Explosive and thermic compositions or charges – Containing free boron or binary compounds of boron or boranes
Reexamination Certificate
2001-11-13
2004-07-20
Carone, Michael J. (Department: 3641)
Explosive and thermic compositions or charges
Containing free boron or binary compounds of boron or boranes
C149S045000, C149S092000
Reexamination Certificate
active
06764562
ABSTRACT:
The function of pyrotechnical gas-generating substances used in air-bag assemblies is to fill the fabric pouch of the air bag with a gas quickly, in order to provide a flexible protecting medium between the passenger and the equipment in the car. Pyrotechnical gas-generating substances and the gas formed by them must meet a number of requirements in order to ensure that the air-bag assembly works properly and reliably, and that the environment is not harmed. The same requirements are also placed on the pyrotechnical gas-generating substances used in other gas-actuated safety devices fitted in cars, such as safety-belt tighteners, inflatable neck supports, etc.
Thus, the gas formed in all such car safety devices should not contain any hot solid particles that could burn through the main part of the system and set fire to the gas-filled fabric pouch and injure the passengers or jeopardize the entire operation of the safety device. Sodium azide, the most common pyrotechnical gas-generating substance used for this purpose nowadays, does not fully meet this requirement and must therefore be employed with specially reinforced fabric pouches to stop the penetration of the solid particles formed in the combustion of sodium azide. The need for this extra reinforcement means that such a safety device is larger and heavier than strictly necessary for its operation.
Furthermore, the environmental requirements placed on the pyrotechnical gas-generating substances used for the purpose in question stipulate that these substances must not form gaseous mixtures that contain poisonous gases in an amount that is harmful to health. The poisonous gases that are mainly relevant in this context because they are formed in the combustion of gas-generating substances are nitrogen oxides (NO
x
) and carbon monoxide. If the gas-generating substance contains chlorine, then hydrochloric acid is also formed.
Furthermore, the pyrotechnical gas-generating substances used in a gas-actuated car safety device must have a high efficiency, i.e. they should form a large amount of gas per unit weight or volume of the gas-generating substance. However, the efficiency of sodium azide is not particularly high, since it only forms gas in an amount of about 40% of the solid substance. This low efficiency makes it difficult to meet the car manufacturers, requirement of car safety devices with a low weight and a small size when sodium azide is employed as a gas-generating substance. The main reason why sodium azide is still so widely used is that no better gas-generating substance has yet been found.
A further requirement placed on pyrotechnical gas-generating substances is that they should all be thermally stable in the sense that they should not be affected much by the high temperatures that can occur in the dashboard in countries with a warm climate. Nitrocellulose is an example of a substance that does not meet this requirement, but which might otherwise be suitable, and in fact it is used nowadays for this purpose, although it limits the service life of the car safety devices in question.
In addition to the above requirements, the product used in car safety devices as a pyrotechnical gas-generating substance must also meet several requirements concerning its combustion characteristics if a fully satisfactory operation is to be ensured. Thus, the ideal pyrotechnical gas-generating substance in this connection should have a high rate of burning and one that does not vary much with the pressure or the temperature. Sodium azide is an ideal substance from this point of view, but it has several disadvantages, as mentioned above.
There is another group of substances that generate gases when combusted and which have been tried as gas-generating materials for car safety devices. This group comprises nitramine-based gunpowder analogue compositions such as RDX, which are used e.g. in a mixture with cellulose acetyl butyrate. However, the disadvantage of nitramine-based gunpowder analogues is that their rate of burning depends on the pressure to a large extent. If the pressure is too low, the burning is completely extinguished, while if the pressure is too high, the combustion has an explosive course. According to U.S. Pat. No. 5,695,216, these disadvantages can be corrected by constructing a powerful container for the gas-generating substance and equipping the container with decompression means. However, even though this works (and works very well), the construction still requires extra parts and costs more.
The developments in the field of gas-actuated car safety devices therefore show that it is very difficult to find a completely ideal gas-releasing substance for this purpose.
The aim of the present invention is to solve this problem by using a substance that is completely new, at least in the context of gas-actuated safety devices and which—especially if combined with one or more other well-defined substances in accordance with the specific rules given below—provides a gas-generating composition (material) for the present purpose, that has almost optimum combustion characteristics and exhibits several other useful properties, described below, irrespective of whether the gas generators used with it are of the hybrid type or not. However, the mixing ratio of the substances according to the invention does depend to some extent on the type of safety device in question and on the protective function envisaged for it.
The first of the pyrotechnical gas-generating substances according to the invention, which is also the main component of the material according to the invention, is guanyl urea dinitramide (GUDN), which has the following chemical formula.
Guanyl urea dinitramide is relatively easily prepared by reacting guanyl urea with ammonium dinitramide. Pure guanyl urea dinitramide burns much less fast than sodium azide. In the pure form, its combustion is fairly independent of the pressure and temperature, and it stable even at a low pressure. Furthermore, guanyl urea dinitramide scores over sodium azide by burning entirely without forming any solid particles, due to its good intrinsic oxygen balance. In addition, it is thermally stable, with a melting point of over 160° C., and a decomposition temperature of 180° C.
As its structural formula shows, guanyl urea dinitramide has an extra carbon atom, which means that it must be burned with an oxygen excess to ensure that no carbon monoxide persists as a residual product. The necessary oxygen excess can come from a solid substance that forms part of the pyrotechnical gas-generating material releasing a gas on its combustion, or else it can come to various extents from a substance supplied in the gaseous phase. This latter is the case with a “hybrid” gas-generating material, which comprises both a pyrotechnical gas-generating part (releasing a gas during its combustion) and a gaseous component that is supplied in the form of a compressed gas from the beginning. The oxygen excess can then be partly provided by this gaseous component, which can be e.g. pure oxygen or nitrous oxide (N
2
O), also called “laughing gas”. The oxygen-rich component is thus the second constituent according to the present invention. When this second component is a solid substance, it can be chosen from one or more of the following three groups of substances:
Group 1: nitrates, perchlorates and permanganates of alkali metals
Group 2: oxides of iron, nickel, cobalt and metals in the manganese group
Group 3: oxides of the transition metals in Groups 7-12 of the Periodic Table.
However, the rate of burning of pure guanyl urea dinitramide is so much lower than that of sodium azide even in the presence of an oxygen excess that in certain cases it can be too low for some of the applications in question. However, it closely resembles chemically another substance—guanidine dinitramide (GDN)—which has been proposed for a similar purpose before and which has a considerably higher rate of burning. This makes both these substances particularly suitable for use as each other's combustion moderators for regulating t
Persson Svante
Sjöqvist Conny
Bofors Bepab AB
Carone Michael J.
Connolly Bove & Lodge & Hutz LLP
Felton Aileen B.
LandOfFree
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