U.S. patent application number 11/789756 was filed with the patent office on 2007-10-25 for gas generant compositions.
Invention is credited to Sean P. Burns, Deborah L. Hordos.
Application Number | 20070246138 11/789756 |
Document ID | / |
Family ID | 38608262 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070246138 |
Kind Code |
A1 |
Hordos; Deborah L. ; et
al. |
October 25, 2007 |
Gas generant compositions
Abstract
An auto ignition/gas generating composition is provided that
contains DL-tartaric acid as a first fuel; a second fuel selected
from carboxylic acids; amino acids; tetrazoles; triazoles;
guanidines; azoamides; metal and nonmetal salts thereof; and
mixtures thereof; and potassium chlorate as a first oxidizer.
Potassium perchlorate is also preferably included as a second
oxidizer. The composition is typically contained within a gas
generating system such as an airbag inflator or seat belt assembly,
or more broadly within a vehicle occupant protection system.
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: |
38608262 |
Appl. No.: |
11/789756 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60795077 |
Apr 25, 2006 |
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Current U.S.
Class: |
149/74 ;
149/36 |
Current CPC
Class: |
C06C 9/00 20130101; C06D
5/06 20130101; B60R 2021/2648 20130101 |
Class at
Publication: |
149/74 ;
149/36 |
International
Class: |
C06B 47/08 20060101
C06B047/08; C06B 47/04 20060101 C06B047/04 |
Claims
1. A composition comprising: DL-tartaric acid as a first fuel
provided at about 5-40 percent; a second fuel selected from
carboxylic acids; amino acids; tetrazoles; triazoles; guanidines;
azoamides; metal and nonmetal salts thereof; and mixtures thereof,
said second fuel provided at about 0.1-30 percent; and potassium
chlorate as a first oxidizer, provided at about 5-70 percent,
wherein said percents are based on the weight of each constituent
as compared to the weight of the total composition.
2. The composition of claim 1 further comprising a secondary
oxidizer provided at about 0.1-50 weight percent of the total
composition, said second oxidizer selected from metal perchlorates,
metal nitrates, metal nitrites, metal oxides, basic metal nitrates,
and mixtures thereof.
3. The composition of claim 1 further comprising a processing aid
provided at about 0.1-15 weight percent of the total
composition.
4. The composition of claim 2 wherein said secondary oxidizer is
selected from potassium perchlorate, strontium nitrate, potassium
nitrate; potassium nitrite; basic copper nitrate; iron oxide,
copper oxide; and mixtures thereof.
5. The composition of claim 1 wherein said second fuel comprises a
carboxylic acid selected from mucic acid, oxalic acid, salicylic
acid, malic acid, fumaric acid, malonic acid, barbituric acid,
glutamic acid, adipic acid, and mixtures thereof.
6. The composition of claim 1 wherein said second fuel comprises an
amino acid selected from glycine, histidine, arginine, and serine,
and mixtures thereof.
7. The composition of claim 1 wherein said second fuel comprises a
tetrazole selected from 5-aminotetrazole; potassium
5-aminotetrazole; 5-aminotetrazole nitrate; 5-nitraminotetrazole;
dipotassium 5-nitraminotetrazole; dipotassium 5-nitraminotetrazole;
and mixtures thereof.
8. The composition of claim 1 wherein said second fuel comprises a
guanidine selected from nitroguanidine, dicyandiaide, guanidine
nitrate, and mixtures thereof.
9. The composition of claim 1 wherein said second fuel comprises an
azoamide selected from azodicarbonamide, azodicarbonamide
dinitrate, and mixtures thereof.
10. A gas generating system containing the composition of claim
1.
11. A vehicle occupant protection system containing the composition
1.
12. A composition comprising: DL-tartaric acid as a first fuel;
succinic acid as a second fuel; and potassium chlorate.
13. The composition of claim 12 further comprising a second
oxidizer selected from metal perchlorates, metal nitrates, metal
nitrites, metal oxides, basic metal nitrates, and mixtures
thereof.
14. The composition of claim 2 wherein said second fuel is succinic
acid and said second oxidizer is potassium perchlorate.
15. The composition of claim 12 further comprising potassium
perchlorate, wherein DL-tartaric acid is provided at about 22-24
weight percent, succinic acid is provided at about 14-16 weight
percent, potassium chlorate is provided at about 20-22 weight
percent, and potassium perchlorate is provided at about 44-46
weight percent.
16. A composition comprising DL-tartaric acid provided at about
5-40 weight percent, succinic acid provided at about 0.1-30 weight
percent, potassium chlorate provided at about 5-70 weight percent,
and potassium perchlorate provided at about 0.1-50 weight percent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/795,077 filed on Apr. 25, 2006.
TECHNICAL FIELD
[0002] The present invention relates generally to gas generating
systems, and to gas generant/auto ignition compositions employed in
gas generator devices for automotive restraint systems, for
example.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to gas generant/auto ignition
compositions that upon combustion produce a relatively smaller
amount of solids and a relatively abundant amount of gas. It is an
ongoing challenge to reduce the amount of solids and increase the
amount of gas thereby decreasing the filtration requirements for an
inflator. As a result, the filter may be either reduced in size or
eliminated altogether thereby reducing the weight and/or size of
the inflator.
[0004] An equally important challenge is to manufacture gas
generants that exhibit relatively low sensitivity with regard to
impact, friction, or electrostatic discharge stimuli.
[0005] It is also required that airbag inflators be subjected to
environmental conditioning, such as high temperature heat aging,
thermal aging, thermal cycling, thermal shock, humidity cycling,
and so forth. These extreme tests can cause many problems, ranging
from failure to inflate the airbag to over-pressurization of the
inflator leading to rupture. It is therefore desirable to have a
gas generant and inflator/gas generating system that performs the
same regardless of conditioning. The present invention provides a
solution to many of these possibilities.
[0006] Related thereto, certain auto ignition compositions, that is
those compositions employed to auto ignite at relatively low
temperatures (below 200 C), are desirable because of their
relatively low melting point and therefore their relatively low
auto ignition temperature. Additionally, another emphasis is
providing dual functionality with regard to gas generation and auto
ignition. Nevertheless, certain chemistry that provides desirable
auto ignition temperature unfortunately also contributes to more
reactive and less stable compositions after USCAR heat aging
testing. Typically, the inflator is subjected to about 400 hours at
107 C, as defined in SAE International Document SAE/USCAR-24 "USCAR
INFLATOR TECHNICAL REQUIREMENTS AND VALIDATION", herein
incorporated by reference.
[0007] It has been found, for example, that otherwise desirable
compositions containing hydroxyl functionality exhibit poor thermal
stability due to more reactive components included therein. More
specifically, and by way of example only, compositions containing
glucose and potassium chlorate function exceptionally well as auto
ignition material. Nevertheless, when subjected to heat aging
testing, the auto ignition temperature is elevated above 200 C and
the thermal stability of this composition is compromised. It is
believed that although hydroxyl functionality through electron
localization increases the acidity of the terminal proton on each
glucose molecule, it may have a propensity to produce water as a
decomposition product over time when subjected to the extreme heat
aging of the USCAR requirements. Glucose in particular has six
hydroxyl groups that provide up to six mols of water per mol of
glucose.
[0008] Accordingly, it would be an improvement in the art to
provide compositions that provide both auto ignition and gas
generating functionality. Furthermore, these compositions must pass
USCAR heat aging requirements while maintaining both thermal
stability and auto ignition temperatures at or below 200 C.
SUMMARY OF THE INVENTION
[0009] The above-referenced concerns are resolved by gas generators
or gas generating systems containing auto ignition/gas generating
compositions including DL-tartaric acid as a primary fuel; a second
fuel selected from carboxylic acids, amino acids, tetrazoles,
triazoles, guanidines, and mixtures thereof; and potassium chlorate
as an oxidizer. A secondary oxidizer selected from metal nitrates,
metal nitrites, metal perchlorates, metal oxides, other known
oxidizers, and mixtures thereof may also be employed.
Non-hygroscopic oxidizers are preferred.
[0010] In further accordance with the present invention, a gas
generator or gas generating system, and a vehicle occupant
protection system incorporating the auto ignition/gas generant
composition are also included.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a cross-sectional side view showing the general
structure of an inflator in accordance with the present
invention.
[0012] 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 INVENTION
[0013] The present invention provides a gas generant system that
includes at least one of the following: auto ignition functionality
for airbag inflators, enhanced thermal stability, reduced component
reactivity, and/or improved sensitivity with respect to impact and
friction. The present gas generating system employs a unique
advantage to the ignition function of a chlorate-based auto
ignition system. This advantage is achieved by reducing the most
reactive components of a chlorate based auto ignition system to
their minimal functional level while increasing gas yield.
Preferred gas generant systems utilize an auto ignition/gas
generating composition formed from a mixture of carboxylic acids as
fuels, and uses one or more oxidizers selected from potassium
chlorate, potassium perchlorate, strontium nitrate, potassium
nitrate, and metal oxides. (See table 1)
[0014] Although not thereby limited, it is believed that the
following explains the theory of operation of the present
invention. The primary fuel of choice is DL-tartaric acid. The
preferred secondary fuel is succinic acid. The combination of these
two carboxylic acids provides the mechanism for desired
functionality to the system based on the acidity of the carboxylic
acids as indicated by pKa value and by melting point. The degree of
hydroxyl substitution on the carboxylic acid provides the necessary
reactivity when coupled with the lower melting point of succinic
acid. It is believed that this combined interaction with potassium
chlorate is the mechanism responsible for auto ignition function.
The D and L forms of tartaric acid function equally well within
this system. However, it is the racemic mixture of tartaric acid
and the effects of hydrogen bonding between the D and L forms that
as presently informed provide optimum thermal stability. It must be
appreciated that a relatively low auto ignition temperature is
achieved by this relationship. The preferred content of tartaric
acid is about 5-40 wt %, and more preferably at about 10-25 wt
%.
[0015] Succinic acid is a preferred co-fuel within this gas
generant/auto ignition (AI) system based upon its melting point and
lack of hydroxyl substitution. While hydroxyl substitution is
typically required for auto ignition function, it is believed that
too much hydroxyl substitution exacerbates decomposition,
particularly when subjected to USCAR heat aging requirements.
Succinic acid, as a co-fuel, provides a preferred compliment to
this auto ignition/gas generant system. The preferred content of
succinic acid is about 5-30 wt % and more preferably at about 5-20
wt %.
[0016] This system will function with other suitable carboxylic
acid co-fuels such as, but not limited to, mucic acid, oxalic acid,
salicylic acid, malic acid, fumaric acid, malonic acid, barbituric
acid, glutamic acid, and adipic acid. Alternate carboxylic acids
are generally provided at about 0-20 wt %.
[0017] Alternate co-fuels such as amino acids may be incorporated
into the gas generant/AI system. Amino acids such as, but not
limited to, Glycine, Histidine, Arginine, and Serine are generally
provided at about 0-20 wt %.
[0018] It has been further demonstrated that carboxylic acid
interaction with other co-fuels such as tetrazoles, triazoles, and
guanidines provides low auto ignition temperatures based upon
depression of melting points between the fuel mixture. For example,
DL-tartaric acid (mp 210 C) and 5AT (mp 206 C) interact to create a
melting point of 151 C. This same phenomenon is observed between
5AT and succinic acid. This forced melting in the presence of
potassium chlorate offers an alternate mechanism for low
temperature auto ignition function.
[0019] Secondary fuels include tetrazoles such as 5-aminotetrazole;
metal salts of azoles such as potassium 5-aminotetrazole; nonmetal
non-ammonium salts of azoles; nitrate salts of azoles such as
5-aminotetrazole; nitramine derivatives of azoles such as
5-aminotetrazole; metal salts of nitramine derivatives of azoles
such as dipotassium 5-aminotetrazole; metal salts of nitramine
derivatives of azoles such as dipotassium 5-aminotetrazole;
nonmetal salts of nitramine derivatives of azoles such as
5-aminotetrazole and; guanidines such as dicyandiamide; salts of
guanidines such as guanidine nitrate; nitro derivatives of
guanidines such as nitroguanidine; azoamides such as
azodicarbonamide; nitrate salts of azoamides such as
azodicarbonamidine dinitrate; and mixtures thereof. The secondary
fuel can be used within this system as co-fuels to tartaric acid.
U.S. Pat. Nos. 5,035,757 and 5,872,329, herein incorporated by
reference, describes and exemplifies certain types of these
fuels.
[0020] Tartaric acid mixtures with potassium chlorate offer
improvements over carbohydrate-chlorate (D-glucose) systems with
respect to a more reliable auto ignition function after aging.
Tartaric acids have less hydroxyl substitution than reducing sugars
such as D-glucose thereby reducing the chemical generation of water
as a decomposition product. The generation of water through the
aging process compromises system stability and function.
[0021] The primary oxidizer of this system is potassium chlorate.
The content of potassium chlorate is critical to auto-ignition
function but also must be attenuated to achieve the most desired
safety factors. Utilization of potassium chlorate to the lowest
functioning level allows for improved impact/friction and
opportunity to increase gas yield by supplementing the oxygen
requirement of the system. This may be achieved by utilization of
secondary oxidizers with higher oxygen content and less solids.
Potassium chlorate is generally provided at about 5-70 wt %.
[0022] The most preferred secondary oxidizer is potassium
perchlorate. Other preferred secondary oxidizers include metal
nitrates such as strontium nitrate and potassium nitrate; metal
nitrite salts such as potassium nitrite; basic metal nitrates such
as copper nitrate; metal oxides such as iron oxide and copper
oxide; and mixtures thereof. The secondary oxidizer is generally
provided at about 0-50 wt %, and more preferably at about 10-40 wt
%.
[0023] Processing aids such as fumed silica, boron nitride, and
graphite may also be employed. Accordingly, the gas generant may be
safely compressed into tablets, or slugged and then granulated. The
gas generant may also include binders such as cellulose
derivatives, cellulose acetate, and cellulose acetate butyrate, and
carboxymethylcellulose, salts of carboxymethylcellulose; silicone;
polyalkene carbonates such as polypropylene carbonate and
polyethylene carbonate. The processing aid and/or binder is
generally provided at about 0-15 wt %, and more preferably at about
0-5 wt %.
[0024] Slag formers may also be provided and are selected from
silicon compounds such as elemental silicone; silicon dioxide;
silicones such as polydimethylsiloxane; silicates such as potassium
silicates; natural minerals such as talc and clay, and other known
slag formers. The slag former is typically provided at about 0-10
wt %, and more preferably at about 0-5 wt %.
TABLE-US-00001 TABLE 1 Preferred Preferred Preferred Ingredient %
Range example % example % example % DL-tartaric 5 40 23 19 24 Acid
Succinic Acid 5 30 15 13 15 Potassium 5 60 20 20 10.5 Chlorate
Potassium 0 55 42 44 50 Perchlorate Potassium 0 55 0 0 0 Nitrate
Strontium 0 55 0 0 0 Nitrate Metal Oxide 0 55 0 0 0.5 CAB 0 15 0 4
0 Hot Plate Temp 175 C. 172 C. 171 C. Gas yield 65.2% 64.2%
66.3%
[0025] It is believed that the reactivity of potassium chlorate in
an auto ignition system creates performance concerns with respect
to impact sensitivity and the detrimental chlorous decomposition
products, particularly when heat aged as per USCAR requirements.
Carbohydrate-chlorate systems decompose significantly upon aging at
107 C for 400 hrs. The baseline auto ignition temperature on Hot
Plate for carbohydrate-chlorate systems is 174 C, but after aging
the auto ignition temperature increases to >220 C. It is
generally recognized that for optimum inflator function, the auto
ignition composition should exhibit an auto ignition temperature
less than 200 C. See table 2.
[0026] Certain known carboxylic acid-chlorate systems offer
improvements for auto ignition systems with respect to thermal
stability, but do not provide the dual functionality of gas
generating compositions. The detrimental decomposition products of
carboxylic-chlorate systems have the potential to interact with
inflator components such as aluminum, steel, EDPM, and plastic.
Because of this reactivity the amount of material is limited for
use only as auto ignition system. Furthermore, certain known
carboxylic acid-chlorate systems also rely upon a vapor scavenger,
unlike the present invention.
[0027] The proposed gas generant/AI system offers up to 75% gas
generation per mol of gas generant/auto ignition composition, with
a baseline hot plate value of 175 C which remains virtually
unchanged (Table 1) after 600 hrs. aging at 107 C. Mass loss due to
decomposition of the proposed system is limited to about 4-20% as
compared to >20% for DL-tartaric/Potassium chlorate systems and
carbohydrate-chlorate systems. (See table 3)
TABLE-US-00002 TABLE 2 Auto ignition function after aging: AIM
Baseline AI Aged Al Carbohydrate-chlorate (D- 174 C >220 C.
glucose) system Aged 400 hrs sometimes does not ignite @ 107 C.
Existing Carboxylic Acid- 177 C. 172 C. 207 C. Chlorate systems
aged 600 hrs Lower Al requires use of @ 107 C. vapor scavenger
Improved Carboxylic- 174 C. 174 C. chlorate systems aged 600 hrs
Does not depend upon a @ 107 C. vapor scavenger
TABLE-US-00003 TABLE 3 Mass loss of 3 gram sample after aging 600
Hrs @ 107 C. in sealed 20 ml vial. AIM % Mass Loss
Carbohydrate-chlorate system Aged 400 hrs 14.2% @ 107 C. Existing
Carboxylic Acid-Chlorate systems 22% aged 600 hrs @ 107 C. Improved
Carboxylic-chlorate systems 2.9% aged 600 hrs @ 107 C.
[0028] It should be appreciated that Example 1 as given below
defines the exemplary "improved carboxylic-chlorate system"
referred to in Tables 2, 3, and 4. Example 2 as given below defines
the "existing carboxylic acid-chlorate systems" referred to in
Tables 2, 3, and 4. Example 9 as given below defines the
"carbohydrate-chlorate system".
[0029] The combined functionality of the auto-ignition and gas
generating composition will reduce cost with respect to inflator
design. An appreciable caveat of this invention is auto ignition
function coupled to good burn rate performance and high gas yields
of about 60-75% as compared to about 50-55% yield of other chlorate
systems.
[0030] Safety margins for these formulations are significantly
improved. Carbohydrate-chlorate systems and previous Carboxylic
acid-chlorate systems have HD50 values of 2.06-2.64 inches.
Friction safety is also a concern. These systems have demonstrated
BAM friction values of 24N-128N. The proposed gas generate system
offers HD50 Values of 4.5-7.3 inches for impact sensitivity and
216N-360N for friction sensitivity. ARC testing of these materials
demonstrates additional advantages. Carbohydrate-Chlorate systems
have a ARC value of 109.84 C and other carboxylic acid-chlorate
systems have an ARC value ranging from 11 C-126 C. The compositions
formed in accordance with the present invention demonstrated an ARC
value of 131 C.
[0031] Inflator component compatibility is also enhanced with the
present gas generant/AI system in that reaction with aluminum,
steel, EDPM, and plastics did not occur after extreme aging for 600
hrs at 107 C. (See table 4)
TABLE-US-00004 TABLE 4 AIM Aging and Component Compatibility
Formulation (1 gram samples) Improved Carboxylic Existing
Carboxylic Acid/Chlorate System - Acid/Chlorate System Post Age
Data Post Age Data % wt. Degree of % wt. Degree of Sample
description loss HP .COPYRGT. Corrosion loss HP .COPYRGT. Corrosion
auto ignition 3.34 174 n/a 22.0 206 n/a material alone auto
ignition 2.02 172 n/a 4.5 170 n/a material + MS 13X auto ignition
4.14 174 None 24.1 198 significant material with steel alone
(contact) auto ignition 4.66 175 None 23.3 202 significant material
with Al alone (contact) auto ignition 3.56 177 None 19.0 205
significant material + shim adhesive (no- contact) auto ignition
3.34 179 None 22.0 205 significant material + SDI initiator
(contact) auto ignition 3.25 178 None 13.6 195 significant material
+ EDPM cushion (contact) auto ignition 1.45 176 None 34.0 >260
significant material + initiator gasket (contact) auto ignition
2.32 175 None 6.8 186 significant material + SDI BBS O-ring
(contact)
[0032] The compositions of the present invention are formed from
constituents as provided by known suppliers such as Aldrich or
Fisher Chemical companies. The compositions may be provided in
granulated form and dry-mixed and compacted in a known manner, or
otherwise mixed as known in the art. The compositions may be
employed in gas generators typically found in airbag devices or
occupant protection systems, or in safety belt devices, or in gas
generating systems such as a vehicle occupant protection system,
all manufactured as known in the art, or as appreciated by one of
ordinary skill. Application within other gas generating systems is
also contemplated.
[0033] The following examples further illustrate the benefits of
the present invention. To form comparative compositions, dry mixes
of formulations containing the various constituents described below
were prepared in a known manner.
EXAMPLE 1
[0034] In accordance with a preferred embodiment of the present
invention, 23 wt. % of DL-tartaric acid (DL-TTA), 15 wt. % of
succinic acid (SA), 20 wt. % potassium chlorate, and 42 wt. % of
potassium perchlorate were provided in granulated form and
homogeneously dry mixed, and then pelletized in a known manner. As
evaluated by a differential scanning calorimeter (DSC), the auto
ignition onset was 157-160 C. The baseline hot plate auto ignition
temperature was 170-172 C. The hot plate auto ignition temperature
of the same composition, after extreme aging for 600 hours at 107 C
within a passenger inflator and a driver side inflator of known
design, was about 174 C. Decomposition of the composition after
aging was relatively minimal. Reactivity of decomposition products
with inflator components was relatively minimal. This example
illustrates how the compositions formed in accordance with the
present invention provide relatively low and similar auto ignition
temperature before and after aging, with limited reactivity.
Furthermore, compositions formed in accordance with the present
invention therefore exhibit excellent thermal stability after
aging.
EXAMPLE 2
[0035] For comparative purposes, 35.0 wt. % of DL-tartaric acid
(DL-TTA) and 65.0 wt. % potassium chlorate were provided in
granulated form and homogeneously dry mixed, and then pelletized in
a known manner. As evaluated by a differential scanning calorimeter
(DSC), the auto ignition onset was 166 C. The baseline hot plate
auto ignition temperature was 177 C. The hot plate auto ignition
temperature of the same composition, after extreme aging for 600
hours at 107 C within the same inflators of Example 1, was 193 C.
Decomposition of the composition after aging was relatively high.
Reactivity of decomposition products with inflator components was
relatively high. This example illustrates how decomposition and
inflator component reactivity is increased by the absence of a
secondary fuel such as succinic acid, and by the increase in the
chlorine-containing oxidizer.
EXAMPLE 3
[0036] For comparative purposes, 44.0 wt. % of DL-tartaric acid
(DL-TTA), 10.0 wt. % potassium chlorate, and 46.0 wt. % potassium
perchlorate were provided in granulated form and homogeneously dry
mixed, and then pelletized in a known manner. As evaluated by a
differential scanning calorimeter (DSC), the auto ignition onset
was 170 C. The baseline hot plate auto ignition temperature was
nonexistent as no flame occurred. The hot plate auto ignition
temperature of the same composition, after aging for 600 hours at
107 C within a 20 ml. vial, was also nonexistent as no flame
occurred. Decomposition of the composition after aging was
relatively minimal. Reactivity of decomposition products with
inflator components was relatively minimal. This example
illustrates how auto ignition functionality is adversely affected
with the increase of chlorine-containing oxidizers, and the absence
of a secondary fuel such as succinic acid.
EXAMPLE 4
[0037] For comparative purposes, 42.5 wt. % of DL-tartaric acid
(DL-TTA), 20 wt. % potassium chlorate, and 36 wt. % of potassium
perchlorate were provided in granulated form and homogeneously dry
mixed, and then pelletized in a known manner. As evaluated by a
differential scanning calorimeter (DSC), the auto ignition onset
was 171 C. The baseline hot plate auto ignition temperature was 176
C. The hot plate auto ignition temperature of the same composition,
after aging for 600 hours at 107 C within a 20 ml. vial, was 175 C.
Decomposition of the composition after aging was relatively
minimal. Reactivity of decomposition products with inflator
components was relatively moderate. This example illustrates how
the absence of succinic acid or a secondary fuel results in
decomposition products that increase the reactivity with inflator
components.
EXAMPLE 5
[0038] For comparative purposes, 12.0 wt. % of DL-tartaric acid
(DL-TTA), 23.5 wt. % of succinic acid (SA), 13.0 wt. % potassium
chlorate, and 51.5 wt. % of potassium perchlorate were provided in
granulated form and homogeneously dry mixed, and then pelletized in
a known manner. As evaluated by a differential scanning calorimeter
(DSC), the auto ignition onset was 159 C. The baseline hot plate
auto ignition temperature, although a weak auto ignition, was 176
C. The hot plate auto ignition temperature of the same composition,
after aging for 600 hours at 107 C within a 20 ml. vial, was
nonexistent as no flame occurred. Decomposition of the composition
after aging was relatively minimal. Reactivity of decomposition
products with inflator components was relatively minimal. This
example illustrates how auto ignition functionality after aging is
affected by variation of the amount of the constituents.
EXAMPLE 6
[0039] For comparative purposes, 31 wt. % of succinic acid (SA), 20
wt. % potassium chlorate, and 49 wt. % of potassium perchlorate
were provided in granulated form and homogeneously dry mixed, and
then pelletized in a known manner. As evaluated by a differential
scanning calorimeter (DSC), the melting point onset was 184 C. The
baseline hot plate melting point temperature was 207 C. The hot
plate melting point temperature of the same composition, after
aging for 600 hours at 107 C within a 20 ml. vial, was 210 C.
Decomposition of the composition after aging was relatively
minimal. Reactivity of decomposition products with inflator
components was relatively minimal. This example illustrates the
auto ignition functionality of DL-tartaric acid, and the absence of
auto ignition functionality without DL-tartaric acid.
EXAMPLE 7
[0040] DSC evaluations of succinic acid, DL-tartaric acid, and
D-tartaric acid resulted in respective melting points of 189.05 C,
212.27 C, and 167.66 C. This supports the belief that hydrogen
bonding increases the melting point of DL-tartaric acid.
EXAMPLE 8
[0041] A composition formed in accordance with EXAMPLE 1 was found
to have a baseline auto ignition temperature ranging from 154-159
C. After aging at 107 C for 400 hours, the composition still
exhibited an auto ignition temperature ranging from 154-159 C. This
composition exhibited 65.2 wt % gaseous products with a combustion
temperature of 1989 C and a heat of reaction (cal/g) of 90.degree..
The combustion temperature and heat of reaction are relatively
lower than known auto ignition materials, as shown in EXAMPLE 9,
thereby mitigating the cooling requirements of the gaseous
effluent.
EXAMPLE 9
[0042] A composition containing 27 wt. % of d-glucose and 73 wt. %
of potassium chlorate was mixed and pelletized as given in EXAMPLE
1. This composition was found to have a baseline auto ignition
temperature ranging from 150-175 C. After aging at 107 C for 400
hours, the carbohydrate-chlorate system exhibited an auto ignition
temperature in excess of 220 C. This composition exhibited 55.5 wt
% gaseous products with a combustion temperature of 2290 C and a
heat of reaction (cal/g) of 1126. The combustion temperature and
heat of reaction of this know composition are relatively higher
than compositions of the present invention, as shown in EXAMPLE 8,
thereby increasing the cooling requirements of the gaseous
effluent.
EXAMPLE 10
[0043] As measured by DSC, a composition containing 25 wt. %
succinic acid and 75 wt. % DL-tartaric acid exhibited a melting
point of 174.67 C. As measured by DSC, a composition containing 10
wt. % succinic acid and 90 wt. % DL-tartaric acid exhibited a
melting point of 180.84 C. As measured by DSC, a composition
containing 75 wt. % succinic acid and 25 wt. % DL-tartaric acid
exhibited a melting point of 176.82 C. As measured by DSC, a
composition containing 50 wt. % succinic acid and 50 wt. %
DL-tartaric acid exhibited a melting point of 176.57 C. This
example illustrates the ability to modulate the auto ignition
temperature while retaining other benefits of the present
invention.
EXAMPLE 11
[0044] As measured by DSC, a composition containing 43 wt. %
D-tartaric acid and 57 wt. % potassium chlorate, exhibited a
melting point of 167.66 C and an auto ignition temperature of 144
C. As measured by DSC, a composition containing 35 wt. %
DL-tartaric acid and 65 wt. % potassium chlorate, exhibited a
melting point of 212.27 C and an auto ignition temperature of 164
C. As measured by DSC, a composition containing 29 wt. % succinic
acid and 71 wt. % potassium chlorate, exhibited a melting point of
189.05 C and an auto ignition temperature of 185 C. As measured by
DSC, a composition containing succinic acid, DL-tartaric acid, and
potassium chlorate exhibited a melting point of 176.57 C and an
auto ignition temperature of 157 C. This example illustrates the
ability to modulate the auto ignition temperature while retaining
other benefits of the present invention.
EXAMPLE 12
[0045] A composition formed in accordance with EXAMPLE 1 exhibited
burn rates of: about 0.3 inches per second (ips) at 100 psig; about
0.45 ips at 500 psig; about 0.59 ips at 1000 psig; about 0.73 ips
at 1500 psig; about 0.75 ips at 2000 psig; about 0.88 ips at 2500
psig; about 0.98 ips at 3000 psig; about 1.05 ips at 3500 psig; and
about 1.07 ips at 4000 psig. Burn rate testing was conducted in a
steel bomb wherein each sample was placed. The bomb may be
pressurized from 0-5500 psi. Propellant samples 0.5 inches in
length are encased along the length in epoxy along with a
thermocouple. The naked end of the propellant is then ignited with
an electric match. The samples were ignited at various pressures
while the testing temperature was maintained at about 20-24 C.
Burns rate were then measured for each trial. This example
illustrates how the present compositions provide acceptable burn
rates for both auto ignition and gas generating functionality.
[0046] In view of the examples, a preferred composition as
exemplified in example 1 will include: 22.0-24.0 wt. % DL-tartaric
acid, 14.0-16.0 wt. % succinic acid, 19.0-21.0 wt. % potassium
chlorate, and 41.0-43.0 wt. % potassium perchlorate. Stated another
way, an optimum ratio of fuels, as exemplified here, results in the
relatively low auto ignition temperatures and excellent thermal
stability after aging. Furthermore, the optimum ratio of oxidizers,
as exemplified here, results in reliable auto ignition
functionality, and limited reactivity after aging.
[0047] It will appreciated that known auto ignition materials such
as carbohydrate-chlorate systems, containing d-glucose and
potassium chlorate for example, are more sensitive and therefore
pose handling concerns. Accordingly, special accommodations must be
made for the transfer of these materials. On the other hand, the
auto ignition/gas generating compositions of the present invention
are non-hygroscopic, more easily transported, and less sensitive
than known auto ignition materials.
[0048] As shown in FIG. 1, an exemplary inflator or gas generating
system 10 incorporates a dual chamber design to tailor containing a
primary gas generating/auto ignition 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.
[0049] Referring now to FIG. 2, the exemplary inflator or gas
generating system 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.
[0050] 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 gas generating/auto ignition composition 12 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.
[0051] 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.
[0052] 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.
[0053] It should further be understood that the preceding is merely
a detailed description of various embodiments of this invention and
that numerous changes to the disclosed embodiments can be made in
accordance with the disclosure herein without departing from the
scope of the invention. The preceding description, therefore, is
not meant to limit the scope of the invention. Rather, the scope of
the invention is to be determined only by the appended claims and
their equivalents.
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