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Offset printing, named for its indirect ink transfer process, uses a three-cylinder system to print images onto paper. This method extends the lifespan of the lithographic printing plate. The three cylinders involved are:
The image and background are printed on the same sheet in offset printing. The process is based on the principle that oil and water do not mix. Plates are designed so that image areas attract oil-based ink, while non-image areas repel it with water. Some offset presses use a silicone layer instead of water, making them "dry" presses.
The process begins with the 'plate' cylinder, enclosed by a plastic or aluminum plate designed specifically for the paper type. The plate cylinder's graphics are prepared to attract ink and repel water.
The second cylinder, the "offset blanket," is covered in a rubber blanket and rotates opposite the plate cylinder. Excess water is removed as these two cylinders roll against each other, and ink is transferred to the rubber sheet, creating a mirrored ink pattern.
The third cylinder, the "impression," is made of polished steel and rotates opposite to the blanket cylinder. As the paper is pressed onto the rubber blanket, ink is transferred from the impression cylinder.
An offset press can produce up to 18,000 sheets per hour, each containing up to 48 pages of A4 or letter-sized text. A standard offset press, printing eight pages per sheet, can produce approximately 120,000 pages per hour.
Web offset lithography, commonly used for packaging and newspapers, can produce over five thousand prints in a single run by continuously feeding paper rolls through the press. The paper is then trimmed to ensure uniform size. Web-fed offset presses can print over 3,000 papers per minute, making them ideal for businesses needing quick, high-volume production.
There are two types of web offset printing:
In contrast to web-fed, sheet-fed offset lithography prints lower volumes due to its sheet-feeding process. However, it's still a fast option, printing between 12,000 and 24,000 sheets per hour. Technological advancements now allow sheet-fed presses to run at speeds similar to web-fed presses.
Standard and custom offset paper sizes include:
These "parent" sheets can be trimmed to letters, legal, and tabloid sizes. Printers select paper based on the artwork's specific needs. Often, multiple copies are printed on a single sheet and trimmed after printing to avoid waste. For instance, four 8.5x11-inch letterheads might be printed on a single 17x22 sheet.
Smaller offset printing companies often use cut sizes of 8.5x11 inches, 8.5x14 inches, and 11x17 inches, as these are well-suited for their sheet-fed printers.
Unlike offset printing, which uses metal plates, digital printing employs various technologies, including toner (as in laser printers) or liquid ink in larger printers.
Digital printing shines when printing smaller quantities, such as 20 greeting cards or 100 flyers. It also allows for variable data, making it the go-to option when each piece needs a unique code, name, or address, a feature not available in offset printing.
For businesses and individuals not requiring large print runs of 500 or more, digital printing is the preferred choice, despite offset printing's capacity for high-quality print projects.
Digital printing sends an image directly to the printer, bypassing the need for a computer. It's ideal for high-detail, low-volume orders, eliminating the need for cumbersome formatting equipment like film plates or photo chemicals. The time from creating a digital document file to printing is significantly reduced compared to traditional printing.
The resulting digital prints should be flawless if the production steps are executed precisely. The image in the file should be clear and sharp, with adequate resolution for the intended print size. Bleed and crop marks are added when necessary to ensure perfect trimming with no unprinted edges.
The next step, imposition, maximize paper use by positioning the print job to fill as much of the page as possible. PDF documents can also be printed, though specifics depend on the software used.
To print your electronic document file, you'll need to convert it to a compatible file format such as BMP, TIFF, GIF, JPEG, or PDF.
Future Trends: According to a report by Smithers, the global print market is forecasted to reach $874 billion by 2024. According to Grand View Research, the digital printing market is expected to grow at a CAGR of 4.4% from 2020 to 2028.
The standard sheet size for digital printing is 19 inches by 29 inches, with some machines handling larger sheets. Offset printing typically uses 29" and 40" sheet presses. Certain types of printing require larger sheets but cannot be done on standard paper. Customers often resort to digital wide-format presses for short-run printing where print size is critical.
Different printing equipment provides slightly different color interpretations and controls. Some digital printing services can't match the precision of offset presses' color controls. Offset presses are better suited for printing Pantone colors because they use Pantone ink, which is significant for major corporate brands where maintaining a consistent color scheme is crucial.
Digital printing allows for faster turnaround times due to the reduced need for setup. Businesses with advanced digital printing capabilities can provide same-day and next-day printing at a fraction of the cost of offset printing. However, using multiple offset presses would require making several plates and allowing extra time for inking.
Each printing method, whether digital or offset, has its unique advantages. Understanding these can help businesses and individuals make informed decisions based on their needs. Here are the key benefits of each method: