Offset printing, also known as offset lithography, is a commonly used printing technique for producing high-quality, large-volume print materials such as newspapers, magazines, brochures, posters, packaging, and more. It is called "offset" because the ink is not directly transferred from the printing plate to the paper but is offset onto an intermediate surface before being applied to the paper.
Here's how offset printing works:
Image Preparation: The first step involves creating a printing plate for each color used in the design. Traditionally, this is done through a photographic process, where a negative image of the content is transferred onto a printing plate. For full-color printing, there are typically four plates: cyan, magenta, yellow, and black (CMYK).
Plate Transfer: Each printing plate is mounted onto a plate cylinder on the offset printing press. The image on the plate is treated to attract ink in the areas where printing is required and repel ink in non-printing areas.
Ink Application: The printing press has a series of rollers. The first roller, called the ink roller, transfers ink onto the image areas of the plate. However, the ink doesn't go directly onto the paper.
Blanket Cylinder: The inked image on the printing plate is then transferred onto a rubber-coated cylinder called the blanket cylinder. The blanket cylinder receives the inked image from the plate and then transfers it to the paper.
Paper Feeding: The paper is fed through the offset press and comes into contact with the blanket cylinder, where the ink is transferred onto the paper. Multiple sheets of paper are fed through the press in rapid succession, making it suitable for high-volume printing.
Drying: After the ink is applied to the paper, it needs to dry. Offset printed materials typically pass through a drying system, which may use heat, air, or ultraviolet (UV) light, depending on the type of ink used.
Finishing: Once the printing is complete, the printed materials can undergo finishing processes such as cutting, folding, binding, or other post-printing treatments, depending on the final product's requirements.
Offset printing offers several advantages, including high-quality, consistent results, the ability to print on a wide range of paper types and sizes, and cost-effectiveness for large print runs. It is a versatile and widely used printing method in the commercial printing industry, although digital printing has gained popularity for short-run and on-demand printing due to its flexibility and speed.