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Why is dispersed emerald blue prone to “discoloration”?

Disperse dyes are nonionic dyes that are highly hydrophobic but have little water solubility. They have no water-soluble groups in their structure but contain many polar groups, such as -NO2, -NH2, -CN, -OG etc…

Disperse dyes are nonionic dyes that are highly hydrophobic but have little water solubility. They have no water-soluble groups in their structure but contain many polar groups, such as -NO2, -NH2, -CN, -OG etc.

Disperse dye dyeing

1. The dyeing rate of disperse dyes varies greatly due to different dye varieties. When color matching Try to use dyes with similar dyeing rates or better compatibility, such as disperse dyes and weakly compatible dyes or neutral dyes, to adjust the color and improve the leveling, so as to learn from each other’s strengths.

2. The dyeing rate of disperse dyes is highly dependent on temperature, so special attention should be paid to temperature control during dyeing.

Therefore, the temperature of the prepared dye solution should be low, and prolonged heating of the dye solution should be avoided before dyeing. Generally, dyeing is started at 40~50℃, and the temperature is raised to boiling at about 0.5℃/min. According to the leveling and exhaustion of the dye, keep it warm and wash it with water.

3. Disperse dyes can dye nylon and polyurethane at the same time.

The active groups in the dye and the large number of amide groups in the PA6 molecule and the amino groups at the end of the molecule are dyed and fixed through hydrogen bonds, van der Waals forces and dipole forces. In addition, the PA6 molecule contains a large number of non-polar hydrocarbon hydrophobic chains, which is why hydrophobic disperse dyes can dye brocade. Disperse dyes have small molecular weight, good diffusion properties, simple dyeing methods, good level dyeing properties, excellent light fastness, and good coverage. They can avoid nylon fibers having different weights during polymerization or different stretch levels during spinning. resulting in uneven dyeing. However, when dyeing PA6 with disperse dyes, its saturation value is very low, making it difficult to dye dark colors.

4. Disperse dyes can color polyurethane better, which is related to the polyurethane’s own molecular structure and relatively tight foaming structure. Polyurethane forms an incompletely coherent polymer film on the surface and inside of the synthetic leather base fabric, and its structure consists of soft segments and hard segments. The soft chain segment has a loose structure and is the main location for disperse dyes to be dyed.

Polyurethane absorbs a large amount of disperse dyes, and the dye residue in the dyeing residue is small, which is very necessary when using high-strength disperse dyes to dye dark colors. Within a certain range, as the dyeing temperature increases, the color yield increases. In addition, the color fastness of disperse dyes on polyurethane is also better.

In the dyeing of island-type microfiber synthetic leather, disperse dyes are the main dye type used for dyeing polyurethane. In comparison, some other types of dyes are poor at coloring polyurethane and, on the contrary, color nylon; while some dyes are good at coloring polyurethane but at the same time color nylon, which is important for uniform dyeing. Finished products that are light and have no color difference are very disadvantageous. Even for disperse dyes, the dosage must be controlled, because the coloring of nylon will not only affect its color light, but also affect the dye fastness of nylon.

Factors that should be considered when dyeing:

1. Select the synchronous high-temperature type of dye in the dyeing formula. Try to avoid incompatible non-high temperature dyes.

2. Cuilan is very sensitive to pH value. The amount of acetic acid should not be less. Ensure that the dyeing pH value is controlled between 4 and 5.5 before and after dyeing. If necessary, add a pH sliding agent.

3. The key factor affecting the dyeing stability of Cuilan is the high-temperature leveling agent, which has an excellent retarding effect, but the amount should not be too much, otherwise the color will become lighter. Salt-resistant leveling dyeing The agent will be better (mainly due to the high salt content of the return water).

4. A large amount of additives such as diffusing agents and anti-settling agents are added to dyes during production, which are sensitive to water quality. Calcium and magnesium ions in the water easily combine with dyes to produce color spots, especially iron ions, which have the greatest impact. It is necessary to add chelating dispersant, which is good for the color purity and brightness of the cloth surface.

5. The glass transition temperature of polyester is as low as 70-80°C. After reaching 80°C, disperse dyes begin to dye. The dyeing speed is fastest at 90° and 110°! At this time, it is easiest to control the temperature rise speed. Within 1°C/min; it is best to keep the temperature for ten minutes at 90°C, 110°C, and 120°C. For high-temperature S-GL dyeing, the dyeing temperature is increased to 135°C, which has the best dye migration, uniform dyeing, and color. Smaller, good fastness!

6. Disperse dyes are different from other dyes when dyeing polyester. They are prone to sublimation and thermal migration, which affect the color fastness and color change. During finishing, the setting temperature cannot be Too high is best around 160℃.

7. Domestic single-component dispersed emerald blue S-GL has a relatively large molecular weight. Ordinary dispersed leveling agents have dispersing properties at medium and low temperatures, but may show weak performance at high temperatures due to cloud point issues. Positive, basic dispersion performance will be lost, which will cause the dye molecules to agglomerate and become larger, and the leveling power will decrease, resulting in colored flowers and stains. Be sure to choose a special leveling agent; the dye is recommended to use two-component emerald blue with good level dyeing, domestic BGE emerald blue and DyStar and Huntsman imported emerald blue, etc.

Acid dye dyeing

1. Acid dye dyeing is an important dye for nylon dyeing. The fibers and dyes are mainly bonded by ionic bonds.

2. If the pH value is low (PH<3=) during dyeing, the imino group in the molecular chain can also be positively ionized (-N+H2-) and combined with the dye anion. In addition, weak When dyeing acid dyes in acid or neutral bath dyeing, hydrogen bonding and van der Waals forces also play an important role, and their dyeing saturation values ​​often exceed the saturation value calculated based on the amino content. Since the amino content at the end of nylon is lighter than the amino content, so when using When two or more dyes are used to match colors, competing dyeing problems often occur. Therefore, when matching colors, attention should be paid to choosing dyes with good compatibility.

3. The molecules of nylon are linear molecules. There are no branches or large side groups on the chain, but there are many groups that can form hydrogen bonds. The dye molecules are easy to interfere with the fiber molecules and have large van der Waals forces. Hydrogen bonds are easy to form between the dye and the fiber. Therefore, Acid dyes generally have a higher affinity for nylon than wool. The saturation value of strong acid dyes for dyeing nylon is 2.3%, and the saturation value of weak acid dyes is 5%~5.2%. Therefore, weak acid dyes are commonly used to dye nylon, and the dyes are improved with the help of van der Waals forces and hydrogen bonds. The dye uptake rate.

4. Nylon is dyed with strong acid dyes and is generally not dyed deeply. This is because the proportion of amphoteric groups is different (acetic acid or benzoic acid is commonly used in polyamide synthesis to adjust the molecular weight, and some The terminal amino group of the macromolecule is acylated and exists in the form of acetyl group and benzamide group. The amino group content is lower than the carboxyl group content. In PA6, cyclic amide group is also found). Therefore, it is dyed with typical leveling acid dyes. , that is, it is difficult to dye deep and rich colors by relying only on Coulomb force.

5. Acid dyes can also dye polyurethane, because there are amide groups, urea groups, and Carbamate acid group, the bonding form is van der Waals force, hydrogen bond and ionic bond, but the dyeing effect is not ideal. Especially for strong acid dyes, the dye will almost all be fixed on the surface of the fiber and rarely penetrate into the interior of the fiber, resulting in serious fading after soaping , the fixation fastness is very poor. The dyeing percentage of weakly matching dyes is slightly higher than that of strong acid dyes, and the washing fastness is also better, but the soaping fastness is still not ideal, and the dye cannot penetrate into the fiber, and the light fastness Degree difference.

Neutral dye dyeing

Neutral dyes are 1:2 type acidic mordant dyes, metal atoms and The dye molecules are combined in a ratio of 1:2. The dye molecules do not contain water-soluble groups such as sulfonic acid groups, but only contain hydrophilic groups with low water solubility, such as sulfonylamino (-SO2NHR), methyl sulfone (-SO2CH3), etc. They are generally dyed in neutral or weakly acidic media, which is where the name comes from.
The molecule of nylon has a large number of aminocarboxyl end groups, so neutral dyes can be used. </p

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Author: clsrich

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