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Basic knowledge of disperse dyes (2)

Views: 60     Author: Site Editor     Publish Time: 2021-01-15      Origin: Site Inquire

1. What is hot melt pad dyeing?


The hot melt pad dyeing process is suitable for continuous dyeing of polyester/cotton blended fabrics. Its dyeing principle is also a kind of high temperature dyeing. The difference from high temperature and high pressure is that the melting and fixing temperature is high (180℃-220℃) and the time is short. (90 seconds).


2. Describe the performance of disperse dyes in high temperature and high pressure dyeing


(1) Physical properties of disperse dyes:


The wettability, dispersibility, particle fineness, stability of the dispersion liquid, etc., these properties will affect the quality of the dye solution preparation, and are the main factors in the formation of dye spots.


(2) High temperature dispersion stability of disperse dyes:


It represents the disperse, agglomerated or decomposed state of the dye during high-temperature and high-pressure dyeing, and is the main cause of staining, surface floating, and staining of the cylinder.

Disperse Dyes

(3) High temperature dyeability:


i. Covering: The polyester fiber has undergone various heat treatments during the manufacturing process, which causes uneven physical structure such as crystallinity, distribution and molecular orientation of the fiber, resulting in differences in dye uptake, resulting in so-called streaks and warp directions. Strip shadow. (The property of covering the dyed flowers due to uneven fiber structure is called hiding.)


ii. Dyeing migration: refers to the phenomenon of dye migration between fibers due to increased temperature or addition of additives after dyes are dyed on fibers. Dyes with good migration properties are easier to obtain level dyeing, so good or bad migration is an important factor in level dyeing. Generally, E-type disperse dyes have good dyeing properties, but S-type disperse dyes have poor migration properties.


iii. Dyeing rate:

The dyeing process of disperse dyes on polyester fibers is divided into three stages:

a. Disperse dyes diffuse to the fiber surface in a dispersed state or a slightly molten state and a dissolved state.

b. Disperse dyes are adsorbed on the surface of polyester fiber.

c. Disperse dyes diffuse into the polyester fiber.


Therefore; the high temperature dyeing speed of disperse dyes has a complicated relationship with the solubility, adsorption and diffusibility of the dye. In order to obtain a good leveling effect for dyes with high dye uptake, the dyeing rate should be large, and the dyeing speed has a small relationship with the temperature rise. When matching colors, you should choose dyes with similar dyeing speed (that is, good compatibility).


iv. Promotion rate:

When dyeing dark colors, dyes with a high lifting rate should be used, otherwise the dye utilization rate will not be high.

Disperse Dyes

(4) Adaptability to process factors:


i. The choice of dyeing auxiliaries: In order to improve the dyeing performance of dyes during the dyeing process, dyeing auxiliaries are usually added. The auxiliaries use anionic and non-anionic leveling agents, the dosage is 0.5g/l-1.0g /l, the high temperature dispersibility will decrease if the dosage is too high.


ii. The choice of dyeing ratio: In high temperature and high pressure dyeing, the change of the ratio will affect the dyeing rate, especially the coverage. Dyes with good migration properties, high solubility, and high affinity for water have a large dependence on the solubility ratio and should be strictly controlled to prevent batch errors.


iii. The choice of dyeing and solvent pH: dyeing water, auxiliaries, residual alkalis in fabric pretreatment and auxiliaries added during dye manufacturing have certain effects on the pH, and excessively high pH will cause some disperse dyes The hydrolysis of the molecular structure causes color change, and the pH is generally controlled between 4.5-5.5.


iv. Selection of dyeing water:

If hard water is used or the metal ions Ca++, Fe+++, Fe++, etc. are mixed into the dyeing solution, the color of the dyed material will be dull, so the hardness of the dyeing water is controlled within 100PPM.


(5) Temperature selection during high temperature and high pressure dyeing:


When high-temperature and high-pressure dyeing with disperse dyes, the temperature is generally controlled at 130°C. Dyes with low temperature sensitivity such as E type or SE type, although the temperature changes greatly, their dye uptake rate changes very little, so not only can obtain better dyeing reproducibility, but also have better level dyeing effect. The dyeing temperature should be strictly controlled during the heating process and heat preservation, and attention should be paid to the cooling process, otherwise it will easily cause batch errors. For this reason, dyes with consistent temperature sensitivity should be selected when matching colors, especially when matching different types of dyes.

Disperse Dyes

3. How fast is the disperse dye?


The dyeing fastness of disperse dyes is mainly the fastness to sunlight, sublimation, rubbing and washing. Of particular importance is the light fastness in application properties and the sublimation fastness in post-processing. Others such as washing fastness and friction fastness can be solved by the method of reductive washing after dyeing.


4. Why should disperse dyes be reduced and cleaned?


Due to the close internal structure of polyester fiber and the relationship of surface charge, anionic reducing agent cannot penetrate into the fiber. Therefore, reduction cleaning can only remove the floating color on the fiber surface without affecting the dye molecules that have penetrated into the fiber. Reduction cleaning is generally used 30Beo caustic soda 2-4ml/l, sodium hydroxide 1-2g/l, detergent 1g/l, temperature 70℃ for ten minutes.


5. How to control the temperature of disperse dyes?


Disperse dyes should be hydrated materials with a temperature lower than 40°C, but it is difficult to control the temperature at 40°C in practice. Therefore, normal temperature materials are recommended. Too high temperature will cause dyes to agglomerate and cause stains.


6. What effect does polyester oligomer have on dyeing?


Oligomers, also known as oligomers, are low-molecular polymers created during the spinning process of synthetic fibers. Generally, polyester fibers contain 1-3% oligomers. When dyeing, under heating, the oligomer migrates from the inside of the fiber to the outside of the fiber. Because the oligomer is slightly soluble at high temperature, when the dyeing temperature is lowered, the oligomer will crystallize out and produce "white" on the yarn surface. "Frost" phenomenon, the greater the amount of dye and the darker the color, the more serious the impact of oligomers.


7. Describe the hot melt dyeing process of disperse dyes:


Pre-treatment--->Padding--->Intermediate drying--->Hot melt--->Reduction cleaning--->Water washing


8. Describe the direct printing process of disperse dye polyester-cotton fabric:


Printing drying, high temperature steaming (180~185℃, 7~8 minutes), washing and drying, finishing.


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