Packaging has a great impact on the quality of its contents and also influences consumer purchasing decisions. Both factors represent major challenges for product design, especially where food packaging is concerned. Packaging for other items must also fulfill numerous additional requirements depending on type and function, for example, packaging for cosmetics, medicine, chemicals, transport packing (pallets and crates), industrial packing (bulk bags, containers, barrels), electronic appliances, and consumer goods.
Packaging products have a great impact on the quality of the contents and also influence consumer purchasing decisions. Both factors represent major challenges for product design, especially where food packaging is concerned. No other product implements as many newly and refined developments to packaging as does food. Nanotechnology, convenience, biodegradable packing, intelligent and active systems are key terms.
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.
Packaging is as varied as the methods for opening them. Individual values are determined because testing standards are rare.
Examples of such tests:
- Piercing beverage cartons with a straw
- Piercing of preperforated openings
- Opening force of ring-pull cans
- Tearing off opening tabs, for example, those on lids
- Tearing off carrying handles
- Opening and closing lids with snap locks
- Actuating force on spray pumps
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. The opening angle is based on the manual opening and can be varied between 90° and 155°. Furthermore the kit enables flexible adjustment to fit to different packaging shapes and heights.
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 up to failure, enabling the maximum stacking height to 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.
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.
The sealed-seam strength of sealings made of flexible packaging material is determined according to DIN 55529 and other standards.
A tensile test is performed on 15-mm wide strips with a peel angle of 180°. This seal must demonstrate a certain stiffness, depending on the type of packaging material used.
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 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.
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.
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.
Basic materials such as plastic, paper, and metals have the most varied material tests performed on them. A few examples:
- Tensile test on plastic foils for determining the stress-strain characteristic
- Determining the coefficient of friction (COF)
- Penetration test on elastic packaging materials for determining the penetration resistance
- 4-point flexure test kit for testing single-wall and multi-wall corrugated cardboard