Differentiate yourself through the quality of your packaging

Why is measuring leaks under known pressure conditions the best way to differentiate yourself by improving the quality of your packaging process, while helping you at every stage of production and decision-making?

Viande emballée - laboratoire

The context

Measuring the leak-tightness of packaging in the biscuit industry is a priority issue, because measuring leak-tightness helps to improve the lifespan of products. But today, it is becoming an essential means of profitability by optimising the quantity of material (size, thickness and type of film) or speeding up machine settings (heat, sealing time).

It is also crucial for preserving flavour and taste, and ensuring total consumer satisfaction. For example, savoury biscuit and snack companies are concerned about product crispness, which deteriorates very quickly in the presence of moisture or O2 absorption, especially if the packaging is perforated and has integrity defects. Damage to the wrapper and inadequate sealing can easily destroy the barrier properties of the film and, in the case of protective atmosphere packaging, increase the cost of maintaining O2 levels (increased gas consumption to achieve a lower initial level, increased headspace, absorption solutions, more complex films, etc.).

Moving from a location-based detection method to instrumented and metrological solutions

Good manufacturing practice for dry foods prohibits the use of water in the production area, mainly for reasons of hygiene and the direct negative effects on the product of the presence of a source of moisture in the workshop. Consequently, measuring leaks using an air-air test method is more relevant than simply detecting leaks using a water basin (bubble tightness test based on ASTM F 2096, or DIN 55508-5).

Having a view of the location of a defect is not a true and complete reflection of the rate of exchange of the internal atmosphere with the external atmosphere, and is not representative of the conditions actually experienced by the packaging. It is simply not possible for bubbles to be produced naturally in conditions where there is no stress, especially as the packaging generally floats. Furthermore, the stress generated on the packaging is often with an uncontrolled pressure differential which can lead to bursting inside the water basin rather than revealing weaknesses in the packaging process.

Limits of the water bath

The external pressure used in the water bath to generate bubbles (or the passage of air through the water) cannot be achieved with a small headspace. In confectionery, for example, there simply isn’t enough headspace to create bubbles. Finally, this technique provides no data on the rate of gas or water vapour exchange. In the real world, food packaging is never delivered in a bucket of water, but is clearly subject to mechanical stress and air diffusion through defects.

The evolution of the packaging industry towards a more paper-based solution represents a new challenge, and the method using buckets of water is no longer relevant and will immediately destroy the packaging structures. An air-to-air technique is therefore the only solution.

The mode and conditions of transport can also affect the rate of exchange of the internal atmosphere through defects in the packaging.

Pressure variations due to altitude, weather conditions and temperature changes can be generated at different rates depending on the means of transport and destination. Consequently, the assessment of exchange rates between the internal atmosphere and the external atmosphere cannot be limited to knowledge of the film’s permeability property alone, but is in fact the result of massive diffusion of gas exchange through the open area of the defects.

Quite simply, the defects generated by the packaging process give a much higher rate of diffusion across their equivalent surface, in a proportion that drastically compromises the exchange rate based on the initial permeability calculation.

But assessing the effects of the defect while waiting for the molecules to equilibrate is a relatively lengthy process, especially when the speed of routine testing is required to launch or release production. It is in this context that measuring the amount of air escaping from the internal volume, by controlling the initial conditions and keeping the internal pressure constant, gives a faster, more consistent and reliable metrological result with a minimum of influencing variables.

Effects of defects on film permeability

By way of example, in the case of a snack pack inert with N2 :

A structural defect in a 10 × 10 × 1 cm package (100 ml headspace volume) consisting of a 100 µm thick plastic film with a defect such as a 100 µm diameter straight pinhole significantly increases both O2 exchange and recovery:

  • 10 times faster than permeability through a single PE film
  • 10,000 to 100,000 times faster than permeability through a single EVOH film.

(with a ratio between the surface area of the film and the surface area of the pinhole of ≈ 5 × 106).

And for water vapour, it’s worse: the diffusion speed of water vapour in air is 2 times faster than that of O2.

Reference method for measuring leaks

Reference method for measuring leaks

In many leak detection and measurement techniques, certain variables remain unknown when it comes to determining the relevant exchange rate. This is mainly because the internal pressure and the volume of the headspace during the test are not known, are influencing variables and do not allow a correct estimation of the leakage rate.

For this reason, DIN55508-1 has been published, which describes a sealing technique using flow measurement at constant pressure. This makes the test consistent, sensitive and versatile for all types of packaging and solid contents.

How can leakage measurement help to manage production?

Faced with the complexity of production, having DIN55508-1 based instruments such as Exos® or Oxylos® makes life easier for the packaging engineer by allowing a minimum of influencing variables, high sensitivity and controlled pressure conditions, whatever the shape and construction of the packaging.

The Exos® solution is versatile, easy to use and can provide key performance indicators to monitor the quality of the production line. Exos® applies a pre-defined test pressure and then calculates the flow rate required to maintain that pressure. The flow rate is an aggregate of all leaks through the package, whereas other techniques provide no data.

You can then easily examine the distribution of leak values and their deviation, as shown in the following figure, the ideal shape being a straight line with a small slope proportional to constant sampling:

graphique débit de fuite - Anéolia

Additional features for MAP applications

What’s more, Exos® and Oxylos® can analyse the gas in the internal atmosphere in addition to measuring the leak, so you know the initial atmosphere of the pack and can anticipate the effect of leak size on gas changes by directly correlating the two values. This means a minimum of influencing variables, high sensitivity and controlled pressure conditions, whatever the shape and construction of the packaging.

The Exos® solution is versatile, easy to use and can provide key performance indicators for production line quality control. Exos® applies a pre-defined test pressure and then calculates the flow rate required to maintain that pressure. The flow rate is an aggregate of all leaks through the package, whereas other techniques provide no data.

You can then easily examine the distribution of leak values and their deviation, as shown in the following figure, the ideal shape being a straight line with a small slope proportional to constant sampling:

Benefits and rewards for the food industry

ECISION SUPPORT

The sensitivity of the device means that experience can be used to discriminate the causes of leakage from the following examples:

  • Film perforation
  • Best film material for leakage level
  • Seal quality
  • Presence of product in seals
  • The effect of machine settings on performance
  • Fatigue phenomena (creep test)

COMMIT TO RELIABLE SPECIFICATIONS

The technique used by Exos® and Oxylos® enables compliance with DIN 55508-1 to be verified:

  • Joint strength
  • Leakage measurement (down to 5µm)
  • Breathability of the packaging
  • Gas absorption over time for modified atmosphere applications

The performance achieved is such that the sensitivity, or detection limit, can go down to a perforation of 5µm equivalent diameter at low stress. It is at this level of effective sensitivity that packaging solutions can be truly evaluated. This instrumentation provides the right tool to measure and control improvements, and ultimately to act on the most cost-effective solution, becoming a true quality differentiator for the development of your strategic markets.

Making food safer

Knowing the modified atmosphere without measuring leaks can lead to the wrong conclusion if contamination is detected in a package while the gas level is still good after a few hours.

Even if a 0.5 to 2 µm pathogen has no chance of passing through a 5 µm perforation, an initial population of Escherichia coli in the package can be multiplied by 10 in 50 hours if a certain mass of O2 is supplied by structural defects. For example, after 15 hours, the headspace can still be measured below 1% O2, but with a defect as low as a leak rate of 1ml/min and maintained for 6 hours under a pressure difference condition of only 10 mbar, provides the necessary number of molecules to grow the pathogen.