1. Let's answer the most practical question first: Can water based ink run at high speed?

Yes, it can. Current mainstream formulations run stably at over 300 m/min on film substrates, and some high-solid products can reach 400 m/min. But there's a precondition — your drying system must keep up. Water based ink dries by evaporation and air convection, not as fast as solvent ink, so if your oven is too short, you'll need to reduce speed.

Based on our measured data: printing on plastic film with 60°C hot air, 450 m/min is near the limit for water based ink, while solvent ink can reach 700 m/min. But water based ink has only about one-tenth the VOC emissions of solvent ink. The trade-off depends on your local environmental regulations and equipment capabilities.

Watch: Water Based Flexo Ink printing process in real production

2. Four critical parameters: Viscosity, pH, Fineness, Surface Tension

Many people think stable viscosity is all that matters. But in production, pH drift also causes unstable printing — along with fineness and surface tension. If these four parameters are off, even expensive ink won't perform. Below are normal ranges and what happens when values go out of spec. Press operators can use this as a quick reference.

Parameter Normal Range Below Lower Limit Above Upper Limit
Viscosity (Zahn #4 cup, 25°C) 14–25 seconds Faint color, thin ink film, missing dots Blurred dots, stringing, uneven ink transfer
pH Value 7.5–9.0 Slow drying, smearing, resin precipitation Excessive foaming, plate damage, strong odor
Fineness (Grindometer) ≤10μm Exceeds 10μm → Clogs anilox rollers, particles on print
Surface Tension 30–35 dyne/cm Higher than substrate → cratering, poor ink wetting; must be lower than substrate

One sentence summary from shop floor experience: Adjust viscosity with water/thickener, pH with amine additives, fineness with grinding equipment and filtration, surface tension with wetting agents. Don't expect one additive to solve all problems.

3. Water based vs Solvent vs UV ink: How to choose

No single ink is "best" — only "most suitable". The table below highlights the key differences.

Comparison Water Based Flexo Ink Solvent Based Flexo Ink UV Flexo Ink
VOC Content <5% 30–60% 0%
Suitable Substrates Paper, non-woven, corona-treated film Films, aluminum foil, self-adhesive labels Almost all (requires UV curing equipment)
Drying Method Hot air + IR Hot air (high volume) UV lamps
Cleaning Cost Low (water) High (solvents + labor) Medium
Food Contact Compliance Easy (low-migration formulations mature) Difficult (residual solvent risk) Possible (after full cure)

Selection advice — straight talk: For food packaging, paper products, hygiene materials (diapers, sanitary napkins, etc.) → water based ink; for self-adhesive films with no environmental restrictions → solvent ink; for high-end labels with UV equipment → UV ink. Trying to use one ink for everything is unrealistic.

4. Common pressroom troubleshooting

If you encounter these problems, don't flip through the manual from the beginning — just match the symptom below.

Problem Most Likely Cause First Action to Try
Print rubs off plastic film Low substrate surface tension (<38 dyne) Corona treat to ≥40 dyne, or switch to high-adhesion resin ink
Excessive foam in ink tank High pH (>9.6) or circulation pump too fast Lower pH to below 9.0, add 0.1-0.3% defoamer, reduce pump speed
Slow drying, smearing on rewinds Low pH (<8.2) or insufficient oven temp/airflow Add amine to raise pH to 8.8-9.2, increase oven temperature 5-10°C
Plugged plate dots Excessive ink fineness or dried ink buildup Check fineness (replace ink if >15μm), stop and wipe plate with damp cloth
Inconsistent color within same job Viscosity or pH drift (water/amine evaporation) Measure viscosity every 30-60 min; best to install automatic top-up system

Honestly, the causes above cover about 70% of daily complaints. If your problem isn't listed, it's likely equipment or plate related — having the press operator look at it for half an hour is more effective than searching documentation.

5. Application scope: Which materials are reliable, which need caution

Recommended (mature solutions):
Kraft paper, solid bleached board, corrugated board (post-print/pre-print), non-woven, paper cups, paper bags, diaper backsheet film (after corona), napkin tissue.

Conditional (requires sample testing):
PE film (surface energy ≥40 dyne), PET film, aluminum foil (requires IR drying), coated paper.

Not recommended:
Untreated PP/PE, highly water-resistant films, oil/wax-contaminated surfaces. Forcing these either fails adhesion or causes drying issues.

Reference data from our customer feedback over the past two years: first-pass yield on paper materials with water based ink is about 94-97%; on plastic films it's about 78-85%, mainly limited by adhesion pretreatment. So if your main orders are films, make sure you leave room for a corona treater.

6. Environmental advantages and trends

The reason water based ink is being promoted is not primarily "best performance" but regulatory friendliness. More than a dozen provinces in China require packaging printers to achieve ≥90% VOC abatement efficiency. A single RTO incinerator costs 2-3 million RMB — small printers simply cannot afford it. Water based ink reduces VOCs at the source, achieving 1-3% VOC content, making it the most realistic compliance path for small and medium enterprises.

On the technology side, resin development has advanced rapidly in recent years. Previously, water based ink on film required slowing to below 150 m/min; now it can easily run at 350-400 m/min. The shortcoming remains — adaptability to high-oil, high-humidity extreme environments still lags behind solvent ink — but for most ordinary orders, it's sufficient.

7. If you're evaluating or trialing, these tips may help

  • Don't switch your entire shop at once. First trial on one line and one common material for 2-4 weeks to get viscosity/pH control working.
  • Don't mix cleaning water lines with solvent residue. Residual solvent will break down the resin system in water based ink, causing flocculation.
  • Ask suppliers for a complete TDS (Technical Data Sheet). Especially look for: solids content, viscosity range, pH window, and thinner ratio. Missing any of these means high risk of problems later.
  • Water quality matters. If tap water hardness exceeds 200 ppm, consider a simple water purifier — otherwise calcium and magnesium ions will react with the resin.
  • If your main business is paper bags, corrugated, or food packaging, prioritize high-solid water based flexo ink; if film orders dominate, choose specialized high-adhesion formulations and use corona treatment.

Frequently Asked Questions (FAQ)

Question Answer
1. What is water based flexo ink used for? Mainly for paper, paperboard, corrugated board, non-woven, and corona-treated films. Typical products: food packaging boxes, paper bags, paper cups, diaper backsheet film, sanitary napkin packaging, courier bags, labels. Not suitable for untreated plastic films.
2. Why is pH important? pH directly determines whether the resin stays dissolved. Below pH 8.2, resin precipitates — ink thickens, dries slowly, or even clumps. Above pH 9.8, excessive foaming and plate damage occur. The optimal range is 8.5–9.5, requiring measurement every 2 hours and timely amine addition.
3. Why does foaming occur? Three main causes: ① High pH (>9.6) ② Circulation pump speed too fast ③ Defoamer failure or insufficient amount. Fix: Lower pH to below 9.2 first, add 0.1-0.3% defoamer, reduce pump speed. Foaming clogs anilox rollers and causes white spots on prints — don't ignore it.
4. Can it print on film? Yes, with conditions. PE, PP, PET and other non-absorbent materials must be corona treated to ≥38 dyne (preferably 40+), otherwise adhesion fails with a simple rub. After proper treatment, some specialized water based inks can run at 250-350 m/min. Without corona equipment, stick to paper.
5. Why is adhesion poor? 95% of the time it's low substrate surface tension (below 38 dyne). The other 5% may be: ink surface tension too high (>35 dyne), oil/dust contamination on substrate, or insufficient drying. First use a dyne pen to check the substrate; if that's fine, then inspect the ink.
6. Which is better, water based or solvent ink? No absolute answer — depends on your environmental pressure, substrate types, and existing equipment.
• Strict environmental requirements, printing on paper → water based is better (low VOC, safe, cheap cleaning)
• Heavy film printing, no environmental inspections → solvent based is better (faster drying, more forgiving adhesion)
One-sentence advice: Use water based when you can, but don't force it on difficult films.