What should I watch when using thiourea dioxide in package and beam dyeing?

Direct answer

Package and beam dyeing circulate liquor through the yarn layers, which is completely different from fabric moving freely in a dyeing machine. When thiourea dioxide is used for reduction clearing or reductive dyeing here, the thing to watch is penetration uniformity: if circulation is uneven, the outer layers clear properly while the inner layers stay under-reduced, and a layer-to-layer difference appears.

1. Three differences from fabric processing

2. Starting parameters

3. Four operating points

1. Circulate to uniformity before dosing: let the bath reach the goods, then raise the temperature

2. Use two-way circulation: one-way circulation tends to create inner-versus-outer differences

3. Control the heating rate: too fast and the outer layers react while the inner layers lag

4. Sample by layer: take samples from the outer, middle and inner layers, not just the surface

4. Common problems

• Layer difference: usually insufficient circulation or too dense a package, so check flow and winding density first
• Increased hairiness: mechanical action or temperature is too high; reduce circulation pressure and temperature
• Inner layers under-reduced: extending the equalisation time is usually more effective than increasing the dose

Sources

Starting values are the recommended ranges from our technical data sheet and published literature. Yarn count, package density and machinery vary widely, so confirm on the actual machine with a bench trial.