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Must the film be blown out by a film blowing machine? People who are unfamiliar with film technology and film characteristics are likely to recommend ordinary blown film machines. As a result, customers may lose money if they fail to meet the requirements after purchasing the machine. In fact, films are divided into many types according to their characteristics. Different types of films require different production equipment. To correctly answer this question, first of all, we must have a correct understanding of the film production process.
Plastic film according to the different production processes are: cast film, blown film. The same raw material, due to different production methods, has a large difference in various properties of the film.
There are two types of cast film: extruded melt cast film and solvent cast film.
Since the cast film produced by the solvent method needs to use a large amount of organic solvent, heating and volatilizing to remove the solvent and recovering the solvent consumes a lot of energy, and also needs to invest in a set of equipment. The operation cost and equipment cost are relatively large. Only a few such as cellophane cannot Or it is difficult to produce the film produced by the extrusion method using the solvent method. Solvent cast film has the following characteristics:
(1) The thickness of the film can be very small, generally 5-8um. The thin film using mercury as a carrier is called molecular film, and its thickness can be as low as 3um.
(2) The film has high transparency and low internal stress, and most of them are used in occasions with high optical performance requirements, such as film interlayer and interlayer film of safety glass.
(3) The uniformity of the film thickness is good, it is not easy to mix impurities, and the film quality is good.
(4) Since the solvent cast film is not subjected to sufficient plasticization and extrusion, the distance between the molecules is large, the structure is relatively loose, and the strength of the film is low.
(5) High production cost, high energy consumption, large solvent consumption, and low production speed.
Extrusion melt casting method is mostly used to produce film by casting film machine. It is the main production method of heat sealing film for plastic packaging. Due to good heat sealability of casting film, balance of vertical and horizontal performance, fast production speed, good transparency The advantages have become one of the main production processes of the flexible plastic packaging industry.
The characteristics of the extrusion cast film are:
(1) The production speed is higher than the inflation method, which can be as high as 60 ~ 80m / min. The extrusion cast film production line recently imported from abroad can be as high as 150 ~ 200m / min, and the inflation method is affected by the cooling rate of the bubble film. Restriction, generally only 30 ~ 60m / min, the temperature of the cooling roller in the extrusion casting process can be 0 ~ -5 ℃, directly attached to the roller, and the cooling effect is good.
(2) The transparency of the extruded cast film is better than that of the blown film. Whether it is PE or PP, a film with good transparency can be produced by the extrusion casting method, and when the air cooling by the blown method, PP cannot have a good Transparency, to get good transparency, you must use the water cooling method.
(3) The thickness uniformity of the film by extrusion casting method is better than that by inflation method.
(4) The vertical and horizontal properties of the extruded cast film are balanced, while the vertical and horizontal properties of the blown film differs depending on the speed of the traction roll and the blow-up ratio. In principle, the film produced by the extrusion casting method is transferred from one roller to another roller, and there should be no pulling force of winding or traction, so the extruded casting film is not stretched in the longitudinal or transverse direction, performance It is balanced.
(5) Just because the extruded cast film is not stretched in any direction, its heat sealing performance is better than that of the blown film, while the biaxially stretched film has no heat sealability. The extruded cast film has the smallest shrinkage when heated, which is beneficial to heat sealing bags.
Blown film is a film produced by extrusion blow molding, and a film blown out by a film blowing machine.
The characteristics of the film produced by the inflation method are:
(1) Compared with the cast film, the inflation film has higher mechanical strength. The transverse inflation and the rapid traction of the traction roller are a two-way stretch of the plastic film, so the mechanical properties are relatively large.
(2) Inflatable films can be used as heat-sealing materials. In fact, most heat-sealing films are inflated films, but their heat-sealability is not as good as cast films.
(3) The production speed of the inflation method is lower than that of the casting method, and the uniformity of the film thickness is not as good as that of the casting film. Since there are many places where films are used in production and life, especially in bags and packaging, many films can be blown out with a blown film machine, so it is still very common to blow films with a blown film machine.
It can be seen from the above that not all films are blown out by a film blowing machine, and some are cast films made by a casting film machine.
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