Views: 2 Author: Site Editor Publish Time: 2023-12-06 Origin: Site
Disperse dyes are a type of dye with smaller molecules (molecular weight 200-500) and relatively simple structure. It does not contain strong hydrophilic groups such as sulfonic acid group so3- and carboxyl COOH. It only contains some weak polar groups such as carboxyl groups, amino groups, and nitro groups, and is a non-ionic dye with very low water activity.
The five major dyeing properties of disperse dyes are listed below.
Lifting power refers to the degree to which the color depth on the fabric (or yarn) increases accordingly when the amount of dye is gradually increased when the dye is used for dyeing or printing. For dyes with good lifting power, the dyeing depth increases in proportion to the dye dosage, indicating better dyeing depth; dyes with poor lifting power have poor dyeing depth. When reaching a certain depth, the color will no longer deepen as the dye dosage increases.
2) Impact on dyeing
The lifting power of disperse dyes varies greatly between specific varieties. When dyeing deep colors, choose dyes with high lifting power; when dyeing bright, light colors, choose dyes with low lifting power. Only by mastering the characteristics of dyes and using them rationally can we achieve the effect of saving dyes and reducing costs.
The dye lifting power of high-temperature and high-pressure dyeing is expressed in %. Under specified dyeing conditions, the exhaustion rate of the dye in the dye solution is measured, or the color depth value of the dyed sample is directly measured. The dyeing depth of each dye can be divided into six levels according to 1, 2, 3.5, 5, 7.5, 10% (O.M.F), and dyeing is carried out in a high-temperature and high-pressure dyeing prototype machine. The dye lifting force of hot melt pad dyeing or fabric printing is expressed in g/L.
From a practical point of view in production, the lifting power of a dye is the change in the concentration of the dye solution, that is, the change in the color depth of the printed and dyed finished product. Use an instrument to accurately measure the color depth value, and then calculate the lifting force curve of the disperse dye through the color depth formula.
The hiding ability of disperse dyes on poor quality polyester is called covering power. Polyester (or acetate) filament fabrics, including knitwear, often have color gaps after piece-dyed with disperse dyes. There are many reasons for color blemishes, some are weaving defects, and some are due to differences in fiber quality that are exposed after dyeing.
If you choose low-quality polyester filament fabrics and dye them with disperse dyes of different colors under the same dyeing conditions, different situations will occur. Some color casts are serious and some are not obvious. This reflects that disperse dyes have different color casts. level of coverage. According to the gray standard rating, serious color difference is grade 1, and no color difference is grade 5.
Disperse dyes are poured into water and immediately dispersed into fine particles. The particle size distribution is expanded according to a binomial equation, with an average value of 0.5 to 1 micron. The particle sizes of high-quality commercial dyes are very similar and have a high percentage, which can be shown by the particle size distribution curve. Dyes with poor particle size distribution contain coarse particles of varying sizes and have poor dispersion stability. If the particle size greatly exceeds the average range, recrystallization of tiny particles may occur. Due to the increase in recrystallized large particles, the dye is precipitated and deposited on the wall of the dyeing machine or on the fiber.
2) Factors affecting dispersion stability:
Impurities in the raw dye may adversely affect the dispersion state. Changes in dye crystallization are also important factors. Some crystalline states are easily dispersed, while other states are not. During the dyeing process, the crystalline state of the dye sometimes changes.
When dyes are dispersed in aqueous solutions, due to the influence of external factors, the stable state of dispersion is destroyed, which may lead to increased dye crystallization, particle aggregation and flocculation.
A. Filter paper method:
Prepare 10 g/L disperse dye solution and add acetic acid to adjust the pH value. Take 500 ml and use filter paper to suction filter on a porcelain funnel and observe the particle fineness. Take another 400 ml and conduct a blank test in a high-temperature and high-pressure dyeing machine. Heat it to 130°C, keep it for 1 hour, cool it down, and then filter it with filter paper to compare the changes in the fineness of the dye particles during boiling dyeing. The dye solution heated at high temperature is filtered and there are no color spots on the paper, indicating good dispersion stability.
B. Color pet method:
The dye concentration is 2.5% (heavy for polyester), the liquor ratio is 1:30, add 1 ml of 10% ammonium sulfate, adjust to pH 5 with 1% acetic acid, take 10 grams of polyester knitted fabric and roll it on the porous wall, place it in the dye liquor for internal and external circulation In a small high-temperature and high-pressure dyeing prototype machine, raise the temperature from 80°C to 130°C, keep it warm for 10 minutes, cool to 100°C, wash and dry, and observe whether there are dye condensed color spots on the fabric.
There are many varieties of disperse dyes with a wide chromatogram, and their sensitivities to pH are very different. Dye solutions with different pH values often lead to different dyeing results, affecting the depth of the color, and even causing discoloration in severe cases. In weakly acidic medium (pH 4.5 ~ 5.5), disperse dyes are in the most stable state.
The pH values of commercial dye solutions vary, some are neutral, and some are slightly alkaline. Before dyeing, acetic acid must be used to adjust the pH to the specified value. During the dyeing process, sometimes the pH value of the dye liquor will gradually increase. If necessary, formic acid and ammonium sulfate can be added to keep the dye liquor in a weakly acidic state.
In large-scale dyeing production, in order to obtain good reproducibility, it is usually required that the dyeing properties of the three primary color dyes used are similar to ensure that the color difference is consistent between batches. Controlling the color difference between batches of dyed finished products within the allowable quality range involves the color compatibility of dyeing prescriptions, which is called dye compatibility (also known as dyeing compatibility). The compatibility of disperse dyes also has a certain relationship with the dyeing depth.
Disperse dyes used for dyeing fiber acetate are usually required to be colored at nearly 80°C. The coloring temperature of the dyes is too high or too low, which is not conducive to color matching.
When polyester is dyed under high temperature and high pressure, the dyeing properties of disperse dyes often change due to the addition of another dye. The general principle is to choose dyes with similar critical dyeing temperatures for color matching. In order to examine the compatibility of dyes, a series of small sample dyeing tests can be carried out under conditions similar to those of the dyeing production equipment. By changing the main process parameters such as prescription concentration, dye solution temperature and dyeing time, the color and light consistency of the dyed cloth samples can be compared. , grouping dyes with good dyeing compatibility into one category.
3) Reasonable selection of dye compatibility
When hot-melt dyeing polyester-cotton blended fabrics, the color-matching dyes must also have the same properties as single-color dyes. The hot melt temperature and time should be compatible with the fixation characteristics of the dye to ensure the highest color yield. Each single-color dye has a specific hot-melt fixation curve, which can be used as the basis for the preliminary selection of color-matching dyes. High-temperature disperse dyes usually cannot be matched with low-temperature disperse dyes because they require different hot melt temperatures. Medium-temperature dyes can match colors with high-temperature dyes and are compatible with low-temperature dyes. Reasonable color matching must consider the consistency between the performance and dye fastness of dyes. The result of arbitrary color matching is unstable color light and poor product color reproducibility.
It is generally believed that the shape of the hot-melt fixation curves of dyes is the same or similar. When two dyes with the same number of monochromatic diffusion layers on a polyester film are dyed together, the color light in each diffusion layer remains unchanged, which means that the two dyes have the same number of monochromatic diffusion layers. Dyes have good color matching compatibility with each other; on the contrary, the shapes of the hot-melt fixation curves of dyes are different (for example, one curve rises with the increase of temperature, and the other curve decreases with the increase of temperature). The single-color diffusion layer on the polyester film When two dyes with different numbers are dyed together, the color light in the diffusion layer is different, so it is not suitable to dye each other, but those with the same hue are not subject to this restriction.
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