An olefin (e.g., propylene) has been polymerized using an olefin polymerization catalyst. The resulting olefin polymer may be melted, molded using a molding machine, a stretching machine, or the like, and used for a variety of applications (e.g., automotive parts, home appliance parts, containers, and films).
A solid catalyst component that includes magnesium, titanium, an electron donor compound, and a halogen atom as essential components has been known as a component of the olefin polymerization catalyst. A number of olefin polymerization catalysts have been proposed that include the solid catalyst component, an organoaluminum compound, and an organosilicon compound.
An olefin polymer has been desired that exhibits higher fluidity (melt flow rate (MFR)) when molded using a molding machine, a stretching machine, or the like.
The MFR of an olefin polymer mainly depends on the molecular weight of the olefin polymer, and an olefin polymer having a low molecular weight tends to have a high MFR. Therefore, the molecular weight of an olefin polymer is normally reduced by adding a large amount of hydrogen during polymerization in order to obtain an olefin polymer having a high MFR.
In recent years, an olefin polymer that has a high MFR, high stereoregularity, a reduced thickness, and high physical strength (i.e., excellent rigidity) has been desired for producing large home appliance parts and automotive parts (particularly a bumper).
In view of the above situation, the applicant of the present application proposed an olefin polymerization catalyst and an olefin polymerization method using the olefin polymerization catalyst, the olefin polymerization catalyst including a solid catalyst component, an organoaluminum compound, and an organosilicon compound, the solid catalyst component being obtained by bringing a magnesium compound, a tetravalent titanium halide compound, a malonic diester (internal electron donor compound), and a phthalic diester (internal electron donor compound) into contact with each other (see Patent Document 1 (JP-A-2004-107462)).