Abstract:
A fabric for use as a base fabric in an air bag comprises a fibrous substrate having adhered to it a covering layer made of a thermoplastic synthetic resin and of 10 μm or less in average thickness. The adhesion between the fibrous substrate and covering layer is effected by causing the thermoplastic synthetic resin material of the covering layer to fill interstices between the fibers of the fibrous substrate. This may be achieved by applying to the fibrous substrate a solution or dispersion of the thermoplastic synthetic resin. An air bag may be constructed entirely from the fabric such that when it comprises sheet material additional to the base fabric, these may also be provided by the same fabric as that used for the base fabric.

Description:
This application is a division of Ser. No. 08/715,231, filed Sep. 18, 1996, now U.S. Pat. No. 5,989,660. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an air bag which absorbs impact when a motor vehicle collides, thus affording passenger protection. In more detail, the invention relates to a fabric for use as a base fabric in an air bag, an air bag comprising the fabric, a method of producing it and its use as a base fabric in an air bag so as to provide an air bag having low air permeability and less susceptible to fraying. 
     BACKGROUND OF THE INVENTION 
     Conventional air bags are produced by coating or laminating a plain weave fabric, formed by weaving nylon 66 or nylon 6 filament yarns of 300 to 1000 deniers (330 to 1100 dtex), with an elastomer resin such as a synthetic rubber, for example chloroprene, chlorosulfonated olefin or silicone, to provide a base fabric with improved heat resistance, flame resistance, gas interceptability, etc., and cutting and sewing the base fabric into bags. 
     When the plain weave fabric is coated or laminated with such an elastomer resin, a coating process such as knife coating, roll coating or reverse coating, is generally adopted. If the plain weave fabric made from filaments is coated with a chloroprene elastomer resin, to make the base fabric, the resin is applied to the surface of the base fabric in an amount of 90 to 120 g/m 2 , and the air bag produced is very heavy, hard and coarse in appearance. If the air bag is inflated to contact the face of the passenger, he/she can be scratched. Furthermore, also when it is folded into a compact standby style, it is hard to fold. If the base fabric is coated with silicone elastomer resin, the air bag is considerably more heat resistant and cold resistant than an air bag having a base fabric coated with chloroprene elastomer resin. Moreover, the amount of resin coated is only 40 to 60 g/m 2 , thus allowing a reduction in weight and an improvement in appearance and foldability. However, as yet, such improvement is not regarded as sufficient. Furthermore, the coating or lamination with an elastomer resin requires a complicated process, with attendant problems in productivity. 
     In addition, it is also demanded that the base fabric for air bags be less expensive and more easily folded for reducing the size of the module cover. Thus, air bags using non-coated base fabrics have attracted attention. In particular, high density non-coated air bags formed from woven fabrics of polyamide fibers such as nylon 66 and nylon 6, and polyester fibers have been tested and found to have improved mechanical properties and foldability as compared with air bags formed from coated base fabrics. However, they become frayed during sewing and are not low enough in air permeability, i.e., not high enough in gas interceptability, and intensive studies are being made to solve these problems. For example, JP-A-64-070247 proposes a pressure-compressed base fabric. However, this does not sufficiently prevent fraying, even though it is lower in air permeability. Furthermore, JP-A-07-040798 and JP-A-0-503763 propose a base fabric formed from a urethane resin. In particular JP-A-07-040798 discloses an air bag having a base fabric coated by dipping into an emulsion of a urethane resin and subsequently treated with a fireproof agent. However, even though such air bags are highly improved from the point of view of prevention of fraying, they are not low enough in air permeability, especially since the air permeability is increased by thermal deterioration, so that maintenance of air permeability at a stable, low level cannot be assured. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to overcome the above mentioned disadvantages of conventional air bags, so as to provide a base fabric for air bags which is prevented from being frayed during sewing, excellent in foldability and low in air permeability while retaining the mechanical properties required for air bags. 
     The present invention enables the above problems to be solved by providing, according to one aspect, a fabric for a base fabric for air bags, which fabric comprises a fibrous substrate and a covering layer, which covering layer is made of a thermoplastic synthetic resin and of 10 μm or less in average thickness and which covering layer is adhered to a surface of a fibrous substrate such that interstices between the fibers are filled with the resin, and also by providing, according to another aspect, an air bag comprising such a fabric. According to yet another aspect, the invention provides a process for producing a base fabric for air bags, comprising the steps of applying a solution or dispersion, in a liquid, preferably aqueous, medium, of a thermoplastic synthetic resin to a fibrous substrate; and heat-treating. 
     Basically, in accordance with the invention, a covering layer made of a thermoplastic synthetic resin is formed in such a way that the covering layer adheres to a fibrous substrate used in a fabric for air bags, and without this configuration, the present invention cannot be achieved. The process of the present invention can provide a fabric for air bags which does not fray during sewing, and from which air bags can be constructed which are excellent in foldability and low in air permeability while retaining the mechanical properties required for air bags. 
     The fibrous substrate of a fabric in accordance with the present invention can be a woven fabric, knitted fabric or non-woven fabric formed from polyamide fibers of nylon 6.6, nylon 6, nylon 12, nylon 4.6, nylon 6-nylon 6.6 copolymer, or any of copolymers of nylon with, for example, a polyalkylene glycol, dicarboxylic acid or amine, polyester fibers of a homopolyester such as polyethylene terephthalate or polybutylene terephthalate, or any copolymer thereof additionally containing units derived from another acid component of a polyester, such as an aliphatic dicarboxylic acid, for example, isophthalic acid, 5-sodiumsulfoisophthalic acid or adipic acid, aramid fibers of, for example, any copolymer formed from paraphenyleneterephthalamide and an aromatic ether, rayon fibers, sulfone based fibers, ultrahigh molecular weight polyethylene fibers, and high polymer fibers arranged within an islands-in-sea structure mainly composed of the above synthetic fibers. As the fabric of the fiber substrate, a woven fabric is preferable. As for the weave, a plain weave, twill weave, satin weave, modified weaves of these types or a multi-axial weave, can be used, but among them a plain weave, is preferable because it is excellent in mechanical properties and thin. Among these woven fabrics, a plain weave of polyamide fibers or polyester fibers is capable of providing an air bag having excellent properties. The fibers can contain various additives usually used for improving productivity and properties in the production and processing of raw filaments. For example, a thermal stabilizer, antioxidant, photo stabilizer, smoothing agent, antistatic agent, plasticizer, thickening agent, pigment or flame retarder, can be present 
     The strength of the mono-filaments constituting the woven fabric is not especially limited, but is preferably 6 g/denier (6.7 g/dtex) or more, more preferably 7 g/denier (7.8 g/dtex) or more. The thickness of each of the mono-filaments and the thickness of each of the filament yarns respectively constituting the woven fabric are not especially limited as far as the mechanical properties required as air bags can be satisfied. However, it is preferable that the thickness of each of the mono-filaments is at least 0.1 denier (0.11 dtex), more preferably at least 0.5 denier (0.55 dtex) up to 7 deniers (7.8 dtex) inclusive, and that the thickness of each of the filament yarns is 200 to 500 deniers (220 to 550 dtex). Furthermore, the cover factor of the woven fabric is preferably 1700 to 2500 denier  0.5  in −1  [(0.9 dtex) 0.5 (2.54 cm.) −1 ]. The cover factor referred to here is expressed by (D1)×N1+(D2)×N2, where D1 is the thickness (denier) (0.9 dtex) of each of the warp filament yarns, N1, the density of the warp filament yarns (number per inch) (number per 2.54 cm), D2, the thickness (denier) (0.9 dtex) of each of the weft filament yarns, and N2, the density of the weft filament yarns (number per inch) (number per 2.54 cm). The loom used for weaving is desirably a water jet loom, air jet loom or rapier loom. 
     The thermoplastic synthetic resin of the covering layer of a fabric in accordance with the present invention can be based on, for example, a polyurethane, polyester, polyamide, acrylic polymer, polyethylene or polypropylene. Among these thermoplastic synthetic resins, polyurethane based resins and polyester based resins are more effective. Having regard to environment resistance, particularly heat resistance of the base fabric for air bags, the softening point of the synthetic resin is preferably 120° C. or higher, more preferably 150° C. or higher. The softening point referred to here is the temperature at which the synthetic resin (solid) begins to flow at a pressure of 10 kg/cm 2 . Among the synthetic resins, a resin formed from a self-dispersible resin is more effective. A self-dispersible resin refers to, for example, a colloid-dispersible resin with hydrophilic groups, for example, a metal sulfonate or carboxylate and dissolved or dispersed as fine grains in water, without requiring any emulsifier. For example, it can be an ionomer type urethane resin, for example, an anionic resin consisting of an aliphatic polyisocyanate and a polyol or an anionic resin consisting of an aromatic polyisocyanate and a polyol. More particularly, the ionomer type urethane resin may be, for example, a polyester based urethane resin, an ionomer type polyether based urethane resin or an ionomer type polycarbonate based urethane resin. Alternatively, the self-dispersible resin may be an ionomer type aliphatic polyester resin or ionomer type aromatic polyester resin composed of, for example, an anionic polyester. As required, the resin can also contain a crosslinking agent such as an epoxy compound, melamine or polyfunctional isocyanate, antioxidant such as an amine based compound or flame retarder such as a halogen compound. One, or a mixture of two or more of these resins can be used. 
     The average thickness of the film made of such a thermoplastic synthetic resin formed on the surface of a fibrous substrate is 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less, especially 1-2 μm. If the thickness is more than 10 μm, the fibrous substrate becomes undesirably coarse and hard, being low in foldability. Furthermore, it is necessary that the film is formed to adhere to the fibrous substrate in a manner such that inter-fibrous meshes are filled with the resin. When the film is formed so as to adhere to the fibrous substrate like this, the film and the fibrous substrate are integrated to assure reinforced covering layer formation. 
     The thermoplastic synthetic resin is preferably deposited in an amount of 0.05 to 20%, more preferably 0.1 to 10% by weight based on the weight of the fibrous substrate alone. If the amount is too small, the effect of preventing fraying and the effect of lowering the air permeability are too small, and if more than necessary, the fibrous substrate becomes coarse and hard, to be undesirably low in foldability. 
     The thermoplastic synthetic resin may be applied as a solution or dispersion thereof in a liquid medium, preferably an aqueous medium. The resin solution or dispersion may exist initially in concentrated form, in which case it can be diluted at will to the desired resin solids concentration suitable for application. To apply the thermoplastic synthetic resin, immersion is usually adopted. In this case, for example, a dipping tank and a mangle or vacuum apparatus to ensure homogeneous impregnation may be used in combination. However, for example, a sprayer or foaming machine can also be used, and the resin application method is not especially limited. When a sprayer or foaming machine is used, the fabric can be coated with the resin on one side only or on both sides. The synthetic resin solution or dispersion, which can be applied directly as such (after dilution where appropriate) or as a liquid resin foam preferably contains 0.1 to 50 wt %, more preferably 0.5 to 20 wt %, of solid resin. The heat treatment is preferably applied at 50 to 200° C., more preferably 100 to 150° C. after completion of application of the synthetic resin coating. As required, the heat treatment can also be applied in two steps, for example at 80° C. at first, and then at 150° C. The impregnation of the fabric with the synthetic resin can be effected after looming, after scouring, after drying or after thermal setting, and physical processing such as pressure compression can also be applied additionally as required. 
     Having regard to air bag inflatability, the air permeability of the base fabric for air bags is preferably 20 cc/cm 2 /sec or less, more preferably 10 cc/cm 2 /sec or less, being the air flow rate through the base fabric measured when air is fed at a pressure of 0.2 kg/cm 2 . The air bag produced using such a base fabric for air bags can be used as an air bag, for example, for a driver&#39;s seat, an air bag for a front passenger&#39;s seat, an air bag for a rear seat or an air bag for expansion from a position laterally of an occupant of a seat. 
     In the above air bag, in addition to the base fabric it is preferable to include, at least in one or more certain selected region(s), a reinforcing fabric layer or layers, superimposed on the base fabric, for example in regions surrounding apertures such as an inflator installing opening, vent holes, etc. and also to include in the bag construction at least one fabric piece which serves to control the configuration of the air bag when in an inflated condition. For ease of sewing, it is preferred that any such fabric layer or piece be of the same fabric as that of the base fabric of the air bag. Furthermore, for constructing the air bag, it is preferable that the or each fabric portion required for the air bag is obtained by punching or heat-cutting it out of a fabric in accordance with the invention, and then sewn at a peripheral region thereof to provide stitching, thereby securing the or each fabric portion in position, in a desired configuration in the air bag. More preferably, the stitching at the peripheral region for forming the air bag is achieved using only a single or double overlapped seam. 
     Advantageous features of a fabric embodying the invention when used at least as a base fabric in an air bag, also embodying the present invention, are freedom from fraying during sewing, excellent foldability, and the possibility of keeping the air permeability low in a range preferable for air bags, while retaining the mechanical properties required for air bags. 
     Thus, according to an especially preferred aspect, the invention provides an air bag comprising a base fabric, which fabric comprises a covering layer made of a thermoplastic synthetic resin and of 10 μm or less in average thickness, which covering layer is adhered to the surface of a fibrous substrate such that interstices between the fibers are filled with the resin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings and the following Examples. 
     In the drawings, 
     FIG. 1 is a perspective view showing an air bag embodying the invention for a driver&#39;s seat; 
     FIG. 2 is a perspective view showing an air bag embodying the invention for a front passenger&#39;s seat; 
     FIGS. 3-5 are respective photomicrographs of fabrics prepared in accordance with Examples 1-3; 
     FIG. 6 is a photomicrograph of a fabric embodying the invention with an ionomer type polyurethane covering layer provided by coating; 
     FIG. 7 is a photomicrograph of a fabric with an ionomer type polyurethane covering layer provided by immersion; and 
     FIG. 8 is a photomicrograph of an uncoated fibrous substrate prior to application thereto of a covering layer; and 
     FIG. 9 is a photomicrograph of a coated fabric produced in accordance with Comparative Example 6. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Thus, referring to FIG. 1, an air bag for a driver&#39;s seat has a base fabric portion  1  which, when fitted in front of the driver&#39;s seat, faces the driver, a fabric portion  2  for contact with an inflator, a circular opening  3  for connection to the inflator and vent holes  4 . 
     Referring to FIG. 2, an air bag for a passenger&#39;s seat has a base fabric portion  5  which, when fitted in front of the passenger&#39;s seat, faces the passenger, a pair of fabric portions  6  providing respective laterally disposed fabric pieces for controlling the configuration of the bag when in an inflated condition, a rectangular opening  3  for connection to an inflator and vent holes  4 . 
     The respective properties referred to in the Examples below were evaluated according to the following methods: 
     Tensile strength: The average of the values of warp and weft directions was obtained according to JIS L 1096 (6.12.1A) method. 
     Breaking elongation: The average of the values of warp and weft directions was obtained according to JIS L 1096 (6.12.1A) method. 
     Bursting strength: The average of the values of warp and weft directions was obtained according to JIS L 1096 (6.12.1A) method. 
     Thickness of covering layer: A photomicrograph of a cross section of the coated fabric was taken and a covering layer portion of a certain length was cut out of it. Then, the average thickness of the covering layer was obtained from the following formula: 
     (Area of covering layer portion)×(Thickness of certain length portion)/(Area of certain length portion). 
     Weight ratio of resin:fabric: This can be determined by multiplication of the cut out area referred to above by the density of the resin. Alternatively, the weight ratio of resin:fabric can be determined merely by measuring the difference between the respective weights of coated and uncoated fabrics. However, this method may sometimes be less accurate because the weight ratio may be very small and the fibrous substrate may not be sufficiently dimensionally stable for an accurate measurement. 
     Air permeability: A laminar flow type air permeability measuring instrument was used, and air was fed at a pressure of 0.2 kg/cm 2 , to measure the flow rate of the air passing through the sample (cc/cm 2 /sec). 
     Environment resistance: The base fabric was treated at 110° C. for 500 hours, then at 80° C. and 95% for 500 hours, and finally at −40° C. for 24 hours respectively in a thermohygrostat, and then the air permeability was measured. 
     Prevention of fraying: The woven fabric was cut into a disc 20 cm in diameter, and placed in a drum type rotating machine, being rotated at 25° C. for 15 minutes. The degree of fraying was expressed in terms of the following grades. 
     Grade 5: No fraying 
     Grade 3: Fraying observed 
     Grade 1: Fraying remarkable 
     (Grade 2 and Grade 4 express the respectively intermediate conditions of fraying.) 
     Foldability: A 60-liter air bag was folded into a predetermined form, and with a pressure of 98N applied, its folded height was measured. It was expressed as a relative value with reference to the folded height of a standard silicone rubber coated air bag (coated by 45 g/m 2 ) as 100. 
     EXAMPLES 1 and 2 
     Nylon 6.6 filament yarns each of 420 deniers 467 dtex and each filament yarn consisting of 72 filaments, 9.5 g/denier (10.6 g/dtex) in strength and 24.1% in elongation were used to obtain a plain weave of 53 yarns/inch (20.9 yarns/cm) in both the warp and weft yarn densities, using a water jet loom. The woven fabric was scoured at 60° C. and dried at 130° C. respectively according to conventional methods. Then, the woven fabric was immersed in a diluted resin solution containing 10 wt %, as solid content, of an anionic ionomer type polyester based urethane resin consisting of an aliphatic polyisocyanate and a polyol and of 150° C. in softening point [Example 1] or a water dispersed polyester based urethane resin with the same composition emulsified by a polyethylene glycol aliphatic ester based emulsifier [Example 2], and pressed and rendered smooth by a mangle at 3 kg/cm 2 . In this case, the softening point was measured as follows. The solid resin to be measured was placed in a tube of 1 mm in inner diameter, and heated at a pressure of 10 kg/cm 2 , and the temperature at which the resin began to flow was measured and identified as the softening point. The coated woven fabric was then dried at 120° C. for 3 minutes and thermally set at 160° C. for 25 seconds, to obtain a base fabric for air bags. Subsequently, from the base fabric for air bags, two base fabric discs of 725 mm in diameter were punched out. At the center of one of the discs, three circular reinforcing fabric sheets of 200 mm in diameter of the same fabric were laminated, and circular lines of 110 mm, 145 mm and 175 mm in diameter were respectively sewn by a lock stitch sewing machine using sewing threads of nylon 6.6 fiber 420D/1×3 as needle and bobbin threads. At the center, a hole of 90 mm in diameter was formed as the inflator installing opening. Furthermore, each one circular reinforcing fabric sheet of 75 mm in diameter of the same fabric was placed at two opposite positions 255 mm from the center in the bias direction, and circles of 50 mm and 60 mm were sewn by a lock stitch sewing machine using sewing threads of nylon 6.6 fiber 420D/1×3 as needle and bobbin threads. At the two positions, holes of 40 mm in diameter were formed as vent holes. Then, on the fabric disc with the reinforcing fabric sheets kept outside, the other fabric disc was overlapped with its warp axis shifted by 45 degrees, and circles of 700 mm and 710 mm in diameter were sewn by a multi-thread chain stitch sewing machine using sewing threads of nylon 6.6 fiber 1260D/1 as needle and looper threads. The bag was reversed, to complete an air bag for the driver&#39;s seat of 60 liters in capacity. 
     The properties of the base fabric for air bags thus obtained are shown in Table 1. The base fabric for air bags of the present invention retained the mechanical properties required for air bags, were free from fraying during sewing, and were excellent in low air permeability and foldability as an air bag. 
     COMPARATIVE EXAMPLE 1 
     The same woven fabric as that used in Example 1 was scoured at 60° C., dried at 130° C. and thermally set at 160° C. for 25 seconds, to obtain a base fabric for air bags. Then, as described for Example 1, an air bag for the driver&#39;s seat of 60 liters in capacity was manufactured. 
     The properties of the base fabric for air bags thus obtained are shown in Table 1. The base fabric for air bags of Comparative Example 1 was excellent in foldability as an air bag, but rather insufficient in low air permeability, and furthermore, when sewn, it was frayed so as also to pose a problem in productivity. 
     EXAMPLE 3 
     Nylon 6.6 filament yarns each of 315 deniers (35 dtex) and each filament yarn consisting of 72 filaments, 9.4 g/denier (10.4 g/dtex) in strength and 23.3% in elongation were used to obtain a plain weave of 60 yarns/inch (23.6 yarns/cm) in both the warp and weft yarn densities, using a water jet loom. Then, the woven fabric was foam-coated, on one side, with a foam diluted solution containing 30 wt %, as solid content, of the same ionomer type polyester based urethane resin as used in Example 1 and 0.1 wt %, as solid content, of a nonionic foaming agent, and of 7 times in expansion ratio. It was dried at 130° C. for 2 hours, and thermally set at 160° C. for 25 seconds, to obtain a base fabric for air bags. From the base fabric for air bags, one main body fabric sheet and two lateral fabric sheets were fusion-cut, and an air bag for the front passenger&#39;s seat of 120 liters in capacity as shown in FIG. 2 was manufactured. 
     The properties of the base fabric for air bags thus obtained were similarly evaluated and found to be as shown in Table 1. The base fabric for air bags of the present invention held the mechanical properties required for air bags, and was free from fraying during sewing, and excellent in low air permeability and foldability as an air bag. 
     COMPARATIVE EXAMPLE 2 
     The same woven fabric as used in Example 1 was thermally set at 160° C. for 25 seconds, to obtain a base fabric for air bags. Then, an air bag for the front passenger&#39;s seat of 120 liters in capacity was manufactured, as described for Example 2. 
     The properties of the base fabric for air bags thus obtained were similarly evaluated and found to be as shown in Table 1. The base fabric for air bags of Comparative Example 2 was excellent in foldability as an air bag, but was rather insufficient in low air permeability, and when sewn, it was frayed so as also to pose a problem in productivity. 
     EXAMPLE 4 
     Polyethylene terephthalate filament yarns each of 420 deniers (467 dtex) and each filament yarn consisting of 144 filaments, 9.0 g/denier (10 g/dtex) in strength and 18.2% in elongation were used to obtain a plain weave of 57 yarns/inch (22.4 yarns/cm) in the warp yarn density and 53 yarns/inch (20.9 yarns/cm) in the weft yarn density, using an air jet loom. Then, the woven fabric was scoured at 80° C., dried at 130° C., thermally set at 180° C. for 25 seconds, immersed in a diluted resin solution containing 12.5 wt %, as solid content, of an anionic ionomer type aliphatic polyester resin of 155° C. in softening point, pressed and rendered smooth by a mangle at 4 kg/cm 2 , dried at 150° C. for 2 minutes, and thermally set at 180° C. for 25 seconds, to obtain a base fabric for air bags. From the base fabric, an air bag for the driver&#39;s seat of 60 liters in capacity was manufactured as described for Example 1. 
     The properties of the base fabric for air bags thus obtained are shown in Table 1. The base fabric for air bags of the present invention were free from fraying during sewing, and excellent in low air permeability and foldability as an air bag. 
     COMPARATIVE EXAMPLE 3 
     The same woven fabric as used in Example 4 was scoured at 80° C., dried at 130° C., and thermally set at 180° C. for 25 seconds, to obtain a base fabric for air bags. From the base fabric, an air bag for the driver&#39;s seat of 60 liters in capacity was manufactured as described for Example 1. 
     The properties of the base fabric for air bags thus obtained were similarly evaluated and found to be as shown in Table 3. The base fabric for air bags of Comparative Example 3 was excellent in foldability as an air bag, but was rather insufficient in low air permeability, and when sewn, it was frayed remarkably, so as to pose a problem in productivity. 
       
     COMPARATIVE EXAMPLE 4 
     The same woven fabric as used in Example 1 was scoured at 80° C., dried at 130° C. and thermally set at 180° C. for 25 seconds. Then, it was pressurized and compressed on one side, between a metallic roll, having a smooth surface, heated to 160° C. and a plastic roll at room temperature at a pressure of 25 tons at a speed of 15 m/min, to produce a base fabric for air bags. Then, as described for Example 1, an air bag for the driver&#39;s seat of 60 liters in capacity was manufactured. 
     The properties of the base-fabric for air bags thus obtained are shown in Table 1. The base fabric for air bags of Comparative Example 4 was rather improved but insufficient in low air permeability. 
       
     COMPARATIVE EXAMPLE 5 
     Nylon 6.6 filament yarns of 840 deniers (933 dtex) and each filament yarn consisting of 136 filaments, 9.4 g/denier (10.4 g/dtex) in strength and 23.8% in elongation were used to obtain a plain weave of 25 yarns/inch (9.8 yarns/cm) in both the warp and weft yarn densities, using a water jet loom. The woven fabric was scoured at 60° C., dried at 130° C. and thermally set at 180° C. for 25 seconds. Then, the woven fabric was coated with 95 g/m 2  of chloroprene rubber by twice coating, using a type of knife coater, dried at 130° C., and vulcanized at 1° C. for 3 minutes, to obtain a base fabric for air bags. Subsequently, as described for Example 1, an air bag for the driver&#39;s seat of 60 liters in capacity was manufactured. 
     The properties of the base fabric for air bags thus obtained were evaluated as described for Example 1 and found to be as shown in Table 1. The base fabric for air bags of Comparative Example 5 was excellent in the prevention of fraying and low air permeability, but was so hard as to impair foldability and to complicate processing disadvantageously having regard to productivity. 
     COMPARATIVE EXAMPLE 6 
     The same nylon 6.6 filament yarns as used in Example 1 were used, to weave a plain weave of 46 yarns/inch (18.1 yarns/cm) in both the warp and weft yarn densities, using a water jet loom. The woven fabric was scoured at 60° C., 20 dried at 130° C. and thermally set at 180° C. for 25 hours. Then, the woven fabric was coated with 45 g/m 2  of a methylvinyl based silicone rubber, using a type of knife coater, dried at 130° C., and vulcanized at 180° C. for 3 minutes, to obtain a base fabric for air bags. Subsequently, as described for Example 1, an air bag for the driver&#39;s seat of 60 liters in capacity was manufactured. 
     The properties of the base fabric for air bags thus obtained were evaluated as described for Example 1 and found to be as shown in Table 1. A photomicrograph of the base fabric for air bags of Comparative Example 6 is shown in FIG.  9 . 
     As can be seen by comparison with FIGS. 3-7, the covering layer of the base fabric of FIG. 9 is particularly thick. 
     As is evident from Table 1, the base fabric of Comparative Example 6 was excellent in the prevention of fraying during sewing, and low air permeability, but was so hard as to impair foldability and also to complicate processing disadvantageously having regard to productivity. 
     EXAMPLE 5 
     Nylon 6.6 filament yarns each having a denier of 420 (467 dtex) and each filament yarn consisting of 72 filaments, having a strength of 9.5 g/denier and an elongation of 24.1% were used to obtain a plain weave having both warp and weft yarn densities of 53 yarns/inch (21 yarns/cm) using a water jet loom. The woven fabric was then knife-coated with a paste-like foam prepared by adding a thickening agent to a solution of an anionic ionomer type polyester based urethane resin having a softening point of 150° C. and dried at 130° C. for three minutes. A photomicrograph of the resulting base fabric is shown in FIG.  6 . 
     EXAMPLE 6 
     Nylon 6.6 filament yarns each having a denier of 420 (467 dtex) and each filament yarn consisting of 72 filaments, having a strength of 9.5 g/denier and an elongation of 24.1% were used to obtain a plain weave having both warp and weft yarn densities of 55 yarns/inch (22 yarns/cm), using a water jet loom. The woven fabric was scoured at 80° C., dried at 130° C. and heat set at 180° C. A photomicrograph of this untreated fabric is shown in FIG.  8 . The woven fabric was then immersed in a diluted resin solution containing 10 wt %, as solid content, of an anionic ionomer type polyester based urethane resin having a softening point of 120° C. and squeezed with a mangle under a pressure of 3 kg/cm 2 . The fabric was dried at 120° C. for three minutes and heat set at 160° C. for 25 seconds. A photomicrograph of the resulting base fabric is shown in FIG.  7 . 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Item 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 Example 
                 Example 
               
               
                   
                   
                 1 
                 2 
               
               
                   
               
               
                 Components 
                 Material 
                 N66 
                 N66 
               
               
                   
                 Thickness of each filament 
                 420 
                 420 
               
               
                   
                 yarn (D) (d) (0.9 dtex) 
               
               
                   
                 Thickness of each mono- 
                 5.8 
                 5.8 
               
               
                   
                 filament (d) (d) (0.9 dtex) 
               
               
                   
                 Number of filaments of each 
                 72 
                 72 
               
               
                   
                 filament yarn 
               
               
                   
                 Strength (g/d) (g/0.9 dtex) 
                 9.5 
                 9.5 
               
               
                   
                 Elongation (%) 
                 24.1 
                 24.1 
               
               
                   
                 Cover factor 
                 2,172 
                 2,172 
               
               
                   
                 Loom 
                 WJL 
                 WJL 
               
               
                 Processing 
                 Resin 
                 Polyurethane 
                 Polyurethane 
               
               
                 conditions 
                   
                 (aqueous) 
                 (water 
               
               
                   
                   
                   
                 dispersed) 
               
               
                   
                 Softening point (° C.) 
                 152 
                 156 
               
               
                   
                 Concentration of diluted 
                 10 
                 10 
               
               
                   
                 solution (wt %) 
               
               
                   
                 Covering layer application 
                 Immersion 
                 Immersion 
               
               
                   
                 method 
               
               
                 Properties 
                 Deposited amount (wt %) 
                 1.2 
                 1.3 
               
               
                 of 
                 Average covering layer 
                 1.1 
                 1.2 
               
               
                 processed 
                 Thickness (μm) 
               
               
                 base 
                 Tensile strength (N/cs) 
                 727 
                 726 
               
               
                 fabric 
                 Breaking elongation (%) 
                 30 
                 31 
               
               
                   
                 Bursting strength (N) 
                 More than 
                 More than 
               
               
                   
                   
                 450 
                 450 
               
               
                   
                 Air permeability 
               
               
                   
                 (cc/cm 2 /sec) 
               
               
                   
                 Initial 
                 6.5 
                 6.7 
               
               
                   
                 Heat 
                 6.7 
                 10.3 
               
               
                   
                 resistance 
               
               
                   
                 Cold 
                 6.1 
                 6.6 
               
               
                   
                 resistance 
               
               
                   
                 Moisture 
                 6.3 
                 6.5 
               
               
                   
                 resistance 
               
               
                   
                 Prevention of fraying 
                 4-5 
                 4-5 
               
               
                   
                 (grade) 
               
               
                   
                 Foldability 
                 87 
                 87 
               
               
                   
                 Productivity 
                 Excellent 
                 Excellent 
               
             
          
           
               
                   
                   
                 Compar- 
                   
                 Compar- 
               
               
                   
                   
                 ative 
                 Exam- 
                 ative 
               
               
                   
                   
                 exam- 
                 ple 
                 exam- 
               
               
                   
                   
                 ple 1 
                 3 
                 ple 2 
               
               
                   
               
               
                 Components 
                 Material 
                 N66 
                 N66 
                 N66 
               
               
                   
                 Thickness of each 
                 420 
                 315 
                 315 
               
               
                   
                 filament yarn 
               
               
                   
                 (D) (d) (0.9 dtex) 
               
               
                   
                 Thickness of each mono- 
                 5.8 
                 4.4 
                 4.4 
               
               
                   
                 filament 
               
               
                   
                 (d) (d) (0.9 dtex) 
               
               
                   
                 Number of filaments of 
                 72 
                 72 
                 72 
               
               
                   
                 each filament yarn 
               
               
                   
                 Strength 
                 9.5 
                 9.4 
                 9.4 
               
               
                   
                 (g/d) (g/0.9 dtex) 
               
               
                   
                 Elongation (%) 
                 24.1 
                 23.3 
                 23.3 
               
               
                   
                 Cover factor 
                 2,172 
                 2,129 
                 2,129 
               
               
                   
                 Loom 
                 WJL 
                 WJL 
                 WJL 
               
               
                 Process 
                 Resin 
                 — 
                 Poly- 
                 — 
               
               
                 ing 
                   
                   
                 ure- 
               
               
                 condi- 
                   
                   
                 thane 
               
               
                 tions 
                   
                   
                 (aque- 
               
               
                   
                   
                   
                 ous) 
               
               
                   
                 Softening point (° C.) 
                 — 
                 145 
                 — 
               
               
                   
                 Concentration of diluted 
                 — 
                 30 
                 — 
               
               
                   
                 solution (wt %) 
               
               
                   
                 Covering layer 
                 — 
                 Foam 
                 — 
               
               
                   
                 application method 
                   
                 coating 
               
               
                 Proper- 
                 Deposited amount (wt %) 
                 — 
                 1.6 
                 — 
               
               
                 ties of 
                 Average covering layer 
                 — 
                 2.8 
                 — 
               
               
                 process 
                 thickness (m) 
               
               
                 ed base 
                 Tensile strength (N/cs) 
                 722 
                 678 
                 680 
               
               
                 fabric 
                 Breaking elongation (%) 
                 28 
                 29 
                 30 
               
               
                   
                 Bursting strength (N) 
                 More 
                 More 
                 More 
               
               
                   
                   
                 than 
                 than 
                 than 
               
               
                   
                   
                 450 
                 450 
                 450 
               
               
                   
                 Air permeability 
               
               
                   
                 (cc/cm 2 /sec) 
               
               
                   
                 Initial 
                 25.3 
                 6.1 
                 24.8 
               
               
                   
                 Heat resistance 
                 32.1 
                 6.3 
                 31.9 
               
               
                   
                 Cold resistance 
                 22.4 
                 5.8 
                 22 
               
               
                   
                 Moisture 
                 23.8 
                 S.9 
                 23.2 
               
               
                   
                 resistance 
               
               
                   
                 Prevenion of fraying 
                 1-2 
                 4-5 
                 1-2 
               
               
                   
                 (grade) 
               
               
                   
                 Foldability 
                 85 
                 79 
                 77 
               
               
                   
                 Productivity 
                 More 
                 Excel- 
                 More 
               
               
                   
                   
                 excel- 
                 lent 
                 excel- 
               
               
                   
                   
                 lent 
                 lent 
               
             
          
           
               
                   
                   
                   
                 Com- 
                 Com- 
                 Com- 
               
               
                   
                   
                   
                 par- 
                 par- 
                 par- 
               
               
                   
                   
                   
                 a- 
                 a- 
                 a- 
               
               
                   
                   
                   
                 tive 
                 tive 
                 tive 
               
               
                   
                   
                 Ex- 
                 ex- 
                 ex- 
                 ex- 
               
               
                   
                   
                 am- 
                 am- 
                 am- 
                 am- 
               
               
                   
                   
                 ple 
                 ple 
                 ple 
                 ple 
               
               
                   
                   
                 4 
                 3 
                 4 
                 5 
               
               
                   
               
               
                 Com- 
                 Material 
                 PET 
                 PET 
                 PET 
                 N66 
               
               
                 po- 
                 Thickness of each 
                 420 
                 420 
                 420 
                 840 
               
               
                 nents 
                 filament yarn 
               
               
                   
                 (D)(d)(0.9 dtex) 
               
               
                   
                 Thickness of each 
                 2.9 
                 2.9 
                 2.9 
                 6.2 
               
               
                   
                 mono-filament 
               
               
                   
                 (d)(d)(0.9 dtex) 
               
               
                   
                 Number of filaments of 
                 144 
                 144 
                 144 
                 136 
               
               
                   
                 each filament yarn 
               
               
                   
                 Strength (g/d)(g/0.9 dtex) 
                 9 
                 9 
                 9 
                 9.4 
               
               
                   
                 Elongation (%) 
                 18.2 
                 18.2 
                 18.2 
                 23.8 
               
               
                   
                 Cover factor 
                 2,254 
                 2,254 
                 2,254 
                 1,449 
               
               
                   
                 Loom 
                 AJL 
                 AJL 
                 AJL 
                 WJL 
               
               
                 Pro- 
                 Resin 
                 poly- 
                 — 
                 — 
                 Chloro- 
               
               
                 ces- 
                   
                 ester 
                   
                   
                 prene 
               
               
                 sing 
                   
                 (aque- 
                   
                   
                 rubber 
               
               
                 con- 
                   
                 ous) 
               
               
                 di 
                 Softening point (° C.) 
                 147 
                 — 
                 — 
                 — 
               
               
                 tions 
                 Concentration of diluted 
                 15 
                 — 
                 — 
                 — 
               
               
                   
                 solution (wt %) 
               
               
                   
                 Covering layer appli- 
                 Immer- 
                 — 
                 Calender 
                 Rubber 
               
               
                   
                 cation method 
                 sion 
                   
                   
                 coating 
               
               
                 Pro- 
                 Deposited amount (wt %) 
                 1.8 
                 — 
                 — 
                 90 
               
               
                 per 
                 Average covering layer 
                 1.6 
                 — 
                 — 
                 85 
               
               
                 ties 
                 thickness (m) 
               
               
                 of 
                 Tensile strength (N/cs) 
                 698 
                 695 
                 685 
                 744 
               
               
                 pro- 
                 Breaking elongation (%) 
                 25 
                 24 
                 23 
                 30 
               
               
                 ces- 
                 Bursting strength (N) 
                 More 
                 More 
                 More 
                 More 
               
               
                 sed 
                   
                 than 
                 than 
                 than 
                 than 
               
               
                 base 
                   
                 450 
                 450 
                 450 
                 450 
               
               
                   
                 Air permeability 
               
               
                   
                 (cc/cm 2 /sec) 
               
               
                   
                 initial 
                 7.1 
                 22.5 
                 13.1 
                 0 
               
               
                   
                 Heat resistance 
                 7.3 
                 24.7 
                 16.9 
                 0 
               
               
                   
                 Cold resistance 
                 7 
                 21.6 
                 13.2 
                 0 
               
               
                   
                 Moisture resistance 
                 7 
                 21.9 
                 13.5 
                 0 
               
               
                   
                 Prevention of fraying 
                 4-5 
                 1-2 2 
                 5 
               
               
                   
                 (grade) 
               
               
                   
                 Foldability 
                 84 
                 82 
                 86 
                 168 
               
               
                   
                 Productivity 
                 Ex- 
                 More 
                 Ex 
                 Poor 
               
               
                   
                   
                 cel 
                 ex 
                 cel 
               
               
                   
                   
                 lent 
                 cel 
                 lent 
               
               
                   
                   
                   
                 lent 
               
               
                   
               
             
          
         
       
     
     As can be seen from the above Examples and Comparative Examples, the present invention enables air bag to be provided which still have the required mechanical properties, while at the same time minimising the incidence of fraying during sewing and exhibiting excellent foldability and low air permeability, all at an expense lower than that of conventional coated air bags and calendered air bags.