Disperse Dyes
High-Performance Disperse Dyes For Textile Dyeing
Core Definition
Disperse dyes are a class of nonionic dyes with simple molecular structures and extremely low water solubility. They are dispersed in water as tiny particles (typically less than 1 μm) to form a suspension, maintained by a dispersant. Under high temperatures, they penetrate the interior of hydrophobic synthetic fibers, achieving dyeing through physical fixation.
In Essence
Simply put, they are not soluble in water, but rather "dispersed" in water and then "dissolved" in the fiber.
Dyeing Mechanism
Dyeing polyester with disperse dyes is a physical process, typically divided into four stages:
Dispersion
Dye particles are uniformly suspended in the dye bath under the action of a dispersant.
Dissolution / Sublimation
At high temperatures (>130°C), a very small amount of dye dissolves in water to form unimolecular states, or sublimates into gaseous molecules.
Adsorption
Dissolved or gaseous dye molecules are adsorbed onto the moving fiber surface.
Diffusion and Fixation
Dye molecules diffuse from the fiber surface into the hydrophobic amorphous region and are "frozen" between fiber segments, fixed by intermolecular forces.
Classification
Dyes are typically classified into three categories based on their application properties (sublimation fastness and raising power) and chemical structure:
| Category | Features | Sublimation Fastness | Dyeing Strength | Leveling |
|---|---|---|---|---|
|
E Type (Low Temp) |
Small molecular weight, fast diffusion, low dyeing temperature. | Poor | Fair | Excellent |
|
SE Type (Medium Temp) |
Performance is intermediate between E-type and S-type. | Moderate | Moderate | Good |
|
S Type (High Temp) |
Large molecular weight, complex structure, slow diffusion. | Excellent | Excellent | Poor |
Main Dyeing Methods
For polyester, there are three core methods:
01
High Temperature High Pressure (HT-HP) Method
Conditions: 125-135°C | > 1.5 atm | 30-60 mins
Principle: Under high temperature, polyester molecular chains move violently, the amorphous region increases, pores open, and the dye can quickly diffuse into the fiber interior.
Advantages: Good leveling properties, excellent hand feel, wide range of applicable dyes; the mainstream method.
Equipment: Requires sealed high-pressure dyeing equipment (HT-HP dyeing machine).
02
Hot Melt Method
Conditions: 190-220°C | 1-2 minutes baking
Process: Fabric is first impregnated with disperse dye → dried → hot melt baked.
Principle: The dye sublimates into a gaseous state at high temperature and diffuses into the fiber interior.
Advantages: Continuous production, extremely high efficiency, suitable for large-volume production.
Disadvantages: High requirements for dye sublimation fastness (must use S-type), slightly stiff hand feel.
03
Carrier Method
Principle: Adding a carrier (e.g., chlorobenzene) causes polyester to "swell" under normal pressure, lowering its glass transition temperature to aid dye uptake.
Advantages: Can be used for dyeing at temperatures below 100°C under normal pressure.
Disadvantages: Carriers are often toxic, odorous, and environmentally unfriendly. (Now largely obsolete)
Application Areas
Primary Area:
Dyeing and printing of various polyester fibers (filament, staple fiber, textured yarn, fabrics).
Secondary Area:
Dyeing of acetate fiber, triacetate fiber, and nylon.
Important Application:
Polyester-cotton (T/C), polyester-viscose blends, etc., often used in one-bath or two-bath dyeing with reactive dyes.
Special Application:
Coloring of plastics (such as ABS) and resins.