There are mainly two types of labels for beverage bottle. They are self-adhesive label and shrink label. The former one employs adhesive to stick to the body of beverage bottle, while the latter one employs shrink film which will attach tightly to the body of beverage bottle when it is heated. The materials of self-adhesive labels are mainly PP. The main materials of shrink labels are PET, PVC and PS.

As one kind of packaging material that is widely used, shrink label is featured with compactness, transparency, decency and high bonding strength. If the shrinkage ratio of the shrink film is too high, the printings on the shrink label may be twisted and deformed. If the shrinkage ratio of the shrink film is too low, the shrink label may not be able to stick to the bottle tightly. Therefore, it is necessary to control the shrinkage ratio of the shrink films that are used in shrink labels so as to maintain a good appearance of the bottle and reduce the production cost.

This article provides a simplified test method for shrinkage ratio of shrink labels for your reference. The sample material is shrink label made from PVC and the testing instrument is Labthink’s C631H Film Thermal Shrinkage Tester.

Figure 1. Shrink Labels of Beverage Bottles

The testing instruments for film thermal shrinkage test on the market mainly employ drying oven or liquid bath to process the testing materials and then measure the size after heat shrinking to calculate the shrinkage ratio wherein only shrinking force can be measured. Labthink’s C631H Film Thermal Shrinkage Tester conforms to ISO 14616, which can measure both shrinking and contracting force of heatshrinkable films.

Before tests, Cut 20 pieces of 15mm wide specimens along the machine direction and transverse direction of the samples of shrink labels, respectively. Divide those specimens into 10 groups, 2 specimens for each group. The length of the specimens should be proper so that the valid specimen length between the sample grips should be not less than 100mm. Measure the thickness of the specimen and calculate the average value of at least 3 points. Use special hole puncher to make two holes in the specimen so that the specimen can be mounted easily in the sample grips.

After preparing the specimens, the tests can be started in the following procedures.

1)     Mount the specimens. One specimen in one group should be mounted in the load cell and no force should be applied on the load cell. The other specimen in the said group should be placed horizontally between the support arm and the displacement sensor with valid length of 100mm.

2)     Set reference temperature for PVC shrink film, test temperature and end temperature, etc. Start test.

3)     Set thermal shrinking temperature. When the temperature inside the heating chamber reaches the preset value, the specimen should be delivered to the heating chamber. The specimen shrinks and the load cell and displacement sensor will record the real-time shrink force and shrinkage ratio.

4)     If the maximum shrink force appear after 15 seconds to 30 seconds since the test starts, record the maximum shrink force and shrinkage ration. Otherwise, adjust the setting of shrinking temperature and do the test again.

For more details about C631H Film Thermal Shrinkage Tester, please visit www.labthink.com

About Labthink Instruments Co., Ltd:

Labthink Instruments Co., Ltd is one leading supplier of packaging testing instruments, which is headquartered in Jinan, China and operated in Boston, U.S.A.