PET sheet

1. Selection of raw materials and their properties

The main raw material of PET sheet is random polyethylene terephthalate (APET).

(1) Intrinsic viscosity. The performance of APET is related to the relative molecular mass, and the relative molecular mass is determined by the intrinsic viscosity. The intrinsic viscosity is low, the physical properties of the sheet are poor, and the impact strength is low; the intrinsic viscosity is high, the physical properties of the sheet are improved, and the impact strength is high, but the fluidity is poor, the extrusion load is large, and molding is difficult. Therefore, it is better to produce APET sheet with polyester resin with intrinsic viscosity of 0.76-0.85.

(2) Melting point. The melting point of PET homopolymer is 263°C-265°C, and the melting point of PET copolymer varies greatly due to the different content of excipients and excipients copolymerized by various raw material manufacturers. Commonly used copolymerization materials include isophthalic acid (IA), cyclohexanedimethanol (CHDM), diethylene glycol (DEG), etc., and the co-condensation polyester resin with a melting point of 242°C-250°C is generally used, so that its melting point is low and convenient. Extrusion processing, high crystallization temperature, slow crystallization speed, convenient for secondary molding of APET sheet.

(3) Acetaldehyde content. Acetaldehyde is generated when polyester is heated and decomposed, and acetaldehyde is odorous and toxic, so its content is required to be less than 2 parts per million.

4) Moisture content. The moisture content of APET resin directly affects its drying effect, and its moisture content is required to be lower than 0.3%.

(5) Yellow index. APT sheet is often used as a visual packaging material, and its yellowness index is required to be L=85, bS.5

(6) Carboxyl terminal content. The content of COOH can be used as an index to measure the thermal stability of PET. Generally, the end group content is required to be less than 0.03moL/kg; in addition, its thermal stability and crystallization performance must also be considered. PET is prone to thermal aging, which reduces the intrinsic viscosity and color Yellowing; the slower the crystallization rate of the polyester resin used to extrude the APET sheet, the better. To sum up, the US Eastman PET9921 was selected. The auxiliary material used for extruded APET sheet is preferably PET or PETG-based masterbatch, and it cannot affect the transparency of the sheet. The dosage is generally 2% to 5%. The selected additives are: anti-sticking agent PETG6763007, denesting agent PET9921c0019, color masterbatch PET9921001 antistatic agent SARMSTAT G33690.