Filter pressure value, why two suppliers' numbers are usually not comparable, and what a lot certificate should actually contain.
Technical white paper by Zoe Lin, Export Manager, E-LUCK (Guangdong Yijuyuan Plastic Industry Technology Co., Ltd.) · September 2026 · Revision 1.0
Download the white paper (PDF, 15 pages) →
Dispersion is the one property of a black masterbatch that cannot be recovered later. A carrier mismatch can be worked around, a moisture problem can be dried out, an MFI difference can sometimes be trimmed with process settings — but if the carbon was never deagglomerated during compounding, no downstream adjustment fixes it. It arrives as specks in a film, gels in a fibre pack, a rising screen-pack pressure, or a mechanical result that never quite reaches the data sheet.
So dispersion is the property buyers most often try to specify. And it is the property they most often specify badly, for a structural reason: the standard method for measuring it is deliberately tied to the equipment and conditions used to run it. Two suppliers can each send a defensible dispersion figure, both correct, neither comparable — and nothing in the numbers themselves tells you so.
The white paper covers three things: what the filter pressure value method actually measures; why an FPV is not a material constant and how to write it into a specification so that it becomes one you can enforce; and what a lot certificate should carry so that a run of them tells you about process control rather than about the day of the audit.
A single-screw extruder melts and homogenises the test material and feeds a melt (gear) pump, which forces it through a filter package in a breaker plate at a constant volume flow. A baseline pressure is established on the base polymer alone; then a mixture of masterbatch and base polymer at a defined pigment content is introduced, and the pressure rise is logged. Agglomerates and other oversize particles lodge in the mesh and reduce its open area, which at constant flow raises the pressure. The result is normalised to the pigment mass:
The method was developed by CEN/TC 298 and published as EN 13900-5:2005, adopted internationally as ISO 23900-5:2015 and republished in Europe as EN ISO 23900-5:2018, which superseded the original European edition. The melt pump is not a refinement — it is what makes the measurement honest. Older arrangements mounted the screen pack directly on the extruder, where a blocking screen raises backpressure, and rising backpressure improves mixing inside the screw. The material was being dispersed more thoroughly because it was being measured, with only a subtle drop in throughput as evidence.
This is the part most buyers have never been shown, and it is why dispersion specifications fail in practice. The scope of the standard is explicit that a filter pressure value is not a property of the material in the abstract:
Read plainly, that says three things a buyer has to act on: the number belongs to the measurement rather than to the material; the compounding route is inside the figure; and comparability requires an identical method. This is not theoretical. Published compounding trials on carbon black in PET show the same carbon black returning 0.53 bar/g by a premix route and 0.84 bar/g by a split-feed route at a 5 µm mesh — roughly a 60% difference from process configuration alone.
Written into the purchase specification, these turn a marketing figure into something enforceable:
No table of "good" filter pressure values transfers between rigs. What transfers is the order of magnitude different product classes occupy — and it is worth seeing those figures with their conditions attached:
| Material / context | Reported FPV | Conditions as stated |
|---|---|---|
| General colour concentrates, industry reference point | around 2 bar/g | Widely quoted order of magnitude; no single standard condition |
| Carbon black masterbatch for fine PET fibre | should not exceed 1 bar/g | 10 µm mesh; stated as the acceptance limit for fibre-grade PET carbon black |
| Carbon black in PET — premix compounding route | 0.53 bar/g | 5 µm mesh; single-screw plus melt pump arrangement |
| Carbon black in PET — split-feed route | 0.84 bar/g | 5 µm mesh; identical carbon black, different feed configuration |
| High-performance organic pigment, supplier claim | 0.2 bar/g | Vendor data sheet; presented as exceptionally low for the pigment class |
Mesh size is not a detail. A figure quoted at 5 µm and one quoted at 10 µm are measuring retention of different particle populations, and the finer mesh always returns the higher number for the same material. When a supplier quotes a low value, the mesh is the first question to ask.
The application sets the target, not the market. Fibre spinning and thin film are where dispersion genuinely dominates, because the process mesh is fine and a defect stops the line. Thick-section pipe or a large moulding can tolerate a materially higher figure and never show a symptom — and specifying fibre-grade dispersion there buys dispersion you cannot use, paid for in compounding energy and colour cost.
Everything that improves deagglomeration is also a way to damage the polymer, and a dispersion specification that ignores the second half of that sentence is incomplete. Dispersion is driven by shear and residence time, and both raise melt temperature and mechanical stress on the chain. Published trials on carbon black in PET show a more aggressive screw configuration at higher speed continuing to heat and shear the material with barely any further dispersion gain, while the intrinsic viscosity fell below the acceptable level — the working requirement in that application being to keep it as far above 0.5 dl/g as achievable while still meeting the dispersion target.
It also follows that a higher FPV is not simply a supplier's failure. Coarse blacks, high loadings and heat-sensitive carriers all push the number up legitimately. The useful question is never "why is your number worse than theirs" but "what does your number do in my process, in my resin, at my mesh".
A certificate of analysis has two jobs. The first is to state what is in the bag. The second — the one that supports process control — is to state it in a form comparable with the previous bag. A certificate without a lot number and a method reference cannot do the second job at all.
| Property | How it is established | What the certificate should state |
|---|---|---|
| Lot identity | Producer's internal lot system | Lot number and production date, traceable to raw material batches |
| Carbon black content | TGA, ashing or dissolution — not interchangeable measurements | The measured value, the tolerance band, and the method used |
| Carrier resin | Formulation record | The carrier and its grade, and whether any regrind is present |
| Melt flow index | Capillary method (ISO 1133 / ASTM D1238 type) | The value with temperature and load stated — an MFI without conditions is not a number |
| Moisture | Loss on drying or Karl Fischer | Measured value and drying conditions |
| Ash content | Ashing at defined temperature | Measured value — the figure that separates carbon loading from carbon plus mineral filler |
| Dispersion | Filter pressure value per EN ISO 23900-5 or an agreed equivalent | FPV in bar/g with mesh size, base polymer and pigment loading of the test mix |
What does not belong on a lot certificate: values described as "typical" with no lot linkage, figures carried over from a qualification trial rather than measured on the shipment, and any dispersion statement that is a sentence rather than a number with conditions.
What a buyer can run without owning a filter pressure rig — and the sequence we would expect a serious customer to run on us:
Filter pressure value is the pressure rise produced when a defined quantity of pigmented polymer is forced through a fine filter mesh at constant volume flow, divided by the mass of pigment in the sample. It is expressed in bar per gram. A lower value means less material was retained by the mesh, which means finer dispersion. The method is standardised as EN 13900-5 and, internationally, EN ISO 23900-5 / ISO 23900-5.
Not unless both were produced under identical conditions. The scope of the standard states that the filter pressure value is valid only for the equipment, conditions and test polymer used, and that results are comparable only when the same method of preparation for the colour concentrate is applied. Mesh size, base polymer, pigment loading, melt temperature and the compounding route all change the number.
The mesh must be named, because the same material gives a higher figure on a finer mesh. Commercial filter testers use meshes broadly in the 5 to 40 micrometre range, and the mesh is chosen according to the fineness the application needs. Fibre and thin film work typically specify finer meshes than pipe or thick-section moulding.
There is no universal figure, because the number is method-bound. What can be used is the application: fibre spinning and thin film are the applications where dispersion dominates and where published acceptance limits are tightest — a common stated limit for carbon black masterbatch in fine PET fibre is not more than 1 bar/g at a 10 micrometre mesh. Thick-section applications tolerate materially higher values without symptoms.
No. Dispersion is driven by shear and residence time, and both also degrade the polymer. Published compounding trials show configurations that keep adding shear and heat with little further dispersion gain, while the polymer's intrinsic viscosity falls below the acceptable level. A dispersion improvement that comes with a viscosity or MFI loss is not automatically an improvement — ask what happened to the polymer at the same time.
A filter pressure value in bar per gram, together with the mesh size, the base polymer the test was run in, and the pigment loading of the test mixture. Without those conditions the figure cannot be checked or reproduced. The certificate should also carry a unique lot number, a production date, and the method used for the carbon content figure.