The PET products of China pet sheet extrusion line have high transparency, good gloss and glass texture. It has the advantages of strong tinting strength, easy molding and processing, good sanitation (in compliance with FDA), etc. It does not contain bisphenol A and belongs to a new generation of environmentally friendly plastics.
China pet sheet extrusion line PET sheet is like other plastics, its performance is closely related to molecular weight, and intrinsic viscosity determines molecular weight. The lower the intrinsic viscosity, the poorer the physical and chemical properties and the poor impact strength. Therefore, the intrinsic viscosity of the PET transparent sheet should be selected from 0.8dl/g to 0.9dl/g.
China pet sheet extrusion line production process
The leading production equipment of China PET transparent sheet is: crystallization tower, drying tower, extruder, die head, three-roll calendar, and coiler.
The production process is raw material crystallization-drying-extrusion plasticization-extrusion molding-calendering-setting-rolling products.
Crystallization. The PET slices are heated and crystallized in the crystallization tower so that the molecules are arranged neatly, and then the glass transition temperature of the slices is increased; the purpose is to prevent sticking during the drying process and block the hopper. Crystallization is generally an indispensable step, crystallization takes 30 minutes to 90 minutes, and the temperature is less than 149 °C.
Dry. Under high temperature conditions, water can hydrolyze and degrade the PET of the China pet sheet extrusion line, resulting in a decrease in its intrinsic viscosity, and its physical properties, especially impact strength, will decrease with the decrease in molecular weight. Therefore, PET must be dried before melt extrusion to reduce the moisture content, and its moisture content should be less than 0.005%. Dehumidification dryer is used for drying. Due to the hygroscopicity of PET material, molecular bonds will be formed when the moisture penetrates the surface of the slice, and another part of the moisture will exist deep inside the piece, making drying difficult. Therefore, ordinary hot air cannot be used. The dew point of the hot air must be below -40C, and the hot air is fed into the drying hopper through a closed loop for continuous drying.
For extrusion moulding. After crystallization and drying, PET is transformed into a high polymer with an obvious melting point. The high polymer has a high moulding temperature and a narrow temperature control range. The China pet sheet extrusion line uses a polyester-specific barrier screw to separate unmelted pellets and melts, which is beneficial to maintain a more extended shear history and increase the output of the extruder.
China pet sheet extrusion line adopts flexible die lip die head with streamline blocking rod; the die head is sharp cone, streamlined runner and scratch-free die lip show good finish, the heater of the die head has a clean. For cleaning, the die lip gap should ensure good uniformity. The uniform dies lip gap of the die directly affects the lateral thickness deviation of the sheet and the smoothness of the calendering.
Cooling and setting. China pet sheet extrusion line The melt comes out of the machine head and directly enters the three-roll calender for calendering and cooling. The distance between the three-roll calendar and the machine head is generally maintained at about 8cm because if the space is too large, the sheet is easy to It sag and wrinkles, resulting in poor sheet finish. In addition, because the distance is too large, the heat dissipation and cooling are too slow, resulting in whitening of crystals, which is not conducive to calendering.
Carry out pulling and coiling. China pet sheet extrusion line sheet comes out through the calender roll and enters the pulling device from the guide roll. The components of the traction device are active rubber rollers and passive rubber rollers. The two rollers are mainly compressed by air pressure to prevent the sheet material from being flattened by the calendering roller while pulling the sheet through the two rollers to the coiling device.
PET transparent sheet production points
(1) The primary conditions for producing PET transparent sheets of China pet sheet extrusion line are the control of drying time and hot air dew point. The drying effect directly determines the sheet's physical and mechanical properties and production. When drying, attention should be paid to controlling drying temperature and time. The drying temperature and time should neither be too high nor too low.
(2) If the melt temperature exceeds 280C, the PET sheet will be discoloured or decomposed, so the melt temperature should be controlled below 280C.
(3) China pet sheet extrusion line die lip gap determines the flatness and thickness uniformity of the sheet. The temperature of the three-roller plays a vital role in the transparency and smoothness of the sheet. The PET melt needs to quickly avoid the fastest crystallization. In the speed temperature zone, the temperature drops from the melting temperature to below the crystallization temperature instantly, so the distance between the die and the calender roll is critical.
China pet sheet extrusion line product advantages
china pet sheet extrusion line, the main advantages of PET transparent sheet are crystal clear appearance, sound gas barrier, good protective drug, toughness and extensibility.
- PET transparent sheet is favored by consumers because it does not contain any stabilizers and plasticizers, does not contain harmful elements, and has a good price.
- JWELL as China pet sheet extrusion line manufacturer, PET transparent sheet can be recycled in production, transportation and use. Therefore, PET transparent sheet has high use value.
- In the PET production process, the drying process and the dew point of the hot air should be mastered in strict accordance with the production process requirements, and the gap between the calendering rollers and the traction speed ratio of the subsequent units should be well controlled, to improve the production quality.
The development prospect of PET sheet
PET can be processed into heat shrinkable film and various injection products, widely used in food packaging, cosmetic packaging, medical packaging and other fields. The average annual growth rate of consumption from 2016 to 2022 is more than 10%. As an environmentally friendly material, PET complies with FDA food contact standards. It is non-toxic and harmless to the human body and the natural environment. It will not produce unpleasant odours during thermal processing, will not release toxic gases during incineration, and will not pollute after landfill treatment—groundwater source. With the consumption upgrade of Chinese residents, the attention to health, environmental protection and high-quality products will continue to increase, which is conducive to the development of PET in food packaging, cosmetic packaging and medical and health care.
As a China pet sheet extrusion line manufacturer, JWELL manufactures plastic extrusion equipment that meets the needs of middle and high-end users. Rigorous design, strict, standardized manufacturing process and perfect after-sales service guarantee system provide users with high efficiency, energy-saving and excellent quality. Advanced production line equipment and considerate service. If necessary, please feel free to contact China JWELL.