Polypropylene resin hollow molded foam article and a process for the production thereof

A process for the production of a polypropylene resin hollow molded foam article, in which a cylindrical foam having a foam layer is formed by extruding from a die a foamable molten resin comprising a base resin containing a foaming agent, and then placing said cylindrical foam in a metal mold while in a softened state, wherein the base resin is one selected from among the following (i), (ii), (iii), and (iv):

• (i) a resin composed of at least 20 wt % and less than 70 wt % (a) polypropylene resin with a melt tension of at least 98 mN at 230° C. and a melt flow rate of 0.5 to 15 g/10 minutes at 230° C. and over 30 wt % and no more than 80 wt % (b) polypropylene resin with a melt tension of less than 30 mN (excluding 0) at 230° C. and a melt flow rate of 2 to 30 g/10 minutes at 230° C. (the combined amount of (a) and (b) being 100 wt %);
• (ii) a resin composed of 30 to 70 wt % (c) polypropylene resin with a melt tension of at least 30 mN and less than 98 mN at 230° C. and a melt flow rate of 2 to 15 g/10 minutes at 230° C. and 30 to 70 wt % (b) polypropylene resin with a melt tension of less than 30 mN (excluding 0) at 230° C. and a melt flow rate of 2 to 30 g/10 minutes at 230° C. (the combined amount of (c) and (b) being 100 wt %);
• (iii) a resin composed of at least 20 wt % and less than 70 wt % (a) polypropylene resin with a melt tension of at least 98 mN at 230° C. and a melt flow rate of 0.5 to 15 g/10 minutes at 230° C. and over 30 wt % and no more than 80 wt % (c) polypropylene resin with a melt tension of at least 30 mN at 230° C. and less than 98 mN and a melt flow rate of 2 to 15 g/10 minutes (the combined amount of (a) and (c) being 100 wt %) at 230° C.;
• (iv) a resin composed of (a) a polypropylene resin with a melt tension of at least 98 mN at 230° C. and a melt flow rate of 0.5 to 15 g/10 minutes at 230° C., (b) a polypropylene resin with a melt tension of less than 30 mN (excluding 0) at 230° C. and a melt flow rate of 2 to 30 g/10 minutes at 230° C., and (c) a polypropylene resin with a melt tension of at least 30 mN and less than 98 mN at 230° C. and a melt flow rate of 2 to 15 g/10 minutes at 230° C., with (a) accounting for 5 to 65 wt %, (b) for 30 to 78 wt %, and (c) for 5 to 65 wt % (with the combined amount of (a), (b), and (c) being 100 wt %), and said resin having a composition within the bounds of a quadrangle ABCD (including on the lines of the quadrangle) drawn by connecting with straight lines the:
• four points A (17, 78, 5), B (5, 72, 23), C (5, 30, 65), and D (65, 30, 5) which are component coordinates (x, y, z) where the polypropylene resin (a) component is given as x wt %, the polypropylene resin (b) component is given as y wt %, and the polypropylene resin (c) component is given as z wt % in a triangular component graph in which the upper vertex of a regular triangle is marked as 100 wt % polypropylene resin (a), the lower left vertex as 100 wt % polypropylene resin (b), and the lower right vertex as 100 wt % polypropylene resin (c).