Printing & Design Tips: AUGUST 2007, #73

Heatset Vs. Non-Heatset Web Presses

Web presses fall into two categories: heatset and non-heatset (also referred to as coldset webs). These presses print on paper rolls fed into the printing equipment instead of on stacks of paper.

Heatset web presses have more components than non-heatset webs. They feature ovens at the delivery end of the press. These ovens flash off the solvent in the ink, effectively drying the ink film on the paper’s surface as the paper runs through the press. Upon leaving the oven, the paper then passes through chill rollers. Many web presses include finishing equipment, such as in-line folders, which allow the final product delivered by the press to be a complete signature ready for binding.

Non-heatset web presses differ from heatset presses in one major way. They do not have ovens or chill rollers. Ink laid down by these presses must be absorbed into the paper to dry (or the solvent must evaporate into the surrounding air).

The distinction between these two types of presses determines the kind of work for which each is best suited. Since intense heat quickly dries the ink printed by a heatset web, the ink can be printed on a coated sheet. The halftone dots and solid ink film will sit up on top of the sheet, and the images will be crisp. Such a press is ideally suited for long-run, high-quality, four-color work. Some presses even have eight units (or more), allowing both sides of the uncut ribbon of paper moving through the press at from 300 fpm (feet per minute) to 3,000 fpm to accept four or more colors of ink at once.

Keep in mind that in most cases paper travels through a web press once. It is a ribbon of paper running from the rolls at the infeed section of the press all the way through the inking units, oven, and chill rollers to the delivery end of the press, where it is cut into sheets (or folded and cut). A sheetfed press, on the other hand, allows the operator to bring back the printed sheets to the infeed section of the press and either print the opposite side of the sheet or add more ink colors or varnish to the first side of the sheet. In contrast, on a web press, all ink colors and varnishes must be printed in a single pass through the press.

Non-heatset webs are ideal for jobs on uncoated paper or the cheap, throw-away newspaper inserts you get on the weekend. For this type of press, quality issues are not paramount. Area screens and halftones printed on such a press (particularly large screens) must be printed with somewhat coarse line-rulings (150 to 175 lpi), because mottling or uneven printing can occur.

If you are cost conscious, web presses are best suited for very long press runs, while sheetfed presses should be used for shorter press runs. For instance, you might produce 5,000 brochures on a sheetfed press, but it would not be economical in most cases to print fewer than 50,000 press sheets of brochures (with perhaps four brochures per sheet, for a total of 200,000 brochures) on a web press.

Another way of looking at this is that 15,000 copies of an 80-page magazine printed on a sheetfed press might be of higher quality (crisper, more vibrant photos, for instance) than the same magazine printed on a heatset web press. However, the magazine printed on the web press might cost several thousand dollars (or even as much as ten thousand dollars) less than the same magazine printed on a sheetfed press. How much is the better quality worth to you?

Regarding quality, though, web presses have improved significantly, and the quality of a four-color printed piece in many cases is comparable to the quality of a sheetfed printed product for pleasing color. However, showcase color, like what you would need for a coffee-table art book, still would require a sheetfed press. Look at a selection of samples from your print providers to help your make your decision.

What is Flying Paster?

A flying paster is a piece of equipment attached to the infeed section of a web press that pastes a new roll of printing paper onto an almost exhausted roll of paper while the press is running. It’s a wonderful invention because rolls of paper at the infeed section of a web press eventually run out, and stopping a web press to reload paper is highly uneconomical, wasting both paper and time. Therefore, this device was invented to allow a new roll of paper to be spliced onto a roll of paper that’s just finishing up without slowing down the press.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]