Milk is a staple in elementary school lunches in Japan. In recent years, its container has changed from glass bottles to paper containers. Now there is a trend towards strawless packaging. This article presents the results of force measurement required to open a milk carton.
Measurement Methods and Conditions
Measurements were performed under the following conditions with reference to ISO 17480 (2015). *1
[Strength Measurement of the Gable Top]
- Create a 4mm hole in the gable top of the milk carton (on the pouring side).
- Put the string of the jig with a catch through the created hole, and connect the other end of the string to the force gauge. *2
- Pull horizontally and measure the force (maximum force value) required until the gable top opens to the sides.
[Strength Measurement of the Carton Spout]
- Pull the two wings of the gable top apart and bend them back as far as you can. Then, create a 2mm hole in the carton spout.
- Insert the jig’s hook into the created hole, and connect the other end of the string to the force gauge.
- Pull horizontally and measure the force (maximum force value) required to open the carton spout.
*1. The measurements above don’t comply with ISO 17480 (2015). On IMADA’s website, you can watch measurement case videos partially compliant with ISO 17480 (2015).
*2. Force gauges are used to measure the force value. The measurement results are displayed in units of Newtons (N).
Measurement Results
This time, we measured three 500ml milk cartons and calculated the average maximum force value. The measurement results are shown in the table below.
 The force to open the gable top sideways |  The force to open the carton spout |
| 30.2N | 9.8N |
Opening the gable top sideways requires a force of about 30N, which is almost the same force required to stretch a bundle of 10 rubber bands (#18) by 20 cm. It may sound that a certain amount of force is actually needed to open the gable top. On the other hand, opening the spout requires about 10N. The result was unexpected because I felt it would be more difficult to open the spout after opening the gable top.
Incidentally, we conducted the measurement under the condition of “fully opening the gable top before pulling out the spout.” Do you make sure to fully open the gable top when opening a milk carton? Many people often try to open the spout while the gable top is just loosely open. So, we also measured how the ease of opening the spout would be affected if the gable top was only opened to the side.
 Firmly bend the gable top back as far as you can. |  The opening of the gable top stops at 180 degrees. |
| Tensile force required to open the carton spout: 9.8N | Tensile force required to open the carton spout: 8.9N |
From the measurement results, the degree of roof opening does not seem to significantly affect the force required to open the spout. However, it may be easier to open the carton spout once the gable top is wide open, because if the spout sticks out, it is easier to apply force in the direction of opening.
The Effect of Milk Carton Opening
In addition to comparing the openability based on the degree of gable top opening, we also measured the difference in openability between the opening side and the opposite side. Here are the measurement results.
| The opening side | The opposite side | |
|---|---|---|
| The force to open the gable top sideways | 30.2N | 36.5N |
| The force to open the carton spout | 9.8N | 25.9N |
The measurement results show that the force required to open the spout differs significantly between the opening side and the opposite side. It is best to follow the package instructions and open the spout from the specified side when opening a milk carton.
Summary: Openability and Sealing Ability
The openability of the milk carton was measured and found to be as follows.
- Compared to the force required to open the spout, a greater force is needed to open the gable top to the sides.
- There is a significant difference in openability between the opening side and the opposite side, particularly in the force required to open the spout.
The figures introduced in the article are limited to the samples measured this time, but we hope you can use them as a reference value. In addition, this time we conducted force measurements focusing on the force required for opening. However, in actual beverage packaging, there is the challenge of ensuring airtightness in addition to ease of opening. As such, the milk carton makers have been pursuing better package shapes to realize both openability and sealing ability.
Please check other related articles on Force Channel and measurement case videos in the packing industry on IMADA’s website, including the measurement of the opening performance of milk cartons.
