Glazing Drying Technology (I)

First, the continuous development of glazing drying technology in the print surface coating (or spray, printing) on ​​a layer of colorless and transparent paint, after leveling, drying, calendering, curing a thin and uniform transparent bright layer on the surface of the printed matter The glazing process, which enhances smoothness of the surface of the carrier and protects the finishing functions of printed graphics, has become an important means of finishing after printing and has achieved great results in the packaging and processing of foreign export products. In the technological innovation of prepress digital network and high-efficiency multi-color printing, post-press processing can only accomplish the complete revolution of printing technology by using high technology to achieve exquisite automation. The glazing process using clean energy and clean raw materials for the production of cleaning products will be used as an important post-print finishing tool for the 21st century to meet the ISO14000 environmental management international standards. It will be fully promoted in the printing and packaging industry.
With the increasing popularity of glazing processing, the research and development of glazing coatings and machinery are increasingly valued by related industries such as printing, packaging, chemicals, and machinery. Glazing coatings have evolved from oxidative, solvent-vapor-soluble to heat-curable and photocurable types. Reliance on oxygen in the air to polymerize the liquid glazing coating to dry the film investment equipment less; rely on the solvent solvent evaporation drying film forming a good leveling, processing performance and a wide range of adaptation, but the need for glazing, Two steps of calendering; Reliance on the active functional groups contained in the film-forming resin in the coating material and the catalyst of the coating in case of thermal cross-linking reactions. The automatic film coating machine has a high production efficiency; After absorbing the radiation energy of the coating, , The molecular internal structure of the polymerization reaction drying the conjunctiva UV glazing mechanism, can be synchronized with the printing, a multi-purpose machine. UV technology allows the printing and coating processes to be performed on a dedicated machine to be integrated into the printing unit at one time.
As an important polishing technology, the drying technology has also been continuously improved and developed. The coating drying process of glazing coatings has evolved from hot-air drying of oxidative polymerization and solvent evaporation to electrothermal and UV drying. With the development of hi-tech and the use of clean energy and the pursuit of clean energy, the electron beam drying method integrated with various advanced scientific and technological means has been used in developed countries in Europe and America. The rapid development of the latest UV/electron beam and thermal/electron beam hybrid drying systems will provide the latest high energy curing fundamentals and technologies for the printing and packaging industries at the turn of the century and the 21st century. The continuous application of technological innovation will make the coating drying process more scientific and further promote the quality improvement and economic development of the printing and packaging industry.
Second, the coating process of several drying methods Comparison of solvent evaporation drying method Solvent-based coating coating for different coating formulations, the type of solvent used and the ratio is different, coating, drying process, the evaporation rate is 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.
Ultraviolet curing drying method UV curing is the use of UV (Uitra Violet or ultraviolet) irradiation energy to make the free-radical polymerization acrylic coating film curing process. 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.
[PI]-------[PI]--------[Free radicals]
Photoinitiator Excited State Photoinitiator [Free radical] + [monomer] + [oligomer] - - - - [polymer]
Cured coating UV curing has the characteristics of fast curing and low temperature curing, which helps to 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. (To be continued)