What is a Thermal printing paper?

The Core Principle: A Chemical Reaction

• The paper is coated with a special, heat-sensitive layer (the “thermal coating”).
• This coating contains colorless dyes (leuco dyes) and developers (often acidic substances like bisphenol-A (BPA) or, increasingly, BPA-free alternatives like Pergafast 201).
• When a specific area of the paper is heated by the thermal printhead, the dye and developer react chemically.
• This reaction causes the dye to change color (typically turning black, but blue or red is also possible), creating the visible mark.

How It’s Used:

• The thermal printer contains a printhead made up of tiny heating elements (pins).
• As the paper passes under the printhead, these heating elements are selectively activated (turned on/off very rapidly) according to the data being printed.
• Wherever a heating element activates, it heats the thermal coating directly beneath it, causing the chemical reaction and producing a dark dot.
• The pattern of these dots forms the text, barcodes, or images.

Key Types:

• Direct Thermal Paper: This is the most common type (used for receipts, tickets, labels). The heat from the printhead acts directly on the coated paper to create the image. It’s simple and cost-effective but has limitations (see pros/cons).
• Thermal Transfer Paper (Receiver): Used in thermal transfer printers. This paper has a special receptive coating designed to accept melted ink (resin or wax) from a separate ribbon when heated by the printhead. The image comes from the ribbon, not the paper’s own coating. This method produces much more durable, long-lasting prints (common for shipping labels, asset tags, product labels).

Common Applications:

• Point-of-Sale (POS) receipts (supermarkets, restaurants, shops)
• Shipping labels & logistics
• Barcode labels
• Admission tickets, boarding passes, luggage tags
• Fax machine paper (though less common now)
• ECG/EKG paper in medical devices
• Credit card terminals & ATM receipts
• Lottery tickets
• Label printers (both direct thermal and thermal transfer)

Pros of Direct Thermal Paper:

• No Ink/Ribbon Needed: Simpler printer design, lower consumable costs (just paper).
• Quiet Operation: No impact mechanism like dot matrix.
• Reliable: Fewer moving parts to jam or break.
• Cost-Effective: Paper itself is relatively inexpensive.
• Fast Printing: Prints almost instantly.

Cons of Direct Thermal Paper:

• Image Fading/Instability: The image is susceptible to fading over time when exposed to:
  • Heat (e.g., left in a hot car, near ovens/heaters)
  • Light (especially UV/sunlight)
  • Friction/abrasion (rubbing in wallets/pockets)
  • Chemicals (alcohol, solvents, plasticizers in PVC receipts holders, oils from skin)
• Limited Archival Quality: Not suitable for long-term records due to fading.
• Sensitivity: Can be scratched or marked before printing if mishandled.
• Environmental Concerns: Traditional coatings using BPA raised health and environmental concerns, leading to increased use of BPA-free alternatives.
• Limited Color: Typically monochrome (black on white/yellowish paper), though some specialty papers exist for limited colors.

Important Considerations:

• Storage: Thermal paper should be stored in a cool, dark, dry place away from chemicals to preserve its lifespan before printing.
• BPA/BPS: Due to health concerns (potential endocrine disruptors), regulations in many regions restrict or ban BPA in thermal paper. Look for “BPA-Free” or “Phenol-Free” labels if this is a concern. Alternatives like Pergafast 201 are common.
• Recycling: Thermal paper coating complicates recycling. Check local guidelines; it’s often not accepted in standard paper recycling streams.