Three-dimensional net-shaped structure and method and apparatus for manufacturing thereof

A method for manufacturing a three-dimensional net-like structure, the three-dimensional net-like structure comprising a surface layer and an inside part, wherein the bulk density of the inside part is 0.045 to 0.085 g/cm3 and the ratio of the bulk density of the surface layer of the three-dimensional net-like structure to the bulk density of the inside part of the three-dimensional net-like structure is 1.5:1 to 6:1, the method comprising the steps of:

• (a) extruding and dropping downward a thermoplastic synthetic resin in a molten state from a nozzle having a plurality of extrusion holes arrayed in an approximately rectangular shape to form a filament assembly of a plurality of filaments;
• (b) supplying cooling water onto upper surfaces of a pair of long chutes that are located below the nozzle, are arranged across longitudinal faces of the filament assembly, are inclined downward toward a center of the filament assembly, are opposed to each other across a distance that is 6 to 25% less than a short side length of the array of the extrusion holes at inclined lower ends of the pair of long chutes, and are submerged at the lower ends by 3 to 45 mm in water of an underlying water tank;
• (c) causing filaments located on the longitudinal faces of the filament assembly to fall into contact with the upper surfaces of the long chutes which are not submerged in the tank water, so as to bend the filaments located on the longitudinal faces of the filament assembly in substantial loops, tangle adjacent filaments located on the longitudinal faces of the filament assembly at random, and make the filaments located on the longitudinal faces of the filament assembly thermally adhere to one another while falling toward the lower ends of the pair of long chutes;
• (d) cooling down the plurality of tangled filaments with the cooling water supplied to the upper surfaces of the long chutes;
• (e) forming the surface layer on the longitudinal faces of the filament assembly, while guiding the plurality of tangled filaments obliquely downward toward the center of the filament assembly along the long chutes;
• and
• (f) compressing and shape-forming the filament assembly by a pair of haul-off machines that are located below the long chutes and are opposed to each other across a distance that is 1 to 30% less than the distance between the pair of opposed long chutes so as to hold the longitudinal faces of the filament assembly therebetween, haul off the filament assembly at a lower haul-off speed than a fall speed of the filament assembly, and submerge the filament assembly into the tank water and cool down and solidify the submerged filament assembly.