The Impact of Prepress Imposition on the Binding Quality of Book and Magazine Printing
Many critical details of the printing production process are determined during the prepress imposition stage, including the unification of trim and register marks for different jobs, the reservation of binding and milling margins, the standardization of process marks, and the handling of cross-spread and bleed images.For saddle-stitched products, special attention must also be paid to page creep, as well as the consistency of page numbers, running heads, and text block positions throughout the publication.
As a key step in implementing production processes, the completeness and accuracy of imposition directly affect the quality of subsequent binding and finishing.
1. Accuracy of Layout Templates and Folding Quality
The layout template (imposition sheet) serves as the basis for manual imposition, and its drawing accuracy directly affects page number alignment, text block positioning, running heads, and the joining accuracy of cross-spread images after folding.The template must be drawn neatly and precisely, with accurate dimensions. The diagonal deviation should be controlled within 1 mm.
Templates should be made on relatively thick paper and stored in a moisture-proof environment. Before use, dimensions should be checked carefully. In principle, templates should be drawn as needed and not reused for long periods, to avoid deformation affecting accuracy.
2. Handling of Cross-Spread and Bleed Images
When imposing cross-spread images, proper top-to-bottom alignment must be ensured, and sufficient allowance should be reserved for the binding edge, milling edge, and spine gluing area to prevent important images or text from being covered during binding.The milling and binding margins reserved during imposition must match the actual milling depth used in binding to ensure accurate image alignment across spreads.
For perfect-bound products, the milling depth is generally designed to be 2.0–3.5 mm. In actual production, due to paper size limitations, the milling depth may be slightly reduced as long as the signatures are fully milled.
In practice, the criterion is that the innermost page of the signature must be firmly bonded:
- For three-fold signatures, the milling depth is typically 1.5–2.0 mm;
- For four-fold signatures, 2.0–2.5 mm is recommended;
- For books with a thick text block, a larger milling allowance should be applied at the plate-making stage.
3. Page Creep Adjustment for Saddle-Stitched Products
When imposing large sheets, paper thickness, number of folds, and the nesting relationship between signatures must be considered, as these factors affect page position.For saddle-stitched products, appropriate page creep compensation must be applied to the inner signatures to ensure consistent alignment of page numbers and text blocks after binding.
For example, when printing a 16mo, three-signature saddle-stitched product on 70 g/m² paper, page creep is usually handled by signature:
- The second signature is shifted outward toward the binding edge by 1 mm;
- The third signature is shifted outward by 2 mm.
4. Principles for Setting Process Marks
Process marks should be standardized and complete, with the primary goal of facilitating printing and binding operations. They should be clear, concise, and easy to identify.When covers, text pages, and color inserts are plated separately, the same gripper and side guide positions should be used, and folding marks must remain consistent.
For double-up products, upper and lower imposition marks must be clearly differentiated.
For series products with similar formats, distinct and easily recognizable characters should be added to the spine text or identification marks to prevent mismatching during gathering and binding.
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