Capama Blog

2026-08-10 | CAPAMA (Shanghai) Machinery Co., Ltd. Technical Team | Reading time approx. 10 min

Introduction

There is an old saying in the printing industry: "Good prepress means half the battle of printing is already won." Whether it is the high-precision multi-color registration of a rotary letterpress (CPM270L) or the print-and-apply workflow of a digital die-cutting machine (ZH-CW65), most of the final print quality — registration accuracy, color fidelity, and die-cut consistency — is determined at the file preparation stage. In this article, we share 8 practical prepress tips drawn from 20 years of hands-on experience, from shrinkage calculation to digital die-cut file standards.

1. What Is Shrinkage Rate and Why Film Labels Cannot Ignore It

Shrinkage rate refers to the amount of shortening in the machine (web) direction of printed artwork. Many first-time film-label users ask: "My design is exactly 1:1, so why does my multi-color registration keep drifting?"

The root cause: the substrate undergoes slight stretching or contraction under printing tension and drying (especially UV curing or hot-air drying). This is particularly noticeable with BOPP, PET, and PE films, as well as self-adhesive label stock. If no shrinkage compensation is applied at the file stage, downstream color stations will show a systematic offset from the first station.

2. How to Apply Shrinkage Compensation to Your Files

2.1 When Is Shrinkage Compensation Needed?

• Film substrates (BOPP/PET/PE): obvious thermal shrinkage — compensation is required.
• Self-adhesive face stock + release liner: more dimensionally stable, but still verify on large-volume or wide-web production.
• Multi-color printing + downstream die-cutting: any product requiring "print + die-cut" precision relies on compensation for yield.

2.2 Step-by-Step Implementation

1. Proof on the real material: run a test and measure the actual stretch/shrink in the web direction.
2. Calculate the shrinkage rate: apply the formula above to get a percentage.
3. Compensate in the design file: in Illustrator/CorelDRAW, compress the artwork in the web direction by the inverse of the shrinkage, and adjust registration marks accordingly.
4. Verify before production: run one proof with the compensated file to confirm registration returns to zero, then start the batch.

Key tip: Shrinkage compensation applies to the printed artwork, while the die-cut line usually stays at original size. This is why layered file management is essential — see Section 7.

3. Setting Up Bleed, Safe Area, and Registration Marks

3.1 Bleed

• Label printing should use ≥2mm bleed to give the die-cutter enough margin and avoid white edges.
• Large solid color blocks should use 3mm bleed to prevent white gaps if die-cutting shifts.
• Name files with the actual bleed value to avoid prepress misjudgment.

3.2 Safe Area

Keep important artwork (logo, text, barcodes) at least 2-3mm from the die-cut line to allow for die-cut tolerance and avoid cutting into critical content.

3.3 Registration Marks

• Multi-color jobs must have cross registration marks — one set per CMY color plus a K-color reference.
• Place registration marks in the waste area outside the die-cut region: do not affect the finished label appearance.
• Use 0.1mm fine cross lines for higher photoelectric detection accuracy.

4. Color Management: Decide Spot vs. Process Color at Prepress

4.1 Spot Color (Pantone)

• Ideal for brand and logo colors — color-consistent and highly reproducible.
• In letterpress, a spot color typically uses a dedicated station for richer ink laydown.
• Supply the Pantone number at prepress and calibrate with a device proof.

4.2 Process Color (CMYK)

• Best for photographs, gradients, and continuous-tone images.
• Watch out for dot gain — preset a compensation curve in the ICC profile at prepress.
• Dark CMYK overprints tend to shift; convert large dark areas to spot color when possible.

Key tip: For label products, spot color first, especially for repeat standardized items. Use CMYK for complex short-run graphics. For both saturation and image detail, combine "CMYK + spot color accent."

5. Trapping: The Key to Avoiding White Gaps in Registration

When adjacent dark and light areas or different spot color blocks meet, imperfect registration often creates a "white hairline." Trapping makes adjacent colors overlap by a small amount (usually 0.1-0.15mm) to hide the registration error.

• Spread lighter color into darker: visually the most natural.
• Choke darker color: shrink the dark area to leave room for the light color.
• Limits of auto commands: Illustrator/CorelDRAW auto trapping suits simple shapes; complex artwork should be hand-checked in critical areas.
• Text over a background: on a light background, dark text should be outlined or untrapped to avoid distorting thin strokes.

6. White Ink Layer: Prepress Notes for Transparent and Metallic Substrates

When printing on transparent film (PET/BOPP) or silver foil, you usually need a white undercoat before the color layers, so the color is opaque and does not "show through."

• Name the white ink layer separately (e.g., "White") for clear prepress recognition.
• White ink may need 2 or even 3 passes for sufficient opacity — factor this into throughput estimates.
• Screen printing machines (RR-320S / CPM 520SX) lay a thicker white layer, ideal for high-coverage requirements; letterpress/digital machines need the white channel planned in the file.
• For a semi-transparent blocking layer (local see-through effects), mark it explicitly as a spot channel with opacity defined.

7. Layer Management for Artwork vs. Die-Cut Lines — Avoid Disastrous Errors

The most frequent label-file mistake is mixing print artwork, die-cut lines, barcodes, and variable data in one layer, leading to accidental deletion or mis-print during prepress or production. The standard practice:

Key tip: With clean layer separation, prepress can "hide all non-print layers" and safely output the print plates; during production, export the die-cut and variable-data layers as needed. This standard is especially useful for the print-and-apply workflow of the digital die-cutting machine (ZH-CW65), where printing, lamination, die-cutting, and waste removal run in one pass.

8. Special Notes for Digital Die-Cutting Files

Digital die-cutting machines (ZH-CW65, 1200×1200 dpi, 120 m/hour) have slightly different prepress file requirements than offset/letterpress:

• Resolution: bitmap images should be ≥300 dpi; use vector for logos/lines to keep small type crisp.
• Variable data templates: for serial numbers or trace codes, build the variable template at prepress rather than editing sheet by sheet.
• Die-cut paths: digital die-cutting demands precise cut lines — closed paths must be complete with no gaps, or cutting becomes discontinuous.
• Color mode: most digital devices support RGB-to-CMYK workflows; calibrate with the device ICC profile and soft-proof so the on-screen preview matches the output.
• Shrinkage still applies: digital web transport also has tension effects — verify shrinkage for integrated devices per Section 1.

9. Quick Self-Check Table for Common Prepress Errors

Conclusion: Prepress Is Both a Craft and a Discipline

Prepress may seem tedious, but it is the dividing line between yield and waste for any printing company. When the shrinkage rate is calculated accurately, layers are managed cleanly, and color and trapping are handled correctly, everything downstream — whether the high-precision registration of the rotary letterpress (CPM270L) or the print-and-apply flow of the digital die-cutting machine (ZH-CW65) — runs smoothly. The technical team at CAPAMA Machinery is happy to share these practical lessons, and we welcome discussions on equipment selection and prepress process.

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