At the same time an earth polarity is assigned to the lower tool
3. Due to this a second, simultaneous primary field is set up between the upper tool
2 and the lower tool
3, which passes through the flat regions
9,
10 of the upper film
7 and the lower film
8. This causes the two films
7,
8 to be securely welded together in the flat regions
9,
10, that is, adjacent to the tube
12.