What are the special requirements for ink in tin box printing?

What are the special requirements for ink in tin box printing?
Ink should have good adhesion and mechanical properties
Due to the fact that tinplate printing materials ultimately need to be made into food cans, toys, metal frames, and barrels and cans of chemical products, which require cutting, bending, and stretching processes, printing ink is required to have good adhesion and corresponding mechanical properties to tinplate. To improve ink adhesion, it is necessary to first apply a white primer to the sheet before printing. White is the fundamental color of all images and has a high brightness. After adding other high-energy colors, the brightness of each color can be increased to form a color scale.
Requirements for white ink
The surface of tinplate is silver white (or yellow) with a metallic luster. Before printing color images and texts, the surface needs to be painted or printed white. Due to the limitation of ink coverage ability, a monochrome machine often needs to go through two white prints, with a whiteness of up to 75%. Whiteness, as an important indicator of the quality of tinplate printing products, requires white ink to have good adhesion with the primer, and to withstand multiple high-temperature baking without yellowing and high-temperature steaming without fading. Applying primer to tinplate can increase its adhesion to tinplate and have good adhesion to white ink. The commonly used primer is epoxy amine based, which has the characteristics of light color, non yellowing after multiple baking, non aging, and good flexibility and impact resistance.
Requirements for color ink
The color ink for sheet printing should not only have a certain degree of water resistance, but also have special requirements. Due to the impermeability of moisture and solvents on the surface of tinplate, it needs to be baked and dried, so its ink should be heat cured. The requirements for the coloring power and durability of pigments are high. In addition to the basic properties of general offset printing ink, printing ink should also have characteristics such as heat resistance, strong ink film adhesion, impact resistance, good hardness, cooking resistance, and light resistance according to the characteristics of printing ink.
Drying process of ink
In the production of tinplate printing, the drying of ink is a complex physicochemical reaction process. To effectively carry out rapid printing operations and ensure product quality, it is necessary to reasonably control the drying speed of ink and grasp the physical and chemical mechanisms involved in ink drying. Drying the ink too quickly will reduce its normal transmission performance and affect the normal production process; Causing blurred imprints, faded ink color, and ink drying on the surface of the printing plate and ink roller, hindering the transfer of ink; Expanding the dry layer of the printing plate image and text outward; Excessive use of desiccant leads to increased ink adsorption and dirty blank areas. And if the ink dries too slowly, it can cause difficulty in overprinting, adhesion, adhesion, and reduced firmness; Easy to cause scratches during transmission. So the drying speed of the ink should be appropriate, as either too fast or too slow is detrimental.
Special structure of printing equipment
Due to the different substrates, the auxiliary mechanism of the sheet printing machine is also different from the paper offset printing machine. Tinplate is insoluble in water and does not adsorb solvents, so printing ink needs to be baked at high temperatures to allow the solvent to evaporate and solidify the film. Therefore, the printing process equipment generally needs to be equipped with a drying room. The total length of the entire tin plate printing automatic line is generally about 50 meters, which has the characteristics of precision and bulkiness. In addition, the sheet printing machine utilizes magnets to split and double