M3 is for controlling metallics
The purpose of this research is to demonstrate that the M3 measurement condition should be used for controlling metallic inks on press. In this research, lithographic and flexographic metallic inks were printed with the PrüfbauPrintability Tester and the Phantom Proofer. The tested inks were also printed on an offset press and on a flexographic label press.
Results showed that the X-Rite eXact and Techkon SpectroDens measuring devices, operating in the M3 mode, best capture the density values regardless of the color of the metallic ink being printed. Legacy densitometers with a polarization filter capture changes in the printed ink film thickness as well, but in future M3 mode compliant measurement devices should be used for controlling metallic inks on press.
The metallic inks were not only printed on coated paper, but also on cardboard stock to simulate the use of this substrate in the folding carton industry. The results demonstrate that the substrate does not influence on the measurability of the metallic inks.
A gloss water-based coating was applied to all printed samples to see if there is any influence on the measurement of the printed ink film density or colorimetric values. Since the results show that the coating has little effect on the measured densitometric or colorimetric values, the M3 mode can be used for controlling metallic inks on press, even with the application of a protective gloss water-based coating, like it is often done in the folding carton industry.
In addition, the ∆E values from the flexographic metallic ink press run illustrate that there were only small color variations between the coated and non-coated print samples. Thus, the application of a gloss water-based coating does not influence the density values and the M3 measurement conditions can be used to measure flexographic metallic inks as well.
The colorimetric values of the printed metallic colors were examined and the results show that the application of the water-based coating does not cause significant change in the L*a*b* values.
The main result from this study is, that a measurement device that is M3 measurement mode compliant, as outlined in ISO 13655, can be used for the control of metallic inks on press. Since modern spectrodensitometers capture the reflectance curve from the color sample, which in turn is converted mathematically into printed ink density, colorimetric values, mainly the L*-value of the sample, or the densitometric values can be used to measure and control metallic inks on press. The measurability of metallic inks is not influenced by the ink type, whether it is offset or flexographic ink.
The M3 measurement mode is the measurement mode of choice for controlling metallic inks on press.
