With the widespread application of digital inkjet technology, water-based inks—thanks to their environmental friendliness and controllable cost—have become key consumables in many fields such as textile printing, packaging printing, and advertising graphics. A thorough understanding of their characteristics and proper usage practices is essential to ensure stable operation of inkjet systems and to achieve high print quality.
This article provides a detailed explanation from two perspectives: ink characteristics and usage precautions.
I. Characteristics of Water-Based Inks in Digital Inkjet Systems
Water-based inks use water as the primary solvent (typically 50–80%), combined with water-soluble resins, pigments or dyes, and functional additives (such as humectants, defoamers, and pH regulators). Their characteristics can be analyzed from three dimensions: physicochemical properties, application compatibility, and environmental & safety performance.
(I) Physicochemical Characteristics
1. Low Viscosity and High Fluidity
To accommodate the precision printheads used in digital inkjet systems—especially piezoelectric printheads—water-based inks typically have viscosities controlled within 5–20 mPa·s at 25 °C, significantly lower than solvent-based inks.
This low viscosity allows inks to pass smoothly through micro-nozzles (usually 10–50 μm in diameter), forming uniform droplets and reducing the risk of nozzle clogging. However, excessively low viscosity may cause ink misting or overspray during printing, which must be balanced through additive formulation.
2. Relatively High Surface Tension and Wettability
Water has a high surface tension (~72 mN/m), so water-based inks typically exhibit surface tensions in the range of 30–50 mN/m.
This enables good spreading and film formation on hydrophilic substrates such as paper and cotton fabrics. However, on hydrophobic substrates (e.g., plastics or metals), edge shrinkage or poor wetting may occur unless surface pretreatment (coatings, corona treatment) or specially modified water-based inks are used.
3. Controlled Volatility
Since water is the primary solvent, evaporation is highly influenced by ambient temperature and humidity. To prevent nozzle drying and clogging caused by rapid water loss, humectants such as glycerol or propylene glycol are added.
Under typical conditions (20–25 °C, 40–60% RH), the evaporation rate is approximately 0.1–0.3 g/(h·cm²)—fast enough for drying after printing while preventing ink solidification inside the printhead.
4. pH Stability
Most water-based inks are maintained at a weakly alkaline pH of 7.5–9.5, which improves resin solubility and pigment dispersion while preventing corrosion of printhead metal components (e.g., stainless-steel nozzles, piezoelectric ceramics).
High-quality inks maintain pH fluctuations within ±0.5 throughout their shelf life (typically 6–12 months), ensuring stable printing performance.
(II) Application Compatibility Characteristics
1. Broad Substrate Compatibility (with Targeted Adaptation)
- Textiles: Reactive, disperse, and acid water-based inks are suitable for cotton, polyester, and wool fabrics respectively. With thermal fixation (100–180 °C), wash fastness of Grade 3–4 and rub fastness of Grade 4 or higher can be achieved.
- Packaging: Water-based inks are well suited for kraft paper and corrugated board, often without additional drying.
- Non-absorbent substrates (e.g., PET films): Require adhesion promoters or pre-coatings to prevent ink delamination.
2. Color Performance and Gamut
- Dye-based inks: Offer high color saturation and wide color gamut (over 90% of sRGB), suitable for photographic and advertising graphics.
- Pigment-based inks: Slightly lower saturation due to pigment opacity (particle size typically 50–200 nm), but superior lightfastness (Grade 5–6), making them ideal for outdoor displays and packaging.
3. Adjustable Drying Speed
Drying speed can be tuned by adjusting humectant content or using drying equipment.
- In textile digital printing, a “print–pre-dry–fix” process typically requires 1–3 minutes at 60–80 °C for pre-drying.
- In high-speed packaging printing (e.g., >300 m/min), reduced humectant content combined with hot-air drying enables surface drying within 1–2 seconds.
(III) Environmental and Safety Characteristics
1. Low VOC Emissions
Water-based inks contain very low VOCs—typically <100 g/L, and in eco-friendly formulations <50 g/L—far lower than solvent-based inks (500–1000 g/L). They comply with regulations such as GB 41616-2022 and reduce health risks and ventilation costs.
2. Low Toxicity and Biodegradability
Most formulations use food-grade or environmentally friendly additives. Acute oral toxicity (LD50) typically exceeds 5000 mg/kg, and biodegradability (BOD₅/COD) can exceed 60%, minimizing environmental impact.
3. Non-flammability
With flash points above 100 °C, water-based inks are non-flammable, simplifying storage and transportation and reducing safety management costs compared to solvent inks.
II. Usage Precautions for Water-Based Inks in Digital Inkjet Systems
Improper storage, operation, or maintenance may lead to nozzle clogging, poor adhesion, or color deviations. Key precautions include the following:
(I) Storage Guidelines
- Temperature, Humidity, and Light Control
Store inks at 5–35 °C and 40–60% RH, away from direct sunlight and heat sources.
High temperatures accelerate evaporation and degradation; freezing (<0 °C) can destabilize the dispersion system. - Sealed Storage and Shelf-Life Management
Unopened inks should remain sealed. Opened inks should be used within 1–2 months, tightly sealed after each use to prevent pH drift and microbial growth. - Avoid Mixing Different Ink Types
Different brands or ink types must not be mixed. When changing ink types, thoroughly flush the entire ink system using cleaning solution before refilling.
(II) Operational Guidelines
- Agitation and Filtration
Shake inks thoroughly before use. For inks stored over one month, filtration through 1–5 μm filters is recommended to remove agglomerates. - Environmental and Printhead Temperature Control
Maintain printing environments at 20–28 °C, 40–60% RH.
Printhead temperatures typically range 30–45 °C, adjusted according to ink type. - Print Speed and Ink Volume Control
Adjust speed and ink laydown according to substrate absorbency. Avoid long continuous operation—pause 10–15 minutes every 4–6 hours.
(III) Maintenance Guidelines
- Regular Printhead Cleaning and Moisturizing
Perform nozzle checks daily. Use gentle cleaning first. After daily operation, apply printhead moisturizing procedures. For downtime over 3 days, flush and seal with maintenance fluid. - Ink Path Inspection and Sealing
Inspect ink tanks and tubes weekly; remove air bubbles promptly. Clean ink paths monthly and replace aging seals. - Prompt Troubleshooting
Address clogging, color deviation, or poor adhesion immediately by cleaning, recalibrating color profiles, or adjusting curing parameters.
(IV) Safety Guidelines
- Personal Protection
Wear gloves and masks. In case of eye contact, rinse with water for at least 15 minutes and seek medical attention. - Waste Disposal
Dispose of waste ink and cleaning fluids through certified waste handlers. Contaminated wipes must be sealed before disposal. - Restricted Access
Store inks securely away from children. Post warning signs and restrict unauthorized access to inkjet equipment.