After testing, most medium-temperature reactive dyes are dyed in dark colors, and the maximum amount of electrolyte should be less than 70g/L; for some reactive dyes with strong personality, such as reactive turquoise blue BGFN for dark colors, the maximum amount of electrolyte must be<60g/L; Reactive brilliant blue KN-R is dyed dark, the maximum amount of electrolyte must be <40g/L. The reason is that if the amount of electrolyte is too high, the color depth is actually not improved much, but in the initial stage of adding alkali to fix the color, the mixed concentration of salt and alkali (sodium ash is also electrolyte) will be too high, resulting in the "aggregation" of the dye. The degree of "sudden dyeing" is too large, which will negatively affect the dyeing quality.
The most worth mentioning here is that in rope dyeing (jet overflow machine dyeing, airflow machine dyeing), the electrolyte must be added first and the dye must be added later (the order of addition is the opposite of jig dyeing). The reason is that, according to the traditional method, the dye is added first, and the electrolyte is dissolved in the dye-containing reflux water. The dye will flocculate and precipitate immediately in the saturated solution of the electrolyte, and it will adhere to the fabric in the tank, which will easily cause color spots and stains. Stained. Add electrolyte first, and use the electrolyte-containing reflux water to dissolve and dilute the pre-mixed dye, then the dye will not "agglomerate" or precipitate (after testing, the commonly used medium-temperature reactive dye is used in a neutral bath with an electrolyte of<80g/L Medium, good solubility stability.)
After testing, the most commonly used medium-temperature reactive dyes for dyeing cotton have the best fixing pH value of 10.5-11.0 (reactive turquoise blue dyeing at 60℃ is 12.0, 80℃ dyeing is 11.0). Lianyungang powdered light soda ash is commonly used 5～25g/L, pH=10.65～10.99, and its pH buffering capacity is great. Therefore, 5-20g/L of soda ash is sufficient according to the depth of dyeing. If the amount is too much, the color depth will not increase significantly, but it will reduce the solubility stability of the dye in the salt-alkali fixation bath and harm the dyeing quality.
Practice has proved that the application of alkaline agents must follow the following two principles:
First, the addition of soda ash must be based on "balanced color absorption and uniform color absorption". That is to say, only in the neutral salt bath (color absorption bath), the color absorption balance is truly achieved and the color absorption is uniform after dyeing before the alkali agent can be added. This is because the residual dye solution concentration is the lowest after the absorption balance is reached, and the lower the dye solution concentration, the less the dye's aggregation tendency after the alkali agent is added, the milder the secondary color absorption rate, and the lower the probability of dye defects. After the alkali agent is added, the dye on the fiber will be fixed and lose the ability to dye migration. This will make the non-uniformity produced in the absorption stage become permanent defects.
The second is that the application of the alkaline agent must be "first less and then more, adding in portions". Because the faster the alkali agent (soda ash) is added, the stronger the alkalinity of the fixing bath is, and the higher the salt-alkali mixing concentration is. The more intense the aggregation behavior and coloring behavior of the dye, the more likely it is to produce dyeing quality problems. Practice has proved that the alkalinity of the fixing bath increases from weak to strong, the mixed concentration of salt and alkali increases from low to high, and the concentration of dye liquor decreases from thick to light, which can effectively alleviate the excessive behavior of dyes due to the addition of alkali agents, thereby ensuring the quality of dyeing Achieve stability.