Color strength

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The color intensity is a colorimetric size that the coloring ability of a coloring agent describes. A distinction is made between absolute and relative color strength. The color strength is the most important property of pigments .

Absolute color strength

The absolute color strength indicates the amount of colored pigment that is necessary to adjust a defined amount of white pigment in a certain application medium to a standard color depth . The color strength is therefore not a fixed parameter, but depends essentially on the application medium (such as paint , plastic , printing ink ) in which the colored pigment is tested and under which conditions it is dispersed . Manufacturer specifications in sample cards are therefore not comparable, as different test systems are used.

The specification of the absolute color strength is usually used for sample cards and technical data sheets , where the same application medium applies to all products in a product group under defined dispersion conditions.

Relative color strength

In the production of pigments it is common to use not the absolute but the relative color strength, measured against a standard. For this purpose, each batch to be tested is dispersed and colored under the same conditions as the standard. The quotient (sample / standard) of the K / S values ​​(according to Kubelka-Munk ), which represent a measure of the light absorption of the overall system, is referred to as the relative color strength and expressed in percent:

A value of 100% means that the sample has the same color strength as the standard; larger values ​​mean a higher color strength, i.e. H. less pigment is required to color a certain shade .

The indication of the relative color strength is used for all types of direct comparisons between two products, e.g. B. when testing alternative products or quality control .

Differentiation from related terms

Color depth

The terms color strength and color depth are often confused with one another. The depth of color describes the visual impression of the same concentrations when comparing two pigments. In reality, however, the pigment concentrations can differ from one another due to different color strengths. Therefore all pigments are set to a standardized color depth for comparative representations (eg. As in sample cards) usually, a standard depth .

Lightening power

The lightening power is used to calculate the "color strength" of white pigments . For this purpose, the color strength is measured, which is achieved by a defined amount of black pigment . The reciprocal of this color strength is therefore the lightening power of the white pigment.

Color strength adjustment

When carrying out a color intensity adjustment , the concentration of the sample is adjusted until both colors are in the same color depth (usually that of the standard). Coloristic differences can only be correctly assessed if the color depth is the same; if the color depth is not the same, they are influenced by the color strength.

The color distance  ∆E after color strength adjustment is called the residual color distance.

Special features of tinting systems

Pigment preparations ("pastes") are used for tinting systems , ie predispersed mixtures of pigment, water or solvent (s), wetting and dispersing agent (s), retention agent (s) and, for certain applications, binder (s). The density of the liquid can vary greatly depending on the type and amount of raw materials added, especially for inorganic pigments.

Two mechanisms have become established on the market for the dosage of pigment preparation on the base color: gravimetric dosage (according to mass ) and volumetric (according to volume ). This in turn requires a more precise specification of the color strength, since for a correct dosage with a different density only volume or mass can be identical, but not both at the same time.

Manufacturers of pigment preparations therefore usually specify both gravimetric and volumetric color strength and thus indirectly also the density.

Gravimetric color strength

The gravimetric color strength is usually the value that is easily determined in the laboratory, since it is easier to weigh in by mass with the relatively highly viscous pigment preparations. With the same gravimetric color strength, the same initial weight (i.e. mass) is required to achieve the same color strength.

Volumetric color strength

In dosing systems , in addition to the gravimetric, the volumetric color strength is important, since it is easily possible with the system to dose constant volumes. In the laboratory, on the other hand, the volumetric color strength is determined from the gravimetric color strength and the quotient of the densities of sample and standard:

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  1. DIN EN ISO 787-24
  2. DIN 53235-2
  3. DIN EN ISO 787-24
  4. ISO 787-26