Method of producing a packaging material

A method of producing a packaging laminate (10) comprising a core layer (1) with through-going holes (2) which are covered by a first outer layer (3) applied on one side of the core layer (1), and a second outer layer (4) applied on the other side of the core layer (1), said first and second outer layers (3 and 4) being sealed to one another within the regions of the through-going holes (2), the method comprising the steps of providing a web of core layer (1) with through-going holes (2), coating the other side of the web (1) with a second outer layer (4) including an aluminium foil (4a) facing towards the web (1) and an outermost layer (4b) applied on the surface of the aluminium foil (4a) facing away from the web (1), and thereafter coating the first side of the web (1) with a first outer layer (3) in such a manner that the first and second outer layers (3 and 4) are sealed to one another within the regions of the opening contour of the through-going holes (2), characterised in that the holed web (1), after coating with the second outer layer (4) but prior to coating with the first outer layer (3), is subjected to treatment by so-called flame-treating during which the web (1) is caused to pass one or more gas flames (9a and 9b) directed at the first, or uncoated, side of the web (1) and by means of which accessible parts of the second outer layer (4) are, for the purpose of promoting adhesion, activated or polarised within the regions of the through-going holes (2).