Plastic bags are widely used, from department stores to corner stores. The key control points of plastic bags in film blowing process are temperature, main engine speed, traction ratio and expansion ratio.
1. Extruder temperature
When blowing low density polyethylene, the extrusion temperature is generally controlled between 160 170 C, and the head temperature must be uniform.
High extrusion temperature: the resin is easy to decompose, and the film is brittle, especially the longitudinal tensile strength is significantly reduced.
Extrusion temperature is too low: resin plasticization is not good, film tensile strength is low, surface gloss and transparency is poor, and even appear like wood ring pattern and melt core.
2. Blowing ratio of plastic bags
Blowing film ratio is a link of blowing film process comparison. It controls the width and thickness of the film, the number of substrates and the traction ratio.
At the same time, the blowing ratio also affects the transverse tensile strength and thickness uniformity of the films. The transverse strength of the films can be increased with the increase of blowing ratio, but not too large. Otherwise, it is easy to cause unstable vesicles, wrinkle and uneven film thickness. In general, LDPE blowing rate should be controlled at 2.5-3.0.
3. traction ratio
The traction ratio refers to the ratio of the traction speed of the membrane to the extrusion speed of the pipe ring. However, if the traction ratio is too large, it will be difficult to control the thickness of the film, and may even lead to film fracture, resulting in the phenomenon of segmental film. The traction force of LDPE film is generally controlled between 4 and 6.