METHOD FOR DETERMINING THE COMPOSITION OF A MULTI-LAYER SYSTEM SHOWING A PREDETERMINED COLOUR FLIP-FLOP EFFECT

The present invention relates to a method for determining the composition of a multi-layer system showing a predetermined colour flip-flop effect, wherein the multi-layer system comprises from bottom to top a) a substrate, b) at least one first colour layer containing a colourant, which is arranged on the substrate a), c) on the at least one first colour layer an effect layer containing at least one platelet-shaped effect pigment, and d) on the effect layer c) at least one second colour layer containing a colourant, wherein each of the at least one first colour layer and of the at least one second colour layer contains a colourant being no platelet-shaped effect pigment, wherein the method comprises the following steps:i) specifying a first target value for the colour shade and/or colour brightness of the top side of the multi-layer system seen at a first observation angle,ii) specifying a second target value for the colour shade and/or colour brightness of the top side of the multi-layer system seen at a second observation angle, wherein the second observation angle is different from the first observation angle, and wherein the second target value is different from the first target value,iii) specifying a colourant system comprising at least one colourant and further comprising one effect pigment layer recipe being suitable for forming the effect layer c),iv) providing at least one empirical model of the relationship between the colour shades and/or colour brightness at at least two different observation angles comprising at least the first observation angle and the second observation angle specified in step ii) of the top side of a first number of multi-layer systems, at least 90% of which comprising at least one first colour layer b) having at least one colourant as specified in step iii), at least one second colour layer d) having at least one colourant as specified in step iii) and an effect layer c) made of the effect pigment layer recipe specified in step iii), andv) determining - making use of the at least one empirical model provided in step iv) - the composition of a multi-layer system (10) having within a predetermined tolerance the first target value specified in step i) and the second target value specified in step ii), or, if none is found, specifying a new tolerance for the first target value specified in step i) and/or the second target value specified in step ii), or specifying in steps i) and ii) a new first target value and/or new the se