Is your Ice Cream Tub at the Top of the Stack?

An ice cream tub has an important job. It must attract the supermarket shopper with an appealing design, often showing off the ice cream through a transparent window. 

The structure of the ice cream should be protected – any decorations or surface construction should remain in place and not be squashed by the lid. At the same time, there are requirements for packaging to be lightweight, stackable and suitable for nesting in pallets during shipping as well as minimising both empty space and material usage.

When designing a new ice cream tub, it is vital to put the new packaging to test to ensure breakage and spillage do not occur during transportation from the factory to shop and onto the customer. Existing packaging designs are subject to similar tests in the quality control process. With millions of tubs produced each year, small weight reductions add up quickly to reduce costs. The design can be adjusted to remove material in areas of lower importance. This reduces the package’s weight but helps maintain functionality. Similar difficulties arise during the design process of each new type of package, with consideration for its functional requirements and the materials used in manufacture. A tub is placed in many different situations during its lifetime, and so conflicting requirements can occur, making the all-important packaging weight reduction more difficult.

Rectangular Compression Platen A/RCP

The materials used to manufacture ice cream tub walls and lids are usually limited to coated cardboard or a small group of thermoplastic polymers. However, sometimes variations on these materials are considered, particularly if a brand is motivated to make the product more sustainable. We are likely to see more eco-friendly packaging coming into the market with pressure on large companies to cut plastic pollution. The UK Plastics Pact earlier this year has been signed by more than 40 large companies, requiring the elimination of single use plastic packaging, 100% of packages to be reusable, recyclable or compostable, and 30% of plastic packaging to include recycled material. Similar initiatives are seen internationally.
These strict guidelines will see a surge in biodegradable plastic and designs altered for multiple uses, so in the next few years, physical testing will become more important than ever before.

Tensile Grips A/TG

A Texture Analyser such as the TA.HDplus is an essential tool in studying the potential weaknesses of a newly designed package, from raw material to crush strength and label adherence.

A good place to start when deciding on a new material for tub manufacture is tensile testing, providing a thorough assessment of the material’s basic properties, including stiffness, yield strength, toughness, tensile strength and strain to failure. This process involves cutting the polymer sheet into thin strips (or dogbone shapes), held in a set of tensile grips and pulled apart.

While the grips separate, the sample begins to stretch elastically before it yields, necks and finally breaks. If the sample dimensions were measured accurately and precisely before the test, the material’s mechanical properties can be calculated from the stress-strain graph. This process can be performed automatically in Exponent software. These parameters allow the raw comparison of candidate materials, helping to narrow down the selection before proceeding to tub manufacture.

As an ice cream tub is intended for a frozen product, it is important to know whether or not the polymer’s glass transition temperature is high enough such that it will cause problems. If the polymer becomes hard, glassy and brittle within the temperature range of use, the tub is more likely to shatter during loading. If the transition temperature is unknown, it is helpful to perform measurements across a range of temperatures. There are thermal control methods available from Stable Micro Systems such as a Peltier cabinet or Peltier platform, but a shortcut method may sometimes be used as a verification, storing samples at a range of temperatures and testing them immediately after removing them from storage. The sample temperature will not be uniform but a thermocouple in contact with the sample during the test will give an indication of its internal temperature.

It is also worth bearing in mind that many materials are anisotropic (their properties vary with test orientation). This is often the case for polymers extended, elongated or extruded in any way during manufacture, as long chain molecules can align in the direction of deformation. Pulling apart a polymer sample in this direction will require higher force than if it was turned 90 degrees. Consequently, it is useful to test samples in both orientations for a full picture of its tensile properties.

Once several candidate materials have been selected and formed into tubs, perhaps the most important indication of whether or not a tub will survive its journey is its top load strength – the amount of force that can be exerted on top of the tub before failure. This strength increases when the tub is filled due to the contribution of the frozen ice cream inside and so an empty tub can be considered a worst case approach. If many tubs are to be stacked on top of each other in transit or storage, the minimum acceptable top load strength can be estimated as a function of parameters such as tub weight and stack height.

Universal Peel Rig (A/UPS)

Top load compression involves the placement of a tub on the Texture Analyser base below a platen large enough to cover the top surface. The platen moves down at a constant speed to a target distance and measures the forces required for permanent deformation. Inspection can help to identify the tub’s weakest spots to allow for reconsideration of the design if necessary – these are often found at the bottom corners, at discontinuities or near the ridge along the top of the lid.

It is possible to predict the behaviour of a tub under top loading using a method such as finite element analysis, and this will tell you where your container is likely to fail first. The material used can be input in the model along with its stiffness, yield stress and strength, so the force at yield and failure can be predicted. However, computer modelling is time consuming and potentially expensive (not to mention it becomes much more difficult to predict behaviour once the tub has been filled with ice cream). Physical testing must always be used, even if it is to confirm the results of a model.

As well as top loading, there are several other important tests that will assess the whole behaviour of the container. Impact loading will help to show a tub’s response to shocks during transport and as the tub is most likely made from a polymer, viscoelasticity is an important consideration. Time-dependent testing involving the measurement of creep under a held force will show what might happen during storage under a heavy stack of boxes. And lastly, forces are exerted on the container during filling, closing and stacking, so some imitative testing can be very useful in these cases.

Film Support Rig (HDP/FSR)

A full assessment of the tub’s performance aside from its bulk strength can also be investigated using a Texture Analyser. For example, peel strength of the label can be measured using a 90 Degree Peel Rig, temperature-dependent adhesive strength of any glues used are measured using a force-hold test on a Peltier platform, and properties of plastic or paper films can be assessed in biaxial tension using a Film Support Rig.


For help putting your packaging to the test, contact Stable Micro Systems today.

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For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

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