Black Sulfide Dye
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Black sulfide, also known as black sulfide BN, black sulfide RN, etc., is a dye produced by the "vulcanization" reaction of aromatic compounds (mainly 2, 4-dinitrochlorobenzene) with sodium polysulfide or sulfur. It is insoluble in water but soluble in sodium sulfide solution, and thus is classified as a sulfur dye.
It is the sulfur dye with the largest output and the widest application in the world, especially renowned for its firm black dyeing on cotton fibers.
Main features
Color: It can dye a very rich and deep dark black.
Low cost: The raw materials for manufacturing are inexpensive and the process is relatively simple, making it one of the most economical black dyes.
Application object:
It is mainly used for dyeing cellulose fibers, such as cotton, linen and viscose fibers.
It can also be used for dyeing vinylon.
Washing fastness: Very good.
Rubbing fastness: Medium to good, but wet rubbing fastness may sometimes be slightly poor and needs to be improved through post-treatment.
Light fastness: Medium.
Dyeing mechanism and process flow
Black sulfide itself is insoluble in water, and its dyeing process is a reduction-oxidation process.
Reductive dissolution
Mix black sulfide dye with a reducing agent (usually alkali sulfide, that is, sodium sulfide Na₂S) in hot water.
Under alkaline reducing conditions, disulfide bonds and other substances in dye molecules are reduced to form cryptochroms.
The cryptochroma is soluble in alkaline solutions and has a good affinity for cellulose fibers.
Dyeing
When the cotton fabric is immersed in the above-mentioned cryptochromic solution, the cryptochromic substances are adsorbed by the fibers and penetrate into the interior.
Oxidation
When the dyed fabric is exposed to the air (or an oxidizing agent such as hydrogen peroxide is used), the latent color on the fibers is oxidized and re-transformed into the insoluble original sulfur black dye, which firmly adheres to the interior of the fibers.
Post-processing
Washing: Remove floating color and residual chemicals.
Anti-brittleness treatment: This is a very special step in sulfur black dyeing.
Oiling/softening: Improves hand feel.
Black sulfide dye has remained popular in the dye industry for a long time due to its unparalleled cost advantage and unique jet-black color. Despite the issues of brittle fabric and environmental protection, it remains one of the top choices for dyeing black cotton fabrics through appropriate post-treatment and improvements in modern environmental protection technologies.
