BAG FOR ABSORBING IMPACT AND PRODUCTION THEREOF

Abstract: This invention relates to an impact absorbing bag for an automobile, that is, an air bag, consisting of circular seamless woven fabric bag bodies (1) which comprises an annular non-hollow-weave part (B1) formed around a circular hollow weave part (B2), is at least partially covered with a polymer film (2) on the surface thereof and has gas inlets (3) on one of its surfaces. The bag body (1) can be prepared by cutting circularly a woven fabric having the weave parts (B2) formed in succession. The bag may be turned inside out so that its inside and outside are reversed.

Description: Field of the Invention The present invention relates to an air bag and a method of manufacturing the same. More particularly, the present invention relates to an impact absorbing bag housed in a center portion of a steering wheel which is capable of sensing impact caused when a car collides with some object and instantaneously inflating to ensure the safety of a driver or the like and to a method for manufacturing the impact absorbing bag. Background Technology When a car collides with an oncoming car or another object, the driver may smash his face strongly onto the steering wheel or the front glass. If the impact generated at that time can be reduced, it is possible to prevent death or serious injury to the driver. In many countries, drivers are obliged by law to use seat belts as one means of safety upon collisions, but the effective reduction of the impact by seat belts is not sufficient when a car collides with an object at a high speed. Therefore, use of an air bag system, i.e., a system capable of sensing an impact caused when a car collides with an object and instantaneously inflating a bag housed in a center portion of a steering wheel or the like to ensure the safety of the driver or the like is now being considered in many countries as a more reliable safety measure. One conventional air bag has been manufactured by forming a polymer layer on a plain woven fabric, providing a gas introducing hole in one of the woven fabrics, superimposing two woven fabrics with polymer layers in a state with the polymer layer sides facing each other, and sewing together circumferential edges of the two woven fabric. For example, Japanese Unexamined Patent Publication JP-A-4742/76 corresponding to DE-A-2528636, in one portion explaining the conventional air bags, describes that conventional air bags are obtained by cutting two circular pieces of woven fabrics from two regular square pieces of woven fabrics and sewing together the circumferential edges of the two circular pieces. In air bags, a gas is instantaneously fed into the bag by explosion of a pyrotechnic, so the air bag must have a strength sufficient to endure the impact force caused by the explosion. The above-mentioned method of manufacturing air bags using a sewing process has several problems in this regard. There are many manual working processes involved, so there is a chance of decreased strength of the sewn portions and inspections of the strength of the sewn portions and the air permeability of the woven fabric take much time. The overall reliability of air bags manufactured by this method is low. A method of manufacturing air bags using a tubular weaving method has been proposed. Japanese Examined Utility Model Publication JP-U-58228/82, corresponding to Japanese Unexamined Utility Model Publication No. 49-56352, discloses an impact absorbing tubular woven fabric having bag portions formed by alternately folding two woven up and down at a middle portion. In this tublar weave, a bag portion A and a bag portion B having a connecting portion C, which consists of the upper woven fabric and lower woven fabric woven together in a jointed weave, are alternately provided. The bag portion B is smaller than the bag portion A. The fact that this tubular woven fabric could be coated was mentioned in this patent publication, but a detailed explanation was only given of a continuous body of an air bag. Further, Japanese Examined Patent Publication JP-A-576/79 corresponding to Japenese Unexamined Patent Publication No. 50-7232, disclose an impact absorbing bag having an upper connecting portion and a lower connecting portion having weft threads with larger shrinkage ratios than their warp threads. In the description of the invention and the drawings of this publication, there was shown an air bag having a square shape in plan view, provided at the outer layer thereof with a covering layer. However, when making separate bags from the impact absorbing tubular woven fabric disclosed in Japanese Examined Utility Model Publication JP-U-58228/82, the above tubular woven fabric should be cut along the widthwise direction in a portion indicated as C in Fig. 9 in the publication, so the shape of the cut fabric necessarily becomes square. An air bag having a square shape has problems such that the air pressure is not applied uniformly over the air bag, the appearance of the air bag is inferior, and it is difficult to neatly house the air bag in the steering wheel. The impact absorbing bag disclosed in Japanese Examined Patent Publication JP-A-576/79 also has a square shape, so it has the same problems. US-A-3991249 describes a fabric material for manufacturing woven air bags. The fabric described is composed of a plurality of tubular weave portions formed along the warp direction and a stitched portion formed between two adjacent tubular weave portions. It is possible to make the chamber into which air is blown an octagon by sewing the four corners of an air bag of a square shape (in this case, the appearance of the air bag is still square), but this sewn air bag has disadvantages of the large cost of the labour to sew the corners, the weaker strength of the sewn portions compared to the other portions, and the lack of uniformity. Even if this air bag is turned inside out by pulling the inside of the air bag through the opening at the center portion of the air bag for the air insertion, only the appearance of the air bag is improved. The other disadvantages, such as the inferior uniformity, are not eliminated. An object of the present invention is to provide an impact absorbing bag having superior uniformity, appearance and reliability and having the ability to be easily manufactured. Disclosure of the Invention According to one aspect of the present invention there is provided an impact absorbing bag formed from a flat, seamless tubular fabric comprising warp and weft yarns, the fabric being obtained by segment cut of a continuous body having a plurality of large, hollow portions circumferentially surrounded by a stitched portion and periodically formed along the warp yarn direction, a polymer covering layer provided on at least one portion of a surface of the fabric before or after segment cut of the continuous body, and a gas introducing hole formed in the hollow portion at one side of the fabric (Bag of the type disclosed e.g. in US-A-3 991 249); characterised in that the fabric is constituted with a hollow and substantially circular-shaped central zone and a ring-like, stitched circumferential zone around the central zone. The impact absorbing bag may be used in practice by turning inside-out the bag described above. This is achieved by pulling the inside of the above-mentioned impact absorbing bag out through the gas introducing hole. The invention also provides a method of manufacturing an impact absorbing bag comprising (i) a step of obtaining a flat, seamless tubular fabric which comprises conducting tubular weaving using a plurality of warp threads with a weft thread according to a tubular weave method to form a continuous body having rows of plurality of large, hollow portions periodically along the warp yarn direction and a stitched portion formed between two adjacent large, hollow portions, followed by segment cutting of the continuous body, (ii) a step of forming a polymer layer on at least a portion of a surface of the fabric before or after segment cut of the continuous body, and (iii) a step of providing a gas introducing hole in the hollow portion at one side of the fabric before or after step (ii); characterised in that the tubular weaving in step (i) is conducted in a manner that the length in the widthwise direction of a non-correcting portion of a tubular weave structure is gradually changed, to form rows of a plurality of large, hollow and substantially circular-shaped portions periodically along the wary yarn direction and a stitched portion is formed between two adjacent large, hollow portions, and the segment cutting of the continuous body in step (i) is conducted in a manner ,that the circular-shaped portions are cut along a portion slightly apart from the circumferential edge of the circular-shaped portions to form the fabric constituted with a hollow and substantially circular-shaped central zone and a ring-like, stitched circumferential zone around the central zone. The present invention will now be described in detail. As a base woven fabric, it is used a flat, seamless tubular fabric (1) which comprises warp and weft yarns. The fabric (1) is obtained by segment cut of a continuous body having a plurality of large, hollow portions periodically formed along the warp yarn direction and a stitched portion formed between two adjacent large, hollow portions. In accordance with the present invention, the above fabric (1) is constituted with a hollow and substantially circular-shaped central zone and a ring-like, stitched circumferential zone around the central zone. The flat, seamless tubular fabric (1) as described hereinbefore can be obtained by conducting tubular weaving using a plurality of warp threads with a weft thread according to a tubular weave method to form a continuous body, followed by segment cutting of the continuous body. The tubular weaving is conducted in a manner that the length in the widthwise direction of a non-connecting portion B2 of a tubular weave structure is gradually changing, to form rows of plurality of large, hollow and substantially circular-shaped portions periodically along the warp yarn direction and a stitched portion formed between two adjacent large, hollow portions. The segment cutting of the continuous body is conducted in a manner that the circular-shaped portions are cut along a position slightly apart from the circumferential edge of the circular-shaped portions to form the fabric (1) constituted with a hollow and substantially circular-shaped central zone and a ring-like, stitched circumferential zone around the central zone. For example, first, the non-tubular weave structure A is formed by repeating a non-tubular weave until the predetermined length is obtained and then the tubular weave structure B having the connection portion B1 and the non-connecting portion B2 of a substantially ring-like shape is manufactured by performing a tubular weave operation, i.e., a warp and weft double weaving weave in which a front layer and a back layer are connected to each other at both edge portions, in such a manner that the longer the length in the widthwise direction of the non-connecting portion B2 and then the shorter the length in the widthwise direction of the non-connecting portion B2. After that, a continuous body in which a plurality of large, hollow and substantially circular-shaped portions are aligned in a row periodically along the warp direction as illustrated in Fig. 1. In this case, when a connecting portion B1 or non-tubular weave structure A having some width is further arranged on a middle portion in the widthwise direction of the continuous body, a continuous body can be obtained in which a plurality of the large, hollow portions are arranged in two rows as illustrated in Fig. 6. A continuous body in which a plurality of large, hollow portions are arranged in rows of three or more can be easily obtained in the same manner as that of the previous case. Further, a continuous body in which a plurality of large, hollow portions are arranged in a zigzag state as illustrated in Fig. 7 can be obtained. The above weaving can be performed by using a jacquard loom, or the like. The shape of the non-connecting portion B2 in the tubular weave structure B is generally circular or nearly circular, but it is possible to make a deformed circle as illustrated in Fig. 8. The impact absorbing bag including the non-connection portion B2 of the deformed circle seat be usefully used as an air bag in the front passenger seat or the rear passenger seats. A plain weave, twill weave, satin weave or the like can be used as the weave in the non-connecting portion and the connecting portion. As the weft thread and the warp thread used for manufacturing the flat, seamless, tubular fabric 1, a thread produced from a polyester fiber, polyamide fiber, including aramide fibers, acrylic fiber, polyvinyl alcohol fiber, polyvinylidene chloride fiber, polyolefin fiber, polyurethane fiber, fluoroplastic fiber, semisynthetic fiber, regenerated fiber, natural fiber, carbon fiber, glass fiber, ceramic fiber, metal fiber or the like can be used. Further, a thread having a suitable elasticity can be used. A polymer layer 2 is provided on at least one portion of a surface of the flat, seamless tubular fabric 1 to prevent permeation of gases through the fabric 1. Generally, the polymer layer 2 is provided on the entire surface of both sides of the fabric 1, but the polymer layer 2 may also be provided on just the surface of the side facing the driver when the air bag is mounted in a steering wheel. As examples of the polymer layer 2, mention may be made of film produced from a polyurethane resin, polyester resin, polyamide resin, polyvinylidene chloride resin, polyvinyl chloride resin, polyolefin resin, fluorine resin, silicone resin, polystyrene resin, cellulose polymer, natural rubber, synthetic rubber, or the like. A polymer capable of forming an elastic film is useful. A polyurethane elastomer, a polyester elastomer, a polyamide elastomer, a polyolefin elastomer, or the like can be used as typical elastic polymers. A polyurethane elastomer is particularly preferable. Where, "polyurethane elastomer" denotes a rubber-like elastic polymer having a urethane radical in its molecular structure and includes an adipate ester type, a polyether type, a caprolactone type, and a polycarbonate type. The polymer is generally applied in a film state, liquid state, solution state, dispersion state, or a molten state on the outer surface of both sides of the fabric 1 and then is made into a laminate or covering by heating, drying, cooling, irradiation by activation energy or the like. Further, if necessary, it is possible to use a method in which the warp thread and/or weft thread is previously coated with the polymer, a fabric is made by the above warp threads and weft threads, and the woven fabric is heated to increase the flowability of the polymer on the surface of the thread so that gaps in the woven fabric structure are filled with the polymer. The polymer layer 2 may be formed on the flat, seamless tubular fabric 1 for individual units of the fabric 1. However, it is more efficient to form the polymer layer 2 on a continuous body having a plurality of large, hollow portions. It is possible to apply the polymer layer to a segment cut from a continuous body, for example, a segment including two hollow portions, a segment including three hollow portions, or a segment having the shape of a square. A gas introducing hole 3 is arranged on the central zone at one side of the flat, seamless woven fabric 1. The gas introducing holes 3 may be made in the continuous body, the segments, or the individual units. To obtain the individual units of the flat, seamless tubular fabric 1 from the continuous body, the connecting portion B1 of the tubular weave structure B and/or the non-tubular weave structure A may be cut in a circular shape along a position slightly apart from the circumferential edge of the non-connecting portion B2 having a substantially circular shape in the tubular weave structure B. It is advantageous to use melting rather than mechanical cutting as a cutting method, thus, individual units including a hollow and substantially circular shaped central zone and a ring-like stitched circumferential zone around the central zone is obtained. The polymer layer 2 is generally formed on the seamless, tubular fabric 1 from the outside of the fabric 1. Therefore, the bag obtained by this method has a slightly inferior feeling. Further, since the circumferential zone is present in a circumferential portion of the bag, the appearance of the bag is not always good. If the bag is turned inside-out by pulling out the inside of the air bag through the gas introducing hole 3, the feeling and the appearance of the obtained air bag are remarkably improved. Therefore, it is advantageous to use an inside-out air bag in terms of the merchandiseability. It is possible to provide one or more strands or strips inside the impact absorbing bag in accordance with the present invention for limiting the infration of the bag between the front of the bag, as seen from the driver's portion, and the opposite side of the bag. The impact absorbing bag in accordance with the present invention is housed in the central portion of the steering wheel with the gas introducing hole 3 connected to a gas generator. When an impact of a predetermined value or more, for example, an impact generated when a car having a speed of 16 km/hr or 25 km/hr collides head on with an object, is sensed by a mechanical sensor or an electrical sensor, gas generated by a pyrotechnic is suddenly fed into the bag, and the bag is simultaneovsly inflated. For example, the bag is inflated in 0.06 seconds after sensing of the impact. It is also possible to feed a gas having a high pressure from a gas cylinder. When the air bag is used for the front passenger seat or rear passenger seats, portions capable of housing the impact absorbing bags may be suitably arranged inside the car. Effects of the Invention The impact absorbing bag according to the present invention uses as a base woven structure a flat, seamless tubular fabric 1 constituted with a hollow and substantially circular-shaped central zone and a ring-like stitched circumferential zone around the central zone. Due to this, it is superior in terms of uniformity, strength, and adjustment of the air-permeability compared with the conventional method of forming a bag by cutting out circular pieces of fabric from two square pieces of fabric and sewing together the circumferences of the same. Therefore, a high degree of reliability can be ensured as an impact absorbing bag. Further, the manufacturing steps are streamlined and inspection time can be reduced, so it is advantageous in terms of productivity as well. Even compared with a square-shaped air bag, seen in plan view, prepared from a tubular weave, the impact absorbing bag of the present invention is far superior in the overall uniformity of application of the air pressure, the external appearance and the capability of housing within a steering wheel. Brief Description of the Drawings Figure 1 is a plan view illustrating an example of a continuous body of a flat, seamless tubular fabric in accordance with the present invention; Figure 2 is a front view illustrating the continuous body illustrated in Figure 1 and provided with a polymer layer; Figure 3 is a plan view illustrating an example of one individual unit of the flat seamless tubular fabric provided with a gas introducing hole; Figure 4 is a cross-sectional view of an example of the impact absorbing bag in accordance with the present invention obtained by turning inside-out an individual unit of the impact absorbing bag illustrated in Figure 3 through the gas introducing hole; Figure 5 is a cross-sectional view of another example of the impact absorbing bag obtained by turning inside-out an individual unit illustrated in Figure 3 through the gas introducing hole; and Figures 6 to 8 are plan view illustrating other examples of the continuous bodies of the impact absorbing bag in accordance with the present invention. In the figures, the reference numeral 1 represents a flat seamless tubular fabric, 2 represents a polymer covering layer, 3 represents a gas introducing hole, 4 represents a strand or strip for limiting the information of the bag, 5 represents a reinforcement piece, A represents a non-tubular weave structure, B represents a tubular weave structure, B1 represents a connecting portion and B2 represents a non-connecting portion. Best Mode for carrying out the Invention The present invention will now be explained in further detail by examples. Example 1 Figures 1 to 4 show an example of the steps for manufacturing an impact absorbing bag according to the present invention. Use was made of polyester multifilament yarn as the warp and weft and weaving was performed using a jacquard loom. First, non-tubular weaving was performed until a predetermined width to form a non-tubular weave structure A, then tubular weaving wherein the upper and lower layers are joined only at the two edge portions was performed so that, first the longer the length in the widthwise direction of the non the non-connecting portion B2 (that is the shorter the length in the widthwise direction of a connecting portion B1), and, then, the shorter the length in the widthwise direction of the non-connecting portion B2 (that is the longer the length in the widthwise direction of the connecting portion B1), so that a tubular weave structure B was formed. This step was repeated. By this procedure, a continuous body of a single row of a plurality of large, hollow portions periodically formed along the weft direction is obtained - (see Fig. 1). From the two sides of the continuous body was coated a polyether type polyurethane elastomer. This was heated to dry and further cured to form a polymer covering layer 2 - (see Fig. 2). Next, separate circular pieces were cut by melting along a portion slightly apart from the circumferential edge of the circular-shaped portions so as to give a diameter somewhat larger than the circular-shaped portions B2. There was thus obtained a flat, seamless tubular fabric 1 having a polymer covering layer 2 with a hollow and circular-shaped central zone and a ring-like stitched circumferential zone - (see Fig. 3). Next, a hole was made in the center portion of the central zone on one side, along with the polymer layer 2, to form the gas introducing hole 3 and thus give an impact absorbing bag - (see Fig. 3). Further, this individual unit was turned inside out from the gas introducing hole 3 to prepare the desired impact absorbing bag - (see Fig. 4). Note that (4) in Fig. 4 is a strip for limiting the inflation of the bag, which is provided according to need. It is attached to inside the bag between the top surface and bottom surface. This inflation limiting strip 4, as shown in Fig. 5, may be attached inside the bag between the top surface and bottom surface by tearing a portion of the top surface and bottom surface of the bag, adhering the two ends of the strip 4 so that they stick outside, then adhering a reinforcement piece 5 over the attached portion. Example 2 Use was made of nylon multifilament yarn as the warp and weft and weaving was performed using a loom. Except for this, the same procedure was followed as in Example 1 so as to prepare a continuous body of a seamless tubular fabric 1. Next, a film of an adipate ester type polyurethane elastomer was laid over the two surfaces of the continuous body. The composite was passed between heating rollers for lamination, thereby forming a polymer covering layer 2. A hole was made in the center portion of the central zone on one side, along with the polymer layer 2, to form the gas introducing hole 3. Finally, this individual unit was turned inside out from the gas introducing hole 3 to prepare the desired impact absorbing bag. Example 3 Figures 6 to 8 are plan views showing other examples of the continuous body of the impact absorbing bag of the present invention. In Examples 1 and 2, a single row of continuous bodies of a seamless tubular woven fabric 1 was obtained and the impact absorbing bag prepared from the same, but by providing a connecting portion B1 at not only the two edges, but also the width at the intermediate portion with the two edges in the tubular weaving step, it is possible to obtain two rows of continuous bodies as shown in Fig. 6. It is also possible to prepare impact absorbing bags similarly from such two rows of continuous bodies. The two rows of continuous bodies in Fig. 7 are prepared by just repeating a necessary number of times just the step of tubular weaving wherein the length is changed in the widthwise direction of the non-connecting portion B2. The continuous body of Fig. 8 was prepared by making the non-connecting portion B2 of the tubular weave structure B a deformed circle in shape. Industrial Utility The impact absorbing bag of the present invention, housed in the center portion of the steering wheel, is useful for the object of instantaneous inflation when sensing an impact of collision of the car and ensuring driver safety. It may be used not only for the object of ensuring driver safety, but also for the object of ensuring the safety of the passengers in the front passenger seat and rear passenger seats.

Claims: An impact absorbing bag formed from a flat, seamless tubular fabric (1) comprising warp and weft yams, the fabric (1) being obtained by segment cut of a continuous body having a plurality of large, hollow portions circumferentially surrounded by a stitched portion and periodically formed along the warp yarn direction, a polymer covering layer (2) provided on at least one portion of a surface of the fabric (1) before or after segment cut of the continuous body, and a gas introducing hole (3) formed in the hollow portion at one side of the fabric (1); characterised in that the fabric (1) is constituted with a hollow and substantially circular-shaped central zone and a ring-like, stitched circumferential zone around the central zone. An impact absorbing bag according to claim 1, wherein at least one strand or strip capable of limiting the inflation of the bag is provided inside the impact absorbing bag between the front of the bag, as seen from the driver's or passenger's position, and the opposite side of the bag. An impact absorbing bag which is formed by turning inside-out the impact absorbing bag according to claim 1 or claim 2 by pulling the inside of the said bag out through the gas introducing hole (3). A method for manufacturing an impact absorbing bag, comprising: (i) a step of obtaining a flat, seamless tubular fabric (1) which comprises conducting tubular weaning using a plurality of warp threads with a weft thread according to a tubular weave method to form a continuous body having rows of a plurality of large, hollow portions circumferentially surrounded by a stitched portion and periodically along the warp yarn direction, followed by segment cutting of the continuous body, (ii) a step of forming a polymer layer (2) on at least a portion of a surface of the fabric (1) before or after segment cut of the continuous body, and (iii) a step of providing a gas introducing hole (3) in the hollow portion at one side of the fabric (1) before or after step (ii); characterised in that the tubular weaving in step (i) is conducted in a manner that the length in the widthwise direction of a non-connecting portion (B2) of a tubular weave structure is gradually changed, to form rows of a plurality of large, hollow and substantially circular-shaped portions periodically along the warp yarn direction and a stitched portion is formed between two adjacent large, hollow portions, and the segment cutting of the continuous body in step (i) is conducted in a manner that the circular-shaped portions are cut along a portion slightly apart from the circumferential edge of the circular-shaped portions to form the fabric (1) constituted with a hollow and substantially circular-shaped central zone and a ring-like, stitched circumferential zone around the central zone. A method for manufacturing an impact absorbing bag including a step of turning the bag obtained according to claim 4 inside out by pulling out an inner side of the bag through the gas introducing hole (3). Use in the manufacture of an impact absorbing bag of a flat, seamless, tubular fabric (1) comprising warp and weft yarns, the fabric (1) being obtained by segment cut of a continuous body having a plurality of large, hollow portions circumferentially surrounded by a stitched portions and periodically formed along the warp yarn direction, a gas introducing hole (3) formed in the hollow portion at one side of the fabric (1); characterised in that the fabric (1) is constituted with a hollow and substantially circular-shaped central zone and a ring-lire, stitched circumferential zone around the central zone.

Inventors: KITAMURA, ATSUSHI
Applicants: ASAHI KASEI KOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: B60R21
IPC codes: D03D1, B60R21, B32B3, D03D11