Identifying Reprocessed Engineering Thermoplastic Additions through Visual Screening
Visual inspection of pellet geometry, color shift, specks, and cross-polar optics rapidly identifies reprocessed additions in engineering resin lots.
Color Drift
Meaning
Process variation across production shifts induces shifting chromaticity coordinates in finished plastic parts beyond allowable colorimetric thresholds. During continuous injection moulding or compounding operations, color drift marks an unintended change in hue or lightness over time. Material lot variations, masterbatch feed inconsistency and thermal degradation of organic colorants drive these gradual chromatic shifts.
The property governs aesthetic uniformity across multi-cavity tools and sequential production lots, ending where deliberate color changes or initial formulation development occur.
Pigment Behavior
Pigment concentration shifts occur when volumetric feeder calibration drifts or when raw resin bulk density fluctuates during hopper feeding. Organic pigments degrade thermally when residence time in the barrel increases, shifting the output hue toward yellow or brown tones. Masterbatch dispersion quality determines whether colorants distribute uniformly across the polymer matrix during screw homogenization.
Recycled content additions introduce variable baseline color, forcing processors to adjust pigment loadings between resin lots. Shear heating at high screw speeds alters heat sensitive dye structures, producing chromatic shifts without changes in pigment loading. Differential cooling rates across mold cavities alter polymer crystallinity, which changes surface light scattering and perceived color tone.
Process Instability
Temperature fluctuations inside barrel zones alter pigment thermal exposure and polymer melt viscosity. Variations in back pressure change the mixing efficiency of the screw, leading to uneven masterbatch distribution. Regrind ratio changes alter melt flow behavior and baseline resin opacity across continuous runs.
Spectrophotometric Tolerance
Color consistency evaluation relies on CIELAB color space measurements using spectrophotometers under standardized lighting conditions. Total color difference delta E quantifies combined shifts in lightness and chromatic axes against an approved master standard. Processors set strict color difference boundaries to prevent visual mismatched assemblies in multi-part product housings.