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Views: 0 Author: Site Editor Publish Time: 2025-02-28 Origin: Site
Water is indispensable in the process of fabric printing and dyeing. In addition to dyes, water quality becomes one of the key factors affecting dyeing. Anyone who knows a little about water will know that water in nature can be divided into soft and hard. Soft water refers to water that contains no or a small amount of calcium, magnesium, and iron ions. On the contrary, it is called hard water. Hard water is divided into temporary hard water and permanent hard water.
(1) Temporary hard water: The hardness component of water. If it is caused by sodium bicarbonate or magnesium bicarbonate, it is temporary hard water (when boiling temporary hard water, the decomposed sodium bicarbonate generates insoluble carbonates and precipitates, and the water changes from hard water to soft water).
(2) Permanent hard water: If it is caused by sulfates or chlorides containing calcium and magnesium, it is permanent hard water and cannot be removed after boiling.
The above two types of hardness are collectively called total hardness, which are roughly divided according to the total hardness value of water:
Total hardness of 0-30ppm is called soft water, total hardness of more than 60ppm is called hard water, high-quality drinking water does not exceed 25ppm, and the total hardness of high-quality soft water is below 10ppm.
In natural water, unpolluted rainwater and snow water far away from cities are soft water; spring water, stream water, river water, and reservoir water are mostly temporary hard water, and some groundwater is high-hardness water.
When water droplets condense in the atmosphere, they dissolve carbon dioxide in the air to form carbonic acid. Carbonic acid eventually falls to the ground with rainwater, then seeps through the soil to the rock layer, dissolving lime (calcium carbonate and magnesium carbonate) to produce temporary hard water. This is how hard water is formed in caves and near caves in some areas.
The water used in printing and dyeing factories has different water quality due to different water sources. The water quality hardness in southern my country is lower, while the water quality hardness in northern China is higher. Generally, printing and dyeing factories use natural surface water or groundwater and tap water.
Untreated natural water contains various chemical substances, mainly calcium, magnesium, iron, sodium, carbonate, sulfate, chloride, which will have a great impact on textile dyeing.
The quality of textile printing and dyeing also has certain requirements relative to water quality. The consequences of hard water: it will affect the bleaching effect, uneven dyeing, poor fabric feel, and yellowing of fabrics. Adding water softeners requires increasing the amount of caustic soda and other additives.
Calcium and magnesium, which are difficult to dissolve in water, will precipitate on the fabric, form scale in alkaline solutions, and adhere to equipment to hinder production. When the iron and manganese salts in the water exceed the standard, rust spots are easily produced during scouring and catalytic oxidation of cotton fibers. When bleaching with oxidants, iron, manganese, and salts also catalyze the decomposition of bleaching agents.
The factors that affect the quality of dyeing in water include: chromaticity, pH value, iron ion content, calcium ion content, etc. When using reactive dyes for dyeing, the impact of water hardness is not significant, but when using acid dyes for dyeing nylon, the impact of water hardness is more prominent. Too hard water not only makes the color of the fabric poor, but the CI in the water also has a great impact on dyeing.
The suspended matter in hard water affects the bleaching whiteness of the fabric. When dyeing cheese yarn, it is easy to reduce the color brightness of the inner and outer layers of the cheese yarn. High water pH value will affect the levelness of light-colored fabrics, because under alkaline conditions, the added dyes will be fixed, resulting in poor levelness and dyeing.
If the water pH value is too high, the dye will be hydrolyzed in the soap washing process, with poor reproducibility, and the pH value of the cloth surface will exceed the standard in the over-softening process. Excessive iron ions will cause color spots, color flowers, and dull color. Excessive manganese ions are the main cause of yellowing of bleached fabrics.
Hard water quality affects the color brightness, causes scaling of the heat exchanger, and causes large energy loss. It will also cause alkaline spots due to insoluble precipitates generated by calcium and magnesium ions and soda ash.
In the process of fabric printing and dyeing, metal ions such as calcium, magnesium, iron, and manganese in hard water, as well as high pH values and suspended solids, can lead to uneven dyeing, dull color, yellowing of fabrics, equipment scaling, and energy loss. In response to this industry pain point, dispersing chelating agents have become an efficient and environmentally friendly solution. Its mechanism of action and advantages are as follows:
Dispersing chelating agents can strongly complex metal ions such as calcium, magnesium, iron, and manganese in water to prevent them from reacting with dyes or auxiliaries to form insoluble precipitates (such as scale and color spots). For example:
In reactive dyeing, reduce the alkaline spots generated by calcium and magnesium ions and soda ash;
When dyeing nylon with acid dyes, avoid the color loss and color flower problems caused by hard water;
Inhibit the decomposition of bleach catalyzed by iron/manganese ions to prevent bleached fabrics from yellowing or rusting.
By adjusting the pH of water to neutral or weakly acidic range, dispersing chelating agents can improve level dyeing and reduce the problem of premature fixation or hydrolysis of dyes caused by alkaline conditions, which is especially important for the color consistency and reproducibility of light-colored fabrics.
Chelating agents can effectively prevent calcium and magnesium salts from scaling on the inner wall of heat exchangers, pipes and dyeing tanks, reduce heat loss and equipment maintenance costs, and prevent insoluble precipitates from adhering to the surface of fabrics and affecting the feel.
By removing the interference of metal ions on dyes, dispersing chelating agents can significantly improve the color fastness, brightness and whiteness of dyed fabrics, especially reducing the color difference between the inner and outer layers in cheese dyeing.
Desizing/scouring process: pre-soften water quality and reduce the oxidative damage of metal ions to fibers;
Bleaching process: inhibit the excessive decomposition of bleaching agents catalyzed by iron/manganese ions to ensure whiteness stability;
Dyeing and soaping: optimize dye uptake, prevent hydrolysis and secondary contamination;
Wastewater treatment: reduce the content of metal ions in wastewater and help meet environmental protection standards.
High efficiency: low addition amount can achieve hard water softening (total hardness ≤ 10ppm), reduce the amount of auxiliaries such as water softeners and caustic soda;
Environmental compatibility: suitable for all kinds of dyes (active, acidic, direct dyes), and does not contain phosphorus and heavy metals, in line with green production standards;
Economic efficiency: extend equipment life, reduce energy consumption and sewage costs, and comprehensively improve printing and dyeing quality and efficiency.
By scientifically adding dispersing chelating agents, printing and dyeing companies can systematically solve process defects caused by water quality, achieve quality control from source to finished product, and respond to the sustainable development needs of the industry.
