21 Applications of NIR Techniques in Polymer Coatings …
477
analytical methods. NIR spectroscopy does not appear to be an obvious method for
in-line analysis of thin coatings due to the rather low extinction coefficients in this
spectral range. Nevertheless, it has been shown during the last two decades that NIR
spectroscopy has great potential for monitoring of the conversion, the thickness and
other properties of polymer coatings if spectroscopic equipment with high sensitivity
is combined with powerful chemometric approaches. Furthermore, the distribution
of the parameters of interest across the coatings may be monitored as well by means
of hyperspectral imaging.
An even greater challenge are printed layers since their thickness is even lower
than those of most coatings. UV-curable printing inks applied for example by offset
printing have typical thicknesses in the range between 0.5 and 3 g/m
2 (which very
roughly corresponds to their thickness in micrometers). Moreover, printing speeds
are at least one order of magnitude higher than in coating technology, which further
increases the specific requirements. Despite these difficulties it has been demonstrated that the conversion in printed layers as well as their thickness may be predicted
with surprisingly high precision from the NIR spectra. The first part of this chapter
will provide a survey on the current state of the art of in-line monitoring of the
properties of polymer coatings and printed layers by NIR spectroscopy.
Synthetic fibers and textiles play an important role in our daily life. They are
widely used not only for clothes, but also for interior design of living rooms, offices,
cars and other means of transportation as well as in numerous technical applications.
Nevertheless, despite their widespread use, the diversified production and processing
technologies and the high quality requirements, synthetic textiles have been rarely the
subject of specific spectroscopic investigations dealing with their characterization or
the monitoring of production and finishing processes. The majority of analytic studies
is dealing with textiles made of natural fibers such as cotton, wool, flax, silk etc.
However, technical textiles, which make particularly high demands on quality and
compliance with the specification, are mostly based on fibers and textiles of synthetic
polymers such as polyethylene terephthalate (PET), polyamide (PA), polypropylene
(PP) or more special materials such as poly(p-phenylene terephthalamide) (paraaramid). Moreover, they are often subject of special treatment and finishing steps
such as impregnation, coating, lamination etc. which have to be controlled in order
to ensure adequate processing. Recently, NIR spectroscopy has been discovered as
an appropriate tool for process monitoring and quality control in textile technology.
Moreover, sorting of textiles with the objective of recycling the materials becomes a
more and more established practice, and NIR spectroscopy is used for identification.
The second part of this chapter will give an overview of the current status of the use
of NIR spectroscopy in textile technology for the characterization of materials and
in-line control of production and converting processes.
477
analytical methods. NIR spectroscopy does not appear to be an obvious method for
in-line analysis of thin coatings due to the rather low extinction coefficients in this
spectral range. Nevertheless, it has been shown during the last two decades that NIR
spectroscopy has great potential for monitoring of the conversion, the thickness and
other properties of polymer coatings if spectroscopic equipment with high sensitivity
is combined with powerful chemometric approaches. Furthermore, the distribution
of the parameters of interest across the coatings may be monitored as well by means
of hyperspectral imaging.
An even greater challenge are printed layers since their thickness is even lower
than those of most coatings. UV-curable printing inks applied for example by offset
printing have typical thicknesses in the range between 0.5 and 3 g/m
2 (which very
roughly corresponds to their thickness in micrometers). Moreover, printing speeds
are at least one order of magnitude higher than in coating technology, which further
increases the specific requirements. Despite these difficulties it has been demonstrated that the conversion in printed layers as well as their thickness may be predicted
with surprisingly high precision from the NIR spectra. The first part of this chapter
will provide a survey on the current state of the art of in-line monitoring of the
properties of polymer coatings and printed layers by NIR spectroscopy.
Synthetic fibers and textiles play an important role in our daily life. They are
widely used not only for clothes, but also for interior design of living rooms, offices,
cars and other means of transportation as well as in numerous technical applications.
Nevertheless, despite their widespread use, the diversified production and processing
technologies and the high quality requirements, synthetic textiles have been rarely the
subject of specific spectroscopic investigations dealing with their characterization or
the monitoring of production and finishing processes. The majority of analytic studies
is dealing with textiles made of natural fibers such as cotton, wool, flax, silk etc.
However, technical textiles, which make particularly high demands on quality and
compliance with the specification, are mostly based on fibers and textiles of synthetic
polymers such as polyethylene terephthalate (PET), polyamide (PA), polypropylene
(PP) or more special materials such as poly(p-phenylene terephthalamide) (paraaramid). Moreover, they are often subject of special treatment and finishing steps
such as impregnation, coating, lamination etc. which have to be controlled in order
to ensure adequate processing. Recently, NIR spectroscopy has been discovered as
an appropriate tool for process monitoring and quality control in textile technology.
Moreover, sorting of textiles with the objective of recycling the materials becomes a
more and more established practice, and NIR spectroscopy is used for identification.
The second part of this chapter will give an overview of the current status of the use
of NIR spectroscopy in textile technology for the characterization of materials and
in-line control of production and converting processes.