Packaging material with integrated pressure relief valve

Packaging material for forming at least a part of a package for a product releasing gasses and being provided with an integral, normally closed pressure relief valve (18) that opens at an excess of pressure within the package overpressure outside the package, said pressure relief valve including a first inner film (10) preferably a polymer film, to be an inner film of the package and having at least one inlet opening (13,14;

• 28:
• 39:
• 41), and a second outer film (11) to be an outer film of the package and covering the inlet opening in the first inner film (10) and being bonded to the first inner film (10) to form a channel or pocket portion (12;
• 32) between the first inner and the second outer film, said channel or pocket portion (12;
• 32) communicating with the surroundings of the package through at least one outlet opening (15;
• 33, 34) spaced apart from the inlet opening, the first inner film (10) having a first surface (20) and a second surface (21) and the second outer film (11) having a first surface (22) and a second surface (3), the second surface (21) of the first inner film (10) facing the second surface (23) of the second outer film (11), said pressure relief valve (18) further comprising a liquid (19) provided in the channel or pocket portion and solid spacer means (17;
• 29:
• 37;
• 40) provided in the channel or pocket portion proximate to the inlet opening (13, 14;
• 28;
• 39;
• 41), said spacer means providing an interspace between the second surface (21) of the first inner film (10) and the second surface (23) of the second outer film (11), wherein the second outer film (11) is a film having such a flexibility or elasticity that in a tensile test a force of less than 5N is needed for elongating a test piece thereof having a width of 15 mm by 5%, the tensile test being carried out according to ISO 527/ASTM D 638, wherein a test piece of a width of 15 mm is gripped between two sets of jaws interspaced by exactly 100 mm and pulled in tension at a speed of 100 mm/min and at 5% elongation, i.e. 5 mm, the force is registered.