Hard water is the enemy of dissolving direct dyes! Softened water must be used or a water softener (0.5-2 g/L sodium hexametaphosphate or EDTA) must be added. Hard water can cause dye precipitation, color change, reduced color yield and uneven dyeing.
Slurry mixing:
This is the key to the success of dissolution! Always use a small amount of cold water to make the dry powder into a uniform, particle-free slurry before diluting. Directly sprinkling the dry powder into a large amount of water will easily cause lumps and it will be extremely difficult to disperse and dissolve.
Temperature:
Dissolution temperature: Warm water (40-60°C) is usually sufficient. Avoid unnecessary long-term high-temperature boiling.
Dye stability: Understand the heat resistance of the specific dye and avoid exceeding its tolerance temperature.
Stirring:
Continuous and sufficient stirring during slurry mixing, dilution and heating is necessary to ensure uniform dissolution and prevent lumps and precipitation.
Concentration:
The solubility of dyes is limited (although usually high). When preparing a very concentrated solution (such as storing a mother liquor), it is necessary to confirm whether the dye can be completely dissolved at the required temperature at this concentration to avoid precipitation after cooling due to oversaturation.
Solvent:
For individual direct dyes with low solubility or that require the preparation of a high-concentration mother liquor, a small amount of solvent can be added to help dissolve. Commonly used ones are:
Urea:
The effect is significant, and the common dosage is 5-20 g/L.
Surfactant: Such as Perchlorate O (fatty alcohol polyoxyethylene ether), which can help disperse and solubilize, with a dosage of 0.1-0.5 g/L.
Stability after dissolution:
Completely dissolved dyes can usually be stored stably for a period of time (several hours to a day) at room temperature, but long-term storage (especially when the temperature changes greatly) may cause some dyes to aggregate or hydrolyze. It is recommended to prepare and use it now. If storage is required, it should be sealed, protected from light, and avoid drastic temperature fluctuations. Recheck the dissolution state before use and heat and stir appropriately.
Addition order:
When adding the dye solution to the dye bath, it should be added slowly under good stirring to avoid excessive local concentration. The dye bath usually contains electrolytes (such as sodium sulfate/salt) to promote dyeing. After the dye solution is added, it needs to be stirred evenly before starting to heat up the dyeing process.
