With the development of automatic packaging machinery, heatsealability of flexible package material has become a key index again. The difference is that the focus is not ultimate strength (sealing place is cooled down) any more but hot tack (sealing place is not cooled down).

Heat-sealing package is extensively used in the fields of daily chemical products, food and medicine. At present, the widely employed form-fill-seal machine could perform a range of activities including forming, filling and sealing. It develops very quickly in recent 20 years, with the development of package material and the increasing demand for small flexible package. Form-fill-seal machine has been widely used in production line such as milk package, coffee powder and other solid beverage.

In production line, the content is often filled by dropping products into package from a certain height, which has strong impact on the package bottom. If package bottom cannot resist the disruptive force of filling content, there will be fracture package. Since the interval between heat-sealing package making and content filling in production line is very short, it is impossible for sealing place to be completely cooled down within such a short period. Therefore, the rate of rupture package is almost determined by hot tack of package. In order to control rupture package effectively, hot tack is greatly concerned when the heat-sealing layer (sealant) is not completely cooled down.

Heatsealability of material includes two aspects: hot tack being tested while the sealing place is still heat (not declined to environment temperature) and ultimate strength being tested after sealing place is cooled down and become stable. Ultimate strength is tested with heat-sealing tester and heat-sealing gradient tester coordinated by pull tester and peeling off tester. With the improvement of hot tack importance, hot tack tester also appears in the package market (the picture below is Labthink HTT-L1 hot tack tester).

 

Then, to what extent is the difference between hot tack and ultimate strength of one material? The author performs testing on three common materials and the data comparison is as bellows:

Table 1 data comparison

In the testing, ultimate strength is tested with Labthink HST-H2 heat-sealing tester and XLW (L) PC intellectronic pull tester, while hot tack is tested with HTT-L1 hot tack tester, recently developed by Labthink. However, the testing are performed with the same heat-sealing temperature of 130℃, and same heat-sealing pressure and dwell time. Table 1 shows that hot tack being tested when sealing place is not cooled down is much lower than ultimate strength being tested after sealing place is completely cooled down. There is certain relationship between hot tack and ultimate strength and detailed information is available in heat-sealing technology and important testing indexes updated on Labthink Lab Forums on October 24, 2005.

For some products, content filling has become one necessary procedure. Therefore, manufactures are exerting their efforts to shorten packaging time to achieve ideal production efficiency. After some time of exploration, they realize that optimizing heat-sealing procedure can shorten cycling time of packaging. Hot tack testing can help operators to select optimal parameter for heat-sealing procedure.