A polypropylene-based resin composition is generally excellent in chemical resistance and mechanical properties and thus used in a wide variety of fields including packaging materials, mechanical parts and car parts. Recently, in order to satisfy the needs for overcoming environmental problems, development of halogen-free transparent polymer materials has been accelerated. Particularly in the fields including sheets, films and tubes, a polypropylene-based resin composition is used and a request for making a polypropylene-based resin composition soft and/or transparent to meet various uses has appeared.
Patent Literature 1 discloses “a hydrogenated block copolymer which comprises at least two polymer blocks A each mainly comprising an aromatic vinyl hydrocarbon compound monomer unit and at least two hydrogenated polymer blocks B each mainly comprising a butadiene monomer unit, at least 90% of the olefinically unsaturated double bonds in said polymer block mainly comprising a butadiene monomer unit before hydrogenation having been hydrogenated, wherein at least one of the block at the terminal of the hydrogenated block copolymer is the polymer block B, wherein the proportion of the terminal polymer blocks B in the hydrogenated block copolymer is at least 0.1 wt % but less than 9.1 wt %, wherein the proportion of the aromatic vinyl hydrocarbon compound in the hydrogenated block copolymer exceeds 10 wt % but less than 25 wt %, wherein the 1,2-bond content of the polymer blocks mainly comprising a butadiene monomer unit before hydrogenation is, on average, at least 62 mol % but less than 99 mol %, and wherein the difference ΔTc (Tc1−Tc2) between the crystallization initiating temperature (Tc1) of the isotactic homopolypropylene and the crystallization initiating temperature (Tc2) of a mixture thereof with 20% by weight of the hydrogenated block copolymer is at least 1.5° C.”.
Patent Literatures 2 and 3 disclose hydrogenated block copolymers comprising a styrene block and a butadiene block.