FILTER MATERIAL

PROBLEM TO BE SOLVED: To obtain a filter material hard to generate fluffing even if exposed to a water flow or wave over a long period of time, generating no perforation and excellent in durability by needling synthetic filaments having a specific number of crimps per a unit length to integrally entangle them. SOLUTION: A nonwoven fabric filter material suitably used for preventing the outflow of soil particles from the shore protection of rivers is formed by needling synthetic filaments having 3-10 crimps/cm to mutually entangle and integrate them. As a method for providing crimps to a ssynthetic filament, a method using a filament having latent crimping capacity to develop the latent crimps thereof is designated. As the filament having latent crimping capacity, a parallelly arranged type conjugate fiber wherein two kinds of fiber forming polymers different in heat shrinkability are arranged in a fiber length direction or an eccentric core-sheath type conjugate fiber wherein two kinds of fiber forming polymers different in heat shrinkability are arranged in an eccentric core-sheath structure is designated.