Not all black is the same black, and the difference is measured in nanometres. The carbon black in a truck tyre, in a UV-stabilised water pipe and in a high-gloss consumer housing are three genuinely different materials that happen to share a name. Choosing the wrong one gives you a part that is grey instead of jet, or a pipe that fails on UV, or a cost that makes no sense.
Here is what the grade codes actually mean and how to pick.
Reading the ASTM code
Rubber-grade carbon blacks are classified under ASTM D1765 with a four-character code such as N330.
The letter describes cure rate in rubber. N means normal curing, S means slow curing. For plastics applications the letter carries no useful information.
The first digit encodes the average primary particle size band. This is the number that matters.
| First digit | Average particle size | Character |
| 1 | 11-19 nm | Very fine, highest jetness, highest cost |
| 2 | 20-25 nm | Fine |
| 3 | 26-30 nm | Fine, the general-purpose reinforcing range |
| 5 | 40-48 nm | Medium |
| 6 | 49-60 nm | Coarse |
| 7 | 61-100 nm | Coarse, semi-reinforcing |
The last two digits relate to structure – how extensively the primary particles are fused into branching aggregates. Higher structure means more branching.
So N330 is a fine 26-30 nm black; N550 is a medium 40-48 nm black; N660 is a coarser 49-60 nm black. Lower number, smaller particle.
The single most useful rule: smaller particles give deeper black, better UV protection and better conductivity – and cost more, disperse harder and thicken the melt more. Almost every trade-off in carbon black selection follows from that sentence.
Why particle size drives everything
Jetness. Colour depth comes from surface area. Smaller particles pack more surface area into the same mass, absorb more light and scatter less, so the black looks deeper and more neutral. Coarse blacks look brownish or greyish by comparison – the “undertone” that a fine black avoids.
UV protection. Carbon black protects by absorbing ultraviolet radiation before it reaches the polymer. Absorption efficiency per unit mass rises as particle size falls. This is why pipe and geomembrane standards call for fine furnace blacks in the 10-25 nm class rather than whatever black is cheapest – a coarse black at the same 2.5% loading simply does not deliver the same protection. We cover the loading requirement in carbon black content in HDPE pipes.
Conductivity. Electrical conductivity needs a continuous network of touching aggregates through the polymer. High-structure, high-surface-area blacks form that network at much lower loading. Conductive and antistatic grades are a distinct class – conductive furnace blacks and specialised carbons – not an ordinary N-series grade used at higher dosage.
Dispersion difficulty. Finer particles have greater surface energy and hold together in agglomerates far more stubbornly. A fine black needs more shear, more energy and better wetting to disperse than a coarse one. This is why fine blacks belong in a properly compounded masterbatch and are close to hopeless as a dry powder addition.
Viscosity. High surface area and high structure both raise melt viscosity. At high loadings a fine, high-structure black can change your processing window noticeably.
Which grade for which job
| Application | Typical grade class | Reason |
| Pipe, geomembrane, outdoor film | Fine furnace, 15-25 nm | Maximum UV absorption per unit mass |
| High-gloss consumer housings | Very fine, high jetness | Deep neutral black, no brown undertone |
| General moulded parts, crates, furniture | Medium, N550 class | Adequate colour at sensible cost and easy dispersion |
| Thick-wall industrial mouldings | Medium to coarse | Colour is cosmetic, cost dominates |
| Conductive and antistatic | Conductive furnace blacks | Network formation at low loading |
| Fibre and thin filament | Very fine, tightly controlled | Coarse particles break filaments |
Two of these deserve expanding.
Fibre and fine filament is the least forgiving application in the list. Any agglomerate approaching the filament diameter is a break point, and a line that breaks is lost production. Fibre-grade black requires both a fine primary particle and exceptionally tight dispersion control.
Conductive grades carry a trade-off people underestimate. The loadings required for true conductivity are high enough to change mechanical properties significantly – the part becomes stiffer and more brittle. If the requirement is only static dissipation rather than genuine conductivity, an antistatic additive is usually a better answer than a heavy conductive black loading.
Furnace, channel, lamp and acetylene
You will see process names as well as grades.
Furnace black dominates. Made by partial combustion of heavy aromatic feedstock in a controlled furnace, it covers essentially the whole range of particle sizes and structures at reasonable cost. Almost everything discussed here is furnace black.
Channel black is an older process producing very fine, oxidised, acidic surfaces. Largely superseded on cost and environmental grounds, occasionally still specified for particular ink and coating requirements.
Lamp black is coarse with a distinctive bluish undertone, used where that specific tone is wanted.
Acetylene black is made by thermal decomposition of acetylene and has very high structure and purity. It is a conductivity material, used in batteries and conductive compounds rather than for colour.
Why dispersion decides the outcome
Two masterbatches can contain the same grade of carbon black at the same loading and perform completely differently, because carbon black arrives as agglomerates that must be broken down and wetted by polymer.
Undispersed carbon black is worse than less carbon black. Agglomerates deliver no UV protection – the material is clumped rather than distributed – and they act as stress concentrators and crack initiation points. In pipe this is why standards specify dispersion grade to ISO 18553 alongside content. In film it shows as specks and, at scale, as filter blockage and pressure rise.
Dispersion is created during compounding, under high shear on a twin-screw line. It cannot be recovered on a single-screw extruder. Your machine distributes what it receives; it does not disperse. That makes dispersion the one black-masterbatch property for which the supplier is unambiguously accountable, and a lot-specific dispersion report is a reasonable thing to require.
Cost, honestly
Finer blacks cost more per kilogram, and the naive response is to move to a coarser grade. Sometimes that is right and sometimes it is a false economy, depending on which property you were buying.
If you were buying UV protection, moving coarser reduces protection at the same loading, and compensating by adding more coarse black raises viscosity, worsens dispersion and often costs more in total than the fine grade would have.
If you were buying jetness, moving coarser needs more loading to reach the same visual depth, and it will still not look the same – the undertone changes and a discerning customer notices.
If black is purely cosmetic on a thick industrial part, a coarser grade is genuinely the right answer and the saving is real.
The question to answer before optimising cost is which property you are actually paying for.
What to put on an enquiry
– The polymer and grade, with MFI – The process – film, pipe, injection, fibre, cable – What the black is for: colour, UV protection, conductivity, or a combination – Part thickness and required service life if outdoor – Jetness or undertone requirement if appearance matters – Dispersion standard you need to meet, and whether a lot report is required – Whether the part must be NIR-detectable for recycling sorting
That last point is increasingly important. Conventional carbon black absorbs across the near-infrared band, so black packaging is invisible to automated sorting lines and is rejected to residue. If your product falls under recycled-content obligations, raise it early – see EPR for plastic packaging in India.
Talk to us
Life Color Pigments & Masterbatches manufactures black masterbatch across the range – UV grades for pipe and outdoor products, high-jetness grades for visible mouldings, and general-purpose grades where cost dominates – under ISO 9001:2015.
Tell us your polymer, process and what the black has to do, and we will specify the grade rather than sell you a number. Related: what is masterbatch, black specks in plastic parts, electrical applications.
FAQs
What does N330 mean in carbon black? It is an ASTM D1765 code. N indicates normal cure rate in rubber, the first digit 3 places the average primary particle size in the 26 to 30 nanometre band, and the last two digits relate to structure. N330 is a fine general-purpose furnace black.
What is the difference between N330, N550 and N660? Particle size. N330 averages 26 to 30 nm, N550 averages 40 to 48 nm and N660 averages 49 to 60 nm. Finer grades give deeper black, better UV protection and better conductivity, and are harder to disperse and more expensive.
Which carbon black grade gives the best UV protection? Fine furnace blacks in roughly the 15 to 25 nanometre class. UV absorption per unit mass rises as particle size falls, which is why pipe and geomembrane standards call for a fine grade rather than any black at the specified percentage.
Why is fine carbon black harder to disperse? Smaller particles have much higher surface energy and hold together in agglomerates more strongly. Breaking them down needs high shear and good wetting, which is available on a compounding line and not on a single-screw production extruder.
Can I improve carbon black dispersion on my own extruder? No. A single-screw extruder distributes what it is given but does not break down agglomerates. Dispersion is created during compounding of the masterbatch, which makes it a supplier responsibility and a fair thing to require a test report for.
What is conductive carbon black? A distinct class of high-structure, high-surface-area carbons that form a continuous conductive network through the polymer at relatively low loading. Ordinary N-series grades used at higher dosage do not achieve the same effect and damage mechanical properties in the attempt.
Why is black packaging a problem for recycling? Because carbon black absorbs near-infrared light and automated sorting lines identify polymers by NIR reflectance. A conventionally blacked package gives no usable signal and is rejected as residue even when the polymer is fully recyclable. NIR-detectable black systems solve this.
Is a cheaper coarse carbon black a false economy? It depends on what you were buying. For UV protection, moving coarser costs more in the end because you need more of it. For jetness, the undertone changes and heavier loading does not fully compensate. For a thick industrial part where black is purely cosmetic, the saving is genuine.