(1) PET sheet produces crystal point impurities. The reason is raw material and corner material. The PET sheet itself does not produce crystallization point impurities, but the impurities or inferior raw materials generated due to the drying problem and the poor environment caused by the addition of leftovers to a certain extent during the processing cannot be removed during the forming process of the PET sheet.

(2) Horizontal and water lines. Water marks are caused by the fact that there is no residue between the calendering rolls when the flow produced by the extruder head enters the calendering rolls, the material is not full, and the surface of the sheet is not as smooth as orange peel. The solution is to have visible residue between the embossing rollers, and the residue to be rotated evenly. It is a process defect of the horizontal extrusion method, just like the nozzle of the rolling method, it is the indentation caused by the speed difference between the two rolls of the calender. The solution is to ensure that the speed control accuracy of the three rolls of the three-roll calender is improved, and the synchronization accuracy is also improved, thereby reducing the horizontal line.

(3) The paper is yellow, with black spots or impurities, streamlines, uneven calendering, etc. The main reason for foaming is that the granules do not dry well and have zero water content. 005% or more, indicating that the water is not dry enough, it will go deep into the slice, form molecular bonds, or stay in the depth of the slice. If the drying temperature is too low or the drying time is too short, the drying effect will be affected. If the chips are blistered, the drying temperature and time should be adjusted immediately. The main reason for the yellowing of 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 sheet yellowing is that the melt temperature is too high and the melt temperature needs to be lowered quickly. The main cause of black spots in the debris is a broken filter or PET decomposed material remaining in the protruding device.

Main points of PET sheet production 

(1) The primary condition for the production of PET transparent sheet is the control of drying time and hot air dew point. The drying effect directly determines the physical and mechanical properties and output of the sheet. When drying, pay attention to adjusting the drying temperature and time. Drying temperature and time should not be too high or too low. If the dew point cannot be lowered, check the molecular sieve. Aged molecular sieves cannot absorb moisture in the air and cannot achieve the purpose of drying slices, so molecular sieves need to be replaced.

(2) When the melt temperature exceeds 280C, the PET sheet will change color 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 plate. The three-roll temperature plays an important role in the transparency and surface finish of the sheet. The melt of PET should quickly avoid the temperature region where the crystallization rate is high. The melt temperature drops below the crystallization temperature instantaneously, so the distance between the die and the embossing roll is particularly important.

The main advantages of PET sheet are beautiful appearance, good gas barrier, good protection, good toughness and good expansion. PET sheet does not contain stabilizers and plasticizers, does not contain harmful elements, and has a very good price, so it is very popular with consumers. PET sheet can be recycled in the process of production, transportation and use, so PET sheet has high use value. In the process of PET sheet production, according to the production process requirements, the drying process and hot air dew point should be correctly grasped, and the calendering roll gap and the traction speed ratio of the subsequent units should be adjusted to improve the production quality.