Date of Award

12-2017

Degree Name

Doctor of Philosophy

Department

Chemical and Paper Engineering

First Advisor

Dr. Paul D. Fleming III

Second Advisor

Dr. Alexandra Pekarovicova

Third Advisor

Dr. Veronika Husovska

Fourth Advisor

Dr. Kiran Deshapande

Keywords

Density, whiteness, tone value, expanded Gamut, Spot color printing, Optical Brightening agents (OBA)

Abstract

In the printing industry, process color printing is a very common way of reproduction of color photographic images. As continuous tone reproduction is not possible, images are converted to halftone format. Process control of a halftone image quality is carried out by measuring optical density of solid patches. ISO 5 defines measurement of optical density, formula, filters and requirements. As per ISO document optical density can be calculated only for the 4 colors cyan, magenta, yellow and black, known as process colors. To enhance quality of color reproduction of images, the number of reproducible colors are increased by gamut expansion. The color gamut of this process color is expanded by adding orange, green and violet along with CMYK. This process is known as CMYKOGV expanded color gamut process. For measurement and control of ink film on substrate, a spectrophotometer is used to measure reflected light from an ink patch and related to its opacity. The range of sensitivity of these instruments is usually from 400 nm to 700 nm. Each color has its own reflection spectrum. The spectrum of each color can be divided in two parts known as reflection and absorption regions. When a color is printed in tonal gradation, then the reflectance spectrum shows change in the absorption region. The optical density is calculated by using data from the change in the absorption region. This change in the absorption region is selected by using a filter in the density calculation. For CMYK inks, this filter is defined in the ISO document, but for orange, green and violet, no filter is available, so optical density calculations are not possible. This research focuses on generation of absorption filters for orange, green violet and other spot inks to measure optical density. Also, it recommends modifications in the ISO 20654 SCTV formula.

In the paper industry, one dimensional scales are widely used for determining optical properties of paper and paperboard. Whiteness, tint, brightness, yellowness and opacity are most common optical properties of paper and paper board. Most papers have a blue cast generated by addition of OBA (Optical Brightening Agent) or blue dye. This blue cast is given because of human perception that bluer is whiter up to certain limit. It is necessary to determine how much blue cast paper and paperboard has. As printing industry follows ISO 3664 standard for viewing, which has a D50 light source, this also plays a very important role in showing blue cast. Color perception is based on light source and light reflected from object. D50 has UV component in it and this interacts with OBAs and provides a blue cast as emission caused by OBA is in blue region. Use of a UV blocking filter results in measurements without effect of emission in blue region. This difference is used in determining the blue cast of the paper. This equation is known as Shendye-Fleming OBA Index.

Access Setting

Dissertation-Open Access

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