Keeping Book Printing Quality Stable from Prepress to Binding

Print quality is what a customer sees on the finished page, and much of it is decided long before the press runs. Artwork, plate quality, the production process, the machinery and the room itself all leave their mark on the sheet. For a book printer, the hard part is not reaching a good result once, but repeating it on every copy of a run. Four areas repay close control.

Check the job before it reaches the press

Prepress review deserves real attention rather than a quick glance. Someone should confirm that the artwork is clear, well proportioned and suited to the process, and predict how the page will look once printed. Sound design keeps type, layout, composition and colour working together, which raises the information value, legibility and appeal of the finished book.

Ink coverage belongs in that review. Very heavy coverage is harder to dry and harder to hold steady through a run. Distributing dark and light inks sensibly across the form helps the press keep a stable colour from the first sheet to the last.

Control the plate making stage

Plate quality sets the ceiling for the printed result, including colour saturation, sharpness and tonal depth. The size of the halftone dots on the plate decides both how dark an area prints and how crisp the image reads. Plate making also has to match the equipment and the consumables in use. Parameters should be adjusted for the plate type, the paper and the artwork, so the job avoids broken contours, ragged type edges, colour shift and ink streaks.

Screen ruling and screen angle matter here as well. The ruling, measured in lines per inch, is the number of dot rows in a grid. A higher ruling carries finer detail and gives a sharper plate. Pushed too far, however, it shrinks the dots, flattens the colour, wears the plate faster and can create printing dead spots. A ruling that is set too low enlarges the dots and can fill in shadow areas. When the ruling does not suit the file or the substrate, colour drift follows. Screen angle, if poorly chosen, produces a moire pattern and shows as streaking on the sheet.

Thermal CTP plates need care in storage, because both time and environment act on them. Heat, high humidity and direct sunlight can corrode, oxidise or yellow the coating. Plates left too long without protection can be scratched or otherwise damaged. Store them in suitable conditions, follow the maker's handling instructions and inspect stock on a regular schedule.

Hold the press and the bindery to the same standard

Equipment and technique decide much of the outcome. Before printing, development time should be checked. During the run, colour and impression pressure need watching so the sheet stays saturated, clean and well defined, with solid lines and smooth type edges. In the bindery, the collating sequence, the strength of the adhesive joint, the trim and the appearance of the finished copy all have to be verified.

Take a six-up exam paper as an example. The finished copy measures 185 mm by 260 mm, the untrimmed sheet before perfect binding is 370 mm by 260 mm, and the real imposition is 555 mm by 260 mm, with no trim at the front edge. The job looks simple. In practice, small details decide whether it works.

That sheet holds three 185 mm by 260 mm pages. The left margin is the binding edge, and the right page folds against the middle page along a line at 185 mm, giving a 373 mm by 266 mm section. After perfect binding, 3 mm is trimmed from head and foot, and the fold becomes the front edge of the paper. If the pages run long or short, that front edge comes out uneven and the copy looks poor.

Three points keep it straight: a paper width of 555 mm with a tolerance no greater than 1.0 mm; registration of the left margin against the left corner marks with 3.0 mm reserved for the milling spine; and steady control of the left corner marks and the right fold line during printing.

Watch temperature and humidity

Conditions in the pressroom affect drying speed, sheet flatness, register and sharpness. When temperature and humidity drift, sheets can curl, shrink or distort, and the whole book suffers. Both the pressroom and the bindery benefit from controlled settings across the day.

The working rule

Many factors touch book quality, and each one matters. Prevention before the run and control during it are the surest route to a stable result. A printer that keeps that discipline is the one that stays competitive.