The current situation and development of multi-layer co extruded cast barrier film Ⅱ

Typical multi-layer co extruded cast barrier film structures：

① Asymmetric structure: The main properties of PA/TIE/PE/PE/PE film are good flexibility, transparency, low temperature resistance, and puncture resistance. The main application of the film is cryogenic vacuum packaging.
② Asymmetric structure: PA/TEE/PA/TIE/PP/PP: The main properties of the film are resistance to cooking above 121 ° C, good transparency, and ability to withstand certain low temperatures. The main application of film is high-temperature steaming and packaging.
③ Symmetric structure: PP/TIE/PA/EVOH/PA/TIE/PP. The main properties of the film are high barrier properties, good transparency, and excellent odor resistance. The main application of the film is chemical packaging.
④ Asymmetric structure: PA/TIE/PA/EVOH/PA/TIE/PE. The main properties of the film are high barrier properties, good transparency, and easy stretching and thermoforming. The main application of the film is deep stretch thermoforming packaging.
⑤ Asymmetric structure: The main properties and applications of PA/PA/TIE/PA/EVOH/PA/TIE/PE film are the same as those of ④.
⑥ Asymmetric mechanism: PBT/TIE/PE/PA/EVOH/PA/TIE/PE/PE. The mechanical properties of the membrane are better than those of structure ⑤, and the membrane does not experience warping. The main properties and structures of the membrane are similar to those of structure ⑤.

The principles of the above structure allocation:
(1) PA, EVOH, and PBT are polar materials, while PE and PP are non-polar materials: according to the principle of similar assembly, they need to be bonded together by TIE, which is modified by PE and PP and has good water resistance. Therefore, the inner layer of PA will not be blocked due to water absorption. Therefore, replacing single-layer materials with multiple layers of the same material in the barrier layer can improve the stability of the film's barrier performance.
(2) Replacing a single type of material with two different materials in the barrier layer can significantly improve the barrier properties of the film. According to the principle of synergistic effect, PA/EVOH/PA has a better barrier to oxygen than EVOH.
(3) Dividing PE or PP into two layers, with one layer using inexpensive materials and the other layer using functional materials that meet their functional requirements, can reduce production costs.
(4) The use of co extruded films with more layers can improve the stress warpage resistance of co extruded films with less than seven layers. Due to the easy deformation of PA after absorbing water, the film may curl, while using PBT instead of PA in structure ⑥ will not cause curling.

The main components of the multi-layer co extrusion casting barrier film equipment：

1. Automatic suction, weighing, and mixing system: Each extruder is equipped with a weight measuring hopper to measure the actual flow rate of raw materials. Based on the deviation between the measured actual value and the set value, the weight measuring system will automatically adjust the speed of the extruder screw, thereby increasing or decreasing the extrusion volume accordingly to control the thickness of the film.
2. Extruder: (1) Barrel: During the plasticization and pressurization process of the resin, it is equipped with external high partition heating and cooling devices, namely heating resistors and air cooling. The purpose of heating is to melt the resin, while the purpose of cooling is to prevent the resin from heating or rapidly cooling during parking, so as to prevent resin degradation or decomposition. The external friction between the barrel and the resin provides heat for the resin, and the flow of the resin in the barrel is also determined by the frictional force between the resin and the barrel. (2) The screw can only move forward by rotating the resin inside the barrel. The ability of the screw to melt depends on the speed of the screw and the temperature of the material barrel, as it generates pressure and partial heat.
3. Filter: Filter impurities that may be mixed in the resin and prevent unplasticized resin from entering the machine head, maintain a certain pressure, and strengthen the plasticization of the resin.
4. Forming device: (1) Online adjustable splitter device (distributor): The core rod inputs the melt from each extruder into the splitter system according to the designed structure, and the splitter blades control the flow of the melt (including flow rate and velocity). The distributor tip adjusts the layer thickness distribution, which is the key to maintaining the uniformity of each layer during co extrusion of resins with different viscosities. By adjusting the splitter blades and distribution tips online, the cross-sectional shape of each layer of melt thickness can be precisely controlled.
2) Automatic flat mold head: The heating system of the mold head maintains the temperature of the melt to prevent adhesion to the mold cavity and a decrease in the flow rate of the melt. The gap between the mold lips is controlled by thermal expansion bolts, which can ensure high control accuracy of the film thickness tolerance. The geometric shape of the flow cavity inside the mold head evenly distributes the melt along the thickness of the mold head, ensuring that the film thickness is uniform throughout the entire processing width.
5. Forming device: ① Needle type electrostatic film end locator: The needle type electrostatic film end locator uses electrostatic charges to generate a force to stick the film to the cold roller. By using a thin film edge positioning device, the necking can be minimized, stable thin film edges can be obtained, and the effective film width can reach the maximum value Double chamber vacuum suction hood: The suction hood is used as a means to reduce melt shaking and improve production line speed. The function of the vacuum chamber is to suck out the entrained air and stabilize the melt film Positive pressure air knife: Press out the entrained air and stabilize the molten film Clean the pressure roller: synchronize the speed of the film with the cooling roller to prevent the film from slipping on the cold roller. By adjusting the pressure, use the film to take away the precipitates on the cold roller. ⑤ Double cold roll: The first cold roll of the casting system is passivated with special beads to ensure the smooth detachment of the viscous film and additives from the roll surface; The diameter of the second branch is usually smaller, and the common surface is subjected to highly polished treatment to further cool the cured film.
6. Thickness measurement device: Multiple infrared measuring heads are used to measure the overall thickness of the film and the thickness of the barrier layer. The uniformity of the film thickness is adjusted by controlling the thermal expansion bolts on the mold head.
7. Edge cutting and recycling device: Cut off thick edges and crush or press the edges into blocks.
8. Corona treatment equipment: By discharging the electrodes, the surface of the film is treated to enhance its adhesion performance during subsequent printing or composite processing.
9. Heat setting device: The film is heated by a hot roller to eliminate internal stress, reduce film curling, promote the precipitation of additives, and improve the quality of the subsequent winding.
10. Winding device: ① Swing mechanism: Before winding, swing the film horizontally to evenly distribute possible deviations in film thickness on the film roll. ② Static eliminator: Eliminate static electricity on the film Tension detection roller: The tension of the film is detected by pressure sensors under the bearings at both ends of the tension roller. The detected signal is controlled by an electronic circuit to regulate the speed of the winding motor, ensuring appropriate winding tension Tracking roller: Its main function is to press the film against the winding core, perform contact winding or small gap winding, and quickly roll the flat film onto the winding core to achieve the purpose of flat winding Automatic film winding machine: The central winding roller is driven by a winding motor, and the speed control system of the winding is connected to the driving system of the cold roller, synchronized with the speed of the cold roller, and controlled by feedback from the tension controller.

Processing technology of multi-layer co extruded cast film barrier film

Selection of raw materials: PA selects viscosity of 3.6-4.0, PBT selects viscosity of 1.2, EVOH selects melt index of 4.0, PE adhesive selects melt index of 2.0, PP adhesive selects melt index of 5.0, LDPE selects melt index of 2.0, LLDPE selects melt index of 2.0, MLLDPE selects melt index of 3.5-4.0, HDPP selects melt index of 3.0-5.0, COPP selects melt index of 7.0.
Temperature control: The melt temperature of PA is 250-260 ° C, the melt temperature of PBT is 250-260 ° C, the melt temperature of EVOH is 220-230C, the melt temperature of PE is 240-245 ° C, the melt temperature of PP is 240-245 ° C, the melt temperature of the die is 250-260 ° C, the temperature of the cold roll is around 25 ° C, and the heat setting temperature is 50-70 ° C.
Pressure control: The control of pressure before the melt mesh is mainly determined by the mesh size and number of layers of the filter screen. Different resins have different requirements for pressure, so different filter combinations need to be selected. PA uses two-layer 80 mesh and one layer 150 mesh filters, PBT uses five layer 300 mesh filters, EVOH uses two-layer 80 mesh and one layer 120 mesh filters, PE uses two-layer 80 mesh and one layer 120 mesh filters, and PP uses two-layer 80 mesh and one layer 300 mesh filters.