If you make black HDPE pipe in India, one line in IS 4984 governs the masterbatch you buy: the pipe must contain 2.5 ± 0.5% carbon black by mass, dispersed satisfactorily.
That is the whole requirement, and almost every pipe rejection traced back to masterbatch comes from misreading one half of it or the other.
Why the number is confusing
Search for it and you will find three different answers on the first page – 2.0 to 3.0%, 2.0 to 2.5%, and 2.5 ± 0.5%. They are not all wrong, they are just quoted from different places.
2.5 ± 0.5% is the same range as 2.0 to 3.0%. They are one statement written two ways. The 2.0-2.5% figure comes from ISO 4427, the international standard for PE pressure pipe, which specifies a narrower band.
What to do about it: quote the range from the amendment currently in force for the grade you are supplying, and put the specific figure on your purchase order. Do not accept “as per IS” on a masterbatch invoice – it does not tell you what was actually dosed.
Why 2.5%, and not more or less
Carbon black in a buried or exposed pipe is not there for looks. It is a UV screen.
Polyethylene has no natural defence against ultraviolet light. Left unprotected outdoors, the polymer chains break down through photo-oxidation, the pipe surfaces chalk, then micro-crack, then fail under pressure. A well-dispersed carbon black loading absorbs UV across the damaging band and stops the reaction before it starts.
Below about 2%, UV screening becomes unreliable. The pipe still looks black – black is a very efficient colour – but the protection is not there and the failure shows up years later, in the field, at a joint.
Above about 3%, you start losing more than you gain. Carbon black is a solid filler. Too much of it stiffens the melt, embrittles the pipe wall, hurts hydrostatic performance, and makes dispersion harder – which is self-defeating, because a poorly dispersed 3.5% protects worse than a well-dispersed 2.5%.
The window exists because both ends of it fail.
Dispersion is the half everybody skips
The standard does not say “shall contain 2.5% carbon black”. It says the carbon black shall be present at 2.5 ± 0.5% and satisfactorily dispersed.
Those are separate tests and a pipe can pass one and fail the other.
Carbon black content is measured by pyrolysis – a sample is heated in an inert atmosphere until the polymer burns off and the residue is weighed. Carbon black dispersion is measured optically, by microtoming a thin slice of the pipe wall and grading the agglomerates under a microscope against a reference chart.
An agglomerate is a clump of carbon black that never broke down in the melt. It contributes its mass to the content test and passes it, but it protects nothing around itself, and it acts as a stress concentrator in the pipe wall. Pipes fail there.
This is the single most useful thing to know about buying black masterbatch for pipe: you are buying dispersion work, not carbon black. Carbon black is a commodity. Getting it fully broken down and evenly distributed in a polyethylene carrier – on a twin-screw line, with the right dispersing package, screened to a filter pressure value that proves it – is not.
Ask any supplier for a dispersion rating and a filter pressure value. A supplier who cannot give you either has not measured them.
Converting the standard into a masterbatch dosage
This is where the arithmetic bites, and where most of the confusion in the market sits.
IS 4984 specifies the carbon black in the finished pipe. Your masterbatch is not 100% carbon black. So:
Masterbatch dosage % = (required carbon black % in pipe) ÷ (carbon black % in masterbatch) × 100
Worked, at the 2.5% midpoint:
| Carbon black loading in the masterbatch | Masterbatch dosage to hit 2.5% in pipe | Let-down ratio |
| 25% | 10.0% | 1 : 9 |
| 30% | 8.33% | 1 : 11 |
| 40% | 6.25% | 1 : 15 |
| 45% | 5.56% | 1 : 17 |
| 50% | 5.0% | 1 : 19 |
So a pipe maker running a 40% black masterbatch needs 6.25% at the hopper, not 2.5%. Dosing 2.5% of a 40% masterbatch puts 1% carbon black in the pipe – comfortably outside the standard, and invisible until the pipe is tested or fails.
If you would rather not do this by hand every time you change grade, use our masterbatch let-down ratio calculator.
The clause nobody costs in: MFR drift
IS 4984 also limits the pipe’s melt flow rate to within ±30% of the base resin’s MFR, measured at 190 °C under 5 kg.
At a 6% masterbatch dosage you are replacing six percent of your compound with a different polymer – the masterbatch carrier. If that carrier has a very different melt flow rate from your pipe resin, it shifts the compound MFR, and at pipe-grade dosages the shift is measurable.
This is why the carrier resin on a pipe-grade black masterbatch matters more than on a general-purpose one. A masterbatch built on a carrier close in MFI to PE 80 / PE 100 pipe resin keeps you inside the ±30% band. A cheap general-purpose carrier may not.
Ask for the carrier polymer and its MFI. It should be on the technical data sheet.
Other IS 4984 parameters your masterbatch touches
Carbon black is not the only line item the colour supply can affect:
| Parameter | Typical requirement | How masterbatch affects it |
| Carbon black content | 2.5 ± 0.5% | Directly – dosage arithmetic above |
| Carbon black dispersion | Satisfactory | Directly – quality of the compounding |
| Density at 27 °C | 940-960 kg/m³ | Carbon black is dense; heavy loadings shift it |
| MFR | Within ±30% of base resin, 190 °C / 5 kg | Carrier resin MFI at pipe dosages |
| OIT | 20 minutes minimum | Antioxidant package; some blacks consume stabiliser |
| Elongation at break | 350% minimum | Poor dispersion embrittles |
| Overall migration | 10 mg/dm² maximum | Pigment and additive selection for potable water |
Confirm the exact values against the amendment currently in force before you quote against them – the standard has been revised, and the older figures still circulate widely online.
What to put on your enquiry
If you are sourcing pipe-grade black masterbatch, a specification this short is enough to get a serious quote and filter out the rest:
- Carbon black loading, stated as a percentage, with tolerance
- Carbon black grade and mean particle size – for UV, you want a fine furnace black, broadly in the 15-25 nm range
- Carrier resin and its MFI
- Dispersion rating and the method used to grade it
- Filter pressure value, with mesh and test conditions
- Recommended dosage to reach 2.5% in the finished pipe
- Confirmation of suitability for potable water contact, if relevant
Then ask for a trial quantity and run the carbon black content and dispersion tests yourself on the first pipe. Any supplier confident in their material will expect you to.
FAQs
How much carbon black does IS 4984 require in black HDPE pipe? 2.5 ± 0.5% by mass – that is, between 2.0% and 3.0% – with satisfactory dispersion. Check the amendment in force for your grade, as ISO 4427 specifies a narrower band.
How much black masterbatch do I need to add? Divide the required carbon black percentage by the carbon black percentage in your masterbatch. For a 40% masterbatch targeting 2.5% in the pipe, that is 6.25% masterbatch at the hopper.
Can I use a general-purpose black masterbatch for pipe? Usually not safely. General-purpose blacks are formulated for appearance, often with coarser carbon black grades that give jetness but weak UV screening, and with carriers not matched to pipe-resin MFI. Both matter under IS 4984.
What is carbon black dispersion and why is it tested separately? Content tells you how much carbon black is present; dispersion tells you whether it broke down into individual particles or survived as clumps. Clumps pass the content test, protect nothing, and act as failure initiation points in the pipe wall.
Does more carbon black mean better UV protection? Only up to a point. Past roughly 3% you lose mechanical performance and dispersion quality faster than you gain protection. A well-dispersed 2.5% outperforms a poorly dispersed 3.5%.
Which carbon black particle size is right for UV protection? Finer grades screen UV better because they present more surface area. Broadly, 15-25 nm mean particle size is the range used for weatherable applications. Coarser blacks are cheaper and look just as black, which is exactly why they get substituted.