[Bite Chemical] Several molding processing methods and precautions for ethylene-vinyl acetate copolymer (EVA)

Ethylene-vinyl acetate copolymer (EVA) is a general-purpose polymer that is flammable and has no irritating burning smell. It is a random copolymer of ethylene and vinyl acetate. It is understood that due to the introduction of short branch chains formed by polar acetate groups in the ethylene chain, the original crystallization state is changed, making EVA more flexible and elastic than polyethylene. EVA resin is characterized by good softness, rubber-like elasticity, good flexibility at -50°C, good transparency and surface gloss, good chemical stability, aging resistance and ozone resistance. OK, non-toxic. Good blendability with fillers, good coloring and molding processability.

The molding processing methods of ethylene-vinyl acetate copolymer (EVA) include the following types and precautions:

1. Injection molding: using general PE or The injection equipment used for PP is sufficient. Because EVA is elastic, it can be made into rubber-like products without the vulcanization process, and it is easy to color and the products are brightly colored. The lower limit of the molding temperature is to maintain a certain degree of fluidity, and the upper limit of the molding temperature is to prevent thermal decomposition of EVA. Its thermal decomposition temperature is about 229~230℃. Under normal circumstances, it is appropriate to control the material temperature at 170—200℃.

2. Vacuum forming: EVA vacuum forming products are smooth and transparent. However, due to its poor thermal conductivity and low melting point, the cavity mold temperature should be low and the molding cycle should be long. Generally, low-temperature cooling of the mold can be used for molding.

3. Blow molding film: General blow molding equipment can be used. Due to the low melting point of EVA, special consideration must be given to the cooling of the material. The traction force should be smaller, otherwise the opening of the film product will be poor. In addition, adding a slip agent should also be considered.

4. Foam molding: Pay attention to adjusting the amount of foaming agent during foam molding. Its foam products have the characteristics of elasticity, light weight, strength and low shrinkage.