TPE encapsulation is familiar to everyone. As the name suggests, it is to encapsulate low-hardness TPE onto the surface of other materials. Processing methods generally include two-shot injection molding process of ordinary injection molding machine and two-color injection molding process of one-time molding. TPE encapsulation materials are widely used in handles, handles and electronic products. Its comfortable touch and softness improve the grip and use comfort of the product.
However, for manufacturers of TPE encapsulated products, TPE encapsulation is actually not easy, and a series of problems often occur. Therefore, let’s learn about common TPE encapsulation problems today, and hope to help everyone.
1. TPE encapsulation has poor adhesion. TPE is usually used in conjunction with other plastics, such as PP, ABS, PC, PA, PC/ABS and other plastics. The solution to the poor adhesion of TPE encapsulation is as follows. In the formulation of TPE materials, there must be components compatible or bonded with plastics. For example, nylon packaging needs to add SEBS compatibilizer and TPU materials to improve compatibility. The injection temperature must ensure that the plastic is completely plasticized to achieve the fluidity required for injection molding. At the same time, the compatibility and activity of other components in the TPE encapsulation formula will increase, and it can interpenetrate and contact with other materials during packaging. The interface only takes tens of seconds. The TPE and hard glue can be firmly bonded together. The greater the thickness and area of the TPE encapsulation, the longer it takes for the TPE to flow in the mold cavity to complete the coating, and the longer the time, the greater the temperature drop during the flow of the rubber in the mold cavity, and lowering the temperature is not conducive to packaging Bond. The thickness design of TPE encapsulation is generally 0.5~3mm. The greater the flow length ratio, the more difficult the packaging. Generally, for the mold design of TPE overmolding, it is recommended that the flow length ratio is less than 1:150. For example, the coating thickness of TPE encapsulation is 0.5mm, and the length of the coating (flow direction) is recommended to be less than 75mm. The greater the encapsulation flow length ratio, the higher the requirements for the fluidity and melt strength of the TPE material. Therefore, for the coating structure of complex products, if conditions permit, it is recommended to use a hot runner mold, which will help achieve thermal coating and obtain a better TPE coating effect.
2. TPE encapsulated hard plastic parts often have deformation problems. Common reasons are: rigid plastic parts are thin in size, or have a large aspect ratio, and the molding temperature is high. In TPE encapsulation molding, higher encapsulation temperature (170~200℃) will easily soften ABS, PP and other plastic parts, thereby deforming them. TPE material has shrinkage, and the thicker the cover layer, the greater the shrinkage rate, and the material's requirements for elasticity and strength properties also enhance the shrinkage of the material. For some narrow and long covering structures, this shrinkage can exacerbate the deformation of rigid plastic parts. The solution is to lower the injection molding temperature and use a TPE material with a lower melting point in the mixing system. However, sometimes lowering the coating temperature may adversely affect adhesion. If necessary, a rib design can be added to the hard plastic mold. Under the premise of considering material properties, minimize material shrinkage. The design of the glue inlet (change the gate position) should make the flow length ratio as small as possible, because when filling the cavity, the longer the melt flow path, the greater the shrinkage. It will aggravate the deformation of hard plastic parts.
The above is a summary of some of the problems of TPE encapsulation. I hope to help you. If you need TPE, TPR, TPV, TPU, TPEE and other thermoplastic elastomer materials, please call Kunshan Kexin Polymer Materials Co., Ltd.