Paper water-based ink printing failure prevention and treatment

Paper, as the core substrate for water-based ink printing, has unique properties such as porosity, ink absorbency, and moisture sensitivity. When interacting with the water-based ink’s “water-borne film-forming” principle, these characteristics can easily lead to printing defects. According to statistics, the defect rate of paper printing with water-based inks is about 8%–12%, with three primary issues—strike-through, poor adhesion, and insufficient drying—accounting for over 60% of the total. Below, we analyze common failures and their solutions.

Core Issue 1: Strike-Through

Symptoms
Ink penetrates through the paper fibers, creating a blurred “shadow” on the reverse side, especially noticeable in dark solid areas or large coverage prints. In severe cases, the back-side ink smudges onto adjacent sheets, causing batch contamination.

Causes

1. Excessive ink absorbency of paper: Low density (≤0.6 g/cm³), high porosity paper allows water and resin in the ink to penetrate quickly.

2. Low ink solids: When ink solids are below 30%, excessive water accelerates fiber swelling and deep penetration, common when inks are over-diluted.

3. Excessive ink film thickness: High-volume anilox rolls (>15 BCM) or excessive printing pressure (>2.5 bar) transfer more than 15 g/m² ink, beyond paper’s capacity.

4. Insufficient drying: Low hot-air temperature (<40°C) or weak airflow (<1 m/s) prevents surface film formation, allowing more penetration.

Solutions

1. Paper optimization: Use paper with density ≥0.7 g/cm³; if low-density paper must be used, pre-coat with a water-based primer (40–50% solids, 0.5–1 μm thickness) to seal pores, reducing strike-through by up to 60%.

2. Ink formulation adjustment: Use high-solids ink (≥45%), raise viscosity (from 20s to 30s, Zahn Cup #4 at 25°C), and avoid over-dilution (>10%).

3. Control ink film thickness: Use high-line, low-volume anilox (e.g., 800 LPI, 6–8 BCM), reduce printing pressure to 1.8–2.2 bar, and keep ink transfer ≤12 g/m². Measure film weight every 50 meters with a thickness gauge, deviation ≤±1 g/m².

4. Accelerate drying: Apply combined IR + hot air drying: IR preheating at 60–70°C, hot air 50–55°C with airflow 2–3 m/s. Drying time shortens to 2–3 seconds, allowing surface film formation.

Core Issue 2: Poor Ink Adhesion

Symptoms
In 3M 610 tape tests, ink film peels off significantly (≤2B level). Stacked sheets smudge, ink transfers, or ink cracks along folds.

Causes

1. Insufficient surface preparation: Dust or oil prevents proper wetting and bonding.

2. Resin-paper mismatch: Acidic paper (pH <6.5) combined with alkaline resin ink (pH >8.5) causes chemical reaction, weakening adhesion.

3. Incomplete drying: Resin not fully crosslinked, leading to weak cohesion.

4. Abnormal moisture content: Too dry (<5%) makes paper brittle; too wet (>10%) causes fiber swelling, reducing bonding strength.

Solutions

1. Paper pretreatment:

   • Clean paper surface of dust/oil.

   • Match ink resin pH with paper (acidic paper with neutral-acidic resin, alkaline paper with alkaline resin).

   • Precondition paper 24h in workshop (23±2°C, 50±5% RH), target moisture 6–8%.

2. Optimize resin system: Use suitable water-based ink resins that improve flexibility and bonding; achieve 4B–5B adhesion in cross-hatch tests.

3. Ensure thorough drying: Dry at 55–60°C for 3–4 seconds; solvent residue ≤1% (verified by GC).

4. Post-treatment reinforcement: For high-end products (e.g., gift boxes, catalogs), apply a compatible water-based overprint varnish (1–1.2 μm). Increases rub resistance from 100 to 500 cycles.

Core Issue 3: Insufficient Drying

Symptoms
Ink film feels tacky, sheets block together during rewinding, “stringing” occurs when separating, and prints remain uncured after 24 hours.

Causes

1. Improper environment: Low workshop temperature (<18°C) or high humidity (>65% RH) slows evaporation.

2. Lack of drying additives: Insufficient fast-drying agents (<3%) worsen problems under low temperature/high humidity.

3. Excessive ink thickness or slow absorbency paper: Ink film >15 μm, or substrates like coated paper slow drying.

4. Weak drying equipment: Hot air <5 kW or aged IR lamps (energy loss >30%).

Solutions

1. Control workshop conditions: Maintain 20–25°C and ≤50% RH. Use dehumidifiers or quick solutions like lime desiccant near the press.

2. Add drying aids: Incorporate 3–5% water-compatible drying agents (e.g., tert-butanol, propylene glycol methyl ether). Always test first to avoid surface defects.

3. Control ink/substrate match: For low-absorbency paper, use finer anilox (e.g., 1000 LPI / 5 BCM), keep film 8–12 μm. For high-absorbency paper, slightly increase ink load but strengthen drying.

4. Upgrade equipment: Use higher power hot-air blowers (≥8 kW), airflow 3–4 m/s; test IR lamps quarterly and replace if energy loss >20%.

Other Common Defects & Quick Fix Table

Conclusion

Defects in water-based ink printing on paper fundamentally stem from a mismatch among ink properties, paper characteristics, and process parameters. Solutions require optimization across the entire chain—from raw material compatibility to process control.

With ongoing advances in water-based ink formulations and paper surface treatment, defect rates are expected to fall below 3%, achieving efficient and high-quality production. For complex cases, collaboration between ink suppliers and paper mills on customized solutions is recommended.

StarColor provides tailored water-based ink solutions to address such challenges—feel free to consult us for customized support.