The whiteness and smoothness of thermal paper are important physical indicators that affect the clarity of printing. The two seem independent, but they are interrelated in the printing process and jointly determine the final imaging effect. When we get a printed thermal ticket or label, the clarity of the handwriting, the depth and contrast of the color, and even the details of the image are inseparable from the performance of these two indicators. Understanding their specific impact on the clarity of printing can help optimize the quality of thermal paper from the source of the material, and can also provide a more accurate basis for selection for actual application scenarios.
Whiteness is directly related to the visual contrast of the content printed on thermal paper. The so-called whiteness refers to the ability of paper to reflect the full wavelength of visible light. thermal paper with high whiteness presents a purer white base when it is not printed. When the thermal print head heats the coating, the color-developing substance reacts chemically to form dark handwriting. At this time, the greater the contrast between the white base and the dark handwriting, the higher the clarity perceived by the human eye. If the thermal paper is not white enough, the base color is gray or has other tones, which will cause the contrast between the handwriting and the background to decrease, just like writing on paper that is not white enough, even if the strokes are clear, they will appear blurry. This weakening of visual contrast not only affects the readability of the text, but also blurs the transition of the image layers, reducing the fineness of the overall printing effect.
Smoothness affects the uniformity of printing from a microscopic structure. Thermal paper with high smoothness has a fine and smooth surface, and the coating particles are evenly distributed. When the print head is heated, the heat can be more evenly transferred to all parts of the coating, making the color reaction consistent, thus forming clear edges and uniform shades of handwriting. On the contrary, paper with low smoothness has microscopic bumps or particle agglomerations on the surface. When heated, the local heat distribution is uneven, which may lead to uneven color depth and burrs or breakpoints on the edges of the handwriting, just like writing with a pen on rough paper, the ink easily penetrates or accumulates, forming blurred strokes. Especially when printing small text or high-precision images, insufficient smoothness will cause details to be lost. For example, the lines of the barcode may be uneven in thickness, making it difficult to scan and recognize. This is particularly critical in scenes with high clarity requirements such as logistics labels and product barcodes.
The synergistic effect of whiteness and smoothness will amplify the impact on print clarity. A thermal paper with high whiteness but low smoothness may have a good contrast between the base and the handwriting, but due to the uneven color development caused by the rough surface, the handwriting may appear "mottled", that is, light spots are mixed in the dark part; while a paper with high smoothness but low whiteness may appear dim and lack transparency even if the color development is uniform. Only when both are at a good level can the ideal printing effect be achieved: the white base is pure and bright, providing a vivid background for the handwriting, while the smooth surface ensures uniform color development, so that every stroke and every pixel can be clearly presented, just like a high-quality canvas can better show the details of the painting.
The impact of environmental factors on the whiteness and smoothness of thermal paper will also indirectly affect the print clarity. For example, if thermal paper is exposed to moisture or pollutants in the air during storage, the whiteness may decrease, and the originally white base will become yellow or gray, resulting in a decrease in contrast when printing; and long-term friction or pressure may destroy the smooth structure of the paper surface, causing the coating particles to shift or agglomerate, affecting the color uniformity when heated. This change is very common in practical applications. For example, if supermarket cash register paper is not stored properly, even if the original whiteness and smoothness meet the standards, the printed characters may be blurred when used. This requires that the protection of these two indicators should be taken seriously in the production, storage and use of thermal paper.
Different application scenarios have different requirements for the whiteness and smoothness of thermal paper. In the bill scene that needs to be preserved for a long time, high whiteness can delay the impact of yellowing of the base on the contrast, while higher smoothness can reduce the surface structure damage caused by paper aging and maintain the clarity of the printed characters; for logistics labels that need to print fine images or barcodes, the importance of smoothness is more prominent, and only a delicate surface can ensure the accurate restoration of lines and patterns; in temporary recording scenes with relatively low requirements for clarity, the whiteness and smoothness indicators can be appropriately relaxed, but basic readability must still be ensured. This difference in scenarios requires thermal paper manufacturers to accurately adjust these two indicators according to customer needs to achieve a balance between cost performance and printing effect.
Improving the whiteness and smoothness of thermal paper requires starting from both raw materials and production processes. In terms of raw material selection, the use of high-purity fillers and high-quality coating raw materials can improve the whiteness of paper and improve the surface fineness; in the production process, the uniformity of the coating thickness is controlled through a precise coating process, and the surface of the paper is treated through processes such as high-temperature calendering, which can effectively improve the smoothness. At the same time, optimizing the pulping and sizing process in the papermaking process can also help improve the whiteness and structural uniformity of the paper matrix. These process improvements can not only directly improve the print clarity, but also enhance the comprehensive performance of thermal paper, so that it can maintain stable performance under different use conditions.
The whiteness and smoothness of thermal paper are like the "basic canvas" of print clarity. They jointly construct the premise of high-quality printing effects from the two levels of macroscopic visual contrast and microscopic color uniformity. Whether it is a cash register receipt in daily consumption or a logistics label in an industrial scene, paying attention to the performance of these two indicators can not only ensure the clarity of instant printing, but also extend the identifiable period of the printed content. With the application of thermal printing technology in more fields, the refined control of the whiteness and smoothness of thermal paper will become a key direction to improve printing quality and promote the deep fit between material performance and printing needs.
