Filter medium

Filter medium comprising:

• a) at least one textile nonwoven layer (layer 1), preferably a spunbonded nonwoven layer, comprising synthetic polymer fibres wherein
• a1) textile nonwoven layer (layer 1), preferably the spunbonded nonwoven layer, has a weight per unit area of 50 to 500 g/m2, preferably 80 to 300 g/m2,
• a2) the fibres of the textile nonwoven layer (layer 1), preferably of the spunbonded nonwoven layer, have a diameter in the range of 0.7 to ≦6 dtex, preferably 1 to ≦4 dtex for polymer fibres,
• a3) textile nonwoven layer (layer 1) has no chemical binders and preferably is a spunbonded nonwoven,
• a4) the textile nonwoven layer (layer 1), preferably the spunbonded nonwoven layer was preferably compacted by means of a calendering to an air permeability of 500-2000 l/m2sec,
• b) at least one further textile layer (layer 2) which is applied to at least one side of the textile nonwoven layer (layer 1) according to a), wherein the further textile nonwoven layer, is preferably a spunbonded nonwoven layer comprising synthetic polymer fibres, wherein
• b1) the further textile nonwoven layer (layer 2), preferably the spunbonded nonwoven layer, has a weight per unit area of 50-500 g/m2, preferably 80 to 300 g/m2,
• b2) the fibres of the further textile nonwoven layer (layer 2), preferably the spunbonded nonwoven layer have a diameter in the range of 3.0 to ≦15 dtex, preferably 4.0 to ≦12 dtex for polymer fibres,
• b3) the further textile nonwoven layer (layer 2) comprises no chemical binders and is preferably a spunbonded nonwoven
• b4) the air permeability of the further textile layer (layer 2) is greater than, preferably by at least 10%, than the air permeability of the textile nonwoven layer (layer 1),
• b5) the further textile nonwoven layer (layer 2), preferably the spunbonded nonwoven preferably has a gradient with regard to the fibre diameter which decreases in the direction of the textile nonwoven layer (layer 1),
• c) wherein the textile nonwoven layer (layer 1) and the further textile nonwoven layer (layer 2) are joined to one another by mechanical needling and the diameter of the holes formed on the outer side of the textile nonwoven layer (layer 1) which faces away from the first textile nonwoven layer (layer 2) is reduced by means of action of a heated surface, preferably a calender, by at least 50%, preferably by at least 80%.