Technical Information

Extrusion/Film Blowing

There are several stages in making any polythene product

Polymerisation

Polyethylene, or polythene is an oil derivative and was first used in the 1930s. Crude oil or natural gas is ‘cracked’ into several commonly known products, including petrol.

One such product, Ethylene, is then subject to heat and other catalysts - the end result is polyethylene in a granular form.

Extrusion

Lincoln Polythene Ltd sources polyethylene in granular form direct from major petro-chemical companies. These granules are then sent through a film extrusion machine. The granules are heated to a molten state and forced through a die. The molten polyethylene is subject to air and appears from the die in the form of a circular tube.

This molten tube has air blown into it - two nip rollers pull the tube upwards. Emerging beyond the nip rollers still as a flattened tube (known as Lay Flat Tubing) this tube can be wound onto a cardboard or plastic core.

Conversion

There are 2 main methods of making bags - sideways or lengthways.

Side Weld

With this method, bags are produced on a machine using a hot knife which simultaneously cuts and seals the film to form the sides of the bag. The bottom of the bag is formed by folding the film.

Bottom Weld

Using this method, layflat tubing is sent through a machine. A hot bar makes a seal across the tube whilst simultaneously a sharp blade cuts the film below the seal. The seal therefore forms the bottom of the bag and the folds of the film form the sides. These are known as bottom-weld (or end-seal) bags.

Slip Level

Low Slip - safe stacking of pallet loads

High Slip - ease of movement between wrapped packs

Shrinkfilm

We are capable of manufacturing shrinkfilms for all of its varied end uses. Shrinkfilm is manufactured against a 4 or 5 letter code depending on the shrink and slip level specifications required. Please refer to the table below for more details.