The adhesion of the ink coating on the surface of tinplate has always been a question that professionals have been discussing and carefully studying in practice for a long time. It is related to the surface properties of the tinplate itself, the type of ink used in the printing process, the type of coating, the temperature of the drying oven, and the thickness of the ink coating and many other factors. Now I will talk about my superficial views on how to control the baking temperature of tinplate after printing.
The object of metal printing is a non-absorbent material-low-carbon tinned sheet steel, commonly known as tinplate. The principle of tinplate printing is similar to that of lithographic offset printing, but there are special aspects in the process, such as:
1. After the tinplate is printed, the ink stays on the surface and must be dried and solidified by some form of heat energy;
2. The tin layer on the surface of the tinplate is bright and shiny, and it belongs to the black phase based on the spectral characteristics. Therefore, before color printing, a layer of white paint must be applied to the surface of the tinplate. Of course, sometimes according to the special artistic effect of the product pattern, it can also be partially painted with white paint or directly use the appearance of the tinplate tin surface itself;
3. After tinplate printing finished product. It needs to be transferred to the next process for mechanical processing to produce various shapes of containers or other packaging. In the process of mechanical processing, the ink coating on the surface of the tinplate must be resistant to mechanical impact and extension. For special products such as canned food containers, the metal offset printing machine ink coating must have physical properties that are resistant to high-pressure cooking. This requires excellent adhesion between the ink coating and the surface of the tinplate.
Tinplate printing, the surface ink is dried by heat curing, which is one of the main characteristics that distinguish metal printing from offset printing.
Because the resin and pigment components of the paint and ink used in each process are different, the baking temperature of the printing dryer is also different. Strictly controlling the baking temperature of each process is the key to the quality of tinplate products, and it will directly affect the adhesion of the entire ink film. If the baking temperature is too low, the chemical molecular bonds in the resin will not be fully cross-linked and cured to form a film. Not only does it have no adhesion, but it will also cause the back of the tinplate to be dirty and reverse printing. The next process will cause the tinplate to separate due to ink adhesion. Difficulty in tensioning, affecting color registration (the back of the tinplate is tied to the inner wall of the container, and dirt will contaminate the contents of the container).
However, the baking temperature of the printing dryer is too high, the chemical bond is broken, the ink film layer is embrittled and cracked, and it cannot withstand mechanical processing and high temperature sterilization and fall off. Therefore, it is necessary to strictly control the baking temperature of each process, and regularly check the temperature in the oven for drying, and strive to achieve the error between the actual temperature value in the drying oven and the temperature value of the oven temperature indicator is between 13°C. As an experienced drying oven factory, RUIYUAN also provides high quality ovens for paint drying.
At the same time, in the printing process, the circulating air volume should reach 21600m3/h. The electric heating tube, automatic temperature controller and temperature display in the drying room must work normally. The operating speed of the machine should also be controlled within a certain range to ensure proper baking time for the ink coating.