Gas Generant Manufacturing Method

Abstract

A method of forming a gas generating composition containing a salt of dinitrosalicylic acid and ammonium nitrate or phase stabilized ammonium nitrate. The method involves the co-precipitation of a salt of 3,5-dinitrosalicylic acid with phase stabilized ammonium nitrate. A gas generating composition 12 is also presented along with a gas generator 10 containing the gas generating composition 12. The gas generator 10 may be contained within a gas generating system 200 such as an airbag inflator 10 or seat belt assembly 150, or more broadly within a vehicle occupant protection system 180.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/318,161 filed on Mar. 26, 2010 and PCT Application Serial No. PCT/US11/00562 filed Mar. 28, 2011.

TECHNICAL FIELD

The present invention relates generally to gas generating systems, and to gas generating compositions employed in gas generator devices for automotive restraint systems, for example.

BACKGROUND OF THE INVENTION

The present invention relates to gas generating compositions that upon combustion produce a relatively smaller amount of solids and a relatively abundant amount of gas. It is an ongoing challenge to reduce the amount of solids and increase the amount of gas thereby decreasing the filtration requirements for an inflator. As a result, the filter may be either reduced in size or eliminated altogether thereby reducing the weight and/or size of the inflator. Additionally, reduction of combustion solids provides relatively greater amounts of gaseous products per gram or unit of gas generating composition. Accordingly, less gas generant is required when greater mols of gas are produced per gram of gas generant. The result is typically a smaller and less expensive inflator due to reduced manufacturing complexity.

In a related challenge, when increasing the amount of gas, the effluent must be tailored to ensure that carbon monoxide or other less-than-desirable gases are attenuated. For example, when increasing the relative amounts of carbon in the gas generant, one concern is whether the gas generant might produce more carbon monoxide as a combustion product. As such, the effort to reduce solids and increase gas production upon combustion, must be balanced with combustion products that meet current effluent standards.

Another challenge is providing gas generating compositions that meet current USCAR requirements for chemical and thermal stability. Chemical stability is indicative of a propellant retaining its structural integrity over time. Dimensional stability is indicative of chemical stability, the retention of density over time for example. Components of the composition must be compatible with each other with a minimum of interaction. Therefore, chemical stability involves the mitigation of interaction of the various constituents that are included in the gas generating composition.

Thermal stability is the ability to retain structural integrity when cycled between −40 C and 107-110 C, for example. For example, the composition may be held at a temperature of −40 C for a period of time and then quickly brought to a temperature of about 107 to 110 C and held there for a period of time. Accordingly, retaining gas generant structural integrity while undergoing periodic cycling between the two temperature regimes over time is yet another challenge. Furthermore, USCAR requirements include thermal testing by holding compositions at about 107 C for about 400 hours without thermal decomposition of the compositions. Certain compositions containing phase stabilized ammonium nitrate, for example, oftentimes present concerns with regard to thermal stability.

Yet another concern is that the compositions must exhibit burn rates that are satisfactory with regard to use in vehicle occupant protection systems. In particular, compositions containing phase stabilized ammonium nitrate may exhibit relatively lower burn rates requiring various measures to improve the burn rate. Accordingly, the development of energetic fuels is one ongoing research emphasis whereby the less aggressive burn characteristics of preferred oxidizers such as phase stabilized ammonium nitrate are accommodated and compensated for by careful blending or combining of new and useful constituents.

Furthermore, it has been found that oftentimes nitrated aromatic compounds combined with ammonium nitrate or phase stabilized ammonium nitrate are not clean burning and may form large amounts of soot-like residues when combusted. Acidic nitro-aromatic compounds provide some measure of catalytic impetus to ammonium nitrate or phase stabilized ammonium nitrate compositions, particularly in view of the ignitability and sustained combustion concerns with some compositions containing ammonium nitrate (stabilized or not).

With regard to gas generant formulation or processing, pyrotechnic constituents may oftentimes be blended as dry powders consisting of fuels, oxidizers, and other known additives. When using acidic fuels or constituents, however, handling and processing concerns due to sensitivity of the acidic compound requires careful handling to prevent any unintended reactions. Oftentimes, when an acidic fuel is employed in a gas generating composition, it may be advisable to form a salt with the acid prior to combining it with the composition. The time constraints, and the additional steps in the processing add cost to the formulation process, and detract from the benefit of the acidic fuel, less combustion solids for example. Yet another challenge is that the composition formed from the acidic fuel must also exhibit favorable impact sensitivity and comply with Department of Transportation regulatory requirements, and exhibit favorable chemical and thermal stability.

In view of these concerns, it would be an improvement in the art to provide a “smokeless” gas generant, or one that upon combustion provides more than 90% of gas as a combustion product without the aforementioned concerns. For example, an ammonium nitrate or phase stabilized ammonium nitrate based composition that meets or exceeds the relative gas output of typical high-nitrogen fuels combined with an ammonium nitrate or phase stabilized ammonium nitrate oxidizer while yet retaining the performance of or improving upon the considerations provided above would be an improvement in the art. It would also be an improvement to simplify the formulation or processing of gas generating compositions that incorporate acidic fuels without the hazards that might be attendant due to the acidity of the fuel.

SUMMARY OF THE INVENTION

The above-referenced concerns are resolved by gas generators or gas generating systems containing a novel fuel constituent, 3,5-dinitrosalicylic acid (DNSA), a metallic salt of DNSA, a non-metallic salt of DNSA, or an adduct of DNSA with another compound that forms a hydrogen bonded complex. When combined with phase stabilized ammonium nitrate (PSAN) (stabilized, for example only, with potassium nitrate provided at 10-15% by weight of the PSAN), one or more of the present fuels result in a gas generant composition that exhibits optimum burn rates at relatively lower operating combustion pressures, and optimum thermal and chemical stability, notwithstanding the use of PSAN. Furthermore, one or more of the present compositions combust readily at relatively lower combustion pressures thereby resulting in relaxed manufacturing and structural requirements for an associated gas generator or airbag inflator. Yet further, one or more of the present compositions when combusted result in relatively greater amounts of gas and lower amounts of solids, and therefore improved effluent quality.

An optional second fuel may be selected from tetrazoles and salts thereof, triazoles and salts thereof, azoles and salts thereof, guanidines and salts thereof, guanidine derivatives, imides, amides, aliphatic carboxylic acids and salts thereof, aromatic carboxylic acids and salts thereof, nitro-aromatic carboxylic acids and salts thereof, nitrosalicylic acids and salts thereof, amines, nitrophenols, pyrazoles, imidazoles, azines, and mixtures thereof.

A primary oxidizer may be selected from metal and nonmetal nitrates, nitrites, chlorates, perchlorates, oxides, other known oxidizers, and mixtures thereof.

If desired, other known constituents may also be utilized in known effective amounts.

In further accordance with the present invention, a wet method of formulating ammonium nitrate and phase stabilized ammonium nitrate (PSAN) based compositions, containing a salt of DNSA, is provided. It is believed that the co-precipitation of PSAN and a salt of DNSA results in an intimate mixture that provides substantial effluent improvements and substantial improvement in ballistic performance, as well.

In further accordance with the present invention, a gas generator or gas generating system, and a vehicle occupant protection system incorporating the gas generant composition are also included.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view showing the general structure of an inflator in accordance with the present invention.

FIG. 2 is a schematic representation of an exemplary vehicle occupant restraint system containing a gas generant composition in accordance with the present invention.

FIG. 3 is a first microstructure of a co-precipitation of ammonium dinitrosalicylic acid and phase stabilized ammonium nitrate.

DETAILED DESCRIPTION OF THE INVENTION

The above-referenced concerns are resolved by gas generators or gas generating systems containing an acidic nitrated aromatic compound as a primary fuel, the primary fuel including a member selected from the group of 3,5-dinitrosalicylic acid (DNSA), a metallic salt of DNSA, a non-metallic salt of DNSA, or an adduct of DNSA with another compound that forms a hydrogen bonded complex. Examples of adducts include an adduct of DNSA and 3-amino-triazole; DNSA and melamine; and DNSA and alkyl amines. When combined with phase stabilized ammonium nitrate (PSAN) (stabilized for example only, with 10-15% by weight of the PSAN with an alkali metal salt such as potassium nitrate), one or more of the present fuels result in a gas generant composition that exhibits optimum burn rates at relatively lower operating combustion pressures, and optimum thermal and chemical stability, notwithstanding the use of PSAN. Furthermore, one or more of the present compositions combust readily at relatively lower combustion pressures thereby resulting in relaxed manufacturing and structural requirements for an associated gas generator or airbag inflator. Yet further, one or more of the present compositions when combusted result in relatively greater amounts of gas and lower amounts of solids, and therefore improved effluent quality. When used without other fuels, the primary fuel may be provided at 20 wt % to 80 wt %, 25 wt % to 75 wt %, or at 40 wt % to 60 wt % of the total composition. All other percentages hereinafter make reference to weight percents of the total composition.

Optional secondary fuels may be selected from tetrazoles such as 5-aminotetrazole; metal salts of azoles such as potassium 5-aminotetrazole; nonmetal salts of azoles such as diammonium salt of 5,5′-bis-1H-tetrazole: nitrate salts of azoles such as 5-aminotetrazole; nitramine derivatives of azoles such as 5-aminotetrazole; metal salts of nitramine derivatives of azoles such as potassium 5-aminotetrazole; nonmetal salts of nitramine derivatives of azoles such as monoammonium 5-aminotetrazole; salts of guanidines such as guanidine nitrate; nitro derivatives of guanidines such as nitroguanidine; azoamides such as azodicarbonamide; nitrate salts of azoamides such as azodicarbonamidine dinitrate; aliphatic carboxylic acids such as fumaric acid, tartaric acid, and succinic acid, and metal and nonmetal salts thereof; aromatic carboxylic acids such as benzoic acid, phtalic acid, and isophthalic acid, and metal and nonmetal salts thereof; nitro-aromatic carboxylic acids such as nitrobenzoic acid, dinitrobenzoic acid, nitroisophthalic acid, and 4-hydroxydinitobenzoic acid, and metal and nonmetal salts thereof; mono-nitrosalicylic acids such as 3-nitrosalicylic acid and 5-nitrosalicylic acid and metal and nonmetal salts thereof; amines such as melamine; amides such as oxamide; imides; nitrophenols such as nitrophenol, 2,4-dinitrophenol, and picric acid, and metal and nonmetal salts thereof; triazoles such as 3-nitrotriazole and nitrotriazolone (NTO); pyrazoles imidazoles; azines; and mixtures thereof. The secondary fuel can be used within this system as co-fuels to the primary fuel. U.S. Pat. Nos. 5,872,329 and 6,210,505 describes the use of these and provision of these fuels and are both herein incorporated by reference in their entirety. When used, the secondary fuel in combination with the primary fuel may constitute about 10-90 wt % of the gas generant composition. Also, when the secondary fuel is employed, the primary fuel may be provided from 5 wt % to 80 wt % of the total composition. By itself, the optional secondary fuel may constitute 0.1-45 wt % when used, and more preferably about 3-30 wt % when used.

An oxidizer is selected from metal and nonmetal nitrates, nitrites, chlorates, perchlorates, oxides, hydroxides, other known oxidizers, and mixtures thereof. The preferred primary oxidizer is selected from ammonium nitrate and phase stabilized ammonium nitrate, and most preferably phase stabilized ammonium nitrate. The primary oxidizer may be provided at 20 wt % to 80 wt %, and more preferably at 50 wt % to 80 wt % of the total composition. All other percentages hereinafter make reference to weight percents of the total composition.

A secondary oxidizer component is optionally selected from at least one exemplary oxidizer selected from basic metal nitrates, and, metal and nonmetal nitrates, chlorates, perchlorates, nitrites, and oxides, including such oxidizers as basic copper (II) nitrate, strontium nitrate, potassium nitrate, potassium nitrite, iron oxide, and copper oxide. Metal-containing oxidizers include those formed from alkali, alkaline earth, and transitional metal oxidizers. Other oxidizers as recognized by one of ordinary skill in the art may also be employed. The secondary oxidizer is generally provided at about 0-50 wt % of the gas generant composition.

If desired, other known constituents may also be utilized in known effective amounts.

Metal and non-metal carbonates such as potassium carbonate and ammonium carbonate may also be employed with an oxidizer such as ammonium nitrate.

Processing aids such as fumed silica, boron nitride, and graphite may also be employed. Accordingly, the gas generant may be safely compressed into tablets, or slugged and then granulated. The processing aid is generally provided at about 0-15 wt %, and more preferably at about 0-5 wt %.

Slag formers may also be provided and are selected from silicon compounds such as elemental silicon; silicon dioxide; silicones such as polydimethylsiloxane; silicates such as potassium silicates; natural minerals such as talc and clay, and other known slag formers. The slag former is typically provided at about 0-10 wt %, and more preferably at about 0-5 wt %.

The compositions of the present invention may be formed from constituents as provided by known suppliers such as Aldrich or Fisher Chemical companies. The compositions may be provided in granulated form and dry-mixed and compacted in a known manner, or, wet-mixed and formulated as described in the examples, or otherwise mixed as known in the art. The compositions may be employed in gas generators typically found in airbag devices or occupant protection systems, or in safety belt devices, or in gas generating systems such as a vehicle occupant protection system, all manufactured as known in the art, or as appreciated by one of ordinary skill.

EXAMPLES

Example 1

Wet Mix Method Including a Secondary Fuel

A composition was made by providing a jacketed mixing vessel containing about two liters of ethanol. To this solution, about 753 grams of dinitrosalicylic acid (DNSA) was added while continuously stirring. The solution was then heated slowly to about 105 C over about thirty minutes and maintained throughout the remaining process. Once the DNSA was completely dissolved, about 4352 grams of ammonium nitrate, about 122 grams of potassium nitrate, about 227 grams of potassium carbonate (whereby potassium nitrate and potassium carbonate taken together provide a potassium source for phase stabilization of the ammonium nitrate), about 595 grams of diammonium bitetrazole, and one liter of water are added together into the vessel, while continuously and mechanically stilling. A bright yellow precipitate forms immediately in a viscous, paint-like consistency. After about one hour, the mix forms crumbly solids. The mixing and heating is continued until the desired dryness is obtained. If desired, the mix may be formed into desired shapes such as pellets or tablets and then dried to a desired moisture content, in an oven for example.

Example 2

Wet Mix Method

A composition was made by providing a jacketed mixing vessel containing about two liters of water or ethanol, or any other suitable solvent such as ethers or alcohols. To this solution, an approximate stoichiometric amount of dinitrosalicylic acid (DNSA) or a metal or nonmetal salt of DNSA was added while continuously stirring. The solution was then heated slowly to about 105 C over about thirty minutes and maintained throughout the remaining process.

Once the DNSA was completely dissolved, an approximate stoichiometric amount of ammonium nitrate was added and stirred into the solution. A potassium source such as potassium nitrate was then added in about 10-15% by weight with regard to the total amount of ammonium nitrate added. The mixture was continually stirred and the heat maintained as a solid formed. The mixing and heating is continued until the desired dryness is obtained. If desired, the mix may be formed into desired shapes such as pellets or tablets and then dried to a desired moisture content, in an oven for example. The resultant solid included stoichiometric amounts of phase stabilized ammonium nitrate (PSAN) and ammonium dinitrosalicylic acid (ADNSA). The resultant ADNSA crystals are comparatively small and therefore form an intimate co-precipitation with the ammonium nitrate.

Example 3

Wet Mix Method Including a Secondary Fuel

A composition was made by providing a stainless steel jacketed mixing vessel containing about two liters of water. To this solution, about 753 grams of dinitrosalicylic acid (DNSA) was added while continuously stirring. The solution was then heated slowly to about 105 C over about thirty minutes and maintained throughout the remaining process. Once the DNSA was completely dissolved, about 4352 grams of ammonium nitrate, about 122 grains of potassium nitrate, about 227 grams of potassium carbonate (whereby potassium nitrate and potassium carbonate taken together provide a potassium source for phase stabilization of the ammonium nitrate), about 595 grams of diammonium bitetrazole, and one liter of water are added together into the vessel, while continuously and mechanically stirring. A bright yellow precipitate forms immediately in a viscous, paint-like consistency. After about one hour, the mix forms crumbly solids. The mixing and heating is continued until the desired dryness is obtained. If desired, the mix may be formed or extruded into desired shapes such as pellets or tablets and then dried to a desired moisture content, in an oven for example.

Example 4

A composition containing about 73 wt % ammonium nitrate and about 27 wt % monopotassium dinitrosalicylic acid was wet mixed and formed into a homogeneous composition in accordance with the present invention. The resultant composition included phase stabilized ammonium nitrate at about 75.20 wt % (the PSAN containing 64.95 wt % of ammonium nitrate and 10.25 wt % potassium nitrate) and ammonium dinitrosalicylic acid at about 24.80 wt %.

Example 5

A composition containing about 76.39 wt % phase stabilized ammonium nitrate (containing about 7.64 wt % potassium nitrate as a phase stabilizer); about 10 wt % di-ammonium salt of 5,5′-bis-1H-tetrazole; and about 13.61 wt % ammonium dinitrosalicylic acid was dry mixed and formed into a homogeneous composition in accordance with the present invention.

Example 6

A composition containing about 68.75 wt % ammonium nitrate; about 7.64 wt % potassium nitrate; about 10 wt % diammonium salt of 5,5′-bis-1H-tetrazole; and about 13.61 wt % ammonium dinitrosalicylic acid was dry mixed and formed into a homogeneous composition in accordance with the present invention.

Example 7

A composition containing about 67.58 wt % ammonium nitrate; about 7.51 wt % potassium nitrate; about 7.0 wt % diammonium salt of 5,5′-his-1H-tetrazole; about 3.0 of dipotassium tartaric acid; and about 1491 wt % ammonium dinitrosalicylic acid was dry mixed and formed into a homogeneous composition in accordance with the present invention.

Example 8

A composition containing about 68.4 wt % ammonium nitrate; about 7.6 wt % potassium nitrate; about 3.5 wt % diammonium salt of 5,5′-bis-1H-tetrazole; and about 20.5 wt % ammonium dinitrosalicylic acid was dry mixed and formed into a homogeneous composition in accordance with the present invention.

Example 9—Comparative Example (PSAN-Tetrazole)

A composition containing about 73.5 wt % phase stabilized ammonium nitrate and about 26.5 wt % ammonium salt of 5,5′-bis-tetrazole amine was dry mixed and formed into a homogeneous composition in accordance with methods known in the art.

Example 10—Comparative Example (PSAN-Tetrazole)

A composition/gas generant formed as provided in Example 9 was evaluated based on gaseous effluent. A given mass of the composition contained about 3.9% carbon and when combusted in a single-stage one mole inflator (that is containing one mole of gas generant and operating at about 33-35 MPa), the parts per million of the following gaseous products were measured from a 100 cubic foot tank: 126 ppm carbon monoxide; 41 ppm ammonia; 13 ppm nitrogen oxide; and 0 ppm nitrogen dioxide. The same mass of the same fuel was also combusted in a double stage one mole inflator (that is containing one mole of gas generant and operating at about 40 MPa), and resulted in the following gaseous products as also measured from a 100 cubic foot tank: 129 ppm carbon monoxide; 35 ppm ammonia; 11 ppm nitrogen oxide; and 0 ppm nitrogen dioxide.

Example 11

A composition/gas generant formed as provided in Example 4 was evaluated based on gaseous effluent. A given mass of the composition contained about 8.5% carbon and when combusted in a single-stage one mole inflator (the same model inflator as used in Example 10, and one that contained one mole of gas generant and operated at about 33-35 MPa), the parts per million of the following gaseous products were measured from a 100 cubic foot tank: 173 ppm carbon monoxide; 14 ppm ammonia; 12 ppm nitrogen oxide; and 0 ppm nitrogen dioxide. In accordance with the present invention, the results illustrate that although this example had more than twice the amount of carbon content in the gas generant composition as compared to Example 10, there was only about a 37% increase in the amount of carbon monoxide produced upon combustion. Furthermore, the ammonia content was about one third or about 33% of the amount of ammonia produced in the composition of Example 10. The results were unexpected and counterintuitive in that the expectation had been to see a linear and increased amount of carbon monoxide produced upon combustion. Instead, useful amounts of acceptable gas such as carbon dioxide were produced while attenuating the production of carbon monoxide as analyzed from the pre-combustion content of carbon in the gas generant. Accordingly, the present invention supplants less desirable gases such as ammonia with acceptable gases such as carbon dioxide, while surprisingly mitigating the production of carbon monoxide.

Example 12

A composition/gas generant formed as provided in Example 4 was evaluated based on gaseous effluent. A given mass of the composition contained about 6.0% carbon and when combusted in a single-stage one mole inflator (the same model inflator as used in Example 10, and one that contained one mole of gas generant and operated at about 33-35 MPa), the parts per million of the following gaseous products were measured from a 100 cubic foot tank: 122 ppm carbon monoxide; 11 ppm ammonia; 20 ppm nitrogen oxide; and 0 ppm nitrogen dioxide. In accordance with the present invention, the results illustrate that although this example had more than 150% if the amount of carbon content in the gas generant composition as compared to Example 10, there was less carbon monoxide (96.8% as compared to Example 10) produced upon combustion. Furthermore, the ammonia content was about 26.8% of the amount of ammonia produced in the composition of Example 10. The results were unexpected and counterintuitive in that the expectation had been to see a linear amount of carbon monoxide produced upon combustion. Instead, useful amounts of acceptable gas such as carbon dioxide were produced while attenuating the production of carbon monoxide as analyzed from the pre-combustion content of carbon in the gas generant. Accordingly, the present invention supplants less desirable gases such as ammonia with acceptable gases such as carbon dioxide, while surprisingly mitigating the production of carbon monoxide.

The same mass of the same fuel was also combusted in a double stage one mole inflator (the same model inflator as used in Example 10, and one that contained one mole of gas generant and operated at about 40 MPa), and resulted in the following gaseous products as also measured from a 100 cubic foot tank: 135 ppm carbon monoxide; 14 ppm ammonia; 12 ppm nitrogen oxide; and 0 ppm nitrogen dioxide. Again, the present invention supplants less desirable gases such as ammonia with acceptable gases such as carbon dioxide, while surprisingly mitigating the production of carbon monoxide.

Example 13—Comparative Example (PSAN-Tetrazole)

A composition/gas generant formed as in Example 10 was combusted within a single stage one mole inflator as employed in Example 10. The peak inflator chamber pressure attained in sustained combustion was about 37 MPa at about 0.015 seconds after combustion began. Gas outputs within a 60-liter ballistic tank were measured from the beginning of combustion at T₀ through 0.1 seconds after combustion. The ballistic tank pressure steadily increased up through 0.05 seconds after combustion began, and then leveled off at a sustained pressure of about 31-32 MPa through 0.1 seconds after combustion began. Sustained pressure indicates suitable gas generating properties that accommodate the sustained pressure utilized in vehicle occupant protection systems.

Example 14

A composition/gas generant formed in accordance with the present invention and as described in Example 4, was combusted within a single stage one mole inflator as employed in Example 10. The peak inflator chamber pressure attained in sustained combustion was about 32 MPa at about 0.013 seconds after combustion began. Gas outputs within a 60-liter ballistic tank were measured from the beginning of combustion at T₀ through 0.1 seconds after combustion. The ballistic tank pressure steadily increased up through 0.05 seconds after combustion began, and then leveled off at a sustained pressure of about 28-31 MPa through 0.1 seconds after combustion began. Sustained pressure indicates suitable gas generating properties that accommodate the sustained pressure utilized in vehicle occupant protection systems. Quite unexpectedly, it has been discovered that compositions provided in accordance with the present invention operate at a peak inflator pressure that is 5 MPa lower than the inflator of Example 13, and yet provide substantially equivalent amounts of sustained pressure in the ballistic tank. Accordingly, it can be seen that the present compositions can sustainably combust at a lower inflator pressure thereby relaxing the structural requirements of the inflator while yet providing similar performance from the standpoint of gas generation over time.

Example 15

A composition/gas generant formed in accordance with the present invention and as described in Example 4, was combusted within a single stage one mole inflator similar or equivalent to the one employed in Example 10. The peak inflator chamber pressure attained in sustained combustion was about 26 MPa at about 0.015 seconds after combustion began. Gas outputs within a 60-liter ballistic tank were measured from the beginning of combustion at T₀ through 0.1 seconds after combustion. The ballistic tank pressure steadily increased up through 0.05 seconds after combustion began, and then leveled off at a sustained pressure of about 30-28 MPa through 0.1 seconds after combustion began. Sustained pressure indicates suitable gas generating properties that accommodate the sustained pressure utilized in vehicle occupant protection systems. Quite unexpectedly, it has been discovered that compositions provided in accordance with the present invention operate at a peak inflator pressure that is about 11 MPa lower than the inflator of Example 13, and yet provide substantially equivalent amounts of sustained pressure in the ballistic tank. Accordingly, it can be seen that the present compositions can sustainably combust at a lower inflator pressure thereby relaxing the structural requirements of the inflator while yet providing similar performance from the standpoint of gas generation over time.

Example 16

A composition/gas generant formed in accordance with the present invention and as described in Example 4, was combusted within a single stage one mole inflator similar or equivalent to the one employed in Example 10. The peak inflator chamber pressure attained in sustained combustion was about 22.5 MPa at about 0.013 seconds after combustion began. Gas outputs within a 60-liter ballistic tank were measured from the beginning of combustion at T₀ through 0.1 seconds after combustion. The ballistic tank pressure steadily increased up through 0.05 seconds after combustion began, and then leveled off at a sustained pressure of about 30-28 MPa through 0.1 seconds after combustion began. Sustained pressure indicates suitable gas generating properties that accommodate the sustained pressure utilized in vehicle occupant protection systems. Quite unexpectedly, it has been discovered that compositions provided in accordance with the present invention operate at a peak inflator pressure that is about 14.5 MPa lower than the inflator of Example 13, and yet provide substantially equivalent amounts of sustained pressure in the ballistic tank. Accordingly, it can be seen that the present compositions can sustainably combust at a lower inflator pressure thereby relaxing the structural requirements of the inflator while yet providing similar performance from the standpoint of gas generation over time.

Example 17

A composition/gas generant formed in accordance with the present invention and as described in Example 4, was combusted within a single stage one mole inflator similar or equivalent to the one employed in Example 10. The peak inflator chamber pressure attained in sustained combustion was about 20 MPa at about 0.015 seconds after combustion began. Gas outputs within a 60-liter ballistic tank were measured from the beginning of combustion at T₀ through 0.1 seconds after combustion. The ballistic tank pressure steadily increased up through 0.05 seconds after combustion began, and then leveled off at a sustained pressure of about 28-30 MPa through 0.1 seconds after combustion began. Sustained pressure indicates suitable gas generating properties that accommodate the sustained pressure utilized in vehicle occupant protection systems. Quite unexpectedly, it has been discovered that compositions provided in accordance with the present invention operate at a peak inflator pressure that is about 17 MPa lower than the inflator of Example 13, and yet provide substantially equivalent amounts of sustained pressure in the ballistic tank. Accordingly, it can be seen that the present compositions can sustainably combust at a lower inflator pressure thereby relaxing the structural requirements of the inflator while yet providing similar performance from the standpoint of gas generation over time.

Example 18

A composition/gas generant formed in accordance with the present invention and as described in Example 4, was combusted within a single stage one mole inflator similar or equivalent to the one employed in Example 10. The peak inflator chamber pressure attained in sustained combustion was about 17.5 MPa at about 0.015 seconds after combustion began. Gas outputs within a 60-liter ballistic tank were measured from the beginning of combustion at T₀ through 0.1 seconds after combustion. The ballistic tank pressure steadily increased up through 0.05 seconds after combustion began, and then leveled off at a sustained pressure of about 28-27 MPa through 0.1 seconds after combustion began. Sustained pressure indicates suitable gas generating properties that accommodate the sustained pressure utilized in vehicle occupant protection systems. Quite unexpectedly, it has been discovered that compositions provided in accordance with the present invention operate at a peak inflator pressure that is about 19.5 MPa lower than the inflator of Example 13, and yet provide substantially equivalent amounts of sustained pressure in the ballistic tank. Accordingly, it can be seen that the present compositions can sustainably combust at a lower inflator pressure thereby relaxing the structural requirements of the inflator while yet providing similar performance from the standpoint of gas generation over time.

Example 19

A composition formed as described in Example 4 exhibited burn rates in inches per second (ips) of about: 0.64 at 1000 pounds per square inch gauge (psig); 0.82 at 2000 psig; 0.98 at 2500 psig; 1.02 at 3500 psig; 1.12 at 4500 psig; and 1.22 at 5500 psig.

Example 20—Comparative Example (PSAN-Tetrazole)

A composition formed as described in Example 10 exhibited burn rates in inches per second (ips) of about: 0.48 at 1000 pounds per square inch gauge (psig); 0.82 at 2000 psig; 0.92 at 2500 psig; 1.02 at 3500 psig; 1.08 at 4500 psig; and 1.12 at 5500 psig.

Example 21

A composition is formed to contain a primary fuel of ammonium dinitrosalicylic acid at about 10-20 weight percent, a secondary fuel of diammonium salt of 5,5′-bis-1H-tetrazole at about 3-15 weight percent, and phase stabilized ammonium nitrate (containing ammonium nitrate and potassium nitrate) as an oxidizer with the ammonium nitrate at about 60-75 weight percent and potassium nitrate at about 5-10 weight percent.

When compared to Example 19, it can be seen that compositions of the present invention exhibit suitable burn rates substantially equivalent to another state-of-the-art gas generant composition as described in Example 10.

As illustrated above, gas generating compositions of the present invention including salts of dinitrosalicylic acid combined with phase stabilized ammonium nitrate result in low combustion solids, with reduced levels of less desirable combustion gases compared to other state-of-the-art gas generants while operating at reduced combustion pressures. Other benefits may include reduced manufacturing costs, improved thermal stability, improved chemical stability, and/or reduced processing costs.

As shown in FIG. 1, an exemplary inflator or gas generating system 10 incorporates a dual chamber design containing a primary gas generating composition 12 formed as described herein, that may be manufactured as known in the art. U.S. Pat. Nos. 6,422,601, 6,805,377, 6,659,500, 6,749,219, and 6,752,421 exemplify typical airbag inflator designs and are each incorporated herein by reference in their entirety.

Referring now to FIG. 2, the exemplary inflator or gas generating system 10 described above may also be incorporated into an airbag system 200. Airbag system 200 includes at least one airbag 202 and an inflator 10 containing a gas generant composition 12 in accordance with the present invention, coupled to airbag 202 so as to enable fluid communication with an interior of the airbag. Airbag system 200 may also include (or be in communication with) a crash event sensor 210. Crash event sensor 210 includes a known crash sensor algorithm that signals actuation of airbag system 200 via, for example, activation of airbag inflator 10 in the event of a collision.

Referring again to FIG. 2, airbag system 200 may also be incorporated into a broader, more comprehensive vehicle occupant restraint system 180 including additional elements such as a safety belt assembly 150. FIG. 2 shows a schematic diagram of one exemplary embodiment of such a restraint system. Safety belt assembly 150 includes a safety belt housing 152 and a safety belt 100 extending from housing 152. A safety belt retractor mechanism 154 (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner 156 containing gas generating composition 12 may be coupled to belt retractor mechanism 154 to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners with which the safety belt embodiments of the present invention may be combined are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference.

Safety belt assembly 150 may also include (or be in communication with) a crash event sensor 158 (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner 156 via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner.

It should be appreciated that safety belt assembly 150, airbag system 200, and more broadly, vehicle occupant protection system 180 exemplify but do not limit gas generating systems contemplated in accordance with the present invention.

In yet another aspect of the invention, a method of making gas generating compositions containing DNSA and PSAN is provided. Because of the acidic nature of DNSA, dry mixing may not be desired. Furthermore, using a salt of DNSA or an adduct of DNSA and another compound may be desirable if dry mixing, however, forming and isolating the respective DNSA derivative may be time consuming and costly. Accordingly, forming a DNSA salt or adduct in situ obviates the need to form the salts or adducts independently. Furthermore, co-crystallization of PSAN can occur at the same time. To begin with, an aqueous slurry of stoichiometric amounts of reactants is prepared including stoichiometrically appropriate, amounts of DNSA, ammonium nitrate, and a potassium source such as potassium nitrate, potassium hydroxide, or potassium carbonate. The resultant formulation as co-precipitated is ammonium DNSA and PSAN. Alternatively, a wet mix of DNSA, an ammonium source such as ammonium hydroxide or di-ammonium carbonate, and PSAN will provide the same results. Even further, a wet mix of DNSA, an ammonium source, a potassium source, and ammonium nitrate would also produce ammonium DNSA and PSAN. All of the aforementioned aqueous mixes provide a base to form a salt of DNSA as a fuel, phase stabilized ammonium nitrate as an oxidizer, wherein sufficient potassium ion is present to stabilize the ammonium nitrate. The aqueous mixture may be blended at room temperature and then gently heated to drive off excess moisture and co-precipitate a blend of DNSA salt and PSAN.

Exemplary Salt-Forming Reactions of DNSA:

DNSA+potassium carbonate=potassium DNSA+water+carbon dioxide

DNSA+potassium hydroxide=potassium DNSA+water

One advantage of the wet mix method is the formation of relatively small DNSA salt crystals. As shown in the microstructure of FIG. 3, PSAN is represented as a plurality of large smooth portions having smaller DNSA salt crystals interspersed within the PSAN. As shown, PSAN grains are relatively large, and because of the relatively smaller size of the DNSA salt crystals, the DNSA salt crystals embed between the relatively larger PSAN grains, thereby providing an intimate mixture or blend of the fuel and the oxidizer. As a result, the resultant free-flowing co-precipitated blend may be pressed or compacted into tablets wafers, or other shapes very readily without having to grind or mill ingredients together as dry ingredients. This eliminates an additional processing step. It is also believed that the small DNSA crystals may contribute to improved or enhanced ballistic and effluent performance of an associated inflator, as described in the examples, particularly because of favorable combustion kinetics due to the intimate mixture of DNSA within PSAN.

Accordingly, a method of processing gas generating compositions of the present invention is provided. Liquid or granulated constituents are preferred in the following steps. The following steps may be followed in all wet method formulations. It should be appreciated that initially, the DNSA must be solvated within the solvent before any other step is conducted. The order of steps 4-8 is not critical, and these steps may be done in any desired order.

• • 1. Provide a solvent within a jacketed mixing vessel. The solvent may, for example, be selected from water, ethanol, propanol, methanol, or some other solvent miscible with water.
  • 2. Place a stoichiometric or predetermined amount of dinitrosalicylic acid in the solvent.
  • 3. Stir the solution.
  • 4. If desired, the solution may be heated and the temperature of the solution may be maintained at temperatures about 100-110 C throughout the process.
  • 5. Add at least one oxidizer selected from ammonium nitrate and phase stabilized ammonium nitrate to the solution and continue to stir.
  • 6. Add a precipitating agent to the composition and continue to stir. The precipitating agent may be a potassium source such as potassium nitrate, potassium hydroxide, or potassium carbonate if ammonium nitrate is added in step five. Alternatively, the precipitating agent may be an ammonium source such as ammonium hydroxide, ammonium bicarbonate, or ammonium carbonate when adding phase stabilized ammonium nitrate in Step 5.
  • 7. If desired, a secondary fuel as described herein, diammonium salt of 5,5′-bis-1H-tetrazole for example, may be added to the slurry while continually stirring.
  • 8. If desired, additional solvent such as distilled water may be added to enhance the solubility of the constituents that are added to the vessel, while continuing to heat and stir the solution. A solid then forms.
  • 9. If desired, the solids and slurry may be continually stirred while heating the solids and slurry, until the desired dryness within the resultant solid is attained.
  • 10. If desired, the solid precipitate may be formed into desired shapes by compression and other known methods of forming tablets or pellets, for example.

Compositions 12 formed by the method provided above are also provided as are gas generators 10 that contain the compositions 12. Further, gas generating systems such as a seat belt assembly 200 or vehicle occupant protection system 180 are also provided, containing a composition 12 formed by the method provided above.

The formation of small particles of DNSA salt crystals is advantageous in that the relatively small particles, equal to or less than 10 microns in length or width or depth, are readily entrained or precipitated or embedded within the much larger ammonium nitrate crystals as shown in FIG. 3. Unlike other precipitates, the microstructure is therefore readily amenable to pressing into tablets, wafers, or other shapes, without having to grind or mill ingredients together as dry ingredients. The wet mix process forms rounded granules that flow well in-bulk in press feeders to make tablets, for example. In essence, the aforementioned process results in reduced processing of raw materials, and fewer number of ingredients compared to dry blending. It is also results in free flowing granules from the wet-mix process and obviating the need to mill the constituents or the composition.

It should further be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents.

Claims

1. A method of forming a gas generating composition comprising the following steps:

providing a solvent within a jacketed mixing vessel;

adding a stoichiometric amount of dinitrosalicylic acid to the solvent and stirring;

adding at least one oxidizer in a stoichiometric amount to the solution and stifling, the oxidizer selected from ammonium nitrate and phase stabilized ammonium nitrate; and

adding a precipitating agent to the composition and continuing to stir, thereby forming solids.

2. The method of claim 1 wherein the solvent is selected from water, ethanol, methanol, propanol, and any other solvent miscible with water.

3. The method of claim 1 wherein the precipitating agent is a potassium source and is added when ammonium nitrate is added to the vessel.

4. The method of claim 3 wherein the precipitating agent is selected from potassium nitrate, potassium hydroxide, and dipotassium carbonate.

5. The method of claim 1 wherein the precipitating agent is an ammonium source and is added when phase stabilized ammonium nitrate is added to the vessel.

6. The method of claim 5 wherein the precipitating agent is selected from ammonium hydroxide and ammonium carbonate.

7. The method of claim 1 further comprising the step of adding a secondary fuel to the vessel and continuing to stir.

8. The method of claim 7 wherein diammonium salt of 5,5′-bis-1H-tetrazole is added as a secondary fuel.

9. The method of claim 7 wherein the secondary fuel that is added to the vessel is selected from tetrazoles and salts thereof; triazoles and salts thereof; azoles and salts thereof; guanidine salts and derivatives; imides; amides; aliphatic carboxylic acids and salts thereof; aromatic carboxylic acids and salts thereof; nitro-aromatic carboxylic acids and salts thereof; nitrosalicylic acids and salts thereof; amines; nitrophenols; pyrazoles;

imidazoles; azines; and mixtures thereof.

10. The method of claim 1 further comprising the step of adding additional solvent after adding the oxidizer to enhance the solubility of the constituents that are added to the vessel, while continuing to heat and stir the solution.

11. The method of claim 1 further comprising the step of forming the solid precipitate into a desired form.

12. The method of claim 11 wherein the method is selected from compression and extrusion methods.

13. A composition formed from the method of claim 1.

14. A composition formed from the method of claim 7.

15. A composition formed from the method of claim 8.

16. A composition formed from the method of claim 9.

17. A gas generator containing a composition formed from the method of claim 1.

18. A vehicle occupant protection system containing a composition formed from the method of claim 1.

19. The method of claim 1 further comprising the step of heating and maintain the temperature of the solution to about 100 C-110 C.

20. The method of claim 1 further comprising the step of stirring and heating the solids until the desired dryness within the resultant solids is attained.