How to read a black masterbatch CoA: certificate of analysis
The data sheet tells you what a grade was designed to be. The CoA tells you what is actually in the bag you received. Buyers who read the CoA properly catch drifting quality months before it becomes a defect claim. Here is what each line means — and what to do when a number moves.
Buyers are usually handed four different documents and expected to read them as one. Before the line-by-line: what a data sheet, a lot certificate, a third-party test report and a management system certificate each prove, and where each one stops.
By Zoe Lin, Export Manager, E-LUCK (Guangdong Yijuyuan Plastic Industry Technology Co., Ltd.)
1. CoA vs data sheet: which document answers which question
A data sheet is a promise: carbon content, melt flow, carrier resin, recommended let-down. It is written once for a grade and rarely changes. A certificate of analysis is a measurement: the results recorded for the specific lot in front of you, tied to a lot number and a test date.
When two shipments behave differently on the same line, the CoA is where you look first. If the supplier cannot produce a lot-specific CoA, you are buying on faith — and "typical values" are not a substitute.
2. Four documents, four jobs: TDS, lot CoA, third-party report, system certificate
Before reading any single line, it helps to know which of four documents you are holding. They are routinely mistaken for one another, and the mistake usually surfaces at the worst moment: a claim that nobody can support.
| Document | What it is | What it proves | What it does not prove |
|---|---|---|---|
| Data sheet (TDS) | Typical values written once for a grade: carbon black loading, carrier resin, melt flow rate, recommended let-down, processing window. | What the grade was designed to be, and the basis for comparing one grade with another. | Anything about the bag you received. A "typical" figure is not a lot result, and it is not a specification limit unless a tolerance band is stated alongside it. |
| Lot certificate of analysis (CoA) | The producer's record of what a named lot measured, on a stated date, by a stated method, against a stated tolerance. | That this lot was tested, and that the results sat inside the agreed band at the time of testing. | Fitness for your process. A lot can sit inside every declared band and still be wrong for your line; suitability is settled by a trial on your equipment. |
| Third-party test report | Testing by an outside laboratory on the sample that laboratory received: RoHS, REACH, PAHs, FDA migration and similar. | That a named laboratory tested a named sample for named substances, and what it found. | Anything about lots other than the sample tested. It is not a lot release record, even when it is issued for the grade you are buying. |
| Management system certificate | ISO 9001, ISO 14001, ISO 45001 or IATF 16949, issued by a certification body against a defined scope. | That the factory's management system was audited against that standard. | That any product, or any lot, passed any test. A system certificate certifies the system; it never certifies the product. |
The rule of thumb worth keeping: a system certificate describes the factory, a data sheet describes the grade, a CoA describes the lot, and a third-party report describes the sample. When a claim jumps one of those levels — a certificate PDF sent where you asked for a lot result, or a data sheet figure presented as a measured value — that is the moment to ask which document actually supports it.
The TDS and SDS for each of our grades, together with the release checks every lot is tested against, are listed on the technical data page.
3. Carbon black content: the number that moves your cost
Carbon content is usually measured by pyrolysis or ash method and reported as a percentage by weight. A "40% grade" might carry a tolerance of ±1–2 points, so a lot measuring 38.5% is within spec for many suppliers — but at a fixed let-down it delivers roughly 4% less carbon into your part than the nameplate number. Ask which method the figure came from: carbon black content by calcination or pyrolysis is a method-defined result, and two competent laboratories using different methods can return different numbers on the same material.
What to do with it:
- Compare the lot value against the grade's stated tolerance, not just the nameplate percentage.
- Watch the trend across lots. One lot at 38.9% is noise. Four consecutive lots drifting down is a process change you should ask about — politely, with the CoAs attached.
- Recalculate let-down on the trend if your part has a color or UV target you must hold.
4. Melt flow rate: read it with the temperature and load
Melt flow rate — still widely called melt flow index — is not a property of the material on its own. It is a result measured under conditions of temperature and load that the test method fixes, not the grade name. ISO 1133-1 specifies the determination of melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics "under specified conditions of temperature and load", reported in grams per 10 minutes; the method used on our own data sheets is GB/T 3682.
So a line reading "MFR 20" is not yet a number you can use. It needs the temperature and the load as well: 190 °C / 2.16 kg and 190 °C / 21.6 kg are both common conditions, and the same compound gives different figures under each. Two parties can each hold a correct result and still appear to disagree, purely because one tested at a different load. This is why our TDS always states the load next to the value.
For masterbatch the practical question is whether the melt will blend evenly with your natural polymer. A masterbatch whose flow is far below that of the resin it colors tends to mix poorly at high let-down; one that is far above can lubricate the melt and change cycle behaviour. Check the CoA value — with its conditions — against the grade's nominal figure and against your own process window, and treat a large lot-to-lot swing the same way you would treat swing on your own incoming resin.
When you write your purchase specification, state the conditions as well as the band. Without them the figure cannot be compared with your own incoming test, or with another supplier's.
5. Filter pressure value: useful, but check the method and the release set
Filter pressure value measures the pressure rise as a diluted sample is extruded through a defined filter. It is one established way to assess dispersibility on the masterbatch itself, and a lower pressure rise generally means fewer coarse agglomerates reaching your screen pack.
Two cautions before you build a specification on it. First, the figure is method-dependent: ISO 23900-5 states that results apply to the equipment, conditions and test polymer used, so mesh and polymer alone do not make two values interchangeable. Second, a filter pressure value printed on a data sheet is not evidence that the test was run on the lot you are buying — it is a separate test from a supplier's routine release set, so ask whether it is actually performed on your lot, to which method, and on which equipment.
Where it is available, three practical uses:
- Lot acceptance: set an internal ceiling with your supplier based on your thinnest product — and record the mesh, polymer and method the ceiling refers to.
- Supplier comparison: useful, but only when both sides tested to the same method, mesh and polymer. Otherwise you are comparing two different tests and calling it one number.
- Early warning: a rising value across lots usually means carbon feedstock or compounding conditions changed upstream — ask before it becomes a screen-pack problem on your extruder.
On our own grades the routine per-lot dispersion check is a simulated-process dispersion rating, rated in three grades. A filter-pressure value is not part of that routine release set. If your specification asks for one, raise it with the quotation and we will confirm then whether we can run it, by which method and on what terms — we do not put a per-lot filter-pressure guarantee on paper that we cannot evidence.
6. Moisture and volatiles: the silent defect source
Moisture content looks like a formality until a black masterbatch that has absorbed humidity starts producing porosity, streaks or bubbles — particularly in PET, PA and other moisture-sensitive processes. Check the moisture line on the CoA, but also check the packaging date and condition when the container is opened. A CoA is a snapshot at the plant gate; sea freight in summer is not the plant gate.
7. A purchasing file checklist you can copy
Use this before you accept a quotation, and again when the shipment lands. Every row is a field to fill in from the documents in front of you, not a value to assume. The blanks are deliberate: a worked example full of invented numbers would look more useful and be less so, because the only numbers that matter are the ones from the lot you are actually buying.
| Field | What to record from the document | If it is missing or unclear, ask |
|---|---|---|
| Grade and lot identity | Grade code: ______ · Lot or batch number: ______ · Same number printed on the bags: ☐ yes ☐ no | "Which lot number will be printed on the bags, and will the certificate be issued for that lot?" |
| Dates | Production date: ______ · Sampling date: ______ · Test date: ______ | "Was the sample taken from the lot being shipped, and how long after production?" |
| Method and conditions | Method or standard for each line: ______ · For melt flow rate, temperature and load: ______ °C / ______ kg | "Which standard was used, and were the conditions the same as the ones in our specification?" |
| Units | % by weight · g/10 min · bar/g · mesh in µm — recorded as: ______ | "Every figure should carry a unit. Which unit is this?" |
| Limits and result | Lower limit: ______ · Upper limit: ______ · Result for this lot: ______ | "Is the band a contractual limit or a typical value? Are the two stated separately?" |
| Who issued it | Issuing body or department: ______ · Name, signature or stamp: ______ · Date issued: ______ | "Was this issued by the producer's own laboratory or by an outside laboratory? Both are legitimate; they mean different things." |
| Which clause it answers | Purchase specification clause or drawing reference: ______ | "Which line of our specification does this document satisfy, and which lines are still open?" |
| When a field stays blank | Note for the file: ______ | "Ask in writing before the shipment, not after the defect." A blank nobody chased is a limit nobody set. |
In practice the two rows most often left empty are method and conditions and limits versus result. A melt flow figure without its temperature and load cannot be compared with anything, and a typical band quoted as a limit quietly widens what you have agreed to accept.
8. A 30-minute incoming inspection protocol
For each new lot, before it goes to the floor:
- Match the lot number on the bag, the CoA and your purchase order. Mismatches happen more often than anyone admits.
- Check the test date is close to the production date. A CoA dated months after the lot was made is a reconstructed document.
- Compare the numbers against your spec band: carbon content, melt flow rate with the temperature and load it was measured at, and the dispersion measure your supplier actually releases. If you are comparing filter pressure values, check first that both figures were run to the same method, mesh and polymer. Log them — a simple spreadsheet, one row per lot.
- File the CoA with the retention sample. If a defect claim ever needs evidence, this is the evidence.
Ten lots in, you will have a better picture of your supplier's real process control than any audit questionnaire.
9. Red flags on a CoA
- Identical values across every lot — real measurements vary slightly; photocopy CoAs do not.
- No lot number, no test date, no method reference.
- Tolerances quoted only verbally. The band should be on the document.
- A dispersion figure with no method, mesh or equipment stated — including a filter pressure value that nobody can say was run on your lot.
- A management system certificate sent where you asked for a lot result. ISO 9001, ISO 14001, ISO 45001 and IATF 16949 describe an audited system; none of them releases a lot.
10. What we put on ours
Every E-LUCK lot is released against ten written in-house checks before it is allowed out, and the certificate of analysis states what that batch measured against them, tied to the lot number and the production date. The ten are: pellet appearance against a visual reference; bulk density (GB/T 23771); true density (GB/T 1033.1); volatiles (GB/T 6284); melt flow rate (GB/T 3682, always reported with its load); carbon black content (GB/T 13021); residue on ignition (GB/T 9345.1); a simulated-process dispersion rating; restricted substances (RoHS, six-substance sum, checked against the SGS reports held for the grade family); and PAHs (EN 16143). A test outside that set appears on your certificate only if it was agreed in writing with the order.
Three things we would rather state plainly than paper over:
- A filter-pressure value is not in that routine set. If your specification needs one, raise it with the quotation and we will confirm then whether we can run it, by which method and on what terms.
- We do not publish a scanned certificate from a past lot on this site. If you want to see the layout and the fields before you commit, ask for a specimen certificate for your grade and we will send one with the quotation — then check it against the table in section 7 rather than taking our word for it.
- A third-party report does not come with every lot. The SGS-CSTC reports we hold are listed with their report numbers on the SGS test reports page; they were issued for the samples and grades named on them, mostly for RoHS, REACH and PAHs, and they are sample documents rather than lot release records. Where your customer needs independent testing on a specific lot, agree it in writing before the order so the sampling and the method can be arranged.
Minimum order quantities and trial lot sizes are confirmed in the quotation for your grade and specification. Lead time is 10–15 days after specification confirmation.
11. What a CoA is — and what it is not
Buyers occasionally treat a CoA as a guarantee, and suppliers occasionally allow them to. It is worth being precise about the document, because the difference shows up the one time it matters.
A certificate of analysis is a record of what was measured on a specific lot, produced by the supplier against a stated method and reported against a stated tolerance. That is all it is — and that is a great deal. What it is not:
- It is not a warranty of fitness for your application. A lot can sit perfectly inside its declared band and still be wrong for your line, because the band was written for a general case. Suitability is settled by a trial on your equipment, not by a CoA.
- It is not necessarily a third-party result. Most CoAs are the producer's own in-house testing. That is normal and useful — but where your customer or your own quality system requires independent verification, that is a separate document. Ask for it rather than assume the CoA covers it.
- It is not the specification. The TDS states what the grade is designed to be; the CoA states what a particular lot measured. Reading one as the other is the most common confusion in incoming inspection.
- It is not a management system certificate, and a system certificate is not a CoA. ISO 9001, ISO 14001, ISO 45001 and IATF 16949 describe a management system audited within a defined scope. None of them certifies a product or releases a lot. When a certificate PDF arrives in answer to a request for lot results, the question has been answered at the wrong level.
- It is only as good as the method behind it. A dispersion figure means nothing unless you know the method and can compare it with your own. Where methods differ between supplier and buyer, two correct numbers can look like a mismatch.
The practical rule: agree the method, agree the tolerance band in writing, then use the CoA to check the lot against that agreement — not to discover the specification for the first time.
12. Reading a CoA against your own incoming test
The CoA and your incoming inspection answer different questions, and the comparison between them is where the value sits.
| Check | What the CoA tells you | What your own test adds |
|---|---|---|
| Carbon content | What the supplier measured on the lot, against the grade band | Whether the lot you actually received matches the lot the document describes — the check that catches a mix-up in despatch |
| Melt flow rate | The flow the grade was compounded to, at the temperature and load stated on the certificate | Whether it flows as expected on your machine, at your temperature profile — the lab figure is only a proxy for this, and it is only comparable if both were run at the same conditions |
| Moisture | The figure at the plant gate | What it is after weeks in a container and a humid warehouse. The number most likely to differ, and the one most likely to cause a defect |
| Dispersion measure | The supplier's dispersion result — a simulated-process rating on our grades, by the method stated on the certificate | Whether that dispersion survives your let-down and your shear history — dispersion is not fixed for all time |
| Ash | Filler content, which drives both cost and surface | Whether the ash level suits the surface the part is actually judged on |
Two habits make this comparison useful rather than ceremonial. Keep the file per lot, not per purchase order — defects are usually discovered months after delivery, and by then the question is which bag the part came from. And record your own numbers, not just pass/fail — a moisture reading that is inside tolerance but drifting upward across three lots tells you about your storage long before it causes a visible defect.
Request a CoA sample with your quote
Questions about reading a lot certificate
A certificate of analysis is only useful if you know which lot it describes and which values were measured rather than promised.
What must a black masterbatch CoA contain to be useful?
The lot number, the production date, and measured values rather than specification ranges. Ranges tell you what the supplier promises; only measured values tell you what is in your silo. Useful additions are carbon black or pigment content, sieve residue, dispersion or filter pressure value with its method stated, moisture, and melt mass flow rate. A lot number is the minimum — without it, the document cannot be matched to the bags you receive.
How do I match a CoA to the shipment I received?
Compare the lot number on the certificate with the lot number printed on the bags, and check the production date against the delivery date. A certificate dated well before the shipment describes a batch that may no longer be the one you have. If the lot numbers do not match, ask for the certificate covering your lot rather than accepting the one that arrived by email.
Why do two suppliers quote very different dispersion values for the same grade?
Because filter pressure value is method-dependent. Different mesh, different filter medium, different test speed and different sample preparation produce different numbers on identical material. A value quoted without its method and unit is not comparable to anything. This is the single most common source of false disputes in black masterbatch sourcing, and it is why we publish a free white paper on how to compare dispersion numbers properly.
What is a sieve residue value and what should I look for?
Sieve residue is the fraction of the compound that does not pass a stated mesh, which is a direct proxy for foreign material and oversized agglomerates that could block a die or a screen pack. Look for the mesh stated on the certificate: a low value on a fine mesh is a stronger claim than the same number on a coarse one. If your line has a known screen pack, the certificate is more useful when the mesh matches what you actually run.
Should a first order be accepted without a CoA?
No. A supplier who cannot produce a lot-specific certificate on request is buying material rather than compounding it, and you have no visibility of the lot you are actually receiving. Ask for the CoA covering your first lot, compare the values against your specification, and keep it. Six months later, when a quality dispute starts, that document is the only factual basis either side has.
What is the difference between a TDS typical value and a CoA result?
A typical value on a data sheet describes what a grade was designed to be, and it is written once. A CoA result is what a named lot measured, on a stated date, by a stated method. Buying against typical values leaves you with no record of what was actually in the bag. Ask for the tolerance band and the measured result as two separate lines, and keep both.
Does an ISO 9001 or IATF 16949 certificate say anything about the lot I am receiving?
No. ISO 9001, ISO 14001, ISO 45001 and IATF 16949 cover a management system audited within a defined scope; none of them certifies a product or releases a lot. For the lot itself you need a lot-specific certificate of analysis, and for independent verification a third-party report on the sample that was tested. A certificate is useful, but it answers a different question.
Will every lot come with a third-party SGS report?
Not as a routine matter. Third-party reports such as the SGS-CSTC RoHS, REACH and PAHs reports are issued for the sample the laboratory received, and they cover that sample rather than each production lot. If your customer requires independent testing on a specific lot, agree it in writing before the order so the sampling and the method can be arranged.
Continue reading
- White paper: measuring dispersion and filter pressure value — why two suppliers' FPV numbers are not comparable, and the eight items to fix in a spec.
- Carbon black content testing in PE — why two correct labs can report different numbers for the same lot.
- PET black masterbatch: gels and high filter pressure — what a filter pressure value does and does not predict.
- How to calculate let-down ratio for black masterbatch — the other number that decides what the bag really costs.
- Black masterbatch defects: gels, streaks and specks — what bad dispersion looks like when it reaches the line.
- Carbon black price outlook 2026 — why carbon content and price drift together.
Related pages
- Is black masterbatch a dangerous good? — the shipping classification, and the UN numbers that get confused with it
- SGS test reports — third-party verification for standard grades
- Black masterbatch pricing — what drives cost per kg
- Film grades — where FPV matters most
- All black masterbatch — full grade range and selection guide
- H6045 grade page — a full TDS laid out line by line, the way we present lot data