Proving a Halogen-Free Centring Adhesive Claim

A halogen-free centring adhesive is one of the few lines on a speaker adhesive datasheet you can settle with a single email, because halogen-free is not an adjective. It is a number — two numbers, in practice: a chlorine limit and a bromine limit, both commonly quoted as 900 mg/kg and both traceable to IEC 61249-2-21. If your supplier sends a test report from a named laboratory showing measured chlorine and bromine values against that threshold, on the grade you are buying, the claim is real and you can pass it on to your own customer. If what comes back is a datasheet line and a sentence about "no added halogen", you have been handed a description, not a determination.

Aosibo Adhesives lists centring adhesive in one-part, epoxy and halogen-free versions, and its own CMH profile makes the same point in the product entry: ask for the test report and the threshold it was measured against. No such report was provided at profile review, so nothing about one is claimed here. What follows is how to get one, and how to read it when it arrives.

The number behind the word

"Halogen-free" entered electronics procurement through printed-board base materials, and the definition most buyers cite comes from there. The thresholds are homogeneous-material limits expressed in mg/kg, which is the same thing as parts per million by mass.

Two standards do most of the work. IEC 61249-2-21 is where the 900/900/1,500 set comes from. The IPC/JEDEC joint standard on low-halogen electronic products, JS-709, carries the same chlorine and bromine limits into a broader electronics scope. Confirm the current edition text of both before you quote them in a contract; they are revised, and a purchase order that names a superseded edition invites an argument later.

Here is the first detail worth knowing: IEC 61249-2-21 is written for copper-clad, glass-reinforced laminate sheet. It is not written for adhesives. Applying its thresholds to a centring adhesive is an industry convention, not a scope statement, and a supplier who reads the standard closely can technically say "that standard does not cover my product" and be correct. The fix is simple and takes one sentence: do not put the standard name in your purchase order on its own. Put the numbers in.

Halogen-free grade: chlorine ≤ 900 mg/kg and bromine ≤ 900 mg/kg, each determined on the cured film, reported as a measured value with the laboratory's limit of quantification stated.

That sentence is enforceable. "Must be halogen-free per IEC 61249-2-21" is an invitation to a scope debate.

Worth saying plainly, because buyers often assume otherwise: no regulation requires halogen-free under that name. It is a customer specification, usually inherited from a brand's own restricted-substance list or from an assembly plant's requirements. Statutory restrictions on specific halogenated substances exist under other regimes and are worded around named substances, not a blanket halogen limit. Treat halogen-free as a contractual requirement between you and your customer, then push it upstream in the same words.

What a real test report contains

Reports arrive as PDFs with a lot of letterhead and very little that matters. Six fields decide whether the document is evidence or decoration.

The reporting-limit trap catches more buyers than any other. A report that says "Cl: not detected, LOQ 900 mg/kg" is arithmetically compatible with a sample sitting at 899 mg/kg. You have paid for a test that measured exactly the thing you already assumed. Ask for the LOQ as a number and check it is far enough below the limit that a marginal batch would show up.

Accredited scope is the second one. A laboratory can be accredited for dozens of tests and not for this one. The general habit of checking the issuing body, the holder name and the validity date on any document a supplier sends applies here too — the approach set out in how to read a China certificate of conformity transfers directly to test reports.

One more thing about the document itself: a test report is a photograph of a single lot. Formulations drift, raw-material suppliers change, and a report dated three years ago on a lot you did not receive is weak evidence about the drum on your dock. Decide up front whether you need a report per shipment, a report per formulation with a change-notification commitment, or an annual re-test — and write the choice into the contract alongside the certificate of analysis and batch-traceability terms you agree for the rest of the order.

Where halogen-free claims quietly fail

Screening is not determination

X-ray fluorescence is fast, non-destructive and cheap, and a lot of "halogen reports" are XRF printouts. In the IEC 62321 framework, XRF sits in the screening part of the series, and screening methods produce a pass, a fail, or an inconclusive band where a confirmatory test is required. Around a 900 mg/kg threshold, an adhesive is very likely to land in that band — polymer matrices, fillers and pigments all interfere. If the report header names an XRF method, you have a screen. Ask for combustion ion chromatography as the confirmation.

Wet basis versus cured basis

This is the detail that separates people who have run this test from people who have read about it. A water-based or solvent-containing adhesive loses most of its carrier during cure. Residual halogen stays behind and concentrates in the cured film. A grade tested as supplied — wet, with the carrier included in the mass — can report a comfortable 400 mg/kg and cure down to a film well over the limit, because the denominator shrank. Your customer's specification almost certainly refers to the material as it exists in the finished driver, which is the cured film. Say which basis you want in writing. If the report does not say, ask; if the laboratory tested the wet material, the number is not the number you need.

Epoxy chemistry carries chloride by construction

Conventional epoxy resins are made by an epichlorohydrin route, and the finished resin carries residual chloride — hydrolysable and total — as a consequence of how it was made, not as an additive someone chose to put in. That is why "no halogenated flame retardant is added" and "this material is below 900 mg/kg chlorine" are different statements, and why an epoxy centring grade is the version most worth testing rather than assuming. A formulation statement describes intent. A measurement describes the material.

The email that settles it

Send this to the supplier before you order the halogen-free grade. It is short on purpose; every line asks for one checkable thing.

1. Grade designation. "Please confirm the exact product code of the halogen-free centring grade, as it will appear on the label and the invoice."
2. Threshold. "Against which chlorine and bromine limits is this grade sold? Please state the mg/kg figures, not only a standard number."
3. Report. "Please send the most recent halogen test report for this grade as a PDF, including the laboratory name, accreditation number, report number and issue date."
4. Method. "Which method was used? If the report is an XRF screen, please also send a combustion ion chromatography determination."
5. Basis. "Was the sample tested as supplied or as a cured film? If as supplied, please advise whether a cured-film result is available."
6. Reporting limit. "Please confirm the limit of quantification stated on the report for chlorine and for bromine."
7. Batch linkage. "Does the report correspond to a specific batch? If so, please give the batch number and confirm whether that batch is still in production."
8. Ongoing. "Will a test report be issued per production batch, per shipment, or on request? And will you notify a formulation change in writing before shipping the changed material?"
9. Scope check. "Do any other grades in the loudspeaker range — lead-wire, damper, surround, magnet-circuit — carry the same claim, or is it specific to the centring grade?"

Nine questions, one email. What comes back tells you as much about the supplier as it does about the adhesive: a house that compounds its own material and sells into electronics customers will have the reports in a folder. A house that has not been asked before will say so, and that answer is also useful — it tells you the claim has not yet been tested by anyone else's procurement department.

Common questions

Does a halogen-free pass also cover RoHS and REACH?

No. It buys you one thing: chlorine and bromine below a stated limit. It does not establish RoHS compliance, which is a separate restricted-substance list with its own limits and its own declaration. It does not address REACH candidate-list substances, which change twice a year. It says nothing about flame retardance, smoke density, outgassing, or any thermal property. And it is not a substitute for a safety data sheet and CLP classification or a dangerous-goods classification — those are separate documents that decide whether the drum can legally move and legally land, and none of them were provided at this factory's profile review.

Buyers assembling a document set for a first chemical order will find the general list in what documents to request from a supplier before your first order a reasonable starting point; halogen testing is an addition to that set, not a replacement for any of it. If you are also weighing whether the company you are talking to compounds the material or buys it in, the checks in the China supplier verification guide matter more here than in most categories, because a repacker cannot answer a formulation question without asking someone else first.

Can I test it myself instead?

Yes, and for a first qualification it is often the faster path. Send a sample of the cured film to a laboratory in your own market, specify combustion ion chromatography, and ask for measured Cl and Br with the LOQ stated. The cost is modest against a requalification. It also gives you an independent baseline to compare against whatever the supplier sends later — and if the two disagree, that gap is the conversation worth having.

The supplier says the raw material is halogen-free. Is that enough?

Not on its own. A raw-material declaration covers a component, and an adhesive is a formulation of several. Contamination during blending, cleaning residues, and fillers or pigments that nobody thought of as a halogen source all sit outside a resin supplier's declaration. Component declarations are supporting evidence; a determination on the finished grade is the evidence.

What to ask this supplier next

If you are evaluating the halogen-free centring grade specifically, the practical sequence is short:

• Confirm the grade code and the mg/kg thresholds it is sold against, in writing.
• Request the test report with laboratory, method, batch, measured values and LOQ.
• Confirm whether the sample was tested wet or cured, and get a cured-film result if not.
• Ask where the material is compounded and under whose licence, so you know whether the formulation answer is coming from the people who make it.
• Ask for the safety data sheet and dangerous-goods classification in the same message, since those decide the shipment regardless of the halogen result.
• Agree the retest and change-notification terms before the first purchase order, not after.

Aosibo Adhesives is a workable example of why the sequence matters: the factory profile lists a halogen-free centring version among three chemistries, records that no product-level compliance documents were sighted at review, and states sampling at 7 days and production at 15 days as company-stated figures. That combination — a specific claim, a short sample lead time, and an open document folder — is exactly the case where one email during the sampling week is worth more than a certificate folder later. Buyers who also need the certification vocabulary for a wider document request will find the groundwork in product certification for China suppliers.