A single screw is an extruder,and a twin screw is two extruders
Single screw cannot make composite membrane,such as coextrusion membrane:black and white membrane,which is used to make express bags or milk bags.Because the express bags contain hard objects or many factors,the bags are easy to break,so it is not possible to use ordinary PE membrane,so coextrusion membrane is needed;Coincidentally,food bags (e.g.pure milk bags)also need to meet food standards and are not easy to break,so coextrusion membranes must be used.Black and white film belongs to double-layer coextrusion film.When plastic is extruded,two heads extrude black PE film and white PE film at the same time.When the film is still in semi-liquid state,it is bonded together without chemicals such as glue.Single screw can't do it Because the composite film is a material fed into an extruder,B material fed into an extruder,and then pasted together on the die head back of the extruder to become a composite film
