Colours without tears

Leading purging compound developer Aquapurge reports that plastics processor versatility and ambition with colour is driving an increased need for vigilance and precision when changing over tools and colour work.

Technical Director John Steadman says that ‘colourants and additives simply don’t always stay inside the polymer carrier: This can be due to a multitude of issues, including; pigment and/or additive type; quantity of each; peak shear rates, residence time and temperatures of processing.’

Since masterbatch suppliers are often reluctant to divulge their exact material formulations, ‘processors seek a universal purging solution that can be guaranteed to shift a multitude of problems; chemical and physical. Our customers want a one-shot deal that frees up their capital equipment in minimum time.’

Aquapurge compounds are therefore designed to succeed in cleaning the production equipment from both the coloured polymer; the plate out (concentrated colourant) and also the carbon residue (degraded plate-out or polymer).

Barrel Blitz and Scrubber Freeze are the two primary Aquapurge products for plastics processors in this regard. They have been joined this month by the new formulation for blow moulders – Poly Clear HMEX.

The ‘hands on’ Aquapurge approach to client work means that the company often gets to witness colour change work from beside the moulding machine. According to Steadman, some ‘black arts’ are still sometimes necessary and advised in order to guarantee successful results.

‘Moulders can do themselves a number of favours in the way they set up their materials handling and equipment before the purging process begins. For example, it’s often a good idea to completely empty and clear one silo feed on a machine, and then start another before then stopping that process in order to clean out the hopper loader
before the next colour run.’

Typically, many colours and formulations are not equal to others, notes Steadman. Many blues and red colourants are bad for plate out, he says. Acetal materials often struggle not to have plate out and some yellows can also degrade easily in processing. Pearlescents and metallics often pose difficulties in clearing and purging. Some
so-called universal carriers won’t work with certain polymers – Nylon and PET to name but two. In general, high temperature polymers don’t like low temperature carriers as they can melt too early in the feed section of the screw, causing cleaning issues.

Liquid colours also need special care in that the colour is an issue from the very start of the process; ie from the feed section. For this reason, Aquapurge Poly Clear or Carbon Clear is best used to wash the liquid colour away from the hopper throat. ‘Masterbatch,’ says Steadman, ‘normally only becomes an issue when it really starts to melt – ie from the start of the compression zone.