Thursday, 1 March 2012

An Offset Press And Four Color Copies

By Phyllis P. Kinder


When a person goes into a printing shop on a regular basis they expect certain things to occur. They know the person working there will look over the documents very carefully to make sure everything is in order. They will be assured of a genuine pick up time for the presentation, brochure, or pamphlet they dropped off. There is no doubt that the color copies will have the look and feel the customer is searching for. What may not be as known is the process the printer takes to turn the order into a stack of printed material.

A common method has been using a lithographic offset printing press. This machine has remained almost virtually unchanged since its inception in 1843. Richard Hoe took two methods that printing was being done and combined them into one mechanism. He found that if one put a negative onto a piece of metal that spun around, they could eventually duplicate that image on a piece of paper.

In the beginning there was a photographic component to the lithographic offset printing process. They had to make a photographic negative that was used to project the image onto the rubber blanket. This aspect is now being done by digital computers that have the ability to make their own negative.

The negative is connected to the cylinder made of metal. The cylinder spins around continuously when the press is working. There are a number of devices that moves the ink the printer places in the machine to where it is applied to the document.

The printer will place some ink into an ink duct. Ink moves onto a roller and gets spread along the surface as the roller rotates. Ink is transferred from one roller to the distribution rollers. These rollers place the ink on the printing plate and then onto the rubber blanket. When paper is pressed against the rubber blanket, then the image is completely transferred.

There are primary colors which are used in printing. The primary colors are cyan, magenta, black, and yellow. With these a printer can easily make blue, green, and red for printing purposes. There are many shades and hues that can also be created when mixing these inks. However, each layer must be put down separately on the paper and each must have their own negative.

Most people are used to printing service companies being around. They understand that this is where you go for professional looking color copies of documents one may want. What they may not know is how those documents are actually made.




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