English to French Tech/Engineering Patents (in a patent) INDIVIDUAL CAVITY FLOW CONTROL METHOD AND SYSTEM FOR CO-INJECTION MOLDING

an example graph of pressure as a function of distance along a flow path for EVOH material flowing as an interior skin layer through a hot runner system and a mold cavity for a thin walled article.

For co-injection molding of multilayer articles, the inventors recognized that a
uniform delay across all cavities in the addition of core material to the flow after initiation of skin material flow into all cavities often results in articles from different cavities having different amounts of core layer coverage, (i.e., different positions for the location of the leading edge of the core layer in different articles). This is especially pronounced for thinwalled articles. The inventors determined that conventional thermal balancing and shooting pot techniques for controlling leading edge positions of skin layers and core layers in coinjected molded articles often provide insufficient control to obtain uniform leading edge positions from cavity to cavity for thin-walled articles (e.g., articles with a wall thickness of less than 0.5 mm, or articles with a wall thickness of between about 0.25 mm and 0.5 mm).

Temperatures throughout the flow path of a melt flow affect the viscosities of the
skin and core materials.

a time delay between initiation of flow of the first material into a cavity and initiation of co-injection of the second material into the cavity is a skin-core time delay for the cavity, and wherein the method further comprises specifying a first skin-core time delay for the first cavity (22a) and specifying a second skin-core time delay different than the first skin-core time delay for the second cavity (22b).