1. Surface properties of tinplate
The surface performance of tinplate, that is, the surface condition and the quality of the surface are poor. The surface of the tinplate may have defects such as scars, pits, wrinkles, dust, and rust. From the structure of the tinplate, the tinplate surface often has a very thin oil film. And it is generally electroplated, so the surface is relatively smooth. From the relationship between the specific surface area of ​​the solid surface and the adsorption force, the adsorption force of tinplate is not very good.
2. Surface properties affect printing fastness
Tinplate printing is dominated by offset printing, and the process is as follows:
The surface roughness of tinplate is one of the important factors affecting printing fastness. The surface of the tinplate substrate is generally smooth. Although some organic coatings also have strong adhesion on a smooth surface, the overall absorption is poor and the adhesion is small, which makes the adhesion fastness and drying performance of the coating layer and the ink layer. affected.
3. Influence of oil film layer
In the tinplate structure, there is an oil film on the surface. This oil film is to prevent the tinplate from rusting during storage and rubbing against each other during transportation, which will greatly reduce the adhesion fastness of the coating and ink. Therefore, the control of the amount of oil film is very important. At present, tinplate produced in various countries in the world does not have a certain standard for the thickness of the oil film. Generally, the amount of oil is controlled at 2 to 4 mg / m2, but some are more than 6 mg / m2. If too much oil is applied, the printing quality of the tinplate will be affected, so that the coating and ink layer cannot completely wet the surface of the tinplate, and the adhesion performance is poor. It is easy to generate "pin holes" in the ink layer after baking and curing. The "pinhole" will cause the adhesion between the ink layer and the tinplate to decrease. Therefore, when the amount of oil on the surface of the tinplate is high, that is, above 6mg / m2, the tinplate should be pre-baked before printing to evaporate too much oil film.
In addition, the smooth tinplate surface will not only reduce the ink's adsorption force, but also reduce the printing fastness. Due to the poor adsorption performance, the ink's drying speed is slow and the conjunctiva is poor, which affects the adhesion fastness and wear resistance of the ink layer. As a metal material, tinplate will form many small water droplets on the surface of tinplate when it encounters high air humidity and large temperature difference, which will also reduce its adsorption force and affect the printing fastness.
4. Effect of oxide layer
In addition to the oil film on the surface of the tinplate will affect the adsorption force, the second layer of oxide film in the tinplate structure will also affect the adhesion of the ink. There is a thin oxide film on the surface of tinplate of tinplate. The structure of this oxide film is unstable, and it will continue to oxidize and thicken, and even cause the ink layer on the oxide film to fall off, so that the ink adhesion performance is lost. Therefore, tinplate should be passivated after tin plating to improve the stability of the oxide layer, hinder the growth of the oxide film, and maintain the stability of the ink adsorption.
Therefore, the surface properties of tinplate will have a greater impact on the printing fastness of the ink. In addition to good quality tinplate, it also needs good performance coatings and inks, and it is best to treat the surface of the tinplate to improve Surface adsorption force.
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