Classification and development trend of Stretch Packaging Films
in terms of manufacturing methods, stretch packaging films can be divided into flat extruded films and blown films. There are two main differences between flat extruded films and blown films that affect the properties of stretched films. One of them is because the cooling and curing methods used are different. Flat film extrusion is a rapid cooling of one or more highly polished rollers containing circulating coolant. The blown film cannot be cooled quickly, usually by high-speed air. Compared with the film made by blow molding of the same material, the flat extruded film has more uniform thickness and higher viscosity and transparency. Another difference is their molecular orientation. The flat extrusion film is in the direction of the machine during the production process (Longitudinal) A certain degree of stretching has been carried out, which we call uniaxial orientation, and its longitudinal ultimate tensile strength is greater than dry transverse tensile strength. Therefore, the transverse stretching spread has strong tearing property, which reduces the breakage in wrapping, storage and transportation. In the production of blown film, it is stretched in both vertical and horizontal directions. We call it bidirectional orientation. This kind of film has small resistance to transverse spread tearing and is easy to be damaged.
purpose, coextrusion film is widely welcomed at home and abroad. It is co-extruded by two or more layers at the same time, so that the multilayer films contact each other in a molten state and permanently adhere-From. This method provides many opportunities for the combination of resin and additives, improves the film properties and increases the film tensile rate by 200%- 300%, becoming the preferred film for stretch packaging.
The International stretch film market generally tends to three types. For the first type of application with less demand, a low stretch rate film is used with a stretch rate of 0-75% or so. These films are used to wrap regular, irregular or arbitrarily shaped cargo, using slower stretch packaging machines. Due to the limitation of equipment, 30% stretch rate is difficult to achieve.
In recent years, with the development of equipment, in the second type of application, the film stretch rate is as high as 120%, irregular cargo load of any shape, goods that include heavy objects or can be displaced tend to use this type of stretch wrap. A typical type of equipment is a semi-automatic high-speed winding machine. The third type of application is high performance. The film stretch rate is as high as 300%, and some are higher. A fully automatic high-speed winding machine usually equipped with a conveyor belt. The development trend is that thin stretch films replace thick films. In 1970s, the standard tensile film thickness was 25um, but now it is 20um, some up to 13um. In the future, with the appearance of new additives, Matrix Resins and New stretching equipment, higher performance stretching films will be produced, and Coextruded films will continue to be widely used as spiral wound films.