Filter medium

A multilayered filter medium whose air permeability is at least 500 l/m2sec and which has a least three concrete layers, wherein

• a first layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 1 to 2 dtex,
• a second layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 2 to 4 dtex,
• a third layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 4 to 12 dtex,
• the first layer of the multilayered filter medium is 20 to 60% by weight, the second layer of the multilayered filter medium is 10 to 40% by weight and the third layer of the multilayered filter medium is 10 to 40% by weight,
• a melt binder portion in the three layers amounts to 5 to 40% by weight in total,
• the filter medium comprises an expanded configuration that is defined by an expanded state of the filter medium after exposure to a hot-air oven having a temperature of at least a melting point of the melt binder portion in the first, second, and third layers,
• in the expanded state the filter medium has a thickness that is at least about 30% larger than a pre-heated thickness exhibited prior to the exposure to the hot-air oven,
• a weight per unit area of the first layer, the second layer, and the third layer amounts to 50 to 400 g/m2 in total, the filter medium further comprises additional melt binder-solidified textile fabrics whose fibres have different titres in the range of 1 to 12 dtex and which have a weight per unit area of 50-400 g/m2, and
• the filter medium, when charged with 5 mg/cm3 SAE dust of a class “fine”, exhibits a pressure increase of no more than 100 Pa.

A multilayered filter medium whose air permeability is at least 500 l/m2 sec and which has a least three concrete layers, wherein

• a first layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 1 to 2 dtex,
• a second layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 2 to 4 dtex,
• a third layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 4 to 12 dtex,
• the first layer of the multilayered filter medium is 20 to 60% by weight, the second layer of the multilayered filter medium is 10 to 40% by weight and the third layer of the multilayered filter medium is 10 to 40% by weight,
• a melt binder portion in the three layers amounts to 5 to 40% by weight in total,
• the filter medium comprises an expanded configuration that is defined by an expanded state of the filter medium after exposure to a hot-air oven having a temperature of at least a melting point of the melt binder portion in the first, second, and third layers,
• in the expanded state the filter medium has a thickness that is at least about 30% larger than a pre-heated thickness exhibited prior to the exposure to the hot-air oven,
• a weight per unit area of the filter medium amounts to 50 to 400 g/m2 in total,
• the fibres of the formed textile fabrics have no texturing, and
• the filter medium, when charged with 5 mg/cm3 SAE dust of a class “fine”, exhibits a pressure increase of no more than 100 Pa.

A multilayered filter medium whose air permeability is at least 500 l/m2 sec and which has a least three concrete layers, wherein

• a first layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 1 to 2 dtex, wherein the fibres comprise carrier fibres and melt binder fibres, and wherein the carrier fibres comprise a polyester and the melt binder fibres comprise a polymer having a melting point at least 5° C. below a melting point of the carrier fibres,
• a second layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 2 to 4 dtex, wherein the fibres comprise carrier fibres and melt binder fibres, and wherein the carrier fibres comprise a polyester and the melt binder fibres comprise a polymer having a melting point at least 5° C. below a melting point of the carrier fibres,
• a third layer is a melt binder-solidified textile fabric whose fibres have a titre in the range of 4 to 12 dtex,
• the first layer of the multilayered filter medium is 20 to 60% by weight, the second layer of the multilayered filter medium is 10 to 40% by weight and the third layer of the multilayered filter medium is 10 to 40% by weight, wherein the fibres comprise carrier fibres and melt binder fibres, and wherein the carrier fibres comprise a polyester and the melt binder fibres comprise a polymer having a melting point at least 5° C. below a melting point of the carrier fibres,
• a melt binder portion in the three layers amounts to 5 to 40% by weight in total,
• the filter medium comprises an expanded configuration that is defined by an expanded state of the filter medium after exposure to a hot-air oven having a temperature of at least a melting point of the melt binder fibres of the first, second, and third layers and at least 10° C. below a melting temperature of the carrier fibres of the first, second, and third layers,
• in the expanded state the filter medium has a thickness that is at least about 30% larger than a pre-heated thickness exhibited prior to the exposure to the hot-air oven,
• a weight per unit area of the filter medium amounts to 50 to 400 g/m2 in total,
• the filter medium is pleatable, and
• the filter medium, when charged with 5 mg/cm3 SAE dust of a class “fine”, exhibits a pressure increase of no more than 100 Pa.