日期：2022/3/15 8:45:37 / 閱讀： / 來源：本站
PET sheet1. Selection and performance of raw materials
Random polyethylene terephthalate (APET) is the main raw material of PET sheet. (1) The characteristic degree t property is related to the relative component mass, and the relative molecular mass is determined by the intrinsic viscosity. Low physical viscosity and poor impact strength of the sheet; High intrinsic viscosity, improved physical properties of the sheet, high impact strength, but poor fluidity. Extrusion load is large and forming is difficult. Therefore, it is better to produce PET sheet with polyester resin with intrinsic viscosity of 0.76-0.85.
(2) Melting point of 263265pet copolymer at point t. Due to the different contents of auxiliary materials and auxiliary materials copolymerized by various raw material manufacturers, there are great changes. Commonly used copolymerization materials include isophthalic acid (IA), cyclohexanedimethanol (CHDM), diethylene glycol (DEG), etc. generally, polycondensated polyester resin with melting point of 242 ~ 250 ℃ is selected, which has low melting point, is convenient for extrusion processing, high crystallization temperature and slow crystallization speed, and is convenient for secondary molding of APET sheet
(3) Acetaldehyde content is decomposed by heating to produce ethylene, which has odor and toxicity, 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 less than 0.3%.
(5) Yellow index APET sheet is commonly used as visual packaging material, and its L value of yellow index is required to be ≥ 85 and b value ≤ 0.5.
(6) The content of terminal carboxyl group and the content of COH can be used as an index to measure the thermal stability of pet. Generally, the content of terminal carboxyl group is required to be less than 0.03mol/kg
In addition, its thermal stability and crystallinity should be considered. Pet is easy to heat aging, which reduces the intrinsic viscosity and turns yellow. The slower the product speed of juku resin used to extrude APET sheet, the better. To sum up, pet9921 of Eastman is selected. It is used for good material and can not affect the transparency of the sheet. The dosage is generally 2% 5%. The selected additives are
(20001: antistatic agent sarmst4tg33690 European patch eg67630047: degumming agent 9921c019 Color Masterbatch pe9)
2. It is mainly equipped with various pieces of European wet and dry air flow drying of Q) system. Need one that can provide a temperature of 10 ° C
Stainless steel heat preservation and drying hopper with polyester resin staying for at least 5h- A dehumidification dryer with air flow of about 0.062m/min at 29-40 ℃ and a set capable of maintaining
(2) The length diameter ratio of T-piece produced by the machine is 241 ~ 30:1, and the short length diameter ratio can not make the output stable and the productivity high. The driving power of the extruder is required to be 0.16 ~ 0.2KW / (kg / h). The screen gauge rod designed for polyester of $100 ~ $150mm is used. The first four screw edges of the screw feeding section need to be cooled. The barrel heating is generally divided into 5-6 sections. The heating power can make the temperature of the machine reach 315 ℃, and each area should be equipped with cooling devices to ensure the temperature control grid. The filter screen adopts 2020 mesh, 120 mesh X120 mesh, 60 mesh X60 mesh and 20 day X20 mesh
Objective stainless steel mesh overlay.
(3) When the volume of the pump is greater than 25% and the return material used is thin, the longitudinal thickness error will be greater than ± 6%. Therefore, a melt metering pump with constant speed and stepless speed regulation is required. A melt pressure controller is equipped between the extruder and the pump to stabilize the extrusion volume.
(4) the section is 2532mm. The surface of all flow channels shall have extremely low roughness (0.05 ~ 0.1pm) and be of streamlined design. The maximum opening of the die head is 125 times the maximum production thickness of the product. The outer surface of the die head shall be conical.
(5) The cooling roller for producing APET sheet with three rollers can be vertical, flat or inclined 45. The roller diameter is 400 ~ 500mm. The surface should be chrome plated and the surface roughness is
0.05 ~ 0.1M, the concentricity and cylindricity of rollers shall not exceed 0.025mm, the mutual matching accuracy of rollers shall be within ± 0.075mm, and the cooling device of three rollers shall be equipped with temperature control device.
3. Process flow and process control
(1) In the process flow, PET sheet polyester pellets are used as raw materials. Polyester auxiliary materials such as color mixing masterbatch, antistatic agent, de nesting agent and anti adhesion agent are mixed according to different purposes. After metering and mixing, they are sent to the flat drying. The dried aggregate is baked, melted and plasticized by the extruder and filtered 329 through the filter screen
The learning body is quantitatively transported to the die head, and flows to the three rollers through the die head. It is cooled and calendered to obtain the recycling process of amorphous and image protecting materials. After cooling, the t-sheet is cut into a roll, and the edge material is crushed, metered and mixed, extruded, cooled and calendered by the metering pump. The edge cutting is pulled to roll the waste edge of the finished product