U.S. patent number RE36,296 [Application Number 08/761,979] was granted by the patent office on 1999-09-14 for propellant composition for automotive safety applications.
This patent grant is currently assigned to Alliant Techsystems, Inc.. Invention is credited to Edward Hays Zeigler.
United States Patent |
RE36,296 |
Zeigler |
September 14, 1999 |
Propellant composition for automotive safety applications
Abstract
Clean burning, non-self extinguishing propellant compositions
for use in hybrid automotive air bag systems are disclosed. The
propellant compositions are based on a mixture of a crystalline
nitramine propellant, an energetic or non-energetic binder and one
or a combination of an oxidizing propellant and an energetic
plasticizer.
Inventors: |
Zeigler; Edward Hays (Radford,
VA) |
Assignee: |
Alliant Techsystems, Inc.
(Hopkins, MN)
|
Family
ID: |
24046155 |
Appl.
No.: |
08/761,979 |
Filed: |
December 11, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
514189 |
Aug 11, 1995 |
05507891 |
Apr 16, 1996 |
|
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Current U.S.
Class: |
149/47; 149/19.6;
280/741; 149/19.91; 149/19.7; 149/93; 149/88; 149/19.9 |
Current CPC
Class: |
C06D
5/06 (20130101); C06B 25/34 (20130101) |
Current International
Class: |
C06B
25/00 (20060101); C06B 25/34 (20060101); C06D
5/00 (20060101); C06D 5/06 (20060101); C06B
031/32 () |
Field of
Search: |
;149/47,19.7,19.9,19.91,19.6,88,93 ;280/741,737,738,739,740
;102/288,289 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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420 726 |
|
Apr 1991 |
|
EP |
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0591119 |
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Apr 1994 |
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EP |
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673 809 |
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Sep 1995 |
|
EP |
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Primary Examiner: Nelson; Peter A.
Attorney, Agent or Firm: Vidas, Arrett & Steinkraus
Claims
What is claimed is:
1. .[.A.]. .Iadd.In a .Iaddend.crash bag propellant system
comprising a source of compressed.[., oxygen-containing inert
gas.]. .Iadd.inert gas/oxygen mixture .Iaddend.and a propellant
composition in functional proximity to ignition means for effecting
ignition of said propellant within said gas, .Iadd.the improvement
wherein .Iaddend.said propellant .Iadd.is a .Iaddend.composition
consisting essentially of a uniform mixture of:
a) from about 40 to about 80% by weight of a crystalline
particulate propellant selected from the group consisting of
cyclotrimethylenetrinitramine, cyclotetramethylenetetranitramine
and mixtures thereof;
b) from 0 up to about 35% by weight of a crystalline particulate
oxidant selected from the group consisting of ammonium nitrate,
triamino-guanidinium nitrate, pentaerythritol tetranitrate and
mixtures thereof;
c) from about 8 to about 30% by weight of an inert or energetic
binder;
d) from 0 to about 15% by weight of an energetic plasticizer
selected from the group consisting of trimethylolethane trinitrate,
tri(ethylene glycol)dinitrate, butane triol trinitrate,
bis-dinitropropyl acetyl, bis-dinitropropyl formal, glycidal azide,
1,5-diazido-3-nitraza pentane, and mixtures thereof;
provided however, that where said binder component (c) does not
comprise an energetic binder, the mixture contains at least about
5% by weight of component (b) or component (d) or a mixture of
components (b) and (d).
2. The system of claim 1 wherein said binder component (c) is an
inert binder selected from the group consisting of cellulose
acetate, cellulose acetate butyrate, ethyl cellulose, an
elastomeric polymer and mixtures thereof.
3. The system of claim 2 wherein said propellant composition
contains from about 5 to 15% by weight of component (d).
4. The system of claim 3 wherein component (d) is trimethylolethane
trinitrate.
5. The system of claim 3 wherein component (d) is glycidal
azide.
6. The system of claim 2 wherein said propellant composition
contains from about 70 to 80% by weight of component (a).
7. The system of claim 2 wherein said propellant composition
contains from about 5 to about 35% by weight of component (b).
8. The system of claim 7 wherein component (b) is ammonium nitrate
present at a level of from about 5 to about 15% by weight.
9. The system of claim 7 wherein component (b) is
triaminoguanidinium nitrate present at a level of from about 20 to
about 35% by weight.
10. The system of claim 2 wherein said binder is cellulose
acetate.
11. The system of claim 1 wherein said binder component (c)
comprises an energetic binder selected from the group consisting of
.[.cured glycidyl azide polymer.]., cured glycidyl nitrate
polymers, cured 3-nitrato-methyl-3-methyl oxetane polymers, and
mixtures thereof. .[.12. The system of claim 11 wherein said
energetic binder comprises a glycidyl
azide polymer..].13. The system of claim 1 wherein said
propellant
composition contains from about 70 to 80% by weight of component
(a). 14. The system of claim 1 wherein said propellant contains
from about 40 to about 55% by weight of component (a) and from
about 20 to about 35% by
weight of component (b). 15. The system of claim 14 wherein
component (b)
is triaminoguanidinium nitrate. 16. The system of claim 1 wherein
said compressed gas is argon containing up to about 20% by volume
of oxygen.
The system of claim 16 wherein said gas is maintained under a
pressure
of from about 2000 to about 5,000 psi. 18. The system of claim 1
comprising a mixture of from about 70 to 80% by weight of
cyclotrimethylenetrinitramine, from about 10 to 15% by weight of
cellulose acetate binder and from about 10 to 15% by weight of a
plasticizer selected from the group consisting of glycidal azide
and trimethylolethane
trinitate. 19. The system of claim 17 wherein said plasticizer
is
trimethylolethane trinitrate. 20. The system of claim 1 wherein
said propellant component (a) is cyclotrimethylenetrinitramine.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to inflator propellant compositions
adapted for use with compressed gas-based air bag automotive safety
systems.
2. Description of Related Art
Current usage of propellants in automotive safety applications
falls into at least two classes: those that serve as inflators for
air bags (either driver, passengers or side impact) and those that
serve to tighten (remove slack from) more conventional restraint
systems such as lap/shoulder belts. This invention addresses
inflator propellants. Current inflator propellants can be further
divided into those for inflators;called pyrotechnic type inflators,
where the propellant provides all of the inflation gas, and those
for so-called hybrid inflators where the propellant heat energy and
gas serves to supplement a pre-pressurized volume of inert gas
contained in a pressure bottle so as to speed up the inflation
process and reduce the volume and size of the pre-pressurized gas
source. This invention further addresses hybrid inflator
systems.
Current state-of-the-art propellants for pyrotechnic inflators,
where all of the gas is provided by the propellant, typically
consist of a tableted mixture of sodium azide and an oxidant such
as iron oxide. The byproducts of such a reaction are free iron,
sodium oxide and gaseous nitrogen. Regardless of the oxidant, solid
residue comprises a substantial proportion of these combustion
products which must be filtered out of the gas stream via an
elaborate filtration system.
The current state-of-the-art propellant for hybrid inflator systems
is comprised of a mixture of polyvinyl chloride, a suitable
plasticizer, and potassium perchlorate as an oxidizer. Although
this propellant is suitable in terms of heat output and burning
rate, a major combustion product is very finely divided potassium
chloride (KCl). The KCl, dispersed as an aerosol, upon exhausting
from the gas bag, acts as an obscurant which may impede occupant
egress from a vehicle and, if inhaled, can cause retentions in
allergic individuals.
The gas used to inflate the gas bag in both pyrotechnic and hybrid
inflators must meet stringent requirements regarding toxic
components such as carbon monoxide (CO) and oxides of nitrogen
(NO.sub.x), as well as thermal stability. These requirements are a
crucial factor mendating the propellant types used to generate the
inflator gas. Clean burning, conventional smokeless propellants
containing nitrocellulose and nitroglycerin are unacceptable for
use in either type because of the significant amounts of CO in
their product gases when used in pyrotechnic inflators and their
poor thermal stability when used in either system.
One type of hybrid inflator utilizes a pre-pressurized mixture of
gaseous oxygen (up to 20%) and Argon. Because of the presence of
oxygen, this type of hybrid inflator is capable of oxidizing carbon
monoxide and hydrogen generated as combustion products in
conventional propellants to the more desirable carbon dioxide and
water, thus making possible the use of more conventional
propellants which are not fully oxygen balanced. Poorly oxygen
balanced propellants of the type commonly known as LOVA, based
primarily on the energetic ingredient cyclo trimethylene
trinitramine (RDX), have been tested and, although they possess the
necessary thermal stability, their burning characteristics, i.e.,
low burning rate and tendency to self-extinguish, make them
unsuitable.
The prior art discloses various other propellant compositions for
use in automotive safety applications. For example, U.S. Pat. No.
5,125,684 discloses a stable, extrudable, non-azide crash bag
propellant composition and a low temperature process for producing
the same from an extrudable mass containing an effective amount of
a cellulose based binder. The composition comprises 45-80 wt. %
oxidizer salt, a cellulose based binder and 10-35 wt. % of an
energetic component selected from a group which includes
cyclotrimethylenetrinitramine (RDX) and
cyclotetramethylenetetranitramine (HMX).
EP 591119 A2 discloses a gas emitting substance for inflating an
accident safety airbag, comprising one or more high energy
explosive(s) including 50 . 95% of (RDX) and/or (HMX) of a mean
particle size of 1-20 microns, up to 5 wt. % of nitrocellulose; and
5-50 wt. % of a combustible, energetic or non-energetic binder,
preferably one or more of polyurethane, cellulose acetate butyrate,
hydroxy terminated polybutadiene, ethyl cellulose, glycidyl acid
polymers and polymers of either 3-nitratemethyl-3-methyl oxymethane
or glycidyl nitrate.
Other prior art patents disclose explosive or rocket propellant
compositions which are not specifically designed as safety air bag
propellants. For example, U.S. Pat. No. 3,954,528 discloses solid
gas generating and gun propellant compositions employing
triamino-guanidine nitrate as a propellant ingredient in admixture
with an oxidant and a compatible synthetic polymer binder material.
The oxidant may be selected from cyclotrimethylenetrinitramine
(RDX) and cyclotetramethylenetetranitramine (HMX).
U.S. Pat. No. 4,689,097 discloses that a mixture of a nitramine and
triaminoguanidium nitrate accelerates the burn rate for certain low
smoke propellants. The nitramine may be selected from
cyclotrimethylenetrinitramine (RDX) and
cyclotetramethylenetetranitramine (HMX) or mixtures thereof. Fine
triaminoguanidium nitrate particles and coarse nitramine particles
are shown to be used in crosslinked propellant compositions.
U.S. Pat. No. 5,061,330 discloses a cast cured propellant and
explosive made from a mixture of a polyglycidal azide polymer, an
energetic plasticizer such as trimethylolethane trinitrate (TMETN)
and HMX or RDX. The composition may also contain aluminum
powder.
In addition, U.S. Pat. No. 5,316,600 discloses a castable,
energetic, plastic-bonded explosive containing glycidyl azide
polymer (GAP) combined with the energetic plasticizers
trimethyloethane trinitrate (TMETN) and triethylene glycol
dinitrate (TEGDN) or bisdinitropropyl formal and acetal mixture
(BDNPF/A), and the explosive solid cyclotetramethylene
tetranitramine (HMX) or cyclotrimethylene trinitramine (RDX).
However, none of these latter references discloses propellants
compositions which are stable enough to function satisfactorily in
hybrid inflator systems in such a way that the burning rates are
increased and their tendency to self-extinguish is reduced.
SUMMARY OF THE INVENTION
The present invention provides for a crash bag propellant system
comprising a source of compressed .[.oxygen-containing inert gas.].
.Iadd.inert gas/oxygen mixture .Iaddend.and a propellant
composition in functional proximity to ignition means for effecting
ignition of said propellant within said gas, said propellant
composition comprising a uniform mixture of: (a) from about 40 to
about 80% by weight of a crystalline particulate propellant
selected from the group consisting of
cyclotrimethylenetrinitramine, cyclotetramethylenetetranitramine
and mixtures thereof; (b) from 0 up to about 35% by weight of a
crystalline particulate oxidant selected from the group consisting
of ammonium nitrate, triamino-quanidinium nitrate, pentaerythritol
tetranitrate and mixtures thereof; (c) from about 8 to about 30% by
weight of an inert or energetic binder; (d) from 0 to about 15% by
weight of an energetic plasticizer selected from the group
consisting of trimethylolethane trinitrate, 1,5-diazido-3-nitraza
pentane, tri(ethylene glycol)dinitrate, butane triol trinitrate,
bis-dinitropropyl acetyl, bis-dinitropropyl formal, glycidal azide,
1,5-diazido-3-nitraza pentane, and mixtures thereof; provided,
however, that where said binder component (c) does not comprise an
energetic binder, the mixture contains at least about 5% by weight
of component (b) or component (d) or a mixture of components (b)
and (d).
Propellants of the invention possess the high thermal stability
required for auto safety applications, high burning rates and fast
ignition reaction times which render them suitable as smokeless
propellants for use in hybrid inflator systems for automotive
safety air bag applications.
DETAILED DESCRIPTION OF THE INVENTION
The propellant which is the energy constituent in the propellant
system of the invention is a crystalline, particulate nitramine
selected from cyclotrimethylenetrinitramine (RDX),
cyclotetramethylene-tetranitramine (HMX) and mixtures thereof. A
minor portion of the RDX or HMX propellant may be replaced by an
auxiliary oxidizer propellant to impart improved oxygen balance to
the system. Suitable oxidizer propellants include crystalline
ammonium nitrate (AN), triaminoguanidinium nitrate (TAGN),
pentaerythitrol tetranitrate (PETN) and mixtures thereof.
Where the propellant consists essentially of HMX or RDX, it is
present in the composition at a preferred level of from about 70 to
80% by weight. Where the propellant comprises a mixture of HMX or
RDX with AN, TAGN, or PETN, the HMX or RDX component is present at
a level of at least about 40% by weight and the auxiliary oxidizer
may be present at a level of from about 5 to 35% by weight. Where
AN is the auxiliary oxidizer propellant it is present at a level of
from about 5 to 15% by weight. Other auxiliary oxidizer propellants
such as TAGN are present at preferred levels of from about 20 to
35% by weight.
These propellants or mixtures thereof should be present in the
composition in the form of relatively finely ground particles
having a median particle size of from about 2 to 30 microns, more
preferably from about 3 to 15 microns, and are uniformly dispersed
in an energetic or non-energetic binder as described hereafter.
Polymers which may be used as a binder for the composition of the
invention include non-energetic (non-energetically combustible)
binders or energetic (energetically combustible) binders. Suitable
non-energetic binders include cellulose acetate, cellulose acetate
butyrate, ethyl cellulose as well as elastomeric binders such as
polyurethanes, polysilicones, gum rubbers of polybutadiene or
polyisoprene, butyl rubbers and polybutadienes containing hydroxy
or carboxy functionality. The most preferred non-energetic binder
for use in the present invention is cellulose acetate because of
its good oxygen combustion balance.
Energetic binders which may be used include glycidal azide polymer
(GAP), glycidal nitrate polymers, 3-nitratomethyl-3-methyl oxetane
polymers and mixtures thereof. These materials are normally liquid
materials and need to be formulated with an appropriate amount of
suitable curative to crosslink the material, e.g., from about
10-15% by weight based on the weight of binder of a multifunctional
isocyanate such as hexamethylene diisocyanate and/or
4,4'-diisocyanatodicyclohexyl-methane.
Binders are present in the composition at a level of from about 8
to about 30% by weight, more preferably from about 10 to 15% by
weight.
Where the binder used to formulate the compositions of this
invention is non-energetic, the composition also preferably
includes an energetic plasticizer. Suitable energetic plasticizers
include liquids such as glycidal azide (GAP), trimethylolethane
trinitrate (TMETN), tri(ethylene glycol) dinitrate (TEGDN), butane
triol trinitrate (BTTN), bis-dinitropropyl acetyl (BDNPA),
bis-dinitropropyl formal (BDNPF), 1,5-diazido-3-nitrazapentane
(DIANP) and mixtures thereof.
Composition, especially those which contain nitrate esters as the
energetic liquid plasticizer, also preferably contain suitable
stabilizers as are known in the prior art. Stabilizers which may be
used include amines such as diphenylamine, 2-nitrodiphenylamine and
N-methyl-p-nitroaniline; urethanes such as 1,3-bis(N-methyl-phenyl
urethane) benzene; phenols such as resorcinol; ureas such as
diethyl diphenyl urea; and mixtures thereof. The stabilizer is
normally used at a level of from about 3 to 15% by weight, based on
the weight of the nitrate ester component present in the
composition.
Where the composition contains one or more energetic plasticizers,
these are generally present in the composition at levels of from
about 5 to about 15% by weight.
The propellant compositions of this invention are specifically
adapted for use in hybrid inflator systems where inflation takes
place as the result of a triggered release of pressurized gas
supplemented by an almost simultaneous firing of the propellant
charge. The use of this combination of gas and heat sources allows
for smaller pressurized gas containers than would be required if
pressurized gas were the sole source of the inflation gas.
The pressurized gas is preferably an inert gas, e.g. argon, mixed
with sufficient air or oxygen (generally up to about 20 volume
percent) to provide sufficient oxygen for the oxidation of
propellant combustion products such as carbon monoxide and hydrogen
to non-toxic and non-flammable carbon dioxide and water. Pressures
within the gas bottle may range from about 2,000 to about 5,000
psi, more preferably about 4,000 psi.
The propellant charge of the invention is positioned within the gas
bottle, for example, in a canister, in functional proximity to an
ignition means for effecting ignition of the propellant within the
volume of pressurized gas.
Generally speaking, from about 2 to about 10 grams of propellant
composition are used per 100 grams of compressed gas.
Actuation of these types of propellant systems generally takes
place as the result of an electrical squib initiated by a crash
sensor after automobile impact has been detected by the sensor. A
biased piston is then actuated which penetrates a sealing diaphragm
in the pressurized gas bottle, starting the release of pressurized
gas which is operatively connected by gas flow lines to a folded
air bag. Almost simultaneously, the piston contacts a firing pin in
the propellant canister which impacts percussion primers, which in
turn fires off an ignition charge, which in turn ignites the
propellant charge. The combination of a relatively low volume of
pressurized gas and the heat and gas generated by the burning
propellant supplement one another to provide high pressures in the
gas bottle sufficient to inflate the associated air bag quickly and
efficiently.
Particularly preferred propellant composition for use in the
present invention comprise mixtures of from about 70-80% by weight
of RDX having a mean particle size of about 4-6 microns with from
about 10-15% by weight of cellulose acetate binder and from about
10-15% by weight of an energetic plasticizer such as TMETN or GAP.
Other preferred compositions comprise a mixture of from about 40 to
55% by weight of 4-6 micron size RDX, about 20 to 35% by weight of
TAGN, about 10-15% by weight cellulose acetate binder and from
about 10 to 15% by weight of TMETN or GAP. These combinations
provide a particularly effective propellant when used in
conjunction with a hybrid inflator system where the pressurized gas
is a mixture of argon and from about 5-15 volume % of oxygen,
providing a clean burning release gas very low in content of
noxious gases such as carbon monoxide and nitrogen oxides.
The propellant composition may be prepared by mixing the components
in a suitable mixing device such as a horizontal sigma blade mixer
to form a dough. Dough formation is facilitated by inclusion of
from about 15 to 35% by weight, based on the weight of the mixture,
of a suitable processing solvent which is later removed after the
dough has been pelletized. Suitable solvents include lower alkyl
acetates, lower alcohols, ketones and mixtures thereof. Mixing is
conducted at temperatures of from about 90.degree.-130.degree. F.
for a period of time sufficient to form a very uniform dispersion
of the solid particles within the dough, generally from about 30 to
120 minutes. The dough is then passed through an extrusion die to
form strands which are cut to form pellets. The resulting pellets
are subsequently dried to remove residual processing solvent.
The following examples are illustrative of the invention.
EXAMPLE 1
A propellant having the following composition was prepared:
______________________________________ Ingredient Percent (Wt.)
______________________________________ RDX (5 micron) 76 Cellulose
Acetate 12 GAP 12 Total 100.0
______________________________________
The propellant ingredients, totalling 12 pounds in weight, were
added to a horizontal sigma blade mixer along with 4.5 pounds of a
processing solvent consisting of equal parts ethyl acetate, ethyl
alcohol, and acetone and then mixed for 90 minutes at 120.degree.
F. The resulting dough was cooled, removed from the mixer and
extruded in a conventional 4 inch extrusion press through an
extrusion die having an inside diameter of 0.147 inch and a central
perforation-forming pin 0.053 inch in diameter. The resulting
strands were cut in a cutting machine to a length of 0.44 inch. The
resulting granules were then dried to remove processing solvent in
a forced air dryer.
After drying, the granules had dimensions of length 0.431 inch,
outside diameter 0.140 inch and the inside diameter 0.047 inch. No
detectable amounts of processing solvent remained. When tested in a
closed vessel, the propellant exhibited a linear burning rate of
about 0.4 inches/second at 3000 psi.
EXAMPLE 2
A propellant having the following composition was prepared as in
Example 1:
______________________________________ Ingredient Percent (WT)
______________________________________ RDX (5 micron) 75 Cellulose
Acetate 12.5 TMETN 11.25 diethyl diphenyl urea 1.25 Total 100.0
______________________________________
When tested in a closed vessel, the propellant exhibited a linear
burning rate of about 0.37 inches/second at 3000 psi.
EXAMPLE 3
A propellant having the following composition was prepared as in
Example 1:
______________________________________ Ingredient Percent (WT)
______________________________________ RDX (5 micron) 47.0 TAGN
27.4 Cellulose Acetate 12.5 GAP 12.5 diethyl diphenyl urea 0.3
resorcinol 0.3 Total 100.0
______________________________________
The propellants of Examples 1-3 were tested by ignition of the
pellets in a pressurized atmosphere of argon and oxygen and found
to possess excellent burning qualities without self extinguishment.
The quantity of carbon monoxide and (NO.sub.x) gases generated was
well below safety maximums, particularly with respect to the
formulation of Example 2.
* * * * *