Robin Meade reviews developments in technology for materials testing and inspection
Paper, board, film and foil were once a constant – purchased in bulk under contract, loaded onto machines and converted into a saleable product. The finer technical points were considered inconsequential or left to the research and development department. With the call for innovative and technically demanding products, converters now need to know a lot more about the materials they rely upon.
At a shrink sleeves and sleeving conference earlier this year, a number of converters were agitated at one aspect of testing films and the fact that the process was not standardized across materials suppliers. Converters in that sector face demands to use new films made from renewable raw materials, and that are thinner and have higher shrink values, among other attributes.
The methods of ensuring they are fit for purpose investigate attributes such as appearance through gloss, haze and image clarity by reflectometer values, density, permeability, friction and strength.
However, the equipment for the standard test for machine direction and transverse direction shrinkage of a film was described at the conference as a bath containing distilled water heated to 90degC, a measuring tape and a clock. After immersing the sample for 15s, the film is removed, cooled and measured with the tape.
When a converter challenged the speaker that other suppliers did use different temperatures over different periods, it was agreed that was the case, but that there were no plans for standardization.
Other tests, however, require greater sophistication. A Systech 8001 oxygen permeation analyser is being used to test Xylophane, a novel biodegradable packaging film being developed in Sweden. The new, environmentally friendly oxygen barrier film, being developed by Xylophane AB, makes use of by products of corn, straw and wood processing that are usually discarded. Processing turns them into xylan, a biopolymer used to produce the film with oxygen barrier properties said to be similar to aluminium foil and plastics film from non renewable sources.
As part of the commercialization process, the Systech 8001 oxygen permeation analyser is used to produce data that allows the performance of Xylophane to be compared directly with that of conventional oxygen barrier films used in the food packaging industry.
Systech has also introduced a testing service for companies that cannot justify the purchase of equipment. The Systech permeation laboratory provides measurement of oxygen permeation in films, bottles and finished packaging.
The laboratory is fully compliant with all major standards, including ASTM 3985 and DIN 53380 (Europe), relevant to the packaging materials industries. Systech says it is able to provide a service for companies with their own test equipment for routine result comparison tests and to absorb excess workload.
Zwick has expanded its range of modular and expandable materials testing systems to enable improvements in plastics film testing. Its horizontally constructed testing system for tensile tests on plastics films and paper simplifies the insertion and gripping of the specimen as two optical sensors detect it, close the pneumatic grips and start the test.
The application software provides parameters such as tensile modulus, yield point, tensile strength, and tear strain, and other results can be calculated from the recorded force extension data. Increased travel load frames are available for high elongation plastics films.
With its ProLine coefficient of friction testing system a sled is connected to the testing machine’s moving crosshead and pulled over a reference surface at a constant speed of 100± 10mm/min or 150± 30mm/min.
The traction system can have a significant impact on the result so the static force required to initiate the sliding process and the kinetic force necessary to maintain motion are determined automatically by the testing software. These forces are combined with the weight of the sled to calculate the static and dynamic coefficients of friction.
The materials testing system can be reconfigured to determine the puncture resistance of plastics films in accordance with EN 14477. The strip samples can be gripped quickly and with ease whilst the testing procedure is controlled by the testXpert II software. The test result is calculated automatically.
Peel tests on adhesive joints, seals and tapes are carried out by mounting the specimen on a stiff carrier which is then peeled off at a constant angle of 90 degrees in order to determine the adhesive force. The peel force is measured and evaluated. Where the unrolling force from a roll is required a special testing module is available.
The viability of new products being developed for packaging or protection, from pre-prepared, microwaveable convenience foods at the supermarket to medicines and other medical products depends on the availability of high barrier materials. As new high barrier materials are developed for these applications, there is a need for highly sensitive permeability measurement methods to test these materials and quantify their barrier properties.
To meet the demands, PBI-Dansensor, the supplier of gas instrumentation equipment, has developed the L80-5000 LP, an enhanced model of the L80-5000 water vapour permeability tester. The new model has been designed for the measurement of high barrier materials with very low water vapour transmission rates.
PBI-Dansensor says the new tester provides the ability to measure WVTR of high barrier films and foils with improved measurement sensitivity, faster measurements, and a better repeatability and reliability of measurement results.
The L80-5000 LP has improved measurement sensitivity to the lower measurement limit 0.003gm2/24 hour, a factor of 10 lower than the conventional L80-5000 tester. It also has improved stability and reproducibility of measurements, said to provide more reliable results. This is achieved by using an optimized chamber with a special anti absorption coating, significantly reduced internal volume, a new sensor design and placement, and special air inlet and outlet valves.
Lloyd Instruments has made its FTPlus friction tester to be configured to operate as two instruments in one. It is a dedicated bench mounted single lead screw instrument that conforms to the requirements of the key ASTM D1894, ISO 8295 and TAPPI T549 friction testing standards and has extensive applications in the packaging and printing industries.
However, it can also be configured as a universal testing machine to perform tensile, compression, flexural and other mechanical tests up to 1kN with the appropriate grips, fixtures, loadcells and software. A friction table is mounted directly onto the machine with a full set of accessories to achieve the ASTM, ISO and TAPPI requirements. A stainless steel table option is now available for ‘film against metal’ friction measurements. A further seven tests are available for user custom configuration.
The statistics for each type of test are automatically calculated including static coefficient of friction, kinetic coefficient of friction, peak load and average load. User defined tests can be configured in terms of final movement limits, relative and absolute calculation limits, sled weights and dimensions. Up to 600 samples can be stored in any of the test set-ups.
A high resolution encoder is used to measure the sample extension and to provide high accuracy speed control. The crosshead is driven by a high precision servomotor and DC servo system to achieve a wide range of speeds throughout the full load range. Three XLC loadcell options are available for friction testing: 10N, 50N and 100N.
The FTPlus friction tester features a dedicated user interface for friction testing. Tests are set up from, and results displayed on, a backlit LCD integrated into the control console. Although the FTPlus is a fully self contained instrument, an RS232 is provided to allow computer control using the latest NEXYGENPlus material test and data analysis software.
Diageo’s Brand Technical Centre in Menstrie, UK, has bought a Lloyd Instruments LRXPlus single column materials testing machine equipped with NEXYGENPlus material test and data analysis software, with a specially designed jig to allow testing of the strength of the base of board presentation boxes for whisky and other beverages.
Boxed drinks have become an increasingly popular gift and are now purchased more and more outside of the Christmas period. It is important to ensure the interlocked flaps that form the base of the box will not give way under the weight of the bottle. The new system measures the load force required to push open the base of the box. The test can be carried out completely automatically using the NEXYGENPlus software.
The test jig is mounted on the baseplate of the LRXPlus, which has two vertical supports for the sides of the box. A lever is moved to adjust the jig sides in or out. This ensures they are the correct distance apart to hold the box in the centre position, leaving space below the bottom of the box. The upper box flaps are opened and held down by a spring loaded toggle/clamp arrangement on either side. The full bottle is then placed inside the secured box.
A compression plate fitted to the moving crosshead of the testing instrument is driven down onto the lid of the bottle. The new test jig is compatible with any of Lloyd Instruments Plus range of materials testing instruments. The LRXPlus can be used for material testing applications up to 5kN and uses high accuracy interchangeable XLC Series loadcells for tension, compression and cycling through zero force measurements. The load measuring system is said to exceed the requirements of all recognized international standards.