INORGANIC PIGMENTS FOR PLASTICS

 

The pigments used for colouring plastics must satisfy a number of exacting technical requirements. Given the usually short dwell times and relatively low shear forces in the processing equipment, the pigments must have good dispersibility, i.e. they must be easy to break down and distribute to reach their final tinting strength quickly. They must also have high thermal stability, and their lightfastness and weather stability must be adequate for the intended application. They should not migrate.

 

Inorganic pigments in general and Lanxess’s range of inorganic colour pigments in particular satisfy these requirements.

 

 

COLORTHERM^® Iron Oxide Pigments 

In terms of volume, iron oxide pigments are the most widely used inorganic colour pigments. The range includes yellows, reds, browns and blacks. Chemically speaking, iron oxide yellows are iron (III) oxide hydrates with acicular particles. Iron oxide reds are iron (III) oxides and iron blacks iron (II, III) oxides, both with spherical particles. The normal iron oxide browns are mixtures of iron oxide red and iron oxide black, possibly also iron oxide yellow. Special heat-stable brown and black pigments are also available. These are (Fe,Mn)₂O₃ mixed phase pigments (COLORTHERM^® Brown 645 T and Black 303 T).

 

COLORTHERM^® pigments are easily dispersed in plastics. Some pigments are available in a micronized version with reduced agglomerates. The COLORTHERM^® pigments are specially pre-tested in PVC to meet the high demands of the colouring of plastics regarding product conformity.

 

The normal iron oxide yellow pigments possess a limited heat stability. By inorganic aftertreatment COLORTHERM^® Yellow 10 and COLORTHERM^® Yellow 20, the latter with hydrophobic properties, were developed. The heat stability of both pigments is up to 260 °C, therefore also suitable for HDPE and PS.

 

COLORTHERM^® Yellow 30, a stabilised iron/zinc oxide, is stable up to 300 °C. It can be used in all engineering plastics, including ABS and PA.

 

Bearing in mind the limited heat stability of the normal yellows, the COLORTHERM^® pigments can be used without restrictions. But careful pre-tests should be done by colouring PVC (a good stabilisation is required) or PP and ABS when demands are high.

 

COLORTHERM^® Chrome Oxide Pigments   

With their excellent resistance properties - heat stability, migration resistance, lightfastness and weather stability - Chrome Oxide Green pigments are suitable for colouring almost any type of plastic. When dispersing these pigments, their relatively high inherent hardness should be borne in mind. This is particularly significant if high-speed mixers are used, e.g. when mixing PVC powders or working with a high-speed extruder, because the metal may be abraded more.

 

Chrome Oxide Green pigments can be mixed with brilliant yellow pigments with good stability to produce the saturated greens required by, for example, the household appliance industry. But generally speaking, Chrome Oxide Green pigments are also used in the technical sector, e.g. for colouring engineering plastics for machine components.

 

COLORTHERM^® Green GN-M is especially recommended for PVC coating pastes, e.g. for truck tarpaulins or floor coverings, because then pastes can also be ground in a dissolver.

 

Because COLORTHERM^® Green pigments contain nearly no chrome (VI), they can be used for the coloration of food packaging.