The Science Behind Thermal Paper: How Chemical Coatings Create Images

Thermal paper, widely used in self-adhesive labels and PSA (pressure-sensitive adhesive) products, relies on a precise chemical reaction to produce images without ink. This article explains the technology behind thermal paper coatings and their role in labels and adhesives.

How Thermal Paper Develops Color

Thermal paper changes color when heated above 70°C, thanks to a two-component coating. The key ingredients are a colorless dye (leuco dye) and a developer. Common dyes include Crystal Violet Lactone (CVL) and fluorane systems, while developers often consist of parabens or salicylic acid. Heat triggers a reaction between them, forming visible text or graphics in blue, black, or purplish-red.

Coatings: More Than Just Color

Special additives ensure performance and durability. Dispersants like polyvinyl alcohols (e.g., L-3266, GL-05) help distribute components evenly. Topcoat agents such as gohsefimer Z-200 or polyvinyl alcohol T-350 improve scratch and moisture resistance—essential for self-adhesive labels exposed to various environments.

Applications in Labels and PSA Products

Thermal technology is valued for its simplicity and speed in many fields:

• Thermal self-adhesive labels: Used in retail, logistics, and healthcare for fast, ink-free printing.

• PSA thermal tapes and tags: Provide instant adhesion and clear prints for industrial or safety labeling.

• Specialty thermal papers: Include high-temperature or anti-counterfeit variants, tailored through coating adjustments.

Conclusion

Understanding thermal paper’s chemistry helps in selecting the right product for specific needs, whether for durable outdoor labels or efficient PSA applications. Continuous innovation in coatings ensures thermal paper remains a reliable and adaptable solution across industries.