Method for manufacturing a container comprising sealing of container parts

A method of preparing a package comprising:

• joining together of a first and a second piece of material, wherein at least the first piece of material is constituted by a multi-layered material of the laminate type comprising a mechanically stabilizing layer, an electrically conducting layer, and a weldable layer,
• where the mechanically stabilizing layer is constituted by a carton material, where the first piece of material is arranged in such a manner that the weldable layer can be melted by supplying energy to the electrically conducting layer, and
• where the joining together comprises that the weldable layer is pressed against the second piece of material and that energy is supplied to the electrically conducting layer,
• wherein the energy supply per time unit to the electrically conducting layer is varied during the period of time in which energy is supplied to the electrically conducting layer, where the power supply is lower at the end of the period of supply than at an earlier stage,
• where the power supply has a maximum, or near maximum, allowed value during a first phase of the period of supply, and
• where the first phase constitutes at least 40% of the period of supply.