(1) PET sheets produce impurities at crystallization points. The reason is due to raw materials and corner materials. PET sheets themselves do not produce impurities at crystallization points, but impurities or inferior raw materials generated during the processing due to drying issues and to some extent the addition of leftover materials in the environment cannot be removed during the PET sheet forming process.
(2) Horizontal and waterline. Water marks are caused by the flow of material generated by the extruder head entering the rolling rolls, where there is no residue between the rolling rolls, the material is not full, and the surface of the board is not as smooth as orange peel. The solution is to have visible residue between the embossing rollers, and the residue should rotate evenly. It is a process defect of the horizontal extrusion method, just like the nozzle of the rolling method, which is caused by the difference in speed between the two rollers of the rolling machine. The solution is to ensure that the speed control accuracy and synchronization accuracy of the three roll rolling machine are improved, thereby reducing the horizontal line.
(3) Paper yellowing, black spots or impurities, streamlines, uneven calendering, etc. The main reason for foaming is poor drying of the particles and zero moisture content. More than 005% indicates that the moisture is not dry enough and will penetrate into the slices, forming molecular bonds, or staying deep in the slices. Low drying temperature or short drying time can affect the drying effect. If the fragments blister, the drying temperature and time should be adjusted immediately. The main reason for the yellowing of bed sheets is that the drying temperature is too high or the drying time is too long, which reduces the drying temperature and drying time. Another reason for the yellowing of the sheet material is that the melt temperature is too high, and it is necessary to quickly reduce the melt temperature. The main reason for the appearance of black spots in the debris is due to filter damage or protruding residual PET decomposition material in the device.
Key points for PET sheet production (1) The primary conditions for PET transparent sheet production are the control of drying time and hot air dew point, and the drying effect directly determines the physical and mechanical properties and yield of the sheet. When drying, pay attention to adjusting the drying temperature and time. The drying temperature and time should not be too high or too low. If the dew point cannot be reduced, check the molecular sieve. Aging molecular sieves cannot absorb moisture from the air and cannot achieve the purpose of drying slices. Therefore, molecular sieves need to be replaced.
(2) When the melt temperature exceeds 280C, PET sheets will discolor or decompose, so the melt temperature should be adjusted below 280C.
(3) The crack gap of the head mold determines the flatness and thickness uniformity of the sheet metal. The temperature of the three rollers plays an important role in the transparency and surface finish of the sheet metal. The melt of PET should quickly avoid temperature regions with fast crystallization rates. The melt temperature instantly drops below the crystallization temperature, so the distance between the mold and the embossing roller is particularly important.
The main advantages of PET sheets are their exquisite appearance, good gas resistance, good protection, good toughness, and good expansion. PET sheets do not contain stabilizers and plasticizers, and do not contain harmful elements. Their prices are very good, so they are very popular among consumers. PET sheets can be recycled and reused during production, transportation, and use, therefore they have high practical value. In the production process of PET sheets, it is necessary to correctly grasp the drying process and hot air dew point according to the production process requirements, adjust the gap between rolling rollers and the subsequent unit traction speed ratio, and improve production quality.