Details:
Summary:
An essential part of four process colour printing, is the need to use inks of a consistent colour and to have a reliable method of defining the ink colorimetrics. Ink colours and transparency measurements recently reported to IS0 TC 130 have highlighted several areas where an apparent inconsistency could occur, particularly with high viscosity inks, such as UV flexographic inks. A significant amount of the difference can be attributed to the execution of the methodology proposed in the IS02847-series of standards. This paper describes an improved methodology for measuring the colour and transparency of the inks, which has been developed to enables a quick, accurate and repeatable measurement. The method uses a preliminary evaluation to define press ready ink and the extension limits. This is then used to produce a further series of colour and transparency measurements that enable the printing range to be accurately covered. The use of a polynomial interpolation, enables an accurate resolution of the colorimetric curve to be obtained with the minimum number of measurements. The influence of the number of samples on the accuracy of the results is discussed. The problems associated with the use of Meyer bar draw down systems for high viscosity inks is highlighted and alternative approaches suggested. Results are presented for different flexographic ink types provided by a range of suppliers. Good agreement was achieved for the measurement of colour and transparency as defined in IS02847. These results show that the same colorimetric targets could be used for all flexographic process ink sets.