CN1169459A - Process for preparation of gas-generating compositions - Google Patents

Abstract

A process for the production fo a gas-generating composition containing a redox-couple including a solutable azide component and an oxidizer component includes forming an aqueous dispersion of the redox-couple wherein the azide component is totally dissolved and the oxidizer is uniformly dispersed and stabilised in the azide solution, passing said aqueous dispersion through a spray nozzle to form a stream of droplets, conducting said droplets with hot air whereby the water is removed to produce solid particles of gas-generating composition.

Description

The preparation method of gas generating composition

The present invention relates to a kind of preparation method of gas generating composition, especially contain the composition of the redox couple of being made up of trinitride and oxygenant, it can discharge nitrogen after burning.This based composition is widely used as propellant compositions, with " air bag " that provide gas to be used for to expand automotive occupant baffle safety system (air-bags), wherein composition is lighted when collision happens, simultaneously because the gas that composition rapid combustion produces charges into air bag.

Successful, the operation fast of gas-bag system when crashing of the combustionproperty of airbag gas generation composition is very crucial.Air bag must be in about 30-40 millisecond time be expanded by the steady air flow of lower temperature, damages air bag or the occupant is produced injury avoiding.Therefore gas generating composition must ignite easily, and rapid combustion and rate of combustion are stable, controlled and can reproduce.Further requiring is the toxic substance that expanding gas can not contain significant quantity, therefore should avoid producing any toxic substance, even or produced, also should leach air-flow.

Present welcome gas generating composition comprises the redox system that contains trinitride, it is based on trinitride such as basic metal and an alkaline earth metal azide, and be mixed with can and trinitride reaction generation heat and discharge the metal oxide of nitrogen, as the oxide compound of iron, aluminium, copper or silicon.Preferred compositions is based on sodiumazide, and preferred oxidant constituents comprises ferric oxide.This based composition also can advantageously contain the highest about 15% silicon-dioxide, so that mix with the sodium oxide that is produced by sodiumazide, thereby it is residual to form the slag that is easy to remove.

In order to satisfy the strict demand of airbag inflation system, each component must be disperseed very thinly, and closely and equably mixes.Mix particle bad and/or the trinitride component and cross senior general and cause reaction not exclusively, and in products of combustion, exist flammable and toxic substance such as sodium Metal 99.5.For reaching a prerequisite that reacts completely is that the blended degree should make each component press the formula rate existence in the space that the linear dimension (the trinitride gas generating composition is about 20 microns) of a reaction zone length is determined.The completeness of reaction depends on that also each component is diffused into the required together time at reaction zone, has only ought obviously be less than diffusion time to react and passes the required time of reaction zone length, and reaction could be carried out fully.The size and the intergranular distance that depend on each component particles diffusion time.Therefore, can make reaction more complete by the degree of mixing that reduces granularity and each component of increase.

Up to now, used the whole bag of tricks to prepare gas generating composition, to obtain the well-mixed fine grain composition of desired form.The method of many prior aries is based on and grinds each component separately or together, each component is mixed and is pressed into sheet or granular, in the gas generating system of packing into.Grinding can be carried out (as USP 3895098,4203787,4243443 and 4376002 in cited) by dry method, also can carry out (as described in USP 5074940,4999063 and 4547235) with wet method.

In a kind of improved wet method (for example described in USP 5143567 and 5223184), each component is ground into wet slurry and spraying drying, the granularity of component, the especially granularity of trinitride component are by the grinding technics decision, rather than the drying process decision.Therefore this process of lapping is very little to the control of size distribution, has caused the trinitride component of the larger particles of higher proportion inevitably, they can not with thinner oxidant constituents thorough mixing.Thereby this composition can not react completely and have unsettled speed of reaction.In addition, in the dry grinding process, also exist and catch fire or the danger of dust explosion.

In another approach, trinitride base gas generation redox couple composition is preparation like this: the trinitride component is soluble in water, in azide solution, disperse or dissolve oxidant constituents, separate out trinitride by solution or dispersion are mixed with the non-solvent (as ethanol) of trinitride.These class methods have narration in USP 4021275 and English Patent Nos GB2270686 and GB 2278840.The shortcoming of these class methods relates to reclaim the expense of solvent, and the efficient that reclaims trinitride is low, and uses combustible solvent also to have the danger of catching fire.

In a kind of method of narration, gas generating composition is preparation like this, by insoluble divided oxide being dispersed in the hot solution of trinitride, separates out trinitride after the cooling, solid particulate is separated from supernatant liquid again in German Patent 4133595.This method process cost costliness is because it is not high to reclaim the efficient of trinitride.And the granularity of the trinitride of separating out can not control, so contains a high proportion of oversized particles in the product, causes reacting incomplete and unsettled rate of combustion simultaneously.

An object of the present invention is to provide a kind of method for preparing trinitride base gas generating composition safely and effectively, it can obtain the thorough mixing of required small particle size He each component, produces gas when making it to be adapted at airbag inflation.

We have found that, advantageously that trinitride is soluble in water fully when preparation trinitride base gas generating composition, in water, be dissolved with or be dispersed with oxygenant, and then with solution or dispersion spraying drying.

Therefore the present invention relates to a kind of preparation method of gas generating composition, said composition contains a kind of by water-soluble trinitride component with can produce the redox couple that the oxidant constituents of gas is formed with described trinitride component reaction, this method may further comprise the steps: form a kind of aqueous based dispersions of described redox couple, wherein the trinitride component dissolve fully and oxidant constituents with form homodisperse and stabilization in azide solution of solution or stable solid granulates dispersion; Described aqueous based dispersions is formed stream of liquid droplets by a nozzle; With described drop is contacted with warm air, to remove the solid particulate anhydrate and to make gas generating composition.

The trinitride component preferably includes a kind of basic metal or alkaline-earth metal, sodium for example, potassium, lithium, the trinitride of calcium or barium, most preferably sodiumazide.Oxygenant if desired, a kind of oxidative compound that can be water-soluble, for example nitrate or perchlorate are as the nitrate or the perchlorate of sodium or potassium.In this case, the particle that is formed by the spraying drying drop comprises the coacervate of very thin redox couple mixed crystal, the about 0.5-5 μ m of minimum size place of the primary crystal of this redox couple, preferred 0.5-1 μ m.But preferably oxygenant that can be water-soluble because can obtain very thin granularity like this and sneak into to form slurry in the azide solution, thereby is reduced in water required when atomizing dispersion.Preferred oxidant constituents be a kind of in electromotive series the oxide compound than the metal of the metal even lower level of trinitride.Preferred metal oxide comprises iron, nickel, vanadium, copper, titanium, manganese, zinc, tantalum, the oxide compound of silicon or aluminium.In them with ferric oxide, Fe ₂O ₃For good.It is 0.1-1.0 μ m that these oxide compounds are easy to obtain granularity, the fine particulate form of preferred 0.1-0.3 μ m.

Advantageously in the slurry of trinitride and metal oxide, add a certain amount of silicon-dioxide, SiO ₂It not only plays the effect of oxidant constituents, and can make slurry more viscous, thereby alleviate or avoid the migration of metal oxide in large quantities of slurry or slurry drip, but also can form glassy residue with metal oxide that in redox reaction, forms such as sodium oxide reaction, this residue can easily leach from the nitrogen that produces.Silicon-dioxide should preferably very thin form.Being easy to obtain particle diameter is other silicon-dioxide of 0.007-0.02 μ m level.

Preferably, redox couple comprises the 50-70 weight part, the more preferably sodiumazide of 60-70 weight part, the ferric oxide of 20-30 weight part, Fe ₂O ₃And the silicon-dioxide of 5-14 weight part, SiO ₂When forming aqueous based dispersions, said composition is sneaked in the water of capacity, and with all trinitride of dissolving under atomization temperature, but the consumption that should limit water is to minimum, so that the water yield of required evaporation when reducing spraying drying.Usually, the trinitride component of every 30-45 weight part can contain the water of 100 weight parts in the dispersion.

Can oxidant constituents be dispersed in the azide solution by the vigorous stirring dispersion, this stirring should make all oxygenant particle separation to enough degree, for water-soluble oxidizers, can reach minimum by the viscosity of dispersion and indicate, the dispersion of the minimum value indication oxygenant of viscosity has reached at utmost.In order to obtain the most effective dispersion, preferred high-shear mixer.The viscosity of dispersion should be enough high, to avoid solid particulate (as ferric oxide) obviously migration from the dispersion of a large amount of drops.

In forming the step of drop, can under pressure, make the nozzle of the aperture of dispersion by having one or more diameter 0.5-2.5mm, thereby make the aqueous based dispersions of redox couple in spray nozzle, be atomized into the small droplets of 40-200 μ m diameter easily.By making drop fall into temperature range is 80-250 ℃, can make drop spraying drying easily in preferred 80-180 ℃ the hot blast.It is different that the temperature in of airflow and temperature out should have, to obtain required heat passage of dry drop.The temperature range of being quoted is to point out mouth and temperature in respectively herein.

The particle of the present invention's preparation consists essentially of the spherical micropore coacervate of trinitride crystalline; wherein coacervate be in for the required very narrow particle size range of oxygenant complete reaction in; 20-100 μ m diameter range for example; at the minimum size place; the trinitride primary crystal is 0.5-5 μ m, is generally 0.5-1 μ m.Generally speaking, all solids oxygenant particle is all wrapped up by the trinitride crystal, and thinks to serve as the nuclear of trinitride crystal growth.This method produces ultrafine dust seldom, and these dust are deleterious in follow-up technology.This product is easy to be pressed into sheet or granular, thereby is used for taking place gas when giving airbag aeration.Compression moulding operation can be carried out easily by after spray-dired redox particle and a certain amount of water or other binder such as Graphite Powder 99 are mixed.Water preferably provides with the form of water and hydrophobic fumed silica mixture, and wherein silicon-dioxide can be sneaked in the redox composition with high-shear mixer.Composition can be pressed into the sheet or the particle of the conventional density of 2.0-2.2g/cc then, they can be by lighter for ignition such as ignition, or more effectively light easily by the igniting blasting agent, wherein the igniting blasting agent comprises the fireworks flaky material, this material is applied by the oxidable metal of one deck such as magnesium by a kind of oxidisability film such as tetrafluoroethylene and forms, and this has narration in EP 505024.

The present invention is further described by the following examples, and wherein all parts and percentage number average are base with weight.

Embodiment 1-5

Table 1

	Embodiment					The comparative example
								Component (%)	???1	???2	???3	???4	????5	????6	????7
??????NaN 3	???61	???63	???63	???63	???69	???64.5	???64.5
								?????Fe 2O 3	???27	???27	???29	???31	??29.5	???26.5	???26.5
??????SiO 2	???12	???10	???8	???6	??1.5	????9	????9
								The reaction heat KJ/g that estimates	??1.60	??1.51	??1.38	??1.26	??1.07	???1.47	???1.47
Test burn linear rate mm/s	??48.2	??43.7	??37.8	??32.8	??15.0	???32.8	???24.4

By sodiumazide is water-soluble with the concentration of every hectogram water 44 gram sodiumazide, the batching of the embodiment 1-5 shown in the preparation table 1.In ratio shown in the table 1 ferric oxide (Har-cros R-1599D, granularity 0.2 μ m) and silicon-dioxide (CAB-O-SIL M-5 type fumed silica, Cabot Corporation, Boston, Mass, nominal granularity 0.014 μ m) are added above-mentioned solution.(MaSS) mixing velocity with 3000rpm is dispersed in oxide particle in 70 liters of azide solutions for Silver-son Machines Inc. manufacturing, East Longmeadow with DX type Silverson high speed shear mixing machine.(made by NIRO Inc., Columbia Maryland), and enters in the counter-flow air of introducing by the 4.47mm diameter by two fluid tips (06-06 type) with 2.18mm bore dia slurry to be pumped into NIRO Mi-nor-5 spray-drier.The intake air temperature of spray-drier is 180 ℃, and temperature out is controlled at 100 ℃.About 11 seconds of the residence time of batching in airflow.Collect the product powder, and in powder, sneak into a spot of moisture (2% weight) as tackiness agent or binder.Moisture is 28.5 gram hydrophobic silicas (Tulco Inc. sells with TULLANOX-500, and from Cabot Corporation, Boston, Mass. secures permission) to be mixed in 100m1 water and when forming by high speed mixer.The moisture of making like this has fine grain consistence, can easily add and mix fully with the fireworks powder of preparation in these embodiments.With powder in hydraulic press with 138MPa pressure pressurize 3 seconds, be pressed into diameter 12.5mm, the right cylinder of high 12.5mm.The right cylinder that is pressed into is dry in baking oven then to be less than 0.1% until moisture.Exsiccant right cylinder nominal density 2g/cc.Cylindrical curved surface and the coated one deck thermosetting epoxy resin of end face are to prevent prematur ignition.Right cylinder burns in 1.8 liters pressurized vessel, and initial nitrogen pressure is 6.9MPa in the container.With lighter for ignition uncoated end face is lighted.Determine the perfect combustion required time by pressure record, by with cylinder length divided by obtaining rate of combustion combustion time.The results are shown in table 1.Find that the experiment rate of combustion is the function of expectation reaction energy, because it increases along with the increase of batching reaction energy.Residue after the test places water.Viewed sodium flame when not observing the similar batching for preparing with other method.This has proved advantageously that by force the degree of mixing that obtains with the inventive method is very high.

The Photomicrograph of the product of embodiment 5 such as Fig. 1, the diameter of spherical as can be seen coacervate formal product are no more than about 20 μ m.Fig. 2 shows the scanning electron microscopy X ray concentration map of the product of embodiment 3.

These figure have shown three kinds of element Na, the concentration of Fe and Si, and this shows three kinds of components, NaN with form intuitively ₃, Fe ₂O ₃And SiO ₂Distribute equably at the spray-dried granules camber.Comparative example 6 (Table I)

With 40 gram sodiumazide, 16.4 gram ferric oxide (Harcros R-1599D) and 5.6 gram silicon-dioxide (CAB-O-SIL M-5) mechanically mixing and ball millings.With the sample that is used to measure rate of combustion in the previous embodiment with the quadrat method preparation.The burning linear rate that obtains is 32.8mm/s, and it is starkly lower than the product made from the inventive method.After residue places water, produce a large amount of sodium flame.Comparative example 7 (table 1)

In the present embodiment, with the sodiumazide of equal amts among the embodiment 6, ferric oxide and silicon oxide mix with 110ml water.Mixture places the steam sleeve container dry then.Test burn speed only is 24.4mm/s.The same with embodiment 6, the present embodiment residue also produces a large amount of sodium flame after placing water.

Claims (12)

1. process gas generation method for compositions, said composition contains the redox couple of being made up of water-soluble trinitride component and oxidant constituents, trinitride component wherein for example is the trinitride of sodium, potassium, lithium, calcium or barium, oxidant constituents for example is the oxide compound of SODIUMNITRATE, sodium perchlorate, saltpetre, potassium perchlorate or iron, nickel, vanadium, copper, titanium, manganese, zinc, tantalum, silicon or aluminium, described oxidant constituents can produce gas with described trinitride component reaction, and this method may further comprise the steps:

Form a kind of aqueous based dispersions of above-mentioned redox couple, wherein the trinitride component is dissolved fully, and oxidant constituents homodisperse and stabilization in azide solution;

Described aqueous based dispersions is formed stream of liquid droplets by a nozzle; With

Described drop is contacted with warm air, to remove the solid particulate that anhydrates and make gas generating composition.

2. according to the method for claim 1, it is characterized in that described oxidant constituents comprises water-soluble oxidizers, and described aqueous based dispersions is the slurry of this oxygenant in stacked oxide solution.

3. according to the method for claim 2, it is characterized in that the oxygenant particle size is that diameter is in the 0.1-1.0 micrometer range.

4. according to the method for claim 2 or 3, it is characterized in that also being added with silicon-dioxide in the aqueous based dispersions, present in an amount at least sufficient to alleviate or prevent the migration of oxidant constituents.

5. according to the method for claim 4, the diameter that it is characterized in that silica dioxide granule is less than 0.02 micron.

6. according to each method in the claim 2 to 5, it is characterized in that described aqueous based dispersions comprises the sodiumazide of 50-70 weight part, the silicon-dioxide of the ferric oxide of 20-30 weight part and 5-14 weight part, they are dispersed in the water of capacity to dissolve all trinitride.

7. according to the method for claim 6, it is characterized in that the trinitride of every 30-45 weight part in the dispersion adds the water of 100 weight parts.

8. according to each method in the claim 2 to 7, it is characterized in that oxygenant being dispersed in the azide solution by vigorous stirring, until the enough height of viscosity of dispersion in case the obvious migration of oxidation agent in dispersion.

9. according to each method in the claim 1 to 8, it is characterized in that, by under pressure, making dispersion by having the nozzle that one or more diameters are the 0.5-2.5mm aperture, thereby make aqueous based dispersions be atomized into the drop that diameter is 40-200 μ m.

10. according to each method in the claim 1 to 9, it is characterized in that, is to make its spraying drying in 80-250 ℃ the airflow by making drop fall into temperature.

11. according to each method in the claim 1 to 10, it is characterized in that, the gas generating composition of above-mentioned solid granular is mixed with binder and tablet forming or particle, and wherein binder comprises for example water, the mixture of graphite or water and hydrophobic fumed silica.

12. the gas generating composition of making by each method in the claim 1 to 11.

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