Offset printing is one of the most common means of printing today. It is adopted so widely because of its ability to produce consistently high quality images. It is quick and easy to produce the printing plates, and it is also the cheapest means of printing high quality images. Its disadvantage is that it is costly and time consuming to set up, making it best for large projects, but inconvenient for smaller ones. This system is used for everything from newspapers to books and here is how it all works.
Instead of going step by step right away, we will begin with the basic concept of this type of printing. It starts with plates. These plates are dampened with water, then ink. The ink does not mix chemically with the water, so the ink adheres to the image area while the water adheres to everywhere else. The image (now covered with ink)is transferred onto a rubber printing blanket and that blanket is what comes in contact with the paper, creating the printed image. This is where offset printing gets its name, as the plates never come into contact with the paper itself.
Printing plates can be made with a variety of materials, the most popular being aluminum and paper as a cheaper alternative. Paper doesn’t produce as high quality of an image though, so it is used sparingly. The plates are prepared in a manner very similar to photography. The plates have a chemical reaction to light, and when filtered through the negatives of the images you wish to print, you can impose that image onto a plate as the light is activating an ink receptive chemical. Now the plates are ready to use.
In order to keep production flowing, the whole process works with rolls. The ink and water are both rolled onto a larger cylinder, which rolls against the blanket cylinder, which is what comes in contact with the paper. This concept is best explained with an image, so here is a little diagram to help understand.
Once through the printing itself, the paper is still a bit wet and risks smudging. To help the paper dry it is run through an oven heated to about 350 –400 degrees Fahrenheit. Once out, the project is run through a series of “chill” rollers. These rollers are metal and have cold water running through them to cool the paper, thus helping the ink set in. Without this process, the ink would stay at risk of smudging. After that there is a quality control section that judges the amount of ink and alignment of the plates, entirely digitalized.
The final step is called bindery. The sheet of paper is cut into pages and placed in order, then bound together. The last moment of this step is cutting the project to its final delivered size.
The project, now completed, can be shipped to wherever it is needed!
How Offset Printing Works
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