LDPE 1C7A is an extrusion coating grade with a published typical melt mass-flow rate of 7.0 g/10 min at 190 °C under 2.16 kg load and a base density of 0.918 g/cm³ at 23 °C. The grade is processed on high-speed lines for paper, paperboard, aluminium foil and flexible film coating. It is supplied as a free-flowing pellet with a defined antioxidant and additive formulation. Because the material is used for liquid cartons, barrier laminates and general packaging, the certificate of analysis is not treated as a routine document: it is the first incoming inspection point. Verification of a COA for LDPE 1C7A should establish that the lot number matches the delivered packaging, that the test methods are named, that the numerical values sit inside the converter’s acceptance window, and that regulatory statements for food contact are present where required.

LDPE 1C7A: Extrusion Coating Grade and What to Verify in the COA

The grade is defined by its balance of melt stability and neck-in control under high-speed extrusion coating. Published datasheet values for LDPE 1C7A typically include a melt mass-flow rate of 6.5–7.5 g/10 min, density of 0.917–0.919 g/cm³, and a melting peak near 106 °C by differential scanning calorimetry under ISO 11357-3:2018. The molecular architecture is long-chain branched polyethylene produced under high pressure. That branching promotes shear-thinning and allows relatively high throughput while retaining melt-curtain stability at low coating weight. The COA verification therefore concentrates on six primary properties: melt-flow rate, density, melting point, antioxidant or additive loading, volatile content, and particulate contamination.

On a monolayer extrusion coating line fitted with a 90 mm single-screw extruder having a 30:1 L/D ratio and a 1,200 mm coat-hanger die, LDPE 1C7A is typically processed at barrel temperatures from 200 °C to 320 °C and a melt temperature of 295–310 °C. The molten film falls through an air gap of 120–200 mm before the substrate and chill-roll nip. At these settings, the melt curtain can be drawn to coating weights from 8 g/m² to 40 g/m². Draw resonance appears as periodic thickness bands when line speed exceeds the melt’s extensional capability; for LDPE 1C7A, die-lip gaps of 0.6–1.2 mm and higher melt temperatures reduce that defect. Neck-in, measured as the difference between die width and coated substrate width, is the most operator-sensitive variable. Universal neck-in data for LDPE exist, but a specific value for this grade must be generated on the same die and air gap because die geometry and edge encapsulation can alter the result by 10–30 mm per side.

Which Values in a Certificate of Analysis Require Immediate Rejection?

Immediate rejection is required when the COA contains a lot number that is not present on the delivered packaging, when the declared melt-flow rate is outside the converter’s purchase specification, or when density differs by more than 0.002 g/cm³ from the approved reference lot. The second-level reject trigger is method mismatch: a COA reporting melt index by ASTM D1238-23a cannot be accepted without review if the purchase order specified ISO 1133-1:2022. Although both methods use 190 °C and 2.16 kg, differences in die dimensions, thermocouple placement, and loading procedure can create inter-laboratory variation of approximately 2–3% at MFR levels near 7 g/10 min. The COA must also confirm whether the grade contains slip, antiblock, or antioxidant levels that differ from the approved formulation. A missing antioxidant declaration is an immediate rejection in food-contact lamination because subsequent extrusion can generate oxidative degradation products that affect organoleptic quality.

For COA density verification, the value 0.918 g/cm³ is not a single-point target but the centre of a narrow acceptance interval. A lot at 0.916 g/cm³ can reduce heat-seal initiation temperature by 1–3 °C, which may be beneficial in some structures but can also lower stiffness and increase oxygen transmission measured by ASTM D3985-17 at 23 °C and 0% RH. A lot at 0.921 g/cm³ can stiffen the coating and increase minimum seal temperature. The COA density should therefore be checked against the original qualification lot. Published data for the specific combination of LDPE 1C7A on high-gloss paperboard are limited, so converters often maintain reference coated sheets at 15 g/m² and 25 g/m² for comparison of gloss, seal strength, and pinhole count.

When Substrate Adhesion Drops Below 2 N/15 mm

Adhesion of extrusion-coated LDPE 1C7A to aluminium foil or paperboard is commonly evaluated by peel testing with a 15 mm wide strip and a separation speed of 100 mm/min; peel strengths above 2 N/15 mm indicate acceptable adhesion for many laminating applications, although the exact limit depends on substrate surface energy and primer. A drop below 2 N/15 mm on the same converting line can be traced to inadequate oxidation of the melt curtain. The COA is not a direct predictor of adhesion, but melt index is indirectly relevant. A lot at 7.5 g/10 min may develop slightly lower melt strength than a lot at 6.5 g/10 min, and if the converter compensates by raising melt temperature above 320 °C, oxidative scission can create low-molecular-weight species that deposit on the die and reduce anchorage. Additional adhesion probes include peel strength after 1 week aging at 23 °C and 50% RH; failure mode should remain cohesive or substrate tear rather than adhesive delamination.

For food-contact extrusion coating, the COA should state the regulatory status of LDPE 1C7A under FDA 21 CFR 177.1520(c) for olefin polymers and, in the European framework, under Commission Regulation (EU) No 10/2011 with overall migration verification by EN 1186-1:2002 or EN 1186-2:2002. The converter verifies that the lot is free of animal-derived slip additives where kosher or halal certificates are required and that the COA includes the manufacturer’s declaration on heavy metals and the absence of intentionally added bisphenol A. A COA lacking these statements does not automatically indicate non-compliance, but the lot cannot be released for food-contact production under current Good Manufacturing Practice until the producer supplies a corrected document.

Tracking Melt-Index Drift Across Production Batches

Production-scale records show that LDPE 1C7A can exhibit lot-to-lot melt-index drift of ±0.2 g/10 min, even when all COA values remain inside the published 6.5–7.5 g/10 min range. On a 120 mm extruder with a screw speed of 120 rpm, a 0.2 g/10 min drift can alter back-pressure by 5–10 bar and shift neck-in by several millimetres. The converter should therefore plot the COA MFR value against internally measured melt-index data from the same lot and stop the line when the difference exceeds the repeatability limit of the method. Under ISO 1133-1:2022, repeatability for polyethylene MFR near 7 g/10 min is typically about 3–5% relative; differences larger than that suggest the COA value does not match the delivered pellets or that the sample was poorly homogenized.

Moisture accumulation in LDPE 1C7A during transport is not visible at pellet-surface moisture below 0.03 wt%, but condensation in silos can raise local moisture to 0.10 wt%. During extrusion, residual moisture in the feed throat lowers extruder output and creates surface voids at coating weights below 12 g/m². The COA moisture value, usually measured by ISO 15512:2019, should be compared with the converter’s incoming loss-on-drying result. A COA value of 0.04 wt% is not automatically safe if the pellet bags have been stored outdoors or in an unheated warehouse; the processor should perform a hopper-dryer check and reject wet lots that produce extruder amperage fluctuations greater than 2%.