To address the issue of poor adhesion of water-based acrylic resin in film PVC and PET printing, a comprehensive approach is required, including substrate pretreatment, resin formula optimization, ink formulation, and process parameter adjustments. Below are specific solutions:

I. Optimization of Substrate Surface Treatment

Corona Treatment

● Purpose: Increase the surface energy of PVC and PET films (to 38-40 dyn/cm or above) to enhance polar bonding between the resin and substrate.

● Parameters: Voltage intensity of 30-50 kV, with treatment speed adjusted based on substrate thickness (lower speeds generally yield better results).

● Note: Treated substrates should be used within 24 hours to prevent surface energy decay.

Flame Treatment (for PET)

● Briefly expose the surface to flames to oxidize and generate carboxyl groups, improving adhesion.

● Control flame temperature (1000-1200°C) and contact time (0.1-0.5 seconds) to avoid substrate deformation.

Chemical Priming

● Apply specialized primers (e.g., chlorinated CPO primers, polyurethane primers) to form an intermediate layer that enhances bonding.

● Choose primers compatible with water-based acrylic resins (e.g., water-based polyurethane).

II. Resin and Ink Formula Adjustments

Selecting Specialized Resins

● Use modified acrylic resins designed for PVC/PET (e.g., epoxy-modified or silicone-modified) to improve adhesion to non-polar substrates.

● Introduce monomers with polar groups such as carboxyl or hydroxyl groups (e.g., acrylic acid, hydroxyethyl methacrylate).

Adding Adhesion Promoters

● Silane coupling agents (e.g., KH-550, KH-560): Dosage of 0.5-2% to enhance chemical bonding between resin and substrate.

● Polyester or polyurethane tackifying resins: Blend with acrylic resin (10-30% ratio) to improve flexibility and anchoring.

Adjusting Ink Parameters

● pH control: Maintain at 8.5-9.5 (adjusted with ammonia or AMP-95) to avoid resin instability causing film defects.

● Wetting agent selection: Add low dynamic surface tension wetting agents (e.g., BYK-349) to improve ink spreading on the substrate.

III. Printing Process Optimization

Drying Condition Adjustments

● Use staged drying: First stage at low temperature (50-60°C) for pre-drying, second stage at high temperature (80-90°C) for complete curing.

● Extend drying time or increase air volume to avoid residual moisture affecting adhesion.

Printing Pressure and Speed

● Appropriately increase printing pressure to ensure sufficient ink transfer to the film surface.

● Reduce printing speed (e.g., from 200 m/min to 150 m/min) to extend ink penetration time.

Post-Curing Treatment

● After printing, use UV curing (for UV-curable modified resins) or thermal curing (60-80°C, 5-10 minutes) to promote resin cross-linking.

IV. Other Key Factors

Impact of Substrate Additives

● Plasticizer migration in PVC can reduce adhesion; choose substrates with low-migration plasticizers or add anti-migration agents (e.g., epoxidized soybean oil).

● For PET, avoid silicone oil residue on the surface; clean with ethanol or isopropyl alcohol before printing.

Ink Layer Thickness Control

● Excessive ink thickness can cause internal stress cracking; recommend dry film thickness of 1-3 μm.

V. Verification and Testing Methods

Adhesion Testing

● Cross-cut test: After scoring, use 3M tape for peeling; ≤5%脱落面积为合格 (≤5% detachment is acceptable).

● Peel strength test: Use a tensile tester (target value ≥1.5 N/15mm).

Simulating Real-World Conditions

● Perform boil resistance testing (100°C/30 min) and damp heat resistance testing (40°C/90% RH/48 h) on printed products to check for delamination.

Summary

By implementing a three-pronged strategy of “substrate treatment – formula optimization – process adjustment,” the adhesion of water-based acrylic resin on PVC and PET films can be significantly improved. It is recommended to first verify the effectiveness of corona treatment and resin modification before gradually optimizing other parameters. If further cost reduction is needed, consider blending with low-cost resins (e.g., styrene-acrylic emulsion) while balancing performance.