U.S. patent application number 11/656319 was filed with the patent office on 2007-07-26 for autoignition main gas generant.
Invention is credited to Sean P. Burns, Deborah L. Hordos.
Application Number | 20070169863 11/656319 |
Document ID | / |
Family ID | 38284370 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070169863 |
Kind Code |
A1 |
Hordos; Deborah L. ; et
al. |
July 26, 2007 |
Autoignition main gas generant
Abstract
A gas generating composition of the present invention contains
at least one fuel selected from amides, imides, and metal
amine-based fuels, ammonium nitrate or phase stabilized ammonium
nitrate, and at least one metal oxide. A gas generating system 200
containing a-gas generant in accordance with the present invention
is also contemplated.
Inventors: |
Hordos; Deborah L.; (Troy,
MI) ; Burns; Sean P.; (Almont, MI) |
Correspondence
Address: |
L.C. Begin & Associates, PLLC
PMB 403
510 Highland Avenue
Milford
MI
48381
US
|
Family ID: |
38284370 |
Appl. No.: |
11/656319 |
Filed: |
January 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60761017 |
Jan 19, 2006 |
|
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Current U.S.
Class: |
149/37 |
Current CPC
Class: |
C06C 9/00 20130101; C06D
5/06 20130101 |
Class at
Publication: |
149/037 |
International
Class: |
C06B 33/00 20060101
C06B033/00 |
Claims
1. A gas generant composition comprising: a fuel selected from the
group of amides, imides, metal amine-based fuels, and mixtures
thereof; ammonium nitrate; and a metal oxide, wherein said gas
generant composition has a non-azole character.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Application No. 60/761,017 having a filing date of Jan.
19, 2006.
TECHNICAL FIELD
[0002] The present invention relates generally to gas generating
systems, and to gas generant compositions employed in gas generator
devices for automotive restraint systems, for example.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to nontoxic gas generating
compositions that upon combustion rapidly generate gases that are
useful for inflating occupant safety restraints in motor vehicles
and specifically, the invention relates to thermally stable
nonazide gas generants having not only acceptable burn rates, but
that also, upon combustion, exhibit a relatively high gas volume to
solid particulate ratio at acceptable flame temperatures.
[0004] The evolution from azide-based gas generants to nonazide gas
generants is well-documented in the prior art. The advantages of
nonazide gas generant compositions in comparison with azide gas
generants have been extensively described in the patent literature,
for example, U.S. Pat. Nos. 4,370,181; 4,909,549; 4,948,439;
5,084,118; 5,139,588 and 5,035,757, the discussions of which are
hereby incorporated by reference.
[0005] In addition to a fuel constituent, pyrotechnic nonazide gas
generants contain ingredients such as oxidizers to provide the
required oxygen for rapid combustion and reduce the quantity of
toxic gases generated, a catalyst to promote the conversion of
toxic oxides of carbon and nitrogen to innocuous gases, and a slag
forming constituent to cause the solid and liquid products formed
during and immediately after combustion to agglomerate into
filterable clinker-like particulates. Other optional additives,
such as burning rate enhancers or ballistic modifiers and ignition
aids, are used to control the ignitability and combustion
properties of the gas generant.
[0006] One of the disadvantages of known nonazide gas generant
compositions is the amount and physical nature of the solid
residues formed during combustion. When employed in a vehicle
occupant protection system, the solids produced as a result of
combustion must be filtered and otherwise kept away from contact
with the occupants of the vehicle. It is therefore highly desirable
to develop compositions that produce a minimum of solid
particulates while still providing adequate quantities of a
nontoxic gas to inflate the safety device at a high rate.
[0007] The use of phase stabilized ammonium nitrate as an oxidizer,
for example, is desirable because it generates abundant nontoxic
gases and minimal solids upon combustion. To be useful, however,
gas generants for automotive applications must be thermally stable
when aged for 400 hours or more at 107 degree C. The compositions
must also retain structural integrity when cycled between -40
degree C. and 107 degree C. Further, gas generant compositions
incorporating phase stabilized or pure ammonium nitrate sometimes
exhibit poor thermal stability, and produce unacceptably high
levels of toxic gases, CO and NO.sub.x for example, depending on
the composition of the associated additives such as plasticizers
and binders.
[0008] Yet another problem that must be addressed is that the
U.S.
[0009] Department of Transportation (DOT) regulations require "cap
testing" for gas generants. Because of the sensitivity to
detonation of fuels often used in conjunction with ammonium
nitrate, many propellants incorporating ammonium nitrate do not
pass the cap test unless shaped into large disks, which in turn
reduces design flexibility of the inflator.
[0010] Yet another concern includes slower cold start ignitions of
typical smokeless gas generant compositions, that is gas generant
compositions that when combusted result in at least 80 weight % of
gaseous combustion products as compared to the overall weight of
the combustion products.
[0011] Many compositions containing phase stabilized ammonium
nitrate contain an azole-based fuel such as a tetrazole. Although
proven to be satisfactory in many applications, one concern is that
azole-based fuels sometimes have a relatively shorter burnout time
thereby complicating the inflation profile requirements.
Furthermore, it is also an ongoing effort to economize the design
of an inflator by increasing the functionality of a given
composition, as an autoignition (less than 160 Celsius, perhaps)
and primary gas generant for example.
[0012] Accordingly, ongoing efforts in the design of automotive gas
generating systems, for example, include other initiatives that
desirably produce more gas and less solids without the drawbacks
mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an exemplary inflator incorporating a composition
of the present invention.
[0014] FIG. 2 is an exemplary gas generating system, in this case a
vehicle occupant protection system, incorporating the inflator of
FIG. 1.
SUMMARY OF THE INVENTION
[0015] The above-referenced concerns are resolved by gas generating
systems including a gas generant composition containing phase
stabilized ammonium nitrate, stabilized in a known manner, metal
oxides including transitional metal oxides such as copper oxide,
and a non-azole fuel, that is a fuel not containing tetrazole,
triazoles, furazans, or azoles. Accordingly, typical fuels include
amides and imides such as azodicarbonamide for example, or metal
amine-based fuels such as copper diamine dinitrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0016] The above-referenced concerns are resolved by gas generating
systems including a gas generant composition containing phase
stabilized ammonium nitrate, stabilized in a known manner, metal
oxides including transitional metal oxides such as copper oxide,
and a fuel having non-azole character, that is a fuel not
containing, or a fuel absent of any tetrazoles, triazoles,
furazans, or azoles. Stated another way, the gas generant
composition may be described as having a non-azole character
because it does not contain an azole-based fuel as described
herein. Accordingly, typical fuels include at least one of amides
and imides such as dihydrazides, hydrazides, succinic dihydrazide,
hydrazodicarbonamide, dicyandiamide, urea, carbohydrazide, oxamide,
oxamic hydrazide, Bi-(carbonamide)amine, azodicarbonamide,
derivatives thereof, d- or l-tartaric acid amide derivatives, and
mixtures thereof, for example; metal amine-based fuels such as
copper diamine di-nitrate; and mixtures thereof. Exemplary methods
of stabilizing the phase stabilized ammonium nitrate include
co-crystallization of the ammonium nitrate with potassium salts
(e.g. KNO3 at about 10-15% by weight of the total weight of the
PSAN), or by the solid-state melting of ammonium nitrate with
transition metal oxides.
[0017] Ammonium nitrate or phase stabilized ammonium nitrate (PSAN)
is provided at about 60-80%, and more preferably at about 65-75% by
weight of the total composition. A metal oxide is provided at about
2-10%, and more preferably at about 3-7%, by weight of the total
composition. The fuel is provided at about 18-38% by weight of the
total composition. It will be appreciated that the various
percentages may be varied based on design requirements such as
autoignition temperature and burn rate.
[0018] One embodiment includes 68.27% PSAN, 3.25% copper oxide, and
27.50% azodicarbonamide. The resulting gas generation is 94.9% of
the total combustion products. It will further be appreciated that
a typical dry blend ratio of PSAN to the metal oxide is about 10 to
1 respectively, but may be modified as per the weight percents
described above. Differential Scanning Calorimeter (DSC) laboratory
results indicate a composition containing ammonium nitrate melt
phase stabilized with copper oxide, combined with azodicarbonamide,
exhibits an autoignition onset temperature of 150.20C, with a peak
autoignition temperature of 155.48C. In contrast, nitrocellulose
(smokeless powder) indicates an onset of 189.35C with a peak
temperature of 214.19C. Accordingly, auto-ignition occurs
relatively lower with compositions of the present invention.
[0019] In yet another aspect of the invention, the present
compositions may be employed within a gas generating system. For
example, a vehicle occupant protection system made in a known way
contains crash sensors in electrical or operable communication with
an airbag inflator in a steering wheel or otherwise within the
vehicle, and also within a seatbelt assembly. The gas generating
compositions of the present invention may be employed in both
subassemblies within the broader vehicle occupant protection system
or gas generating system. More specifically, each gas generator
employed in the automotive gas generating system may contain a gas
generating composition as described herein.
[0020] It should be noted that all percents given herein are weight
percents based on the total weight of the gas generant composition.
The chemicals described herein may be supplied by companies such as
Aldrich Chemical Company and Polysciences, Inc. for example.
[0021] As shown in FIG. 1, an exemplary inflator incorporates a
dual chamber design to tailor the force of deployment an associated
airbag. In general, an inflator, containing a primary autoigniting
gas generating composition 12 formed as described herein, 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. It should also be appreciated that
with regard to thermal stability and USCAR requirements, it has
been found that the use of desiccant, such as zeolite, provided at
about 1:1 weight ratios with regard to the gas generant 12,
improves the thermal stability of the present compositions.
Co-owned and co-pending U.S. application Ser. No. 11/604,628 filed
on Nov. 27, 2006, incorporated herein by reference, further
explains how the use of a desiccant may provide thermal stability
advantage.
[0022] Referring now to FIG. 2, the exemplary inflator 10 described
above may also be incorporated into a gas generating system such as
an airbag or vehicle occupant protection 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.
[0023] 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.
[0024] 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
propellant 12 and autoignition 14 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.
[0025] Safety belt assembly 150 may also include (or be in operable
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.
[0026] 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.
[0027] The compositions may be dry or wet mixed using methods known
in the art. The various constituents are generally provided in
particulate form and mixed to form a uniform mixture with the other
gas generant constituents. The mixture is then pelletized or formed
into other useful shapes in a safe manner known in the art.
[0028] In one aspect of the invention, it has been found that
forming a complex between ammonium nitrate and the metal oxide,
copper oxide for example, may best be accomplished by melting the
two compounds and then homogeneously mixing the melt. A
heating/mixing vessel may be employed wherein ammonium nitrate, or
phase stabilized ammonium nitrate, is heated to its melting point.
It has been found that heating ammonium nitrate or phase stabilized
ammonium nitrate (co-precipitated with 10-15 wt % potassium nitrate
for example) at about 150-175C provides a sufficient melt. Copper
oxide, or any other metal oxide such as a transitional metal oxide,
is then mixed in and melted as well. The contents of the vessel may
be stirred and heated to complex the copper or copper oxide with
the ammonium nitrate or phase stabilized ammonium nitrate. After
stirring to provide a substantially homogeneous mixture, about
15-20 minutes for example, the heat is removed and the melt is
preferably slowly cooled to room temperature. After the melt
solidifies into the copper complex, the solid may be ground by
mortar and pestle, or other known grinding techniques. Powdered
fuel and powdered complex may then be homogeneously mixed in a
planetary mixer for example, and then compacted and pelletized in a
known manner. The melt constituents are of course provided in the
weight percents characterized herein.
[0029] It should be noted that all percents given herein are weight
percents based on the total weight of the gas generant composition.
The chemicals described herein may be supplied by companies such as
Aldrich Chemical Company and Polysciences, Inc., or Toyo Kasie
Kogyo Co. of Takasago City, Japan, for example. Or, the various
constituents may be made as known in the art. For example, d- or
l-tartaric acid amide derivatives may be formed as described in
U.S. Pat. No. 5,306,844, herein incorporated by reference in its
entirety.
[0030] In sum, the present invention provides simplification of the
inflator design by only requiring a gas generating composition
(auto-igniting below 200C), rather than an auto-ignition
composition and a separate gas generating composition. Furthermore,
in many gas generators or inflators, a booster composition must
also be employed to provide the energy needed to combust the
primary gas generant in the event of a fire. By eliminating the
need for an auto-igniting composition, the need for a booster
composition may also be eliminated if desired. Furthermore,
decomposition products typically associated with the decomposition
of the auto-ignition composition in typical inflators is avoided.
As such, the integrity of the propellant and the performance
reliability of the inflator are favorably enhanced.
[0031] The present description is for illustrative purposes only,
and should not be construed to limit the breadth of the present
invention in any way. Thus, those skilled in the art will
appreciate that various modifications could be made to the
presently disclosed embodiments without departing from the scope of
the present invention as defined in the appended claims.
* * * * *