Disperse dyes were produced by Baden aniline soda ash company in Germany in 1922. They are mainly used for dyeing polyester fiber and acetate fiber. At that time, it was mainly used for dyeing acetate fibers. After the 1950s, with the emergence of polyester fiber, it has developed rapidly and become a large category of products in the dye industry.
What is disperse dye? Which fibers are suitable for dyeing?
- Disperse dyes are a kind of non-ionic dyes with low solubility in water and high dispersion.Disperse dyes are usually mixed with dispersants and are suspended in water.Disperse dyes are suitable for the dyeing of acetate fiber, polyester, nylon, spandex, PTT fiber and DLA fiber. They can also be used for the original pulp coloring of nylon and polypropylene fiber and the coloring of plastics.
What is the classification and performance of disperse dyes?
- According to chemical structure:
- There are mainly azo type and anthraquinone type, as well as nitrostyrene, benzoimidazole and other heterocyclic structures.
- According to the application performance and color fastness, it is generally divided into:
- (1) Low temperature type (E type) is suitable for high temperature and high pressure dyeing and carrier dyeing. The dye has poor sublimation fastness and good levelness.
- (2) Medium temperature type (SE type, M type) is suitable for high temperature and high pressure, hot melt pad dyeing, and can also be used for carrier dyeing. It has medium sublimation fastness and medium levelness.
- (3) High temperature type (s type, H type) is suitable for high temperature and high pressure, hot melt pad dyeing, good sublimation fastness and poor levelness.
What are the common methods of dyeing polyester with disperse dyes?
- A. Carrier dyeing
- B. High temperature and high pressure dyeing
- C. Hot melt pad dyeing
Dyeing mechanism of disperse dyes
- Because disperse dyes are insoluble in water and only use water as the medium, they are directly dissolved in fiber when dyeing, fiber is used as the solvent, and dye is used as the solute. Because both solvent and solute are solids, it is called “solid solution theory”.
- Polyester fiber has the characteristics of compact molecular structure, high crystallinity, strong hydrophobicity and high negative potential. At the same time, it lacks functional genes combined with ionic dyes. Therefore, in order to solve the difficult dyeability of polyester fiber and improve the diffusion rate of dyes in the fiber, in addition to selecting disperse dyes with small molecular weight and micro molecules, the above three dyeing methods should be adopted in dyeing methods.
What is carrier staining?
Polyester can be dyed by adding chemical agents such as organic acids, alcohols, lipids and benzene compounds into disperse dye solution under atmospheric pressure boiling dyeing conditions. The carrier plays the role of expanding fiber and carrying dye, so it is called carrier dyeing method.
What are the commonly used carriers?
- When using carrier dyeing, the carrier with no toxicity, no serious irritating smell, excellent levelness, good fastness to sunlight and soaping, and maximum expansion performance and dye guiding capacity for polyester fiber should be selected.
- Common carriers include methyl salicylate (Holly oil), sodium o-phenylphenol, methylnaphthalene, etc.
What is high temperature and high pressure dyeing?
- The diffusivity of disperse dyes is closely related to temperature. The higher the temperature, the greater the kinetic energy of dye molecules, that is, the faster the diffusion speed of dyes. For polyester fiber, high temperature can make the fiber “thermally expand”, so as to improve the vibration frequency of fiber molecules, increase the amorphous area of fiber dimension, increase the gap and relax the structure. Therefore, the increase of dyeing rate is conducive to the diffusion of dyes and enter the fiber, Therefore, high temperature and high pressure dyeing is a common process of polyester fiber dyeing. The dyeing temperature is 130 ℃, and the holding time is 15-60 minutes.
What is hot melt pad dyeing?
- 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 lies in high melting color temperature (180 ℃ – 220 ℃) and short time (90 seconds).
Properties of disperse dyes in high temperature and high pressure dyeing
- (1) Physical properties of disperse dyes:
- Wettability, dispersibility, particle fineness, stability of dispersion, etc. these properties will affect the preparation of dyeing solution and are the main factors for the formation of dyeing spots.
- (2) High temperature dispersion stability of disperse dyes:
- It represents the dispersion, condensation or decomposition state of dyes during high temperature and high pressure dyeing. It is the main factor to form dyeing spots, surface floating color and cylinder contamination.
- (3) High temperature dyeability:
- i. Covering ability: polyester fiber has undergone various heat treatments in the manufacturing process, resulting in uneven physical structures such as crystallinity, distribution and molecular orientation of the fiber, resulting in differences in dye uptake and so-called streaking and meridional streaking. (the nature of the dye that covers the flowers caused by uneven fiber structure is called covering.)
- II. Migration: refers to the migration of dyes between fibers due to the increase of temperature or the addition of additives after dyes are dyed on fibers. Dyestuffs with good migration are easy to obtain level dyeing, so good migration and bad migration are important factors for level dyeing. Generally, E-type disperse dyes have good migration and S-type disperse dyes have poor migration.
- III. dye uptake rate:
- The dyeing process of disperse dyes on polyester fiber is divided into three stages:
- a. Disperse dyes diffuse to the fiber surface in dispersed state, micro molten state and dissolved state.
- b. Disperse dyes are adsorbed on the surface of polyester fiber.
- c. Disperse dyes diffuse into polyester fibers.
- Therefore; The high-temperature dyeing speed of disperse dyes has a complex relationship with the solubility, adsorption and diffusion of dyes. In order to obtain good leveling effect, dyes with high dyeing rate and less relationship between dyeing speed and temperature rise should be selected. Dyes with similar dyeing speed (i.e. good compatibility) should be selected during color matching.
- IV. promotion rate:
- When dyeing dark colors, dyes with high promotion rate should be selected, otherwise the utilization rate of dyes is not high.
- (4) Adaptability to process factors:
- i. Selection of dyeing auxiliaries: in order to improve the dyeing performance of dyes in the dyeing process, dyeing auxiliaries are usually added. Anionic and non anionic leveling agents are used as auxiliaries, and the dosage is 0.5g/l-1.0g/l. If the dosage is too large, the high-temperature dispersion will be reduced.
- II. Selection of dyeing solution ratio: in high temperature and high pressure dyeing, the change of solution ratio will affect the dyeing rate, especially the coverage. Dyes with good migration, high solubility and high affinity for water are highly dependent on the solubility ratio. They should be strictly controlled to prevent batch difference.
- III. selection of dyeing solution pH value: dyeing water, auxiliaries, residual alkali agent in fabric pretreatment and auxiliaries added in dye manufacturing have a certain impact on the pH value. Too high pH value will cause the hydrolysis of the molecular structure of some disperse dyes and cause color change. Generally, the pH is controlled between 4.5 and 5.5.
- IV. selection of dyeing water:
- If hard water is used or metal ions Ca + +, Fe + + +, Fe + + are mixed into the dye solution, the color of the dye will fade, so the hardness of the dyeing water is controlled within 100ppm.
- (5) Selection of temperature during high temperature and high pressure dyeing:
- When disperse dyes are dyed at high temperature and high pressure, the temperature is generally controlled at 130 ℃. For dyes with low temperature sensitivity, such as E-type or Se type, although the temperature changes greatly, then their dye uptake changes very little, so they can not only obtain better dyeing reproducibility, but also have better leveling effect. In addition to strictly controlling the heating process and heat preservation, the dyeing temperature should also pay attention to the cooling process, otherwise it will easily cause batch difference. Therefore, dyes with consistent temperature sensitivity should be selected during color matching, especially for different types of dyes.
What is the fastness of disperse dyes?
- The dyeing fastness of disperse dyes is mainly the fastness to sunlight, sublimation, friction and washing. Among them, the sun fastness in application performance and sublimation fastness in post-processing are particularly important. Others, such as washing fastness and rubbing fastness, can be solved by reducing washing after dyeing.
Why should disperse dyes be reduced and cleaned?
- Due to the close internal structure and surface charge relationship of polyester fiber, anionic reducing agent cannot penetrate into the fiber. Therefore, through reduction cleaning, only the floating color on the fiber surface can be removed and the dye molecules that have penetrated into the fiber will not be affected. Generally, 30beo caustic soda 2-4ml / L, insurance powder 1-2g / L, detergent 1g / L and temperature 70 ℃ for ten minutes are selected for reduction cleaning.
How to control the temperature of disperse dyes?
- Disperse dyes should be hydrated at a temperature lower than 40 ℃, but in practice, the temperature of 40 ℃ is difficult to control, so it is recommended to use chemicals at room temperature. Too high temperature will cause dye condensation and color spots.
What effect does polyester oligomer have on dyeing?
- Oligomer, also known as oligomer, is a low molecular polymer caused by the spinning process of synthetic fiber. Generally, it contains about 1-3% oligomer in polyester fiber. When dyeing, under the condition of 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 decreases, the oligomer crystallizes and precipitates, resulting in a “white frost” phenomenon on the yarn surface. The greater the amount of dye and the darker the color, the more serious the influence of the oligomer.
The hot melt dyeing process with disperse dyes:
- Pretreatment — > dip rolling — > intermediate drying — > hot melt — > reduction cleaning — > water washing
The direct printing process of disperse dye polyester cotton fabric:
- Printing → drying → high temperature steaming (180 ~ 185 ℃, 7 ~ 8 minutes) → flat washing → drying → finishing.
