Black Masterbatch Selection — Carbon Black Type, Loading and the UV Question

Direct answer

Two numbers decide a black masterbatch: the carbon black particle size and the loading. Small-particle furnace blacks give jetness and the highest UV protection per kilogram, and they are what a PE100 pipe or a geomembrane needs. Large-particle blacks disperse more easily, cost less and are adequate where the part is indoors or the black is cosmetic. A 40% black on a fine-particle grade and a 40% black on a coarse grade are not interchangeable, even though the datasheet headline looks identical.

Why "40% black" tells you almost nothing

Loading describes how much carbon black is in the pellet, not how well it is dispersed or how it will behave in your line. Two failures dominate:

• Undispersed agglomerates. They show as specks in film, as screen-pack pressure rise, and as failure points in thin-wall parts. Dispersion is a property of the compounding, not of the loading.
• Wrong particle size for the duty. Pipe and outdoor film buy carbon black as a UV absorber. That job needs fine particles well dispersed at roughly 2 to 2.5% carbon black in the finished article — the figure written into pressure-pipe specifications. A coarse cosmetic black at the same weight percentage does not deliver the same protection.

Carrier before colour

The carrier resin has to melt and mix inside your process window. A PE-carrier black in a PP raffia line will usually run, but it can cost you tape strength and gloss; an HDPE-carrier black in a soft LDPE film can leave gels. When the host polymer is PET, PA or PC, a polyolefin carrier is the wrong tool entirely — those need a compatible or polymer-specific carrier.

What changes when the part goes outdoors

Outdoor service moves the decision from appearance to lifetime. Ask for:

• the carbon black type and, where the supplier states it, the particle size;
• the carbon black content the supplier expects in the finished article, not in the pellet;
• dispersion evidence for the grade;
• whether the formulation also carries a stabiliser package, since carbon black alone protects the polymer surface but does not replace an antioxidant system for long thermal exposure.

Where black masterbatch is the wrong purchase

If the requirement is a dark grey, a specific brand shade or a soft-touch matte appearance, that is a colour masterbatch project with a submitted reference, not a black concentrate. If the driver is cost per kilogram of finished part, the lever is usually the filler or down-gauging strategy, not the black.

What to send with the enquiry

Host polymer and MFI, process, wall thickness or film gauge, whether the part is outdoors and for how long, any pipe or geomembrane standard you must satisfy, annual volume, and packaging. With those six lines a supplier can quote a grade instead of a category.