Method and apparatus for manufacturing a hollow plastic product

A method for manufacturing a hollow plastic product having at least two kinds of material portions characterized by:

• supplying a first kind of molten raw material to a first annular passage having a common annular discharge opening at a bottom end thereof;
• supplying a second kind of molten raw material to a second annular passage concentric with said first annular passage and having said common annular discharge opening at a bottom end thereof;
• switchingly and selectively discharging the first kind and the second kind of molten raw materials through said common annular discharge opening so as to control the discharge of said first kind and said second kind of raw materials so as to form a fundamentally single layer parison differing in material along a center line of the parison, wherein at least one interface is formed between said first kind and said second kind of materials, said at least one interface being tapered along and substantially circumferentially uniform around said center line;
• placing said parison within a mold;
• and
• blow molding said parison to form from said parison said hollow plastic product with sections of differing dimensions.