The multi-layer co-extrusion barrier should have a certain gas barrier function. The barrier property of multi-layer co-extruded film here refers to the shielding ability of plastic products (containers, films) to small molecular gases and odors. We generally use gas permeability to measure the size of the barrier function of plastic products. General-purpose plastics such as PE and PP have large gas permeability values, that is, the gas barrier function is poor, while resin materials such as PA, PVDC, and EVOH have a much lower gas permeability value than general-purpose plastics, and the barrier function is better. Therefore, we generally refer to the multi-layer co-extruded film containing at least one resin material among PA, PVDC and EVOH as the multi-layer co-extrusion barrier.
The top-blown co-extrusion barrier is a multi-layer co-extrusion barrier produced by the top-blowing process. The multi-layer co-extruded film top-blowing method has the lowest production capacity, and the top-blowing production line with a general width of 1.6 m has a daily production capacity of less than 5 tons.
However, the upper blowing method is simple in operation and low in equipment investment, and is the most common process for producing multi-layer co-extrusion barriers. In addition, the upper blowing method has the advantage of being more sensitive in the processing of some special small quantities of packaging materials due to the lower output.
The water-cooled down-blowing co-extrusion barrier is a multi-layer co-extrusion barrier produced by the down-blowing process, and the multi-layer co-extrusion film is cooled by water. The water-cooled down-blowing method produces a multi-layer co-extrusion barrier with moderate production capacity. The general width is 1.6m. The down-blown water-cooled production line has a daily production capacity of nearly 8 tons. In addition, the multi-layer co-extrusion barrier is produced by the down-blowing method, and the melt can be rapidly crystallized by cooling water, so that the transparency of the film is very high and the elongation rate is large, so it is very popular in the field of meat food packaging. However, due to special reasons such as the film needs to overcome the influence of downward gravity, the thickness uniformity of the film product is poor, generally about 5%.
