Comparison of Drying Methods of Three Coating Processes
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Solvent-based glazing coatings have different types and proportions of solvents for different coating formulations, and the evaporation rate during coating and drying is also different. The evaporation speed of the solvent is too fast, the leveling property of the coating material is not good, and the quality problems such as streaks and tresses that affect the surface smoothness appear on the surface after the film is dried. And in the process of solvent evaporation, it absorbs external heat and induces condensation of moisture, causing cracking or whitening of the dried coating. Solvent evaporation is too slow and can cause problems such as insufficient curing of the conjunctiva, poor resistance to stickiness, and the like.
UV curing drying method
UV curing is a glazing process that uses UV (Uitraviolet, ie, ultraviolet) irradiation energy to cure a film of a free-radical-polymerized acrylic ester. Photoinitiators in the components of this type of coating absorb the light energy of the ultraviolet light and generate free radicals in the excited state, which leads to a polymerization reaction.
Photoinitiator excited photoinitiator
UV curing has the characteristics of rapid curing and low temperature curing, which helps improve product quality, maintain consistent color, shorten printing time, prevent air pollution, reduce fire risk and improve working environment. Solve the adhesion of solvent-based glazing coating due to temperature and humidity changes.
The use of UV curing technology in China's printing and packaging industry has developed rapidly, mostly used in printing and finishing after printing. In 1994, UV-curable coatings for paper processing increased by 100% compared with 1993. The annual consumption has reached 50 tons. It will increase year after year. In addition to ultraviolet radiation-excited fluorescent powder developed by Peking University as its main raw material, the mainland itself needs to be purchased from Hong Kong, Taiwan, Japan and other places to meet demand.
UV curing light sources generally use high-pressure mercury lamps or metal halide lamps. The output power must be controlled at 80-120W/cm to ensure that the UV coating cure speed is < 0.5s. At the same time there is the problem of the depth of cure, the degree of curing, and the post-curing lag time.
Electron beam (EB) heating drying method
Electron beam drying treatment method is a new type of energy conversion processing method used by foreign developed countries in recent years for the application of electron beam processing technology such as perforation, notching, cutting and other mechanical processing to a multi-color high-efficiency printing process. Electron beam (EB) is a polymerized, dense, directional electron flow generated by an electrical vacuum device. Using the high power density electron beam processing method, the electrons emitted from the hot cathode are controlled by the electrostatic field of the control electrode and the accelerating anode to be condensed into a dense, small-surface-mounted electron beam that moves in the same direction. When the electron beam hits the workpiece, the kinetic energy becomes thermal energy, producing an extremely high temperature that can instantaneously melt or vaporize any material. It is considered by the scientific community as a drying technology with the best processing consistency in the near future. Allows inks and coatings to be maximally crosslinked and polymerized without post cure and solvent residue. At the same time, the use of heat energy is highest.
Most high-speed production line printing operations require that the inks, adhesives, and coatings be dried in the unit. The use of electron beam (EB) alone as a dry treatment method is not economical in terms of price and space utilization.
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