Patent Application
20060102258
This invention relates generally to gas generant materials such as are used to inflate automotive inflatable restraint airbag cushions and, more particularly, to enhancement of the stability of gas generant materials containing basic copper nitrate.
Gas generating materials are useful in a variety of different contexts. One significant use for such compositions is in the operation of automotive vehicle restraint systems. It is well know to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion” that is inflated or expanded with a gas when a vehicle experiences sudden deceleration, such as in the event of a collision. Such airbag restraint systems normally include: one or more airbag cushions, housed in an uninflated and folded condition to minimize space requirements; one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden deceleration of the vehicle; an activation system electronically triggered by the crash sensors; and an inflator device that produces or supplies a gas to inflate the airbag cushion. In the event of a sudden deceleration of the vehicle, the crash sensors trigger the activation system which in turn triggers the inflator device which begins to inflate the airbag cushion in a matter of milliseconds.
Gas generant compositions utilized in such inflator devices generally include at least a fuel and an oxidizer. Desirably such fuels are non-azide based materials composed of carbon, hydrogen, nitrogen and oxygen atoms which typically yield primarily gaseous products upon combustion. As will be appreciated by those skilled in the art, fuels with high nitrogen and hydrogen contents and a low carbon content are generally attractive for use in such inflatable restraint applications due to their relatively high gas outputs (such as measured in terms of moles of gas produced per 100 grams of gas generant material). Unfortunately, various non-azide based fuels such as, for example, guanidine nitrate, suffer from a lower burn rate than may be desired in many applications.
For some inflator applications a low gas generant composition burn rate may be at least partially compensated for by reducing the size of the shape or form of the gas generant material such as to provide the gas generant material in a shape or form having a relatively larger surface area. In practice, however, there are practical limits to the minimum size of the shape or form to which gas generant materials can reproducibly be manufactured.
For other inflator applications a low gas generant composition burn rate can be at least partially compensated for by including a burn rate enhancer such as, for example, a transition metal complex of diammonium bitetrazole, in the composition. These compounds, when used as part of a gas generant formulation, in conjunction with a primary non-azide fuel, can desirably serve to enhance the burn rate of the composition.
Most oxidizers known in the art and commonly employed in such gas generant compositions are metal salts of oxygen-bearing anions (such as nitrates, chlorates and perchlorates, for example) or metal oxides. Basic copper nitrate is one such oxidizer employed in such gas generant compositions. Basic copper nitrate advantageously imparts desirable properties to such gas generant compositions such as, for example, high gas yield, thermal stability, and good slagging properties due to the formation of molten copper metal during combustion which is readily filterable from a gas stream.
Basic copper nitrate is a double salt of copper hydroxide and copper nitrate having the structure (1), below.
3Cu(OH)2.Cu(NO3)2 (1)
The double salt nature of basic copper nitrate imparts unique chemistry to the compound. For example, certain weak acids can react with the hydroxyl groups on the copper hydroxide forming substituted basic copper nitrates. Other chemical reactions include anion exchange with anions of strong acids, and hydrolysis by water at elevated temperatures resulting in a mixture of basic copper nitrate, cupric oxide and nitric acid. As one skilled in the art would appreciate, particular of such chemical reactions of the basic copper nitrate can be desirable or undesirable depending upon the resulting reaction products.
A number of gas generant formulations have been proposed to take advantage of various of the desirable properties of basic copper nitrate. For example, gas generant compositions have been proposed wherein certain ingredients, such as, for example, non-azide fuels and burn rate enhancers, are combined with basic copper nitrate to impart desirable characteristics to the gas generant composition such as, for example, increased burn rate and/or improved ignitability. Such gas generant compositions including basic copper nitrate are disclosed, for example, in commonly assigned Mendenhall, U.S. Pat. No. 6,689,237 issued 10 Feb. 2004 and commonly assigned Mendenhall et al., U.S. Pat. No. 6,712,918 issued 30 Mar. 2004.
Unfortunately, under certain conditions, one or more deleterious reaction can occur between basic copper nitrate and other gas generant composition components. For example, in the presence of moisture, basic copper nitrate can deleteriously react with gas generant composition components that contain ammine containing ligands. One such moisture induced deleterious interaction has been observed between basic copper nitrate and diammonium bitetrazole, wherein the basic copper nitrate reacts with the diammonium bitetrazole to form copper oxide and ammonium nitrate, as shown below (2):
Cu(NH3)2C2N8+3Cu(OH)2.Cu(NO3)2→CuC2N8+4CuO+2NH4NO3 (2)
Such moisture-induced deleterious interaction between basic copper nitrate and other gas generant composition components can result in undesirable variations in the color, density and hygroscopicity of the gas generant composition. Moreover, such moisture-induced deleterious interactions can result in unacceptable variation in inflator performance.
Thus, there is a need and a demand for gas generant compositions and related methods such as allow or permit taking advantage of desirable properties or characteristics of the inclusion of basic copper nitrate while minimizing or avoiding deleterious interactions between basic copper nitrate and other components of the gas generating composition. There is a further need and demand for a gas generant composition including basic copper nitrate having desirable performance attributes and reduced performance and/or lot to lot production variability.
A general object of the invention is to provide an improved gas generant composition.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through a gas generant composition that includes basic copper nitrate, at least one fuel material and a phosphate stabilizer, wherein the phosphate stabilizer inhibits moisture induced deleterious interaction between the basic copper nitrate and other of the gas generant composition components. Suitably, and in accordance with one preferred embodiment, the phosphate stabilizer is present in a concentration of at least about 1 part by weight phosphate per about 770 parts by weight basic copper nitrate.
The prior art generally fails to provide a basic copper nitrate containing gas generant composition, such as for use in the inflation of automotive inflatable restraint air bag cushions, having improved stability and reduced lot to lot production variation as compared to conventionally produced materials or compositions. The prior art further generally fails to provide a basic copper nitrate containing gas generant composition including a phosphate stabilizer material.
The invention further comprehends a stabilized gas generant composition comprising:
a fuel;
a burn rate enhancer including a transition metal complex of tetrazole containing at least one ammine-containing ligand;
basic copper nitrate oxidizer; and
a phosphate stabilizer,
wherein the phosphate stabilizer inhibits moisture induced deleterious interaction between the basic copper nitrate and the transition metal complex of tetrazole containing at least one ammine-containing ligand.
The invention still further comprehends a method for making a stabilized gas generant composition comprising the steps of: preparing an aqueous slurry including a fuel and a burn rate enhancer; adding an amount of a phosphate stabilizer to the aqueous slurry; preparing a dry blend of basic copper nitrate; mixing the dry blend into the aqueous slurry; and drying the aqueous slurry to form the stabilized gas generant composition.
As used herein, references to a specific composition, component or material as a “fuel” are to be understood to refer to a chemical that generally lacks sufficient oxygen to bum completely to CO2, H2O and N2.
Correspondingly, references herein to a specific composition, component or material as an “oxidizer” are to be understood to refer to a chemical generally having more than sufficient oxygen to burn completely to CO2, H2O and N2.
References to a component or material as a “burn rate catalyst”, a “burn rate enhancer” or the like are to be understood to refer to such a component or material, when added or included as a minor ingredient, i.e., typically in an amount of less than 30 composition weight percent and, more commonly, in an amount of less than 20 composition weight percent, produces or results in a significant effect on the burn rate of the composition in which the component or material has been added, where a significant effect on burn rate generally involves an increase in burn rate of at least about 20 percent. It will be understood that such burn rate catalyst or enhancer materials can and typically do undergo reaction when in normal use in a combustion reaction.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.
The present invention provides improved gas generant compositions such as are used to inflate automotive inflatable restraint air bag cushions and, more particularly, to enhancement of the stability of gas generant materials containing basic copper nitrate. As described in greater detail below and in accordance with one preferred embodiment of the invention, such improved gas generant composition desirably contains or includes components including basic copper nitrate, at least one fuel material and a phosphate stabilizer.
It is generally desirable in the production of gas generant compositions that the final product of the compounding process possess various desirable characteristics such as, for example, suitable bum rate and stability in the presence of moisture. It is additionally desirable that lot to lot variations of gas generant compositions be kept to a minimum in order to reproducibly prepare suitable gas generant materials which meet or exceed industry and federal safety standards and limit costs associated with waste and reduced performance. While it is known to incorporate basic copper nitrate into various compositions, the use of basic copper nitrate in gas generant compositions is a relatively new development within the field of automotive inflatable restraint systems. However, gas generant compositions containing basic copper nitrate, as described above, can be susceptible to moisture induced deleterious interaction between basic copper nitrate and other components of the gas generant composition that can result in variations in color, density and hygroscopicity of the gas generant material as well as reduced performance of the gas generant material as measured by, for example, reduced burn rate. Therefore, what is needed to curb or eliminate such moisture induced deleterious interactions is a gas generant material which is stabilized or buffered. Thus, it has been discovered that the inclusion of a phosphate stabilizer within a gas generant composition including basic copper nitrate inhibits moisture induced deleterious interaction between the basic copper nitrate and other gas generant components thereby providing an improved gas generant material. In certain formulations including basic copper nitrate and ammine-containing ligand bearing materials such as, for example, burn rate enhancers and/or fuel materials, it is generally believed that the inclusion of a phosphate stabilizer within the gas generant composition inhibits moisture induced deleterious interactions between the basic copper nitrate and the ammine-containing ligands which results in increased composition variability and reduced performance. Heretofore, such a stabilized gas generant composition has been unknown in the art.
In accordance with the invention, an improved gas generant composition contains components including basic copper nitrate, at least one fuel material and a phosphate stabilizer, wherein the phosphate stabilizer inhibits moisture induced deleterious interaction between the basic copper nitrate and other components of the gas generant composition. In particular, the gas generant composition includes a phosphate stabilizer in a concentration of at least about 1 part by weight phosphate per about 770 parts by weight basic copper nitrate. More particularly, the gas generant composition includes a phosphate stabilizer in a concentration of about 1 part by weight phosphate per about 770 parts by weight basic copper to about 1 part by weight phosphate per about 15 parts by weight basic copper nitrate; suitably, about 1 part by weight phosphate per 770 parts by weight basic copper nitrate to about 1 part by weight phosphate per 150 parts by weight basic copper nitrate.
Useful phosphate stabilizers that may be included in the gas generant compositions of the invention include tetrasodium pyrophosphate, sodium phosphate dibasic, phosphoric acid and combinations thereof. In accordance with one preferred embodiment of the invention the phosphate stabilizer comprises tetrasodium pyrophosphate. Suitably, such tetrasodium pyrophosphate stabilizer is present in a concentration of at least about 0.1 composition weight percent; particularly, in a concentration of about 0.1 to about 5 composition weight percent; and, in accordance with certain preferred embodiments, in a concentration of about 0.1 to about 0.5 composition weight percent.
As discussed above, basic copper nitrate is a double salt of copper hydroxide and copper nitrate which imparts a unique chemistry to the compound and which has been found to be a particularly effective oxidizer for certain application such as, for example, in gas generant compositions for use in the inflation of an associated automotive inflatable airbag restraint cushion. Suitably, the basic copper nitrate is present in a concentration of at least about 10 composition weight percent; particularly, in a concentration of about 10 to about 60 composition weight percent; and, more particularly, in a concentration of about 25 to about 50 composition weight percent.
The gas generant compositions of the invention desirably include at least one non-azide fuel material. Such non-azide fuel materials, as discussed above, generally impart desirable attributes to the gas generant composition such as, for example, increased gas yield. While the broader practice of the invention is not necessarily limited to or by practice with specific non-azide fuels, the invention has been found or is believed to be particularly attractive for use in conjunction with non-azide fuel materials such as, for example, guanidine nitrate and transition metal complexes of nitrate such as, for example, cobalt (III) hexamine nitrate and copper bis-guanyl urea dinitrate. Suitably, such non-azide fuel is present in a concentration of at least about 10 composition weight percent; particularly, in a concentration of about 10 to about 50 composition weight percent; and, more particularly, in a concentration of about 10 to about 25 composition weight percent.
Gas generant compositions in accordance with the invention may desirably further include at least one burn rate enhancer. Suitably, such burn rate enhancer comprises a transition metal complex of a tetrazole containing at least one ammine-containing ligand. Suitable transition metals for use in the practice of the invention include copper, zinc, cobalt, nickel and chromium. Preferred transition metals used in the practice of the invention include zinc and copper. One particularly preferred transition metal complex of a tetrazole containing at least one ammine-containing ligand for use in the practice of the invention is a copper complex of diammonium bitetrazole having an empirical formula of CuC2H6N10. Another particularly preferred transition metal complex of a tetrazole containing at least one ammine-containing ligand for use in the practice of the invention is a copper complex of ethylenediamine 5,5′-bitetrazole, i.e., copper bis ethylenediamine 5,5′-bitetrazole, having an empirical formula of Cu(C2H8N2)2C2N8.
Those skilled in the art and guided by the teachings herein provided will appreciate that the invention can desirably be practiced via the inclusion of a sufficient quantity of a burn rate enhancer in the gas generant formulation to effect a desirable increase in the burn rate exhibited by the resulting formulation, as compared to the same formulation without the inclusion of such bum rate enhancer. In general, however, it has been found preferable for a gas generant composition in accordance with a preferred embodiment of the invention to include or incorporate the burn rate enhancer in a relative amount of about 1 to 100 weight percent of the fuel component, and particularly in a relative amount of about 1 to about 25 weight percent of the fuel component. In specific preferred embodiments, the burn rate enhancer is desirably present in a concentration of at least about 10 composition weight percent and, more preferably, in a concentration of at least about 15 composition weight percent in order to provide gas generant compositions evidencing a sufficiently increased burn rate effective for such inflatable restraint system applications.
In addition, gas generant compositions in accordance with the invention may, if desired, include one or more additional components or ingredients such as, for example, one or more metal oxide burn rate enhancing and slag formation additive. Suitable such metal oxide burn rate enhancing and slag formation additives may include silicon dioxide, aluminum oxide, titanium dioxide, boron oxide and combinations thereof, for example. Suitably, such burn rate enhancing and slag formation additive is included in the gas generant composition in a relatively minor amount, e.g., in a concentration of less than about 10 composition weight percent and typically less than about 5 composition weight percent.
Those skilled in the art and guided by the teachings herein provided will appreciate that suitable stabilized gas generant compositions in accordance with the invention can be prepared by various methods and the broader practice of the invention is not necessarily limited by or to specific methods of preparation. A preferred method for preparing a stabilized gas generant composition includes the steps of: preparing an aqueous slurry including a fuel and a burn rate enhancer; adding an amount of a phosphate stabilizer to the aqueous slurry; preparing a dry blend of basic copper nitrate; mixing the dry blend into the aqueous slurry; and drying the aqueous slurry to form the stabilized gas generant composition.
As will be appreciated, gas generant compositions or materials prepared in accordance with the invention can be incorporated, utilized or practiced in conjunction with a variety of different structures, assemblies and systems. As representative,
The vehicle occupant safety restraint system 14 includes an open-mouthed reaction canister 16 which forms a housing for an inflatable vehicle occupant restraint 20, e.g., an inflatable airbag cushion, and an apparatus, generally designated by the reference numeral 22, for generating or supplying inflation gas for the inflation of an associated occupant restraint. As identified above, such a gas generating device is commonly referred to as an “inflator.”
The inflator 22 contains a quantity of a gas generant composition or formulation in accordance with the invention and such as suited, upon ignition, to produce or form a quantity of gas such as to be used in the inflation of the inflatable vehicle occupant restraint 20. As will be appreciated, the specific construction of the inflator device does not form a limitation on the broader practice of the invention and such inflator devices can be variously constructed such as is also known in the art.
In practice, the airbag cushion 20 upon deployment desirably provides for the protection of a vehicle occupant 24 by restraining movement of the occupant in a direction toward the front of the vehicle, i.e., in the direction toward the right as viewed in
The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.
Gas generant formulations having the compositions identified in TABLE 1 below were prepared as follows.
Diammonium 5,5′-bitetrazole (C2H8N10) and guanidine nitrate (GN) were dissolved in 60 ml of water equilibrated to 90° C. in a jacketed reaction vessel equipped with a mechanical stirring device and a pH probe. Cupric oxide was added to the solution and the mixture was stirred and held at 90° C. for 1 hour while the diammonium 5,5′-bitetrazole and the cupric oxide reacted to form copper diammine bitetrazole (CuC2H6N10). After completion of this reaction, a dry blend of basic copper nitrate (BCN) and aluminum oxide (Al2O3) was added to the reaction mixture and incorporated with stirring.
The above procedure was repeated in an identical manner except that tetrasodium pyrophosphate (Na4P2O7) was added to the reaction mixture prior to the addition of the basic copper nitrate and the aluminum oxide.
Test Methods and Data:
The pH of each reaction mixture was monitored continuously for 200 minutes and visual observations were recorded. The pH profile for each gas generant composition is shown in
Each gas generant composition was also tested to determine the burn rate and density (ρ) values for the compositions. The results are shown in TABLE 2 below. In particular, the bum rate data was obtained by first pressing samples of the respective gas generant compositions into the shape or form of a 0.5 inch diameter cylinder using a hydraulic press (12,000 lbs. force). Typically enough powder was used to result in a cylinder length of 0.5 inch. The cylinders were then each coated on all surfaces except the top one with a krylon ignition inhibitor to help ensure a linear burn in the test fixture. In each case, the so coated cylinder was placed in a 1-liter closed test vessel capable of being pressurized to several thousand psi with nitrogen 5 and equipped with a pressure transducer for accurate measurement of pressure within the test vessel. A small sample of igniter powder was placed on top of the cylinder and a nichrome wire was passed through the igniter powder and connected to electrodes mounted in the lid of the test vessel. The test vessel was then pressurized to the desired pressure and the sample ignited by passing a current through the nichrome wire. Pressure versus time data was collected as each of the respective samples were burned. Since combustion of each of the samples generated gas, an increase in pressure within the test vessel signaled the start of combustion. The time required for combustion was equal to (t2−t1) where t2 is the time at the end of combustion and t1 is the time at the start of combustion. The sample weight was divided by combustion time to give a burning rate in grams per second. Burning rates were measured at two pressures, 1000 psi and 3000 psi. The log of burn rate versus the log of average pressure was then plotted. From this line the burn rate at any pressure can be calculated using gas generant composition burn rate equation (3), below:
rb=k(P)″ (3)
where,
n=pressure exponent, where the pressure exponent is the slope of a linear regression line drawn through a log-log plot of burn rate versus pressure.
Discussion of Results:
As shown in
As shown in TABLE 2, the presence of tetrasodium pyrophosphate in the gas generant composition of Example 1 has a minimal effect upon the burn rate of the formulation as compared to the gas generant composition of Comparative Example 1. Other forms of phosphate such as, for example, sodium phosphate dibasic and phosphoric acid were found to have a comparable effect.
Thus, the invention provides an improved gas generant composition suitable for use in the inflation of an associated automotive inflatable airbag restraint cushion, and, more particularly, a basic copper nitrate containing gas generant composition having improved stability and reduced variability. Further, the invention provides gas generant composition including basic copper nitrate that is stabilized to curb or eliminate moisture induced deleterious interactions between the basic copper nitrate and other gas generant composition components.
The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.
While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
