EP1110929A1

EP1110929A1 - Gas generator composition

Info

Publication number: EP1110929A1
Application number: EP99921250A
Authority: EP
Inventors: Kenjiro Himeji Factory of Nippon Kayaku K.K IKEDA; Eishi Himeji Factory of Nippon Kayaku K.K. SATO; Makoto Himeji Fac. of Nippon Kayaku K.K. IWASAKI; Dairi Himeji Factory of Nippon Kayaku K.K. KUBO; Eiichiro Kobe C.R.L. in Kobe Steel Ltd YOSHIKAWA; Ryo 1-401 Shinonotsubo 1379 MINOGUCHI
Original assignee: Nippon Kayaku Co Ltd
Current assignee: Nippon Kayaku Co Ltd
Priority date: 1999-05-24
Filing date: 1999-05-24
Publication date: 2001-06-27
Also published as: WO2000071491A1; KR20010106408A

Abstract

The object of the present invention is to provide nitrogenous organic compound that is effective for solving the problem of harmfulness of the known metallic azide, to solve the contradictory problems of the generation of harmful gases such as NOx and CO and the slag collecting capability, and further the problem involved in the conventional automatic ignition mechanism at one stroke.

A composition of a gas generating agent of the present invention contains a fuel component, an oxidizing agent and a catalyst component as its main components. The composition comprises 20-45 weight % of aminotetrazole as the fuel component, 50-75 weight % of oxidizing agent, 0.05-5 weight % of molybdenum trioxide as a component of an automatic ignition capability developing catalyst. The oxidizing agent comprises strontium nitrate, and nitrate of alkali metal or barium, or strontium nitrate, and perchlorate of alkali metal or barium, and the strontium nitrate content in the oxidizing agent is in a range of 75 to 95 weight %.

Description

Technical Field

The present invention relates to a gas generating agent for use in an airbag and particularly to a non-azide gas generating agent for use in an airbag. More particularly, the present invention relates to a novel composition of gas generating agent that contains a small quantity of detrimental constituents, such as nitrogen oxide and carbon monoxide, in generated gas and has excellent slag collecting properties and further has automatic ignition capability.

Background Art

An airbag system is a rider protecting system that has been widely adopted in recent years as one of measures to improve safety of the riders in an automobile. The airbag system operates on the principle that a gas producer is operated under control of signals from a sensor detecting a collision, to inflate an airbag between riders and a car body. The gas producer is required to have a capability of producing a required and sufficient amount of clean gas containing no harmful gas in a short time.
On the other hand, the gas generating agents are press-formed into a pellet form for stability to the burning and are required to maintain their initial flammability characteristics over a long time even under various harsh environments. In the event that the pellets or equivalents decay or decrease in strength due to deterioration with age, change of environments and the like, the flammability of the explosive composition will vary from that of the initial design and exhibit an abnormally rapid flammability characteristics. As a result of this, there is a fear that the airbag or the gas producer itself may be broken by the abnormal burning of the gas generating agents in a car collision, to fail in accomplishing the aim of protecting the riders or even cause them injury.
To satisfy those required functions, gas generating agents containing metallic azide (compound), such as sodium azide and potassium azide, as their major components have been used hitherto. These known gas generating agents are widely used in terms of their advantages that they are burnt momentarily; that the component of combustion gas is substantially nitrogen gas only, so that no harmful gas such as CO (carbon monoxide) or NOx (nitrogen oxide) is produced; and that since the burning velocity is little influenced by the environment or the structure of the gas producer, it is easy to design the gas producer. On the other hand, the conventional gas generating agent has the notable problems that the azide produced by the contact with heavy metal has the property of being easily exploded on impact and friction and thus must be handled with the greatest possible caution; that the metallic azide and the metallic azide itself are harmful materials and that they can decompose in the presence of water and acid to produce harmful gas.
As the substitution of metallic azide, gas generating agents containing tetrazoles, azodicarbonamides and other nitrogenous organic compounds as fuel components were proposed by, for example, Japanese Laid-open Patent Publications No. Hei 2(1990)-225159, No. Hei 2(1990)-225389, No. Hei 3(1991)-20888, No. Hei 5(1993)-213687 and No. Hei 6(1994)-80492, No. Hei 6(1994)-239684, No. Hei 6(1994)-298587. Of the various nitrogenous organic compounds, the tetrazoles in particular are thermally stable and have a high proportion of atoms of nitrogen in their molecular structure, and thus have the property of inherently suppressing the production of CO. However, they have the problem of readily producing NOx. So then, as disclosed by Japanese Laid-open Patent Publications No. Hei 2(1990)-225159 and No. Hei 3(1991)-20888, there was proposed a method in which the gas producer is provided with a venturi means to feed air into the combustion gas from outside, so as to reduce the concentration of NOx on the whole. However, this method did not essentially provide complete solution to that problem.
When a nitrogenous organic compound is used as fuel, chlorate, perchlorate or nitrate of alkaline metal or alkaline earth metal is generally used as an oxidizing agent for the nitrogenous organic compound to be burnt. The salts of alkaline metal or alkaline earth metal produce oxides as a result of the burning, and the oxides produced are harmful materials for a human body and environment. Accordingly, the oxides must be converted into slag of an easily collectable form so that it can easily be collected in the gas producer to prevent the oxides from being discharged into the airbag. However, since many of the gas generating agents using the nitrogenous organic compound as fuel have the heat of combustion as high as 2,000-2,500 joule/g or more, the gas generated becomes high in temperature and pressure. As a result of this, the slag which is a by-product made in the burning of the gas generating agents increases in temperature and thus increases in flowability. Because of this, the slag collection efficiency of a filter fitted in a conventional type of gas producer tends to reduce. To increase the slag collection efficiency, the method is conceivable of arranging an increased number of filtering members in the filter to cool and solidify the slag, but such a method has a disadvantage of increasing the size of the gas producer, going against the trend toward the size reduction and weight reduction of the gas producer.
There were proposed various methods in which a slag forming agent is added to efficiently collect the oxides of alkaline metal or alkaline earth metal in the form of the slag that can easily be collected in the filtering part. These proposed methods use substantially the same principle that silicone dioxide or aluminum oxide is added as an acid material or neutral material that can easily react with the oxides of the basic materials to produce the slag and thus are the same in concept as the conventional slag forming methods using the gas generating agents using the metallic azide as the fuel. In other words, the proposed methods are based on the principle that the oxides are converted into silicate or aluminate, so that they are converted into the glassy material of high viscosity and high melt point to be easily collected. Japanese Laid-open Patent Publication No. Hei 4(1992)-265292 discloses the method in which a low temperature slag forming material typified by silicon dioxide and a high temperature slag forming material (e.g. oxides such as alkaline earth metal and transition metals) that produces solid substance having a melting point close to or not less than a reaction temperature are both added, so that high-melting point particles as solid material produced by the combustion reaction are allowed to react with the low temperature slag forming material which is in the melted state and also the particles produced as a result of the reaction are fused together, so as to improve the slag collection efficiency.
Japanese Laid-open Patent Publications No. Hei 4(1992)-265292, No. Hei 5(1993)-117070 and No. Hei 5(1993)-21368 disclose that strontium nitrate is a preferable material as the oxidizing agent having the property of forming the high temperature slag. It is true that the use of strontium nitrate is effective means as far as the property of forming the high temperature slag is concerned. But, the use of strontium nitrate as the oxidizing agent presents the practical problem that no matter how the stoichiometric ratio between the oxidizing agent and the fuel component is varied, the concentration of NOx is not lowered to a desirable level. Japanese Laid-open Patent Publication No. Hei 5(1993)-117070 discloses the method as the countermeasure therefor, according to which chemical additives are used with carbonate of the alkaline metal or alkaline earth metal as fuel component. However, this method leads to increase of cost and also reduction of gasification efficiency of the gas generating agent and thus it is not a desirable method.
On the other hand, when potassium nitrate is used in place of strontium nitrate, it is possible to lower the concentration of NOx to an acceptable level for the human body, but the outflow of the slag increases significantly which is due to a white-smoke-like mist derived from potassium oxide produced from potassium nitrate. As a result, there is the possibility that the airbag may be fused and damaged by the mist or, if the worst happens, the airbag may be staved to burn the riders. For avoidance of this, there was proposed the method that a large amount of slag forming agents of silicon dioxide and the like are added and further the filtering members in the gas producer are increased in thickness. This method can suppress the outflow of slag to a considerable extent, though the slag collecting performance is reduced, as compared with the method using the strontium nitrate. However, this method has a practical problem of increasing the size of the gas producer, going against the trend toward the size reduction and weight reduction of the gas producer.
As mentioned above, the use of strontium nitrate can reduce the outflow of the slag, but it increases NOx over the maximum permissible level. On the other hand, when potassium nitrate is used in place of strontium nitrate to suppress the generation of NOx, the outflow of slag is increased. Thus, it was very difficult to solve this antinomy problem.
Further, as a substitute for conventional stainless steel (SUS), aluminum is in widespread use as a container material of the gas producer, for the purpose of weight saving of the gas producer. In the case of the container made of SUS, because of its excellent strength in high temperature, even when a temperature rise is caused by car fire, incineration of the gas producer or the like, no fracture of the container is caused and the composition of the gunpowder can be burnt out. In the case of the container made of aluminum, since its strength reduces significantly in high temperature, when the gas producer is exposed to flame of the car fire and the like and the composition of the gunpowder loaded in the interior is burnt, it is feared that the container cannot withstand the burning pressure and thus may be broken so that the fragments may be flied off to the surrounding to kill and wound riders and persons around them. Accordingly, it is cited as the required term for the gas producer for use in the airbag that the critical condition of the container, such as the fracture of the container, can be prevented even in such circumstances. To take measures to meet that situation, U.S. PAT. No. 4,561,675 proposed a system for the aluminum container, according to which the gunpowder that ignites automatically at a temperature lower than the temperature at which reduction of strength of aluminum is caused is arranged in close contact with an inner surface of the container. The automatic igniting gunpowder used therein includes nitrocellulose as a major component. Nitrocellulose itself lacks long-term stabilization under high temperature and further may ignite automatically due to that deterioration.
The gunpowder preferably ignites automatically at a temperature of 150-210°C in terms of strength of aluminum. The material that ignites at a temperature lower than that has trouble with long-term stabilization. The disclosure on the automatic ignition composition is given by Japanese Laid-open Patent Publications No. Hei 4(1992)-265289, No. Hei 7(1995)-232989, No. Hei 8(1996)-508972 and No. Hei 8(1996)-511233. However, these publications teach that some structure must be arranged therefor in the interior of the gas producer, as is the case with the above-mentioned U.S. Patent, or the automatic ignition composition is required to be incorporated in igniting charge or transfer charge, thus involving factors to complication in structure and increase in cost. Also, all but Japanese Laid-open Patent Publication No. Hei 8(1996)-508972 use a sensitive chlorate as the oxidizing agent, thus having a possible risk in the manufacturing process. Further, Japanese Laid-open Patent Publication No. Hei 7(1995)-257986 teaches the gas generating agent holding automatic ignition capability in itself, but the composition described therein as an example of this composition contains 70 weight % of inorganic oxide, so that the gasification rate is low, thus having the problem that it is difficult to reduce the size and weight of the gas producer.
It is object of the present invention to solve the problems on the choice of a component of oxidizing agent of the gas generating agent containing nitrogenous organic compound, such as aminotetrazole, in particular, as a fuel component that is effective for solving the problem of harmfulness of the known metallic azide, in other words, the contradictory problems of the generation of harmful gases such as NOx and CO and the slag collecting capability, and further the problem involved in the conventional automatic ignition mechanism at one stroke.
Specifically, it is the object of the present invention to provide a novel composition of gas generating agent that is low in quantity of harmful NOx and CO which are harmful gas components contained in the generated gas, high in gasification rate and small in outflow of the slag and also holds an automatic ignition capability in the gas generating agent itself.

Disclosure of the Invention

The present invention, which aims to solve the above-noted problems, is directed to a composition of a gas generating agent containing a fuel component, an oxidizing agent and a catalyst component as its main components, wherein the composition comprises 20-45 weight % of aminotetrazole as the fuel component, 50-75 weight % of oxidizing agent, 0.05-5 weight % of molybdenum trioxide as an automatic ignition capability developing catalyst (a catalyst for enabling the automatic ignition of the composition of the gas generating agent), the oxidizing agent comprising strontium nitrate, and nitrate of alkali metal or barium, or strontium nitrate, and perchlorate of alkali metal or barium, and the strontium nitrate content in the oxidizing agent is in a range of 75 to 95 weight %. This produces the composition of the gas generating agent that produces a reduced amount of NOx generated and a reduced outflow of slag and also has an automatic ignition capability. The composition of the gas generating agent may comprise, as a substitute for molybdenum trioxide, a molybdenum compound, such as molybdic acid, sodium molybdate and ammonium phosphomolybdate, that produces the molybdenum trioxide by application of heat in a range of 0.05-5 weight % in terms of the molybdenum trioxide.
Hydrotalcites expressed by the followi-ng formula may be mixed into the composition comprising the fuel component, the oxidizing agent and the catalyst component as a binder in a ratio of 2-10 weight % to the total composition and formed as a desirable composition: [M²⁺ _1-xM³⁺ _x (OH)₂] ^x+ [A^n- _x/n • mH₂O] ^x- where M²⁺ represents bivalent metal including Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺;
M³⁺ represents trivalent metal including Al³⁺, Fe³⁺, Cr³⁺, CO³⁺ and In³⁺;
A^n- represents an n-valence anion including OH^-, F^-, Cl^-, NO₃ ^- , CO₃ ^2-, SO₄ ^2-, Fe(CN)₆ ^3-, CH₃COO^-, ion oxalate and ion salicylate; and
x:0<x≦0.33.
Preferably, the hydrotalcites are synthetic hydrotalcite expressed by the chemical formula: Mg₆Al₂(OH)₁₆CO₃ · 4H₂O or pyroaurite expressed by the chemical formula: Mg₆Fe₂(OH)₁₆CO₃ · 4H₂O
Further, it is of preferable that at least one material of metallic nitride or metallic carbide as a slag collector is mixed in the composition in a ratio of 2-10 weight % to the total composition, to improve the slag collecting capability. Also, it is of preferable that at least one material of magnesium stearate, zinc stearate, graphite, boron nitride and molybdenum disulfide is mixed in the composition as a lubricant in a ratio of 0.1-1 weight % to the total composition, to produce improved moldability. The metallic nitride or the metallic carbide may be mixed when either or both of the fuel component and the oxidizing agent is pulverized. In this case, the metallic nitride or the metallic carbide is uniformly dispersed, and as such can produce uniformity of the slag reaction and can serve as an anticaking agent.

Brief Description of the Drawings

FIG. 1 is a schematic sectional view of a gas producer used in an embodiment of the present invention;
FIG. 2 is a graph showing the relation between the time (t) in a 60 liter tank test and the pressure (P) in the tank;
FIG. 3 is a schematic sectional view of an automatic ignition capability test equipment used in an embodiment of the present invention
FIG. 4 is a diagram showing TABLE giving the results of the 60 liter tank test and the automatic ignition capability test; and
FIG. 5 is a diagram showing TABLE giving the results of the automatic ignition performance test.

Best Mode for Carrying out the Invention

In the following, the present invention will be described in detail. A gas generating agent of the present invention has a fundamental structure comprising aminotetrazole as a combustion fuel; mixture of an oxidizing agent for burning the combustion fuel; and molybdenum trioxide for allowing the automatic ignittion capability to develop, as the major components, and further mixes therein hydrotalcites as a binder and other additives as occasion demands.
The description on aminotetrazole used as the fuel component in the present invention will be given first. The aminotetrazoles that may be used include 5-aminotetrazole. The aminotetrazoles have a high proportion of an atom of nitrogen in the molecular structure and have the structure of inherently restraining production of harmful CO gas and also are easy to handle including thermal stability and safety and low in price. Of various nitrogenous organic compounds, the aminotetrazoles are the most preferable material. The aminotetrazole content is preferably between 20 and 45 weight % to the total composition. With the content of not more than 20 weight %, a limited amount of gas is generated, so that an inflating failure of the air bag may possibly be caused. On the other hand, with the content added in excess of 45 weight %, the added amount of oxidizing agent is relatively reduced to cause incomplete combustion and, as a result of this, there is a possible fear that a large amount of harmful CO gas may be generated. Further, in the extreme, there is a possible fear that unburned material may be produced.
Then, the oxidizing agent used in the gas generating agent of the present invention will be described. As mentioned above, the combination of aminotetrazole and strontium nitrate generates increased NOx gas, and the combination of aminotetrazole and potassium nitrate has the contradictory problem that it generates a reduced amount of NOx and an increased slag overflow. From various studies the inventors have found that in the case where strontium nitrate and potassium nitrate are used in combination, when the both are mixed in a specific mixing proportion range, the NOx lowering effect and the outflow slag lowering effect can both be produced of vastly different from the mixing effects which are expected from the additivity of the both. The mixing proportion to the total oxidizing agent is in the range of 75-95 weight % strontium nitrate and 5-25 weight % potassium nitrate. It should be noted that when nitrate of other alkali metals or barium or perchlorate of other alkali metals or barium is used in place of potassium nitrate, a similar effect can be obtained, but potassium nitrate is the most preferable. The oxidizing agent content is preferably in the ratio of 50 to 75 weight % to the total composition of the gas generating agent. With the oxidizing agent content of less than 50 weight %, the amount of oxygen supplied falls short to cause incomplete combustion and thus there is a possible fear that a large amount of harmful CO gas may be generated, or in the extreme, unburned material may be produced, so that an inflating failure of the air bag may possibly be caused. On the other hand, with the oxidizing agent content over 75 weight %, there is a possible fear that a short of fuel component may be caused inversely, so that an inflating failure of the air bag may possibly be caused, as is the case with the former case.
Then, the composition of an automatic ignition capability manifesting catalyst used in the present invention will be described below. The study was made on whether or not the automatic ignition capabilities are produced by adding various kinds of metallic oxides, metallic sulphide and metallic powder to the compositions of aminotetrazoles and strontium nitrates and potassium nitrates. This study showed astonishingly that only molybdenum trioxide has the property of manifesting the automatic ignition capability. The study also showed that even an addition of a very small quantity of 0.05 weight % of molybdenum trioxide developed the automatic ignition capability and that the capability was kept substantially unchanged in the range of 0.05 weight % to 5 weight %. Thus, the molybdenum trioxide is preferably added as the automatic ignition capability developing catalyst in the range of 0.05 weight % to 5 weight %. With a less than 0.05 weight % addition, no automatic ignition capability develops, while on the other hand, with a more than 5 weight % addition, the tendency of decreasing the gasification rate develops.
Also, the inventors checked to see whether or not the automatic ignition capability develops in combination of the molybdenum trioxide and other fuel components. It was found therefrom that the automatic ignition capability was not developed when nitroguanidine, dicyandiamide and azodicarbonamide were used as the fuel components and that the automatic ignition capability was best developed when combination of strontium nitrate and potassium nitrate was used as the oxidizing agent. Though the automatic ignition capability was found to develop in the combination of nitrate or perchlorate of other alkali metals or barium and strontium nitrate, the automatic ignition capability was not found to develop when strontium nitrate was used singly. It can be said from this that the molybdenum trioxide is a peculiar catalyst that manifests the automatic ignition capability only when it is combined with aminotetrazole of the fuel component and strontium nitrate and nitrate or perchlorate of alkali metals or barium.
As a substitute for molybdenum trioxide, the molybdenum compounds that produce molybdenum trioxide at 180°C or less which is less than a deterioration temperature of aluminum, such as molybdic acid, sodium molybdate, and ammonium phosphomolybdate, may be used to obtain the automatic ignition capability. Those molybdenum compounds may be used in the present invention. When the molybdenum compounds are added as a substitute for the molybdenum trioxide, the addition should preferably be in the range of 0.05 weight % to 5 weight % in terms of the molybdenum trioxide produced.
Then, the description on the composition of other additives used in the present invention will be given. One of the additives used in the present invention covers metallic nitride or metallic carbide as the slag collector. The description on the metallic nitride will be described, first. The other additives used in the present invention include metallic nitride as the slag collector. At least one material selected from the group consisting of silicon nitride (Si₃N₄), boron nitride (BN), aluminum nitride (AlN), magnesium nitride (Mg₃N₂), molybdenum nitride (Mon/Mo₂N), tungsten nitride (WN₂/W₂N,W₂N₃), potassium nitride (Ca₃N₂), barium nitride (Ba₃N₂), strontium nitride (Sr₃N₂), zinc nitride (Zn₃N₂), sodium nitride (Na₃N), copper nitride (Cu₃N), titanium nitride (TiN), manganese nitride (Mn₄N), vanadium nitride (VN), nickel nitride (Ni₃N/Ni₃N₂), cobalt nitride (CoN/Co₂N/Co₃N₂), iron nitride (Fe₂N/Fe₃N/Fe₄N), zirconium nitride (ZrN), chromium nitride (CrN/Cr₂N), tantalum nitride (TaN), niobium nitride (NbN), cerium nitride (CeN), scandium nitride (ScN), yttrium nitride (YN) and germanium nitride (Ge₃N₄) may be used as the metallic nitride. Of the metallic nitrides mentioned above, sodium nitride (Na₃N) is a compound fundamentally different from sodium azide (NaN₃) that have been used as the fuel of the gas generating agent so far. The metallic nitrides defined in the present invention do not cover the sodium azide.
Of these compounds, silicon nitride, boron nitride, aluminum nitride, molybdenum nitride, tungsten nitride, titanium nitride, vanadium nitride, zirconium nitride, chromium nitride, tantalum nitride, and niobium nitride, which are called fine ceramics, are used as heat-resistant materials which are thermally stable and high resistant, but they have the property of burning in high-temperature oxidizing atmospheres, as is the case with the other metallic nitrides. In the present invention, the slag forming and the gas generation are both provided through the use of their burning property. For example, in the case of silicon nitride, nitrogen gas, silicate and oxygen are produced by the reaction with the strontium nitrate as expressed by the following reaction formula (1). 2Si₃N₄+6Sr(NO₃)₂→6SrSiO₃+10N₂+9O₂
The nitrogen gas produced is discharged into the airbag together with nitrogen gas and carbon dioxide produced by the burning of the fuel components, so as to be effectively used for the inflation of the airbag, and the oxygen gas is used for the burning of the fuel components.
The reaction formula of Si₃N₄ of two molecules and Sr(NO₃)₂ of six molecules is expressed by the formula (1) for convenience of explanation, but actually, since the strontium nitrate added as the oxidizing agent is overwhelmingly larger in amount than the silicon nitride added to collect the slag, though the formula as expressed above can be partly established stoichiometrically, it is probable that strontium silicate shown in the general formula as expressed by the following formula (3) is produced on surface layers of particles of strontium oxide produced by the decomposition of the strontium nitrate as expressed by the following formula (2). 2Sr(NO₃)₂→2SrO + 2N₂+ 5O₂ SrO+SrSiO₃→Sr_xSiO_y (where (x, y)=(2, 4), (3, 5); the coefficient in the reaction formulas is omitted).
The strontium oxide produced by the decomposition of strontium nitrate is oxide having a high melt point (2,430°C), which is produced in the form of fine solid particles in the combustion process in the gas producer. Various silicates having a melt point of around 1,600°C are formed on surfaces of the particles in accordance with the reaction formulas (1) and (3) given above. The silicates are put in the melted state with high viscosity under environmental reaction temperature, so the particles are melted and aggregated into large particles, so that they are easily collected with the filtering members in the gas producer.
In the case where the metallic nitride is aluminum nitride (AlN), the formulas (1) and (3) are rewritten as the following. It is noted that the coefficient of the formula (5) is omitted. 2AlN+Sr(NO₃)₂→Sr(AlO₂)₂+2N₂+O₂ SrO+Sr(AlO₂)₂→Sr_x(AlO₂)_y
The aluminate produced herein also forms a slag layer of high viscosity on the solid slag (SrO), as is the case with the silicate, so that the fine particles are melted and aggregated to form the slag of such a form as to be easily collected with the filtering members.
The metallic nitride is preferably added in the ratio of 0.5 to 10 weight % to the total composition of the gas generating agent. With a less than 0.5 weight % metallic nitride, the expected slag collecting effect cannot be produced. On the other hand, with a more than 10 weight % metallic nitride, the amount of fuel and oxidizing agent added is limited, so that there is the possibility of short amount of gas generated or incomplete combustion. The finer the particle size of the particles, the more the effect is produced. Accordingly, it is preferable that the metallic nitride is of not more than 5 µ m, or preferably not more than 1 µ m, in a 50% average particle diameter of number of reference. It is noted that the 50% average particle diameter of number of reference is a measurement by which a size distribution is expressed on the basis of number: when the total number of particles is taken as 100, the particle size obtained when the particles integrated from the smaller number reach 50 is called the 50% average particle diameter of number of reference. When a small amount of the fine particles of the metallic nitride are added in the pulverizing process of the fuel components and the components of the oxidizing agent, they act as an anticaking agent of the pulverized components and also they can be uniformly dispersed in the oxidizing agent and fuel, so that uniformity of the slag reaction can also be expected. The metallic nitride may be used in combination with powdered silica of the fine powder of silica dioxide when the metallic nitride is used as the anti-caking agent.
The use of the metallic nitride for the gas generating agent is described, for example, by Japanese Patent Publication No. Hei 6(1994)-84274. However, the gas generating agent disclosed therein uses aluminum nitride, boron nitride, silicon nitride or transition metallic nitride as a substitute for the metallic azide and it is disclosed that the metallic nitrides are used as the fuel components. Hence, this prior art is fundamentally different in concept from the present invention disclosing that the metallic nitride is used for the purpose of improving the slag collecting property.
Then, the description on the metallic carbide used as the slag collector in the present invention, as is the case with the metallic nitride, will be given. At least one material selected from the group consisting of silicon carbide (SiC), boron carbide (B₄C), aluminum carbide (Al₄C₃), magnesium carbide (MgC₂/Mg₂C₃), molybdenum carbide (MoC/Mo₂C), tungsten carbide (WC/W₂C), potassium carbide (CaC₂), barium carbide (BaC₂), strontium carbide (SrC₂), zinc carbide (ZnC₂), sodium carbide (Na₂C₂), copper carbide (Cu₂C₂), titanium carbide (TiC), manganese carbide (Mn₃C), vanadium carbide (VC), nickel carbide (Ni₃C), cobalt carbide (Co₂C,CoC₂), iron carbide (Fe₂C/Fe₃C), zirconium carbide (ZrC), chromium carbide (Cr₃C₂/Cr₇C₃/Cr₂₃C₆), tantalum carbide (TaC), niobium carbide (NbC), cerium carbide (CeC₂), scandium carbide (ScC₂), yttrium carbide (YC₂) and germanium carbide (GeC) may be used as the metallic nitride.
Of these compounds, silicon carbide, boron carbide, molybdenum carbide, tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, chromium carbide, tantalum carbide, and niobium carbide, which are called fine ceramics, are used as heat-resistant materials which are thermally stable and high resistant, but they have the property of burning in high-temperature oxidizing atmospheres, as is the case with the other metallic carbides. In the present invention, the slag forming and the gas generation are both provided through the use of their burning property. For example, in the case of silicon carbide, carbon dioxide gas and silicate are produced by the oxidation reaction as expressed by the following reaction formula (6). 2SiC + 2Sr(NO₃)₂→2SrSiO₃ + 2CO₂ + 2N₂ + O₂
The carbon dioxide gas and nitrogen produced are discharged into the airbag together with the nitrogen gas, carbon dioxide gas and vapor produced by the burning of the fuel components, so as to be effectively used for the inflation of the airbag, and the oxygen is used for the burning of the fuel components.
On the other hand, the by-product, silicate, is allowed to react with SrO produced as the combustion residue by the decomposition of strontium nitrate, as expressed by the reaction formulas (3), (5) given above, to form the slag of high viscosity, so as to be easily collected with the filtering members in the gas producer, as is the case with the above-mentioned case. In this stage, the SrO produced as the combustion residue produces strontium carbide by the reaction with the carbon dioxide gas produced as expressed by the reaction formula (6) given above, as expressed by the following reaction formula. SrO+CO₂→SrCO₃
The strontium carbide thus produced is also brought into the melted state with high viscosity at around 1,500°C, as is the case with the strontium silicate, and accordingly it operates so that the strontium carbide of high viscosity is formed on the surface of solid strontium oxide of high-melt-point particle so that the fine particles of combustion residues can be melted and aggregated to be easily collected with the filtering members in the gas producer.
The metallic carbide is preferably added in the ratio of 0.5 to 10 weight % to the total composition of the gas generating agent, as is the case with the metallic nitride. With a less than 0.5 weight % metallic carbide, the expected slag collecting effect cannot fully be produced. On the other hand, with a more than 10 weight % metallic carbide, the amount of fuel and oxidizing agent added is limited, so that there is the possibility of short amount of gas generated or incomplete combustion. Further, the finer the particle size of the particles, the more the effect is produced. Accordingly, it is preferable that the metallic carbide is of not more than 5 µ m, or preferably not more than 1 µ m, in a 50% average particle diameter of number of reference. When a small amount of the fine particles of the metallic carbide are added in the pulverizing process of the fuel components and the components of the oxidizing agent, they act as an anti-caking agent of the pulverized components and also they can be uniformly dispersed in the oxidizing agent and fuel, so that uniformity of the slag reaction can also be expected. The metallic carbide may be used in combination with powdered silica of the fine powder of silica dioxide when the metallic carbide is used as the anti-caking agent. This enables the slag collection efficiency to be further improved, as mentioned above. The metallic carbide may, of course, be used in combination with the metallic nitride mentioned above.
Then, the other additives that may be used in the present invention include hydrotalcites expressed by the following general formula as the binder. [M²⁺ _1-xM³⁺ _x (OH)₂] ^x+ [A^n- _x/n • mH₂O] ^x- where M²⁺ represents bivalent metals including Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺;
M³⁺ represents trivalent metals including Al³⁺, Fe³⁺, Cr³⁺, CO³⁺ and In³⁺;
A^n- represents n-valence anions including OH^-, F^-, Cl^-, NO₃ ^-, CO₃ ² ^-, SO₄ ^2-, Fe(CN)₆ ^3-, CH₃COO^-, ion oxalate and ion salicylate; and
x: 0<x≦0.33.
The hydrotalcites, which are a porous material having water of crystallization, are very useful as a binder for a gas generating agent of nitrogenous organic compound. As described in detail by the applicant's earlier application of Japanese Patent Application No. Hei 8-277066, the gas generating agent containing the hydrotalcites as the binder can provide a degree of hardness (25-30kg) much higher than a degree of hardness of 10-15kg (Monsant type hardness meter) of a pellet of a general type of azide base gas generating agent even in a low pelletizanon pressure, particularly when the aminotetrazole is used as the main component of the fuel composition. This seems to be because the hydrotalcites have the common property of being liable to absorb moisture and that property serves to firmly bind the components of the composition. Also. the pellets using this binder keep their characteristic and flammability characteristic unchanged against the thermal shock caused by temperature being raised and fallen repeatedly, thus enabling the pellets to be minimized in deterioration with age after practical installation on a vehicle. to be very stable in properties.
Typical of the hydrotalcites are synthetic hydrotalcite expressed by the chemical formula of Mg₆Al₂(OH)₁₆CO₃ • 4H₂O or pyroaurite expressed by the chemical formula of Mg₆Fe₂(OH)₁₆CO₃ • 4H₂O. The synthetic hydrotalcite is of preferable in terms of availability and costs.
In the combustion of the gas generating agent, for example the synthetic hydrotalcite of the hydrotalcites decomposes as expressed by the following reaction formula and thus produces no harmful gas. Also. the reaction itself is an endothermic reaction, thus providing an advantageous effect of reducing the heat value. Mg₆Al₂(OH)₁₆CO₃•4H₂O→6MgO+Al₂O₃+CO₂+12H₂O
Further, the MgO and Al₂O₃ obtained by the decomposition reaction are high-melt-point oxides of the metallic compound having the slag forming property and are allowed to react with silicate of the metallic components (e.g. Sr_xSiO_y) contained in the nitride or carbide, as expressed by the following formula, to form glassy double salt of silicate of magnesium that can be easily filtered with the filtering members to be collected as the slag. MgO+Sr_xSiO_y→MgO • Sr_xSiO_y
In addition, the decomposition product itself of the synthetic hydrotalcite forms spinel that can be easily filtered by the slag reaction of the acid base reaction expressed by the following formula. MgO+Al₂O₃→MgAl₂O₄
When the hydrotalcites are added as the binder, they are contained in the ratio of 2 to 10 weight % to the total composition of the gas generating agent. With the hydrotalcites content of less than 2 weight %, the function as the binder is achieved with difficulty. On the other hand, with the hydrotalcites content of more than 10 weight %, the amount of the other components added is reduced, such that the function as the composition of the gas generating agent is achieved with difficulty. The hydrotalcites are preferably added particularly in the range of 3 to 8 weight %.
In general, the gas generating agents are press-formed into a pellet form or a disk-like form having a diameter of 4-10mm and thickness of 2-5mm or proper size, for their intended use. For the purpose of providing improved fluidity of powder or granules in the molding, lubricant, such as stearic acid, zinc stearate, magnesium stearate, calsium stearate, aluminum stearate, molybdenum disulfide, graphite, and boron nitride is preferably added in the ratio of 0.1 to 1 weight % to the total gas generating agent. This enables further improvement of the moldability.
The gas generating agents thus formed are heat-treated at 100-120°C for about 2 to about 24 hours after formed to thereby produce the gas generating agents that are resistant to deterioration with age. The heat-treatment is very effective particularly for allowing the gas generating agents to have the property of passing harsh heat and aging tests of 107°C × 400hrs.. The heat-treatment for less than 2 hours is insufficient and that for more than 24 hours will be of meaningless, for the reason of which the heat-treatment time should be selected from the range of 2-24 hours, or preferably 5-20 hours. Also, the heat-treatment at less than 100°C is not effective and that at more than 120°C may cause deterioration rather than improvement, for the reason of which the heat-treatment temperature should be selected from the range of 100-120°C, or preferably 105-115°C.
Then, the description on the preferable combination of the respective components of the present invention will be given. First of all, preferable as the fuel component is 5-aminotetrazole which is material stable and high in safety and have a high proportion of atoms of nitrogen in their molecular structure and, as a result of this, have the properties of decomposing to discharge a large amount of nitrogen gas and also inherently suppressing the production of CO. Preferable as the oxidizing agent is nitrate having the capability of suppressing the generation of NO_x. Particularly, the mixture of strontium nitrate that produces easy-collectable, high-viscosity slag and potassium nitrate that develops the NOx lowering effect and the automatic ignition capability by the combination of aminotetrazole and molybdenum trioxide is optimum. The content of these components is as mentioned above.
Silicon nitride is preferable as the metallic nitride, and carbon nitride is preferable as the metallic carbide. This is because the silicon content produces silicon dioxide in the combustion process and the silicon dioxide thus produced is allowed to react with strontium oxide produced from strontium nitrate or metallic component contained in the hydrotalcites added as the binder to form an easy-collectable, high-viscosity slag. The amount of these components added is as mentioned above.
Most desirable as the binder for binding those particle mixtures to be molded is synthetic hydrotalcite that can produce MgO and Al₂O₃ which are high-melt-point oxides. These are allowed to react with the silicon dioxide produced from silicon nitride or silicon carbide to produce the high-viscosity slag that can be easily collected by the filtering part of the gas producer. Optimum as the lubricant for improving moldability is magnesium stearate. The amount of these components added is as mentioned above.
In the following, the description on the embodiments of the present invention will be given.

[Example 1]

32.2 parts by weight of 5-aminotetrazole used as the fuel component, 53.4 parts by weight of strontium nitrate used as the oxidizing agent, 5.8 parts by weight of potassium nitrate (rate of strontium nitrate content in the oxidizing agent: 90.2 parts by weight), 0.5 parts by weight of molybdenum trioxide used as the catalyst, 3.3 parts by weight of silicon nitride used as the metallic nitride, 4.6 parts by weight of synthetic hydrotalcite used as the binder, and 0.2 parts by weight of magnesium stearate used as the lubricant were formulated and dryblended with a V-type stirring machine. Before the stirring, fine powders of the silicon nitride (0.2 µ m in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile, strontium nitrate and potassium nitrate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The mixture was press-formed with a rotary type tablet making apparatus to obtain the gas generating pellets of 5 mm in diameter, 2.3 mm in thickness and 100 mg in weight. Then, the pellets were heat-treated at 110°C for 10 hours.
46g of the pellets thus obtained were loaded in the test-use gas producer 1 having the structure shown in FIG. 1. The test-use gas producer 1 comprises a central ignition chamber 7 placing therein an igniter 2 and a transfer charge 3; a combustion chamber 8 provided around the ignition chamber and loading therein the gas generating agents 4; and a cooling/filtering chamber 9 provided outside of the combustion chamber and disposing therein a metallic filter 5. The combustion gas is exhausted outside from gas exhausting holes 6 in a housing, passing through the cooling/filtering chamber 9. The 60 liter tank test was carried out by using the gas producer 1. In the 60 liter tank test, the gas producer placed in a high pressure tank having an internal volume of 60 liter is put in action to release the gas in the tank, and changes of the internal pressure with time as shown in FIG. 2 and the quantity of slag flown into the tank are measured. In FIG. 2, an ordinate represents the internal pressure P of the tank; an abscissa represents time t; P₁ represents a maximum range pressure in the tank (Kpa); t₁ represents the time (ms:millisecond) from the power supply to the igniter 2 to the start of operation of the gas producer; and t₂ represents a required time (ms) for the pressure to reach P₁ after the operation of the gas producer. The results of the 60 liter tank test is shown as TABLE 1 in FIG. 4. Further, the automatic ignition capability was tested by use of the pellets of the gas generating agents, the results being also shown in TABLE 1.
In TABLE 1, the outflow of slag is expressed in weight (g) by collecting the solid residues exhausted from the gas discharging holes 6 of the test-use gas producer 1 which is collected from the interior of the tank. The quantity (ppm) of CO and NO_x (including NO and NO₂) which are harmful gas for the human body was determined by analyzing the gas accumulated in the 60 liter tank after the actuation of the gas producer by use of a prescribed gas detecting tube. Further, AI capability means the automatic ignition capability. The test-use gas producer is tested by the method which is called the external flame test, to detect the presence of the automatic ignition capability for the flame. The external flame test is the test in which after the test-use gas producer is put on cumulated timbers and lamp oil is poured to the timbers and is ignited, the gas producer is allowed to stand in the flame for 10-30 minutes to examine on whether or not the gas producer is broken by the burning of the gas generating agents. For the test-use gas producer of this Example, the burning of the gas generating agents was started about 8 minutes later after the timbers were ignited, but the gas producer was not broken, from which it was confirmed that the pellets of the composition of the gas generating agent of Example 1 had the automatic ignition capability.

[Example 2]

32.2 parts by weight of 5-aminotetrazole used as the fuel component, 48.4 parts by weight of strontium nitrate used as the oxidizing agent, 10.8 parts by weight of potassium nitrate (rate of strontium nitrate content in the oxidizing agent: 81.8 parts by weight), 0.5 parts by weight of molybdenum trioxide, 3.0 parts by weight of silicon nitride, 4.9 parts by weight of synthetic hydrotalcite, and 0.2 parts by weight of magnesium stearate were formulated, mixed and formed into pellets in the same manner as in Example 1, to obtain the pellets of the gas generating agent. Before the mixing, fine powders of the silicon nitride (0.2 µ m in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile, strontium nitrate and potassium nitrate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The same test as that of Example 1 was made of the pellets obtained, the results being shown in TABLE 1.

[Example 3]

32.0 parts by weight of 5-aminotetrazole used as the fuel component, 50.4 parts by weight of strontium nitrate used as the oxidizing agent, 9.0 parts by weight of sodium nitrate (rate of strontium nitrate content in the oxidizing agent: 84.3 parts by weight), 0.5 parts by weight of molybdenum trioxide, 3.6 parts by weight of silicon nitride, 4.3 parts by weight of synthetic hydrotalcite, and 0.2 parts by weight of magnesium stearate were formulated, mixed and formed into pellets in the same manner as in Example 1, to obtain the pellets of the gas generating agent. Before the mixing, fine powders of the silicon nitride (0.2 µ m in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile, strontium nitrate and sodium nitrate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The same test as that of Example 1 was made of the pellets obtained, the results being shown in TABLE 1.

[Example 4)

31.6 parts by weight of 5-aminotetrazole used as the fuel component, 53.6 parts by weight of strontium nitrate used as the oxidizing agent, 6.2 parts by weight of potassium perchlorate (rate of strontium nitrate content in the oxidizing agent: 90.5 parts by weight), 0.5 parts by weight of molybdenum trioxide, 4.0 parts by weight of silicon nitride, 3.9 parts by weight of synthetic hydrotalcite, and 0.2 parts by weight of magnesium stearate used as the lubricant were formulated, mixed and formed into pellets in the same manner as in Example 1, to obtain the pellets of the gas generating agent. Before the mixing, fine powders of the silicon nitride (0.2 µ m in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile, strontium nitrate and potassium perchlorate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The same test as that of Example 1 was made of the pellets obtained, the results being shown in TABLE 1.

(Comparative Example 1]

32.2 parts by weight of 5-aminotetrazole used as the fuel component, 59.2 parts by weight of strontium nitrate used as the oxidizing agent (no other oxidizing agents were contained), 0.5 parts by weight of molybdenum trioxide, 3.3 parts by weight of silicon nitride, 4.6 parts by weight of synthetic hydrotalcite, and 0.2 parts by weight of magnesium stearate used as the lubricant were formulated, mixed and formed into pellets in the same manner as in Example 1, to obtain the pellets of the gas generating agent. Before the mixing, fine powders of the silicon nitride (0.2 µ m in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile and strontium nitrate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The same test as that of Example 1 was made of the pellets obtained, the results being shown in TABLE 1.

[Comparative Example 2]

32.2 parts by weight of 5-aminotetrazole used as the fuel component, 30.2 parts by weight of strontium nitrate used as the oxidizing agent, 29.0 parts by weight of potassium nitrate (rate of strontium nitrate content in the oxidizing agent: 51.0 parts by weight), 0.5 parts by weight of molybdenum trioxide, 3.3 parts by weight of silicon nitride, 4.6 parts by weight of synthetic hydrotalcite, and 0.2 parts by weight of magnesium stearate used as the lubricant were formulated, mixed and formed into pellets in the same manner as in Example 1, to obtain the pellets of the gas generating agent. Before the mixing, fine powders of the silicon nitride (0.2 µ m in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile, strontium nitrate and potassium nitrate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The same test as that of Example 1 was made of the pellets obtained, the results being shown in TABLE 1.

[Comparative Example 3]

33.7 parts by weight of 5-aminotetrazole used as the fuel component, 56.6 parts by weight of potassium nitrate used as the oxidizing agent (no strontium nitrate was contained in the oxidizing agent), 0.5 parts by weight of molybdenum trioxide, 4.2 parts by weight of silicon nitride, 4.8 parts by weight of synthetic hydrotalcite, and 0.2 parts by weight of magnesium stearate used as the lubricant were formulated, mixed and formed into pellets in the same manner as in Example 1, to obtain the pellets of the gas generating agent. Before the mixing, fine powders of the silicon nitride (0.2 µm in the 50% average particle diameter of number of reference) were added in advance to the 5-aminotetrazile and potassium nitrate by the amount generally prorated in correspondence with their respective weights. Then, the mixture was pulverized to about 12 µ m in the 50% average particle diameter of number of reference. The same test as that of Example 1 was made of the pellets obtained, the results being shown in TABLE 1.
As seen from TABLE 1, since all Examples and Comparative examples use the same fuel component and select the compositions on the good burning condition, there is little difference therebetween in t₂ and P₁. Similarly, since all of them use 5-aminotetrazole (5-ATZ) as the fuel component which has the property of structurally suppressing the generation of CO, as mentioned above, there is little difference therebetween in CO and also the CO is not in a harmful level for the human body.
Reference is given to strontium nitrate and potassium nitrate used as the oxidizing agent. Comparative example 1 using only the strontium nitrate as the oxidizing agent produces the effect of lowering the outflow of slag but produces NOx of a non-negligible level. On the other hand, Comparative example 3 using only the potassium nitrate as the oxidizing agent produces the effect of suppressing the amount of NOx generated to a low value but shows a high value of the outflow of slag. This shows that the both are in the relation of antinomy, as aforementioned.
Reference is now given to the NOx lowering effect provided by the mixture of strontium nitrate and potassium nitrate used as the oxidizing agent. In Comparative example 3 of the strontium nitrate content of 0 part by weight in the oxidizing agents and the potassium nitrate content of 100 parts by weight in the oxidizing agents, the NOx content reaches the bottom of 80 ppm. In Comparative example 1 of the strontium nitrate content of 100 parts by weight in the oxidizing agents, the NOx content reaches the top of 650 ppm. Referring to Comparative example 2 using the generally half-and-half mixture of the both oxidizing agents, if additivity is held between the mixing ratio of the both oxidizing agents and the amount of NOx generated, Comparative example 2 should show an intermediate NOx generation level of about 360-370 ppm, but actually it shows 120 ppm. It is found from this that the mixture of the both oxidizing agents generates the amount of NOx largely deviating from the expected additivity line and produces the unexpected lowering effect. This can also be seen from Examples 1 and 2 in which even with a high ratio of strontium nitrate content of 80-90 parts by weight in the oxidizing agents, the NOx content is at a level of 150-170 ppm deviating from the additivity line toward a lower concentration of NOx. Similarly, even when sodium nitrate (Example 3) or potassium perchlorate (Example 4) is used in combination with strontium nitrate as the oxidizing agent, the NOx content deviates from the additivity line toward a lower concentration of NOx, which shows that even the combined use of these oxidizing agents produces effectiveness.
Reference is now given to the outflow of slag. Since an adequate amount of silicon nitride is mixed as the slag collector in all Examples and Comparative examples mix, no excessive outflow of slag is found in any of Examples and Comparative examples. So then, the examine is made of the relation between the mixing ratio between strontium nitrate and potassium nitrate in the oxidizing agents and the outflow of slag, as is the case with the case of NOx. In Comparative example 3 of the strontium nitrate content of 0 part by weight (potassium nitrate content of 100 parts by weight) in the oxidizing agents, the outflow of slag reaches the top of 8.0g. In Comparative example 1 of the strontium nitrate content of 100 parts by weight in the oxidizing agents, the outflow of slag reaches the bottom of 1.4g. Referring to Comparative example 2 using the generally half-and-half mixture of the both oxidizing agents, it shows 4.6g that is at an intermediate level between the both. Though it appears that the additivity is held between the mixture of both oxidizing agents and the outflow of slag in this mixture region, the outflow of slag is 1.8-2.2g, deviating from the additivity line toward a reduction of the outflow of slag, in the region in which a ratio of strontium nitrate content in the oxidizing agents is as high as 80-90 parts by weight in Examples 1 and 2. It is confirmed from this that the mixture of the both oxidizing agents produces the unexpected effect on the outflow of slag as well. Similarly, even when sodium nitrate (Example 3) or potassium perchlorate (Example 4) is used in combination with strontium nitrate as the oxidizing agent, the outflow of slag is suppressed to a low value.
For reference's sake, reference will be given to CO. It is found that the combined use of sodium nitrate as the oxidizing agent (Example 3) produces an increased effect of lowering the generation of CO, as compared with the other examples. Also, it is found that the combined use of potassium perchlorate as the oxidizing agent (Example 4) shows the smallest value t₂, thus producing an improved combustion speed with efficiency.
Reference is now given to the automatic ignition performance. In the external flame test, the gas generating agent of Examples 1-3 started to burn within 10 minutes after ignition of the timbers, without breaking the gas producer. The same applied to Comparative examples 2 and 3. On the other hand, in Comparative example 1, the gas producer was exploded with a loud noise and broken in pieces at the point of time after 23 minutes passed from the ignition of timbers. It is found from this fact that only the singular use of strontium nitrate as the oxidizing agent does not provide any automatic ignition performance even in the presence of molybdenum trioxide of the automatic ignition capability developing catalyst and that the automatic ignition capability is produced in the presence of molybdenum trioxide coexistent with any of potassium nitrate, sodium nitrate and potassium perchlorate.

[Automatic ignition performance test)

In the following, various test results on the automatic ignition capability are described. The automatic ignition performance test was performed by using the same composition of the gas generating agent as that of Example 1, i.e., the pellets of the gas generating agent formed in the same manner as in Example 1 by using 32.2 parts by weight of 5-aminotetrazole used as the fuel component, 53.4 parts by weight of strontium nitrate used as the oxidizing agent, 5.8 parts by weight of potassium nitrate, 0.5 parts by weight of molybdenum trioxide used as the component of the automatic ignition capability developing catalyst, 3.3 parts by weight of silicon nitride used as the metallic nitride, 4.6 parts by weight of synthetic hydrotalcite used as the binder, and 0.2 parts by weight of magnesium stearate used as the lubricant, and the pellets of the gas generating agents formed in the same manner as in Example 1 by changing the fuel component (X), the component (Y) combined with strontium nitrate in the oxidizing agents and the catalyst component (Z) of the composition of Example 1 into other component one by one for each component. The results are shown in TABLE 2 in FIG. 5. The components examined are the fuel components (X) including four components of aminotetrazole, nitroguanidine, dicyandiamide and azodicarbonamide; the components (Y) to be combined with strontium nitrate in the oxidizing agent including four components of potassium nitrate, sodium nitrate, barium nitrate, potassium perchlorate and one component not combined therewith; and the catalyst components (Z) including twenty-three components of molybdenum trioxide, iron oxide, tri-iron tetroxide, nickel oxide, vanadium pentoxide, copper oxide, calcium oxide, manganese dioxide, tungsten oxide, chromium oxide, potassium permanganate, molybdic acid, sodium molybdate, ammonium phosphomolybdate, molybdenum disulfide, iron sulfide, zinc sulfide, aluminum, iron, molybdenum, sulfur, activated carbon, and graphite.
The automatic ignition performance test was carried out in the following way. After an oil bath 11 with an automatic temperature control device shown in FIG. 3 was prepared, a bottomed steel pipe 10 having an inner diameter of 2 cm and a length of 20 cm was immersed in silicon oil 14 which can be automatically controlled by a heater 12. Then, one pellet of each kind of gas generating agent was thrown in the steel pipe 10 under stable temperature of the silicon oil 14 of 200±2°C and the time for the pellet to be ignited was measured to confirm the automatic ignition performance. The results of the automatic ignition test shown in TABLE 2 in FIG. 5 are classified by using the mark ○ which indicates that the pellet is ignited within 3 minutes after it is thrown in; the mark Δ which indicates that the pellet is ignited within 5 minutes; and the mark X which indicates all but those results. In FIG. 3, 13 designates a thermometer.
As seen from TABLE 2, the automatic ignition performance is produced only by the combination of the fuel component of aminotetrazole; the oxidizing agent of strontium nitrate and any of potassium nitrate, sodium nitrate, barium nitrate and potassium perchlorate as the component to be combined with the strontium nitrate; and the catalyst component of any of molybdenum trioxide, molybdic acid, sodium molybdate and ammonium phosphomolybdate. For molybdic acid, sodium molybdate and ammonium phosphomolybdate, they are decomposed by the application of heat at 200 °C to produce molybdenum trioxide, for the reason of which it seems that the automatic ignition performance is produced from that point of time. Accordingly, somewhat delay is caused in the ignition time in this combination, when compared with the case of the addition as molybdenum trioxide.

[Effect]

As described above, according to the composition of the gas generating agent of the present invention, the following marked effects can be expected.
(1) Since aminotetrazole that restrains production of harmful CO gas is used for the fuel component, the clean gas having little CO is generated to inflate the airbag, so that the safety for riders is improved.
(2) In the gas generating agent of high gasification efficiency having aminotetrazole and the oxidizing agent as the main components, strontium nitrate is used as the main component of the oxidizing agent and also metallic nitride or metallic carbide is added thereto as the slag collector, thus providing significantly improved collectivity of the slag produced and thus reduced outflow of slag. This enables the airbag to be inflated with clean gas. Further, this enables the filtering members for collecting the slag to be reduced in quantity, thus contributing to the reduction in size and weight of the gas producer.
(3) The metallic nitride or the metallic carbide is decomposed to produce nitrogen gas or carbon dioxide, which contributes to the inflation of the airbag as the gas component effective for the inflation of the airbag. This enables the aminotetrazole content as the fuel component to be saved and, as a result of this, the contribution to the reduction of size and weight of the gas producer can be expected.
(4) A small amount of potassium nitrate, sodium nitrate, barium nitrate or potassium perchlorate is added to the strontium-nitrate-based oxidizing agent to obtain the mixed oxidizing agent. This enables the generation of NOx to be suppressed significantly, though it is hard to suppress the generation of NOx by use of the strontium nitrate only.
(5) Further, a small amount of molybdenum trioxide or the molybdenum component that produces the molybdenum trioxide by the application of heat is added to the composition of the gas generating agent and thereby the gas generating agent can develop the automatic ignition capability in itself without reducing the gasification efficiency. This can eliminate the need to additionally provide the automatic ignition mechanism in the gas producer, as in the prior art, thus enabling a simplified structure of the gas producer and reduction of costs.

Capabilities of Exploitation in Industry

The composition of the present invention is optimum as the composition of the gas generating agent that is low in quantity of harmful NOx and CO which are harmful gas components contained in the generated gas, high in gasification rate and small in outflow of the slag and also holds the automatic ignition capability in the gas generating agent itself.

Claims

A composition of a gas generating agent containing a fuel component, an oxidizing agent and a catalyst component as its main components, wherein the composition comprises 20-45 weight % of aminotetrazole as the fuel component, 50-75 weight % of oxidizing agent, 0.05-5 weight % of molybdenum trioxide as a component of an automatic ignition capability developing catalyst, the oxidizing agent comprising strontium nitrate and nitrate of alkali metal or barium, or strontium nitrate and perchlorate of alkali metal or barium, and the strontium nitrate content in the oxidizing agent is in a range of 75 to 95 weight %.
The composition of the gas generating agent as set forth in Claim 1, which comprises, as a substitute for molybdenum trioxide, a molybdenum compound that produces the molybdenum trioxide by application of heat in a range of 0.05-5 weight % in terms of the molybdenum trioxide.
The composition of the gas generating agent as set forth in Claim 2, wherein the molybdenum compound comprises at least one compound selected from the group consisting of molybdic acid, sodium molybdate and ammonium phosphomolybdate.
The composition of the gas generating agent as set forth in any of Claims 1-3, wherein hydrotalcites expressed by the following formula is added to the composition of the gas generating agent as a binder in a ratio of 2-10 weight % to the total composition and mixed and formed: [M²⁺ _1-xM³⁺ _x (OH)₂] ^x+ [A^n- _x/n • mH₂O] ^x- where M²⁺ represents bivalent metal including Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺;

M³⁺ represents trivalent metal including Al³⁺, Fe³⁺, Cr³⁺, CO³⁺ and In³⁺;

A^n- represents an n-valence anion including OH^-, F^-, Cl^-, NO₃ ^-, CO₃ ^2-, SO₄ ^2-, Fe(CN)₆ ^3-, CH₃COO^-, ion oxalate and ion salicylate; and

x:0<x≦0.33.
The composition of the gas generating agent as set forth in Claim 4, wherein the hydrotalcites are synthetic hydrotalcite expressed by the chemical formula: Mg₆Al₂(OH)₁₆CO₃ • 4H₂O or pyroaurite expressed by the chemical formula: Mg₆Fe₂(OH)₁₆CO₃ • 4H₂O
The composition of the gas generating agent as set forth in any of Claims 1 to 3, wherein at least one material of metallic nitride or metallic carbide as a slag collector is mixed in the composition in a ratio of 2-10 weight % to the total composition.
The composition of the gas generating agent as set forth in Claim 6, wherein the metallic nitride or the metallic carbide is of not more than 5 µ m in a 50% average particle diameter of number of reference.
The composition of the gas generating agent as set forth in Claim 6, wherein the metallic nitride or the metallic carbide is of not more than 1 µ m in a 50% average particle diameter of number of reference and is mixed when either or both of the fuel component and the oxidizing agent is pulverized.
The composition of the gas generating agent as set forth in any of Claims 1 to 3, wherein at least one material selected from the group consisting of magnesium stearate, zinc stearate, graphite, boron nitride and molybdenum disulfide is mixed in the composition as a lubricant in a ratio of 0.1-1 weight % to the total composition.