Hot Fill Changes the Rules

A cold drink cup never sees more than room temperature. A hot-fill cup is filled at 85–95°C, cooled, transported and sometimes reheated by the consumer. That cycle eliminates half the material list immediately: PS and PET soften or haze near filling temperature, so the workhorse becomes polypropylene.

Shantou Longsheng Industry Co., Ltd. builds the equipment for this segment in Shantou City, Guangdong Province: PP sheet extrusion, cup making machines and the molds that define each cup.

What a Hot-Fill Cup Must Survive

• Filling temperature — the cup must hold its geometry while the drink is poured in hot
• Vacuum panel — as the drink cools, internal pressure drops and thin side walls can panel inward
• Sealing rim flatness — the lid or foil must seal on a hot, soft rim
• Stacking under load — filled cups are cased and palletised while still warm

Each of these is answered in tooling and process rather than by material choice alone. Vacuum panels are designed into the wall as ribs. Rim geometry is machined flat and round. Wall thickness is distributed so the base stays rigid at temperature.

Where the Line Starts: the Sheet

PP sheet for hot-fill is usually produced with a multilayer structure: a core of regrind or lower-cost resin between two skins of virgin food-contact PP. This is exactly what the DSI-PP multilayer co-extrusion line from Longsheng is built for. Layer ratios tune stiffness and cost; skin quality keeps the cup printable and glossy.

Gauge consistency matters more than for cold cups, because a thin spot that is invisible at room temperature becomes a soft zone at 90°C. The extruder's melt pressure control and three-roll calibration are what keep the profile flat.

Forming on the Machine

Longsheng cup machines — FS-8556 full servo, HSS-8556 hydraulic servo and HAI-8556 hydraulic — all process PP. For hot-fill formats the practical differences show up in cycle control: servo machines hold dwell and plug-assist timing precisely, which keeps wall distribution repeatable across high-cavity molds.

Founded in 1998, Longsheng operates a 30,000 square metre plant, holds 25 authorised patents (1 invention, 24 utility model) and is a high-tech enterprise.

For hot-fill cup projects, visit the official website: https://www.stlongsheng.com