The difference between near-infrared rays and far-infrared rays is that the energy density is different. The longer the wavelength, the lower the energy density. Therefore, near-infrared rays have higher energy density.
Near-infrared (.NIR) emitters basically emit near-infrared rays with high energy density. This radiation drying technology has been applied to the curing of powder coatings, and it can complete the whole process of melting, flowing and curing of powder coatings in about 10s, and make the coatings have excellent appearance. Since the emitted energy is almost completely absorbed into the powder coating, the curing speed is extremely fast, so it can be used to dry powder coatings on heat-sensitive substrates.
In fact, far-infrared radiation and near-infrared radiation only use the characteristics of a certain range of infrared rays, so in recent years people have developed a high-infrared radiation drying technology with a higher utilization rate of infrared energy.
High infrared radiation heating technology is a new infrared radiation technology developed in the 1990s. Far-infrared heating technology is developed on the basis of the theory that the infrared radiation spectrum of the radiator matches the absorption spectrum of the irradiated coating. Studies have shown that the absorption wavelength sensitive region of the coating film is mostly in the far-infrared band, so choosing a far-infrared heater is beneficial to accelerate the curing of the coating film. But the obvious disadvantage of far-infrared radiation is that the energy density of radiation is low (the energy of electromagnetic waves is inversely proportional to its wavelength or proportional to frequency, the longer the wavelength, the lower the energy of light, so the energy density of far-infrared rays is the lowest in infrared rays. ). It is difficult to achieve a good match in industrial applications, so its practical application effect is not good in many occasions. The high infrared radiation technology is a new technology that can instantly provide high-intensity, high-energy, high-density full-band infrared radiation.
(1) The structure of the high-infrared radiator. The high-infrared radiator is composed of a lamp tube and a reflective screen. It is a special quartz tube lamp with a power of 3~5kW. The filament of the tube lamp is made of tungsten. The tungsten wire of the tube lamp is the heat source, the working temperature can reach 2000~2400°C, and radiate near-infrared rays outward. The temperature of the directional reflective screen behind the lamp can reach 500~600°C when it works, and it can radiate far infrared rays outward. Therefore, this kind of infrared radiator can radiate infrared rays of all bands outward, reaching the maximum radiation output state, and the emitted energy is 80% The above is infrared radiation energy.
(2) Advantages of high infrared radiator Its remarkable features are short start-up time, small thermal inertia, can be quickly heated to the rated temperature in an instant, and emit full-band infrared rays. When infrared rays irradiate the surface to be coated, infrared rays of different wavelengths play their respective roles synergistically. Among them, mid- and far-infrared rays are easily absorbed by the coating and converted into heat to heat the coating film, while most of the near-infrared rays with high energy density pass through. The coating film heats up the substrate, heats the coating film from the inside, and accelerates the evaporation of the solvent in the coating. Therefore, it can transfer heat much faster than hot air convection, so that the temperature of the workpiece can rise much faster. Drying with high infrared rays within 3~4 minutes can achieve the same drying effect as hot air convection drying at 180°C and 30 minutes. It is very efficient for drying coatings on planar structures. However, due to the straight-forward characteristic of infrared radiation, the drying effect on places where the light does not reach or dead angles is slightly poor. Therefore, when drying the coating film with a three-dimensional structure, it is necessary to cooperate with hot air convection circulation to obtain a more satisfactory effect.
High infrared radiation is more suitable for film drying of thermosetting coatings, water-based coatings and powder coatings. On the one hand, because these coatings have good absorption characteristics for infrared rays with a wavelength around 3 μm, and the infrared rays emitted by high-infrared radiators that match it are absorbed by the coating film, which stimulates the chemical activity of the crosslinking groups in the coating film and promotes the coating process. The membrane crosslinking (curing) reaction occurs more quickly. On the other hand, the radiated high-energy-density near-infrared rays are absorbed by the powder coating and converted into heat energy, which promotes the melting and leveling process of the powder coating particles, and promotes the volatilization of water in the water-based coating and the combination of coating particles to form a film. Due to the high infrared radiation efficiency, fast curing speed and short action time, it has very little effect on the performance of the coated substrate, so it is suitable for drying the coating film on the heat sensitive substrate.