Composite propellant

Abstract

To provide a composite propellant having excellent manufacturability and good mechanical properties.SOLUTION: A composite propellant contains hydroxyl-terminated polybutadiene (HTPB), ammonium perchlorate (AP) and a phosphate, wherein the content of the phosphate is 0.02-0.50% by mass. This invention makes it possible to provide a composite propellant having excellent manufacturability and good mechanical properties by the addition of 0.02 to 0.50 mass% of phosphate to a composite propellant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composite propellant having excellent manufacturability and good mechanical properties. [Background technology]

[0002] Composite propellants are widely used as rocket motor propellants due to their excellent combustion and mechanical properties. Composite propellants are primarily composed of an oxidizer and a binder, which acts as both a fuel and a binder. Metal powder is usually added as a combustion improver to improve combustion performance. Examples of oxidizers include ammonium perchlorate (AP), nitramine, and ammonium nitrate. Examples of binders include polybutadiene and polyurethane, and examples of combustion improvers include aluminum powder.

[0003] Composite propellant manufacturing methods can be broadly divided into direct loading and block bonding. Direct loading involves mixing the raw materials of the composite propellant until they become a slurry, then pouring the mixture into a motor case and thermally curing it. For composite propellants manufactured using the direct loading method, manufacturability—i.e., the fluidity of the composite propellant slurry—is a key factor. During pouring, the motor case is depressurized to prevent air bubbles from being mixed into the composite propellant slurry, but tiny air bubbles can still be mixed in. The mixed air bubbles are compressed and collapsed when the motor case is returned to normal pressure. However, if the composite propellant slurry has lost its fluidity at that point, it will harden while still containing the air bubbles. This type of composite propellant results in unstable combustion and reduced mechanical properties. Therefore, good manufacturability is required for composite propellants.

[0004] On the other hand, the composite propellant filled in the motor case is subjected to various loads during manufacturing, storage, and firing, so the composite propellant must have sufficient mechanical properties to withstand these external loads.

[0005] Given the above background, composite propellants are desired to have both excellent manufacturability and mechanical properties.

[0006] For example, Patent Document 1 discloses a composite propellant that uses inexpensive, general-purpose hydroxyl-terminated liquid polybutadiene and a hexamethylene diisocyanate-based curing agent. While this document acknowledges improvements in elongation properties, the strain at maximum stress relative to the modulus of elasticity is significantly reduced, and although the range of raw material options has expanded, the mechanical properties are not sufficient. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-11624 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a composite propellant having excellent manufacturability and good mechanical properties. [Means for solving the problem]

[0009] As a result of intensive research into the above-mentioned problems, the inventors discovered that excellent manufacturability and good mechanical properties can be achieved by containing a binder containing hydroxyl-terminated polybutadiene (HTPB), ammonium perchlorate (AP), and a phosphate, with the phosphate content limited to 0.02 to 0.50 mass%, and thus completed the present invention. That is, the present invention is the following composite propellant.

[0010] A composite propellant comprising a binder containing hydroxyl-terminated polybutadiene (HTPB), ammonium perchlorate (AP), and a phosphate, the phosphate content being 0.02 to 0.50 mass%. [Effects of the Invention]

[0011] According to the composite propellant of the present invention, by adding 0.02 to 0.50 mass% of phosphate to the composite propellant, it is possible to provide a composite propellant with excellent manufacturability and good mechanical properties. Furthermore, by setting the proportion of phosphate to 0.05 to 0.50 mass%, these effects can be further exhibited. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Composite propellant] The composite propellant of the present invention is used as an auxiliary booster for large rockets and as the main fuel for medium and small rockets. It contains a binder whose basic composition is hydroxyl-terminated polybutadiene (HTPB) as the main raw material, a binding agent, and a curing agent, ammonium perchlorate (AP) as an oxidizer, aluminum powder as a combustion improver, and phosphate and iron oxide as additives. Other additives can be added depending on the application. The composite propellant of the present invention can simultaneously achieve both excellent manufacturability and good mechanical properties.

[0013] Items used to evaluate manufacturability include fluidity and pot life. Fluidity refers to the fluidity of the composite propellant slurry immediately after mixing, and is evaluated by the distance the composite propellant slurry flows at a specified temperature. For example, if the distance traveled in 5 minutes at 52°C is 140 mm or more, the fluidity is high and casting is deemed easy. Casting is possible when the distance is 120 mm or more or less than 140 mm, but if it is less than 120 mm, there is a high risk of air bubbles being entrained during casting. The time during which the composite propellant slurry has fluidity that allows it to be poured without entraining large air bubbles is referred to as the pot life. There are no particular limitations on the pot life, but it is preferably 500 minutes or more and less than 950 minutes. A pot life of 500 minutes or more can prevent the composite propellant from hardening during the pouring process. On the other hand, a pot life of less than 950 minutes has the effect of allowing the composite propellant to harden quickly after pouring, thereby improving productivity. From the perspective of even better productivity, the upper limit of the pot life is preferably less than 800 minutes.

[0014] Regarding mechanical properties, the elastic modulus is not particularly limited, but is, for example, 3 MPa or more and 11 MPa or less. Preferably, it is 4 MPa or more and 9 MPa or less. When it is 3 MPa or more, it has sufficient strength and can withstand various loads. When it is 11 MPa or less, the elongation properties are improved and it becomes less likely to break. The maximum elongation under load of the composite propellant of the present invention is not particularly limited, but is, for example, 25% or more. It is preferably 30% or more, and more preferably 40% or more. If it is 25% or more, it can deform in response to the load and is less likely to break. The true stress of the composite propellant of the present invention is not particularly limited, but is, for example, 0.8 MPa or more, preferably 0.9 MPa or more, and more preferably 1.0 MPa or more. At 0.8 MPa or more, the composite propellant can withstand various loads.

[0015] <Binder> The composite propellant of the present invention comprises a binder containing a fuel / binder, a binder, a curing agent, and a plasticizer. The binder is a component for binding the oxidizer, combustion improver, and other components. The binder content of the total composite propellant is typically 7 to 25 mass%. Each component in the binder will be described below.

[0016] (fuel and binder) Examples of fuel / binder materials include hydroxyl-terminated polybutadiene (HTPB), hydroxyl-terminated polyethers having azidomethyl groups, such as glycidyl azide polymer (GAP), and 3,3-bisazidomethyloxetane / tetrahydrofuran copolymer (BAMO / THF copolymer).

[0017] The binder used in the composite propellant of the present invention contains hydroxyl-terminated polybutadiene (HTPB). The content of hydroxyl-terminated polybutadiene (HTPB) in the binder is not particularly limited, but is, for example, 50 to 90% by mass. The lower limit is preferably 60% by mass or more, and the upper limit is preferably 85% by mass or less.

[0018] The hydroxyl-terminated polybutadiene (HTPB) according to this embodiment is, for example, a hydroxyl-terminated polybutadiene (HTPB) having an average of 2 to 4 hydroxyl groups at the molecular terminals and a number average molecular weight of 2000 to 4000. The number average molecular weight (Mn) was measured by the VPO method.

[0019] (binder) Examples of binders include aziridines such as tris[1-(2-methyl)-aziridinyl]phosphine oxide (MAPO) and bisisophthaloyl 1-(2-methyl)aziridine (HX-752), amines such as N-methyldiethanolamine (MDA), N-ethyldiethanolamine (EDA), reaction products of tetraethylenepentamine and acrylonitrile (TEPAN or HX-879), and reaction products of tetraethylenepentamine, acrylonitrile, and glycidol (TEPANOL or HX-878), hydantoins such as dihydroxyethyl-5,5-dimethylhydantoin (DHE), and silane coupling agents (A-1100). do.

[0020] The content of tris[1-(2-methyl)-aziridinyl]phosphine oxide (MAPO) relative to the total amount of the binder is preferably 0.3 to 0.8% by mass, and more preferably 0.5 to 0.7% by mass. When the content of tris[1-(2-methyl)-aziridinyl]phosphine oxide (MAPO) relative to the total amount of the binder is 0.3% by mass or more, the tensile strength of the composite propellant is improved, and when it is 0.8% by mass or less, the elongation of the composite propellant is improved.

[0021] The content of tris[1-(2-methyl)-aziridinyl]phosphine oxide (MAPO) relative to the total amount of the composite propellant is preferably 0.04 to 0.18 mass%, more preferably 0.07 to 0.12 mass%, and even more preferably 0.08 to 0.10 mass%.

[0022] The content of N-methyldiethanolamine (MDA) relative to the total amount of the binder is preferably 0.1 to 0.5% by mass, and more preferably 0.2 to 0.4% by mass. When the content of N-methyldiethanolamine (MDA) relative to the total amount of the binder is 0.1% by mass or more, the elongation percentage of the physical properties of the composite propellant is improved, and when it is 0.5% by mass or less, the tensile strength of the physical properties of the composite propellant is improved.

[0023] (hardening agent) 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.

[0024] The content of the curing agent, expressed as the ratio of isocyanate groups to hydroxyl groups in the fuel / binder, is preferably in the range of isocyanate groups / hydroxyl groups=0.6 to 1.1, more preferably 0.7 to 1.0.

[0025] (plasticizer) Examples of plasticizers that can be used include esters such as dioctyl adipate (DOA), dioctyl sebacate (DOS), diisodecyl adipate (DIDA), and isodecyl pelargonate, 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. The content of the plasticizer relative to the total amount of the binder is preferably 1 to 20% by mass, and more preferably 5 to 15% by mass.

[0026] <Oxidizing agent> Examples of oxidizers that can be used include ammonium perchlorate (AP), cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetetranitramine (RDX), and ammonium nitrate. The oxidizer of the present invention contains ammonium perchlorate (AP) as an essential component, but it does not necessarily need to contain only one of the above oxidizers. The oxidizer content is at least 50% by mass, preferably 60% by mass, of the total amount of the composite propellant. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0027] Furthermore, the oxidizer may have a plurality of different particle sizes to adjust the viscosity of the composite propellant to facilitate the casting process, adjust the burning rate, and chemically bond with the binder to improve mechanical properties. The oxidizer particles are preferably small particles with an average particle size of 1 to 30 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 mechanical properties, it is particularly preferable to mix 10 to 30% by mass of each of the small and large types and 40 to 80% by mass of one medium type per 100% by mass of oxidizer. The average particle size is measured using a "Microtrac particle size distribution analyzer" (manufactured by Nikkiso).

[0028] <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. The content of the combustion improver is not particularly limited, but is, for example, 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less, relative to the total amount of the composite propellant. The lower limit is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more.

[0029] <Phosphate> When producing a composite propellant, examples of phosphates include tricalcium phosphate, tetracalcium phosphate, octacalcium phosphate, monomagnesium phosphate, dimagnesium phosphate, trimagnesium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate. Among these, tricalcium phosphate is preferred in the present invention. The shape and particle size of tricalcium phosphate are not particularly limited, but the content must be 0.02 to 0.50 mass% of the total amount of the composite propellant. Furthermore, the effects of the present invention are further enhanced by setting the content to 0.05 to 0.50 mass%.

[0030] <Other additives> In addition, additives may be added depending on the combustion characteristics, mechanical properties, and manufacturability required of the composite propellant.

[0031] 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.

[0032] Examples of antioxidants include 2,2'-methylene-bis(4-methyl-6-t-butylphenol), phenyl-β-naphthylamine, and reaction products of diphenylamine and acetone.

[0033] Examples of the burning rate modifier include iron oxide, ferrocene derivatives, carborane derivatives, lead salts, carbon, etc. Among these, iron oxide (Fe2O3) is preferred in the present invention. The content of the burn rate modifier is not particularly limited, but is, for example, 0.01 to 0.1% by mass relative to the total amount of the composite propellant.

[0034] [Composite propellant manufacturing method] The method for producing a composite propellant of the present invention is characterized in that 0.02 to 0.50 mass % of a phosphate is added to the total amount of the composite propellant, thereby providing a method for producing a composite propellant with excellent manufacturability.

[0035] When producing the composite propellant of the present invention, for example, the raw materials and, if necessary, various additives are charged into 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]

[0036] 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.

[0037] <Examples 1 to 6> The compounding compositions of the composite propellants of Examples 1 to 6 are shown in Table 1. The manufacturability and mechanical properties of the composite propellants were measured using the methods described below. The results are also shown in Table 1.

[0038] Example 1 578.6 g of hydroxyl-terminated polybutadiene (HTPB) (82.7% by mass in the binder; the same applies below) was mixed with 69.4 g (9.9% by mass) of dioctyl adipate (DOA) as a plasticizer and 6.0 g of tricalcium phosphate. 900.0 g of aluminum powder as a combustion improver was added and mixed, followed by 1.5 g of iron oxide (Fe2O3) as a burning rate modifier. 4.6 g (0.7% by mass) of tris[1-(2-methyl)aziridinyl]phosphine oxide (MAPO) and 1.7 g (0.2% by mass) of N-methyldiethanolamine (MDA) as binders were then added and mixed.

[0039] Next, 45.7 g (6.5 mass%) of the curing agent isophorone diisocyanate (IPDI) was added and mixed under vacuum, after which the oxidizing agent ammonium perchlorate (AP) was added to bring the total amount to 5000 g, and the mixture was heated to 60°C and mixed under vacuum to obtain a slurry mixture. This mixture was then poured into a specified container under a reduced pressure of 10 mmHg or less, left to stand under the same pressure for 20 minutes to degas any tiny air bubbles remaining in the composite propellant, and cured at 60°C for 7 days to obtain a composite propellant.

[0040] [Examples 2 to 6, Comparative Examples 1 and 2] Composite propellants were produced in the same manner according to the formulations in Tables 1 and 2, and their manufacturability and mechanical properties were evaluated by the following tests.

[0041] [Manufacturability] <Pot life> Using an RE80 viscometer, viscosity was measured over time after the hardener was added at 52°C and a spindle rotation speed of 5 rpm. The time during which a composite propellant retains fluidity sufficient for casting into a rocket motor is called pot life. In the manufacture of medium- to large-sized rocket motors using the direct filling method, a pot life of 500 to 950 minutes with a viscosity of 10 kP or less is preferred. If the pot life is less than 500 minutes, the composite propellant will lose fluidity before casting is complete, increasing the risk of air bubbles remaining. On the other hand, if the pot life is more than 950 minutes, the time until curing is long, extending the construction period and making this undesirable from the standpoint of productivity. <Fluidity test> Approximately 500 g of composite propellant was poured into a 300 ml cylindrical polypropylene container under atmospheric pressure. The container was then leveled and the top surface of the composite propellant was smoothed. The container was then placed on its side in a thermostatic chamber maintained at 52°C, and the distance traveled by the composite propellant was measured after 5 minutes. The travel distance was measured from the top of the container to the farthest point on the composite propellant's outflow end. This test evaluated the ease of casting the composite propellant. A composite propellant travel distance of 140 mm or more after 5 minutes indicates high fluidity and easy casting. A composite propellant travel distance of 120 mm or more but less than 140 mm was also acceptable. A composite propellant travel distance of less than 120 mm lacked fluidity and increased the risk of air bubbles being trapped during casting. Therefore, a three-point rating system was used: "Excellent," "Good," or "Bad." ◎: Composite propellant travel distance is 140mm or more (easy to pour) 〇: The composite propellant travel distance is 120mm or more and less than 140mm (casting possible) ×: The composite propellant travels less than 120 mm (casting is possible, but there is a risk of air bubbles remaining)

[0042] [Mechanical properties] Tensile test specimens were prepared in accordance with the plastic tensile testing method "ASTM D638-84," and tensile tests were conducted at a tensile speed of 50 mm / min and a test temperature of 20°C to determine the elastic modulus, elongation at maximum load, and true stress. The tensile test specimen was 125 mm long, 25 mm wide at both ends, and 10 mm thick with a central straight section 50 mm long and 10 mm wide between the ends.

[0043] [Table 1]

[0044] [Table 2]

[0045] The test results in Table 1 reveal the following: The composite propellants of Examples 1 to 6 were found to have good manufacturability, maintaining high fluidity while satisfying the pot life of 500 to 950 minutes. Furthermore, the results showed that they satisfied the mechanical properties required for rocket motor propellants in all of the items of elastic modulus, elongation at maximum load, and true stress. When the composite propellant of Example 4 was compared with Examples 1 to 3, it was found that the composite propellants of Examples 1 to 3 had better fluidity, and therefore the tricalcium phosphate content was preferably 0.05 to 0.50 mass %. The composite propellant of Example 5 has a compounding composition with a higher binder ratio compared to Example 1. In this case, the pot life generally tends to be longer and the elastic modulus lower, but it was found that by setting the tricalcium phosphate content to 0.12 mass%, both the pot life and mechanical properties could be adjusted to ranges applicable to rocket motors. The composite propellant of Example 6 has a blend composition in which the binder ratio is reduced compared to Example 1. In this case, there is a general tendency for the pot life to be shorter and the elongation at maximum load to be lower. However, it was found that by setting the tricalcium phosphate content to 0.12 mass%, both the pot life and mechanical properties could be adjusted to ranges applicable to rocket motors. In Comparative Example 1, a composite propellant was produced by increasing the tricalcium phosphate content to 1.00 mass%, but results showed that it was unsuitable for both manufacturability and mechanical properties. In Comparative Example 2, a composite propellant containing no tricalcium phosphate was produced, and although good results were obtained for pot life and mechanical properties, results showed that it was unsuitable for fluidity.

Claims

[Claim 1] A composite propellant comprising a binder containing hydroxyl-terminated polybutadiene, ammonium perchlorate, and a phosphate, the phosphate content being 0.02 to 0.12 mass% based on the total mass of the composite propellant.

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