JP2001048690A - Gas generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an increase of a combustion rate and good gas generation efficiency and to decrease undesirable gaseous components by compounding the simple substance, alloy or compound of elements forming a nitrate specified in a pyrolysis temperature under containing ammonium nitrate. SOLUTION: This gas generating agent is prepared by compounding the simple substance, alloy or compound (effective matter for compounding) of the elements which have the pyrolysis temperature above the pyrolysis temperature of ammonium nitrate and form the nitrate with the ammonium nitrate. The elements used for the compounding are preferably magnesium, calcium and strontium. The elements are preferably stabilized by coating the elements with a polymer, or the like, when the elements are added to the ammonium nitrate in the form of the simple substance. In the case of the alloy, the elements are preferably the alloy powder of the magnesium and aluminum. In the case of the compound, organic acids and borides are preferable. The amount of the effective matter for the compounding to be added is preferably 0.05 to 1.0 mol to 1 mol ammonium nitrate. The combustion rate increases as a result of a rise in the combustion surface temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a gas generator for a vehicle safety device such as an air bag, a gas utilization propulsion device, a high-pressure device, and the like. The present invention relates to a gas generating composition which is a good solid gas generating agent and is improved so that gas can be generated at a high speed.

[0002]

2. Description of the Related Art Solid gas generating agents include gas generating devices for vehicle safety devices such as airbags, propulsion devices such as rockets (gas generating agents for rockets are called propellants),
It is often used for automatic control pressure generators. The gas generating agents used in these devices are small and lightweight, using a gas generating agent with high gas generation efficiency, which generates little harmful gas to the living body and generates a large amount of gas per unit weight or unit volume. It is important that the gas is supplied at a sufficient rate, in other words, that the gas generation rate is high, that it is stable against heat and impact, that it is easy to handle and that it can withstand long-term storage. Gases that are not preferred for living organisms are generally, for example, nitrogen oxides, halogenated gases, carbon monoxide, high-concentration carbon dioxide, and the like. Generates a lot of gas. For this reason, gas generators containing sodium azide have been used in gas generators for airbags, but sodium azide itself is toxic and therefore difficult to handle and has low gas generation efficiency. Gas generating agents that do not use this are being used. Also,
In propulsion devices such as rockets, a propellant containing ammonium perchlorate as a main component is used as an oxidizing agent.
This propellant generates a large amount of hydrogen chloride gas during combustion, has a possibility of causing strong acid rain, and there is a concern that environmental destruction may occur. In order to improve this point, studies have been made using an inorganic oxidizing agent containing no halogen, an organic nitro compound, a nitramine compound, and the like. In particular, ammonium nitrate has been attracting attention as an inorganic oxidizing agent that is stable without halogen, generates less undesirable gas, and has good gas generation efficiency. Under such circumstances, the inventor has previously invented a gas generating composition composed of ammonium nitrate and metal nitride, which has extremely low undesired gas generation (Patent Application No. 10-323718). However, a gas generating agent using ammonium nitrate as an oxidizing agent does not always have a sufficient gas generating speed, and further improvement is required when a large amount of gas is required to be generated at a high speed. It is known that increasing the surface area of the gas generating agent and increasing the burning rate are effective in improving the gas generation rate. It has been reported that the addition of an organic substance containing an azide group, such as a glycidyl azide polymer, to ammonium nitrate is effective in increasing the burning rate of a gas generating agent. Ammonium nitrate contains three oxygens in one molecule, but uses two to oxidize its own ammonia group, so the other one oxidizes the other.
Only one can be used. In order to sufficiently increase the burning rate, it is necessary to increase the amount of the azide group-containing organic substance. However, in this case, a large amount of undesirable carbon monoxide is generated. Although a certain amount of carbon monoxide is allowed to be emitted as a rocket propellant, it is not suitable for use in airbags, and inorganic oxidants other than azide group-containing organic substances and nitrogen-containing organic substances and ammonium nitrate, such as strontium nitrate and potassium nitrate Gas generating agents in combination with potassium perchlorate and the like have been studied. Comparing the gas generating agent containing sodium azide with the gas generating agent currently used, the gas generating agent using sodium azide has less undesirable gas generation, but the gas generation efficiency is lower than the weight of the gas component. It is 40 to 60% in terms of rate (weight% of generated gas with respect to the weight of gas generating agent), and 14 to 19 mol / kg in terms of gas generation amount (number of moles generated per kg of gas generating agent).
On the other hand, the gas generating efficiencies of currently used gas generating agents composed of nitrogen-containing organic substances and inorganic oxidizing agents are 55 to 65% and 20 to 25 mol / kg, respectively, which are considerably improved. The gas contains an undesirable gas.

[0003]

As described above, there is a demand for a solid gas generating agent which is stable, has excellent gas generation efficiency, and has an improved gas generation rate, with little generation of gas which is undesirable for living organisms. However, these have not yet been fully achieved.

It is an object of the present invention to provide a gas generating composition having these characteristics.

[0005]

As a result of intensive studies, the present inventors have invented a gas generating composition which can achieve this object.

That is, the present invention provides (1) a gas generating agent containing ammonium nitrate, which is composed of a simple substance, an alloy of the element and a compound of the element, which form a nitrate having a thermal decomposition temperature higher than the thermal decomposition temperature of ammonium nitrate. A gas generating agent comprising at least one selected from the group consisting of: (2) the gas generating agent according to (1), wherein the element is magnesium, calcium or strontium;
(3) The gas generating agent according to the above (1) or (2), wherein the compound of the element is a boride, a nitride, a halide, or an organic acid salt, (4) a nitrogen-containing organic material, a binder, an auxiliary oxidizing agent, and The gas generating agent according to any one of (1) to (3), further including at least one metal nitride.

According to the present invention, the burning rate can be greatly increased, the gas generation efficiency is good, and the undesirable gas components can be substantially reduced as compared with the conventional gas generating agents using ammonium nitrate.

The present invention will be described in detail. The ammonium nitrate used in the present invention is not particularly limited, but generally,
For example, industrial-use ammonium nitrate, microcrystalline ammonium nitrate, and phase-stabilized ammonium nitrate are suitable.

The present invention relates to these ammonium nitrates,
Thermal decomposition temperature of ammonium nitrate (210
℃), which is selected from the group consisting of simple substances of the elements that form nitrates with a thermal decomposition temperature of over (referred to as effective compounding elements), alloys of the elements, and compounds of the elements (these are collectively referred to as effective compounding substances). It is characterized by blending at least one kind. In general, when a gas generating agent burns, the combustion surface is heated and the surface temperature rises, thereby decomposing the gas generating agent, generating a flammable gas, and causing a combustion reaction in the gas phase to cause a gas temperature. Rise and develop into a flame. At this time, it is said that the higher the combustion surface temperature and the flame temperature, the higher the combustion speed. The present invention relates to a method for measuring a differential scanning calorimeter (hereinafter referred to as DSC), in which, in the case of a generator containing ammonium nitrate, an element which produces a nitrate having a thermal decomposition temperature higher than the thermal decomposition temperature of ammonium nitrate is added. Decomposition in the thermal decomposition temperature range is based on the discovery that disappearance or a significant decrease in the calorific value has occurred, and a new peak appears on the higher temperature side, which indicates that new decomposition occurs. This raises the combustion surface temperature in the combustion and, as a result, increases the combustion rate. The reason why the thermal decomposition temperature of the product of the present invention is increased is that ammonium nitrate is melted on the combustion surface, and at this time, the compounded effective element reacts with ammonium nitrate, and the thermal decomposition temperature is higher than that of ammonium nitrate. In the present invention, nitrite is also included in nitrate). In such a case, in general, the theoretical amount of the compounded effective substance necessary for the ammonium nitrate to react to form a nitrate having a high decomposition point (for example, when the compounded effective substance is magnesium alone, ammonium nitrate 2 Since 1 mol of magnesium reacts with 1 mol of mol to produce 1 mol of magnesium nitrate, the theoretical ratio is 2 g of ammonium nitrate (molecular weight: 80) and 160 g of 2 mol of ammonium nitrate (molecular weight: 2).
4.3) It is thought that it is necessary to add 24.3 g) of 1 mol, but contrary to this expectation, even at a very small amount of addition, it is further confirmed that the burning rate increases dramatically. discovered. On the other hand, when the compounded effective substance does not react with ammonium nitrate to become nitrate or nitrite of the compounded effective element, the reaction rate of the combustion reaction phase does not increase and it is not effective, and the gas generation efficiency of ammonium nitrate is good. May not be able to survive. In addition, the compounded effective substance and ammonium nitrate are the main components, but the surface of the compounded effective substance should be stable so that they do not react in the required temperature range and become unstable such as partial or total decomposition. Processing such as surface inactivation such as covering with a molecular substance, stabilization as a compound, and alloying with a stable metal can be performed by common sense.

[0010] Typical effective elements to be blended include lithium, sodium, potassium, silver, magnesium, calcium, strontium, cadmium, lead and bismuth. Among them, magnesium is relatively inexpensive, has good availability, and has low metal toxicity.
Calcium and strontium are preferred.

[0011] When these compounded effective elements are added alone, for example, in a stabilized form such as a surface-inactivated powder whose surface is covered with a polymer or the like well known in this technical field. It is preferred to add. When the element is added as an alloy, a powder of magnesium and an aluminum alloy (magnalium) is typical.

When the effective compound is a compound, the compound may be mixed with ammonium nitrate and heated at the melting temperature of ammonium nitrate (chemical temperature) as in the case of using the compound in the form of an element or an alloy of the element. Any material that reacts at a temperature of about 169.6 ° C. or higher in Handbook Basic Edition, page I-178) or higher to generate nitrate or nitrite having a decomposition point equal to or higher than the decomposition point of ammonium nitrate may be used. This phenomenon can be easily measured by, for example, DSC. For example, with a sample amount of 1 to 4 mg, D
When the SC was measured, an endotherm for melting appeared at about 150 to 165 ° C for the phase-stabilized ammonium nitrate with potassium nitrate, and then at about 265 to 297 ° C (hereinafter about 28 to 297 ° C).
(At 0 ° C.), the decomposition peak appears at about 280 ° C. in the mixture containing the effective compound, or the peak does not appear at all at about 280 ° C.
A new decomposition peak appears at ~ 450 ° C. When the compounded effective substance is a compound, examples of the compounded effective element are organic acid salts such as formic acid, oxalic acid, and acetic acid, boride, nitride, halide, thiosulfate, metaborate, chromate, and bichromium. Inorganic salts and compounds other than nitrates such as acid salts and molybdates. Among them, organic salts, borides and nitrides are preferable because they have high gas generation efficiency and are stable.

[0013] The amount of the effective compound added is 1 part of ammonium nitrate.
The effective amount of the compounded element is from 0.05 mol to 1.1 mol, preferably from 0.08 mol to 1 mol, per mol (80 g). If the range is less than this, the effect of increasing the combustion speed is small. If it is more than this, the gas generation efficiency will be equal to or lower than the conventional product.

A composition obtained by adding an effective compound to ammonium nitrate is further added with one or more of a nitrogen-containing organic substance, a binder, an auxiliary oxidizing agent, and a metal nitride to have a gas composition, a gas generating agent shape and strength, and the like. It is possible to adjust as follows.

As the nitrogen-containing organic substance, those generally used for a gas generating agent for an air bag, for example, nitroguanidine, guanidine nitrate, tetrazole derivatives such as amitotetrazole, and azodicarbonamide are representative.

As the binder, an inorganic binder and an organic binder can be used. A typical example of the inorganic binder is water glass, and a molded product can be obtained by adding, mixing, and press-molding. When a resin containing a liquid polymer and a curing agent as main components is used as an organic binder, for example, a urethane system composed of a prepolymer having a hydroxyl group and an isocyanate, an epoxy system composed of an epoxy resin and its curing agent, and an unsaturated bond Generally, polyester-based products consisting of a prepolymer, a radical generator such as a peroxide, and an auxiliary agent, and the like, are added, mixed, molded into a specified shape, and then cured. Can be obtained. When a thermoplastic resin is used for the organic binder, for example, acetyl cellulose, a thermoplastic resin soluble in a solvent such as butyl cellulose,
After mixing a plasticizer, a solvent, and the like with the gas generating composition of the present invention, forming the mixture into a specified shape, followed by heating and drying, a gas generating agent molded product can be obtained.

Auxiliary oxidants, as noted above, can be added to help ammonium nitrate because it has less oxygen to oxidize others. Examples of this are generally potassium nitrate, sodium nitrate, strontium nitrate and the like. Note that potassium nitrate is preferably added to stabilize the phase change of ammonium nitrate.

The metal nitride combines with the oxygen of ammonium nitrate to generate heat, and does not generate carbon oxides during combustion. Therefore, it is easy to obtain an extremely small amount of undesired gas and the gas generation efficiency is high. It is effective when used as a gas generating agent for airbags. Metal nitrides do not contain azide. Examples of this are boron nitride, silicon nitride,
A typical example is aluminum nitride.

In addition to the gas generating agent of the present invention, other materials generally added to the gas generating agent, such as metal powder, molding aid, and slag forming agent, may be added according to the purpose.

Example 1 Ammonium nitrate undergoes a phase change accompanied by a volume change at 30 to 80 ° C. When the phase change affects the characteristics like a gas generating agent, it is prevented and stabilized. It is preferred to use phase stabilized ammonium nitrate (PSAN). Also in this embodiment, potassium nitrate is used to form P.
A SAN was created and used. PSAN is 90% ammonium nitrate and 10% potassium nitrate (both in weight%,
The same applies hereinafter) and water is added to the mixture of the two in an outer ratio of 20 to 50%.
In addition, it was prepared by heating and melting at 100 ° C. to 140 ° C., drying and pulverizing. The other components are commonly used chemicals, and a sample having the composition shown in Table 1 was prepared using these components. Data on the thermal decomposition of this sample was obtained. In this measurement, 1.5 to 3.5 mg of a sample was packed in an aluminum sealed container, heated at a heating rate of 10 ° C./min using a DSC (manufactured by Shimadzu Corporation), and the decomposition state was measured. Table 1 shows the results. In Table 1, decomposition peak 1 is indicated in units of J / g by decomposing temperature, peak temperature, and heat of decomposition in the decomposition temperature range of ammonium nitrate (the calorific value is determined from the area of the peak, and the calorific value is divided by the sample amount). ),
In addition, those of newly appeared decomposition peaks are described in decomposition peak 2. Under this condition, as shown in Comparative Example 1, ammonium nitrate decomposes at a temperature higher than the thermal decomposition temperature shown in the Chemical Handbook. Even when a relatively oxidizable substance such as the composition of Comparative Examples 2 to 5 is blended,
A decomposition peak appears as if ammonium nitrate had been decomposed first without increasing the calorific value in the same pyrolysis temperature range as SAN alone and without burning the added fuel component. In the case of the gas generating agent of the present invention, a decomposition peak having a small heat of decomposition and thus a small amount of decomposition may appear in the same temperature range as the decomposition peak of ammonium nitrate as in Example 1-2, but in many cases, The peak in the decomposition range of ammonium nitrate disappears,
It is shown that a new decomposition peak having a heat of decomposition equivalent to that of PSAN appears at 70 to 130 ° C. higher.

[0021]

[Table 1]

Example 2 The combustion state of the gas generating agent of the present invention was measured. The gas generating compositions shown in Table 2 were mixed, and a disc-shaped tablet having a diameter of 5 mm and a maximum thickness of about 1 mm was prepared by a press. In addition, a disc-shaped tablet having a particle size of 150 mg and a diameter of 5 mm was prepared by a press using a mixture of 22% boron and 78% potassium nitrate as an igniting agent. Also, titanium powder 45 is used as an ignition charge.
% And potassium perchlorate 55%. Approximately 15m internal volume with safety valve, venting pipe with valve, internal pressure measurement sensor and ignition current terminal for combustion rate measurement
1 pressure vessel and a pressure measuring device were prepared. Further, an undesirable gas contained in the generated gas, namely, C
A detection tube gas measuring device and a detection tube manufactured by GASTECH, which can measure O, Cl, NO, and NH _3, were prepared.

In the composition of Table 2, as described in the column of the number of moles of gas, the amount of generated gas is calculated from a basic chemical formula, and the amount of generated gas of a gas generating agent generally used at present is calculated. A composition capable of obtaining several 25 mol / kg or more was selected.

About 0.4 m in diameter to the ignition power supply terminal of the pressure vessel
m and a pressure sensor, and the thickness of the gas generating agent tablet was measured. Then, 0.5 to 1 g was weighed and filled in the pressure vessel (the weight of the charged gas generating agent was W And). One tablet of the igniting powder and 100 mg of the igniting powder were added thereto, the pressure vessel was sealed, the valve of the gas vent pipe was closed, and the pressure sensor was connected to a pressure measuring device so that the pressure could be measured. An AC power supply of about 30 volts was supplied to the ignition power supply to ignite the gas generating agent, and the relationship between pressure and time (referred to as pressure time data) was measured and recorded. After the combustion was completed, a gas detector was attached to the gas vent pipe, the valve was opened, and the gas concentration was measured by the detector tube. The results are shown in the column of toxic gas concentration in Table 2. The pressure time data gradually increases with time from the initial pressure (0 atm), shows the maximum pressure (Pmax), and reaches an equilibrium. From this data, the burning rate in the closed vessel test was calculated. This principle is based on the maximum pressure (Pma
It is assumed that the entire amount (W) of the gas generant charged in x) has burned. The value (Pi / Pmax) obtained by dividing the pressure (Pi) at each time (ti) by Pmax is the ratio of the amount (Wi) of the gas generating agent burned up to each time (ti) to the total amount (Wi / W).
Is considered to be equivalent to That is, Pi / Pmax =
Wi / W is established. Here, Pi, Pma
Since x and W can be measured, Wi can be calculated. The amount (Wr) of the gas generating agent remaining at each time (ti) and Wi
Is W, and therefore Wr = W−Wi, so that Wr can also be obtained. The diameter of the initial gas generating agent is Do, the thickness is To, the burning distance burned by each time (ti) is hi,
If the density of the gas generating agent is d and the number of particles of the gas generating agent is n, W = (π / 4) × n × d × Do ² × To, Wr = (π / 4) × n × d × ( Do−2 × hi) ² × (To−2 × hi) = W−Wi.

From this relationship, Wi / W = 1− (Wr / W) = 1− (Do−2 × hi) ² × (To−2 × hi) / (Do ² × To), and other than hi are known. So that hi can also be calculated,
The combustion distance (hi) for each time (ti) can be calculated. For example, the combustion rate at a pressure of 150 atm (about 15 MPa) is determined by the time (ti) at the pressure of 148 atm, the combustion distance (hi) at that time, and the time (t) at the pressure of 152 atm.
_{i + 1)} and when determining the combustion distance at that time (h _{i + 1),} a _{(h i + 1 -hi) /} (t i + 1 -ti). Thus, the burning rate at a pressure of 150 atm was obtained. The results are shown in the column of combustion rate in Table 2. As a result, the gas generating agent of the present invention has a better gas generating efficiency than the conventional gas generating agent, and has extremely few undesired gases.
O is contained in the order of 1000 ppm), and the burning rate is also increased by 2 to 10 times that of the comparative example. Table 2
ND means “not detected” and NM means “not measured”.

[0026]

[Table 2]

[0027]

As described above, the gas generating agent of the present invention is more effective than the conventional ammonium nitrate based gas generating agent.
Its pyrolysis temperature can be raised, and thus the surface temperature of the gas generant can be raised,
The burning rate can be increased.

Therefore, the gas generating agent of the present invention has a remarkably improved gas generating speed and excellent gas generating efficiency, and can suppress generation of gas components which are not desirable for living organisms.

Therefore, the gas generating agent of the present invention has a high gas generation efficiency, such as an airbag device and a rocket propellant,
And it is useful in the field where high-speed gas generation is required.

Claims (4)

[Claims] 1. A gas generating agent containing ammonium nitrate, wherein at least one selected from the group consisting of a simple substance of an element generating a nitrate having a thermal decomposition temperature higher than the thermal decomposition temperature of ammonium nitrate, an alloy of the element, and a compound of the element A gas generating agent containing seeds. 2. The gas generating agent according to claim 1, wherein the element is magnesium, calcium or strontium. 3. The gas generating agent according to claim 1, wherein the compound of the element is a boride, a nitride, a halide, or an organic acid salt. 4. The gas generating agent according to claim 1, further comprising at least one of a nitrogen-containing organic substance, a binder, an auxiliary oxidizing agent, and a metal nitride.