Is the elastomer material TPE encapsulated bad? Find the reason from the craft!
There are two main ways in which TPE can be overmolded
1. A two-component molding or two-color injection molding, that is, on a two-color injection molding machine, a material is injection molded into a product, and then a mold is applied on the two-color machine. The flipping jumps to the corresponding mold cavity of the other plastic injection cylinder, and the component is used as an insert, and another material is injected thereon to form an integrated double-material product. The injection molding machine is a double barrel and a double mold cavity. The injection molding process is simultaneous production of two kinds of materials, but only one cavity product will enter the next cavity as an insert.
2. The other is a two-step injection molding in which a part of a material is formed on an injection molding machine, and the part is placed as an insert in another mold. Re-inject the second material.
Methods for achieving overmolding (including encapsulation) can be physically snapped and chemically.
The former, for example, by snap design, surface roll, surface tapping, and then coated with a second material to achieve overmolding (encapsulation). The feature of material bonding by this method is that the physical joint has strong adhesion, and the part outside the physical joint has little adhesion.
The chemical method relies on the molecular affinity between the two materials, the bonding force of the chemical bond, the two materials are bonded together to form a single part, two And even more.
Although physical snapping and chemical bonding are often used together in practice, it is clear that chemical bonding between the two materials is more robust, A preferred method of greater freedom of design.
This strong chemical bonding involves the mutual dissolution, penetration, penetration, and molecular entanglement of molecular or molecular segments.
To achieve TPE/hard plastic molecular layer bonding, the key is to do the following three things:
1. The TPE material is similar in polarity to the hard plastic (otherwise it cannot dissolve, penetrate, penetrate in the melt state);
2. The surface tension of the TPE material is less than the surface tension of the hard plastic (otherwise the TPE melt will not spread over the surface of the hard plastic insert);
With regard to surface tension, think about the fact that mercury shrinks on the surface of the glass, and the water droplets spread out on the surface of the glass, which is easy to understand;
3. When the TPE melt flows along the hard plastic surface in the mold cavity, the cooling process releases heat, which can quickly and effectively melt the hard plastic surface to form a thin inter-wearable Floor.
The reason why the cover can not be covered is definitely the first reason is that the TPE material formula is not good, this is also the customer's first reaction, then change the factory to find the sample, waste A lot of time and energy, but if it is an experienced salesperson and a modified manufacturer, when you receive the customer's demand, you will definitely understand the customer's situation and then make recommendations, so generally speaking, unless it is really because the technology is not mature, the material The wrapping should be no problem, because it can't be covered, so it is not only the customer's time but also the time and sample cost of the salesman. So many times we have to analyze the reasons why we can't cover it from the injection molding process.
In terms of craftsmanship, the following points are worthy of reference.
One: Two-color injection molding (2K molding) is better than 2-step molding.
Reason: To put it simply, the first step of the hard plastic is still hot when it is injection molded. It immediately enters the second cavity of the 2K injection molding machine, and the intermediate transfer process does not suck. Tidal, it is easy to be ablated by the high temperature TPE melt on the surface of the ultra-thin layer, and there is no effect of moisture on the surface;
2: In the processing allowable range of TPE material, use a higher barrel (melt) temperature as much as possible, otherwise TPE is easy to have enough heat Ablation of hard plastic surfaces.
Three: When the second step of encapsulation, the hard mold is used as the cavity of the insert as much as possible. The hard plastic temperature is high, and the TPE high temperature melt is cooled slowly, and there is enough heat and enough time to ablate the hard plastic to form a super soluble thin layer.
Four: In the second step of encapsulation, the TPE melt is injected at a high rate of fire as much as possible without generating a TPE flash.
1) High rate of fire, TPE has a short spreading time on hard plastic surfaces and a longer ablation of hard surfaces during the molding cycle;
2) High rate of fire, friction between TPE and hard plastic surface causes frictional heat generation, TPE melt temperature is also slowed down, and longer time is used for contact and ablation Plastic surface;
3) High rate of fire, most TPE (except TPU, TPU melt viscosity is more sensitive to temperature). The melt viscosity is shear thinning and the surface tension is reduced. Conducive to spreading on hard plastic surfaces.
Five: To avoid the moisture absorption or staining of the hard plastic surface, especially in the two-step injection molding, the hard plastic is in the middle of the stop and transfer process, which is even more It is easy to happen. Polar hard plastics such as PC, PBT, PET, POM, especially strong polar hard plastics such as nylon 6, nylon 66, the surface moisture absorption leads to the formation of hydrogen molecules with the adsorption of hydrogen molecules, TPE can not effectively form molecules with hard plastic surface molecules Inter-bonding, the natural bonding power of the bonding force is reduced; the surface of the hard plastic part is dirty, such as the workshop worker's gloves are not clean or the glove cotton fiber adheres to the surface of the polar hard plastic part, which naturally affects the encapsulation of the TPE melt; The hard-plastic TPE is definitely a polar formula, which does not pay attention to moisture, and also affects the cohesion effect of the rubber.
Six: Pay attention to the problem of washing the barrel in the early stage of the test.
1, before the use of PVC plastic
2, before is the production of hard rubber machine
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