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Dry double drawing process
The dry double pull process is developed by the Institute of Chemistry, Chinese Academy of Sciences, which has independent intellectual property rights and is also a unique diaphragm manufacturing process in China. Because the β crystal of PP is a hexagonal crystal system, single crystal nucleation and loose wafer arrangement, it has a radial growth into a dispersive bundle of wafer structure and does not have a complete spherical crystal structure. Under the action of heat and stress, it will transform into a more compact and stable α crystal, and will produce holes in the material after absorbing a large amount of impact energy. In this process, β crystal modifier with nucleation effect was added to PP, and the density difference between different phases of PP was used to generate crystal transformation to form micropores during the stretching process.
The process flow of dry double drawing
1) Feeding: the raw materials such as PP and pore-forming agent are pretreated according to the formula and transported to the extrusion system.
2) Flow casting: get the PP flow casting sheet with high content of β crystal and good uniformity of β crystal morphology.
3) Longitudinal stretching: longitudinally stretching the cast at a certain temperature, and using the characteristics of β crystal easy to form holes under tensile stress to cause holes.
4) Lateral stretching: the sample is laterally stretched at a higher temperature to reexpand the pores, while improving the uniformity of the pore size distribution.
5) Finalization winding: through heat treatment of the diaphragm at high temperature, reduce its thermal shrinkage rate and improve dimensional stability.
Characteristics of dry double drawing process
Excellent mechanical properties
Through biaxial stretching, the molecular chains of the material are arranged and oriented to the maximum extent in both directions, which significantly improves the tensile strength, tear strength and puncture resistance of the film, especially for the application scenarios that need to bear high loads.
Improved air permeability and moisture permeability
Compared with unidirectional stretching, bidirectional stretching effectively optimizes the pore structure of the membrane, improves the air permeability and moisture permeability, and makes it widely used in fields that require good gas exchange such as medical treatment and food packaging.
Enhanced thermal and dimensional stability
After biaxial stretching, the heat setting treatment of the film significantly improves the resistance of the material to temperature changes, ensuring that it can maintain stable size and performance in high temperature or extreme environments.
High production efficiency
The dry double drawing process is relatively simple, and can achieve efficient large-scale production, meet industrial needs, and reduce production costs.
Application of dry double drawing process
Lithium battery separator: widely used in lithium ion batteries, greatly improve the electrochemical performance and safety of the diaphragm.
Packaging materials: In the packaging of food, medicine and other industries, dry double pull film can effectively improve the fresh-keeping effect of products and extend the shelf life.
Optical thin films: Used in the manufacture of displays, solar cells and optical devices. The dry double drawing process can optimize the optical properties of thin films to meet the needs of various applications.
Electronic products: widely used in the manufacture of conductive film, insulation film and other electronic components, improve the performance of electronic equipment.
conclusion
As an efficient and environmentally friendly film manufacturing technology, the dry double drawing process plays an increasingly important role in modern industry with its excellent performance and wide application prospects. With the continuous progress of material science and manufacturing technology, the dry double drawing process will show greater potential and value in the future advanced material manufacturing.
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