Flexography, or flexo for short, is a form of printing that is common in packaging. The printing plate is the heart of the process and is essentially a high-tech flexible rubber stamp made of a plastic material. The image area (the area that will print the image) is raised up so that ink can be applied to it without the non-image recessed area (the area that will not print) receiving ink.
Take a look at the “FLEXO” rubber stamp and the image it produced. The word “FLEXO” is raised to receive ink from the ink pad and to transfer the image to the paper.
Now look at the nutrition facts panels on the green flexo plate images above. The raised image area accepts ink and then transfers that ink to the paperboard. The non-image recessed area does not receive ink and does not contact the paperboard. Note that the image is reversed on the stamp and plate so that they print positive on the paper.
The printed nutrition facts panel is above.
The flexo plate gets wrapped around the plate cylinder before going into the press.
An inking cylinder called the anilox contacts and transfers ink to the plate. The inked plate contacts the paperboard and transfers the image to the sheet much the same way the rubber stamp makes contact with, and transfers its image, to the paper.
The image above shows the anilox in the foreground, the plate wrapped around the plate cylinder in the middle and the image printed on the substrate in the background.
Flexo plates are made of a special material called photopolymer. That material allows the plate to carry images with very small dots so that it can print process work (see our four-color process printing blog). See the dots that make up the words “Est. 1905” in the image above.
The photopolymer plates are so advanced that they can print images that are at least 133 line screen. That means that in one linear inch the plate can hold 133 dots and each of those dots can be one or two percent of that. They can be as small as .0002” inches.