Свойства при растяжении
For example, intelligent systems show the conditions of packaged food and the environment; gas indicators detect when the gas concentration has exceeded limits in the interior packaging. For example, active systems help extend the shelf life, for example, sprayed plastics that absorb ethylene or a filter against light and radiation generated from the near UV spectrum.
Due to the growing desire for convenience, packaging should be easy to handle, easy to open, resealable or should be able to be heated directly in a microwave so food does not have to be transfered. Packaging that is easy to open is important in the cosmetic and pharmaceutical fields. Additionally, packaging for medical devices must be tightly sealed and withstand sterilization.
Packaging comes in different forms and materials thus requiring specially adapted, flexible fixtures. The following are just some examples of test fixtures for the many testing solutions ZwickRoell offers.
Function testing on the entire packaging
Packaging is as varied as the methods for opening them. Individual values are determined because testing standards are rare.
Examples of such tests:
Peel test on lid or sealing material
The ability to peel off dimensionally stable or rigid packaging depends on material combinations, machine parameters, and on sealed seam and tear-off geometries. Performing a test of the peel forces with a special peel test kit can help to optimize these elements. The most important value is the cracking force, but the regularity of the sealing is also significant.
A benefit of the ZwickRoell peel test kit is the exact alignment of the delaminated area with the test axis: The packaging is tracked automatically by the sliding specimen table and this ensures a consistent and reproducible measurement of the load because a peeling angle of 90° is always guaranteed. Furthermore the kit enables flexible adjustment to fit to different packaging shapes and heights.
Compression tests on plastic beakers, buckets, boxes, containers, barrels and similar dimensionally stable packaging
Compression tests have different purposes, for example:
Determination of stacking characteristics: There are different methods, depending on the standard and material being used. One or more packages are loaded until failure, from which the maximum stacking height can be determined. This test can also be performed on plastic cups with completely filled trays. Or a certain load may be applied for a preset length of time or until failure.
Determining the inherent stiffness: This test provides information for the packaging manufacturing process. The package is loaded with a defined force on closing (lid attachment) and must withstand this process without becoming damaged.
Fatigue tests: A hysteresis test is performed on a pail to see with what frequency a certain load can be applied before it breaks. In practice this happens when palettes are loaded and unloaded. Not every loading and unloading cycle is shown. Only the 1st, 100th, 500th, and 1,000th cycles are displayed for monitoring.
Tear tests on plastic foils
Standards ISO 34-1, ISO 6383-1, EN 495-2 and DIN 53363 relate to tear tests on plastic foils.
The test simulates the behavior of packaging foils when the package is opened. When opening a plastic bag, the initial tearing strength should be approximately as much as the remaining tearing strength. If the maximum force at initial tearing is too high, the danger exists that the plastic bag will suddenly tear open completely and the contents will spill out. The ideal behavior is not easy to adjust because the tear resistance (as well as the tensile strength), is very direction dependent with stretched foils.
90°/180° peel tests
This type of test is used to determine the adhesive characteristics as adhesion and tear strength. There are many peel and tear tests that use the same principle. Examples: EN 1939, EN 1719, DIN 30646, DIN 55475, DIN 55477, FINAT test method no. 2.
There are so many because different substrate materials and adhesives are used for many different applications. Test plates made of glass or stainless steel with a standardized surface are used to compare the adhesion properties of the different materials.
The tests determine the adhesive or adhesion strength: The force that is necessary to tear a strip of a tape constantly from a test plate or glass. The result is the force referred to the width of the tape.
The tack test is often important: It determines the ability to adhere to a surface and to obtain a measurable tearing force. The adhesion on a substrate is achieved by touching or having little contact without applying a force.
Tack loop test for testing the adhesive strength of adhesive tape
Tack is the initial adhesion. It is expressed as the tearing force of a loop material which has been brought into contact with the surface of a test plate.
A strip of a pressure-sensitive material is formed into a loop with the adhesive side outwards. The testing machine brings the loop in contact with a test plate. When a defined contact area is reached, the loop is pulled off. This test is described in FINAT test method No. 9.
Unscrewing lids/torsion testing
A torsion drive is used in conjunction with a linear axis for opening a sealing cap. With this test, tightening and loosening torques and the ease of the closure cap can be tested, taking into consideration the thread pitch. This is implemented via a corresponding testXpert III Master Test Program.
ZwickRoell torsion drives can perform single-axis and multiple-axes testing combining tension or compression test with torsion. For example, safety packaging can be checked requiring simultaneous pushing and twisting for opening.
Customized test tools
According to customer-specific requirements, ZwickRoell develops and produces various testing tools and fixtures optimally designed for your specimen packaging and testing on short notice.
Some examples are fixtures to determine the push-out force on blister packs, fixtures for special-shape containers or testing tools to test the pull-out force of wine corks as seen in the illustration on the right.
Frictional properties of spaghetti packaging
zwickiLine materials testing machine, determination of the frictional properties, food industry