Table of Contents

1. Why Print Specifications Matter for Retort Packaging

2. File Format Requirements

3. Color Mode: CMYK and Pantone Standards

4. Resolution and Image Quality Requirements

5. The Dieline: Safe Zones, Bleed, and Seal Area Restrictions

6. Surface Print vs. Reverse Print — Which Side Goes to the Laminator

7. White Ink: When It Is Required and How to Specify It

8. Retort-Resistant Ink Selection

9. Special Finishes: Matte, Gloss, and Spot UV

10. Artwork Submission Process and Common Rejection Reasons

11. Frequently Asked Questions

Artwork rejection is the single most common cause of production delays in retort pouch manufacturing — a rejected file adds 2 to 4 weeks to your timeline before a single pouch is produced. Unlike standard flexible packaging, retort pouches undergo 121°C or 135°C sterilization cycles that impose strict constraints on ink chemistry, laminate structure, and color registration that most general packaging design guidelines do not cover. This guide delivers the complete set of technical print specifications required to submit production-ready artwork to Sunkey Packaging: file formats, color standards, resolution requirements, dieline rules for seal zones, ink selection for retort conditions, and the artwork submission workflow — applicable to food, pet food, baby food, and ready-to-eat meal retort pouch orders.

1. Why Print Specifications Matter for Retort Packaging

Retort pouch printing operates under constraints that standard food packaging does not share. The 121°C or 135°C moist-heat sterilization cycle subjects the laminate structure — including every ink layer — to conditions that will cause poorly specified inks to migrate, bleed, or delaminate. Beyond ink chemistry, the multi-layer laminate structure means that artwork is printed on an inner surface of the film stack, not on the outer surface that consumers touch. This reverse-print geometry fundamentally changes how colors appear, how registration is maintained across layers, and how special finishes interact with the substrate.

There is also a commercial dimension: retort pouch printing is typically performed using rotogravure (intaglio) or flexographic presses producing runs from 30,000 to several million units. At these volumes, a 1 mm misregistration in the artwork file compounds into significant material waste. The specifications in this guide exist to prevent four categories of failure: artwork rejection before production begins, color deviation discovered after production, ink delamination discovered after sterilization, and print registration errors visible to the consumer.

Table 1. The four categories of print failure in retort pouch production, their commercial consequences, and their root causes in artwork file submission.

2. File Format Requirements

Retort pouch printing presses require vector-based artwork files. Raster-only file formats (JPEG, PNG, TIFF) are not accepted as primary files because they cannot be scaled without quality loss and do not support the layer structure required for color separation.

2.1 Accepted Primary File Formats

Table 2. Accepted and rejected file formats for retort pouch artwork submission.

2.2 File Preparation Checklist Before Submission

• All fonts converted to outlines (Create Outlines / Convert to Curves)

• All linked images embedded (not externally linked)

• Document color mode set to CMYK (not RGB)

• All spot colors (Pantone) converted to CMYK process unless requesting a spot color separation

• Trim marks and bleed included in the document setup

• Layers labeled by color or function (e.g., 'CMYK Print', 'White Ink', 'Dieline', 'Varnish')

• Dieline on a separate, clearly labeled, non-printing layer

• File resolution: embedded raster elements at minimum 300 DPI at 100% final print size

3. Color Mode: CMYK and Pantone Standards

Retort pouch printing uses four-color process (CMYK) as the baseline color system. RGB is a screen color model and does not correspond to any physical ink formulation — RGB values submitted in artwork files will be automatically converted to CMYK by the pre-press department, almost always producing colors that differ from the designer's intent.

3.1 CMYK Specifications

Table 3. CMYK color specifications for retort pouch print files. TIC = Total Ink Coverage.

3.2 Pantone Colors and Spot Color Separations

Pantone colors (Pantone Matching System, PMS) require conversion to CMYK before submission unless a spot color separation is explicitly ordered. Spot color printing adds an additional ink station on the press and typically adds 8–12% to print unit cost. When requesting spot color printing for brand-critical colors (e.g., brand green, metallic gold), the following must be provided:

• PMS color code (e.g., PMS 348 C)

• Whether the color requires a metallic Pantone ink (PMS Metallic series)

• Confirmation of whether the spot color overprints or knocks out underlying CMYK layers

Table 4. CMYK conversion targets for common Pantone colors. ΔE values achievable on rotogravure press with standard retort inks.

4. Resolution and Image Quality Requirements

Resolution applies only to raster (bitmap) elements embedded in the artwork file — photographs, textures, and gradient mesh rasters. Pure vector elements (paths, shapes, text outlines) are resolution-independent and have no minimum DPI requirement.

Table 5. Minimum resolution requirements for raster elements in retort pouch artwork. All measurements at 100% final print size.

5. The Dieline: Safe Zones, Bleed, and Seal Area Restrictions

The dieline is the technical template that defines the exact dimensions of the pouch: the cut edges, fold lines, seal zones, zipper position, valve position (if applicable), and hanging hole. Every retort pouch artwork file must be built within a dieline supplied by Sunkey. Do not create your own dieline from pouch dimensions — production tolerances and machine-specific parameters must be incorporated.

5.1 Bleed Requirements

Bleed extends the background design beyond the trim edge to account for ±1.5 mm cutting tolerance in the pouch-making machine. Without bleed, cutting tolerance creates white unprinted edges on finished pouches.

Table 6. Dieline zone requirements for retort pouch artwork. All measurements from the structural feature (cut edge, seal seam, zipper) inward into the print area.

5.2 Seal Area Rules in Detail

The bottom seal, side seals, and top seal of a retort pouch are formed by pressing two laminate surfaces together under heat and pressure. Any ink or coating between the two sealing surfaces acts as a contaminant that reduces seal strength, increases the risk of seal failure under retort pressure, and may cause void channels that allow post-retort contamination.

The 10 mm exclusion zone applies to all critical design elements — text, barcodes, nutritional information panels, logos, and product photography. Background color may extend into the seal area but must be a solid, single-layer color (no gradients, no halftones) to avoid ink accumulation at the seal interface.

6. Surface Print vs. Reverse Print — Which Side Goes to the Laminator

Most retort pouch structures use reverse printing: the artwork is printed on the inside surface of the outer film layer (PET or BOPP), which is then laminated face-down so the print is sandwiched between film layers and protected from abrasion. The consumer sees the design through the transparent outer film.

Surface printing (printing on the outside surface of the finished pouch) is not used for retort applications because retort conditions destroy any unprotected ink layer. Surface printing is limited to cold-fill pouches and ambient-temperature stand-up pouches.

Table 7. Comparison of reverse print and surface print for retort pouch production. Reverse print is the required method for retort applications.

7. White Ink: When It Is Required and How to Specify It

White ink is a separate ink station on the press that prints an opaque white layer beneath the CMYK color layers. It is required whenever the substrate is not a clear film — specifically for aluminum foil laminates, metallized PET, and kraft paper substrates where the substrate color would show through and alter color appearance.

7.1 When White Ink Is Required vs. Optional

Table 8. White ink requirements by substrate type for retort pouch reverse printing.

7.2 How to Specify White Ink in Your Artwork File

White ink must be specified as a separate spot color layer in the artwork file, not as CMYK white (C0 M0 Y0 K0 — which is simply transparent). The standard approach is:

• Create a separate layer named 'White Ink' or 'W' in your artwork file

• Color all white ink areas with a custom spot color named exactly: 'White' (this is the pre-press system trigger)

• Overprint setting: white ink should be set to 'Overprint OFF' (knockout, not overprint)

• White ink opacity: specify as 100% opaque (standard) or as a percentage if a translucent white effect is intended

• White ink coverage: white areas typically require 2 passes (double-strike) for full opacity — specify if single-pass white is acceptable

8. Retort-Resistant Ink Selection

Standard gravure or flexo inks used in ambient-temperature food packaging will not survive retort conditions. The 121°C or 135°C moist-heat cycle causes three failure modes in non-retort inks: color migration through the laminate adhesive layer into the food product, delamination of the ink layer from the substrate, and color shift (yellowing of cyan inks, browning of magenta inks).

8.1 Ink Systems Approved for Retort Conditions

Table 9. Ink system retort compatibility. Non-retort-rated inks are not acceptable regardless of application — they present food safety and structural failure risks.

8.2 Regulatory Requirements for Retort Inks

Retort pouch inks must comply with food contact migration regulations. The applicable standards depend on the target market:

• FDA (USA): 21 CFR §175.300 (resinous and polymeric coatings) and 21 CFR §178.3800 (adjuvants and production aids) — ink components must appear on FDA food contact substance notification lists

• EU: EU Regulation 10/2011 (plastic food contact materials) and Council of Europe Resolution AP(2005)2 — ink components must comply with migration limits (10 mg/kg for overall migration, substance-specific SML values)

• China: GB 9685-2016 (Standards for the Use of Additives in Food Contact Materials) — relevant for packaging produced in China and exported, or sold domestically

• Sunkey's standard ink suppliers provide migration compliance declarations (conformity certificates) upon request — these should be included in your regulatory dossier

9. Special Finishes: Matte, Gloss, and Spot UV

Special finishes modify the surface feel and light reflection of the finished pouch. Not all finishes are compatible with retort conditions, and some require modification of the laminate structure.

Table 10. Special finish compatibility with retort conditions and artwork file specification requirements.

10. Artwork Submission Process and Common Rejection Reasons

10.1 Submission Process

Sunkey's artwork submission and pre-press review process follows five steps from file receipt to production sign-off:

1. File upload: Submit artwork file via Sunkey's shared link or FTP. Include a low-res visual reference PDF.

2. Pre-press check (24–48 hours): Sunkey pre-press team checks file against specifications. Issues are reported via markup PDF.

3. Client correction round: Client revises file and resubmits. One revision round included; additional rounds are billable.

4. Digital proof approval: A digital proof (soft proof or hard copy) is sent to the client for sign-off. No production begins without written approval.

5. Plate production and press scheduling: After approval, plates are produced and the order is scheduled. Standard lead time from approval to production start: 7–10 business days.

10.2 Most Common Artwork Rejection Reasons

Table 11. Most common artwork rejection reasons at Sunkey pre-press review, listed by frequency.

11. Frequently Asked Questions

Q1: Can I use Pantone metallic inks on a retort pouch?

Pantone Metallic inks (the PMS Metallic series) can be used on retort pouches when applied as a spot color in the reverse-print layer, provided the ink is rated for retort conditions by the ink manufacturer. Standard Pantone Metallic inks available in commercial ink libraries are not automatically retort-rated — confirm retort compatibility with Sunkey before ordering a spot metallic color. An alternative that achieves a similar metallic appearance without a separate ink station is a metallized PET outer film combined with a standard white ink base.

Q2: What is the minimum barcode size for a retort pouch, and how should it be set up?

The minimum readable barcode size for a GS1-128 or EAN-13 barcode on a retort pouch is 80% of the nominal size (nominal = 100% magnification per GS1 specifications). At this magnification, the narrow bar width is approximately 0.264 mm. Barcodes must be set up in vector format, printed in single-color black (K100 only — never CMYK composite black), and positioned in the non-seal, non-zipper area of the pouch with a minimum quiet zone of 2.5 mm on each side. Never place a barcode within 10 mm of a heat-seal seam.

Q3: How do gradients and vignettes perform after retort sterilization?

Smooth gradients and vignettes generally survive retort sterilization without significant color shift, provided they are built with retort-rated inks and the total ink coverage at any point in the gradient does not exceed 300%. The primary risk is in very light gradient tones (below 5% dot) where the halftone dots may consolidate during retort, creating a slightly banded appearance in the lightest areas. For premium packaging, test a press proof at 121°C before committing to a full run with complex gradients in critical areas.

Q4: We need nutritional information panels on the pouch. What are the minimum font sizes?

Nutritional information panels must meet FDA (21 CFR Part 101) or local regulatory minimum font size requirements regardless of the pouch size. For US market products, the minimum font size for nutritional information is 6 pt for standard Nutrition Facts panels. From a print quality standpoint, the practical minimum for legible printing on a retort pouch is 6 pt for black-on-white text (K100 only) and 8 pt for colored text. Text below 6 pt is not printable at acceptable quality on retort pouch substrates using gravure printing.

Q5: What happens if we use standard packaging inks instead of retort-rated inks?

Standard packaging inks not rated for retort conditions will fail during the 121°C or 135°C sterilization cycle in one or more ways: color migration through the laminate adhesive layer into the product (a food safety violation), delamination of the ink film from the substrate (structural failure), and visible color shift — typically yellowing of cyan areas and browning of magenta areas. Using non-retort inks to reduce cost eliminates any cost savings through the certain production failure and regulatory risk.

Q6: How long does Sunkey's pre-press review process take, and what does it cost?

Sunkey's standard pre-press review (artwork check, digital proof generation) is completed within 24–48 hours of receiving the artwork file. One revision round is included in the order. Additional revision rounds are charged at $50 per round to cover pre-press staff time. Digital proofing (standard soft proof) is included. Physical press proofs can be arranged at additional cost — typically $200–400 depending on structure and quantity — and are recommended for brand-critical or first-time order verification.

Q7: Can we submit artwork in a language other than English for the pre-press team?

Sunkey's pre-press team handles artwork files in English and Chinese. For Russian, German, Spanish, and other language artwork, the pre-press technical check (dimensions, color mode, resolution, seal zones) is performed normally — the team does not read the text content for correctness. Clients are responsible for text accuracy in all languages. If your artwork contains Arabic, Hebrew, or other right-to-left script, notify the pre-press team to ensure text direction is not mirrored during the reverse-print plate setup.

Q8: Is there a difference in print specifications for 121°C vs. 135°C retort applications?

The print file specifications (file format, CMYK, resolution, bleed, seal zones) are identical for 121°C and 135°C retort applications. The difference is in the ink formulation required: inks must be rated for the specific sterilization temperature. Sunkey uses exclusively 135°C-rated inks as standard for all retort pouch orders, which provides full compatibility with both 121°C and 135°C processes and eliminates the risk of using 121°C-rated inks in a higher-temperature application.

Related Articles

• Retort Pouch Materials Guide: Choosing the Right Structure for 121°C and 135°C → /retort-pouch-materials-guide

• Retort Pouches: The Complete Guide to Heat-Resistant Flexible Packaging → /retort-pouch-complete-guide

• Retort Pouch Quality Assurance: Preventing Seal Failures and Delamination → /retort-pouch-seal-integrity-testing

• Can to Pouch Conversion: The Complete Step-by-Step Transition Guide → /can-to-pouch-conversion-guide

• Retort Pouch for Pet Food: Structure Selection by Product Type → /retort-pouch-pet-food-packaging

© 2026 Sunkey Packaging. All rights reserved.

The technical specifications in this article reflect Sunkey Packaging's standard production parameters as of 2026. Specifications may vary based on specific pouch structure, press configuration, and customer requirements. Always confirm final specifications with Sunkey's technical team before artwork preparation.