POF shrink film is a three-layer co-extruded film. The two surface layers are polypropylene and the core layer is polyethylene. The typical layer thickness ratio is 15:70:15. The production process is rough as follows.
1. polymerized polypropylene and polyethylene enter the surface layer and core layer extruder respectively. After screw plasticization, it enters the ring coextrusion die.
2、The first film bubble of PP/PE/PP triple co-extrusion is extruded from the ring die head, sized and water-cooled, then flattened and hauled out of the water tank.
3、The first film bubble is heated by infrared ray to soften it properly and inflated to blow it to form the second film bubble. In the second film bubble blowing process, realize the polyolefin
stretching.
4. After the second film bubble is cooled by air, it is flattened to enter the trimming and winding process.
Since the double-bubble film blowing process is different from the ordinary film blowing process, the requirements for the production raw materials are quite special. The surface layer of polypropylene usually uses copolymer PP with lower melting point and wider melting range.
copolymer PP is used for the surface layer to facilitate the blowing and stretching of the second film bubble and low temperature heat sealing. The core layer of polyethylene is typically linear low density polyethylene to provide second film bubble stability and high tear strength.
POF Shrink Film Performance Requirements
Because POF shrink film is manufactured in a different way than regular film, and because it is heated for shrink packaging applications, it requires a very high level of performance. Therefore, the film itself has extremely high performance requirements
Low shrinkage temperature: to help end-users improve packaging speed and reduce packaging costs.
Wide working range of shrinkage temperatures: improves the film's machineability and allows the film to be easily adapted to various shrink packaging equipment of old and new designs without significant adjustments to packaging conditions
Appropriate shrinkage rate and force: Different packaging contents may require different shrinkage properties to match, which must be adjusted using formulation and processing conditions.
High heat sealing strength and heat sealing strength: for high-speed automatic packaging equipment, higher heat sealing strength and heat sealing strength is particularly important to effectively reduce the rate of packaging breakage.