The goal of our Film Lab is to gather data, utilize the knowledge and experience of our film technicians, analyze the results, and make recommendations that match the best film to a particular application.
Our stretch film testing utilizes the following variables:
On our Semi-Automatic Power Prestretch Machine utilizing dual electric drives, we can run stretch levels from 0 to 600% with digital settings. Stretch levels can be adjusted at various points on the load during the wrap cycle if desired.
Turntable speed can be varied from 0 to 42 rpm with the capability of adjusting that speed while the machine is in motion. This allows some degree of simulation of high speed automatic machine conditions.
Film Tension (F2)
F2 allows us to fully measure the capabilities of a candidate stretch wrap by determining how it responds to a range of low to high post stretch conditions at a variety of prestretch levels and turntable speeds. Film tension is developed by slowing the film output of the stretch carriage relative to the speed of the turntable.
As we apply the above variables to the stretch wrapping process, we map the responses of candidate films by using load cells to measure the following:
Load compression is the force the film applies to the load as a result of the wrapping process and is chiefly responsible for what we term load unitization. If you have insufficient load compression, the load will be loose and not properly unitized. If you have too much load compression, some loads can be damaged by the crushing aspect of the compressive force. We measure this using 3 load cells arranged vertically on 1 corner of our test box.
We have a puncture probe that can extend from 0 to 5.5 inches. This enables us to simulate characteristics of different types of loads we encounter. The puncture test captures the ability of wrapped film to resist puncture from sharp corners when a load attempts to shift during transit, much like the containment test captures the ability of the film to resist further stretching during the transportation cycle.
Puncture Propagated Tear Resistance
We added a plate to our test box that is used to observe puncture propagated tear characteristics. This plate is 16" square, 3/8" thick, and extends out from 1 corner of the box 1.5". As film tension is increased during the testing cycles, the corner plate will eventually puncture the film (this will vary with film type, prestretch level, and turntable speed). High performance films will accept this puncture but the initial hole initiated in the film will not grow or propagate. As the film tension increases during subsequent test cycles, the hole will increase in size, eventually leading to our proscribed failure level (approximately 4" tear) or actual breaking of the film web. This is the test we use to determine the maximum film tension any individual film can withstand at a given prestretch level and turntable speed. In turn, this allows us to predict the maximum load containment available from a given film.
Load containment is the ability of the film to prevent palletized loads from shifting by offering enhanced resistance to being further stretched and is measured by a load cell attached to a ram/plate combination which is extended into the film a specified distance. (This simulates and correlates well with the ASTM 4649 pull test for load containment). At a given turntable speed, we will determine what prestretch level and F2 setting will provide the best balance of puncture propagated tear resistance and load containment for a particular film.
Our test box has an electrically driven ram that will push that disc out the same distance each time, at the same speed, with the same force each time, so there's no bias. Our test environment removes inconsistencies so we’re able to capture an accurate measurement for comparing films.
Both load compression and load containment are very highly influenced by the film tension (F2) setting. Higher F2 settings results in higher compression and also greater containment force. Offsetting this relationship results in a loss in propagated tear resistance for some film formulations. By this we mean that some films, when punctured during the wrapping process, have significantly reduced resistance to tearing across the film web as film tension is increased. Basically some films are more prone to film web breaks after puncture than high performance films, limiting the amount of load containment which can be developed in the wrapping process.
As we run these tests, we acquire data which can be graphed that will show the compression force the film applies to the load during the wrapping process, puncture resistance of the final wraps, and resistance to further stretching of the wrapped film (containment force) versus time. We can also measure the force required to stretch the film. We can get a real time graph of this data and we can see how it changes at different points in cycles.
This gives us the capability to simulate what occurs on some of the high-speed automatic stretch wrap equipment and to gather accurate data on pre stretch levels.
In the non- stretch film portion of our lab, we have the ability to run additional tests to measure the tensile properties of film (the amount of force a film can absorb before yielding, and/or breaking, and how far it will elongate prior to breaking), tear properties of film (both machine direction and cross direction), and the toughness of the film with either the Spencer Impact or falling dart impact test, both high-speed puncture tests. We can also very accurately determine the thickness of film and shrink properties of packaging films (machine and cross direction). We can measure the stiffness of films and also determine the strength of heat seals.