shaping table a spraying tank a hauler and a cutter the specific preparation process was as follows 1 the randomly copolymerized polypropylene with melt index of 1 0 g 10 min was premixed with the necessary aids in the blender drawn into the hopper of the crew extruder and dried at 80 u00b0 c where for the weight ratio of the homopolymerized polypropylene to the aids the inorganic filler was 10 parts by weight and the fire retardant was 15 parts by weight on a basis of 100 parts by weight of the raw material polypropylene 2 the dried raw material was passed through the crew extruder for plasticizing and mixing with the parameters of the crew extruder being set as the screw temperature of 250 u00b0 c the die head temperature of 160 u00b0 c the molten mass pressure of 15 mpa and the host rotation rate of 30 rpm 3 the plasticized polypropylene molten mass was passed through the special flat extrusion die for molding to form the polypropylene extrusion board at fusion state bearing pore space in the core where the special flat extrusion die was one having one or more rows of core rods in the center and the core rods were used to provide the pore canal structure in the center of the polypropylene extrusion board and had the cross section in the shape of circle and the pore canals had the height of 5 mm the width of 0 5 mm and the pitch of 3 mm between the pore canals 4 the polypropylene extrusion board at fusion state having pore space in the.