Calendered transparent pvc sheet is one of the main varieties of rigid PVC. It is usually produced by conical twin-screw extrusion. Common problems encountered in the production process are: bubbles, more crystal points, and yellowing of the sheet. Yellow color

The causes and solutions are:

First, the PVC itself is poorly stable

If it is a new PVC resin manufacturer, the stability of the PVC itself may be poor. You can change the PVC and try it. However, even the brand of PVC that has been used may be caused by the PVC resin itself, because even if the same manufacturer produces PVC, the quality may vary from batch to batch.

Second, insufficient stabilizer

Third, the temperature controller has a problem

The displayed temperature is lower than the actual temperature. If the temperature is too high, the PVC will decompose and yellow. In this case, you need to re-check the calibration temperature controller. The method is very simple. In actual production, due to loose thermocouples, sticking materials, etc., the temperature display of the temperature controller will be different from the actual temperature. It is also recommended to use a high-quality temperature controller.

2. Sheets have small bubbles

Causes:

①. Excessive moisture in PVC raw materials: If the raw materials are damp in the rainy summer days, the water may not be fully discharged in the barrel, expand by heating, and then form bubbles in the sheet.

② In addition, there may be too high moisture content in the auxiliary.

In summary, the solution can be adopted: Properly extend the mixing time of the hot mixer and use a cooling mixer. Can effectively remove the moisture of raw materials.

3. The number of crystal points in the sheet exceeds the standard, also known as fisheye

The common cause of crystal point is: some PVC resin particles are not plasticized, or plasticization is not good. The reasons for this are: the quality of the PVC resin itself is not good. Without changing the PVC resin, the solutions are:

First, appropriately extend the mixing time and increase the mixing temperature to promote the absorption of additives. And the use of high-quality mixing unit, the pre-plasticizing effect of the mixing unit on the material is irreplaceable.

Second, the mixed raw materials can be left for half a day or one day to be matured and then used.

Third, the set temperature of the barrel can be appropriately increased, the screw rotation speed can be increased, and the head pressure can be increased to further improve the plasticizing performance.

Fourth, in the formulation, we must carefully choose the appropriate additives, and the amount of additives. At present, the market for additives is very chaotic, and the quality of the products varies widely. We must carefully choose and find a good balance between price and performance .

In summary, we must comprehensively consider the above multiple reasons and choose the optimal solution. Some solutions have contradictory relations, such as increasing the temperature may cause the sheet to yellow, and adding more stabilizers may cause the cost to rise. Only in practice can we explore the way forward.