Statistical Variable Acceptance Plans for Transverse Chemical Skew in Wet Processing
Variable acceptance plans under ISO 3951-1 quantify transverse wet-processing skew through across-width chemical assay data, preventing border detentions.
Thermal Redistribution
Heat Migration
Movement of dyes or finishing chemicals from the interior of a fibre to the surface during a high-temperature process describes this physical phenomenon. Dryers and curing ovens often trigger thermal redistribution when the heat level exceeds the glass transition temperature of the polymer. Internal shifts change the colour fastness and handle of the fabric by concentrating the active ingredients on the outer layer.
Managing this effect is a critical part of the finishing stage for synthetic and blended textiles. Finishing plants must control dwell times precisely to prevent the degradation of surface-active properties.
Colour Shift
Pigments and disperse dyes are particularly susceptible to this movement during the heat setting of polyester fabrics. When the dye migrates to the surface, it becomes more vulnerable to rubbing and laundering. This often results in a lower fastness rating despite the fabric passing initial lab tests.
Finish Modification
Softeners and water repellents also move through the yarn structure when exposed to intense heat. An uneven distribution of these chemicals creates patches of different absorbency or stiffness across the width of the roll. Mill operators monitor the air velocity and temperature profile in the stenter to minimize these variations.
Quality Control
Testing for fastness after the final finishing step captures any negative impacts of this internal migration. If the chemicals have shifted significantly, the garment may fail to meet the brand’s performance standards. Careful selection of dye molecules with high molecular weight helps reduce the tendency of the colour to move under heat.