Characteristics of extrusion casting film

Is the film blown out by the film blowing machine? Those who are unfamiliar with the film process and film properties are likely to recommend a common blown film machine. As a result, the customer may lose money due to the inability to meet the requirements after purchasing the machine. In fact, films are classified into many categories 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 films vary according to the production process: cast film, inflated film. The same raw material has a large difference in various properties of the film due to different production methods.

The cast film has two types of extruded melt cast film and solvent cast film.

The cast film produced by the solvent method requires a large amount of organic solvent to be used. Heating and volatilizing to remove the solvent and recovering the solvent requires a large amount of energy. It also requires investment in a set of equipment. The operating cost and equipment cost are relatively large, and only a few such as cellophane cannot be used. It is also difficult to produce a film produced by extrusion using a solvent method. Solvent cast film has the following characteristics:

(1) The thickness of the film can be small, generally 5-8 um, and a film using mercury as a carrier, called a molecular film, can be as low as 3 um thick.

(2) The film has high transparency and small internal stress, and most of them are used in applications where optical performance is high, such as film film, interlayer film of safety glass, and the like.

(3) The uniformity of the film thickness is good, it is not easy to be mixed with impurities, and the film quality is good.

(4) Since the solvent cast film is not sufficiently plasticized and extruded, the distance between 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 uses cast film machine to produce film, which is the main production method of heat sealing film for plastic packaging. Due to good heat sealing property of cast film, balance of vertical and horizontal properties, fast production speed, good transparency, etc. Advantages have become one of the main production processes in the soft plastic packaging industry.

The characteristics of the extrusion casting film are:

(1) The production speed is higher than the inflation method, which can be as high as 60~80m/min. Recently, the extrusion casting film production line imported from abroad can be as high as 150~200m/min, and the inflation method is due to the cooling rate of the film. The limit is generally only 30~60m/min. In the extrusion casting process, the cooling roll temperature can be 0~-5°C, which is 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. Both PE and PP can be used to produce a film with good transparency by extrusion casting. When the air is cooled by inflation, the PP cannot have a good PP. For transparency, to achieve good transparency, water cooling must be used.

(3) The thickness uniformity of the extrusion casting film is better than the inflation method.

(4) The longitudinal and transverse properties of the extruded cast film are balanced, and the longitudinal and transverse properties of the blown film differ depending on the speed of the take-up roll and the blow ratio. In principle, the film produced by the extrusion casting method is transferred from one roller to the other, and there should be no pulling or pulling tension, so the extruded cast film is not stretched in the longitudinal or transverse direction. It is balanced.

(5) Just because the extruded cast film is not subjected to stretching in any direction, its heat sealing performance is better than that of the inflation film, and the biaxially stretched film is not heat-sealed. The extruded cast film has the least shrinkage when heated, which is advantageous for heat sealing the bag.

The inflation film is a film produced by an extrusion blow molding method, and a film blown out by a film blowing machine.

The characteristics of the film produced by the inflation method are:

(1) The inflation film has higher mechanical strength than the cast film, and the lateral inflation and the rapid traction of the traction roller are a two-way stretching of the plastic film, and thus the mechanical properties are relatively large.

(2) The inflation film can be used as a heat sealing material. In fact, most of the heat sealing film is an inflation film used, but its heat sealability is inferior to that of a cast film.

(3) The inflation method is produced at a lower speed than the casting method, and the uniformity of the film thickness is not as good as that of the cast film. Since there are many places where film is used in production and life, especially in bag packaging, many films can be blown out by a film blowing machine, so it is still common to blow film with a film blowing machine.

It can be seen from the above that the film is not all blown out by a film blowing machine, and there is a cast film made by a cast film machine.

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