CZ20024237A3 - Premature firing powder for thermal fuses for airbag gas generators - Google Patents

Abstract

The present invention relates to a rapid ignition powder for thermal fuses intended for use in airbag gas generators, which powder is capable of a thermally controlled ignition of gas-producing mixtures far below the critical temperature, said mixtures usually being used in gas generators. The inventive powder has a weight loss substantially lower than 3 %percent by weight when kept for more than 400 hours at warm storage temperatures of 110 degC and still remains completely functional. The inventive rapid ignition powder contain at least one fuel selected from the group including 2-thiohydantoin and 2-thiobarbituric acid, at least one oxidant, at least one stabilizing agent and optionally processing agents, auxiliary fuels and filling agents.

Description

Premature igniting powder for thermal fuses for airbag gas generators

Technical field

BACKGROUND OF THE INVENTION The present invention relates to premature igniting powder for thermal fuses for the instantaneous ignition of gas charges used in automobile airbag gas generators.

BACKGROUND OF THE INVENTION

The gas charges used in gas generators for car airbags usually have high thermal stability. The so-called thermal fuses are used for the controlled ignition of the gas charge at high ambient temperatures, for example in the event of a car fire. Such a thermal fuse ensures that before and after installation, i.e. in a car, the resulting gas generator does not ignite only at an uncontrolled elevated temperature, which could then lead to leakage or even tearing of the gas generator housing, especially in the case of an aluminum housing. Thus, the thermal fuse ensures that the gas charge reaction is thermally triggered well below this critical temperature. Thus, by premature reaction and controlled ignition of the gas charge, destruction of the gas generator housing is prevented and the associated hazards are eliminated.

One possible embodiment of the thermal fuse consists of a housing filled with a premature igniting powder, which is a pyrotechnic mixture in an amount of 0.1 to 0.5 g, for example in the form of a granulate, which ignites itself at a temperature between 150 ° C and 200 ° C and releases sufficient heat to ignite the igniter and / or gas charge.

• * · · · · · · · · · · · · ·

- 2 In the event of a vehicle collision, pyrotechnic airbag gas generators are usually ignited by a current pulse from the sensor. The ignition is supported by an igniter which, together with the hot gas and the solid particles produced in this situation, ignites the gas mixture present almost synchronously, which is mostly in the form of tablets. The gas charge, when burned, creates gas to fill the protective cushion. The auto-ignition temperature of the gas feedstocks now in use is about 400 ° C for azide-containing gas feedstocks and up to about 300 ° C for azide-free gas feedstocks.

In the prior art, stabilized nitrocellulose powder having a self-igniting temperature (decomposition point) in the range of 150 ° C to 200 ° C has hitherto been used as a premature igniting powder for thermal fuses. However, the nitrocellulose powder does not meet the stability requirements recently imposed by the automotive industry. The thermal fuse should withstand storage for more than 400 hours at 107 ° C (224 ° F, US-Patent 5,460,671, column 3) with a weight loss of less than 3% while maintaining full functionality. However, nitrocellulose tends to decompose slowly even at lower temperatures and thus does not provide functionality as a premature igniting powder for a longer period of time, which is required for cars.

DE 197 30 873 discloses thermal fuses which are said to be capable of thermally controlled ignition of gas generating compositions commonly used in gas generators, well below a critical temperature while allegedly not suffering from deficiencies such as nitrocellulose. Substances or mixtures of substances selected from the group of compounds containing oxalates, peroxodisulphates (persulphates), permanganates, nitrides, borates, bismutites, formates, nitrates, sulphamates are used for these thermal fuses.

- 3 bromates or peroxides. According to DE 197 30 873, oxidizable components can also be used, for example explosives with a low detonation or decomposition point, preferably calciumumbistetrazolamine, 3-nitro-1,2,4-triazol-5-one (ΝΤΟ), 5 aminotetrazolonitrate, nitroguanidine ( NIGU), guanidine nitrate or bis-tetrazolamine. Substances with a lower detonation or decomposition point than the gas generating mixture used, but which decompose themselves endothermally, require at least one fuel and possibly a reducing agent if they are to be used in a thermal fuse. Examples of fuels are the oxidizable components mentioned above. For example, a metal powder, preferably a titanium powder, may be used as the reducing agent. Oxidizing agents, for example potassium nitrate or potassium perchlorate or mixtures of these oxidizing agents, may be added to influence the detonation points.

US Patent 5,460,671 discloses an ignition powder consisting of a mixture of an explosive and an oxidizing agent. The oxidizing agents are selected from the group consisting of alkali metal or alkali earth metal chlorates or mixtures thereof, especially potassium or sodium chlorate. Examples of fuels are hydrocarbons such as D-glucose, D-galactose, D-ribose and the like.

WO 99/41213 discloses a premature igniting powder consisting of a mixture of at least one fuel, at least one oxidizing agent, at least one stabilizing agent and optionally processing aids, auxiliary fuels and fillers. The fuel is selected from the group consisting of thiourea and its derivatives, such as Ν, N'-diphenylthiourea. Sodium, potassium and strontium chlorates, perchlorates and nitrates can be used as oxidizing agents. Examples of stabilizing agents are, among others, cellulose derivatives, polystyrol and polystyrol copolymers, polyamides and polyacrylates. These powders are suitable for •

The above-mentioned stability requirements in the automotive industry, while maintaining full functionality, can withstand bearings for 400 hours at 107 ° C with a weight loss of less than 3% by weight.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a premature igniting powder which has an increased stability which is higher than the aforementioned stability and which meets the increasingly stringent stability requirements in the automotive industry. In particular, it is intended that the weight loss when stored at a temperature exceeding 107 ° C for at least 400 hours is less than 3% by weight. After the gas generator has overheated to a temperature above 240 ° C, this premature igniting powder, to which a small amount of 0.1 to 0.5 g is to be used in the premature ignition unit, is capable of igniting the airbag gas charge.

SUMMARY OF THE INVENTION

A premature igniting powder for thermal safety devices comprising:

(A) at least one fuel selected from the group consisting of 2-thiohydantoin (1) and 2-thiobarbituric acid (2),

(B) at least one oxidizing agent selected from the group consisting of sodium, potassium and strontium chlorates, perchlorates and nitrates, i.e. NaNO ₃ , KNO ₃ , Sr (NO ₃ ) ₂ , NaClO ₃ , KClO ₃ , Sr (CO ₃ ) ₂ , NaC10 ₄ , KC1O ₄ , Sr (C10 ₄ ) ₂

- (C) at least one stabilizing agent selected from the group comprising cellulose derivatives such as cellulose ethers and esters, polystyrene and polystyrene copolymers, polyamides, polyacrylates, polycarbonates, polypropylenes, polybutylenes, polyoxymethylenes, polyacetates and polyvinyl compounds.

The oxidizing agent (B) is preferably selected from the group consisting of KClO ₃ and KNO ₃ and mixtures thereof.

The stabilizing agent (C) is preferably selected from the group consisting of cellulose acetobutyrate and dicyanodiamide and mixtures thereof.

Preferably, the fuel (A) is 2-thiohydantoin, the oxidizing agent (B) is KNO ₃ and / or KCl _3, and the stabilizing agent (C) is dicyanodiamide and / or cellulose acetobutyrate.

Another preferred option is that the fuel (A) is 2-thiobarbituric acid, the oxidizing agent (B) is KNO ₃ and / or KClO _3, and the stabilizing agent (C) is dicyanodiamide and / or cellulose acetobutyrate.

In addition, it is preferred that the premix igniting powder further comprises processing ingredients (D) selected from the group consisting of calcium and magnesium stearates, graphite, high boiling paraffins and citric and acyl citric acid esters in an amount of 0.5 to 5, preferably 0, 5 to 3 parts by weight.

In addition, the premature igniting powder may contain auxiliary fuels (E) selected from the group consisting of elemental aluminum, zirconium, titanium, magnesium, zinc and iron in an amount of 0.5 to 20, preferably 0.5 to 10 and especially 0.5 to 5 parts by weight.

«*

Further, the premature igniting powder may also contain fillers (F) selected from the group consisting of Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Si ₃ N ₄ and boron nitride in an amount of 0.5 to 12, preferably 0.5 to 10 and in particular 0.5 to 5 parts by weight.

The stabilizing agent (C) is preferably cellulose acetobutyrate, which contains as processing additive (D) triethyl citrate, particularly in a ratio of cellulose acetobutyrate: triethyl citrate of about 3: 1.

The fuel (A) is present in the premature igniting powder in an amount of 20 to 40, preferably 25 to 35, and especially 27 to 32 parts by weight.

The oxidizing agent (B) is present in the premature igniting powder in an amount of 40 to 80, preferably 50 to 75 and especially 60 to 75 parts by weight.

The stabilizing agent (C) is present in the premix igniting powder in an amount of 0.5 to 20, preferably 0.5 to 10, and in particular 0.5 to 5 parts by weight.

The invention also relates to the use of the described premature igniting powder for the thermal fuses of gas generators for airbags.

The fuel (A) is present in the premature igniting powder according to the invention for thermal fuses in an amount of 20 to 40 parts by weight, preferably 25 to 35 parts and in particular 27 to 32 parts by weight. The oxidizing agent (Β), preferably potassium chlorate and potassium nitrate, is present in an amount of 40 to 80, preferably 50 to 75 and especially 60 to 75 parts by weight. Of stabilizing agents (C) • ·

- Ί · · *

Cellulose acetobutyrate is particularly suitable. The polyamides as stabilizing agents (C) include, in addition to the conventional polyamides according to the invention, also amide derivatives such as dicyandiamide (cyanoguanidine). The stabilizing agents (C) are present in the premix igniting powder in an amount of 0.5 to 20, preferably 0.5 to 10, and in particular 0.5 to 5 parts by weight. The processing additives are optionally present in an amount of from 0.5 to 5, preferably from 0.5 to 3, parts by weight in the premature igniting powder. The stabilizing agent (C) may be cellulose acetobutyrate which contains processing additive (D) with triethyl citrate, particularly in a ratio of cellulose acetobutyrate: triethyl citrate of about 3: 1. In addition, the premature ignition powder may contain auxiliary fuels (E) in an amount of 0.5 to 20, preferably 0.5 to 10, and in particular 0.5 to 5 parts by weight. Furthermore, the premature igniting powder may also contain fillers (F) in an amount of 0.5 to 12, preferably 0.5 to 10, and in particular 0.5 to 5 parts by weight.

The use of premature igniting powders for the thermal fuses according to the invention is not limited to the airbag area, since they can also be used for triggering mechanical movements and also as pressure and locking elements.

The toxicity of all the raw materials used in the thermal safety devices according to the invention corresponds to Swiss classes 3, 4 and 5 of the poisons. When using these combinations of raw materials and their small quantities, there is no risk of endangering the occupants of the motor vehicle by the reaction of said mixtures. Mixtures that have not been used can be easily processed or recycled by conventional means. The thermal safety device according to the invention is very well compatible with other gas generating mixtures or pyrotechnic charges, for example boron nitrate or

Potassium nitrate and may be applied as a granulate or tablet additive or may be housed in a housing preferably of aluminum or steel. The temperature and course of the decomposition of the premature igniting powder are influenced by the purity and particle size of said raw materials, as well as by the various mixtures of oxidizing agents and explosives used.

The long-term thermal stability and the ignition temperature are mainly influenced by the type of stabilizing agent and its proportion in the mixture.

In the case of pyrotechnic mixtures it is known from DE 195 05 568 to combine, for example, thiourea with potassium chlorate. However, these mixtures do not meet the automotive storage stability requirements of 400 hours at 107 ° C (see Comparative Example 1 in Table I.). (WO 99/41213). In this regard, it is known to combine thiourea with potassium chlorate as an oxidizing agent with dicyandiamide and cellulose acetobutyrate as a stabilizing agent. These mixtures currently meet the automotive industry's 400 hour shelf life at 107 ° C - see Comparative Examples 2, 3, 4 in Table I.

However, only the use of special cyclic thiourea derivatives according to the invention which contain at least one carbonyl group in the core as fuels bound in a temperature-resistant stabilizing agent can, however, meet the increased stability requirements in the future.

• · • ♦

A system which reacts strongly exothermically between 150 and 230 ° C and meets even more stringent stability requirements can be formed from 2-thiohydantoin (1) or 2-thiobarbituric acid, in combination with oxidizing agents and suitable stabilizing agents.

Addition of auxiliary fuels (Ε) such as metal powders of aluminum, zirconium, titanium, magnesium, zinc, iron and the like may favor the formation of hot particles. Another possibility of forming hot particles, which, however, at the expense of the total energy of the thermal fuse mixtures, consists in the addition of fillers (F) such as Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Si ₃ N ₄ , nitride boron and the like. The use of processing agents (D), such as calcium and magnesium stearates, graphite, high boiling paraffins and citric and acylcitronic acid esters, generally increases the ignition temperature.

Examples

The following examples illustrate the nature of the invention without limiting the scope of the invention.

Comparative Examples 1 to 4 and Examples 5, 6:

The ground solids of the mixture shown in Table I were premixed in the proportions in a vertical mixer and treated for one hour with the addition of water and / or solvent such as C1-C4 alcohols such as methanol, ethanol, iso- / n-propanol %, n-butanol and acetone - see Comparative Example 3, in an amount of 10 - 20 wt. and optionally adding a stabilizing agent in a heterogeneous mixture. Depending on the type and amount of the stabilizing agent, granules or tablets ready for use can only be sieved. Can be · · · · · · · · · · · · ·

- 10 • · ♦ • · · ···· <

however, a highly viscous mixture can also be prepared which can be extruded and then cut. The preparation is completed by drying at 90 ° C for one to two hours.

Before and after storage for 400 hours at 107 ° C (comparative examples) or for 400 hours at 110 ° C (examples), the heat performance of the mixture was evaluated by differential measurement calorimetry (DSC method).

Table I

example 1 (comparison) wt. 2 (comparison) wt. parts parts KC1O ₃ 70 44 KNO ₃ 0 26 thio- urea 30 30 2-thiohy- dantoin 0 0 acid 2-thio- barbiturová 0 0 dikyandi- amid 0 0 hydroxy- 0 3

3 4 5 6 (comparison) wt. (comparison) wt. wt. wt parts parts parts parts 55 70 42 44 15 Dec 0 25 26 28 28 0 0 0 0 27 Mar: 0 0 0 0 28

2 2 2 2 3 0 0 0

ethylcellulose • · · ·

(Natrosole 250 HR from Aqualon Co.) aceto- butyrate cellulose * 0 0 0 1.7 3 3 loss Mon 216 po 400 po 400 Mon 4 00 po 400 po 400 weight throw. throw. throw. throw. throw. throw. after hour (100 ° C) (110 ° C) for 107 ° C in% (or after > 3% 1.3% 1.9% 2.4% 0.15% 0.25% 110 ° C) Mon 620 Mon 620 throw. throw (100 ° C) (100 ° C) 0.24% 0,30% top before before before before before before reaction testem testem testem testem testem testem at DSC analysis; speed 170 [deg.] C 197 ° C Mp 172 ° C 170 [deg.] C 184 ° C 227 ° C heating after AFTER AFTER After AFTER AFTER 10 ° C / min test test test test test test - 190 ° C 165 [deg.] C Mp 164 ° C 178 ° C 225 [deg.] C

* contains triethyl citrate as processing aid (cellulose acetobutyrate: triethyl citrate 3: 1 ratio)

Comparison of Comparative Example 1 with Comparative Examples 2 to 4 and Examples 5 and 6 shows that the desired stability is only achieved by the addition of a stabilizing agent. The composition of Comparative Example 1 showed a weight loss of greater than 3% as early as 216 hours. Composition of Comparative Examples 2 · · · · · · · srovn

Up to 4, after 400 hours at 107 ° C, the weight loss between

1.3 and 2.4%, thus meeting the current stability requirements. When stored hot at 110 ° C, i.e. at a temperature of 3 ° C higher than existing requirements, the premature igniting powders of the present invention exhibit substantially lower weight loss between 0.15 and 0.30%, which is still clearly apparent even after 620 hours less than the weight loss in Comparative Examples 2 to 4.

In addition, the ignition or decomposition temperatures of the pre-igniting powders according to the invention are both in the desired range of 150 to 230 ° C both before and after thermal stress. The pre-igniting powders of the invention of Examples 5 and 6 showed a change in decomposition temperature between 0 and 6 ° C after 400 hours at 110 ° C. The decomposition point was determined by differential calorimetry (DSC method). The decomposition temperature bandwidth was 10 ° C / min at the heating rate used. ± 5 ° C.

Claims (13)

PATENT CLAIMS 1. Premature igniting thermal fuse powder, comprising: (A) at least one fuel selected from the group consisting of 2-thiohydantoin and 2-thiobarbituric acid, in an amount of 20 to 40 parts by weight, (B) at least one oxidizing agent selected from the group consisting of NaNO ₃ , KNO ₃ , Sr (NO ₃ ) ₂ , NaC10 ₃ KC1O _3, Sr (C 10 -C _{3) 2,} NaC10 ₄ KC1O _4, Sr (C10 _{4) 2} in an amount of 40 to 80 parts by weight, (C) at least one stabilizing agent selected from the group comprising derivatives Cellulose such as ethers and cellulose esters, polystyrene and polystyrene copolymers, polyamides, polyacrylates, polycarbonates, polypropylenes, polybutylenes, polyoxymethylenes, polyacetates and polyvinyl compounds in an amount of 0.5 to 20 parts by weight. Premature igniting powder according to claim 1, characterized in that the oxidizing agent (B) is selected from the group consisting of KClO ₃ and KNO ₃ and mixtures thereof. The premature ignition powder according to claim 1 or 2, characterized in that the stabilizing agent (C) is selected from the group comprising cellulose acetobutyrate and dicyanodiamide and mixtures thereof. A premature igniting powder according to claim 1, characterized in that the fuel (A) is 99 9 9 9 9 9 9 9 9 · 9999 98 • · 2-thiohydantoin, the oxidizing agent (B) is KNO ₃ and / or KClO ₃ and the stabilizing agent (C) is dicyanodiamide and / or cellulose acetobutyrate. A premature igniting powder according to claim 1, characterized in that the fuel (A) is 2-thiobarbituric acid, the oxidizing agent (B) is KNO ₃ and / or KClO ₃ and the stabilizing agent (C) is dicyanodiamide and / or cellulose acetobutyrate. . Premature igniting powder according to any one of claims 1 to 6 5, characterized in that it further comprises processing additives (D) selected from the group comprising calcium and magnesium stearates, graphite, high boiling paraffins and citric and acylcitronic acid esters in an amount of 0.5 to 5, preferably 0.5 to 5, 3 parts by weight. Premature igniting powder according to any one of claims 1 to 7 6, characterized in that it further comprises auxiliary fuels (E) selected from the group consisting of elemental aluminum, zirconium, titanium, magnesium, zinc and iron in an amount of 0.5 to 20, preferably 0.5 to 10 and in particular 0.5 up to 5 parts by weight. A premature igniting powder according to any one of claims 1 to 8 7, characterized in that it further contains fillers (F) selected from the group comprising Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Si ₃ N ₄ and boron nitride in an amount of 0.5 to 12, preferably 0.5 to 10, and in particular 0.5 to 5 parts by weight. A premature igniting powder according to any one of claims 1 to 9 8, characterized in that 9 9 9 9 9 e • • • The agent (C) is cellulose acetobutyrate, which contains as processing additive (D) triethyl citrate, in particular in the ratio of cellulose acetobutyrate: triethyl citrate. about 3: 1. A premature igniting powder according to any one of claims 1 to 10 9, characterized in that the fuel (A) is present in an amount of 25 to 35 parts by weight. A premature igniting powder according to any one of claims 1 to 11 10, characterized in that the oxidizing agent (B) is present in an amount of 50 to 75 parts by weight, in particular 60 to 75 parts by weight. A premature igniting powder according to any one of claims 1 to 12 11, characterized in that the stabilizing agent (C) is present in an amount of 0.5 to 10, in particular 0.5 to 5 parts by weight. Use of a premature igniting powder according to any one of claims 1 to 12 for thermal fuses of gas generators for airbags.