| 摘要 |
A filter element includes an upstream side layer structure disposed on an upstream side in a flow direction of air to be filtrated and formed of a non woven fabric formed by laminating chemical fibers, and a downstream side layer structure disposed on a downstream side in the flow direction of the air and including a plurality of layers including chemical fiber non woven fabric layers formed by laminating chemical fibers. The upstream side layer structure has a fiber density relatively smaller than that of the downstream side layer structure. The downstream side layer structure includes a natural fiber layer such as cotton layer disposed between the chemical fiber non fabric layers, and an oil is impregnated from the upstream side layer structure to the natural fiber layer in the downstream side layer structure.
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