Silicone tube with inner braided structure and preparation method thereof

Abstract

The invention discloses a silicone tube with an internal braided structure and a preparation method thereof. The preparation method comprises the following steps: 1) preparing modified silicone rubber; 2) mixing the fluorosilicone rubber composite material; 3) extrusion molding and weaving reinforcement; and 4) vulcanization molding. The preparation method comprises the following steps: synthesizing high vinyl MVQ, grafting side chain amino, generating a benzoxazine group, and obtaining the modified silicone rubber with the benzoxazine group; a rigid phenolic network is obtained creatively through high-temperature self-ring-opening cross-linking of benzoxazine, and interpenetrates with a fluorine-silicon covalent bonding cross-linked network to form an interpenetrating polymer network structure; then aramid fiber weaving, filler anchoring and other means are used, so that the silicone tube with the inner weaving structure can normally work at the extreme temperature of-60-200 DEG C, the small size change rate is kept, the excellent mechanical property and chemical medium resistance are achieved, and the problems of high-temperature deformation and low-temperature embrittlement of the silicone tube in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of silicone tube manufacturing technology, and in particular to an internally braided silicone tube and its manufacturing method. Background Technology

[0002] Silicone rubber tubing is widely used in medical, food, industrial, and electronics fields due to its excellent resistance to high and low temperatures, weather resistance, biocompatibility, electrical insulation, and flexibility. However, traditional silicone tubing technology has the following key drawbacks:

[0003] Silicone rubber has a low Si-O bond energy (≈444kJ / mol) in its main chain, and undergoes rearrangement degradation at 180℃. It also becomes brittle and fractures at temperatures below -40℃. Existing technologies enhance the heat resistance of the tubing by adding heat-resistant fillers, such as silica, but this can only delay softening and cannot break through the 200℃ service limit.

[0004] The high degree of freedom of motion in siloxane segments results in a thermal expansion coefficient >250×10⁻⁶. -6 / K, free state deformation at 150℃ >10%; aramid braided reinforcement uses physical coating, interlayer shear strength ≤5MPa, interface delamination easily occurs after thermal cycling, and high-temperature dimensional instability is serious.

[0005] Compared to many other synthetic rubbers, silicone rubber has lower tensile and tear strength, especially at stress points or edges, making it more susceptible to stretching, scratching, or tearing, and also more easily punctured by sharp objects.

[0006] Poor heat and cold resistance, severe dimensional instability at high temperatures, and no significant advantage in mechanical properties compared to other synthetic rubbers limit the application of silicone tubes in high-end fields such as aerospace and new energy. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing an internally braided silicone tube and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention first proposes an internally braided silicone tube, comprising the following steps:

[0010] S1. Preparation of modified silicone rubber

[0011] S1.1, Synthesis of High Vinyl MVQ:

[0012] Methylvinyl dichlorosilane, dimethyl dichlorosilane and vinyl dimethyl methoxysilane were dissolved in tetrahydrofuran and cooled to 0-5℃ in an ice bath; deionized water was added dropwise for hydrolysis, and the temperature was maintained at ≤10℃. 10% NaHCO3 solution was added and stirred for 30 min. The aqueous layer was removed by separation.

[0013] KOH was added, the temperature was raised to 60℃ and the reaction was carried out for 4 hours. Acetic acid was added dropwise until the reaction solution was neutral to terminate the reaction. After filtration, the solid phase was washed with tetrahydrofuran to obtain methyl vinyl silicone rubber with high vinyl content, namely high vinyl MVQ.

[0014] Methylvinyldichlorosilane and dimethyldichlorosilane are hydrolyzed at low temperature (≤10℃) in THF to generate silanols, avoiding side reactions. NaHCO3 neutralizes HCl to prevent runaway silanol condensation polymerization, and finally, vinyldimethylmethoxysilane is used for end-capping. KOH catalyzes siloxane bond rearrangement to form high molecular weight linear silicone rubber (MVQ). The vinyl monomers provide side-chain double bonds, laying the foundation for subsequent click chemistry grafting.

[0015]

[0016] S1.2, Amino grafting:

[0017] High-vinyl MVQ was dissolved in tetrahydrofuran and stirred for 30 min under nitrogen protection; 2-aminoethanethiol was added and stirred for 10 min in the dark; 4-dimethylaminopyridine was added, and the mixture was transferred to a 365 nm UV reactor with a UV frequency of 50 mW / cm². 2 Irradiate with light intensity for 5 min; pour the product into ethanol, and repeat the flocculation and THF dissolution process 3 times; dry in a vacuum oven at 55℃ until constant weight, to obtain MVQ-g-NH2;

[0018] 365nm ultraviolet light excites 4-dimethylaminopyridine (DMAP) to generate free radicals, which initiate the nucleophilic addition of thiols (-SH) to vinyl groups (-CH=CH2), achieving efficient grafting;

[0019] S1.3 Synthesis of benzoxazine group:

[0020] 3-Pentadecylphenol, paraformaldehyde, and MVQ-g-NH2 were dissolved in tetrahydrofuran and refluxed at 80°C and 100 rpm under nitrogen protection with magnetic stirring for 6 h. After cooling to room temperature, a 1% NaOH aqueous solution was added dropwise to neutralize to pH 7. The product was then poured into ethanol, and the flocculation and THF dissolution processes were repeated three times. The product was then dried in a vacuum oven at 55°C to constant weight to obtain MVQ-benzoxazine.

[0021] The Mannich reaction synthesizes benzoxazine. Simultaneously, the hydrophobic long chain of 3-pentadecanylphenol enhances compatibility with silicone rubber, prevents phase separation, and serves as a flexible block reinforcing agent for the mechanical properties of the tubing.

[0022]

[0023] S2, fluorosilicone rubber composite compound

[0024] S2.1, Silicone rubber phase compounding:

[0025] MVQ-benzoxazine, fumed silica, and hydroxyl silicone oil were added sequentially to the open mill for mixing. The mixture was then passed through the mill 5 times at 40°C until it wrapped around the rollers. The left and right cutters were used 10 times each, followed by 3 passes through the mill to obtain a silicone rubber sheet.

[0026] S2.2, Fluororubber blend:

[0027] At 60℃, fluororubber is plasticized in a thin pass for 5 minutes, then silicone rubber sheets are added and mixed. After mixing, the temperature is lowered to 40℃ and a vulcanizing agent is added. The mixture is then cut with a knife until no particles are visible, thus obtaining fluorosilicone composite rubber.

[0028] S3, Extrusion Molding and Braiding Reinforcement

[0029] S3.1 Inner layer tube blank extrusion and cooling / shaping:

[0030] Fluorosilicone composite rubber is pre-cut into strips and preheated at a constant temperature of 50℃ for 1 hour; the tube blank is extruded through an extruder and shaped by a vacuum sizing sleeve under a vacuum degree of -0.08MPa; it is then traction-speeded at 2m / min into a cooling water tank with a water temperature of 20±2℃ and a length of 6m to obtain the inner tube blank.

[0031] S3.2, Aramid fiber braiding reinforcement:

[0032] Aramid fibers are coated with a silane coupling agent ethanol solution, dried in a 70°C oven for 1 minute, and then woven using a 24-spindle high-speed braiding machine.

[0033] S3.3, Outer Coating and Composite Tube Molding

[0034] Using the same extruder, change the die, lower the temperature setting by 5℃, keep the traction speed consistent with the weaving step at 2m / min, and control the outer layer rubber thickness at 0.5±0.05mm to obtain the composite tube rough product;

[0035] S4, vulcanization molding

[0036] S4.1, First stage of vulcanization:

[0037] The first stage of vulcanization of the composite pipe rough was carried out using a horizontal steam vulcanizing tank.

[0038] The platinum catalytic system catalyzes the crosslinking of the fluorosilicone rubber blend phase. The platinum complex activates the Si-H bond, lowers the reaction energy barrier, and achieves low-temperature and high-efficiency addition crosslinking. A Si-C covalent bridge is formed between the silicone rubber phase (MVQ-benzoxazine) and the fluororubber phase (FVMQ), eliminating phase separation and improving the media resistance and mechanical strength of the composite material.

[0039] S4.2, Second stage vulcanization:

[0040] After the first stage of vulcanization, it needs to be left to stand for 4 hours before the second stage of vulcanization is carried out using a hot air circulating oven.

[0041]

[0042] The side chain of benzoxazine endows silicone rubber with the ability of self-catalytic ring-opening polymerization. The benzoxazine group undergoes a ring-opening reaction during heating. The active group generated after ring opening can automatically catalyze the unreacted benzoxazine to continue to open the ring and crosslink, forming a dense thermosetting network.

[0043] Essentially, the phenolic hydroxyl and secondary amine groups generated by the ring opening of benzoxazine act as proton donors, initiating a chain reaction that opens the ring of the adjacent benzoxazine ring.

[0044] The phenolic cross-linked network formed by the reaction has a decomposition temperature >300℃ and can inhibit the rearrangement and degradation of the siloxane backbone.

[0045] Meanwhile, the benzoxazine network and SiO2 filler are bonded together through -OH hydrogen bonds, thereby enhancing the interaction between the filler and the matrix and greatly improving the performance of silicone rubber.

[0046] In addition, the synergistic effect of the rigid phenolic network (heat resistant) and the flexible siloxane chain (cold resistant) enables the silicone tube of the present invention to have wide temperature range flexibility, with an operating temperature of -60℃ to 200℃, and simultaneously improves the heat resistance, dimensional stability and mechanical strength of the tube.

[0047] After vulcanization, an internally braided silicone tube is obtained.

[0048] Preferably, in step S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 solution is 4-6:5:0.5-1:5;

[0049] The NaHCO3 solution is a 10% (w / w) NaHCO3 aqueous solution;

[0050] The amount of KOH added is 1.5% of the total mass of methylvinyldichlorosilane, dimethyldichlorosilane, and vinyldimethylmethoxysilane.

[0051] Preferably, in step S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyldichlorosilane and vinyldimethylmethoxysilane is 1.5-1.7:2;

[0052] The amount of 4-dimethylaminopyridine added is 1%-2% of the reaction substrate.

[0053] Preferably, in step S1.3, the molar ratio of 3-pentadecanylphenol, paraformaldehyde, and 2-aminoethanethiol added in step S1.2 is 3.2:3:1.1.

[0054] Preferably, in step S2.1, the mass ratio of MVQ-benzoxazine, fumed silica, and hydroxyl silicone oil during silicone rubber phase compounding is 100:20-30:4; the open mill roll temperature is 25°C; the thin pass roll gap is 0.5 mm; and the compounding roll gap is 1.5 mm.

[0055] Preferably, in step S2.2, the fluororubber is fluorosilicone rubber FVMQ, and when the fluororubber is blended, the mass ratio of silicone rubber sheet to fluororubber is 100:50-70.

[0056] The vulcanizing agents are hydrogen-containing silicone oil crosslinking agent, platinum-vinylsiloxane complex, and 1-ethynylcyclohexanol;

[0057] The amount of hydrogen-containing silicone oil crosslinking agent is 1.5% of the total mass of the rubber compound, the amount of platinum-vinylsiloxane complex added is 0.5% of the total mass of the rubber compound, and the amount of 1-ethynylcyclohexanol added is 1% of the total mass of the rubber compound.

[0058] Preferably, in step S3.2, the silane coupling agent is KH-792, and the mass concentration of the KH-792 ethanol solution is 5%.

[0059] The parameters for the knitting machine are set as follows:

[0060] The fiber pretension is 10±0.5N / spindle, the weaving density is 16±0.5picks / cm, and the weaving layer coverage needs to be ≥80%.

[0061] Preferably, in step S4, the parameters for the first stage of vulcanization are set as follows:

[0062] ① Heat from room temperature to 140℃ at a heating rate of 2℃ / min and hold for 15min;

[0063] ② Cool down from 140℃ to 80℃ at a heating rate of 1℃ / min, and hold for 8 minutes;

[0064] ③ Allow to cool naturally to room temperature;

[0065] The second stage of vulcanization is programmed as follows:

[0066] ① Heat from room temperature to 160℃ at a heating rate of 5℃ / min and hold for 1 hour;

[0067] ② Increase the temperature from 160℃ to 200℃ at a rate of 1℃ / min and hold for 2 hours;

[0068] ③ Allow to cool naturally to room temperature.

[0069] The present invention also proposes an internally braided silicone tube prepared by the aforementioned preparation method, wherein the thickness ratio of the inner layer adhesive to the outer layer adhesive is 0.8-1.2:1.

[0070] Compared with the prior art, the beneficial effects of the present invention are:

[0071] 1. Benzooxazine ring-opening forms a rigid three-dimensional phenolic cross-linked network.

[0072] This invention first synthesizes methyl vinyl silicone rubber with dense double bonds in the side chain, which serves as a "molecular anchor" for subsequent functionalization. Then, 2-aminoethanethiol is efficiently grafted onto the silicone molecular chain through "click chemistry". The grafted amino group reacts with the long-chain phenol to generate a benzoxazine ring, which undergoes a ring-opening reaction when heated. The active groups generated after ring opening can automatically catalyze the unreacted benzoxazine to continue to open the ring and crosslink, forming a dense thermosetting network.

[0073] Essentially, the phenolic hydroxyl and secondary amine groups generated by the ring-opening of benzoxazine act as proton donors, initiating a chain reaction of ring-opening of adjacent benzoxazine rings to form a rigid three-dimensional phenolic cross-linked network; and it combines with SiO2 filler through -OH hydrogen bonds, thereby enhancing the interaction between the filler and the matrix, which greatly improves the performance of silicone rubber.

[0074] 2. Interpenetrating polymer network structure

[0075] In the first stage of vulcanization, a platinum catalyst activates the hydrogen-containing silicone oil at 80-140℃, causing it to form a strong Si-C covalent bond with the double bonds of fluororubber and silicone rubber, which greatly improves the interfacial bonding strength. Moreover, the platinum catalytic addition reaction is an ionic mechanism and is not inhibited by oxygen, which can achieve deep and uniform vulcanization in thick-walled rubber hoses.

[0076] In the second stage of vulcanization, benzoxazine ring-opening forms a phenolic network. The Si-C bonds generated in the first stage of vulcanization do not break below 250°C. The two networks interpenetrate to form an interpenetrating polymer network structure, making the crosslinking point density far exceed that of traditional silicone tubes, further shielding the main chain from thermal and oxygen attacks, and achieving "dual-network thermal protection".

[0077] The synergistic effect of the rigid phenolic network (heat resistant) and the flexible siloxane chain (cold resistant) gives the silicone tube of the present invention a wide temperature range of flexibility, applicable to temperatures from -60℃ to 200℃.

[0078] 3. Superior dimensional stability

[0079] The phenolic network, acting as a "molecular backbone," divides the flexible siloxane segments into confined micro-regions, significantly reducing the material's coefficient of thermal expansion. At 200℃, the thermal kinetic energy of the molecular chains is approximately 25 kJ / mol, while the bond energy of the phenolic network is >350 kJ / mol, effectively locking up chain segment slippage. Furthermore, the axial coefficient of thermal expansion of aramid fibers is -6 × 10⁻⁶. -6 / K exhibits negative expansion characteristics, which can counteract the positive expansion of the hose when heated; the amino (-NH2) part of the KH-792 silane coupling agent participates in the ring-opening reaction of benzoxazine to form fiber-matrix covalent bonds, and the interfacial shear strength is far superior to physical bonding.

[0080] The phenolic hydroxyl groups (-OH) generated by the ring opening of benzoxazine form a high-density hydrogen bond network with the silanol groups (Si-OH) on the surface of gaseous SiO2, making the filler an anchor point for the rigid network. The two networks form a topologically interlocked structure. The flexible Si-C network absorbs the initial strain through entropic elasticity, while the rigid phenolic network resists plastic deformation through covalent bonds. Stress is transferred at the interface between the two networks through chemical bonds, preventing interface slip.

[0081] In summary, this invention synthesizes high-vinyl MVQ, grafts side-chain amino groups, and generates benzoxazine groups to obtain modified silicone rubber with benzoxazine groups. It creatively obtains a rigid phenolic network through high-temperature self-ring-opening crosslinking of benzoxazine, and interpenetrates with a fluorosilicone covalently bonded crosslinked network to form an interpenetrating polymer network structure. Subsequently, using aramid braiding, filler anchoring, and other methods, the internally braided silicone tube of this invention can operate normally in extreme temperatures ranging from -60 to 200°C, maintaining a small dimensional change rate, possessing excellent mechanical properties and chemical resistance, and solving the problems of high-temperature deformation and low-temperature embrittlement of silicone tubes in the prior art. Attached Figure Description

[0082] Figure 1 The 1H NMR spectrum of MVQ-benzoxazine prepared in this invention. Detailed Implementation

[0083] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0084] The purity and manufacturers of the various drugs used in the experiment are shown in Table 1.

[0085] Table 1. Raw Material Drug Information

[0086]

[0087] Example 1:

[0088] A method for preparing an internally braided silicone tube includes the following steps:

[0089] S1. Preparation of modified silicone rubber

[0090] S1.1, Synthesis of High Vinyl MVQ:

[0091] Methylvinyl dichlorosilane, dimethyl dichlorosilane and vinyl dimethyl methoxysilane were dissolved in tetrahydrofuran and cooled to 0-5℃ in an ice bath; deionized water was added dropwise for hydrolysis, and the temperature was maintained at ≤10℃. 10% NaHCO3 solution was added and stirred for 30 min. The aqueous layer was removed by separation.

[0092] KOH was added, the temperature was raised to 60℃ and the reaction was carried out for 4 hours. Acetic acid was added dropwise until the reaction solution was neutral to terminate the reaction. After filtration, the solid phase was washed with tetrahydrofuran to obtain methyl vinyl silicone rubber with high vinyl content, namely high vinyl MVQ.

[0093] S1.2, Amino grafting:

[0094] High-vinyl MVQ was dissolved in tetrahydrofuran and stirred for 30 min under nitrogen protection; 2-aminoethanethiol was added and stirred for 10 min in the dark; 4-dimethylaminopyridine was added, and the mixture was transferred to a 365 nm UV reactor with a UV frequency of 50 mW / cm². 2 Irradiate with light intensity for 5 min; pour the product into ethanol, and repeat the flocculation and THF dissolution process 3 times; dry in a vacuum oven at 55℃ until constant weight, to obtain MVQ-g-NH2;

[0095] S1.3 Synthesis of benzoxazine group:

[0096] 3-Pentadecylphenol, paraformaldehyde, and MVQ-g-NH2 were dissolved in tetrahydrofuran and refluxed at 80°C and 100 rpm under nitrogen protection with magnetic stirring for 6 h. After cooling to room temperature, a 1% NaOH aqueous solution was added dropwise to neutralize to pH 7. The product was then poured into ethanol, and the flocculation and THF dissolution processes were repeated three times. The product was then dried in a vacuum oven at 55°C to constant weight to obtain MVQ-benzoxazine.

[0097] A portion of MVQ-benzoxazine was dissolved in DMF, purified, and then analyzed by 1H NMR. The results are as follows: Figure 1 As shown;

[0098] The peaks at 5.5-6.0 ppm indicate that double bonds remain in the system, but most of the double bonds have been grafted with amino groups and cyclized to form benzoxazine structures. The absence of obvious amino peaks at 1.5 ppm indicates that most amino groups have been reacted.

[0099] S2, fluorosilicone rubber composite compound

[0100] S2.1, Silicone rubber phase compounding:

[0101] MVQ-benzoxazine, fumed silica, and hydroxyl silicone oil were added sequentially to the open mill for mixing. The mixture was then passed through the mill 5 times at 40°C until it wrapped around the rollers. The left and right cutters were used 10 times each, followed by 3 passes through the mill to obtain a silicone rubber sheet.

[0102] S2.2, Fluororubber blend:

[0103] At 60℃, fluororubber is plasticized in a thin pass for 5 minutes, then silicone rubber sheets are added and mixed. After mixing, the temperature is lowered to 40℃ and a vulcanizing agent is added. The mixture is then cut with a knife until no particles are visible, thus obtaining fluorosilicone composite rubber.

[0104] S3, Extrusion Molding and Braiding Reinforcement

[0105] S3.1 Inner layer tube blank extrusion and cooling / shaping:

[0106] Fluorosilicone composite rubber is pre-cut into strips and preheated at a constant temperature of 50℃ for 1 hour; the tube blank is extruded through an extruder and shaped by a vacuum sizing sleeve under a vacuum degree of -0.08MPa; it is then traction-speeded at 2m / min into a cooling water tank with a water temperature of 20±2℃ and a length of 6m to obtain the inner tube blank.

[0107] S3.2, Aramid fiber braiding reinforcement:

[0108] Aramid fibers are coated with a silane coupling agent ethanol solution, dried in a 70°C oven for 1 minute, and then woven using a 24-spindle high-speed braiding machine.

[0109] S3.3, Outer Coating and Composite Tube Molding

[0110] Using the same extruder, change the die, lower the temperature setting by 5℃, keep the traction speed consistent with the weaving step at 2m / min, and control the outer layer rubber thickness at 0.5±0.05mm to obtain the composite tube rough product;

[0111] S4, vulcanization molding

[0112] S4.1, First stage of vulcanization

[0113] The first stage of vulcanization of the composite pipe rough was carried out using a horizontal steam vulcanizing tank.

[0114] S4.2, Second stage vulcanization

[0115] After the first stage of vulcanization, it needs to be left to stand for 4 hours before the second stage of vulcanization is carried out using a hot air circulating oven.

[0116] After vulcanization, an internally braided silicone tube is obtained.

[0117] In S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 6:5:1:5;

[0118] The amount of KOH added is 1.5% of the total mass of methylvinyldichlorosilane, dimethyldichlorosilane, and vinyldimethylmethoxysilane.

[0119] In S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyldichlorosilane and vinyldimethylmethoxysilane is 1.5:2;

[0120] The amount of 4-dimethylaminopyridine added is 1% of the reaction substrate.

[0121] In step S1.3, the molar ratio of 3-pentadecanylphenol, paraformaldehyde, and 2-aminoethanethiol added in step S1.2 is 3.2:3:1.1.

[0122] In step S2.1, the mass ratio of MVQ-benzoxazine, fumed silica, and hydroxyl silicone oil during silicone rubber phase compounding is 100:30:4; the open mill roll temperature is 25℃, the thin pass roll gap is 0.5mm, and the compounding roll gap is 1.5mm.

[0123] In S2.2, when fluororubber is blended, the mass ratio of silicone rubber sheet to fluororubber is 100:50.

[0124] The vulcanizing agents are hydrogen-containing silicone oil crosslinking agent, platinum-vinylsiloxane complex, and 1-ethynylcyclohexanol;

[0125] The amount of hydrogen-containing silicone oil crosslinking agent is 1.5% of the total mass of the rubber compound, the amount of platinum-vinylsiloxane complex added is 0.5% of the total mass of the rubber compound, and the amount of 1-ethynylcyclohexanol added is 1% of the total mass of the rubber compound.

[0126] In step S3.2, the silane coupling agent is KH-792, and the mass concentration of the ethanol solution is 5%.

[0127] The parameters for the knitting machine are set as follows:

[0128] The fiber pretension is 10±0.5N / spindle, the weaving density is 16±0.5picks / cm, and the weaving layer coverage needs to be ≥80%.

[0129] In step S4, the parameters for the first stage of vulcanization are set as follows:

[0130] ① Heat from room temperature to 140℃ at a heating rate of 2℃ / min and hold for 15min;

[0131] ② Cool down from 140℃ to 80℃ at a heating rate of 1℃ / min, and hold for 8 minutes;

[0132] ③ Allow to cool naturally to room temperature;

[0133] The second stage of vulcanization is programmed as follows:

[0134] ① Heat from room temperature to 160℃ at a heating rate of 5℃ / min and hold for 1 hour;

[0135] ② Increase the temperature from 160℃ to 200℃ at a rate of 1℃ / min and hold for 2 hours;

[0136] ③ Allow to cool naturally to room temperature.

[0137] The thickness ratio of the inner layer adhesive to the outer layer adhesive in the braided silicone tube is 1.2:1.

[0138] Example 2:

[0139] The implementation method is the same as in Example 1, but...

[0140] In S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 5:5:0.75:5;

[0141] In S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyldichlorosilane and vinyldimethylmethoxysilane is 1.6:2;

[0142] The amount of 4-dimethylaminopyridine added was 1.5% of the reaction substrate.

[0143] In step S2.1, the mass ratio of MVQ-benzoxazine, fumed silica, and hydroxyl silicone oil during silicone rubber phase compounding is 100:25:4; the open mill roll temperature is 25℃, the thin pass roll gap is 0.5mm, and the compounding roll gap is 1.5mm.

[0144] In S2.2, when fluororubber is blended, the mass ratio of silicone rubber sheet to fluororubber is 100:60.

[0145] The thickness ratio of the inner layer adhesive to the outer layer adhesive in the braided silicone tube is 1:1.

[0146] Example 3:

[0147] The implementation method is the same as in Example 1, but...

[0148] In S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 4:5:0.5:5;

[0149] In S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyldichlorosilane and vinyldimethylmethoxysilane is 1.7:2;

[0150] The amount of 4-dimethylaminopyridine added was 2% of the reaction substrate.

[0151] In step S2.1, the mass ratio of MVQ-benzoxazine, fumed silica, and hydroxyl silicone oil during silicone rubber phase mixing is 100:20:4; the open mill roll temperature is 25℃, the thin pass roll gap is 0.5mm, and the mixing roll gap is 1.5mm.

[0152] In S2.2, when fluororubber is blended, the mass ratio of silicone rubber sheet to fluororubber is 100:70.

[0153] The thickness ratio of the inner layer adhesive to the outer layer adhesive in the braided silicone tube is 0.8:1.

[0154] Unlike the embodiments, the following comparative experiments were also designed:

[0155] Comparative Example 1: The formulation and experimental method are the same as those in Example 2, but in S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 15:5:0.75:5;

[0156] Comparative Example 2: The formulation and experimental method are the same as in Example 2, but in S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 1:5:0.75:5;

[0157] Comparative Example 3: The formulation and experimental method are the same as those in Example 2, but in S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 5:5:0.1:5;

[0158] Comparative Example 4: The formulation and experimental method are the same as in Example 2, but in S1.1, the mass ratio of methylvinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane, and NaHCO3 aqueous solution is 5:5:2:5;

[0159] Comparative Example 5: The formulation and experimental method are the same as those in Example 2, but in S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyldichlorosilane and vinyldimethylmethoxysilane is 0.5:2;

[0160] Comparative Example 6: The formulation and experimental method are the same as those in Example 2, but in S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyldichlorosilane and vinyldimethylmethoxysilane is 3:2;

[0161] Comparative Example 7: The formulation and experimental methods are the same as in Example 2, but the thickness ratio of the inner layer adhesive to the outer layer adhesive of the braided silicone tube is 0.4:1;

[0162] Comparative Example 8: The formulation and experimental methods are the same as in Example 2, but the thickness ratio of the inner layer adhesive to the outer layer adhesive of the braided silicone tube is 2:1.

[0163] According to standards such as ISO 37, GB / T 531.1, ISO 11359-2, ISO 815, ISO 4639, and GJB150.5, the present invention was tested for tensile strength, hardness (Shore A), coefficient of thermal expansion, degree of compressive set, long-term resistance to media, and resistance to temperature shock. The corresponding results are summarized in Table 2.

[0164] Table 2. Performance test data of silicone tubing with internal braided structure

[0165]

[0166] Data Analysis:

[0167] By comparing Example 2, Comparative Example 1, and Comparative Example 2, it can be seen that the proportion of vinyl monomers has an impact on the balance of crosslinking network construction. Excess or deficiency of vinyl monomers will destroy the regularity of molecular chains, resulting in uneven stress distribution, defects in the crosslinking network, increased freedom of thermal motion of molecular chain segments, and a surge in expansion rate, which in turn determines the interfacial bonding strength between benzoxazine and fluororubber. Excess vinyl monomers will lead to excessively high crosslinking density, a surge in hose hardness, increased brittleness, and even cracking of the inner layer, as well as a deterioration of the coefficient of thermal expansion. When vinyl monomers are insufficient, the crosslinking points are sparse, the interlayer bonding force of the hose is severely lost, delamination is obvious, thermal stability collapses, and strength drops sharply.

[0168] By comparing Example 2, Comparative Example 3, and Comparative Example 4, it can be seen that vinyl monomers are key performance regulators. The amount of vinyl dimethyl methoxysilane determines the number of vinyl groups on the silicone rubber backbone. A suitable ratio can ensure that there are enough active sites in the system for subsequent functionalization, while avoiding excessive crosslinking, and achieving synergistic optimization of strength, flexibility, and interface stability.

[0169] In Comparative Example 3, the amount of vinyl dimethyl methoxysilane was insufficient. Excessive vinyl content would cause local over-crosslinking, resulting in uneven distribution of crosslinking points, stress concentration points, and a sharp drop in tensile strength. Furthermore, during the vulcanization process, the difference in shrinkage rates between the inner and outer layers of the adhesive intensified, the flexibility of the molecular chains was lost, and the solvent could more easily penetrate from the microcracks, leading to a decrease in resistance to media.

[0170] The excessive amount of vinyl dimethyl methoxysilane in Comparative Example 4 resulted in insufficient active vinyl groups in the silicone rubber molecular chain, decreased amino grafting rate, reduced active sites synthesized with benzoxazine, decreased crosslinking density between molecular chains, and insufficient polar groups. This led to poor interfacial compatibility between the rubber and aramid fiber braided layer, causing outer layer peeling under temperature shock, easy medium penetration, and a significant increase in volume change rate.

[0171] By comparing Example 2, Comparative Example 5, and Comparative Example 6, it can be seen that the amount of amino grafting in Comparative Example 5 is insufficient, which leads to the inability of the active vinyl groups of the MVQ molecular chain to be fully grafted with amino groups. Since amino groups are the key reaction sites for the subsequent synthesis of benzoxazine rings, their deficiency directly leads to a sharp drop in the grafting rate of benzoxazine groups and insufficient cross-linking density between molecular chains. Although there is a platinum vulcanization system in the system to construct a fluorosilicone rubber network, its strength is far inferior to that of the double cross-linked network. The loose cross-linked network cannot prevent the penetration of the medium, the volume change rate increases significantly, and the tensile strength decreases accordingly.

[0172] In Comparative Example 6, excessive amino grafting caused the benzoxazine groups to aggregate densely, forming rigid micro-regions that disrupted the flexibility of the molecular chain. During vulcanization, the ring-opening polymerization rate of benzoxazine was uneven, generating internal stress. When subjected to temperature shock, the stress was released, resulting in hardening and cracking of the hose surface and a significant increase in the brittleness of the material.

[0173] By comparing Example 2, Comparative Example 7, and Comparative Example 8, it can be seen that the inner layer adhesive acts as a stress buffer and a medium barrier, while the outer layer adhesive acts as an environmental protection and restrains the inner layer. A sufficiently thick inner layer adhesive can effectively wrap the fibers and block the medium, while a sufficiently thick outer layer adhesive will provide mechanical protection and balance the internal stress.

[0174] The inner layer of Comparative Example 7 is too thin and cannot effectively wrap the aramid braided layer. The bonding area between the fiber and the rubber interface is reduced sharply, which makes it impossible to evenly distribute the stress to the braided layer. When stretched, the stress is concentrated in the local fibers, the braided layer debonds, and the appearance is severe delamination. In addition, the ability of the tube to block solvents is weakened, and the medium will directly erode the fiber-rubber interface, resulting in a collapse in strength and loss of structural load-bearing capacity, accompanied by a surge in the volume change rate of the tube.

[0175] In Comparative Example 8, the inner layer of adhesive was too thick, and the inner layer of adhesive was more prone to accumulating shrinkage stress. The difference in thermal shrinkage was amplified. During vulcanization and cooling, the shrinkage rate of the inner layer of adhesive was greater than that of the outer layer of adhesive. Shear stress was generated at the interface. When subjected to temperature shock, the stress was released, and the inner layer of adhesive itself cracked. The microcracks became solvent penetration channels, and the system lacked toughness.

[0176] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing an internally braided structure silicone tube, characterized by, Comprising the following steps: S1, preparation of modified silicone rubber S1.1, synthesis of high-vinyl MVQ: Methyl vinyl dichlorosilane, dimethyl dichlorosilane and vinyl dimethyl methoxysilane are dissolved in tetrahydrofuran, cooled to 0-5℃ in an ice bath; add deionized water dropwise, maintain the temperature ≤10℃, add NaHCO3 solution, stir for 30min, remove the water layer by liquid-liquid separation; Add KOH, heat to 60℃ for 4h, add acetic acid to neutralize the reaction solution, filter the solid phase with tetrahydrofuran, and obtain high-vinyl methyl vinyl silicone rubber, i.e. high-vinyl MVQ; S1.2, amino grafting: The high-vinyl MVQ was dissolved in THF and stirred for 30 min under nitrogen protection; 2-aminoethanethiol was added and stirred for 10 min in the dark; 4-dimethylaminopyridine was added and transferred into a 365 nm UV reactor, irradiated for 5 min at a light intensity of 50 mW / cm 2 ; the product was poured into ethanol and the process of flocculation and THF dissolution was repeated 3 times; vacuum oven at 55°C until constant weight to obtain MVQ-g-NH2; S1.3, synthesis of benzoxazine group: Dissolve 3-pentadecyl phenol, paraformaldehyde and MVQ-g-NH2 in tetrahydrofuran under nitrogen protection, 80℃, 100rpm magnetic stirring reflux for 6h; cool to room temperature, add 1% mass fraction of NaOH aqueous solution dropwise to neutralize to pH=7; pour the product into ethanol, repeat the process of flocculation and THF dissolution for 3 times; vacuum oven at 55℃ until constant weight to obtain MVQ-benzoxazine; S2, mixing of fluorosilicone rubber composite S2.1, mixing of silicone rubber phase: Add MVQ-benzoxazine, fumed silica and hydroxyl silicone oil in the open mill in turn for mixing, thin pass 5 times at 40℃ until the roll is wrapped; left and right cutter each 10 times, thin pass 3 times, to obtain silicone rubber sheet; S2.2, fluororubber blending: At 60℃, plasticize the fluororubber and thin pass for 5min, add silicone rubber sheet for blending, after mixing, add vulcanizing agent at 40℃; left and right cutter until no particles, to obtain fluorosilicon composite rubber; S3, extrusion molding and woven reinforcement S3.1, inner layer pipe blank extrusion and cooling shaping: Cut the fluorosilicon composite rubber into strips, preheat at 50℃ for 1h; extrude the pipe blank through the extruder, shape through the vacuum sizing sleeve under a vacuum degree of-0.08MPa; enter the cooling water tank with water temperature of 20±2℃ and length of 6m at a pulling speed of 2m / min to obtain the inner layer pipe blank; S3.2, aramid fiber woven reinforcement: Coat the aramid fiber with silane coupling agent ethanol solution on the surface, dry at 70℃ for 1min, then use 24 spindle high-speed weaving machine for weaving; S3.3, outer layer rubber coating and composite pipe forming: Use the same set of extruder, replace the die, set the temperature 5℃ lower, the pulling speed is consistent with the weaving step, maintain 2m / min, the outer layer rubber thickness is controlled at 0.5±0.05mm, to obtain the composite pipe crude product; S4, vulcanization molding S4.1, first stage vulcanization: Use horizontal steam vulcanization tank for first stage vulcanization of the composite pipe crude product; S4.2, second stage vulcanization: After the first stage vulcanization, stand for 4h, then use hot air circulating oven for second stage vulcanization; Vulcanization is completed, to obtain the inner woven structure silicone tube.

2. The method of claim 1, wherein: In S1.1, the mass ratio of methyl vinyl dichlorosilane, dimethyl dichlorosilane, vinyl dimethyl methoxysilane and NaHCO3 solution is 4-6:5:0.5-1:5; The NaHCO3 solution is 10% mass fraction NaHCO3 aqueous solution; The amount of KOH added is 1.5% of the total mass of methylvinyl dichlorosilane, dimethyl dichlorosilane and vinyl dimethyl methoxysilane.

3. The method of claim 1, wherein: In S1.2, the molar ratio of 2-aminoethanethiol to the added methylvinyl dichlorosilane and vinyl dimethyl methoxysilane is 1.5-1.7:

2. The amount of 4-dimethylamino pyridine added is 1%-2% of the reaction substrate.

4. The method of claim 1, wherein: In S1.3, the molar ratio of 3-pentadecyl phenol, paraformaldehyde to 2-aminoethanethiol added in S1.2 is 3.2:3:1.

1.

5. The method of claim 1, wherein: In S2.1, the mass ratio of MVQ-benzoxazine, fumed silica and hydroxyl silicone oil in the mixing of silicone rubber is 100:20-30:4; the roll temperature of the open mill is 25℃, the thin pass roll gap is 0.5mm and the mixing roll gap is 1.5mm.

6. The method of claim 1, wherein: In S2.2, the fluororubber is fluorosilicone rubber FVMQ, and the mass ratio of silicone rubber sheet to fluororubber during blending of the fluororubber is 100:50-70. The vulcanizing agent is hydrogen-containing silicone oil crosslinking agent, platinum-vinyl siloxane complex and 1-ethynylcyclohexanol. Among them, the amount of hydrogen-containing silicone oil crosslinking agent is 1.5% of the total mass of the rubber compound, the amount of platinum-vinyl siloxane complex is 0.5% of the total mass of the rubber compound, and the amount of 1-ethynylcyclohexanol is 1% of the total mass of the rubber compound.

7. The method of claim 1, wherein: In S3.2, the silane coupling agent is KH-792, and the mass concentration of KH-792 ethanol solution is 5%. The parameters of the braider are set as follows: The fiber pretension is 10±0.5N / spool, the braiding density is 16±0.5picks / cm, and the braided layer coverage needs to be ≥80%.

8. The method of claim 1, wherein: In S4, the first stage of vulcanization is set as follows: ①Rise from room temperature to 140℃ at a rate of 2℃ / min, and keep the temperature for 15min; ②Cool from 140℃ to 80℃ at a rate of 1℃ / min, and keep the temperature for 8min; ③Cool naturally to room temperature; The second stage of vulcanization is set as follows: ①Rise from room temperature to 160℃ at a rate of 5℃ / min, and keep the temperature for 1h; ②Rise from 160℃ to 200℃ at a rate of 1℃ / min, and keep the temperature for 2h; ③Cool naturally to room temperature.

9. A braided-in structure silicone tube prepared by the production method according to any one of claims 1 to 8, characterized in that, The thickness ratio of the inner layer rubber to the outer layer rubber of the inner braided structure silicone tube is 0.8-1.2:1.

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