How to solve the problem of yellowing of PVC transparent sheets (plates)?

How to solve the problem of yellowing of PVC transparent sheets (plates)?

During the production of PVC transparent sheets (plates), due to the poor thermal stability of PVC itself, when the extrusion temperature is too high or the heating time is too long, it is easy to cause the transparent sheets (plates) to turn yellow. 
The main measures usually adopted to solve the problem of yellowing in actual production are: 
① Strictly control the heating-up time in accordance with the process requirements. The heating-up time should not be too long. If a malfunction or other reasons cause a temporary shutdown, all the materials in the barrel should be extruded out immediately, and the temperature of each section of the extruder should be reduced for cooling. 
② Appropriately reduce the temperature of the extruder barrel; 
③ Adjust the raw material formula, improve the thermal stability of the raw materials, and increase lubricity. 
④ Adding a trace amount of blue or purple pigment or fluorescent brightener in the range of a few parts per ten thousand can mask the slight yellowish tint of the resin itself, but the usage should not be excessive as it may affect transparency.
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