Technical Talk

This is a broad subject and we have endeavored to provide basic information of most of the common Polymers used in films.

PE

• LDPE Low Density Polyethylene. Common material used in general packaging that is a polymer of ethylene.
• HDPE High Density Polyethylene. Similar to LDPE in terms of chemical make up but has a higher density and produces a stiffer film with superior moisture barrier properties.
• LLDPE Linear Low Density Polyethylene. These materials are a Copolymer of Ethylene and either butene, hexene or octene. These materials are generally tougher than LDPE and yield better sealability and optical properties.
• mLLDPE Metallocene Linear Low Density Polyethylene. Specialised Coploymers manufactured to yield enhanced toughness, optics and particularly sealability properties. Many different types are available. Has replaced "older" Polymers such as Ionomer, EVA, and EAA resins

PP

• Polypropylene is a copolymer of ethylene and propylene. As a film it is used in laminates and coextrusions for good stiffness, moisture barrier, good optics and cost reduction. Appears in many general packaging applications

Nylon

• Generic name for a variety of Polymers derived from Caprolactum. Most common nylon used in laminates and coextrusions is Nylon 6 but Copolymer Nylons (Nylon 6, 66), Amorphous Nylons and Aromatic Nylons can be used.
• Nylons have good toughness, heat resistance, formability and medium Oxygen Barrier performance.

EVOH

• Ethylene Vinyl Alcohol Copolymer. Specialised resin used primarily because of its excellent oxygen barrier properties. There are many (ethylene mol%) varieties providing a balance of flex crack resistance, softness, and oxygen barrier to suit the application. Normally used in a coextruded films encapsulated by other resins as is moisture sensitive with regard barrier properties.

PET (Polyester)

• Polyethylene Terephthalate in films is a clear material that has medium oxygen barrier properties, good heat resistance and high stiffness. Very commonly used in laminate films. Can be used as uncoated or coated (with PVDC) or metallised (thin aluminium coating)

PVDC

• Poly vinylidene Chloride is typically used as an aqueous coating against BON or PET, but can be extruded as a discreet layer in coextruded shrink films. Its main property is oxygen barrier which, although is not as effective as EVOH, is not moisture sensitive.

Pigments

• This is a generic name for the additives used to colour a film. Commonly called masterbatches.

This information explains some of the technical terms used when describing resins (and thus finished films) properties.

• Gauge Term used to quantify a films thickness usually specified in microns (1 micron = 0.001 mm)
• Sealability This describes a materials ability to seal to itself or another substrate. It can encompass several criteria:

  Sealing through contamination, heat seal temperature range, ultimate seal strength, hot tack seal strength.

• COF Coefficient of friction. This is a measure of a films “slipperiness” which is critical in a number of packaging applications
• Tensile Strength A measure of a films strength when a strip is pulled apart in a controlled fashion
• Elongation A measure of a films stretch ability when pulled apart in a controlled fashion
• Tear Strength A measure of a films resistance to tearing once notched and subjected to force
• Puncture Resistance A measure of a films resistance to puncture under controlled conditions
• Impact Strength A measure of a films resistance to impact when a given weight is dropped on the film from a set height.
• RH Relative Humidity or % RH. Measure of moisture presence in air. Important when measuring film properties
• Moisture Barrier A measure of a films ability to prevent moisture vapour passing through it. This is normally specified in units grams of H2O / m² / 24 hrs at 37ºC and 98% RH
• Oxygen Barrier A measure of a films ability to prevent oxygen gas passing through it. Oxygen Transmission Rate (OTR) is a term commonly used and is normally expressed in units cc/m²/24hrs at specified temperature and RH. RH is very important when interpreting OTR.

The following information explains some of the terms used for a variety of packaging processes

• VFFS Vertical Form Fill and Seal. Product is packaged using reel stock film and assisted by gravity to form a pouch, fill the pouch then seal the pouch. Frozen Vegetables is a good example of the end result.
• HFFS Horizontal Form Fill and Seal. Similar to VFFS but performed on the horizontal plane. Used when more fragile or hard to handle items are being packaged. Sometimes termed Flow Wrapping.
• Lidding Description of goods being packaged (normally in some form of tray) and a film lid is heat sealed to the perimeter of the tray. Sometimes the pack is gas flushed prior to sealing to extend shelf life
• MAP / CAP Modified Atmosphere or Controlled Atmosphere Packaging. Normally involves a pouch that, once the product is placed inside, is flushed with a gas mixture to expel oxygen and replace it with nitrogen / carbon dioxide to extend shelf life. Particularly useful in lamb, beef and poultry food service applications.
• Skin Packing When a forming web is heated, placed over the product (in a tray or another base web) then evacuated. The film cools and thus hugs the contour of the product with no air encapsulated.
• Thermoforming When a thick web is heated, formed to make a desired shape, the goods placed in this formed shape and then a Top Web welded to the formed shape. Bacon packaging is a good example of this technique.
• Vacuum Packaging Very common method of packing goods sensitive to oxygen. Goods are placed into a premade pouch, placed in a chamber machine that evacuates the air and seals the pouch – thus creating a vacuum in the pouch.