JP2008538348A - Gas generating composition - Google Patents

Abstract

  The present invention relates generally to gas generant compositions for inflators such as occupant restraint systems. The gas generant composition 12 formed in accordance with the present invention includes an alkyl cellulose fuel / binder, an oxidizer, and a combustion inhibitor or ignition catalyst. The vehicle occupant protection system 180, other gas generation systems, incorporate the compositions of the present invention.

Description

Related Application Cross Reference This application claims the benefit of US Provisional Application No. 60 / 666,964, filed March 31, 2005.

TECHNICAL FIELD The present invention relates to general gas generation systems and gas generant compositions used in gas generators, for example for automobile restraint systems.

BACKGROUND OF THE INVENTION The present invention relates to a non-toxic gas generating composition that rapidly generates a gas that serves to inflate an automobile occupant safety restraint device upon combustion. In particular, the present invention provides a thermally stable non-azide gas that exhibits a relatively high gas volume to solid particulate ratio at an acceptable flame temperature during combustion as well as an acceptable combustion rate. Related to the product. Generation of non-azide gas products from azide-based gas generants is well described in the prior art. The advantages of non-azide gas generant compositions compared to azide gas generants are, for example, U.S. Patents 4,370,181; 4,909,549; 4,948,439; 5,084,118; 5,139,588 and No. 5,035,757 is widely disclosed. These patents are referenced and incorporated as part of this specification.

  In addition to fuel components, pyrotechnic non-azide gas generants provide oxygen necessary for rapid combustion and components such as oxidants, carbon and nitrogen to reduce the amount of toxic gases produced And a slag-forming component that causes agglomeration of solid and liquid products formed during or immediately after combustion into filterable clinker-like particulate masses. Other optional additives such as burn rate improvers or ballistic property improvers, and ignition aids are used to control the ignitability and flammability of the gas generant.

  One of the disadvantages of known non-azide gas generant compositions is the amount and physical characteristics of the solid residue formed during combustion. When used in a vehicle occupant protection system, solids resulting from combustion must be filtered or otherwise kept out of contact with the vehicle occupant. It is therefore highly desirable to develop a composition that minimizes the production of solid particulates while providing an appropriate amount of non-toxic gas to inflate the safety device at high speed.

  The use of, for example, phase-stabilized ammonium nitrate as an oxidant is desirable because it produces abundant non-toxic gases and minimal solids upon combustion. However, in order to be useful in automotive applications, the gas generant must be thermally stable when aged at a temperature of 107 ° C. for more than 400 hours. The composition must also retain structural integrity when cycled between -40 ° C and 107 ° C. In addition, gas generant compositions incorporating phase stabilized ammonium nitrate or pure ammonium nitrate sometimes exhibit poor thermal stability, depending on the composition of the additive being combined, such as plasticizer and binder, It produces unfortunately high levels of toxic gases such as CO and NOx.

  Nevertheless, the addition of additives such as binders is often necessary to preserve the shape of the propellant or gas generant tablet and to prevent their fragmentation over time. Certain water soluble binders, such as carboxyl cellulose binders, exhibit the hygroscopicity afforded by their water solubility. Accordingly, these types of binders often result in compositions having poor thermal stability. This occurs in particular with compositions containing preferred oxidants such as, for example, phase stabilized ammonium nitrate. Thus, ongoing efforts in the design of automotive gas generation systems, for example, have the initiative to produce more gas and less solids and without the disadvantages mentioned above.

SUMMARY OF THE INVENTION The above problems are solved by a gas generating system comprising a gas generating composition comprising an alkyl cellulose binder, such as cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate. In other words, the composition of the present invention comprises a cellulosic binder comprising an alkyl substituent as a main component, an oxidizing agent, and molybdenum trioxide and other molybdenum compounds, dibutyl taleate, dicyclohexurea, triacetin and Including an ignition catalyst or combustion inhibitor selected from a mixture thereof. Known fuels, oxidants and other additives can be incorporated into these compositions as is known in the art and as determined by design criteria. The present invention provides gas generation systems such as airbag inflators and vehicle occupant protection systems having these gas generating compositions.

  A typical micro gas generator uses nitrocellulose or a smokeless explosive composition for gas generation in the device. These compositions often result in relatively higher amounts of carbon monoxide. In addition, the use of nitrocellulose does not facilitate ballistic customization. These are non-nitrocellulose compositions that contain an oxidant, a fuel and a binder. The performance characteristics related to the burning rate (ie ballistic power) can be varied by the particle size distribution of the oxidant component. Generally, when the particle size distribution of the oxidizer is reduced, the burning rate of the propellant composition increase is improved, and therefore the ballistic characteristics are also improved. As the particle size increases, the burning rate decreases and, therefore, the ballistic properties also deteriorate. Therefore, the ballistic characteristics can be adjusted in this way. The average particle size is in the range of 10 to 150 microns. Combinations of particle size distributions within the aforementioned range can also be considered for the purpose of changing performance. Adjustment of the ballistic properties can also be achieved by changing the shape, size and surface treatment of the propellant grains, or any combination thereof. Various propellant processes and techniques that affect propellant particle density, porosity, and surface finish (ie, whether the exposed combustion surface area is large or low) are also variable, for example, to achieve a reversible combustion profile. Can be used to adjust stick output. Propellant geometries such as small cylinders machined in a specific way, such as extrusion, exhibit a porous center and a reversible type combustion profile. This makes it easier to limit damage to equipment incorporating gas generants, such as seat belt pretensioners.

  In summary, the present invention optimizes the production of gas combustion products, minimizes solid combustion products, and retains other design requirements such as reduced hygroscopicity and thermal stability. Offer things. These and other advantages will be apparent from the detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention generally includes a gas generant composition comprising a fuel, an oxidant, molybdenum trioxide, and a first binder. The first binder is selected from the group of cellulose binders such as cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate. In other words, the composition of the present invention preferably comprises a first cellulose binder having an alkyl substituent. Examples of the alkyl substituent include an acetyl group, a propionyl group, and a butyryl group having a hydroxyl group. The first binder is generally provided at about 5-30% based on the weight of the composition.

  In the present invention, a combustion inhibitor and a combustion inhibitor are also included. This is selected from the group comprising dibutyl taleate, dicyclohexurea, triacetin and other known combustion inhibitors and mixtures thereof. The combustion inhibitor or ignition catalyst can be provided at about 0.1-20% weight percent. By inhibiting combustion, possible damage to devices with gas generation systems such as seat belt assemblies and pretensioners is mitigated. In accordance with one aspect of the present invention, it has been found that the addition of combustion described substantially reduces the overall ignition temperature, thereby maintaining the integrity of related equipment such as, for example, a seat belt pretensioner.

Example 1:
A composition comprising nitroguanidine, potassium perchlorate and cellulose acetate butyrate was intimately mixed in a known manner. Although heat was applied from a hot plate, the composition did not ignite automatically at 320 ° C., producing black charcoal.

Example 2:
To the composition of Example 1 containing cellulose acetate butyrate, nitroguanidine, and potassium perchlorate, about 1 wt% ammonium molybdate was added. It was an ignition temperature of 260 ° C. when measured with a hot plate.

Example 3 and Example 4:
To the composition of Example 1 containing cellulose acetate butyrate, nitroguanidine, and potassium perchlorate, about 1 wt% or 2 wt% molybdenum trioxide was added. It was an ignition temperature of 262 ° C. when measured with a hot plate.
It can be seen from the examples that the use of a combustion inhibitor or ignition catalyst in accordance with the present invention results in an ignitable composition that effectively mitigates the harm to the associated equipment.

  In a different aspect of the invention, a carbon monoxide scavenger can be provided. Thereby, the required outflow rate is maintained despite the use of the cellulose binder. When used optionally, metal oxides such as manganese oxide and cupric oxide, sulfates such as ammonium sulfate and other scavengers are contemplated for use at about 0.1-20% by weight of the composition. Is done. By using a CO scavenger, the overall cost of the gas generant composition is increased by increasing the relative amount of binder / fuel and reducing the amount of other fuels typically used in the gas generant composition. Can be reduced. The gas generant composition of the present invention may further include the following components in the indicated weight percentages. A second fuel selected from the group comprising the following compounds; azoles such as 5-aminotetrazole; non-metal salts of azoles such as potassium 5-aminotetrazole; 5,5′-bis-1H-tetrazole Non-metal salts of azoles such as mono- or diammonium salts of; nitrites of azoles such as 5-aminotetrazole nitrate; nitroamine derivatives of azoles such as 5-nitroaminotetrazole; dipotassium such as 5-nitroaminotetrazole Metal salts of nitroamine derivatives of azoles; metal salts of nitroamine derivatives of azoles such as dipotassium 5-nitroaminotetrazole; non-metal salts of nitroamine derivatives such as mono- or diammonium 5-nitroaminotetrazole; and dicyandiamide, nitro Guanidines such as anidine and guanidine nitrate; guanidine salts such as guanidine nitrate; nitro derivatives of guanidine such as nitroguanidine; azoamides such as azodicarbonamide; azoamides such as azodicarbonamidine dinitrate Nitrates; and mixtures thereof. The second fuel is typically used at 0.1-50 wt%, more preferably about 5-40 wt%, based on the total weight of the gas generant composition. It will be appreciated that in certain compositions, the binder may function as a binder / fuel, and the amount of binder used may further provide an effective amount of fuel. Thus, in that case, the second fuel may not be included in the composition. An optional third fuel selected from the same group of fuels is typically provided at about 0-50% by weight, more preferably about 0-30% by weight.

  The non-metallic or metallic first oxidant can be selected, for example, from the following compounds: ammonium nitrate, a phase-stabilized ammonium nitrate stabilized in a known manner, more preferably about 10% by weight potassium nitrate Nitrates such as potassium nitrate and strontium nitrate; nitrites such as potassium nitrite; chlorates such as potassium chlorate; perchlorates such as ammonium perchlorate and potassium perchlorate; iron oxide and Oxides such as copper oxide; basic nitrates such as basic copper nitrate and basic iron nitrate; and mixtures thereof. The first oxidant can be provided at about 0.1-70% by weight, more preferably about 30-70% by weight. A second oxidant can also be used and is selected from the oxidants described above. The second oxidant is typically provided at about 0-50 wt%, more preferably 0-30 wt%, based on the weight of the gas generant composition.

  The optional second binder can be selected from the following compounds; cellulose derivatives such as cellulose acetate, cellulose acetate butyrate, carboxymethyl cellulose, salts of carboxymethyl cellulose; silicones; polyalkenes such as polypropylene carbonate and polyethylene carbonate Carbonates; and mixtures thereof. If used, the second binder can be provided at about 0-10% by weight, more preferably 0-5% by weight.

  The optional slag former can be selected from the following compounds; silicon compounds such as silicon atoms and silicon dioxide; silicones such as polydimethylsiloxane; silicates such as potassium silicate; clays, talc and Natural minerals such as mica; fumed metal oxides such as fumed silica and fumed alumina. If used, the slag former may be provided at about 0-10% by weight, more preferably 0-5% by weight.

  Other exemplary fuels, oxidants, and other gas generant components are described in U.S. Pat. Nos. 5,035,757, 5,756,929, 5,872,329, incorporated herein by reference. 6,074,502, 6,287,400, 6,210,505 and 6,306,232. The gas generant components of the present invention can be provided by known suppliers such as Aldrich Chemical Company, Fisher Chemical Company and Eastman Chemical Company.

  The gas generant composition of the present invention can be formed as is known in the art. A typical manufacturing process includes the following steps: (1) Mixing and / or milling of oxidizer, fuel, binder and other components in the absence of solvent and compacting the powder material in a press; (2 Depending on the binder chemistry and functional groups, the cellulose binder is solvated with an organic, aqueous, or aqueous / organic solution, and the desired components such as fuel, oxidant and other additives are added to the propeller. Then the solvent is dried off; (3) solvate the cellulose binder, add oxidant, fuel and other ingredients, extrude the propellant through the die under pressure, various shapes To form. Thereafter, the molded product is cut into a predetermined length, and the solvent is removed by evaporation or heating. It will be appreciated that an oxidant is selected to adjust the overall oxygen balance by known methods to reduce CO and other undesirable effluents.

  The drying process can be accelerated by applying heat to the final homogeneous mixture. Or, for example, according to design criteria, the drying process can be extended without heating. Other blending methods are contemplated to include other known wet and dry mixing and consolidation methods. The compositions of the present invention are contemplated for use in gas generation systems. Exemplary gas generation systems include an airbag device or the vehicle occupant protection system shown in FIG. 2, including an airbag module, airbag inflator, or gas generator. More generally, it includes a vehicle occupant restraint system constructed or designed as is known in the art.

  As shown in FIG. 1, the exemplary inflator incorporates a dual chamber design to adjust the deployment force of the associated airbag. In general, an inflator including a gas generant 12 formed as described herein can be manufactured by known techniques. US Pat. Nos. 6,422,601, 6,805,377, 6,659,500, 6,749,219 and 6,752,421 illustrate typical airbag inflator designs, which are referenced and described herein. Incorporated as part of the book.

  Please refer to FIG. The exemplary inflator 10 described above can be incorporated into the airbag system 200. The airbag system 200 includes at least one airbag 202 and an inflator 10 that includes the gas generant composition 12 of the present invention, the inflator being associated with the airbag 202 in fluid communication with the interior of the airbag. The airbag system 200 includes or is connected to a crash sensor 210. The crash sensor 210 includes a known crash sensor algorithm and signals activation of the airbag system 200 in the event of a crash, for example by activation of the airbag inflator 10.

  Please refer to FIG. The airbag system 200 can be incorporated into a wider and more comprehensive vehicle occupant restraint system 180 that includes 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 (eg, a spring-type mechanism) can be coupled to the end portion of the belt. Further, a safety belt pretensioner 156 including a propellant 12 can be coupled to the belt retractor mechanism 154 to start the retractor mechanism in the event of a collision. Exemplary seat belt retractor mechanisms that can be used with the safety belt embodiment of the present invention are US Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546. These patents are referenced and incorporated as part of this specification. Examples of typical pretensioners with which safety belt embodiments of the present invention can be combined are disclosed in US Pat. Nos. 6,505,790 and 6,419,177. These patents are referenced and incorporated as part of this specification.

  The safety belt assembly 150 includes a crash sensor algorithm 158 (e.g., a known crash sensor algorithm that generates an activation signal for the belt pretensioner 156, e.g., upon activation of a pyrotechnic igniter (not shown) incorporated in the pretensioner. Inertial sensors or accelerometers) or can be connected thereto. US Pat. Nos. 6,505,790 and 6,419,177, referenced above and incorporated as part of this specification, provide examples of pretensioners that start in such a manner.

  Although the safety belt assembly 150, the airbag system 200, and the wider vehicle occupant protection system 180 are illustrated, the gas generation system contemplated by the present invention is not limited thereto.

  It will be further understood that the foregoing descriptions of embodiments of the present invention are for illustrative purposes only and do not limit the scope of the invention in any way. As such, the various structural operational features shown herein can be modified in many ways by those skilled in the art without departing from the scope of the invention as defined by the claims. .

FIG. 1 illustrates an exemplary airbag inflator that includes a gas generant composition formed in accordance with the present invention. FIG. 2 is a schematic diagram of an exemplary vehicle occupant restraint system incorporating the inflator of FIG. 1 and a gas generant according to the present invention.

Claims (12)

A gas generating system comprising a gas generating composition, wherein the composition comprises:
A fuel / binder selected from the group consisting of cellulosic binders containing alkyl substituents;
An oxidizing agent; and an additive selected from dibutyltalates, dicyclohexurea, triacetin, molybdenum trioxide, molybdic acid, ammonium molybdate, sodium molybdate, phosphomolybdic acid, molybdenum disulfide and sodium phosphomolybdate;
Wherein the additive is provided at about 0.05 to 20 weight percent of the weight of the composition. The gas of claim 1, further comprising a second additive selected from metal oxides and sulfates, wherein the second additive is provided at about 0.1 to 20 wt% of the weight of the composition. Generation system. The gas generating system of claim 2, wherein the second additive is selected from manganese oxide, cupric oxide and ammonium sulfate. The oxidant is selected from a metal oxidant or a non-metal oxidant, and the oxidant is selected from nitrate, nitrite, perchlorate, chlorate, oxide and basic metal nitrate. A gas generation system as described. The oxidant is ammonium nitrate, phase stabilized stabilized ammonium nitrate, potassium nitrate and strontium; nitrites such as potassium nitrite; chlorates such as potassium chlorate; such as ammonium perchlorate and potassium perchlorate Selected from perchlorates; oxides such as iron oxide and copper oxide; basic nitrates such as basic copper nitrate and basic iron nitrate; and mixtures thereof;
The gas generating system of claim 4, wherein the oxidant is provided at about 0.1-70 wt%. Non-metal salts and metal salts of azoles; azoles, guanidines, nitroamine derivatives and salts of guanidine derivatives; guanidines, salts of azoamides; nitrates of azoamides; and mixtures thereof The gas generation system of claim 1, further comprising: about 0.1-50 wt% of the second fuel. The azole is selected from 5-aminotetrazole; the non-metal salts of the azoles are selected from monoammonium or diammonium salts of 5,5′-bis-1H-tetrazole, and 5-aminotetrazole nitrate; Nitroamine derivatives and salts are selected from 5-nitroaminotetrazole, dipotassium 5-nitroaminotetrazole, monoammonium 5-nitroaminotetrazole and diammonium 5-nitroaminotetrazole; said guanidines, guanidine derivatives and guanidine salts are dicyandiamide Nitroguanidine and guanidine nitrate; the azoamides and nitrates of azoamides are selected from azodicarbonamide and azodicarbonamidine dinitrate Item 7. The gas generation system according to Item 6. The gas generating system according to claim 1, wherein the cellulose-based binder containing an alkyl substituent is selected from cellulose-based binders containing an alkyl substituent selected from acetyl, propionyl, and a butyryl group having a hydroxyl group. The gas generation system according to claim 1, wherein the cellulose-based binder is selected from cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl hydroxyethyl cellulose. The gas generating system of claim 1, further comprising about 0.1-20 wt% metal oxide based on the weight of the gas generating composition. A vehicle occupant protection system comprising the gas generation system of claim 1. A gas generant composition comprising:
A fuel / binder selected from the group consisting of cellulosic binders containing alkyl substituents;
An oxidizing agent; and an additive selected from dibutyltalates, dicyclohexurea, triacetin, molybdenum trioxide, molybdic acid, ammonium molybdate, sodium molybdate, phosphomolybdic acid, molybdenum disulfide and sodium phosphomolybdate;
Wherein the additive is provided at about 0.05 to 20 weight percent of the weight of the composition.

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