Vacuum winding and coating technology
In this paper, the development of vacuum winding coating technology is reviewed from the aspects of system structure, parameter control and coating methods. According to the structure, it can be divided into single chamber, double chamber and multi-chamber vacuum winding system, the latter two can solve the problem of uncoiling and deflating, and respectively control the vacuum degree of winding and coating chamber. The taper, indirect and direct control models of winding tension control can solve the problems of film folding and uneven distribution of radial force. No sensor is needed for indirect tension control, which can be replaced by vector converter with built-in tension control module. Direct tension control accurately measures the tension value through the tension sensor, but requires various parameters such as moment of inertia and angular velocity.Vacuum coiling coating mainly includes vacuum evaporation, magnetron sputtering and other methods, which can be used to prepare new high refractive index films, nanomaterials such as graphene and semiconductor devices such as flexible solar cells. In view of the research status of vacuum winding coating technology and the problems existing in the transition to industrialization, a brief analysis and prospect are made at last.
Vacuum coiling coating (roll to roll) is a technology to realize continuous coating on flexible substrate by different methods under vacuum. It covers vacuum acquisition, electromechanical control, high precision transmission and surface analysis. The key point is to improve the winding rate, control the stability of the coating and implement the on-line monitoring on the premise of guaranteeing the quality of the coating. Roll-to-roll technology has the advantages of low cost, easy operation, compatibility with flexible substrate, high productivity and continuous multi-layer coating. The first vacuum evaporation coiling and coating machine was made in 1935, and now the plating width can be from 500 to 2500mm. In recent years, the application of roll-to-roll technology has gradually expanded from packaging and decorative film to laser anti-counterfeiting film, conductive film and other functional film, which is one of the mainstream technologies in the future flexible electronics industry.
1. Classification of vacuum winding and coating equipment
Vacuum coil to coil equipment consists of vacuum pumping, winding, coating and electrical control systems. According to the vacuum chamber without baffle, it can be divided into single chamber, double chamber and multi-chamber structure. Single chamber rollers and rollers in the same room, simple structure but uncoiling air will pollute the vacuum environment. The double-chamber structure divides the system into a winding and coating chamber with baffle plate, and the gap between the roller and baffle plate is about 1.5mm, which avoids similar uncoiling deflating problem. Multi-chamber is often used to prepare composite films. On the basis of double-chamber, adjacent coating areas are separated by baffles to avoid interference. For example, Krebs et al. fixed the cape tuna Flexibles AB baffle between two magnetron sputtering targets, and coated 50 m copper layer on both sides of the plate.
The smaller the gap between the baffle and the wall of the vacuum chamber, the better. According to the coating roller action is divided into a single main roll and multi main roll winding coating machine. According to the number of motor, it can be divided into two motor, three motor and four motor drive system.
2. summary and outlook
3. Because of its large area, low cost, continuity and other characteristics, vacuum winding coating has a great advantage over intermittent coating, and is widely concerned by researchers and enterprises at home and abroad. At present, the winding and coating technology has made rapid progress and solved the problems such as hollow lines, white stripes and folds. It has been used to prepare new functional media and devices such as graphene, organic solar cells and transparent conductive films. Therefore, higher requirements are put forward for the film-making process and film-forming quality. The main pump of the vacuum unit is developed from the large-pumping speed diffuser pump to the oil-free ultra-high vacuum molecular pump and the cryogenic pump, and the double-cooling roll coating machine with large wrap Angle is developed to reduce the tensile deformation of the film. The winding model considering the pinch induced tension and the single span nonlinear dynamic model are widely used in tension control.
At present, the precision control of winding and coating needs to be improved. For example, when graphene is transferred, it is difficult to completely remove the pyrolytic adhesive between the substrate and graphene, and the shear stress caused by excessive winding speed or hard substrate will cause cracks or holes in the graphene layer. For another example, the surface defects of the organic film prepared by vacuum winding hair are many and the carrier mobility is low, which seriously affects the photoelectric characteristics of the device. In the future, the measurement and control units such as film stress should be added, and the film forming technologies such as CVD, ion plating, high-voltage electrostatic spinning, vacuum injection and in-situ polymerization should be integrated to provide guarantee for the development of new organic and inorganic composite functional films and devices.