Air bag made of resin

Abstract: An air bag made of thermoplastic urethane resin. In the air bag, the thermoplastic urethane resin has properties presented in the following table with the values indicated in the table measured by the testing method indicated in the table.

Description: FIELD OF THE INVENTION The present invention relates to an air bag of an air bag device installed into a motor vehicle to protect a vehicle occupant when the vehicle comes into collision and, more particularly, to an air bag made of thermoplastic urethane resin. DESCRIPTION OF THE RELATED ART An air bag device for a driver (hereinafter, referred to as the "driver air bag device") installed in the center of a steering wheel comprises a retainer, an air bag attached to the retainer, a gas generator (inflator) for deploying the air bag, and a module cover for covering the air bag. When the vehicle comes into collision, the inflator generates gases and the air bag is then deployed into the vehicle cabin while breaking the module cover. A conventional air bag used in the driver air bag is made of fabrics and has a circular front panel and a circular rear panel having a center opening into which an inflator is inserted. The front panel and the rear panel are sewn together around the peripheries thereof. As for an air bag device for an occupant in a passenger seat (hereinafter, referred to as the "passenger air bag device") which is mounted in an instrument panel, an air bag and an inflator are installed in a container and a module cover is placed in such a way as to cover an opening of the container. The module cover is also called the "lid" or the "deployment door". In a collision of a vehicle, the inflator is actuated to deploy the air bag. The module cover is then pushed by the deploying air bag to open up into the vehicle cabin. Then, the air bag is deployed fully into the vehicle cabin. A conventional air bag used in the passenger air bag device is also made of fabrics. An air bag made of thermoplastic urethane resin such as thermoplastic polyurethane is disclosed in Japanese Patent Laid-Open No. 4-266544 (the asignee: BASF). An air bag made of fabric has disadvantages of requiring more processing steps and extra cost for sewing the panels, while the air bag made of thermoplastic urethane resin disclosed in Japanese Patent Laid-Open No. 4-266544 is simple in terms of its fabrication owing to the use of fusion instead of sewing. However, the air bag made of thermoplastic urethane resin has a problem to be solved that the air bag is not capable of being satisfactorily and quickly deployed in a wide temperature range of an extreme low degree to a high degree (for example, -40°C to +100°C). OBJECT AND SUMMARY OF THE INVENTION The object of the present invention is to solve the problem of the conventional air bag made of thermoplastic urethane resin and to provide an air bag made of thermoplastic urethane resin capable of being efficiently and quickly deployed at the ambient temperature ranging from an extreme low degree to a high degree. . In the air bag made of thermoplastic urethane resin of the present invention, the thermoplastic urethane resin has properties presented in Table 1 with the values indicated in Table 1 measured by the testing method indicated in Table 1. items testing method values hardness (Shore scale A) JIS K 7311 88 - 92 tensile strength (kg/cm 2 ) JIS K 7311 400 or more breaking elongation (%) JIS K 7311 400 or more 100% modulus (kg/cm 2 ) JIS K 7311 70 or more 300% modulus (kg/cm 2 ) JIS K 7311 150 or more tearing strength (kg/cm) JIS K 7311 75 or more pour point (°C) Flow Tester 182 - 188 melting viscosity (Pas/190°C) Flow Tester 2.5 - 45 × 10 5 It is known that thermoplastic urethane resin is preferable as material of the air bag. However, the known thermoplastic urethane resin has the property of crystallizing at a low temperature so as to be easy to destroy and of softening at a high temperature so as to reduce its strength. Conventionally, there is no material satisfying the requirements of deploying at the ambient temperature ranging from -40°C to +100°C. After various examinations with regard to thermoplastic urethane resin, the inventors have accomplished this invention upon discovering that the air bag made of the thermoplastic urethane resin having the aforementioned properties satisfactorily quickly deploys in a wide temperature range -40°C to +100°C. In the air bag made of thermoplastic urethane resin of the present invention, the resin having A-scale Shore hardness of less than 88 is not able to provide satisfactory efficiency at a high temperature, while the resin having A-scale Shore hardness of more than 92 makes the air bag too hard to be folded and is then unable to provide satisfactory efficiency at a low temperature. The resin having tensile strength of less than 400 kg/cm 2 is unable to provide satisfactory strength at a high temperature so that the air bag of this resin breaks during deploying at a high temperature. The resin having breaking elongation, one of indications for the fragility of the film, of less than 400% easily allows the film to break at a low temperature so that the air bag of the resin is unable to withstand the deployment at a low temperature. The resin having 100% modulus of less than 70 kg/cm 2 is unable to allow the air bag to hold the necessary inner pressure so that the air bag of this resin can not receive the occupant. The resin having 300% modulus of less than 150 kg/cm 2 allows the air bag to be elongated during the deployment at a high temperature so that the deployment configuration is quite disorganized. Therefore, it is not preferable. The resin having tearing strength of less than 75 kg/cm easily allows the air bag to break during the deployment. The resin having a pour point of less than 182°C is unable to provide satisfactory efficiency at low and high temperatures, while the resin having pour point of more than 188°C makes the hardness high and is then unable to provide satisfactory efficiency at a low temperature. The resin having melting viscosity of less than 2.5 × 10 5 Pas/200°C is unable to provide satisfactory efficiency at low and high temperatures, while the resin having melting viscosity of more than 45 × 10 5 Pas/200°C makes the hardness high and is then unable to provide satisfactory efficiency at a low temperature. In the above description, the high temperature means from +80°C to +100°C and the low temperature means from -40°C to -30°C. The air bag of the present invention is preferably manufactured upon making a film or sheet from thermoplastic urethane resin pellet having properties indicated in Table 2 by T-die extrusion or manufactured by blow molding. items testing method values hardness (Shore scale A) JIS K 7311 89 - 93 tensile strength (kg/cm 2 ) JIS K 7311 300 or more breaking elongation (%) JIS K 7311 400 or more 100% modulus (kg/cm 2 ) JIS K 7311 75 or more 300% modulus (kg/cm 2 ) JIS K 7311 140 or more tearing strength (kg/cm) JIS K 7311 90 or more pour point (°C) Flow Tester 192 - 198 melting viscosity (Pas/200°C) Flow Tester 2.5 - 25 × 10 5 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing an embodiment of a driver air bag to which the present invention is applied; Fig. 2 is a perspective sectional view with main parts of the driver air bag of Fig. 1 enlarged; and Fig. 3 is a perspective view showing an embodiment of a passenger air bag to which the present invention is applied. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Fig. 1 is a sectional view showing an embodiment of a driver air bag to which the present invention is applied, and Fig. 2 is a perspective sectional view with the main parts of the driver air bag enlarged. Fig. 3 is a perspective view showing an embodiment of a passenger air bag to which the present invention is applied. The driver air bag 1 shown in Figs. 1 and 2 is made of thermoplastic urethane resin films and comprises a circular front panel 2 and a circular rear panel 3 having a central opening 3A into which an inflator (not shown) is inserted. The periphery 2a of the front panel 2 and the periphery 3a of the rear panel 3 are fused together (reference numeral 4 designates the fused part in Fig. 1). Around the periphery of the opening 3A of the rear panel 3, films 5 made of polyimide resin having higher heat resistance than thermoplastic urethane resin are fused to the outer surface and the inner surface of the rear panel 3. The method used for fusing may be heat sealing, impulse sealing, or high-frequency sealing. In Figs. 1 and 2, reference numeral 3B designates vent holes, and 5A and 3C designate fixing holes formed in the films 5 and the rear panel 3 for attaching the air bag to the inflator (not shown). The highly heat-resistant film which is attached to the inner surface of the rear panel around the periphery of the opening may be silicone resin, fluororesin such as PFA, polyphenylenesulfide resin, polyamideimide resin, aramid resin, polyparabanic acid resin, polysulfone resin, amorphous polyallylate resin, polyethersulfone resin, polyetherimide resin, polyethylenenaphthalate resin, polyetherketone resin, as well as polyimide resin. The optimum thickness and outside diameter of this type of film depends on the performance of the employed inflator and the physical properties of the film (particularly the pour point and the tearing strength). Usually, it is preferable that the thickness is in a range of 0.02 to 0.1 mm and the width W as shown in Fig. 2 is in a range of 50 to 200 mm. It should be understood that the resin air bag of the present invention is not limited to be applied to a driver air bag device and may be applied to a passenger air bag device, like a passenger air bag 9 (Fig 3) comprising a center panel 6, side panels 7, and an attachment 8 for a container (not shown). Reference numeral 7A designates a vent hole, and 8A designates fixing holes for attaching the passenger air bag 9 to the container. It should be noted that the passenger air bag 9 is also easily manufactured by fusing the center panel 6 with the side panels 7. The aforementioned air bags are manufactured upon making a film or sheet of resin by T-die extrusion, then cutting the film or sheet into predetermined configurations and fusing the cut films or sheets. The resin air bag of the present invention may be formed by blow molding. However, it needs special attention to forming the air bag by blow molding from thermoplastic urethane resin having properties indicated in Table 1. Because the thermoplastic urethane resin with the properties of Table 2 has hygroscopicity, a dry environment is necessary to perform extrusion of the thermoplastic urethane resin. Particularly in case of blow molding, the reduced degree of viscosity due to the moisture in the resin easily causes draw down. To prevent the draw down, it is preferable that the resin pellets are dried more than 2 hours at 80°C. In normal blow molding, an accumulator head is employed in parison molding. However, since the resin with the properties of Table 2 is easily deteriorated by heat in the accumulator, a direct blowing machine or an injection molding machine is preferably employed. To prevent the deterioration while efficiently melting and kneading the resin, the L/D of the extruding machine is preferably between 20 and 26 and the compression ratio is preferably between 3.0 and 3.5. The temperature of the resin extruded from the head is preferably its pour point + 10°C or less. The higher temperature of the resin easily causes draw down, thereby making the molding impossible. The blowing pressure is preferably between 290 and 590 kPa. The temperature of the mold is preferably between 20 and 60°C. The lower temperature of the mold easily produces mottles while the higher temperature easily makes the resin adhere to the mold. The air bag formed by the blow molding as mentioned above is characterized in that there is no reduced strength due to the sealed portion of the air bag formed by heat sealing and no different thickness around the periphery of the sealed portion. Turning to some embodiments, the present invention will now be described in more detail. (Embodiments 1 - 3, Comparative Examples 1 - 9) Driver air bags as shown in Fig. 1 have been made of thermoplastic urethane resin films having properties indicated in Table 1, respectively, by heat sealing. Each of the driver air bags is provided with, as the highly heat-resistant film, a polyimide resin film having a thickness of 0.1 mm and a width of 200 mm attached on the inner surface of the air bag and a polyimide resin film having a width of 50 attached on the outer surface of the air bag. The results of inflation tests with the respective air bags thus formed are presented in Table 4. In this table, mark "E" indicates a large breakage, "F" indicates a small breakage, and "G" indicates no breakage. As seen from Table 3, in the air bags of the present invention, the breakage is securely prevented in a wide temperature range of -40°C to +100°C. As described above, the present invention can provide an air bag made of thermoplastic urethane resin which is capable of efficiently protecting the occupant in the wide temperature range of an extreme low degree to a high degree as -40°C to +100°C.

Claims: An air bag made of thermoplastic urethane resin, wherein said thermoplastic urethane resin has a hardness (Shore scale A) of 88 to 92 measured by JIS K-7311, a tensile strength of 400 kg/cm 2 or more measured by JIS K-7311, a breaking elongation of 400 % or more measured by JIS K-7311, a 100% modulus of 70 kg/cm 2 or more measured by JIS K-7311, a 300% modulus of 150 kg/cm 2 or more measured by JIS K-7311, a tearing strength of 75 kg/cm or more measured by JIS K-7311 a pour point of 182°C to 188°C measured by Flow Tester, and a melting viscosity of 2.5 × 10 5 Pas/190°C to 45 × 10 5 Pas/190°C measured by Flow Tester.

Inventors: HIRAI KINJI, TOMITA HIROSHI, TSUJI ATSUSHI, HIRAI, KINJI, TOMITA, HIROSHI, TSUJI, ATSUSHI
Applicants: TAKATA CORP, TAKATA CORPORATION
Application year: 1995
Main classification: B60R21
IPC codes: C08L75, B60R21, B29D22, B29K75