Can the CPET Tray be used with automated filling and sealing machinery?

CPET trays are fully compatible with automated filling and sealing machinery, and they are in fact one of the most widely used substrates on high-speed ready-meal production lines worldwide. However, successful integration depends on precise dimensional tolerances, correct material specifications, and proper machine configuration. Understanding these requirements before committing to a CPET tray format can save significant time, cost, and production downtime.

Why CPET Trays Are Designed for Automation

CPET (Crystallised Polyethylene Terephthalate) trays are thermoformed under high heat and pressure, which gives them a rigid, dimensionally stable structure. This rigidity is precisely what makes them ideal for automated handling. Unlike flexible packaging formats, a CPET tray maintains its shape consistently throughout filling, sealing, labelling, and distribution — a critical requirement for any automated line running at speed.

Most CPET trays are manufactured to tolerances of ±0.3 mm to ±0.5 mm on critical dimensions such as flange width, overall length, and rim height. These tight tolerances are necessary to ensure repeatable registration on tray-sealing equipment. A flange width that is inconsistent — even by 1 mm — can result in incomplete seals, seal leakage, or machine stoppages.

Major tray-sealing machine manufacturers, including Multivac, Ulma Packaging, Mondini, and Ishida, all list CPET as a supported substrate in their equipment specifications. This broad compatibility reflects the material's established role in the food manufacturing industry, particularly for chilled and frozen ready meals.

Key Dimensional Tolerances for Machine Compatibility

When specifying a CPET tray for use on an automated line, the following dimensional parameters must be validated against the sealing machine's tooling specifications:

Rim flatness is particularly critical. A warped or uneven flange surface — even one that appears acceptable to the naked eye — can cause micro-leaks in the sealed atmosphere, compromising MAP (Modified Atmosphere Packaging) integrity and reducing product shelf life by several days.

Compatible Sealing Equipment and Line Speeds

CPET trays are routinely run on two primary categories of tray-sealing machines:

• In-line (indexing) tray sealers — these machines advance trays in a step-and-seal motion and are suitable for medium-output lines, typically achieving 20 to 60 trays per minute depending on tray size and format.
• Rotary tray sealers — used on high-volume production lines, these machines can process up to 120 trays per minute with consistent seal quality, making them the preferred choice for large-scale ready-meal manufacturers.

Equipment suppliers such as Mondini (Trave series) and Multivac (T 200 series) offer dedicated tooling formats engineered specifically for CPET tray geometries. When ordering tooling, the manufacturer will typically require a physical sample of the CPET tray along with a dimensional drawing to ensure proper nest fit and sealing head alignment.

Sealing temperatures for CPET trays with standard PET-based lidding films typically range from 140°C to 180°C, with dwell times of 0.8 to 2.0 seconds. These parameters must be validated for each tray-film combination, as variations in CPET crystallinity or surface treatment can affect seal strength and peel force.

Lidding Film Compatibility with CPET Trays

Not all lidding films perform equally on a CPET tray. The choice of film directly affects seal strength, peelability, and the overall appearance of the finished package. The most commonly used lidding films with CPET trays include:

• PET/PE laminates — provide a strong, reliable seal with good barrier properties; widely used for chilled ready meals.
• PET/EVOH/PE structures — offer enhanced oxygen barrier performance, extending shelf life in MAP applications to up to 21 days for certain protein-based products.
• Dual-ovenable lidding films — heat-resistant films that can remain on the CPET tray during oven cooking, eliminating the need for the consumer to remove the lid before heating.
• Peelable easy-open films — engineered with a controlled peel force of 8 N to 15 N per 25 mm width, meeting consumer convenience standards without compromising seal integrity during distribution.

It is strongly recommended to conduct seal strength testing — typically a T-peel test per ASTM F88 — on every new tray-film combination before committing to full production runs. A minimum seal strength of 1.5 N/15 mm is generally considered the baseline for distribution-safe packaging, though requirements vary by product type and retailer specification.

Automated Filling Considerations for CPET Trays

Beyond sealing, the filling stage also requires careful attention when working with CPET trays on automated lines. The following factors influence filling performance:

Tray Denesting Performance

CPET trays are supplied in nested stacks and must be reliably separated (denested) one at a time by the automated line's denesting unit. The draft angle of the tray — typically between 3° and 7° — directly affects how easily trays release from the stack. Insufficient draft angle leads to double-feeding or jamming, which can halt production. Specifying the correct draft angle for your denesting equipment is a non-negotiable step in tray selection.

Tray Stability During Filling

The rigidity of a CPET tray means it can be conveyed and filled without deforming under the weight of the product — an important advantage over thinner-gauge or flexible substrates. A standard CPET tray with a wall thickness of 0.45 mm can typically support a filled product weight of 400 g to 900 g without base deflection exceeding 2 mm, which is within the acceptable range for most sealing tooling clearances.

Contamination Control on the Flange

Food contamination on the tray flange is one of the most common causes of seal failure on automated lines. Production lines handling saucy or liquid-rich products should incorporate flange-wiping stations or recessed filling nozzles that direct product away from the sealing rim. Even small amounts of oil or protein residue on a CPET tray flange can reduce seal bond strength by 30% to 50%, according to packaging validation data from leading ready-meal manufacturers.

Validation Steps Before Running CPET Trays on a New Line

Before committing a new CPET tray format to full-scale automated production, the following validation steps are strongly recommended:

1. Dimensional audit — measure a statistically significant sample (minimum 30 trays per batch) across all critical dimensions and compare against tooling specifications.
2. Denesting trial — run a denesting trial at target line speed with full stack heights to confirm reliable single-tray separation without jamming.
3. Seal parameter optimisation — conduct a design of experiment (DOE) varying sealing temperature, pressure, and dwell time to identify the optimal sealing window for your CPET tray and lidding film combination.
4. Seal integrity testing — perform bubble emission testing (ASTM D3078) or dye penetration testing on sealed CPET trays to confirm hermetic seal quality across the full range of sealing parameters.
5. Transit simulation — subject filled and sealed CPET trays to ISTA 2A or equivalent transit simulation testing to validate that seals remain intact under real-world distribution conditions, including vibration, compression, and temperature cycling.