4.7. Cationic dyes
Cationic dyes are modified basic dyes, they are used for dyeing poliacrilic fiber by different methods and for printing as well.
For the purpose of creating a wide range of colors, it is recommended using mixtures of cationic dyes. Compatibility factor is the va characterizing dye behavior in mixtures. In triple combinations variation the compatibility factor by 0,5 is allowed, in double combinations – by 1,5.
Dyeing by fast-fixing dyes
In general fiber ane carded ribbon are dyed by this method without using the leveling agents. While tinting with light and medium shades by fast-fixing dyes sulfuric acid (pH 3,5) or dyeing inhibitor (1-2 is added to the dye bath to provide even coloring.
Fig. 4.3. Dyeing of fiber and ribbon
By the pad-steaming method
The dyes with high fixation rate are used for dyeing by this method.
Optimum composition of the pad liquor (g/L) is:
Dye. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X
Thickening agent (indalka PR-90 or solvitosa OFA) . . . 4-6
Propylene carbonate or tanapal AWS . . . . . . . . . . . . . .10-20
Leveling agent A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Acetic acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pH 4,5
Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Y
After padding at temperature of 25-30°C the braid is wringed out г steamed in saturated steam at 102-103°C during 30-40 min or in high preheated steam at 110-120°C during 15-20 min. Washing is carried by the countercurrent flow in five boxes of washing machine at 60-65°C unionogenized detergent is added to the second box (5 g/l); antistatic agent is added to the fifth box.
Dyeing of newly-formed braid
While making the poliacrilic fiber, it leaves the setting bath in h swelled amorphous state and it can readily sorb the dye. It gives opportunity of dyeing the fiber within several seconds in warm dye bath, directly in the process of its manufacturing.
4.8. Disperse dyes
Disperse dyes have low solubility in water, but they can interact with the polyester chains by forming dispersed particles. Their main use is the dyeing of polyesters, and they find minor use dyeing cellulose acetates and polyamides. The general structure of disperse dyes is small, planar and non-ionic, with attached polar functional groups like -NO2 and -CN. The shape makes it easier for the dye to slide between the tightly-packed polymer chains, and the polar groups improve the water solubility, improve the dipolar bonding between dye and polymer and affect the color of the dye. However, their small size means that disperse dyes are quite volatile, and tend to sublime out of the polymer at sufficiently high temperatures.
The dye is generally applied under pressure, at temperatures of about 130oC. At this temperature, thermal agitation causes the polymer's structure to become looser and less crystalline, opening gaps for the dye molecules to enter. The interactions between dye and polymer are thought to be Van-der-Waals and dipole forces.
The volatility of the dye can cause loss of color density, and staining of other materials at high temperatures. This can be counteracted by using larger molecules or making the dye more polar (or both). This has a drawback, however, in that this new larger, more polar molecule will need more extreme forcing conditions to dye the polymer2. The most important class is the azo class. This class of azo disperse dyes may be further sub-divided into four groups, the most numerous of which is the aminoazobenzene class. This class of dye can be altered as mentioned before, to produce bathochromic shifts. A range of heterocyclic aminoazobenzene dyes are also available. These give bright dyes, and are bathochromically shifted to give blues. The third class of disperse dye is based on heterocyclic coupling components, which produce bright yellow dyes. The fourth class is disazo dyes. These tend to be quite simple in structure. Other than these, there are disperse dyes of the carbonyl class, and a few from the nitro and polymethine classes. Below is an example of a disperse dye. It is the same as the chime molecule at the top of the page.
Dyeing conditions
Material: a polyester fabric
Temperature, °С. . . . . . . . . . . . . . . . . . . . . . ..130
Time, min. . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
Bath Modulus. . . . . . . . . . . . . . . . . . . . . . . . . 1:40
Leveling agent, 1g/l. . . . . . . . . . . . . . . . . . . . . 1-2
PН . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4,5
After dyeing
Reducing agent. . . . . . . . . . . . . . . . . . . . . . . . X
Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Y