Injection molding of multilayer articles with post-pullback pressure monitoring

A method (1000) of molding a multilayer article (200), comprising:

• providing a mold cavity (800), a surface layer material injection unit (104), an internal layer material injection unit (106), and a coinjection nozzle (400) having a surface layer material channel (424, 428) and an internal layer material channel (426);
• causing (1002) the surface layer material injection unit to commence injecting a surface layer material (455) into the mold cavity via the surface layer material channel;
• then
• causing (1004) the internal layer material injection unit to commence injecting an internal layer material (466) into the mold cavity via the internal layer material channel;
• then
• during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, causing (1006) a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material;
• then
• after a delay interval, detecting (1008) at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit;
• and
• generating (1010) an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure (PT).