Tray Sealing Machine Product

Overview

A tray sealer is a finishing machine for thermoformed trays (prepared by a Tray Forming Machine), applying a flexible film lid and sealing the perimeter to create a barrier pack. The machine is commonly found in fresh food (meats, seafood, deli items, ready meals, bakery), dairy (yogurt, cheese), and pharmaceutical packaging. A tray laden with product arrives on a conveyor, is stopped under a heated Sealing Platen, a film is positioned over the tray opening, and the platen clamps down at 150–220 °C for 1–4 seconds, heat-sealing the film to the tray rim. Modern tray sealers optionally include Vacuum System (air evacuation for longer shelf life) and Gas Injection System (nitrogen or CO2 flush for modified atmosphere packaging). Speed ranges from 20–60 trays per minute, and the sealed trays emerge ready for labelling, case packing or immediate shipment.

Tray infeed and positioning

Filled trays arrive from upstream (a product-loading station or from manual placement) on the Infeed Conveyor. A Tray Stop (a pneumatic pusher) indexes the tray into exact position beneath the Sealing Platen. A Stop Sensor confirms positioning. The tray must be stationary and square to the sealing head for consistent seal strength; precise mechanical stops ensure repeatability. Some machines use a rotary carousel instead of linear indexing, allowing continuous feed with intermittent pausing at the sealing station.

Film supply and positioning

Lidding film (typically 30–100 microns: polypropylene PP, PET/PE laminate, or BOPP — biaxially oriented polypropylene) is unwound from the Film Unwind System reel. A Film Motor with encoder feedback controls advance speed. A Film Tension arm maintains constant tension. The film web advances into precise registration over the tray, and a mechanical blade or web-guide cuts or separates one tray-sized portion. The film drapes over the tray opening, held in place by gravity or light vacuum.

Sealing and platen design

The Sealing Platen descends from above and clamps the film to the tray rim. The platen is a precision-engineered block (typically aluminum or hardened steel, 100–300 mm × 100–300 mm) heated by embedded Heater Element cartridges to 150–220 °C depending on film type (PP reseals at ~160 °C, PET at ~180 °C). A Temperature Sensor (thermocouple or RTD) measures platen surface temperature, and a Temperature Controller (a PID loop) adjusts heater power to maintain setpoint ±5 °C. The platen face is precisely machined or coated (often PTFE or hard anodised) to release sealed trays without sticking.

Sealing occurs in the overlap zone where the film drapes over the tray rim. Heat softens the film and the tray rim (usually the tray's edge is slightly raised as a flange). Pressure (100–300 psi, applied by a Platen Actuator) fuses the film and tray rim together. Dwell time is typically 1–4 seconds; the shorter the dwell, the faster the throughput, but very short dwells risk weak seals if the film does not reach equilibrium temperature. Longer dwells with lower temperature may reduce seal strength but improve thermal stability.

Vacuum and modified atmosphere

The Vacuum System is optional but increasingly common for fresh-food applications. A Vacuum Pump (rotary vane or piston pump) evacuates air from the tray headspace before the platen descends and seals. Vacuum level is typically 600–800 mbar (60–80 kPa below atmosphere). Vacuum removal extends shelf life by inhibiting oxygen-dependent spoilage (oxidation, microbial growth). Once vacuumed and sealed, the pack is a barrier to gas exchange.

The Gas Injection System system uses a Gas Source (bottled nitrogen, CO2, or blended gas) regulated by a Gas Regulator. A Gas Injector nozzle (positioned inside the tray chamber or above the rim) injects 30–100 mL of gas per tray immediately after vacuum (or as an alternative to vacuum). This modified-atmosphere packaging (MAP) fills the headspace with nitrogen (inert, extends shelf life) or a mix of nitrogen and CO2 (CO2 is antimicrobial and keeps fresh meats pink). The Gas Timer controls injection duration.

Platen clamping and release

The Platen Clamp (a mechanical jaw or pneumatic band) applies clamping force as the platen lowers. Pressure distribution is critical: uneven force creates weak spots in the seal. Some machines use a flexible gasket or compliant clamping head to accommodate small tray height variations. After the dwell period, the platen retracts and the tray is released. A dwell too short allows the seal to cool insufficiently and may re-open on handling; too long wastes cycle time and can over-soften the film, tearing it.

Cooling and discharge

Sealed trays are hot (120–150 °C) when they leave the platen. They advance onto the Discharge Conveyor, which carries them away. Some designs include a cooling tunnel (optional air jets or passive cooling zone) to speed setting, though ambient air works if downstream operators can handle warm trays. The conveyor speed must match the sealing cycle to prevent jams.

Control and flexibility

The Control System (a Control PLC) orchestrates the entire cycle: conveyor feed, tray stop, film advance/cut, vacuum (if used), gas injection (if used), platen descent, hold dwell, platen ascent, release. Tray size changes require mechanical changeover (new platen, adjusted tray guides and film cutter) and PLC recipe change (dwell time, platen temperature, vacuum level, gas volume). Quick-change platen tooling and modular tray fixtures reduce changeover time to 15–30 minutes for similar-sized trays.

Heat sealing principles and seal quality

A strong seal requires three conditions: adequate temperature (film must soften), adequate pressure (force film onto rim) and adequate dwell (time for heat transfer and cooling). Weak seals result from too-cold platen, insufficient dwell, or low pressure. Strong seals resist thermal abuse and mechanical stress. Seal strength is tested by peel testing (pulling the film away from the tray rim after sealing and measuring the force required); a good seal might resist 2–5 kg/25 mm of peel force.

Why tray sealing dominates fresh food

Sealed trays are rigid, stack-able, display-ready, and create a tamper-evident package. The seal protects product from oxygen and contamination. Vacuum and gas options extend shelf life significantly (fresh meat from 2 days to 10+ days, yogurt from 2 weeks to 8 weeks). The combination of thermoforming (low equipment cost, low tray cost) and inline tray sealing (fast, high-volume) makes this the standard for fresh-food retail in developed markets.