Coinjection Molding
“Coinjection molding is typically used to mold multi-layered plastic packaging articles having a laminated wall structure. Each layer is typically passed through a different annular or circular passageway in a single nozzle structure and each layer is partially, sequentially, injected through the same gate. Some coinjection hot runner systems include shooting pots to meter material of one plastic resin so that each cavity of a multi-cavity mold receives an accurate dose of that resin in the molding cycle. Such systems may also use shooting pots to exert supplementary pressure on the melt during the molding process.”( (Sicilia; US Patent 7,559,756; July 14, 2009)
Coinjection molding is a process by which at least two separate injection moldable materials are combined just prior to the mold gate in an orderly one step molding operation, in which the materials co-flow for at least a portion of the operation. In particular, coinjection molding makes it possible to form an entire tube, including a closed, rounded bottom, in a single step, with desired coverage and desired encapsulation. No preform is needed. The bottom wall can be provided by using a mold cavity having a region for forming the closed bottom wall during the polymer flow into the mold cavity. Desired coverage and/or encapsulation is achieved by controlling the flow of the various materials.
(Ahern et al, US Patent 7,803,305, 9/28/2010)
Recent US Patents
1/4/2011
7,862,760
Co-injection nozzle, method of its use, and resulting golf ball
Puniello, Cavallaro and Morgan of Acushnet, Massachusetts, developed a nozzle for an injection molding machine consisting of a nozzle body, an inner nozzle, and an outer nozzle with two independent flow paths. This nozzle can simultaneously discharge two materials for a golf ball. (RDC 7/18/2011)
12/28/2010
7,858,013
Injection molding method
Izumo of Suzuki Motor, Japan, has developed a two part injection molding system in which two sections are indepently molded onto a single connecting film. (RDC 7/6/2011)
9/28/2010
7,803,305
Process for forming multilayer containers
Ahern et al of Becton, Dickinson and Company has developed a co-injection molding process for molding multilayer containers such as blood collection tubes, evacuated blood collection tubes, culture bottles, centrifuges tubes, and syringe barrels with improved gas and liquid vapor barriers. (RDC 12/8/2010)
7/14/2010
7,559,756
Apparatus and method for actuation of injection molding shooting pots
Sicilia of Husky Injection Molding Systems, Canada has developed a coinjection hot runner with a coinjection nozzle. The coinjection nozzle has at least two melt channels ending at the same gate. A shooting pot piston is configured to discharge a melt from the shooting pot. An actuation structure is on the opposite side of the mold cavity half from the coinjection hot runner, and provides the force to the piston. (RDC 1/23/2011)
Recent Journal Articles
Effects of Process Parameters on the Skin/Core Distribution in Co-Injection: Experiments and Simulations Using a Simple Geometry
(1314-1322) Polymer - Plastics Technology and Engineering 50 #13 (2011)
Abstract
Vangosa of thePolitecnico di Milano, Italy, studied the effect of processing parameters on core breakthrough and material distribution during co-injection in a model mould. PMMA was used for the skin and ABS for the core. To identify the influences of the core volumetric fraction, its injection rate and temperature and the skin injection temperature a series of computer simulations and experimental tests were performed according to the design of experiments statistical approach. The results of statistical analysis performed on data coming from experiments and simulations are consistent, even if simulations overestimate the ABS content at which the breakthrough takes place. (RDC 9/16/2011)