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[...] Some Basics

It is absolutely necessary to pay attention to the absorption of the lacquer. It is a matter of common knowledge, that light short-wave infrared has the great advantage to penetrate much deeper into a good, such as lacquer coatings, plastic foil or the like. For specific coatings it simultaneously enforces a heating of the substrate. It is public as well, that the typical absorption bands of water […] and many plastics (among others the solid percentage in water-based varnishes) lies especially within in a wavelength range of 3 to 6 μm. For the required energy for drying, heating and/or cross-linking of coats, there needs to be affected an infrared radiation source, which emits the principal part of its power exactly within this spectrum. […]

About selective radiation characteristics

If the heaters (according to illustration 2)would show some additive characteristics analog to a distinctively selective radiation characteristic, a further approximation of emission and absorption in terms of improvements for energy efficiency could be effected. The STIR®-technology is working with ceramics presenting these characteristics. The advantage are […] the different selective radiation spectra of STIR®-ceramics in comparison to full radiators (ε = 1) and steel. […] The coating of a conventional steel heater with STIR®-ceramics increases the approximation to the ideal full radiator significantly. The goal of the STIR®-technology is to achieve an optimal accordance of emission of the heaters and absorption of the good (here the coating on the substrate). You can name it rational energy transfer at resonance. […]

ill. 2: emissions performance and absorption spectrum of three typical infrared heaters and the absorption of water
–––– light infrared (e.g. NIR) with 2500 °C max. performance at ë = 1.00 ìm
–––– medium infrared with 1600 °C max. performance at ë = 1.55 ìm
–––– dark infrared (e.g. STIR®) with 600 °C max. performance at ë = 3.32 ìm
–––– absorption of water with maximum at ë = 3.0 ìm (schematic)

...read it up on:

application/pdf Holztechnologie 50/2009; Peter John, Winfried Reh, Ulrich Putzschke (1.0 MB)

Application orientation and absorption bands

Groups of moleculesPhase wavelengths (µm)temperature (°C)Intersectional
temperature (°C)
-CH3,5-3,1555-662608
-OH; -NH3,12-2,85654-744699
-NCO4,54-4,42365-383374
-NH25,91-6,0217-211214
-C=O5,88220220
aromatic ring6,25190190
-CO (epoxide ring)8,068787

The needed λ max. by the good as well as the strongest absorption bands for typical OH- and CH-groups are around 3 to 8 µm (application-oriented selection of the relevant functional ceramics).

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