What are the specific requirements for printing food packaging bags? The printing plate is used to transfer ink to the graphic carrier of the substrate. During printing, the ink adhered to the graphic part is transferred to the food packaging bag substrate under the action of pressure.

1. Letterpress: The blank part on the printing plate is concave, the graphic part is convex and on the same plane or the same radius of the arc, the height difference between the graphic part and the blank part is very different. Commonly used printing plates are type plate, zinc plate, and rubber letterpress.

2. Plate: There is no obvious difference between the graphic part and the blank part on the printing plate, and they are almost on the same plane. The graphic part is lipophilic and hydrophobic, and the blank part is hydrophilic and oleophobic.

3. The graphic part on the printing plate is concave, the blank part is raised and is on the same plane or the same radius of the arc, the structure of the layout is opposite to that of the letterpress. The depth of the depression in the graphic and text part of the layout corresponds to the level of the original image. The darker the image, the greater the depression depth. Commonly used printing plates are manual or mechanical engraving gravure, face gravure, and electronic gravure.

4. Stencil plate: The graphics on the plate are composed of holes that can print the ink onto the substrate, while the blank part cannot penetrate the ink. Commonly used printing plates include writing plate, hollow plate, silk screen plate, etc.