Paper Dye Direct Black EX Direct Black 38.
Product Features
Direct Black 38 is a commonly used black dye for paper, cotton, linen, and viscose. It has a greenish black color, fast coloration, and low price.
Basic Physical and Chemical Properties
Appearance: Uniform brownish black powder
Color: Standard greenish black (in water)
Solubility (water): Approximately 40g/L at 85℃; soluble in cold water and more soluble in hot water
Solvent solubility: Direct Black EX is slightly soluble in ethanol (greenish blue black) and soluble in cellulose; insoluble in other organic solvents
Acid-base reaction:
Concentrated sulfuric acid: Deep redish blue, dilution turns to purple-brown → redish black precipitate
Concentrated hydrochloric acid: Dark redish black; water solution with hydrochloric acid → purple-brown precipitate
Concentrated NaOH: Blue-gray precipitate
Dyeing Performance (Paper / Fiber)
Affinity: Direct Black 38 has good absorption to cellulose (cotton / linen / viscose / paper), with the highest affinity at 80℃; coloration is slightly lower at low temperatures
Color yield: High color yield and low loss in paper dyeing; Direct Black 38 is suitable for cultural paper / packaging paper / boxboard paper
Color fastness (paper):
Lightfastness: 4–5 grades (medium, lower than Direct Black 17's 7–8 grades)
Water fastness: 3–4 grades; Rub fastness: 3 grades
Dischargeability: Dischargeable; Direct Black EX is suitable for reprocessing of printed paper / colored paper
pH range: Neutral to weakly alkaline (pH 6.5–8.5), moderate resistance to hard water
Form and Quality Indicators (Industrial Grade)
Form: Powder (mainstream), liquid (less common)
Quality standards (reference):
Moisture: ≤1.0%
Insoluble matter in water: ≤0.5%
Color strength: 100±3%
Fineness (80 mesh): Residue ≤5%
Core Advantages and Disadvantages
Advantages
Low price: Direct Black 38 is 30%–40% cheaper than Direct Black 17, offering high cost performance
Fast coloration: Dyeing completed in 30–40 minutes at 80℃, suitable for high-speed paper machines
Pure color: Greenish black with no red / brown impurities, uniform paper surface color
Wide application: Direct Black EX can be used in paper, cotton, linen, viscose, leather, wood, and ink
Disadvantages
Moderate lightfastness of Direct Black EX: 4–5 grades, not suitable for long-term outdoor / high lightfastness requirements
Poor resistance to hard water of Direct Black 38: Easy to precipitate in high-hardness water, requires soft water / chelating agents
- Key Points for Paper Dyeing Application
Applicable paper types for Direct Black EX: Cultural paper, packaging paper, boxboard paper, tissue paper, colored paper
Process parameters:
Temperature: 75–85℃ (optimal 80℃)
Time: 30–40 minutes
pH: 7.0–8.0
Dosage: 1%–3% (based on absolute dry pulp)
Compatibility: Direct Black 38 can be mixed with Direct Yellow / Red / Blue for color matching, to achieve gray / brown / black tones