Five main properties of disperse dyes:

Lifting power, covering power, dispersion stability, PH sensitivity, compatibility.

1. Lifting power
1. The definition of lifting power:
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 is gradually increased, and the degree of color depth on the fabric (or yarn) increases accordingly. For dyes with good lifting power, the depth of dyeing increases according to the proportion of the amount of dye, indicating that there is better deep dyeing; dyes with poor lifting power have poor deep dyeing. When reaching a certain depth, the color will no longer deepen as the amount of dye increases.
2. The effect of lifting power on dyeing:
The lifting power of disperse dyes varies greatly among specific varieties. Dyes with high lifting power should be used for deep and thick colors, and dyes with low lifting rate can be used for bright light and light colors. Only by mastering the characteristics of dyes and using them reasonably can the effect of saving dyes and reducing costs can be achieved.
3. Lifting test:
The dye lifting power of high temperature and high pressure dyeing is expressed in %. Under the 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 small sample machine of high temperature and high pressure. The dye lifting power of hot melt pad dyeing or textile printing is expressed in g/L.
In terms of actual production, the lifting power of the dye is the change in the concentration of the dye solution, that is, the change in the shade of the finished product relative to the dyed product. This change can not only be unpredictable, but also can accurately measure the color depth value with the aid of an instrument, and then calculate the lifting force curve of the disperse dye through the color depth formula.
2. Covering power

1. What is the covering power of the dye?

Just like the concealment of dead cotton by reactive dyes or vat dyes when dyeing cotton, the concealment of disperse dyes on poor quality polyester is called coverage here. Polyester (or acetate fiber) filament fabrics, including knitwear, often have color shading after they are piece-dyed with disperse dyes. There are many reasons for the color profile, some are weaving defects, and some are exposed after dyeing because of the difference in fiber quality.

2. Coverage test:

Choosing low-quality polyester filament fabrics, dyeing with disperse dyes of different colors and varieties under the same dyeing conditions, different situations will occur. Some color grades are serious and some are not obvious, which reflects that the disperse dyes have different color grades. Degree of coverage. According to the gray standard, grade 1 with serious color difference and grade 5 without color difference.

The covering power of disperse dyes on the color file is determined by the dye structure itself. Most dyes with high initial dyeing rate, slow diffusion and poor migration have poor coverage on the color file. Covering power is also related to sublimation fastness.

3. Inspection of dyeing performance of polyester filament:

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. Dyeability quality inspection of polyester filaments is usually done with the typical poor covering dye Eastman Fast Blue GLF (CI Disperse Blue 27), dyeing depth 1%, boiling at 95～100℃ for 30 minutes, washing and drying according to the degree of color difference Rating grading.

4. Prevention in production:

In order to prevent the occurrence of color shading in actual production, the first step is to strengthen the management of the quality of polyester fiber raw materials. The weaving mill must use up the surplus yarn before changing the product. For the known poor quality raw material, disperse dyes with good covering power can be selected to avoid mass degradation of the finished product.

3. Dispersion stability

1. Dispersion stability of disperse dyes:

Disperse dyes are poured into water and then dispersed into fine particles. The particle size distribution is expanded according to the binomial formula, with an average value of 0.5 to 1 micron. The particle size of high-quality commercial dyes is very close, and there is a high percentage, which can be indicated by the particle size distribution curve. Dyes with poor particle size distribution have coarse particles of different sizes and poor dispersion stability. If the particle size greatly exceeds the average range, recrystallization of tiny particles may occur. Due to the increase of large recrystallized particles, the dyes are precipitated and deposited on the walls of the dyeing machine or on the fibers.

In order to make the fine 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 the dispersant, which prevents the dyes from getting close to each other, preventing mutual aggregation or agglomeration. The charge repulsion of the anion helps stabilize the dispersion. Commonly used anionic dispersants include natural lignosulfonates or synthetic naphthalene sulfonic acid dispersants: there are also non-ionic dispersants, most of which are alkylphenol polyoxyethylene derivatives, which are specially used for synthetic paste printing.

2. Factors affecting the dispersion stability of disperse dyes:

Impurities in the original dye may adversely affect the dispersion state. The change of dye crystal is also an important factor. Some crystal states are easy to disperse, while others are not easy. During the dyeing process, the crystal state of the dye sometimes changes.

When the dye is dispersed in the aqueous solution, due to the influence of external factors, the stable state of the dispersion is destroyed, which may cause the phenomenon of dye crystal 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 by stirring, while the flocculated dye is a dispersion that cannot be restored to stability. The consequences caused by the flocculation of dye particles include: color spots, slower coloring, lower color yield, uneven dyeing, and staining tank fouling.

The factors that cause the instability of the dye liquor dispersion are roughly as follows: poor dye quality, high dye liquor temperature, too long time, too fast pump speed, low pH value, improper auxiliaries, and dirty fabrics.

3. Test of dispersion stability:

A. Filter paper method:
With 10 g/L disperse dye solution, add acetic acid to adjust the pH value. Take 500 ml and filter with #2 filter paper on a porcelain funnel to observe the particle fineness. Take another 400 ml in a high temperature and high pressure dyeing machine for a blank test, heat it to 130°C, keep it warm for 1 hour, cool it down, and filter it with filter paper to compare the changes in dye particle fineness. After the dye liquor heated at high temperature is filtered, there are no color spots on the paper, indicating that the dispersion stability is good.

B. Colour pet method:
Dye concentration 2.5% (weight to polyester), bath ratio 1:30, add 1 ml of 10% ammonium sulfate, adjust to pH 5 with 1% acetic acid, take 10 grams of polyester knitted fabric, roll it on the porous wall, and circulate inside and outside the dye solution In the high-temperature and high-pressure dyeing small sample machine, the temperature is increased to 130°C at 80°C, kept for 10 minutes, cooled to 100°C, washed and dried in water, and observed whether there are dye condensed color spots on the fabric.

Fourth, pH sensitivity

1. What is pH sensitivity?

There are many varieties of disperse dyes, wide chromatograms, and very different sensitivity to pH. Dyeing solutions with different pH values ​​often result in different dyeing results, affecting the color depth, and even causing serious color changes. In a weakly acidic medium (pH4.5～5.5), disperse dyes are in the most stable state.

The pH values ​​of commercial dye solutions are not the same, some are neutral, and some are slightly alkaline. Before dyeing, adjust to the specified pH with acetic acid. During the dyeing process, sometimes the pH value of the dye solution will gradually increase. If necessary, formic acid and ammonium sulfate can be added to keep the dye solution in a weak acid 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 of the disperse dyes with ester groups, cyano groups or amide groups will be affected by alkaline hydrolysis, which will affect the normal shade. Some varieties can be dyed in the same bath with direct dyes or pad dyed in the same bath with reactive dyes even if they are dyed at high temperature under neutral or weak alkaline conditions without color change.

When printing colorants need to use disperse dyes and reactive dyes to print at the same size, only alkali-stable dyes can be used to avoid the influence of baking soda or soda ash on the shade. Pay special attention to color matching. It is necessary to pass a test before changing the dye variety, and find out the range of pH stability of the dye.
5. Compatibility

1. Definition of compatibility:

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 before and after batches. How to control the color difference between batches of dyed finished products within the allowable range of quality? This is the same question involving the color matching compatibility of dyeing prescriptions, which is called dye compatibility (also known as dyeing compatibility). The compatibility of disperse dyes is also related to the depth of dyeing.

The disperse dyes used for dyeing of cellulose 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. Compatibility test:

When polyester is dyed at high temperature and high pressure, the dyeing characteristics of disperse dyes are often changed due to the incorporation of another dye. The general principle is to select dyes with similar critical dyeing temperatures for color matching. In order to investigate the compatibility of dyestuffs, a series of small sample dyeing tests can be done under conditions similar to the dyeing production equipment, and the main process parameters such as the concentration of the recipe, the temperature of the dyeing solution and the dyeing time are changed to compare the color and light consistency of the dyed fabric samples. , Put the dyes with better dyeing compatibility into one category.

3. How to choose the compatibility of dyes reasonably?

When polyester-cotton blended fabrics are dyed in hot melt, the color matching dyes must also have the same properties as the monochromatic dyes. The melting temperature and time should be compatible with the fixing 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 type disperse dyes usually cannot match colors with low-temperature type, because they require different melting temperatures. Moderate temperature dyes can not only match colors with high temperature dyes, but also have compatibility with low temperature dyes. Reasonable color matching must consider the consistency between the properties of dyes and the color fastness. The result of arbitrary color matching is that the shade is unstable and the color reproducibility of the product is not good.

It is generally believed that the shape of the hot-melt fixing curve of the dyes is the same or similar, and the number of monochromatic diffusion layers on the polyester film is also the same. When two dyes are dyed together, the color light in each diffusion layer remains unchanged, indicating that the two The dyes have good compatibility with each other in color matching; on the contrary, the shape of the hot-melt fixation curve of the dye is different (for example, one curve rises with the increase of temperature, and the other curve decreases with the increase of temperature), the monochromatic diffusion layer on the polyester film When two dyes with different numbers are dyed together, the shades in the diffusion layer are different, so it is not suitable for each other to match colors, but the same hue is not subject to this restriction. Take a chestnut: Disperse dark blue HGL and disperse red 3B or disperse yellow RGFL have completely different hot-melt fixation curves, and the number of diffusion layers on the polyester film is quite different, and they cannot match colors. Since Disperse Red M-BL and Disperse Red 3B have similar hues, they can still be used in color matching even though their hot-melt properties are inconsistent.