Combining the core root causes of yellowing in PVC foam shoe soles, this analysis delves into the reasons behind PVC yellowing and preventive measures. By focusing on two key dimensions—"raw material control + process optimization"—it delivers a practical anti-yellowing solution that balances environmental sustainability with production efficiency. The specifics are as follows:
1. Select the right core raw materials to lay the foundation for anti-yellowing (source blocking)
- Prioritize the use of specialized high-temperature calcium-zinc thermal stabilizers: This is the core step for yellowing resistance. The preferred choice is environmentally friendly calcium-zinc thermal stabilizers specifically for footwear materials (e.g., Rongjia RJ-902, RJ-903), which offer excellent thermal stability, light initial coloring, and high whiteness. They can withstand high-temperature processing around 200°C, effectively preventing PVC resin decomposition and yellowing. Additionally, they reduce mold carbon buildup, decrease demolding frequency, and save energy and labor costs.
- Select low-migration environmentally friendly plasticizers: Avoid phthalate-based plasticizers and prioritize the use of environmentally friendly, low-migration types such as DOTP and polyester-based plasticizers. If epoxy-based plasticizers are used, strictly control the dosage and adhere to the principle of "just enough," avoiding excessive amounts that may trigger yellowing.
- Matching foaming agent and processing temperature: Select a foaming agent with the same decomposition temperature based on the processing temperature of PVC resin; Small batch testing must be conducted before production to ensure complete decomposition of the foaming agent, reduce residual amounts, and lower the risk of yellowing from the source.
- Optimize microsphere and regulator parameters: Based on the flowability requirements of the formula, accurately control the amount of microspheres used to avoid affecting material flow; Simultaneously selecting viscosity modifiers to ensure stable material flowability, uniform heating during processing, and reduced local degradation and yellowing.
2、 Optimize production processes and safeguard the key to anti yellowing (process protection)
- Segmented precise temperature control+timely cooling: Combining equipment characteristics and formula requirements, refine the temperature settings of each section of the screw, shorten unnecessary high temperature zones, and prevent excessive degradation of materials; Strictly control the temperature of the mold, immediately perform cooling treatment after processing, quickly dissipate residual heat inside the sole, and protect the integrity of the material structure.
- Precise control of formula ratio+process sampling: Before production, the optimal ratio of stabilizer, plasticizer, and foaming agent is determined through professional calculation and small-scale testing to avoid yellowing caused by excessive or insufficient single raw materials; Regular spot checks are conducted during the production process to ensure stable formula ratios and eliminate the risk of yellowing at the process level.
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