The production of thermal paper is a complex process involving multiple layers and processes. The base paper, as the underlying material carrying the thermal coating and protective layer, significantly impacts the final product's performance across various dimensions, including print clarity, preservation stability, environmental resistance, and equipment compatibility. The physical properties, chemical stability, and surface treatment processes of the base paper directly determine the final performance of the thermal paper through their interaction with the coating.
The smoothness of the base paper is a core factor affecting print clarity. Thermal coatings typically employ a lightweight coating process, with a coating weight between 5-6 g/m². In this case, the surface smoothness of the base paper directly reflects the uniformity of the coating. If the base paper has microscopic irregularities or loose fibers, the coating is prone to localized thickness variations during drying, leading to uneven heat transfer during printing and resulting in blurred text, rough edges, or uneven color distribution. Conversely, high-smoothness base paper (e.g., base paper with a smoothness ≥ 80s) ensures sufficient contact between the coating and the thermal printhead, allowing for efficient heat transfer to the heat-sensitive layer, accelerating the color development reaction, and thus improving image resolution and printing speed. This is especially suitable for scenarios with stringent detail requirements, such as high-speed fax machines or high-precision label printers.
The water absorption and deformability of the base paper are crucial to the dimensional stability of the thermal paper and the adhesion of the coating. If the base paper is too absorbent, it is prone to curling and coating cracking due to moisture absorption and expansion in humid environments, and may even cause poor contact between the printhead and the paper, resulting in broken lines or ghosting. Conversely, insufficient water absorption may cause the coating to dry too quickly, producing surface defects such as "orange peel" or streaks. Furthermore, the tensile strength and stiffness of the base paper must match the weight of the coating. If the base paper is not strong enough, it is prone to breakage or deformation during coating, slitting, or printing, affecting production efficiency and the yield of finished products. For example, in the roller coating process, the base paper must withstand the pressure and tension of the coating roller. If its tensile strength is lower than the combined force of the friction between the coating and the roller surface, it may cause paper stretching or coating peeling, leading to batch quality incidents.
The chemical stability of the base paper directly affects the shelf life of thermal paper. The colorless dyes and developers in the thermal coating are extremely sensitive to pH. If the pH value of the base paper deviates from the neutral range (e.g., is acidic), it may cause the coating to develop color prematurely or accelerate aging, resulting in fading of printed text within months. Furthermore, impurities in the base paper (such as metal ions) may catalyze the oxidation reaction of the coating, shortening its shelf life. High-quality base paper requires rigorous chemical treatment to ensure a stable pH value within the slightly alkaline range and to remove impurities that may interfere with the coating reaction, thus providing a fundamental guarantee for long-lasting thermal paper (e.g., products with a shelf life of 5-10 years).
The surface treatment process of the base paper plays a decisive role in the adhesion of the coating and protective layer. Untreated base paper has low surface energy, making the coating prone to peeling or powdering, especially under frequent friction or high-temperature environments, where protective layer particles may detach and damage the printhead. Base paper treated with corona or coated with a primer, however, has significantly increased surface energy, forming a tightly bonded interface with the coating and enhancing abrasion and water resistance. For example, in extreme environments such as cold storage or outdoor labeling, specially treated base paper ensures that thermal paper maintains print clarity and structural integrity even under low temperature and high humidity conditions.
The basis weight (weight per unit area) and thickness of the base paper must be precisely matched to the intended use of the thermal paper. Low basis weight base paper (e.g., 40-50 g/m²) is often used for disposable labels or short-term stored receipts; it is inexpensive but lacks stiffness, making the coating susceptible to damage from folding or crumpling. High basis weight base paper (e.g., 70-90 g/m²) is suitable for archival labels requiring long-term storage or frequent handling; it has stronger tear and deformation resistance, better protecting the coating from mechanical damage. Furthermore, the thickness uniformity of the base paper must be controlled within ±5%, otherwise it may lead to fluctuations in coating amount, causing differences in printing quality within the same roll of paper.
The quality of the base paper affects the performance of thermal paper throughout the entire production process and its entire lifecycle. From coating uniformity to print clarity, from storage stability to equipment compatibility, the physical, chemical, and surface properties of the base paper must work synergistically with the coating process to produce high-quality thermal paper that meets the needs of different scenarios.
