Plastic Film Extrusion Molding
DATE：2022/10/13 8:50:34 / READ： / SOURCE：This station
Plastic Film Extrusion Molding
③ Pay attention to the temperature control of the cylinder when the resin is plasticized. As PS material is a thermosensitive resin melt, its temperature is too high or it stays in the cylinder for too long, which will easily cause the melt to decompose. ④ When extruding and blowing PS resin to form the film, the air ring shall be used to cool and expand the film bubble. The gap between the blowing ports shall be smaller, the wind speed shall be stable, and the air volume blowing around the film bubble shall be uniform to maintain the stable operation of the film bubble. The blowing expansion ratio shall be less than 2.5 times, and the height of condensate line shall be controlled at100~150mm.
⑤ In order to ensure the full cooling of the blown film, it should be noted that the distance between the traction roller and the outlet of the forming die should not be less than 15% of the die mouth diameter.
⑥ For the stretching of polystyrene sheets, it is appropriate to control the stretching ratio within the range of 2.0~2.5 times; The longitudinal and transverse stretching ratio of the membrane should be close (preferably 1:1), which is conducive to the improvement of the membrane performance.
The preheating temperature of the longitudinal stretching roll is 100~110 ℃, and the speed of the preheating roll is slightly faster than that of the casting cooling roll. The temperature of the longitudinal stretching roll is about 110 ℃, the transverse stretching preheating temperature is about 120 ℃, the temperature of the stretching section is about 125 ℃, and the temperature of the setting section is about 110 ℃.
⑦ The polystyrene film with thickness no more than 0025mm can also be produced by extrusion flat tube stretching method. The production mode is shown in Figure 6-38. The heating temperature of extruder barrel is 130~160 ℃, 160~180 ℃, 180~200 ℃. The membrane tube bubble is extruded from the forming die and introduced into the guide roller composed of several small holes. The membrane tube is drawn by the guide roller at the temperature of 100~130 ℃, and cooled and shaped with cold air. Longitudinal and transverse stretching of film produced by this method
Figure 6-38 Schematic Diagram of Polystyrene Extruded Flat Tube Stretch Film
1 - Forming mold; 2 - Stretch guide roller frame; 3 - Guide roller; 4 - Traction roller; 5 Plastic extrusion molding technologist manual of one coiler roll
The multiples are all 3 times.
(5) The quality requirements of polystyrene film (sheet) are specified in B/T7191996. See Table 6-46 for the thickness and deviation values of biaxial stretch film (sheet). See Table 6-47 for the physical and mechanical property indexes of film (sheet).
Table 6-46 Thickness and Deviation of Biaxially Stretched BOPS Film (Sheet)
6.6 Extrusion and stretch molding of polyethylene terephthalate (PET) film
Polyethylene terephthalate (PET) is one of the most widely used polymers in polyester industry. The film produced by PET is generally extruded and cast, and then biaxially stretched into a stretched PET film, which is called BOPET film for short.
(1) Application Characteristics of BOPET Film
① BOPET film has no peculiar smell, odor and high transparency, and the film thickness is usually in the range of 0.01~0.10mm.
② BOPET film has a wide range of application temperatures, which can be used at 150 ℃, and can be used for a long time at temperatures below 120 ℃; Low temperature resistance to - 70 ℃.
③ It has excellent mechanical properties, and the tensile strength can reach above 200MPa. ④ It is moisture-proof, waterproof and has less air permeability. ⑤ Excellent electrical insulation performance.
Chapter 6 Plastic Film Extrusion Molding
⑥ In addition to being able to crack under the action of strong acid, strong alkali and water vapor, it has good chemical resistance.
⑦ The product is not easy to burn (ignition point 480 ℃), and cracking starts when the temperature is above 420 ℃. (2) Application of BOPET film Due to its high strength, excellent solvent resistance, weak acid and alkali resistance, good heat resistance and electrical insulation, BOPET film is widely used in various electrical equipment and instruments. For example, it is used as packaging film in motors, capacitors and transformers; It is used as film, X-ray film, etc. in photosensitive materials; Make the base material of audio and video tapes and the packing film of various articles; Vacuum aluminized film, such as gold foil and silver foil, can be used as gold and silver thread and other decorative products of 8 ± 7.
(3) Forming process
① Biaxially stretched BOPET film (sheet) shall be selected as raw materials for production, and PET raw materials with intrinsic viscosity of 0.59~0.69 n shall be selected. Generally, raw materials are selected according to the purpose of the film (film): for example, PET film (film) products can be produced by selecting video tape base grade, packaging film grade, audio tape base grade and other polyester chips produced by Shantou Ocean (Group) Co., Ltd. Polyester Chip Factory. Note: The raw materials shall be dried in an oven at 140~160 ℃ for 4h before being put into production.
② The equipment conditions are the same as those for biaxial stretching of polypropylene, as shown in Fig. 6-35.
③ The production process uses the most raw materials for drying treatment → extruded raw materials are in molten liquid → molten materials are filtered and then enter the forming mold → cast onto the cooling roller to cool and shape the film → longitudinal stretching → transverse stretching → traction → thickness measurement → trimming → PET thin limit is rolled with the extrusion flow shop
④ Extrusion drawing process temperature
a. Extruded melt temperature 260~280 ℃ Application film
b. The temperature of casting cooling shaping roller is - 60~70 ℃.
c. The stretching temperature of the diaphragm is about 90 ℃ for longitudinal stretching and about 100 ℃ for stretching; Transverse stretching preheat 95~100 ℃, stretching 100~105 ℃. d. The heat setting temperature of BOPET film is 220~240 ℃. The tensile ratio is 2.5~4 times, and the longitudinal and transverse tensile ratios are close.
(4) Key points of process operation for extruding biaxially oriented BOPET film: ① The moisture content of raw materials after drying shall not exceed 0.095%. ② The screw structure suitable for the viscosity of raw materials shall be selected.
③ The material extrusion shall be controlled by a metering pump to ensure that the flow rate and flow rate of the molten material in sheets are uniform, so as to obtain a diaphragm with small thickness error. The thickness of the membrane is 12-15 times that of the tensile membrane.
④ The temperature of the cooling roller of the forming diaphragm is constant, the speed is stable, the roller surface is flat and smooth, and the roughness is R. It shall not be greater than 0.2 μ m。
⑤ The forming die structure shall be manifold type or coat hanger type, and the temperature shall be low in the middle and slightly higher at both ends.
⑥ The stretching preheating temperature shall be stable, and the heating temperature fluctuation of the stretching roll and the transverse stretching oven shall not exceed ± 2 ℃.
⑦ The traction and winding tension of BOPET film shall be controlled and balanced.
⑧ Note that the temperature of each heating process shall not exceed 304 ℃ to avoid decomposition of raw materials.
(5) Quality requirements The quality of PET biaxially stretched film (sheet) shall comply with GB T16958-1997. The thickness, deviation, appearance quality and physical and mechanical properties of the film are shown in Table 6-48~Table 6-50.
Table 6-48 Thickness deviation of polyester film Nominal thickness Average thickness deviation/% Thickness deviation/%
60~7537~5917~368~16/ μ M x 4 x 3 x 2 ± 2 superior quality 6 x 5 x 4 ± 4 superior quality 10 x 10 qualified products ± 6 ± 6 x 6 ± 5 superior quality 5 ± 7 x 8 first-class quality 7 x 7 x 9 ± 12 qualified quality 10 x 12 ± 10
Table 6-49 Appearance Quality of Finished Film
First class qualified products
Different points/(piece/m ²) 10 Do not affect the use
The curling surface is smooth and clean, and petals are allowed
No scar and wrinkle is allowed, which will not affect the use of uneven end face ≤ 2mm ≤ 4mm Chapter 7 Plastic sheet (sheet) extrusion molding
There are no specific provisions on the classification of plates, sheets and films in plastic products. Generally, people refer to thin sheet products with thickness less than 0.25mm as plastic film; Products with a thickness greater than 1mm are called plastic plates; Products with a thickness of 0.25~1mm are called sheets.
The production process of plastic sheet (sheet) extrusion molding is basically the same as that of plastic film extrusion molding. The layout of extrusion plate (sheet) production equipment with more applications is shown in Figure 6-3. The structure requirements and equipment layout of the extruder and auxiliary machine in the plastic sheet (sheet) molding extruder production line are also identical to those of the extruder and auxiliary machine for plastic film extrusion and traction molding. Die structures for plate (sheet) forming can be branch pipe type, coat hanger type or screw distribution T-shaped die according to the width of products (see Fig. 6-13~Fig. 6-16). See Table 7-1 for technical parameters of some domestic plate (sheet) extrusion auxiliary machines
Plastics commonly used for extrusion molding of plastic plates (sheets) include polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, etc. The purpose of plastic plates (sheets) is mainly to make various structures and packaging materials. For example, it is used in the manufacture of chemical containers, electrical insulation plate (sheet) materials, building or traffic vehicles, wall panels, partitions, floors in ships, or refrigerator linings formed by blistering, and food and medicine packaging.
7.1 Extrusion molding of polyethylene sheet (sheet)
(1) Raw materials for extrusion forming of polyethylene sheet (sheet) shall be special resin for sheet forming. For example, 5000H high-density polyethylene produced by Sinopec Beijing Yanshan Petrochemical Co., Ltd. and DGDS-6097 (MFR=0.4g/10min, density 0.948g/cm) PE resin produced by Sinopec Guangzhou Petrochemical Company. LDPE resin is selected, MFR=0.4~0.6g/10min; HDPE resin, MFR=0.1~
0.4g/10min, it can also be used to extrude plates (sheets)- 450-
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