In the field of injection molding and injection mold processing, two-color injection molding and secondary injection molding are the core processes to achieve multi-material combination. With the upgrading of intelligent manufacturing, the technical connotation and application scenarios of the two continue to iterate. This paper compares the principle, process, application and other dimensions, combined with the latest technology trends in 2024 and 2025, to provide a clear selection reference for the industry.
First, the core principle: a molding vs step-by-step composite
(A) Two-color injection molding (melting state integration)
Technical path: Through the dual-color injection molding machine double injection glue unit, the two materials are successively injected into the rotating mold, and the molecular diffusion is used to realize the jointless combination.
Typical cases:
The smart hand case (PC outer layer + PMMA inner layer) is formed at one time, and the no-spray process meets the RoHS 3.0 standard
Multi-color components of automobile dashboard, through the layered cavity to achieve color and texture integration
(2) Secondary injection molding (cured coating)
Technical path: the first step is to form hard basic parts (such as PA66 gear), and then the second pair of molds is coated with soft materials (such as TPU-ECO degradable elastomer produced in mass production in 2024), and the second molding of two materials is formed.
Industry breakthrough:
In the medical field, nano-coating pretreatment can increase the bonding strength of PE and silica gel by 40%
Metal substrates (such as aluminum alloy) can be directly coated with PPS high temperature materials to expand to industrial temperature resistant parts
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Two, process upgrading: equipment and mold technology comparison
Dimension of technology
Two-color injection molding (Latest progress)
Secondary injection molding (Latest progress)
Mold innovation
Multi-station rotary mold (support injection molding of more than 3 colors) in-mold heating technology (material utilization rate 98%)
Intelligent positioning mold (integrated visual recognition) embedded sensors monitor coating thickness
Intelligent equipment
AI temperature control system + servo hydraulic hybrid drive (response speed ↑50%)
Automatic loading and unloading
Green technology
Energy saving glue shooting unit
Waste heat recovery of die temperature machine (energy consumption reduced by 25%)
Iii. Material and combination technology: compatibility vs functionality
(1) Differences in material selection
process
Material requirements
Typical combination
Emerging Material Applications
Two-color injection molding
Compatibility (shrinkage difference < 5%)
ABS+PC, PC+PMMA (consumer electronics case)
OBC compatibilizer helps PP to combine with PC (automotive lightweight components)
Secondary injection molding
Structural suitability (no material limit)
Rigid plastic + TPU/TPE (tool handle)
Degradable PLA+PBS (medical stapler), conductive TPE (robotic joint)
(2) Innovation of combination methods
Two-color injection molding:
Traditional: molecular diffusion in molten state (the binding surface is smooth without joints)
Upgrade: ultrasonic assisted fusion (local heating promotes fusion, bond strength ↑25%)
Secondary injection molding:
Traditional: mechanical occlusion (dependent on notch design)
Upgrade: laser micro/nano structured processing (surface roughness Ra3.2, stripping force ↑30%, ISO 8510 standard)
Two colors (3)
Iv. Application scenarios: appearance driven vs function driven
(1) The core scene of two-color injection molding
Precision field of appearance
Consumer electronics: mobile phone case multi-color gradient, smart glasses TR90+TPU lightweight frame
Automotive interior: Instrument panel multi-texture components (matte + high-gloss surface integrated molding)
Advantages: Spray free process, in line with the latest EU environmental directives (such as RoHS 3.0 new restricted substances in 2024)
(2) The core scene of secondary injection molding
Functional composite domain
Tools and instruments: screwdriver soft adhesive non-slip handle (hard body + TPU coating)
Medical device: Biodegradable PLA stapler (PBS elastomer coated, FDA approved in 2024)
Industrial components: 5G base station copper substrate coated with high thermal conductivity silica gel (thermal resistance reduction 15%)
Advantages: Support any combination of metal-plastic, hard-soft materials to meet special requirements such as conductivity/insulation/biocompatibility
(3) The trend of technology integration
Multi-process composite: two-color injection molding + IMD mold interior decoration, realize the integration of "three-color injection molding + mold interior coating" (applied to high-end home appliance panel)
Green manufacturing: water-assisted cooling technology (70% water saving) is popular, and both processes promote closed-loop recycling of waste
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Summary: Precise selection in technology iteration
In 2025, dual-color injection molding will continue to deepen the advantages of high-speed and multi-color in the fields of consumer electronics and automotive appearance parts, while secondary injection molding will open new space through special material cladding in high-end fields such as medical treatment and new energy. Enterprises or injection mold factory selection should pay attention to:
Material compatibility: Two-color injection molding depends on formulation design, secondary injection molding depends on structural innovation
Intelligent level: large batch priority two-color injection molding intelligent production line, small batch priority secondary injection molding flexible production
Environmental protection trend: no spraying, biodegradable materials application has become the industry access threshold
With the popularization of AI process optimization, digital twin mold and other technologies, the boundaries of the two processes are gradually merging. The core of future competition lies in whether it can find a dynamic balance between efficiency, function and cost, and at the same time meet the upgrading needs of global manufacturing industry for green and intelligent.
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