会社のニュース UV Curing on Flexible Materials: How to Avoid Film Curling and Thermal Deformation

In fields such as film coating, flexible electronics, label printing, and medical packaging, flexible substrates like PET, PI, PP, and PVC are becoming increasingly vital. However, during the UV photo-curing process, manufacturers frequently encounter a frustrating bottleneck: after passing through the UV irradiation zone, thin films are highly prone to curling, wrinkling, or even melting and deforming.

Flexible materials are extremely heat-sensitive. Even minor deformation can lead to immediate product scrapping, poor registration, or air bubbles during subsequent lamination. How can production lines achieve the perfect balance between high-efficiency curing and "zero deformation"? This article explores the root causes of heat and stress, along with four key engineering strategies to solve the issue.

To prevent film curling, it is essential to understand where the heat and physical stress originate during UV curing. There are two primary drivers:

1. The Thermal Effect:

   • Infrared Radiation Heat: Traditional mercury lamps emit a massive amount of infrared (IR) light alongside UV rays, creating intense heat.

   • Photon Energy Conversion: Even with pure UV light, a portion of the energy absorbed by the substrate and the chemistry is inevitably converted into thermal energy, causing the substrate's surface temperature to spike instantly.

2. Polymerization Shrinkage Stress:

   • At the exact moment UV adhesives or inks cure, monomers polymerize into cross-linked networks, causing a volume shrinkage (typically between 2% and 10%). If this shrinkage force is too aggressive while the film is thin or lacks rigidity, it literally pulls and warps the film, causing it to curl.

To combat thermal and physical deformation, modern manufacturing lines utilize the following advanced technical solutions:

This is the most effective thermal management upgrade available. Unlike traditional mercury lamps, UV-LED curing systems emit a narrow, single wavelength of ultraviolet light (typically 365nm or 395nm), completely eliminating infrared (IR) wavelengths from the spectrum.

• • The Result: The substrate surface temperature drops by 30°C to 50°C compared to mercury lamps, cutting off the primary external heat source.

In continuous Roll-to-Roll (R2R) production lines, relying solely on the LED head's internal cooling is not enough. The substrate itself must be actively cooled.

• How it works: The UV-LED head is positioned directly above a precision chill roller. As the thin film travels tightly wrapped around the water-cooled metal roller, the UV light cures it from above while the heat generated on the back of the film is instantly conducted away by the continuously circulating chilled water.

• The Result: The film remains near room temperature throughout the entire curing process.

• Manufacturers should prioritize cationic curing systems (which exhibit exceptionally low shrinkage, usually under 1% to 2%) or specify free-radical UV adhesives/inks with low-shrinkage additives.

• Carefully control the coating thickness. Thicker coatings exhibit more pronounced shrinkage stress; keep coatings as thin and uniform as performance requirements allow.

Avoid trying to fully cure the chemistry instantly with brute-force, high-intensity UV exposure.

• • Process Optimization: Implement a dual-zone layout featuring "Pinning (Pre-curing) + Final Curing." The first stage uses low-power UV light to lock the chemistry in place and prevent running, allowing internal stress to release gradually. The second stage applies high-power UV to achieve a full cure. This stepped energy input prevents a sudden burst of internal stress, drastically reducing film wrinkling.

Conclusion: UV curing on flexible materials is an art of balance. By combining UV-LED cold light technology with high-precision water-cooled transmission mechanisms, manufacturing enterprises can permanently resolve film curling and deformation without sacrificing line speed—paving the way for higher yields and greater commercial value in high-end flexible electronics and film manufacturing.