Note: Descriptions are shown in the official language in which they were submitted.
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WO 95/09825 PCT/DE94/01184
Gas generator propellant
The invention relates to solid gas generator propellants based
on guanidine compounds on suitable carriers.
JP H5-254977 discloses gas generator propellants for airbags
based on triaminoguanidine nitrate (TAGN), which may additionally
contain oxidizing agents such as alkali-metal and alkaline-earth-
metal nitrates, nitrites, chlorates or perchlorates. Molybdenum
sulphide may be present as a further component. The advantage
of using TAGN instead of the known sodium azides is the nontoxic
nature and also the good stability of TAGN, which, in addition,
does not form any salts which are sensitive to friction and
impact in combination with heavy metals. The burn-up rate of the
gas generator propellants should be possible via a variation in
the compression pressure during the production of pellets or
tablets from the component mixture.
Disadvantages of such gas generator propellants are a still
inadequate controllability of the burn-up, the development of
toxic gases such as CO and an imperfect formation of slag during
burn-up, which results in an increased development of dusts, some
of which enter the lungs.
Compared with JP H5-254977, the object of the present invention
is to provide improved gas generator propellants whose burn-up
behaviour can be systematically adjusted and which form readily
retainable slags during burn-up and minimize the production of
toxic gases. The gas generator propellants are intended to be
thermally stable, readily ignitable, fast-burning, even at low
temperature, and satisfactorily storable and to ensure a high gas
yield. In addition, said gas generator propellants are intended
to make it possible to reduce the size of the generator casing
and consequently reduce its weight compared with known generators
operated with sodium azide.
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According to the invention, these objects are achieved by a gas
generator propellant, comprising
(A) at least one carbonate, hydrogen carbonate or nitrate of
guanidine, aminoguanidine, diaminoguanidine or triamino-
guanldlne,
(B) at least one alkali-metal or alkaline-earth-metal nitrate
or ammonium nitrate as oxidizing agent, and
(C) at least one carrier substance selected from silicon
dioxide, alkali-metal silicates, alkaline-earth-metal
silicates or aluminosilicates and/or at least one oxygen-
supplying carrier substance selected from iron(III) oxide,
cobalt oxides, manganese dioxide and copper(II) oxide, to
moderate burn-up and improve slag formation.
Carbonates, hydrogen carbonates or nitrates of guanidine,
aminoguanidine, diaminoguanidine or triaminoguanidine (TAGN) or
its mixtures can be used as component (A). TAGN is preferably
used. TAGN is virtually nontoxic (LD50 ' 3500 mg/kg rat),
nonhygroscopic, sparingly soluble in water, thermally stable,
combustible at low temperature and has low sensitivity to impact
and friction. The gas yield in the burn-up of TAGN is very high,
in which process a large proportion of nitrogen gas is produced.
Optionally, the TAGN may be replaced by 1 to 50% by weight of
nitroguanidine. The cost of the component (A) can thereby be
reduced and a beneficial burn-up behaviour achieved, since
nitroguanidine has a lower burn-up rate than TAGN.
Alkali-metal or alkaline-earth-metal nitrates, ammonium nitrate
and mixtures thereof can be used as oxidizing agents, component
(B). Potassium nitrate is preferably used. Potassium nitrate
is nonhygroscopic, nontoxic and makes possible a high gas yield
during burn-up and a low burn-up temperature.
In the mixture of (A) and (B), component (A) is present in a
quantity of about 20 to 55, preferably about 50 to 55% by weight,
and component (B) in a quantity of about 80 to 45, preferably
about 50 to 45% by weight. Preferably, component (A) is present
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in a quantity of about 50 to 55~ by weight and component (B) in
a quantity of about 50 to 45~ by weight.
Silicon dioxide, alkali-metal silicates, alkaline-earth-metal
silicates or aluminosilicates or mixtures thereof can be used as
carrier substance, component (C). Examples of these are Aerosil
200 and Aerosil 300, highly disperse silicic acid and kieselgur
(diatomaceous earth). Preferred carrier substance is silicic
acid having a pH of about 7.
Iron(III) oxide, cobalt oxides, manganese dioxide and copper(II)
oxide or mixtures thereof can also be used as component (C). The
preferred oxygen-supplying carrier substance is iron(III) oxide.
Relative to the total quantity of the components (A) and (B),
component (C) is present in a quantity of about 5 to 45,
preferably about 8 to 20% by weight. If iron(III) oxide is used
as oxygen-supplying carrier substance (C), it is present in a
quantity of about 20 to 40, preferably about 25 to 35~ by weight,
relative to the total quantity of the components (A) and (B).
Component (C) serves to moderate burn-up, i.e. to adjust the
burn-up rate. Simultaneously, the slag or melt formation is
improved. The slag formation is absolutely necessary, for
example, in the case of an airbag.
An airbag essentially comprises a gas generator casing filled
with the gas generator propellant, generally in tablet form, and
an initial detonator (squib) for detonating the gas generator
propellant, and also a gas bag. Suitable detonators are
disclosed, for example, in US-PS 49 31 111. The gas bag, which
is initially folded into a small pack, is filled, after the
initial detonation, with the gases produced in the burn-up of the
gas generator propellant and reaches its full volume in a time
period of about 10 - 50 ms. The escape of hot sparks, molten
material or solids from the gas generator into the gas bag has
to be largely prevented, since it could result in a destruction
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of the gas bag or in injury to the vehicle occupants. Thls is
achieved by the slag formation.
The formation of slags simultaneously reduces the production of
dust-type components which enter the lungs and which could escape
from the gas generator of an airbag. Dust-type particles which
enter the lungs have a diameter of about 6 ~m or less. The
oxygen-supplying carrier substances additionally suppress the
formation of toxic gases, such as carbon monoxide, during burn-
up .
Optionally, the gas generator propellant may furthermore contain,as component (D), a binder which is soluble in water at room
temperature. Preferred binders are cellulose compounds or
polymers of one or more polymerizable olefinic unsaturated
monomers. Examples of cellulose compounds are cellulose ethers,
such as carboxymethylcellulose, methylcellulose ether, in
particular methylhydroxyethylcellulose. A methylhydroxyethyl-
cellulose which can be used satisfactorily is CULMINAL(R) MHEC
30000 PR supplied by the company Aqualon. Suitable polymers
having binding action are polyvinylpyrrolidone, polyvinyl
acetate, polyvinyl alcohol and polycarbonates.
Relative to the total quantity of components (A) and (B),
component (D) is present in a quantity of about 0.1 to 5,
preferably about 1.5 to 2.5~ by weight.
The binder (D) serves as desensitizing agent and as processing
aid in the production of granular material or tablets from the
gas generator propellant. It furthermore serves to reduce the
hydrophilic nature of the gas generator propellant and to
stabilize it.
The tablets or pellets of the gas generator propellant used in
the gas generator can be produced by known methods, for instance
by hot press working, extrusion, in rotary compression presses
or in tableting machines. The size of the pellets or tablets
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depends on the desired burn time in the particular application
case.
Working Examples
The calculated quantities of triaminoguanidine nitrate (TAGN),
optionally also nitroguanidine, and also potassium nitrate and
optionally cellulose ether are dissolved in as little water as
possible at 90C and iron oxide and/or silicon dioxide having a
mean particle size of approximately 1 ~m is stirred into the
solution. After predrying at 60C and 16 hPa with mechanical
agitation, the mixture is comminuted in the still moist state and
then, after drying at 60C, is compressed into tablets having a
diameter of 6 mm and a height of 2 mm using a tableting machine.
The tested mixtures are listed in Table I. Mixture 1 does not
contain any silicon dioxide and Mixture 5 does not contain any
iron(III) oxide. As a comparison mixture, Mixture 6 does not
contain either silicon dioxide or iron(III) oxide.
Table I: Composition of the mixtures in percentaqe by weiqht
1 2 3 4 5 6
TAGN 39.1 39.1 39.1 29.1 47.3 53.0
Nitroguanidine - - - 10.0 -
KNO3 30.9 30.9 30.9 30.9 40.7 47.0
Fe2O3 30.0 20.0 14.0 14.0 -
SiO2 - 10.0 14.0 14.0 12.0 -
Cellulose ether - - 2.0 2.0 -
Table II shows an overview of the reaction parameters determined
by calculation. A high reaction temperature occurs in Mixture 5
and particularly in Mixture 6.
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Table II: Calculated values
2 balance % +2.13 +1.13 -1.84 -1.57 +0.25 +0.84
Volume ccm 1000 1000 1000 1000 10001000
Charging density (g/ccm)0.1 0.1 0.1 0.10.1 0.1
Pressure bar 427 444 470 457 654810
Temperature K 1973 2116 2116 2116 24682666
Number of moles of
the gases used mol/kg21.1 22.6 23.9 23.427.5 28.8
Heat of explosion J/g 3369 3092 29982913 3852 4566
Table III shows an overview of the reaction products produced
during burn-up and their quantities.
Table III: Reaction products at 298 K, freeze-out temperature
1,500 K
Compound 1 2 3 4 5 6
(% by wt)
C2 3.604 10.086 11.538 13.228 12.408 3.768
H2O 18.952 18.817 18.828 17.711 22.935 26.692
N2 27.219 27.219 27.217 26.735 33.383 37.596
CO 0.000 0.134 1.283 1.223 0.0000.000
H2 - 0.017 0.139 0.109 0.0000.000
NO 0.001 0.000 0.000 0.000 0.0090.018
2 0.001 0.000 0.000 0.000 0.2480.826
HCN 0.000 0.000 0.000 0.000 0.0000.000
NH3 0.000 0.000 0.003 0.002 0.0000.000
KOH 0.086 0.000 0.003 0.003 0.0530.101
K2CO3 21.014 0.000 0.000 0.000 0.150 31.997
FeO - - 12.597 12.597 - -
Fe2O3 3.726 0.000 0.000 0.000 - 0.000
Fe3O4 25.396 19.331 0.000 0.000 - 0.000
K2SiO3 - 23.572 23.572 23.572 30.813
SiO2 - 0.820 4.820 4.820
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,
Table IV shows the test results on the susceptibility to
decomposition, stability, slag formation and burn-up behaviour
of the various mixtures. Mixtures 1 to 5 exhibited good to very
good burn-up behaviour, in particular in relation to a constant,
high burn rate. Only inadequate slag formation and inadequate
burn-up behaviour was observed for the comparison Mixture 6,
which did not contain either silicon dioxide or iron(III) oxide
as component (C).
Table IV: Test results
Mixture 1 2 3 4 5 6
Decomposition temperature C *) - 207 178 203
Measurement conditions:
Heating rate 2C/min
from 15C below
decomposition temperature
Stability : Holland test
Sample weight : 2.5 g
Test temperature: 105C
Test time : 72 h
Weight loss (~ by weight) - - 0.28 0.40 0.13 -
Slag formation ++ ++ ++ ++ ++
Burn-up behaviour + ++ ++ ++ +
Note: ++ very good; + good; - inadequate
*) For Mixture 1, other stability tests were performed:
Stability tests on Mixture 1
1. Differential thermal analysis
Apparatus: HERAEUS - FUS-O-MAT
Heating rate 10C/min, initial sample mass 10 mg
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'L 8
Result: KNO3 conversion: 129/130C
Start of exothermic reaction: 168C
2. Differential thermogravimetry
Apparatus: LINSEIS - Simultan DTA/TG
Heating rate 5C/min, initial sample mass 20 mg
Result: KNO3 conversion: 127C
Start of exothermic reaction: 135C
Deflagration: 158C
Test burn-uP of Mixture 1
A test burn-up of Mixture 1 was carried out in a normal aluminium
gas generator casing for a 60 litre airbag, provided with a bore
for pressure measurement, in a 60 litre can. The test
temperature for Test 1 was -35C and the propellant charge weight
was 51.0 g. The propellant charge was composed of tablets having
a diameter of 6 mm and a height of 2 mm.
Figure 1 shows the pressure in the burn-up chamber in units of
105 pascals as a function of the time after detonation in
milliseconds for Test 1.
The pressure build-up takes place within approximately 1.5 ms and
the pressure drop to half the maximum pressure takes place after
approximately 27 ms. The maximum pressure is 1.88*107 Pa and is
reached after 12.3 ms.
Analysis of the toxic qas components formed in ppm
CO 300 NH3 > 70 NOx 60
Test burn-up of Mixture 2
The test burn-up of Mixture 2 was carried out in an aluminium
Euro gas generator casing for a 35 litre airbag, provided with
a bore for pressure measurement, in a 60 litre can. The test
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g
temperature was -35C in Test 2 and +20C in Test 3. The
propellant charge weight was 41.0 g in Test 2 and 30.0 g in Test
3. The propellant charge was composed of tablets having a
diameter of 6 mm and a height of 2 mm.
Figure 2 shows the pressure in the burn-up chamber in units of
105 pascals as a function of the time after the detonation in
milliseconds for Test 2.
The pressure build-up takes place within approximately 1.5 ms and
the pressure drop to half the maximum pressure takes place after
approximately 27 ms. The maximum pressure was 1.45*107 Pa and
was reached after 15.7 ms.
Figure 3 shows the pressure in the burn-up chamber in units of
105 pascals as a function of the time after the detonation in
milliseconds for Test 3.
The pressure build-up takes place within approximately 1.5 ms and
the pressure drop to half the maximum pressure takes place after
approximately 27 ms. The maximum pressure was 1.33*107 Pa and
was reached after 7.5 ms.
The gas generator propellant according to the invention is
composed of nontoxic, easily producible and inexpensive
components whose processing does not present problems. Their
thermal stability results in good storage capability. Despite
low burn-up temperature, the ignitability of the mixtures is
good. They burn rapidly and provide high gas yield with very low
CO and NO components. The mixtures according to the invention
are therefore particularly suitable for use as gas generating
agents in the various airbag systems, as extinguishing agents or
propellants. In addition, the gas generator propellants are
readily recyclable.
