U.S. patent application number 11/497149 was filed with the patent office on 2007-02-15 for autoignition/booster composition.
Invention is credited to Deborah L. Hordos.
Application Number | 20070034307 11/497149 |
Document ID | / |
Family ID | 37709331 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070034307 |
Kind Code |
A1 |
Hordos; Deborah L. |
February 15, 2007 |
Autoignition/booster composition
Abstract
A gas generator 10 includes a composition that contains a metal
chlorate such as potassium chlorate as an oxidizer, a carboxylic
acid such as DL-tartaric acid as a primary fuel, a secondary
oxidizer such as strontium nitrate, and if desired, a secondary
fuel such as 5-aminotetrazole. Gas generating systems 180 such as
vehicle occupant protection systems 180, containing the gas
generator 10, are also provided.
Inventors: |
Hordos; Deborah L.; (Troy,
MI) |
Correspondence
Address: |
L.C. Regin & Associates, PLLC
510 Highland Avenue
PMB 403
Milford
MI
48381
US
|
Family ID: |
37709331 |
Appl. No.: |
11/497149 |
Filed: |
July 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60703998 |
Jul 29, 2005 |
|
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Current U.S.
Class: |
149/36 |
Current CPC
Class: |
C06C 9/00 20130101; C06D
5/06 20130101 |
Class at
Publication: |
149/036 |
International
Class: |
C06B 47/08 20060101
C06B047/08 |
Claims
1. A composition comprising: a metal chlorate as a first oxidizer;
a primary fuel selected from carboxylic acids, dicarboxylic acids,
and mixtures thereof; and a second oxidizer not having perchlorate
character.
2. The composition of claim 1 wherein said metal chlorate is
provided at about 10-20 wt%, and said primary fuel is provided at
about 15-45 wt%, and said second oxidizer is provided at about
30-50 wt%, said percentages stated by weight of the total
composition.
3. The composition of claim 1 wherein said composition further
comprises a secondary fuel selected from tetrazoles, triazoles,
furazans, and salts thereof, said secondary fuel provided at about
0.1-30 wt%.
4. A vehicle occupant protection system comprising the composition
of claim 1.
5. A gas generating system comprising the composition of claim
1.
6. The composition of claim 1 wherein said primary fuel is selected
from tartaric acid and its isomers, succinic acid, glutamic acid,
adipic acid, mucic acid, oxalic acid, malonic acid, fumaric acid,
galactaric acid, glycolic acid, citric acid, L-malic acid, and
mixtures thereof.
7. The composition of claim 3 comprising DL-tartaric acid at about
19-28 wt%, potassium chlorate at about 12-30 wt%, 5-aminotetrazole
at about 15-25 wt%, and strontium nitrate at about 30-50 wt%, said
percentages stated by weight of the total composition.
8. The composition of claim 1 wherein said secondary oxidizer is
selected from metal, basic metal, and nonmetal nitrates, nitrites,
oxides, and chlorates.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/703,998 filed on Jul. 29, 2005.
TECHNICAL FIELD
[0002] The present invention relates generally to gas generating
systems, and to autoignition compositions employed in gas generator
devices for automotive restraint systems, for example.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to autoignition compositions
that upon ignition provide the flame front and pressure front
necessary to safely ignite gas generant compositions in combustible
communication therewith. As known in the art, gas generators are
typically provided with an autoignition composition that in the
event of a fire ignites responsive to a desired threshold
temperature. As a result, the gas generant is ignited prior to
melting for example, thereby safely igniting the main gas generant
composition to inhibit or prevent the likelihood of an explosive
event once the gas generant begins to combust.
[0004] An ongoing challenge is to simplify the manufacture of a gas
generator by reducing the constituents required in the production
thereof. For example, in many gas generators used in vehicle
occupant protection systems, several discrete compositions are
provided to serve correspondingly discrete functions. These
compositions often include a primary gas generating composition
that when combusted is employed to provide sufficient quantities of
gaseous products to operate the associated restraint device, such
as an airbag or seatbelt pretensioner. A booster composition is
utilized to elevate the pressure and heat within the gas generator
prior to combustion of the primary gas generant, thereby creating
favorable conditions within the inflator for acceptable combustion
of the primary gas generant. Of course, still yet another
composition is the auto-ignition composition employed to provide
safe combustion of the other compositions in the event of a fire.
The auto-ignition composition is designed to ignite at temperatures
below the melting point of the primary gas generant for example,
thereby ensuring the controlled combustion of the primary gas
generant, as opposed to an explosive reaction perhaps.
[0005] The use of potassium chlorate within an autoignition
composition has been considered given the autoignition properties
of this oxidizer. Furthermore, carboxylic acid in combination with
potassium chlorate typically provides a desired autoignition
temperature of 200 degrees Celsius or less. Nevertheless, these
types of compositions typically do not provide anything but
auto-ignition function when employed in gas generators used in
vehicle occupant protection systems, for example.
SUMMARY OF THE INVENTION
[0006] The above-referenced concerns and others may be resolved by
gas generating systems including an autoignition composition
containing a first oxidizer selected from metal chlorates, such as
potassium chlorate, a carboxylic acid or dicarboxylic acid as a
primary fuel, a secondary oxidizer selected from metal and nonmetal
nitrates, nitrites, oxides, basic metal nitrates, and other known
oxidizers, and a secondary fuel selected from azoles including
tetrazoles, triazoles, and furazans, and salts thereof. Other
constituents including extrusion aids, such as fumed silica and/or
graphite, may be included in relatively small amounts. In further
accordance with the present invention, a gas generator and a
vehicle occupant protection system incorporating the autoignition
system are also included.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional side view showing the general
structure of an inflator in accordance with the present
invention;
[0008] FIG. 2 is a schematic representation of an exemplary vehicle
occupant restraint system containing a gas generant composition in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0009] The present compositions contain a first oxidizer selected
from alkali, alkaline earth, and transitional metal chlorates, and
mixtures thereof, such as potassium chlorate, at about 10-60
weight%; a primary fuel selected from carboxylic acids and
dicarboxylic acids, such as DL-tartaric acid, at about 15-45
weight%; a secondary oxidizer selected from metal and nonmetal
nitrates, nitrites, oxides, and other known oxidizers at about
30-50%; and a secondary fuel selected from tetrazoles, triazoles,
furazans, and salts thereof at about 0-30 weight %, said weight
percent calculated with regard to the weight of the total
composition. Extrusion aids or processing additives such as
graphite or fumed silica may be added in relatively smaller
amounts, such as 0.1-2% by weight of the total composition for
example.
[0010] The present compositions contain a metal chlorate such as
potassium chlorate; a primary fuel selected from carboxylic acids
and dicarboxylic including DL-tartaric acid, L-tartaric acid,
D-tartaric acid, succinic acid, glutamic acid, adipic acid, mucic
acid, fumaric acid, oxalic acid, galactaric acid, citric acid,
glycolic acid, L-malic acid, and compounds having at least
one--COOH--group, and mixtures thereof; a second fuel selected from
an azole including tetrazoles, triazoles, furazans, salts thereof,
and mixtures thereof; a secondary oxidizer selected from metal and
nonmetal nitrates or other known oxidizers not containing a
perchlorate. The carboxylic acid or dicarboxylic acid will
preferably have a primary hydrogen or PKA less than or equal to 3.
Nevertheless, it has been found that with certain fuels/salts, the
pKa of the base acid may range up to 5.0 or less.
[0011] In one embodiment, the total fuel constituent including he
carboxylic fuel and the second fuel is provided at about 20-45% by
weight of the total composition; the oxidizer constituent is
provided at about 20-50% by weight of the total composition; and
the potassium chlorate or metal chlorate is provided at about
10-60% by weight of the total composition wherein the weight
percent of the chlorate is separately calculated from that of the
oxidizer. The composition may be formed by wet or dry mixing the
constituents in a granulated form in a known manner, and then
pelletizing or otherwise forming the composition for further use.
The constituents may be provided by Fisher Chemical, Aldrich
Chemical, GFS, and other known suppliers.
[0012] The present invention is exemplified by the following
Examples:
Comparative Example 1
[0013] A known autoignition composition was prepared by
homogeneously mixing dried and granulated D-glucose at about 26.875
wt% and potassium chlorate at about 73.125 wt%, the percents stated
by weight of the total composition. The composition autoignited at
about 144 C. as measured by DSC analysis. The propellant formed
from the constituents resulted in an approximate 55.5% gas yield.
The impact sensitivity of this formulation had an HD50 of 2.0
inches as conducted in conformance with the Bruceton Test.
Example 2
[0014] An exemplary formulation was provided that functions as a
booster, an autoignition, and a gas generant composition. The
formulation contains 5-aminotetrazole at about 19.0 wt%,
DL-tartaric acid at about 20.0 wt%, strontium nitrate at about 35.0
wt%, and potassium chlorate at about 26.0 wt%. The constituents
were previously and separately ground to a relatively small size in
a known manner. They were then dry-mixed to form a substantially
homogeneous composition. The composition autoignited at about 140
C. as measured by DSC analysis. The propellant formed from the
constituents resulted in an approximate 67% gas yield. The impact
sensitivity of this formulation had an HD50 of 11.5 inches as
conducted in conformance with the Bruceton Test. The composition
was aged for about 480 hours at 107C. and still autoignited at
about 145.1C. as determined by DSC analysis.
Example 3
[0015] An exemplary formulation was provided that functions as a
booster, an autoignition, and a gas generant composition. The
formulation contains 5-aminotetrazole at about 19.0 wt%,
DL-tartaric acid at about 19.0 wt%, strontium nitrate at about 50.0
wt%, and potassium chlorate at about 12.0 wt%. The constituents
were granulated and dry-mixed to form a substantially homogeneous
composition. The composition autoignited at about 141 C. as
measured by DSC analysis. The propellant formed from the
constituents resulted in an approximate 68.2% gas yield. The impact
sensitivity of this formulation had an HD50 of 8.8 inches as
conducted in conformance with the Bruceton Test. As shown in FIG.
3, the composition reflected a relatively strong burn rate across
several pressure regimes, and in particular indicated burn rates of
over 0.8 inches per second (ips). Again referring to FIG. 3, it can
be seen that the composition exhibited a burn rate of about 0.2 ips
at about 200 psig, about 0.35 ips at about 550 psig, about 0.5 ips
at about 1000 psig, about 0.55 ips at about 1500 psig, about 0.85
ips at about 2000 psig, about 0.9 ips at about 2500 psig, about
0.85 ips at about 3000 psig; and about 1.2 ips at about 3900 psig.
It can therefore be seen that a composition in accordance with the
present invention exhibits a satisfactory burn rate (typically 0.4
ips or more at about 2500-3000 psig) thereby ensuring satisfactory
functionality as a primary gas generant. The composition was aged
for about 480 hours at 107C. and still autoignited at about 174.7C.
as determined by DSC analysis.
Example 4
[0016] An exemplary formulation was provided that functions as a
booster, an autoignition, and a gas generant composition. The
formulation contains DL-tartaric acid at about 28.0 wt%, strontium
nitrate at about 32.0 wt%, and potassium chlorate at about 30.0
wt%. The constituents were previously and separately ground to a
relatively small size in a known manner. They were then dry-mixed
to form a substantially homogeneous composition. The composition
autoignited at about 153 C. as measured by DSC analysis. The
propellant formed from the constituents resulted in an approximate
66.1% gas yield. The impact sensitivity of this formulation had an
HD50 of 8.1 inches as conducted in conformance with the Bruceton
Test.
[0017] As indicates in Examples 1-4, compositions formed in
accordance with the present invention (Examples 2-4) preferably
autoignite at or below about 180C. and provide a booster function
as well. The compositions of the present invention may also produce
substantial quantities of gas, and exhibit sufficient burn rates
thereby producing sufficient amounts of gas when activated.
Compositions employing a secondary oxidizer, such as strontium
nitrate, provide relative increased quantities of gas and an
improved sensitivity. A Bruceton sensitivity result wherein
H.sub.50=3.9 or more relaxes the packaging requirements as per
U.S.D.O.T regulations. Accordingly, compositions having a
sensitivity result of 3.9 or greater provide substantial packaging
advantages. It will further be appreciated that the use of a
secondary fuel, such as 5-aminotetrazole, in conjunction with the
carboxylic or dicarboxylic acid, the secondary oxidizer, and the
potassium chlorate produces greater amounts of gas, acceptable
autoignition temperatures, and booster functionality. As such,
compositions formed in this manner may be provided to singularly
replace the three discrete booster, autoignition, and primary gas
generant compositions normally found in a gas generator.
Examples 5-16
[0018] As shown in Table 1 below, the various acids shown, when
converted to salts and mixed with potassium chlorate in
stoichiometric amounts exhibit acceptable autoignition temperatures
for a variety of uses. Certain autoignition temperatures exceed 180
C. but may still be useful in selected applications such as hybrid
inflators and seatbelt pretensioners for example. It will be
appreciated that these Examples reflect the autoignition character
imparted by the resulting salts and the potassium chlorate. As
further shown, acids exhibiting a pKa of about 3.05 or less
generally provide autoignition temperatures generally less than
170-180C. However, acids exhibiting a pKa of about 5.0 or less may
still be acceptable wherein autoignition temperatures of 250 or so
are acceptable, for example. It will be appreciated that certain
acids such as citric acid and malonic acid when stoichiometrically
combined with potassium chlorate may not satisfy the autoignition
function, but still when combined with at least a second oxidizer
function as a booster oxidizer and a primary gas generant. It has
further been determined that the use of a desiccant as described in
co-owned and co-pending U.S. Ser. No. 11/479,493, herein
incorporated by reference, may in certain circumstances maintain
optimum environmental conditions within the gas generator thereby
facilitating the tri-functionality of the composition when used as
an autoignition, booster, and primary gas generating composition.
TABLE-US-00001 TABLE I Stoichiometric Mixture w KC Lit. Hot Name
Structure mp DSC/TGA Plate PKa L-Tartaric Acid ##STR1## 168-170 Al
142 154 3.02 D-Tartaric 168-170 2.98 Acid DL- 206 Al 171 185
Tartaric Acid Meso- 140 3.22 Tartaric Acid Succinic Acid ##STR2##
188-190 mp 184 followed by small exo; no TGA step function 210 4.16
Diglycolic Acid ##STR3## 142-145 mp 130 followed by small exo: TGA
slow dec. 155 3.28 Malonic Acid ##STR4## 135-137 mp 124 followed by
small exo; TGA slow dec. >250 2.83 Trans- Glutaconic Acid
##STR5## 137-139 mp 136; Al 166 188 D- Glutamic Acid ##STR6##
200-202 mp 206; Al 213 235 2.13 Adipic Acid ##STR7## 152-154 mp
153; Al 222 237 4.43 Mucic Acid ##STR8## 215 Al 200 223 3.08 Citric
Acid ##STR9## 152-154 mp 141 followed by small exo; no TGA step
function >250 3.12
[0019] It will be appreciated that in further accordance with the
present invention, gas generators made as known in the art and also
vehicle occupant protection systems manufactured as known in the
art are also contemplated. As such, autoignition compositions of
the present invention are employed in gas generators, seat belt
assemblies, and/or vehicle occupant protection systems, all
manufactured as known in the art.
[0020] In yet another aspect of the invention, the present
compositions may be employed within a gas generating system. For
example, as schematically shown in FIG. 2, a vehicle occupant
protection system made in a known way contains crash sensors in
electrical communication with an airbag inflator in the steering
wheel, and also with 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.
[0021] Extrusion aides may be selected from the group including
talc, graphite, borazine [(BN).sub.3], boron nitride, fumed silica,
and fumed alumina. The extrusion aid preferably constitutes 0-10%
and more preferably constitutes 0-5% of the total composition.
[0022] 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.
[0023] 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 for example.
[0024] As shown in FIG. 1, an exemplary inflator incorporates a
dual chamber design to tailor the force of deployment of an
associated airbag. In general, an inflator containing a primary gas
generant 12 and an autoignition/booster composition 14 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.
[0025] Referring now to FIG. 2, the exemplary inflator 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.
[0026] 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 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, each
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.
[0027] 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.
[0028] 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.
[0029] 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.
* * * * *