Process conditions and process control for the production of PET sheets
DATE：2019/10/17 8:54:05 / READ： / SOURCE：This station
Process conditions and process control for the production of PET sheets
(1) Dry. PET resin is a highly water-absorbing polymer, and the polycondensation reaction of synthetic PET is a reversible reaction. Therefore, the presence of moisture in the melt extrusion process of PET will promote the hydrolysis of PET molecules. Hydrolysis reduces the relative molecular mass of PET, resulting in a decrease in physical properties, particularly impact strength, causing bubbles, streaks, blurring, etc. in the sheet. PET must be dried prior to melt extrusion to a moisture content of less than 0.005%, especially for high viscosity resins used in the production of sheets. PET will age during the drying process, the drying is not complete, and it will be hydrolyzed during processing. The effect of the drying process on it is: use large air flow rate, high drying temperature and long-term drying will age; use low drying temperature, low Air flow and short drying can cause hydrolysis.
Drying process conditions: air inlet temperature is 150 ° C, dew point is -29 ° C ~ -40 ° C, air flow is about 0.62 m 3 / min, drying time is about 5 h - 6 h. The moisture content after drying should be less than 0.05%.
(2) Extrusion. PolyPET resin is a crystalline resin with a melting point of 242 ° C -250 ° C, the operating temperature must be greater than the melting point, but PET is very easy to thermally degrade above 280 ° C, so the material temperature should not exceed 280 ° C. The barrier type screw is used, and the heating in the second zone is the initial stage of the compression section, and the temperature should be set higher, so that the PET is not aged due to excessive frictional heat generated by excessive shearing. The die temperature setting is about 5 ° C below the feed temperature, and the ends are slightly higher than the middle, and the slab is slightly lower than the sheet temperature. The extrusion temperature is set to:
One zone, 260°C-270°C; ニ zone, 275°C-290°C; three zones, 270°C～280°C; four zones, 255°C-265°C; five zones, 255°C-265°C; six zones, 255°C -265 ° C; connector, 255 ° C ~ 265 ° C; die area, 255 ° C -265 ° C.
Since molten PET is easier to bond metal, PP, PE, PETG are used to rinse the barrel and flow path during long shutdowns. Since the PET remains in the crystal state after being cooled in the barrel and the flow channel, the reheating heat requires a large heat of fusion, and needs to be preheated to 270 ° C to 280 ° C to ensure complete melting of the PET resin in the entire flow path.
The die opening is 1.2 times to 1.3 times the maximum production thickness of the product. The front die and lip area of the leader must be thoroughly cleaned with a brass knife, and any debris in the lip area will cause longitudinal streaks in the sheet.
(1) Dry. PET resin is a highly water-absorbing polymer, and the polycondensation reaction of synthetic PET is a reversible reaction. Therefore, the presence of moisture in the melt extrusion process of PET will promote the hydrolysis of PET molecules. Hydrolysis reduces the relative molecular mass of PET, resulting in a decrease in physical properties, particularly impact strength, causing bubbles, streaks, blurring, etc. in the sheet. PET must be dried prior to melt extrusion to a moisture content of less than 0.005%, especially for high viscosity resins used in the production of sheets. PET will age during the drying process, the drying is not complete, and it will be hydrolyzed during processing. The effect of the drying process on it is: use large air flow rate, high drying temperature and long-term drying will age; use low drying temperature, low Air flow and short drying can cause hydrolysis.
Drying process conditions: air inlet temperature is 150 ° C, dew point is -29 ° C ~ -40 ° C, air flow is about 0.62 m 3 / min, drying time is about 5 h - 6 h. The moisture content after drying should be less than 0.05%.
(2) Extrusion. PolyPET resin is a crystalline resin with a melting point of 242 ° C -250 ° C, the operating temperature must be greater than the melting point, but PET is very easy to thermally degrade above 280 ° C, so the material temperature should not exceed 280 ° C. The barrier type screw is used, and the heating in the second zone is the initial stage of the compression section, and the temperature should be set higher, so that the PET is not aged due to excessive frictional heat generated by excessive shearing. The die temperature setting is about 5 ° C below the feed temperature, and the ends are slightly higher than the middle, and the slab is slightly lower than the sheet temperature. The extrusion temperature is set to:
One zone, 260°C-270°C; ニ zone, 275°C-290°C; three zones, 270°C～280°C; four zones, 255°C-265°C; five zones, 255°C-265°C; six zones, 255°C -265 ° C; connector, 255 ° C ~ 265 ° C; die area, 255 ° C -265 ° C.
Since molten PET is easier to bond metal, PP, PE, PETG are used to rinse the barrel and flow path during long shutdowns. Since the PET remains in the crystal state after being cooled in the barrel and the flow channel, the reheating heat requires a large heat of fusion, and needs to be preheated to 270 ° C to 280 ° C to ensure complete melting of the PET resin in the entire flow path.
The die opening is 1.2 times to 1.3 times the maximum production thickness of the product. The front die and lip area of the leader must be thoroughly cleaned with a brass knife, and any debris in the lip area will cause longitudinal streaks in the sheet.
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