Diagnostic Technique
Optical analysis using oblique illumination and high-frequency light isolates surface contamination on undyed fabrics. Dark field ultraviolet inspection utilizes a light source positioned at a shallow angle to the fabric surface. This arrangement ensures that only light scattered by surface irregularities or fluorescent contaminants reaches the detector.
It is a critical quality checkpoint before dyeing and finishing.
Mechanism Action
Fluorescent materials like machine oils, synthetic sizing agents, and plastic microfibers absorb the ultraviolet light and re-emit it as visible light. The dark background provided by the oblique illumination makes these glowing contaminants stand out with high contrast. Operators can locate microscopic contamination that would remain invisible under standard white light.
This allows for localized treatment or sorting of defective rolls.
Defect Isolation
Pre-dyeing evaluation using this technique prevents the formation of light or dark spots on the finished garment. Synthetic fiber contamination is particularly troublesome because it fails to absorb cotton dyes. Identifying these fibers before the dye bath saves chemical and fabric costs.
Physical Constraint
Ambient light must be completely excluded from the inspection area to ensure high contrast. If the room is not dark, weak fluorescence from small particles cannot be detected. This requirement restricts the method to dedicated inspection cabins.
