web
A long sheet of paper which is fed from a roll into a printing press, as opposed to individual sheets of paper.
web: continuous paper from roll to press
In web printing, the web is the long continuous strip of paper (or film, or fabric) that unwinds from a large roll, passes through the printing press, and is either cut into sheets or rolled up again at the output. Unlike sheetfed presses that handle one individual sheet at a time, web presses maintain constant forward motion through the press unit, making them faster and more suited to high-volume jobs like newspapers, magazines, and packaging.
Web widths vary widely by press size and application. A typical coldset offset web press might run webs between 30 and 54 inches wide, though narrower web presses for labels start around 8 inches. The paper itself is wound on large cylindrical cores: rolls for newsprint or tissue may weigh 1000 pounds or more. The web speed directly affects production rate, measured in impressions per minute or linear feet per minute; a high-speed coldset web press typically runs 1500 to 2500 feet per minute.
Web tension and registration are critical during production. Excessive tension stretches the paper and causes wrinkles or tears; too little tension causes slack and misalignment. The press operator monitors this constantly through tension sensors and dancer rolls (idler rollers that move to compensate for slight variations). Registration, the alignment of different color layers, depends on maintaining consistent web pull and cannot be adjusted as easily as on a sheetfed press once the job is running.
Common web printing methods include offset lithography (coldset or heatset), flexography, and gravure. Coldset offset dries mainly through absorption into absorbent substrates like newsprint; heatset uses heated rollers and is faster but requires coated stock. After printing, the web moves to the folder and cutter section, where it is usually folded lengthwise and cross-cut into pages. Some products are rewound as rolls rather than cut.
Problems specific to web printing include web breaks (sudden tears during a run, requiring threading and restart), ink misting (spray) at high speeds, and moisture-related dimensional changes that worsen registration errors. Newspaper and magazine production is the classic web printing domain, though food packaging, labels, and commercial printing increasingly use web technology for cost and speed advantages on long runs.