Cationic dyes are a kind of textile dyes, also known as basic dyes and base dyes. It is in the state of cation dissolved in water. The cation dye can be dissolved in water and ionized in water to form a dye with positive charge. The cationic dye can combine with the acid group of the third monomer in the fabric to dye the fiber. It is a special dye for acrylic fiber dyeing. It has the advantages of high strength, bright color and good light fastness.
Types of cationic dyes
Cationic dyes can be classified according to their application properties and chemical structure. According to the application properties, the existing dyestuffs in China are divided into ordinary type, X type and M type. According to the chemical structure, there are two types: isolated type and conjugated type.
(1) Isolated cationic dye: the positive charge in the dye molecule is connected with the conjugated system of the chromophore of the dye through the isolation group, and the positive charge is fixed on the nitrogen atom of the quaternary ammonium salt. Cationic dyes are characterized by a slightly lower amount of color, not very bright color, but heat, sun, acid and alkali resistance, good stability. For example, cation red GTL (C.I. basic red 18 (c.i.11085) (English Name: Cationic Red GTL) has the following structural formula:
Cationic red GTL is dark red powder, soluble in water, dark red, red light orange in concentrated sulfuric acid, red after dilution, dark red in dyed acrylic fiber. N-ethylaniline was hydroethylated, chlorinated and ammoniated; 2-chloro-4-nitroaniline was diazotized and coupled with the above ammoniated compound, then methylated, filtered and dried. It can be used for printing and dyeing of acrylic fiber and its blends, modified acrylic fiber and polyester fiber, and acetate fiber fabric.
(2) Conjugated cationic dye: the positive charge in the dye molecule is a part of the dye chromophore conjugation system. The positive charge is not fixed on an atom, but can be shifted. This kind of dyestuff is characterized by bright color, high coloring power, but medium light fastness. For example, cation yellow x-6g (c.i.48056) (English Name: Basic yellow 13), its structural formula is as follows:
Cationic yellow x-6g is brownish yellow powder, slightly soluble in cold water and hot water, dyeing acrylic fiber is bright green yellow. 1,3,3-trimethylindoline acetaldehyde was condensed with p-aminoanisole, filtered and dried. It can be used in the printing and dyeing of acrylic fiber and its blends, as well as the printing of acetate fiber, PVC fiber and modified acrylic fiber.
Dyeing method and mechanism of cationic dyes
Cationic dye is a special dye for acrylonitrile fiber. The dyeing method is to use acetic acid and sodium acetate as buffers in bathtub with weak acidity (pH value is about 4.5). In the presence of dielectrics and appropriate auxiliaries, it is close to boiling dyeing. The dyeing mechanism can be divided into three steps: [1]
(1) The dye cations in the dye bath are adsorbed on the fiber surface.
(2) The dye cation diffuses from the fiber surface to the interior.
(3) The dye cation and the anion group in the fiber form a salt bond.
Under normal dyeing conditions, the salt formation in the last step is irreversible, which can lead to high fastness and uneven dyeing. The first two steps react fast and the second one diffuses slowly, which determines the whole dyeing speed. Due to the high affinity between dyes and fibers, it is necessary to strictly control the bath temperature, pH value, electrolyte, retarder, etc.
Influencing factors of cationic dyes
Cationic dyes have a large affinity for acrylic fibers, which are easy to cause dyeing unevenness due to fast adsorption and slow diffusion. Once dyeing unevenness occurs, it is difficult to correct it by prolonging dyeing time. In order to get uniform dyeing results, the dyeing rate should be reduced properly. In addition to the types of acrylic fibers, the factors that affect the dyeing rate of cationic dyes are as follows:
1. temperature
Temperature is an important factor to control level dyeing. When acrylic fibers are dyed with cationic dyes, the dye uptake rate increases rapidly when the dyeing temperature reaches the glass transition temperature (75-85 ℃). Therefore, when the dyeing temperature reaches the glass transition temperature of the fiber, the temperature should be raised slowly, generally 1 ℃ every 2-4 min. It can also be dyed at 85-90 ℃ for a period of time and then heated to boiling.
2. PH value of dye bath
The addition of acid in the dye bath can inhibit the dissociation of acid groups in acrylic fibers, reduce the number of anion groups on fibers, reduce the Coulomb force between dyes and fibers, and reduce the dyeing rate. The effect of pH value on the dyeing rate of acrylic fiber with carboxylic acid group is more significant, and the effect of pH value on the dyeing rate of acrylic fiber with sulfonic acid group is less. The pH value of dyeing bath should be controlled reasonably. Cationic dyes are generally not alkali resistant, and the optimal pH value of dyeing is generally 4-4.5. When dyeing in dark color, the pH value of dyeing bath can be higher, and when dyeing in light color, it should be carried out at a lower pH value. The pH value of dye bath is generally regulated by acetic acid, which can not only reduce the pH value of dye bath, but also improve the solubility of dye. When sodium acetate is added to the dye bath, the pH value of the dye bath can be kept within the required range.
3. electrolyte
Adding electrolytes, such as sodium chloride and salt, in the dye bath can reduce the dye uptake rate of cationic dyes and has the function of slow dyeing. The electrolyte has no obvious retarding effect on the dyes with K value 1 ~ 1.5, but has retarding effect on the dyes with K value 3 ~ 5. The retarding effect of electrolyte decreased with the increase of dyeing temperature. When dyeing light color, the amount o f electrolyte can be higher, about 5% - 10% (o.w.f.), but not when dyeing dark color.
4. retarding agent
In cationic dyeing, retarder is often added to reduce the dyeing rate and get uniform dyeing effect. There are two kinds of Retarders for cationic dyes: cationic retarder and anionic retarder.
Cationic retarder is the most commonly used retarder for cationic dyeing, most of which are cationic surfactants, such as 1227 (leveler tan), 1631 (leveler IV). Cationic retarder has affinity for acrylic fiber. For the cationic retarder with smaller molecule and less affinity with fiber, because of its fast diffusion rate, it first occupies the fiber during dyeing
EMPEROR company stroingly for those Cationic dye:
Cationic Red 1, Cationic Red 14, Cationic Red 18, Cationic Red 46
Cationic Yellow 2, Cationic Yellow 13, Cationic Yellow 28, Cationic Yellow 40, Cationic Yellow 51
Cationic Blue 7, Cationic Blue 9, Cationic Blue 26
Cationic Green 4
Cationic Violet 1, Cationic Violet 3, Cationic Violet 10, Cationic Violet 14
Cationic Brown 14
if you are interested Cationic dyes, pls feel free to contact us. our TEL is 0086-15958136613 Ms Gloria Xu(7X24hours)
