Determining Masterbatch Letdown Ratios for Recycled Polyethylene Compounds
Determining masterbatch letdown ratios for recycled polyethylene requires MFR matching, antioxidant depletion testing, and gravimetric dosing adjustments.
Delta E CIE Lab
Meaning
Colorimetric testing measures the total color difference between a produced plastic part and its established reference standard using a three-dimensional color space. This delta e cie lab metric quantifies the distance between two color points, combining variations in lightness, redness-greenness, and yellowness-blueness. Manufacturers use this value to determine whether a moulded part meets the visual specifications required for final assembly.
Tolerance Limits
Acceptable variation depends on the final application of the plastic part and the sensitivity of the human eye to specific hues. In automotive interior trim, a delta e cie lab value below zero point five is often required for adjacent parts to prevent visible mismatch. For consumer housewares, the threshold frequently expands to one point zero or higher before consumers perceive a difference.
Processing Influence
Melt temperature, residence time, and shear stress within the injection barrel can degrade heat-sensitive pigments and alter the final appearance of the part. If the operator runs the machine at an excessive temperature, the delta e cie lab value will rise due to polymer yellowing or pigment degradation. This problem is particularly acute in light-colored polymers like white or grey ABS where small color shifts are easily noticeable.
Regular calibration of colorimeters ensures that these drift issues are caught before bulk shipment.
Sourcing Economics
Sourcing masterbatches from multiple suppliers often introduces color variations due to different pigment concentrations or carrier resins. Utilizing a standard delta e cie lab measurement during incoming inspection allows molders to reject out-of-spec color concentrates before they enter production. This proactive testing prevents expensive scraps and avoids the need to run corrective color adjustments during molding.