why tinplate bottom always need clear coating

Clear coating commonly includes epoxy resin, alkyd resin, acrylic resin, acrylic amino, etc., with different components, different properties, and different uses. Usually, different types of varnishes should be selected according to whether there is deep stamping deformation in the subsequent process, local high-temperature heating of welding and whether high-pressure cooking is required.
To increase production efficiency and save energy, the last printing process is usually combined with the varnishing process.
In addition to roller coating, glazing can also be printed with bright ink. There is not much difference in gloss between the two, but the processing resistance is not as good as roller coating.
In addition to bright varnish, there are matte oil, wrinkle oil, pearl varnish. Bright oil achieves a high gloss effect, which is in line with people's traditional aesthetic habits. On the contrary, matt oil can make the surface of printed iron products matt, with paper texture and elegant decorative effect. After the wrinkle oil is painted and formed, it is in the shape of crystal-transparent scales, and the reflection of light makes the exquisite patterns printed on the tinplate full of three-dimensional effect. From different angles, it has a high artistic appreciation value. The pearl varnish is coated on a large area of white layout, with a pearl-like luster, which sets off the brilliance of the printed graphics and has a high aesthetic value.