Abstract: A thin and uniform nonwoven fabric air filter for an internal combustion engine with a pleated form which comprises an air-laid nonwoven fabric obtained by forming a plurality of layers mainly composed of polyester-based binder fibers having a fiber length of 1 to 10 mm by an air-laid nonwoven fabric production process and performing heat adhesion, wherein an upper layer side (fluid inflow side) comprises large fibers, a lower layer side (fluid outflow side) comprises fine fibers, a final fluid outflow side comprises 100% of the polyester-based binder fibers, the basis weight (METSUKE) is from 100 to 350 g/m2, the apparent density is from 0.04 g/cm3 to 0.3 g/cm3, and the dry-heat shrinkage factor after 300 hours at 100° C. is 3% or less. The air filter induces no environmental pollution, is high in dust collection efficiency, and has long life.

Abstract: Disclosed is a dry-process nonwoven pulp fabric composed of united layer structures, which contains heat-bondable synthetic fibers and comprises surface layer portions on both sides in which the synthetic fibers are heat bonded to one another and which has a basis weight of more than 5 g/m2 to 12 g/m2, and an internal layer portion in which heat-bondable synthetic fibers and pulp fibers are mixed at a ratio of 20/80 to 60/40% by weight and the synthetic fibers and/or the synthetic fibers and pulp fibers are heat bonded to one another and which has a basis weight of 8 to 240 g/m2, wherein the front and back surface layers and the internal layer portion are united as a whole by heat bonding of the synthetic fibers to one another, the ratio of a strength in a lengthwise direction to that in a crosswise direction is from 0.8 to 1.2 in both dry and wet states, the ratio of a strength in a dry state to that in a wet state is from 0.6 to 1.