What are the components of the thermal coating on thermal label paper?

The thermal coating of thermal label paper is mainly composed of various chemical substances, which can undergo chemical reactions under heating conditions, thereby releasing colors. Specifically, the components of thermal sensitive coatings mainly include the following:

Colorless dye (also known as latent dye): This is one of the key components in thermal sensitive coatings, and it is a stable powder that is colorless or light colored. Under certain conditions (such as thermal energy), colorless dyes will undergo chemical reactions with color developing agents, resulting in the appearance of color. Commonly used colorless dyes include crystal violet lactone (CVL) from the triphenylalkylphthalein system, fluoranthene system, colorless benzoyl methylene blue (BLMB), or spiropyran system.

Color developer: Color developer is another important chemical component in thermal sensitive coatings, accounting for less than 20% of the total composition of the coating. When colorless dyes and colorants come into contact under heating conditions, they undergo a chemical reaction to produce colored products. Common colorants include para hydroxybenzoic acid and its esters (PHB, PHB), salicylic acid, 2,4-dihydroxybenzoic acid, or aromatic sulfones.

Sensitizer: The function of sensitizers in thermal sensitive coatings is to enhance the chemical reactivity between colorless dyes and color developing agents, thereby improving the sensitivity of thermal sensitive paper. Sensitizers usually account for less than 10% of the coating composition, and commonly used sensitizers include benzenesulfonic acid amide compounds.

Filler: Filler mainly plays a role in improving the opacity of paper and enhancing the contrast between image and background color in thermal sensitive coatings. Common fillers include calcium carbonate (particles), which account for less than 50% of the coating composition.

Adhesive: Adhesives provide coatings with good surface strength and printing performance, while also forming a colloidal protective film between dyes and colorants to prevent premature reactions. It accounts for less than 10% of the coating composition, and commonly used ones include polyvinyl acetate.

Stabilizer: The function of stabilizers is to improve the chemical stability of thermosensitive coatings and prevent unnecessary chemical reactions during storage or use. Common stabilizers include phthalic acid dibenzoyl, etc.

Lubricant: Lubricants are usually waxy materials that can be used to prevent hot heads from sticking.

In addition, depending on specific requirements, thermal sensitive coatings may also contain other additives such as antioxidants, antistatic agents, etc. These components work together to enable thermal label paper to quickly and clearly display graphic and textual information when heated.

In general, the thermal coating of thermal label paper is a complex chemical system, and its composition and formula are often adjusted and optimized by various manufacturers according to specific needs.