WHAT IS CO-INJECTION?
It is the simultaneous injection of two compatible thermoplastic materials where one material engulfs or encapsulates the other. This is accomplished with the use of two separate injection units and a single injection nozzle. The two materials flow into the mold together as skin and core and maintain this configuration throughout the injection. The core foams and pushes to fill the mold cavity. This process should not be confused with two-shot or two-color molding where two colors and/or two materials are injected separately.
In co-injection with gas assist, a gas enters the mold at the end of the injection, further pushing the material to fill the cavity, but also limiting the expansion of the foam core, leaving a hollow volume inside the object. The result is a material with variable density:
• compact skin or high density foam
• low density foam
• high density foam
• hollow inner core
The advantages of co-injection and co-injection with gas, over traditional injection molding, are several:
• Increase product performances leveraging on the multi-component nature of co-injection (example: extreme UV protection or fire extinguishing properties on the skin, and a fiberglass compound in the inner core for resistance). The skin can be hard and shiny with a Class "A" finish, or even provide a different surface such as a "soft touch" material, while the inner core can be a different material. Colorant are required only on the skin, thus reducing costs.
• Possible use of cheaper material in the core. The possible inferior materials of the core do not flow in direct contact with the walls of the mold which facilitates their use in the molding. For the same reason, difficult mixes such as material loaded with wood flour and fiberglass can be easily injected as the core with minimal shrinkage problems.
• Reduced part weight and ability to manufacture very thick part that resemble wood and other material, with improved qualities and efficiencies (antibacterial properties of plastic versus wood for example) The inner core can be foamed, or the entire part can be foamed with a range of different densities, while the use of gas enhances greatly the possibility of having rigid high volume parts emptied on the inside by the use of the gas assist molding.
• Dimensional stability, low warpage during cooling time. Problems of shrinkage, sinking, warping and internal stress are greatly reduced.
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OF MOLDING
DPS MOLDING, Inc.
276 Bailey Lane
Vanceboro NC 28586-8226
USA
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THE TECHNOLOGY
DPS Molding is going to process composite multilayer techno-polymers, manufactured with a TWO COMPONENT RESIN (CO-INJECTION) system, or with a TWO COMPONENT RESIN (CO-INJECTION) PLUS GAS system on special Injection molding machines. It is going to use the highest standards in plastic manufacturing.
