Two-injection molding (also known as two-color injection molding or two-material injection molding) is a process that uses two sets of molds on the same injection molding machine to form plastic products with two different colors or materials in two separate injections. It has high process requirements, involving mold design, material selection, equipment configuration, and molding parameter control.
Material Compatibility: The two materials must meet the requirements for adhesion and processing compatibility. Generally, the melting point of the first injection material should be higher than that of the second injection, with a recommended temperature difference of at least 30°C, often 60°C, to prevent the molten B material from damaging the already formed A material in the first injection during the second injection.
Molding Sequence: In most cases, rigid materials (such as PC, ABS) are injected first, followed by soft materials (such as TPU, TPE), because soft plastics are more prone to deformation under subsequent high temperature and pressure.
Mold and Cooling: Since different materials may be used in the two injections, the mold often needs to be equipped with two independent cooling systems to control the temperature in different areas. The product size of the first injection needs to be slightly larger to allow for compression and sealing during the second injection.
