Surface Treatment Essentials for Printing on Clear PET Films
Printing on clear PET films requires precise surface preparation to ensure print durability, clarity, and ink adhesion. One of the most crucial steps in this process is PET surface treatment, a set of techniques designed to modify the film’s surface energy. This article will walk you through the requirements and techniques involved in optimizing printable PET film for high-quality printing.
1. Why Surface Treatment is Critical for PET Films
Polyethylene terephthalate (PET) is naturally a low surface energy material, meaning inks have difficulty adhering to it. Untreated PET surfaces result in issues like ink smearing, poor color density, and flaking.
A proper PET surface treatment ensures:
- Strong ink adhesion
- Reduced drying time
- Enhanced image clarity
- Compatibility with various inks (UV, solvent, water-based)
Without surface treatment, even the best printable PET film cannot deliver professional-quality results.
2. Types of Surface Treatments for PET
Several methods can be used to treat PET surfaces for printing. Each has its own strengths depending on the printing application.
a. Corona Treatment
The most widely used method is corona treatment. In this technique, a high-frequency electrical discharge is applied to the film's surface, increasing its surface energy.
Benefits of corona treated PET film:
- Inexpensive and fast
- Effective for short- and long-run jobs
- Compatible with roll-to-roll processing
Corona treatment is especially popular for printable PET film used in label printing, electronics overlays, and packaging.
b. Plasma Treatment
Atmospheric plasma offers a more controlled surface activation and deeper cleaning compared to corona. It's useful for sensitive applications or when higher bond strength is needed.
c. Chemical Priming
Involves coating the PET film with a primer layer that promotes ink adhesion. Often combined with other treatments for enhanced results.
3. Measuring Surface Energy
After performing PET surface treatment, it's important to verify effectiveness. The surface energy should be around 38-42 dynes/cm for most printable PET film applications.
How to test:
- Dyne Pens: Simple and quick surface energy verification.
- Contact Angle Measurement: More accurate lab method.
A corona treated PET film should consistently test above 38 dynes/cm for optimal ink bonding.
4. Storage and Handling of Treated Films
Even after successful surface treatment, improper storage can reverse the effects, a phenomenon known as “aging.”
Best Practices:
- Use treated films within 6 months
- Store in cool, dry, dust-free environments
- Avoid direct sunlight or moisture
- Keep rolls in sealed packaging
For printable PET film, it’s advised to perform a quick dyne test before printing if the film has been in storage for a long period.
5. Ink Compatibility and Selection
The surface energy of a corona treated PET film must match the surface tension of the ink for proper adhesion.
Recommendations:
- UV inks for fast curing and abrasion resistance
- Solvent-based inks for high coverage
- Water-based inks for eco-friendlier jobs (if compatible with primer-treated PET)
Always run a print adhesion test before starting large production batches.
6. Use Cases for Printable PET Film with Surface Treatment
Treated PET films are used in diverse industries:
- Labeling: Transparent labels for bottles and jars
- Electronics: Overlays for control panels and touch interfaces
- Retail Displays: Clear shelf signage and promotional materials
- Industrial Graphics: Long-life outdoor applications
In each of these, PET surface treatment directly affects product performance and longevity.
7. Partnering with the Right Supplier
A reliable supplier will offer:
- Consistent corona treated PET film quality
- Surface energy data sheets
- Custom roll sizes
- Technical support for surface treatment
Purchasing printable PET film from a reputable manufacturer ensures consistency across batches.
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