Offset printing is a printing technique where you have a plate covered in ink that transfers, or offsets, the image to a rubber blanket, and from the blanket to the medium. Although in 2011 you can have other forms of printing that are more advanced, many industries still use offset printing. Because of its varied applications, you use a number of different plates in offset printing.
Offset Printing
Offset printing is a process that involves a number of steps. The technique applies ink to a plate, the plate presses against the rubber mat and the mat presses against the medium to transfer the image that was originally on the plate. Because of their central role in the printing process, the plates have evolved into a variety of types, each with specific uses and materials.
Aluminum Plates
Aluminum is the most common metal for offset printing plates, although you can also use ceramic plates or older-style copper plates. Lightweight and immune to oxidation, you can anodize aluminum with special treatments and or use special coatings to ensure that it lasts as a plate material and that it will react favorably to inks and other printing chemicals.
Lithographic Plates
The theory behind offset lithographic plates is that oil repels water. You treat all of the non-printing areas of a lithographic plate with a substance that will attract a water-based film. All of the areas that you don't treat will attract ink, ensuring that the ink won't bleed into the non-printing areas because the water-based film repulses the oil in it.
Wipe-Off Plates
Offset printing plates that you use to recreate images in great detail have anodized coatings, special inks, film treatments and other chemical enhancements to make sure the images you transfer are as crisp and clean as possible. You can also use plain, untreated plates. These plates have raised letters, and you use these plates most often in letterpress and newspaper printing. Often referred to as wipe-off plates, they are the most simple and straightforward to use. You coat the plate with ink, use the plate and wipe off the ink after use.
