Sleeve molding

An apparatus for making multilayer injection-molded plastic articles comprising:

• a first mold cavity set (11) and a second mold cavity set (12), each first cavity being adapted to form a relatively thin inner sleeve layer (20) and each second cavity being adapted to form a relatively thick outer layer (22):
• a transfer mechanism (2) with first and second core sets (9, 10) for successively positioning the first and second core sets in the first and second cavity sets;
• wherein the first core set (9) is positionable in the first cavity set (11) for molding a set of inner sleeve layers (20) on the first core set, while the second core set (10) is positionable in the second cavity set (12) for molding, over a previously-molded set of inner sleeve layers on the second core set, a second set of outer layers (22);
• and
• means for heating (15) the first cavity set so as to maintain an outer surface of the inner sleeve layer (20) at an elevated temperature during transfer and molding of the outer layer (22) thereover, the elevated temperature being selected to provide melt adhesion between the inner sleeve and outer layer.

A method of injection molding a multilayer plastic article comprising:

• first molding an inner sleeve (20) on a core (9) positioned in a first mold cavity (11), the first molding step including a filling stage and a pressure boost stage but substantially no holding and cooling stage so as to maintain an outer surface of the inner sleeve at an elevated temperature for a second molding step;
• removing the sleeve (20) on the core (9) and transferring the same without substantial delay to a second mold cavity (12);
• and
• second molding an outer layer (22) over the sleeve (20) in the second mold cavity (12) to form the multilayer injection molded article, wherein the elevated temperature of the outer surface promotes layer adhesion between the inner sleeve and outer layer.