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Whiteness and Fluorescence in Paper: Perception and Optical Modelling
Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik. (DPC)
2010 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. This includes psycho-physical modelling of perceived whiteness from measurable light reflectance properties, and physical modelling of light scattering and fluorescence from the paper composition.

Existing models are first tested and improvements are suggested and evaluated. The standardised and widely used CIE whiteness equation is first tested on commercial office papers with visual evaluations by different panels of observers, and improved models are validated. Simultaneous contrast effects, known to affect the appearance of coloured surfaces depending on the surrounding colour, are shown to significantly affect the perceived whiteness. A colour appearance model including simultaneous contrast effects  (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. A recently proposed extension of the Kubelka-Munk light scattering model including fluorescence for turbid media of finite thickness is successfully tested for the first time on real papers.

It is shown that the linear CIE whiteness equation fails to predict the perceived whiteness of highly white papers with distinct bluish tint. This equation is applicable only in a defined region of the colour space, a condition that is shown to be not fulfilled by many commercial office papers, although they appear white to most observers. The proposed non-linear whiteness equations give to these papers a whiteness value that correlates with their perceived whiteness, while application of the CIE whiteness equation outside its region of validity overestimates perceived whiteness.

It is shown that the quantum efficiency of two different fluorescent whitening agents (FWA) in plain paper is rather constant with FWA type, FWA concentration, filler content, and fibre type. Hence, the fluorescence efficiency is essentially dependent only on the ability of the FWA to absorb light in its absorption band.  Increased FWA concentration leads accordingly to increased whiteness. However, since FWA absorbs light in the violet-blue region of the electromagnetic spectrum, the reflectance factor decreases in that region with increasing FWA amount. This violet-blue absorption tends to give a greener shade to the paper and explains most of the observed greening and whiteness saturation at larger FWA concentrations. A red-ward shift of the quantum efficiency is observed with increasing FWA concentration, but this is shown to have a negligible effect on the whiteness value.

The results are directly applicable to industrial applications for better instrumental measurement of whiteness and thereby optimising the use of FWA with the goal to improve the perceived whiteness. In addition, a modular Monte Carlo simulation tool, Open PaperOpt, is developed to allow future spatial- and angle-resolved particle level light scattering simulation.

 

Ort, förlag, år, upplaga, sidor
Sundsvall: Mid Sweden University , 2010. , s. 94
Serie
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 47
Nyckelord [en]
Paper Whiteness, Fluorescence Whitening Agents, Kubelka-Munk, light scattering, paper industry applications, Colour Appearance Models, CIECAM02, Monte Carlo
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:miun:diva-12143ISBN: 978-91-86073-97-8 (tryckt)OAI: oai:DiVA.org:miun-12143DiVA, id: diva2:357563
Presentation
2010-11-09, O111, Mid Sweden University, Sundsvall, 20:30 (Engelska)
Opponent
Handledare
Projekt
PaperOptTillgänglig från: 2010-10-19 Skapad: 2010-10-18 Senast uppdaterad: 2010-10-19Bibliografiskt granskad
Delarbeten
1. Whiteness assessment of paper samples at the vicinity of the upper CIE whiteness limit
Öppna denna publikation i ny flik eller fönster >>Whiteness assessment of paper samples at the vicinity of the upper CIE whiteness limit
2007 (Engelska)Ingår i: 26th Session of the CIE, 2007Konferensbidrag, Publicerat paper (Refereegranskat)
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:miun:diva-6824 (URN)6006 (Lokalt ID)6006 (Arkivnummer)6006 (OAI)
Tillgänglig från: 2008-12-08 Skapad: 2008-11-02 Senast uppdaterad: 2012-12-20Bibliografiskt granskad
2. Modelling the effect of simultaneous contrast on perceived whiteness
Öppna denna publikation i ny flik eller fönster >>Modelling the effect of simultaneous contrast on perceived whiteness
2008 (Engelska)Ingår i: Society for Imaging Science and Technology - 4th European Conference on Colour in Graphics, Imaging, and Vision and 10th International Symposium on Multispectral Colour Science, CGIV 2008/MCS'08, The Society for Imaging Science and Technology, 2008, s. 183-188Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

The perceived colour from a surface does not only depend on its optical properties and the illumination. Several studies have demonstrated the simultaneous contrast effect that makes the appearance of coloured patches depend on neighbouring colours. In this study the perceived whiteness of white patches surrounded by induction fields of different shades was evaluated by asking observers to give a magnitude estimate of perceived whiteness of the patches in comparison to a white reference. The perceived whiteness of patches with identical tristimulus values was highly dependent on the shade of the induction field and the patch size did not significantly affect the perceived whiteness. The recent CIECAM02-m2 colour appearance model was tested together with two whiteness equations. A combination of ClECAM02-m2 and a non-linear whiteness equation defined in the whole colour space predicted much of the observed simultaneous contrast effect. However, the model performed better for dark induction fields than for light induction fields. The model rated patches surrounded by light blue and light yellow equally, whereas the observers clearly rated the patches with light yellow induction field as whiter than the patches with light blue induction field. A deeper analysis of the CIECAM02-m2 model indicated that the simultaneous contrast model used cannot accurately predict the change in hue for high lightness induction fields. A potential improvement for predicting contrast simultaneous effect would be to base the calculations not only on the difference between the induction field and the background, but on the difference between the patch stimulus and the induction field.

Ort, förlag, år, upplaga, sidor
The Society for Imaging Science and Technology, 2008
Nyckelord
simultaneous contrast effect, whiteness, colour appearance modelling, CIECAM02
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:miun:diva-6825 (URN)2-s2.0-70349971071 (Scopus ID)6007 (Lokalt ID)978-160560702-3 (ISBN)6007 (Arkivnummer)6007 (OAI)
Konferens
4th European Conference on Colour in Graphics, Imaging, and Vision and 10th International Symposium on Multispectral Colour Science, CGIV 2008/MCS'08; Terrassa; Spain; 9 June 2008 through 13 June 2008; Code 77574
Tillgänglig från: 2008-12-08 Skapad: 2008-11-02 Senast uppdaterad: 2016-09-26Bibliografiskt granskad
3. Quantum efficiency of fluorescent dyesin different furnishes
Öppna denna publikation i ny flik eller fönster >>Quantum efficiency of fluorescent dyesin different furnishes
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

A recently proposed model for the radiative properties of optically thick fluorescentturbid media of finite thickness (Kokhanovsky, JOSA A, 26(8), p1896) is successfullyapplied to uncoated papers produced at different thicknesses. It is found that thequantum efficiency of the FWA is almost independent of the fibre type, FWA type,FWA concentration and filler additive concentrations used in this study. The scatteringcoefficient is however dependent on the FWA concentration. The absorptioncoefficient depends on the adsorption of the FWA in the furnish and is function ofthe sample thickness and of the FWA type, at equal amount of FWA used in the papermakingprocess. The results open for a estimation of the model parameters asfunction of the FWA concentration and furnish. This is necessary in order to use themodel for optimizing fluorescence in the paper and textile industries.

Nyckelord
Fluorrescence whitening agents, Kubelka-Munk, paper, light scattering modelling, fluorescence
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:miun:diva-12141 (URN)
Projekt
PaperOpt
Tillgänglig från: 2010-10-18 Skapad: 2010-10-18 Senast uppdaterad: 2010-11-29Bibliografiskt granskad
4. Limitations of the efficiency of fluorescent whitening agents in uncoated paper
Öppna denna publikation i ny flik eller fönster >>Limitations of the efficiency of fluorescent whitening agents in uncoated paper
2011 (Engelska)Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, nr 3, s. 319-328Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The fluorescence efficiency of one fluorescent whitening agent (FWA) inuncoated and unfilled paper was characterised at different FWA concentrations. An extendedKubelka-Munk model proposed earlier by several authors was applied to quantify the effect onCIE whiteness of absorption of the FWA in the visible spectrum . At high FWA concentration,chemical interactions slightly modify the emission spectrum of the FWA, and the quantumefficiency depends on the FWA concentration. This effect has however a negligible effect onthe CIE whiteness for FWA concentrations used in practice. The overlap of the absorption andemission bands of the FWA is shown to be the main cause of greening (a shift of thechromaticity towards green) and saturation of the fluorescence effect. With increasing FWAconcentration, the positive effect of fluorescence is neutralised by the reduction of thereflectance factor in the violet-blue region of the spectrum induced by a significant absorptionof the FWA in that region.

Nyckelord
Fluorescence, paper, fluorescence whitening agents, greening, whiteness
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:miun:diva-12142 (URN)10.3183/NPPRJ-2011-26-03-p319-328 (DOI)000294524200010 ()2-s2.0-80052349477 (Scopus ID)
Projekt
PaperOpt
Tillgänglig från: 2010-10-18 Skapad: 2010-10-18 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
5. Open source Monte carlo simulation platform for particle level simulation of light scattering from generated paper structures
Öppna denna publikation i ny flik eller fönster >>Open source Monte carlo simulation platform for particle level simulation of light scattering from generated paper structures
2009 (Engelska)Ingår i: Papermaking Research Symposium, 2009Konferensbidrag, Publicerat paper (Refereegranskat)
Nyckelord
light scattering, fluorescence, paper strucutre modelling
Nationell ämneskategori
Pappers-, massa- och fiberteknik
Identifikatorer
urn:nbn:se:miun:diva-9122 (URN)978-951-27-1038-6 (ISBN)
Projekt
PaperOpt
Tillgänglig från: 2009-10-02 Skapad: 2009-06-09 Senast uppdaterad: 2012-12-20Bibliografiskt granskad

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