Water Hardness
It is generally acknowledged that water hardness below 50 ppm exerts no adverse effects, and water with a hardness of 20 ppm is considered excellent.
Such water quality is sufficient for cheese dyeing, yet the concentrations of copper and iron ions in water must be closely monitored.
A hardness level below 50 ppm is ideal for reactive dyeing. The critical factor lies in metal ion content, especially iron ions, which alter shade tones. Conductivity testing of water is recommended.
When wastewater that meets discharge standards is recycled for bleaching and dyeing, uneven dyeing (speckled fabrics) frequently occurs primarily due to excessive water conductivity. Operators should prioritize monitoring the conductivity of recycled bleaching and dyeing wastewater. Conventional wastewater treatment processes cannot effectively remove metal ions that drive high conductivity; treatment via reverse osmosis membranes is mandatory for their elimination.
Excessively hard water leads to limescale buildup on boiler walls. Calcium and magnesium ions in hard water cause soap precipitation, resulting in uneven dyeing, poor fabric hand feel, and fabric yellowing. Hard water also deactivates desizing enzymes, reduces the solubility of sizing agents, and causes incompatibility with chemicals in finishing formulations.
Treatment options include adding EDTA or sodium tripolyphosphate at a dosage of 2 g/L. A superior alternative is to purchase specialized metal ion sequestering agents. Undertreated dyeing water or thick fabrics carrying inherent metal ions commonly trigger uneven dyeing defects. Therefore, chelating dispersants are added during dyeing to offset metal ion interference and enhance washing-off efficiency.
However, chelating dispersants such as EDTA (Ethylenediaminetetraacetic acid), DTPA, NTA, phosphates and gluconates may strip metal ions from dyes, lowering light fastness and triggering discoloration. For this reason, industry practitioners recommend polyphosphate and polyhydroxycarboxylic acid-based chelating dispersants instead.
Practical Case
A factory currently uses untreated groundwater (without softening or filtration) for cotton cheese dyeing. Previously, a visible layer of sludge scale formed on the inner layers of dyed cheese yarn. Minor improvements were achieved by adding a small dose of bleaching powder to the water, yet persistent defects remain: stiff hand feel, dull and pale shade on the inner layers of cheese yarn. Adjustments to forward/reverse rotation and additional softening agents yielded minimal improvement. Further inspection revealed layer-to-layer shade discrepancies arising from pre-scouring processes, with water hardness measured at approximately 130 ppm.
Root Cause
Excessively hard groundwater laden with abundant impurities stains the inner yarn layers of cheese packages. The optimal solution involves pumping groundwater to holding tanks for sedimentation, followed by water softening and fine filtration. This process eliminates the defects, albeit with relatively high upfront investment costs.
Impurities & Microorganisms
Cationic softener working baths become unstable in river water. They flocculate with aquatic microorganisms to form yellow flocculent deposits that adhere to fabrics. After drying and heat setting, these deposits leave permanent yellow spots on textiles. This explains why quality issues surge from May to June, when water temperatures favor algae proliferation, while such defects rarely emerge in autumn and winter.
Water quality strongly impacts the stability of diluted softener baths and the whiteness of finished soft-treated fabrics. Printing and dyeing plants are therefore advised to utilize fully treated process water in production.
Some manufacturers still encounter yellow spot defects even with activated carbon filtered water, as microorganisms are microscopic and cannot be fully adsorbed or filtered out by activated carbon. To boost treatment efficiency, cationic surfactants are dosed into pre-filtration sedimentation tanks to flocculate microorganisms prior to activated carbon filtration. In addition, activated carbon filters require regular cleaning or replacement.
If the above measures fail to eradicate quality defects, plants are advised to switch to nonionic or anionic softeners during algae bloom seasons, or blend nonionic softeners with silicone oil for hand feel finishing.
Factories suffering severe yellow spot issues reported zero such defects when applying amino silicone oil finishing.
Winter also presents challenges for printing and dyeing facilities, as raw water quality tends to degrade during cold months.
pH Value
For reactive dyeing, a pH range of 7–9 produces consistent fabric color difference, indicating minimal impact within this window. Trace alkali does not alter or destroy the chromophoric groups of reactive dye molecules.
At pH 8.5, fabric soaping fastness and wet rubbing fastness only reach Grade 3, failing customer specifications. Further pH elevation degrades color fastness, proving elevated alkalinity in water impairs dyeing performance.
Recycled wastewater treatment plants generally require influent pH <9 to sustain normal microbial activity without alkali-induced damage to treatment systems. The standard for recycled process water stipulates a pH value close to 7 (original text “落 85″ presumed typo for ≤8.5).
Salinity
Sodium sulfate constitutes the primary salt in water recycling systems, originating from two sources:
- Addition as a dye accelerating agent during exhaustion processes;
- Caustic soda and soda ash dosed in scouring, bleaching and fixation stages, neutralized with sulfuric acid to form sodium sulfate.
The threshold salinity limit for recycling systems is 924 mg/L, which does not compromise fabric dyeing quality.
Iron Ions
Iron ions in pre-treatment water accelerate hydrogen peroxide decomposition and aggregation, creating pinholes on fabric surfaces.
Iron ions dull dyed fabrics and trigger speckling defects. For removal reference: concentrations below 15 ppm pose no risks; chelating agents can be added for slightly elevated iron levels.
Chloride Ions
Pure chloride ions do not interfere with reactive dyeing (sodium chloride is widely used as a dye accelerant). However, chloride corrodes dye vats, dependent on the chlorine resistance grade of the vat steel material.
Tap water contains free chlorine from disinfection and bleaching. If free chlorine concentrations exceed threshold limits, it will degrade dye colorants.
Clarification of definite & pending information
- Definite information: All technical parameters (hardness threshold, conductivity issue, pH range, salinity limit, ion hazards), chemical names, process defects, treatment methods, factory case phenomenon translation are fully confirmed based on textile dyeing industry standard terminology.
- Pending information: The original text “pH 值落 85″ is inferred as a typo of “≤8.5″, without access to the factory’s official water quality standard document to verify the exact standard figure.
Post time: Jun-29-2026