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Date: Mar 21 2025 From: Star Color
In the printing industry, PET (polyethylene terephthalate) film is widely used in packaging, electronics, decoration, and other sectors due to its excellent properties such as high strength, high transparency, and good chemical resistance. However, when it comes to printing on PET film, particularly using water-based inks, there are several challenges. This article will explore the characteristics of PET film and the printing challenges it presents, while also delving into technological breakthroughs in water-based ink printing on PET. It will compare the performance of water-based, solvent-based, and UV inks and discuss the feasibility of using water-based inks for PET film printing.
1. Characteristics of PET Film and Printing Challenges Why is it difficult to use water-based ink on PET film? PET film has some unique characteristics that make it more suitable for solvent-based or UV inks rather than water-based inks, presenting several difficulties.
Firstly, PET film has a non-absorbent surface. Unlike materials such as paper, it cannot allow ink to penetrate; it relies on physical adhesion to achieve the printing effect. This requires water-based inks to form a strong bond on the film surface, which is no easy task.
Secondly, PET film has a relatively low surface energy, with a dyne level ranging between 38-42 mN/m, whereas ideal printing conditions require a surface energy of ≥48 mN/m. The low surface energy makes it difficult for water-based ink to spread evenly and adhere to the film, often resulting in issues such as ink shrinkage and poor leveling.
Additionally, PET film has strong chemical resistance. Conventional water-based resins struggle to form stable layers on such a chemically resistant surface, making it hard to ensure the durability and quality of the printed pattern.
2. Four Technological Breakthroughs for Water-based Ink Printing on PET
Surface Pretreatment: Enhancing Adhesion
Corona Treatment (Mainstream Solution): Corona treatment is the most common method to increase the surface energy of PET film and enhance the adhesion of water-based inks. The goal is to raise the dyne level of the PET film to 48-52 mN/m. During corona treatment, real-time monitoring of the dyne level is required to ensure the stability of the effect. Typically, the corona equipment operates with a power range of 1.5-2.5 kW and an electrode gap of 1-2 mm.
Chemical Primer: In addition to corona treatment, using a chemical primer is an effective way to improve adhesion. A two-component polyurethane primer is widely used in PET film printing. The dry film thickness is usually controlled between 0.5-1μm, creating a transitional layer on the PET surface that enhances the bond between the water-based ink and the film.
Modification of Water-based Ink Formulation
Resin Selection: Resin selection plays a crucial role in the formulation of water-based ink. Water-based polyurethane-acrylic hybrid resins are ideal because they can form good adhesion on PET film surfaces, with adhesion levels reaching ≥4B according to ASTM D3359 testing. Adding silane coupling agents can further improve the bond between the ink and PET molecules. Silane coupling agents have a special molecular structure, with one end reacting chemically with the resin in the ink, and the other end bonding with groups on the PET film surface, forming strong chemical bonds and greatly enhancing adhesion.
Functional Additives: Various functional additives can be incorporated to improve the properties of the ink, including flow agents, defoamers, and curing agents.
Printing Process Optimization
Flexographic Printing Parameters: For flexographic printing, proper parameter settings can improve both print quality and efficiency. The recommended anilox roller line count is 150-180 LPI, ensuring an appropriate ink transfer. The printing pressure should be controlled between 0.12-0.18 MPa, ensuring sufficient ink transfer to the PET film without damaging it. The drying temperature should use a three-stage drying process, with temperatures of 70°C, 80°C, and 90°C, respectively. This gradual heating ensures the even evaporation of moisture in the ink, preventing issues like uneven drying or surface bubbling.
Gravure Printing Adaptation: When using gravure printing, water-based ink's corrosiveness requires the use of laser-engraved ceramic anilox rollers to improve resistance to ink corrosion. The ink viscosity should be strictly controlled using a Zahn cup #3 at 25°C, with viscosity between 18-22 seconds. Proper ink viscosity ensures good transfer in the cells and even coating on the PET film surface.
Post-Curing to Enhance Durability
UV-Curable Water-based Ink: UV-curable water-based ink uses a dual curing mechanism—first through moisture evaporation for initial drying, followed by UV cross-linking curing. This curing method creates highly cross-linked films with excellent durability. Testing shows that the ink has a resistance of more than 50 alcohol wipe cycles (ISO 15790).
Thermal Curing: Thermal curing is also an effective way to enhance ink durability. Treating the printed PET film at 130°C for 3 minutes in a curing oven significantly improves the scratch resistance of the ink film. Pencil hardness testing shows hardness ≥2H, effectively protecting the printed pattern during subsequent use and processing.
3. Comparison of Water-based, Solvent-based, and UV Ink Performance
| Metric | Water-based Ink | Solvent-based Ink | UV Ink |
|---|---|---|---|
| Adhesion (PET) | ★★★☆☆ (Requires Pretreatment) | ★★★★★ | ★★★★☆ |
| VOCs Emission | <5% | 40%-60% | <1% (Curing Agent Residue) |
| Drying Energy Consumption | Medium (0.8 kW・h/m²) | Low (0.3 kW・h/m²) | High (1.2 kW・h/m²) |
| Overall Cost (RMB/m²) | 0.15-0.25 | 0.10-0.18 | 0.30-0.50 |
| Environmental Certification | REACH, GB 38507 | Requires Exhaust Treatment | MSDS Component Review |
In terms of adhesion, solvent-based inks perform the best, followed by UV inks, while water-based inks also provide good adhesion when surface pretreatment is applied. In terms of VOC emissions, water-based inks and UV inks have a clear advantage, with water-based inks emitting <5% VOCs, UV inks having less than 1% curing agent residue, while solvent-based inks emit 40%-60% VOCs, creating significant environmental pressure. In terms of drying energy consumption, solvent-based inks require the least energy, followed by water-based inks, with UV inks consuming the most. In terms of overall cost, solvent-based inks are the cheapest, water-based inks are moderately priced, and UV inks are the most expensive. Water-based inks meet environmental standards such as REACH and GB 38507, while solvent-based inks require exhaust treatment and UV inks require MSDS component reviews.
Conclusion Although PET film printing presents challenges when using water-based inks, technological breakthroughs such as surface pretreatment, ink formulation modification, process optimization, and post-curing have made it possible. With growing environmental regulations, water-based inks, with their low VOC emissions, have significant potential. Printing companies can choose the most suitable ink type based on their needs and conditions to achieve high-quality, efficient, and environmentally friendly printing production.
An example of a water-based ink specially developed for PET film printing by Huizhou Zhongzhixing Color Technology Co., Ltd. has demonstrated outstanding performance in adhesion, abrasion resistance, and color concentration. It is safe, environmentally friendly, non-flammable, and non-explosive, with appropriate viscosity (20±5s), fineness (≤8 microns), and pH value (8.5-9.0). The drying speed is 40-150m/min, and the printing speed can reach 300 meters, meeting production efficiency demands with a shelf life of up to 12 months.
In practice, many companies have achieved excellent results and feedback by using Zhongzhixing water-based ink for PET film printing. If you are looking for a suitable water-based ink for PET film printing, consider Zhongzhixing's products. They also offer free samples and tailored environmental solutions, helping you better assess whether the product meets your needs.
