Metal working – Method of mechanical manufacture – Valve or choke making
Reexamination Certificate
2000-11-03
2001-12-04
Cuda Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Valve or choke making
C280S741000, C073S15000R
Reexamination Certificate
active
06324760
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to an air bag system for protecting a passenger from impacts, and in particular to a gas generator for an air bag which effectively prevents a gas generating agent from absorbing moisture or water vapors in the atmosphere, and has a stable operating capability.
2. Description of the Prior Art
When a motor vehicle, such as an automobile, collides with something at a high speed, passengers in the vehicle may crash into hard or dangerous parts, such as a steering wheel or front glass, inside the vehicles, due to inertia. To prevent the passengers from being injured or killed by such crashes, an air bag system for an automobile has been developed wherein a bag is rapidly inflated by gases generated by a gas generating agent. The gas generating agent suitable for the automobile air bag system is required to satisfy very severe conditions. First, the bag must be inflated in a considerably short period of time, normally within 40 to 50 milliseconds. Gas generating agents generally used at present, which contain alkali metal salt or alkaline earth metal salt of hydrazoic acid, such as sodium azide, as a base, satisfy those conditions, and exhibit excellent characteristics.
Non-azide gas generating agents have also been developed which may replace the agents containing sodium azide as a base. For instance, Japanese laid-open Patent Publication No. 3-208878 discloses compositions containing tetrazole, triazole, or their metallic salts, and an oxygen containing oxidizing agent containing alkali metal nitrate, such as sodium nitrate, as major components. On the other hand, Japanese Patent Nos. 64-6156, 64-6157 disclose a gas generating agent having a metallic salt of bitetrazole compound containing no hydrogen as a major component. Further, Japanese laid-open Patent Publication No. 3-208878 discloses a gas generating agent having a transition metal complex of aminotetrazole as a main component. Many of the above-indicated compositions for the gas generating agent, however, contain oxidizing agents or others which exhibit considerably high degrees of hygroscopic property or deliquescence. Since the amount of water contained in the gas generating agent has a great influence on its burning characteristic, the conventional gas generator employs various methods for preventing the gas generating agent stored therein from absorbing moisture or water vapors. For example, the gas generating agent is contained in a thin, aluminum container, which is air-tightly closed by a lid with a sealing agent, and this container is mounted in the gas generator. This method, however, results in an increased cost, and makes it difficult to reduce the size of the inflator container. To solve this problem, a gas generator having a seal tape attached to its gas discharge ports has been employed, so as to prevent moisture from entering the generator. The seal tape is formed by coating a moisture-proof film with an adhesive, such as a thermosetting adhesive or pressure sensitive adhesive. The use of such a seal tape makes it possible to significantly reduce the cost, and reduce the size of the gas generator. However, this seal tape is not so good in terms of a water vapor permeability, as compared with the above-described moisture-preventing method. Namely, the gas generator to which the seal tape is attached has a portion (side face of the tape) where the interior of the gas generator is shield from the exterior thereof strictly only by the adhesive of the seal tape. However, generally these adhesives contain chemical substances, such as those containing rubber, acrylic, silicone, or polyvinyl ether, as major components, for improving the adhesive strength or shear adhesion, and these chemical substances have relatively high water solubility or water dispersibility, thus allowing more or less water vapors to pass through the portion of the seal tape where only the adhesive is present, into the interior. Thus, the known seal tape cannot completely prevent moisture from entering the generator, and there is a possibility that water vapors permeate through the seal tape when the moisture reaches a certain level.
As described above, the main component of the adhesive generally used in the seal tape contains rubber, acrylic, silicone, or polyvinyl ether having relatively high water solubility or water dispersibility, so as to improve the adhesive strength or shear adhesion. When the seal tape is attached to a housing wall of the gas generator to close gas discharge ports formed therethrough, and left under normal environments, for example, water vapors in the atmosphere are more or less moved through a portion where only the adhesive serves to block the water vapors, and enter the interior of the gas generator. When the seal tape is used for blocking entry of the water vapors, therefore, it is necessary to use a material having an excellent moisture-preventive property, while assuring the bonding and holding functions of the seal tape.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a gas generator for an air bag using a seal tape for preventing water vapors from entering an inflator, so that it is free from the above problems encountered in the prior art.
As a result of diligent studies in an attempt to solve the above problems, the present inventirs surprisingly found that if an opening of the gas generator that communicates with the atmosphere is closed by a seal tape which provides 2.0% or less of increase in the weight of the gas generator due to moisture absorption by its gas generating agent after the generator is left for a while under humidified environments, the seal tape can accomplish moisture-proofing of the gas generating agent, with a significantly small influence on the performance of the gas generator for an air bag. The inventors have reached the present invention based on this finding.
Namely, the present invention relates to a gas generator for an air bag characterized in the tan opening formed through the gas generator to communicate with the atmosphere is closed by a moisture-proof seal tape comprising a substrate and an adhesive, a rate of increase in a weight due to moisture absorption by a gas generating agent stored in the gas generator is not higher than 2.0% when the gas generator is left for 20 days in a constant-temperature, constant-humidity chamber kept at a temperature of 80° C. and a humidity of 90%.
In the gas generator of the present invention, the seal tape is firmly pressed by hand and attached to its inner cylindrical portion or housing to completely close communication holes open to the atmosphere, such as through-holes formed in the inner cylindrical portion, and gas discharge ports formed through the housing. The above-indicated rate of increase in the weight is obtained by measuring the weight of this gas generator after leaving it for 20 days in a constant-temperature, constant-humidity chamber kept at a temperature of 80° C. and humidity of 90%, and calculating a difference between the thus measured weight and the weight measured before it is left in the constant-temperature, constant-humidity chamber, so as to obtain a percentage of this difference with respect to the gas generating agent. In this case, in particular, the rate of increase in the weight is considered as the rate of water-vapor absorption of the gas generator.
Before and after the gas generator of the present invention is subjected to the above-described test, the combustion evaluation of the gas generator was carried out. As a result, a significant difference was not observed between the performance of the gas generator before the humidified-condition test, and that after the test. Thus, the gas generator, in which the seal tape of the present invention prevents moisture from entering the housing, exhibits stable operating capability or performance without being affected by water vapors in the atmosphere.
In particular, the seal tape used in the present invention preferably has a water v
Cuda Rosenbaum I
Daicel Chemical Industries Ltd.
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