Which date coder is suitable for jam jars and sauce bottles?
The choice depends on where the code will be printed. Continuous inkjet can mark many moving glass, plastic or metal surfaces; thermal-transfer overprinting is commonly used on flexible film or label webs; laser may suit compatible materials where a permanent mark is required; and hot-foil or contact coders can suit defined labels and lower-speed equipment. The production substrate and intended storage route must be tested.
Write the code brief before selecting printing technology
List every data element: best-before or use-by date, batch or lot number, time, line identifier, price, allergen statement, barcode, 2D code or customer-specific text. Define the largest number of lines and characters, variable-data source, font size and minimum acceptable contrast.
The code position should be visible to consumers and inspectors without interfering with branding, closure checks or label readability. Curved shoulders, ribbed plastic, embossed glass, coloured products and reflective metal lids can make an apparently simple position difficult to print and inspect.
Direct to container
Inkjet or laser can mark glass, plastic, metal or coated surfaces when material compatibility and contrast are proven.
Onto the label web
Thermal-transfer or hot-foil coding can print before label application, giving a controlled flat substrate.
Onto a lid or closure
Top coding can be easy to view but must cope with coating, curvature, vibration and changing closure orientation.
Flexible pack coding
Thermal-transfer, inkjet or integrated VFFS coding must be synchronised with film registration and seal areas.
Compare coding technologies against the substrate and production conditions
There is no universally best coder. Ink and ribbon chemistry, laser wavelength, printhead distance, line speed and environmental conditions influence the result. A code that appears dark immediately after printing may smear, fade, rub off or become difficult to read after condensation, oil exposure or abrasion.
| Coding route | Selection considerations |
|---|---|
| Continuous inkjet | Flexible direct marking at line speed; prove adhesion, contrast, solvent management, print distance and start-up behaviour. |
| Thermal inkjet | High-resolution text and codes on receptive surfaces; control cartridge distance, surface condition and ink compatibility. |
| Thermal-transfer overprinter | Strong option for flexible film and label webs; define ribbon grade, print area, intermittent or continuous motion and web tension. |
| Laser marking | Permanent non-contact mark on compatible substrates; assess material response, contrast, extraction, guarding and change-part implications. |
| Hot foil or contact coder | Defined characters on labels or film at lower or indexed speeds; manage type changes, temperature and consumables. |
| Print-and-apply label | Useful when larger variable information is required; adds label stock, application and label-presence verification to the task. |
Integrate triggers, encoders, product detection and data control
The coder needs a reliable trigger and a stable product path. Variations in conveyor speed or product position can stretch or move the code unless an encoder and appropriate tracking are used. The printhead should be protected from impacts while remaining accessible for cleaning and consumable changes.
Data entry is also a production risk. Decide whether operators enter codes locally, select a protected recipe or receive data from a central system. Access control, line clearance and first-off verification are as important as print resolution.
Fix the print window
Document the acceptable code area for every pack and label format.
Control product presentation
Use guides, sensors and encoders to maintain print distance and position.
Control data selection
Minimise free typing and define who can create, approve and recall code formats.
Verify first-off production
Check content, format, readability and permanence before releasing a run.
Manage faults and rejects
Define the response to no-print, low-contrast, incorrect-data or unreadable-code conditions.
Plan human and automatic verification at the required risk level
A basic system may rely on documented first-off and periodic checks. Higher-risk or retailer-driven applications may require vision inspection of presence, legibility, content or 1D/2D code quality. The inspection method should be selected from the real risk and specification rather than added as an undefined “camera check”.
If an automatic system rejects packs, prove the reject timing across line-speed changes and closely spaced containers. Confirm that the rejected pack is contained and that a full reject bin or air-pressure loss produces the required controlled response.
- Define whether verification checks presence, readable text, exact content or code grade.
- Use the worst normal background colour, reflectivity and print contrast in trials.
- Challenge the system with missing, partial, wrong and deliberately poor codes.
- Link reject confirmation and bin-full monitoring where required.
- Retain records and approved samples in line with the customer quality plan.
Test the code after the real storage and distribution route
Code samples should be assessed after the intended cooling, chilling, freezing, wiping, abrasion, handling and shelf period. This is especially important where sauces, oils or condensation may contact the marked surface.
The acceptance test should include start-up, normal running, a stop and restart, consumable replacement and a format change. Record printhead settings, substrate batch, ink or ribbon grade and the approved code result.
Agree a measurable date-coding acceptance plan
The coder should be accepted using production packs, final data formats and the intended inspection method.
- Every required line of text or machine-readable data is supported.
- Position, character size and contrast meet the documented specification.
- The code remains legible after the agreed cooling, storage and abrasion tests.
- Triggers and encoders maintain position through normal speed variation.
- Wrong, missing or unreadable codes generate the specified response.
- Operator data access and recipe selection follow the agreed control method.
- Consumable changes and printhead cleaning can be completed safely.
- Approved code samples and settings are recorded for commissioning.
Common questions
Often yes, provided a suitable ink is selected and the glass surface is clean and at an appropriate temperature. Production jars should be tested for adhesion and readability after the intended storage route.
Coding the label web gives a controlled flat surface, while direct container coding may reduce dependence on a particular label position. The best choice depends on pack design, substrate, line layout and inspection requirements.
Many modern systems can, but code size, resolution, substrate contrast, line speed and verification grade must be defined. A small machine-readable code needs a more controlled print and inspection setup than plain text.
Depending on the chosen equipment, codes can be selected or populated from line controls or external systems. The required interface, permissions, data ownership and validation should be specified before purchase.