Abstract: A filter pleat pack of the present disclosure includes an air filter medium folded into pleats. The air filter medium includes a laminate of a polytetrafluoroethylene (PTFE) porous membrane and an air-permeable supporting member. When a cut surface of the filter pleat pack is observed, the cut surface being taken along a plane perpendicularly crossing a pleat line of the filter pleat pack, the PTFE porous membrane has a first converging portion, a split portion, and a second converging portion in this order in a direction in which the membrane extends. In the split portion, the PTFE porous membrane is split into a plurality of layers in a thickness direction of the membrane and the plurality of layers are spaced apart from each other. At the first converging portion and the second converging portion, the plurality of layers converge into one layer. The filter pleat pack of the present disclosure is a filter pleat pack for which a collection efficiency decrease resulting from pleating is reduced.

Abstract: A filter pleat pack of the present disclosure includes an air filter medium folded into pleats, wherein the air filter medium includes a laminate of a polytetrafluoroethylene (PTFE) porous membrane and an air-permeable supporting member, and the air filter medium has a shrinkage rate of 50% or more, the shrinkage rate being determined by a formula (d2?d1)/d2, where d1 is a smallest thickness of the PTFE porous membrane in a folding area of the air filter medium folded into pleats and d2 is a thickness of the PTFE porous membrane in a flat area of the air filter medium. The filter pleat pack of the present disclosure is a filter pleat pack for which a collection efficiency decrease resulting from pleating is reduced.

Abstract: The filter medium of the present disclosure includes a base layer having air permeability, and the base layer has a modified surface by fibrils of polytetrafluoroethylene. The modified surface of the base layer may be exposed. A modification amount of the fibrils in the modified surface is, for example, less than 0.5 g/m2. The base layer may include a fiber material, and an example of the base layer including a fiber material is a non-woven fabric. In the filter medium of the present disclosure, permeation of water into the inside of the medium can be inhibited.

Abstract: The filter medium of the present disclosure includes a polytetrafluoroethylene porous membrane and an air-permeable base layer, has a pressure loss PLF of less than 40 Pa when air is passed therethrough at a linear velocity of 5.3 cm/sec, and has a collection efficiency CEF of 65% or more when a linear velocity of a gas to be filtered is set to 5.3 cm/sec and particle diameters of particles to be collected are set to be within a range of 0.3 to 0.5 ?m. The filter medium of the present disclosure is a novel filter medium that can replace an electret medium and that can prevent a decrease in collection performance due to water vapor in the air, which is unavoidable in an electret medium.

Abstract: Provided is a moisture permeable filter medium formed by laminating a hydrophobic layer having hydrophobicity and a hydrophilic layer having hydrophilicity together, in which one of the hydrophobic layer and the hydrophilic layer is composed of a PTFE porous film formed using PTFE, and the other of the hydrophobic layer and the hydrophilic layer is composed of an air permeable sheet to which air is permeable.

Abstract: Provided is a moisture permeable filter medium formed by laminating a hydrophobic layer having hydrophobicity and a hydrophilic layer having hydrophilicity together, in which one of the hydrophobic layer and the hydrophilic layer is composed of a PTFE porous film formed using PTFE, and the other of the hydrophobic layer and the hydrophilic layer is composed of an air permeable sheet to which air is permeable.

Abstract: Provided is a method including: a step A of extruding a mixture containing a fine PTFE powder and a liquid lubricant into a sheet form so as to obtain a PTFE sheet; a step B of rolling the PTFE sheet by passing the sheet between a pair of rolls in the longitudinal direction of the sheet; a step C of heating the rolled PTFE sheet to a temperature of 19° C. or higher; a step D of stretching the rolled PTFE sheet having a temperature of 19° C. or higher in the width direction of the sheet; a step E of removing the liquid lubricant from the PTFE sheet; and a step F of stretching the PTFE sheet, from which the liquid lubricant has been removed, in both the longitudinal direction and the width direction so as to form pores in the sheet.

Abstract: Provided is a moisture permeable filter medium formed by laminating a hydrophobic layer having hydrophobicity and a hydrophilic layer having hydrophilicity together, in which one of the hydrophobic layer and the hydrophilic layer is composed of a PTFE porous film formed using PTFE, and the other of the hydrophobic layer and the hydrophilic layer is composed of an air permeable sheet to which air is permeable.

Abstract: The present invention provides a filter medium causing a low pressure drop. The present invention is a filter medium including a porous fluororesin membrane and an air-permeable support member laminated on at least one surface of the porous fluororesin membrane. In this filter medium, the air-permeable support member is a blended nonwoven fabric containing: core-sheath fibers (A) having a polyester core and a polyolefin sheath; polyester fibers (B); and core-sheath fibers (C) having a polyester core and a copolymerized polyester sheath.

Abstract: The present invention provides a filter medium causing a low pressure drop. The present invention is a filter medium including a porous fluororesin membrane and an air-permeable support member laminated on at least one surface of the porous fluororesin membrane. In this filter medium, the air-permeable support member is a blended nonwoven fabric containing: core-sheath fibers (A) having a polyester core and a polyolefin sheath; polyester fibers (B); and core-sheath fibers (C) having a polyester core and a copolymerized polyester sheath.