Packaging printing is an important means and way to increase the added value of goods, enhance product competitiveness and expand the market. Designers should understand the necessary packaging printing process knowledge to make the designed packaging works more functional and beautiful. Different packaging materials will have different printing processes. This issue collects and organizes the content to share the relevant knowledge of printing process.

Paper packaging printing process
1. Printing method
There are many methods for paper packaging printing. Different methods have different operations and different printing effects. The traditional printing methods are mainly divided into the following four categories:
(1) Letterpress printing
Letterpress printing means that the image part on the printing plate is higher than the non-image part. The ink on the ink roller can only be transferred to the image part of the printing plate, while the non-image part has no ink, thus completing the printing of the printed product.
If the back of the printed product has a slight impression, the edges of the lines or dots are neat, and the ink appears light in the center, it is a letterpress print.
(2) Gravure printing
In contrast to letterpress printing, the image part of the printing plate is lower than the non-image part, forming a groove shape. The ink is only applied in the grooves, and there is no ink on the surface of the printing plate. The paper is applied to the upper part of the printing plate, and the printing plate and the paper are pressed to transfer the ink from the concave part of the printing plate to the paper.
The printed products of gravure printing have a thick ink layer and bright colors, and the printing plate has the advantages of high printing durability, stable print quality, and fast printing speed, so it has been widely used in practice.
(3) Planographic printing
The image and non-image parts of the printing plate keep the surface flat, the image part is covered with a layer of oil film rich in grease, and the non-image part absorbs appropriate moisture. When applying ink, the image part repels moisture and absorbs ink, and the non-image part forms an ink-resistant effect due to the absorption of moisture.
(4) Screen printing
Screen printing refers to the process in which the ink leaks from the mesh of the image part to the substrate under the extrusion of the scraper, while the mesh of the non-image part is blocked, so that the ink cannot leak to the substrate, thereby completing the printing of the printed product.

2. Printing process
There are many printing processes for paper packaging. Here are some commonly used printing processes:
(1) Hot stamping process
The hot stamping process is to make the required hot stamping or silver stamping pattern into a convex plate and heat it, then place the required color of aluminum foil on the printed material, and then apply pressure to make the aluminum foil adhere to the printed material.
(2) Laminating process
Laminating process is a surface processing process after printing. It refers to a product processing technology that uses a laminating machine to cover the surface of the printed product with a layer of transparent plastic film.
(3) Concave and convex embossing process
This process uses the greater pressure of the relief printing machine to press the local pattern or text on the printed semi-finished product into a concave and convex image with a three-dimensional sense.
(4) UV anti-metal etching printing process
UV anti-metal etching printing, also known as frosted or sand surface printing, is a process in which a layer of uneven translucent ink is printed on a substrate with a metallic mirror luster (such as gold or silver cardboard), and then cured by ultraviolet light (UV) to produce an effect similar to that of a shiny metal surface after etching or frosting.