Net fabric for processing

Abstract: A net fabric for processing capable of simplifying processing during manufacturing of a net product, leading to a reduction in manufacturing cost of the net product. The net fabric is so constructed that side edge portions thereof to be subjected to processing such as cutting, vibrational welding or the like are increased in compressibility in a thickness direction thereof as compared with or relatively to intermediate portions thereof. This ensures that the net fabric exhibits increased workability during manufacturing of the fabric into a net product in spite of having a three-dimensional structure, to thereby simplify the manufacturing, leading to a reduction in manufacturing cost.

Description: BACKGROUND OF THE INVENTION This invention relates to a net fabric for processing which has a three-dimensional structure. 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 properties of satisfactorily distributing a pressure of the body and impact absorbing properties. Net products made of such a net material 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 for processing (a net fabric for processing) prior to manufacturing of the material 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 for processing, a configuration of each of the front and rear mesh layers and a size thereof, as well as knitting or weaving conditions such as the number of piles knitted or woven between both mesh layers are inevitably rendered substantially constant over a whole region of the net fabric. This causes compressibility of the net fabric in a 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 for 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 of a three-dimensional structure therefor is so manufactured that a whole thereof may exhibit compressibility suitable for the automobile seat. Thus, when the net fabric is made so as to exhibit compressibility suitable for properties required for the net product, a portion of the net fabric to be processed is relatively reduced in compressibility and relatively increased in compressive elastic modulus, to thereby render operation of cutting the portion troublesome because elasticity thereof offers resistance to the cutting. The cutting operation is generally carried out in a manner to cut the roll fabric into the net fabrics of a predetermined length and then cut the net fabrics into a desired shape 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, in cutting of the net fabrics laminated on each other, the resistance described above is apt to cause positional misregistration therebetween. Also, a reduction in compressibility causes vibrational welding operation which is a treatment of processing ends of the net fabric (end treatment) or sewing operation to be troublesome. GB 2 009 266 A discloses a net fabric according to the preamble of claim 1. 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 for processing which is capable of facilitating processing of the net fabric such as cutting, welding or sewing during manufacturing of the net fabric used as a material for processing into a net product. It is another object of the present invention to provide a net fabric of a three-dimensional structure for processing 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 for processing which is used as a material for any 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 portion of the net fabric to be processed in processing steps for manufacturing of the net product is relatively increased in compressibility in a thickness direction thereof as compared with that of a remaining portion thereof. In a preferred embodiment of the present invention, a 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 preferred embodiment of the present invention, a difference in compressibility between the portion of the net fabric to be processed and the remaining 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 density of a net structure of the net fabric. In a preferred embodiment of the present invention, density of the net structure is adjusted by adjusting any one selected from the group of elements consisting of a mesh configuration of the front mesh layer, a mesh size of the front mesh layer, a mesh configuration of the rear mesh layer, a mesh size of the rear mesh layer, density at which the piles are arranged, a length of the piles between the front mesh layer and the rear mesh layer and a thickness of the piles, or any combination of the elements. In a preferred embodiment of the present invention, the compressibility is adjusted by varying a material of fibers for 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 a type of 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 cut 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 fragmentary sectional view showing an embodiment of a net fabric for processing 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 plan view showing the net fabric for processing 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 plan view showing another embodiment of a net fabric for processing according to the present invention; and Figs. 10(a) to 10(e) each are a schematic view showing a type of a pile structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now, a net fabric for processing according to the present invention will be described with reference to the accompanying drawings. Referring first to Figs. 1 to 3, an embodiment of a net fabric for processing according to the present invention is illustrated. A net fabric of the illustrated embodiment which is generally designated at reference numeral 10, 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 to each other, resulting in being configured into a steric truss structure (three-dimensional structure). 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 subjecting yarns obtained by twisting monofilaments to rib knitting and formed into a structure having a small mesh (fine mesh structure), as compared with the honeycomb mesh of the front mesh layer 11. The piles 13 may be formed of monofilaments or yarns and knittedly incorporated between the front mesh layer 11 and the rear mesh layer 12 so as to hold both mesh layers spaced from each other at a predetermined interval, resulting in providing the net fabric 10 which is a steric knitted mesh structure with 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 a 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 including the small mesh may be used as the front layer. A structure for the mesh layer may be formed into any desired mesh configuration other than the above-described honeycomb-like mesh shape and fine mesh shape, as described hereinafter with reference to Table 1. The front mesh layer 11, rear mesh layer 12 and piles 13 each may be preferably made of thermoplastic resin. For example, 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 may be used for this purpose. 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 a 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 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 falling of the piles 13, so that the net fabric may provide a flexible structure which prevents stress concentration. Fig. 4 shows the net fabric 10 for precessing which is formed into a continuous length and which is in the form of a material to be manufactured 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. To this end, the net fabric 10 is cut at a central portion thereof defined in a width direction thereof into two pieces, so that one of the two pieces of the net fabric may be used as a net for a back portion of the automobile seat or a back seat 10a and the other piece of the net fabric 10 may be used as a net for a cushioning portion of the automobile seat or a cushioning seat 10b. In Fig. 4, reference numerals 20 to 22 each designate a portion of the net fabric 10 which is relatively increased in compressibility in a thickness direction thereof and reference numerals 23 and 24 each designate a 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 20a and 21a thereof and having a predetermined width and a first cut portion 22 positioned between the side lines 20a and 21a 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 formed so as to exhibit a relatively increased compressibility in the thickness direction, to thereby facilitate processing of the portions. The compressibility may be measured according to a procedure described in "Compressibility and Compressive Modulus" defined in JASO Standard M404-84. More specifically, three specimens cut into dimensions of 50mm x 50mm each are subjected to measurement of a thickness thereof obtained after initial load of 3.5 g/cm 2 (0.343 kPa) is applied thereto in a thickness direction thereof for 30 seconds and that obtained after a pressure of 200 g/cm 2 (19.6 kPa) is then applied thereto in the thickness direction for 10 minutes. Then, a thickness thereof is measured which is obtained when a pressure of 3.5 g/cm 2 (0.343 kPa) is applied thereto for 30 seconds after it is left to stand for 10 minutes while being kept released from load. 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 } x 100 B (%) = {(t' 0 -t 1 )/(t 0 -t 1 )} x 100 wherein t 0 is a thickness (mm) of the specimen obtained when a pressure or load of 3.5 g/cm 2 (0.343 kPa) is applied thereto, t 1 is its thickness (mm) obtained when load of 200 g/cm 2 is applied thereto, and t' 0 is its thickness (mm) when load of 3.5 g/cm 2 (0.343 kPa) is applied thereto again. 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 executed. 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. The difference in compressibility is more preferably 10% or more. 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 execute the vibrational welding operation. Thus, the difference in compressibility is preferably 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 a means of varying density of a 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 reduced in density as compared with that of the intermediate portions 23 and 24. A variation in density of the net structure by the density varying means may be accomplished by adjusting any one element selected from the group consisting of a mesh configuration of the front mesh layer 11, a mesh size of the front mesh layer 11, a mesh configuration of the rear mesh layer 12, a mesh size of the rear mesh layer 12, density at which the piles 13 are arranged, a length of the piles 13 between the front mesh layer 11 and the rear mesh layer 12 (a thickness of the pile layer) and a thickness of the piles 13, or any combination of the elements. More particularly, at the time of starting a 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 treatment of, for example, increasing a mesh size of the front mesh layer 11 or rear mesh layer 12, changing a fine mesh shape of the net fabric to a honeycomb mesh shape or increasing an 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 previously setting various factors such as a position of the net fabric at which 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 30mm from one side line 20a except one grip margin 20b 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 10a. Thereafter, the number of piles 13 knitted is reduced within a region of 50mm at a 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 10b and then the number of piles 13 knitted is decreased in a region inwardly extending by 30mm from the other side line 21a except the other grip margin 21b 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 been knitted while stretching it by gripping each of the grip margins 20b and 21b by means of a fixture or gripper (not shown), resulting in correcting 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 be decreased in warpage due to shrinkage as compared with 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 a 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 is increased in rigidity as compared with 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 be relatively increased in compressibility as compared with 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 with each other. For example, the side edge portions 20, 21 and first cut portion 22 may be made of a multifilament, wherein the multifilament may be reduced in thickness or thinned as compared with that of a monofilament constituting the piles 13 incorporated in the intermediate portions 23 and 24. Alternatively, in this instance, the multifilament may be made of a material decreased in rigidity or a means of reducing density of the net structure may be employed. Further, 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. In Table 1, "d" is an abbreviation of "denier". "1d" indicates a thickness of fibers of 1g obtained when they are stretched by 9,000m. For example, "220d" means a thickness of fibers of 1g obtained when they are stretched by 9,000/220=40.9m. "f" means the number of monofilaments. For example, "70f" indicates that 70 monofilaments constitute a single yarn. The unit "kg/5cm" 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 to each other do not intersect each other as viewed sideward. "Cross" indicates that they intersect each other as viewed sideward. Arrangement of the piles 13 (pile structure) may be carried out in each of manners classified 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 to each other are sideward viewed. 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 for the rear mesh layer 12 opposite thereto, wherein Fig. 10(a) shows the piles 13 straightly knitted in an 8-shaped manner and Fig. 10(b) shows the piles 13 straightly knitted in a simple manner. 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 each are arranged so as to describe a figure 8. In Fig. 10(d), the piles 13 are knitted in a simple cross manner. In Fig. 10(e), the piles 13 are arranged in a double cross manner. Now, manufacturing of the net fabric of the illustrated embodiment constructed as described above into an automobile seat will be described. First, as shown in Fig. 4, the net fabric 10 is drawn out of the roll fabric and cut by a length easy to handle in a width direction thereof. Then, as shown in Fig. 5, each set of seat nets 10c in which the back net 10a and cushioning net 10b are integrated with each other are cut from the cut net fabric 10. Then, as shown in Fig. 6, the each set of the seat nets 10c 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 22a and 22b 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 problems due to 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 a level sufficient to permit characteristics suitable for the cushioning portion and back portion to be satisfactorily exhibited. 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 elastic force thereof to act as resistance, leading to curving 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 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 previously formed 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 misregistration between the net fabrics. As will be 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 a degree. Thus, the back and cushioning nets 10a and 10b are separated from each other at the first cut portion 22 for formation of the back portion and cushioning portion of the automobile seat. Then, a plurality of back nets 10a and 10b are superposed on each other, respectively, and cut along cutting lines 20c and 21c 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 readily and accurately attained as in the cutting along the first cut portion 22. The back nets 10a and cushioning nets 10b which have been thus cut out each are then subjected to fine cutting operation, to thereby be formed into a desired shape as indicated in a first step shown in Fig. 7. Then, the back net 10a is transferred to a second step, wherein washers 61 for connection of the back net to a seat frame are mounted on both sides of the back net 10a by sewing. Then, a trim 63 for decoration is attached to an end of the back net 10a by sewing. The cushioning portion 10b has an unnecessary end portion removed by cutting in a second step and then has trims 64 for decoration attached to ends thereof by sewing in a third step. When the trims 63 and 64 for decoration are provided 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 thereof is reduced in density. In addition to the back net 10a and cushioning net 10b, a base net 30 is prepared by cutting the net fabric 10 in substantially the same manner as the nets 10a and 10b as indicated in a first step. The base net is likewise constructed so that portions thereof to be processed are increased in compressibility in a thickness direction thereof as compared with remaining portions thereof. In a second step, side edge portions of the base net 30 which are formed so as to exhibit increased 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 10a, cushioning net 10b 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 10a or cushioning net 10b to a portion 30a of the base net 30 which is formed so as to exhibit increased compressibility by vibrational welding to integrate them with each other, as shown in Fig. 8. At this time, a plate 40 made of synthetic resin is arranged between fixtures 50 for vibrational welding and 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 are increased in compressibility in a thickness direction thereof as compared with that of 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 causes direct application of vibrational welding to the base net 30 after the cutting operation as in the illustrated embodiment to fail to facilitate bonding therebetween. In order to eliminate such a disadvantage, the prior art requires that a treatment or processing of previously subjecting the portions of the back net 10a and cushioning net 10b which are to be subjected to vibrational welding during assembling of the net product to vibrational welding independently, to thereby render the portions semi-crushed is carried out, for example, between the first step and the second step shown in Fig. 7 after the cutting operation. The prior art also requires that processing of previously subjecting the portions of the base net 30 which are to be subjected to vibrational welding during assembling of the net product to vibrational welding independently, to thereby render the portions semi-crushed is carried out, for example, after attachment of the reinforcing belt 65 thereto in the third step. However, the illustrated embodiment eliminates a necessity of such previous treatments, 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 are relatively increased in compressibility, to thereby ensure satisfactory vibrational welding, resulting in effectively preventing 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 fixing of the net product onto the seat frame or the like by screwing, hitching or the like, predetermined sites of end portions of the back net 10a, cushioning net 10b or the like may be independently 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 to each other, so that the front mesh layer 11 and rear mesh layer 12 may be fixed to each other while being kept in proximity to each other, to thereby be provided with hardness at a predetermined level. Also, the above-described plate made of synthetic resin (Fig. 8) may be additionally fixed thereto by vibrational welding. The illustrated embodiment facilitates even such an end treatment, because the portions to be processed are increased in compressibility. Referring now to Fig. 9, another embodiment of a net fabric for processing according to the present invention is illustrated. A net fabric of the illustrated embodiment generally designated at reference numeral 10 in Fig. 9 includes second cut portions 25 along each of which respective sets of seat nets 10c (Fig. 5) having a back net 10a and a cushioning net 10b integrated with each other are cut from the net fabric 10. The second cut portions 25 each are formed into a predetermined width and increased in compressibility in a thickness direction thereof as compared with intermediate portions 23 and 24 of the net fabric 10. Such construction of the illustrated embodiment facilitates operation of cutting the net fabric 10 along predetermined cutting lines in the second cut portions 25 as in operation of cutting it along first cut portion 22. Also, vibrational welding for an end treatment on each of the second cut portions 25 may be enhanced in workability as in vibrational welding on 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 are increased in compressibility as compared with 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 which are to be increased in compressibility are determined depending on the portions to be processed. Also, the above description has been made in connection with processing for an automobile seat. However, it is a matter of course that the net fabric of the present invention may 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 form the foregoing, the net fabric for processing 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 are increased in compressibility as compared with or relatively to the remaining portions thereof. Such construction ensures that the net fabric exhibits increased workability during manufacturing thereof into a net product in spite of having a three-dimensional structure, to thereby simplify the manufacturing, 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 within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims: A net fabric (10) of a three-dimensional structure for processing which is used as a material for any net product, comprising: a front mesh layer (11); a rear mesh layer (12); and a plurality of piles (13) for coupling said front mesh layer and rear mesh layer to each other therethrough; characterized in that a portion (20-22) of the net fabric to be processed in processing steps for manufacturing of the net product is relatively increased in compressibility in a thickness direction thereof as compared with that of a remaining portion (23, 24) thereof. A net fabric (10) as defined in claim 1, wherein a difference in compressibility between said portion (20-22) of said net fabric to be processed and said remaining portion (23, 24) thereof is set to be 5% or more. A net fabric (10) as defined in claim 2, wherein a difference in compressibility between said portion (20-22) of said net fabric to be processed and said remaining portion (23, 24) thereof is set to be within a range between 10% and 70%. A net fabric (10) as defined in any one of claims 1 to 3, wherein said compressibility is adjusted by density of a net structure of the net fabric. A net fabric (10) as defined in claim 4, wherein said density of said net structure is adjusted by adjusting any one selected from the group of elements consisting of a mesh configuration of the front mesh layer (11), a mesh size of the front mesh layer (11), a mesh configuration of the rear mesh layer (12), a mesh size of the rear mesh layer (12), density at which the piles (13) are arranged, a length of the piles (13) between the front mesh layer (11) and the rear mesh layer (12) and a thickness of the piles (13), or any combination of the elements. A net fabric (10) as defined in any one of claims 1 to 5, wherein said compressibility is adjusted by varying a material of fibers for at least one of the front mesh layer (11), rear mesh layer (12) and piles (13). A net fabric (10) as defined in any one of claims 1 to 6, wherein said compressibility is adjusted by varying a type of fibers for at least one of the front mesh layer (11), rear mesh layer (12) and piles (13). A net fabric (10) as defined in any one of claims 1 to 7, wherein said portion of the net fabric to be processed includes at least a side edge portion of the net fabric (10) of a predetermined width which is defined along each of side lines thereof. A net fabric (10) as defined in any one of claims 1 td 8, wherein said portion of the net fabric (10) to be processed includes at least a cut portion of a predetermined width defined along each of cut lines thereof.

Inventors: FUJITA ETSUNORI, KOYAMA EIICHI, NISHINO MASAKI, OGURA YUMI, TSUMURA YOSHIO, UEDA KAZUHIRO, FUJITA, ETSUNORI, KOYAMA, EIICHI, NISHINO, MASAKI, OGURA, YUMI, TSUMURA, YOSHIO, UEDA, KAZUHIRO
Applicants: DELTA TOOLING CO LTD, DELTA TOOLING CO., LTD.
Application year: 2001
Main classification: D04B21
IPC codes: D04B21