TPE over molding technology introduction
Encapsulation, also known as overmolding, usually refers to two-color injection molding or overmolding. The TPE composite adheres to the surface of another material to meet certain performance requirements of the material, which can provide soft touch, anti-slip, abrasion, shock absorption, elasticity, sealing, waterproof and other functional properties.
2. Over molding equipment
2.1 ordinary injection molding machine
Ordinary injection molding machine + two sets of molds (usually hard plastic base injection molds and TPE plastic molds).
2.2 two-color injection molding machine
The device contains two or more hoppers as well as a screw and glue injection port. Two sets of molds for hard plastic and TPE injection were loaded into two molds. When injection molding, the first injection is hard plastic, then the rotary mold is used and the other screw will be used. The soft rubber is injected into the soft mold without removing the hard plastic sheet to complete the rubber quickly.
3. Overmolding process
TPE encapsulation generally does not use vacuum aluminum film paper bags. Whether to bake depends on whether the composite TPE is easily absorbed or not to determine whether to bake the sample. If the TPE is water absorbing, it should be baked at a temperature of 80-90 ° C for about 2-3 hours. If not baked, the moisture in the material will affect the adhesion or cause surface wrinkles or water on the rubber surface.
Hard plastic parts should be cleaned before being placed in plastic molds, free of moisture, garbage and oil. For nylon parts, if placed in the air for more than two hours after injection molding, we recommend preheating the nylon parts (the two-color injection molding machine can be ignored). Baking temperature is 100~140°C, baking time is 2~4 hours. The meaning of baking: remove moisture from the nylon parts and increase the surface temperature of the nylon parts. Because nylon has a higher melting point and stronger polarity, and preheating before packaging is beneficial to improve the bonding strength of the package molding.
The injection pressure and speed should be adjusted by the injection molding master according to the product structure, mold flow path structure and material flowability. The injection temperature can be negotiated with the TPE supplier to provide a reference processing temperature.
4. Rubber classification
According to the encapsulation mechanism, true encapsulation refers to a strong encapsulation bond between TPE and hard plastic with similar polarity. Currently, TPE and many plastics can be used for true encapsulation, such as TPE encapsulation (pp.pe, abs, pc, pa, ps, etc.). Fake rubber, which refers to the difference in polarity between TPE and hard plastic, does not form ablation and inter-melting layers, and does not have any adhesion. However, special hard plastic structures, such as snap-on designs, improve the robustness of the TPE and hard plastic coatings through the structure.
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