P-01Undispersed specks and fisheyes in film or thin wall parts

Cause: pellets added downstream of the melting zone, carrier melt index too low for the process temperature, or a package stored above 35 °C and partly fused.

Solution: move the dosing point to the main feed throat, confirm the carrier MI against the resin, and lower the last barrel zone by 5–10 °C so the pellets melt before the mixing section. In film, add a 40/80 mesh screen pack and re-check the fisheye count on a 60 µm drawdown.

P-02Black specks and carbon build-up at the die

Cause: degraded material held in a dead spot, usually at a poorly swept screw element or at the die adapter; aggravated by over-dosing lubricant in the package.

Solution: purge with a high-viscosity purging compound, inspect and polish the adapter, and reduce the package dosage to the lower half of its window. If specks return within a shift, the cause is residence time, not the additive: shorten the barrel or raise the output.

P-03Plate-out and die build-up on film lines

Cause: low-molecular-weight lubricant or slip agent migrating to the surface faster than the line can carry it away; common when a slip-rich package is dosed into a formulation that already contains erucamide.

Solution: switch to the film grade with a balanced slip level, remove the duplicate slip masterbatch, and clean the die lips every 8 hours during the transition. Check the deposit by FTIR: an ester or amide peak confirms migration rather than degradation.

P-04Colour shift or yellowing after the package is introduced

Cause: acid scavenger reacting with a pigment or with a residual catalyst in the resin; or an antioxidant system consumed by excessive heat history.

Solution: run a colour panel against the previous lot, verify the pigment type against the package's acid scavenger, and lower the melt temperature by 10 °C. Where yellowing appears only after oven ageing, move to the low-yellowing variant of the grade.

P-05Viscosity drift during the run

Cause: impact modifier or peroxide-carrying component interacting with a resin whose melt index varies lot to lot; also uneven dosing from a volumetric feeder on a shallow hopper.

Solution: verify the resin MI on arrival, use a gravimetric feeder with a 20-shot weight check, and hold the package dosage constant while the resin MI is trimmed. Log the melt pressure every hour: a drift above 5% signals the cause before the parts do.

P-06Blocking and caking of the bags in storage

Cause: bags stacked above 8 high in a warehouse above 35 °C, or pellets still warm from production packed too early.

Solution: cool the pellets below 40 °C before packing, keep the stack to 8 bags, and store away from sunlight and heaters. Re-condition caked bags at 25 °C for 24 hours before use; do not break them by impact.

P-07Voids, silver streaks and bubbles

Cause: moisture in the resin, not in the package; the package's own moisture is ≤ 0.3% but a hygroscopic resin at 0.3% will still foam.

Solution: dry PA, PBT and ABS to ≤ 0.1% before extrusion, check the dryer dew point, and vent the first 30 seconds of each run. Add a vacuum vent if the line has one.

P-08Odour and VOC complaints on finished parts

Cause: residual monomer or amine-based stabiliser, or degradation products from an overheated barrel; intensified in recycled feedstock.

Solution: request the low-odour version of the grade, add a vented barrel section, and cap the melt temperature. For automotive interior parts, run a VOC chamber test on the first lot rather than after the part is tooled.

P-09Screw slip and unstable feeding

Cause: over-lubrication from dosing above the window, or a carrier whose MI is far above the resin's, which reduces the friction the screw needs to convey solids.

Solution: cut the dosage by 0.5% absolute, match the carrier MI to the resin, and check the feed throat for bridging. In starve-fed lines, verify that the feeder output matches the screw's conveying capacity at the new dosage.

P-10Weld-line weakness and low impact on moulded parts

Cause: impact modifier poorly dispersed, or too high a filler loading competing with the modifier for the interface.

Solution: use the toughening grade with a compatibiliser, raise the mixing-section temperature slightly to improve dispersion, and re-check notched Izod at the weld line, not on a random specimen.

P-11Batch-to-batch inconsistency between deliveries

Cause: active content or pellet size distribution drifting between production lots; sometimes the customer's own feeder calibration rather than the product.

Solution: compare the COA of the new lot with the retained standard, weigh 20 shots of the new lot on the customer's feeder before running, and keep one sealed reference bag per lot. If the COA is inside limits and the fault persists, the feeder or the resin lot is the variable — request a joint trial rather than a replacement.