From department stores to corner stores, plastic bags are widely used. In the process of film blowing, the key control points of plastic bags are: temperature, rotating speed of main machine, traction ratio and blowing expansion ratio. Today, I will introduce the precautions during film blowing:
1. Extruder temperature
During the blowing of LDPE, the extrusion temperature is generally controlled between 160 ℃ and 170 ℃, and the head temperature must be kept uniform.
Extrusion temperature is too high: the resin is easy to decompose, the film is easy to be brittle, especially the longitudinal tensile strength is significantly reduced.
Low extrusion temperature: poor plasticization of resin, low tensile strength of film, poor glossiness and transparency of surface, even the appearance of wood ring pattern and melting crystal core
2. Blowing ratio
Film blowing ratio is a link in the process of film blowing. It controls the width and thickness of film blowing, as well as the base weight and traction ratio.
At the same time, the blowing ratio also affects the transverse tensile strength and the thickness of the film. Increasing blowing ratio can improve the transverse strength of the film, but not too much, otherwise it is easy to cause the instability of the film bubble, and the film is easy to wrinkle, and the film thickness will be uneven. Generally speaking, it is suitable to control the film blowing rate of LDPE at 2.5-3.0
3. Traction ratio
Traction ratio refers to the ratio of the traction speed of the membrane to the extrusion speed of the ring. As the traction ratio increases, the longitudinal strength increases and the thickness of the film becomes thinner. However, if the traction ratio is too large, the thickness of the film will be difficult to control, and it may even break the film, resulting in film phenomenon. The traction of LDPE film is generally controlled between 4-6.