Gas Generant Composition

Abstract

To provide a gas-forming agent composition having a high combustion rate.SOLUTION: Provided is a gas-forming agent composition including the following components (a)-(d): (a) guanidine nitrate; (b) basic metal nitrate; (c) binder; and (d) basic magnesium carbonate, wherein (d) the basic magnesium carbonate has an average particle diameter of 12 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to gas generant compositions. [Background technology]

[0002] Attempts have been made to ensure the reliability of inflators that use gas generant compositions and are used in vehicle safety devices such as airbag devices mounted on vehicles. For example, attempts have been made to lower the combustion temperature of the gas generant composition, improve ignition properties, and reduce the pressure index (Patent Document 1). It is known that the burning rate of a gas generant composition fluctuates over a range of powers of the pressure index n due to pressure fluctuations within the inflator, as shown in the following equation: The invention described in Patent Document 1 solves the problem by setting the ratio of melamine cyanurate to nitroguanidine within a specific range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-211064 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the characteristics of a gas generant composition is its burning rate. If the burning rate of a gas generant composition is low, it is necessary to reduce the shape of the gas generant composition when molding it to compensate for this drawback. Reducing the shape of the gas generant composition when molding it can make the manufacturing process complicated. Furthermore, a gas generant composition with a low burning rate cannot be used as a gas generant for an inflator that requires rapid deployment. In addition, the gas generant composition is also required to have good ignition properties. In view of the above, an object of the present disclosure is to provide a gas generating composition that has a high burning rate and good ignition properties. [Means for solving the problem]

[0005] As a result of extensive research to solve the above problems, the inventors have found that by using basic magnesium carbonate as an additive to a gas generant composition and using one with an average particle size within a predetermined range, it is possible to obtain a gas generant composition having a high burning rate and a short ignition time. In particular, it has been found that the addition of basic magnesium carbonate to a gas generant composition containing guanidine nitrate as a fuel and a basic metal nitrate as an oxidizer increases the burning rate of the gas generant composition. Furthermore, it has been found that when the average particle size of the basic magnesium carbonate in the gas generant composition is within a predetermined range, the composition has a high burning rate and good ignition properties. In this specification, good ignition properties are synonymous with short ignition time.

[0006] The present disclosure relates to the following: [1] A gas generant composition comprising the following components (a) to (d), wherein the average particle size of the following (d) basic magnesium carbonate is 12 μm or less. (a) guanidine nitrate, (b) Basic metal nitrates (c) Binder (d) Basic magnesium carbonate [2] The content of (a) guanidine nitrate is 20% by mass or more and 60% by mass or less, the content of the (b) basic metal nitrate is 35% by mass or more and 75% by mass or less, The content of the binder (c) is 0.1% by mass or more and 10% by mass or less, The gas generant composition according to [1], wherein the content of (d) basic magnesium carbonate is 6% by mass or less. [3] The gas generant composition according to [1] or [2], wherein the (b) basic metal nitrate is basic copper nitrate, and the (c) binder is carboxymethyl cellulose. [4] The gas generating composition according to any one of [1] to [3], wherein the content of the (d) basic magnesium carbonate is 0.1 mass % or more and 6 mass % or less. [5] An inflator comprising the gas generating composition according to any one of [1] to [4]. [Effects of the Invention]

[0007] According to an embodiment of the present disclosure, a gas generant composition having a high burning rate and good ignition properties can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a graph showing the relationship between the content of basic magnesium carbonate and the burning rate of the molded gas generating composition. [Figure 2] FIG. 1 is a graph showing the relationship between the content of basic magnesium carbonate and the ignition time of the gas generating composition after molding. [Figure 3] FIG. 2 is a graph showing the relationship between the average particle size of basic magnesium carbonate and the burning rate of the gas generating composition after molding. [Figure 4] FIG. 1 is a graph showing the relationship between the average particle size of basic magnesium carbonate and the ignition time of the gas generating composition after molding. [Figure 5] FIG. 1 is a graph showing the relationship between the content of basic magnesium carbonate having an average particle size of 12 μm or 13 μm and the burning rate of the gas generant composition after molding. [Figure 6] FIG. 1 is a graph showing the relationship between the content of basic magnesium carbonate having an average particle size of 12 μm or 13 μm and the ignition time of the gas generating composition after molding. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure will be described below based on specific embodiments.

[0010] (a)Fuel The fuel (a) according to an embodiment of the present disclosure contains guanidine nitrate, which has the advantages of allowing for a reduction in the amount of oxidizer component blended due to the inclusion of oxygen in the molecule, good thermal stability, low cost, and the potential for a high gasification rate upon combustion. In the present disclosure, guanidine nitrate is preferably in a powder or granular form for ease of handling, and the lower limit of its 50% particle size is usually 5 μm or more, and in a preferred embodiment, 10 μm or more, while the upper limit is usually 80 μm or less, and in a preferred embodiment, 50 μm or less. If the 50% particle size of guanidine nitrate is too large, the strength of the gas generant composition molded article decreases, while if it is too small, significant costs are required for pulverization. In the present disclosure, the 50% particle size refers to the 50% particle size based on the number of particles measured, and can be measured, for example, by a laser diffraction / scattering method or the like.

[0011] The lower limit of the content (mixing ratio) of guanidine nitrate in the gas generant composition according to the embodiment of the present disclosure is usually 20% by mass or more, and in a preferred embodiment, 30% by mass or more, while the upper limit is usually 60% by mass or less, and in a preferred embodiment, 55% by mass or less. If the content (mixing ratio) of guanidine nitrate is less than 20% by mass, the number of moles of gas generated per 100 g of the gas generant composition decreases, and there is a tendency for excess oxygen to increase the generation of nitrogen oxides. On the other hand, if the content (mixing ratio) of guanidine nitrate exceeds 60% by mass, there is a shortage of the oxidizer component, This tends to produce a lot of harmful carbon monoxide. Furthermore, other known fuels may also be contained within the range in which the object of the present invention can be achieved. Other known fuels include at least one selected from the group consisting of tetrazole compounds including 5-aminotetrazole and bitetrazole ammonium salt; guanidine compounds including guanidine nitrate and dicyandiamide (excluding nitroguanidine); and triazine compounds including melamine, trimethylolmelamine, alkylated methylolmelamine, ammeline, ammeland, melamine nitrate, melamine perchlorate, trihydrazinotriazine, and melamine nitrate compounds.

[0012] (b) Oxidizing agent The oxidizing agent of component (b) according to an embodiment of the present disclosure contains a basic metal nitrate and, if necessary, other oxidizing agents. By using a basic metal nitrate as component (b), the combustion temperature can be lowered. The basic metal nitrate may be at least one selected from basic copper nitrate, basic cobalt nitrate, basic zinc nitrate, and basic manganese nitrate, and among these, basic copper nitrate is preferred.Other oxidizing agents may include metal nitrates, ammonium nitrate, metal perchlorates, ammonium perchlorate, metal nitrites, and metal chlorates. The content of the oxidizer relative to the gas generant composition is usually in a range of 35 mass% or more and 75 mass% or less in a preferred embodiment, and in another preferred embodiment, it is more preferable to set it in a range of 40 mass% or more and 75 mass% or less in order to particularly reduce the concentrations of carbon monoxide and nitrogen oxides in the generated gas.

[0013] (c) Binder Examples of the binder of component (c) according to an embodiment of the present disclosure include one or more selected from carboxymethyl cellulose (CMC), carboxymethyl cellulose sodium salt (CMCNa), carboxymethyl cellulose potassium salt, carboxymethyl cellulose ammonium salt, cellulose acetate, cellulose acetate butyrate (CAB), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), microcrystalline cellulose, polyacrylhydrazide, acrylamide-acrylic acid metal salt copolymer, polyacrylamide-polyacrylic acid ester compound copolymer, acrylic rubber, and silicone. Among these, CMCNa is preferred. The lower limit of the content of the binder of component (c) in the gas generant composition according to the embodiment of the present disclosure is usually 0.1 mass% or more, and in a preferred embodiment, 1 mass% or more, and the upper limit is usually 10 mass% or less, and in a preferred embodiment, 8 mass% or less.

[0014] (d) Basic magnesium carbonate The basic magnesium carbonate as component (d) according to an embodiment of the present disclosure is added to ensure a high burning rate of the gas generant composition. The content of (d) basic magnesium carbonate in the gas generant composition according to the embodiment of the present disclosure is 11% by mass or less in one preferred embodiment, 10% by mass or less in another preferred embodiment, 6% by mass or less in another preferred embodiment, less than 5% by mass in another preferred embodiment, and less than 2% by mass in yet another preferred embodiment. During combustion of the gas generant, the base of the basic magnesium carbonate promotes the rate-determining process of the combustion reaction, thereby improving ignition ability. In particular, even a relatively small amount of basic magnesium carbonate can control the pH of the entire gas generant composition, so even a content of 6 mass% or less can be sufficiently effective. On the other hand, if the content of basic magnesium carbonate exceeds 11 mass %, the burning rate and ignition ability of the gas generating composition may decrease. On the other hand, from the viewpoint of maintaining good ignition properties of the gas generating composition, the content of basic magnesium carbonate is 0.1 mass % or more in a preferred embodiment. The basic magnesium carbonate according to the embodiment of the present disclosure may be commercially available. The average particle size of the basic magnesium carbonate according to the embodiment of the present disclosure is 12 μm or less. In a more preferred embodiment, it is 11 μm or less. In order to consistently obtain the effect of improving ignition performance even with a small amount of basic magnesium carbonate during scale-up, it is necessary to increase the contact between the fuel and oxidizer and the basic magnesium carbonate. Therefore, by having an average particle size of 12 μm or less, which is equal to or smaller than the average particle size of the fuel and oxidizer, the ignition performance of the gas generant composition, particularly in a low-temperature environment, is improved. Meanwhile, the average particle size of the basic magnesium carbonate is typically 5 μm or more, and in a preferred embodiment, it is 8 μm or more. The combustion of gas generant compositions is easily affected by the external environment, and generally, ignition and continued combustion are less favorable in low-temperature environments than at room or high temperatures. In order to minimize performance differences due to temperature, it is important to improve ignition performance in low-temperature environments. The average particle size of basic magnesium carbonate can be measured using a particle size distribution analyzer that uses a laser diffraction / scattering method. Specifically, it can be measured using a precision particle size distribution analyzer (such as Microtrac HRA or 3000II manufactured by Microtrac Bell Corporation). The average particle size of basic magnesium carbonate can be adjusted during its production, for example, by controlling the initial concentration of magnesium hydroxide used as a raw material and the reaction temperature when basic magnesium carbonate is obtained by reactive crystallization using a carbonation method.

[0015] (e) Other ingredients The gas generant composition according to the embodiment of the present disclosure may contain various known additives for the purposes of adjusting the combustion rate of the gas generant composition, purifying the combustion gas, etc., to the extent that the problems of the present invention can be solved. Examples of known additives include metal oxides such as cupric oxide, iron oxide, zinc oxide, cobalt oxide, manganese oxide, molybdenum oxide, nickel oxide, bismuth oxide, silica, and alumina; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, cobalt hydroxide, and iron hydroxide; cobalt carbonate and calcium carbonate; complex compounds of metal oxides or hydroxides such as acid clay, kaolin, talc, bentonite, and diatomaceous earth; metal acid salts such as sodium silicate, mica molybdate, cobalt molybdate, and ammonium molybdate; molybdenum disulfide, calcium stearate, silicon nitride, silicon carbide, metaboric acid, boric acid, boric anhydride, and glass.

[0016] The gas generant composition according to the embodiment of the present disclosure may be substantially free of phosphate. salt "Substantially free of phosphate" means that the content of phosphate in the gas generant composition is below the detection limit. Examples of phosphates referred to in this specification include potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, calcium dihydrogen phosphate, calcium monohydrogen phosphate, tricalcium phosphate, magnesium dihydrogen phosphate, magnesium monohydrogen phosphate, trimagnesium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, and ammonium magnesium phosphate. Even if the gas generant composition according to the embodiment of the present disclosure does not contain a phosphate, the combustion temperature does not become higher than necessary. Furthermore, if the gas generant composition according to the embodiment of the present disclosure does not contain a phosphate, the ignition ability at low temperatures is improved.

[0017] The gas generant composition according to the embodiment of the present disclosure can be molded into a desired shape, such as a single-hole cylindrical body, a porous cylindrical body, or a pellet-shaped body. These molded bodies can be produced by adding and mixing water or an organic solvent to the gas generant composition, followed by extrusion molding (single-hole cylindrical body, porous cylindrical body) or compression molding using a tablet press or the like (pellet-shaped body). Since the gas generant composition according to the embodiment of the present disclosure has a high burning rate, it is not necessary to make the molded body small, and the manufacturing process is not complicated.

[0018] The gas generant composition according to the embodiment of the present disclosure or a molded article obtained therefrom can be applied to, for example, driver's seat airbag inflators, passenger seat airbag inflators, side airbag inflators, inflatable curtain inflators, knee bolster inflators, inflatable seatbelt inflators, tubular system inflators, and pretensioner inflators for various vehicles. Among these, the gas generant composition according to the embodiment of the present disclosure or a molded article obtained therefrom can be preferably applied to side airbag inflators, which require early deployment.

[0019] Furthermore, an inflator including a gas generant composition according to an embodiment of the present disclosure or a molded article obtained therefrom may be either a pyrotype in which gas is supplied only from a gas generant, or a hybrid type in which gas is supplied from both a compressed gas such as argon and a gas generant.

[0020] The gas generant composition according to the embodiment of the present disclosure or a molded article obtained therefrom can also be used as an ignition agent called an enhancer agent (or booster) for transferring the energy of a detonator or squib to a gas generant. The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope of the spirit of the present invention. The present disclosure is not limited to the embodiments, but is limited only by the scope of the claims. [Example]

[0021] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to the aspects of the following examples. <Preparation of Gas Generant Composition> Pre-molded gas generant compositions having the compositions shown in Table 1 were prepared. [Table 1] *Binder is carboxymethyl cellulose **Average particle size of basic magnesium carbonate in Example 1: 10 μm, average particle size of basic magnesium carbonate in Comparative Example 1: 14 μm

[0022] <Forming into cylindrical strands> Water was added to each of the gas generating compositions of the Examples and Comparative Examples shown in Table 1, and the mixture was extrusion-molded, cut, and dried to obtain a single-porous molded article. The obtained single-porous molded body was pulverized in an agate mortar, and the powder was passed through a wire mesh with 500 μm openings and filled into the mortar side of a predetermined mold. Next, the mixture was compressed and held at a pressure of 14.7 MPa from the punch end face using a hydraulic pump for 5 seconds, then removed and molded into a cylindrical strand with an outer diameter of 9.6±0.1 mm and a length of 12.7±1.0 mm, thereby obtaining a molded gas generating composition.

[0023] <Method for measuring burning rate> The sample cylindrical strand was placed in a 1-liter sealed stainless steel bomb, and the bomb was completely purged with nitrogen while the pressure was stabilized at 5 MPa, 7 MPa, or 9 MPa. A predetermined current was then passed through a nichrome wire in contact with the end of the strand, causing it to ignite and burn due to the resulting fusing energy. The pressure behavior over time inside the bomb was confirmed on a recorder chart, and the elapsed time from the start of combustion to the peak pressure rise was confirmed on the chart scale. The value calculated by dividing the strand length before combustion by this elapsed time was used as the combustion rate. The test results for the examples and comparative examples are shown in Table 1.

[0024] <Method for measuring ignition time> A predetermined amount of the gas generating agent for evaluation, a single-porous molded body obtained by extrusion molding, was placed in a 5cc bomb test jig and ignited with an ignition charge containing ZPP in a low-temperature environment (-35°C) or at room temperature (26°C). The time required for the pressure to reach 10% of the maximum pressure was defined as the ignition time.

[0025] A comparison of the results of Example 1 and Comparative Examples 1 and 2 in Table 1 shows that when basic magnesium carbonate is added to the gas generating composition, the burning rate increases and the ignition time decreases. Furthermore, when the results of Example 1 and Comparative Example 1 are compared, it is found that when the average particle size of the basic magnesium carbonate is 12 μm or less, the burning rate of the gas generating composition is high and the ignition time is short.

[0026] <Burning rate and ignition time when the content of basic magnesium carbonate is changed> Pre-molded gas generant compositions having the compositions shown in Table 2 were prepared. The preparation method was the same as that for the gas generant compositions in Table 1. The materials used were the same as those listed in Table 1, and the average particle size of the basic magnesium carbonate was 10 μm. These pre-molded gas generant compositions were molded into cylindrical strands in the same manner as in Example 1 above, etc., to obtain molded gas generant compositions. The burning rate and ignition time of each molded gas generant composition were measured using the methods described above. The results are shown in Table 2. The burning rate and ignition time are shown as percentages (%) of the burning rate (mm / sec) and ignition time (msec) of Comparative Example 3. The results of Examples 2 to 6 and Comparative Example 3 are summarized in Figures 1 and 2. The horizontal axis of Figure 1 shows the content of basic magnesium carbonate, and the vertical axis shows the rate of change (%) in the burning rate from Comparative Example 3. The horizontal axis of Figure 2 shows the content of basic magnesium carbonate, and the vertical axis shows the rate of change (%) in the ignition time from Comparative Example 3. [Table 2]

[0027] <Burning rate and ignition time when the average particle size of basic magnesium carbonate is changed> Pre-molded gas generant compositions having the compositions shown in Table 3 were prepared. The preparation method was the same as that of the gas generant compositions in Table 1. Materials other than the basic magnesium carbonate were the same as those listed in Table 1, with the average particle size of the basic magnesium carbonate being changed. These pre-molded gas generant compositions were molded into cylindrical strands in the same manner as in Example 1 above, etc., to obtain molded gas generant compositions. The burning rate of each molded gas generant composition was measured using the above method. The time to ignition was measured, and the results are shown in Table 3. The burning rate and ignition time are shown as percentages (%) of the burning rate (mm / sec) and ignition time (msec) of Example 9, respectively. The results of Examples 7 to 9 and Comparative Example 4 are summarized in Figures 3 and 4. The horizontal axis of Figure 3 shows the average particle size (µm) of basic magnesium carbonate, and the vertical axis shows the rate of change (%) in the burning rate from Example 9. The horizontal axis of Figure 4 shows the average particle size (µm) of basic magnesium carbonate, and the vertical axis shows the rate of change (%) in the ignition time from Example 9. [Table 3]

[0028] <Burning rate and ignition time when the average particle size of basic magnesium carbonate is changed> Pre-molded gas generant compositions having the compositions shown in Table 3 were prepared. The preparation method was the same as that for the gas generant compositions in Table 1. The materials other than the basic magnesium carbonate were the same as those listed in Table 1, with the average particle size of the basic magnesium carbonate being changed. These pre-molded gas generant compositions were molded into cylindrical strands in the same manner as in Example 1 above, etc., to obtain molded gas generant compositions. The burning rate and ignition time of each molded gas generant composition were measured using the methods described above. The results are shown in Table 3. The burning rate and ignition time are shown as percentages (%) of the burning rate (mm / sec) and ignition time (msec) of Example 9, respectively. The results of Examples 7 to 9 and Comparative Example 4 are summarized in Figures 3 and 4. The horizontal axis of Figure 3 shows the average particle size (µm) of basic magnesium carbonate, and the vertical axis shows the rate of change (%) in the burning rate from Example 9. The horizontal axis of Figure 4 shows the average particle size (µm) of basic magnesium carbonate, and the vertical axis shows the rate of change (%) in the ignition time from Example 9. [Table 3]

[0029] The results in Table 3 and Figures 3 and 4 show that when the average particle size of basic magnesium carbonate exceeds 12 μm, the burning rate drops sharply and the ignition time increases sharply. On the other hand, when the average particle size of basic magnesium carbonate is 12 μm or less, good burning rates and short ignition times were observed in all cases.

[0030] <Burning rate and ignition time when the average particle size and content of basic magnesium carbonate are changed> Basic magnesium carbonates with average particle sizes of 12 μm and 13 μm were prepared, and the content of basic magnesium carbonate in the gas generant composition was adjusted to 0.1 mass%, 2 mass%, 6 mass%, 7 mass%, and 10 mass%, to prepare pre-molded gas generant compositions having the compositions shown in Table 4. Materials other than the basic magnesium carbonate were the same as those listed in Table 1. These pre-molded gas generant compositions were molded into cylindrical strands in the same manner as in Example 1 above, etc., to obtain molded gas generant compositions. The burning rate and ignition time of each molded gas generant composition were measured using the methods described above. The results are shown in Table 4. The burning rate and ignition time are shown as percentages (%) of the burning rate (mm / sec) and ignition time (msec) of Comparative Example 5. The results of Examples 10 to 14 and Comparative Examples 5 to 10 are summarized in Figures 5 and 6. The horizontal axis of Figure 5 shows the basic magnesium carbonate content (mass%), and the vertical axis shows the rate of change (%) in the burning rate from Comparative Example 5. The horizontal axis of Figure 6 shows the basic magnesium carbonate content (mass%), and the vertical axis shows the rate of change (%) in the ignition time from Comparative Example 5. [Table 4] The results in Table 4 and Figures 5 and 6 show that when basic magnesium carbonate with an average particle size of 12 μm was used, a good burning rate and short ignition time were achieved regardless of the content. On the other hand, when basic magnesium carbonate with an average particle size of 13 μm was used, a short ignition time was not always achieved depending on the content. The results in Tables 1 to 3 and Figures 1 to 6 show that in the gas generating composition, the use of basic magnesium carbonate with an average particle size of 12 μm or less is an important requirement for achieving a good burning rate and a short ignition time. [Industrial Applicability]

[0031] According to the present disclosure, a gas generant composition having a high burning rate and a short ignition time can be provided.

Claims

1. A gas generant composition comprising the following components (a) to (d), wherein the average particle size of the following (d) basic magnesium carbonate is 7 μm or more and 12 μm or less, and the gas generant composition is substantially free of phosphate. (a) Guanidine nitrate (content is 20% by mass or more and 60% by mass or less) (b) Basic metal nitrate (content of 35% by mass or more and 75% by mass or less) (c) Binder (content is 0.1% by mass or more and 10% by mass or less) (d) basic magnesium carbonate (content of 0.1% by mass or more and 10% by mass or less)

2. 2. The gas generant composition according to claim 1, wherein the (b) basic metal nitrate is basic copper nitrate, and the (c) binder is carboxymethyl cellulose.

3. 3. The gas generant composition according to claim 1, wherein the content of the (d) basic magnesium carbonate is 0.1% by mass or more and 11% by mass or less.

4. An inflator comprising the gas generant composition according to any one of claims 1 to 3.

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