Monitoring of the Thickness of Ultraviolet-Cured Pigmented Coatings and Printed Layers by Near-Infrared Spectroscopy

Heymann, Katja; Mirschel, Gabriele; Scherzer, Tom

doi:10.1366/000370210791114310

Cited by 16 publications

(10 citation statements)

References 29 publications

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“…Recently, an in-line monitoring method based on NIR reflection or transflection spectroscopy has been developed, and it was shown that it can be used for the direct determination of the coating thickness of acrylate coatings with thicknesses in the range of about 5 to 50 lm. [19][20][21][22] In printing technology, transparent lacquers are used as protective and decorative layers as well. In particular, they can be utilized for the creation of specific design effects on the print image.…”

Section: Introductionmentioning

confidence: 99%

In-Line Monitoring of the Thickness of Printed Layers by Near-Infrared (NIR) Spectroscopy at a Printing Press

et al. 2012

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In this work, it is demonstrated that the coating weight of printed layers can be determined in-line in a running printing press by near-infrared (NIR) reflection spectroscopy assisted by chemometric methods. Three different unpigmented lacquer systems, i.e., a conventional oil-based printing lacquer, an ultraviolet (UV)-curable formulation, and a water-based dispersion varnish, were printed on paper with coating weights between about 0.5 and 7 g m(-2). NIR spectra for calibration were recorded with a special metal reflector simulating the mounting conditions of the probe head at the printing press. Calibration models were developed on the basis of the partial least squares (PLS) algorithm and evaluated by independent test samples. The prediction performance of the developed models was examined at a sheet-fed offset printing press at line speeds between 90 and 180 m min(-1). Results show an excellent correlation of data predicted in-line from the NIR spectra with reference values obtained off-line by gravimetry. The prediction errors were found to be ≤ 0.2 g m(-2), which confirms the suitability of the developed spectroscopic method for process control in technical printing processes.

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Section: Introductionmentioning

confidence: 99%

In-Line Monitoring of the Thickness of Printed Layers by Near-Infrared (NIR) Spectroscopy at a Printing Press

et al. 2012

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“…The change in absorption of this CH oscillation is a direct measure of the degree of polymerization and accordingly an indicator for remaining acrylic C‐double bonds in the coating. Furthermore, an overall attenuation of the reflection is observed, as a result of the coating shrinkage in combination with a change of the refractive index,11, 12 and a change in molecular scattering. Consequently, a discrete measurement of the absorption at 1620 nm is only possible by compensating for these changes.…”

Section: Resultsmentioning

confidence: 99%

NIR‐laser based detection of the photopolymerization state of acrylate coatings suitable for in situ measurements

Bach

Heering

2011

J of Applied Polymer Sci

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The present article describes a method for the determination of the radical photopolymerization conversion of acrylic coatings suitable for an in situ monitoring during the coating process. Acrylate based coatings are increasingly used in many kinds of industrial coating processes, because of advantages of the solvent-free application process. The applied method is based on 1620 nm light absorption of the acrylate. To overcome the disadvantages of a common NIR spectrometer, only the diffuse reflection of the relevant discrete wavelength at 1620 nm and of a reference wavelength is measured. A sophisticated sensor setup including an optical spatial filter and lock-in amplified signal processing is used to achieve a sufficient signal to noise ratio. The capability of the sensor to discriminate between polymerized and unpolymerized coatings on metal substrates down to a coating thickness of 16 lm is demonstrated. Furthermore, the information on polymerization from larger depth in TiO 2 pigmented coatings is investigated. The results can be analytically modeled in analogy to the Lambert-Beer's law, resulting in a detection limit of a maximum pigment concentration of 15 wt % with 100 lm coating thickness. The presented sensor design is suitable to be used in an industrial production environment for example in screen printing applications as a monitoring and quality control tool.

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“…The reduction of sampling errors facilitates the study of the effect of: (1) scattering and depth of penetration, (2) the selection of spectral regions and (3) the effect of spectral preprocessing on the performance of the PLS models. <2 TF ternary fuel blends Rohe et al 21 <2 T polymer blends Heymann et al 13 <2 TF polymer film coatings Sulub and Derudder 22 <3 DR polymer blends Rosas et al 23 6.2 DR ternary mixture pellets Colón et al 24 2.5 DR pharm. powder blends Vanarase et al 25 7.5 DR pharm.…”

Section: Introductionmentioning

confidence: 99%

“…5 Nevertheless, NIR spectroscopy is considered as one of the most suitable and fast non-destructive methods for analysis of materials. NIR scattering is affected by physical differences of the materials, such as particle size, 6–9 density 10–12 and thickness, 13–15 This scattered radiation was studied using different numbers of layers of similar polymer sheets to describe the representative layer theory 16 and to find the absorption and remission fractions of layers which best fit the observed Log 1/R values. 17,18 In spite of the complexity of the interaction between radiation and particles, NIR spectroscopy is applied in many industries.…”

Section: Introductionmentioning

confidence: 99%

Study of near infrared chemometric models with low heterogeneity films: The role of optical sampling and spectral preprocessing on partial least squares errors

Ortega-Zúñiga

Reyes-Maldonado

Méndez

et al. 2017

Journal of Near Infrared Spectroscopy

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This study is focused on understanding absorption and scattering effects and their impact on the errors observed in near infrared calibration models developed using partial least squares regression able to predict the number of polypropylene film layers stacked together. The films provided a system with reduced heterogeneity to study the sources of error due to light scattering, selection of spectral preprocessing and spectral region on near infrared calibrations. Near infrared spectra were acquired using two experimental setups with the integrating sphere module of the FT-NIR spectrometer. The first setup consisted in stacking the polymer films to determine the penetration of the near infrared radiation. The second setup was a variation using a reflective surface on the top of the films in transflection mode, increasing the pathlength and therefore transmission and absorption of the material. The estimation of the penetration of radiation was performed using talc placed over the polymers films. The narrow bands of talc, related to first and second overtones of the O-H stretching mode, were used to estimate the near infrared sampling depth into polymer film layers, which ranged from 2.95 to 3.12 mm. Partial least square calibrations developed with up to 30 film layers were accurate with bias values that were not significantly different from zero at the 95% confidence level. Statistical errors were calculated for seven near infrared regions using different spectral preprocessing and the confidence interval of the bias showed that optical sampling is unbiased and there is an absence of systematic error by the near infrared method. A calibration model developed with 50 film layers presented high statistical errors and bias different from zero, indicating a sampling error due the depth of penetration of near infrared radiation. The impact of number of samples in the calibration and validation set was also evaluated. The results showed that bias was significant when the number of samples was less than 11. This finding highlights the lack of systematic error in the near infrared method, as long as the number of samples in the calibration set is representative of the variation to be modelled by a partial least squares regression and the sampling error is reduced.

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Monitoring of the Thickness of Ultraviolet-Cured Pigmented Coatings and Printed Layers by Near-Infrared Spectroscopy

Cited by 16 publications

References 29 publications

In-Line Monitoring of the Thickness of Printed Layers by Near-Infrared (NIR) Spectroscopy at a Printing Press

In-Line Monitoring of the Thickness of Printed Layers by Near-Infrared (NIR) Spectroscopy at a Printing Press

NIR‐laser based detection of the photopolymerization state of acrylate coatings suitable for in situ measurements

Study of near infrared chemometric models with low heterogeneity films: The role of optical sampling and spectral preprocessing on partial least squares errors

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