Vacuum roll-to-roll coating (roll-to-roll) is a technology that applies different methods to achieve continuous coating on flexible substrates under a vacuum. It covers vacuum acquisition, electromechanical control, high-precision transmission, and surface analysis. The focus is to increase the winding rate, control the stability of the coating and implement online monitoring under the premise of ensuring the quality of the coating. The roll-to-roll technology has the advantages of low cost, easy operation, compatibility with flexible substrates, high productivity, and continuous multi-layer coating. The first vacuum evaporation roll-to-roll coating machine was made in 1935, and now the coating width is from 500 to 2500mm.
The application of roll-to-roll technology has gradually expanded from packaging and decorative films to functional films such as laser anti-counterfeiting films and conductive films in recent years. It is one of the mainstream technologies in the future of flexible electronics and other industries.
At present, the international frontier is to study the characteristics of functional thin films under different preparation processes and to improve the preparation of composite films. There are two trends in the direction of large-scale industrialization and small-scale scientific research.
The roll-to-roll vacuum coating equipment consists of vacuuming, winding, coating, and electrical control systems. Whether the vacuum chamber has baffles or not, it can be divided into single-chamber, double-chamber, and multi-chamber structures. The single-chamber rewinding and unwinding roller and the coating roller are in the same chamber, and the structure is simple, but the outgassing during unwinding will pollute the vacuum environment. The double-chamber structure separates the system into winding and coating chambers with baffles, and the gap between the roll and the baffles is about 1.5mm, which avoids similar unwinding and outgassing problems. Multi-chamber is often used to prepare composite films. On the basis of dual-chamber, adjacent coating areas are separated by baffles to avoid interference.
The smaller the slit separating the baffle and the vacuum chamber wall, the better. According to the role of the roller during coating, it is divided into a single main roller and a multi-main roller winding coating machine. According to the number of motors, it can be divided into two-motor, three-motor, and four-motor drive systems.
Because of its large area, low cost, and continuity, vacuum roll-to-roll coating has great advantages over batch coating and is widely concerned by domestic and foreign researchers and enterprises. At present, the winding coating technology has progressed rapidly, solving the problems of hollow lines, white strips, wrinkles, etc., and has begun to be 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-forming process and film-forming quality. The main pump of the vacuum unit is developed from a large pumping speed diffusion pump to an oil-free ultra-high vacuum molecular pump and a cryogenic pump, and a large angle double cooling roller coating machine is developed. In order to reduce the stretch deformation of the film. Tension control mostly uses a winding model that considers clip-induced tension and an unwinding model that considers single-span nonlinear dynamics.