What are the main reasons for the excessive density of surface skinning core layer microfoamed profiles? How to solve it?

What are the main reasons for the excessive density of surface skinning core layer microfoamed profiles? How to solve it?


The main reason is: 
① If the amount of foaming agent in the formula is too small or the dosage of foaming accelerator is improper, the density of the product will be too high. When the foaming accelerator is insufficient, the decomposition temperature of the foaming agent is higher than the extrusion temperature, which will cause the surface skin core layer micro-foamed product density to be too large. When the foaming accelerator is excessive, the foaming agent will decompose in large quantities in the barrel before the resin is plasticized, and the gas will escape from the feed port and the vacuum system of the main machine, resulting in a large density of the surface skin core layer micro-foamed product.
② The temperature control is unreasonable. The temperature at the front end of the screw is too high, causing the foaming agent to decompose prematurely, or the temperature of the melt is too low, resulting in insufficient decomposition of the foaming agent.

③ The melt pressure is too low; If the length of the cooling skinning system is too long, the cooling water volume is too large, or the cooling water temperature is too low, it will cause the skinning layer to be too thick, resulting in a higher density.


The solutions are as follows:
①Adjust the dosage of the foaming agent or foaming accelerator in the formula.
②Adjust to the appropriate process temperature.
③ By adjusting the relationship between the main machine's rotational speed and the feeding rate, increasing the length of the straight section of the die, and reducing the gap of the die lip, the melt pressure can be increased.
④ Shorten the length of the cooling skin system, adjust the temperature of the cooling medium and the amount of cooling water.
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