Dyes are substances that can attach a certain color to fibers and prevent them from falling off or changing color. Dyes are usually soluble in water, and some dyes require a mordant to allow the dye to adhere to the fiber. Early human dyes were obtained directly from plants, animals and minerals.
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 carboxyl groups; amino, nitro and other weak polar groups, and is a non-ionic dye with very low water activity. Let’s talk about the five major dyeing properties of disperse dyes:
Lifting power
1. Definition:
Lifting power is one of the important properties of disperse dyes. This characteristic indicates that when each dye is used for dyeing or printing, the amount of dye gradually increases, and the depth of color on the fabric (or yarn) increases accordingly. 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.
3. Test:
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. This change can be unpredictable, or the color depth value can be accurately measured with the help of instruments, and then the lifting force curve of disperse dyes can be obtained by calculating the color depth formula.
coverage
1. What is the covering power of dye?
Just like the coverage of dead cotton by reactive dyes or vat dyes when dyeing cotton, the coverage of disperse dyes on poor quality polyester is here 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.
2. Coverage test:
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.
The coverage of color stops by disperse dyes depends on the dye structure itself. Most varieties of dyes with high initial dyeing rate, slow diffusion and poor migration have poor coverage of color stops. There is also a certain relationship between covering power and sublimation fastness.
3. Inspection of polyester filament dyeing performance:
On the contrary, disperse dyes with poor covering power can be used to detect the quality of polyester fibers. Unstable fiber manufacturing processes, including changes in drafting and setting parameters, will cause inconsistencies in fiber affinity. To test the dyeability and quality of polyester filament, a typical dye with poor coverage, Eastman Fast Blue GLF (C.I. Disperse Blue 27), is usually used. The dyeing depth is 1% and boiled and dyed at 95-100°C for 30 minutes. After washing and drying, the color difference is determined according to the degree of color difference. Rating scale.
4. Prevention during production:
In order to prevent the occurrence of color blemishes in actual production, the first step is to strengthen the quality management of polyester fiber raw materials. The weaving mill must use up the remaining yarn before changing products. For raw materials that are known to be of poor quality, disperse dyes with good coverage can be selected to avoid downgrading the finished product in large quantities.
Dispersion stability
1. Dispersion stability:
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 fibers.
In order to make the tiny particles of dye into a stable water dispersion, there must be a sufficient concentration of boiling dye dispersant in the water. The dye particles are surrounded by a dispersant, which prevents the dyes from getting close to each other and preventing them from aggregating with each other or clumping into clumps. The charge repulsion of the anions contributes to the stability of the dispersion. Commonly used anionic dispersants include natural lignin sulfonates or synthetic naphthalene sulfonic acid dispersants: there are also nonionic dispersants, most of which are alkylphenol polyoxyethylene derivatives, specially used for synthetic paste printing.
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.
The dye is dispersed in the aqueous solution. Due to the influence of external factors, the stable state of dispersion is destroyed.��It may cause dye crystallization to increase, particle aggregation and flocculation.
The difference between aggregation and flocculation is that the former can disappear again, is reversible, and can be dispersed again through stirring, while the flocculated dye cannot return to a stable dispersion. The consequences caused by the flocculation of dye particles include: color spots, slowed down coloring, reduced color yield, uneven dyeing, fouling in the dyeing tank, etc.
The factors that cause the dye liquor dispersion to be unstable include: poor dye quality, high dye liquor temperature, too long time, too fast pump speed, low pH value, improper additives, dirty fabrics, etc.
3. Test of dispersion stability:
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 #2 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.
pH sensitivity
1. What is pH sensitivity?
There are many varieties of disperse dyes with wide chromatograms, 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 a 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.
2. The influence of dye structure on pH sensitivity:
Some disperse dyes with azo structure are very sensitive to alkali and are not resistant to reduction. Most disperse dyes with ester, cyano or amide groups will be hydrolyzed by alkali and affect the normal color light. There are also some varieties that have no color change even when dyed at high temperatures under neutral or weakly alkaline conditions. They can be dyed in the same bath with direct dyes or pad-dyed in the same bath with reactive dyes.
When the printing paste needs to be printed with disperse dyes and reactive dyes at the same paste, only dyes that are stable to alkali can be used so that the color will not be affected by the effects of baking soda or soda ash. Pay special attention to the color matching. Before changing the dye type, you must pass the test and find out the stable pH range of the dye.
Compatibility
1. Definition:
In mass 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. How to control the color difference between batches of dyed finished products within the allowable quality range is a problem involving 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.
2. Test:
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. How to reasonably choose 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 high color yield. Each single-color dye has a specific hot-melt fixation curve, which can be used as a 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 and light, and the reproducibility of product color is poor.
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 does not change, which means that the two dyes have the same color. 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. For example: the shapes of the hot melt solid color curves of dispersed dark blue HGL and dispersed red 3B or dispersed yellow RGFL are completely different. The number of diffusion layers on the polyester film is also quite different, and they cannot be mutually exclusive.Color blocking. Since Disperse Red M-BL and Disperse Red 3B have similar hues, although their hot-melt properties are inconsistent, they can still be used for color matching. Extended reading: https://www.china-fire-retardant.com/post/9577.html
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