Лако-красочные материалы — производство

Pigment blacks have a number of advantages compared to other black pigments and black organic dyes:

— Color stability

— Solvent resistance

— Acid and alkaline resistance

— Thermal stability

— Hiding power

Though not considered as an international standard, the following classification system serves as the main reference for most manufacturers. This system contains four groups:

High Color (HC), Medium Color (MC), Regular Color (RC) and Low Color (LC). A third letter refers to the manufacturing process: (F) for furnace black and (C) for channel or gas black. Finally, oxidative aftertreatment is indicated by the suffix (o) for “oxidized” (Table 4.6).

The most important coloristic properties of carbon blacks are jetness and tinting strength. The jetness refers to the achievable intensity of blackness. A method for

measuring residual refraction (<0.5%) invented by Degussa became a standard as DIN 55979. Here, a carbon black sample mixed with linseed oil and measured with a spectral photometer results in a My-value. The finer the carbon black particles, the higher the My-value, corresponding to a higher blackness. A refined version of the paste method described above consists of determining the My-factor in an alkyd/melamine resin system (PA 1540). The jetness achieved is mapped against various group standards and indicated as a relative blackness value My for optimum reproducibility and consistency [4.27, 4.28].

Measuring of the blackness:

Without colored undertone My = 100 log (100/y)

Contribution of the colored undertone dM = 100 (log Xn/X — log Zn/Z)

blue dM >0 brown dM <0

Tinting strength is the coloring ability of a carbon black as measured against a white pigment (titanium dioxide, zinc oxide). However, tinting strength is not only influenced by particle size and structure but also to some extent by particle size distribution. The finer the carbon black particles, the greater the tinting strength, an indirect indicator of surface or particle size specification.

In addition to the particle size expressed in the jetness (My-value), the surface chemistry of the pigment blacks has a decisive influence on their processing behavior. The effect of surface treatment on the performance of pigment black in coatings was shown in Section 4.4.7.

4.7.2.2