Patent Publication Number: US-2007123128-A1

Title: Webbing for occupant restraint belt

Description:
BACKGROUND  
      The present invention relates to a technology for developing an occupant restraint belt used for restraining an occupant in a vehicle in the event of a collision.  
      For example, Japanese Unexamined Patent Publication No. 2004-315984, which is incorporated by reference herein in its entirety, discloses a conventional technology for developing such an occupant restraint belt. Japanese Unexamined Patent Publication No. 2004-315984 discloses a technology which relates to a seat belt that can have improved retractability and comfort by improving filament bundle and weaving arrangement thereof.  
     SUMMARY OF THE INVENTION  
      One embodiment of the invention relates to a webbing material for an occupant restraint belt that restrains a vehicle occupant. The webbing material comprises warp yarns and weft yarns woven together to form the webbing. The warp yarns and weft yarns being made of synthetic filaments such that the warp yarns and weft yarns extend perpendicular to each other. At least either of the warp yarns and the weft yarns are made of synthetic filaments with thermal adhesiveness. The synthetic filaments are formed by bundling a plurality of filament bodies. Each of the filament bodies includes a first filament and a second filament attached to an outer surface of the first filament. The second filament has a melting point lower than a melting point of the first filament. The second filaments melt when heated to temperature of 150° C. or more and a process time of 180 seconds or more such that the filament bodies are welded to each other. The webbing has a weight of 60 g/m or less, tensile strength of 25 kN or more, and retention rate after hexagonal bar abrasion of 70% or more.  
      Another embodiment of the invention relates to a seat belt. The seat belt comprises a webbing material that is configured to restrain an occupant in a vehicle. The webbing includes warp yarns and weft yarns woven together to form the webbing. The warp yarns and weft yarns are made of synthetic filaments such that the warp yarns and weft yarns extend perpendicular to each other. At least either of the warp yarns and the weft yarns are made of synthetic filaments with thermal adhesiveness. The synthetic filaments are formed by bundling a plurality of filament bodies. Each of the filament bodies includes a first filament and a second filament attached to an outer surface of the first filament. The second filament has a melting point lower than a melting point of the first filament. The second filaments melt when heated to a temperature of 150° C. or more and a process time of 180 seconds or more such that the filament bodies are welded to each other. The webbing has a weight of 60 g/m or less, tensile strength of 25 kN or more, and retention rate after hexagonal bar abrasion of 70% or more.  
      Yet another embodiment of the invention relates to a seat belt apparatus. The seat belt apparatus comprises a seat belt comprising a webbing material, a seat belt retractor capable of winding and unwinding the seat belt, a buckle fixed to a vehicle, and a tongue attached to the seat belt and latched to the seat belt buckle when the seat belt is worn by a vehicle occupant. The webbing material comprises warp yarns and weft yarns woven together to form the webbing. The warp yarns and weft yarns are made of synthetic filaments such that the warp yarns and weft yarns extend perpendicular to each other. At least either of the warp yarns and the weft yarns are made of synthetic filaments with thermal adhesiveness. The synthetic filaments are formed by bundling a plurality of filament bodies. Each of the filament bodies includes a first filament and a second filament attached to an outer surface of the first filament. The second filament has a melting point lower than a melting point of the first filament. The second filaments melt when heated to a temperature of 150° C. or more and a process time of 180 seconds or more such that the filament bodies are welded to each other. The webbing material has a weight of 60 g/m or less, tensile strength of 25 kN or more, and retention rate after hexagonal bar abrasion of 70% or more.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
       FIG. 1  is an illustration schematically showing the structure of a seat belt apparatus according to an embodiment.  
       FIG. 2  is a table indicating weaving conditions and webbing properties of seat belt webbing composing a seat belt shown in  FIG. 1  with regard to examples (Example 1 through Example 4) and a comparative example.  
       FIG. 3  is an illustration showing a brief overview of the low melting point polyester filaments (thermal adhesion yarns). 
    
    
     DETAILED DESCRIPTION  
      When designing a seat belt of this kind, it is required to apply stiffness to the seat belt in order to restrain the occupant in the event of a vehicle collision. In addition, taking into consideration the occupant&#39;s comfort while wearing the seat belt and the ease of withdrawing the seat belt from a retractor, it is also required to reduce the weight of the seat belt (which is a long belt). To reduce the weight of the seat belt, the number of filaments in the filament yarns of the seat belt can be reduced. Though the technique of simply reducing the number of filaments achieves the reduction in weight, the technique has a risk of causing the reduction in stiffness according to the reduction in the number of filaments. In this case, it is difficult to achieve the desired performance of restraining the occupant.  
      An object of the present invention is provide a technology which is effective both for applying stiffness and for reducing the weight of an occupant restraint belt to be installed in a vehicle.  
      Embodiments of the present invention can be typically adapted to a seat belt or a safety belt as a mechanism for restraining an occupant in a vehicle, such as an automobile.  
      The webbing for occupant restraint belt of a first embodiment is used for an occupant restraint belt (such as a seat belt), which is a long belt to be wound and unwound by a seat belt retractor, and a safety belt for an aircraft. The webbing for occupant restraint belt is webbing which is woven from warp yarns and weft yarns made of synthetic filaments such that the warp yarns and the weft yarns extend perpendicular to each other.  
      In the webbing for an occupant restraint belt, at least either of the warp yarns and the weft yarns are made of synthetic filaments having thermal adhesiveness which are made by bundling a plurality of filament bodies each of which comprises a first filament and a second filament which is attached to the outer surface of the first filament and has a melting point lower than that of the first filament. The second filaments are melted when heated under a condition of a temperature of 150° C. or more and a process time of 180 seconds or more so that the filament bodies are welded. The configuration of the filament bodies used here includes an embodiment in which the second filament is attached partially to the outer surface of the first filament and an embodiment in which the entire outer surface of the first filament is enclosed by a layer of the second filament, that is, a double layer structure. The synthetic filaments having thermal adhesiveness can be called “thermal welding type synthetic filaments” or “thermal adhesion yarns”. In one alternative, either of the warp yarns and the weft yarns are made of synthetic filaments having thermal adhesiveness. In another alternative, both the warp yarns and the weft yarns are made of synthetic filaments having thermal adhesiveness. In this case, parts or all of the warp yarns and the weft yarns may be made of synthetic filaments having thermal adhesiveness. As a specific example of the synthetic filament having thermal adhesiveness, polyester filament may be employed.  
      In the webbing of an occupant restraint belt, at least either of the warp yarns and the weft yarns are made of synthetic filaments having thermal adhesiveness which are made by bundling a plurality of filament bodies in which the second filaments are melted when heated under a condition of a temperature of 150° C. or more and a process time of 180 seconds or more so that the filament bodies are welded to each other, whereby the second filaments (low melting point filaments) having lower melting point in the synthetic filaments having thermal adhesiveness are preferentially melted when heated under the aforementioned condition so that the adjacent filament bodies, i.e. the first filaments which are high melting point filaments, are welded to each other. That is, the second filaments having low melting point in the synthetic filaments having thermal adhesiveness exhibits works and effect as a binder for connecting the first filaments. Therefore, since the filament bodies are welded to each other, the overall stiffness of the webbing is enhanced. Thus, since the stiffness of the webbing is enhanced because of the yarns including the synthetic filaments having thermal adhesiveness, it allows reduction in number of filaments of warp yarns and weft yarns so as to achieve the weight saving. Accordingly, webbing for occupant restraint belt having weight of 60 g/m or less, tensile strength of 25 kN or more, and retention rate after hexagonal bar abrasion of 70% or more is obtained, thereby providing a seat belt having both sufficient stiffness and light weight properties. The measurement of tensile strength (force) of webbing was carried out by a method according to JIS L1096 8.12.1A and the measurement of retention rate after hexagonal bar abrasion of webbing was carried out by a method according to JIS D4604.  
      The webbing for occupant restraint belt in a second embodiment of the invention has the same structure the first embodiment and is adapted such that the weft density is 20 picks per inch or less.  
      As for the sectional configuration of webbing of this kind, the warp yarns are curved so as to form “crimps (ruffling)”, while weft yarns extend linearly. This is a phenomenon unique to a weaving method (weaving structure) of woven fabric in which weft yarns are inserted into portions formed by spacing warp yarns alternately. In such an arrangement, the wavy profile of the crimps as curves of warp yarns can be smoothened by reducing weft density to 20 picks per inch or less, preferably 17 or less, thereby reducing stress concentration on the curves. Therefore, with regard to satisfaction of both stiffness and weight saving of webbing, a further improvement of performance can be obtained.  
      The webbing for occupant restraint belt of the third embodiment has the same structure the first or second embodiments and is adapted such that at least either of the warp yarns and the weft yarns are made of filament yarn material of twist yarns or filament yarn material made of entangled non-twist yarn. In one alternative, the warp yarns or the weft yarns are made of filament yarn material of twist yarns or filament yarn material made of entangled non-twist yarn. In another alternative, both the warp yarns and the weft yarns are made of filament yarn material of twist yarns or filament yarn material made of entangled non-twist yarn. This increases the tangles of filaments so as to improve the cohesion thereof, thereby enhancing the stiffness of the webbing. Especially, using the filament yarn material made of entangled non-twist yarn contributes lower material cost than a case using the filament yarn material of twist yarns, thereby reducing the manufacturing cost of the webbing for occupant restraint belt.  
      The seat belt of the fourth embodiment is an occupant restraint belt which comprises the webbing for occupant restraint belt as disclosed in any one of the first, second, or third embodiments. This arrangement allows satisfaction of both stiffness and weight saving of the seat belt.  
      The seat belt apparatus of fifth embodiment comprises: at least a seat belt as disclosed in the fourth embodiment; a seat belt retractor; a buckle, and a tongue. The seat belt retractor has a function of winding and unwinding the seat belt and has a retractor housing and a spool which is accommodated in the retractor housing. The seat belt retractor may be provided with a driving mechanism for driving the spool and a control mechanism for controlling the driving. The tongue which is attached to the seat belt is latched to the buckle fixed to the vehicle when the seat belt is worn. According to this arrangement, there can be provided a seat belt apparatus in which stiffness and weight saving of the seat belt are both satisfied.  
      As mentioned above, embodiments of the present invention relate to webbing for occupant restraint belt which is woven from warp yarns and weft yarns made of synthetic filaments such that the warp yarns and the weft yarns extend perpendicular to each other and provides a technology which is effective both for applying stiffness and for reducing the weight of an occupant restraint belt by such an arrangement that at least either of the warp yarns and the weft yarns are made of synthetic filaments having thermal adhesiveness.  
      Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The embodiment relates to a seat belt apparatus to be installed in an automobile and proposes a seat belt which is suitable for composing the seat belt apparatus, and a method for manufacturing the same.  
      First, description will be made with regard to a seat belt apparatus  100  as an embodiment of “seat belt apparatus” of the present invention with reference to  FIG. 1 .  FIG. 1  is an illustration schematically showing the structure of the seat belt apparatus  100  of this embodiment according to the present invention.  
      As shown in  FIG. 1 , the seat belt apparatus  100  of this embodiment is a seat belt apparatus which is installed in a vehicle and mainly comprises a seat belt retractor  101 , a seat belt  10 , a tongue  104 , and a buckle  106  and such.  
      The seat belt retractor  101  of this embodiment comprises a retractor housing  101   a  in which at least a cylindrical spool  102  is accommodated and is capable of winding and unwinding the seat belt  110  by the spool  102 . The spool  102  is driven by a driving mechanism composed of a spring or a motor. In the example illustrated in  FIG. 1 , the seat belt retractor  101  is attached in an accommodating space in a B-pillar  10  of a vehicle. The seat belt retractor  101  corresponds to the “seat belt retractor” of the present invention.  
      The seat belt  110  of this embodiment is a long belt which is used for restraining a vehicle occupant C and is made by forming webbing made of synthetic filaments into a long strip. The seat belt  110  corresponds to the “occupant restraint belt” and the “seat belt” of the present invention. The seat belt  110  is withdrawn from the seat belt retractor  101  fixed relative to the vehicle and extends through a shoulder guide anchor  103  provided around an area about the shoulder of the vehicle occupant C and is connected to an outer anchor  105  through the tongue  104 . By inserting (engaging) the tongue  104  to the buckle  106  fixed to the vehicle, the seat belt  110  becomes into the state worn by the vehicle occupant C. The tongue  104  corresponds to the “tongue” in embodiments of the present invention and the buckle  106  corresponds to the “buckle” in embodiments of the present invention. The seat belt webbing corresponds to the “webbing for occupant restraint belt” in embodiments of the present invention.  
       FIG. 2  is a table indicating weaving conditions and webbing properties of seat belt webbing composing the seat belt  110  shown in  FIG. 1  with regard to examples (Example 1 through Example 4) and a comparative example. The seat belt webbing of any of the examples and the comparative example is a woven fabric which is woven from warp yarns and weft yarns made of synthetic filaments filament such that the warp yarns and the weft yarns extend perpendicular to each other. Especially, thermal adhesion yarns having thermal adhesiveness are used as the weft yarns in the examples (Example 1 through Example 4), while the weft yarns are not thermal adhesion yarns in the comparative example.  
      As shown in  FIG. 2 , in Example 1, a filament bundle of warp yarns of 1670 dtex and 144 filaments, which was a weight-reduced filament yarn bundle obtained by reducing 34 warp yarns from a normal product (in which the number of warp yarns was 280), was used as a first filament yarn bundle. By this reduction, the number of the warp yarns was decreased to 246. As the first filament bundle, filament yarn material in which non-twist yarns were interlaced was used. In addition, used as a second filament bundle was weft yarns composed of high melting point polyester filaments of 560 dtex and 96 filaments and low melting point polyester filaments of 280 dtex and 16 filaments, specifically thermal adhesion yarns of which heat shrinkage factor was 30% when heated under a condition of a temperature of 210° C. and a process time of 180 seconds (filaments corresponding to “synthetic filaments having thermal adhesiveness”). As for the mixture between the high melting point polyester filaments and the low melting point polyester filaments of the weft yarn, for example, one low melting point polyester filament (highly shrinkable yarn) of 280 dtex and 16 filaments is mixed per one high melting point polyester filament of 560 dtex and 96 filaments. In this case, the mixing ratio of the high melting point polyester filament relative to the low melting point polyester filament (highly shrinkable yarn) is set to 2:1.  
      The heat shrinkage factor of filaments is the degree of shrinkage in the longitudinal direction of filaments. As the thermal adhesion yarn, one of which heat shrinkage factor ranges of from 20% to 60% when heated under a condition of a temperature of 150° C. or more and a process time of 180 seconds or more is selected. The heat shrinkage factor of filaments, i.e. the degree of shrinkage in the longitudinal direction of filaments, is obtained from the lengths before and after the process under the aforementioned condition. That is, the heat shrinkage factor is indicated by ((length after process—length before process)/length after process)×100. The lengths are obtained by process method or measuring method based on, for example, JIS L 1909.  
      The aforementioned high melting point polyester filaments composing the weft yarn are typically made of a polymer of polyethylene terephthalate which is manufactured by esterification of terephthalic acid and ethylene glycol. On the other hand, the aforementioned low melting point polyester filaments (thermal adhesion yarns) composing the weft yarn are typically made of a polymer of polyethylene terephthalate and a copolymer of polyethylene isophthalate with the aforementioned polyethylene terephthalate, which is manufactured by esterification of terephthalic acid, isophthalic acid and ethylene glycol.  
      The schematic illustration of the low melting point polyester filaments (thermal adhesion yarns) is shown in  FIG. 3 . As shown in  FIG. 3 , the low melting point polyester filaments are composed of filament bodies each of which comprises a polymer of polyethylene terephthalate and a copolymer of polyethylene isophthalate with polyethylene terephthalate coating the entire outer surface of the polymer of polyethylene terephthalate. That is, the low melting point polyester filaments are structured as double-layered copolymer in which the high melting point polymer of polyethylene terephthalate as a core is enclosed by the copolymer of polyethylene isophthalate with polyethylene terephthalate as a sheath. The low melting point polyester filaments correspond to the “filament bodies each of which comprises a first filament and a second filament which is attached to the outer surface of the first filament and has a lower melting point than that of the first filament” of the present invention. In this embodiment, multi-filaments made by bundling a plurality of low melting point polyester filaments (monofilaments) are used as some of the weft yarns. When the webbing using the weft yarns is heated, the copolymer of polyethylene isophthalate with polyethylene terephthalate (low melting point filaments) having a lower melting point than that of the polymer of polyethylene terephthalate is preferentially melted so that the polyethylene terephthalate as the high melting point filaments are welded and the adjacent monofilaments and multi-filaments are thus welded to each other. That is, the low melting point copolymer of polyethylene isophthalate with polyethylene terephthalate in the low melting polyester filaments exhibits works and effects as a binder for connecting filaments. Therefore, since the adjacent monofilaments and multi-filaments are welded to each other, the overall stiffness of the webbing is enhanced. The polymer of polyethylene terephthalate corresponds to the “first filaments” in embodiments of the present invention and the copolymer of polyethylene isophthalate with polyethylene terephthalate corresponds to the “second filaments having a melting point lower than that of the first filaments” of the present invention.  
      As the copolymerization rate, i.e. the used amount, of polyethylene isophthalate (isophthalic acid) is increased in the low melting point polyester filaments, the melting point of the original yarns is lowered. For instance, when the copolymerization rate of polyethylene isophthalate is 10% (the rate of polyethylene terephthalate is 90%), the melting point of the low melting point polyester filaments is 230° C. When the copolymerization rate of polyethylene isophthalate is 30% (the rate of polyethylene terephthalate is 70%), the melting point of the low melting point polyester filaments is 160° C. In this embodiment, the low melting point polyester filaments in which the copolymerization ratio of polyethylene isophthalate is 30% and the melting point is thus 160° C. are used as the thermal adhesion yarns.  
      The first filament bundle and the second filament bundle of the aforementioned Example 1 were processed by a needle-type weaving machine based on the weaving conditions shown in  FIG. 2  so as to make a seat belt webbing (evaluation webbing). In the weaving process, the weft density was 19 picks per inch. After that, the evaluation webbing was processed by dyeing and predrying, if necessary, and was then processed by heat stabilization. The heat stabilization was conducted by passing the evaluation webbing in a heating furnace, which was controlled to have a temperature in the vicinity of 210° C., taking about 180 seconds. The process condition for the heat stabilization may be suitably set by selecting a temperature from a range equal to and higher than 150° C. and selecting a process time from a range equal to and greater than 180 seconds. For example, a process condition that the temperature is 150° C. and the process time is 300 seconds may be selected. Further, for measuring the properties of webbing shown in  FIG. 2 , the evaluation webbing was cut to be a test piece of given dimensions and the test piece was dried naturally and was exposed to a predetermined condition with constant temperature and humidity (20° C., 65% RH).  
      In Example 1, the weight per unit length of the entire seat belt webbing was 52.80 g/m because of the reduction of warp yarns in the first filament bundle and such. In this case, the weight saving ratio was 14.29%.  
      In Example 2, a filament bundle of warp yarns of 1670 dtex and 144 filaments, which was a weight-reduced filament yarn bundle obtained by reducing 34 warp yarns from a normal product (in which the number of warp yarns was 280), was used as the first filament yarn bundle. By this reduction in number of the warp yarns, the number of the warp yarns was set to 246. As this first filament yarn bundle, a yarn material made of entangled non-twist yarns was used. In addition, as the second filament yarn bundle, the same filament yarn bundle as that in example-1 was used, and the weft density was set to 20 picks per inch. The other conditions were the same as those of Example 1.  
      In Example 2, the weight per unit length of the entire seat belt webbing was 53.73 g/m because of the reduction of the first filament bundle. In this case, the weight saving ratio was 12.78%.  
      In Example 3, a filament bundle of warp yarns of 1670 dtex and 144 filaments, which was a weight-reduced filament yarn bundle obtained by reducing 26 warp yarns from a normal product (in which the number of warp yarns was 280), was used as the first filament yarn bundle. By this reduction in number of the warp yarns, the number of the warp yarns was set to 254. As this first filament yarn bundle, a yarn material made of entangled non-twist yarns was used. In addition, as the second filament yarn bundle, the same filament yarn bundle as that in example-1 was used, and the weft density was set to 17 picks per inch. The other conditions were the same as those of Example 1.  
      In Example 3, the weight per unit length of the entire seat belt webbing was 54.02 g/m because of the reduction of warp yarns in the first filament bundle and reduction in weft density in the second bundle. In this case, the weight saving ratio was 12.31%.  
      In Example 4, a filament bundle of warp yarns of 1670 dtex and 144 filaments, which was a weight-reduced filament yarn bundle obtained by reducing 26 warp yarns from a normal product (in which the number of warp yarns was 280), was used as the first filament yarn bundle. By this reduction in number of the warp yarns, the number of the warp yarns was set to 254. As this first filament yarn bundle, a yarn material made of entangled non-twist yarns was used. In addition, as the second filament yarn bundle, the same filament yarn bundle as that in example-1 was used, and the weft density was set to 18 picks per inch. The other conditions were the same as those of Example 1.  
      In Example 4, the weight per unit length of the entire seat belt webbing was 54.59 g/m because of the reduction of warp yarns in the first filament bundle and reduction in weft density in the second bundle. In this case, the weight saving ratio was 11.38%.  
      In a Comparative Example, used as a first filament bundle was a filament bundle of warp yarns of 1670 dtex and 144 filaments, in which the number of warp yarns was the same of the number (280) of warp yarns of a normal product. As this first filament yarn bundle, a yarn material made of entangled non-twist yarns was used. In addition, used as a second filament bundle was a filament bundle of weft yarns of 830 dtex and 96 filaments, not including any thermal adhesion yarn as used in Example 1 through Example 4. The weft density in the second filament bundle was 19 picks per inch.  
      In the Comparative Example, the weight per unit length of the entire seat belt webbing was 61.60 g/m. This weight was defined as the reference value for weight saving.  
      With regard to the respective seat belt webbings of Example 1 through Example 4 and the Comparative Example, which were woven based on the aforementioned weaving condition, measurements of the following items for the purpose of evaluating the webbing properties were taken. Each measurement was taken using at least five test pieces for each webbing, and the results of the measurements were confirmed to have reproducibility.  
     Measurement Items  
      In this embodiment, as the measurement items for evaluating the webbing properties of seat belt webbing, “tensile strength” (sometimes referred to “force” or “strength”) and “retention rate after hexagonal bar abrasion” were used.  
     Measurement of Force  
      In this embodiment, the measurement of tensile strength (force) of webbing was carried out by a method according to JIS L1096 8.12.1A. By designing seat belt webbing to have tensile strength exceeding, for example, 25 kN, it is ensured to provide a desired load capacity required for seat belt.  
     Measurement of Retention Rate after Hexagonal Bar Abrasion  
      In this embodiment, the measurement of retention rate after hexagonal bar abrasion of webbing was carried out by a method according to JIS D4604. By designing seat belt webbing to have retention rate after hexagonal bar abrasion exceeding, for example, 70%, it is ensured to provide a desired abrasion resistance required for seat belt.  
     Evaluation Items  
      The seat belt webbings of Example 1 through Example 4 and the Comparative Example were evaluated based on the results of the aforementioned measurements. As the evaluation items, “lightweight properties”, “strength”, and “abrasion resistance” of webbing were used.  
      Since, as shown in  FIG. 2 , the webbing of Example 1 had a weight saving ratio of 14.29% relative to Comparative Example because of the thinning of the first filament bundle by reducing 34 warp yarns, it was confirmed that the webbing was superior especially in lightweight properties. Though the webbing of Example 1 was slightly inferior to Comparative Example with regard to the tensile strength and the retention rate after hexagonal bar abrasion, the webbing satisfied the required levels, i.e. tensile strength greater than 25 kN and retention rate after hexagonal bar abrasion greater than 70%. That is, it was confirmed that the webbing of Example 1 was also excellent in strength and abrasion resistance.  
      Since the webbing of Example 2 had a weight saving ratio of 12.78% relative to Comparative Example because of the thinning of the first filament bundle by reducing 34 warp yarns, it was confirmed that the webbing was superior in light weight properties. Thought the webbing of Example 2 was slightly inferior to the Comparative Example with regard to the tensile strength, the webbing satisfied the required level, i.e. tensile strength greater than 25 kN. That is, it was confirmed that the webbing of Example 2 was also excellent in strength. Further, since the retention rate after hexagonal bar abrasion of the webbing was 83.43% which was larger than that of the Comparative Example, it is also confirmed that the webbing was excellent in abrasion resistance.  
      Since the webbing of Example 3 had a weight saving ratio of 12.31% relative to the Comparative Example because of the thinning of the first filament bundle by reducing 26 warp yarns and the reduction in weft density per inch of the second filament bundle (17 picks per inch), it was confirmed that the webbing was superior in light weight properties. Though the webbing of Example 3 was slightly inferior to the Comparative Example with regard to the tensile strength and the retention rate after hexagonal bar abrasion, the webbing satisfied the required levels, i.e. tensile strength greater than 25 kN and retention rate after hexagonal bar abrasion greater than 70%. That is, it was confirmed that the webbing of Example 3 was also excellent in strength and abrasion resistance.  
      Since the webbing of Example 4 had a weight saving ratio of 11.38% relative to the Comparative Example because of the thinning of the first filament bundle by reducing 26 warp yarns and the reduction in weft density per inch of the second filament bundle (18 picks per inch), it was confirmed that the webbing was superior in light weight properties. Thought the webbing of Example 2 was slightly inferior to the Comparative Example with regard to the tensile strength, the webbing satisfied the required level, i.e. tensile strength greater than 25 kN. That is, it was confirmed that the webbing of Example 4 was also excellent in strength. Further, since the retention rate after hexagonal bar abrasion of the webbing was 83.48% which was larger than that of the Comparative Example, it is also confirmed that the webbing was excellent in abrasion resistance.  
     Comprehensive Evaluation  
      Based on the aforementioned results of evaluation, in  FIG. 2 , the comprehensive evaluation of each seat belt webbing of Example 1 through Example 4 was “□” because each of them was excellent in all of light weight properties, strength, and abrasion resistance, while the comprehensive evaluation of the seat belt webbing of the Comparative Example was “×” because it did not satisfy the desired level as the comprehensive level relating to the light weight properties, the strength, and the abrasion resistance. Especially, since the weight of the seat belt webbing of the Comparative Example exceeds 60 g/m, it had trouble with light weight properties.  
      As mentioned above, the embodiment provides a seat belt (webbing) which is excellent in practicality such as light weight properties, strength, and abrasion resistance, and provides a seat belt apparatus using the seat belt.  
      That is, the seat belt webbings of Example 1 through Example 4 which were woven according to the embodiment are excellent overall such as weight, tensile strength, retention rate after hexagonal bar abrasion as compared to the Comparative Example and, thus, are effective in weight saving while preventing the reduction in seat belt strength.  
      Especially, the webbing of each of Example 1 through Example 4 uses the weft yarns in which the low melting point polyester filaments (thermal adhesion yarns) having thermal adhesiveness which are melt when heated under a condition of a temperature of 210° C. or more and a process time of 180 seconds or more so as to contribute filament welding are mixed with the high melting point polyester filaments. Therefore, when the webbing is heated under the aforementioned condition, the polyethylene isophthalate having a lower melting point than the other synthetic filaments having thermal adhesiveness is preferentially melted so that the adjacent filaments are welded to each other by the effect as a binder. Therefore, the high melting point polyester filaments are welded to each other, thereby enhancing the overall stiffness of the webbing. Thus, since the stiffness of the webbing is enhanced because of the yarns including the synthetic filaments having thermal adhesiveness, it allows reduction in number of filaments of warp yarns and weft yarns so as to achieve the weight saving. Accordingly, seat belt webbing having weight of 60 g/m or less, tensile strength of 25 kN or more, and retention rate after hexagonal bar abrasion of 70% or more is obtained, thereby providing a seat belt having both stiffness and light weight properties.  
      An object of embodiments of the present invention is to obtain a seat belt webbing having weight of 60 g/m or less, tensile strength of 25 kN or more, and retention rate after hexagonal bar abrasion of 70% or more by suitably employing synthetic filaments having thermal adhesiveness in which low melting point filaments are melted to weld high melting point filaments when heated under a condition of a temperature of 150° C. or more and a process time of 180 seconds or more. In embodiments of the present invention, the kinds of filaments to be used in warp yarns and weft yarns and the process condition may be suitably changed, if necessary. Though the weft yarns are made by mixing the low melting point polyester filaments (thermal adhesion yarns) with the high melting point polyester filaments in the aforementioned embodiment, the kinds of high melting point filaments and low melting point filaments, the combination and the mixing ratio of the high melting point filaments and the low melting point filaments may be suitably changed, if necessary.  
      In the seat belt webbings of Example 1 through Example 4 which are woven according to this embodiment, the warp yarns may be made of filament yarn material of twist yarns or material made of entangled non-twist yarn. This increases the tangles of filaments so as to improve the cohesion thereof, thereby enhancing the stiffness of the webbing. Especially, using the material made of entangled non-twist yarn contributes lower material cost than a case using the filament yarn material of twist yarns, thereby reducing the manufacturing cost of the webbing.  
      As for the sectional configuration of webbing of this kind, warp yarns are curved so as to form “crimps (ruffling)”, while weft yarns extend linearly. This is a phenomenon unique to a weaving method (weaving structure) of woven fabric in which weft yarns are inserted into shed of warp yarns alternately. The wavy profile of the crimps as curves of warp yarns can be smoothened by reducing the weft density to 20 picks per inch or less like the seat belt webbings of Example 1 through Example 4, especially by reducing the weft density to 17 or 18 picks per inch as Example 3 or Example 4, thereby reducing stress concentration on the curves. Therefore, with regard to satisfaction of both stiffness and weight saving of webbing, further improvement of performance can be obtained. In the present invention, the weft density per inch may be suitably set within a range equal to and smaller than 20. Further, the weft density may be set to exceed 20 picks per inch when desired webbing properties can be obtained by employing synthetic filaments having thermal adhesiveness.  
      The present invention is not limited to the aforementioned embodiment, so various variations and modifications may be made. For example, the following embodiments as variations of the aforementioned embodiment may be carried out.  
      Though the above embodiment has been described with regard to a case that only weft yarns among warp yarns and weft yarns are structured to include synthetic filaments having thermal adhesiveness, only warp yarns or both warp yarns and weft yarns may be structured to include synthetic filaments having thermal adhesiveness in the present invention.  
      Though the above embodiment has been described with regard to a case that only warp yarns among warp yarns and weft yarns are made of material made of entangled non-twist yarn, only weft yarns or both warp yarns and weft yarns may be made of filament yarn material of twist yarns or material made of entangled non-twist yarn in the present invention. In embodiments of the present invention, warp yarns and weft yarns may be made without using the filament yarn material of twist yarns or the material made of entangled non-twist yarn when desired webbing properties can be obtained by employing synthetic filaments having thermal adhesiveness.  
      Though the above embodiment has been described with regard to the seat belt apparatus  100  to be installed in an automobile, the present invention can be adapted to seat belts for restraining occupants in a driver seat, a front passenger seat, and a rear seat, and seat belts to be installed in vehicles such as aircraft and boat other than the automobile.  
      Japan Priority Application 2005-342920, filed Nov. 28, 2005 including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.  
      Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.