Sample Request & RFQ Guide for Adhesives UV Curing & Surface Chemicals

What Your Inquiry Needs to Contain Before You Hit Send #

Most delayed RFQ cycles we see are not caused by slow suppliers. They are caused by incomplete inquiry briefs that force multiple back-and-forth clarification rounds before a supplier can even pull a candidate product from their portfolio.

For UV-cure adhesives and surface treatment chemicals, the minimum technical brief that a Chinese supplier needs to quote accurately includes: substrate type (and surface energy if known), bond-line thickness or coating weight, cure equipment type (conveyor UV lamp, LED spot, flood), peak irradiance available at the substrate surface (mW/cm²), line speed or dwell time, and end-use service conditions including temperature range and any chemical exposure.

If you are sourcing a surface treatment chemical — a plasma pretreatment aid, silane coupling agent, or surface activator — replace the cure parameters with: surface material and finish, treatment method (wipe, dip, spray), open time before bonding, and the adhesive system being applied on top.

For UV-cure adhesives and surface treatment chemicals, the parameter that gets omitted most often is peak irradiance at surface — not lamp wattage, which is a lamp spec, not a substrate spec. A 200 W/cm lamp producing only 80 mW/cm² at 10 cm working distance will under-cure a formulation designed for 150 mW/cm² regardless of exposure time. Suppliers who do not receive this number will quote based on lamp wattage alone, and the sample they send will be tuned to the wrong cure window.

Viscosity requirement is the second most-omitted parameter. For dispensing applications, you need to specify not just the viscosity range (typically 500–50,000 mPa·s depending on method) but also the shear rate at which you’re measuring — many Chinese supplier COAs report Brookfield viscosity at 20 rpm, which is not comparable to cone-plate measurements at higher shear rates used in automated dispensing qualification.

Symptoms of an Incomplete RFQ — and What Each Missing Parameter Triggers #

When we audit RFQ documents that stalled or returned non-conforming samples, the failure mode almost always maps back to one of three missing parameters. This diagnostic table covers the most common gaps:

This is not an exhaustive list, but these six parameters account for the majority of misquoted samples we receive in our category QC-07 material risk intake procedure. If your inquiry covers all six, you are already ahead of roughly two-thirds of the briefs suppliers in this category receive from overseas buyers.

Root Cause of Most Sample Failures: The Grade-Substitution Gap #

There is a failure mode specific to this product category that does not appear in the RFQ stage but surfaces 3–4 weeks into sample testing, and it causes more qualification delays than any other single issue.

Chinese UV-cure adhesive and surface chemical suppliers typically maintain two to three tiers within a single product family: a laboratory-developed formulation, a standard production grade, and what some suppliers internally describe as an “export grade” that uses a partially substituted photoinitiator package. The distinction matters because photoinitiator selection directly controls cure speed, depth of cure in pigmented or filled systems, and long-term yellowing behavior.

When a buyer submits an RFQ without specifying photoinitiator type restrictions — or without knowing to ask — some suppliers will quote a price based on their lowest-cost photoinitiator combination. Type II photoinitiators (benzophenone-based systems) are substantially cheaper than Type I alpha-cleavage systems and are more widely produced in China. However, Type II initiators require hydrogen donors to function and perform poorly in thick-section cure applications, in systems with amine-incompatible substrates, and in any application where residual surface tack is unacceptable.

The sample you receive will be formulated correctly. The problem appears at production volume, when raw material costs are being managed and the compounder introduces a partial photoinitiator substitution that is within their internal tolerance but outside yours. Your incoming testing at sample approval did not catch it because you were testing cure speed and adhesion — not photoinitiator type or residual monomer content by HPLC. The COA from the supplier shows cure speed as “pass” and viscosity within range, but the actual photoinitiator system has shifted.

Confirming photoinitiator class requires either direct disclosure in the technical data sheet or, where that is not available, GC-MS or HPLC testing of a dissolved film extract. We set the threshold for batch-to-batch photoinitiator consistency at ±10% relative area under the relevant HPLC peak when comparing qualification lot to production lot. Deviation beyond that threshold triggers a requalification hold under our intake protocol.

This is the mechanism behind a pattern we see roughly once per quarter in incoming adhesive qualifications: a supplier passes initial sample approval at 95%+ bond strength retention after 72h humidity aging, then delivers production lots showing 70–75% retention. The formulation looks correct on the COA. The viscosity is within spec. The cure speed passes. What changed was the photoinitiator blend — specifically, the ratio of Type I to Type II initiator — and nothing in a standard COA will reveal that shift.

For high-yellowing-sensitivity applications (optical bonding, display assembly), specifying a maximum CIE b* shift of ≤2.0 after 500h UV aging per ASTM D4329 in your RFQ forces the supplier to commit to a photoinitiator package that can meet the threshold, not just one that cures fast enough to pass your first incoming test.

Corrective Actions When Your RFQ Returns the Wrong Sample #

1. Reissue with the diagnostic table completed. Before rejecting the supplier, send back the completed parameter table from the first section. Ask them to re-map their quoted product against each row. In our experience, this single step resolves mismatches in roughly half of cases without needing a new sample. It also reveals whether the supplier understood your application or was simply quoting on price.

2. Request the full TDS and SDS simultaneously. The Technical Data Sheet and Safety Data Sheet together reveal more than either document alone. The SDS will disclose whether the formulation contains restricted substances under REACH Regulation (EC) No 1907/2006 — relevant if you are selling assembled goods into the EU. The TDS will show whether the quoted viscosity, cure speed, and shore hardness were measured at conditions comparable to yours. If the supplier cannot provide both documents, that is the more important data point.

3. Run incoming lap-shear at your cure conditions, not theirs. ASTM D1002 lap-shear on your substrate using your cure lamp at your irradiance is the single most reliable incoming test for UV-cure adhesives. We set a minimum threshold of 8 MPa for structural bonding applications on metal substrates and 4 MPa for flexible substrate assemblies as a first-pass qualifier. If the supplier’s TDS shows higher values and your incoming test does not match, the cure conditions used in their testing differ from yours.

4. Request three consecutive production batch COAs before committing to volume. This is not about distrust — it is about establishing a baseline for lot-to-lot consistency. Viscosity should not vary by more than ±8% between batches for a formulation in steady production. Wider variation indicates raw material sourcing instability at the compounder level.

5. If the issue is surface chemical compatibility, not cure performance, bring in a silane coupling agent qualification check before re-running adhesion tests. Silane hydrolysis and condensation chemistry is sensitive to pH, temperature, and substrate hydroxyl density. A surface treatment chemical that passed testing on your lab coupons may fail on production parts if surface cleanliness, temperature, or humidity conditions are not controlled to the same standard. Specify application conditions in the RFQ, not just the product grade.

Prevention: What to Lock Into Your PO and Spec Sheet Upfront #

The parameters that prevent sample-failure loops are not the ones that end up on most POs. Buyers routinely specify product code, quantity, and delivery — and leave off the three fields that actually govern product performance: cure irradiance at substrate (mW/cm²), bond-line thickness range, and service temperature ceiling.

Add these three fields to your standard PO as a supplier-acknowledgment requirement. Require the supplier to confirm in writing that their quoted product is suitable for the specified conditions before the PO is accepted. This is a one-line addition to your terms, and it shifts the burden of fit-for-purpose confirmation to the correct party.

For surface chemicals, also specify concentration range for use solution and application method (wipe, spray, immersion) — these two parameters alone determine whether a dilutable product will perform consistently across shifts.

The document to request before final supplier selection: a completed application questionnaire with performance test data at your specified conditions, not a generic TDS. If the supplier cannot produce application-specific data, that is your answer.

Practical Guidance for Buyers #

When sourcing UV-cure adhesives or surface treatment chemicals from China, the first document to request is not the product TDS — it is the supplier’s application questionnaire. Most Chinese suppliers in this category maintain internal application checklists that map product grades to substrate type, cure equipment, and end-use conditions. A supplier who cannot or will not share this form is quoting on product code, not on your application.

The risk scenario worth flagging here: if your cure lamp delivers less than 100 mW/cm² at substrate surface and you are bonding a low-surface-energy polymer (surface energy below 36 mN/m), you are operating at the intersection of the two most common failure conditions in this category. A product that passes lap-shear at 12 MPa in the supplier’s lab may deliver 5–6 MPa in your assembly line — not because the adhesive is wrong, but because the cure energy and surface preparation were not specified clearly enough for the supplier to tune the formulation.

Before committing to volume, insist on a minimum of five production-representative samples (not lab samples) tested under your cure conditions per ASTM D1002 lap-shear and your relevant thermal aging protocol. Three days is not enough aging for structural bond qualification — use 72h minimum at 85°C/85% RH for electronic assembly applications, and confirm CIE b* yellowing shift if optical clarity is a requirement.

Frequently Asked Questions

What sample quantity should I request for initial qualification of a UV adhesive?
Request 500g to 1 kg for adhesives in the 500–5,000 mPa·s viscosity range — enough to run lap-shear, humidity aging, and process trials without exhausting the sample on a single test method. For high-viscosity paste adhesives above 50,000 mPa·s, 200–300g is typically sufficient for a full qualification panel.

How long does a typical RFQ-to-first-order cycle take for this category?
From a complete inquiry brief to first production order, plan for 7–11 weeks: 1–2 weeks for supplier response and sample preparation, 2–3 weeks for shipping, and 3–6 weeks for incoming qualification testing depending on your aging protocol. Incomplete briefs add 2–4 weeks to the front end.

Should I ask for REACH compliance documents before or after sample testing?
Before. If the formulation contains substances of very high concern (SVHCs) listed on the ECHA REACH candidate list, testing the sample is a waste of time if the product cannot be imported or used in your target market. Request the SDS and SVHC declaration in your initial inquiry, not as a post-approval step.

Does specifying a higher Shore A hardness in my RFQ guarantee better bond performance?
No — and this is a premise worth challenging. Shore A hardness is a cured-film property that correlates with stiffness, not bond strength or cohesive integrity. For UV adhesives, the parameter that predicts bond durability in thermal cycling is Tg (glass transition temperature), not Shore A. Specify Tg range and compression set behavior if your application involves temperature variation above 60°C.

How many suppliers should I run RFQs with in parallel for this category?
Three to four suppliers is the practical range for a serious qualification. Running fewer than three gives you no competitive basis for negotiation on price or lead time. Running more than five creates a qualification workload that exceeds what most incoming inspection teams can handle concurrently without cutting corners on testing depth — and in this category, the testing depth is where qualification value actually comes from.

Published by sinoraw.com Technical Team | Request a sourcing consultation