Polypropylene resin composition and injection-molded article

A resin composition based on polypropylene comprising a predominant proportion of polypropylene and having the following characteristic features C to H, namely,

• C:
• an isotactic pentad proportion (mmmm proportion) determined by 13C-NMR of 98.0% or higher,
• D:
• a molecular weight distribution expressed by Mw/Mn determined by gel permeation chromatography (GPC) of 20 or higher and a molecular weight distribution expressed by Mz/Mw of 7 or higher,
• E:
• a specific gravity determined by water-displacement method (ASTM D 1505) of 0.915 or lower,
• F:
• a flexural modulus (ASTM D 790) of 2600 MPa or higher,
• G:
• a thickness of the skin layer of at least 300 μm, which is formed on an injection-molded article when the resin composition of 190° C. is injected into a mold of 60° C. and held therein for 30 seconds, and
• H:
• a heat distortion temperature (ASTM D 648, under a load of 0.45 MPa) of 145° C. or higher.

A resin composition based on polypropylene, comprising a predominant proportion of polypropylene and having the following characteristic features C to H, namely,

• C:
• an isotactic pentad proportion (mmmm proportion) determined by 13C-NMR of 98.0% or higher,
• D:
• a molecular weight distribution expressed by Mw/Mn determined by gel permeation chromatography (GPC) of 20 or higher and a molecular weight distribution expressed by Mz/Mw of 8 or higher,
• E:
• a specific gravity determined by water-displacement method (ASTM D 1505) of 0.910 or lower,
• F:
• a flexural modulus (ASTM D 790) of 2500 MPa or higher,
• G:
• a thickness of, the skin layer of at least 380 μm, which is formed on an injection-molded article when the resin composition of 190° C. is injected into a mold of 60° C. and held therein for 30 seconds, and
• H:
• a heat distortion temperature (ASTM D 648, under a load of 0.45 MPa) of 150° C. or higher.