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The cells within the foam board vary in size, with some cells being unusually large and unevenly distributed. This can lead to large density fluctuations, a rough surface, and a significant decrease in mechanical properties (such as impact strength and flexural strength). In severe cases, it can even cause cell breakage or perforation.

This problem is directly related to the synergistic effect of the foaming regulator (ACR processing aid) and the foaming agent.

1. Insufficient or ineffective foaming regulator: The core function of foaming regulators (typically ACR processing aids) is to improve the melt strength and elasticity of PVC during the cell growth phase. If they are insufficiently added, unevenly dispersed, or the product itself is of poor quality, the melt strength will be insufficient to contain the gases generated by the decomposition of the foaming agent. The gases easily coalesce, break through the melt, and form large bubbles.

2. Poor compatibility between the foaming agent and the substrate: If the foaming agent is unevenly dispersed in the melt, this can lead to localized excessive gas concentrations, which can also easily form concentrated, large bubbles.

Appropriately increase the amount of foaming regulator to significantly enhance melt strength and elastic modulus, allowing the cell walls to withstand greater gas expansion forces without rupture.

Or, consider upgrading the product: choose an ACR product with a higher molecular weight or one specifically designed for high-efficiency foaming. These additives more effectively stabilize the cell structure and promote the formation of fine, uniform cells.

Check the mixing process to ensure that the foaming regulator is thoroughly mixed with other components (such as blowing agent, stabilizer, and PVC resin) to avoid inconsistent performance due to local concentration differences.

Appropriately lower the processing temperature to prevent premature or excessive decomposition of the foaming agent.

Adjust the screw speed and back pressure to ensure a more uniform plasticized melt, creating optimal conditions for bubble nucleation and uniform growth.