The board produces crystal point impurities. The reason is that PET sheets do not produce crystal point impurities due to raw materials. However, impurities or inferior raw materials introduced during the processing due to drying and environmental issues can result in the formation of crystal point impurity horizontal lines and water lines (orange peel lines) during the sheet forming process.

Water streaks are caused by the material flowing out of the PET sheet extruder die and entering the calendering roller. As there is no remaining material, the material is not compacted, and the surface of the sheet exhibits poor smoothness like orange peel. The solution is that there must be visible residue between the calendering rollers, and the residue should rotate evenly. Horizontal stripes are a process defect in the extrusion method, just like the water ripples in the calendering method, which are caused by the indentation due to the speed difference between the two calendering rollers. The solution is to require an increase in the three roll speed control accuracy of the three roll calender, while also improving the accuracy to reduce horizontal stripes& nbsp;

PET sheet yellowing, black spots or impurities, streamline, uneven calendering. The main reason for the formation of bubbles in the sheet is that the granules are not completely dried and have a moisture content exceeding 0.005%. If the moisture is not sufficiently dried, it will penetrate deep into the slice, indicating the formation or retention of molecular bonds. If the drying temperature is too low or the drying time is too short, it will affect the drying effect. When water bubbles appear on the sheet, the drying temperature and time should be adjusted immediately. The main reason for paper yellowing is that the drying temperature is too high or the drying time is too long. The main measure at this time is to lower the drying temperature and reduce the drying time. Another reason for board yellowing is that the melt temperature is too high. At this time, the melt temperature should be quickly lowered. The main reasons for black spots and impurities on the sheet are filter damage or residual PET decomposition products in the PET extrusion line.