Depending on the standard and on its calibration values used for the UV adjustment a different percentage was determined as being the adequate. In general the UV setting was lower for the new scales. This indicates that the FWA of the original scales probably had already deteriorated due to extensive use and more UV energy was required from the lamp to excite the fluorescence necessary to achieve the indicated whiteness value.
3. Measurement Results
After having adjusted the instruments as mentioned previously, the samples were then measured. The 10 samples, five standards each of the cotton and the polyester calibration scales, were measured and compared to their values as given in the calibration certificate. Table 2 shows the average differences from the calibration values of the standard samples measured on the different instruments/settings. Calibration with the original scale is slightly better than with the new scale and the cotton scale also resulted in a smaller difference from the calibration values than the PES scale.
The comparison of the three different whiteness values in Table 3 shows that the adjusted instrument-specific parameters lead to better W GG results than the standard values. These W GG adj values are better than the W CIE values, especially when taking into consideration that the W GG and W CIE scales are different. An evaluation as a percentage of the average whiteness value in the certificates, as shown in the right-hand column of Table 3 is more adequate.
A second requirement, apart from a measurement error as small as possible, where one expects the measurement results to be as close as possible to the calibration values, is the reproducibility amongst instruments. The same sample measured on different instruments should lead to results as similar as possible. The standard deviation of the average measurement results obtained on the four instruments shown in Table 4 is reasonably small. For the Ganz-Griesser whiteness values the adjusted parameters lead to closer results amongst the instruments, as is the purpose of the adjustment.
4. Conclusions
The study confirmed that it is really necessary to adjust the UV radiation of the sample illumination when fluorescent samples are to be measured a basic fact not always so obvious for the industrial user. It shows that it is necessary to adjust the instrument-specific parameters when using the Ganz-Griesser whiteness formula. If for some reason this not possible it is then more appropriate to use the CIE whiteness formula than to use the standard parameters for the Ganz-Griesser whiteness formula.
Comparing the two different types of UV setting, the filter adjustment and the numerical UV setting, it can be said that both lead to good results. From a users point of view the NUVC is much faster and easier.
We found that the portable instrument is highly compatible with the bench top instruments, even when measuring FWA-treated samples.
Our results show that the inter-instrument agreement of instrumental whiteness evaluation might not yet be as good as desirable, but compared to the visual reproducibility these results are already a significant improvement, considering that a group of observers was able to repeat their own whiteness evaluations only in approximately 50% of the cases (Gay 2004).
Acknowledgments
All the spectrophotometers used in this study are long-term loans to the Colour Institute of SENAI/CETIQT from Konica Minolta with whom SENAI/CETIQT is proud to have a cooperation agreement. The samples used in this work were prepared by Cssia Cristina Melo as part of an applied research project for which the authors acknowledge the financial help provided by FAPERJ (Fundao Carlos Chagas Filho de Amparo Pesquisa do Estado do Rio de Janeiro).
References
- ASTM (American Society for Testing and Materials). 1992. ASTM E 991 98, Standard practice for color measurement of fluorescent specimens. West Conshohocken: ASTM.
- Ganz, E. 1972. Whiteness measurement. The Journal of Color and Appearance 1 (5): 33-41.
- Grtner, F., and R. Griesser. 1975. Eine Vorrichtung zur Messung von optischen Aufhellern mit konstanter UV-Anregung. Die Farbe 24: 199-207.
- Gay, J. 2004. Controle metrolgico e instrumental da avaliao de amostras brancas tratadas com alvejante ptico. Rio de Janeiro: Pontfica Universiadade Catlica, MSc Dissertation.
- Hayhurst, R., and K. Smith. 1995. Instrumental evaluation of whiteness. Journal of the Society of Dyers and Colourists 111: 263-266.
- Imura, K. 1997. Numerical calibration of UV energy in illumination for color measurements of fluorescent samples. Minolta Radiometric Operation, private communication.
- USPTO (United States Patent and Trademark Office). 1997. United States Patent 5,636,015, Imura et al., Measuring apparatus for measuring an optical property of a fluorescent sample. Attlington: USPTO.
- 2000. United States Patent 6,020,959, Imura, Apparatus and method for measuring spectral characteristics of fluorescent sample. Attlington: USPTO.
To read more articles on Textile, Industry, Technical Textile, Dyes & Chemicals, Machinery, Fashion, Apparel, Technology, Retail, Leather, Footwear & Jewellery, Software and General please visit https://articles.fibre2fashion.com
To promote your company, product and services via promotional article, follow
this link: https://www.fibre2fashion.com/services/article-writing-service/content-promotion-services.asp
Comments