Analysis of diffusion mechanism between gas and melt in gas-assisted injection molding

In the process of gas-assisted injection molding (GAIM), the high-pressure gas such as N2 comes to a supercritical state. The supercritical N2 diffuses into the polymer melt. After unloading the pressure, the N2 in the polymer melt achieves a super-saturation state. The super-saturated N2 close to the gas–melt interface diffuses through it, and the N2 close to the internal wall delays to diffuse and remains in the polymer melt to form the small bubble, the inner pressure of small bubbles is bigger than outside pressure, so the small bubble has grown up gradually. Finally the cellular gas bubble blemish was formed. To decrease the gas bubble blemish, the gas holding pressure should be reduced in the precondition of the product quality is reached. And to eliminate the gas bubble blemish, the gas holding time should be increased as long as possible, and gas pressure should vent until molding part temperature comes down below its glassily temperature.