Composite propellant

Abstract

To provide a composite propellant which is improved in both combustion characteristics and manufacturability and has high flowability.SOLUTION: A composite propellant contains a hydroxyl-terminated polybutadiene, ammonium perchlorate, and an iron oxide having a tap density of 0.3-1.3 g / ml. This composite propellant enables the improvement in both combustion characteristics and manufacturability and a high flowability by using the iron oxide having the tap density of 0.3-1.3 g / ml as a combustion catalyst in the propellant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composite propellant having good manufacturability and combustion characteristics. [Background technology]

[0002] Composite propellants are widely used as propellants for high-performance rocket motors due to their excellent combustion and physical properties. Composite propellants are primarily composed of an oxidizer and a binder, which acts as both a fuel and a binder. Metal powder is typically added as a combustion improver to improve combustion performance. Examples of oxidizers include ammonium perchlorate, nitramine, and ammonium nitrate. Examples of binders include polybutadiene and polyurethane. Examples of combustion improvers include aluminum powder.

[0003] In recent years, in order to expand the design range and improve the performance of rocket motors, there has been a demand for a wide range of burn rates for composite propellants, and combustion catalysts are added as additives to achieve this. Granular or rod-shaped iron oxide is widely known as an additive that increases the burn rate of composite propellants containing ammonium perchlorate.

[0004] Generally, the relationship between the burning rate of a propellant and the combustion pressure is given by equation (1): r=aP n -(1) It is empirically known that the burning rate r can be expressed as follows (where r is the burning rate, P is the burning pressure, n is the pressure exponent, and a is a constant determined by the type of propellant). This equation means that when the pressure exponent n is large, a slight increase in pressure P results in a large exponential increase in the burning rate r. In other words, if an abnormality such as a crack occurs accidentally in the propellant and the pressure inside the rocket motor deviates from the set value, the burning rate will differ significantly from the desired value. Furthermore, a sudden increase in the burning rate may even lead to an explosion. Therefore, to avoid this and control the burning rate to achieve stable combustion, it is desirable to use a propellant with a smaller pressure exponent.

[0005] However, conventional composite propellants using iron oxide require an increased amount of iron oxide to increase the burning rate, which is known to cause problems such as reduced manufacturability. To solve this problem, various studies have been conducted to improve manufacturability and combustion characteristics while increasing the burning rate by changing the particle size and shape of the iron oxide.

[0006] Such a propellant is disclosed, for example, in Patent Document 1 as a composite solid propellant containing a binder and an oxidizer as main components, characterized in that it contains rod-shaped iron oxide having a length-to-diameter ratio of 1000 or less, a length of 10 μm or less, and a diameter of 0.01 μm or more.

[0007] However, in the composite propellant of Patent Document 1, which uses rod-shaped iron oxide of different lengths and diameters, although the burning rate as a combustion characteristic is improved, the pot life as a manufacturability characteristic is insufficient. In addition, among the manufacturability characteristics, the flowability, which indicates the ease of casting, could not be improved even when rod-shaped iron oxide of different lengths and diameters was used. Therefore, there has been a demand for a composite propellant that uses iron oxide as a combustion catalyst and improves manufacturability while maintaining the combustion characteristics. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 3-97687 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a composite propellant which has improved combustion characteristics, manufacturability, and high fluidity. [Means for solving the problem]

[0010] As a result of intensive investigation into the above-mentioned problems, the inventors discovered that in a composite propellant containing a binder primarily composed of hydroxyl-terminated polybutadiene and an oxidizer composed of ammonium perchlorate, the addition of iron oxide having a tap density of 0.3 to 1.3 g / ml as a combustion catalyst, and further setting the proportion of iron oxide to a specific ratio, can result in a composite propellant that has both improved combustion characteristics and manufacturability and also has high fluidity, and have completed the present invention. That is, the present invention is the following composite propellant.

[0011] [1] A composite propellant comprising hydroxyl-terminated polybutadiene, ammonium perchlorate, and iron oxide having a tap density of 0.3 to 1.3 g / ml. [2] 2. The composite propellant according to claim 1, wherein the content of the iron oxide is 0.006 to 0.5 mass % with respect to the total amount of the composite propellant. [Effects of the Invention]

[0012] The composite propellant of the present invention uses iron oxide with a tap density of 0.3 to 1.3 g / ml as a combustion catalyst in the propellant, thereby improving both combustion characteristics and manufacturability, and providing a composite propellant with high fluidity. Furthermore, by setting the ratio of iron oxide to the propellant to 0.006 to 0.5 mass%, these effects can be further enhanced. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Composite propellant] The composite propellant of the present invention is used, for example, as a propellant for high-performance rocket motors, and has a basic composition consisting of ammonium perchlorate as an oxidizer, hydroxyl-terminated polybutadiene in a binder, a bonding agent, and a curing agent, while also containing aluminum powder as a combustion improver and iron oxide as an additive. Depending on the application, other additives may be added.

[0014] <Hydroxyl-terminated polybutadiene> When manufacturing a composite propellant, the binder contains hydroxyl-terminated polybutadiene (HTPB) as a fuel and binder, hydroxyl-terminated polyethers having azidomethyl groups, such as glycidyl azide polymer (GAP), and 3,3-bisazidomethylmethyloxetane / tetrahydrofuran copolymer (BAMO / THF copolymer), etc. Among these, the present invention prefers the use of hydroxyl-terminated polybutadiene (HTPB), which is widely used in general composite propellants.

[0015] The hydroxyl-terminated polybutadiene according to the present embodiment is, for example, a hydroxyl-terminated polybutadiene having an average of 2 to 4 hydroxyl groups at the molecular terminals and a number average molecular weight of 2000 to 4000. The content of the hydroxyl-terminated polybutadiene is usually 50 to 90% by mass, preferably 60 to 85% by mass, of the total amount of the binder. An example of commercially available hydroxyl-terminated polybutadiene is "Poly bd R-45M" (manufactured by Total Petrochemicals & Refining USA Inc.).

[0016] <Oxidizing agent> When producing a composite propellant, ammonium perchlorate (AP), cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetetranitramine (RDX), ammonium nitrate, etc. are used as oxidizers. The oxidizer of the present invention is ammonium perchlorate (manufactured by Nippon Carlit Co., Ltd.), but it does not necessarily have to be a single oxidizer and may contain multiple oxidizers. The oxidizer content is at least 50% by mass, and preferably 60% by mass or more, of the total amount of the propellant.

[0017] Furthermore, the oxidizer may have a plurality of different particle sizes to adjust the propellant viscosity to facilitate the casting process, adjust the burning rate, and chemically bond with the binder to improve physical properties. The oxidizer particles are preferably small particles with an average particle size of 1 to 60 μm, medium particles with an average particle size of 150 to 300 μm, and large particles with an average particle size of 350 to 600 μm, each in two types (large / medium), large / small, or medium / small, or three types (large / medium / small). From the perspectives of adjusting the viscosity of the composite propellant to facilitate the casting process, adjusting the burning rate, and chemically bonding with the binder to improve physical properties, it is particularly preferable to mix 20 to 60% by mass of each of the two medium / large types and 10 to 30% by mass of one small type relative to 100% by mass of oxidizer. The average particle size is measured using a "Microtrac particle size distribution analyzer" (manufactured by Nikkiso).

[0018] <Iron oxide> When producing a composite propellant, examples of iron oxide include FeO, Fe2O3, and Fe3O4. Among these, Fe2O3 is preferred in the present invention. While the particle shape and particle size of the iron oxide are not particularly limited, the tap density of the iron oxide to be blended must be 0.3 to 1.3 g / ml. A tap density of less than 0.3 g / ml increases dispersibility within the propellant, reduces particle repulsion, and increases the fluidity of the propellant. This reduces the initial viscosity of the propellant and tends to result in a longer pot life than desired. Furthermore, increased dispersibility within the propellant results in the iron oxide's effect of increasing the decomposition rate within the propellant manifesting throughout the propellant, tending to increase the burn rate and pressure index. A tap density greater than 1.3 g / ml reduces the dispersion of the iron oxide within the propellant, increases particle repulsion, reduces the fluidity of the propellant, and increases the initial viscosity of the propellant, tending to result in a shorter pot life than desired. Furthermore, if the iron oxide becomes difficult to disperse within the propellant, the effect of increasing the decomposition rate of the iron oxide within the propellant will appear locally, and although the pressure exponent will decrease, the burning rate will tend not to increase.From the viewpoint of improving the fluidity of the propellant, the upper limit of the tap density is preferably 1.0 g / ml.

[0019] The tap density of iron oxide is calculated by weighing a predetermined amount of iron oxide, putting it into a measuring cylinder of a predetermined volume, tapping it under predetermined tapping conditions, measuring the volume of the iron oxide after tapping, and dividing the mass of the iron oxide by the volume of the iron oxide after tapping (apparent volume). The tap density is measured according to JIS K The test was carried out in accordance with the pigment test method specified in 5101:2004.

[0020] The iron oxide content is preferably 0.006 to 0.5% by mass, and more preferably 0.01 to 0.4% by mass, based on the total amount of propellant. Furthermore, from the viewpoint of improving the fluidity of the propellant, the upper limit of the iron oxide content is preferably 0.3% by mass or less, and more preferably 0.1% by mass or less. If the iron oxide content is 0.006% by mass or less based on the total amount of propellant, the effect of increasing the burning rate is small, and if it exceeds 0.5% by mass, manufacturability decreases and the pressure index tends to increase. Examples of commercially available iron oxides include R-516-L (particle size: length 0.7 × diameter 0.07 μm, manufactured by Titan Kogyo Co., Ltd.), R2899 (average particle size: 0.3 μm, manufactured by HUNTSMAN Corporation), Bayferrox 140 (average particle size: 0.3 μm, manufactured by LANXESS Deutschland GmbH), and Bayferrox 180 (average particle size: 1.5 μm, manufactured by LANXESS Deutschland GmbH). If the desired tap density cannot be obtained with commercially available iron oxide, iron oxide having the desired tap density can be obtained by classification according to a wet sedimentation classification method.

[0021] <Binder> The binder is added for the purpose of imparting adhesion to the oxidizer particles. When manufacturing composite propellants, the binder used is aziridine, such as tris[1-(2-methyl)-aziridinyl]phosphine oxide (MAPO) or bisisophthaloyl 1-(2-methyl)aziridine (HX-752). system, N amine-based compounds such as ethyldiethanolamine (EDA), reaction products of tetraethylenepentamine and acrylonitrile (TEPAN or HX-879), reaction products of tetraethylenepentamine, acrylonitrile and glycidol (TEPANOL or HX-878); hydantoin-based compounds such as dihydroxyethyl-5,5-dimethylhydantoin (DHE); and silane coupling agents (A-1100). do.

[0022] <Curing agent> When producing a composite propellant, examples of the curing agent include diisocyanate compounds such as isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), dicyclohexylmethane-4,4-diisocyanate (hydrogenated MDI), etc. Among these, isophorone diisocyanate (IPDI) is preferred in the present invention.

[0023] The content of the curing agent, expressed as the equivalent ratio of isocyanate group to hydroxyl group in terms of NCO / OH, is in the range of 0.7 to 1.1, preferably 0.8 to 1.0.

[0024] <Combustion improver> Examples of combustion improvers include powders of metals such as aluminum, boron, magnesium, etc. Among these, aluminum powder is preferably used in the present invention. Examples of aluminum powder include X-65 (manufactured by Toyal America, Inc.) and H-5 (manufactured by VALIMET, Inc.).

[0025] <Other additives> In addition, additives may be added depending on the combustion characteristics, physical properties, and manufacturability required of the composite propellant. Examples of plasticizers that can be used include esters such as dioctyl adipate (DOA), dioctyl sebacate (DOS), diisodecyl adipate (DIDA), and isodecyl pelagonate, as well as nitroplasticizers such as 1,2,4-butanetriol trinitrate (BTTN), trimethylolethane trinitrate (TMETN), and triethylene glycol dinitrate (TEGDN). Among these, dioctyl adipate (DOA) is preferred for use in the present invention.

[0026] Examples of the curing catalyst include organotin compounds such as dibutyltin dilaurate (DBTDL) and dibutyltin di(2-ethylhexoate), organobismuth compounds such as triphenylbismuth, and amines such as triethylenediamine.

[0027] Examples of antioxidants include 2,2'-methylene-bis(4-methyl-6-t-butylphenol), phenyl-β-naphthylamine, and reaction products of diphenylamine and acetone (Nonflex BA, manufactured by Seiko Chemical Co., Ltd.).

[0028] [Composite propellant manufacturing method] The method for producing a composite propellant of the present invention is characterized by adding iron oxide having a tap density of 0.3 to 1.3 g / ml, thereby providing a method for producing a composite propellant with excellent manufacturability.

[0029] When producing the composite propellant of the present invention, for example, the raw materials and, if necessary, various additives are placed in a mixer so as to have predetermined contents, and the mixture is uniformly mixed at a predetermined temperature to form a slurry. The mixture is then poured into a predetermined mold and cured at a predetermined temperature for a predetermined time, thereby producing the composite propellant. [Example]

[0030] The composite propellant of the present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the scope of these examples. The abbreviations in Tables 1 and 2 have the following meanings. HTPB: Hydroxyl-terminated polybutadiene MAPO: Tris[1-(2-methyl)-aziridinyl]phosphine oxide MDA: N-methyldiethanolamine IPDI: Isophorone diisocyanate DOA: Dioctyl adipate

[0031] <Examples 1 to 5> The compounding compositions of the composite propellants of Examples 1 to 5 are shown in Table 1. In addition, the manufacturability and combustion characteristics of the composite propellants of Examples 1 to 5 were measured by the methods described below, and the results are also shown in Table 1.

[0032] [Table 1]

[0033] [Manufacturability] <Liquidity> A cylindrical core with an outer diameter of 40 mm was attached to the bottom plate of a predetermined casting mold, and a piece of ABS resin with an outer diameter of 84 mm, an inner diameter of 80 mm, and a length of 140 mm was applied to the inner surface of the casting mold. The composite propellant slurry of each example and comparative example was then poured into the mold, and the ease of pouring into the mold was evaluated according to the following evaluation criteria. ◎: The propellant slurry had high fluidity and was extremely easy to cast. 〇: The propellant slurry had good fluidity and could be easily poured. △: The fluidity of the propellant slurry was poor, and it took time to cast.

[0034] <Pot life> Using an RE80 viscometer, the viscosity was measured at specified intervals at 54°C with a spindle rotation speed of 5 rpm, and the pot life was calculated as the time from when the curing agent was added until the viscosity reached 1 kPa·s at 54°C. The calculated pot life is preferably between 500 and 900 minutes. A pot life of less than 500 minutes is short, making casting difficult, while a pot life of more than 900 minutes is undesirable because the pot life is long, curing does not complete within the specified curing time, and physical properties change due to post-curing.

[0035] [Combustion characteristics] A cylindrical core with an outer diameter of 40 mm was attached to the bottom plate of a specified casting mold. A sheet of ABS resin with an outer diameter of 84 mm, an inner diameter of 80 mm, and a length of 140 mm was applied to the inner surface of the casting mold. The propellant slurry was poured into the mold and allowed to harden. After demolding, a cylindrical propellant with a diameter of 80 mm, an inner diameter of 40 mm, and a length of 140 mm was formed. The propellant was then processed to be flush with the ABS resin. The propellant web (thickness from the propellant bore surface to the outer surface of the ABS resin minus the thickness of the ABS resin) was recorded. The prepared propellant was loaded into a standard rocket motor chamber with an inner diameter of 84 mm, and the nozzle throat diameter was adjusted to combustion pressures of 6.86, 8.83, and 10.79 MPa. Combustion tests were conducted using a standard small rocket motor combustion stand device as specified. The time periods for 10% (early combustion) and 75% (late combustion) of the maximum pressure (excluding the initial peak pressure) were calculated from the pressure-time curves obtained in the combustion tests. The difference between these values ​​was taken as the average combustion time tb, and the propellant's burning rate rb (rb = Web / tb) was calculated from the propellant's Web and tb. Furthermore, since it is empirically known that the logarithm of the average combustion pressure Pb, obtained by dividing the integral value of each pressure-time curve in the tb section by tb, and the logarithm of rb obtained at each combustion pressure have an approximately linear relationship using equation (1), the slope n (pressure exponent) of this line was calculated. The nozzle throat diameter was then adjusted so that the combustion pressure was 8.83 MPa, and the burning rate at 8.83 MPa was calculated using the calculated rb, Pb, and pressure exponent n.

[0036] Example 1 11.55 parts by mass of hydroxyl-terminated polybutadiene (HTPB) (number of terminal hydroxyl groups: average 2.3, average molecular weight: 2800) (content in the binder: 82.5% by mass; same below), and 1.39 parts by mass (9.9% by mass) of dioctyl adipate (DOA) as a plasticizer were added and mixed. A predetermined amount of aluminum powder as a combustion improver was added and mixed, and 0.02% by mass of iron oxide (Fe2O3) with a tap density of 0.4 g / ml was added and mixed as a combustion catalyst. Later,0.1 parts by mass (0.7% by mass) of thris[1-(2-methyl)-aziridinyl]phosphine oxide (MAPO) and 0.03 parts by mass (0.2% by mass) of N-methyldiethanolamine (MDA) were added and mixed.

[0037] Next, 0.94 parts by mass (6.7% by mass) of isophorone diisocyanate (IPDI) as a curing agent was added and mixed under vacuum, after which a predetermined amount of ammonium perchlorate as an oxidizing agent was added and heated to 54°C, followed by vacuum mixing to obtain a slurry mixture. This mixture was then poured into a predetermined container under reduced pressure, degassed, and cured at 54°C for 12 days to obtain a composite propellant.

[0038] Examples 2 and 3 Composite propellants were manufactured in the same manner as in Example 1 for cases where the tap density of the combustion catalyst, iron oxide (Fe2O3), was set to 0.8 g / ml (Example 2) and 1.2 g / ml (Example 3), and their manufacturability and combustion characteristics were measured.

[0039] Examples 4 and 5 A composite propellant was produced in the same manner as in Example 1, except that the blending amount of iron oxide (Fe2O3) with a tap density of 0.4 g / ml was changed as shown in Table 1, and its manufacturability and combustion characteristics were measured.

[0040] <Comparative Examples 1 to 6> Composite propellants according to Comparative Examples 1 to 6 were produced using the propellant blend compositions shown in Table 2 in the same manner as in Examples 1 to 5. The manufacturability and combustion characteristics of the composite propellants were measured, and the results are shown in Table 2.

[0041] [Table 2]

[0042] Comparative Example 1 A composite propellant was produced in the same manner as in Example 1, except that iron oxide (Fe2O3) was not added, and its manufacturability and combustion characteristics were measured.

[0043] Comparative Examples 2 to 6 Composite propellants were manufactured using the formulations shown in Table 2 in the same manner as in Example 1, for the cases where iron oxide (Fe2O3) with a tap density of 0.2 g / ml was used instead of iron oxide (Fe2O3) with a tap density of 0.4 g / ml (Comparative Examples 2 to 4), and where iron oxide (Fe2O3) with a tap density of 1.5 g / ml was used (Comparative Examples 5 and 6), and their manufacturability and combustion characteristics were measured.

[0044] The test results in Table 1 reveal the following: The composite propellants of Examples 1 to 5 maintained high fluidity and all had pot lives of 500 minutes or more and 900 minutes or less, demonstrating good manufacturability. Furthermore, they exhibited good burning rates of 7.0 to 12.0 mm / s and pressure exponents of 0.4 or less, confirming that they also had good combustion characteristics.

[0045] On the other hand, as shown in Table 2, Comparative Example 1, which did not contain iron oxide, had no problems with fluidity and pressure index, but had a lower burning rate than any of the composite propellants of Examples 1 to 5 and a pot life exceeding 900 minutes, indicating problems due to post-curing. Comparative Examples 2 and 3, which contained iron oxide with a tap density of 0.2 g / ml, had no problems with combustion characteristics and fluidity, but had a pot life exceeding 900 minutes, indicating problems due to post-curing. Comparative Example 4, which contained iron oxide with a tap density of 0.2 g / ml, had no problems with fluidity or manufacturability, but had a burning rate exceeding 12.0 mm / s and a pressure index exceeding 0.4, indicating problems with combustion characteristics. Comparative Example 5, which contained iron oxide with a tap density of 1.5 g / ml, had no problems with pot life and pressure index, but had a lower burning rate than any of the composite propellants of Examples 1 to 5, indicating problems with fluidity. In Comparative Example 6, which contained iron oxide with a tap density of 1.5 g / ml, there was no problem with the combustion characteristics, but the fluidity was low and the pot life was less than 500 minutes, which indicated a problem with manufacturability.

[0046] The above results clarified that in order to obtain a composite propellant with improved combustion characteristics, manufacturability, and high fluidity, it is essential to use iron oxide with a tap density of 0.3 to 1.3 g / ml, and that the content of the iron oxide relative to the total amount of the composite propellant is preferably 0.006 to 0.5 mass%.

Claims

[Claim 1] A composite propellant comprising: a binder containing hydroxyl-terminated polybutadiene; ammonium perchlorate; and iron oxide having a tap density of 0.3 to 0.8 g / ml as measured in accordance with JIS K5101; The content of the hydroxyl-terminated polybutadiene is 50 to 90 mass % of the total amount of the binder, The content of the ammonium perchlorate is 50% by mass or more based on the total amount of the composite propellant, A composite propellant characterized in that the content of the iron oxide is 0.006 to 0.1 mass% relative to the total amount of the composite propellant.

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