Holliday Pigments’ Technical Support Manager, Dave Masterman, has developed a bank of white papers exploring the pigment properties required for the company’s signature Ultramarine’s many and varied applications - each of which has its own particular demands.
The first in the series (extract below) explores what is required of an Ultramarine pigment when used for colouring plastics and is available to download in full from the ‘publications’ section on the company’s website ( www.holliday-pigments.com/publications).
Ultramarine for colouring plastics
When used to colour plastics, it is important that a grade of Ultramarine pigment has consistent colour and dispersion properties. It must be low in unreacted sulphur so that odours are not released when it is heated to plastics processing temperatures and it must not contain excessively high moisture. For sensitive applications where regulatory approval is required, it must also have a low trace metal content.
While general purpose grades of Ultramarine can be used to colour plastics, manufacturers should recommend a specific range of grades in which the above properties have been optimised.
Holliday Pigments’ Premier range for plastics, for example, features excellent colour specification for achieving consistency in plastics applications. The total colour difference (DE) for a production lot is guaranteed within 0.5 units CIELAB, whereas general purpose grades are specified to wider tolerances which may require corrections in sensitive applications to compensate for the differences in colour between production lots.
In terms of colour consistency, masterbatch manufacturers should also consider that high strength grades of red and green shades are ideal when maximum colour strength is the main objective, but medium strength grades are preferred when this is not so key because the lower surface area makes them slightly easier to disperse.
Moisture content can present another potential challenge. For example, at high concentrations where masterbatches contain 30% or more Ultramarine, it can be difficult to remove the amount of moisture generated without adequately vented processing equipment.
To counteract this, Holliday Pigments dries its Premier D range at higher temperatures to give exceptionally low moisture content. The specially dried Ultramarine is so hydrophilic that it would slowly re-absorb moisture from the atmosphere, so needs to be packed in moisture proof plastic sacks. The moisture content is less than 0.05%, and with Premier D versions it is possible to manufacture good quality masterbatch at pigment content in excess of 60% - even when vented equipment is not available.
(396 words)-ENDS- |