Machine pummels crisp bags

Packets for crisps or other types of products must be strong enough to prevent accidental tearing or bursting and to ensure that no air or moisture enters to affect the product's shelf life. Theymust also be relatively easy to open by hand, yet not tear suddenly on opening. Industry standard tests are available for measuring opening strength, seam strength and peel strength, but individual manufacturers often set their own pass and fail tolerances. Lloyd Instruments' 1 kN LFPlus machine can be used to test a wide range of packets for potato crisps, the company stated in a press release. The machine tests burst strength, openingstrength, seam strength and tear and peel pressure. Peel tests determine how easy it is to open the packet. The instrument can also be used to measure the friction on the plastic film used for crisp packets. The majority of crisp packets are manufactured from polypropylene. A "pull-tobreak" test measures the tensile strength of the plastic film, whilst elongation tests measure the percentage extension of the film, which indicates how much it will stretch before it will break, Lloyd Instruments stated. The LFPlus' tests for static and kinetic friction can be made on the plastic film if the instrument is fitted with a special sliding friction part. The part measures the coefficient of friction todetermine how easily the plastic passes over the rollers in the high speed, high volume packaging machines used in the production process. If the film does not move at the correct speed, the process can get out of synchronisation, leading to slowed production and possible damage and wastage, the company stated. The plastic film can be tested to various ASTM, ISO and TAPPI standards by holding it on a horizontal bed and exerting a known force. This is done using a sled to which is attached a furthersample of the same material. The sled is pulled across the bed either at rates defined by the required standards or at user-selectable speeds. The instrument measures friction on both unmodified and printed films. The amountof ink on the film influences the amount of friction it generates on the production line. External links to companies or organisations mentioned in this story: Central Science Laboratory