In the private label segment for two-component epoxy resin systems, the industrial phrase Private Label Epoxy Resin: OEM Filling, Labelling & REACH Duty Split describes a contract-manufacturing arrangement in which the resin formulation may be owned or specified by one legal entity, the filling and assembly operation is performed by a separate filler, and the regulatory responsibilities under EC 1907/2006 are allocated by written agreement rather than assumed from physical custody. A typical system is a bisphenol A/F diglycidyl ether resin combined with a polyamidoamine or modified cycloaliphatic amine hardener, supplied as a two-component kit or as a filled single-component heat-cure system depending on the target end use. The private label structure changes the legal point of market placement: the brand owner may be the importer of record, the downstream user, or the only-representative appointee, while the OEM filler may act as a toll blender, repacker, or contract packager under Article 3(13) of REACH. This allocation determines which party authorises label artwork, verifies child-resistant closures, files poison centre notifications, and holds the registration dossier linkage. A recurring contract defect is the assumption that the filler’s quality-control release data automatically satisfies the brand owner’s legal obligations under EC 1272/2008; it does not.

What restricts rotary filler output when the epoxy component contains a platelet thickener?

In a 12-head rotary filling machine using positive-displacement pistons and a 500 mL target fill volume, the maximum sustained cycle rate is not set solely by the servo-drive speed; it is governed by the recovery time of the resin surface after each piston intake stroke, the air entrainment rate in the hopper, and the yield stress produced by organoclay or fumed-silica thixotropes. Commercial liquid bisphenol A resins with an epoxy equivalent weight of 184–190 g/eq typically exhibit a neat viscosity of 11,000–14,000 mPa·s at 25°C when measured by ASTM D2196 with spindle 7 at 20 rpm. Addition of 2–4 wt% fumed silica can raise low-shear viscosity above 80,000 mPa·s and create a gel-like structure that feeds unevenly into volumetric cavities. Cavitation at the suck-back port occurs when the product clings to the hopper wall and a vacuum pocket forms behind the piston; this failure is more frequent at fill temperatures below 20°C and when the hopper level falls below 15% of working volume. Production-scale monitoring therefore uses a vibrating rod or tuning-fork level switch rather than a float to avoid false dry signals caused by resin coating. Deaeration is conducted in a jacketed vacuum vessel at 30–40°C and 50–100 mbar absolute pressure, but prolonged vacuum stripping removes reactive diluents such as C12–C14 glycidyl ether and shifts the stoichiometric ratio unless the hardener weight is recalculated after degassing. Batch-to-batch variation at the filling head is most visible as a ±1.5% fill-volume drift when the resin temperature drops from 25°C to 18°C because viscosity changes the piston-chamber fill time; gravimetric checkweighers reject capsules outside the 1.0% tolerance window required by many private-label purchase specifications.

Filled epoxy resin used in private-label electrical potting often contains aluminium trihydroxide at 40–65 phr or calcium carbonate at 30–50 phr; the density differential between ATH at approximately 2.4 g/cm³ and the resin at 1.16 g/cm³ produces hard settling within 24–72 h if the anti-settling package is not matched to the storage interval. Re-homogenisation requires an air-powered propeller at 300–600 rpm or a low-shear planetary paddle, but a high-speed disperser above 1,500 rpm can generate local shear heating and initiate premature reaction in one-component dicyandiamide-catalysed systems. Published data for this specific configuration is limited because filler settling is highly dependent on particle-size distribution and surface treatment; the safe default is to commission a short settling-column study before freezing the filling recipe, with gel time checked according to ASTM D2471.

Under EC 1272/2008, a private-label epoxy resin supplied as a two-component kit generally carries a label for each component, while the final mixed system is addressed in the safety data sheet and on the kit outer packaging if the components are packaged together and intended to be mixed before use. Legal responsibility for label accuracy does not transfer to the contract filler merely because the filler prints and applies the label; the brand owner or importer placing the product on the market in the EU remains responsible for classification and labelling under Article 17 and for poison-centre notification under Annex VIII to EU Regulation 2017/542. The label must show the UFI code for products classified for health or physical hazards, with the UFI placed on the label or in an adjacent field; the OEM filler’s role is usually limited to verifying the UFI is present in the artwork, checking varnish adhesion, and confirming that hazard pictograms remain legible after solvent exposure. A labelling non-conformance that recurs on packaging lines is the use of polyester or glycol-modified polyethylene terephthalate labels on filled metal cans exposed to amine vapour; the label adhesive may soften and allow the CLP pictogram to slip. For this reason, private-label filling contracts often specify a label peel-adhesion test according to ISO 2409 or ASTM D3330 with 24 h conditioning at 40°C and 90% RH, followed by visual inspection for signal-word legibility. Child-resistant closures are mandatory when the component meets the criteria for acute toxicity, specific target organ toxicity, aspiration, or corrosivity; the standard reference for reclosable packages is ISO 8317. The label must also show the nominal quantity under EC 76/211/EEC or national metrology rules, the mixture identity, hazard statements, precautionary statements, and the responsible person’s name, address and telephone number. The OEM filler cannot legally substitute its own legal entity on the label unless it is the importer or distributor placing the kit on the market under its own name.

If the non-EU manufacturer appoints an only representative, where does the OEM filler sit in the REACH allocation?

The REACH position of the OEM filler changes with the contractual configuration. When a non-EU epoxy resin producer appoints an only representative under Article 8 of EC 1907/2006, the only representative assumes the registration and communication duties of the non-EU manufacturer for substances imported into the EU. The EU brand owner that imports the resin mixture may be an importer for the formulation if the only representative does not cover that specific mixture; the OEM filler that blends, fills and labels under tolling instructions is usually a downstream user under Article 3(13), provided the filler does not place the product on the market under its own name. However, if the OEM filler re-imports or buys the resin in its own name for the sole purpose of filling for a brand owner, it may itself become an importer, and the registration obligation under Article 6 attaches unless an only representative covers the import. Written duty-split clauses therefore assign four distinct functions: registration data linkage, exposure-scenario use mapping, safety-data-sheet authoring, and label/package conformity. Without such a clause, the duty is determined by default legal definitions, which can create duplication or omission at the warehouse boundary. The table below supplies a compliance-assignment matrix for a typical private-label kit.

The only-representative structure is not a transfer of downstream-user obligations to the filler. If the filling operation uses a process category such as PROC 8b for transfer of a substance or mixture into small containers, and the supplier’s exposure scenario does not list that process category or the associated concentration band, the OEM filler is obligated under Article 37(4) to either implement conditions that bring the use within the exposure scenario, prepare a downstream-user chemical safety report, or request the supplier to add the use under Article 37(2). In practice, filling lines running at 20–25°C with local exhaust ventilation velocities of 0.5–1.0 m/s at the fill head usually fall within the supplier’s defined operational conditions, but the private-label contract must record the applicable use-descriptor string so that audit evidence is not assembled retrospectively. A common unsupported claim is that the OEM filler’s ISO 9001 certificate covers REACH use mapping; it does not, because ISO 9001 addresses quality management, not chemical-safety assessment.

Viscosity ratio, epoxy equivalent weight drift and side-by-side cartridge release limits

After the filling campaign, release testing for a private-label two-component epoxy kit typically compares the batch-average viscosity against the formulation reference using ASTM D2196, a Brookfield RV viscometer, spindle 7, 20 rpm, 25°C. The acceptance band for unfilled resin is often ±10% of the reference viscosity, while the mixed cartridge output must not exceed ±15% of the reference gel time determined by ASTM D2471 at 25°C on a 100 g mass. Epoxy equivalent weight is checked by ASTM D1652 using perchloric acid titration or a near-infrared prediction calibrated against the titration; the release band of 184–190 g/eq for a standard bisphenol A resin is tightened to ±2 g/eq in many private-label specifications because a drift of +3 g/eq shifts the stoichiometric hardener demand by 1–2 phr and alters crosslink density. For filled systems, the ratio of low-shear viscosity at 0.5 rpm to high-shear viscosity at 20 rpm is monitored as a thixotropy index; values below 1.5 suggest insufficient anti-settling behaviour, while values above 6.0 may cause pump cavitation and poor levelling in self-levelling floor formulations. The test sample is conditioned in a water bath for 2 h at 25°C before measurement because a temperature offset of ±1°C can move epoxy viscosity by approximately 7–10%. Batch records from twin-screw filling lines show that the highest release failure rate occurs not in the resin component but in the amine hardener after humid exposure; the hardener viscosity can increase by 20–50% without visible colour change. The OEM filler therefore pre-checks the hardener with 0.5 mm sieve filtration and measures the amine value before connecting the feed vessel to the filling line.

At relative humidity above 60% RH, the exposed surface of an amine hardener in an open-top pressure vessel absorbs carbon dioxide and forms a viscous carbamate film, which can block 50 μm inline filters and alter the stoichiometric mixing ratio by removing active amine hydrogen from the bulk. This failure mode is observable in two-component filling cells where the resin and hardener are deaerated separately and then metered through a static mixer with 32 elements; if the hardener feed has not been nitrogen-blanketed at 0.1–0.2 barg, the mixed output may show intermittent gel particles that contaminate the fill nozzle. Private-label OEM lines that package 50 mL side-by-side cartridges use static mixers with an internal diameter of 10–16 mm and a length-to-diameter ratio of approximately 15:1, but the critical parameter is not mixer length alone; it is the pressure drop between the metering pump and the outlet, which rises sharply when the mixed viscosity exceeds 200,000 mPa·s. On high-speed lines, in-line pressure transmitters are located 100 mm upstream of the static mixer to detect filter blocking before failure reaches the dispensing tip. Shelf-life prediction for an unfilled bisphenol A/F resin is typically based on accelerated storage at 40°C and 75% RH for 8 weeks or 50°C for 4 weeks, with epoxy equivalent weight drift and viscosity ratio measured against ASTM D1652 and ASTM D2196. Published data for this specific configuration is limited when the formulation contains latent accelerators, because the accelerator’s deactivation rate under humid packaging conditions depends on the exact tertiary amine or imidazole used; release for production should therefore be based on the supplier’s batch-specific data and not on generic epoxy shelf-life tables. Incompatibility with amine-based accelerators must be stated in the private-label specification because mistaken addition of benzyl alcohol or unreactive solvents to manage viscosity can lower glass transition temperature below the end-use requirement and produce a resin that passes the gel-time check but fails the final thermal performance standard.