Ink Adhesion to Non-Absorbent Substrates: Corona Treatment, Primers, and Adhesion Additives
Why Non-Absorbent Substrates Are Problematic for Ink Adhesion
Ink adhesion on non-absorbent substrates such as polyolefin films (PE, PP), polyester (PET), nylon, and coated papers remains one of the most persistent challenges in printing and packaging. Unlike absorbent substrates like uncoated paper, non-absorbent surfaces lack micropores to mechanically interlock ink, leading to poor wetting, low surface energy, and eventual delamination under stress.
Surface energy mismatch is the primary culprit. Polyolefins typically exhibit surface energies of 28–32 mN/m, well below the 38–42 mN/m threshold required for optimal wetting by most solvent-based and UV-curable inks. Even treated films rarely exceed 44 mN/m after corona or flame treatment, often decaying over time due to additive migration or surface contamination.
This article examines three practical strategies to improve ink adhesion on non-absorbent substrates:
- Corona surface treatment: the industry standard for in-line activation
- Primer systems: solvent-based, water-based, and UV-curable options
- Adhesion additives: polymeric and reactive chemistries integrated into ink formulations
We provide actionable data on performance benchmarks, dosage ranges, and formulation strategies based on real-world case studies from packaging and industrial printing applications.
1. Corona Treatment: The First Line of Defense
How It Works
Corona treatment uses high-voltage electrical discharge (typically 10–25 kV) to generate ozone and ionized gas that oxidize the substrate surface, introducing polar functional groups (e.g., hydroxyl, carbonyl, carboxyl) and increasing surface energy. This enhances wetting and provides chemical sites for adhesion.
Treatment Parameters and Performance
| Parameter | Typical Range | Notes |
|---|---|---|
| Power density | 0.5–3.0 W·min/m² | Higher for high-speed lines |
| Electrode gap | 2–5 mm | Critical for uniform treatment |
| Line speed | Up to 500 m/min | Depends on power supply |
| Half-life | 4–24 hours | Decay rate varies by polymer |
Effectiveness by substrate:
- PE/PP: Surface energy increases from ~30 mN/m to 38–44 mN/m
- PET: Rises from ~40 mN/m to 46–50 mN/m
- Nylon: From ~36 mN/m to 42–48 mN/m
Dosage Guidelines
- Low-density PE (LDPE): 1.2–1.8 W·min/m²
- High-density PE (HDPE): 1.5–2.2 W·min/m²
- Polypropylene (PP): 1.8–2.5 W·min/m² (heterogeneous surface requires higher energy)
- PET: 0.8–1.5 W·min/m² (already high energy)
⚠️ Caution: Over-treatment can cause thermal damage, pinholes, or excessive oxidation leading to poor ink anchorage.
Best Practices
- Use inline treatment systems (not offline) to minimize surface contamination and oxidation decay.
- Maintain electrode cleanliness to prevent arcing and uneven treatment.
- Monitor surface energy using dyne test pens (e.g., 38, 40, 42, 44 mN/m solutions).
- Re-treat if surface energy drops below 38 mN/m before printing.
Limitations
Corona treatment is temporary and substrate-specific. It does not address:
- Low surface energy after extrusion coating
- Additive migration (e.g., slip agents, antiblock agents)
- Contamination from processing aids
It is best used as a prerequisite, not a standalone solution.
2. Primer Systems: Bridging the Energy Gap
Primer systems provide a chemically reactive or highly polar interlayer between substrate and ink, enhancing both adhesion and barrier performance. Primers can be applied via roll coating, spray, or inline gravure.
Primer Types and Applications
| Primer Type | Chemistry | Substrate Compatibility | Ink Compatibility |
|---|---|---|---|
| Solvent-based | Chlorinated polyolefin (CPO), acrylic | PE, PP, OPP | Solvent, UV, water |
| Water-based | Acrylic emulsion, polyurethane dispersion | PE, PP, PET | Water, UV |
| UV-curable | Epoxy acrylate, polyester acrylate | PET, nylon, coated film | UV, EB |
| Two-part | Epoxy-amine, PU | Rigid substrates (e.g., automotive trim) | 2K systems |
Dosage and Performance Data
Solvent-Based Chlorinated Polyolefin (CPO) Primer
- Dosage: 0.5–1.5 g/m² (dry weight)
- Solids: 5–15%
- Solvent: Toluene, MEK, or blends
Adhesion Results (ASTM D3359 Crosshatch, 5B = best):
| Substrate | Corona Energy (mN/m) | Primer Dosage | Adhesion (ASTM) |
|---|---|---|---|
| LDPE | 38 | 0.8 g/m² | 4B |
| LDPE | 42 | 0.8 g/m² | 5B |
| PP | 36 | 1.2 g/m² | 4B |
| PP | 40 | 1.2 g/m² | 5B |
✅ Note: CPO primers bond via hydrogen bonding and van der Waals interactions with oxidized surface and ink resin.
Water-Based Acrylic Primer
- Dosage: 1.0–2.0 g/m² (dry weight)
- Solids: 12–20%
- pH: 7.5–9.0
Adhesion Results (ASTM D3359, 1000 g load):
| Substrate | Primer Type | Adhesion (ASTM) | Tape Test |
|---|---|---|---|
| OPP | Water-based acrylic | 5B | Pass |
| PET | Water-based acrylic | 4B | Pass |
| Nylon | Water-based acrylic | 3B | Fail (needs 2K PU) |
⚠️ Limitation: Water-based primers may not penetrate well into low-surface-energy PP without corona pre-treatment.
UV-Curable Primer
- Dosage: 0.3–1.0 g/m² (wet)
- Viscosity: 20–50 mPa·s
- Cure dose: 100–300 mJ/cm² (UVA, 365 nm)
Adhesion Results (ASTM D3359, after boiling test):
| Substrate | Primer | Ink System | Adhesion (After Boil) |
|---|---|---|---|
| PET | UV-epoxy acrylate | UV-ink | 5B |
| Nylon | UV-PU acrylate | UV-ink | 4B |
| OPP | UV-epoxy acrylate | UV-ink | 3B (improves to 5B with corona) |
✅ Advantage: Fast cure, solvent-free, high chemical resistance.
Formulation Tips
- Use blocked isocyanates in water-based primers to improve storage stability.
- Add surfactants (e.g., 0.1–0.3%) to enhance wetting on low-energy surfaces.
- Consider primer + adhesion promoter systems for extreme conditions (e.g., sterilized medical packaging).
3. Adhesion Additives in Ink Formulations
For inks that must perform without primers or where inline treatment is impractical, adhesion additives are blended directly into the ink formulation. These additives migrate to the interface and form covalent or strong polar interactions.
Types of Adhesion Additives
| Additive Type | Chemistry | Recommended Dosage (wt%) | Substrate Target |
|---|---|---|---|
| Polyolefin graft copolymer | Maleic anhydride-grafted PE | 1–4% | PE, PP |
| Acrylic copolymer | Styrene-acrylic or MMA copolymer | 2–5% | PET, OPP |
| Silane coupling agent | Aminopropyltriethoxysilane (APTES) | 0.5–2% | Glass, PET, nylon |
| Polyurethane dispersion | Aqueous PU dispersion | 3–8% | General films |
Performance Data: Solvent-Based Ink with PE Graft Copolymer
Test: ASTM D3359, 1000 g load
| Additive Level | PE Film (Corona 38 mN/m) | PP Film (Corona 40 mN/m) |
|---|---|---|
| 0% | 1B | 2B |
| 1% | 3B | 3B |
| 2% | 4B | 4B |
| 3% | 5B | 4B |
| 4% | 5B | 5B |
✅ Effective range: 2–3% for most applications
Water-Based Ink with Acrylic Copolymer
- Dosage: 3–5%
- Compatibility: Stable in acrylic and styrene-acrylic emulsions
- Adhesion (ASTM D3359):
- PET: 5B
- OPP: 4B
- Nylon: 3B (requires silane or PU dispersion)
Reactive Silane Coupling Agents
- Dosage: 0.5–1.5%
- Mechanism: Hydrolyzes to silanol, bonds to hydroxyl groups on treated surface and ink resin
- Best for: Glass, PET, nylon
⚠️ Note: Silanes require moisture for activation. Avoid in solvent-based systems unless water is co-solvent.
Practical Considerations
- Compatibility: Test additive solubility and stability in full ink system.
- Viscosity: High levels may increase viscosity; use rheology modifiers if needed.
- Regulatory: Ensure compliance for food packaging (e.g., FDA 21 CFR, EU 10/2011)
Comparative Analysis: Corona, Primers, Additives
| Criteria | Corona Treatment | Primer Systems | Adhesion Additives |
|---|---|---|---|
| Initial Cost | Low | High | Medium |
| Operational Complexity | Low | High | Low |
| Permanence | Temporary | Permanent | Permanent |
| Substrate Flexibility | High | Medium | High |
| Speed Impact | Minimal | Moderate (drying/curing) | None |
| Best Use Case | Inline activation, PE/PP | High-end packaging, medical | Inks without primers |
| Side Effects | Oxidation decay | VOCs (if solvent-based) | Viscosity change, cost |
📌 Recommendation: Use corona treatment as a foundation, primer for critical applications, and adhesion additives as cost-effective inks boosters.
Case Study: Improving Adhesion on OPP Film for Flexible Packaging
Challenge: A converter printing UV-curable inks on oriented polypropylene (OPP) film experienced 30% adhesion failure in tape tests after 24 hours.
Substrate: OPP, surface energy 36 mN/m
Solution Applied:
- Corona treatment: 2.0 W·min/m² → surface energy 42 mN/m
- Water-based acrylic primer: 1.5 g/m² → cured at 60°C
- Ink formulation: Added 2.5% PE-graft copolymer adhesion promoter
Results (ASTM D3359):
- After 1 hour: 5B
- After 7 days: 5B
- After boiling (60°C, 30 min): 5B
Failure Rate: <1% (down from 30%)
Cost Increase: ~$0.08/m² (primer + additive)
ROI: Reduced rework and customer complaints by 95%.
Troubleshooting Guide
| Symptom | Likely Cause | Solution |
|---|---|---|
| Poor initial adhesion | Low surface energy | Re-treat with corona; check dyne level |
| Adhesion failure after storage | Additive migration or primer degradation | Use higher MW primer; avoid low-Tg polymers |
| Ink crawling/beading | Contamination or low surface energy | Clean substrate; add surfactant to ink |
| Delamination after boiling | Weak interlayer | Increase primer dosage; use crosslinked primer |
| Poor UV ink adhesion | Insufficient cure or oxygen inhibition | Increase UV dose; add amine synergist |
Formulation Checklist for Non-Absorbent Substrates
✅ Substrate Characterization
- Identify polymer type (PE, PP, PET, etc.)
- Measure surface energy (dyne test)
- Check for additives (slip agents, antiblock agents)
✅ Surface Preparation
- Corona or flame treat inline
- Clean with isopropyl alcohol or plasma if needed
- Test dyne level before printing
✅ Primer Selection
- Match primer chemistry to substrate and ink system
- Test adhesion before full production
- Consider VOC compliance for food/medical
✅ Additive Integration
- Add adhesion promoter to ink (typically 2–4%)
- Ensure compatibility and stability
- Monitor viscosity and printability
✅ Validation
- Perform initial adhesion tests (ASTM D3359)
- Conduct accelerated aging (heat, humidity, boiling)
- Perform customer end-use tests (flex, rub, sterilization)
Conclusion: A Layered Approach to Reliable Adhesion
Achieving durable ink adhesion on non-absorbent substrates demands a multi-layer strategy, not a single solution. While corona treatment remains essential for activating polymer surfaces, primers and adhesion additives provide the chemical and mechanical reinforcement needed for long-term performance—especially in high-value applications like flexible packaging, medical devices, and automotive trim.
Start with corona treatment as baseline, then select primers for critical substrates (e.g., nylon, PP, low-energy PE), and integrate adhesion additives into inks for cost-effective enhancement without compromising print quality or regulatory compliance.
By combining surface science with practical formulation, converters and ink manufacturers can eliminate adhesion failures, reduce waste, and deliver products that meet the highest durability standards.
Final Tip: Always validate adhesion under real-world conditions—heat sealing, sterilization, or flexing often reveal weaknesses not seen in lab tests.
Chemzip offers a curated portfolio of adhesion promoters, primers, and corona treatment enhancers designed for the printing and packaging industry. Our technical team supports formulation optimization, regulatory guidance, and application testing to ensure consistent ink performance across challenging substrates.
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