What Is the Protective Layer of Thermal Label Paper? And What Are the Common Materials?
In daily life, thermal label paper is extremely common. It can be found everywhere, from supermarket price tags to logistics waybills. The protective layer, as an important part of thermal label paper, plays a key role in the performance and lifespan of the label. So, what are the common materials used for the protective layer of thermal label paper? Today, let’s delve into the common materials and their functions for the protective layer of thermal label paper.

What Is the Protective Layer of Thermal Label Paper?

The core of thermal label paper is the thermal coating. When the print head heats up, the coating undergoes a chemical reaction to produce color. However, the thermal coating itself is quite fragile and is susceptible to external factors such as friction, light exposure, moisture, and chemical solvents. These factors can cause the image to fade or become blurry. To extend the lifespan of the label and enhance its durability, manufacturers apply a transparent protective layer on top of the thermal coating.

Common Materials for the Protective Layer

At present, the protective layer of thermal label paper mainly uses the following types of materials:
Acrylic Resin (Acrylic Resin)
This is one of the most commonly used materials for the protective layer. Acrylic resin has good transparency, wear resistance, and chemical resistance. It can effectively prevent daily friction and minor solvent erosion. Moreover, it is environmentally friendly and non-toxic, making it suitable for fields with high safety requirements, such as food and pharmaceuticals.

Polyvinyl Alcohol (PVA, Polyvinyl Alcohol)

PVA has excellent film-forming and water-soluble properties. It is often used in ordinary thermal paper that requires certain moisture-proof performance but does not pursue extreme durability. However, PVA has poor stability in high humidity environments. Therefore, it is mostly used in short-term label scenarios.

Styrene-Acrylic Copolymer (Styrene-Acrylic Copolymer)

This type of material combines the hardness of styrene with the flexibility of acrylic. The protective film formed is both wear-resistant and light-resistant. It is particularly suitable for thermal labels that need to be preserved for a long time or exposed to outdoor environments, such as logistics waybills and warehouse labels.

Silicone-based Materials

In some high-end applications, silicone-based materials are used as the protective layer to provide excellent heat resistance, UV resistance, and anti-adhesion properties. These materials are costly and are usually used for special industrial labels or medical record labels.

Wax Emulsion

Some economical thermal papers use wax emulsion as a simple protective layer. It mainly improves surface smoothness and minor scratch resistance. However, its durability is limited and is not suitable for long-term archiving or harsh environments.

Fillers

In the protective layer of thermal label paper, fillers such as kaolin, ground calcium carbonate, precipitated calcium carbonate, silica, and alumina are also added. These fillers can not only reduce the cost of the protective layer but also improve its physical properties. For example, kaolin and calcium carbonate can increase the hardness and wear resistance of the protective layer, while silica can enhance its water and oil resistance. This allows the label to maintain good condition in various environments.

Other Additives

In addition to the above main materials, other additives such as wet strength agents and lubricants are also added to the protective layer. Wet strength agents, such as polyamide/epichlorohydrin and adipic acid dihydrazide, can enhance the strength and toughness of the protective layer in humid environments. Lubricants, such as zinc stearate, paraffin wax, and calcium stearate, can improve the surface properties of the protective layer, reduce friction, and enhance the printing and processing performance of the label.

Summary of the Functions of the Protective Layer

•  Scratch and Wear Resistance: Prevents the printed content from being erased during transportation or use.
•  UV Resistance: Slows down image fading caused by light exposure.
•  Moisture and Chemical Resistance: Blocks the erosion of moisture, grease, alcohol, and other substances on the thermal coating.
•  Print Quality Improvement: Optimizes surface tension to produce clearer and more uniform printing.

The protective layer of thermal label paper has a wide variety of materials. Different material combinations can meet various usage requirements. With the continuous advancement of technology, it is believed that more new materials will be applied to the production of the protective layer of thermal label paper in the future. This will further enhance the performance and application scope of thermal label paper.