1. Printing ink:
a) Dryness and heat resistance of the ink, the curing of the printing ink must be heated and dried, so the white ink after heating is required to be unchanged, not yellow, the color ink does not fade, does not change color, the coating oil does not lose light, iron printing ink Generally cured by 150°C, 10-12 minutes, but usually after the process such as Varnish baking high frequency resistance welding, internal coating, full spray baking, the temperature should reach 180-220°C, therefore, the ink heat resistance It is even more important.
b) Solvent resistance. After the printing, the coating oil contains various solvents. In order to prevent bleeding when the coating is applied, the ink must have good solvent resistance.
c) Resistance to retort: Containers filled with food must be sterilized at high temperatures. Therefore, printing ink should not be bleeded, faded or softly detached due to wet steam.
d) Process resistance. Most of the printed iron products have to undergo stamping, punching, bending, flanging, crimping and other processes, so the ink layer on the surface of the metal sheet should have a strong structure, requiring the printing iron ink has good adhesion, flexibility, surface hardness and impact resistance strength.
e) Light and weather resistance. Various daily necessities are generally stored for a long time, so it is required that the printing ink cannot fade and deteriorate due to light irradiation or climatic factors.
f) The ink layer does not contain heavy metals. Many Indian iron products such as toy boxes, chess boxes, battery shells and other export products, the heavy metal content in the ink should also meet the United States, Japan, the European Union's corresponding standards.
Finished all printed tinplate prints, need to be covered with a layer of bright oil, in order to increase the surface gloss and scratch resistance of the print, but also increase the hardness, so that the printed surface coating has a certain degree of flexibility and corrosion resistance. Varnish should have the following properties:
a) The color retention performance is good, and the solvent in the varnish cannot make the ink bleed or fade.
b) Has sufficient hardness and firmness to withstand the processing distortion of the subsequent process.
c) Match white or base oils and do not attack white or base oils.
Bright oil common epoxy resin, alkyd resin, acrylic resin, amino acid and other amino acid, the composition is different, the performance is also different, the use is not the same. Usually, different types of varnish are used depending on whether there is deep stamping deformation in the post-process, local high-temperature heating of the welding and whether high pressure cooking is required.
In order to increase production efficiency and save energy, the final printing process is generally combined with the coating process.
In addition to coating with a roller, coating can also be used for printing glossy inks. There is not much difference in gloss between the two, but the processing performance is not as good as roller coating.
In addition to bright oil, there are matte oils, wrinkle oils, and pearlescent oils. Bright oil has a high gloss effect, which is in line with people's traditional aesthetic habits. Matte oil, on the other hand, can make the surface of printed iron products dull, with a papery texture and elegant decorative effect. After the wrinkle oil coating is formed, it is shaped like crystal transparent scaly. The light reflection makes the beautifully printed pattern on the tinsel three-dimensional. From a different point of view, it is rich in art appreciation value. The pearl varnish is applied to a large area of the exposed white plate with a pearl-like luster to set off the bright and bright printed artwork. It also has high aesthetic value.
3. Drying process and requirements
All paints and inks need to be dried. The drying process is determined by the following three parameters: A. The temperature set by the oven, B. The time for maintaining the peak temperature.
Drying room is usually composed of three parts: warming zone, constant temperature zone, cooling zone. The main function of the temperature rising zone is to raise the iron sheet from room temperature to a set temperature. The main function of the constant temperature zone is to maintain the temperature reached in the temperature rise zone. The role of the cooling zone is to allow the dried iron sheet to be sufficiently cooled. If the cooling is insufficient, the paint film is easily scratched when the iron sheet is collected, and the sticky sheet easily occurs after the stacking.
If the peak temperature is kept too low, the paint or ink will not be fully baked, which will cause the ink and paint to be soft and unable to fully exert its protection or other functions. After high-temperature cooking tests, adhesion is often poor. If the peak temperature is kept too long, excessive baking will occur, the paint will become brittle, and it will break easily during processing. Overbaking will also cause yellowing of the paint and ink.
In order to avoid insufficient baking and excessive baking, the oven temperature profile must be checked regularly to determine the temperature peak time at the standard machine speed.