Patent Publication Number: US-6663373-B2

Title: Apparatus for making nonwoven fabric

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for making a nonwoven fabric from continuous fibers. 
     There have already been proposed a process as well as an apparatus adapted to accumulate continuous fibers discharged from spinning nozzles of an extruder onto a top surface of an endless belt running in one direction and thereby to make a nonwoven fabric. The endless belt in the known apparatus is air-permeable and there is provided below this endless belt with a suction zone. It is well known in the known apparatus to provide an air gun or suckers serving to blow pressurized air against the continuous fibers, to provide a relatively narrow duct below the air gun or the suckers and to provide a hood below the duct so that the endless belt may be partially covered with the hood. 
     Provision of the duct and the hood in accordance with the prior art enables a stretching ratio for the fibers to be improved and thereby a desired nonwoven fabric to be made from the continuous fibers having a relatively small denier number. However, the fibers discharged from the spinning nozzles must be previously thinned in order to obtain the fibers having a fineness smaller than 1 d and this requirement deteriorates a production efficiency of a nonwoven fabric per unit time. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to improve the known apparatus so that the nonwoven fabric may be efficiently made from the continuous fibers of a fineness less than 1 d. 
     According to this invention, there is provided an apparatus for making a nonwoven fabric adapted to accumulate continuous fibers discharged from a plurality of spinning nozzles onto a top surface of an air-permeable endless belt running in one direction under a suction effect exerted from below the endless belt, wherein: between the nozzles and the endless belt, the apparatus comprises means adapted to blow pressurized air against the continuous fibers, a duct having a relatively small dimension as viewed in running direction of the endless belt and directly connected to the means so as to extend downward and a hood having a relatively large dimension as viewed in the running direction and directly connected to the duct so as to cover a vicinity of the endless belt&#39;s top surface so that an interior of the hood may be subjected to the suction effect exerted through the endless belt from below the endless belt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary perspective view showing an apparatus for making a nonwoven fabric; 
     FIG. 2 is a sectional view taken along a line II—II in FIG. 1; and 
     FIG. 3 is a fragmentary sectional view showing an alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Details of an apparatus for making a nonwoven fabric according to this invention will be more fully understood from the description given hereunder with reference to the accompanying drawings. 
     FIG. 1 is a fragmentary perspective view showing an apparatus for making a nonwoven fabric  1  and FIG. 2 is a sectional view taken along a line II—II in FIG.  1 . The apparatus  1  includes an extruder  2  and an array comprising a plurality of spinning nozzles  4  arranged transversely of an endless belt  3  running in a direction indicated by an arrow Q. Between the array of nozzles  4  and the endless belt  3 , an air gun  6 , a duct  7  and a hood  8  are connected one to another in this order so as to establish a substantially air tight condition. A box  9  underlies the hood  8  with the endless belt  3  therebetween and an exhaust duct  11  extends from the box  9  in a direction indicated by an arrow X. The exhaust duct  11  has its distal end connected to a blower (not shown). 
     The array of nozzles  4  each having an orifice diameter of 0.3˜0.7 mm are arranged on a nozzle plate  2   a  of the extruder  2 , which nozzle plate  2   a  extends transversely of the endless belt  3  having a width of 250˜3000 mm. The array comprises 200˜25000 nozzles  4  over a length of 200˜25000 mm. The air gun  6  is spaced from the array of nozzles  4  by a distance L of 100˜1500 mm. The duct  7  has a dimension A of 5˜20 mm as measured in a running direction of the endless belt  3 , a dimension B of 200˜2500 mm as measured transversely of the endless belt  3  and a dimension C of 50˜1000 mm as measured vertically of FIG.  1 . The hood  8  has a dimension D of 50˜1500 mm as measured in the running direction of the endless belt, a dimension E of 200˜2500 mm as measured transversely of the endless belt  3  and a dimension F of 50˜2000 mm as measured vertically of FIG. 1, and extends above the top surface of the endless belt  3  with a clearance  22 . The box  9  has a dimension G of 50˜1500 mm as measured in the running direction of the endless belt  3 , a dimension H of 200˜2500 mm as measured transversely of the endless belt  3  and a vertical dimension as viewed in FIG. 1 which may be optionally selected. The duct  7  is located at the middle of the hood  8  as viewed in the running direction of the endless belt  3  and the hood  8  is positioned substantially in vertical alignment with the box  9 . In front and behind the endless hood  8 , there are provided rollers  21 . The rollers  21  function to close the clearance between the endless belt  3  and the hood  8  so that a negative pressure within the hood  8  may be maintained sufficiently high even during running of the endless belt  3 . These rollers  21  are adapted to move vertically of the endless belt  3  as the rollers  21  rotate in the running direction of the endless belt  3 . 
     The nozzles  4  continuously discharge a plurality of thermoplastic synthetic resin fibers  16  downward as viewed in figures, which are then introduced into an upper end portion  17  of the air gun  6 . In the vertically middle portion  18  of the air gun  6 , a flow of pressurized air supplied in a direction indicated by an arrow P and blows against the fibers  16  which are thereby accelerated downward into the duct  7 . The fibers  16  pass straight through the relatively narrow duct  7  into the relatively wide hood  8  in which the fibers  16  are correspondingly decelerated. The hood  8  is vertically opposed to the box  9  having an open top with the air-permeable endless belt  3  therebetween. The box  9  is in fluid communication with the blower so that the interior of the hood  8  is maintained at a desired level of negative pressure under a suction by the box  9 . The hood  8  at the desired level of negative pressure functions to pull the fibers  16  within the duct  7  so that these fibers  16  may be directed to the hood  8 . The fibers  16  which have passed straight through the relatively narrow duct  7  in parallel one to another oscillate longitudinally as well as transversely of the endless belt  3  as these fibers  16  enter the hood  8  which lies adjacent the top surface of the endless belt  3  and is enlarged in the running direction of the endless belt  3 . As a result, the fibers  16  are intertwined and accumulated on the top surface of the endless belt  3 . The fibers  16  accumulated on the endless belt  3  in this manner are conveyed through the clearance  22  between the endless belt  3  and the hood  8  and then between the endless belt  3  and roller  21  to be brought out from the hood  8  and to be taken up in a roll of nonwoven fabric  31 . Assumed that the fibers  16  are in molten or softened state as the fibers  16  are accumulated on the endless belt  3 , the fibers  16  can be bonded one to another at their contacting points. Furthermore, oscillation of the fibers  16  within the hood  8  enables them to be mechanically intertwined. 
     During the process for making the nonwoven fabric  31  in this manner, the fibers  16  are stretched at a high ratio in the course from the nozzles  4  to the hood  8 , particularly during a period elapsing from a point at which the fibers  16  have been discharged from the nozzles  4  to a point at which the fibers  16  begin to be accelerated by the air gun  6  period starting from being discharged from the nozzles  4 . Such stretching is achieved by cooperation of a pressure of air blown from the air gun  6  with a pulling force of the hood  8  sucking this air. The gun  6 , the duct  7  and the hood  8  may be directly connected one to another and the clearance  22  defined between the hood  8  and the endless belt  3  may be closed by the respective rollers  21  to ensure the pulling force to act upon the fibers  16 . 
     In order to ensure that the fibers  16  are stretched at a desired high ratio and, after having stretched, oscillate over a relatively large extent as measured longitudinally as well as transversely of the endless belt  3 , A:C, a ratio of a dimension A of the duct  7  to a dimension C of the duct  7  is preferably in a range of 1:2.5˜1:200, C:D, a ratio of the dimension C of the duct  7  to a dimension D of the hood  8  is preferably in a range of 1:1˜1:1.5. F:D, a ratio of the dimension F of the hood to a dimension D of the hood  8  is preferably in a range of 1:1˜1:1.3. A suction capacity of the box  9  is preferably in a range of 8˜30 times the air discharge from the air gun  6 . 
     FIG. 3 is a fragmentary sectional view schematically showing a part of the apparatus similar to the embodiment of the invention shown in FIGS. 1 and 2. This apparatus  1  is similar to the apparatus shown in FIGS. 1 and 2 except that the air gun  6  is replaced by sucker  33  placed in a laterally symmetric relationship about the fibers  16  as the means to blow the pressurized air against the fibers  16 . A clearance R of each blow nozzle  34  in each of the suckers  33  is adjusted in a range of 0.1˜1.0 mm so that a stretching ratio of the fibers  16  may be controlled in this range. 
     EXAMPLE 
     Polypropylene having a melt flow rate of 70 as measured in accordance with the prescription of JIS K 7210 was extruded and stretched to obtain continuous fibers and a nonwoven fabric formed with these continuous fibers using the apparatus of FIG.  3 . Table 1 shows a relationship between conditions under which the continuous fibers are made and fineness (d). 
     Control 1 
     Using polypropylene similarly to the EXAMPLE, the continuous fibers were obtained by the apparatus of FIG. 3 deprived of the hood and the nonwoven fabric was made from these continuous fibers. CONTROL 1 in Table 1 shows a relationship between conditions under which the continuous fibers are made and fineness. 
     Control 2 
     Using polypropylene similarly to the EXAMPLE, the continuous fibers were obtained by the apparatus of FIG. 3 deprived of the suckers and the nonwoven fabric was made from these continuous fibers. CONTROL 2 in Table 1 shows a relationship between conditions under which the continuous fibers are made and fineness. 
     Control 3 
     Using polypropylene similarly to the EXAMPLE, the continuous fibers were obtained by the apparatus of FIG. 3 in which the suckers were spaced apart from the duct by 30 mm and the nonwoven fabric was made from these continuous fibers. CONTROL 3 in Table 1 shows a relationship between conditions under which the continuous fibers are made and fineness. 
     Control 4 
     Using polypropylene similarly to the EXAMPLE, the continuous fibers were obtained by the apparatus of FIG. 3 in which a suckers air flow was adjusted to be 4.8 times a suction air flow and the nonwoven fabric was made from these continuous fibers. CONTROL 4 in Table 1 shows a relationship between conditions under which the continuous fibers are made and fineness. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 EXAMPLE 
                 CONTROL 1 
                 CONTROL 2 
                 CONTROL 3 
                 CONTROL 4 
               
               
                   
               
             
            
               
                 Resin 
                 Polypropylene 
                 Polypropylene 
                 Polypropylene 
                 Polypropylene 
                 Polypropylene 
               
               
                 Nozzle Discharge 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
               
               
                 (g/min/hole) 
               
               
                 Nozzle ˜ Sucker 
                 1000 
                 1000 
                 — 
                 1000 
                 1000 
               
               
                 Distance 
                 — 
                 — 
                 1000 
                 — 
                 — 
               
               
                 (mm) 
               
               
                 Sucker Clearance 
                 0.15 
                 0.15 
                 — 
                 0.15 
                 0.15 
               
               
                 (mm) 
               
               
                 Sucker ˜ Duct 
                 0 
                 0 
                 — 
                 30 
                 0 
               
               
                 Distance 
               
               
                 (mm) 
               
               
                 Duct Dimensions: A 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
               
               
                 (mm) 
               
               
                 C 
                 300 
                 300 
                 300 
                 300 
                 300 
               
               
                 Hood Dimensions: D 
                 500 
                 — 
                 500 
                 500 
                 500 
               
               
                 F 
                 600 
                 — 
                 600 
                 600 
                 600 
               
               
                 Sucker Air Flow 
                 9.3 
                 9.3 
                 — 
                 9.3 
                 9.3 
               
               
                 (Nm 3 /min/m) 
               
               
                 Suction Air Flow 
                 133.3 
                 133.3 
                 133.3 
                 133.3 
                 45 
               
               
                 (Nm 3 /min/m) 
               
               
                 Suction Air Flow to 
                 14.3 
                 14.3 
                 — 
                 14.3 
                 4.8 
               
               
                 Sucker Air Flow 
               
               
                 (times) 
               
               
                 Fineness 
                 0.97 
                 1.59 
                 1.89 
                 1.19 
                 1.60 
               
               
                 (d) 
               
               
                   
               
            
           
         
       
     
     As will be apparent from comparison of these examples with controls 1˜4, the apparatus  1  according to this invention is able to obtain the continuous fibers having a fineness of 1 d or less and to make desired nonwoven fabric from these continuous fibers. 
     The apparatus for making a nonwoven fabric according to this invention enables nonwoven fabric to be easily made from continuous fibers having a fineness of 1 d or less.