Technical breakthrough in liquid silicone molding in secondary injection molding

As consumers' requirements for product feel, tightness, and aesthetics continue to increase, it is difficult for a single material to meet complex functional needs. The application of liquid silicone molding in the field of overmolding has realized the perfect combination of hard plastics and soft silicone, becoming the core process of high-end product design. Dongguan Fengyanda Life Technology Co., Ltd. will deeply explore the engineering logic and innovation practice behind this "soft and hard combination" technology. LSR secondary injection molding refers to placing a preformed rigid plastic skeleton (such as PC, ABS, PA) into a mold, and then wrapping the LSR outside the plastic through a liquid silicone molding process. This process not only retains the structural strength and rigidity of the plastic, but also gives the product a unique skin-friendly touch, excellent sealing and impact resistance. In smartphones, smart wearables and automotive interiors, this composite structure has become a standard feature that enhances the texture and functionality of the product. However, there are two core challenges to achieving high quality plastic-coated liquid silicone: interlayer bond strength and dimensional accuracy control. Silica gel and most engineering plastics are non-polar materials, and they naturally lack chemical affinity. If not handled properly, delamination and degumming are very likely to occur. The key to solving this problem lies in surface pretreatment and material modification. Current mainstream solutions include the addition of special adhesion promoters to plastic substrates, plasma cleaning or flame treatment of plastic surfaces to increase surface energy, and the use of specially designed self-adhesive LSR materials. Through years of process accumulation, Fengyanda has established a complete set of surface treatment standards to ensure that silicone and plastic can remain firmly combined under extreme temperature differences and high-frequency bending environments. In addition, dimensional accuracy control is also a difficult point for secondary injection molding of liquid silicone molding. Plastics have a significant difference in shrinkage from LSR (plastics typically range from 0.5% -1.5%, while LSR is about 2% -3%). If the mold design does not fully consider the thermal expansion coefficient matching, internal stress is easily generated after cooling, resulting in product warping or cracking at the joint. Fengyanda uses high-precision CNC machining center and slow wire cutting equipment to control the mold tolerance within ± 0.01 mm, and compensates for the prediction through mold flow analysis software to ensure the consistency of finished product dimensions. In terms of application scenarios, LSR secondary injection molding technology is widely used in many fields. In the medical industry, the hard frame and cushion of the respirator mask are integrally formed through this process, which not only ensures the comfort of wearing, but also improves the durability of the structure. In automotive electronics, the hard shell of the touch panel and the waterproof seal ring are combined through secondary injection molding to achieve the IP67 dustproof and waterproof effect. In consumer electronics, the hard plastic bracket of the charging interface and the dustproof plug are combined through this process to improve the plugging life and aesthetics. In the future, with the development of microfoaming technology and multi-color injection molding technology, liquid silicone molding will show more possibilities in the field of secondary injection molding. Through the introduction of microfoamed LSR materials, a lighter product structure can be achieved; through multi-color injection molding, richer visual effects can be achieved. Fengyanda Life Science and Technology will continue to pay attention to this trend and provide high-quality, high-value-added plastic packaging liquid silicone solutions to customers around the world through technological innovation and process optimization.