Preparation method of environment-friendly halogen-free low-smoke flame-retardant silicone rubber cable insulating material

Abstract

The invention discloses a preparation method of an environment-friendly halogen-free low-smoke flame-retardant silicone rubber cable insulating material, and relates to the technical field of silicone rubber cable insulating materials. Performing premixing; carrying out supercritical CO2 pretreatment; and vulcanizing. According to the halogen-free low-smoke and high-flame-retardancy flame-retardant composite material disclosed by the invention, by adopting the hydroxyapatite core-boron nitride shell composite filler, matching with the ammonium polyphosphate and silicon-nitrogen resin compounded flame-retardant system and combining the synergistic effect of the dynamic compatibilizer and the hydroxyl-terminated polybutadiene siloxane block copolymer, the synchronous improvement of the halogen-free low-smoke and high-flame-retardancy properties of the material is realized; the smoke suppression effect and the flame-retardant efficiency of the material during combustion can be remarkably improved, and meanwhile, the harm of halogen release to the environment and a human body is avoided, so that the problem that a traditional silicone rubber cable insulating material is difficult to consider both the environmental protection property and the high flame-retardant property can be solved.

Description

Technical Field

[0001] This invention relates to the field of silicone rubber cable insulation materials, specifically to a method for preparing environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation materials. Background Technology

[0002] The core function of cable insulation material is to isolate the cable conductor from the external environment and other conductors, thereby ensuring the safe transmission of electrical energy. It not only prevents current leakage through electrical insulation performance, avoiding the risk of short circuits or electric shock, but also provides physical protection against external mechanical damage, moisture intrusion and chemical corrosion, reducing the impact of external factors on the conductor, ultimately extending the service life of the cable and ensuring its stable operation under complex conditions.

[0003] In existing technologies, traditional flame-retardant systems for cable insulation materials often rely on halogen-containing components. These release toxic and corrosive gases and substances during combustion, harming human health and polluting the environment, thus failing to meet current environmental protection requirements. Furthermore, the pursuit of environmental friendliness by reducing or eliminating halogens often leads to a significant decrease in the flame-retardant efficiency of the material, accompanied by poor smoke suppression and high smoke concentration during combustion. Therefore, this invention provides a method for preparing an environmentally friendly halogen-free, low-smoke flame-retardant silicone rubber cable insulation material. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material. This invention uses a hydroxyapatite core-boron nitride shell composite filler, combined with a flame-retardant system of ammonium polyphosphate and silicon nitrogen resin, and combines the synergistic effect of dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer to simultaneously improve flame retardant efficiency and smoke suppression effect on the basis of halogen-free. In addition, a supercritical CO2 pretreatment process is introduced, along with a staged mixing method to optimize the dispersion of internal components of the material and improve structural uniformity. At the same time, an organotin titanate composite catalyst is added in two stages, and a gradient temperature-pressure vulcanization regime is designed to precisely control the crosslinking density of the material. Finally, the material achieves simultaneous improvement in environmental protection, flame retardancy, mechanical properties, insulation properties and anti-aging properties.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The preparation method of environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material includes: step (1): by weight, take 96-104 parts of methyl vinyl vulcanized silicone rubber raw rubber, 4-7 parts of composite filler, 9-11 parts of ammonium polyphosphate and silicon nitrogen resin compound flame retardant system, 0.6-1.1 parts of dynamic compatibilizer, 0.9-1.4 parts of hydroxyl-terminated polybutadiene siloxane block copolymer and 0.12-0.28 parts of organotin titanate composite catalyst; The composite filler is a hydroxyapatite core-boron nitride shell composite filler; Step (2): Under the conditions of temperature 58℃~63℃ and vacuum degree -0.088MPa~-0.072MPa, methyl vinyl vulcanized silicone rubber raw rubber, composite filler, dynamic compatibilizer, hydroxyl-terminated polybutadiene siloxane block copolymer, polyphosphate ammonium and silicon nitrogen resin compound flame retardant system and 50% of organotin titanate composite catalyst are added in sequence and mixed in stages to obtain premixed rubber; Step (3): Place the premixed adhesive obtained in step (2) in a supercritical CO2 environment with a temperature of 34℃~46℃ and a pressure of 8MPa~12MPa, keep it at the temperature and pressure for 20~30min, release the pressure and then introduce inert nitrogen gas for replacement to obtain the pretreated premixed adhesive. Step (4): Add the remaining 50% of the organic tin titanate composite catalyst to the pretreated premixed adhesive obtained in step (3) and vulcanize to obtain vulcanized silicone rubber cable insulation material.

[0006] Preferably, the vinyl content of the raw methyl vinyl vulcanized silicone rubber in step (1) is 0.16% to 0.24% by mass.

[0007] Preferably, the structure of the composite filler in step (1) is as follows: the core is hydroxyapatite microspheres, the particle size of the microspheres is 1.6μm to 2.1μm, and the porosity is 34% to 41%; The outer shell is an amino-modified boron nitride nanosheet layer, the thickness of which is 6nm to 8nm and the number of layers is 3 to 5; The core and shell are bonded by γ-aminopropyltriethoxysilane, and the grafting rate of γ-aminopropyltriethoxysilane on the surface of the composite filler is 68% to 95%.

[0008] Preferably, the dynamic compatibilizer in step (1) is a physical blend of γ-chloropropylmethyldimethoxysilane and maleic anhydride-grafted ethylene-vinyl acetate copolymer, wherein the molar ratio of γ-chloropropylmethyldimethoxysilane to maleic anhydride-grafted ethylene-vinyl acetate copolymer is 1:0.72 to 1:0.88.

[0009] Preferably, the parameters of the polyphosphate and silica-nitrogen resin composite flame retardant system in step (1) are as follows: the degree of polymerization of polyphosphate n = 1020 to 1180, the mass fraction of nitrogen content of silica-nitrogen resin is 39% to 41%, and the mass ratio of polyphosphate to silica-nitrogen resin is 1:1.42 to 1:1.58.

[0010] Preferably, the parameters of the hydroxyl-terminated polybutadiene siloxane block copolymer in step (1) are as follows: the block ratio is hydroxyl-terminated polybutadiene segments: siloxane segments = 2:0.92 to 2:1.08; The number-average molecular weight is 3.0 × 10⁻⁶. 4 ~5.0×104 Da; The mass ratio of the hydroxyl-terminated polybutadiene siloxane block copolymer to the composite filler in step (1) is 1:4.2 to 1:5.8.

[0011] Preferably, the parameters of the organotin titanate composite catalyst in step (1) are as follows: the components include dibutyltin dilaurate and tetrabutyl titanate, and the mass fraction of the purity of dibutyltin dilaurate is 99.6% to 99.8%; The degree of hydrolysis of tetrabutyl titanate is 14%–21% by mass; The molar ratio of dibutyltin dilaurate to tetrabutyl titanate is 1:1.12 to 1:1.28.

[0012] Preferably, the specific process of staged mixing in step (2) is as follows: Add methyl vinyl vulcanized silicone rubber raw material and composite filler, and mix at a speed of 30 r / min to 36 r / min for 7.5 min to 8.5 min; Add dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer, increase the rotation speed to 44 r / min to 50 r / min, and mix for 3.2 min to 3.8 min; Add a flame retardant system of ammonium polyphosphate and silicon nitride resin and 50% of an organotin titanate composite catalyst, maintain a rotation speed of 44 r / min to 50 r / min, and simultaneously raise the temperature to 87℃ to 93℃, and mix for 4.5 min to 5.5 min to obtain a premixed rubber.

[0013] Preferably, in step (3), the inert nitrogen flow rate is 1.2 L / min to 1.8 L / min, and the replacement time is 8 min to 12 min; During the replacement process, the temperature of the premixed rubber material treated with supercritical CO2 was maintained at 34℃~46℃.

[0014] Preferably, in step (4), the vulcanization adopts a gradient temperature-pressure regime, specifically: maintaining the temperature at 117℃~123℃ and the pressure at 0.95MPa~1.05MPa for 4.5min~5.5min; The temperature is increased to 157℃ to 163℃ at a heating rate of 4.5℃ / min to 5.5℃ / min, while the pressure is adjusted to 1.35MPa to 1.45MPa and held for 7.5min to 8.5min. Cool to 137℃~143℃ at a cooling rate of 1.5℃ / min~2.5℃ / min, while adjusting the pressure to 1.15MPa~1.25MPa and holding for 2.5min~3.5min; The vulcanization process is completed by allowing the temperature to cool naturally to room temperature.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a hydroxyapatite core-boron nitride shell composite filler, combined with a flame-retardant system of ammonium polyphosphate and silicon nitrogen resin, and integrates the synergistic effect of dynamic compatibilizers and hydroxyl-terminated polybutadiene siloxane block copolymers. This achieves simultaneous improvement in halogen-free, low-smoke, and high flame-retardant properties of the material. Compared with existing technologies, it can significantly improve the smoke suppression effect and flame-retardant efficiency of the material during combustion, while avoiding the harm of halogen release to the environment and human body. Therefore, it can solve the problem that traditional silicone rubber cable insulation materials cannot simultaneously achieve both environmental protection and high flame-retardant performance.

[0016] 2. This invention pre-treats the premixed rubber in a supercritical CO2 environment, and then combines it with a staged mixing and gradient temperature-pressure vulcanization process to achieve precise control of the uniformity of the internal structure and crosslinking density of the material. Compared with the prior art, it can improve the stability of the mechanical and insulation properties of the material and reduce performance fluctuations caused by uneven mixing or improper vulcanization process. Therefore, it can solve the problems of poor material performance consistency and easy occurrence of local defects under traditional preparation processes.

[0017] 3. This invention improves the compatibility of each component by adding the organotin titanate composite catalyst in two stages, combined with a specific dynamic compatibilizer, thereby achieving a balance between material processing flowability and final product performance. Compared with the prior art, this invention can improve the forming efficiency of the material during processing, while ensuring the anti-aging performance and interfacial bonding strength of the finished product. Therefore, it can solve the problem of processing difficulties or product performance degradation caused by the one-time addition of traditional catalysts. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This embodiment provides a method for preparing an environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material, including: step (1): by weight, take 96-104 parts of methyl vinyl vulcanized silicone rubber raw rubber, 4-7 parts of composite filler, 9-11 parts of ammonium polyphosphate and silicon nitrogen resin compound flame retardant system, 0.6-1.1 parts of dynamic compatibilizer, 0.9-1.4 parts of hydroxyl-terminated polybutadiene siloxane block copolymer and 0.12-0.28 parts of organotin titanate composite catalyst; The composite filler is a hydroxyapatite core-boron nitride shell composite filler; Step (2): Under the conditions of temperature 58℃~63℃ and vacuum degree -0.088MPa~-0.072MPa, methyl vinyl vulcanized silicone rubber raw rubber, composite filler, dynamic compatibilizer, hydroxyl-terminated polybutadiene siloxane block copolymer, polyphosphate ammonium and silicon nitrogen resin compound flame retardant system and 50% of organotin titanate composite catalyst are added in sequence and mixed in stages to obtain premixed rubber; Step (3): Place the premixed adhesive obtained in step (2) in a supercritical CO2 environment with a temperature of 34℃~46℃ and a pressure of 8MPa~12MPa, keep it at the temperature and pressure for 20~30min, release the pressure and then introduce inert nitrogen gas for replacement to obtain the pretreated premixed adhesive. Step (4): Add the remaining 50% of the organic tin titanate composite catalyst to the pretreated premixed adhesive obtained in step (3) and vulcanize to obtain vulcanized silicone rubber cable insulation material.

[0020] In some embodiments, the mass fraction of vinyl content in the raw methyl vinyl vulcanized silicone rubber in step (1) is 0.16% to 0.24%.

[0021] In some embodiments, the structure of the composite filler in step (1) is as follows: the core is hydroxyapatite microspheres with a particle size of 1.6 μm to 2.1 μm and a porosity of 34% to 41%; The outer shell is composed of amino-modified boron nitride nanosheets with a thickness of 6 nm to 8 nm and 3 to 5 layers. The core and shell are bonded by γ-aminopropyltriethoxysilane, and the grafting rate of γ-aminopropyltriethoxysilane on the surface of the composite filler is 68% to 95%.

[0022] In some embodiments, the dynamic compatibilizer in step (1) is a physical blend of γ-chloropropylmethyldimethoxysilane and maleic anhydride-grafted ethylene-vinyl acetate copolymer, wherein the molar ratio of γ-chloropropylmethyldimethoxysilane to maleic anhydride-grafted ethylene-vinyl acetate copolymer is 1:0.72 to 1:0.88.

[0023] In some embodiments, the parameters of the flame retardant system of ammonium polyphosphate and silica-nitrogen resin in step (1) are as follows: the degree of polymerization of ammonium polyphosphate n = 1020 to 1180, the mass fraction of nitrogen content of silica-nitrogen resin is 39% to 41%, and the mass ratio of ammonium polyphosphate to silica-nitrogen resin is 1:1.42 to 1:1.58.

[0024] In some embodiments, the parameters of the hydroxyl-terminated polybutadiene siloxane block copolymer in step (1) are as follows: the block ratio is hydroxyl-terminated polybutadiene segments: siloxane segments = 2:0.92 to 2:1.08; The number-average molecular weight is 3.0 × 10⁻⁶. 4 ~5.0×104 Da; The mass ratio of the hydroxyl-terminated polybutadiene siloxane block copolymer to the composite filler in step (1) is 1:4.2 to 1:5.8.

[0025] In some embodiments, the parameters of the organotin titanate composite catalyst in step (1) are as follows: the components include dibutyltin dilaurate and tetrabutyl titanate, and the mass fraction of the purity of dibutyltin dilaurate is 99.6% to 99.8%; The degree of hydrolysis of tetrabutyl titanate is 14%–21% by mass; The molar ratio of dibutyltin dilaurate to tetrabutyl titanate is 1:1.12 to 1:1.28.

[0026] In some embodiments, the specific process of staged mixing in step (2) is as follows: Add methyl vinyl vulcanized silicone rubber raw material and composite filler, and mix at a speed of 30 r / min to 36 r / min for 7.5 min to 8.5 min; Add dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer, increase the rotation speed to 44 r / min to 50 r / min, and mix for 3.2 min to 3.8 min; Add a flame retardant system of ammonium polyphosphate and silicon nitride resin and 50% of an organotin titanate composite catalyst, maintain a rotation speed of 44 r / min to 50 r / min, and simultaneously raise the temperature to 87℃ to 93℃, and mix for 4.5 min to 5.5 min to obtain a premixed rubber.

[0027] In some embodiments, the inert nitrogen flow rate in step (3) is 1.2 L / min to 1.8 L / min, and the replacement time is 8 min to 12 min; During the replacement process, the temperature of the premixed rubber material treated with supercritical CO2 was maintained at 34℃~46℃.

[0028] In some embodiments, the vulcanization in step (4) adopts a gradient temperature-pressure regime, specifically: maintaining the temperature at 117℃~123℃ and the pressure at 0.95MPa~1.05MPa for 4.5min~5.5min; The temperature is increased to 157℃ to 163℃ at a heating rate of 4.5℃ / min to 5.5℃ / min, while the pressure is adjusted to 1.35MPa to 1.45MPa and held for 7.5min to 8.5min. Cool to 137℃~143℃ at a cooling rate of 1.5℃ / min~2.5℃ / min, while adjusting the pressure to 1.15MPa~1.25MPa and holding for 2.5min~3.5min; The vulcanization process is completed by allowing the temperature to cool naturally to room temperature.

[0029] Based on the foregoing embodiments, the following sets of experiments were conducted: It should be noted that the raw materials used in the following embodiments are all commercially available.

[0030] Example 1: A method for preparing environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material, comprising: Step (1) Raw material selection: By weight, take 98 parts of methyl vinyl vulcanized silicone rubber raw rubber with a vinyl content of 0.20%; take 5 parts of composite filler; take 10 parts of ammonium polyphosphate and silicon nitrogen resin compound flame retardant system; take 0.8 parts of dynamic compatibilizer; take 1.0 parts of hydroxyl-terminated polybutadiene siloxane block copolymer; take 0.20 parts of organotin titanate composite catalyst.

[0031] Composite filler: The hydroxyapatite microspheres are commercially available medical grade, model HA-MS-18, with a particle size of 1.8 μm and a porosity of 37%; the outer shell is an amino-modified boron nitride nanosheet layer with a thickness of 7 nm and 4 layers; the core and outer shell are bonded by γ-aminopropyltriethoxysilane, which is purchased from Sinopharm Group with a purity of 98%; the grafting rate was determined to be 82% by X-ray photoelectron spectroscopy.

[0032] Dynamic compatibilizer: a physical blend of γ-chloropropylmethyldimethoxysilane and maleic anhydride-grafted ethylene-vinyl acetate copolymer. The γ-chloropropylmethyldimethoxysilane was purchased from Aladdin with a purity of 97%. The maleic anhydride-grafted ethylene-vinyl acetate copolymer is a commercially available model, model EVA-g-MAH, with a grafting rate of 1.5%. The molar ratio of the two is 1:0.80.

[0033] Flame retardant system of ammonium polyphosphate and silica-nitrogen resin: ammonium polyphosphate degree of polymerization 1100, commercially available model is APP-1000; silica-nitrogen resin nitrogen content 40%, commercially available model is SN-601; mass ratio of ammonium polyphosphate to silica-nitrogen resin is 1:1.50.

[0034] Hydroxyl-terminated polybutadiene-siloxane block copolymer: Prepared by free radical polymerization, using hydroxyl-terminated polybutadiene and octamethylcyclotetrasiloxane as raw materials. The hydroxyl-terminated polybutadiene (Mn=2000) was purchased from Aldrich; the octamethylcyclotetrasiloxane was purchased from Sinopharm Group with a purity of 99%. Polymerization was carried out under the catalysis of stannous octoate, with a stannous octoate purity of 98%. The number-average molecular weight was determined to be 4.0 × 10⁻¹⁰ by gel permeation chromatography. Da; The mass ratio of the block copolymer to the composite filler is 1:5.0.

[0035] Organotin titanate composite catalyst: composed of dibutyltin dilaurate and tetrabutyl titanate. The dibutyltin dilaurate was purchased from Aladdin with a purity of 99.7%; the tetrabutyl titanate had a degree of hydrolysis of 18% and was purchased from Sinopharm Group; the molar ratio of the two was 1:1.20.

[0036] Step (2) Preparation of premixed rubber: Under the conditions of 60℃ and vacuum degree -0.080MPa, methyl vinyl vulcanized silicone rubber raw rubber, composite filler, dynamic compatibilizer, hydroxyl-terminated polybutadiene siloxane block copolymer, polyphosphate ammonium and silicon nitrogen resin compound flame retardant system and 50% of organotin titanate composite catalyst are added in sequence. The 50% of organotin titanate composite catalyst is 0.10 parts. After staged mixing, the premixed rubber is obtained.

[0037] The specific process of phased mixing is as follows: Add methyl vinyl vulcanized silicone rubber raw material and composite filler, and mix at 33 r / min for 8 min; Add dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer, increase the rotation speed to 47 r / min, and mix for 3.5 min; Add a flame retardant system of ammonium polyphosphate and silicon nitride resin and 50% of an organotin titanate composite catalyst, maintain a rotation speed of 47 r / min, and simultaneously heat to 90℃, mix for 5 min to obtain a premixed adhesive.

[0038] Step (3) Supercritical pretreatment: The premixed adhesive obtained in step (2) is placed in a supercritical CO2 environment at a temperature of 38℃ and a pressure of 10MPa, and kept at the temperature and pressure for 25min. After depressurization, inert nitrogen is introduced for replacement. The inert nitrogen flow rate is 1.5L / min and the replacement time is 10min. The material temperature is maintained at 38℃ during the replacement process to obtain the pretreated premixed adhesive.

[0039] Step (4) Vulcanization molding: Add the remaining 50% of the organic tin titanate composite catalyst to the pretreated premixed rubber obtained in step (3). The remaining 50% of the organic tin titanate composite catalyst is 0.10 parts. Vulcanize to obtain vulcanized silicone rubber cable insulation material.

[0040] The vulcanization process employs a gradient temperature-pressure regime, specifically: Maintain at 120℃ and 1.0MPa for 5 minutes; The temperature was increased to 160℃ at a rate of 5℃ / min, while the pressure was adjusted to 1.4MPa and held for 8min. Cool to 140℃ at a cooling rate of 2℃ / min, while adjusting the pressure to 1.2MPa and holding for 3min; The vulcanization process is completed by allowing the temperature to cool naturally to room temperature.

[0041] Example 2: A method for preparing environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material, comprising: Step (1) Raw material selection: By weight, take 102 parts of methyl vinyl vulcanized silicone rubber raw rubber with a vinyl content of 0.22%; take 6 parts of composite filler; take 10.5 parts of ammonium polyphosphate and silicon nitrogen resin compound flame retardant system; take 1.0 parts of dynamic compatibilizer; take 1.2 parts of hydroxyl-terminated polybutadiene siloxane block copolymer; take 0.25 parts of organotin titanate composite catalyst.

[0042] Composite filler: The hydroxyapatite microspheres are commercially available medical grade, model HA-MS-18, with a particle size of 1.8 μm and a porosity of 37%; the outer shell is an amino-modified boron nitride nanosheet, which is prepared according to the method of Example 1 of patent CN202310245678.9, with a thickness of 7 nm and 4 layers; the core and the outer shell are bonded by γ-aminopropyltriethoxysilane, which is purchased from Sinopharm Group with a purity of 98%; the grafting rate is 90% as determined by X-ray photoelectron spectroscopy.

[0043] Dynamic compatibilizer: a physical blend of γ-chloropropylmethyldimethoxysilane and maleic anhydride-grafted ethylene-vinyl acetate copolymer. The γ-chloropropylmethyldimethoxysilane was purchased from Aladdin with a purity of 97%. The maleic anhydride-grafted ethylene-vinyl acetate copolymer is a commercially available model, model EVA-g-MAH, with a grafting rate of 1.5%. The molar ratio of the two is 1:0.80.

[0044] Flame retardant system of ammonium polyphosphate and silica-nitrogen resin: ammonium polyphosphate degree of polymerization 1100, commercially available model is APP-1000; silica-nitrogen resin nitrogen content 40%, commercially available model is SN-601; mass ratio of ammonium polyphosphate to silica-nitrogen resin is 1:1.50.

[0045] Hydroxyl-terminated polybutadiene-siloxane block copolymer: Prepared by free radical polymerization, using hydroxyl-terminated polybutadiene and octamethylcyclotetrasiloxane as raw materials. The hydroxyl-terminated polybutadiene (Mn=2000) was purchased from Aldrich; the octamethylcyclotetrasiloxane was purchased from Sinopharm Group with a purity of 99%. Polymerization was carried out under the catalysis of stannous octoate, with a stannous octoate purity of 98%. The number-average molecular weight was determined to be 4.8 × 10⁻⁶ m³ / s by gel permeation chromatography. Da; The mass ratio of the block copolymer to the composite filler is 1:5.0.

[0046] Organotin titanate composite catalyst: composed of dibutyltin dilaurate and tetrabutyl titanate. The dibutyltin dilaurate was purchased from Aladdin with a purity of 99.7%; the tetrabutyl titanate had a degree of hydrolysis of 18% and was purchased from Sinopharm Group; the molar ratio of the two was 1:1.20.

[0047] Step (2) Preparation of premixed rubber: Under the conditions of 60℃ and vacuum degree -0.080MPa, methyl vinyl vulcanized silicone rubber raw rubber, composite filler, dynamic compatibilizer, hydroxyl-terminated polybutadiene siloxane block copolymer, polyphosphate ammonium and silicon nitrogen resin compound flame retardant system and 50% of organotin titanate composite catalyst are added in sequence. The 50% of organotin titanate composite catalyst is 0.125 parts. After staged mixing, the premixed rubber is obtained.

[0048] The specific process of phased mixing is as follows: Add methyl vinyl vulcanized silicone rubber raw rubber and composite filler, and mix at 35 r / min for 8 min; Add dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer, increase the rotation speed to 49 r / min, and mix for 3.5 min; Add a flame retardant system of ammonium polyphosphate and silicon nitride resin and 50% of an organotin titanate composite catalyst, maintain a rotation speed of 49 r / min, and simultaneously heat to 90℃, mix for 5 min to obtain a premixed adhesive.

[0049] Step (3) Supercritical pretreatment: The premixed adhesive obtained in step (2) is placed in a supercritical CO2 environment at a temperature of 42℃ and a pressure of 10MPa for 25 minutes. After depressurization, inert nitrogen gas is introduced for replacement. The inert nitrogen gas flow rate is 1.5L / min and the replacement time is 10 minutes. The material temperature is maintained at 42℃ during the replacement process to obtain the pretreated premixed adhesive.

[0050] Step (4) Vulcanization molding: Add the remaining 50% of the organic tin titanate composite catalyst to the pretreated premixed rubber obtained in step (3). The remaining 50% of the organic tin titanate composite catalyst is 0.125 parts. Vulcanize to obtain vulcanized silicone rubber cable insulation material.

[0051] The vulcanization process employs a gradient temperature-pressure regime, specifically: Maintain at 120℃ and 1.0MPa for 5 minutes; The temperature was increased to 162℃ at a rate of 5℃ / min, while the pressure was adjusted to 1.4MPa and held for 8min. Cool to 140℃ at a cooling rate of 2℃ / min, while adjusting the pressure to 1.2MPa and holding for 3min; The vulcanization process is completed by allowing the temperature to cool naturally to room temperature.

[0052] Example 3: A method for preparing environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material, comprising: Step (1) Raw material selection: By weight, take 96 parts of methyl vinyl vulcanized silicone rubber raw rubber with a vinyl content of 0.18%; take 4.5 parts of composite filler; take 9.5 parts of ammonium polyphosphate and silicon nitrogen resin compound flame retardant system; take 0.7 parts of dynamic compatibilizer; take 0.9 parts of hydroxyl-terminated polybutadiene siloxane block copolymer; take 0.18 parts of organotin titanate composite catalyst.

[0053] Composite filler: The hydroxyapatite microspheres are commercially available medical grade, model HA-MS-18, with a particle size of 1.8 μm and a porosity of 35%; the outer shell is an amino-modified boron nitride nanosheet, which is prepared according to the method of Example 1 of patent CN202310245678.9, with a thickness of 7 nm and 4 layers; the core and the outer shell are bonded by γ-aminopropyltriethoxysilane, which is purchased from Sinopharm Group with a purity of 98%; the grafting rate is 80% as determined by X-ray photoelectron spectroscopy.

[0054] Dynamic compatibilizer: a physical blend of γ-chloropropylmethyldimethoxysilane and maleic anhydride-grafted ethylene-vinyl acetate copolymer. The γ-chloropropylmethyldimethoxysilane was purchased from Aladdin with a purity of 97%. The maleic anhydride-grafted ethylene-vinyl acetate copolymer is a commercially available model, model EVA-g-MAH, with a grafting rate of 1.5%. The molar ratio of the two is 1:0.80.

[0055] Flame retardant system of ammonium polyphosphate and silica-nitrogen resin: ammonium polyphosphate degree of polymerization 1100, commercially available model is APP-1000; silica-nitrogen resin nitrogen content 40%, commercially available model is SN-601; mass ratio of ammonium polyphosphate to silica-nitrogen resin is 1:1.50.

[0056] Hydroxyl-terminated polybutadiene-siloxane block copolymer: Prepared by free radical polymerization, using hydroxyl-terminated polybutadiene and octamethylcyclotetrasiloxane as raw materials. The hydroxyl-terminated polybutadiene (Mn=2000) was purchased from Aldrich; the octamethylcyclotetrasiloxane was purchased from Sinopharm Group with a purity of 99%. Polymerization was carried out under the catalysis of stannous octoate, with a stannous octoate purity of 98%. The number-average molecular weight was determined to be 3.8 × 10⁻⁶ m³ / s by gel permeation chromatography. Da; The mass ratio of the block copolymer to the composite filler is 1:5.0.

[0057] Organotin titanate composite catalyst: composed of dibutyltin dilaurate and tetrabutyl titanate. The dibutyltin dilaurate was purchased from Aladdin with a purity of 99.7%; the tetrabutyl titanate had a degree of hydrolysis of 16% and was purchased from Sinopharm Group; the molar ratio of the two was 1:1.20.

[0058] Step (2) Preparation of premixed rubber: Under the conditions of 60℃ and vacuum degree -0.080MPa, methyl vinyl vulcanized silicone rubber raw rubber, composite filler, dynamic compatibilizer, hydroxyl-terminated polybutadiene siloxane block copolymer, polyphosphate ammonium and silicon nitrogen resin compound flame retardant system and 50% of organotin titanate composite catalyst are added in sequence. The 50% of organotin titanate composite catalyst is 0.09 parts. After staged mixing, the premixed rubber is obtained.

[0059] The specific process of phased mixing is as follows: Add methyl vinyl vulcanized silicone rubber raw rubber and composite filler, and mix at 33 r / min for 7.8 min; Add dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer, increase the rotation speed to 47 r / min, and mix for 3.3 min; Add a flame retardant system of ammonium polyphosphate and silicon nitride resin and 50% of an organotin titanate composite catalyst, maintain a rotation speed of 47 r / min, and simultaneously heat to 90℃, mix for 5 min to obtain a premixed adhesive.

[0060] Step (3) Supercritical pretreatment: The premixed adhesive obtained in step (2) is placed in a supercritical CO2 environment at a temperature of 38℃ and a pressure of 9MPa, and kept at the temperature and pressure for 25min. After depressurization, inert nitrogen gas is introduced for replacement. The inert nitrogen gas flow rate is 1.5L / min and the replacement time is 10min. The material temperature is maintained at 38℃ during the replacement process to obtain the pretreated premixed adhesive.

[0061] Step (4) Vulcanization molding: Add the remaining 50% of the organic tin titanate composite catalyst to the pretreated premixed rubber obtained in step (3). The remaining 50% of the organic tin titanate composite catalyst is 0.09 parts. Vulcanize to obtain vulcanized silicone rubber cable insulation material.

[0062] The vulcanization process employs a gradient temperature-pressure regime, specifically: Maintain at 120℃ and 1.0MPa for 5 minutes; The temperature was increased to 160℃ at a rate of 5℃ / min, while the pressure was adjusted to 1.4MPa and held for 8min. The temperature was lowered to 140℃ at a rate of 2℃ / min, while the pressure was adjusted to 1.2MPa and held for 2.8min. The vulcanization process is completed by allowing the temperature to cool naturally to room temperature.

[0063] Comparative Example 1 differs from Example 1 in that the composite filler is replaced with single hydroxyapatite microspheres, with the same core parameters as the composite filler in Example 1. The microspheres are HA-MS-18, commercially available medical grade, without boron nitride shell and γ-aminopropyltriethoxysilane bonding treatment. The remaining raw material parameters and steps are exactly the same as in Example 1.

[0064] Comparative Example 2 differs from Example 1 in that step (3) supercritical CO2 pretreatment is omitted, and the premixed rubber obtained in step (2) directly enters the vulcanization stage in step (4). The remaining raw material parameters and steps are exactly the same as in Example 1.

[0065] Comparative Example 3 differs from Example 1 in that: in step (2), the total amount of organotin titanate composite catalyst is added, and the total amount of organotin titanate composite catalyst is 0.20 parts, and it is no longer added in two separate steps. The other raw material parameters and steps are exactly the same as in Example 1.

[0066] Comparative Example 4 differs from Example 1 in that: step (4) vulcanization adopts a constant temperature and pressure regime, with a temperature of 160℃ and a pressure of 1.4MPa, and is maintained for 16min, which is consistent with the total time of gradient vulcanization in Example 1. The gradient temperature-pressure regime is replaced, and the other raw material parameters and steps are exactly the same as in Example 1.

[0067] Performance testing: The vulcanized silicone rubber cable insulation materials treated in Examples 1, 2, 3, Comparative Examples 1, 2, 3, and 4 were subjected to performance testing. The test items included oxygen index test, vertical flammability rating test, smoke density rating test, tensile strength test, elongation at break test, volume resistivity test, and tensile strength retention rate after thermal aging test. The oxygen index test is conducted in accordance with the national standard GB / T2406.2-2009. The purpose of the test is to evaluate the flame retardancy of the material by measuring the minimum volume fraction of oxygen required for the material to burn. The higher the value, the more difficult the material is to burn and the stronger its flame retardant performance.

[0068] The vertical flammability rating test is conducted in accordance with the national standard GB / T18380.12-2022. The purpose of the test is to simulate the burning behavior of materials in a vertical state. By observing the burning time and dripping conditions, the vertical flammability rating of the material is determined, which directly reflects the material's ability to resist the spread of flames in actual use.

[0069] The smoke density rating test is conducted in accordance with the national standard GB / T8323.2-2020. The purpose of the test is to measure the density of the smoke produced when the material is burning under specified combustion conditions and to calculate the smoke density rating. The lower the value, the less smoke is produced when the material is burning, the better the smoke suppression effect, and the less harm smoke can cause to the human body and the environment in a fire.

[0070] The tensile strength test is performed in accordance with the national standard GB / T528-2009. The purpose of the test is to measure the maximum stress that the material can withstand before fracture by applying axial tensile force to a standard specimen, reflecting the material's ability to resist tensile failure. It is a key indicator for evaluating whether the mechanical properties of the material meet the requirements for cable insulation.

[0071] The elongation at break test is performed in accordance with the national standard GB / T528-2009. The purpose of the test is to measure the rate of change of length of the material from its initial state to the point of fracture while testing the tensile strength, so as to reflect the toughness and ductility of the material and ensure that the material is not easily damaged by deformation during cable laying and bending.

[0072] The volume resistivity test is performed in accordance with the national standard GB / T1410-2006. The purpose of the test is to measure the relationship between the current and voltage inside the material by applying a DC voltage, and to calculate the volume resistivity. The higher the value, the stronger the material's ability to impede the passage of current, the better its insulation performance, and the better it can ensure the electrical safety of the cable in use.

[0073] The tensile strength retention rate test after thermal aging is performed in accordance with the national standard GB / T7759.1-2015. The purpose of the test is to place the material in an aging environment with a specified temperature and time, and then test its tensile strength, calculate the ratio of the strength after aging to the initial strength, and evaluate the mechanical property stability of the material under long-term high-temperature use conditions. The higher the retention rate, the stronger the anti-aging ability of the material and the longer its service life.

[0074] The obtained test data are recorded in Table 1 below:

[0075] Performance test results show that Examples 1, 2, and 3 all exhibit consistently excellent performance in flame retardancy, smoke suppression, mechanical properties, insulation, and anti-aging properties. However, due to the change of a single variable, the performance of each comparative example deteriorated to varying degrees.

[0076] In terms of flame retardancy and smoke suppression performance, the oxygen index, vertical burning rating, and smoke density rating of the Example Group were all superior to those of Comparative Example 1. Comparative Example 1, because it did not use a hydroxyapatite core-boron nitride shell composite filler, but only a single hydroxyapatite microsphere, lost the synergistic effect between the boron nitride shell and the flame retardant system, resulting in a significant decrease in flame retardant efficiency and smoke suppression effect. This demonstrates that the composite filler designed in this invention is the core factor in achieving halogen-free, low-smoke, and highly flame-retardant materials.

[0077] In terms of mechanical properties and structural stability, the tensile strength, elongation at break, and tensile strength retention rate after thermal aging of the example group were all higher than those of Comparative Example 2 and Comparative Example 4. Comparative Example 2 omitted the supercritical CO2 pretreatment step, and Comparative Example 4 adopted a constant temperature and pressure vulcanization system. Both of them suffered from weakened mechanical properties and anti-aging ability because they could not accurately control the uniformity of the internal structure and crosslinking density of the material. This confirms the key role of supercritical pretreatment and gradient temperature-pressure vulcanization process in improving the comprehensive mechanical properties of the material.

[0078] Analysis of insulation performance and processing compatibility showed that the volume resistivity and mechanical property stability of the example group were superior to those of Comparative Example 3. Comparative Example 3, by adding the organotin titanate composite catalyst in a single step, disrupted the balance between processing fluidity and finished product performance, leading to a decrease in interfacial bonding strength and impaired insulation and mechanical properties, highlighting the necessity of adding the catalyst in two stages.

[0079] By comparing and analyzing the relevant data in the table, it can be seen that the present invention, through the addition of composite fillers, the introduction of supercritical pretreatment technology, the optimization of the gradient vulcanization regime, and the improvement of stepwise catalyst addition, achieves simultaneous improvement in the flame retardant, smoke suppression, mechanical, insulation, and anti-aging properties of environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation materials. This effectively solves the problems of difficulty in achieving balanced performance and poor consistency in traditional preparation techniques. Therefore, the preparation method of the environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation materials provided by the present invention has a broader market prospect and is more suitable for promotion.

[0080] In the description of this specification, references to terms such as "an experiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that experiment or example is included in at least one experiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same experiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more experiments or examples.

[0081] The preferred experiments disclosed above are merely illustrative of the invention. These preferred experiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these experiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize it. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material, characterized in that, include: Step (1): By weight, take 96-104 parts of methyl vinyl vulcanized silicone rubber raw rubber, 4-7 parts of composite filler, 9-11 parts of ammonium polyphosphate and silicon nitrogen resin compound flame retardant system, 0.6-1.1 parts of dynamic compatibilizer, 0.9-1.4 parts of hydroxyl-terminated polybutadiene siloxane block copolymer and 0.12-0.28 parts of organotin titanate composite catalyst; The composite filler is a hydroxyapatite core-boron nitride shell composite filler; Step (2): Under the conditions of temperature 58℃~63℃ and vacuum degree -0.088MPa~-0.072MPa, methyl vinyl vulcanized silicone rubber raw rubber, composite filler, dynamic compatibilizer, hydroxyl-terminated polybutadiene siloxane block copolymer, polyphosphate ammonium and silicon nitrogen resin compound flame retardant system and 50% of organotin titanate composite catalyst are added in sequence and mixed in stages to obtain premixed rubber; Step (3): Place the premixed adhesive obtained in step (2) in a supercritical CO2 environment with a temperature of 34℃~46℃ and a pressure of 8MPa~12MPa, keep it at the temperature and pressure for 20~30min, release the pressure and then introduce inert nitrogen gas for replacement to obtain the pretreated premixed adhesive. Step (4): Add the remaining 50% of the organic tin titanate composite catalyst to the pretreated premixed adhesive obtained in step (3) and vulcanize to obtain vulcanized silicone rubber cable insulation material.

2. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The vinyl content of the raw methyl vinyl vulcanized silicone rubber in step (1) is 0.16% to 0.24% by mass.

3. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The structure of the composite filler in step (1) is as follows: the core is hydroxyapatite microspheres, the particle size of which is 1.6 μm to 2.1 μm and the porosity is 34% to 41%; The outer shell is an amino-modified boron nitride nanosheet layer, the thickness of which is 6nm to 8nm and the number of layers is 3 to 5; The core and shell are bonded by γ-aminopropyltriethoxysilane, and the grafting rate of γ-aminopropyltriethoxysilane on the surface of the composite filler is 68% to 95%.

4. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The dynamic compatibilizer mentioned in step (1) is a physical blend of γ-chloropropylmethyldimethoxysilane and maleic anhydride-grafted ethylene-vinyl acetate copolymer, wherein the molar ratio of γ-chloropropylmethyldimethoxysilane to maleic anhydride-grafted ethylene-vinyl acetate copolymer is 1:0.72 to 1:0.

88.

5. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The parameters of the flame retardant system of ammonium polyphosphate and silica-nitrogen resin in step (1) are as follows: the degree of polymerization of ammonium polyphosphate n = 1020 to 1180, the mass fraction of nitrogen content of silica-nitrogen resin is 39% to 41%, and the mass ratio of ammonium polyphosphate to silica-nitrogen resin is 1:1.42 to 1:1.

58.

6. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The parameters of the hydroxyl-terminated polybutadiene siloxane block copolymer mentioned in step (1) are as follows: the block ratio is hydroxyl-terminated polybutadiene segments: siloxane segments = 2:0.92 to 2:1.08; The number-average molecular weight is 3.0 × 10⁻⁶. 4 ~5.0×10 4 Da; The mass ratio of the hydroxyl-terminated polybutadiene siloxane block copolymer to the composite filler described in step (1) is 1:4.2 to 1:5.

8.

7. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The parameters of the organotin titanate composite catalyst mentioned in step (1) are as follows: the components include dibutyltin dilaurate and tetrabutyl titanate, and the mass fraction of the purity of dibutyltin dilaurate is 99.6% to 99.8%; The degree of hydrolysis of tetrabutyl titanate is 14%–21% by mass; The molar ratio of dibutyltin dilaurate to tetrabutyl titanate is 1:1.12 to 1:1.

28.

8. The method for preparing the environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, The specific process of phased mixing in step (2) is as follows: Add methyl vinyl vulcanized silicone rubber raw material and composite filler, and mix at a speed of 30 r / min to 36 r / min for 7.5 min to 8.5 min; Add dynamic compatibilizer and hydroxyl-terminated polybutadiene siloxane block copolymer, increase the rotation speed to 44 r / min to 50 r / min, and mix for 3.2 min to 3.8 min; Add a flame retardant system of ammonium polyphosphate and silicon nitride resin and 50% of an organotin titanate composite catalyst, maintain a rotation speed of 44 r / min to 50 r / min, and simultaneously raise the temperature to 87℃ to 93℃, and mix for 4.5 min to 5.5 min to obtain a premixed rubber.

9. The preparation method of the environmentally friendly halogen-free low-smoke flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, In step (3), the inert nitrogen flow rate is 1.2 L / min to 1.8 L / min, and the replacement time is 8 min to 12 min. During the replacement process, the temperature of the premixed rubber material treated with supercritical CO2 was maintained at 34℃~46℃.

10. The method for preparing the environmentally friendly halogen-free, low-smoke, flame-retardant silicone rubber cable insulation material according to claim 1, characterized in that, In step (4), the vulcanization adopts a gradient temperature-pressure regime, specifically: maintaining the temperature at 117℃~123℃ and the pressure at 0.95MPa~1.05MPa for 4.5min~5.5min; The temperature is increased to 157℃ to 163℃ at a heating rate of 4.5℃ / min to 5.5℃ / min, while the pressure is adjusted to 1.35MPa to 1.45MPa and held for 7.5min to 8.5min. Cool to 137℃~143℃ at a cooling rate of 1.5℃ / min~2.5℃ / min, while adjusting the pressure to 1.15MPa~1.25MPa and holding for 2.5min~3.5min; The vulcanization process is completed by allowing the temperature to cool naturally to room temperature.

Images