484
T. Scherzer
0
100
200
300
400
0
50
100
150
200
Integrated Intensity (1650-1850 nm)
Actual Thickness [µm]
Fig. 21.3 Integrated intensity of the absorbance in the first overtone region of C-H stretching
vibrations in dependence on the coating thickness of a red pigmented PUR varnish applied to steel
sheets by spray painting
PUR coatings with thicknesses higher than 100 μm may be used for example for
protective coatings against weathering in demanding outdoor applications.
In case of very thin coatings, the sensitivity becomes an issue that has to be considered with respect to the detection limit of the NIR method, since the low extinction
coefficients in the NIR region pose a considerable challenge. For example, thin
acrylate layers with a thickness of a few microns only can be photopolymerized
without addition of a photoinitiator by irradiation with short-wavelength UV radiation. The initiating mechanism is based on direct excitation of the acrylate molecules
by photons with high energy. An investigation by NIR in-line monitoring at a roll
coating machine [22] demonstrated that a photoinitiator-free acrylate coating with
an application weight of 4 g/m
2 can be cured by irradiation at 222 nm under inert
conditions using a KrCl* excimer double lamp system (175 mW/cm
2 ). Adequate
conversion was achieved at line speeds up to 30 m/min. Despite the low thickness
of the coating, spectra were found to show sufficient signal-to-noise ratio to provide
significant conversion data.
Ink jet printing is widely used not only in home office applications, but also for
labeling in packaging technology, in electronics, nanotechnology and similar applications. Inks for such applications are aqueous systems, which poorly wet most polymer
surfaces. Therefore, very thin hydrophilic ink absorption layers have to be applied
to polymers to make them printable. The typical thickness of such coatings may be
1 g/m
2 or less. Jiang et al. [23] applied polyvinyl alcohol layers with nanoscale
titania particles to PET films with thicknesses between 0.25 and 1.25 g/m
2 . For
T. Scherzer
0
100
200
300
400
0
50
100
150
200
Integrated Intensity (1650-1850 nm)
Actual Thickness [µm]
Fig. 21.3 Integrated intensity of the absorbance in the first overtone region of C-H stretching
vibrations in dependence on the coating thickness of a red pigmented PUR varnish applied to steel
sheets by spray painting
PUR coatings with thicknesses higher than 100 μm may be used for example for
protective coatings against weathering in demanding outdoor applications.
In case of very thin coatings, the sensitivity becomes an issue that has to be considered with respect to the detection limit of the NIR method, since the low extinction
coefficients in the NIR region pose a considerable challenge. For example, thin
acrylate layers with a thickness of a few microns only can be photopolymerized
without addition of a photoinitiator by irradiation with short-wavelength UV radiation. The initiating mechanism is based on direct excitation of the acrylate molecules
by photons with high energy. An investigation by NIR in-line monitoring at a roll
coating machine [22] demonstrated that a photoinitiator-free acrylate coating with
an application weight of 4 g/m
2 can be cured by irradiation at 222 nm under inert
conditions using a KrCl* excimer double lamp system (175 mW/cm
2 ). Adequate
conversion was achieved at line speeds up to 30 m/min. Despite the low thickness
of the coating, spectra were found to show sufficient signal-to-noise ratio to provide
significant conversion data.
Ink jet printing is widely used not only in home office applications, but also for
labeling in packaging technology, in electronics, nanotechnology and similar applications. Inks for such applications are aqueous systems, which poorly wet most polymer
surfaces. Therefore, very thin hydrophilic ink absorption layers have to be applied
to polymers to make them printable. The typical thickness of such coatings may be
1 g/m
2 or less. Jiang et al. [23] applied polyvinyl alcohol layers with nanoscale
titania particles to PET films with thicknesses between 0.25 and 1.25 g/m
2 . For