The theory holds that the selective absorption of different light by a substance will present various colors, and the color of the substance is the complementary color of the light wave it absorbs. The same is true of dyes. The color of dyes is also the complementary color of the color of the light waves they absorb.
In the molecular structure of dyes, there are chromophoric groups with wavelengths ranging from 380 to 780 nm. In addition, there are auxochromic groups that promote the chromophore groups, such as -NH2, -NR2, etc.
The synergistic effect of the chromophore group and the auxochrome group enables the dye to selectively absorb light waves. When certain groups in the structure produce color that is beneficial to the dye, the dye absorbs light waves in the direction of increasing the wavelength. Color theory calls this effect of increasing absorption wavelengths the dark color effect.
This theory is of great help to the research and development of dark dyes. For example, the dark effect on nylon and acetate fabrics is not ideal, and generally only light and medium colors can be dyed.
In the traditional process, acid and disperse dyes are used for dyeing. In order to obtain deep and strong colors, it is only necessary to increase the amount of dyes. The effect is not obvious, and the waste of dyes is very large. It has been reported abroad that the use of triazole disperse dyes to dye nylon fibers has obvious deepening effect, and the dyed fabrics have high fastness to washing and sunlight. The main method is to replace the hydrogen atom on the triazole ring with the thiomethyl group (CH3S-) of the dye structure, so that the absorption of the light wave by the dye moves to the long wave direction, thereby producing a dark color effect. Under the premise of dyeing, it can achieve a deeper dyeing effect than the original dye.
1. Surface color and reflection theory
This is the most widely used method for evaluating the color depth of dyed fabrics. Generally, the K/S value (KabelKamunk function value) is calculated at the maximum absorption wavelength (λmax) of the reflection or projection spectrum of the colored object, and this value is used to represent the relative depth of the color. Under the guidance of the theory, through the finishing technology of the fabric after dyeing, the microscopic result of the surface of the dyed fabric is changed, so that it produces a certain diffuse reflection to the light wave, so as to obtain a dark color effect.
2. Dyeing diffusion theory
Dyeing theory believes that to achieve a dark color effect on the dyed object, the key is to improve the dyeing rate of the dye on the fabric. Dyeing rate refers to the ratio of the amount of dye dyed on the fabric to the amount of dye put into the dyebath. Since this evaluation method for obtaining a dark color effect is very clear and the reflection result is obvious, it is always one of the primary considerations in the dyeing process in the dyeing process. Some studies on dark colors and dyeing of dark colors mostly start from improving the dyeing rate of fabrics, which has guiding significance for actual production.