Low temperature burning gas generant formulations for airbags with low burn rate gradients.

Abstract

A gas generant formulation for a side impact airbag is provided. The invention provides a gas generant formulation for a side impact airbag, comprising a primary fuel, a primary oxidizer, a secondary fuel, and a secondary oxidizer. The secondary fuel comprises at least melamine nitrate in an amount ranging from about 1.00% to about 10.00% by weight. The secondary oxidizer comprises at least potassium perchlorate in an amount ranging from about 1.00% to about 10.00% by weight. The formulation provides a burn velocity of at least 50 mm / sec at 40 MPa and a burn velocity slope of 0.40 or less.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application Publication No. 17 / 886,536, filed August 12, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] FIELD OF THE INVENTION FIELD OF THE DISCLOSURE The present disclosure relates to gas generating compositions for airbags and airbags including the gas generating compositions. [Background technology]

[0003] This section provides background information related to the present disclosure; background information is not necessarily prior art.

[0004] Airbag systems have been used in vehicles for many years, and significant research has been conducted on these systems. Generally, the goals associated with airbag system research are directed toward improving performance, reducing the size and weight of the system, and reducing the manufacturing costs of the airbag system. More specifically, significant research has been directed toward improving the functionality and reducing the cost of the gas generant used to inflate the airbags in the airbag system.

[0005] Optimized gas generant performance and subsequent system cost reduction can be achieved by pyrotechnic formulations that can burn with desirable ballistic performance characteristics at low flame temperatures. Such desirable ballistic performance characteristics include a fast burn rate and a low burn rate gradient. A low flame temperature and a lower burn rate gradient allow for a reduction in the required airbag cushion reinforcement and a reduction in pressure vessel (combustion chamber) wall thickness, effectively reducing system cost and weight. However, this approach presents the challenge of reducing the flame temperature and gradient while maintaining a burn rate high enough to inflate the airbag cushion within the required time.

[0006] The heat sink in the inflator is typically in the form of a metal screen pack, which also serves to filter solid combustion residues from the gas stream. In an efficient inflator design, the amount of screen pack used is sufficient to effectively filter solid combustion products from the gas stream and cool the gas from its combustion flame temperature to a desired lower temperature that minimizes damage to the airbag. The desired combustion flame temperature for "high velocity, low temperature" gas generant formulations used in secondary applications is 1800K to 1950K.

[0007] Current technology for side-impact inflator applications uses an alkali metal perchlorate co-oxidizer, such as potassium perchlorate, along with a basic copper nitrate oxidizer, guanidine nitrate fuel, and an optional co-fuel. The burn rate achieved is a function of the amount of potassium perchlorate used. Unfortunately, the amount of potassium perchlorate used is also directly proportional to the combustion flame temperature. Reducing the amount of potassium perchlorate in the formulation lowers the flame temperature and desirably reduces the amount of condensable potassium chloride gas in the combustion products. Gaseous potassium chloride can pass through filters, condense, and then form solids within the cushion itself, making it difficult to meet customer limits on airborne particulates. However, reducing the amount of potassium perchlorate to achieve a target flame temperature can reduce the burn rate to the point that it is no longer useful, for example, in side-impact applications. An additive that, when added to other components of the formulation, lowers the combustion flame temperature and positively impacts ballistic properties, thereby allowing for a reduction in the amount of potassium perchlorate in the formulation, would be a "high-speed, low-temperature" solution and an improvement in the art. Summary of the Invention

[0008] This section provides an overview of the disclosure and is not an exhaustive disclosure of the entire scope or all of the features of the disclosure.

[0009] According to a first aspect, the present disclosure provides a gas generant formulation for a side impact airbag that may include a primary fuel, a primary oxidizer, a secondary fuel that may include at least melamine nitrate, wherein the melamine nitrate is present in an amount ranging from about 1.00% to about 10.00% by weight, and a secondary oxidizer that may include at least potassium perchlorate, wherein the potassium perchlorate is present in an amount ranging from about 1.00% to about 10.00% by weight, wherein the formulation has a burn velocity of at least 50 mm / sec at 40 MPa and a burn velocity slope of 0.40 or less.

[0010] According to a first embodiment, the primary fuel may include at least guanidine nitrate, and the amount of guanidine nitrate may range from about 35% to about 55% by weight.

[0011] According to the first embodiment, the primary oxidant may include at least basic copper nitrate, and the amount of basic copper nitrate may range from about 25% to about 50% by weight.

[0012] According to a first aspect, the formulation may further comprise at least one additive in an amount of up to about 11.0 wt. % configured to reduce the gas temperature generated by the formulation, improve slugging of the formulation, or act as a pressing aid for the formulation.

[0013] According to a first aspect, the formulation may include an additive that improves slugging, and the additive that improves slugging may include at least one of a metal oxide and / or a metal hydroxide.

[0014] According to a first aspect, the formulation may include an additive configured to act as a pressing aid, and the pressing aid may include at least one of a lubricant and / or a mold release agent. The lubricant may include at least one of molybdenum disulfide and graphite, and the mold release agent may include at least one of calcium stearate and magnesium stearate.

[0015] According to a second aspect of the present disclosure, there is provided a gas generant formulation for a side impact airbag that may include: a primary fuel including at least guanidine nitrate; a primary oxidizer including at least basic copper nitrate; a secondary fuel including at least melamine nitrate, wherein the melamine nitrate is present in an amount ranging from about 5.00% to about 10.00% by weight; and a secondary oxidizer including at least potassium perchlorate, wherein the potassium perchlorate is present in an amount ranging from about 5.00% to about 10.00% by weight, wherein the formulation has a burn velocity of at least 50 mm / sec at 40 MPa and a burn velocity slope of 0.40 or less.

[0016] According to a second embodiment, the amount of guanidine nitrate can range from about 35% to about 55% by weight.

[0017] According to a second embodiment, the amount of basic copper nitrate can range from about 25% to about 50% by weight.

[0018] According to a second embodiment, the formulation may further comprise at least one additive in an amount of up to about 11.0 wt. % configured to reduce the gas temperature generated by the formulation, improve slugging of the formulation, or act as a pressing aid for the formulation.

[0019] According to a second aspect, the formulation includes an additive that improves slugging, and the additive that improves slugging may include at least one of a metal oxide and / or a metal hydroxide.

[0020] According to a second aspect, the formulation includes an additive configured to act as a pressing aid, the pressing aid may include at least one of a lubricant and / or a mold release agent, the lubricant may include at least one of molybdenum disulfide and graphite, and the mold release agent may include at least one of calcium stearate and magnesium stearate.

[0021] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] Exemplary embodiments will now be described more fully with reference to the accompanying drawings.

[0023] The present disclosure provides gas generating compositions. Gas generating compositions, also known as propellants, gas generating materials, and pyrotechnic materials, are used in inflators of airbag modules used in vehicle occupant inflatable restraint systems. The selection of a gas generating composition or material involves a variety of factors, including, among other considerations, meeting current industry performance specifications, guidelines, and standards, producing a safe gas or effluent, safe handling of the gas generating material, stability of the material over long periods of time, and cost-effectiveness in manufacturing. Preferably, the gas generating composition is safe during handling, storage, and disposal.

[0024] Improved gas generator performance in an inflatable restraint system can be achieved in a variety of ways, many of which ultimately depend on the formulation of the gas generating composition to provide the desired characteristics. Ideally, the gas generating composition provides a sufficient gas mass flow rate over a desired time interval to achieve the necessary work impulse on an inflator (e.g., an airbag) within the inflatable restraint system. The temperature of the gas generated by the gas generating composition affects the amount of work the gas can do, and high gas temperatures may be undesirable due to the potential for combustion and associated thermal damage. Furthermore, high gas temperatures may also potentially lead to excessive gas reliance or sensitivity to heat transfer and an overly rapid contraction profile, which may also be undesirable. Therefore, minimizing flame temperatures is advantageous.

[0025] The desirable combustion flame temperature for a "high-velocity, low-temperature" gas generating composition used in a side inflatable restraint system is in the range of 1800 K to 1950 K (i.e., 1526.85°C to 1676.85°C). Therefore, a high flame temperature can be considered any temperature exceeding approximately 1950°K (1676.85°C) upon combustion. To mitigate the effects of high flame temperatures, the inflator may include a heat sink, which can also function as a filter or screen for the inflator. However, a significant portion of the inflator's mass is often devoted to incorporating a heat sink, which can affect the system's efficiency and, more significantly, the inflator's weight. In light of the above, the present disclosure aims to provide a gas generating composition for a side inflatable restraint system that can achieve high gas output at a high mass flow rate at a relatively low flame temperature (i.e., below approximately 1950°K). This is achieved by using a gas generating composition that includes at least one primary oxidizer, at least one secondary oxidizer, at least one primary fuel, and at least one secondary fuel. Although not required, the gas generating composition may also include various additives.

[0026] Primary Oxidizer Gas generant compositions according to the present disclosure include at least one primary oxidizer. Exemplary primary oxidizers that may be used in the gas generant compositions of the present disclosure include metal nitrates. Preferably, the at least one primary oxidizer comprises a basic metal nitrate. The amount of primary oxidizer may range from about 25.00 to about 50.00 wt. % (inclusive). Exemplary basic metal nitrates include basic copper nitrate, basic cobalt nitrate, basic zinc nitrate, basic manganese nitrate, basic iron nitrate, basic molybdenum nitrate, basic bismuth nitrate, and basic cerium nitrate. While more than one primary oxidizer may be used, it is particularly preferred that the primary oxidizer comprises at least basic copper nitrate.

[0027] Secondary Oxidizer The gas generant compositions of the present disclosure include at least one secondary oxidizer. The at least one secondary oxidizer may be present in an amount ranging from about 1.00 to about 10.00 weight percent, inclusive. Exemplary secondary oxidizers include alkali metal and alkaline earth metal salts of perchloric acid. Specific examples of these materials suitable for use herein include ammonium perchlorate, sodium perchlorate, potassium perchlorate, magnesium perchlorate, and barium perchlorate. While more than one secondary oxidizer can be used, it is particularly preferred that the secondary oxidizer include at least potassium perchlorate.

[0028] primary fuel Gas generant compositions according to the present disclosure include at least one primary fuel. The at least one primary fuel may be present in an amount ranging from about 35.00 to about 55.00 wt. %, inclusive. Exemplary primary fuels may include a nitrogen-containing organic compound. In specific examples, the nitrogen-containing organic compound may be guanidine or a guanidine derivative. The guanidine derivative may be selected from nitroguanidine, guanidine nitrate, aminoguanidine, aminoguanidine nitrate, copper bisguanylurea dinitrate (CuGUN), and aminoguanidine bicarbonate. Other examples of primary fuels include tetrazole or a tetrazole derivative selected from aminotetrazole, bitetrazole, azobitrazole, nitrotetrazole, and nitroaminotetrazole. While more than one primary fuel may be used, it is particularly preferred that the primary fuel include at least guanidine nitrate.

[0029] secondary fuel Gas generant compositions according to the present disclosure include at least one secondary fuel. The at least one secondary fuel may be present in an amount ranging from about 1.00 to about 10.00 wt. %, inclusive. Any of the primary fuels described above may be used as the secondary fuel, albeit in reduced amounts relative to the amount of the primary fuel. Preferably, however, the secondary fuel includes at least melamine nitrate.

[0030] additives Although not required, gas generant compositions according to the present disclosure may contain at least one additive. If desired, the total amount of additives contained in the gas generant composition may range up to about 11.00% by weight. Additives may be used to reduce gas temperature, improve slugging, improve effluent, improve bonding, and improve powder flow. Lubricating additives (i.e., pressing aids) may also be optionally added, which may allow for improved powder flow during processing and pressing and improve slugging.

[0031] Additives that can be used as coolants to reduce gas temperatures include materials such as basic copper carbonate or other suitable carbonates, copper glycolate, melamine copper oxalate, copper cyanurate dihydrate, and other suitable coolants.

[0032] Additives that may be used as pressing aids include, by way of non-limiting example, lubricants and / or mold release agents such as molybdenum disulfide and graphite, metal salts of fatty acids such as calcium stearate and magnesium stearate, and / or graphitic boron nitride. When used as an additive, the pressing aid may be present in the gas generant composition in an amount up to about 1% by weight.

[0033] Additives that can be used to improve slagging include metal oxides such as aluminum oxide, silicon dioxide, cerium oxide, ferric oxide, zinc oxide, titanium oxide, zirconium oxide, bismuth oxide, molybdenum oxide, lanthanum oxide, e-glass, and the like. Metal hydroxides, such as aluminum hydroxide and other metal hydroxides known to those skilled in the art, can also be used as additives to improve slagging. When used as an additive, the slag generating agent can be present in the gas generant composition in an amount of up to about 10% by weight.

[0034] While in certain embodiments it is preferred that the gas generant composition be substantially free of binders, in certain alternative embodiments the gas generant composition may include a binding agent additive to improve crush strength without significantly impairing effluent and burn characteristics. Exemplary additives that may be used as binding agents include, and are suggested to be, carboxymethyl cellulose, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, ammonium carboxymethyl cellulose, cellulose acetate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl ethyl cellulose, microcrystalline cellulose, polyacrylamide, amine products of polyacrylamide, polyacrylic hydrazide, copolymers of acrylamide and metal salts of acrylic acid, copolymers of polyacrylamide and polyacrylic acid ester compounds, polyvinyl alcohol, acrylic rubber, guar gum, starch, and silicone.

[0035] As noted above, gas generant compositions according to the present disclosure preferably include at least potassium perchlorate as a secondary oxidizer and melamine nitrate as a secondary fuel. It has been discovered that the use of melamine nitrate with potassium perchlorate, when used together, achieves a synergistic effect on ballistic performance when each of these materials is included in the gas generant composition in an amount ranging from about 1.00% to about 10.00% by weight, inclusive. Preferably, each of these materials is included in the gas generant composition in an amount ranging from about 5.00% to about 10.00% by weight, inclusive.

[0036] When a gas generant composition includes potassium perchlorate, the burn rate of the gas generant composition containing potassium perchlorate may be a function of the amount of potassium perchlorate used. Additionally, the amount of potassium perchlorate used may be proportional to the flame temperature. In other words, the burn rate and flame temperature increase with increasing amounts of potassium perchlorate in the gas generant composition. Therefore, it would be expected that decreasing the amount of potassium perchlorate in the gas generant composition would lower the flame temperature while also reducing the amount of condensable potassium chloride gas generated as a combustion product (potassium chloride gas can pass through the inflator filter and condense to form solids in the cushion, which is typically desirable to avoid in order to limit the amount of airborne particulates as required by vehicle manufacturers). Unfortunately, it has been found that decreasing the amount of potassium perchlorate in the gas generant composition reduces the burn rate to the extent that compositions using lower amounts of potassium perchlorate may not be useful in side inflatable restraint systems. This is evidenced by Table 1 below.

[0037] [Table 1]

[0038] Each of the above formulations was mixed and then spray dried. As can be seen from Table 1 above, when the amount of potassium perchlorate in the side inflator formulation was reduced from 12.52% to less than 7%, the slope decreased, but the formulation did not produce a sufficient burn rate to match the baseline comparison, and therefore the reduced amount of potassium perchlorate would not be useful for side inflator applications.

[0039] However, as noted above, when a reduced amount of potassium perchlorate as a secondary oxidizer is used in conjunction with a reduced amount of melamine nitrate as a secondary fuel, a low-temperature burning gas generant formulation is achieved that has a low burn rate gradient and a burn rate sufficient to be useful in side-impact inflator applications. In this regard, as can be seen in Table 2 below, the use of potassium perchlorate as a secondary oxidizer in a gas generant formulation containing basic copper nitrate as the primary oxidizer and guanidine nitrate as the primary fuel significantly increases the burn rate of the formulation, but also significantly increases the pressure sensitivity of the burn rate, as can be seen by comparing Formulation 1 and Formulation 2 in Table 2.

[0040] [Table 2]

[0041] Furthermore, as can be seen in Table 2 above, the addition of melamine nitrate as a secondary fuel to a gas generant formulation containing basic copper nitrate as the primary oxidizer and guanidine nitrate as the primary fuel slightly increases both the burn rate and burn rate slope of the formulation, as can be seen by comparing Formulations 1 and 3 in Table 2. However, it can also be seen in Table 2 that when a combination of melamine nitrate and potassium perchlorate is added to a formulation containing basic copper nitrate as the primary oxidizer and guanidine nitrate as the primary fuel, the burn rate of Formulation 4 is greater than the burn rate of Formulation 2. In addition, the slope achieved by Formulation 3 is maintained in Formulation 4, indicating a synergistic relationship between the use of melamine nitrate and potassium perchlorate in reduced amounts (i.e., in amounts ranging from about 1.00% by weight to about 10.00% by weight, preferably in amounts ranging from about 5.00% by weight to about 10.00% by weight, inclusive).

[0042] It should be understood that each of the formulations in Table 2 was made as a sub-scale laboratory mix and was not subsequently spray dried as were the formulations in Table 1. Nevertheless, the use of the sub-scale laboratory mixes is useful for relative comparisons between a formulation that does not contain potassium perchlorate and melamine nitrate (i.e., Formulation 1 in Table 2), a formulation that contains each of potassium perchlorate and melamine nitrate (i.e., Formulation 4 in Table 2), and a formulation that includes one of potassium perchlorate (i.e., in the case of Formulation 2 in Table 2) and melamine nitrate (i.e., in the case of Formulation 3 in Table 2).

[0043] However, when Formulation 4 in Table 2 is spray dried and compared to the baseline composition in Table 1, it is found that the flame temperature and slope are each reduced to a level suitable for use in side impact inflator systems as shown in Table 3 (below) without sacrificing burn rate. For formulations according to the present disclosure containing reduced amounts of potassium perchlorate and melamine nitrate, the burn rate is at least 50 mm / sec at 40 MPa and the slope is 0.40 or less.

[0044] [Table 3]

[0045] It should be understood that the amounts of the various components of Formulation 4 in Table 2 have been reduced to account for the addition of pressing aids required to spray dry the formulation.

[0046] As evidenced above, the formulation of the present disclosure, which includes reduced amounts of potassium perchlorate and melamine nitrate, is beneficial in gas generant performance and reduces the overall cost of systems incorporating the formulation. In this regard, the lower flame temperature falls within the desired combustion flame temperature range (i.e., 1800 K to 1950 K) for "high-speed, low-temperature" gas generant formulations that may be used in side-impact applications, and the burn velocity of at least 50 mm / sec at 40 MPa and a slope of 0.40 or less allows for reduced airbag cushion reinforcement and reduced pressure vessel (combustion chamber) wall thickness, effectively reducing system cost and weight. Furthermore, despite the lower flame temperature and burn velocity slope, the burn velocity remains high enough to inflate the airbag cushion within the required time.

[0047] The foregoing description of the embodiments is provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in selected embodiments even if not specifically shown or described. The same can also be varied in many ways. Such variations should not be considered a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

1. A gas generating agent formulation for side impact airbags, Primary fuels and Primary oxidizing agent, In a compound containing, A secondary fuel comprising at least melamine nitrate, wherein the amount of melamine nitrate is in the range of about 1.00% by weight to about 10.00% by weight, A secondary oxidizing agent comprising at least potassium perchlorate, wherein the amount of potassium perchlorate is in the range of about 1.00% by weight to about 10.00% by weight, Includes, The combustion rate of the aforementioned compound is at least 50 mm / second at 40 MPa, and the combustion rate gradient is 0.40 or less. compound.

2. The formulation according to claim 1, wherein the primary fuel comprises at least guanidine nitrate.

3. The formulation according to claim 2, wherein the amount of guanidine nitrate is in the range of about 35% by weight to about 55% by weight.

4. The formulation according to claim 1, wherein the primary oxidizing agent comprises at least basic copper nitrate.

5. The formulation according to claim 4, wherein the amount of basic copper nitrate is in the range of about 25% by weight to about 50% by weight.

6. The formulation according to claim 1, further comprising at least one additive in an amount of up to about 11.0% by weight, configured to lower the gas temperature produced by the formulation, improve the slugging of the formulation, or act as a press aid for the formulation.

7. The formulation according to claim 1, further comprising an additive for improving slugging, comprising at least one of a metal oxide and / or a metal hydroxide.

8. The formulation according to claim 1, further comprising a press-assisted additive containing at least one of a lubricant and / or a mold release agent.

9. The press-assisted additive comprises at least one of a lubricant and / or a mold release agent. The lubricant comprises at least one of molybdenum disulfide and graphite. The formulation according to claim 8, wherein the mold release agent comprises at least one of calcium stearate and magnesium stearate.