INDUSTRY NEWS
The Surface Properties and Printing Fastness of Tinplate
1. Surface properties of tinplate
The surface performance of tinplate is the difference between the surface state and surface quality. There may be defects such as scars, pits, wrinkles, dust, and rust on the surface of tinplate. From the perspective of tinplate layout, there is often a very thin layer of oil film on the surface of tinplate. And it is generally made of electroplating, so the surface is smoother. Judging 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 mainly lithographic offset printing, and its process is as follows:
The surface roughness of tinplate is one of the important factors affecting printing fastness. The surface of the tinplate base material is relatively smooth as a whole. Although some organic coatings also have strong adhesion on the smooth surface, the overall absorption is poor and the adhesion is small, which makes the adhesion fastness and drying performance of the paint layer and ink layer affected.
3. The influence of oil film layer
In the tinplate structure, the surface layer is an oil film. This layer of oil film is to prevent the tinplate from rusting during storage and conflicting with each other during transportation, which will greatly reduce the adhesion fastness of the coating and ink. Therefore, it is very important to control the amount of oil film. At present, tinplate manufactured in various countries in the world does not have a certain standard for the thickness of the oil film. Generally, the amount of oil applied is controlled at 2-4mg/m2, but some are above 6mg/m2. If the amount of oil is too much, it will affect the printing quality of the tinplate, so that the coating and ink layer cannot completely wet the surface of the tinplate, the adhesion performance is poor, and "pinholes" are easy to form on the ink layer after baking and curing. The "pinhole" will cause the adhesion between the ink layer and the tinplate to drop. Therefore, when the amount of oil applied to the surface of the tinplate is high, that is, above 6mg/m2, the tinplate should be pre-baked once before printing to evaporate the excess oil film.
In addition, the smooth tinplate surface will not only reduce the ink adsorption force and print fastness, but also cause the ink drying rate to be slow and the conjunctiva to be poor due to poor adsorption performance, thereby affecting the adhesion fastness and wear resistance of the ink layer. As a metal material, tinplate will form a lot of fine water droplets on the surface of the tinplate when it encounters high air humidity and relatively large temperature difference, which will also reduce its adsorption force and affect the printing fastness.
4. Influence 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 layout of the tinplate will also affect the adhesion of the ink. There is a very thin oxide film on the surface of the tin layer 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, causing the ink adhesion to disappear. Therefore, passivation treatment must be carried out after tin plating to improve the stability of the oxide layer, prevent the growth of the oxide film, and maintain the stability of 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, there must also be coatings and inks with good performance, and it is best to treat the surface of the tinplate to improve Surface adsorption benefits.
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