Water-based coating drying method – microwave drying

2021-10-12   Pageview:658

Microwave is an electromagnetic wave with a wavelength of 1mm-1m and a frequency of 300mhz-300ghz, which has the ability to penetrate. The commonly used microwave frequency is 915-2450mhz.

Microwave heating uses the principle of dielectric loss, the dielectric constant of water is much greater than the dielectric constant of dry matter. Most of the energy released by the electromagnetic field is absorbed by the water in the coating.

The microwave field periodically changes the direction of the applied electric field at a high speed of hundreds of millions of times per second, causing the water molecules to swing rapidly, producing a significant thermal effect and causing the temperature inside and outside the coating to rise rapidly at the same time. The advantages of microwave heating are fast drying speed, different substances have selective absorption of microwaves; no shape requirements for dry materials; film heating is very uniform, no temperature gradient, thick film can be dried. For water molecules, 2450MHz microwave has the best balance of energy conversion and loss. This frequency of microwave can penetrate 30mm thick water layer, which can be applied to dry various thicknesses of coatings of water-based coatings.












Characteristics and varieties of matting agents

1. The characteristics of matting agents for coatings
1. High chemical inertness, does not react with any components in the coating film
Micron-sized synthetic silica has this feature. They are insoluble in water and various solvents, and do not react with common acids, alkalis, and salts. They are only soluble in strong bases and hydrofluoric acid. Micron-sized synthetic silica contains very few impurities, which further guarantees its high chemical stability. From the chemical composition of the Sy series matting agent announced by Fuji sy lysia, Japan, the main component of silicon dioxide is 99.7%.

The analysis results of the matting agent Syl oid series products announced by Grace Company of the United States.
Its main component silica reaches 99.6%.
The high-quality matting agents produced by famous manufacturers in the world have high purity. The impurities that affect the hinge are titanium dioxide and iron trioxide. The former affects the transparency of the coating film, and the latter affects the color of the coating film.

Little interference to the transparency of the coating film
The refractive index of micron-level synthetic silica is 1.46, while the average refractive index of the various resins forming the coating film is 1.40~1.55. The refractive index of the two is similar, ptfe micronized wax which ensures the transparency of the coating film. In addition, the high chemical purity of the silica matting agent further ensures the stability of the refractive index.

Easy to disperse
Before the 1980s, the dispersion of matting agents required long-term grinding and dispersion with three-roll mills, sand mills and ball mills. The preparation of matting coatings had high energy consumption and low production capacity. After the 1980s, matting agent manufacturers improved the preparation process, and currently only high-speed dispersers can be used to complete dispersion.


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