Lamination Strength Problems in Water-Based Gravure Inks

In the food flexible packaging sector, gravure reverse printing combined with lamination is often adopted to ensure food safety, effectively blocking ink migration into food. However, this brings a new challenge: lamination strength. As a key indicator of packaging quality (typically required to be ≥3N/15mm), laminationstrength determines whether the package can withstand transportation, resist delamination, and prevent leakage. Insufficient strength may cause delamination, wrinkling, or even packaging failure.

Industry surveys indicate that around 35% of lamination failures with water-based gravure inks are caused by inadequate bond strength, far higher than solvent-based inks (15%). This article analyzes the core causes affecting lamination strength and provides practical solutions to help converters overcome lamination challenges.

1. What is lamination Strength in Water-Based Gravure Inks?

The lamination process with water-based gravure inks involves forming a stable structure of substrate + ink layer + adhesive + secondary substrate through physical adsorption and chemical bonding. lamination strength depends on two main factors:

1. Ink-to-substrate adhesion – The water-based ink resin must bond with polar groups on the substrate surface via hydrogen or covalent bonds.

2. Ink-to-adhesive compatibility – The ink’s surface energy must closely match the adhesive (difference ≤5 dyn/cm), with no residual low-molecular substances that could block adhesive penetration.

Any weakness in these links will directly reduce lamination strength.

2. Six Core Causes of Weak lamination Strength

(1) Inadequate Substrate Pretreatment

• Issue: Non-absorbent substrates (BOPP, PE) with surface tension ≤34 dyn/cm prevent proper ink wetting, reducing adhesion to just 2B grade. Ink easily peels off during lamination.

• Causes:

  • Insufficient or aged corona treatment.

  • Residual oil, slip agents, or contaminants forming an isolation layer.

• Data: BOPP film with 34 dyn/cm surface tension achieved only 2.1N/15mm adhesion; after corona treatment to 38 dyn/cm, adhesion improved to 4.5N/15mm (+60% lamination strength).

• Solution:

  • Corona treatment: BOPP/PET ≥38–42 dyn/cm; PE ≥36–38 dyn/cm.

  • Print within 4 hours post-treatment (otherwise re-treat).

  • Clean surface oil and slip agents using alcohol wipes or plasma cleaning.

(2) Poor Resin System Compatibility

• Issue: Ink layers are either too brittle (cracking) or overly soft (poor bonding with adhesive).

• Causes:

  • Single acrylic resin = brittle film, low flexibility.

  • Lack of polar groups = poor hydrogen bonding with adhesive.

  • Resin content too low: solids <40%, resin <30%, porous ink layer → “false bonding.”

• Case: A converter using pure acrylic resin (solids 35%) achieved only 2.2N/15mm on PE film; switching to acrylic–polyurethane hybrid resin (solids 45%) improved strength to 3.8N/15mm.

• Solution:

  • Use acrylic–polyurethane hybrid resins (Tg 30–40℃) for balance of adhesion and flexibility.

  • Ensure solids ≥45%, resin ≥35%.

  • Maintain viscosity 25–35 s (DIN 4 cup, 25℃).

  • Add coupling agents/surface modifiers to boost bonding.

(3) Incomplete Drying of Ink Layer

• Issue: Residual water >5% causes bubbles and weak adhesive penetration during lamination.

• Data: With residual moisture at 2%, lamination strength = 3.5N/15mm; at 6%, it dropped to 1.8N/15mm with visible bubbles.

• Solution:

  • Optimize drying parameters (temperature, air speed, dwell time).

  • Keep residual moisture ≤2% (regular sampling check).

(4) Mismatch of Adhesive Selection and Process

• Issue: Adhesive shrinks or fails to spread, creating spot-bonding instead of uniform bonding; lamination strength fluctuates (±1N/15mm).

• Causes:

  • Ink–adhesive polarity mismatch (water-based inks = polar; rubber adhesives = nonpolar → shrinkage).

  • Insufficient adhesive coating or low lamination pressure.

• Data: Polar polyurethane adhesive (3 g/m²) achieved 95% coverage and 3.6N/15mm strength; nonpolar rubber adhesive achieved only 60% coverage and 1.9N/15mm strength.

• Solution:

  • Select polar polyurethane adhesives with strong ink compatibility.

  • Control adhesive coating at 3–4 g/m².

  • Maintain lamination pressure 0.4–0.6 MPa, temperature 45–55℃.

(5) Insufficient Post-Curing of Adhesives

• Issue: Without post-curing or with inadequate curing conditions, adhesives do not fully crosslink. Initial strength may pass, but drops >30% after one week.

• Data: Post-cured at 45℃ × 12h → 95% strength retention after 1 week; room temperature storage → only 68% retention.

• Solution:

  • Ensure post-curing at 40–50℃ for 8–12h.

  • Maintain humidity <65% during curing.

  • Verify retention: ≥90% strength after 1 week.

3. Case Study: Lamination Strength Upgrade in Snack Packaging

• Background: A food packaging company used water-based gravure ink on BOPP laminated to PE for snack packs. lamination strength was only 2.3N/15mm (requirement ≥3N/15mm). Delamination caused 15% transport rejection rate and frequent complaints.

• Problems Identified:

  1. Substrate: BOPP corona only 35 dyn/cm, stored >24h (tension decay).

  2. Ink: Pure acrylic resin, solids 38%, residual moisture 4.5%.

  3. Adhesive: Nonpolar rubber adhesive, 2 g/m² coating, no post-curing.

• Optimization Plan:

  1. Substrate: Re-treated corona to 39 dyn/cm, printed within 4h.

  2. Ink: Switched to acrylic–PU hybrid resin (45% solids), added 1.5% silane coupling agent, optimized drying (50℃ → 65℃ → 55℃, air speed 3 m/s).

  3. Adhesive: Polar PU adhesive, 3.5 g/m² coating, lamination pressure 0.5 MPa, post-cured at 45℃ × 10h.

• Results:

  • Lamination strength increased from 2.3N/15mm → 4.1N/15mm (above standard).

  • Transport rejection rate reduced from 15% → 0.8%.

  • Customer complaints eliminated.

  • After 1 month, 96% strength retention, no delamination.

4. Conclusion: Core Logic for Improving Lamination Strength

The key to enhancing lamination strength in water-based gravure printing lies in:

1. Substrate pretreatment – building a solid foundation for adhesion.

2. Ink formulation optimization – ensuring dense film formation and chemical compatibility.

3. Process control – complete drying, correct adhesive application, and proper lamination pressure.

4. Post-curing – securing long-term durability and stability.

With continuous improvement in ink formulation and lamination equipment, the lamination strength of water-based gravure inks will increasingly match that of solvent-based inks, making them a reliable, eco-friendly choice for food packaging.