• Categories:IR Lamp Technologies & News
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• Time of issue:2024-02-29
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(Summary description)Infrared Heating In Coating Film Drying Application

1. Absorption of infrared rays by coating film

 

Infrared ray is a kind of ray invisible to the naked eye. It propagates in a straight line like visible light, and has phenomena such as wave reflection, refraction, absorption and transmission. Its main energy wavelength is in the range of 1.0 to 16 microns. Resins, solvents, and even inorganic substances such as pigments in paints have wider and stronger absorption bands in this wavelength range. Usually, 50% of infrared rays are absorbed by the coating film, and the rest passes through the coating film and is absorbed by the coating. The coating film absorbs infrared rays, which intensifies the vibration of internal molecules and increases energy, accelerating the polymerization of organic resin and the use of solvents, achieving the purpose of rapid drying. The infrared rays that pass through the coating film and are absorbed by the coating material cause the temperature of the coating material to rise. Accordingly, the temperature of the inner layer of the coating film is slightly higher than that of the outer layer, forming a process in which the inner layer of the coating film gradually dries toward the outer layer, and the solvent flows through without hindrance. It evaporates from the inside out, shortening the drying process and making the coating film hard and bright.

 



 

2. Comparison between infrared heating and hot air heating

Hot air drying uses conductive convection to heat the coating, which is much slower than infrared radiation heating. In particular, hot air drying uses convection hot air to transfer heat to the coating film. The outermost layer of the coating film is first exposed to the hot air, so the outer layer of the coating film is the first to solidify. This hinders the evaporation of the solvent in the inner layer of the coating film and the entry of oxygen in the air (for oxygen polymerized resin), and reduces the drying speed. When the solvent in the inner layer finally breaks through the outer coating and evaporates, it leaves micropores in the outer coating and makes the coating loose.

 



 

There is obvious absorption efficiency difference caused by different colors of the coating film. The darker the color, the greater the absorption rate, and the lighter the color, the smaller the absorption rate. This causes uneven curing of the coating film due to different colors. Our quartz infrared radiators are made by high temperature tungsten alloy or nickel and chromium high temperaure alloy, which heating elements are vacuum sealed or unsealed in quartz glass. The infrared wavelengths they radiated are from 1.0～16.0 microns, which can match coating films in different colors.

 

 

Infrared heating and drying technology shortens the drying time of the coating film from dozens of minutes to a few minutes, and reduces the length of the effective drying tunnel from a dozen meters to a few meters. The power saving is generally 35~40%, and some are as high as 70%. Due to infrared heating is efficient and quick-drying, takes up less space in the drying tunnel, has good drying quality, and saves energy, so it is quickly adopted in coating film drying.