 |
 |
 |
 |
 |
 |
 |
A Walk Through the
Offset Printing Process
In our last issue of the newsletter, we compared digital and offset printing. Since offset printing is a little more complex, we thought we would walk you through the process in more detail.
In a nutshell, an image is burned onto a plate, then it is transferred from the plate to the rubber blanket (cylinder), and then offset to the paper. But how is the plate made? And why does the ink only adhere to the image?At HPI, we have a computer-to-plate (CTP) process. The digital file is sent from the computer to the plate output device. Each plate can be used for only one color of ink. For example, four-color process uses four plates: Cyan, Magenta, Yellow, and Black. Let’s say you are printing a four-color newsletter. When the newsletter is sent to the plate output device, the “image” of the newsletter file is separated out by color. As the individual plates pass through the CTP output device, each is exposed by laser to light, burning the image of the newsletter onto each corresponding plate.
The “magic” of the process is that ink and water do not mix. The chemically treated plate attracts the ink to the burned, or image, area. The smooth, non-image area of the plate attracts the water, forming a film that will repel the ink.
The plates are placed on cylinders within the press. As ink is applied to the plate, it transfers onto the rubber blanket. The plate does not have direct contact with the paper, since paper can wear down the metal plate and cause inconsistencies in the image. The rubber blanket is used to lessen the friction and keep the plate from wearing. As sheets of paper are fed through the press, the rubber blanket offsets the image to the paper.
Because of the nature of the process, we have a few tips to help you save money with offset printing:
• It is more cost effective to print larger quantities at the same time. The more you run at the same time, the lower the per-unit cost will be.
• Another great way to save is to have multiple pieces running together on the same press sheet. For example, run your business cards and a rack card together. (See the article, “Ganging up jobs can save dollars,” in our summer 2008 newsletter, archived online.)
• Utilize spot screens to add the look of multiple colors to your project without the added cost. (Learn more about spot screens in our fall 2008 newsletter online.)
