Adhesive Films – the Technology

Film manufacture
Adhesive Films are made by adding the ingredients (especially polymers and additives in pellets to extruders, where they are melted and thoroughly mixed as they are moved forward by the extruder screw. The resultant melt is distributed in the die such that it yields a film of the desired thickness when drawn off and cooled. The die determines the shape of the film: a slot die yields a flat film and an annular die is used to produce a blown film.

Diagram of flat film extrusion.

Flat film extrusion (see schematic diagram on the right) is ideal for coating customer’s substrates because these act as carrier at the die. It can also be used to process tacky raw materials, in which case the coated substrate is a release carrier, such as siliconized paper. Pontacol produces coatings and flat films as mono or multilayer.

Schematic structure of a 5-layer blown film die.

Diagram of blown film extrusion.

Blown film (see schematic diagram, right) exits the die in tubular form and is cut to rolls of the desired width by knives. Maximum use of the parison circumference is obtained by subsequently cutting the wound tube at one side and opening it over a triangle. Pontacol can produce blown film in one, three and five layers.

Technologies

Flat film or sheet extrusion	Mono Coex Coatings
Blown film extrusion	Mono Coex
Slit film extrusion	Mono Coex

Raw material classes

Polyethylene, grafted	PE, PE-LD, PE-LLD, PE-HD
Polypropylene, grafted	PP
Ethylene copolymers	EVA, EAA, ethylene terpolymers
Copolyesters	CoPES
Copolyamides	CoPA
Thermoplastic polyurethanes	TPU

A speciality of Pontacol is film slitting, in which we cut slits 4–8 mm in length into the film. This not only makes the film softer and air permeable, but also allows it to be heat-shrunk – which causes the slits to open (see diagram at the bottom right).

Advantages of adhesive film technology

Clean, efficient, ecologically sound processing
Slit films are air permeable, have a softer feel and are easier to process
Blocking and non-blocking types can be produced
Pre-tested quality
Can be reactivated with heat (80–180 °C) and pressure
Bonded joint can be separated again by heat
Long storage times possible
Variable gauge and width
Seals, protects or blocks reliably
Uniform application of adhesive layer
High level of automation at short cycle times
Simple and inexpensive handling
Hardly any cleaning; little scrap
Processing of large surfaces combined with simple logistics
End product has no known harmful effects
Little or no odour
No emission of harmful substances during processing

Advantages of multilayer films

Several production steps possible concurrently, e.g. bonding and finishing in one step
Different adhesive properties in one step
Reliable bond, even between incompatible substrates
Opens scope for new combinations of materials
Clean edges
Enhanced surface finishes
Thermoformable in three dimensions
Two layers in a single pass

Bonding applications