Production process sequence of biaxially oriented polypropylene film
DATE：2022/10/10 8:27:04 / READ： / SOURCE：This station
Production process sequence of biaxially oriented polypropylene film
As shown in Fig. 6-35. The product forming process is as follows.Polypropylene resin and auxiliary materials shall be measured according to the formula requirements, and then mixed evenly → single screw extruder shall blend and plasticize the raw materials into molten state → extrude a forming die through perforated plate and filter screen to extrude the forming membrane → cool down and shape on the roller profile → measure the thickness of the thickness gauge piece → longitudinal tension → transverse tension → heat setting → trimming → thickness measurement → corona treatment → winding
Figure 6-35 Schematic Diagram of BOPP Film Forming Production Process 1 - Feeding Hopper; 2 - Extruder; 3 - Quick screen changing device; 4 - Forming mould; 5 - Cooling shaping roller; 6 - Preheating roll; 7 - Longitudinal stretching roll; 8 - Preheating section;
9 - Transverse tension section; 10 - Heat setting section; 11 - Coiler
③ Equipment conditions
a. Extruder Single screw extruder, the screw diameter shall be selected according to the width and thickness of the extruded film, refer to Table 6-1. The screw structure is of equal distance and unequal depth gradual type (generally used separation type or high efficiency screw structure with mixing section), with length diameter ratio greater than 30:1 and compression ratio greater than 3:1. A perforated plate and a filter screen shall be added in front of the barrel. The mesh number of the filter screen shall be 80~120 according to the product requirements. If co extrusion production line is selected, there is one main extruder and one auxiliary extruder. The auxiliary extruder has small specifications and low extrusion capacity. The main extruder is used to produce sheet substrate. It is required that the screw speed is stable, the amount of molten material extruded is uniform, the pressure is stable, the raw material is mixed and plasticized evenly, the exhaust is good, and there is no bubble in the material, so as to ensure the production quality of the stretch film in the next process.
b. Molding die Biaxially stretched film is usually extruded from sheet base by using straight manifold and coat hanger structure dies. The coat hanger mold is widely used. It is required that the working surface of the cavity of the molten material runner in the mold body is smooth, without stagnation area, and the die lip gap at the molten material outlet of the mold is adjustable.
c. The cooling shaping roller is used to hold the sheet shaped molten material flow from the die lip with the roller surface, and at the same time, under the pressure of compressed air blown by the air knife, make it close to the surface of the low-temperature cooling shaping roller, so that the molten material can be cooled and shaped into a membrane. It is required that the working surface of the cooling shaping roller shall be smooth and smooth, the operation shall be stable, the roller surface temperature shall be uniform, and the allowable temperature difference at each point shall be ± 1 ℃.
d. Thickness gauge The thickness gauge is used to measure the thickness of the cast film when it leaves the cooling roll after cooling the setting roller. The thickness of the diaphragm here has a great influence on the thickness of the finished film when it is stretched. Therefore, through the detection of the thickness of the diaphragm here, the control error of the thickness of the diaphragm can be found in time. Then, the clearance of the die lip at the discharge port in the mold for diaphragm forming can be adjusted at any time according to the process requirements to ensure the quality requirements of the thickness tolerance of the stretched film in the later process.
For example, production 30 μ The thickness tolerance of the m-thick stretch film is required to be ± 6%. If the longitudinal stretch of the film is set to be 5 times and the transverse stretch is set to be 7 times, the thickness of the extruded cast film is required to be:
Tensile film thickness ≈ film thickness
Longitudinal tensile ratio x transverse tensile ratio
Then thickness of thick sheet ≈ tensile film thickness x longitudinal tensile ratio x transverse tensile ratio=30 μ mX5x7=1050 μ M (approximate)
If the thickness tolerance of the stretched film ≈ 2x the thickness tolerance of the thick sheet, the thickness tolerance ≈ ± 6% ÷ 2=± 3%. If the thickness tolerance of the thick sheet is 1050pm and ± 3%, the thick sheet forming is controlled between 1018~1080pm.
Longitudinal stretching device The longitudinal stretching device is 7) in the electrogram 6-35 of the cooling setting roller and thickness gauge. It is mainly composed of several smaller diameter rollers, such as preheating roller, stretching roller, heat treatment roller and clamping and mixing roller. The cooled and shaped substrate is added by the preheating roller
Extrusion then stretches the membrane longitudinally depending on the speed difference of multiple rollers in the stretching roller. When necessary, the space between the screw row extractors shall be as small as possible, the roll surface shall be smooth and clean, the temperature shall be uniform, and the temperature difference on the roll surface is allowed to be ± 1 ℃. To prevent the film surface from sticking to the roll, the roll surface shall also be coated with a layer of polytetrafluoroethylene when necessary. Molded resin heat treatment roll is used to anneal the longitudinally stretched film, so as to reduce the internal stress caused by the longitudinally stretched film. The clamping traction roller at is composed of a steel roller and a rubber roller. The stretched membrane is pressed and pulled forward from between the two rollers to prevent the membrane from slipping when it is longitudinally stretched. The heat conduction medium used for heating the roller can be oil, steam or superheated water and heated in the furnace by resistance or oil pan.
f. The transverse tensioning device is behind the longitudinal tensioning device. The longitudinally stretched diaphragm is preheated into the transverse stretching oven, and the two ends of the diaphragm are clamped by the tenter clamp. The diaphragm is gradually expanded by running along the track. At the same time, hot air is blown to the membrane surface until the diaphragm is pulled to the width required by the process. The stenter in the oven can be divided into feeding section, preheating section, stretching section and hot spot thin inspection
The processing and setting sections are divided according to different temperature regions.
The requirements for the production and working conditions of the transverse stretching device are: the tenting clip works reliably (the clamping film does not fall off and crack), and the running speed is stable; The temperature control of each section is accurate, and the temperature error of each point in the temperature thickness section is small; The hot air flow to the film surface is evenly distributed with small temperature difference; Pay attention to the filling of lubricating oil in the clip running track, fill the high-temperature resistant lubricating oil, and maintain good lubrication between the high-speed running clip and the track plane.
g. The BOPP film of the trimming device that is stretched laterally, the film near the clamp opening and the inside of the clamp opening, whose thickness does not meet the dimensional tolerance requirements, shall be cut off. The cut edge strip can be directly mixed in the new material for recycling after being rolled and crushed.
h. The BOPP film cut by the finished thickness gauge needs to be inspected by the ray thickness gauge. The longitudinal and transverse comprehensive thickness of the film is scanned by an automatic recorder,
Within the tolerance range, properly adjust the discharge lip clearance of the die if necessary. I The electric treatment of biaxially oriented polypropylene film is an indispensable process when it is used for printing, gluing or electroplating metal layers. The effect of corona treatment is to increase the surface wetting tension of biaxial oriented polypropylene film. The surface wetting tension of the biaxially stretched polypropylene film is required to be greater than 38mN/m, so as to ensure the adsorption of the film on processing materials such as ink when printing or gluing. Corona treatment is to use high frequency and high voltage generator to generate uniform discharge between electrode and treatment roller, so as to form polar groups such as carbonyl groups on the surface of the film under the effect of corona, and improve the wetting tension of the film surface. The key points for operation of film corona treatment are as follows. The higher voltage and current shall be selected as far as possible within the rated allowable value. To ensure the treatment effect, the distance between the electrode and the roller shall be adjusted as small as possible during corona treatment. Note that the ambient humidity for corona treatment shall not be greater than 60%. If the effect of corona treatment is not good, the film production speed can be appropriately reduced.
E Pay attention to the air exhaust at the work site to eliminate the discharge, condensation and gas generated in the electrode tube. In order to minimize the adhesion of the rolled film, the surface wetting tension of the corona treated BOPP film should not exceed 44mN/m.
j. The film reeling device is generally used for the reeling of biaxial oriented polypropylene film. In order to ensure the flatness and proper tightness of the finished film, an automatic detector for the film winding tension is also set in front of the winding device to feed back the size of the film winding tension to the driving motor used to control the winding device at any time, so that its output power can be adjusted accordingly.
④ Processing parameters of biaxial oriented polypropylene film (reference value)
a. The process temperature of the raw material plasticizing machine barrel (starting from the feeding port of the barrel) is 190~200 ℃ for the first section, 200~220 ℃ for the second section, 230~240 ℃ for the third section, 240~250 ℃ for the fourth section, and 255~270 ℃ for the fifth section.
b. Mold temperature 250~260 ℃
c. The temperature of the working surface of the cooling shaping roller is 15~20 ℃.
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