Analysis of TPE Soft Rubber Overmolding: Material Selection Principles and Practical Applications
Time of issue:2025-05-15
In the process of two-color injection molding and overmolding, material compounding mostly revolves around two major categories: rigid plastics and soft rubbers. However, in some two-color injection molding scenarios, there are also cases where rigid plastics are compounded through special structural designs. The method of soft rubber overmolding with soft rubber not only brings a more comfortable experience to users from the perspective of product design innovation but also attracts more consumers' attention through micro-innovations, providing new choices in today's highly competitive market. Today, Subo will deeply analyze a unique material combination in two-color injection overmolding - TPE soft rubber adhesive overmolding with soft rubber.
The term "soft rubber" does not have an exact and unified definition. For example, PP is considered a soft rubber compared to ABS, but its hardness is significantly higher than that of TPE soft rubber. In the field of two-color injection overmolding, "soft rubber" refers to a type of thermoplastic soft material with a hardness lower than 95A (this value is set by Subo based on industry experience). Common soft rubbers include elastomers such as TPE, TPU, TPV, and silicone. Considering environmental protection factors, the application of soft PVC in two-color injection molding is relatively limited.
During the two-color injection molding process of TPE soft rubber overmolding with soft rubber, the selection of raw materials should follow two principles:First, the two soft rubbers used for overmolding should preferably be of the same or similar compounding systems, such as both being TPE or both being TPU. Only with similar compounding systems can good adhesion between the two be ensured. If it is necessary to use two different soft rubbers due to special requirements, one of the soft rubbers needs to be modified.Second, the hardness and high-temperature resistance of the first-injected soft material should theoretically be better than those of the second-injected soft rubber material. This can prevent the soft rubber part to be bonded from deforming in the mold cavity due to the high overmolding temperature and injection pressure during the second injection.
In practical cases of two-color injection molding, more than 95% involve the compounding of soft rubber and rigid plastics. Rigid plastics endow products with basic functional properties, while soft rubbers focus on enhancing product functionality and added value. Although the application of two-color molding with soft rubber and soft rubber is relatively rare, in recent years, Subo has encountered many practical cases. Applications of TPE soft rubber overmolding with soft rubber include: mobile phone cases, tool handles, composite suction cups, medical teething toys, and toy products, among others.
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