Lidding applications
Dry food
Dry food products, such as coffee lightener or powdered drink mix, place minimal demands on the peelable heat seal coating, Dry food constructions include
Paper / XLDPE / HS – HIPS
Paper / adhesive / OPP / HS – PVC
X = EXTRUDED
For this end use, a water based EVA dispersion would function quite well. There is no toluene to absorb into the LDPE, and the EVA provides an easily peelable bond to the cup stock. An EVA provides an easily peeable bond to the cup stock. An EVA coating can be applied by any method and requires a relatively low drying temperature that will not distort the polyolefin film. FDA compliance on paper and / or polyolefin is also assured with this type of coating.
Diary Creamer
There are several types of dairy creamer lid stock. The simplest is
Paper / XLDPE / HS – HIPS
For this application, a moisture – resistant, peelable seal is required. An EVA – based gel lacquer is one of the most widely used heat seals. Gel lacquers are a solvent solution of a hot melt. The most common method of application is by directly heated gravure. Here again, a coating with direct food contact compliance on polyolefin film is required. A more sophisticated creamer lid structure is
Paper / XLDPE / AF / HS – HIPS or
Paper / XLDPE / AF / primer / HS – HIPS
An EVA based gel lacquer works well for such applications, but it sometimes bridges or membranes when it is peeled. One such case, a vinyl primer and heat seal must comply with FDA regulation 21CFR175.300.
Jelly and condiments
Jellies, jams. Pancake syrup, fast food sauces are often filled at 170-200 f. Sauces are often acidic and contain aggressive components such as mustard oil. The heat seals used to hold these products must have good hot tack at 200 F to prevent leaking lids, good moisture resistance, moderate grease resistance, and good chemical resistance. One type of construction is
PEST / adhesive / AF / primer / HS – HIPSPVC
Here the heat seal can be a vinyl or vinyl – acrylic applied over a vinyl primer. The primer is important to protect the foil from corrosion by the product. Another approach is
AF / adhesive / PEST / HS – HIPS or PVDC / HIPS PVC PP HDPE
A reinforced EVA gel lacquer will provide good adhesion to the PEST lid substrate as well as good salability to a broad range of cup stocks and good heat resistance for hot fill. Compliance with FDA regulation 21CFR177.1630 is an important factor in these applications. Lidding for fresh and frozen citrus juices is a large and important market. The most common construction is
Print / AF primer / HS – PVC
Where the primer and heat seal are both solvent based vinyls. A pinhole free coating is important to protect the foil from the corrosive citrus juices. Low temperature adhesion is a must for frozen products. Both must comply with FDA regulation 21CFR175.300
Greasy or oily foods
Lidding on a clear substrate for greasy foods such as cheese or peanut butter is a challenge. An often used construction is
OPP / print / PEOT / HE – PETC PVC
This heat seal coating is a solvent based EVA / nitrocellulose hybrid with excellent film clarity and grease resistance. It complies with FDA regulation 21CFR177.1630
Dual Ovenable trays
Ovenable trays are either PET or SBS board / PET in which food production are either microwaved or heated in a thermal oven up to 400 F. The cover can be
PEST / HS – PET or
SBS / PET / HS – PET
Where SBS = solid bleached sulfite
The heat seal for the film lid mist be clear, have heat resistance to 400 F, and still be peelable after heating. A board lid heat seal need not be clear, but it must have all the other attributes. Polyester – based coatings that comply with FDA regulation 21CFR177.1630 are used in these applications.
Autoclavable and aseptic lidding
Lidding for autoclavable and aseptic applications presents some unique problems. The heat – seal coating must have good adhesion to foil, and they must be sealable to poly propylene for steam sterilization. The coating must also be stable to radiation sterilization. The construction is
AF / HS –PP
And the heat seal is a specially reinforced EVA gel lacquer, which provides a controlled peel. This type of package is used for medical applications, such as sterile – water and hydrogen – peroxide – sterilized aseptic packaging. The FDA regulation for the latter is 21CFR178.1005
Retorable Lidding
Few packaging concepts can match restorable lidding for extreme performance requirements. A retortable lid must withstand 121 C, 15 psi steam for 80 min without losing seal integrity and yet remain peeable after long term shelf storage. The special heat seal coating that can function in this environment is a modified polypropylene dispersion known as Morprime. A typical lidding construction could be
0.5 mil PEST / 1 mil AF / Morprime – PP or 2 mil AF / Morprime – PP
This coating is also unique in its selectivity. It must be applied to a metal substrate, such as aluminum foil, and requires drying / curing temperatures of 400 F for 30 – 35 seconds. It is sealable to either cast or molded polypropylene or to another Morprime surface at 450 F for 1 second. Typical food products packaged in retortable cups including apple sauce, orange juice, yogurt and cheese food spreads. Moprime complies with FDA regulation 21CFR175.300
Medical packaging
Heat – seal coating for lidding of disposable packages for medical devices are applied onto Tyvek or surgical kraft paper, which is then sealed to several different plastic tray materials. Typical constructions are
Tyvek / primer / HS – PET HIPS HDPE PP
The heat seal coating must have adequate porosity to allow efficient entry and removal or ethylene oxide gas during sterilization, as well as good humidity resistance and sufficient heat resistance to overcome “sterilizer creep” When peeled from the tray, the coating should transfer completely from the lid to the tray flange to show evidence of closure. Specially formulated EVA dispersions have been successful in this application. The large particle size of the dispersion provides good porosity, and the EVA polymer provides a good peelable bond to almost all of the commercially used tray stocks. These EVA coatings are also stable under radiation sterilization. FDA compliance for direct food contact on any substrate makes these waterborne coatings suitable for lidding or medical package. Although this survey of heat seal coatings for lidding has covered a variety of materials, applications, and usage parameters, it is by no means exhaustive. As new lidding substrates and containers materials become available, new heat seal coatings will be required to meet the needs of the converters and end-users
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