Fuel element for a gas generator, method for producing same, and use of the fuel element

Abstract

The invention relates to a fuel element (10) in the form of a tablet for a gas generator for use in a safety device. The tablet has a core (12) made of a pyrotechnic material and a coating (14) which is applied onto the core (12) and is made of a pyrotechnic pre-ignition agent, wherein the pyrotechnic material and the pyrotechnic pre-ignition agent differ from each other, and the pyrotechnic pre-ignition agent has a deflagration point of 500 K or lower. The invention additionally relates to a method for producing such a fuel element (10) and to the use of such a fuel element (10).

Description

[0001] Fuel element for a gas generator, method for its production and use of the fuel element

[0002] The invention relates to a fuel element for a gas generator for use in a safety device, a method for producing such a fuel element and the use of such a fuel element in a safety device.

[0003] Fuel elements for gas generators are known from the prior art. To protect vehicle occupants in the event of an accident, various safety devices are provided in vehicles. One such safety device could be, for example, a gas bag module equipped with a gas generator. In the event of an imminent collision between the vehicle and another object, the gas generator releases a pressurized gas that deploys a gas bag from the gas bag module, thereby restraining the vehicle occupants.

[0004] Gas generators are used to generate a pressurized gas and are known in various designs. Basically, gas generators use a propellant element made of a pyrotechnic composition, which is located inside the gas generator. When activated by an electrical igniter, it undergoes an exothermic reaction, releasing the pressurized gas in the gas bag.

[0005] Propellant elements are usually in the form of tablets, which can be manufactured in a variety of ways. These tablets generally have a multi-component structure. For example, propellant elements in the form of tablets are known, which are made up of two or more pyrotechnic components. The integration of various pyrotechnic components or compositions in one tablet serves to specifically influence the combustion characteristics of the propellant element. By optimizing the combustion characteristics, among other things, an improved inflation behavior of the gas bag can be achieved. The term combustion characteristics is understood below to refer to a series of properties that a propellant tablet or propellant element for a gas generator exhibits during operation, i.e. during combustion.Burning characteristics include, for example, the burning rate, the burning velocity, the burning velocity at the surface, the gas yield, the autoignition temperature, the ignitability, the superignitability, the pressure exponents and the general burning behavior (degressive or progressive).

[0006] The state of the art reveals various possibilities to influence the combustion characteristics of a fuel element.

[0007] A coated pellet for a gas generator is disclosed in DE 10 2012 024 799 A1. A propellant element is proposed that is designed as a pellet having a core made of a pyrotechnic material, wherein the core is at least partially surrounded by a shell made of a material that delays the combustion of the core.

[0008] JP 2001-278690 A discloses propellant elements with various tablet shapes for use in gas generators. The tablets consist of a first and a second pyrotechnic material laminated together. The first pyrotechnic material differs from the second pyrotechnic material in its burning rate. This document primarily discloses multilayer tablets that have a multilayer structure consisting of the first and second pyrotechnic materials.

[0009] German patent application 10 2022 108 291.1 describes propellant elements in the form of a jacketed pellet, comprising a core made of a pyrotechnic material and a jacket layer surrounding the core, made of a second pyrotechnic material different from the first pyrotechnic material. The core extends over a protruding edge portion along a circumferential direction through the jacket layer, so that the combustion of the core can occur parallel to the combustion of the jacket layer. In this way, undesirable degressive combustion of the jacketed pellet can be avoided or at least limited, and the ignitability of the jacketed pellet can be adjusted. To further influence the combustion characteristics, propellant elements are desirable that ignite reliably even at the lowest possible temperatures and enable rapid pressure buildup.The problem here is that pyrotechnic compositions with corresponding ignition behavior have an undesirably high combustion temperature, require ignition with hot particles and / or produce a comparatively large number of particulate, i.e. solid, combustion products, which have a detrimental effect on the smoke development of the gas generator.

[0010] In tablet bulk materials, for example, in a gas generator, different tablet sizes and / or tablet densities (due to different chemical formulations) can lead to segregation and / or unfavorable installation conditions, which must be compensated for by appropriate compromises in the design of the respective propellant elements. This increases the effort involved in manufacturing the propellant element and in designing the gas generator in which the propellant element is to be used, and limits the freedom of formulation.

[0011] The object of the invention is to provide a fuel element that ignites even at low temperatures and has a defined combustion characteristic.

[0012] The object is achieved according to the invention by a fuel element according to claim 1, a method for producing a fuel element according to claim 9 and the use of a fuel element according to claim 10.

[0013] Advantageous embodiments of the fuel element according to the invention are specified in the subclaims, the features of which can be optionally combined with one another.

[0014] According to the invention, this object is achieved by a propellant element for a gas generator for use in a safety device in the form of a tablet. The tablet has a core made of pyrotechnic material and a coating of a pyrotechnic pre-ignition agent applied to the core, wherein the pyrotechnic material and the pyrotechnic pre-ignition agent differ from one another. The pyrotechnic pre-ignition agent has a deflagration temperature of 500 K or less. The invention is based on the fundamental idea of ​​improving the ignition behavior of the entire propellant element at low temperatures by using a pyrotechnic pre-ignition agent that has a deflagration temperature of 500 K or less, which is comparatively low for pyrotechnic compositions, and thus being able to specifically adjust the combustion characteristics.In particular, the low deflagration temperature of the pyrotechnic pre-ignition agent enables the propellant element to ignite particularly reliably and early upon mere temperature increase, without having to rely on the use of hot particles to activate the propellant element or at least being able to reduce their quantity.

[0015] In this context, the term "pure temperature increase" means that the temperature increase is achieved through the influence of radiation and / or a gas mixture surrounding the propellant element is heated, and the heat transferred from the gas mixture to the propellant element by means of diffusion and / or convection processes is sufficient to ignite the propellant element, specifically the early ignition layer. Thus, in particular, hot particles are not used to ignite the early ignition layer. However, this does not preclude the additional use of hot particles to further influence the ignition behavior of the propellant element, even if this is not preferred. However, the adjustment options for the ignition behavior and combustion characteristics of the propellant element are expanded compared to propellant elements known in the prior art, thus increasing the freedom of formulation.

[0016] It has also been found that the deflagration temperature is a particularly suitable parameter for testing the suitability of a pyrotechnic composition for use as an early ignition layer. This effect is attributed to the fact that, with the same type of components used in the pyrotechnic composition, the proportions of these components can be varied within a wide range without significantly affecting the deflagration temperature. This makes it possible to vary the respective chemical composition of the early ignition layer within a wide range in order to adjust or adapt other parameters of the early ignition layer that influence the combustion characteristics. In this sense, the deflagration temperature essentially represents a type of "early ignition eutectic."

[0017] According to the invention, the deflagration temperature of the pyrotechnic material used in the core is above the deflagration temperature of the pre-ignition agent.

[0018] The improved pre-ignition behavior of the fuel element thus makes it possible to vary the other parameters of the fuel element that influence the combustion characteristics to a greater extent and still achieve improved or similar combustion behavior.

[0019] In particular, the geometry of the pellet can be varied to a greater extent while maintaining comparable combustion characteristics, or it can be maintained while maintaining improved combustion characteristics compared to existing propellant elements. For example, so-called ignition sleeves in the gas generator, in which pressure and temperature develop separately from the rest of the gas chamber, can be omitted.

[0020] Because the fuel element is in tablet form, it can be produced particularly cost-effectively, for example by a compression process.

[0021] The geometric shape of the tablet is not further restricted. In particular, the tablet has a cylindrical shape.

[0022] The pyrotechnic pre-ignition agent may have a deflagration temperature of 450 K or less, preferably 435 K or less. This allows the propellant element to be activated at even lower temperatures.

[0023] The minimum required deflagration temperature is not further restricted, as long as the propellant element has sufficient storage stability over the intended service life of the safety device in which the propellant element is used. For this purpose, the pre-ignition agent can have a deflagration temperature of at least 381.15 K, in particular of at least 403.15 K. Accordingly, the pyrotechnic pre-ignition agent can have a deflagration temperature in the range of 381.15 to 450 K, preferably from 403.15 to 435 K.

[0024] In one variant, the pyrotechnic pre-ignition agent has a combustion temperature of 2000 K or more, and preferably a combustion temperature in the range of 2100 K to 2800 K. Lower combustion temperatures may result in pre-ignition agents that have too low a combustion rate and / or explosion heat, whereby the ignition of the pyrotechnic material may be delayed by the triggered pre-ignition layer.

[0025] The relative arrangement of pyrotechnic pre-ignition agent and pyrotechnic composition within the tablet is in principle not further restricted as long as the desired combustion characteristics can be achieved.

[0026] For example, the coating of pyrotechnic pre-ignition agent is applied to a top side, a bottom side and / or a shell side of the core.

[0027] At the contact surface between the pyrotechnic pre-ignition agent and the core, the propellant element can have a contact-enhancing surface design. For example, the core has recesses into which the pyrotechnic pre-ignition agent is incorporated and / or the core has a roughened contact surface that is in contact with the pre-ignition agent. This further improves the transfer of the pyrotechnic pre-ignition agent to the pyrotechnic composition.

[0028] In principle, the thickness of the coating of the pyrotechnic pre-ignition agent can be chosen arbitrarily, depending on the desired combustion characteristics of the propellant element.

[0029] In one variant, the thickness of the coating of the pyrotechnic pre-ignition agent is 10% or less of the thickness of the tablet. This makes it particularly easy to ensure that the tablet as a whole is ignited by the pyrotechnic pre-ignition agent even at a low temperature, while the subsequent behavior of the tablet is largely determined by the pyrotechnic composition of the core.

[0030] If the tablet has several spatially separated areas with the coating of the pyrotechnic pre-ignition agent, the thickness of the part of the coating with the greatest thickness is counted.

[0031] For example, the thickness of the coating of the pyrotechnic pre-ignition agent is in the range of 0.5 to 3.0 mm.

[0032] The pyrotechnic pre-ignition agent comprises a fuel as component (A) and an oxidising agent as component (B) and optionally further additives as component (C).

[0033] The fuel (A) of the pyrotechnic pre-ignition agent is in particular selected from the group consisting of 1-nitroguanidine, guanidinium nitrate, nitrotriazolone, nitrocellulose, metals, in particular boron, aluminum, titanium, zirconium, tungsten, and combinations thereof.

[0034] The oxidizing agent (B) of the pyrotechnic pre-ignition agent is in particular selected from the group of chlorates, perchlorates, metal oxides, and combinations thereof. The oxidizing agent of the pyrotechnic pre-ignition agent preferably comprises or consists of potassium perchlorate.

[0035] In one variant, the pyrotechnic pre-ignition agent comprises the following components:

[0036] (A) 60 to 95% by weight, preferably 60 to 92% by weight of at least one fuel selected from the group consisting of 1-nitroguanidine, guanidinium nitrate, nitrotriazolone, nitrocellulose, metals, in particular boron, aluminum, titanium, zirconium and / or tungsten and combinations thereof,

[0037] (B) 2 to 40% by weight, preferably 6 to 40% by weight, of at least one oxidizing agent selected from the group of chlorates, perchlorates, metal oxides and combinations thereof, preferably potassium perchlorate, and (C) 0 to 3% by weight, preferably 0 to 2% by weight, of further additives selected from the group of metal oxides, silica, stearates, lubricating oils and combinations thereof, preferably from the group consisting of iron oxide, magnesium oxide, amorphous silica, hydrophobic silica, calcium stearate, C15-C30 lubricating oils and combinations thereof, in each case based on the total weight of the pyrotechnic pre-ignition agent, wherein the proportions of components (A) to (C) add up to 100% by weight.

[0038] The core can have a first core region made of a first pyrotechnic material and a second core region made of a second pyrotechnic material, wherein the first pyrotechnic material and the second pyrotechnic material differ from each other. In this way, the combustion characteristics of the propellant element can be influenced by the choice of the first and second pyrotechnic materials in addition to the selected coating of the pyrotechnic pre-ignition agent.

[0039] The two pyrotechnic materials, i.e., the first pyrotechnic material and the second pyrotechnic material, differ in particular with respect to at least one of the following properties: chemical composition, combustion rate, combustion temperature, gas yield, average grain size, particle distribution, particle morphology, hygroscopicity, autoignition temperature, ignitability, deflagration temperature, and overignitability. The two pyrotechnic materials may also differ in two or more of the aforementioned properties.

[0040] According to the invention, the deflagration temperature of both the first pyrotechnic material and the second pyrotechnic material is above the deflagration temperature of the pyrotechnic pre-ignition agent.

[0041] Advantageously, the first pyrotechnic material has a higher burning rate than the second pyrotechnic material. For example, the first pyrotechnic material can have a burning rate in a range of 20 to 60 mm / s at 20 MPa, preferably 25 to 55 mm / s at 20 MPa, and the second pyrotechnic material can have a burning rate in a range of 5 to 30 mm / s at 20 MPa, preferably 15 to 25 mm / s at 20 MPa. In this way, a degressive burning of the first core region can be avoided, thereby achieving an even more uniform burning of the tablet.

[0042] According to a further aspect, the first pyrotechnic material has a grain size that differs from the grain size of the second pyrotechnic material, wherein in particular the first pyrotechnic material has an average grain size (D50) in a range from 1 to 30 pm and the second pyrotechnic material has an average grain size (D50) in a range from 3 to 100 pm.

[0043] The first pyrotechnic material and the second pyrotechnic material each comprise at least a fuel and an oxidizer.

[0044] In principle, the invention is not limited with regard to the fuel and oxidizer of the first and second pyrotechnic materials. Any fuel and oxidizer known in the art that are suitable for forming a propellant element for a gas generator can be used.

[0045] Advantageously, the fuel of the first and / or second pyrotechnic material is selected from the group consisting of guanidinium salts, aluminum, polyvinyl acetate, 1-nitroguanidine, nitrotriazolone, tetrazoles, bitetrazoles and nitrocellulose and combinations thereof.

[0046] Such fuels can generate a large gas volume upon activation and enable pyrotechnic compositions in which the burning rate can be adjusted over a wide range.

[0047] The oxidizing agent of the first and / or second pyrotechnic material is selected in particular from the group consisting of perchlorates, copper oxide, basic copper nitrate, basic copper zinc nitrate, sodium nitrate, potassium nitrate, and combinations thereof. The oxidizing agent serves in particular to increase the burning rate of the respective pyrotechnic material. Depending on the selection of the oxidizing agent, the burning rate of the propellant element can therefore be influenced. Furthermore, the first and second pyrotechnic materials can each contain at least one further additive, which is selected in particular from the group consisting of stabilizers, burn rate modifiers, binders, compression additives, and combinations thereof. The properties of the propellant element can be modified by adding one of the above-mentioned additives.

[0048] In particular, iron(II) oxide, magnesium oxide, titanium oxide, aluminum oxide and combinations thereof can be used as burn rate modifiers.

[0049] As a pressing additive, in particular amorphous silica, calcium stearate and hydrocarbon-based lubricating oil, preferably lubricating oil based on aliphatic hydrocarbon compounds having 15 to 30 carbon atoms, as well as combinations thereof, can be used.

[0050] For example, Akardit II (3-methyl-1,1-diphenylurea) can be used as a stabilizer.

[0051] Binders that can be used include, for example, alkylcelluloses, hydroxyalkylcelluloses, carboxymethylcelluloses, cellulose carboxylates, xanthan, hydroxyl-terminated polybutadiene (HTPB) and carboxyl-terminated polybutadiene (CTPB) and combinations thereof.

[0052] Advantageously, the chemical compositions of the first and second pyrotechnic materials differ from each other.

[0053] According to one aspect, the first pyrotechnic material and the second pyrotechnic material differ in the selection of at least one of the components such as fuel, oxidizer and an additive.

[0054] The first and second pyrotechnic materials can also be based on the same components, but differ in their component proportions. This can also change the combustion characteristics. For example, the first pyrotechnic material can have a higher proportion of oxidizer, which can lead to an increase in the combustion rate compared to the second pyrotechnic material. According to a further aspect of the invention, the first pyrotechnic material comprises the following components:

[0055] (A) 10 to 95 wt.%, preferably 33 to 66 wt.%, of at least one

[0056] Fuel selected from the group consisting of

[0057] Guanidinium nitrate, aluminum, polyvinyl acetate, nitrotriazolone,

[0058] 1-Nitroguanidine, tetrazoles, bitetrazoles, nitrocellulose and combinations thereof;

[0059] (B) 5 to 90% by weight, preferably 25 to 85% by weight, of at least one oxidizing agent selected from the group consisting of potassium perchlorate, ammonium perchlorate, perchlorates, copper oxide, basic copper nitrate, basic copper zinc nitrate, sodium nitrate, potassium nitrate, other nitrate salts, and combinations thereof; and

[0060] (C) 0 to 15% by weight, preferably 0 to 5% by weight, of further additives selected from the group consisting of iron oxide, magnesium oxide, amorphous silica, hydrophobic silica, calcium stearate, other stearate salts, fatty acid salts, lubricating oil and combinations thereof, in each case based on the total weight of the first core region, wherein the proportions of components (A) to (C) add up to 100% by weight.

[0061] According to a further aspect, the second pyrotechnic material comprises the following components:

[0062] (A) 20 to 75 wt.%, preferably 45 to 65 wt.%, of at least one fuel selected from the group consisting of guanidinium nitrate and bitetrazole, and combinations thereof;

[0063] (B) 25 to 60% by weight, preferably 39 to 56% by weight, of at least one oxidizing agent selected from the group consisting of ammonium perchlorate, potassium perchlorate, perchlorates, sodium nitrate, copper oxide, basic copper nitrate, basic copper zinc nitrate, other nitrate salts and combinations thereof; and

[0064] (C) 0 to 15% by weight, preferably 0 to 5% by weight, of further additives selected from the group consisting of iron oxide, titanium oxide, aluminum oxide, calcium stearate, other stearate salts, fatty acid salts and combinations thereof, in each case based on the total weight of the second core region, wherein the proportions of components (A) to (C) add up to 100% by weight.

[0065] In order to further improve the ignitability of the propellant element, the tablet can be a jacketed tablet in which the first core region is at least partially provided with a casing which is formed by the second core region and / or the coating of the pyrotechnic pre-ignition agent, wherein the first core region has an edge section which projects in the radial direction and extends through the casing to an outer contour of the jacketed tablet, wherein the edge section is formed along a circumferential direction of the jacketed tablet and has a smaller extent in the axial direction of the jacketed tablet than the first core region.

[0066] In principle, the casing can be designed analogously to the shell region of the shell-shaped pellet described in German patent application 10 2022 108 291.1. However, according to the invention, the coating of the pyrotechnic pre-ignition agent is either a component of the casing or is provided in addition to a casing made of a second pyrotechnic material. In this way, the pre-ignition behavior of the propellant element according to the invention is further improved.

[0067] In this variant, an opening in the form of a gap is provided in the casing, which connects the first core region to the outer contour of the coated tablet via the edge section. In this way, only a part of the first core region can be exposed to the environment without making the entire first core region accessible. This is achieved in particular by the edge section having a smaller extent in the axial direction of the coated tablet than the first core region. The presence of an edge section therefore ensures that the combustion of the first core region takes place essentially parallel to the combustion of the casing, but is nevertheless delayed by the geometric design of the tablet, whereby undesirable degressive combustion of the tablet can be prevented.In addition to the basic use of the coating of the pyrotechnic pre-ignition agent, the ignitability of the coated tablet according to the invention can be specifically adjusted in this way. This can be achieved by selecting the axial extent of the gap, which changes the accessibility of the first core region in the form of the edge section. Choosing a larger gap allows more of the edge section and thus a larger part of the core to be made accessible for ignition, whereas a smaller axial extent of the gap has the opposite effect, reducing the ignitability of the first core region. This advantageous control of the properties is not limited to the above-mentioned example of ignitability, but also applies generally to other combustion characteristics such as the degressiveness of the combustion.The coated tablet proposed here can therefore be understood as a hybrid form between known coated tablets and multi-layer tablets.

[0068] If the autoignition temperature of the first pyrotechnic material is lower than that of the second pyrotechnic material, an improved early ignition function can be enabled by the exposed web.

[0069] Consequently, the geometric design of the proposed coated pellet can achieve improved control over the combustion characteristics.

[0070] The above-proposed compositions of the first and second pyrotechnic materials are particularly suitable for use in a coated tablet for a gas generator. The composition of the first pyrotechnic material exhibits a faster burning rate than the composition of the second pyrotechnic material. A tablet containing the above-mentioned compositions exhibits, in particular, a reduced degressivity of burning.

[0071] If the coated tablet has a cylindrical shape with a tablet top and a tablet bottom opposite the tablet top, a web section can be arranged between the tablet top and bottom. This web section runs as a band-shaped boundary ring around the tablet and limits the radial extent of the first core region. The shape of the web section is determined by a die wall during compression. The height of the web section can be freely selected and limits the axial extent of the edge section of the first core region. However, there can also be two webs that limit the axial extent of the edge section of the core on both sides.

[0072] The top and bottom of the tablet may be curved or faceted. A curved tablet has a biconvex shape. The top and bottom of the tablet, in particular, form spherical caps. The curvature has a radius of curvature, which represents the radius of the spherical cap.

[0073] As described above, the tablet according to the invention can have a coating. The invention is not restricted with regard to the coating. In principle, the coating can be of any shape. Furthermore, the coating forms, in particular, the outer contour of the coated tablet, with the exception of the edge portion that extends through it. Therefore, the coating can also encompass the web as well as the top and bottom of the tablet.

[0074] In addition to the coating shape, the coating thickness can also be freely selected. The burning characteristics of the tablet can be influenced by the selected layer thickness.

[0075] The sheathing completely surrounds the core, with the exception of the edge section. The positioning of the edge section relative to the core is arbitrary. For example, the edge section can be positioned centrally or slightly offset from the core. In general, multiple edge sections can also be provided. These can, in particular, run parallel to one another or intersect.

[0076] In addition, the axial extent of the edge section is also arbitrary, as long as the axial extent of the edge section is lower than that of the first core area.

[0077] For example, the axial extent of the edge portion may be at most 80% of the axial extent of the first core region, preferably 60%, more preferably 40%, most preferably 10%. The edge portion may preferably have an axial extent of 100 to 3000 μm, preferably 100 to 800 μm.

[0078] The burning characteristics of the tablet can be further influenced by the axial extension of the edge section.

[0079] Any shape can be chosen for the first core region with the edge section, as long as the above-mentioned conditions are met. Advantageously, the core with the edge section has a shape that can be produced by compression.

[0080] One aspect of the invention provides that the first core region with the edge portion has a T-shaped cross-section. This offers the advantage that such a shaped first core region with edge portion can be manufactured particularly easily.

[0081] According to another aspect of the invention, it is provided that the first core region with the edge portion has a wedge-shaped cross-section.

[0082] According to another aspect, the first core region with the edge portion is convexly shaped, more preferably the first core region with the edge portion is biconvexly shaped.

[0083] According to a further embodiment, the first core region with the edge section is shaped asymmetrically biconvex. An asymmetrical biconvex shape of the first core region with the edge section offers the advantage that, when manufactured by compression, a particularly compact compaction can be achieved. This can, in particular, prevent unwanted air inclusions in the compact.

[0084] According to a further aspect, the edge portion is designed to be continuous along a circumferential direction of the coated tablet. This ensures particularly uniform ignitability.

[0085] The tablet can be provided with an additional coating on at least one of its end faces and / or the shell sides. This additional coating can provide additional functionality for the tablet. If a tablet with a coating interrupted by the edge section is used, it is advantageous to apply the additional coating to one of the end faces, as this way the edge section is not covered by the additional coating. This ensures that accessibility to the first core area is not compromised.

[0086] However, it is also conceivable that the additional coating covers the entire tablet, i.e. is arranged on the shell sides as well as the end faces, or that only the shell sides are provided with the additional coating.

[0087] The additional coating may, in particular, comprise a moisture-protection coating. A tablet provided with such an additional coating advantageously exhibits greater storage stability at high humidity.

[0088] Hydrophobic polymers, especially silicones, polyurethanes and / or polyesters, can be used as moisture protection coatings.

[0089] The additional coating may further comprise an ignition layer, which also improves the ignitability of the propellant element, but differs from the pyrotechnic pre-ignition layer, in particular chemically. According to the invention, the ignition layer has a higher deflagration temperature than the coating made of the pyrotechnic pre-ignition agent.

[0090] The object is also achieved according to the invention by a method for producing a propellant element as described above, wherein the pyrotechnic material and / or the pyrotechnic pre-ignition agent are pressed in a press die to form the core of pyrotechnic material or the coating of the pyrotechnic pre-ignition agent.

[0091] The features and properties of the fuel element according to the invention apply accordingly to the process according to the invention and vice versa.

[0092] The process according to the invention enables the production of the tablet according to the invention using compression machines. The production of tablets using compression machines is known and has long been used in the pharmaceutical industry. Thus, the propellant element according to the invention and the process for producing the propellant element are particularly cost-effective.

[0093] In particular, the components of the propellant element are joined together to form the propellant element exclusively by compression. This avoids the costly coating or lamination of the pre-ignition layer onto the pyrotechnic material of the core, or vice versa.

[0094] Furthermore, the invention relates to the use of a fuel element as described above in a safety device in a vehicle, in particular in a gas generator.

[0095] The features and properties of the fuel element according to the invention apply accordingly to the use according to the invention and vice versa.

[0096] The invention is explained below with reference to selected embodiments and examples, which, however, are not intended to be limiting, as well as the drawings. In these, the following figures show:

[0097] - Fig. 1 Pressure / time curves of tests in a standard combustion chamber of selected components of fuel elements according to the invention,

[0098] - Fig. 2 further pressure / time curves of tests in a standard combustion chamber of selected fuel elements according to the invention and of comparative examples,

[0099] - Fig. 3 to Fig. 14 are schematic representations of fuel elements according to the invention,

[0100] - Fig. 15 schematically shows a sequence of a first embodiment of a method according to the invention for producing the fuel element according to the invention, and

[0101] - Fig. 16 schematically shows a sequence of a second embodiment of the method according to the invention for producing the fuel element according to the invention.

[0102] A propellant element 10 according to the invention for a gas generator for use in a safety device is in the form of a tablet having a core 12 made of pyrotechnic material and a coating 14 made of a pyrotechnic pre-ignition agent applied to the core 12 (cf. Fig. 3).

[0103] The pyrotechnic material and the pyrotechnic pre-ignition agent differ from each other, particularly with regard to their deflagration temperature. The pyrotechnic pre-ignition agent has a deflagration temperature of 500 K or less, so that, according to the invention, the pyrotechnic pre-ignition agent can be activated at a lower temperature than the pyrotechnic material.

[0104] The features and properties of the pre-ignition agent in comparison to suitable pyrotechnic materials are explained in more detail below using examples.

[0105] Examples

[0106] Tables 1 to 3 show exemplary compositions which are suitable as pyrotechnic material in the core 12 of a propellant element 10 according to the invention or as pyrotechnic pre-ignition agent in the coating 14 applied to the core 12.

[0107] The abbreviations used in the tables mean:

[0108] GuNi = Guanidinium nitrate

[0109] AI = aluminum

[0110] NiGu = 1-Nitroguanidine

[0111] PVA = polyvinyl acetate

[0112] NTO = Nitrotriazolone bCN = basic copper nitrate

[0113] Table 4 lists the ballistic properties of the respective compositions.

[0114] The pyrotechnic material is further differentiated into a first pyrotechnic material and a second pyrotechnic material, which differ in their respective ballistic properties and thus in their combustion characteristics. In other words, the core 12 of the propellant element 10 can have a first core region 15 made of the first pyrotechnic material and a second core region 16 made of the second pyrotechnic material.

[0115] In principle, both the first pyrotechnic material and the second pyrotechnic material can also be present as the only pyrotechnic material in the core 12.

[0116] Table 4 shows that the first pyrotechnic material (Examples A to D) and the second pyrotechnic material (Examples E to H) differ significantly in their ballistic properties. The first pyrotechnic material exhibits a higher combustion temperature, a higher to comparable combustion rate at a pressure of 5 MPa, a higher combustion rate at a pressure of 20 MPa, a higher to comparable deflagration temperature, and a higher explosion heat than the second pyrotechnic material. Accordingly, the combustion characteristics of a propellant element can be adjusted to a large extent by selecting the pyrotechnic material used or by combining the various pyrotechnic materials.

[0117] The pyrotechnic pre-ignition agents (Examples I and J) have a significantly lower deflagration temperature of less than 500 K, namely 433 K, compared to the other pyrotechnic compositions of Examples A to H. Other ballistic properties can be varied within a wide range without any significant change in the deflagration temperature.

[0118] Table 1 : First pyrotechnic compositions.

[0119] Table 2: Second pyrotechnic compositions.

[0120]

[0121] Table 3: Pyrotechnic pre-ignition agents.

[0122] Table 4: Ballistic properties of the compositions according to Tables 1 to 3.

[0123] Table 5: Test data on pressure build-up in the standard combustion chamber.

[0124] The differences in the behavior of a first pyrotechnic composition "fuel 1" and a second pyrotechnic composition "fuel 2", which are suitable for use as pyrotechnic material in the core 12 of the fuel element 10 according to the invention, compared to a pyrotechnic pre-ignition agent were further determined by tests in a standard combustion chamber.

[0125] The first pyrotechnic material according to Example A was used as propellant 1, the second pyrotechnic material according to Example G was used as propellant 2, and the pre-ignition agent according to Example I was used as pre-ignition agent.

[0126] A “standard combustion chamber” is a closed vessel with a defined volume of 100 cm 3at which the respective propellant is burned. The pressure / time curves resulting from combustion characterize the respective composition ballistically. Table 5 lists the resulting tsobar values, i.e., the time required to reach a pressure of 50 bar (5 MPa) in the standard combustion chamber. A low tsobar value is desirable to enable rapid pressure buildup in a gas generator.

[0127] In all tests, the standard combustion chamber was filled with cylindrical tablets having a diameter of 6.0 mm and a height of 1.45 mm, with tablets having a total mass of 5 g.

[0128] The tablets presented were ignited by a booster charge, which in turn was activated by an electrically ignited igniter.

[0129] The igniter contained an igniter mass with a composition of 53 to 58 wt% zirconium as fuel, 34 to 42 wt% potassium perchlorate as oxidizer and 4 to 5 wt% fluororubber (FKM) as binder.

[0130] Either a "particle-generating" booster charge or a "gas-generating" booster charge was used to investigate the ballistic behavior of the respective propellant element to be characterized as a function of the ignition type. The behavior with a gas-generating booster charge corresponds to a case in which the respective pyrotechnic composition essentially only needs to ignite via the temperature rise, since no, or at least significantly lower, quantities of hot particles are present that could assist ignition.

[0131] The particle-generating booster charge comprised 27 to 33 wt% boron as fuel and 67 to 73 wt% potassium nitrate as oxidizer.

[0132] The gas-generating booster charge comprised 96 wt% nitrocellulose as fuel, 1 to 3 wt% 3-methyl-1,1-diphenylurea as stabilizer, and 0 to 2 wt% disodium oxalate and 0 to 2 wt% graphite as burn rate modifier.

[0133] Tests conducted with the particle-generating booster charge are also labeled “particle” in Table 5 and the figures, while tests conducted with the gas-generating booster charge are also labeled “gas” in Table 5 and the figures.

[0134] Fig. 1 shows pressure / time curves for individual components as they can be used in a fuel element 10 according to the invention, in each case when ignited with a particle-generating booster charge and when ignited with a gas-generating booster charge.

[0135] Curves 18 and 20 show the behavior of a first pyrotechnic composition, i.e., a composition characterized in particular by a high burning rate, a high burning temperature, and a high heat of explosion. As can be seen, such a composition exhibits the fastest pressure buildup when activated by a particle-generating booster charge, but this buildup is considerably delayed when a gas-generating booster charge is used.

[0136] Curves 22 and 24, in turn, show the behavior of a second pyrotechnic composition, i.e., a composition characterized in particular by a low burning rate, a low burning temperature, and a low heat of explosion. This composition exhibits both a significantly delayed pressure buildup and a significantly lower maximum pressure than the first pyrotechnic composition. When a gas-generating booster charge is used, the pressure buildup is delayed even further.

[0137] Curves 26 and 28 represent the behavior of a pyrotechnic pre-ignition agent characterized by a low deflagration temperature. As can be seen in Fig. 1, the pre-ignition agent almost achieves the behavior of the first pyrotechnic composition when using a particle-generating booster charge. However, when using a gas-generating booster charge, the pre-ignition agent exhibits by far the fastest pressure buildup and the highest maximum pressure of the tested examples.

[0138] Thus, the pre-ignition agent is particularly suitable for improving the ignition behavior of a fuel element if hot particles are not to be used to activate the fuel element.

[0139] Fig. 2 shows further pressure / time curves demonstrating the behavior of bilayer pellets. On the one hand, a first bilayer pellet with a first layer of "propellant 1" and a second layer of "propellant 2" was tested, and on the other hand, a second bilayer pellet with a first layer of "propellant 2" and a second layer of the pre-ignition agent was tested. For reference to Fig. 1, curves 18 and 20 are also shown in Fig. 2.

[0140] Curves 30 and 32 show the behavior of the first bilayer pellet when using a particle-generating and a gas-generating booster charge, respectively. Both the pressure buildup and the maximum pressure are significantly reduced compared to a pellet containing only propellant 1 due to the less ignitable propellant 2, especially in the case of the gas-generating booster charge.

[0141] The second bi-layer tablet, which uses the pyrotechnic pre-ignition agent, exhibits a faster pressure build-up for both the particle-generating and the gas-generating booster charge than is the case for the first bi-layer tablet, especially in the case of the gas-generating booster charge.

[0142] These test results demonstrate that the use of a coating containing the pre-ignition agent can improve the ignition behavior of a fuel element, particularly when activation without hot particles is desired. This expands the formulation flexibility in the design of the fuel element, allowing for the targeted adjustment of other properties necessary for a desired combustion characteristic while improving ignition behavior.

[0143] In the following, exemplary embodiments of fuel elements 10 according to the invention are described with reference to the schematic sectional views in Figs. 3 to 14.

[0144] It is understood that the embodiments shown are not to be considered exhaustive. Rather, propellant elements 10 with different structures are also within the meaning of the invention, in particular those that have combinations of the layer structures shown in Figs. 3 and 14 and / or in which the respective first pyrotechnic material used is replaced by a second pyrotechnic material, and vice versa.

[0145] Identical or equivalent components are provided with the same reference numerals in all embodiments and the described properties apply accordingly to the other embodiments.

[0146] In Fig. 3, a first embodiment of the propellant element 10 is shown, in which the propellant element 10 has a core 12 which is formed only from a single pyrotechnic material, in this case from the first pyrotechnic material.

[0147] The coating 14 of the pyrotechnic pre-ignition agent is applied to an upper side 38 of the core 12, while a lower side 39 of the core 12 opposite the upper side 38 and a shell side 40 connecting the upper side 38 and the lower side 39 are not coated.

[0148] The thickness of the coating 14 can be varied within wide ranges. For example, the thickness of the coating 14 is 10% or less of the thickness of the entire propellant element 10.

[0149] In Fig. 3, the entire upper side 38 is covered by the coating 14. It is understood that only partial areas of the upper side 38 may be provided with the coating 14. Likewise, instead of the upper side 38, only the underside 39 or only the shell side 40 may be provided with the coating 14.

[0150] As an alternative to the embodiment shown in Fig. 3, the core 12 may also consist of the second pyrotechnic composition instead of the first pyrotechnic composition.

[0151] Fig. 4 shows a second embodiment of the propellant element 10, in which the propellant element 10 is a shell tablet and the coating 14 surrounds the core 12 on all sides, i.e. is applied to the top side 38 as well as to the bottom side 39 and the shell side 40.

[0152] In such an embodiment, the coating 14 thus simultaneously represents a covering 42 of the core 12.

[0153] Such a propellant element 10 has an even better ignitability, since the ignition behavior of the pyrotechnic pre-ignition agent to the pyrotechnic material of the core 12 is further improved.

[0154] Fig. 5 illustrates a third embodiment in which the propellant element 10 is a shell pellet, and the core 12 made of first pyrotechnic material, also referred to as the first core region 15, has an edge portion 46 that protrudes in the radial direction r and extends through the casing 42 to an outer contour on the shell sides. In this way, in addition to the coating 14 of pyrotechnic pre-ignition agent, the core 12 is directly exposed to the outside via the edge portion 46. The edge portion 46 is formed integrally with the core 12.

[0155] In particular, the edge portion 46 extends continuously along a circumferential direction of the fuel element 10. In other words, the casing 42 has an ignition gap 48 surrounding the fuel element 10, which is filled by the edge portion 46 of the core 12.

[0156] The edge portion 46 has a smaller extension in an axial direction A of the coated tablet than the core 12. More precisely, the edge portion 46 has an axial extension in the axial direction A of the coated tablet that is smaller than an axial extension of the core 12 in the axial direction A of the coated tablet. The positioning of the edge portion 46 with respect to the core 12 is arbitrary. For example, the edge portion 46 can be arranged offset from the center of the core 12, as can be clearly seen in Fig. 5. Of course, the edge portion 46 can also enclose the core 12 centrally.

[0157] Through the edge section 46, at least a portion of the core 12 is directly accessible via the surroundings of the propellant element 10. In this way, the ignition behavior of the propellant element 10 can be influenced more strongly by the pyrotechnic material of the core 12, in addition to the pyrotechnic pre-ignition agent.

[0158] Fig. 6 shows a fourth embodiment of the propellant element 10, in which the core 12 is composed of the first core region 15 and a second core region 16, wherein the second core region 16 is applied to the underside 39 of the first core region 15.

[0159] On the upper side 38 of the first core region 15, the coating 14 of pyrotechnic pre-ignition agent is again applied, analogously to Fig. 3.

[0160] By using different pyrotechnic compositions in the core 12, the behavior of the propellant element 10 can be further adapted.

[0161] Fig. 7 shows a fifth embodiment of the propellant element 10, in which the core 12 also has the first core region 15 and the second core region 16, but the first core region 15 surrounds the second core region 16.

[0162] On the upper side 38 of the first core region 15, the coating 14 made of the pyrotechnic pre-ignition agent is again applied.

[0163] Fig. 8 illustrates a sixth embodiment of the propellant element 10, in which, in addition to the configuration of the fifth embodiment, the second core region 16 made of a second pyrotechnic material continues on the underside 39 of the first core region 15. In other words, the underside 39 can be coated with additional second pyrotechnic material.

[0164] Fig. 9 shows a seventh embodiment of the propellant element 10, which is constructed similarly to the third embodiment of Fig. 5. However, in the seventh embodiment, only a portion of the casing 42 is formed by the coating 14 of pyrotechnic pre-ignition agent, namely that portion of the casing 42 which is applied to the upper side 38 of the first core region 15.

[0165] The remaining part of the casing 42 is formed from a second pyrotechnic material, i.e. from the second core region 16.

[0166] Fig. 10 shows an eighth embodiment of the propellant element 10, which is constructed similarly to the third and seventh embodiments of Figs. 5 and 9, respectively, but in which the entire casing 42 is formed by the second core region 15, i.e. second pyrotechnic material.

[0167] The coating 14 of pyrotechnic pre-ignition agent is also applied to the upper side of the casing 42.

[0168] Fig. 11 shows a ninth embodiment of the propellant element 10, in which the core 12 consisting of the first core region 15 and the second core region 16 is completely provided with the coating 14, i.e. on the tablet top side, the tablet bottom side and the tablet shell sides.

[0169] At the same time, however, the first core region 15 has the edge sections 46, which in this case extend through the casing 42 in the form of the second core region 16 to the coating 14 of pyrotechnic pre-ignition agent.

[0170] Fig. 12 shows a tenth embodiment of the fuel element 10, which is analogous to the third embodiment of Fig. 5.

[0171] In the tenth embodiment, however, the edge portion 46 encloses the core 12 centrally.

[0172] It is understood that the edge portion 46 may also be arranged non-axially symmetrically. For example, the edge portion 46 may be offset relative to the core 12 or be shaped spindle-like around the core 12, or regions of the edge portion 46 may be offset from one another. Fig. 13 shows an eleventh embodiment of the propellant element 10, in which the illustrated shell tablet has a first core region 15 and an edge portion 46, which together form a biconvex shape.

[0173] In addition, the casing 42, which is formed by a second core region 16 and the coating 14 of pyrotechnic pre-ignition agent, in particular the upper and lower sides of the casing 42, also has a biconvex shape.

[0174] The first core region 15 and the shell 42 can have the same radius. This particularly simplifies the production of such a coated tablet. However, the first core region 15 and the shell 42 can also have different radii from each other.

[0175] In this embodiment, the edge portions 46 are formed by the pointed ends of the biconvex first core region 15.

[0176] Fig. 14 shows a twelfth embodiment of the fuel element 10, in which further additional coatings are used.

[0177] The core 12 is formed from the core region 15 and the second core region 16, which also forms the casing 42, which is perforated by the edge sections 46.

[0178] Furthermore, the coating 14 of the pyrotechnic pre-ignition agent is applied to the upper side of the casing 42.

[0179] An ignition layer 50 is provided as an additional coating on the underside of the casing 42. The ignition layer 50 consists of a further pyrotechnic composition, which differs from both the first pyrotechnic composition and the second pyrotechnic composition and simultaneously has a higher deflagration temperature than the pyrotechnic pre-ignition agent.

[0180] The additional pyrotechnic composition is characterized in particular by a burning rate that is greater than the burning rate of the second pyrotechnic composition, but not necessarily greater than that of the first pyrotechnic composition. Additionally, a moisture protection layer 52 is provided as an additional coating, which completely envelops the coated tablet. For example, the moisture protection layer 52 comprises hydrophobic polymers, in particular silicones, polyurethanes, and / or polyesters.

[0181] By using additional coatings, the behavior of the fuel element 10 can be further adjusted and varied.

[0182] Figure 15 shows a method for producing a fuel element 10 according to the invention in the form of a coated tablet using the embodiment from Fig. 5. The method is explained in more detail below.

[0183] The fuel element 10 according to the invention is produced in a press 54.

[0184] The press 54 includes an upper punch 56, a press die 58 and a lower punch 60.

[0185] The upper punch 56 and the lower punch 60 are arranged opposite each other.

[0186] The pressing die 58 and the lower punch 60 define a receiving chamber 62, in particular a cylindrically shaped or an elliptically shaped receiving chamber 62. In addition, the lower punch 60 can be moved against the pressing die 58.

[0187] In particular, the receiving chamber 62 can form a negative to the upper punch 56.

[0188] The upper punch 56 is designed to be displaced in the direction of the pressing die 58 and to engage into the receiving chamber 62.

[0189] Basically, the upper punch 56 has a cylindrical shape and comprises an inner punch 64 and an outer punch 66.

[0190] The outer punch 66 laterally encloses the inner punch 64, with the inner punch 64 being slidably mounted within the outer punch 66. Thus, the inner punch 64 can be displaced against the outer punch 66. Furthermore, the outer punch 66 and the inner punch 64 form a common end face 68, with which the upper punch 56 engages the receiving chamber 62 of the pressing die 58 during a compression process.

[0191] However, it is also conceivable that different upper punches 56 are used for the individual process steps, each of which differs in the extent of displacement of the inner punch 64 relative to the outer punch 66. In this case, the inner punch 64 is formed integrally with the outer punch 66. For example, a separate upper punch 56 can be used for each of the process steps S2, S5, S6, and S10.

[0192] In a first step, the receiving chamber 62 is filled with the pyrotechnic pre-ignition agent (S1).

[0193] Subsequently, the upper punch 56 is pressed into the receiving chamber 62 of the compression die 58, and the pyrotechnic pre-ignition agent is compressed (S2). During this compression process, the inner punch 64 is pushed further into the receiving chamber 62 than the outer punch 66. In this way, the pyrotechnic pre-ignition agent 14 can be formed while retaining a casing bottom 70. Since the outer punch 66 is pushed into the receiving chamber 62 offset from the inner punch 64, a casing bottom 70 with a U-shaped cross-section is formed. The casing bottom 70 is open toward the upper punch 56.

[0194] Thereafter, the upper punch 56 is withdrawn from the pressing die 58 (S3) and the finished pressed casing bottom 70 remains in the pressing die 58.

[0195] Subsequently, the receiving chamber 62 is filled with the first pyrotechnic material (S4). It is understood that, depending on the desired embodiment, a second pyrotechnic material may also be used.

[0196] In the next step, the upper punch 56 is pressed back into the receiving chamber 62, with initially only the outer punch 66 being pressed into the receiving chamber 62 (S5). In this way, an edge section 46 made of the first pyrotechnic material is pressed onto laterally projecting areas of the casing bottom 70. The inner punch 64 is then pressed far enough into the receiving chamber 62 (S6) until it again forms a common end face with the outer punch 66. Thus, the core 12 is pressed into the casing bottom 70, which is open toward the upper punch 56.

[0197] The upper punch 56 is then withdrawn from the pressing die 58 again (S7) to obtain a compact consisting of the casing bottom 70, which comprises a pre-compacted core 12 with edge section 46.

[0198] The compact is moved by the lower punch 60 in the receiving chamber 62 in the direction of the upper punch 56 (S8).

[0199] Finally, the pyrotechnic pre-ignition agent 14 is filled into the receiving chamber 62 again (S9).

[0200] Finally, the upper punch 56 is pressed back into the receiving chamber 62 or the pressing die 58 is moved or, generally speaking, the distance between the upper punch 56 and the pressing die 58 is reduced to such an extent that the pyrotechnic pre-ignition agent is pressed in the form of a jacketed tablet, obtaining a casing top 72 and thus the finished propellant element 10 (S10).

[0201] In the final step, the upper punch 56 is retracted from the receiving chamber 62. Furthermore, the lower punch 60 is moved toward the upper punch 56 until the receiving chamber 62 is completely occupied by the lower punch 60 (S11). The coated tablet can be removed from the press 54.

[0202] Analogous intermediate steps can be used to produce further layers or partial layers by means of pressing, for example by producing the casing underside 70 from the second pyrotechnic material.

[0203] Figure 16 describes the sequences of a method for producing a fuel element 10 according to the invention in a shell tablet with a biconvex, optionally an asymmetrically biconvex, shaped core 12 with edge portion 46.

[0204] The sequences of this method are explained in more detail below. First, the same press 54 is provided as in Figure 15, with the difference that a convex upper punch 74 and a concave upper punch 76 are used. In addition, a concave lower punch 78 is used in the press 54.

[0205] In this sense, convex and concave means that only the respective end faces of punches 74, 76, and 78 have a curvature. For the production of a biconvex coated tablet, the curvature of the convex upper punch 74 corresponds to that of the concave lower punch 78. The production of an asymmetrically biconvex coated tablet is achieved by using a concave lower punch 78 and a concave upper punch 76, which do not have the same curvature on their end faces.

[0206] The front side of the convex upper punch 76 has a curvature with a radius that corresponds to the curvature of the front side of the concave lower punch 78. The concave lower punch 78 is curved such that the convex upper punch 74 can engage with the lower punch 52, in particular such that the convex upper punch 74 can engage with the lower punch 52 in a form-fitting manner.

[0207] In other words, the front side of the upper punch 74 preferably has a convex shape that is complementary to a concave shape of the lower punch 78.

[0208] In a first step, the receiving chamber 62 is filled with the pyrotechnic pre-ignition agent (S1).

[0209] Subsequently, a convex upper punch 74 is pressed into the receiving chamber 62 and the pyrotechnic pre-ignition agent 14 is compressed to obtain a casing bottom 70 (S2).

[0210] Since both the concave lower punch 78 and the convex upper punch 74 are complementarily shaped on their end faces, the casing bottom 70 resulting from the pressing is also convexly shaped.

[0211] The convex upper punch 74 is first pushed back from the receiving chamber 62 and removed from the press (S3). The receiving chamber 62 is then filled with the first pyrotechnic material (S4).

[0212] In the next step, the first pyrotechnic material is compressed by pushing the concave upper punch 76 into the receiving chamber 62, thereby obtaining the core 12 with an edge section 46 (S5).

[0213] Since the casing underside 70 present in the pressing die 58 prescribes a convex shape and the concave upper punch 76 pushed into the receiving chamber 62 from the other side prescribes a concave shape, this pressing process results in a core 12 with an edge section 46 which has a biconvex shape.

[0214] Optionally, a concave upper punch 76 can be used for the above step, which has a curvature that differs from the curvature of the concave lower punch 78. Thus, an asymmetrically biconvex shaped core 12 can be pressed.

[0215] In the next step, the concave upper punch 76 can be pushed out of the press die 58 again and the pyrotechnic pre-ignition agent can be filled into the receiving chamber 62 again (S6).

[0216] Finally, the pyrotechnic pre-ignition agent 14 can be fully pressed by the concave upper punch 76 or the lower punch 78 is moved or, generally speaking, the distance between the upper and lower punches is reduced in order to achieve compression, while maintaining a convexly shaped casing upper side 72 (S7).

[0217] Optionally, a concave upper punch 76 can be used for the above step, which has a different curvature than the concave lower punch 78. This results in an asymmetrically biconvex-shaped coated tablet.

[0218] In the last step, the biconvex, optionally asymmetrically biconvex, shaped coated tablet can be removed from the compression die 58 (S8).

[0219] The methods described above enable the simple production of propellant elements with a layer structure tailored to a desired combustion characteristic through the use of various stampers and sequences of compositions presented in the receiving chamber 62.

[0220] In particular, the propellant elements 10 according to the invention are suitable for applications in which the propellant elements 10 are to be ignited essentially by increasing the temperature due to the use of the coating 14 made of pyrotechnic pre-ignition agent.

Claims

Patent claims 1. A propellant element (10) for a gas generator for use in a safety device in the form of a tablet, wherein the tablet has a core (12) of pyrotechnic material and a coating (14) of a pyrotechnic pre-ignition agent applied to the core (12), wherein the pyrotechnic material and the pyrotechnic pre-ignition agent differ from one another, and wherein the pyrotechnic pre-ignition agent has a deflagration temperature of 500 K or less.

2. Propellant element (10) according to claim 1, wherein the pre-ignition agent has a deflagration temperature of 450 K or less, preferably 435 K or less.

3. Propellant element (10) according to claim 1 or 2, wherein the pre-ignition agent has a combustion temperature of 2000 K or more, preferably a combustion temperature in the range of 2100 K to 2800 K.

4. Propellant element (10) according to one of the preceding claims, wherein the coating (14) of the pyrotechnic pre-ignition agent is applied to an upper side (38), a lower side (39) and / or a shell side (40) of the core (12).

5. A propellant element (10) according to any one of the preceding claims, wherein the thickness of the coating (14) of a pyrotechnic pre-ignition agent is 10% or less of the thickness of the pellet.

6. Propellant element (10) according to one of the preceding claims, wherein the pyrotechnic pre-ignition means comprises the following components: (D) 60 to 95% by weight, preferably 60 to 92% by weight of at least one fuel selected from the group consisting of 1-nitroguanidine, guanidinium nitrate, nitrotriazolone, nitrocellulose, metals, in particular boron, aluminum, titanium, zirconium, and / or tungsten and combinations thereof, (E) 2 to 40 wt.%, preferably 6 to 40 wt.%, of at least one oxidizing agent selected from the group of chlorates, perchlorates, metal oxides and combinations thereof, preferably potassium perchlorate, and (F) 0 to 3% by weight, preferably 0 to 2% by weight, of further additives selected from the group of metal oxides, silica, stearates, lubricating oils and combinations thereof, preferably from the group consisting of iron oxide, magnesium oxide, amorphous silica, hydrophobic silica, calcium stearate, C15-C30 lubricating oils and combinations thereof, in each case based on the total weight of the pyrotechnic pre-ignition agent, wherein the proportions of components (A) to (C) add up to 100% by weight.

7. Propellant element (10) according to one of the preceding claims, wherein the core (12) has a first core region (15) made of a first pyrotechnic material and a second core region (16) made of a second pyrotechnic material, wherein the first pyrotechnic material and the second pyrotechnic material differ from one another.

8. Propellant element (10) according to claim 7, wherein the tablet is a jacketed tablet in which the first core region (15) is at least partially provided with a casing (42) which is formed by the second core region (16) and / or the coating (14) of the pyrotechnic pre-ignition agent, wherein the first core region (15) has an edge portion (46) which projects in the radial direction and extends through the casing (42) to an outer contour of the jacketed tablet, wherein the edge portion (46) is formed along a circumferential direction of the jacketed tablet and has a smaller extent in the axial direction of the jacketed tablet than the first core region (15).

9. A method for producing a propellant element (10) according to one of the preceding claims, wherein the pyrotechnic material and / or the pyrotechnic pre-ignition agent are pressed in a press die (58) to form the core (12) of pyrotechnic material or the coating (14) of the pyrotechnic pre-ignition agent.

10. Use of a fuel element (10) according to one of the preceding claims in a safety device in a vehicle, in particular in a gas generator.

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