Gas Generant Composition

Abstract

To provide a gas-forming agent composition having a low combustion rate and high ignitability.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) calcium carbonate, wherein the (d) calcium carbonate content is 5 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a gas generant composition. [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 required for an airbag device to be mounted on a vehicle is that the retention time after activation be as long as possible. The retention time can be extended by adjusting the burn completion time of the inflator. The burn completion time of the inflator can be adjusted by adjusting the burn rate or shape of the gas generant composition, for example. When a certain burn completion time is targeted, if a gas generant composition with a slow burn rate is used, the shape of the gas generant composition can be made smaller. If the shape of the gas generant composition can be made smaller, a small and lightweight inflator can be provided. Therefore, technology for controlling the burn rate of the gas generant composition to be low is desired. On the other hand, from the viewpoint of the stability of the continued combustion of the gas generant composition, it is also desired that the gas generant composition have good ignition properties. In view of the above, an object of the present invention is to provide a gas generating composition that has a low 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 calcium carbonate as an additive to a gas generant composition and adding it in a predetermined amount, it is possible to obtain a gas generant composition that has a low burning rate and good ignition properties. In particular, it has been found that in a gas generant composition containing guanidine nitrate as a fuel and a basic metal nitrate as an oxidizer, the addition of calcium carbonate reduces the burning rate of the gas generant composition, while an excessively high calcium carbonate content prevents a low burning rate. It has also been found that when the calcium carbonate content in the gas generant composition is a predetermined amount, the composition has good ignition properties. In this specification, good ignition properties are synonymous with a short ignition time.

[0006] The present invention is as follows. [1] A gas generant composition comprising the following components (a) to (d), wherein the content of the following (d) calcium carbonate is 5 mass % or less. (a) guanidine nitrate, (b) Basic metal nitrates (c) Binder (d) Calcium 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 gas generant composition according to [1], wherein the content of the binder (c) is 0.1% by mass or more and 10% 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 (d) calcium carbonate is 0.1 mass % or more and 5 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 the present invention, a gas generating composition having a low burning rate and good ignition properties can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a graph showing the relationship between the content of calcium 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 calcium carbonate and the ignition time of the gas generating composition after molding. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] (a)Fuel The fuel (a) according to an embodiment of the present invention contains guanidine nitrate, which contains oxygen in its molecule, allowing for a reduction in the amount of oxidizer component added, and has other advantages, such as good thermal stability, low cost, and the potential for a high gasification rate during combustion. In the present invention, 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, preferably 10 μm or more, and the upper limit is usually 80 μm or less, preferably 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, it requires a great deal of cost for pulverization. In the present invention, the 50% particle size means the 50% particle size based on the number of measured particles, 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 an embodiment of the present invention is usually 20% by mass or more, preferably 30% by mass or more, and the upper limit is usually 60% by mass or less, preferably 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 tendency for a shortage of oxidizer components to result in the generation of large amounts 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 invention 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 is usually preferably in the range of 35% by mass or more and 75% by mass or less relative to the gas generating composition, and more preferably in the range of 40% by mass or more and 75% by mass or less in order to 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 invention 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 copolymers, polyacrylamide-polyacrylic acid ester compound copolymers, acrylic rubber, and silicone. Among these, CMCNa is preferred. The lower limit of the content of the binder (c) component in the gas generant composition of the present invention is usually 0.1 mass% or more, preferably 1 mass% or more, and the upper limit is usually 10 mass% or less, preferably 8 mass% or less.

[0014] (d) Calcium carbonate Calcium carbonate as component (d) according to an embodiment of the present invention is added to ensure a low burning rate of the gas generating composition while also ensuring a short ignition time. The content of (d) calcium carbonate in the gas generant composition of the present invention is 5% by mass or less, preferably less than 4% by mass, more preferably less than 3% by mass, and may be less than 2% by mass. When the gas generant composition is burned, the base of calcium carbonate promotes the rate-determining process of the combustion reaction, thereby improving ignition ability. In particular, calcium carbonate can control the pH of the entire gas generant composition with a relatively small amount, so a sufficient effect can be obtained even with a content of 5 mass% or less. On the other hand, if the amount of calcium carbonate added to the gas generant composition is too large, the combustion temperature during combustion tends to decrease, and as the combustion rate decreases, the ignition ability of the gas generant composition also tends to decrease. Therefore, it is important that the content of calcium carbonate in the gas generant composition according to the embodiment of the present invention is 5% by mass or less. Within this range, the ignition time is significantly improved, particularly in low-temperature environments. 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 compared to room temperature or high temperatures. Improving ignition ability in low-temperature environments is also important in order to minimize performance differences due to temperature. From the viewpoint of maintaining a low burning rate and good ignition properties of the gas generating composition, the content of calcium carbonate is preferably 0.1% by mass or more, more preferably 0.3% by weight or more, and even more preferably 0.5% by weight or more. The calcium carbonate according to the embodiment of the present invention can be commercially available.

[0015] <Other ingredients> The gas generating composition of the present invention is a gas generating composition having the following properties within a range that can solve the problems of the present invention. Various known additives may be contained for the purposes of adjusting the combustion rate, purifying the combustion gas, etc. 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, and boric acid anhydride.

[0016] The gas generant composition of the present invention 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 and then extrusion-molding the mixture (single-hole cylindrical body or porous cylindrical body) or by compression-molding the mixture using a tablet press or the like (pellet-shaped body).

[0017] The gas generant composition of the present invention 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 of the present invention or a molded article obtained therefrom can be preferably applied to side airbag inflators, which require early deployment.

[0018] Furthermore, an inflator containing the gas generant composition of the present invention or a molded article obtained therefrom may be either a pyrotype in which gas is supplied only from the gas generant, or a hybrid type in which gas is supplied from both a compressed gas such as argon and the gas generant.

[0019] The gas generant composition of the present invention or a molded article obtained therefrom can also be used as an ignition agent called an enhancer (or booster) for transmitting the energy of a detonator or squib to a gas generant. [Example]

[0020] The present invention will be specifically described below with reference to examples, but the present invention is not limited to 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

[0021] <Forming into cylindrical strands> Water was added to each gas generating composition 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.

[0022] <Method for measuring burning rate> The cylindrical strand sample was placed in a 1-liter sealed stainless steel bomb, and the bomb was completely purged with nitrogen while the pressure was stabilized at 7 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 burning rate. The test results for each example and comparative example are shown in Table 1. Note that the burning rate is not an absolute value, but rather a percentage (%) relative to the burning rate (mm / sec) of Comparative Example 1.

[0023] <Method for measuring ignition time> A predetermined amount of the gas generating agent for evaluation, which was a single-porous molded product obtained by extrusion molding, was placed in a 5 cc bomb test jig and ignited in a low-temperature environment (-35°C) using an ignition charge containing ZPP. The time required for the pressure to reach 10% of the maximum pressure was defined as the ignition time. Note that the ignition time is not an absolute value, but rather a ratio (%) to the ignition time (msec) of Comparative Example 1.

[0024] A comparison of the results of Examples 1 and 2 with those of Comparative Example 1 in Table 1 reveals that when calcium carbonate is added to the gas generating composition, the burning rate decreases and the ignition time decreases. Comparing the results of Examples 1 and 2 with those of Comparative Examples 2 to 5, it was found that when the calcium carbonate content was 5% by mass or less, the burning rate of the gas generant composition was low and the ignition time was short. On the other hand, when the calcium carbonate content exceeded 5% by mass, the low burning rate and short ignition time of the gas generant composition were not obtained.

[0025] <Preparation of Comparative Examples 3 to 5> 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. 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 1. The results of Examples 1 and 2 and Comparative Examples 1 to 5 are summarized in Figures 1 and 2. The horizontal axis of Figure 1 shows the calcium carbonate content, and the vertical axis shows the rate of change (%) in the burning rate from Comparative Example 1. The horizontal axis of Figure 2 shows the calcium carbonate content, and the vertical axis shows the rate of change (%) in the ignition time from Comparative Example 1. [Table 2]

[0026] From the results in Tables 1 and 2 and Figures 1 and 2, it was found that when the content of calcium carbonate in the gas generant composition exceeds 5% by weight, the burning rate decreases, but the ignition time becomes significantly longer than in Examples 1 and 2. In other words, it was confirmed that a reduction in the burning rate and a short ignition time can only be achieved if the content of calcium carbonate is 5% by weight or less. [Industrial Applicability]

[0027] According to the present invention, a gas generant composition having a low burning rate and a short ignition time can be provided.

Claims

1. A gas generant composition comprising the following components (a) to (d): (a) the content of guanidine nitrate is 20% by mass or more and 60% by mass or less; The content of the following (b) basic metal nitrate is 35% by mass or more and 75% by mass or less, The content of the following (c) binder is 0.1% by mass or more and 10% by mass or less, A gas generating composition having a calcium carbonate content of 2.7 mass % or more and 4.9 mass % or less as follows: (d) (a) guanidine nitrate, (b) Basic metal nitrates (c) Binder (d) calcium carbonate

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. An inflator comprising the gas generant composition of claim 1 or 2.

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