Process for producing polyolefin resin composition and polypropylene composition

A process for producing a polyolefin-based resin composition, the process comprising:

• in a first polymerization stage, polymerizing or copolymerizing at least one monomer selected from ethylene, propylene and α-olefins having 4 to 20 carbon atoms in a presence of a catalyst comprising a combination of a catalyst component (X) comprising a titanium trichloride-based compound or a component comprising titanium, magnesium and a halogen as essential components and an organoaluminum compound (Y), and
• in a second polymerization stage, copolymerizing the homopolymer or the copolymer obtained in the first polymerization stage with at least one monomer selected from ethylene, propylene and α-olefins having 4 to 20 carbon atoms in a presence of a polyene having at least two polymerizable carbon-carbon double bonds in one molecule;
• and
• the produced composition satisfying following requirements (a) to (c):
• (a) a ratio [η]2/[η]1=]1.05 to 10, wherein [η]1 represents an intrinsic viscosity of a polyolefin obtained in the first polymerization stage and [η]2 represents an intrinsic viscosity of a polyolefin obtained in the second polymerization stage,
• (b) a content of the polyolefin obtained in the second polymerization stage in the polyolefin-based resin composition is 0.01 to 80% by weight, and
• (c) no insoluble components are present in a dissolution test of the polyolefin-based resin composition using decaline at 135° C. as a solvent.

A polypropylene composition which satisfies following requirements (i) to (iv):

• (i) a branching parameter a is in a range of:
• 0.35<a≦0.57
• (ii) an branching index g is in a range of:
• 0.75≦g<1.0
• (when a molecular weight measured in accordance with a light scattering method is 2,000,000 to 10,000,000)
• 090≦g<1.0
• (when a molecular weight measured in accordance with a light scattering method is 500,000 to a value smaller than 2,000,000)
• (iii) an upturn from an inflection point is present in a curve showing a change in viscosity under extension with time, and
• (iv) a degradation parameter D is:
• D≧0.7

A polypropylene composition which satisfies following requirements (i) to (iii):

• (i) a branching parameter a is in a range of:
• 0.35<a≦0.57
• (ii) an branching index g is in a range of:
• 0.75≦g<1.0
• (when a molecular weight measured in accordance with a light scattering method is 2,000,000 to 10,000,000)
• 090≦g<1.0
• (when a molecular weight measured in accordance with a light scattering method is 500,000 to a value smaller than 2,000,000)
• (iii) a content of a high molecular weight component having a molecular weight of 1,000,000 or greater as measured in accordance with a light scattering method is 10% by weight or smaller.