colour & masterbatch | Pigments
stability, for example. As previously mentioned, it is practically impossible
to produce pigments that contain zero halogens. Even though, on paper, the chemical structure of the pigment is entirely halogen-free, halogens are inevitably involved in the manufacturing process. Production of organic pigments involves the use of solvents such as hydro- chloric acid, for example, and even if multiple washing steps are used, minute traces remain in the finished pigment. These can be quite easily detected by modern analysis equipment that is capable of spotting elements in the parts-per-billion range. Even the trace levels of common salt in the water used in the washing process- es can be picked up.
Clariant says that the consumer goods and food packaging industries are also looking to reduce halogens in pigments
halogens. Pigments are now in that spotlight. The law of diminishing returns is clearly at play here.
Coloured plastics compounds contain only small amounts of pigment after all. But with some well-estab- lished pigments such as Pigment Green 7, a phthalocya- nine pigment containing as much as 45% of chlorine, the limit of 900 ppm can be surpassed, even at pigment addition rates in the final compound as low as 1%. It is clear that the electronics industry has taken the
lead in pushing for reductions in halogens in pigments. Individual manufacturers have set their own standards: For example, one large mobile phone producer has banned the use of Pigment Green 7 in any of its products. The electronics industry is not alone however.
Europe and North America are replacing
lead chromate, the traditional source of yellows,
oranges and reds
Clariant has also noticed a strong will to cut down on these chemicals in consumer goods markets and in food packaging, even if, for the moment at least, there are no legal limits. More often, it is individual companies that set their own limits. One large famous beverage company, for example, specifies that pigments used in its caps and closures are non-halogenated. This transition is not the sort of thing that can be
accomplished with the flick of a switch. Halogenated pigments have held their position in the market for many years because they provide high performance at a reason- able price. It has not been easy to find replacements. Historically, pigment producers have used halogens
for a variety of reasons. Halogens influence the shade of a pigment, so that, for example, chlorine in yellow pigments adds a green hue. They are particularly important for outdoor applications, since they have a positive influence on weather stability. But today, for any given chlorinated pigment, there is
an equivalent non-halogenated version. They can be considered more or less as drop-in replacements: processors do not have to worry about lower thermal
34 INJECTION WORLD | April 2015
www.injectionworld.com
Taking halogens out of the process The best that the pigment producer can do is to start with halogen-free building blocks, and ensure that halo- gen levels are kept below very tight limits during the production process of every single batch. In the case of Clariant, the limit for its LHC (Low Halogen Controlled) pigments is 500 ppm. Today, Clariant believes it is the only company in the
world that ensures this low level of halogens. This assurance is important. Specifiers need to be aware that using a pigment described as non-halogenated may not be sufficient for them to meet their environmental targets: they also need to look closely at the levels of halogens in impurities that accompany the pigments. Sod’s law determines that the colour most difficult to
make in an LHC version is the one that is used in the highest volumes, Pigment Green 7. Traditionally, this is made by starting with a blue pigment, which contains
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