The production process of flexible plastic films is a complex and meticulous craft involving multiple stages.
1. Selection and Preparation of Raw Materials
Types of Raw Materials: Common raw materials include polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), which are petrochemical products obtained through oil cracking and refining.
Form: Raw materials usually exist in the form of granules or powder, requiring further processing to produce films.
2. Melt Extrusion
Process Description: Raw materials are fed into the hopper of an extruder. The extruder melts the raw materials into a flowing plastic melt through heating and mechanical action. Temperature control during this process is crucial, as it directly affects the flowability of the melt and the quality of the film.
Equipment: The primary equipment used for melt extrusion is the extruder.
3. Film Formation
Formation Method: The molten plastic melt is extruded through the die of the extruder into film form. The design of the die determines the thickness and width of the film.
Process Key Points: To ensure the uniformity and flatness of the film, appropriate stretching and cooling are necessary during the forming process.
4. Cooling and Curing
Cooling Method: The formed film needs to be rapidly cooled using cooling devices to prevent the melt from re-solidifying.
Curing Effect: The cooling process also helps in curing the film, giving it sufficient strength and stability.
5. Surface Treatment
Purpose of Treatment: Depending on the intended use, the film's surface may need treatment to enhance characteristics such as gloss, anti-static properties, and printability.
Methods of Treatment: Common surface treatment methods include corona treatment and plasma treatment.
6. Winding and Packaging
Winding: After the above steps, the produced film is wound into rolls by a winding device.
Packaging: The wound film is appropriately packaged to prevent damage during transport and storage.
7. Quality Inspection
Inspection Content: The produced plastic film undergoes strict quality inspection to ensure that its thickness, width, strength, temperature resistance, and other indicators meet standard requirements.
Importance: Only films that pass inspection can proceed to the next production stage or be sold directly to the market.
8. Special Processes (such as Lamination and Printing)
For flexible plastic films, special processes like lamination and printing may also be required:
Lamination: Different materials are laminated together using adhesives or other methods to create composite films with special properties. For example, a printed film may be laminated with a heat-sealable inner film to create materials with special heat-adhesive functions.
Printing: Color printing is performed on the film to attract consumers' attention and enhance the product's quality. Gravure printing is the primary method used for plastic film printing, known for its speed, rich colors, and clarity.