Why ink plays an important role in tinplate printing?

Tinplate printing employs the lithographic offset printing principle, leveraging the natural repulsion between ink and water. This method utilizes printing pressure to transfer images and text onto tinplate via a rubber blanket. Due to tinplate's unique physical and chemical attributes and its reprocessing capabilities, its printing process differs from standard offset printing.

Special ink requirements for tinplate printing are as follows:

Adhesion and Mechanical Properties:

Tinplate must undergo cutting, bending, and stretching before being fashioned into boxes. Consequently, the printing ink must exhibit strong adhesion and mechanical properties. To enhance ink adhesion, tinplate is often coated with a white primer before printing. White serves as the foundational color for all images, boasting high brightness. When combined with other high-energy hues, it elevates the value of each color, creating a spectrum of shades.

White Ink Specifications:

To achieve a metallic sheen on the tinplate's silver (or yellow) surface, a varnishing step is necessary prior to printing. Given the limitations of ink coverage, monochromatic prints often require double varnishing to achieve a whiteness level of 75%. Whiteness is a critical quality metric for tinplate printed products, necessitating that white ink maintains good cohesion with the ground ink, resisting yellowing or fading even after multiple high-temperature baking and steaming processes. Applying ground ink to tinplate enhances its adhesion, which is beneficial for white ink adherence. The typical ground ink is of the epoxy amine type, characterized by its light color, resistance to yellowing and aging after multiple bakings, and its processing properties of flexibility and impact resistance.

Color Ink Requirements:

The color ink used for tinplate printing should not only be water-resistant but also possess certain special characteristics. Since tinplate surfaces do not absorb water or solvents, the ink must be baked and dried, thus requiring it to be thermosetting. It demands high tinting strength and durability. Beyond the basic properties of general offset ink, iron ink should also exhibit heat resistance, strong adhesion of the ink film, impact resistance, good hardness, cooking resistance, and light resistance.

Ink Drying Process:

In tinplate printing production, ink drying involves a complex interplay of physical and chemical reactions. To manage the ink drying spread and its underlying mechanisms effectively, one can ensure swift and high-quality printing operations. If the ink dries too quickly, it can impair the ink's normal transmission performance and disrupt the production process, such as causing printing voids or light colors.

Overly rapid drying can lead to ink desiccation on the rollers and forme, obstructing ink transfer and resulting in the expansion of dry knot layers on the printing plate graphics;

Conversely, if the ink dries too slowly, it can cause poor trapping, inadequate adhesion, and reduced firmness, making the print susceptible to scratches during transmission. Therefore, the ink drying speed should be moderate, as both excessively fast and slow drying are detrimental.

Unique Structure of Printing Equipment:

Due to the diversity of printed products, the auxiliary machinery for tinplate printing presses differs from that of paper offset presses. Tinplate is insoluble in water and does not absorb solvents, so the printing ink must be baked at high temperatures to facilitate its volatilization, film formation, and curing. Thus, a drying room is essential in the printing process.

The total length of the tinplate printing automatic line is approximately 50 meters, highlighting its large scale and precision. Additionally, tinplate printing machines are controlled by magnetic splitting and double splitting, and the high hardness of tinplate dictates that an advanced continuous iron conveying system cannot be employed in the printing process. This differs from paper offset presses in the structure of the feeding section, alignment system, and stacking section.