Patent Publication Number: US-6670018-B2

Title: Net fabric to be processed into net product

Description:
BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     This invention relates to a net fabric with a three-dimensional structure to be processed into a net product. 
     B. Description of the Prior Art 
     There has been recently known in the art a net product made of a three-dimensional net material which exhibits increased cushioning properties in spite of being formed into a reduced thickness as compared with a pad material such as urethane or the like and has a number of voids formed therein to a degree sufficient to permit it to exhibit enhanced breathability. The net material is so constructed that a front mesh layer and a rear mesh layer are connected to each other by means of a number of piles arranged therebetween, resulting in being configured into a truss structure (three-dimensional structure). Such construction permits the net product to provide an elastic structure which has resistance to setting and exhibits both a property of satisfactorily distributing a pressure of the body and a property of impact absorbing. Net products made of such a net fabric include, for example, a seat for a vehicle such as an automobile and the like. 
     The net material of a three-dimensional structure, as described above, includes the front mesh layer, the rear mesh layer, and the piles knittedly incorporated between the front mesh layer and the rear mesh layer and acting as an intermediate layer. When it is in the form of a starting material (a net fabric to be processed into a net product) prior to being converted into any desired net product, it has a strip-like configuration of a continuous length and a required width. The net fabric is generally provided in the form of a roll fabric wound in a roll-like shape. A processor or manufacturer of such a net product rotates the roll fabric in a direction of unwinding it, to thereby draw out it. Then, the roll fabric thus drawn out is cut into a required length and subjected to any desired processing such as vibrational welding, sewing or the like, to thereby provide a desired net product. 
     Unfortunately, in the conventional net fabric to be processed into a net product, the configuration of each of the front and rear mesh layers and the size thereof, as well as the knitting or weaving conditions such as the number of piles knitted or woven between both mesh layers are inevitably rendered substantially constant throughout the whole region of the net fabric. This causes the compressibility of the net fabric in the thickness direction thereof to be substantially constant over the whole region. The compressibility is determined in view of various properties such as elasticity, damping properties and the like demanded by applications of a net product made of the net fabric. Thus, when the net product is used for a seat for an automobile, the net fabric with a three-dimensional structure therefor is so manufactured that the entire net fabric may exhibit compressibility suitable for the automobile seat. 
     Thus, in order to make the net fabric with compressibility suitable for the properties required for the net product, in the portion of the net fabric to be processed, the compressibility is relatively low and the compressive elastic modulus is relatively high, to thereby render operation of cutting the portion troublesome because the elasticity of the portion being cut causes a resistance to the cutting. The cutting operation generally involves cutting a roll of the net fabric into net fabrics with a predetermined length and then cutting the net fabrics into desired shapes by means of a press machine, a cutter equipped with a cutting blade, a water jet type cutter using pressurized water or the like while keeping them laminated or superposed on each other. Unfortunately, during the cutting of the net fabrics laminated on top of each other, the resistance described above is apt to cause positional mismatch therebetween. Also, a reduction in compressibility causes vibrational welding operation, which is a treatment of processing ends of the net fabric (end treatment) or sawing operation to be troublesome. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the foregoing disadvantage of the prior art. 
     Accordingly, it is an object of the present invention to provide a net fabric of a three-dimensional structure which is capable of facilitating processing of the net fabric such as cutting, welding or sewing during manufacturing of a net product made from the net fabric. 
     It is another object of the present invention to provide a net fabric of a three-dimensional structure which is capable of simplifying processing of the net fabric such as cutting, welding or sewing, leading to a reduction in manufacturing cost of a net product made of the net fabric. 
     In accordance with the present invention, a net fabric of a three-dimensional structure, which can be used as a raw material for a net product, is provided. The net fabric includes a front mesh layer, a rear mesh layer, and a plurality of piles for coupling the front mesh layer and rear mesh layer to each other therethrough. In the net fabric thus generally constructed, a first portion of the net fabric to be processed in processing steps for manufacturing of the net product is relatively increased in compressibility in the thickness direction thereof as compared with that of the remaining or second portion thereof. 
     In a preferred embodiment of the present invention, the difference in compressibility between the portion of the net fabric to be processed and the remaining portion thereof is set to be 5% or more. 
     In a more preferred embodiment of the present invention, the difference in compressibility between the first portion of the net fabric to be processed and the remaining or second portion thereof is set to be within a range between 10% and 70%. 
     In a preferred embodiment of the present invention, the compressibility is adjusted by the density of the net structure of the net fabric. 
     In a preferred embodiment of the present invention, the density of the net structure is adjusted by adjusting any one element selected from the group consisting of the mesh configuration of the front mesh layer, the mesh size of the front mesh layer, the mesh configuration of the rear mesh layer, the mesh size of the rear mesh layer, the density at which the piles are arranged, the length of the piles between the front mesh layer and the rear mesh layer, the thickness of the piles, and any combination of these elements. 
     In a preferred embodiment of the present invention, the compressibility is adjusted by varying the material of construction for the fibers used in at least one of the front mesh layer, rear mesh layer and piles. 
     In a preferred embodiment of the present invention, the compressibility is adjusted by varying the type of the fibers for at least one of the front mesh layer, rear mesh layer and piles. 
     In a preferred embodiment of the present invention, the portion of the net fabric to be processed includes at least a side edge portion of the net fabric of a predetermined width which is defined along each of side lines thereof. 
     In a preferred embodiment of the present invention, the portion of the net fabric to be processed includes at least a cut portion of a predetermined width defined along each of cutting lines thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a cross sectional view showing an embodiment of a portion of a net fabric to be processed into a net product according to the present invention; 
     FIG. 2 is an enlarged view showing a front mesh layer incorporated in the net fabric shown in FIG. 1; 
     FIG. 3 is an enlarged view showing a rear mesh layer incorporated in the net fabric shown in FIG. 1; 
     FIG. 4 is a plane view showing the net fabric to be processed into a net product of FIG. 1 which is formed into a continuous length; 
     FIG. 5 is a plan view showing a set of seat nets cut out of the net fabric shown in FIG. 1; 
     FIG. 6 is a schematic view showing a step of cutting a plurality of seat nets while keeping them superposed on each other; 
     FIG. 7 is a schematic view showing a step of manufacturing a cut back net and a cut cushioning net into an automobile seat which is a net product; 
     FIG. 8 is a schematic view showing a vibrational welding step; 
     FIG. 9 is a plane view showing another embodiment of a net fabric to be processed into a net product according to the present invention; and 
     Each of FIGS.  10 ( a ) to  10 ( e ) is a schematic view showing a type of a pile structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A net fabric to be processed into a net product according to the present invention will now be described with reference to the accompanying drawings. 
     Referring first to FIGS. 1 to  3 , an embodiment of a net fabric to be processed into a net product according to the present invention is illustrated. A net fabric of the illustrated embodiment which is designated with reference numeral  10  throughout this specification, as shown in FIG. 1, generally includes a front mesh layer  11 , a rear mesh layer  12  and a plurality of piles  13  arranged between both layers  11  and  12  to couple them together, resulting a steric truss structure (three-dimensional structure) of the net fabric. 
     The front mesh layer  11 , as shown in, for example, FIG. 2, may be formed of yarns obtained by twisting monofilaments into a honeycomb-like (hexagonal) mesh structure. The rear mesh layer  12 , as shown in, for example, FIG. 3, may be made by rib knitting yarns obtained by twisting monofilaments form a structure having a smaller mesh (fine mesh structure) than the honeycomb mesh of front mesh layer  11 . Piles  13  may be formed of monofilaments or yarns and knittedly incorporated between front mesh layer  11  and rear mesh layer  12  so as to hold both mesh layers spaced from each other at a predetermined interval to provide net fabric  10 , which has a steric knitted mesh structure, with a rigidity at a predetermined level. 
     The term “fiber” used herein means both a monofilament and a multifilament, as well as a spun yarn and the like. 
     In the illustrated embodiment, the layer including the honeycomb mesh is defined to be the front layer which is contacted with a human body when the net fabric is used in a cushion for an automobile seat. Alternatively, the layer may be used as a rear layer, wherein the layer with the smaller mesh may be used as the front layer. Any desired mesh configuration in addition to the above-described honeycomb-like mesh shape and fine mesh shape, as described hereinafter with reference to Table 1, may be used in both the front and the rear layers. 
     Each of the front mesh layer  11 , rear mesh layer  12  and piles  13  each may be preferably made of thermoplastic resin, such as thermoplastic polyester resins represented by polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and the like; polyamide resins represented by nylon 6, nylon 66 and the like; polyolefin resins represented by polyethylene, polypropylene and the like; and any combinations thereof. 
     The fiber for each of the front mesh layer  11 , rear mesh layer  12  and piles  13  may have any desired thickness, which may be varied depending on the net product to be manufactured from the net fabric. For example, the fiber for the piles  13  has a thickness of 380d or more and preferably 600d or more, when the net fabric is manufactured into a cushioning portion of an automobile seat. Such arrangement permits the load of a person sitting on the seat to be supported by deformation of the mesh constituting each of the mesh layers  11  and  12  and compression of the piles  13 , so that the net fabric may provide a flexible structure which prevents stress concentration. 
     FIG. 4 shows net fabric  10  for processing which is formed into a continuous length and ready to be converted into a net product. As described above, the net fabric  10  is actually provided in the form of a roll fabric wound in a roll-like manner. In the illustrated embodiment, the net fabric  10  for processing is adapted to be processed into an automobile seat. Net fabric  10  is cut at the center of the net fabric  10  along a first cut (or first) portion  22  into two pieces, so that one of the two pieces of the net fabric may be used as a net for the back portion of the automobile seat or a back seat  10   a  and the other piece of net fabric  10  may be used as a net for a cushioning portion of the automobile seat or a cushioning seat  10   b.    
     In FIG. 4, each of reference numerals  20  to  22  designates a first cut or a first portion of the net fabric  10  which is relatively increased in compressibility in the thickness direction thereof and reference numerals  23  and  24  each designate a second portion thereof relatively reduced in compressibility in the thickness direction. More particularly, the net fabric  10  of a continuous length is so configured that side edge portions  20  and  21  thereof respectively defined along side lines  20   a  and  21   a  thereof and having a predetermined width and the first cut portion  22  positioned between the side lines  20   a  and  21   a  in a manner to be parallel thereto and having a predetermined width are increased in compressibility as compared with or relatively to intermediate portions  23  and  24  thereof respectively positioned between the side edge portions  20  and  21  and the first cut portion  22 . The side edge portions  20  and  21  and first cut portion  22  each are subjected to various kinds of processing such as cutting, a treatment carried out on ends of the net fabric (“end treatment”) and the like during manufacturing of a net product. The portions  20 ,  21  and  22  are constructed to exhibit a relatively increased compressibility in the thickness direction, thereby, to facilitate the processing of these portions. 
     The compressibility may be measured according to a procedure described in “Compressibility and Compressive Modulus” defined in JASO Standard M404-84. More specifically, the thickness of three specimens cut into dimensions of 50 mm×50 mm each are measured after being applied an initial load of 3.5 g/cm 2  (0.343 kPa) in the thickness direction of the specimens for 30 seconds and measured again after being applied a pressure of 200 g/cm 2  (19.6 kPa) again in the thickness direction for 10 minutes. Then, the thickness of the specimens is measured again after the pressure of 3.5 g/cm 2  (0.343 kPa) applied in the previous step being removed for 10 minutes followed by being applied another pressure of 3.5 g/cm 2  again for additional 30 seconds. Thereafter, both compressibility (A) and compressive elastic modulus (B) are calculated according to the following expressions (1) and (2): 
     
       
           A (%)={( t   0   −t   1 )/ t   0 }×100  (1)  
       
     
     
       
           B (%)={( t′   0   −t   1 )/( t   0   −t   1 )}×100  (2)  
       
     
     wherein t 0  is the thickness (mm) of the specimens after the initial application of the pressure or load of 3.5 g/cm 2  (0.343 kPa), wherein t 1  is the thickness (mm) of the specimens after the application of the load of 200 g/cm 2 , and wherein t′ 0  is its thickness (mm) after the second application of the load of 3.5 g/cm 2  (0.343 kPa). 
     A difference in compressibility between the side portions  20 ,  21  and first cut portion  22  and the intermediate portions  23 ,  24  is preferably 5% or more. Such arrangement that the side portions  20 ,  21  and first cut portion  22  is increased in compressibility by 5% or more as compared with the intermediate portions  23  and  24  permits the portions to act like a cutout, for example, during the cutting operation, so that the net fabric may be readily cut irrespective of cutting techniques. Also, it permits the end treatment to be advantageously carried out. More specifically, it significantly facilitates the vibrational welding operation which permits a thickness between the front mesh layer  11  and rear mesh layer  12  to be reduced to provide the portions with increased rigidity. More preferably, the difference in compressibility is at least 10%. 
     In this regard, an excessive increase in compressibility of the side edge portions  20 ,  21  and first cut portion  22  to a degree of causing an excessive reduction in rigidity thereof fails to ensure rigidity required to effectively carry out the vibrational welding operation. Thus, most preferably, the difference in compressibility is between 10% and 70%. 
     A difference in compressibility between the side edge portions  20 ,  21  and first cut portion  22  to be processed and the intermediate portions  23  and  24  to be processed may be obtained by any suitable means. 
     More particularly, one of such means is means of varying density of the net structure of the portions (density varying means), wherein the net structure of the side edge portions  20 ,  21  and first cut portion  22  to be processed is a reduced density as compared with that of the intermediate portions  23  and  24 . 
     A variation in the density of the net structure by the density varying means may be accomplished by adjusting any one element selected from the group consisting of the mesh configuration of the front mesh layer  11 , the mesh size of the front mesh layer  11 , the mesh configuration of the rear mesh layer  12 , the mesh size of the rear mesh layer  12 , the density at which the piles  13  are arranged, the length of the piles  13  between the front mesh layer  11  and the rear mesh layer  12  (the thickness of the pile layer) and the thickness of the piles  13 , or any combination of the elements. 
     More particularly, at the time of starting the step of forming the side edge portions  20 ,  21  and first cut portion  22  in knitting or weaving of the net fabric  10  for processing, a process such as increasing a mesh size of the front mesh layer  11  or rear mesh layer  12 , changing the fine mesh shape of the net fabric to a honeycomb mesh shape or increasing the interval of knitting or weaving of the piles  13  to reduce the number of piles knitted or woven per unit length is employed to vary at least one of the above-described elements. 
     More specifically, adjustment in the number of piles  13  knitted permits manufacturing of the three-dimensional net fabric  10  to be carried out by presetting various factors such as the position of the net fabric where the number of piles  13  knitted is reduced, the number of piles  13  knitted and the like in a microcomputer incorporated in a knitting machine. Supposing that, for example, the net fabric  10  for processing of 970 mm in width is made by knitting, the number of piles  13  knitted is reduced within a region of the net fabric  10  inwardly extending by 30 mm from one side line  20   a  except one grip margin  20   b  of several millimeters for a heat-set fixture, to thereby provide one side edge portion  20 . Then, the number of piles  13  knitted is increased to form the intermediate portion  23  which is used for constituting the back net  10   a . Thereafter, the number of piles  13  knitted is reduced within the region of 50 mm from the center of the net fabric, to thereby form the first cut portion  22 . Subsequently, the number of piles  13  knitted is increased to form the intermediate portion  24  constituting the cushioning net  10   b  and then the number of piles  13  knitted is decreased in the region inwardly extending by 30 mm from the other side line  21   a  except the other grip margin  21   b  for the heat-set fixture, to thereby form the other side edge portion  21 . 
     The term “heat set” or “heat setting” referred to herein means that heat is applied to the net fabric which has already been knitted while the net fabric being stretched by gripping each of the grip margins  20   b  and  21   b  by means of a fixture or gripper (not shown), to correct the shrinkage of the net fabric due to knitting. After the heat setting, the net fabric  10  is generally wound in the form of a roll fabric for shipping. In this regard, the illustrated embodiment is so constructed that the net structure is reduced in density as seen in the side edge portions  20 ,  21  and first cut portion  22 , resulting in the net fabric having a portion relatively increased in compressibility. This permits the net fabric  10  of the illustrated embodiment to have less warpage due to shrinkage than the conventional net fabric having uniform or equal compressibility or density, so that the heat setting operation may be facilitated in a short period of time. 
     Another means for partially varying compressibility of the net fabric  10  in a thickness direction thereof may be also used, wherein a material of fibers for at least one of the front mesh layer  11 , rear mesh layer  12  and piles  13  is varied. For example, the piles  13  may be so constructed that the intermediate portions  23  and  24  are formed of a material exhibiting increased rigidity such as polyester, polypropylene or the like and the side edge portions  20 ,  21  and first cut portion  22  are formed of a material reduced in rigidity as compared with the portions  23  and  24 , such as nylon, PBT or the like. 
     Alternatively, the compressibility may be adjusted by varying the type of fibers for at least one of the front mesh layer  11 , rear mesh layer  12  and piles  13 . The term “type of fibers” referred to herein means a monofilament, a multifilament, a spun yarn and the like. When fibers have the same material and thickness (outer diameter), a monofilament has a higher rigidity than a multifilament. For example, when the piles  13  are constructed in such a manner that the intermediate portions  23  and  24  are made of a monofilament and the side edge portions  20 ,  21  and first cut portion  22  are made of a multifilament having the same material and thickness as the monofilament, the portions  20  to  22  may have a relatively higher compressibility than the portions  23  and  24 . 
     Also, a variation in compressibility of the net fabric  10  may be carried out by suitably combining two or more of the above-described means together. For example, the side edge portions  20 ,  21  and first cut portion  22  may be made of a multifilament, wherein the multifilament may be thinner than the monofilament used in the piles  13  incorporated in the intermediate portions  23  and  24 . Alternatively, in this instance, the multifilament may be made of a material having a lower rigidity. Optionally, means of reducing density of the net structure may be employed for this purpose. Furthermore, any combination of these approaches may be employed. 
     The following Table 1 illustrates characteristics of the net fabrics  10 , each of which permits the intermediate portions  23  and  24  to exhibit properties or characteristics suitable for use for a back portion of an automobile seat or a cushioning portion thereof and permits the side edge portions  20 ,  21  and first cut portion  22  to exhibit characteristics for easy processing. In each of the net fabrics  10  shown in Table 1, compressibility is adjusted by adjusting the number of piles  13  arranged per unit length. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Number 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Material 
                 Front 
                 Nylon 
                 Polyester 
                 ← 
                 ← 
                 ← 
                 ← 
               
               
                   
                 Rear 
                 Nylon 
                 Polyester 
                 ← 
                 ← 
                 ← 
                 ← 
               
               
                   
                 Piles 
                 Nylon 
                 Polyester 
                 ← 
                 PBT 
                 Polyester 
                 ← 
               
               
                 Weight (g/m 2 ) 
                   
                 888 
                 968 
                 1132 
                 1168 
                 1160 
                 1152 
               
               
                 Density of 
                 Longitudinal (fibers/inch) 
                 7 
                 8 
                 9 
                 9 
                 10 
                 8 
               
               
                 Portions 23, 24 
                 Lateral (fibers/inch) 
                 13 
                 15 
                 14 
                 13 
                 131 
                 14 
               
               
                 Density of 
                 Longitudinal (fibers/inch) 
                 6 
                 6 
                 7 
                 8 
                 8 
                 6 
               
               
                 Portions 20 to 22 
                 Lateral (Fibers/inch) 
                 13 
                 15 
                 14 
                 13 
                 13 
                 14 
               
               
                 Thickness of 
                 Front 
                 220d/1f 
                 1300d/96f 
                 1300d/96f 
                 1300d/96f 
                 1300d/96f 
                 1300d/96f 
               
               
                 Fibers 
                 Rear 
                 220d/1f 
                  500d/70f 
                  500d/70f 
                 1300d/96f 
                  500d/70f 
                 1300d/96f 
               
               
                   
                 Piles 
                 880d/1f 
                 600d/1f 
                 600d/1f 
                 800d/1f 
                 800d/1f 
                 800d/1f 
               
               
                 Tensile Strength 
                 Longitudinal 
                 38.0 
                 147.5 
                 173.4 
                 117.2 
                 205.9 
                 162.8 
               
               
                 (Kg/5 cm) 
                 Lateral 
                 24.8 
                 75.5 
                 180.4 
                 117.2 
                 49.1 
                 79.5 
               
               
                 Elongation (%) 
                 Longitudinal 
                 111.1 
                 67.1 
                 72.7 
                 63.2 
                 61.8 
                 65.8 
               
               
                   
                 Lateral 
                 189.3 
                 111.2 
                 109.9 
                 82.5 
                 133.8 
                 117.2 
               
               
                 Tear Strength (kg) 
                 Longitudinal 
                 33.8 
                 78.3 
                 78.3 
                 117.3 
                 119.4 
                 106.8 
               
               
                   
                 Lateral 
                 26.2 
                 76.2 
                 76.2 
                 73.2 
                 48.9 
                 73.3 
               
               
                 Distortion Ratio 
                 Longitudinal 
                 — 
                 2.3 
                 2.3 
                 2.1 
                 0.2 
                 0.7 
               
               
                 by Repeating Loading 
                 Lateral 
                 — 
                 2.5 
                 2.5 
                 1.4 
                 23.2 
                 9.2 
               
               
                 Portions 23 &amp; 24 
                 Thickness (mm) 
                 12.5 
                 13.1 
                 13 
                 12.1 
                 11.7 
                 12.7 
               
               
                   
                 Compressibility (%) 
                 65.7 
                 64.2 
                 54.7 
                 38.9 
                 62.1 
                 12.7 
               
               
                   
                 Elastic Modulus (%) 
                 95.2 
                 93.9 
                 95.0 
                 95.1 
                 94.1 
                 88.8 
               
               
                 Portions 20 to 22 
                 Thickness (mm) 
                 12.5 
                 12.8 
                 13.0 
                 12.0 
                 11.5 
                 12.5 
               
               
                   
                 Compressibility (%) 
                 85.2 
                 80.9 
                 80.7 
                 79.3 
                 78.6 
                 80.3 
               
               
                   
                 Elastic Modulus (%) 
                 45.0 
                 39 
                 42.9 
                 46.9 
                 48.9 
                 44.1 
               
               
                 Structure of 
                 Front 
                 Mesh 
                 Honeycomb 
                 Mesh 
                 Honeycomb 
                 Honeycomb 
                 Honeycomb 
               
               
                 Mesh Layer 
                 Rear 
                 Mesh 
                 Fine mesh 
                 Fine mesh 
                 Mesh 
                 Fine mesh 
                 Mesh 
               
               
                 Structure of Piles 
                   
                 Parallel 
                 Cross 
                 Cross 
                 Cross 
                 Cross 
                 Cross 
               
               
                   
               
            
           
         
       
     
     In Table 1, “d” is an abbreviation of “denier”. “1d” equals to the thickness of a fiber weighing 1 g for each 9,000 m of the fiber. For example, “220d” equals the thickness of a fiber weighing 1 g for each 9,000/220=40.9 m. “f” means the number of monofilaments. For example, “70f” means that there are 70 monofilaments in a single yarn. The unit “kg/5 cm” for tensile strength indicates strength of the net fabric of 5 cm in width. The term “parallel” in the pile structure means that the piles  13  for coupling the front mesh layer  11  and rear mesh layer  12  together do not intersect each other as viewed sideward. “Cross” indicates that they do intersect each other when being viewed sideway. 
     Arrangement of the piles  13  (pile structure) may be carried out in each of the configurations as shown in FIGS.  10 ( a ) to  10 ( e ), wherein the piles  13  through which the front mesh layer  11  and rear mesh layer  12  are coupled together are viewed sideway. FIGS.  10 ( a ) and  10 ( b ) each shows a straight arrangement manner in which the piles  13  each are arranged between each of yarns constituting the front mesh layer  11  and each of yarns constituting the rear mesh layer  12  opposite thereto, wherein FIG.  10 ( a ) shows the piles  13  straightly knitted in an 8-shaped configuration and FIG.  10 ( b ) shows the piles  13  straightly knitted in a simple configuration. FIGS.  10 ( c ) to  10 ( e ) each show the piles  13  each arranged so as to extend between each of yarns of the front mesh layer  11  and each of yarns of the rear mesh layer  12  adjacent to each of yarns of the rear mesh layer  12  opposite to each of the yarns of the front mesh layer  11  while intersecting each adjacent pile  13 . More particularly, in FIG.  10 ( c ), the piles  13  are arranged to show the shape of the numeral “8.” In FIG.  10 ( d ), the piles  13  are knitted in a simple cross configuration. In FIG.  10 ( e ), the piles  13  are arranged in a double cross configuration. 
     Now, manufacturing an automobile seat using the net fabric of the illustrated embodiment constructed as described above will be described. 
     First, as shown in FIG. 4, the net fabric  10  is drawn out of the roll fabric and cut into a length which is easy to handle in the width direction thereof. Then, as shown in FIG. 5, each set of seat nets  10   c  in which the back net  10   a  and cushioning net  10   b  are integrated with each other are cut out from the cut net fabric  10 . 
     Then, as shown in FIG. 6, the each set of the seat nets  10   c  thus cut are laminated on each other on a processing pedestal of any suitable cutting machine such as, for example, a water jet type cutter while being aligned with each other. Then, the cutter is activated to cut the seat nets along predetermined cutting lines  22   a  and  22   b  by means of high-pressure water. In the illustrated embodiment, the first cut portion  22  is increased in compressibility as compared with the intermediate portions  23  and  24 , to thereby be readily compressed. Also, the net fabric  10  is configured into a three-dimensional structure. Such construction substantially eliminates the problems of elastic force which deteriorates cut properties of the net fabric. More particularly, the conventional net fabric is so configured that the intermediate portions  23  and  24  has the same compressibility as the first cut portion  22  and the compressibility is set at such a level that the compressibility is suitable for portions  23  and  24  to be used as a cushioning portion and a back portion. Thus, the conventional net fabric has compressibility set at a relatively low level and a compressive modulus set at a relatively high level. Thus, cutting of a plurality of the conventional net fabrics laminated or superposed on each other causes an elastic force thereof to act as a resistance, leading to the curvature of the cutting line. Also, cutting of the conventional net fabrics laminated on each other by means of a water jet type cutter fails to cut the upper net fabrics. On the contrary, in the illustrated embodiment, the first cut portion  22  is increased in compressibility, to thereby exhibit a function similar to that obtained when a cutout is preformed on the net fabric, so that a plurality of net fabrics laminated on each other may be accurately cut at a predetermined position without substantially causing positional mismatch between the net fabrics. 
     As being noted from Table 1 described above, the compressibility and compressive modulus are not necessarily inversely proportional to each other. Thus, both compressibility and compressive modulus may be increased. Alternatively, both may be reduced. In any event, a relative increase in compressibility facilitates the cutting operation and/or vibrational welding operation even when the compressive modulus is not reduced to the same degree. 
     Thus, the back and cushioning nets  10   a  and  10   b  are separated from each other at the first cut portion  22  to form the back portion and cushioning portion of the automobile seat. Then, a plurality of back nets  10   a  and cushioning net  10   b  are superposed on each other, respectively, and cut along cutting lines  20   c  and  21   c  indicated at broken lines in the side edge portions  20  and  21  (FIGS. 4 to  6 ). In this instance as well, the side edge portions  20  and  21  have compressibility set as described above, so that the cutting may be carried out readily and accurately as in the cutting along the first cut portion  22 . 
     Each of the back nets  10   a  and cushioning nets  10   b  which have been thus cut out is then subjected to a fine cutting operation, to thereby be cut into a desired shape as indicated in a first step shown in FIG.  7 . 
     During the second step, washers  61  for connecting the back net to a seat frame are mounted on both sides of the back net  10   a  by sewing. Then, a trim  63  for decoration is attached to the end of the back net  10   a  by sewing. The cushioning portion  10   b  has an unnecessary end portion removed by cutting in the second step. Then trims  64  for decoration are attached to the ends of the cushioning portion  10   b  by sewing during the third step. 
     When the trims  63  and  64  for decoration are attached on the side edge portions  20  and  21  or the like having compressibility set at a relatively high level, the illustrated embodiment facilitates the sewing operation while preventing breaking of a sewing needle or the like during the operation because the net structure of the net fabric has a lower density. 
     In addition to the back net  10   a  and cushioning net  10   b , a base net  30  is prepared by cutting the net fabric  10  in substantially the same manner as the nets  10   a  and  10   b  as indicated in a first step. The base net is likewise constructed so that portions thereof to be processed have a higher compressibility in the thickness direction than the remaining portions thereof. In a second step, side edge portions of the base net  30 , which are made to have a higher compressibility are inwardly folded at parts  31  and  32  thereof, which are then subjected to vibrational welding. Then, in a third step, a reinforcing belt  65  is attached to a suitable portion of the base net  30  by vibrational welding. 
     The back net  10   a , cushioning net  10   b  and base net  30  which have been thus processed are assembled together in a common fourth step. The assembling is carried out by fixing the side edge portions  20 ,  21  or first cut portion  22  of the back net  10   a  or cushioning net  10   b  to a portion  30   a  of the base net  30 , which has a higher compressibility by vibrational welding to integrate them together, as shown in FIG.  8 . At this time, a plate  40  made of synthetic resin is arranged between fixtures  50  for vibrational welding and is concurrently subjected to vibrational welding. 
     Vibrational welding exhibits large bonding strength. Thus, portions of the front mesh layer  11 , rear mesh layer  12  and piles  13  which have been subjected to vibrational welding are joined together, so that parts of the front mesh layer  11  and rear mesh layer  12  constituting the side edge portions  20 ,  21  and first cut portion  22  are fixed together and hardened while being kept in proximity to each other. This permits the portions of the net fabric subjected to the vibrational welding operation or end treatment to be held on the seat frame by screwing, hitching or the like. In this regard, in the illustrated embodiment, the side edge portions  20 ,  21  and first cut portion  22  which are to be subjected to vibrational welding have a higher compressibility in the thickness direction thereof than the intermediate portions  23  and  24 , so that vibrational welding of the base net  30  may be directly carried out after cutting thereof. 
     On the contrary, in the conventional net fabric, the portions to be subjected to vibrational welding are identical in compressibility with the other portions. Such construction of the prior art makes the direct application of vibrational welding to the base net  30  after the cutting operation as in the illustrated embodiment to form a bonding therebetween difficult. In order to eliminate such a disadvantage, the prior art requires an extra step, during which the back net  10   a  and cushioning net  10   b  are vibrationally welded separately so that the welded portions of the back net  10   a  and the cushioning net  10   b  are semi-crushed, between the first step and the second step shown in FIG. 7 after the cutting operation. The prior art also requires an extra step, during which the base net  30  is vibrationally welded so that the welded portion of base net  30  is semi-crushed after the third step when the reinforcing belt  65  is attached. The illustrated embodiment eliminates the need of such extra steps, to thereby significantly simplify manufacturing of the net product, leading to a reduction in manufacturing cost. Also, the illustrated embodiment minimizes a reduction in mechanical characteristics of the fibers because vibrational welding generally reduces mechanical characteristics of the fibers. 
     Further, in the illustrated embodiment, the portions of the net fabric which are to be subjected to vibrational welding have a relatively high compressibility, to thereby ensure satisfactory vibrational welding, to effectively prevent the piles  13  from partially projecting from an end surface of the net product due to a failure in vibrational welding. 
     In the illustrated embodiment, the end treatment by vibrational welding is not limited to the fourth step shown in FIG.  7 . Thus, in order to enhance rigidity of the end portions or side edge portions  20 ,  21  or the first cut portion  22  to ensure the fixing of the net product onto the seat frame or the like by screwing, hitching or the like, some predetermined sites of end portions of the back net  10   a , cushioning net  10   b  or the like may be individually subjected to vibrational welding. For example, portions of the front mesh layer  11 , rear mesh layer  12  and piles  13  corresponding to the end portions may be welded together to provide a predetermined hardness. Also, the above-described plate made of synthetic resin (FIG. 8) may be additionally fixed thereto by vibrational welding. The illustrated embodiment even facilitates the end treatment, because the portions to be processed have a higher compressibility. 
     Referring now to FIG. 9, another embodiment of a net fabric to be processed into a net product according to the present invention is illustrated. A net fabric of the illustrated embodiment generally designated by reference numeral  10  in FIG. 9 includes second cut portions  25  along each of which respective sets of seat nets  10   c  (FIG. 5) having a back net  10   a  and a cushioning net  10   b  integrated together are cut from the net fabric  10 . Each of the second cut portions  25  is formed into a predetermined width and has a higher compressibility in a thickness direction thereof than the intermediate portions  23  and  24  of the net fabric  10 . 
     Such construction of the illustrated embodiment facilitates the operation of cutting the net fabric  10  along the predetermined cutting lines in the second cut portions  25  as in the operation of cutting it along the first cut portion  22 . Also, the vibrational welding to end-treat each of the second cut portions  25  may be as workable as the vibrational welding to the first cut portion  22 . 
     In the net fabric  10  for processing according to the present invention, it is merely required that the portions thereof to be subjected to processing such as cutting, vibrational welding or the like have a higher compressibility than the other portions thereof. Thus, the portions of the net fabric  10  which are to be processed are not limited to those in the embodiments described above. The portions of the net fabric to be processed are varied depending on a target net product desired. Thus, the portions that require a higher compressibility are determined based on the portions that need to be processed. 
     Even though the above description has been made in connection with processing for an automobile seat, the net fabric of the present invention may also be effectively applied to any other suitable seat such as a seat for a wheelchair, a seat for a chair for a learning desk, a seat for a chair for an office desk or the like. 
     As can be seen from the foregoing, the net fabric to be processed into a net product according to the present invention is so constructed that the portions thereof to be subjected to processing such as cutting, vibrational welding or the like have a relatively higher compressibility than the remaining portions thereof. Such construction ensures that the net fabric exhibits a better workability during the manufacturing of a net product using the net fabric in spite of the fabric&#39;s having a three-dimensional structure, to thereby simplify the manufacturing process, leading to a reduction in manufacturing cost of the net product. 
     While preferred embodiment of the invention have been described with a certain degree of particularity with reference to the drawings, obvious modifications and variations are possible in light of the above teachings. It is therefore to be understood that the scope of the invention is to be determined from the claims appended hereto.