technical paper | Carbon black
Figure 7: Relationship between external surface area (STSA) and Hunter L and b
increased UV absorption and improved weathering. A second mechanism of UV protection is that the carbon exhibits antioxidative behaviour. The carbon black surface acts as a radical trap and stabilizer. Typically a carbon black loading of 1% or above is enough to protect against UV degradation. Good dispersion and distribution of the black are essential for full protection.
Conductivity: Conductivity relies on a continuous network of carbon black transferring electrons throughout the resin through two methods: Electron tunnelling – across gaps between spatially distributed aggregates Graphitic conduction – along chains of aggregates When enough carbon black is added to form the network the conductivity increases dramatically. This is known as the percolation point (Figure 9). At equal dispersion, the onset of percolation depends on the
morphology (surface area and structure) of a carbon black. Finer and more porous carbon blacks have more aggregates per unit weight to form the network. High structure carbon blacks form better networks by providing long three dimensional conductive paths.
4) Application requirements
Colour concentrates: The selection of a carbon black grade here primarily depends on the coloristic performance required. The spectrum can be roughly divided into tinting and low/medium colour for polyole- fi ns (STSA <150m2 resins (STSA >150m2 >200m2
/g), medium colour for engineering /g) and piano blacks (STSA
/g). Figure 7 shows the jetness for different carbon blacks.
Fibres: This can be an extremely demanding applica- tion; here two levels are identifi ed: Primary considerations:
Carbon black fi lterability and dispersability. This is infl uenced by carbon black morphology – fi ner, low structure carbon blacks will be harder to disperse, while very clean carbon blacks ensure low levels of impurities. Physical form and bead quality also play a role. Colour strength and blue tone - higher surface area for stronger jetness and tone. Secondary considerations:
Carbon black moisture pick-up (MPU) - polyester and polyamide are sensitive to moisture during processing, so a low MPU carbon black is preferable.
Guide wear or abrasion - carbon black can increase the abrasiveness of a fi bre and low residue is vital.
Figure 8: Coeffi cient of absorptivity (COA) versus external surface area (STSA) 42 COMPOUNDING WORLD | November 2013
Pipes: Carbon black is used in pipe for UV protection (outdoor pipe), coloration and reduction of static charge.
www.compoundingworld.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82
