Two different materials through the secondary injection molding, usually we call overmolding. The first reason is that the TPE material formula does not work, this is the customer's first reaction, but if it is an experienced sales staff and modification manufacturers, when receiving customer demand will be in-depth understanding of the customer's situation and then make recommendations. So generally speaking, unless it is really because of technical immaturity, the material coating should not be a problem, because the coating can not be, then the waste is not only the customer's time but also a waste of time and sample cost of the sales staff. Therefore, we often need to analyze the reasons for not being able to wrap from the injection molding process.

　　From the process, there are the following points are worth your reference.

　　One: Two-color injection molding (2K molding) is better than two-step molding (2-step molding) effect.

　　Reason: simply put, the first step of the hard plastic is still hot when injected out, immediately into the second cavity of the 2K injection molding machine, the middle of the transfer process also did not absorb moisture, both easy to be a high temperature TPE melt in the surface ablation of ultra-thin layer, but also no water vapor on the surface is adsorbed effects;

　　Second: in the processing of TPE material within the allowable range, as far as possible to choose a higher barrel (melt) temperature, otherwise TPE easy how to have enough heat to ablate the surface of hard plastic material?

　　Third: the second step of overmolding, hard plastic as a mold cavity of the insert as high as possible mold temperature. Hard plastic temperature is high, TPE high-temperature melt cooling is slow, there is enough heat, enough time to erode the hard plastic to form a super-thin layer of mutual solubility;

　　Fourth: when the second step of overmolding, under the premise of not producing TPE flying edge, as far as possible to use high injection speed will be TPE melt injection.

　　(1) high injection speed, TPE in the hard plastic surface spread time is short, in the molding cycle has more time to ablate the hard plastic surface;

　　(2) High injection speed, the friction between the TPE and the hard plastic surface leads to frictional heat generation, and the TPE melt temperature cooling is also slowed down, which is used to contact and ablate the hard plastic surface for a longer period of time;

　　(3) high shooting speed, most of the TPE (except TPU, TPU melt viscosity is more sensitive to temperature) melt viscosity occurs shear thinning, surface tension decreases, conducive to spread in the hard plastic surface;

　　Fifth: to avoid the hard plastic surface of the moisture absorption or staining, especially in the two-step injection molding, hard plastic in the middle of the stop hair, transfer process, which is more likely to happen. Polar hard plastic such as PC, PBT, PET, POM, especially strong polar hard plastic such as nylon 6, nylon 66, surface hygroscopicity leads to the formation of water molecules with adsorption trip hydrogen bonding, TPE can not be effective with the hard plastic surface layer of the molecules between the formation of intermolecular bonding, the natural overmolding of the bonding force is reduced; hard plastic parts surface pollution, such as workers in the workshop gloves are not clean or gloves cotton fiber adhering to the polarity of the surface of the hard plastic parts, the natural impact of the TPE melt overmolding. Naturally affect the TPE melt adhesive package; wrapped polar hard plastic TPE, certainly also polar formula, do not pay attention to moisture, also affects the adhesive package bonding (cohesion) effect.

　　Sixth: the pre-test machine to pay attention to the problem of washing barrels

　　1, before there is PVC covered with glue.

　　2, before the production of hard rubber machine

　　If there really can not wrap the situation, so the first time to get in touch with the material supplier to get technical support. Of course, because in recent years the new TPE material dealers continue to emerge, the technology is constantly updated, but also a mixture of fish and dragons, do not rule out that some companies are trying to take chances to test whether they can meet the needs of customers, and the same sales staff is also in the technical aspects of half-knowledge, so there is a waste of customers' valuable time to test the material situation.