Water-based ink has become the preferred material in the packaging, labeling, and printing industries due to its environmental protection advantages such as being eco-friendly and having low VOC emissions. However, when used on non-absorbent materials, there may be problems of insufficient adhesion, such as color fading and poor scratch resistance. So, how can we improve the adhesion of water-based ink? We can systematically analyze the scientific methods to enhance the adhesion of water-based ink from three major dimensions: substrate treatment, ink formula optimization, and printing process adjustment, and provide implementable solutions.

I. Substrate Surface Treatment to Improve Adhesion

1. Surface Energy Enhancement Technology
   The adhesion of water-based ink is directly related to the surface tension (dyne value) of the substrate. Materials with a surface tension lower than 36 dynes (such as PE, PP, and PET films) need to be pretreated to improve wettability.
   (1) Corona Treatment
   • Principle: By means of high-frequency and high-voltage discharge, polar groups (such as hydroxyl groups and carboxyl groups) are generated on the substrate surface.
   • Parameters: The dyne value should be ≥ 38 mN/m (test liquids such as a mixture of formamide and ethylene glycol).
     (2) Flame Treatment
   • Applicable Scenarios: Thick-walled plastic containers (such as HDPE bottles).
   • Advantages: It has a large treatment depth, and its resistance to aging is better than that of corona treatment.
   • Parameters: The flame temperature is 900-1200°C, and the contact time is 0.1-0.5 seconds.
     (3) Coating Primer
   • Principle: A primer containing polar groups (such as polyurethane and acrylic) is coated on the substrate surface.
   • Formula Example: Water-based polyurethane primer (solid content 20%-30%), with a thickness of 1-3μm after drying.
   • Cost-benefit: It increases about 0.5 yuan per square meter, but can increase the adhesion by 50%-80%.

II. Ink Formula Optimization to Improve Ink Performance

1. Resin Selection: The Core of Adhesion
   Resin is the “skeleton” of water-based ink, directly affecting the adhesion and water resistance of the formed film.
   | Resin Type | Characteristics | Applicable Substrates |
   |–|–|–|
   | Acrylic Resin | Moderate adhesion, low cost, good weather resistance | Paper, cardboard |
   | Polyurethane Dispersion | High adhesion, good flexibility, excellent chemical resistance | PE/PP films, metal foils |
   | Epoxy-modified Resin | High temperature resistance (≤120°C), strong solvent resistance | Retort pouches, medical device packaging |
   | Water-based Vinyl Chloride Copolymer | High hardness, excellent wear resistance | Labels, outdoor advertising materials |

Formula Suggestions:

• For PE films: Use a hybrid resin of polyurethane and acrylic (ratio 7:3), and the adhesion can reach above 4B.
• Add a coupling agent (such as silane coupling agent KH-550): The dosage is 0.5%-1.5%, which can enhance the chemical bonding between the resin and the substrate.

2. Additives: Precisely Regulate Performance
   • Wetting Agent: Reduces the surface tension of the ink (such as BYK-348, with an addition amount of 0.1%-0.3%) to improve the wettability of the substrate.
   • Adhesion Promoter: Contains phosphate ester groups (such as BYK-220S), with a dosage of 0.5%-2%, to enhance the interfacial bonding.
   • Crosslinking Agent: Water-based isocyanate, with an addition of 2%-5%, to improve water resistance and hardness.
3. Pigment Dispersion: Avoid the “Weak Interface Layer”
   • Dispersant Selection: Polymer-type dispersant, with a dosage of 20%-30% of the pigment amount.
   • Grinding Process: Use a sand mill to control the pigment particle size to ≤ 5μm, reducing the decrease in adhesion caused by agglomeration.

III. Printing Process Adjustment: Details Determine Success or Failure

1. Ink Viscosity Control
   • Target Range: Using a No. 4 cup, it should be 30-50 seconds at 25°C. Too high a viscosity will lead to poor leveling, and too low a viscosity will result in a weak film formation.
   • Adjustment Method: Add deionized water or a thickener.
2. Optimization of Drying Parameters
   • Hot Air Drying: The temperature is 80-100°C, and the wind speed is 8-12 m/s to ensure that the ink forms a complete film.
   • Infrared Assistance: Use IR pre-drying for thick ink layers (such as UV primer) to avoid surface skinning while the bottom layer remains undried.
3. Printing Pressure and Speed
   • Pressure Setting: The flexographic printing pressure is 0.1-0.3 MPa, and the gravure printing pressure is 0.3-0.5 MPa. Excessive pressure will squeeze the ink, leading to interface weakening.
   • Speed Matching: Adjust according to the drying capacity. It is recommended that the flexographic printing speed be ≤ 150 meters per minute.

IV. Targeted Solutions for Special Substrates

1. Polyethylene (PE) Film
   • Challenge: Low surface energy (≤34 mN/m), prone to ink detachment.
   • Solution: Corona treatment (dyne value ≥ 40) + polyurethane resin ink + 1% silane coupling agent.
2. Metal Foil (Aluminum Foil)
   • Challenge: Smooth surface, large ink shrinkage stress.
   • Solution: Coat with a water-based epoxy primer (thickness 2μm) + epoxy-modified ink.
3. Recycled Paper
   • Challenge: Porous surface, ink penetration leads to a decrease in adhesion.
   • Solution: Pre-coat with a water-based sealer (solid content 10%-15%) + high-solid-content acrylic ink (solid content ≥ 40%).

Conclusion

Improving the adhesion of water-based ink is a systematic project that requires coordinated optimization from three aspects: substrate, formula, and process. With the tightening of environmental protection regulations and technological progress, water-based ink is developing towards high performance, functionality, and sustainability. Enterprises need to combine their own needs, select scientific solutions, and achieve a win-win situation between quality and environmental protection.

For non-absorbent substrates such as plastic films, Zhongzhixing water-based ink closely combines with the surface of plastic films through a unique formula design and advanced production technology, creating a firm adhesion effect. Whether it is common plastic film materials such as PET, PE, or PP, Zhongzhixing water-based ink can be perfectly adapted, ensuring that the ink is evenly distributed on the film surface without concerns about peeling or color fading.