Low Pressure Injection Molding

Low-pressure injection molding process is a kind of encapsulation process that uses very low injection pressure (0.15-4MPa) to inject hot melt material into the mold and cures it quickly. The skin is put into the mold in advance, and then the molten plastic is injected into the closed cavity by the thrust of the screw, and then the product is obtained after curing and shaping. The material used for low pressure injection skin can be fabric or PVC fabric.

The excellent physical and chemical properties of the hot melt material are used to achieve insulation, temperature resistance, impact resistance, vibration damping, moisture resistance, water resistance, dust resistance, chemical corrosion resistance and other effects, which play a good role in protecting electronic components.

At present, this process has been widely used in the production of automobile door guards, column guards and parcel shelf guards, etc.

(1) Low-pressure injection molding is to fuse the skin material with the plastic base material, so there is no possibility of peeling off.

(2) The process of low pressure injection molding is more environmental friendly because there is no glue application process which is necessary for the over molding process.

(3) The internal structure of low-pressure double-layer injection molded parts can be designed arbitrarily, and the freedom of surface modeling is greater than that of the overmolding process, and the modeling features are clearer and more rigid.

(4) Low-pressure injection molding does not require additional secondary cladding, which improves production efficiency.

(5)Low-pressure injection molding products have good handfeel and appearance.

(6)Low pressure injection molding products have low injection pressure, which can effectively protect the internal parts of the product and low scrap rate.

1) Fabric ductility and tension

Nowadays, the fabrics used in low-pressure injection molding are the bottom non-woven fabric + foam layer + surface fabric layer. Due to the compression of the mold and the extrusion of molten plastic, the longitudinal and lateral extension of the fabrics are different, and the phenomenon reflected on the products is also different. One of the most prominent problems is: seepage of material, breakdown, breakage. That is, in the case of constant die state and constant process conditions, the characteristics of the fabric have a great impact on the quality of the product. The same elongation longitudinal and transverse to different molds also have different adaptability, some molds may have high requirements for longitudinal elongation due to design limitations, and some molds may have high requirements for transverse elongation. So in the trial production of new products, new molds need to consider this issue.

2）Flowability of plastic

The index to evaluate the fluidity of plastic is: melt index MI value. We all know that the flow of plastic on the fabric is much slower than on the smooth mold cavity, which is why the fabric low pressure injection mold has more gates than the ordinary mold. The slow flow rate will inevitably affect other appearance problems of the product, such as bond marks, missing material, etc.

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