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Development of the ISO 2846-1 in support of the standardization concept for offset printing


Research report

42.027

Author

Gemeinhardt, J.; Zins, L.; Zimmermann, Chr.

Year of publication

2017

Abstract

The colour shifts in a primary colour when switching from the APCO test substrate to another specified substrate depend upon the transparency of the inks and the change in the print gloss. It is not therefore possible to define a generally applicable and ISO 2846-1 compliant aim colour values on another substrate.

Since the substrates used for offset printing generally differ significantly from APCO, the question therefore arises as to whether it makes sense to retain the standard’s existing specifications. Inks may, for example, behave very similarly in laboratory tests but differ significantly in actual practice.

Solid colouring is considerably influenced by such substrate properties as colour values, gloss, roughness and absorption behaviour. A mathematical relationship has been derived that uses these characteristic figures to calculate colour values for average inks.

Application of this formula makes it clear that the ISO 2846-1 test substrate tolerances are too large for checking colour. This is especially true for lightness. But further limitations are also recommended for b* and gloss.

Although it is not absolute colour differences measured by printing on a black test substrate that are used for determining transparency but film thickness dependent changes, print gloss continues to exert a certain influence. The guidance in the standard that a test substrate should be chosen so as to achieve the smallest possible gloss changes does not seem to be compatible with practice.

By specifying a defined gloss range for transparency determination it is possible to standardize the results for different laboratories. However, this does not allow misinterpretations stemming from gloss changes to be avoided completely.

In addition, values referred to as the gloss index and gloss constant have been defined for ink gloss. These are substrate independent characteristic values and can be determined from prints on a series of substrates exhibiting a graduated range of gloss.

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