A Dielectric application

A-l Applied amount of dielectric

After testing, most medium-temperature reactive dyes dye dark colors, and the maximum amount of dielectric should be < 70 g/L. For some reactive dyes with strong personality, such as reactive green blue BGFN dyeing dark colors, the maximum amount of dielectric must be < 60g/L, and reactive brilliant blue KN-R dyeing dark colors, the maximum amount of dielectric must be < 40g/L. The reason is that if the amount of dielectric is too high, the actual color gain depth will not increase much, but in the early stage of alkali color fixation, the mixing concentration of salt and alkali (soda ash is also a dielectric) will be too high, resulting in the degree of "agglomeration" of the dye and The degree of "sudden dyeing" is too large, which will have a negative impact on the dyeing quality (especially the leveling effect and wet fastness of dyeing).

A-2 Application method of dielectric

The most worth mentioning here is that during rope dyeing (jet overflow machine dyeing, air flow machine dyeing), the dielectric must be added first, and the dye must be added later (the order of addition is opposite to that of jigger dyeing). The reason is that according to the traditional method, the dye is added first, and the dielectric medium is dissolved in the reflux water containing the dye. The dye will immediately flocculate and precipitate in the saturated solution of the dielectric, and it will be pressed into the cylinder and adhere to the fabric, which is very easy to cause discoloration. Spots and stains. And first add the dielectric, and use the reflux water containing the dielectric to dissolve and dilute the pre-mixed dye, then the dye will not cause harmful "coagulation" or precipitation (after testing, the commonly used medium-temperature reactive dyes are neutral in the dielectric < 80g/L bath, good solvent stability).

B Application of alkaline agent

B-l Application amount of soda ash

After testing, the commonly used medium-temperature reactive dyes for cotton dyeing have an optimal pH value of 10.5-11.0 for color fixation (12 for dyeing at 60°C and 11 for dyeing at 80°C).

B-2 Application method of soda ash

The application of alkali agent must follow the following two principles:

First, the addition of soda ash must be based on "balanced and uniform color absorption". That is to say, the alkaline agent can be added only after the neutral salt bath (color-absorbing bath) has truly reached the balance of color absorption and achieved uniform color absorption through dye transfer.

This is because:

① After the color absorption balance is reached, the concentration of the residual dye solution is the lowest, and the lower the concentration of the dye solution, the smaller the aggregation tendency of the dye after adding the alkali agent, the milder the secondary color absorption rate, and the better the level dyeing effect and color fastness.

② After the alkali agent is added, the dye on the fiber will lose its ability to migrate due to fixation. This can turn any unevenness created during the absorbing stage into a permanent blemish.

The second is that the application of alkali agent must be "first less and then more, adding in stages". Because the faster the alkali agent (soda ash) is added, the stronger the alkalinity of the color-fixing bath and the higher the concentration of salt-alkali mixture, the more intense the aggregation and coloring behavior of the dye, and the easier it is to cause dyeing quality problems. Practice has proved that the alkalinity of the color-fixing bath increases from weak to strong, the concentration of salt-alkali mixture from low to high, and the dyeing concentration from thick to light, which can effectively alleviate the excessive behavior of dyes caused by the addition of alkali agents and ensure uniform coloring of dyes , fully fixed, thus effectively improving the wet rubbing fastness of dyeing