U.S. patent application number 11/092377 was filed with the patent office on 2005-11-24 for gas generant and manufacturing method thereof.
Invention is credited to Matlock, Robert J., Williams, Graylon K..
Application Number | 20050257866 11/092377 |
Document ID | / |
Family ID | 35125660 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050257866 |
Kind Code |
A1 |
Williams, Graylon K. ; et
al. |
November 24, 2005 |
Gas generant and manufacturing method thereof
Abstract
The present invention generally relates to gas generant
compositions for inflators of occupant restraint systems, for
example. An extrudable pyrotechnic composition includes
polyvinylazoles for use within an airbag gas generator. The fuel
may be selected from exemplary polyvinylazoles including
5-amino-1-vinyltetrazole, poly(5-vinyltetrazole),
poly(2-methyl-5-vinyl) tetrazole, poly(1-vinyl) tetrazole,
poly(3-vinyl) 1,2,5 oxadiazole, and poly(3-vinyl) 1,2,4-triazole.
An oxidizer is combined with the fuel and preferably contains phase
stabilized ammonium nitrate. A novel method of forming the
compositions is also presented wherein the various constituents are
wetted and/or dissolved, and then cured within the polyvinylazole
matrix thereby forming a more intimate combination within the gas
generant composition. A vehicle occupant protection system 180, and
other gas generating systems, incorporate the compositions of the
present invention.
Inventors: |
Williams, Graylon K.;
(Warren, MI) ; Matlock, Robert J.; (Southfield,
MI) |
Correspondence
Address: |
L.C. BEGIN & ASSOCIATES, PLLC
510 HIGHLAND AVENUE
PMB 403
MILFORD
MI
48381
US
|
Family ID: |
35125660 |
Appl. No.: |
11/092377 |
Filed: |
March 29, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60557279 |
Mar 29, 2004 |
|
|
|
Current U.S.
Class: |
149/36 |
Current CPC
Class: |
C06D 5/06 20130101; C06B
21/0025 20130101; C06B 45/10 20130101 |
Class at
Publication: |
149/036 |
International
Class: |
C06B 047/08 |
Claims
We claim:
1. A method of forming a gas generating composition comprising the
steps of: providing a solvent effective to dissolve a fuel
comprising a polymeric azole selected from the group consisting of
vinyl tetrazoles, vinyl triazoles and vinyl furazans, the solvent
selected with regard to the solvability of the functional group(s)
that may be present on the polymeric azole, the solvent placed in a
mixing vessel; adding the fuel to the mixing vessel; adding an
oxidizer to the mixing vessel; stirring the mixture; adding an
initiator to the mixing vessel to initiate polymerization of the
slurry; and curing the mixture.
2. The method of claim 1 further comprising the step of adding an
additive to the mixing vessel prior to adding the initiator.
3. The method of claim 1 further comprising the step of heating the
mixing vessel below boiling.
4. The method of claim 1 wherein adding the solvent and adding the
fuel to the mixing vessel comprises the same step whereby the fuel
also functions as the solvent.
5. A gas generating system containing a gas generant produced by
the method of claim 1.
6. A gas generating system containing a gas generant formed by the
method comprising the steps of: providing a solvent effective to
dissolve a fuel comprising a polymeric azole selected from the
group consisting of vinyl tetrazoles, vinyl triazoles and vinyl
furazans, the solvent selected with regard to the solvability of
the functional group(s) that may be present on the polymeric azole,
the solvent placed in a mixing vessel; adding the fuel to the
mixing vessel; adding an oxidizer to the mixing vessel; stirring
the mixture; adding an initiator to the mixing vessel to initiate
polymerization of the slurry; and curing the mixture.
7. The gas generating system of claim 6 wherein said system is a
vehicle occupant protection system.
8. The gas generating system of claim 6 wherein said system is an
airbag system.
9. The gas generating system of claim 6 wherein said system is a
seatbelt assembly system.
10. The gas generating system of claim 6 wherein said system
activates an inflatable floatable device.
11. The gas generating system of claim 6 wherein said system is a
fire extinguishing system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/557,279 filed on Mar. 29, 2004.
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.
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.
[0009] Yet another concern includes slower cold start ignitions of
typical smokeless gas generant compositions, that is gas generant
compositions that result in less than 10% of solid combustion
products.
[0010] Yet another concern regards the environmental impact of
manufacturing gas generant compositions. In many manufacturing
processes, the gas generant is formed in a solvent-based process.
As such, the organic solvent remnant must be disposed of with the
attendant environmental concerns.
[0011] 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.
SUMMARY OF THE INVENTION
[0012] The above-referenced concerns are resolved by gas generating
systems including a gas generant composition containing an
extrudable polyvinylazole fuel such as a polyvinyltetrazole,
polyvinyltriazole, or polyvinyldiazole. Preferred oxidizers include
nonmetal oxidizers such as ammonium nitrate and ammonium
perchlorate. Other oxidizers include alkali and alkaline earth
metal nitrates.
[0013] The fuel is selected from the group of polyvinyltetrazoles,
polyvinyltriazoles, polyvinyldiazoles or polyvinylfurazans, and
mixtures thereof. A preferred group of fuels includes polymeric
tetrazoles, triazoles, and oxadiazoles (furazans), having
functional groups on the azole pendants. Although compositions
containing NH.sub.3 linkages and carbon/hydrogen content are
generally useful, preferred compositions will not contain NH.sub.3
linkages due to handling concerns, and the carbon and hydrogen
content will be minimized to inhibit the formation of carbon
dioxide and water. Preferred vinyl tetrazoles include
5-Amino-1-vinyltetrazole and poly(5-vinyltetrazole), both
exhibiting self-propagating thermolysis or thermal decomposition.
Other fuels include poly(2-methyl-5-vinyl) tetrazole, poly(1-vinyl)
tetrazole, poly(3-vinyl) 1,2,5-oxadiazole, and poly(3-vinyl)
1,2,4-triazole. These and other possible fuels are structurally
illustrated in the figures included herewith. The fuel preferably
constitutes 10-40% by weight of the gas generant composition.
[0014] An oxidizer is preferably selected from the group of
nonmetal, and alkali and alkaline earth metal nitrates, and
mixtures thereof. Nonmetal nitrates include ammonium nitrate and
phase stabilized ammonium nitrate, stabilized as known in the art.
Alkali and alkaline earth metal nitrates include potassium nitrate
and strontium nitrate. Other oxidizers known for their utility in
air bag gas generating compositions are also contemplated. The
oxidizer preferably constitutes 60-90% by weight of the gas
generant composition.
[0015] Other gas generant constituents known for their utility in
air bag gas generant compositions may be employed in effective
amounts in the compositions of the present invention. These
include, but are not limited to, coolants, slag formers, and
ballistic modifiers known in the art.
[0016] In sum, the present invention includes gas generant
compositions that maximize gas combustion products and minimize
solid combustion products while retaining other design requirements
such as thermal stability. These and other advantages will be
apparent upon a review of the detailed description.
[0017] In yet another aspect of the invention, a method of
manufacturing a gas generant composition incorporating a
polyvinylazole is described. A vinyl azole is first added to a
vessel. If necessary, an aqueous, organic, or aqueous/organic
solvent is provided in an amount effective to dissolve all
constituents to be added to the vessel. In preferred embodiments, a
liquid vinyl azole will complete wet and/or facilitate the
solubility of the other gas generant constituents without the use
of a solvent. An oxidizer, preferably nonmetallic, is next added.
Other constituents/solutes such as a secondary fuel(s), a secondary
oxidizer(s), slag former(s), processing aid(s), coolant(s), and/or
burn rate modifier(s) may be added to the slurry and stirred to a
substantially uniform or homogeneous mixture. Next, an initiator is
added to facilitate the curing or polymerization of the mixture.
The mixture is then cured either statically, or without stirring,
wherein a solid is then formed, or, while stirring wherein granules
may then be formed. If cured statically, the mixture may be poured
within molds, for example, to form the desired propellant shape(s).
If cured while stirring, crushing and formation of the granules is
not necessary given the inherent formation of the granules.
Thermoplastic polymers facilitate melt processing for further
shaping of the propellant if desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is an exemplary airbag inflator containing a gas
generant composition formed in accordance with the present
invention.
[0019] FIG. 2 is a schematic representation of an exemplary vehicle
occupant restraint system incorporating the inflator of FIG. 1 and
a gas generant in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0020] The present invention generally relates to gas generant
compositions for inflators of occupant restraint systems. In
accordance with the present invention, a pyrotechnic composition
includes extrudable fuels such as polyvinyltetrazoles (PVT) for use
within a gas generating system, such as that exemplified by a high
gas yield automotive airbag propellant in a vehicle occupant
protection system. The fuel also functions as a binder. Preferred
oxidizers include nonmetal oxidizers such as ammonium nitrate and
ammonium perchlorate. Other oxidizers include alkali and alkaline
earth metal nitrates.
[0021] The fuel is selected from the group of polyvinyltetrazoles,
polyvinyltriazoles, polyvinyldiazoles or polyvinylfurazans, and
mixtures thereof. A preferred group of fuels includes polymeric
tetrazoles, triazoles, and oxadiazoles (furazans), having
functional groups on the azole pendants. Although compositions
containing HN.sub.3 linkages and carbon/hydrogen content are
generally useful, preferred compositions will not contain HN.sub.3
linkages due to handling concerns, and the carbon and hydrogen
content will be minimized to inhibit the formation of carbon
monoxide, carbon dioxide, and water. In general, the consumption of
oxygen from the oxidizer is preferentially inhibited with regard to
the formation of these gaseous or vapor products. Preferred vinyl
tetrazoles include 5-Amino-1-vinyltetrazole and
poly(5-vinyltetrazole), both exhibiting self-propagating
thermolysis or thermal decomposition. Other fuels include
poly(2-methyl-5-vinyl) tetrazole, poly(1-vinyl) tetrazole,
poly(3-vinyl) 1,2,5-oxadiazole, and poly(3-vinyl) 1,2,4-triazole.
These and other possible fuels are exemplified by, but not limited
to, the structures shown below. 1
[0022] Other Possible Tetrazole Polymers:
[0023] As such, it has been discovered that an additional benefit
with the present fuels is that compositions resulting in difficult
cold-start ignitions that necessitate more powerful ignition trains
and boosters, are avoided. Poly(5-amino-1-vinyl) tetrazole, for
example, has no endothermic process before exothermic decomposition
begins. Therefore, the heat-consuming step normally attendant prior
to the energy releasing steps of combustion (that acts as an energy
barrier) is not present in the present compositions. It is believed
that other polymeric azoles functioning as fuels in the present
invention have the same benefit. The polyvinylazole fuel preferably
constitutes 5-40% by weight of the gas generant composition.
[0024] An oxidizer is preferably selected from the group of
nonmetal, and alkali and alkaline earth metal nitrates, and
mixtures thereof. Nonmetal nitrates include ammonium nitrate and
phase stabilized ammonium nitrate, stabilized as known in the art.
Alkali and alkaline earth metal nitrates include potassium nitrate
and strontium nitrate. Other oxidizers known for their utility in
air bag gas generating compositions are also contemplated. The
oxidizer preferably constitutes 60-95% by weight of the gas
generant composition.
[0025] Other gas generant constituents known for their utility in
air bag gas generant compositions may be employed in effective
amounts in the compositions of the present invention. These
include, but are not limited to, coolants, slag formers, and
ballistic modifiers known in the art.
[0026] The gas generant constituents of the present invention are
supplied by suppliers known in the art and are preferably blended
by a wet method. A solvent chosen with regard to the group(s)
substituted on the polymeric fuel is heated to a temperature
sufficient to dissolve the fuel but below boiling, for example just
below 100.degree. C., but low enough to prevent autoignition of any
of the constituents as they are added and then later precipitate.
Hydrophilic groups, for example, may be more efficiently dissolved
by the use of water as a solvent. Other groups may be more
efficiently dissolved in an acidic solution, nitric acid for
example. Other solvents include alcohols and plasticizers such as
polyethylene glycol. Once a suitable solvent is chosen and heated,
the fuel is slowly added and dissolved. The oxidizer is then slowly
added and also dissolved. Any other desirable constituents are
likewise dissolved. The solution is heated and continually stirred.
As the solvent is cooked off over time, the fuel and oxidizer, and
any other constituents, are co-precipitated in a homogeneous solid
solution. The precipitate is removed from the heat once the solvent
has been at least substantially volatilized, but more preferably
completely volatilized. The composition may then be extruded into
pellets or any other useful shape.
[0027] The polymeric fuels may be manufactured by known processes.
For example, vinylation of a tetrazole with vinyl acetate, followed
by polymerization is described in Vereshchagin, et al., J. Org.
Chem. USSR (Engl. Transl.) 22(9), 1777-83, (1987). The synthesis of
various vinyltetrazoles is also described in Russian Chemical
Reviews 72(2), pages 143-164 (2003), herein incorporated by
reference. The methyl-group of the starting tetrazole can be
exchanged for an amino group. The vinyltetrazoles are then
polymerized using a common polymerization initiator such as
azoisobutyronitrile (AIBN). It is believed that similar vinylation
of furazans and triazoles will also yield the polyvinyldiazoles and
polyvinyltriazoles of the present invention. Exemplary reactions
given below illustrate how various polyvinyldiazoles,
polyvinyltriazoles and polyvinyltetrazoles may be formed. Reaction
1 illustrates how polyvinyldiazoles may be formed. Reaction 2
illustrates how polyvinyltriazoles may be formed. Reaction 3
exemplifies how polyvinyltetrazoles may be formed. 2
[0028] Reaction 1: This synthesis is for a
poly(vinyl-1,2,5-oxadiazole) and exemplifies or blueprints a
general method of forming polyvinyidiazoles. 3
[0029] Reaction 2: This synthesis is for an ionic polymer version
of poly(vinyl-1,2,4-triazole) and exemplifies or blueprints a
method of forming other polyvinyltriazoles. 4
[0030] Reaction 3: This synthesis is for a substituted
polyvinyltetrazole and exemplifies or blueprints a method of
forming other polyvinyltetrazoles.
[0031] A generic polyvinylazole, or a structure that generically
represents the polyvinyltetrazoles, polyvinyltriazoles, and
polyvinyldiazoles of the present invention, may be represented by
an aromatic ring having five cites that contains, 5
[0032] Stated another way, the aromatic ring will contain from zero
to a single oxygen atom, will contain at least two nitrogen atoms,
and will contain at least one carbon atom. More preferably, a gas
generant composition of the present invention will contain a
polymeric azole and phase stabilized ammonium nitrate. The
advantages are high gas yield and low solids production, a high
energy fuel/binder, and a low-cost oxidizer thereby obviating the
need for filtration of the gas given that little if any solids are
produced upon combustion. The compositions of the present invention
may be extruded given the pliant nature of the polymeric fuels.
[0033] The gas generant compositions of the present invention may
also contain a secondary fuel formed from amine salts of tetrazoles
and triazoles. These are described and exemplified in co-owned U.S.
Pat. Nos. 5,872,329, 6,074,502, 6,210,505, and 6,306,232, each
herein incorporated by reference. The total weight percent of both
the first and second fuels, or the fuel component of the present
compositions, is about 10 to 40 weight % of the total gas generant
composition.
[0034] More specifically, nonmetal salts of tetrazoles include in
particular, amine, amino, and amide salts of tetrazole and triazole
selected from the group including monoguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.1GAD), diguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.2GAD), monoaminoguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.1AGAD), diaminoguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.2AGAD), monohydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT.1HH), dihydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT.2HH), monoammonium salt of
5,5'-bis-1H-tetrazole (BHT.1NH.sub.3), diammonium salt of
5,5'-bis-1H-tetrazole (BHT.2NH.sub.3),
mono-3-amino-1,2,4-triazolium salt of 5,5'-bis-1H-tetrazole
(BHT.1ATAZ), di-3-amino-1,2,4-triazolium salt of
5,5'-bis-1H-tetrazole (BHT.2ATAZ), and diguanidinium salt of
5,5'-Azobis-1H-tetrazole (ABHT.2GAD).
[0035] Amine salts of triazoles include monoammonium salt of
3-nitro-1,2,4-triazole (NTA.1NH.sub.3), monoguanidinium salt of
3-nitro-1,2,4-triazole (NTA.1GAD), diammonium salt of
dinitrobitriazole (DNBTR.2NH.sub.3), diguanidinium salt of
dinitrobitriazole (DNBTR.2GAD), and monoammonium salt of
3,5-dinitro-1,2,4-triazole (DNTR.1NH.sub.3). 6
[0036] A generic nonmetal salt of tetrazole as shown in Formula I
includes a cationic nitrogen containing component, Z, and an
anionic component comprising a tetrazole ring and an R group
substituted on the 5-position of the tetrazole ring. A generic
nonmetal salt of triazole as shown in Formula II includes a
cationic nitrogen containing component, Z, and an anionic component
comprising a triazole ring and two R groups substituted on the 3-
and 5-positions of the triazole ring, wherein R.sub.1 may or may
not be structurally synonymous with R.sub.2. An R component is
selected from a group including hydrogen or any nitrogen-containing
compound such as an amino, nitro, nitramino, or a tetrazolyl or
triazolyl group as shown in Formula I or II, respectively,
substituted directly or via amine, diazo, or triazo groups. The
compound Z is substituted at the 1-position of either formula, and
is formed from a member of the group comprising amines, aminos, and
amides including ammonia, carbohydrazide, oxamic hydrazide, and
hydrazine; guanidine compounds such as guanidine, aminoguanidine,
diaminoguanidine, triaminoguanidine, dicyandiamide and
nitroguanidine; nitrogen substituted carbonyl compounds or amides
such as urea, oxamide, bis-(carbonamide) amine, azodicarbonamide,
and hydrazodicarbonamide; and, amino azoles such as
3-amino-1,2,4-triazole, 3-amino-5-nitro-1,2,4-triazole,
5-aminotetrazole, 3-nitramino-1,2,4-triaz- ole,
5-nitraminotetrazole, and melamine.
EXAMPLE 1
[0037] A gas generant composition of the present invention is
formed by first synthesizing a polyvinyltetrazole. A generic
substituted tetrazole and vinyl acetate are combined to vinylate
the tetrazole. The vinylated tetrazole is added to a molar
equivalent of mercury acetate and boron trifluoride-etherate for
polymerization thereof. The resulting products may then be
separated by oil distillation for example. The polyvinyltetrazoles
illustrated in the drawings may be formed in the same way. Reaction
3 exemplifies the process described above.
EXAMPLE 2
[0038] A gas generant composition of the present invention is
formed by first synthesizing a polyvinyltriazole. A generic
substituted triazole metal or nonmetal salt is added to a molar
equivalent amount of a free radical brominating reagent such as
n-bromo-succinamide and to a benzoyl-peroxide free radical
initiator to form a brominated triazole. The brominated triazole is
then added to triphenyl phosphine to form a Wittig salt group on
the substituted triazole salt. The triazole salt is then added to a
metal or nonmetal organic or inorganic base, and also to
formaldehyde to form a vinylated triazole salt. The vinylated
triazole salt is next added to a free radical polymerization
reagent such as azoisobutyronitrile and a catalytic amount of a
cationic polmerizer or Ziegler-Natta catalyst such as a metal or
titanium complex. Reaction 2 exemplifies the process described
above wherein the synthesis of poly(vinyl-1,2,4-triazole) is
described.
EXAMPLE 3
[0039] A gas generant composition of the present invention is
formed by first synthesizing a polyvinyldiazole. An alkenol
containing two --OH groups is added to acetic anhydride to form a
substituted diazole. The substituted diazole is then added to a
molar equivalent amount of a free radical brominating reagent such
as n-bromo-succinamide and to a free radical initiator such as
benzoyl-peroxide to form a brominated diazole. The substituted
diazole is then added to triphenyl phosphine to form a Wittig salt
group on the substituted diazole salt. The diazole salt is then
added to a metal or nonmetal organic or inorganic base, and also to
formaldehyde to form a vinylated diazole salt. The vinylated
diazole salt is next added to a free radical polymerization reagent
such as azoisobutyronitrile and a catalytic amount of a cationic
polymerizer or Ziegler-Natta reagent such as a metal complex.
Reaction 1 exemplifies the process described above wherein the
synthesis of poly(vinyl-1,2,5-oxadiaz- ole) is described.
Examples 4-9
[0040] Examples 4-9 are tabulated below and provide a comparative
view of the different types and amounts of gas produced with regard
to several known gas generant compositions and a gas generant
formed in accordance with the present invention. Example 4 is a
representative gas generant composition formed from
5-aminotetrazole and strontium nitrate, in accordance with U.S.
Pat. No. 5,035,757 herein incorporated by reference. Example 5 is a
representative gas generant composition formed from an amine salt
of tetrazole such as diammonium salt of 5,5'-bi-1H-tetrazole, phase
stabilized ammonium nitrate, strontium nitrate, and clay in
accordance with U.S. Pat. No. 6,210,505 herein incorporated by
reference. Example 6 is a representative gas generant composition
formed from an amine salt of tetrazole such as diammonium salt of
5,5'-bi-1H-tetrazole and phase stabilized ammonium nitrate in
accordance with U.S. Pat. No. 5,872,329 herein incorporated by
reference. Example 7 is a representative gas generant composition
formed from ammonium nitramine tetrazole and phase stabilized
ammonium nitrate in accordance with U.S. Pat. No. 5,872,329 herein
incorporated by reference. Example 8 is a representative gas
generant composition formed from ammonium nitramine tetrazole,
phase stabilized ammonium nitrate, and a slag former in accordance
with U.S. Pat. No. 5,872,329 herein incorporated by reference.
Example 9 is a representative composition formed in accordance with
the present invention containing ammonium polyvinyl tetrazole and
phase stabilized ammonium nitrate (ammonium nitrate coprecipitated
with 10% potassium nitrate).
[0041] Table 1 details the relative amounts produced (ppm) of
carbon monoxide (CO), ammonia (NH3), nitrogen monoxide (NO), and
nitrogen dioxide (NO2) with regard to each example and the amount
of gas generant in grams (Gg). All examples were combusted in a gas
generator of substantially the same design.
1TABLE 1 Example Gg P.sub.c CO NH3 NO NO2 4 45 15 125 10 49 9 5 25
36 109 65 29 4 6 25 29 111 29 37 5 7 25 36 62 10 28 3 8 25 37 98 35
33 4 9 25 34 129 4 28 4
[0042] The data collected indicates that the composition of Example
9, formed in accordance with the present invention, results in far
less ammonia than the other examples, well below the industry
standard of 35 ppm. It has been discovered that compositions of the
present invention result in substantially less amounts of ammonia
as compared to other known gas generants. In many known gas
generant compositions, it is often difficult to reduce the total
amount of ammonia produced upon combustion, even though other
performance criteria remain favorable.
Examples 10-14
[0043] Theoretical examples 10-14 are tabulated below and provide a
comparative view of the different amounts and types of gas produced
with regard to several gas generant compositions formed in
accordance with the present invention. All phase stabilized
ammonium nitrate (PSAN10) referred to in Table 2 has been
stabilized with 10% by weight potassium nitrate of the total PSAN.
All examples employ ammonium poly(C-vinyltetrazole) (APV) as the
primary fuel. Certain examples employ nonmetal diammonium salt of
5,5'-Bis-1H-tetrazole (BHT.2NH3) as a secondary fuel. All examples
reflect results generated by combustion of the gas generant
constituents (propellant composition) within a similarly designed
inflator or gas generator with equivalent heat sink design.
2TABLE 2 Gas Constituents Flame Exhaust Combustion (wt % of Temp.
Temp. Products Example 100 g) (K) (K) (mol) 10 15% APV 2222 857
2.25 H2O 85% PSAN10 1.33 N2 0.39 CO2 11 16% APV 2057 900 2.25 H20
40% PSAN10 1.33 N2 10% Strontium Nitrate 0.39 CO2 05% Clay 12 22%
APV 2054 1225 0.64 H2O 73% Strontium Nitrate 0.83 N2 05% Clay 0.52
CO2 13 08% APV 2036 874 1.86 H20 64.60% PSAN10 1.34 N2 10%
Strontium Nitrate 0.35 CO2 05% Clay 12.40% BHT.2NH3 14 08% APV 2206
835 2.20 H2O 80.60% PSAN10 1.45 N2 11.40% BHT.2NH3 0.34 CO2
[0044] Example 10 has been found to be thermally stable at 105
degrees Celsius for 400 hours with only a 0.5% mass loss.
Accordingly, Example 10 exemplifies the unexpected thermal
stability of gas generant compositions of the present invention,
particularly those incorporating a polyvinylazole as defined herein
and phase stabilized ammonium nitrate (stabilized with 10%
potassium nitrate). It should be emphasized that other phase
stabilizers are also contemplated as known or recognized in the
art.
[0045] Examples 11 through 13 exemplify the use of a polyvinylazole
with metallic oxidizers. In certain applications, the use of a
metallic oxidizer may be desired for optimization of ignitability,
burn rate exponent, gas generant burn rate, and other design
criteria. The examples illustrate that the more metallic oxidizer
is used the less mols of gas produced upon combustion.
[0046] In contrast, Examples 1 0 and 14 illustrate that molar
amounts of gas combustion products are maximized when nonmetal gas
generant constituents are employed. Accordingly, preferred gas
generant compositions of the present invention contain at least one
polyvinylazole as a fuel component and a nonmetal oxidizer as an
oxidizer component.
[0047] Finally, with regard to Example 14, it has been found that
the gas generant burn rate may be enhanced by adding another
nonmetal fuel, BHT.2NH3, to APV and PSAN10, thereby optimizing the
combustion profile of the gas generant composition. The burn rate
of Example 14 is recorded at 1.2 inches per second at 5500 psi. It
can be concluded therefore, that the addition of nonmetal amine
salts of tetrazoles and/or nonmetal amine salts of triazoles as
described in U.S. Pat. No. 5,872,329 may be advantageous with
regard to burn rate and gas generation. Furthermore, the pliant
nature of the APV provides extrudability of the propellant
composition.
EXAMPLES 15 and 16
[0048] Examples 15 and 16 exemplify the cold start advantage of gas
generant compositions containing a polyvinylazole. As shown by
differential scanning calorimetry (DSR), typical smokeless or
nonmetal compositions may exhibit an endothermic trend prior to
exothermic combustion. As a result, relatively greater amounts of
energy must be available to ignite the gas generant and sustain
combustion of the same. Oftentimes, a more aggressive ignition
train, to include an aggressive booster composition perhaps, is
required to attain the energy level necessary to ignite the gas
generant and sustain combustion. Example 15 pertains to a
composition containing 65% PSAN10 and about 35% BHT.2NH3. As shown
in FIG. 1, an endotherm is maximized at 253.12 degrees Celsius,
thereby representing a recorded loss of about 508.30 joules/gram of
gas generant. In comparison, Example 16 pertains to a composition
containing about 15% poly(C-vinyltetrazole) and about 85% PSAN10.
Most unexpectedly, there is no endothermic process and accordingly,
combustion proceeds in an uninhibited manner. As a result, less
energy is required to combust the gas generant composition thereby
reducing the ignition train or ignition and booster
requirements.
[0049] In yet another aspect of the invention, the present
compositions as exemplified herein 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 an automotive gas generating system may
contain a gas generating composition as described herein.
[0050] In yet another aspect of the invention, a method of
manufacturing a gas generant composition includes polymerizing a
monomer component of a polymeric binder/fuel in the presence of at
least an oxidizer thereby forming a homogeneous solid composite gas
generant formulation. The polymeric binder/fuel is generally
selected from a myriad of polymeric azoles including vinyl
tetrazoles, vinyl triazoles, vinyl oxadiazoles (furazans),
copolymers thereof, as described above for example. Functional
groups may be present on the azole pendants, however, preferred
compositions avoid HN.sub.3 linkages due to sensitivity issues.
Furthermore, preferred compositions will also have relatively lower
amounts of carbon/hydrogen content thereby facilitating cooler
formulations upon combustion believed attributable to the lower
amounts of water and carbon dioxide formed. The polymeric
binder/fuel is exemplified by any of several polyvinyl tetrazole
compounds including poly(vinyl-5-amino)tetrazole,
poly(vinyl-5-methyl)tetrazole, poly(5-amino-l-vinyltetrazole),
poly(5-vinyltetrazole) and poly(vinyl-bitetrazolamine), or mixtures
thereof. Other polymeric azole fuels are illustrated in the
discussion given above. Other fuels contemplated as useful in the
present invention include metal salts and complexes of the azole
polymers described above.
[0051] The polymeric azoles may be purchased from suppliers known
in the art. They may also be manufactured by vinylation of an azole
with vinyl acetate. For example, the vinylation of a tetrazole with
vinyl acetate, followed by polymerization, yields desirable poly
vinyl tetrazoles. 7
[0052] The procedure is detailed in Vereshchagin, et al., J. Org.
Chem. USSR (Engl. Transl.), 22(9), 177-83, (1987), herein
incorporated by reference. The methyl-group of the starting
tetrazole may be exchanged for an amino-group. The vinyltetrazoles
are then polymerized using a common polymerization initiator such
as azoisobutyronitrile (AIBN). Other syntheses may be employed. It
is believed that vinylation of furazans and triazoles would
similarly yield desirable polymers.
[0053] The oxidizer is preferably selected from exemplary compounds
to include alkali metal, alkaline earth metal, transitional metal,
and nonmetal nitrates and perchlorates. Specific oxidizers include
ammonium nitrate, phase stabilized ammonium nitrate, potassium
nitrate, strontium nitrate, potassium perchlorate, ammonium
perchlorate, sodium nitrate, sodium perchlorate, and mixtures
thereof.
[0054] When preparing the compositions, the monomer(s)/copolymer(s)
and oxidizer(s) are added to an inorganic solvent such as water, or
to an organic solvent such as dimethylformamide, depending on the
chemistry of the monomer/copolymers. If water is used, a
water-based polymerization initiator such as ammonium persulfate is
employed in the aqueous slurry resulting in a relatively thinner or
less rigid slurry. If an organic-based solvent is used, an organic
solvent based initiator such as azobisisobutyronitrile (AIBN) is
employed in the organic slurry resulting in relatively thicker or
more viscous slurry.
[0055] Typically, the azole monomer or azole copolymer is solvated
in an appropriate solvent, either water, a mixture of water and
miscible solvent (ethanol, methanol, or other alcohols; acetone,
tetrahydrofuran (THF), dimethylformamide (DMF), dimethylsulfoxide
(DMSO), or a non-water miscible organic solvent selected from the
group including ethers, such as dimethylether and diethylether, and
also from the group including aromatics, such as toluene and
benzene. Other known additives such as slag formers, coolants, burn
rate modifiers, secondary fuels, and secondary oxidizers may be
added to the solvent in known effective amounts to make a slurry in
the solvent. The slag formers, processing aids, coolants, and/or
burn rate modifiers include stearates such as magnesium stearate,
graphite, clays, micas, talcs, silicates, aluminates, and other
functionally similar constituents. The secondary fuels include
tetrazoles, triazoles, imidazoles, pyrazoles, oxiadiazoles,
guanidines such as nitroguanidine and guanidine nitrate, and other
constituents functional as fuel components in the present
invention. Secondary oxidizers include metal and nonmetal
chlorates, perchlorates, nitrates, nitrites, oxides, and other
compounds having an oxidizing function.
[0056] The polymerization initiator is then added after the
addition of all of the other constituents, and is selected from
known initiators. For example, a preferred free radical initiator
is 2,2'-azobisisobutyronitril- e (AIBN) and may be employed in a
known manner. Other types of initiators such as ammonium persulfate
are also contemplated. In general, the polymerization initiator is
provided at about 100-250 mg per batch. Nevertheless, all that is
required is that is a relatively small amount as compared to the
overall weight of the mix whereby the formation of free radicals is
facilitated. After that, the polymerization reaction self
propagates. Temperature may be increased or lowered to tailor the
desired cure time. At room temperature, curing may take from three
to twenty-four hours. A preferred temperature range is from
10-90.degree. C. Although an apparently cured material may be
obtained in a relatively short time, the curing process may
continue for a number of hours. After mixing the constituents to
form a substantially homogeneous slurry, curing in a static state
produces a solid block of finished propellant while stirring during
the curing process forms granules.
[0057] Depending on the monomer/copolymer and the solvent
temperature, 10-50% propellant mixture per unit solvent weight is
desirable. The solvent can be removed during or after the curing
process by evaporation. Note that if the monomer/copolymer is a
liquid, a solvent may not be necessary. In essence, the liquid
monomer or copolymer must be in an amount effective to "wet" the
solids to be added thereto. "Wet" as used herein is meant as at
least partially solvating, and more preferably completely
solvating, the constituents added to the fuel. The effective liquid
monomer/copolymer amount can therefore be iteratively determined
based on the weight percent desired relative to the fuel function
and relative to the propensity of the fuel to wet the rest of the
constituents. If a solvent is still required to wet the
constituents, the solvent may be added to ensure wetting of the
solid constituents within the vessel. In general, the various
constituents may be added to the slurry at the following weight
percents: 5-20% of the azole monomer/copolymer(s); 50-90% of the
oxidizer(s); 0-25% additional fuels; and 0-10% processing aids,
slag formers, and/or burning rate modifiers. Note that the weight
percents represent the total weight prior to addition to the
slurry, or prior to combination thereof.
[0058] Compositions formed in this manner result in consistent
repeatable performance based on the intimate combination of the
constituents resulting from the mixing and curing process.
Furthermore, the manufacturing process of the gas generant is
simplified as compared to other gas generant syntheses thereby
reducing the associated costs. In addition to the advantages stated
above, other advantages include the ability to melt form many of
the compositions when the monomer/copolymer employed is
thermoplastic in nature. Furthermore, the pliant nature of the
compositions facilitates containment flexibility with many of the
present compositions whereby the propellant or gas generant 12 may
be compressively stored in cavities within the inflator thereby
optimizing the use of available space. As a result, the size of the
inflator may be effectively reduced while still retaining the same
effective amount of gas generation, thereby retaining the same
inflation pressure profile that would typically be represented by a
relatively larger inflator.
[0059] Stoichiometric amounts of fuel and oxidizer are preferably
combined in the slurry thereby resulting in a balanced combustion
reaction. An exemplary balanced combustion reaction of
poly(5-amino-1-vinyl) tetrazole with ammonium nitrate is shown
below:
2C.sub.3H.sub.5N.sub.5+17NH.sub.4NO.sub.3.multidot.6CO.sub.2+22N.sub.2+39H-
.sub.2O
[0060] The weight percents of the fuel and oxidizer are about 14%
PV5AT and about 86% AN. Other oxidizers including strontium
nitrate, potassium perchlorate, ammonium perchlorate, and so forth
may also be employed depending on application design criteria. In
general, the fuel/oxidizer weight percent ratio ranges from 45/50
to 5/90, respectively.
[0061] The polymerization process may be accelerated by the amount
of initiator employed and also by the application of heat, for
example. Other acceleration methods are contemplated.
[0062] It is also contemplated that the present compositions be
employed in an airbag device to include airbag modules, airbag
inflators, seatbelt pretensioners, or, vehicle occupant restraint
systems, all schematically represented in FIG. 2 and all built or
designed as well known in the art. Furthermore, the present
compositions may more generally be provided in gas generating
systems designed for a variety of applications such as inflatable
flotation devices, inflatable aircraft slides, fire extinguishers,
and vehicle occupant protection systems that include airbag devices
and/or seatbelt assemblies with pretensioners, for example.
[0063] 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 gas generant 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.
[0064] 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.
[0065] 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 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.
[0066] 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.
[0067] 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.
[0068] It will be understood that the foregoing descriptions of
various embodiments of the present invention are for illustrative
purposes only, and should not be construed to limit the breadth of
the present invention in any way. As such, the various structural
and operational features disclosed herein are susceptible to a
number of modifications, none of which departs from the scope of
the present invention as defined in the appended claims.
* * * * *