Hot-Selling Textile Dye Direct Red 31
Direct Red 31 is a disazo direct dye used for dyeing cellulosic fibers such as cotton and viscose. As an anionic dye, it binds firmly to cellulose fibers via hydrogen bonds and Van der Waals forces, yielding a bright blue-red shade. It is also commonly used as a colorant and stain in scientific research.
Physicochemical Properties
1) Chemical Properties
● Good water solubility: ≥ 40 g/L at 80°C; aqueous solution is bluered.
● Concentrated HCl: forms claretred precipitate.
● Concentrated alkali: turns orangebrown.
● Soluble in ethylene glycol ethyl ether; slightly soluble in ethanol (redorange); insoluble in other organic solvents.
● Concentrated sulfuric acid: orange to brown; dark bluered precipitate upon dilution.
● Concentrated nitric acid: brown solution with precipitate.
● Insoluble in concentrated alkali; claretred in concentrated ammonia water.
2) Ion Effects
● Copper ions: shade darkens significantly
● Iron ions: almost no effect
● Hard water (Ca²⁺/Mg²⁺): prone to precipitation; soft water + chelating agent recommended
Fastness Properties (Standard Grades)
●Light fastness: Grade 3–4
● Washing fastness: Grade 3
● Dry rubbing fastness: Grade 3–4
● Wet rubbing fastness: Grade 2–3
● Perspiration fastness: Medium
Core Dyeing Characteristics
1.Directness: Medium, stable uptake
2.Migration / Leveling: Good
3.Salt sensitivity: Promoted by sodium sulfate; can be added in one batch
4.pH preference: Neutral to weakly alkaline (pH 7–8)
5.Compatibility
● Can be combined with direct yellow, orange, red, blue, brown
● Not compatible in one bath with reactive, vat, or disperse dyes
6. Staining behavior
● Silk / wool: lightly dyed
● Polyamide: stained
● Diacetate, polyester, acrylic: slightly stained
Applications
Direct Red 31 is a major red dye widely used for dyeing and printing cotton and viscose fabrics, as well as silkviscose blended fabrics. It features good migration, excellent leveling, and high exhaustion.
Direct Red 31 is also used for dyeing silk, vinylon, and direct printing on silk fabrics.
On blended fabrics of cotton/viscose with other fibers: On silk it gives a lighter shade; and on wool and polyamide will get colored. Diacetate is stained by Direct Red 31, polyester and acrylic are slightly stained.
