Propylene-based block copolymer, production method therefor, and solid titanium catalyst ingredient for olefin polymerization

A method for producing a propylene block copolymer, the method comprising:

• a first polymerization step of preparing a crystalline propylene (co)polymer by polymerizing propylene and an optional α-olefin in the presence of a solid titanium catalyst component (i) produced by bringing
• a solid compound (S) containing a magnesium compound (II-0) and having a first pore distribution index of 2 or more and a second pore distribution index of more than 0.5,
• the first pore distribution index being represented by formula I:
• First pore distribution index=x/y (I)
• where x is a cumulative pore volume of pores with a size of 0.001 to 0.1 μm, and y is a cumulative pore volume of pores with a size of 0.1 to 1.0 μm, the cumulative pore volumes being measured with a mercury porosimeter,
• the second pore distribution index being represented by formula I′:
• Second pore distribution index=xα/xβ (I′)
• where xα is a cumulative pore volume of pores with a size of 0.01 to 0.1 μm, and xβ is a cumulative pore volume of pores with a size of 0.001 to 1.0 μm, the cumulative pore volumes being measured with a mercury porosimeter,
• a titanium compound represented by formula IV:
• Ti(OR)gX4-g (IV)
• where R is a hydrocarbon group, X is a halogen atom, and g is an integer satisfying 0≤g≤4, and
• an electron donor
• into contact with each other;
• and
• a second polymerization step of polymerizing the crystalline propylene (co)polymer prepared in the first polymerization step and a raw material of a polymer selected from the group consisting of rubber components, amorphous or low-crystallinity ethylenepropylene copolymers (EPR), and amorphous ethylenea-α-olefin copolymers.