When flatbed UV printer directly print onto smooth materials like glass and metal, the ink spreads out and the images can't be well-shaped. Painting a layer of coating onto the surface of the material, the surface will be slightly corroded and the smoothness will be decreased, then a solid continuous film formed. This film in fact is the coating itself, it not only increases the adsorption of ink and develop the image quality, but also avoid the shedding and color fade of images.

Not all materials need coatings. Such as phone cases printing and textile printing. But when it comes to leather printing and some advertising printing etc., the coating is indispensable. And what are the main types of coatings? Here Yueda Printing Technology(YOTTA) lists some common ones:

1. Glass coating: mainly applied to ceramic tiles, glass, background walls, tempered glass, crystals, sliding doors, screens and more. It has two colors: transparent and white. Both of them can be used for gloss and matte finishes. The adsorption of ink becomes very important when the material demands high boiling-water resistance and the coating is generally equipped with mineral oil. Noted the mineral oil can't be too concentrated.

2. Leather coating: mainly applied to bags, shoes, PVC leather, PU leather and more. It's transparent or white and can be used for gloss and matte finishes.

3. Silicone coating: mainly applied to toys and rubbers etc. These materials need flame process and the coating can't be too thick, otherwise it is hard to be dried.

4. PC coating: mainly applied to PS, PP, PVC materials.

5. Metal coating: mainly applied to aluminum, copper, tin and when special treatment is needed for ceramic and tempered glass. It's white or transparent and can be used for gloss and matte finishes. CP metal coating dries quickly, spray it thickly and DY metal coating dries slowly, spray it thinly.

6. ABS coating: mainly applied to wood, PVC, ABS, plasterboard, acrylic, PS, PVC, regular rubbers and more.

In conclusion, each coating has its own feature and we cannot use them arbitrarily during UV printing process, otherwise the ink adsorption decreases or even worse, the ink dissolves into the coating.