The key technical terms of the blown film machine are analyzed as follows:
The blow-up ratio is a crucial parameter in the blown film production process. It refers to the ratio between the diameter of the inflated bubble and the diameter of the extruded tube before inflation. This ratio represents the transverse stretching of the film, which helps align the polymer molecules, thereby enhancing the film's transverse strength. However, if the blow-up ratio is too high, the bubble becomes unstable, leading to wrinkles or even ruptures. Therefore, it should be balanced with the take-off ratio. For low-density polyethylene (LDPE) films, the blow-up ratio is typically maintained between 2.5 and 3.0 for optimal performance.
The take-off ratio, also known as the draw ratio, is the ratio between the speed at which the film is pulled and the extrusion speed of the tube. This ratio determines the longitudinal stretching of the film, which increases its tensile strength but reduces its thickness. If the take-off ratio is too high, the film may become too thin to control, potentially leading to tearing or breakage. For LDPE films, the take-off ratio is generally kept within the range of 4 to 6.
The dew point, or frost line, marks the transition of the polymer from a viscous flow state to a high elastic state. During the film-blowing process, the extruded LDPE is in a molten state, giving it good transparency. As it exits the die, it is cooled by an air ring. When cool air is directed at the hot bubble, the temperature drops rapidly, causing the material to solidify. At this point, a visible line appears on the bubble, separating the transparent and cloudy areas—this is the dew point.
The position of the dew point significantly affects the film’s properties. If the dew point is high, meaning the bubble remains in a molten state during inflation, the film is only stretched without molecular orientation, resulting in properties similar to cast films. Conversely, if the dew point is low, the inflation occurs in a solid or high elastic state, leading to transverse stretching and molecular orientation, which improves the film’s mechanical properties, making it more akin to biaxially oriented films. Understanding and controlling these parameters is essential for producing high-quality blown films with desired characteristics.
The blow-up ratio is a crucial parameter in the blown film production process. It refers to the ratio between the diameter of the inflated bubble and the diameter of the extruded tube before inflation. This ratio represents the transverse stretching of the film, which helps align the polymer molecules, thereby enhancing the film's transverse strength. However, if the blow-up ratio is too high, the bubble becomes unstable, leading to wrinkles or even ruptures. Therefore, it should be balanced with the take-off ratio. For low-density polyethylene (LDPE) films, the blow-up ratio is typically maintained between 2.5 and 3.0 for optimal performance.
The take-off ratio, also known as the draw ratio, is the ratio between the speed at which the film is pulled and the extrusion speed of the tube. This ratio determines the longitudinal stretching of the film, which increases its tensile strength but reduces its thickness. If the take-off ratio is too high, the film may become too thin to control, potentially leading to tearing or breakage. For LDPE films, the take-off ratio is generally kept within the range of 4 to 6.
The dew point, or frost line, marks the transition of the polymer from a viscous flow state to a high elastic state. During the film-blowing process, the extruded LDPE is in a molten state, giving it good transparency. As it exits the die, it is cooled by an air ring. When cool air is directed at the hot bubble, the temperature drops rapidly, causing the material to solidify. At this point, a visible line appears on the bubble, separating the transparent and cloudy areas—this is the dew point.
The position of the dew point significantly affects the film’s properties. If the dew point is high, meaning the bubble remains in a molten state during inflation, the film is only stretched without molecular orientation, resulting in properties similar to cast films. Conversely, if the dew point is low, the inflation occurs in a solid or high elastic state, leading to transverse stretching and molecular orientation, which improves the film’s mechanical properties, making it more akin to biaxially oriented films. Understanding and controlling these parameters is essential for producing high-quality blown films with desired characteristics.
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