3D printing formula and preparation method of flexible detonating cord

Abstract

The invention discloses a flexible detonating cord 3D printing formula and a preparation method. A cladding formula of a flexible detonating cord comprises 85-90 parts by mass of modified acrylate, 3-5 parts by mass of 1, 6-hexanediol diacrylate and 5-8 parts by mass of diphenyl phosphine oxide; the core material formula comprises 86 to 94 parts by mass of a basic explosive, 4.5 to 11 parts by mass of hydroxyl-terminated polybutadiene, 1 to 2.5 parts by mass of triphenyl bismuth, 0.5 to 1 part by mass of toluene-2, 4-diisocyanate and 30 to 70 parts by mass of a bonding pore-foaming agent. The detonating cord is further prepared by taking the formula as raw materials and adopting photocuring 3D coaxial printing. Core medicine pores are effectively eliminated through a physical synergistic volatilization mechanism, and a firm interpenetrating network structure is formed on a core-shell interface through a chemical copolymerization reaction, so that the technical problems of poor compactness of the core medicine, weak interface bonding and insufficient shell mechanical strength are synchronously solved.

Description

Technical Field

[0001] This invention relates to a 3D printing flexible detonating cord formulation and preparation process, which is applied to the field of micro-sized pyrotechnic charges and can be used as a charge in microelectromechanical systems. Background Technology

[0002] Flexible detonating cords are widely used in aerospace, aviation, and missile weapon systems due to their excellent flexibility, ability to transmit detonation waves over long distances, and high reliability. However, current research indicates that flexible detonating cords suffer from complex manufacturing processes and slightly inconsistent detonation velocities. Their use is particularly limited in the application of miniature pyrotechnic devices. Traditional manufacturing processes struggle to simultaneously ensure charge uniformity, structural integrity, and detonation performance within extremely small dimensions, resulting in less than ideal performance in miniaturized and integrated systems.

[0003] With the development of additive manufacturing technology, direct-write molding technology can be used to achieve miniaturization of detonating cords, consistency of explosive charge, and rapid prototyping, thereby exploring an efficient and high-quality method for preparing detonating cords. Currently, there are still some key technical challenges in preparing flexible detonating cords using direct-write molding technology. Due to differences in material properties, the core layer and shell layer exhibit weak interfacial bonding and are prone to debonding. Summary of the Invention

[0004] In view of the defects or deficiencies of the existing technology, the present invention provides a 3D printing formula for flexible detonating cord.

[0005] Therefore, the flexible detonating cord provided by the present invention includes a core material and a cladding covering the core material, wherein: the raw materials for preparing the cladding include 85-90 parts by weight of modified acrylate, 3-5 parts by weight of 1,6-hexanediol diacrylate, and 5-8 parts by weight of diphenylphosphine oxide; the raw materials for preparing the core material include 86-94 parts by weight of basic explosive, 4.5-11 parts by weight of hydroxyl-terminated polybutadiene, 1-2.5 parts by weight of triphenylbismuth, 0.5-1 parts by weight of toluene-2,4-diisocyanate, and 30-70 parts by weight of bonding pore-forming agent; the basic explosive is CL-20, HMX, or RDX; the bonding pore-forming agent is a mixture of acetone, n-butyl acetate, and hydroxyethyl acrylate.

[0006] An optional embodiment is that the sum of the mass percentages of the various substances in the bonding porogen is 100%, wherein the acetone content is 60%~67%, the n-butyl acetate content is 25%~30%, and the hydroxyethyl acrylate content is 8%~10%.

[0007] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0008] Preferably, the modified acrylate in the coating material is 85 to 90 parts by mass, for example, 85, 87, 89 or 90 parts by mass, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0009] Preferably, the amount of 1,6-hexanediol diacrylate in the coating material is 3 to 5 parts by mass, for example, 3 parts by mass, 4 parts by mass or 5 parts by mass.

[0010] Preferably, the amount of diphenylphosphine oxide in the coating material is 5 to 8 parts by mass, for example, 5 parts by mass, 6 parts by mass, 7 parts by mass or 8 parts by mass.

[0011] Preferably, the amount of basic explosive in the core material is 86 to 94 parts by weight, for example, 86, 88, 90, 92 or 94 parts by weight, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0012] Preferably, the amount of hydroxyl-terminated polybutadiene in the core material raw material is 4.5 to 11 parts by mass, for example, 4.5 parts by mass, 6 parts by mass, 7.5 parts by mass or 11 parts by mass, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0013] Preferably, the triphenylbismuth content in the core material is 1 to 2.5 parts by mass, for example, it can be 1 part by mass, 1.5 parts by mass, 2 parts by mass or 2.5 parts by mass, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0014] Preferably, the amount of toluene-2,4-diisocyanate in the core material is 0.5 to 1 part by mass, for example, 0.5 parts by mass, 0.6 parts by mass, 0.7 parts by mass or 1 part by mass, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0015] Preferably, the bonding pore-forming agent in the core material raw material is 30 to 70 parts by weight, for example, 30, 40, 50, 60 or 70 parts by weight, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0016] The present invention also provides a method for preparing a flexible detonating cord. The method uses the above-mentioned formula as the raw material and employs a photopolymerization 3D printing device to prepare the flexible detonating cord by coaxial printing. The coaxial printing is performed using a coaxial printing needle, which includes a core material needle and a cladding needle disposed outside the core material needle.

[0017] Optionally, the extrusion speed of the core material in the coaxial printing is 2.7–3.0 mm. 3 The extrusion speed ratio of the cladding material to the core material is (1~1.5):4. The lateral movement speed of the printing needle is 1.5~2.0 mm / s. The printing temperature is 40~60℃. The light source for photocuring is an ultraviolet light source. The light intensity is 1400~1600 mw·cm. -2 .

[0018] Preferably, the following steps are taken: acetone and n-butyl acetate are mixed; hydroxyethyl acrylate is added dropwise, and after mixing, explosive, hydroxyl-terminated polybutadiene, triphenylbismuth and toluene-2,4-diisocyanate are added and mixed.

[0019] Preferably, the extrusion speed of the core material in the coaxial printing is 2.8 mm. 3 / s, the extrusion ratio of cladding material to core material is (1~1.5):4, for example, it can be 1:4, 1.1:4, 1.2:4, 1.3:4, 1.4:4 and 1.5:4.

[0020] Compared to existing technologies, this invention, through the use of a composite functional additive system, achieves a leapfrog improvement in the bonding between the core charge and the shell, moving from physical adsorption to chemical bonding. This ensures the compactness of the charge structure and the reliability of detonation, and significantly enhances the bonding strength and structural integrity of the core-shell interface. The sample showed no obvious delamination or debonding, with an elongation at break ≥10% and a detonation velocity ≥7000 m / s. Attached Figure Description

[0021] Figure 1 shows electron microscope (EM) images of the products of the examples and comparative examples; Figure 1(a) is an EEM cross-sectional view of the flexible detonating cord formed in Example 1 with the addition of a bonding porogen; Figure 1(b) is an EEM longitudinal section of the flexible detonating cord formed in Comparative Example 1 using ethanol instead of the bonding porogen; Figure 1(c) is an EEM cross-sectional view of the flexible detonating cord formed in Comparative Example 1 using ethanol instead of the bonding porogen; Figure 1(d) is an EEM longitudinal section of the flexible detonating cord formed in Comparative Example 2 without the addition of a bonding porogen; Figure 1(e) is an EEM longitudinal section of the flexible detonating cord formed in Comparative Example 3 without the use of acetone as the bonding porogen; Figure 1(f) is an EEM longitudinal section of the flexible detonating cord formed in Comparative Example 4 without the use of n-butyl acetate as the bonding porogen; Figure 1(g) is an EEM longitudinal section of the flexible detonating cord formed in Comparative Example 5 without the use of hydroxyethyl acrylate as the bonding porogen.

[0022] Figure 2 shows microscopic images of the examples and comparative examples; Figure 2(a) is a microscopic image of the flexible detonating cord formed when the extrusion ratio of component A and component B ink in Example 1 is 1.5:4; Figure 2(b) is a microscopic image of the flexible detonating cord formed when the bonding pore-forming agent in Example 2 is 30g; Figure 2(c) is a microscopic image of the flexible detonating cord formed when the bonding pore-forming agent in Example 3 is 70g; Figure 2(d) is a schematic diagram of the printed products of Examples 1, 2 and 3.

[0023] Figure 3 shows the detonation velocity test principle and results of the product in Example 1; Figure 3(a) is a detonation velocity principle test diagram; Figure 3(b) is a detonation velocity test diagram of the detonating cord made in Example 1.

[0024] Figure 4 Stress-strain curves of the flexible detonating cord prepared for the examples and comparative examples. Detailed Implementation

[0025] Unless otherwise specified, the scientific and technical terms used in this article are intended for understanding by those skilled in the art.

[0026] In the fabrication of detonating cord using direct-write molding technology, problems exist such as poor interfacial compatibility between the core and shell materials, easy formation of porosity in the core layer, and core-shell interface separation. Existing technologies initially focused on optimizing the explosive ratio in the core charge and adjusting the shell ink formulation. However, fundamental differences remain between the core charge ink (primarily composed of explosives) and the shell ink (often based on photocurable polymers) in terms of material chemistry, curing mechanism, and interfacial compatibility. This makes it difficult to achieve a stable interfacial bond, easily leading to debonding between the core and shell layers, thus affecting the reliable transmission of the detonation wave. To address this interface problem, the industry has further explored replacing traditional photocurable shells with materials that have better interfacial compatibility with the core charge (such as inert explosives or other inert materials). Therefore, the industry believes that using such highly compatible alternative materials can solve the problem of poor core-shell interfacial bonding. However, this technology inevitably leads to a decrease in the mechanical strength of the shell, making it difficult to provide effective physical protection and environmental isolation for sensitive charges in practical applications, limiting the overall reliability of the component, and thus hindering its practical application.

[0027] This invention uses photocurable ink as the shell material for flexible detonating cord, and the core material ink is configured into a thermosetting adhesive system with the addition of a bonding pore-forming agent. This not only improves the interfacial chemical bonding between the shell and the core charge, but also eliminates pores in the core charge. At the same time, based on photothermal dual curing and using coaxial printing, high-quality and rapid prototyping of flexible detonating cord is achieved, ultimately solving the problems of poor core-shell interface bonding, core layer porosity, and insufficient shell mechanical strength.

[0028] Specifically, in this invention, the packaging material uses modified acrylate as the oligomer of the outer shell photocurable adhesive system, 1,6-hexanediol diacrylate as the photoinitiator, and diphenylphosphine oxide as the reactive diluent; the core material explosive is a high-energy explosive, and a thermosetting adhesive terminal hydroxyl polybutadiene is introduced, toluene-2,4-diisocyanate is used as the curing agent, triphenylbismuth is used as the curing catalyst, and a bonding pore-forming agent is introduced to improve the quality of the core material ink, enhance the internal cross-linking effect of the core material, and improve the chemical bonding between the core material and the outer shell.

[0029] The feeding sequence during the preparation of the packaging material in this invention follows the classic principles of photocurable adhesive system configuration: high-viscosity modified acrylate oligomers are mixed with low-viscosity 1,6-hexanediol diacrylate reactive diluent to significantly reduce the system viscosity and create a basic fluid environment for subsequent uniform dispersion. After thorough mixing, a photosensitive diphenylphosphine oxide initiator is added to ensure rapid and uniform dispersion of the initiator. The feeding sequence during the mixing of core material raw materials must ensure a uniform and stable bonding pore-forming agent solution. Specifically: acetone and n-butyl acetate are premixed to establish a uniform solvent environment. Hydroxyethyl acrylate (HEA) is introduced by a dropwise addition method, which effectively controls the heat of mixing and prevents excessively high local concentrations of HEA. Finally, thorough stirring eliminates any phase separation or dripping phenomena, ensuring the repeatability and stability of the subsequent pore-forming function.

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments. These embodiments are merely illustrative of the invention and should not be considered as specific limitations thereof. All raw materials used in the following embodiments are commercially available products.

[0031] The printing device used in this invention is an Axolotl Biosystems A3 printer, wherein the inner diameter of the coaxial printing needle core material is 0.8 mm, the inner diameter of the cladding needle is 1.0 mm, and the cladding thickness is 0.1 mm.

[0032] Example 1: The raw materials prepared in this embodiment are measured by mass, wherein: Component A ink (coating material) is composed of the following raw materials: 89g of modified acrylate, 4g of 1,6-hexanediol diacrylate, and 7g of diphenylphosphine oxide. Preparation of Component A ink: Mix the modified acrylate and 1,6-hexanediol diacrylate; then add diphenylphosphine oxide and continue mixing until there are no obvious particles and bubbles present to obtain Component A ink. Component B ink (core material raw material) is composed of the following raw materials: 94g of CL-20 explosive, 7.5g of hydroxyl-terminated polybutadiene, 2g of triphenylbismuth, 0.5g of toluene-2,4-diisocyanate, and 60g of bonding pore-forming agent, wherein the bonding pore-forming agent includes 38g of acetone, 16.5g of n-butyl acetate, and 5.5g of hydroxyethyl acrylate. Preparation of Component B ink: Acetone and n-butyl acetate are mixed evenly; the weighed hydroxyethyl acrylate is slowly added dropwise using a pipette and mixed thoroughly; the rotation speed is set to 1200 rpm, the time to 60s, and the vacuum degree to 6kPa, and the explosive, hydroxyl-terminated polybutadiene, triphenylbismuth, and toluene-2,4-diisocyanate are added to the bonding pore-forming agent for fusion using a gravity disperser to obtain Component B ink.

[0033] 3D printing: The ink component A is injected into the cartridge A of the printing device, and the cartridge A is in communication with the cladding of the coaxial printing needle; the ink component B is injected into the cartridge B of the printing device, and the cartridge B is in communication with the core layer of the coaxial printing needle. Set the extrusion speed of component B ink to 2.8 mm. 3 The extrusion speed ratio of component A ink to component B ink is 1.5:4, the lateral movement speed of the printing needle is 1.8 mm / s, the printing temperature is 50℃, and the ultraviolet light intensity is 1500 mw·cm². -2 ; After the sample is extruded, the shell is photocured by ultraviolet light. The printing length of the sample is selected according to the requirements. After the sample is printed, it is placed in an oven and cured at 60°C for 6 hours to complete the preparation of the flexible detonating cord.

[0034] Comparative Example 1: Flexible detonating cord was prepared according to the formulation and proportions of Example 1, except that 60g of ethanol was used instead of the bonding pore-forming agent.

[0035] Comparative Example 2: Flexible detonating cords were prepared according to the formulation and proportions of Example 1, except that bonding pore-forming agents were not used.

[0036] Comparative Example 3: Flexible detonating cords were prepared according to the formulation and proportions of Example 1, except that acetone was not used as the bonding pore-forming agent.

[0037] Comparative Example 4: Flexible detonating cord was prepared according to the formulation and proportions of Example 1, except that n-butyl acetate was not used as the bonding pore-forming agent.

[0038] Comparative Example 5: Flexible detonating cord was prepared according to the formulation and proportions of Example 1, except that hydroxyethyl acrylate was not used as the bonding pore-forming agent.

[0039] Example 2: Flexible detonating cord was prepared according to the formulation of Example 1, except that the bonding pore-forming agent was 30g and the proportions of each component were the same as in Example 1.

[0040] Example 3: Flexible detonating cord was prepared according to the formulation of Example 1, except that the bonding pore-forming agent was 70g and the proportions of each component were the same as in Example 1.

[0041] The detonating cords prepared in the above embodiments and comparative examples were analyzed by electron microscopy, microscopy, detonation velocity, and mechanical properties. The detonation velocity test was conducted in accordance with GJB 772A-1997 Test Methods for Explosives. Figure 3a The diagram illustrates the detonation velocity testing principle. The detonation velocity testing device mainly consists of a detonator 1, an aluminum substrate, bolts, target wires 2, and an external oscilloscope. The charge size on the test substrate is 100×1×1mm. Target wires are installed on the cover plate at intervals of I1-3 (30mm) as probes. During testing, the sample to be tested 3 is mounted on the aluminum substrate, with one end connected to the detonator and the other end extending along I1-3. After the detonator is detonated, the time (t1-4) for the detonation wave to reach each probe is recorded. The time difference (Δt) between adjacent probes is calculated using the formula... Calculate the detonation velocity. Mechanical property testing was performed according to GB / T528-2009. Relevant results are as follows: Regarding electron microscopy morphology: As shown in Figure 1, in Example 1, the bonding pore-forming agent effectively controlled the forming process of the flexible detonating cord under heating conditions, resulting in no significant defects and excellent forming integrity and regularity. In Comparative Example 1, ethanol rapidly evaporated upon heating, causing numerous pores to form inside the core of the flexible detonating cord, resulting in a rough, loose, granular aggregate on the surface and a disordered microstructure. Comparative analysis of the cross-sectional views of the flexible detonating cords in Example 1 and Comparative Example 1 shows that the addition of the bonding pore-forming agent in this invention can greatly improve the bonding between the core and the shell, forming a robust, three-dimensional, integrated network structure, significantly improving the quality of the flexible detonating cord and ensuring its reliable operation.

[0042] In Comparative Example 2, no bonding porogen was added, resulting in uneven mixing of the core charge and a rough, loose, granular aggregate appearance on the surface. Compared to Example 1, a clearly visible gap existed between the shell and the core charge, indicating significant interfacial separation and poor interfacial bonding. In Comparative Example 3, acetone was omitted from the bonding porogen, disrupting the solvent system's dissolution balance and leading to uneven dispersion of the bonding porogen in the core charge ink, resulting in pores during curing. In Comparative Example 4, butyl acetate was omitted from the bonding porogen, resulting in a high polarity of the solvent system and excessively rapid evaporation, also causing defects and pores within the core charge. In Comparative Example 5, hydroxyethyl acrylate was omitted from the bonding porogen, preventing the establishment of a chemical bridge between the shell and the core charge, hindering the formation of a homogeneous, dense structure within the core charge, and making pore elimination difficult. During the printing of flexible detonating cord, each component of the bonding porogen is indispensable for achieving interfacial strengthening and pore elimination; the absence of any component directly affects molding quality, structural reliability, and detonation performance.

[0043] Regarding microscopic morphology: As shown in Figure 2, the sample in Example 1 exhibits excellent molding performance. The shell structure provides reliable support for the stable molding of the core charge, effectively ensuring the preparation accuracy and overall quality of the flexible detonating cord. In Examples 2 and 3, after curing, the shell also provides reliable support for the core charge, but the molding quality is lower than that of Example 1. In Example 2, due to the relatively small amount of bonding pore-forming agent, the viscosity of component B ink is relatively high, easily leading to uneven ink distribution during printing and reducing sample uniformity. In Example 3, the amount of bonding pore-forming agent is large, resulting in a lower viscosity of component B ink, causing thinning after printing and hindering the rapid curing of the flexible detonating cord.

[0044] Regarding the detonation velocity test: As shown in Figure 3, the flexible detonating cord prepared in Example 1 was filled into an aluminum substrate, detonated by a detonator, and the detonation velocity of the detonating cord was measured using the probe method. The detonation process of the detonating cord was smooth, and the average detonation velocity reached 7115 m / s.

[0045] Regarding elongation at break, see Figure 4 As shown in the stress-strain curves, the flexible detonating cord exhibits both high strength and high toughness after the addition of the bonding pore-forming agent. The area under its stress-strain curve (representing fracture energy) is much larger than that of the other two groups, indicating that it has the strongest ability to absorb mechanical energy and is not prone to damage, with a fracture elongation of 11.2%. The formulation with added ethanol achieves a significant improvement in toughness with only a slight loss in strength. Although the formulation without additives has the best initial strength and stiffness, its extremely low fracture toughness makes it difficult to use as a structural material, becoming a core weakness.

[0046] In summary, the addition of the bonding pore-forming agent in this invention can greatly improve the bonding between the core charge and the shell, forming a strong, three-dimensional, integrated network structure, which greatly improves the quality of the flexible detonating cord and ensures the reliability of the flexible detonating cord.

Claims

1. A 3D printing formulation for flexible detonating cord, characterized in that, The flexible detonating cord includes a core material and a cladding layer covering the core material, wherein: The coating preparation raw materials include 85-90 parts by weight of modified acrylate, 3-5 parts by weight of 1,6-hexanediol diacrylate and 5-8 parts by weight of diphenylphosphine oxide; The raw materials for core material preparation include 86-94 parts by weight of basic explosive, 4.5-11 parts by weight of hydroxyl-terminated polybutadiene, 1-2.5 parts by weight of triphenylbismuth, 0.5-1 parts by weight of toluene-2,4-diisocyanate and 30-70 parts by weight of bonding pore-forming agent; The base explosive is CL-20, HMX, or RDX; the bonding pore-forming agent is a mixture of acetone, n-butyl acetate, and hydroxyethyl acrylate.

2. The 3D printing formulation for flexible detonating cord according to claim 1, characterized in that, The total mass percentage of each component in the bonding porogen is 100%, wherein the acetone content is 60%~67%, the n-butyl acetate content is 25%~30%, and the hydroxyethyl acrylate content is 8%~10%.

3. A method for preparing a flexible detonating cord, characterized in that, The method uses the formulation described in claim 1 as the raw material and employs a photopolymerization 3D printing device to prepare a flexible detonating cord through coaxial printing. The coaxial printing is performed using a coaxial printing needle, which includes a core material needle and a cladding needle disposed outside the core material needle.

4. The method for preparing the flexible detonating cord according to claim 3, characterized in that, The extrusion speed of the core material in the coaxial printing process is 2.7–3.0 mm. 3 / s, the extrusion speed ratio of cladding material to core material is (1~1.5):

4.

5. The method for preparing the flexible detonating cord according to claim 3, characterized in that, The lateral movement speed of the printing needle is 1.5–2.0 mm / s.

6. The method for preparing the flexible detonating cord according to claim 3, characterized in that, Printing temperature: 40-60℃.

7. The method for preparing the flexible detonating cord according to claim 3, characterized in that, The light source for photocuring is an ultraviolet light source.

8. The method for preparing the flexible detonating cord according to claim 3, characterized in that, Illumination intensity is 1400–1600 mW·cm -2 .

9. The method for preparing the flexible detonating cord according to claim 3, characterized in that, The mixing method of the core material raw materials includes: mixing acetone and n-butyl acetate; adding hydroxyethyl acrylate dropwise, mixing well, and then adding explosives, hydroxyl-terminated polybutadiene, triphenylbismuth and toluene-2,4-diisocyanate.

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