Selection of the appropriate peelable heat seal coating for any lidding application is a challenging process and is influenced by a multitude of parameters.
We present here some of the major parameters that a converter must consider in selecting a heat seal coating for lidding applications.
Lid film or lamination
Coating can be applied to a variety of substrates
- Aluminum foil (AF)
- Polyester film (PEST)
- Oriented polypropylene (OPP)
- Polyethylene (PE)
- Paper or paperboard
- Polyvinylidene chloride (PVDC)
Cup stock, tray stock, or bottom web
A variety of rigid materials are used as cup or tray stock
- Aluminum foilPolyester (PET OR PETG)
- Polyvinyl chloride (PVC)
- Polystyrene (PS)
- High impact polystyrene (HIPS)
- Cast polypropylene (PP)
- High density Polyethylene (HDPE)
- XT polymer
Food, Pharmaceutical, or medical products
The heat seal must be compatible with the contents or the cup or tray
The heat seal coating must be selected to withstand one or more of the following conditions.
Jellies, jams, syrup, sauces are often filled at 170-200 F the heat seal must have adequate hot tack at this temperature to resist leaking.
Refrigerated or freezing temperatures
citrus juices and concentrates are refrigerated or frozen. The heat seal must maintain its flexibility and adhesion to both surfaces at low temperatures.
This property is important for retortable, autoclaavable, or oven able products. The heat seal must have bond integrity up to 350 – 450 F
The coating may be in contact with greasy, oily, acidic, or corrosive food products, perhaps at elevated temperatures.
The sealed package may be exposed to a vacuum during sterilization or another process.
Disposable medical devices are often sterilized by ethylene oxide gas. The heat seal coating must have adequate oxide gas. The heat seal coating must have adequate porosity to permit entry and exit of the gas and not react with it.
Stability to radiation
For certain medical devices or pharmaceutical uses, the heat seal coating must not degrade or react under gamma radiation.
Heat seal coating must comply with the pertinent Food and Drug Administration (FDA) regulation for the lidding substrate, food type, and services conditions.
Type of bond
The packager must be specified low, moderate, or high peel strengths as well as the amount of coating transfer desired. Sometimes a destruct bond is required.
The coating must function within the limits imposed by available heat. Pressure, and dwell time at the bond line. This also includes considerations of sealing equipment.
The converters equipment – gravure, flexo, roller coater will have a strong influence on coating selection.
Sometimes the choice between a solvent or water based heat seal has more influence than all of the others. Solvent recovery equipment can also dictate the solvent to be used.