Polyethylene film extrusion molding

日期:2022/9/23 9:11:02 / 阅读: / 来源:本站

                                                                                                                                                     Polyethylene film extrusion molding
Among such products as plastic film, polyethylene plastic film is a plastic product with the highest output and a wide range of applications. The molding method of polyethylene film is mostly extrusion blow molding, and casting method and calendering method can also be used.
Polyethylene film extrusion blow molding production process sequence:
PE material → extruder plasticizing and melting → mold forming tubular film blank running forward (at the same time, the film blank is pressed and collared
Traction → coiling (refer to Figure 6-1 for the production process sequence). Air inflation and longitudinal stretching make it thin and cylindrical, and cold air cools the cylindrical film bubble and solidifies it)
There are many varieties of polyethylene film. At present, the most widely used polyethylene films include low-density polyethylene film, linear low-density polyethylene film, high-density polyethylene film, and polyethylene field film formed by extrusion blow molding after mixing three or two raw materials. . The main uses of Kang vinyl film: used for agricultural mulch film, greenhouse film and top-loading application film of various items, and polyethylene film with a thickness range of 0.008-0.150mm and a polyethylene film larger than 0.15mm is also used, but the application amount is relatively high. few. The comparison of application characteristics of low density is shown in Table 6-10. Three kinds of thin films: Kang vinyl film, linear low density polyethylene film and high density polyethylene film
Table 6-10 Comparison of application characteristics of several polyethylene films
6.2.1 Low density polyethylene film
Low density polyethylene film is one of the most widely used polyethylene films. The thickness is generally 0.02~0.15mm, and it has good transparency and flexibility. It is often used in an environment of 30~70 °C and has good electrical insulation, moisture resistance and radiation resistance. Generally used for mulch film, greenhouse film, industrial products and food packaging in agricultural production; as wood,
The composite film of paper and aluminum foil and the moisture-proof and anti-electromagnetic radiation film of military articles, etc.
(1) Raw material selection Select the melt flow rate (MFR) as 0.5~4g/out
10min polyethylene resin; the raw material density is about 0.92g/cm3. There are various grades of special resins for LDPE film extrusion blow molding.
material.
(2) The equipment conditions use a general-purpose single-screw extruder, and the screw structure is equidistant gradient type or mutation type. Try to choose a high-speed new structure screw with a barrier at the screw head (homogenization section), and the length-diameter ratio is greater than 20. : 1, the compression ratio is 3~4; when adding more time to the front of the barrel, it is 8100/80 days - the craftsmanship of Duhai
A 1010-10130-150℃, the temperature of the forming mold is 130-15 yuan (special section) 115-135C, 120-150℃, 130-160, the process temperature of the inland is moderate 0-008m
160-170℃. The melt flow is about 160°C. Lishen therapy section) 180-1404, 150-160℃, 170-180C, Han-type teaching aids 908-0.15mm
100-100t.
(4) Process
The application of the seamold needs to add some anti-linking agents and lubricants (such as the raw materials used in the extrusion blow molding of the low-grade seamolecules.
②Choose LDPE grease particles, impurities, non-particulate Lianli and erucic acid deamination lubricant) to reduce the friction coefficient of the product surface and reduce adhesion. The LDPE film with high transparency requirements should be selected with a density of 092
0.925g/cm" of resin.
The melt flow rate (MFR) of the raw material for general LDPE film forming is 20g/10min; the MFR of the high-speed LDPE film can be selected from 0.3 to 1.0g10min; the melt flow rate (MFR) of the raw material for the extremely thin LDPE film can be selected as 6.0 g/10min. The traction speed should be able to smoothly rise and fall depending on the thickness of the film.
⑤ The pulling speed of the blown film bubble should match the speed at which the film blank is extruded from the die mouth
⑥ In order to make the vertical and horizontal strength of the extrusion blown film close to the same, it is necessary to be careful during production. The ratio of the speed of the bubble and the extrusion speed of the film tube blank from the die mouth is the same. ⑦ Note that the inflation ratio should be controlled within the range of 1.5~3, the inflation ratio is small, and the transverse strength of the film after forming is low; the inflation ratio is too large, The film bubble is not running smoothly, and the thickness of the film is wrong
big. The optimum blow-up ratios for several plastics are shown in Table 6-11.
Chapter 6 Plastic Film Extrusion
The best blow-up ratio for several plastics
PP PA PA/adhesive layer/PE
1.0~2.5
Table 6-11
LDPE LLDPE HDPE
020-301.5-2.03.0~5.00.9~1.51.0~1.5
The pulling speed of the film bubble tube by the Li Yin device requires that the draft ratio be controlled in the range of 3 to 7. When the draft ratio is too large, the film bubble tube is easily broken; if the draft ratio is too small, the extrusion blowing film production , a porous plate and a filter should be added in front of the barrel to ensure
poor mechanical properties.
Uniform plasticizing quality and avoid impurities in raw materials affecting the quality of the formed film. When the raw material for blown film is PVC, use 60/80 mesh; when the raw material is PE, use 60/80/100 mesh; when PP, use 80/100/120 mesh. When installing, pay attention to the filter with small mesh on the perforated plate and the feed end, and the filter with large mesh in the middle to improve the filtering effect of large mesh.
expected to be
⑩The upper die gap of the forming die should be based on the different extrusion raw materials before production, and refer to the working strength of the health net.
When the molten material is extruded from the die mouth, pay attention to use a copper tool to remove the residual material at the die mouth, and adjust the gap evenly in Table 6-3.
Prevent scratching of die lips. When the extrusion speed of the melt from the die gap is uneven, adjust the die gap at the part where the material flow speed is fast, or increase the die gap at the part where the material flow speed is slow. If the melt flow rate is affected by the uneven temperature of the mold, the part where the material flow rate is slow should
⑫ Note that the air volume of the cooling air ring is 5~10m/min, and the air pressure is 0.3~0.4MPa; the temperature is increased.
The air volume should spread evenly and softly to ensure that the film bubble is not deformed and the operation is not shaken.
⑬ The pressure of the compressed air blown into the film blank tube is 0.02~0.03MPa, and the amount of air blown into the film tube is subject to the expansion of the film tube. When the film bubble is pulled to operate normally, the film bubble tube can increase the air supply until the film bubble folded diameter as required by the process is reached.
⑭ Pay attention to the shape of the bubble tube. As shown in Figure 6-24(a), it is the shape of the slow cooling film bubble tube. This shape indicates that the position of the air ring is low, the air volume is small, and the cooling air temperature is high; Figure 6-24(b) is the rapid cooling film Bubble tube shape; as shown in Figure 6-24(c), the shape of the film tube after the film tube is separated from the mold for a certain distance and then rapidly cooled. This shape of the film tube indicates that the position of the air ring is higher and the blowing air volume is larger. , while 62 the effect of air ring work on the shape of the film bubble tube 1-membrane governance: 2-condensation line, 3-mould range. And the wind temperature is lower. The height of the cold-fixing line of the film bubble tube should be controlled at 250~300mm (the production and application of packaging film for 5 sub-animal products is the largest. The quality requirements of these types of films are basically close. The appearance quality of blown film and the production of several other raw materials See Table 6-12 for the appearance and quality of blown film according to GBI2025-1989 standard. The quantity requirements are basically close to the appearance quality requirements of high-density polyethylene blown film. The polyethylene resin used for extruding food packaging films should not have peculiar smell , foreign body, the physical and chemical indicators of its hygienic standards should comply with GB9691-1988 standard regulations

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