Plastic film extrusion
DATE：2022/10/7 8:52:49 / READ： / SOURCE：This station
Plastic film extrusion
The tubular membrane blank is extruded, compressed air is pumped into the tubular membrane blank, and the membrane blank is inflated or the membrane bubble with a certain thickness and diameter is formed after air cooling and temperature setting (IPP membrane for short).③ A film or sheet formed by extrusion, tape casting, or blow molding
MOPP, biaxially oriented film (BOPP for short). Material, film made by unidirectional or biaxial stretching
④ Composite molding film Polypropylene composite film is formed by co extrusion casting or co extrusion blow molding of polypropylene resin and other resins (PE PVDC).
⑤ Other methods are used to form films, such as polypropylene aluminum coating formed by vacuum aluminum plating on polypropylene film and polypropylene coating formed by coating a layer of special material on the film.
6.3.1 Extrusion blow molding of polypropylene film
Polypropylene extrusion blown film, like polyethylene blown film, is a versatile film with wide applications. Polypropylene blown film is the lightest, non-toxic film with good mechanical properties, transparency and heat resistance. It can be cooked at 100 ℃ without deformation. Polypropylene blown film is mainly used to package various articles, especially suitable for various clothing and food packaging applications.
The extrusion blow molding of polypropylene film generally adopts the down blowing method as shown in Fig. 6-33. The production process sequence is as follows.
Polypropylene resin → raw materials are plasticized and melted by single screw extruder → tubular film blank is extruded by forming die → the tractor pulls the film blank to run (at the same time, the film cylinder is blown into film bubbles, the film is blown by cold air or cooled by water) → the traction device → drying → corona treatment (according to the use) → finished film reeling
Polypropylene film extrusion blow molding production line can also adopt the up blowing method and flat blowing method in addition to the down blowing method as shown in Figure 6-33. The structure of the mold for forming film blank by down blowing is shown in Figure 6-34. Other equipment (main machine and auxiliary machine) are identical with those used for extrusion blow molding of polyethylene film.
(1) Polypropylene resin shall be selected as raw material for extrusion blow molding film, and resin with melt flow rate of 4~10g/10min and density of 0.89~0.91g/cm shall be selected. For example, F600 and F650 produced by PetroChina Panjin Ethylene Co., Ltd., PPH-I-075 produced by PetroChina Xinjiang Dushanzi Petrochemical Company, and tubular membrane blanks produced by Zhongyuan Petrochemical Changling Refining and Chemical Co., Ltd. are extruded, compressed air is pumped into the tubular membrane blank, and the membrane blank is blown or has a membrane bubble of a certain thickness and diameter, which is formed after air cooling and cooling.
③ A film or sheet formed by extrusion, tape casting, or blow molding
MOPP, biaxially oriented film (BOPP for short). Material, film made by unidirectional or biaxial stretching
④ Composite molding film Polypropylene composite film is formed by co extrusion casting or co extrusion blow molding of polypropylene resin and other resins (PE PVDC).
⑤ Other methods are used to form films, such as polypropylene aluminum coating formed by vacuum aluminum plating on polypropylene film and polypropylene coating formed by coating a layer of special material on the film.
6.3.1 Extrusion blow molding of polypropylene film
Polypropylene extrusion blown film, like polyethylene blown film, is a versatile film with wide applications. Polypropylene blown film is the lightest, non-toxic film with good mechanical properties, transparency and heat resistance. It can be cooked at 100 ℃ without deformation. Polypropylene blown film is mainly used to package various articles, especially suitable for various clothing and food packaging applications.
The extrusion blow molding of polypropylene film generally adopts the down blowing method as shown in Fig. 6-33. The production process sequence is as follows.
Polypropylene resin → raw materials are plasticized and melted by single screw extruder → tubular film blank is extruded by forming die → the tractor pulls the film blank to run (at the same time, the film cylinder is blown into film bubbles, the film is blown by cold air or cooled by water) → the traction device → drying → corona treatment (according to the use) → finished film reeling
Polypropylene film extrusion blow molding production line can also adopt the up blowing method and flat blowing method in addition to the down blowing method as shown in Figure 6-33. The structure of the mold for forming film blank by down blowing is shown in Figure 6-34. Other equipment (main machine and auxiliary machine) are identical with those used for extrusion blow molding of polyethylene film.
(1) Polypropylene resin shall be selected as raw material for extrusion blow molding film, and resin with melt flow rate of 4~10g/10min and density of 0.89~0.91g/cm shall be selected. For example, PetroChina Panjin Ethylene Co., Ltd. produces F600 and F650, PetroChina Xinjiang Dushanzi Petrochemical Company produces PPH-I-075, and Sinopec Changling Petrochemical Co., Ltd. produces
-415 Plastic Extrusion Molding Technician Manual
Figure 6-33 Equipment composition of polypropylene film extrusion downblowing production line 1-single screw extruder; 2 - Forming mould; 3 - Wind ring; 4 - Cooling water ring; 5 - Herringbone guide plate; 6 - traction roll; 7 - Guide roller; 8 - Finished film reeling device
Fig. 6-34 Structural Diagram of Forming Mold for Angle Blowdown Method
1 - Mandrel; 2 - Split cone; 3 - Molten material inlet; 4. One module is specific; 5 - Compressed air inlet; 6 One die
PP resin such as X37F can be used for extrusion blow molding film.
The film used for food packaging shall comply with the provisions of GB9688-88 health standard. See Table 5-26 for specific conditions.
(2) Equipment conditions Polypropylene film extrusion blow molding, select a universal single screw extruder, and refer to Table 6-1 for screw diameter selection; Screw structure can be of equidistant gradual change type or equidistant sudden change type. The length diameter ratio L/D should be greater than or equal to 25:1, and the compression ratio should be less than 4. The structure of the forming die is the same as that of the die used for polyethylene film extrusion blow molding, and the core rod is usually used as a spiral structure die.
(3) Process temperature (from feeding section to homogenizing section) 140~~215 ℃; The mold temperature is 210~225 ℃. Whether the corona treatment process in the extrusion molding production process sequence is adopted. For the extrusion molding of Mody, a mesh of 80/100/100/80 mesh four layers shall be added in front of the barrel of the extruder. Extrusion molding is 120 meshes. The die clearance should be controlled within 0.8~the circumferential clearance of Italian die lip should be uniform. The air pressure control shall be stable, Blowing ratio of membrane preform to bubble (Between the speed of pulling the film bubble and the speed of extruding the film blank from the die mouth. The flow of cooling water in the water ring used for sizing shall be controlled evenly, and the water temperature shall be generally controlled within the range of 15~20 ℃. The water temperature is high, monthly, and the water temperature is low. The film is sticky. The selection method shall pay attention to the influence of the dimensional shrinkage change of the products within 24h. The polypropylene film used for packaging shall meet the requirements of GB9688-1988 standard. The resin performance index of film, blown film, and coated film molding See the sensory index requirements in the table below: normal color, no odor, odor and foreign matters.
(5) The quality requirements for the extrusion molding of polypropylene plastic film shall conform to the provisions of QB/T1956-94 standard.
See Table 6-31 for the thickness and deviation requirements of polypropylene blown film. See Table 6-32 for width and deviation requirements of polypropylene blown film. See Table 6-33 for the physical and mechanical properties of polypropylene blown film. If it is used for food packaging, the film shall comply with GB9688-88.
Table 6-31 Thickness and Deviation Requirements of Polypropylene Blown Film (from QB1956-94)
(6) Quality problem analysis During the production of polypropylene resin extrusion blow molding film, some product quality problems sometimes occur, such as the film folding width or thickness size error exceeds the standard requirements; The film surface has too many crystal points, yellow stripes, black focus, or the surface is dull and dark. After these quality faults occur, the production operator should analyze and find out several possibilities of production quality problems according to the quality of the products, and then modify the process or adjust the equipment item by item, and then observe the changes in product quality until the production quality faults are eliminated.
The causes of specific quality problems of products are analyzed as follows.
① The longitudinal thickness error of the film is too large
a. The working speed of the screw is not stable, and the amount of molten material extruded is uneven.
b. The air cooling or water cooling temperature of the expanded membrane bubble is unstable, and the air volume or water flow is not stable
stable.
c. The running speed of the traction film bubble varies from fast to slow and is unstable.
d. Excessive impurities at the filter screen block the flow rate of molten materials, which is unstable. ② The lateral thickness error of the film is too large
a. Uneven adjustment of the gap between the melt extrusion die in the molding die or the upper parts of the die
Bit temperature error is large.
b. There is blockage at the molten material flow channel in the mold.
C. The cooling speed around the membrane bubble is inconsistent, that is, the air flow or water flow of the air ring or water ring around the membrane bubble is uneven.
③ There are wrinkles on the membrane surface
a. The gap between the openings is not uniform, resulting in uneven thickness and wrinkles at the thin parts.
b. The lip surface of the forming die is not horizontal, which causes the blown film bubble to run unevenly. Line C does not coincide with the center line of the row. The center line of the die mouth and the half line of the opening angle of the herringbone plate shall be adjusted to be on a coincident line.
d. If the installation position of the water ring is incorrect, the setting sleeve and the mold should be adjusted to be concentric, and the cooling water level should be vertical to the center line of the setting sleeve.
e. There is air flow in the production workshop, and the blown film bubble runs unevenly.
f. The working surface of the traction roller is uneven, and the clamping traction force of the working surface of the traction roller is uneven.
④ There are longitudinal stripes on the film surface
a. There are scratches on the die lip.
b. There is a stagnation area in the cavity of the molten material runner of the die.
c. The inner surface of the water ring cooling shaping sleeve is damaged and scratched. d. The working surface of the herringbone plate is not smooth and clean, and the film surface is scratched.
⑤ There are black spots and stains on the membrane surface. a. The filter screen is broken. b. There are many impurities in raw materials.
c. The machine barrel is not cleaned before production or there are foreign matters in the mold.
⑥ There are confluent stripes on the film surface
a. The structure of the forming die is unreasonable, the compression ratio is small, and the molten material confluence stripes appear. b. There are foreign matters in the mold.
c. There are some sticky blocks or scratches on the die lip. d. The temperature of the forming die is too high.
⑦ The transparency of the film is poor and the surface is matt
a. The temperature of plasticizing melt is low, and the plasticizing of raw materials is uneven. b. Screw working speed is too fast
b. The temperature of circulating water in the cooling water ring is too high, or the distance between the water ring and the die mouth
unreasonable.
The working surface of the traction roller has poor finish or there is residue adhering to the roller surface. The ratio between the film bubble ratio and the traction speed ratio of the membrane blank is not properly selected, and the blowing ratio of the film should be selected. The die clearance is adjusted too large. The temperature of molten material is high.
c. The easy cracking at the crease of the membrane cylinder is related to the excessive clamping force of the traction roller.
⑨ The strength index of the film decreases
The plasticizing temperature of the melt is low and the plasticizing is uneven.
b. The ratio between the draft ratio and the expansion ratio of the membrane blank is unreasonable. Generally, the expansion ratio of the membrane blank is too small. Therefore, the expansion ratio should be appropriately increased or reduced.
C Increase the mold temperature appropriately to reduce the orientation of the film longitudinal molecules.
d. The water flow in the cooling ring is small or the water temperature is high.
⑩ Unstable operation of blown film bubble
A. The air flow intensity in the production workshop is too high.
b. The air volume of the cooling air ring is too large or the air volume of the air ring is unevenly distributed around the membrane bubble.
C. The installation position between the mold, wind ring and traction roller is unreasonable or the three are concentric
d. The melting material film forming temperature is on the high side.
Extrusion casting of polypropylene film
Compared with the extruded blown film, the transparent thickness uniformity and surface gloss of the PP extruded cast film are better than those of the blown film; In addition, the film has a slight improvement in its manufacturability and tensile strength. Therefore, the amount of plastic film used in the packaging application of various products is large; The tape cast film can also be used as a base material for composite films and aluminized films.
(1) Polypropylene tape casting film shall be selected as the material, and resin with melt flow rate FR) of 3~12g/10min shall be selected. Modified blend resin, antistatic agent and color masterbatch can be added properly according to the requirements of application conditions during film production.
The best choice for extrusion molding of polypropylene cast film is the special cast film molding resin F850EBA, F800E (DF), FC801 produced by Sinopec Shanghai Petrochemical Company; X37F, T30S, EP2C37F produced by Sinopec Qilu Petrochemical Co., Ltd
And EP2C37F of Fushun Petrochemical Company.
(2) Equipment conditions The equipment production line for polypropylene film extrusion tape casting is shown in Figure 6-2. The equipment to be composed includes extruder, molding die, cooling setting roller and corona
Device, trimming device, winding device, etc.
① The extruder is a common type extruder. The screw structure can be a new type of high efficiency screw with mixing head. The length diameter ratio should be ≥ 25 and the compression ratio should be 4.
② Three to five layers of filter screen can be used, and the mesh number is 80/120/120/80. Its function is to clear
Remove the sundries in the melted materials to ensure the product quality.
③ When the width of forming die products is large, manifold type forming die is used; When the width and size of products are small, coat hanger type molding die is used. The die structure is shown in Figure 6-13~Figure 6-15.
(3) Process temperature: barrel process temperature (from feeding section to homogenizing section): 160~230 ℃, 210~225 ℃, 210~220 ℃. Forming mold temperature: about 210~215 ℃ at the middle part and 215~220 ℃ at both ends. Cooling roller temperature: 15~20 ℃.
(4) Key points of process operation
Pay attention to the influence of the temperature of the plasticizing melt on the quality of the products. The temperature of the melt is on the high side, and the surface of the products has good gloss and high transparency. However, it should also be noted that the impact strength of the product tends to decline when the temperature of the molten material exceeds 290 ℃, and the molten material is easy to decompose.
② The surface temperature of the cooling and setting roller should not be too high, and should be controlled below 25 ℃. Too high roller surface temperature will easily reduce the surface gloss and transparency of products.
③ The speed of the cooling shaping roller shall be stable and constant. The working speed is fast and slow, so that the thickness and width of the product cannot meet the quality requirements.
④ The traction speed of the product is determined by the apparent quality of the product: the traction speed is too fast, the cooling and shaping effect of the film is poor, and the transparency and glossiness are reduced; The traction speed is too slow, which will affect the production efficiency.
⑤ Note that the distance from the die casting nozzle to the cooling and setting roller should not be too large (generally controlled at about 3mm). If the distance is too large, the surface gloss of the product will also decrease.
⑥ The air jet gap is about 2.5mm, and this gap should not be too large to avoid adding film
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