In the first half of 2006, the total industrial output value of all plastic film production and supply enterprises in China reached 439,5981110,000 yuan, a year-on-year increase of 17.3 1%, and the total number of enterprises was 1299, with total product sales revenue of 44040 10. The per capita sales rate of the whole industry is 889,069.85 yuan. Generally speaking, the national plastic film production and supply enterprises are in good operating condition.
The output of plastic film in China accounts for about 20% of the total output of plastic products, which is one of the categories with rapid growth in the output of plastic products. Judging from the application fields of plastic films (thickness 0.06 mm ~ 0.26 mm) in China, the packaging industry has the largest consumption, the largest variety and the widest application, accounting for about 2/3, followed by agriculture, accounting for about 30%, and functional films, such as microporous films, shielding films and geomembranes. In theory, almost all synthetic resins can be formed into films, but the resins with economic significance, commercial use and the largest amount are polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), ethylene/vinyl acetate (EVA) and polyamide (PA). If proper plastic additives are added to the resin matrix, various functional films can be prepared. There are two industrial production methods of plastic film: calendering and extrusion, among which extrusion can be divided into extrusion blow molding, extrusion casting and extrusion stretching (also known as secondary molding). At present, extrusion is the most widely used, especially the processing of polyolefin films, and calendering is mainly used for the production of some PVC films.
The plastic film industry in China is in a booming stage. It is reported that the demand for plastic film in China will increase by more than 9% every year. Moreover, with the continuous emergence of various new materials, new equipment and new technologies, China's plastic films will develop towards diversified, specialized and multifunctional composite films. [Edit this paragraph] Surface properties of plastic film and its treatment Plastic film is widely used in the field of packaging. Plastic film can be used in food packaging, electrical products packaging, daily necessities packaging, clothing packaging and so on. They have a * * * similarity, that is, plastic films should be printed in color, and multi-layer composite or vacuum aluminum plating should be carried out as food packaging. Therefore, the surface free energy and wet tension of plastic film are required to be high, which is beneficial to the firm adhesion of ink, adhesive or aluminized layer with plastic film. In the process of winding and high-speed packaging of plastic film production, it is required that the film surface has certain friction performance to prevent the film from sticking or slipping; When used in the packaging of electrical appliances and electronic products, the film is required to have certain antistatic properties and so on.
Surface tension of plastic film
The surface tension of plastic film depends on the surface free energy of plastic film, and the surface energy of film depends on the molecular structure of film material itself. Most plastic films such as polyolefin films (LDPE, HDPE, LLDPE, PP) belong to non-polar polymer, and their surface free energy is small, and their surface wet tension is low, generally around 30 dynes/cm. Theoretically, if the surface tension of an object is lower than 33 dynes/cm, ordinary ink or adhesive can't be firmly attached, so its surface must be treated. Polyester (PET, PBT, PEN, PETG) is a polar polymer with high surface free energy and surface wet tension higher than 40 dynes/cm. However, for high-speed color printing or increasing the adhesion between vacuum aluminized layer and BOPET film surface, surface treatment of BOPET film is needed to further improve its surface wet tension.
The surface treatment methods of plastic film include corona treatment, chemical treatment, mechanical roughening and coating, among which corona treatment is the most commonly used.
The basic principle of corona treatment is to apply high-frequency and high-voltage power supply between metal electrode and corona treatment roller (generally silicone rubber roller with high temperature resistance, ozone resistance and high insulation) to generate discharge, which ionizes air and forms a large amount of ozone. At the same time, high-energy EDM impacts the film surface. Under their interaction, the surface of plastic film is activated and the surface energy is increased. Corona treatment can increase the wet tension of polyolefin film to 38 dynes/cm. The surface wet tension of polyester film can reach above 52-56 dynes/cm. The wet tension on the surface of corona treated plastic film is related to the voltage applied to the electrode and the distance between the electrode and the corona treated roller. Of course, corona treatment should be moderate, not the higher the intensity of corona treatment, the better. It is worth noting that air should be avoided between the plastic film and the corona treatment roller, otherwise the reverse side of the film may be corona treated. The consequences caused by back corona are: 1 may cause anti-sticking phenomenon in ink printing; 2 When aluminizing, the aluminizing layer will be transferred, and when gluing, the gluing layer will be transferred. The main measure to prevent corona on the reverse side of the film is to adjust the pressure of the rubber press roller in front of the corona treatment roller, and the pressure at both ends of the press roller should be consistent and appropriate. In addition, the corona roller and the pressure roller must undergo a rigorous dynamic-static balance test, and the radial runout is required to be less than 0.05 mm, so as to ensure that the plastic film can smoothly enter the corona roller, prevent air from being trapped, and thus avoid the phenomenon of corona on the reverse side. Related production methods, that is somebody else's patent. If you really want to do it, buy some teaching materials ~~ 《 Plastic Film Production Technology and Plastic Film Manufacturing Method 》.
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