Food Container bases are produced in polypropylene while most lids are made in polyethylene.

 

Polymer Types

Block Copolymer Polypropylene (PP)

§         General purpose type of material

§         Freezing type of applications

§         Types Used:

High Impact PP

• Translucent
• High degree of flexibility
• -35°C – 100°C
• Used for large tubs, ice-cream  tubs and lids

 

Medium Impact PP

• Translucent
• Firm material
• -18°C - 130°C
• Used for large tubs, frozen products

 

Low Impact PP

• Translucent
• Very stiff
• -0°C - 135°C
• Used for chilled and re-heatable products, general goods application

 

Random Copolymer Polypropylene

§         Homo-polymer with the addition of up to 7% PE (polyethylene)

§         High Degree of Clarity

§         Compared to Block Copolymer Relatively Low Impact

§         4°C up to 90°C (Hot Fill to 90°C)

 

Polyethylene (PE)

Types of Polyethylene:

§         High Density Polyethylene (HDPE)

§         Medium Density Polyethylene (LLDPE)

§         Low Density Polyethylene (LDPE)

 

HDPE

• Opaque in Natural Form

• High Impact Strength in Freezing Conditions

• –35° to 85°C

 

HDPE tends to have high shrinkage rates which create problems.

 

LLDPE

• Translucent in Natural Form

• Flexible

• –35° to 70°C

 

Good at low temperatures with good impact strength and flexibility.  Often plastic bottles are made from LLDPE  as it can achieve a thin wall on the container and have good impact strength and flexibility.

 

LDPE

• Clear in Natural Form

• Flexible

• –40° to 70°C

 

Greater clarity achievable but loses hot fill capabilities.

 

 

Maximum baking temperature recommended for dry heat or steam injected ovens is 125°C.  Some bakeries have successfully baked containers up to 150°C but caution should prevail during trial process.

 

Facts and Recommendations

• Polyethylene lids will distort at the maximum temperatures that PP is subjected to so Bowls must be baked with the associated lids off.
• Bake on a flat tray
• It is important that the oven door is not opened during the baking process.  Temperature surges may result in distortion
• Clear polymers have a lower temperature tolerance than natural & colours
• Allow cooked pudding and bowl to cool before applying the lid
• Overlid only fits when the bowls have been cooked
• As with all cooking methods the optimum baking time and temperature can vary with each recipe, preparation and oven type
• All containers can be microwaved

 

PP is capable of hot filling at temperatures of around 95°C. The temperature of material being filled and headspace between the product and lid is crucial to the integrity of the foil or membrane seal.

 

Too much headspace will draw excessive vacuum, causing distortion to the tub sealing flange, effecting the seal and overlid fit.  Inadequate headspace will also contribute to the success or failure of the seal.

 

Extensive trials should be conducted with various products and temperatures to satisfy the specific requirements of each application.

 

Under normal circumstances, PP & PE can be frozen to a temperature of 30°C without adverse affect.  Any lower temperatures would necessitate the addition of an additive to retain polymer pliability.

 

As with baking, clear polymers do not have the same performance tolerance as containers in natural or coloured materials in freezer conditions.

 

 

Product Shelf Life 

 

Where there are issues concerning shelf life, integrity of the product invaluably it is a function of the customer’s process that must be assessed due to the many variables within the filling and packaging process.

 

Lids are designed to be ‘burped’ when applied.  Whether manual or automatic application occurs the lid is designed to be pressed in the centre when applied.

 

Procedure for applying lids

§         Place the lid on the tub

§         Using your two (2) thumbs, pointing away from you, depress the centre of the lid.  This should snap the lid down onto the tub

§         To ensure the lid is properly fitted, turn the tub 90° and repeat the step above.

 

What the packaging will not do:

Do Not::		Cook higher than 150°C and even this needs a special polymer.
Do Not:		Expect random co-polymer PP (clear) to stand over about 110°
Do Not:		Expect LLDPE (lids) to be able to be cooked or heat treated.  Melts at 120° and softens less than 80°C.
Do Not:		Expect it to retain normal strength when frozen
Do Not:		Expect the lid to stay on when the pot is violently deformed, especially when empty
Do Not:		Expect it to be watertight when deformed or squashed
Do Not:		Expect it to be unbreakable
Do Not:		Expect it not to condensate when lid is put on product over 25°C
Do Not:		Expect the Overlid or HL to be watertight
Do Not:		Expect a hermetic seal without film, foil or aluminium end
Do Not:		Expect our products to gain Dangerous Goods (DG) rating

 

 

 

Product List Terminology

 

MTE		Mechanical Tamper Evident – Tear Downwards
NMTE		Non Mechanical Tamper Evident
SAP Lid		Stiff, High Integrity Seal for Liquids, Oils, etc
SL Lid		Pliable Medium Integrity Seal for Semi Solids.  Consumer Friendly
HL Lid		Low Security Seal (originally developed for the Honey Industry)
Overlid		Foil / Membrane Sealing
IML able		Capable of Moulding with an In Mould Label
Full Wrap		The IML extends to the full height of the tub and wraps around the full circumference of the tub leaving no area to view the contents of the tub
Short Wrap		The IML extends to the full height of the tub, but does not wrap around the full circumference of the tub.  This enables the product to be seen.
Short Label (Height)		The IML does not extend to the full height of the tub but does wrap around the full circumference of the tub.  The label is situated at the base of the container allowing product to be viewed at the top.  This is not possible to place the label at the top of the container in order to allow the contents to be viewed at the bottom of the tub.