Colourants | materials feature
Formulating superior colour compounds for polyolefin pipe
Although smaller in volume than the market for black pipe, a substantial amount of high density polyethylene (HDPE) pipe manufactured in North America is colour-coded – and much of that is for non-pressure applications. When formulating colour masterbatches for these applications – such as conduit – a variety of organic and inorganic additives are used. Unlike carbon black, these additives will not always enhance pipe performance in the field – and can actually detract from it. However, adding certain ingredients to the master- batch can improve production, and enhance the pipe’s performance for both pressure and non-pressure applications.
Let-down ratios A major difference between black and colour master- batches is in their let-down ratios. Black concentrates are typically let down in polyolefin resins at relatively high mix ratios between 4% (24:1) and 6.5% (14:1). This is because a greater concentration of carbon black (usually 2-2.5% in the pipe) is necessary to achieve the right amount of UV protection. Let-down ratios for
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Joseph Serbaroli of Ampacet lays down some guidelines to help ensure that polyolefin pipe does not lose performance when adding colour to it
colour masterbatches are lower: for colours such as yellow, blue or lavender, these typically need around 1% (99:1) or 2% (49:1) ratios, for applications such as corrugated duct, smooth wall conduit and gas pipe. For pressure-rated water or gas pipe, the dispersion of the pigments in the matrix is critical. If small agglomerates become embedded in the wall of a yellow gas pipe, it could lead to a brittle failure or Stage Two mechanical failure – in which a tiny hole forms in the wall. As pressurised gas or water spurts through the pipe wall, the opening will become larger until the pipe loses pressure completely. If a compounder cannot attain optimum dispersion of the pigments in a yellow
Extruders must take care when formulating colour for
polyolefin pipe
November/December 2016 | PIPE & PROFILE EXTRUSION 19
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