Offset printing is a commonly used printing technique in which the inked image is transferred (or “offset”) from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called “fountain solution”), keeping the non-printing areas ink-free.
Development of the offset press came in two versions: In 1875 by Robert Barclay of England for printing on tin, and in 1903 by Ira Washington Rubel of the United States for printing on paper.
Offset Printing Today
Offset lithography is one of the most common ways of creating printed matter. A few of its common applications include: newspapers, magazines, brochures, stationery, and books. Compared to other printing methods, offset printing is best suited for economically producing large volumes of high quality prints in a manner that requires little maintenance. Many modern offset presses use computer to plate systems as opposed to the older computer to film work flows, which further increases their quality.
Advantages of offset printing compared to other printing methods include:
- Consistent high image quality. Offset printing produces sharp and clean images and type more easily than, for example, letterpress printing; this is because the rubber blanket conforms to the texture of the printing surface.
- Quick and easy production of printing plates.
- Longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface. Properly developed plates used with optimized inks and fountain solution may achieve run lengths of more than a million impressions.
- Cost. Offset printing is the cheapest method for producing high quality prints in commercial printing quantities.
A further advantage of offset printing is the possibility of adjusting the amount of ink on the fountain roller with screw keys. Most commonly, a metal blade controls the amount of ink transferred from the ink trough to the fountain roller. By adjusting the screws, the gap between the blade and the fountain roller is altered, leading to the amount of ink applied to the roller to be increased or decreased in certain areas. Consequently the density of the colour in the respective area of the image is modified. On older machines the screws are adjusted manually, but on modern machines the screw keys are operated electronically by the printer controlling the machine, enabling a much more precise result.
Disadvantages of offset printing compared to other printing methods include:
- Slightly inferior image quality compared to rotogravure or photogravure printing.
- Propensity for anodized aluminum printing plates to become sensitive (due to chemical oxidation) and print in non-image/background areas when developed plates are not cared for properly.
- Time and cost associated with producing plates and printing press setup. As a result, very small quantity printing jobs may now use digital offset machines.
Digital vs. Offset Printing:
Advantages of each and how to decide which is right for your project.
The growth of digital printing technology has brought technical advancements, more options, and exciting new features to today’s commercial printing. It’s also brought some confusion. An understanding of the advantages and disadvantages of digital printing and how those compare to traditional offset lithography is critical in making the right choice.
Offset lithography is the most common high volume commercial printing technology. In offset printing, the desired print image is burned onto a plate and is then transferred (or offset) from the plate to a rubber blanket, and then to the printing surface. The lithographic process is based on the repulsion of oil and water. The image to be printed gets ink from ink rollers, while the non printing area attracts a film of water, keeping the non printing areas ink-free.
Mechanical Steps Eliminated in Digital Printing
Digital printing eliminates many of the mechanical steps required for conventional printing, including making films and color proofs, manually stripping the pieces together and making plates.
Advantages of Digital
- Shorter turnaround.
- Every print is the same. More accurate counts, less waste and fewer variations, due to not having to balance ink and water during press run.
- Cheaper low volume printing. While the unit cost of each piece may be higher than with offset printing, when setup costs are included digital printing provides lower per unit costs for very small print runs.
- Variable Data Printing is a form of customizable digital printing. Using information from a database or external file, text and graphics can be changed on each piece without stopping or slowing down the press. For example, personalized letters can be printed with a different name and address on each letter. Variable data printing is used primarily for direct marketing, customer relationship development and advertising.
Advantages of Offset
- High image quality.
- Works on a wide range of printing surfaces including paper, wood, cloth, metal, leather, rough paper and plastic.
- The unit cost goes down as the quantity goes up.
- Quality and cost-effectiveness in high volume jobs. While today’s digital presses are close to the cost/benefit ratio of offset for high quality work, they are not yet able to compete with the volume an offset press can produce.
- Many modern offset presses use computer-to-plate systems as opposed to the older computer-to-film work flows, further increasing quality.
Still Not Sure Which is Right?
Use this checklist to help decide:
- Quantity. Offset printing has a front-end cost load. Short runs may have a high unit cost. But as quantities increase, the unit cost goes down with offset printing. Very short runs can be much more cost effective with digital printing; while larger quantities are likely to have a lower unit cost with offset printing.
- Printing medium. Do you need or want a special paper, finish or unusual printing surface, or unique size? The options are increasing continually for digital, but offset printing still offers the most flexibility.
- Color. Digital presses use four-color process printing. If you need only black ink or one or two ink colors, offset printing may offer a more cost-effective solution. If you need four-color printing, digital may offer advantages in lower up-front costs.
- More on color. If you’re planning to print using the Pantone® Matching System, offset printing will give you the best match, since it uses actual Pantone® ink. Digital printing simulates the color using a four-color matching process, so some digital printers may offer less accurate color matching on projects.
- Turnaround. If you need it fast, digital usually offers quicker delivery.
- Proofing. Digital offers accurate proofs since you see an actual sample of the printed piece. Accurate color proofing for offset printing can be expensive.
- Customization. Without question, digital printing offers the most affordable way to customize marketing materials, direct mail pieces, letters, etc.