The main contaminant which may be present in a plastic masterbatch based on Ultramarine pigment is sulphide. There are two possible reasons for its presence.
Firstly, Ultramarine pigments contain sulphur chromophores, plus small quantities of unreacted sulphur. These unreacted species are volatile at plastics processing temperatures and are released as sulphides. Normally the amount of free sulphur present even in the general purpose grades manufactured by Holliday Pigments is not enough to cause any objectionable taint or odour as it is removed along with the other volatiles such as moisture during the production process.
However, food contact plastics are especially sensitive to taint and for these applications even well processed standard grades may not be pure enough. For that reason Holliday Pigments Premier BC ranges for severely demanding food contact applications are free from unreacted sulphur and superior performance is ensured by improving the specification for volatiles to 0.05% maximum at 150°c (standard grades are tested at 105°c) and the un-reacted sulphur to 20ppm maximum (standard grades 200ppm). After thorough independent testing of bottle caps coloured with this grade and immersed in pure mineral water, no evidence of taint in the water could be detected.
Secondly, Ultramarine is sensitive to attack by acids which release sulphides. Such acids may be present as breakdown products of the polymer (such as PVC) or in some foods (sparkling mineral water and fruit juices). While the polymer may protect standard grades of Ultramarine against such weak acids for a period, it is much better to use an Ultramarine which has its own protective coating to resist such attack.
Abelly chemical www.abellychemical.com
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