass %, and more preferably from 27 to 33 mass %.
When the content is at least 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 blockage of flow paths in production equipment due to deterioration of powder fluidity during production of the polypropylene-based resin (A) can be reduced, so that the polypropylene-based resin (A) can be stably and continuously produced.

The polypropylene resin (A) has an MFR of 20 to 100 g/10 min at a temperature of 230° C. and a load of 2.16 kg, preferably 25 to 50 g/10 min, more preferably 30 to 45 g/10 min, and even more preferably 32 to 42 g/10 min. Here, the MFR is a value measured by the measurement method described later.
When the resin composition is equal to or greater than the lower limit of the above range, even when manufacturing large-area parts, poor filling of the mold due to insufficient melt fluidity during injection molding does not occur, and the molten resin can reach particularly narrow parts and end parts of the mold.
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.

[Propylene homopolymer (B)]
The propylene homopolymer (B) is a polypropylene homopolymer (HOMO) as defined in JIS K6921-1.

The MFR of the propylene homopolymer (B) at a temperature of 230° C. and a load of 2.16 kg is 500 to 3000 g/10 min, preferably 1000 to 2500 g/10 min, and more preferably 1500 to 2000 g/10 min. Here, the MFR is a value measured by the measurement method described later.
When the content is equal to or more than the lower limit of the above range, the fluidity of the polypropylene resin composition is increased.
When the content is equal to or less than the upper limit of the above range, the propylene homopolymer (B) can be produced stably, and therefore a high-quality propylene homopolymer (B) can be used.

The xylene insoluble matter (XI) of the propylene homopolymer (B) is preferably 95% by mass or more, more preferably 96% by mass or more, and even more preferably 97% by mass or more.
When XI is at least the lower limit of the above range, the composition has excellent rigidity.
XI is a component obtained by dissolving a sample of propylene homopolymer (B) in o-xylene at 135° C., cooling the solution to 25° C., filtering the cooled solution through filter paper, and collecting the residue on the filter paper. The amount of XI is a value measured by the method described below.

The ratio (Mw/Mn) of the weight average molecular weight Mw to the number average molecular weight Mn of XI of the propylene homopolymer (B) is preferably from 2.0 to 5.0, more preferably from 2.5 to 5.0.
When the content is at least as large as the lower limit of the above range, the appearance of the injection-molded article can be made more excellent.
When it is equal to or less than the upper limit of the above range, the injection molded article has better low-temperature impact resistance and tensile properties.

Propylene homopolymer (B) may contain units derived from monomers other than propylene in an amount of less than 0.5% by mass relative to the total mass of component (B) due to recycled gases or the like generated during the production of a polymer containing a copolymer component.

[Ethylene-α-olefin copolymer (C)]
The ethylene/α-olefin copolymer (C) 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 (C) include ethylene/butene copolymers, ethylene/pentene copolymers, ethylene/hexene copolymers, and ethylene/octene copolymers.
Among these, in consideration of the ease of procurement as a raw material, economic efficiency, and the like, ethylene-butene copolymers and ethylene-octene copolymers are preferred.

The MFR of the ethylene/α-olefin copolymer (C) is 2.0 to 10 g/10 min at 190° C. and a load of 2.16 kg, preferably 3.0 to 7.0 g/10 min, and more preferably 3.5 to 6.0 g/10 min.
When the content is equal to or more than the lower limit of the above range, the fluidity of the polypropylene resin composition is increased.
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, and continuous production of the composition can be improved. Also, the low-temperature impact resistance of the injection-molded article can be improved.

[Inorganic filler (D)]
Examples of the inorganic filler (D) include natural silicic acid or silicates such as talc, kaolinite, clay, bilophyllite, selinite, wollastonite, and mica; synthetic silicic acid or silicates such as calcium silicate hydrate, aluminum silicate hydrate, silicic acid hydrate, 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.
From the viewpoint of shape, examples of the inorganic filler include the following:
Powdered fillers such as synthetic silicic acids or silicates 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 fibers.
The inorganic filler may be used alone or in combination with two or more kinds. In order to improve the dispersibility of these fillers, the inorganic fillers may be surface-treated as necessary. The inorganic fillers used in the present invention are not limited, but from the viewpoint of enhancing the balance of mechanical properties by promoting the orientation of polypropylene crystals in injection molding, plate-like inorganic fillers are preferred. As the plate-like inorganic filler, known materials such as talc, kaolinite, clay, and mica can be used, but considering the affinity with polypropylene resins, ease of procurement as a raw material, and economic efficiency, talc and mica are preferred, and talc is more preferred.

The volume average particle diameter of the inorganic filler (D) is preferably 1 to 10 μm, more preferably 2 to 7 μm. If the volume average particle diameter is within the above range, the mechanical property balance of the injection molded article is improved. The volume average particle diameter can be measured as the 50% diameter in the cumulative volume fraction by the laser diffraction method (based on JIS R1629).

[Other ingredients]
The polypropylene resin composition of the present invention may contain, as optional components, resins or elastomers other than the polypropylene resin (A), the propylene homopolymer (B), and the ethylene-α-olefin copolymer (C), and additives other than the inorganic filler (D), within a range that does not impair the effects of the present invention.
Examples of additives other than the inorganic filler (D) include antioxidants, neutralizing agents, nucleating agents, weathering agents, pigments (organic or inorganic), internal lubricants, external lubricants, antiblocking agents, antistatic agents, chlorine absorbers, heat stabilizers, light stabilizers, ultraviolet absorbers, slip agents, antifogging agents, flame retardants, dispersants, copper inhibitors, plasticizers, foaming agents, bubble inhibitors, crosslinking agents, peroxides, oil extenders, etc. The polypropylene resin composition may contain only one type of resin, elastomer, or additive, or two or more types. The content may be a known amount.

<Method of producing polypropylene resin composition>
As a method for producing the above-mentioned polypropylene-based resin composition, a method of mixing the polypropylene-based resin (A), the propylene homopolymer (B), the ethylene-α-olefin copolymer (C), and the optional inorganic filler (D) and then melt-kneading the mixture can be mentioned.
The mixing method may be a dry blending method using a mixer such as a Henschel mixer, a tumbler, or a ribbon mixer.
The melt-kneading method includes 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 case of 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 a propylene polymer and an ethylene-propylene copolymer during polymerization, or by mixing a propylene polymer and an ethylene-propylene copolymer which have been separately produced, by melt kneading.
The polypropylene-based resin (A) is preferably a polymerization mixture in which a propylene polymer and an ethylene-propylene copolymer are mixed during polymerization.
Such a polymerization mixture is obtained by polymerizing ethylene monomers and propylene monomers in the presence of a propylene polymer. In this method, the ethylene-propylene copolymer is produced in the presence of a propylene polymer, which not only increases the productivity but also increases the dispersibility of the ethylene-propylene copolymer in the propylene polymer, thereby improving the balance of mechanical properties of the injection molded article obtained using the ethylene-propylene copolymer.

As a method for producing the polymerization mixture, a multi-stage polymerization method is typically used. For example, in a first-stage polymerization reactor of a polymerization apparatus equipped with two-stage polymerization reactors, a propylene monomer and, if necessary, an ethylene monomer are polymerized to obtain a propylene polymer, and the obtained propylene polymer is supplied to a second-stage polymerization reactor, and the ethylene monomer and the propylene monomer are polymerized in the second-stage 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 include a slurry polymerization method in which propylene is in a liquid phase and has high monomer density and productivity. The second-stage polymerization conditions include a gas phase polymerization method, which generally makes it easy to produce a copolymer that is highly soluble 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 equal to or higher than the lower limit of the above range, the productivity and the stereoregularity of the obtained polypropylene are superior.
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 as necessary to adjust the molecular weight. By adjusting the molecular weight of the propylene polymer or ethylene-propylene copolymer, the MFR of the polypropylene resin and therefore the MFR of the polypropylene resin composition can be adjusted.
Before the polymerization in the first-stage polymerization reactor, propylene may be prepolymerized in order to form polymer chains on the solid catalyst component as a foothold for the subsequent main polymerization. The prepolymerization is usually carried out at 40° C. or less, preferably 30° C. or less, more preferably 20° C. or less.

As the catalyst, a known olefin polymerization catalyst can be used.
As a catalyst for polymerizing an ethylene monomer and a propylene monomer in the presence of the propylene polymer, a stereospecific Ziegler-Natta catalyst is preferable, and a catalyst containing the following components (A), (B), and (C) (hereinafter also referred to as "catalyst (X)") is particularly preferable.
(a) A solid catalyst containing, as essential components, 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.

The polypropylene-based resin (A) is preferably produced by a process including a step of polymerizing an ethylene monomer and a propylene monomer in the presence of the propylene polymer using a catalyst (X) to obtain the polypropylene-based resin. By using the catalyst (X), a polypropylene-based resin (A) having each physical property within the above-mentioned range can be easily obtained.
The distribution of stereoregularity of the propylene polymer obtained varies depending on the catalyst used (especially the electron donor compound of component (A)), and this difference affects the crystallization behavior, but the details of the relationship have not been clarified. In order to clarify this, it is necessary to analyze the molecular weight distribution and stereoregularity distribution together as molecular structures, but it is complicated because components with different molecular weights and stereoregularities affect each other in the crystallization process, making it more difficult to interpret the effect of stereoregularity distribution on crystallization behavior. Furthermore, since actual injection molding is performed at a very high speed and in a fluid state, it is not easy to grasp the phenomenon even if advanced analytical techniques are used. Therefore, it is almost impossible to specify the difference in crystallization behavior due to the stereoregularity distribution in terms of numerical values, etc., in a polypropylene resin composition obtained using a specific catalyst.

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 ; alkoxy titanium 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 ; alkoxy titanium 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 alkoxy titanium dihalides such as Ti(OCH ₃ ) ₃ Cl and Ti(OC ₂ H ₅ ). 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 alone} or in combination of _two or more.
Among the above titanium compounds, preferred are halogen-containing titanium compounds, more preferred are titanium tetrahalides, and particularly preferred is titanium tetrachloride (TiCl ₄ ).

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, butylmagnesium hydride, etc. These magnesium compounds can also be used in the form of a complex compound with, for example, organoaluminum, etc., 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; alkoxy magnesium halides such as methoxy magnesium chloride, ethoxy magnesium chloride, isopropoxy magnesium chloride, butoxy magnesium chloride, and octoxy magnesium chloride; aryloxy magnesium halides such as phenoxy magnesium chloride and methylphenoxy magnesium chloride; alkoxy magnesium such as ethoxy magnesium, isopropoxy magnesium, butoxy magnesium, n-octoxy magnesium, and 2-ethylhexoxy magnesium; dialkoxy magnesium such as dimethoxy magnesium, diethoxy magnesium, dipropoxy magnesium, dibutoxy magnesium, and ethoxy methoxy magnesium; and aryloxy magnesium such as ethoxypropoxy magnesium, butoxyethoxy magnesium, phenoxy magnesium, and dimethylphenoxy magnesium. 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 compound as an essential component. By using catalyst (X) containing a phthalate compound as an electron donor, a polypropylene resin having a propylene polymer _Mw / _Mn 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, diphenyl phthalate, etc. Among these, diisobutyl phthalate is particularly preferred.

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

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.

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, 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 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-iso 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-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.

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, R ¹ _2.5 Al(OR ² ) _0.5 (R ¹ , R ² are hydrocarbon groups which may be different or the same. ) 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, alkylaluminum dihalides such as ethylaluminum dichloride, propylaluminum dichloride, and butylaluminum dibromide, partially halogenated alkylaluminums such as dialkylaluminum hydrides such as diethylaluminum hydride and dibutylaluminum hydride, alkylaluminum dihydrides such as ethylaluminum dihydride and propylaluminum dihydride, partially hydrogenated alkylaluminums such as ethylaluminum ethoxychloride, butylaluminum butoxychloride, and partially alkoxylated and halogenated alkylaluminums such as ethylaluminum ethoxybromide, butylaluminum butoxychloride, and ethylaluminum ethoxybromide, etc. may be mentioned. The above component (I) may be used alone or in combination of two or more kinds.

As the external electron donor compound of component (c), an organosilicon compound is used.
Preferred organic silicon 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, gamma-chloropropyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, t-butyltriethoxysilane, thexyltrimethoxysilane, n-butyltriethoxysilane, iso-butyltriethoxysilane, phenyltriethoxysilane, gamma-aminopropyltriethoxysilane, chlorotriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, 2-norbornanetrimethoxysilane, 2-norbornanetriethoxysilane, 2-norbornanemethyl 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-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 kinds.

The organosilicon compound plays an important role in adjusting the amount of xylene insoluble matter to the range specified in the present invention. When other catalyst components are the same, the amount of xylene insoluble matter depends on the type and amount of organosilicon compound and polymerization temperature, but even when a suitable organosilicon compound is used, the amount of organosilicon compound is significantly reduced when the amount of organosilicon compound is 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 using a phthalate-based compound as an internal 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) are reduced.Specifically, when using a phthalate-based compound 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.

As the catalyst (X), it is preferable that 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 a propylene polymer may be polymerized in a plurality of polymerization reactors, or an ethylene-propylene copolymer may be polymerized in a plurality of polymerization reactors.
The polymerization mixture may be obtained by 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 an uprising pipe and polymerized, and a monomer is supplied to a downcomer pipe connected to the uprising pipe and polymerized, and a polymerization product is recovered while circulating between the uprising pipe and the downcomer pipe. In this method, a means is provided for completely or partially preventing the gas mixture present in the uprising pipe from entering the downcomer pipe. Also, a gas and/or liquid mixture having a composition different from that of the gas mixture present in the uprising pipe is introduced into the downcomer pipe. For example, the method described in JP-A-2002-520426 can be applied to this polymerization method.

(Method for producing propylene homopolymer (B))
The method for producing the propylene homopolymer (B) is not particularly limited, and for example, it can be produced by polymerizing a monomer using a catalyst containing (a) a solid catalyst component containing magnesium, titanium, a halogen, and an internal electron donor compound as essential components, (b) an organoaluminum compound, and (c) an external electron donor compound. Known components can be used as these components. However, from the viewpoint of achieving a relatively high MFR, it is preferable that the internal electron donor compound is the above-mentioned 1,3-diether. Alternatively, the propylene homopolymer (B) used in the present invention may be produced using a metallocene catalyst.

(Method for producing ethylene/α-olefin copolymer (C))
The ethylene/α-olefin copolymer (C) 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.

<Molded body for automobile interior parts>
The molded article for automobile interior parts of the present invention can be produced by injection molding the above polypropylene resin composition.
The molding temperature is generally 150 to 350 ° C, preferably 170 to 250 ° C. If the molding temperature exceeds 350 ° C, it will cause deterioration of the resin composition and molding defects, and if it is lower than 150 ° C, the fluidity will decrease, causing poor appearance and molding defects due to insufficient filling into the mold. It is preferable to carry out the molding temperature in the range of 10 to 60 ° C. If the mold temperature exceeds 60 ° C, the molded body will have an excellent surface finish and a molded body with excellent rigidity will be obtained, but the molding cycle will be long and productivity will decrease. On the other hand, if the mold temperature is set to a temperature lower than 10 ° C, warping and shrinkage will become significant, making it difficult to obtain a satisfactory molded body, and condensation will easily occur on the mold, causing mold corrosion to progress. It is also not suitable from the viewpoint of energy costs related to cooling.

In order to increase the strength of the product, it is preferable that the molded body for automobile interior parts of the present invention has ribs formed on the non-design surface. By using the polypropylene resin composition of the present invention, even when ribs are formed, the molten resin can be sufficiently filled into the grooves for forming the ribs, and the occurrence of silver streaks and wrinkles can be suppressed, resulting in a molded body with excellent appearance. Specifically, the composition can be applied to automobile interior parts that are generally manufactured by injection molding using polypropylene resin compositions, such as door trims, glove boxes, column covers, instrument panels, package trays, rear trays, pillar garnishes, and console boxes for passenger cars. In particular, the effect is remarkable when applied to door trims, which have a large design surface area.

The flexural modulus of the molded article for automobile interior parts of the present invention is preferably 900 MPa or more, more preferably 950 MPa or more, and even more preferably 1000 MPa or more.
It can be said that the higher the flexural modulus value, the more excellent the rigidity of the molded article for automobile interior parts.

The Charpy impact strength at −20° C. of the molded article for automobile interior parts of the present invention is preferably 4.0 kJ/m ² or more, more preferably 4.5 kJ/m ² or more, and even more preferably 5.0 kJ/m ² or more.
It can be said that the higher the value of the Charpy impact strength at low temperature, the more excellent the low-temperature impact resistance of the molded article for automobile interior parts.

For automobile interior parts, it is preferable that the mode of fracture is ductile rather than brittle fracture. In other words, it is preferable that there is little risk of injury to the human body from the fracture surface due to sudden fracture or explosion, and tensile properties such as the nominal tensile fracture strain are sometimes emphasized as a safety design index. The nominal tensile fracture strain of the molded body for automobile interior parts of the present invention is preferably 30% or more, more preferably 40% or more, and even more preferably 45% or more. It can be said that the higher the nominal tensile fracture strain value, the more excellent the tensile properties of the molded body for automobile interior parts.

The following are examples and comparative examples, but the present invention is not limited to the following examples.

<Preparation of Copolymer 1>
A solid catalyst supported on _MgCl2 with _TiCl4 and diisobutylphthalate as an internal donor was prepared according to the method described in Example 5 of EP 728769.
Next, the solid catalyst was contacted with triethylaluminum (TEAL) as an organoaluminum compound and dicyclopentyldimethoxysilane (DCPMS) as an external electron donor compound at 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 the organosilicon compound/organoaluminum described above of 0.05).
The obtained catalyst (X) was kept in a suspended state in liquid propylene at 20° C. for 5 minutes to carry out prepolymerization.
The obtained prepolymer was introduced into the first polymerization reactor of a polymerization apparatus equipped with two polymerization reactors in series to produce a propylene homopolymer, and a propylene-ethylene copolymer was produced in the second polymerization reactor. During the polymerization, the temperature and pressure were adjusted, and hydrogen was used as a molecular weight regulator.
The polymerization temperature and the ratio of reactants were 80°C, 2.24 mol% in the first reactor, and 80°C, 1.75 mol% in the second reactor, and 0.21 mol% in the second reactor. The residence time distribution of the first and second reactors was adjusted so that the amount of the copolymer component was 30% by mass. The copolymer 1 was obtained by the above method.
The obtained copolymer 1 is a polymer mixture of component (1), which is a propylene polymer constituting the continuous phase, and component (2), which is an ethylene-propylene copolymer constituting the rubber phase, and is the above-mentioned polypropylene-based resin (A).
With respect to copolymer 1, the MFR of component (1), the XI of component (1), the Mw/Mn 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 polymer, component (2) is an ethylene-propylene copolymer, and component (1)+component (2) is a polypropylene-based resin (A).
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".

<Preparation of Copolymer 2>
Copolymer 2 consisting of a polymerization mixture of component (1) and component (2) was 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 a molar ratio of 0.41 so that the content of ethylene-derived units in component (2) was 42 mass%.
Copolymer 2 was measured in the same manner as copolymer 1. The measured values are shown in Table 1.
Incidentally, component (1) is a propylene polymer, component (2) is an ethylene-propylene copolymer, and component (1)+component (2) is a polypropylene-based resin (A).

<Preparation of Copolymer 3>
Copolymer 3 consisting of a polymerization mixture of component (1) and component (2) was obtained by the same production method as for copolymer 1, except that the hydrogen concentration in the first reactor was changed to 2.00 mol %, the hydrogen concentration in the second reactor was changed to 2.04 mol %, and the ratio of ethylene to the total of ethylene and propylene was changed to 0.45 mol %, respectively.
With respect to copolymer 3, the MFR of component (1), the XI of component (1), the Mw/Mn 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) were as shown in Table 1.
Incidentally, component (1) is a propylene polymer, component (2) is an ethylene-propylene copolymer, and component (1)+component (2) is a polypropylene-based resin (A).

<Preparation of Copolymer 4>
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-neck round-bottom flask purged with nitrogen, 250 mL of _TiCl4 was introduced at 0°C. With stirring, 10.0 g of finely divided spherical _MgCl2 · _1.8C2H5OH (prepared according to the method described in Example 2 of USP- _4,399,054 , but operating at 3000 rpm instead of 10000 rpm) and 9.1 mmol of diethyl-2,3-(diisopropyl)succinate were added. The temperature was raised to 100°C and held for 120 minutes. Then, the stirring was stopped, the solid product was allowed to settle, and the supernatant liquid was siphoned off. The following operation 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 x 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 mass ratio of TEAL to the solid catalyst was 18 and the mass ratio of TEAL/DCPMS was 10. The obtained catalyst system was prepolymerized by holding it in a suspended state in liquid propylene at 20° C. for 5 minutes. The obtained prepolymer was introduced into a liquid-phase polymerization reactor of a polymerization apparatus equipped with a liquid-phase polymerization reactor and a gas-phase polymerization reactor in series, and a propylene polymer was produced in the liquid phase state of propylene in the first-stage polymerization reactor, and an ethylene-propylene copolymer was produced in the second-stage gas-phase polymerization reactor. During polymerization, the polymerization temperature was set to 80° C., and the polymerization pressure and the amount of catalyst added were adjusted, and the ratio of ethylene to the total of ethylene and propylene was adjusted to 0.35 molar ratio by adjusting the ethylene supply amount and the propylene supply amount in the second stage so that the ethylene-derived unit content of component (2) was a predetermined amount. In addition, hydrogen was used as a molecular weight regulator, and the hydrogen concentration was set to 0.60 mol% in the first stage and 2.45 mol% in the second stage so that the MFR and XSIV of component (1) + component (2) were set to the specified values. In addition, the residence time distribution of the first and second stages was adjusted so that the mass ratio of component (2) / [component (1) + component (2)] was set to the specified amount. By the above method, the target copolymer 4 was obtained.
With respect to copolymer 4, the MFR of component (1), the XI of component (1), the Mw/Mn 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) were as shown in Table 1.
Incidentally, component (1) is a propylene polymer, component (2) is an ethylene-propylene copolymer, and component (1)+component (2) is a polypropylene-based resin (A).

<Preparation of Copolymer 5>
Copolymer 5, consisting of a polymerization mixture of component (1) and component (2), was obtained by the same production method as for copolymer 1, except that the same prepolymer as copolymer 4 was used and the hydrogen concentration in the first reactor was changed to 1.11 mol %, the hydrogen concentration in the second reactor, and the ratio of ethylene to the total of ethylene and propylene were changed to 1.75 mol % and 0.22 molar ratio, respectively.
With respect to copolymer 5, the MFR of component (1), the XI of component (1), the Mw/Mn 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.
Incidentally, component (1) is a propylene polymer, component (2) is an ethylene-propylene copolymer, and component (1)+component (2) is a polypropylene-based resin (A).

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, 0.05 g of H-BHT manufactured by Honshu Chemical Industry Co., Ltd. was added, and the mixture was homogenized using a dry bland. Then, measurements were performed at a temperature of 230° C. and a load of 2.16 kg in accordance with JIS K6921-2.

<Component (1) XI>
A 2.5 g sample of component (1) polymerized in the first reactor was dissolved in 250 mL of xylene at 135° C. with stirring. After 20 minutes, the solution was cooled to 25° C. with stirring and then allowed to stand for 30 minutes. The precipitate was filtered through a paper filter, the solution was evaporated in a nitrogen stream, and the residue was dried under vacuum at 80° C. until a constant weight was reached. The mass % of the polymer soluble in xylene at 25° C. was thus calculated.
The amount of xylene insolubles (XI) (mass % of polymer insoluble in xylene at 25° C.) is calculated by subtracting "mass % of soluble polymer" from "100" and is considered to be the amount of isotactic components of the polymer.

<Mw/Mn of component (1)>
The component (1) collected as described above was used as a sample, and the number average molecular weight (Mn) and weight average molecular weight (Mw) were measured as described below. The weight average molecular weight (Mw) was divided by the number average molecular weight (Mn) to determine the molecular weight distribution (Mw/Mn).
The apparatus used was a PL GPC220 manufactured by Polymer Laboratories, Inc., and 1,2,4-trichlorobenzene containing an antioxidant was used as the mobile phase. The columns used were UT-G (1 column), UT-807 (1 column), and UT-806M (2 columns) manufactured by Showa Denko K.K. connected in series, and a differential refractometer was used as the detector. The same solvent as that of the mobile phase was used for the sample solution of component (1), and the measurement sample was prepared by dissolving the sample at a sample concentration of 1 mg/mL for 2 hours while shaking at a temperature of 150°C. 500 μL of the sample solution thus obtained was injected into the column, and the measurement was performed at a flow rate of 1.0 mL/min, a temperature of 145°C, and a data acquisition interval of 1 second. For column calibration, polystyrene standard samples (Shodex) with molecular weights of 5.8 to 7.45 million were used.
The measurement was performed using a cubic approximation using a standard polystyrene sample (STANDARD, manufactured by Showa Denko K.K.). The Mark-Houwink-Sakurada coefficients used were K=1.21×10-4, α=0.707 for the polystyrene standard sample, and K=1.37×10-4, α=0.75 for the propylene polymer.

<Total Ethylene Content of Copolymers 1 to 5 and Ethylene-Derived Unit Content of Component (1)>
For each sample of copolymers 1 to 5 dissolved in a mixed solvent of 1,2,4-trichlorobenzene/deuterated benzene, a 13 C-NMR spectrum was obtained using a Bruker AVANCEIII HD400 (13 C resonance frequency 100 MHz) under the conditions of a measurement temperature of ¹²⁰ ° C., a flip angle of 45 degrees, a pulse interval of 7 seconds, a sample rotation speed of 20 Hz, and an accumulation number of 5000.
Using the spectrum obtained above, the total ethylene content (mass%) of Copolymers 1 to 5 was determined by the method described in M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 15, 1150-1152 (1982).
When component (1) 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 (1).

<Content of Ethylene-Derived Units in Component (2)>
The ethylene-derived unit content (mass%) of component (2) was calculated in the same manner as for the total ethylene amount, 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 amount of copolymers 1 to 5 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.

<Mass ratio component (2)/[component (1)+component (2)]>
The mass ratio was calculated according to the following formula.
Component (2)/[Component (1)+Component (2)] (unit: mass%)=
Total ethylene content of copolymers 1 to 5/(content of ethylene-derived units in component (2)/100)

<XSIV of component (1) + component (2)>
The xylene soluble fractions of Copolymers 1 to 5 were obtained by the following method, and the intrinsic viscosity (XSIV) of the xylene soluble fractions was measured.
2.5 g of each sample of copolymers 1 to 5 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 a reflux device while purging with nitrogen at 135°C until completely dissolved, and then cooled at 25°C for 1 hour. The solution thus obtained was filtered using filter paper. 100 mL of the filtrate after filtration 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 a 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 each of Copolymers 1 to 5, 0.05 g of H-BHT manufactured by Honshu Chemical Industry Co., Ltd. was added, and the mixture was homogenized using a dry bland, and then measured at a temperature of 230° C. and a load of 2.16 kg according to JIS K6921-2.

[Examples 1 to 6, Comparative Examples 1 to 5]
As a polypropylene-based resin composition intended for automobile interior parts such as door trim, components (A) to (D) were blended in the composition shown in Table 2, and 0.2 parts by mass of B225 manufactured by BASF as an antioxidant, 0.05 parts by mass of DHT-4A manufactured by Kyowa Chemical Industry Co., Ltd. as a neutralizing agent, 0.1 parts by mass of ADK STAB NA11 manufactured by ADEKA CORPORATION as a nucleating agent, 0.3 parts by mass of ADK STAB LA502XP manufactured by ADEKA CORPORATION as a weather resistance agent, 0.3 parts by mass of TS-5 manufactured by Kao Corporation as an antistatic agent, and 0.5 parts by mass of an inorganic pigment (a mixture of 60% by mass of Carbon Black IP-1000 manufactured by Cabot Corporation and 40% by mass of Titanium White CR-60 manufactured by Ishihara Sangyo Kaisha, Ltd.) were added relative to 100 parts by mass of the total amount of components (A) to (D), and 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 manufactured by JSW Corp. The strand was cooled in water and then cut with a pelletizer to obtain pellets of a polypropylene-based resin composition.
The polypropylene resin compositions thus produced and the injection molded articles obtained using them were evaluated for various physical properties. The results are shown in Table 2.

The components in Table 2 are as follows.
Component (A) is Copolymers 1 to 5 in Table 1.

Component (B) is a powdery propylene homopolymer 1 (MFR=1800 g/10 min, XI=97.7% by mass, Mw/Mn of XI=4.5) produced by the following method.
1) Preparation of solid catalyst component A solid catalyst component was prepared according to Example 1 of European Patent Application EP 728769. Specifically, it was prepared as follows.
225 ml of _TiCl4 was introduced into a 500 ml reactor equipped with a porous barrier at 0°C. 10.1 (54 _mmol ) g of microspherical _MgCl2 · _2.1C2H5OH was added in 15 minutes under nitrogen atmosphere while stirring the contents. The preparation method of said _MgCl2 · _2.1C2H5OH will be described later. At the end of _the addition, the temperature was brought to 70°C, 9 mmol of 9,9-bis(methoxymethyl)fluorene was added, the contents were heated to 100°C and reacted at this temperature for 2 hours. _TiCl4 was then filtered off. 200 ml of _TiCl4 and 9 mmol of 9,9-bis(methoxymethyl)fluorene were added again and the contents were reacted at 120°C for 1 hour. It was then filtered again, 200 ml of fresh _TiCl4 was added, and the contents were reacted at 120° C. for an additional hour, then filtered and washed with n-heptane at 60° C. until all chloride ions were absent from the filtrate. The solid component was analyzed and found to contain 3.5% by weight Ti and 16.2% by weight 9,9-bis(methoxymethyl)fluorene.
The microspherical _{MgCl2.2.1C2H5OH} adduct was prepared as follows: _{48 g} of _MgCl2 , 77 g of anhydrous _C2H5OH and 830 _ml of _kerosene were introduced into a 2 liter autoclave, complete with turbine agitator and dip pipe, at ambient temperature under an inert gas atmosphere. The contents were heated to 120°C with stirring, resulting in the formation of an adduct between _MgCl2 and the alcohol. The adduct was melted and mixed with the dispersant. A nitrogen pressure of 15 atmospheres was maintained inside the autoclave. The dip pipe of the autoclave was heated to 120°C externally by a heating jacket. The inside diameter of the heating jacket was 1 mm and its length from end to end was 3 m. The mixture was circulated through the pipe at a speed of 7 m/s. The dispersion was collected in a 5 liter flask with stirring. The flask contained 2.5 liters of kerosene and was cooled externally by a jacket maintained at an initial temperature of -40°C. The final temperature of the emulsion was 0°C. The spherical solid product, constituting the dispersed phase of the emulsion _, was separated by settling and filtration, then washed with heptane and dried. All the above operations were carried out in an inert atmosphere. 130 g of _{MgCl2.3.0C2H5OH} were obtained in the form of solid spherical particles with a maximum diameter of less than 50μ. The product was then de-alcoholized in a nitrogen stream at a temperature gradually increasing from 50°C to 100°C until _the alcohol content was 2.1 moles per mole of _MgCl2 .
2) Polymerization In a pre-contact vessel, 7 mg of the solid catalyst component obtained above was contacted with 0.56 mmol of dicyclopentylmethoxysilane (DCPMS) and 7 mmol of TEAL in 80 ml of anhydrous n-hexane at 10° C. for 20 minutes. The obtained catalyst system was introduced into a 4-liter stainless steel autoclave equipped with a horseshoe stirrer and purged with a nitrogen flow for 1 hour, and prepolymerization was carried out by maintaining the suspension in liquid propylene at 20° C. for 10 minutes. Subsequently, hydrogen (used for the purpose of adjusting MFR) was fed to the liquid propylene so as to be 1.50 mol %, and the contents were polymerized at a polymerization temperature of 70° C. using the obtained prepolymer. Thereafter, unreacted monomers were removed, and the target polymer was recovered and dried in an oven at 70° C. under a nitrogen flow for 3 hours.

<XI and Mw/Mn of XI of component (B)>
The amount of XI and Mw/Mn of XI of component (B) were determined by the same method as for XI and Mw/Mn of component (1) described above. XI is a component obtained by dissolving a sample of component (B) in o-xylene at 135°C, cooling to 25°C, filtering the cooled solution using filter paper, and collecting the precipitate remaining on the filter paper, as described above. XI was obtained by thoroughly washing away the xylene remaining in the precipitate with methanol, and then drying at 80°C under vacuum.

Component (C) is the following ethylene/α-olefin copolymer.
C-1: Engage 8200, ethylene-octene copolymer, MFR = 5.0 g/10 min, manufactured by The Dow Chemical Company. C-2: Tafmer A-4050S, ethylene-butene copolymer, MFR = 3.6 g/10 min, manufactured by Mitsui Chemicals, Inc. Component (D) is an inorganic filler, specifically the following talc.
Talc: Neotalc UNI05, manufactured by Neolite Kosan Co., Ltd. Volume average particle size measured by laser diffraction method: 5 μm
The other components are the following additives:
Antioxidant: BASF B225
Neutralizer: Kyowa Chemical Industry Co., Ltd. DHT-4A
Nucleating agent: Adeka STAB NA11 manufactured by ADEKA CORPORATION
Weatherproofing agent: Adeka STAB LA502XP manufactured by ADEKA CORPORATION
Antistatic agent: Kao Corporation TS-5
Inorganic pigment: a mixture of 60% by mass of carbon black IP-1000 manufactured by Cabot Corporation and 40% by mass of titanium white CR-60 manufactured by Ishihara Sangyo Kaisha, Ltd.

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

<Liquidity MFR>
For component (B), 0.05 g of H-BHT manufactured by Honshu Chemical Industry Co., Ltd. was added to 5 g of the sample, which was then homogenized using a dry bland, and the measurement was performed at a temperature of 230° C. and a load of 2.16 kg in accordance with JIS K6921-2.
For component (C), the measurement was performed according to JIS K6922-2 under conditions of a temperature of 190° C. and a load of 2.16 kg.
For the polypropylene resin composition, the measurement was performed under conditions of a temperature of 230° C. and a load of 2.16 kg in accordance with JIS K6921-2.

<Rigidity and bending modulus>
In accordance with JIS K6921-2, a multipurpose test piece (Type A1) as defined in JIS K7139 was injection molded from the polypropylene resin composition using an injection molding machine (FANUC ROBOSHOT S2000i manufactured by FANUC CORPORATION) under conditions of a molten resin temperature of 200° C., a mold temperature of 40° C., an average injection speed of 200 mm/sec, a pressure retention time of 40 sec, and a total cycle time of 60 sec. The multipurpose test piece (Type A1) as defined in JIS K7139 was then processed to a width of 10 mm, a thickness of 4 mm, and a length of 80 mm to obtain a measurement test piece (Type B2).
Using a precision universal testing machine (Autograph AG-X 10 kN) manufactured by Shimadzu Corporation, the flexural modulus of the Type B2 measurement specimen was measured under conditions of a temperature of 23°C, a relative humidity of 50%, a support distance of 64 mm, and a test speed of 2 mm/min, and used as an index of rigidity of the injection molded article obtained from the polypropylene-based resin composition.

<Low temperature impact resistance Charpy impact strength [-20℃]>
According to JIS K6921-2, the measurement was performed using a type A1 test piece obtained by the same procedure as the test piece used for measuring the flexural modulus. That is, according to JIS K7111-1, the test piece was processed to a width of 10 mm, a thickness of 4 mm, and a length of 80 mm using a notching tool A-4 manufactured by Toyo Seiki Seisakusho Co., Ltd., and a notch of 2 mm was then made in the width direction to obtain a measurement test piece of shape A.
The Charpy impact strength (edgewise impact, 1 eA method) of the test specimen was measured at a temperature of -20°C using a fully automatic impact tester with a low temperature chamber (No. 258-ZA) manufactured by Yasuda Seiki Seisakusho Co., Ltd.

<Tensile properties: Nominal tensile strain at break>
According to JIS K6921-2, the measurement was performed using a type A1 test piece obtained by the same procedure as the test piece used for measuring the flexural modulus. That is, according to JIS K7161-2, the nominal tensile break strain was measured using a precision universal testing machine (Autograph AG-X 10 kN) manufactured by Shimadzu Corporation under conditions of a temperature of 23°C, a relative humidity of 50%, and a test speed of 50 mm/min.

<Appearance>
A mirror-finished flat plate molding die having dimensions of 200 mm x 400 mm x 3 mm, an opening (40 mmΦ) in the center, and a strength reinforcing rib (height 10 mm x thickness 1 mm) on one side was attached to an injection molding machine (J220ELIII, manufactured by Japan Steel Works, Ltd.) A pellet-shaped polypropylene-based resin composition was used and injection molding was performed under the conditions of a molding temperature of 230°C, a die temperature of 40°C, and an injection time of 1 second.
The appearance of the injection molded products simulating automobile interior parts was evaluated by visually observing the conspicuousness of flow marks, the conspicuousness of welds near the openings, and the conspicuousness of silver streaks on the back surface where the strength reinforcing ribs were formed. The evaluation criteria were as follows:

(Flow mark)
“1”: No flow marks are observed.
“2”: Flow marks are slight and inconspicuous.
"3": Flow marks are noticeable.

(Weld)
"1": No welds are formed.
"2": The welds are slight and not noticeable.
"3": Welds are noticeable.

(Silver Streak)
“1”: No silver streaks occur.
"2": Silver streaks are few and not noticeable.
"3": Silver streaks always occur and are noticeable.

(Scratch resistance)
A specimen measuring 80 mm x 80 mm was cut out from the mirror-finished smooth portion of the plate used for the appearance evaluation to prepare a test piece for evaluating scratch resistance.
Using a surface property measuring instrument (HEIDON-14D manufactured by Shinto Scientific Co., Ltd.) equipped with a tungsten steel needle (R = 0.1 mm), 20 scratches of 50 mm in length were made at 1 mm intervals at a speed of 550 mm / min in a direction perpendicular to the flow direction during injection molding under conditions of a temperature of 23 ° C. and a load of 0.5 N. The lightness difference ΔL * between the scratched part and the normal part of the flat plate was measured using a spectrophotometer (SE2000 manufactured by Nippon Denshoku Kogyo Co., Ltd.) based on JIS Z8730. ΔL * is an index of scratch resistance, and the smaller this value, the better the scratch resistance.

The injection molded articles of Examples 1 to 6, which used polypropylene-based resin compositions with the specified physical properties, had better appearances and suppressed the occurrence of flow marks, welds, silver streaks, etc., compared to Comparative Examples 1 to 5. Furthermore, they also had an excellent balance of mechanical properties such as rigidity, low-temperature impact resistance, and tensile properties.

The injection molded article of Comparative Example 1 using Copolymer 2, in which the content of ethylene-derived units in the ethylene-propylene copolymer in the polypropylene resin (A) was outside the specified range, had poor tensile properties.
The injection-molded article of Comparative Example 2 using Copolymer 3, in which the content of ethylene-derived units in the ethylene-propylene copolymer in the polypropylene-based resin (A) was outside the specified range and the content of the ethylene-propylene copolymer was outside the specified range relative to the total mass of the polypropylene-based resin (A), was inferior in low-temperature impact resistance and tensile properties.
The injection-molded article of Comparative Example 3 using Copolymer 4, in which the content of ethylene-derived units in the ethylene-propylene copolymer in the polypropylene-based resin (A) was outside the specified range and the content of the ethylene-propylene copolymer was outside the specified range with respect to the total mass of the polypropylene-based resin (A), was inferior in low-temperature impact resistance and tensile properties.
In Comparative Example 4, in which the content of the propylene homopolymer (B) was outside the prescribed range, the flowability of the polypropylene-based resin composition was poor.
The injection molded article of Comparative Example 5, in which the content of the inorganic filler (D) was outside the prescribed range, was inferior in low-temperature impact resistance, appearance and scratch resistance.

Claims (7)

A polypropylene-based resin composition comprising: (A) a polypropylene-based resin including a continuous phase made of a propylene polymer and a rubber phase made of an ethylene-propylene copolymer; (B) a propylene homopolymer; (C) an ethylene-α-olefin copolymer which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms; and (D) an inorganic filler as required,
The content of the polypropylene resin (A) is 63 to 85 % by mass based on the total mass of the polypropylene resins (A) to (D),
The content of the propylene homopolymer (B) is 10 to 20% by mass based on the total mass of the (A) to (D),
The content of the ethylene-α-olefin copolymer (C) is 5 to 15 mass% based on the total mass of the (A) to (D),
In the case where the polypropylene-based resin composition contains an inorganic filler (D), the content of the inorganic filler (D) is 2 mass% or less based on the total mass of the (A) to (D),
The polypropylene resin composition has an MFR of more than 50 to 80 g/10 min at a temperature of 230° C. and a load of 2.16 kg,
The propylene polymer has a xylene insoluble content of 97.5% by mass or more based on the total mass of the propylene polymer;
the ratio (Mw/Mn) of the weight average molecular weight Mw to the number average molecular weight Mn of the propylene polymer is 3 to 10;
The propylene polymer has an ethylene-derived unit content of 0.5% by mass or less based on the total mass of the propylene polymer,
The propylene polymer has a propylene-derived unit content of 99.5% by mass or more,
the content of the ethylene-propylene copolymer is 25 to 35% by mass based on the total mass of the polypropylene-based resin (A);
the ethylene-propylene copolymer has an ethylene-derived unit content of 20 to 40% by mass based on the total mass of the ethylene-propylene copolymer;
The polypropylene-based resin (A) has a xylene-soluble portion having an intrinsic viscosity of 1.5 to 4.0 dl/g in tetrahydronaphthalene at 135° C.;
The polypropylene-based resin (A) has an MFR of 20 to 100 g/10 min at a temperature of 230° C. and a load of 2.16 kg;
The propylene homopolymer (B) has an MFR of 500 to 3,000 g/10 min at a temperature of 230° C. and a load of 2.16 kg;
The ethylene/α-olefin copolymer (C) has an MFR of 2.0 to 10 g/10 min at a temperature of 190° C. and a load of 2.16 kg.
Polypropylene resin composition for automotive interior parts.
2. The polypropylene resin composition for automobile interior parts according to claim 1, wherein the ratio of the weight average molecular weight _Mw to the number average molecular weight _Mn ( _Mw / _Mn ) of the propylene polymer is 4-7. The polypropylene-based resin composition for automobile interior parts according to claim 1 or 2, wherein the propylene polymer and the ethylene-propylene 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 a phthalate-based compound as an electron donor compound. (b) An organoaluminum compound. (c) An organosilicon compound as an external electron donor compound. A method for producing the polypropylene-based resin composition for automobile interior parts according to any one of claims 1 to 3, comprising the steps of: polymerizing an ethylene monomer and a propylene monomer in the presence of the propylene polymer using a catalyst containing the following components (a) to (c) to obtain the polypropylene-based resin:
(a) A solid catalyst containing magnesium, titanium, halogen, and a phthalate-based compound as an electron donor compound as essential components. (b) An organoaluminum compound. (c) An organosilicon compound as an external electron donor compound. A molded article for automobile interior parts obtained by injection molding the polypropylene-based resin composition for automobile interior parts according to any one of claims 1 to 3. The molded article for automobile interior parts according to claim 5, wherein the molded article for automobile interior parts is a door trim, a glove box, a column cover, an instrument panel, a package tray, a rear tray, a pillar garnish, or a console box. The molded article for automobile interior parts according to claim 6, wherein the molded article for automobile interior parts is a door trim.