TPE Overmolding and Injection Adhesion Processing Technique and Introduction to Common Materials for Overmolding
Time of issue:2024-03-29
TPE Overmolding and Injection Adhesion Process
TPE overmolding and injection adhesion processes typically employ a two-shot molding technique, wherein a previously molded (injected) rigid plastic part is secured in an overmolding tool, after which TPE soft rubber is injection molded onto the hard plastic part under appropriate temperatures, followed by cooling to produce the final product. The injection molding temperature for overmolding depends on the type of hard plastic material being coated. The temperature must be set to soften both the hard plastic and TPE so that they can achieve a certain level of compatibility at the contact interface. To accomplish true bonding, typical injection molding temperatures for TPE overmolding PP are around 170 to 190 degrees Celsius; for ABS, around 220 to 220 degrees Celsius; for PC, slightly higher than that for ABS; and for PA Nylon, the temperature should be around 240 degrees Celsius.
Common Materials Used in TPE Overmolding
In TPE overmolding applications, TPE serves as the outer soft covering layer and is commonly paired with rigid materials such as plastics, metals, and fabrics. TPE bonding with fabrics mainly takes place in luggage manufacturing, similarly to its bonding with metals, which is generally classified as false bonding. True bonding is more prevalent in secondary injection and dual-color injection molding, where the primary material for TPE overmolding is plastic. TPE can adhere firmly to common general-purpose plastics like PP, GPPS, HIPS, ABS, and engineering plastics like PC, PC/ABS, PA, and their modified versions. However, achieving good adhesion between TPE and POM (Polyoxymethylene) remains a challenge in the elastomers industry. Given the significant difference in their solubility parameters (SP), with POM having an SP of 22.6 and TPE having an SP of 7.2 to 7.6, these materials inherently lack compatibility, and currently, no suitable compatibilizer has been found to promote effective bonding between the two.
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