Against the backdrop of growing demand for precision and multifunctionality in plastic products, the two-color injection molding process addresses limitations of traditional single-material injection molding in performance integration and surface texture through its integrated molding advantage. Widely used in automotive, consumer electronics, and daily necessities sectors, it enables precise fusion of two different materials or the same material in different colors via specialized equipment and mold design, enhancing product value while simplifying subsequent assembly processes, aligning with the efficient and energy-saving development concept of modern manufacturing.
The core of two-color injection molding lies in two injection units of a two-color injection molding machine cooperating with a rotatable or translatable two-color mold cavity to complete injection molding in two stages. In the first injection, the first material is injected into part of the mold cavity to form the product’s base blank. The mold cavity then switches position via mechanical structure, and the second material is injected into the reserved cavity in the second injection. The two materials fuse at the interface inside the mold and cool to form an integrated two-color plastic product. The entire process requires precise matching of injection timing, pressure, and mold positioning to ensure tight bonding without delamination.
Compared with traditional single-color injection molding, this process offers three key advantages: integrated molding enabling seamless combination of two materials, eliminating subsequent bonding/assembly processes and reducing production cycle and costs; performance integration by combining rigid/flexible or heat/weather-resistant materials for multifunctional products; and controllable precision with positioning errors within 0.02mm via mold guide mechanisms and servo systems, ensuring dimensional stability.
Molds are the core carrier of two-color injection molding, and their design directly determines molding quality. Key considerations include cavity structure design to rationally plan injection areas and fusion interfaces for two materials, avoiding flow interference; and reliable rotation/translation mechanisms (e.g., gear rack or servo motor-driven) for stable cavity switching. Mold manufacturing requires strict control of parting surface and guide precision, with micron-level tolerances for key mating surfaces to prevent flash and mold mismatch.
Specialized two-color injection molding machines are required, with high coordination between two injection units and sufficient clamping system rigidity to withstand pressure impacts from two injections. Parameter control must balance material characteristics, focusing on injection temperature, pressure, and holding time: the first injection ensures full filling without excessive shrinkage of the base blank, while the second injection uses slightly higher pressure for tight bonding without damaging the blank. Additionally, mold temperature is zone-controlled via temperature control systems to adapt to molding requirements of two materials.
Materials must meet compatibility and molding adaptability requirements. Compatible combinations (e.g., PP/TPE, ABS/PC) are preferred for stable interfacial fusion; for incompatible materials, compatibilizers or optimized interface design enhance bonding strength. The melt flow index difference between two materials should not exceed 10g/10min to avoid filling unevenness caused by mismatched flow speeds.
A major application area, two-color injection molding is used for automotive interior and functional parts (e.g., two-color buttons, door handles, dashboard trim). Combining rigid and flexible materials delivers both support and comfort—for example, automotive buttons use hard plastic as the base and soft plastic for the pressing surface, ensuring structural strength, improved touch, and reduced loosening risks in assembly.
In consumer electronics, it enhances product appearance and grip experience (e.g., mobile phone frames/buttons, headphone shells, power bank casings). Two-color/multi-color matching enables personalized design, while material combinations improve functionality (e.g., hard plastic for headphone shell stability and soft plastic for wear comfort), meeting consumer demands for aesthetics and practicality.
Applied in toothbrush handles, kitchen utensil grips, and children’s toys. For instance, two-color toothbrush handles use hard plastic for rigidity and soft plastic for slip resistance; children’s toys adopt multi-color materials for visual appeal and food-grade flexible materials for safety, aligning with practicality and safety requirements of daily necessities.
Integrated with industrial internet and IoT technologies, two-color injection molding production is becoming intelligent. Sensors on equipment and molds collect real-time data (injection pressure, temperature, mold positioning) for data-driven dynamic parameter optimization, reducing human error and improving stability. Some high-end production lines achieve fully automated processes from material feeding to molding and inspection.
Driven by green manufacturing, eco-friendly materials (biodegradable, recycled plastics) are increasingly used in two-color injection molding. Mature molding technologies for eco-materials and process optimization (e.g., precise injection volume control to reduce waste) align with low-carbon industry needs.
To meet demand for miniaturized, high-precision plastic products, two-color injection molding is advancing toward higher precision with improved mold and equipment control accuracy for stable production of micro two-color parts (e.g., medical devices, microelectronic components). Integration trends are evident, with more functional structures integrated in a single molding process via mold and process optimization to boost efficiency.
