PET sheet

日期:2019/6/11 8:53:15 / 阅读: / 来源:本站

PET sheet
1. Selection of raw materials and their performance
PET sheet raw materials mainly choose random polyethylene terephthalate (APET).
(1) Characteristic viscosity. The performance of APET is related to the relative molecular mass, and the relative molecular mass is determined by the intrinsic viscosity. The characteristic viscosity is low, the physical properties of the sheet are poor, the impact strength is low, the characteristic viscosity is high, the physical properties of the sheet are improved, the impact strength is large, but the fluidity is poor, the extrusion load is large, and the molding is difficult. Therefore, it is preferable to produce an APET sheet with a polyester resin having an intrinsic viscosity of 0.76 to 0.85.
(2) Melting point. The homopolymer melting point of PET is 263 ° C - 265 ° C, and the melting point of PET copolymer varies greatly due to the content of excipients and auxiliary materials copolymerized by various raw material manufacturers. Commonly used copolymer materials are isophthalic acid (1A), cyclohexanedimethanol (CHDM), diethylene glycol (DEG), etc., generally use a confocal polyester resin with a melting point of 242 ° C -250 ° C, so that its melting point is low, easy Extrusion processing, high crystallization temperature, slow crystallization rate, and easy secondary molding of APET sheet.
(3) Acetaldehyde content. The thermal decomposition of the polyester produces acetaldehyde, which is odorous and toxic, so it is required to be less than two parts per million.
(4) Moisture content. The moisture content of the APET resin directly affects its drying effect, requiring a moisture content of less than 0.3%.
(5) Yellow index. APT sheets are often used as visual packaging materials, requiring a yellow index of L greater than or equal to 85, b ≤ 0.5
6) The content of carboxyl groups at the end, the content of COOH can be used as an index to measure the thermal stability of PET. Generally, the end group carboxy content is less than 0.03 mol/kg. In addition, the thermal stability and crystallization properties should be considered. The heat aging causes the intrinsic viscosity to decrease and the color to become yellow; the crystallization speed of the polyester resin used for extruding the APET sheet is as slow as possible.
 

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