A clear, short, human-readable date code is one of the fastest quality checks on a busy line. Operators, auditors, and retail inspectors rely on it to validate sell-by/use-by and expiration dates in seconds. When codes are concise, placed consistently, and set before rails or accumulation, you reduce smears, misreads, and rework.
This playbook outlines how to design short, inspectable date codes and set up equipment so marks are readable at a glance and repeatable across SKUs. It covers code content, character height, placement, timing, mounting near fillers and seamers, cold-start reliability, quick-change reservoirs for color swaps, and practical compliance pointers.
If you are planning a changeover or standardizing formats across plants, use this as a checklist, then schedule an application review to validate ink, placement, and timing with demo prints.
What date coding is and why it matters
Date coding is the practice of marking primary packaging with a human-readable sell-by/use-by or expiration date, often paired with a short process identifier that links back to batch records. It matters for three reasons. First, consumer safety and brand trust depend on preventing expired product from reaching shelves. Second, production and QA teams need a visible link from a pulled sample to batch sheets, tank logs, and pallet IDs. Third, retailers and regulators expect consistent, legible codes that can be verified without tools.
Best practice is a short format: a date element plus one or two process identifiers. Examples include MM/DD/YY + line letter, or YYMMDD + shift. Keep it consistent across an SKU family so operators and inspectors find it in the same place every time.
The different types of date coders
Multiple technologies can apply date and lot codes. Each excels in specific conditions.
- Contact reciprocating coders: Mechanical heads advance, touch the substrate, transfer quick-drying ink, then retract. Ideal for short, human-readable date and lot marks on curved or flat surfaces, near seamers, and in tight spaces. Rugged, low maintenance, reliable in cold starts thanks to sealed reservoirs and quick-drying inks. Sprinter Marking Models 66, 44, and 416 are representative.
- Continuous inkjet (CIJ): Non-contact droplets deflected to form characters. Flexible for variable data and higher character counts. Requires more environmental control and service.
- Thermal transfer overprinters (TTO): Ribbon-based, excellent on flexible films and webs for longer variable content.
- Laser: Permanent, no consumables, but requires compatible substrates and fume extraction.
- Thermal inkjet: Cartridge based, high-resolution on porous cartoning or labels.
For many food and beverage lines, pair contact coders for human-readable fields with non-contact systems when you need scannable barcodes or long variable messages. To explore options and fit, see our guidance on date coders and code date printers, and consider a dedicated inkjet coder when variable text is frequent.
Internal links for more detail:
- Learn about date coders and code date printers at Sprinter Marking.
- Explore inkjet coder options when variable data is required.
- See how coding and marking equipment integrates on production lines.
How batch and expiration coding works on the line
On a typical primary packaging line, the coding sequence is straightforward:
- A sensor or mechanical trigger detects the package in a controlled, supported position.
- The coder advances and transfers ink as the part is backed by a guide, pocket, starwheel, or plate to prevent deflection and bounce.
- Characters set and dry as the product leaves the strike point, ideally before any side contact at rails or during accumulation.
With reciprocating contact coders, slight head rotation on contact aligns strokes to curved surfaces, producing uniform characters on bottles, cans, and caps. Sealed ink systems stabilize viscosity and reduce dry-outs, which improves cold-start performance in drafty areas or cold rooms. Quick-change reservoirs let operators swap ink colors or formulations quickly during SKU or seasonal changes without remounting the head or re-priming for long periods.
Code design: keep it short and inspectable
Design the code first, then select tooling. Keep the human-readable field minimal and operator friendly:
- Date element: choose MM/DD/YY, DD/MM/YY, or ISO (YYYY-MM-DD). Pick one, document it, and stay consistent across sites.
- Minimal process identifier: add 1 to 2 characters for line, shift, or filler. Examples, L2 or A.
- Character height: select the smallest height that remains readable at expected viewing distance and line speed. Typical ranges are 1.6 to 3.2 mm for small primary codes, larger if operators verify from a distance or through condensation. Validate with demo prints on actual parts.
Avoid long codes that invite placement drift or partial impressions. If you need barcodes or QR codes, put those on labels or cartons via non-contact printers, and keep the primary package code short and human readable.
Character height, placement, and timing
Character height and placement should be locked at the SKU family level. For curved and glossy surfaces, run demo prints and confirm the following:
- Characters are visible against the substrate color. Choose dye-based quick-dry inks for thin, crisp text on clear or light surfaces; choose pigmented inks for high contrast on dark plastics or lacquered metals.
- Set time completes before the first rail or accumulation point. On glass and metal, set times are often under 2 seconds; on PET, expect roughly 2 to 5 seconds in standard conditions. Your environment and ink family drive the final value.
- Placement avoids seams, ridges, and high-traffic handling zones. Near seamers and fillers, mount off the seam path to reduce abrasion during transfers and rinses.
Support the substrate at the strike point. Guides, pockets, starwheels, and backing plates eliminate deflection, bounce, double impressions, and ghosting. Dial in contact pressure and dwell using fine-adjust slides so impressions are complete but not distorted.
Reliability at startup and during changeovers
Cold-start reliability depends on stable ink flow and sound seals. Sealed reservoirs reduce solvent loss, stabilize viscosity, and help coders start clean after downtime, even in cold or drafty rooms. Prepare quick-change reservoirs before shifts so operators can swap colors for promotions or contrast adjustments without lengthy priming.
Removable marking heads and rubber character kits simplify message updates. Offline tooling swaps preserve the mount and timing, which means the coder goes back online with minimal adjustment.
Mounting near fillers and seamers
Coding near a filler or seamer requires rigid mounting and precise timing. Use sturdy brackets and fine-adjust slides to position the head so contact occurs at a supported, repeatable location. Verify that the head’s approach avoids side loads from starwheels and that the message completes before any downstream handling. Compact, orientation-flexible mounts are advantageous in tight retrofits.
For cans, a dedicated can coder mounted just downstream of the seamer can deliver consistent end codes with quick-drying, high-contrast inks. For bottles and pouches, benchtop or in-line pockets and backing plates keep thin films and curved sidewalls stable.
Compliance pointers and audit readiness
This guidance is non-legal. Always confirm regional and customer requirements. Practical steps that support audits:
- Standardize the date format and the minimal process identifier per SKU family, document it on batch sheets, and apply it consistently.
- Map visible codes to production logs so a field sample traces upstream in one step.
- Confirm rollover logic at month-end and year-end to avoid incorrect dates.
- Retain demo print records that document ink choice, character height, placement, and set time under expected conditions.
If your retailer requires scannable barcodes or GS1 2D symbols, place those on labels or secondary packaging using non-contact printers while keeping human-readable date and lot fields on the primary package.
How to print expiration dates on products reliably
Reliable coding is the product of controllable variables:
- Ink and substrate match: select dye-based quick-dry inks for clear/light materials when fine text is required; use pigmented inks for dark or coated surfaces where high contrast and smear resistance are priorities.
- Mechanical control: rigid mounts, fine-adjust slides, correct pressure and dwell, and robust support at the strike point.
- Environmental readiness: sealed reservoirs for cold starts, validated set time before rails or accumulation, periodic wick replacement if pigments are used.
- Operational discipline: preflight date formats and rollover, verify character health, and inspect impressions at startup and after changeovers.
Plan a short on-line validation with demo prints to lock in timing and placement, then record the settings.
FAQ
- What are the different types of date coders?
Contact reciprocating coders for short human-readable marks, CIJ for flexible variable data, TTO for films and webs, laser for permanent marks on compatible substrates, and thermal inkjet for high-resolution on porous cartons or labels.
- What is date coding and why does it matter?
It is the placement of a readable sell-by/use-by or expiration date, often plus a brief process identifier, on primary packaging. It supports consumer safety, rapid QA checks, retailer expectations, and fast audit traceability.
- How does a batch or expiration coding machine work on the line?
A sensor or trigger times the strike, the coder transfers ink as the product is supported to prevent movement, and the mark sets before the package contacts rails or accumulates downstream.
- How do you reliably print expiration dates?
Match ink to substrate, stabilize mechanics with rigid fixtures and correct pressure, validate set time in your environment, and maintain sealed reservoirs and consumables. Confirm date logic and character condition during changeovers.
- Is the batch code the same as the barcode?
No. The batch code is a short human-readable string that links to production records. A barcode or 2D symbol is scannable machine-readable data, typically applied by non-contact printers on labels or cartons.
Summary and next step
Short, inspectable codes win. Choose a concise date format with a minimal process identifier, fix character height and placement per SKU family, and validate set time so marks are dry before rails or accumulation. Use sealed reservoirs and quick-change components for cold-start reliability and fast color swaps, and mount coders near fillers and seamers with rigid brackets and fine-adjust slides.
To de-risk your rollout, book an application review. We will validate ink selection, character height, placement, and timing with demo prints on your actual parts and line speeds, then recommend the right equipment and ink family for consistent, readable codes. Contact us for a consultation today.