A brief discussion on TPE two-color injection molding process and precautions
What is overmolding? In short, overmolding can be plastic overmolding, soft plastic molding or soft plastic soft rubber. TPE two-color injection molding encapsulation process is mainly divided into two types: one is two-component molding or called two-color injection molding, which is realized on a two-color injection molding machine. One material is injected into a product, and then the mold is flipped and jumped on the two-color machine. Into the mold cavity corresponding to another injection plastic barrel, this part is used as an insert, and another material is injected on it to form an integrated dual-material product. The injection molding machine has dual barrels and dual mold cavities. The injection molding process is to produce products of two materials at the same time, but the products in one cavity will be used as inserts to enter the next cavity. The other is two-step injection molding. A component of one material is molded on an injection molding machine. The component is placed as an insert in another mold, and then a second material is injected.
From a technical perspective, the following points are worthy of reference:
One: Two-color injection is better than two-step injection. Simply put, when injection molding, the hard plastic is hot and immediately enters the second cavity of the 2K injection molding machine. The intermediate transfer process does not absorb moisture and is easily ablated by the high-temperature TPE melt on the surface. Ultra-thin layer, no moisture on the surface;
Two: Within the processing range of TPE materials, try to use a higher barrel (melting) temperature, otherwise TPE will easily have enough heat to ablate hard plastic material surface.
Three: When applying the second step of rubber, use hard plastic as the insert The cavity is as high as possible. Hard plastic is at high temperature, and TPE melts at high temperature and cools slowly. There is enough heat and enough time to ablate the hard plastic and form a miscible ultra-thin layer.
Four: In the second step of encapsulation, the TPE melt is injected at the highest possible rate without causing TPE flash.
1. At high rates, TPE has a short diffusion time on the hard plastic surface and a longer time to ablate the hard plastic surface during the molding cycle;
2. High-speed shooting, the friction between TPE and the hard plastic surface causes friction heat to be generated, the cooling of the TPE melt temperature also slows down, and it is used to contact and ablate the hard plastic surface for a longer period of time. Time;
Five: In order to avoid moisture absorption or staining on the hard plastic surface, especially in the case of two-step injection molding, the hard plastic is interrupted and transferred in the middle, which is more likely to happen. Polar hard plastics such as PC, PBT, PET, POM, especially highly polar hard plastics such as nylon 6, nylon 66, surface moisture absorption leads to the formation and adsorption of hydrogen molecules, and TPE cannot effectively form intermolecular bonding hard plastics. Plastic surface molecules, the natural bonding force of the bonding force is reduced; if the workshop workers’ gloves are not clean or the cotton fiber of the gloves adheres to the hard plastic part of the polar surface, this will naturally affect the encapsulation of the TPE melt. The polarity of hard plastic TPE is definitely a polarity formula. Moisture resistance also affects the bonding effect of rubber.
