engleski

The Importance of Surface Structure Influence in Application of Kubelka - Munk Theory

Reflection, absorption and scattering occur when opaque surfaces are exposed to light. Light interacting with a textile material involves absorption and scattering of light by dye molecules and fibres. These two phenomena, exactly, are incorporated in the Kubelka– Munk colour model which describes the reflectance of a colour sample as a function of an absorption spectrum K(λ )and a scattering spectrum of substrate S(λ ). In this paper the aim was to analyse the performance of K– M theory on yellow shaded samples of different surface structure influenced by the measurement geometry. Six different woollen fabrics of different surface structure characteristics (weaving structure) were studied through the application of Kubelka– Munk theory, in correlation with size and the direction of a measured surface. Samples were measured in CIELAB mode spectrophotometrically by means of DataColor type SF600+CT. In order to analyse the influence of a size of the measured surface, samples were measured with three instrument apertures of different sizes (aperture “ M” =2 cm, aperture “ S” =0, 9 cm and aperture “ US” =0, 6 cm) and in a three different directions (direction of warp, direction of weft and diagonal direction). The K– M coefficients K/S were determined, dK/S values were calculated and were showed in a relationship to a dE(CIELAB) values. In further work, substrate 6 was chosen due to the smallest discrepancies obtained in prior analyses of dE/dKS relationship, and was dyed with acid dyestuff in concentration of 0, 5% and 2%, in yellow hue. Based on the results of K/S values obtained for the dyed samples, the optical data of the dyestuff, (k/s)dye, were calculated. For the samples dyed by 0, 5% dyestuff concentration, the values of optical characteristics (k/s)dye are dominant in compare to K/S value and certain differences obtained for the (k/s)dye values considering the measurement direction and size of measuring surface proved the significant influence of the substrate itself. With 2% dyesuff concentration, optical characteristic values (k/s)dye are lower then K/S values and represent the optical characteristic of dyestuff itself. Differences obtained are influenced by the surface direction measurement and the surface structure of the substrate. Dyestuff optical data values (k/s)dye were further used for calculation of predicted K/S values for the rest of five analysed woollen samples of different structure and surface appearance. Certain differences obtained for the results for 2% of dyestuff proved the significant influence of surface structure characteristics on K/S values regarding deeper shades of samples. While defining dyestuff optical characteristic (k/s)dye and K/S values, certain errors and problems may occur especially for samples of low dyestuff concentrations because of the importance of substrate surface influence. That means that colour of the sample dyed with low concentration of dyestuff while considering yellow hues cannot be defined only based on optical data of the dyestuff. When there is a variation in substrate quality it is recommended to evaluate the correction factor to predicted K/S values calculated in order to evaluate the appearance of different substrates to be dyed with same group of dyestuff especially in lower concentration.

K– M theory; lightness; optical data of dyes; measurement geometry; surface influence

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