Radiation-proof high-flame-retardant special optical cable and preparation method thereof

Abstract

The application discloses a kind of radiation protection high flame-retardant special optical cable and preparation method, bismuth oxide and barium sulfate are first mixed with matrix resin to form a basic shielding premix, then tungsten oxide is synchronously post-added with zinc borate and aluminum diethyl phosphinate, and the outer sheath layer is formed by flame-retardant system dispersion, homogenization granulation, extrusion coating and crosslinking. The method improves the dispersion stability, extrusion stability and flame-retardant carbonization holding effect of high filler sheath material through stage wetting and torque process control, so that the outer sheath layer still maintains high radiation shielding ability after burning.

Description

Technical Field

[0001] This invention relates to the technical field of special optical cables, and in particular to a radiation-resistant and highly flame-retardant special optical cable and its preparation method. Background Technology

[0002] Optical cables, as a fundamental component of information transmission systems, are widely used in communication networks, industrial control, rail transportation, energy facilities, and special equipment. With increasingly complex operating environments, some optical cables need to operate for extended periods in environments characterized by high temperatures, humidity, fire risks, mechanical disturbances, and radiation. These environments not only require stable optical signal transmission capabilities but also demand that their outer sheath possess excellent flame retardancy, heat resistance, mechanical protection, and environmental adaptability to minimize the impact of external conditions on the cable core and fiber optic units.

[0003] Special optical cables with radiation protection and flame retardant functions have been proposed in the prior art. For example, Chinese patent application CN112415695A discloses a radiation-protected, highly flame-retardant special optical cable and its manufacturing method. This cable improves its radiation protection, flame retardancy, high-temperature resistance, waterproofing, and abrasion resistance through a multi-layered structure consisting of an FRP reinforcing core, radiation-protecting optical fiber, foam layer, tensile layer, radiation-protecting outer layer, flame-retardant layer, high-temperature resistant waterproof layer, and abrasion-resistant layer. This type of solution mainly improves overall protection capabilities through the layered structure and functional layer stacking of the optical cable.

[0004] In the field of optical cable sheath materials, low-smoke halogen-free flame-retardant polyolefin systems have also been used to improve the flame retardancy, processability, and mechanical properties of the sheath. For example, Chinese patent application CN102977451B discloses a low-smoke halogen-free flame-retardant sheath layer for optical cables, which uses ethylene-vinyl acetate, modified polyethylene, etc. as matrix materials, and adds inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide, as well as silicone masterbatch, polyethylene wax, flow agent, and other additives to improve extrusion stability, outer diameter uniformity, and flame retardant properties.

[0005] However, in radiation-resistant and flame-retardant optical cables, the outer sheath material typically needs to accommodate both high levels of radiation-resistant and flame-retardant fillers. These inorganic fillers have high density and are used in large quantities, which can easily increase the melt flow burden during processing and affect the uniformity of sheath dispersion, extrusion stability, and structural retention after thermal effects. Especially under heated or burning conditions, if the high-density inorganic filler is difficult to effectively retain within the residual sheath layer, the outer sheath layer is prone to localized defects, filler migration, or discontinuous residual structures, thus affecting the overall reliability of the optical cable's protection in complex environments.

[0006] Therefore, how to improve the dispersion stability and structural retention capability of the outer sheath layer of radiation-proof and flame-retardant optical cables in a high-filler system is a technical problem that needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a radiation-proof and flame-retardant special optical cable and its preparation method, so as to improve the dispersion stability of high-content radiation-proof filler and flame-retardant filler in the outer sheath layer and improve the structural retention ability of the outer sheath layer after thermal action.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a radiation-resistant, highly flame-retardant special optical cable, comprising the following steps: S1: Bismuth oxide, barium sulfate, epoxy-containing silane coupling agent and phosphate-containing dispersant are mixed to obtain the treated basic shielding filler; S2: Tungsten oxide and an aminosilane coupling agent are mixed to obtain the treated post-rewetting filler; S3: Ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, silicone rubber elastomer and compatibilizer are added to a mixing equipment and mixed to obtain a matrix premix. S4: Add the treated basic shielding filler to the matrix premix for the first stage of intensive mixing to obtain the basic shielding premix. S5: The treated post-rewetting filler, zinc borate and aluminum diethylphosphinate are simultaneously added to the basic shielding premix for the second stage of intensive mixing to obtain the rewetting premix. S6: Add the metal hydroxide flame retardant and phosphorus-nitrogen charring agent to the rewetting premix and carry out the third stage of intensive mixing to obtain the flame retardant and shielding mixture; S7: Add antioxidants, lubricants and crosslinking aids to the flame-retardant shielding mixture, homogenize it under the conditions of rotor speed of 20-45 r / min and discharge temperature of 115-130℃, and then extrude and granulate it to obtain radiation-proof high flame-retardant optical cable sheath material. S8: The fiber unit and reinforcing member are assembled into a cable core, a water-blocking layer is set on the outside of the cable core, an inner sheath layer is formed by extrusion on the outside of the water-blocking layer, and radiation-proof high flame-retardant optical cable sheath material is extruded and wrapped on the outside of the inner sheath layer to form a radiation-proof high flame-retardant outer sheath layer. S9: The radiation-resistant and flame-retardant outer sheath is cross-linked with warm water or steam to obtain a radiation-resistant and flame-retardant special optical cable.

[0009] Through the aforementioned segmented entry and wetting method, bismuth oxide and barium sulfate first complete initial wetting, interfacial coating, and load-bearing dispersion in the matrix resin, forming a continuous distribution base for the basic shielding filler. Tungsten oxide, however, is not added simultaneously with bismuth oxide and barium sulfate, but rather in the second stage, added later along with zinc borate and aluminum diethylphosphinate, making it easier to distribute in the gaps between the basic shielding fillers and the resin interface transition area. Thus, tungsten oxide not only enhances the radiation attenuation capability of the outer sheath layer but also participates in the construction of the subsequent flame-retardant charring and retention system under the combined action of zinc borate and aluminum diethylphosphinate. This makes the residual char layer formed during combustion more likely to coat, clamp, and retain the high-density shielding fillers such as bismuth oxide, barium sulfate, and tungsten oxide. This process establishes a correlation between the flame-retardant charring behavior and the continuity of the radiation-shielding filler, thereby ensuring good shielding retention capability of the outer sheath layer in both the intact sheath state and the residual state after combustion.

[0010] Preferably, in step S1, the mass ratio of bismuth oxide to barium sulfate is 1:0.55 to 1.35; The mass ratio of the epoxy-containing silane coupling agent to the phosphate-containing dispersant is 1:0.30 to 0.85, and the total mass of the two is 0.8% to 2.2% of the total mass of bismuth oxide and barium sulfate. In step S2, the mass of the aminosilane coupling agent is 0.3% to 1.2% of the mass of tungsten oxide.

[0011] The combination of bismuth oxide and barium sulfate within the aforementioned ratio range enables the basic shielding filler to possess both high radiation attenuation carrying capacity and good resin wetting space. The epoxy-containing silane coupling agent enhances the interfacial bonding between the basic shielding filler and the resin phase, while the phosphate-based dispersant reduces the agglomeration tendency of bismuth oxide and barium sulfate under high-fill conditions, allowing the basic shielding filler to form a stable initial wetting and dispersion state during the first-stage mixing process. Tungsten oxide, treated alone with an amino-containing silane coupling agent, facilitates interfacial contact with zinc borate and aluminum diethylphosphinate when added later in the second stage, and smoothly enters the void regions between the basic shielding fillers, thus providing a more stable interfacial foundation for the subsequent carbon layer to hold the shielding filler.

[0012] Preferably, in step S1, the average particle size D50 of bismuth oxide is 0.8–2.8 μm, and the average particle size D50 of barium sulfate is 1.2–4.0 μm; In step S2, the average particle size D50 of tungsten oxide is 0.4–1.8 μm; The average particle size D50 of the tungsten oxide is smaller than that of the bismuth oxide, and the ratio of the average particle size D50 of the tungsten oxide to that of the bismuth oxide is 0.25 to 0.75.

[0013] With the aforementioned particle size configuration, bismuth oxide and barium sulfate primarily form the basic shielding load distribution. Smaller-sized tungsten oxide particles more easily enter the gaps between bismuth oxide and barium sulfate, as well as near the resin coating interface, in the second stage. This particle size difference, combined with the subsequent addition sequence, allows tungsten oxide to fill in the shielding path and rewet the interface, rather than simply being uniformly mixed into the system as ordinary powder. The resulting filler distribution is more conducive to improving the continuity of the shielding path within the outer sheath layer and makes it easier for the residual layer formed by subsequent flame retardant charring to coat, hold, and connect the shielding filler, thereby reducing the risk of discontinuous shielding filler distribution after combustion.

[0014] Preferably, in step S3, the mass ratio of ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene and silicone rubber elastomer is 38-52:22-34:12-22:6-14. The vinyl acetate content in the ethylene-vinyl acetate copolymer is 24% to 33%; The silane grafting rate of the silane-grafted polyethylene is 0.6% to 1.6%. The compatibilizer comprises maleic anhydride-grafted polyethylene and ethylene-vinyl acetate-maleic anhydride graft, wherein the mass ratio of the maleic anhydride-grafted polyethylene and the ethylene-vinyl acetate-maleic anhydride graft is 1:0.35 to 1.10, and the total acid value of the compatibilizer is 3 to 12 mg KOH / g.

[0015] The aforementioned resin system provides flexibility, polar wetting ability, and crosslinking support for the high-filler outer sheath material. Ethylene-vinyl acetate copolymer facilitates the coating of inorganic fillers such as bismuth oxide, barium sulfate, and tungsten oxide. Polyolefin elastomers mitigate the increased rigidity caused by high-density shielding fillers and flame-retardant fillers. Silane-grafted polyethylene provides reactive sites for warm water or steam crosslinking, and silicone rubber elastomers improve the deformation stability of the outer sheath layer under bending, thermal shock, and high-filling conditions. With the compatibilizer's acid value controlled within the aforementioned range, a suitable interfacial interaction can be formed between the filler surface and the resin phase, allowing the initial wetting of the basic shielding filler, the subsequent rewetting of tungsten oxide, and the subsequent flame-retardant charring and fixation to all occur within a relatively stable continuous resin phase.

[0016] Preferably, in step S5, the mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphinate is 1:0.25-0.75:0.20-0.65; In step S6, the metal hydroxide flame retardant includes magnesium hydroxide and aluminum hydroxide, wherein the mass ratio of magnesium hydroxide to aluminum hydroxide is 1:0.40 to 0.85; The phosphorus-nitrogen charring agent includes ammonium polyphosphate and triazine charring agent, wherein the mass ratio of ammonium polyphosphate to triazine charring agent is 1:0.25 to 0.60; The total mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphonate to the phosphorus-nitrogen char-forming agent is 1:0.55 to 1.40.

[0017] Tungsten oxide, zinc borate, and aluminum diethylphosphinate are simultaneously incorporated into the second-stage mixing process. This allows tungsten oxide to reinforce the shielding pathway while pre-establishing interfacial contact with the flame-retardant synergistic components. Zinc borate enhances the inorganic density and thermal stability of the combustion residue layer, while aluminum diethylphosphinate participates in the phosphorus-based flame-retardant reaction and, together with subsequently added ammonium polyphosphate and triazine charring agents, promotes the formation of the char layer. Since tungsten oxide is already dispersed synchronously with zinc borate and aluminum diethylphosphinate in the second stage, the subsequent phosphorus-nitrogen charring system more easily forms a coating and retention around the tungsten oxide and the basic shielding filler when forming the char layer, ensuring a relatively continuous shielding filler distribution in the post-combustion residual sheath layer.

[0018] Preferably, the radiation-resistant and flame-retardant optical cable sheath material obtained in step S7 comprises the following components by weight: 100 parts of matrix resin; 70–125 parts of a basic shielding filler composed of bismuth oxide and barium sulfate; 8–28 parts of post-rewetting filler composed of tungsten oxide; 65-115 parts of metal hydroxide flame retardant; 8-20 parts of phosphorus and nitrogen charring agent; 3-9 parts zinc borate; 2-8 parts of aluminum diethylphosphinate; 5-14 parts compatibilizer; Antioxidant 1-4 parts; 1-5 parts lubricant; Crosslinking aid 0.3 to 1.5 parts.

[0019] This formulation range ensures a balance between the content of shielding filler, flame-retardant filler, and continuous resin phase. The basic amount of shielding filler guarantees a stable radiation attenuation base for the outer sheath. Controlling the amount of rewetting filler within the aforementioned range facilitates its role in shielding reinforcement, interface rewetting, and charring retention without significantly disrupting melt flow stability. The metal hydroxide flame retardant, phosphorus-nitrogen charring agent, zinc borate, and aluminum diethylphosphonate together form a flame-retardant charring system. This system enables the outer sheath to not only form a flame-retardant residual layer during combustion but also to retain the high-density radiation-shielding filler through this residual layer, thereby improving the shielding retention capability of the residual sheath layer after combustion.

[0020] Preferably, in step S4, the discharge temperature of the first stage of internal mixing is 120-135°C; In step S5, the discharge temperature of the second stage internal mixing is 128-142℃; In step S6, the discharge temperature of the third stage internal mixing is 132-148℃; The discharge temperature of the second stage internal mixing is 4-15°C higher than that of the first stage internal mixing, the discharge temperature of the third stage internal mixing is 2-10°C higher than that of the second stage internal mixing, and the discharge temperature in step S7 is 8-25°C lower than that of the third stage internal mixing.

[0021] This temperature progression method is coordinated with the staged feeding sequence. The first stage temperature allows bismuth oxide and barium sulfate to be fully wetted by the matrix resin and form a basic shielding premixed state. The second stage moderately increases the temperature, allowing tungsten oxide, zinc borate, and aluminum diethylphosphinate to enter the gaps and interface regions between the basic shielding fillers under good melt flow conditions. The third stage continues to increase the temperature, which is conducive to the coating and dispersion of the metal hydroxide flame retardant and phosphorus-nitrogen charring agent, and connects with the distribution state of tungsten oxide, zinc borate, and aluminum diethylphosphinate established in the previous stage. Finally, lowering the homogenization discharge temperature can reduce the premature reaction of crosslinking aids before granulation and reduce the thermal shear damage of the high filler system, so that the outer sheath material maintains a stable processing state during subsequent extrusion and crosslinking processes.

[0022] Preferably, in steps S4, S5 and S7, the stable value of the torque is the average torque when the torque fluctuation amplitude does not exceed 5% of the average torque within 60 seconds after the torque peak occurs in the corresponding step. In step S4, the torque during the first stage of internal mixing decreases from its peak value to a stable value by 20% to 38%. In step S5, during the second stage of internal mixing, the torque decreases from its peak value to a stable value by 12% to 28%. In step S7, the torque decreases from its peak value to its stable value during homogenization by 6% to 16%. The torque decreases sequentially during the first stage of intensive mixing, the second stage of intensive mixing, and the homogenization process.

[0023] By controlling the torque stability and decrease rate as described above, the wetting, rewetting, and homogenization states of the filler can be transformed into directly recordable processing responses. The larger torque decrease in the first stage corresponds to the gradual transformation of bismuth oxide and barium sulfate from a high-resistance powder state to a basic shielded dispersion state coated with resin. The moderate torque decrease in the second stage corresponds to the interfacial redistribution of tungsten oxide, zinc borate, and aluminum diethylphosphinate in the basic shielded premix system and the filling of filler gaps. The smaller torque decrease in the homogenization stage indicates that the system has entered a relatively stable melt flow state. The decreasing torque decrease in each of the three stages allows the process to exhibit a continuous change: the basic shielded filler is first wetted, then re-wetted to fill the gaps, and finally, the flame-retardant charring system achieves a stable distribution.

[0024] Preferably, in step S4, the time required for the torque to reach a stable value during the first stage of internal mixing is the first stabilization time, which is 180 to 420 seconds. In step S5, the time required for the torque to reach a stable value during the second stage of internal mixing is the second stabilization time, which is 100 to 260 seconds. In step S7, the time required for the torque to reach a stable value during homogenization is the third stabilization time, which is 60 to 180 seconds. The first stabilization time, the second stabilization time, and the third stabilization time are successively shortened; The torque reduction in the second stage of internal mixing is 0.50 to 0.78 of the torque reduction in the first stage of internal mixing. The ratio of the torque reduction during homogenization to the torque reduction during the second stage of internal mixing is 0.45 to 0.82. The ratio of the second settling time to the first settling time is 0.45 to 0.75; The ratio of the third stable time to the second stable time is 0.40 to 0.80; The ratio of the torque decrease during the second stage of intensive mixing to the torque decrease during the first stage of intensive mixing is greater than the ratio of the second stabilization time to the first stabilization time.

[0025] The progressively shorter stabilization times indicate that the subsequent additions of tungsten oxide, zinc borate, aluminum diethylphosphinate, and crosslinking aids complete rewetting and homogenization on the existing basic shielding dispersion, rather than causing the system to re-enter a prolonged unstable dispersion state. The first stage allows for a longer stabilization time, which is beneficial for bismuth oxide and barium sulfate to form a fully resin-coated interface. The shortened stabilization time in the second stage indicates that the simultaneous addition of tungsten oxide, zinc borate, and aluminum diethylphosphinate allows for rapid embedding into the basic shielding premixed system and completion of interface filling. The further shortening of the third stage indicates that the homogenization process is mainly used for flow regulation and crosslinking aid dispersion, without disrupting the continuity of the previously formed shielding filler or the distribution of flame-retardant synergistic components.

[0026] The second aspect of the present invention provides a radiation-resistant and flame-retardant special optical cable, comprising a cable core, a water-blocking layer covering the outside of the cable core, an inner sheath covering the outside of the water-blocking layer, and a radiation-resistant and flame-retardant outer sheath covering the outside of the inner sheath. The radiation-resistant and flame-retardant outer sheath layer is formed by extrusion cross-linking of the radiation-resistant and flame-retardant optical cable sheath material prepared by the method described above. The cable core includes optical fiber units and reinforcing components; The inner sheath layer is formed by extrusion of low-smoke halogen-free flame-retardant sheath material; The thickness of the inner sheath layer is 0.4–1.2 mm, and the thickness of the radiation-proof and highly flame-retardant outer sheath layer is 1.0–3.5 mm. A fiberglass tape, mica tape, or low-smoke halogen-free flame-retardant wrapping tape is provided between the inner sheath layer and the radiation-proof, high-flame-retardant outer sheath layer, and the overlap rate of the fiberglass tape, mica tape, or low-smoke halogen-free flame-retardant wrapping tape is 15% to 35%. This optical cable structure achieves a layered approach, integrating core protection, interlayer isolation, and outer functional protection. The inner sheath provides basic mechanical protection and flame-retardant buffering for the core. The wrapping layer enhances the heat resistance and structural stability between the inner sheath and the radiation-resistant, highly flame-retardant outer sheath. The outer sheath provides radiation protection, flame retardancy, heat resistance, and environmental protection. The outer sheath thickness is controlled within the aforementioned range to provide sufficient space for the shielding filler and flame-retardant charring system, while avoiding excessive sheath thickness that could lead to decreased bending performance, increased cooling stress, or poor extrusion dimensional stability.

[0027] The thermal elongation of the cross-linked radiation-proof and flame-retardant outer sheath is 38% to 68% of that of the uncross-linked radiation-proof and flame-retardant outer sheath. The oxygen index of the cross-linked radiation-proof and flame-retardant outer sheath is 0.6 to 2.2 higher than that of the uncross-linked radiation-proof and flame-retardant outer sheath. After a vertical combustion test, the radiation shielding efficiency of the residual outer sheath layer is no less than 82% of the radiation shielding efficiency of the radiation shielding high flame retardant outer sheath layer before combustion.

[0028] The decrease in thermal elongation after cross-linking indicates the formation of a relatively stable cross-linked support network within the outer sheath, enabling the high-filler sheath to maintain good dimensional stability under thermal load. The increased oxygen index indicates that the cross-linked network and the flame-retardant charring system jointly enhance the thermal response stability of the outer sheath. The residual sheath layer after combustion maintains a radiation shielding rate of no less than 82% of its pre-combustion level, demonstrating that the residual char layer formed during combustion not only provides heat and oxygen insulation but also retains the shielding fillers such as bismuth oxide, barium sulfate, and tungsten oxide, ensuring their continuous distribution within the residual sheath layer. This effect reflects the role of the flame-retardant charring process in maintaining radiation protection continuity, allowing the outer sheath layer to maintain a high proportion of shielding function even after thermal shock and combustion.

[0029] The present invention, by adopting the above technical solution, has the following beneficial effects: (1) In this invention, the radiation shielding filler is divided into a basic shielding filler and a post-wetting filler. Bismuth oxide and barium sulfate are first initially wetted, coated at the interface, and dispersed in the matrix resin. Tungsten oxide is then added simultaneously with zinc borate and aluminum diethylphosphinate, making it easier for tungsten oxide to enter the gaps between the basic shielding fillers and the transition area of ​​the resin interface. Thus, tungsten oxide not only enhances the radiation attenuation capability but also participates in the construction of the flame-retardant char-forming and holding system, enabling the outer sheath layer to maintain good radiation shielding capability in both the intact state and the residual state after combustion.

[0030] (2) In this invention, tungsten oxide, zinc borate, and aluminum diethylphosphinate are added simultaneously and subsequently, and metal hydroxide flame retardants and phosphorus-nitrogen charring agents are introduced. This allows the flame-retardant charring system to be established on the basis of a mixture that has already completed basic shielding dispersion and tungsten oxide rewetting. The residual char layer formed during combustion not only serves as heat insulation and oxygen barrier, but also coats, clamps, and fixes the high-density shielding fillers such as bismuth oxide, barium sulfate, and tungsten oxide, ensuring that the residual sheath layer after combustion maintains a high proportion of continuous shielding filler distribution.

[0031] (3) By combining different surface treatments, particle size relationships and resin systems, this invention makes the basic shielding filler more suitable for early wetting and dispersion, and makes tungsten oxide more suitable for post-positioning and interface rewetting. At the same time, by combining ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, silicone rubber elastomer and compatibilizer, the resin coating, extrusion stability, crosslinking support and bending adaptability of the high filler sheath material are improved, thus taking into account radiation protection, high flame retardancy, processing stability and sheath flexibility.

[0032] (4) This invention controls the process by progressively increasing the mixing temperature, decreasing the homogenization temperature, and controlling the torque reduction and stabilization time in stages. This ensures that the wetting of the basic shielding filler, the subsequent rewetting of tungsten oxide, the dispersion of the flame-retardant filler, and the homogenization of the crosslinking aid are all within a predictable and controllable processing window. This process control helps reduce local agglomeration, thermal shear damage, and extrusion fluctuations in the high-filler system, resulting in a more stable dispersion structure in the outer sheath layer. Furthermore, it achieves better dimensional retention and post-combustion shielding retention capabilities after crosslinking. Detailed Implementation

[0033] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0034] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specified, all materials and reagents used in the following examples are commercially available; all raw materials are selected from wire and cable sheathing materials or industrial-grade raw materials commonly used in plastic processing. To ensure that those skilled in the art can implement this method, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 24%–33%, and the melt flow rate is 1.2–4.0 g / 10 min; the polyolefin elastomer can be selected from ethylene-octene copolymer elastomer or ethylene-butene copolymer elastomer, with a density of 0.860–0.885 g / cm³. 3 The silane grafting rate of silane-grafted polyethylene is 0.6%–1.6%; the total acid value of maleic anhydride-grafted compatibilizers is controlled at 3–12 mg KOH / g. Phosphate-based dispersants can be selected from polyether phosphate esters or alkyl polyoxyethylene ether phosphate esters, with an acid value of 45–135 mg KOH / g; triazine charring agents can be selected from pentaerythritol charring agents containing triazine rings or triazine macromolecular charring agents. Antioxidants, lubricants, water-blocking tapes, mica tapes, and low-smoke halogen-free flame-retardant sheathing materials for inner sheaths, unless otherwise specified, can all be commercially available products that meet the processing requirements of optical cable sheaths.

[0037] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0038] In the following examples and comparative examples, the surface treatment agent is added as an auxiliary agent for filler treatment based on the mass of the filler being treated, and is not included in the main weight of the radiation-proof, high flame-retardant optical cable sheath material.

[0039] The silicone rubber elastomer uses silicone rubber elastomer masterbatch with methyl vinyl silicone rubber as the main body, and the carrier is ethylene-vinyl acetate copolymer. The silicone rubber mass content is 50%, and the vinyl content in the methyl vinyl silicone rubber is 0.15%.

[0040] The crosslinking aid uses dioctyltin dilaurate masterbatch, which uses ethylene-vinyl acetate copolymer as a carrier and has a dioctyltin dilaurate content of 10% by mass. The amount of crosslinking aid used is based on the mass of the masterbatch.

[0041] The torque stability value is the average torque when the torque fluctuation amplitude does not exceed 5% of the average torque within 60 seconds after the torque peak occurs in the corresponding step.

[0042] Example 1 This embodiment discloses a radiation-resistant and flame-retardant special optical cable and its preparation method. The radiation-resistant and flame-retardant special optical cable includes a cable core, a water-blocking layer covering the outside of the cable core, an inner sheath covering the outside of the water-blocking layer, and a radiation-resistant and flame-retardant outer sheath covering the outside of the inner sheath. The radiation-resistant and flame-retardant outer sheath is formed by extrusion cross-linking of radiation-resistant and flame-retardant optical cable sheath material.

[0043] The radiation-resistant and flame-retardant optical cable sheath material comprises the following components by weight: 100 parts of matrix resin; 100 parts of a basic shielding filler composed of bismuth oxide and barium sulfate; 18 parts of post-rewetting filler composed of tungsten oxide; 90 parts of metal hydroxide flame retardant; 18 parts of phosphorus and nitrogen charring agent; 8 parts zinc borate; 5 parts of aluminum diethylphosphinate; 9 parts compatibilizer; Two parts antioxidant; 3 parts lubricant; One part of crosslinking aid.

[0044] In this embodiment, epoxy-containing silane coupling agents, phosphate-based dispersants, and amino-containing silane coupling agents are used as additives for filler surface treatment. Their dosage is based on the mass of the filler being treated and is not included in the main weight percentage of the radiation-resistant, flame-retardant optical cable sheath material. The matrix resin consists of ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, and silicone rubber elastomer masterbatch. The ethylene-vinyl acetate copolymer contains 28% vinyl acetate by mass, and its melt flow rate (measured at 190°C and 2.16 kg) is 2.5 g / 10 min. The polyolefin elastomer is an ethylene-octene copolymer elastomer with a density of 0.868 g / cm³. 3 The melt flow rate (measured at 190℃ and 2.16 kg) was 1.0 g / 10 min. The silane grafting rate of the silane-grafted polyethylene was 1.0%, and the melt flow rate (measured at 190℃ and 2.16 kg) was 1.5 g / 10 min. The mass fractions of the ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, and silicone rubber elastomer masterbatch were 45 parts, 28 parts, 17 parts, and 10 parts, respectively. The silicone rubber elastomer masterbatch was mainly composed of methyl vinyl silicone rubber, with ethylene-vinyl acetate copolymer as the carrier. The silicone rubber mass content was 50%, and the vinyl content in the methyl vinyl silicone rubber was 0.15%.

[0045] The basic shielding filler consists of bismuth oxide and barium sulfate. The bismuth oxide has a purity of 99.5% and an average particle size D50 of 1.8 μm; the barium sulfate is precipitated barium sulfate with a purity of 98.8% and an average particle size D50 of 2.5 μm. The mass ratios of bismuth oxide and barium sulfate are 54.05 parts and 45.95 parts, respectively, with a mass ratio of 1:0.85.

[0046] The rewetting filler is tungsten oxide with a purity of 99.0% and an average particle size D50 of 1.0 μm. The average particle size D50 of tungsten oxide is smaller than that of bismuth oxide, and the ratio of the average particle size D50 of tungsten oxide to that of bismuth oxide is 0.56.

[0047] The epoxy-containing silane coupling agent is γ-glycidoxypropyltrimethoxysilane, and the phosphate-containing dispersant is polyether phosphate dispersant. The amount of epoxy-containing silane coupling agent is 1.0 part, and the amount of phosphate-containing dispersant is 0.55 parts, with a mass ratio of 1:0.55. The total mass of the two is 1.55% of the total mass of bismuth oxide and barium sulfate. The amino-containing silane coupling agent is γ-aminopropyltriethoxysilane, used in an amount of 0.15 parts, with a mass of 0.83% of the mass of tungsten oxide.

[0048] The metal hydroxide flame retardant is composed of magnesium hydroxide and aluminum hydroxide. The average particle size D50 of magnesium hydroxide is 1.8 μm, and the purity is 98.5%; the average particle size D50 of aluminum hydroxide is 2.2 μm, and the purity is 99.0%. The mass ratios of magnesium hydroxide and aluminum hydroxide are 56.25 parts and 33.75 parts, respectively, with a mass ratio of 1:0.60.

[0049] The phosphorus-nitrogen charring agent consists of ammonium polyphosphate and a triazine charring agent. The ammonium polyphosphate is type II, with a degree of polymerization of not less than 1000 and an average particle size D50 of 8.0 μm. The triazine charring agent is a pentaerythritol-based charring agent containing a triazine ring, with a nitrogen content of 25%–30%. The mass ratio of ammonium polyphosphate to triazine charring agent is 12 parts to 6 parts, with a mass ratio of 1:0.5.

[0050] The zinc borate used is hydrated zinc borate, with a chemical composition of 2ZnO·3B2O3·3.5H2O and an average particle size D50 of 3.0μm.

[0051] The average particle size D50 of aluminum diethylphosphonate is 3.5 μm. The mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphonate is 18:8:5, or 1:0.44:0.28. The mass ratio of the total mass of tungsten oxide, zinc borate, and aluminum diethylphosphonate to the mass of the phosphorus-nitrogen charring agent is 31:18, or 1:0.58.

[0052] The compatibilizer consists of maleic anhydride-grafted polyethylene and ethylene-vinyl acetate-maleic anhydride graft. The maleic anhydride grafting rate of the maleic anhydride-grafted polyethylene is 1.0%, and that of the ethylene-vinyl acetate-maleic anhydride graft is 0.8%. The total acid value of the compatibilizer is 7 mg KOH / g. The mass ratio of maleic anhydride-grafted polyethylene to ethylene-vinyl acetate-maleic anhydride graft is 1:0.8, with 5 parts maleic anhydride-grafted polyethylene and 4 parts ethylene-vinyl acetate-maleic anhydride graft.

[0053] The antioxidant consists of hindered phenolic antioxidants and phosphite antioxidants. The hindered phenolic antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], with a mass of 1.2 parts; the phosphite antioxidant is tris[2,4-di-tert-butylphenyl]phosphite, with a mass of 0.8 parts.

[0054] The lubricant consists of polyethylene wax and calcium stearate. The number average molecular weight of the polyethylene wax is 3000, and its mass is 2 parts; the mass of the calcium stearate is 1 part.

[0055] The preparation method of radiation-proof and flame-retardant special optical cable is as follows.

[0056] S1: 54.05 parts of bismuth oxide, 45.95 parts of barium sulfate, 1.0 part of γ-glycidyl etheroxypropyltrimethoxysilane, and 0.55 parts of polyether phosphate dispersant were added to a high-speed mixer. The mixture was premixed at 300 rpm for 5 minutes, then heated to 100°C and mixed at 900 rpm for 30 minutes. The mixture was then cooled to below 45°C and discharged to obtain the treated basic shielding filler. Bismuth oxide and barium sulfate were dried at 105°C for 2 hours before being added to the high-speed mixer.

[0057] S2: 18 parts of tungsten oxide and 0.15 parts of γ-aminopropyltriethoxysilane were added to a high-speed mixer. The mixture was premixed at 300 rpm for 3 minutes, then heated to 95°C and mixed at 800 rpm for 20 minutes. The mixture was then cooled to below 45°C and discharged to obtain the treated rewetting packing. The tungsten oxide was dried at 105°C for 2 hours before being added to the high-speed mixer.

[0058] S3: Add 45 parts of ethylene-vinyl acetate copolymer, 28 parts of polyolefin elastomer, 17 parts of silane-grafted polyethylene, 10 parts of silicone rubber elastomer masterbatch, 5 parts of maleic anhydride-grafted polyethylene, and 4 parts of ethylene-vinyl acetate-maleic anhydride graft to a mixer. Set the initial temperature of the mixer to 95°C and the rotor speed to 45 r / min. Mix for 6 min to allow the resin components and compatibilizer to form a uniform melt mixture, thus obtaining the matrix premix.

[0059] S4: The treated basic shielding filler obtained in S1 is added to the matrix premix obtained in S3 for the first stage of intensive mixing. The treated basic shielding filler is added in two stages: first, 60 parts of the corresponding treated material are added, followed by intensive mixing for 3 minutes; second, 40 parts of the corresponding treated material are added, followed by intensive mixing for another 5 minutes. The rotor speed for the first stage of intensive mixing is 45 r / min, and the discharge temperature is 128℃, yielding the basic shielding premix. In this step, the peak torque recorded by the intensive mixer is 824 N·m, the stable torque value is 593 N·m, the torque decrease from the peak value to the stable value is 28.0%, and the first stabilization time is 303 s.

[0060] S5: The 18 parts of the post-rewetting filler material obtained in S2, 8 parts of zinc borate, and 5 parts of aluminum diethylphosphinate were dry-mixed at room temperature for 2 minutes. This mixture was then added all at once to the basic shielding premix obtained in S4 for the second stage of intensive mixing. This ensured that tungsten oxide, zinc borate, and aluminum diethylphosphinate were incorporated into the basic shielding premix at the same stage. The rotor speed for the second stage of intensive mixing was 42 r / min, the mixing time was 5 minutes, and the discharge temperature was 136℃, yielding the rewetting premix. In this step, the peak torque recorded by the intensive mixer was 763 N·m, the stable torque value was 611 N·m, the torque decreased by 19.9% ​​from the peak value to the stable value, and the second stabilization time was 189 s.

[0061] S6: 56.25 parts magnesium hydroxide, 33.75 parts aluminum hydroxide, 12 parts ammonium polyphosphate, and 6 parts triazine charring agent were added to the rewetted premix obtained in S5 for the third stage of intensive mixing. The above components were dried at 80°C for 2 hours before being added to the intensive mixer in a single feeding manner. The rotor speed of the third stage intensive mixing was 40 r / min, the mixing time was 6 minutes, and the discharge temperature was 142°C, yielding a flame-retardant and shielding mixture.

[0062] S7: 1.2 parts of hindered phenolic antioxidant, 0.8 parts of phosphite antioxidant, 2 parts of polyethylene wax, 1 part of calcium stearate, and 1 part of dioctyltin dilaurate masterbatch were added to the flame-retardant shielding mixture obtained in S6. The mixture was homogenized for 4 minutes at a rotor speed of 30 r / min and a discharge temperature of 122℃. Then, it was extruded and granulated using a twin-screw extruder to obtain a radiation-resistant, high-flame-retardant optical cable sheath material. The temperatures from zone one to the die head of the twin-screw extruder were set sequentially to 115℃, 125℃, 135℃, 140℃, and 145℃, with a screw speed of 120 r / min. After pelleting, the material was dried in hot air at 45℃ for 3 hours. In this step, the peak torque recorded by the internal mixer was 523 N·m, the stable torque value was 467 N·m, the torque decreased by 10.7% from the peak value to the stable value, and the third stabilization time was 108 s.

[0063] In this embodiment, the torque decrease rate during the first stage of internal mixing, the second stage of internal mixing, and the homogenization process decreases sequentially, and the first stabilization time, the second stabilization time, and the third stabilization time shorten sequentially. Specifically, the ratio of the torque decrease rate during the second stage of internal mixing to the torque decrease rate during the first stage of internal mixing is 0.71, and the ratio of the torque decrease rate during homogenization to the torque decrease rate during the second stage of internal mixing is 0.54; the ratio of the second stabilization time to the first stabilization time is 0.62, and the ratio of the third stabilization time to the second stabilization time is 0.57; the ratio of the torque decrease rate during the second stage of internal mixing to the torque decrease rate during the first stage of internal mixing is greater than the ratio of the second stabilization time to the first stabilization time.

[0064] S8: A 12-core single-mode optical fiber unit and two aramid reinforcing members are assembled into a cable core. A water-blocking tape is wrapped around the outside of the cable core to form a water-blocking layer with an overlap rate of 20%. Low-smoke halogen-free flame-retardant polyolefin sheath material is extruded outside the water-blocking layer to form an inner sheath layer with a thickness of 0.8 mm. Subsequently, mica tape is wrapped around the outside of the inner sheath layer with an overlap rate of 25%. The radiation-resistant, high flame-retardant optical cable sheath material obtained in S7 is then extruded through a single-screw extruder to cover the outside of the mica tape, forming a radiation-resistant, high flame-retardant outer sheath layer with a thickness of 2.2 mm. The temperatures from zone one to the die head of the single-screw extruder are set sequentially to 120℃, 130℃, 140℃, 150℃, and 155℃, the screw speed is 35 r / min, and the traction speed is 18 m / min.

[0065] S9: The optical cable with radiation-proof and flame-retardant outer sheath obtained in S8 is placed in 90℃ warm water for 6 hours for cross-linking. After being taken out, it is placed in an environment of 25℃ and 50% relative humidity for 24 hours to obtain radiation-proof and flame-retardant special optical cable.

[0066] Example 2 This embodiment discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference between this embodiment and Embodiment 1 is the formula of the radiation-resistant, high flame-retardant optical cable sheath material, the proportion of some fillers, and the parameters of the mixing process.

[0067] The radiation-resistant and flame-retardant optical cable sheath material comprises the following components by weight: 100 parts of matrix resin; 80 parts of basic shielding filler; 12 parts of post-rewetting filler; 75 parts of metal hydroxide flame retardant; 14 parts of phosphorus and nitrogen charring agent; 5 parts zinc borate; 3 parts of aluminum diethylphosphinate; 7 parts compatibilizer; Two parts antioxidant; 3 parts lubricant; One part of crosslinking aid.

[0068] In the matrix resin, the mass of ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, and silicone rubber elastomer masterbatch are 42 parts, 32 parts, 16 parts, and 10 parts, respectively.

[0069] In the basic shielding filler, the mass ratios of bismuth oxide and barium sulfate are 48.48 parts and 31.52 parts, respectively, with a mass ratio of 1:0.65. The average particle size D50 of bismuth oxide is 1.6 μm, and the average particle size D50 of barium sulfate is 2.3 μm.

[0070] The average particle size D50 of tungsten oxide is 0.9 μm, and the ratio of the average particle size D50 of tungsten oxide to that of bismuth oxide is 0.56.

[0071] The amount of epoxy-containing silane coupling agent is 0.80 parts, and the amount of phosphate ester-based dispersant is 0.40 parts, with a mass ratio of 1:0.50. The total mass of the two is 1.50% of the mass of the basic shielding filler. The amount of amino-containing silane coupling agent is 0.10 parts, and its mass is 0.83% of the mass of tungsten oxide.

[0072] In the metal hydroxide flame retardant, the mass of magnesium hydroxide and aluminum hydroxide are 48.39 parts and 26.61 parts, respectively, with a mass ratio of 1:0.55.

[0073] In the phosphorus-nitrogen charring agent, the mass of ammonium polyphosphate and triazine charring agent are 9.66 parts and 4.34 parts, respectively, with a mass ratio of 1:0.45.

[0074] The mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphonate is 12:5:3, or 1:0.42:0.25. The mass ratio of the total mass of tungsten oxide, zinc borate, and aluminum diethylphosphonate to the mass of the phosphorus-nitrogen charring agent is 20:14, or 1:0.70.

[0075] In the compatibilizer, the mass of maleic anhydride-grafted polyethylene and ethylene-vinyl acetate-maleic anhydride grafts are 4 parts and 3 parts, respectively, with a mass ratio of 1:0.75. The total acid value of the compatibilizer is 6 mg KOH / g.

[0076] The operation methods for S1 to S3 are the same as in Example 1, except that the amount of feed is adjusted according to the formula of this example.

[0077] S4: The treated base shielding filler was added to the matrix premix in two stages. The first addition consisted of 48 parts of the treated base shielding filler based on the total amount of bismuth oxide and barium sulfate, and the second addition consisted of 32 parts of the treated base shielding filler based on the total amount of bismuth oxide and barium sulfate. The rotor speed during the first stage of internal mixing was 43 r / min, and the discharge temperature was 124℃. The peak torque recorded on the internal mixer was 758 N·m, the stable torque value was 537 N·m, the torque decrease was 29.2%, and the first stabilization time was 276 s.

[0078] S5: The pre-wetted filler (calculated as 12 parts tungsten oxide), 5 parts zinc borate, and 3 parts aluminum diethylphosphonate were dry-mixed at room temperature for 2 minutes, and then added to the base shielding premix in one go. The rotor speed for the second stage of internal mixing was 40 r / min, the mixing time was 5 minutes, and the discharge temperature was 132℃. The peak torque recorded by the internal mixer was 704 N·m, the stable torque value was 561 N·m, the torque decrease was 20.3%, and the second stabilization time was 173 s.

[0079] S6: The rotor speed for the third stage of internal mixing is 38 r / min, the mixing time is 6 min, and the discharge temperature is 138℃.

[0080] S7: The homogenizing rotor speed was 28 r / min, the discharge temperature was 120℃, and the homogenization time was 4 min. The peak torque recorded by the internal mixer was 482 N·m, the stable torque value was 431 N·m, the torque decrease was 10.6%, and the third stabilization time was 99 s.

[0081] In this embodiment, the ratio of the torque decrease in the second stage of internal mixing to the torque decrease in the first stage of internal mixing is 0.70, and the ratio of the torque decrease in homogenization to the torque decrease in the second stage of internal mixing is 0.52; the ratio of the second stabilization time to the first stabilization time is 0.63, and the ratio of the third stabilization time to the second stabilization time is 0.57; the ratio of the torque decrease in the second stage of internal mixing to the torque decrease in the first stage of internal mixing is greater than the ratio of the second stabilization time to the first stabilization time.

[0082] The operation methods of S8 and S9 are the same as those in Example 1, except that the thickness of the radiation-proof and flame-retardant outer sheath is adjusted to 2.0 mm and the warm water crosslinking time is adjusted to 5.5 h.

[0083] Example 3 This embodiment discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference between this embodiment and Embodiment 1 is the formula of the radiation-resistant, high flame-retardant optical cable sheath material, the proportion of some fillers, and the parameters of the mixing process.

[0084] The radiation-resistant and flame-retardant optical cable sheath material comprises the following components by weight: 100 parts of matrix resin; 120 parts of basic shielding filler; 24 parts of post-rewetting filler; 105 parts of metal hydroxide flame retardant; 20 parts of phosphorus and nitrogen charring agent; 9 parts zinc borate; 7 parts of aluminum diethylphosphinate; 12 parts compatibilizer; Antioxidant 3 parts; 4 parts lubricant; 1.2 parts of crosslinking aid.

[0085] In the matrix resin, the mass of ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, and silicone rubber elastomer masterbatch are 48 parts, 24 parts, 18 parts, and 10 parts, respectively.

[0086] In the basic shielding filler, bismuth oxide and barium sulfate are present in 60 parts by mass and 60 parts by mass, respectively, with a mass ratio of 1:1.0. The average particle size D50 of bismuth oxide is 2.0 μm, and the average particle size D50 of barium sulfate is 2.8 μm.

[0087] The average particle size D50 of tungsten oxide is 1.1 μm, and the ratio of the average particle size D50 of tungsten oxide to that of bismuth oxide is 0.55.

[0088] The amount of epoxy-containing silane coupling agent is 1.20 parts, and the amount of phosphate ester-based dispersant is 0.72 parts, with a mass ratio of 1:0.60. The total mass of the two is 1.60% of the mass of the basic shielding filler. The amount of amino-containing silane coupling agent is 0.22 parts, and its mass is 0.92% of the mass of tungsten oxide.

[0089] In the metal hydroxide flame retardant, the mass of magnesium hydroxide and aluminum hydroxide are 63.64 parts and 41.36 parts, respectively, and the mass ratio of the two is 1:0.65.

[0090] In the phosphorus-nitrogen charring agent, the mass of ammonium polyphosphate and triazine charring agent are 13.33 parts and 6.67 parts, respectively, with a mass ratio of 1:0.50.

[0091] The mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphonate is 24:9:7, or 1:0.38:0.29. The mass ratio of the total mass of tungsten oxide, zinc borate, and aluminum diethylphosphonate to the mass of the phosphorus-nitrogen charring agent is 40:20, or 1:0.50.

[0092] In the compatibilizer, the mass of maleic anhydride-grafted polyethylene and ethylene-vinyl acetate-maleic anhydride grafts are 7 parts and 5 parts, respectively, with a mass ratio of 1:0.71. The total acid value of the compatibilizer is 8 mg KOH / g.

[0093] The operation methods for S1 to S3 are the same as in Example 1, except that the amount of feed is adjusted according to the formula of this example.

[0094] S4: The treated base shielding filler was added to the matrix premix in two stages. The first addition consisted of 72 parts of the treated base shielding filler based on the total amount of bismuth oxide and barium sulfate, and the second addition consisted of 48 parts of the treated base shielding filler based on the total amount of bismuth oxide and barium sulfate. The rotor speed during the first stage of internal mixing was 45 r / min, and the discharge temperature was 132℃. The peak torque recorded on the internal mixer was 887 N·m, the stable torque value was 637 N·m, the torque decrease was 28.2%, and the first stabilization time was 342 s.

[0095] S5: The pre-wetted filler (based on 24 parts tungsten oxide), 9 parts zinc borate, and 7 parts aluminum diethylphosphonate were dry-mixed at room temperature for 2 minutes, and then added to the base shielding premix in one go. The rotor speed for the second stage of internal mixing was 42 r / min, the mixing time was 6 minutes, and the discharge temperature was 140℃. The peak torque recorded by the internal mixer was 827 N·m, the stable torque value was 663 N·m, the torque decrease was 19.8%, and the second stabilization time was 218 s.

[0096] S6: The rotor speed for the third stage of internal mixing is 40 r / min, the mixing time is 7 min, and the discharge temperature is 146℃.

[0097] S7: The homogenizing rotor speed was 30 r / min, the discharge temperature was 126℃, and the homogenization time was 5 min. The peak torque recorded by the internal mixer was 579 N·m, the stable torque value was 519 N·m, the torque decrease was 10.4%, and the third stabilization time was 131 s.

[0098] In this embodiment, the ratio of the torque decrease in the second stage of internal mixing to the torque decrease in the first stage of internal mixing is 0.70, and the ratio of the torque decrease in homogenization to the torque decrease in the second stage of internal mixing is 0.53; the ratio of the second stabilization time to the first stabilization time is 0.64, and the ratio of the third stabilization time to the second stabilization time is 0.60; the ratio of the torque decrease in the second stage of internal mixing to the torque decrease in the first stage of internal mixing is greater than the ratio of the second stabilization time to the first stabilization time.

[0099] The operation methods for S8 and S9 are the same as in Example 1, except that the thickness of the radiation-proof and flame-retardant outer sheath is adjusted to 2.5 mm and the warm water crosslinking time is adjusted to 7 h.

[0100] Comparative Example 1 This comparative example discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference from Example 1 is that bismuth oxide, barium sulfate, and tungsten oxide are not added in stages, but are added to the matrix premix as radiation-resistant fillers all at once.

[0101] In this comparative example, the amounts, particle sizes, and purities of bismuth oxide, barium sulfate, and tungsten oxide are the same as in Example 1. The amounts of zinc borate, aluminum diethylphosphinate, metal hydroxide flame retardant, phosphorus-nitrogen charring agent, matrix resin, compatibilizer, antioxidant, lubricant, and crosslinking aid are also the same as in Example 1.

[0102] S1: Add 54.05 parts of bismuth oxide, 45.95 parts of barium sulfate, 18 parts of tungsten oxide, 1.0 part of γ-glycidyl etheroxypropyltrimethoxysilane, 0.55 parts of polyether phosphate dispersant and 0.15 parts of γ-aminopropyltriethoxysilane to a high-speed mixer, premix at 300 r / min for 5 min, then heat to 100℃ and mix at 900 r / min for 30 min, then cool to below 45℃ and discharge to obtain the treated radiation-shielding mixed filler.

[0103] S2: Post-rewetting filler that is not prepared separately.

[0104] S3: Prepare the matrix premix according to the method of Example 1.

[0105] S4: The treated radiation-shielding mixed filler obtained in S1 is added to the matrix premix obtained in S3 in one step for internal mixing. The rotor speed is 45 r / min, the discharge temperature is 128℃, and the radiation-shielding premix is ​​obtained. In this step, the peak torque recorded by the internal mixer is 913 N·m, the stable torque value is 657 N·m, the torque decrease is 28.0%, and the stabilization time is 382 s.

[0106] S5: Add 8 parts zinc borate and 5 parts aluminum diethylphosphonate to the radiation-shielding premix obtained in S4 and perform intensive mixing. The rotor speed is 42 r / min, the mixing time is 5 min, and the discharge temperature is 136℃ to obtain a synergistic premix. In this step, the peak torque recorded by the intensive mixer is 768 N·m, the stable torque value is 644 N·m, the torque decrease is 16.1%, and the stabilization time is 247 s.

[0107] S6~S9: The operation method is the same as in Example 1.

[0108] Comparative Example 2 This comparative example discloses a radiation-resistant, highly flame-retardant special optical cable and its preparation method. The only difference from Example 1 is that tungsten oxide, bismuth oxide, and barium sulfate are added simultaneously, while zinc borate and aluminum diethylphosphinate are added in the second stage.

[0109] S1: Add 54.05 parts of bismuth oxide, 45.95 parts of barium sulfate, 18 parts of tungsten oxide, 1.0 part of γ-glycidyl etheroxypropyltrimethoxysilane, 0.55 parts of polyether phosphate dispersant and 0.15 parts of γ-aminopropyltriethoxysilane to a high-speed mixer, premix at 300 r / min for 5 min, then heat to 100℃ and mix at 900 r / min for 30 min, then cool to below 45℃ and discharge to obtain the treated radiation-shielding mixed filler.

[0110] S2: Post-rewetting filler that is not prepared separately.

[0111] S3: Prepare the matrix premix according to the method of Example 1.

[0112] S4: The treated radiation-shielding mixed filler obtained in S1 is added to the matrix premix obtained in S3 and subjected to intensive mixing. The rotor speed is 45 r / min, the discharge temperature is 128℃, and the radiation-shielding premix is ​​obtained. In this step, the peak torque recorded by the intensive mixer is 878 N·m, the stable torque value is 621 N·m, the torque decrease is 29.3%, and the stabilization time is 347 s.

[0113] S5: Add 8 parts zinc borate and 5 parts aluminum diethylphosphonate to the radiation-shielding premix obtained in S4 and perform intensive mixing. The rotor speed is 42 r / min, the mixing time is 5 min, and the discharge temperature is 136℃ to obtain a synergistic premix. In this step, the peak torque recorded by the intensive mixer is 742 N·m, the stable torque value is 611 N·m, the torque decrease is 17.7%, and the stabilization time is 228 s.

[0114] S6~S9: The operation method is the same as in Example 1.

[0115] Comparative Example 3 This comparative example discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference from Example 1 is that tungsten oxide is added later, but zinc borate and aluminum diethylphosphinate are not added simultaneously with tungsten oxide. Instead, they are added in the third stage along with the metal hydroxide flame retardant and the phosphorus-nitrogen charring agent.

[0116] S1~S4: The operation method is the same as in Example 1.

[0117] S5: The 18 portions of post-rewetting filler obtained in S2 are added to the basic shielding premix obtained in S4 for the second stage of intensive mixing, without adding zinc borate and aluminum diethylphosphinate. The rotor speed of the second stage intensive mixing is 42 r / min, the mixing time is 5 min, and the discharge temperature is 136℃, resulting in the rewetting premix. In this step, the peak torque recorded by the intensive mixer is 738 N·m, the stable torque value is 609 N·m, the torque decrease is 17.5%, and the second stabilization time is 211 s.

[0118] S6: 56.25 parts magnesium hydroxide, 33.75 parts aluminum hydroxide, 12 parts ammonium polyphosphate, 6 parts triazine charring agent, 8 parts zinc borate, and 5 parts aluminum diethylphosphonate were added to the rewetting premix obtained in S5 for the third stage of intensive mixing. The rotor speed of the third stage intensive mixing was 40 r / min, the mixing time was 6 min, and the discharge temperature was 142℃, resulting in a flame-retardant and shielding mixture.

[0119] S7~S9: The operation method is the same as in Example 1.

[0120] Comparative Example 4 This comparative example discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference from Example 1 is that the formula of the radiation-resistant, high flame-retardant optical cable sheath material is the same as that in Example 1, but the mixing process is not controlled according to the torque drop and stabilization time relationship in Example 1.

[0121] S1~S3: The operation method is the same as in Example 1.

[0122] S4: The treated basic shielding filler is added to the matrix premix in one go for the first stage of intensive mixing. The rotor speed of the first stage intensive mixing is 60 r / min, the mixing time is 4 min, the discharge temperature is 132℃, and the basic shielding premix is ​​obtained. In this step, the peak torque recorded by the intensive mixer is 853 N·m, the stable torque value is 666 N·m, the torque decrease is 21.9%, and the first stabilization time is 232 s.

[0123] S5: 18 parts of the post-rewetting filler corresponding to the treated material, 8 parts of zinc borate, and 5 parts of aluminum diethylphosphinate were dry-mixed at room temperature for 2 minutes, and then added to the basic shielding premix for the second stage of intensive mixing. The rotor speed of the second stage intensive mixing was 58 r / min, the mixing time was 3 minutes, and the discharge temperature was 143℃, yielding the rewetting premix. In this step, the peak torque recorded by the intensive mixer was 793 N·m, the stable torque value was 692 N·m, the torque decrease was 12.7%, and the second stabilization time was 162 s.

[0124] S6: The rotor speed for the third stage of internal mixing is 55 r / min, the mixing time is 4 min, and the discharge temperature is 150℃.

[0125] S7: The homogenization rotor speed is 50 r / min, the discharge temperature is 135℃, and the homogenization time is 2 min. In this step, the peak torque recorded by the internal mixer is 563 N·m, the stable torque value is 521 N·m, the torque decrease is 7.5%, and the third stabilization time is 121 s.

[0126] In this comparative example, the ratio of the torque decrease during the second stage of internal mixing to the torque decrease during the first stage of internal mixing is 0.58, and the ratio of the second stabilization time to the first stabilization time is 0.70, with the former being less than the latter.

[0127] S8 and S9: The operation method is the same as in Example 1.

[0128] Comparative Example 5 This comparative example discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference from Example 1 is that tungsten oxide is not added, and an equal amount of barium sulfate is used to make up the corresponding mass of the rewetting filler.

[0129] In the radiation-resistant, flame-retardant optical cable sheath material, bismuth oxide is used in a quantity of 54.05 parts, and barium sulfate is used in a total quantity of 63.95 parts. Among them, 45.95 parts of barium sulfate and bismuth oxide are used together as the basic shielding filler, and 18 parts of barium sulfate replace tungsten oxide as the post-added filler. Other components and quantities are the same as in Example 1.

[0130] S1: 54.05 parts of bismuth oxide, 45.95 parts of barium sulfate, 1.0 part of γ-glycidyl etheroxypropyltrimethoxysilane and 0.55 parts of polyether phosphate dispersant were added to a high-speed mixer and processed in the manner of Example 1 to obtain the treated basic shielding filler.

[0131] S2: Add 18 parts of barium sulfate and 0.15 parts of γ-aminopropyltriethoxysilane to a high-speed mixer and process them according to the tungsten oxide treatment method in Example 1 to obtain the treated post-filler.

[0132] S3~S4: The operation method is the same as in Example 1.

[0133] S5: The 18 parts of the post-filler corresponding to the treated material obtained in S2, 8 parts of zinc borate, and 5 parts of aluminum diethylphosphinate were dry-mixed at room temperature for 2 minutes, and then added to the basic shielding premix for the second stage of intensive mixing. The rotor speed of the second stage intensive mixing was 42 r / min, the mixing time was 5 minutes, and the discharge temperature was 136℃, resulting in a re-wetted premix. In this step, the peak torque recorded by the intensive mixer was 746 N·m, the stable torque value was 609 N·m, the torque decrease was 18.4%, and the second stabilization time was 198 s.

[0134] S6~S9: The operation method is the same as in Example 1.

[0135] Comparative Example 6 This comparative example discloses a radiation-resistant, high flame-retardant special optical cable and its preparation method. The only difference from Example 1 is that zinc borate is not added, and an equal amount of magnesium hydroxide is used to make up the mass of the flame-retardant filler.

[0136] In the radiation-resistant and flame-retardant optical cable sheath material, the amount of zinc borate is 0 parts, the amount of magnesium hydroxide is adjusted from 56.25 parts to 64.25 parts, and the other components and amounts are the same as in Example 1.

[0137] S1~S4: The operation method is the same as in Example 1.

[0138] S5: The 18 parts of the post-rewetting filler obtained in S2 and 5 parts of aluminum diethylphosphonate were dry-mixed at room temperature for 2 minutes, and then added to the basic shielding premix for the second stage of intensive mixing. Zinc borate was not added. The rotor speed of the second stage intensive mixing was 42 r / min, the mixing time was 5 minutes, and the discharge temperature was 136℃, resulting in the rewetting premix. In this step, the peak torque recorded by the intensive mixer was 752 N·m, the stable torque value was 621 N·m, the torque decrease was 17.4%, and the second stabilization time was 197 s.

[0139] S6: 64.25 parts magnesium hydroxide, 33.75 parts aluminum hydroxide, 12 parts ammonium polyphosphate, and 6 parts triazine charring agent were added to the rewetting premix obtained in S5 for the third stage of intensive mixing. The rotor speed of the third stage intensive mixing was 40 r / min, the mixing time was 6 min, and the discharge temperature was 142℃, to obtain a flame-retardant shielding mixture.

[0140] S7~S9: The operation method is the same as in Example 1.

[0141] Performance testing To verify the comprehensive performance of the radiation-resistant and flame-retardant special optical cable prepared according to this invention, performance tests were conducted on the optical cable samples prepared in Examples 1-3 and Comparative Examples 1-6. The test items included oxygen index, vertical flammability rating, smoke density rating, tensile strength, elongation at break, thermal elongation, outer diameter fluctuation, surface particle defects, radiation shielding efficiency before combustion, and radiation shielding efficiency of the residual sheath layer after combustion. All samples were placed in an environment of 25°C and 50% relative humidity for 24 hours before testing.

[0142] 1. Oxygen Index Testing: Samples were cut from sheets prepared simultaneously using the same sheath material and cross-linking conditions as those used in the embodiments and comparative examples. The sample thickness was 3.0 mm, width was 6.5 mm, and length was 100 mm. Oxygen index testing was conducted according to GB / T 2406.2-2009. Five samples were tested for each sample, and the average value was taken as the oxygen index of that sample. A higher oxygen index indicates a higher oxygen concentration required for the outer sheath material to sustain combustion in an oxygen-nitrogen mixed atmosphere, and thus better flame retardant performance.

[0143] 2. Vertical Burning Test: Strip-shaped samples were cut from sheets prepared simultaneously with the same sheath material and cross-linking conditions as the outer sheath layer of each sample. The sample thickness was 3.0 mm, the width was 13 mm, and the length was 125 mm. The vertical burning test was conducted according to the vertical method in GB / T2408-2021. Five samples were tested for each sample. The V-0, V-1, or V-2 rating was evaluated based on the afterflame time, smoldering time, and drip ignition. The test results were used to determine the self-extinguishing nature and drip risk of the outer sheath layer under fire conditions.

[0144] 3. Smoke Density Test: Samples measuring 75mm × 75mm × 3mm were prepared simultaneously using sheets made from the same sheath material and under the same cross-linking conditions as the outer sheath layer of each sample. A single-chamber smoke generation test was conducted according to GB / T 8323.2-2008. Three samples were tested for each sample, and the average value was recorded as the maximum smoke density Ds,max. The lower the Ds,max, the lower the light-blocking effect of the smoke produced during combustion.

[0145] 4. Tensile strength and elongation at break testing: Dumbbell-shaped specimens were cut from the radiation-proof, high-flame-retardant outer sheath of each sample. Specimen preparation and testing were performed according to GB / T 2951.11-2008. The tensile speed was 250 mm / min, and five specimens were tested for each sample, with the average value taken. This test was used to evaluate the mechanical integrity and flexibility of the high-filler sheath after extrusion crosslinking.

[0146] 5. Thermal Elongation Test: Dumbbell-shaped specimens were cut from the radiation-proof and flame-retardant outer sheath of each sample and tested according to the thermal elongation test in GB / T 2951.21-2008. The test temperature was 200℃, the load was 20 N / cm², and the holding time was 15 min. The thermal elongation under the load was recorded. The lower the thermal elongation, the better the dimensional retention capability of the cross-linked outer sheath under thermal load.

[0147] 6. Outer Diameter Fluctuation Detection: Take 10m of optical cable samples prepared in each embodiment and comparative example, and measure the outer diameter every 0.5m along the length of the optical cable, for a total of 20 measurement points for each sample. Use a digital caliper with an accuracy of 0.01mm to measure, and record the difference between the maximum and minimum outer diameter as the outer diameter fluctuation value. The smaller the outer diameter fluctuation value, the better the extrusion stability of the sheath material.

[0148] 7. Surface Particle Defect Detection: Take 10m of each sample optical cable and observe the surface of the radiation-proof, flame-retardant outer sheath layer under natural light and a magnification of 10x. Count the number of visible particle protrusions, hard spots, and local rough points per meter along the length direction, and take the average value over 10m as the number of surface particle defects. This test is used to evaluate the dispersion stability of high-density inorganic fillers in the outer sheath material and the extrusion surface quality.

[0149] 8. X-ray Shielding Rate Testing: Sheets made simultaneously using the same sheath material and cross-linking conditions as the outer sheath layer of each sample were cut to size 100mm × 100mm, with a uniform sheet thickness of 2.2mm. An X-ray source was used for testing, with a tube voltage of 80kV, a tube current of 5mA, and a distance of 500mm between the source and detector. First, the dose rate received by the detector without a sample was measured and recorded as I0. Then, the sample was placed between the source and detector, and the dose rate after passing through the sample was measured and recorded as I1. The X-ray shielding rate was calculated using the following formula: X-ray shielding rate = (I0 - I1) / I0 × 100%.

[0150] Three samples were tested for each sample, and the average value was taken as the radiation shielding rate before combustion.

[0151] 9. Detection of Residual Radiation Shielding Rate of Sheath Layer After Combustion: The high-flame-retardant outer sheath sheet of each sample was subjected to combustion testing using a vertical combustion method. The residual sheath layer, remaining as a continuous sheet or block after combustion, was collected. The residual sheath layer was lightly pressed and leveled without grinding or adding additional resin or filler. The dose rate transmitted through the residual sheath layer was measured under the same radiation source conditions, test area, and detection distance as the pre-combustion radiation shielding rate test, and the radiation shielding rate of the residual sheath layer after combustion was calculated using the same formula. The ratio of the radiation shielding rate of the residual sheath layer after combustion to the radiation shielding rate before combustion was recorded as the shielding rate retention rate. The residual sheath layer may change due to variations in thickness and surface flatness after combustion; this test is used for relative comparison between samples from the same batch.

[0152] The test results are shown in Table 1 below.

[0153] Table 1. Overall performance test results of the examples and comparative examples. The results above show that Examples 1-3 are superior to the corresponding comparative examples in terms of oxygen index, smoke density, extrusion dimensional stability, number of surface particle defects, and post-combustion shielding retention rate. Although Comparative Examples 1 and 2 have similar pre-combustion shielding rates, their post-combustion shielding retention rates are significantly lower, indicating that simply increasing the total amount of shielding filler or simultaneously adding tungsten oxide cannot form an effective post-combustion retention structure. Comparative Example 3 shows that even with the addition of tungsten oxide post-combustion, the post-combustion shielding retention rate is still lower than that of Example 1 when zinc borate and aluminum diethylphosphonate are not simultaneously introduced into the second stage, indicating that the simultaneous post-dispersion of tungsten oxide and flame-retardant synergistic components contributes to char retention. Comparative Example 4 shows higher outer diameter fluctuations and a higher number of surface defects, indicating that uncontrolled torque reduction and stabilization time relationships weaken the processing stability of the high-filler system. Comparative Examples 5 and 6 respectively demonstrate that the filling effect of tungsten oxide and the densifying char formation effect of zinc borate both support the technical effects of this invention.

[0154] To further illustrate the effects of staged wetting of the filler, post-addition of tungsten oxide, and simultaneous addition of zinc borate and aluminum diethylphosphinate on the dispersion of the filler inside the radiation-resistant and flame-retardant outer sheath and the retention state of the residual layer after combustion, supplementary tests were conducted on Example 1 and related comparative examples. The proportion of filler agglomeration area was statistically analyzed based on the cross-sectional scanning electron microscope images of the outer sheath. The in-plane coefficient of variation of the shielding rate was calculated based on the X-ray shielding rate of 9 test points on the same sheet. The continuous area ratio of residual char was analyzed based on the orthographic projection image of the residual sheath after combustion. The residual mass retention rate was calculated based on the mass weighing results before and after combustion. This supplementary test focused on key variables such as the order of addition, post-addition of tungsten oxide, and simultaneous addition of zinc borate and aluminum diethylphosphinate. Therefore, Example 1 was selected for comparison with Comparative Examples 1-3, 5, and 6. The test results are shown in Table 2.

[0155] Table 2. Validation results of filler dispersion and residual carbon retention in Example 1 and related comparative examples. As shown in Table 2, the packing agglomeration area ratio and in-plane coefficient of variation of shielding efficiency in Example 1 are both lower than those in the relevant comparative examples, indicating that the pre-wetting of the basic shielding packing and the subsequent placement of tungsten oxide to fill the gaps improve the continuity of packing distribution. The high residual carbon continuous area ratio and residual mass retention rate in Example 1 indicate that the combination of zinc borate, aluminum diethylphosphonate and the subsequent phosphorus and nitrogen carbonization system can form a more effective coating and retention of high-density shielding packing.

[0156] To further illustrate the effect of warm water crosslinking on the thermal dimensional retention and flame retardant stability of the radiation-proof, high-flame-retardant outer sheath layer, samples prepared from the same batch of outer sheath material before and after crosslinking in Examples 1-3 were tested. Thermal elongation was determined according to GB / T 2951.21-2008, and oxygen index was determined according to GB / T 2406.2-2009. The test results are shown in Table 3.

[0157] Table 3. Results of thermal elongation and oxygen index tests before and after crosslinking in Examples 1-3 The data before and after crosslinking described above are used to verify the contribution of warm water crosslinking to the thermal dimensional retention and flame retardant stability of the outer sheath layer. Only tests on Examples 1-3 are required. The thermal elongation after crosslinking in Examples 1-3 was 56.7%-57.9% before crosslinking, falling within the range of 38%-68% defined in this invention; the oxygen index increased by 1.0-1.3 after crosslinking, falling within the range of 0.6-2.2 defined in this invention, indicating a synergistic stabilizing effect between the crosslinking network and the high-filler flame retardant system.

[0158] To evaluate the impact of the matching relationship between torque reduction and stabilization time during the internal mixing process on the extrusion stability of the radiation-resistant, flame-retardant outer sheath material, Example 1 and Comparative Example 4 were selected for testing. During the testing process, die head pressure data were continuously collected during the extrusion stage of the radiation-resistant, flame-retardant outer sheath layer, and the difference between the maximum and minimum pressures during the stable extrusion stage was used to characterize the extrusion pressure fluctuation; outer diameter fluctuation and the number of surface particle defects were determined according to the aforementioned method. The test results are shown in Table 4.

[0159] Table 4. Extrusion stability test results of Example 1 and Comparative Example 4 The test results above indicate that Comparative Example 4 uses a higher rotation speed and a higher discharge temperature, and the ratio of the torque decrease in the second stage to the torque decrease in the first stage is less than the ratio of the second stabilization time to the first stabilization time. This results in the high filler system entering the subsequent homogenization without forming a stable rewetting state, thus significantly increasing the extrusion pressure fluctuation, outer diameter fluctuation, and surface particle defects.

[0160] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a radiation-resistant, high flame-retardant special optical cable, characterized in that, Includes the following steps: S1: Bismuth oxide, barium sulfate, epoxy-containing silane coupling agent and phosphate-containing dispersant are mixed to obtain the treated basic shielding filler; S2: Tungsten oxide and an aminosilane coupling agent are mixed to obtain the treated post-rewetting filler; S3: Ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene, silicone rubber elastomer and compatibilizer are added to a mixing equipment and mixed to obtain a matrix premix. S4: Add the treated basic shielding filler to the matrix premix for the first stage of intensive mixing to obtain the basic shielding premix. S5: The treated post-rewetting filler, zinc borate and aluminum diethylphosphinate are simultaneously added to the basic shielding premix for the second stage of intensive mixing to obtain the rewetting premix. S6: Add the metal hydroxide flame retardant and phosphorus-nitrogen charring agent to the rewetting premix and carry out the third stage of intensive mixing to obtain the flame retardant and shielding mixture; S7: Add antioxidants, lubricants and crosslinking aids to the flame-retardant shielding mixture, homogenize it under the conditions of rotor speed of 20-45 r / min and discharge temperature of 115-130℃, and then extrude and granulate it to obtain radiation-proof high flame-retardant optical cable sheath material. S8: The fiber unit and reinforcing member are assembled into a cable core, a water-blocking layer is set on the outside of the cable core, an inner sheath layer is formed by extrusion on the outside of the water-blocking layer, and radiation-proof high flame-retardant optical cable sheath material is extruded and wrapped on the outside of the inner sheath layer to form a radiation-proof high flame-retardant outer sheath layer. S9: The radiation-resistant and flame-retardant outer sheath is cross-linked with warm water or steam to obtain a radiation-resistant and flame-retardant special optical cable.

2. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, In step S1, the mass ratio of bismuth oxide to barium sulfate is 1:0.55 to 1.35; The mass ratio of the epoxy-containing silane coupling agent to the phosphate-containing dispersant is 1:0.30 to 0.85, and the total mass of the two is 0.8% to 2.2% of the total mass of bismuth oxide and barium sulfate. In step S2, the mass of the aminosilane coupling agent is 0.3% to 1.2% of the mass of tungsten oxide.

3. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, In step S1, the average particle size D50 of bismuth oxide is 0.8–2.8 μm, and the average particle size D50 of barium sulfate is 1.2–4.0 μm. In step S2, the average particle size D50 of tungsten oxide is 0.4–1.8 μm; The average particle size D50 of the tungsten oxide is smaller than that of the bismuth oxide, and the ratio of the average particle size D50 of the tungsten oxide to that of the bismuth oxide is 0.25 to 0.

75.

4. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, In step S3, the mass ratio of ethylene-vinyl acetate copolymer, polyolefin elastomer, silane-grafted polyethylene and silicone rubber elastomer is 38-52:22-34:12-22:6-14. The vinyl acetate content in the ethylene-vinyl acetate copolymer is 24% to 33%; The silane grafting rate of the silane-grafted polyethylene is 0.6% to 1.6%. The compatibilizer comprises maleic anhydride-grafted polyethylene and ethylene-vinyl acetate-maleic anhydride graft, wherein the mass ratio of the maleic anhydride-grafted polyethylene and the ethylene-vinyl acetate-maleic anhydride graft is 1:0.35 to 1.10, and the total acid value of the compatibilizer is 3 to 12 mg KOH / g.

5. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, In step S5, the mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphinate is 1:0.25-0.75:0.20-0.65; In step S6, the metal hydroxide flame retardant includes magnesium hydroxide and aluminum hydroxide, wherein the mass ratio of magnesium hydroxide to aluminum hydroxide is 1:0.40 to 0.85; The phosphorus-nitrogen charring agent includes ammonium polyphosphate and triazine charring agent, wherein the mass ratio of ammonium polyphosphate to triazine charring agent is 1:0.25 to 0.60; The total mass ratio of tungsten oxide, zinc borate, and aluminum diethylphosphonate to the phosphorus-nitrogen char-forming agent is 1:0.55 to 1.

40.

6. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, The radiation-resistant, flame-retardant optical cable sheath material obtained in step S7 comprises the following components by weight: 100 parts of matrix resin; 70–125 parts of a basic shielding filler composed of bismuth oxide and barium sulfate; 8–28 parts of post-rewetting filler composed of tungsten oxide; 65-115 parts of metal hydroxide flame retardant; 8-20 parts of phosphorus and nitrogen charring agent; 3-9 parts zinc borate; 2-8 parts of aluminum diethylphosphinate; 5-14 parts compatibilizer; Antioxidant 1-4 parts; 1-5 parts lubricant; Crosslinking aid 0.3 to 1.5 parts.

7. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, In step S4, the discharge temperature of the first stage internal mixing is 120-135℃; In step S5, the discharge temperature of the second stage internal mixing is 128-142℃; In step S6, the discharge temperature of the third stage internal mixing is 132-148℃; The discharge temperature of the second stage internal mixing is 4-15°C higher than that of the first stage internal mixing, the discharge temperature of the third stage internal mixing is 2-10°C higher than that of the second stage internal mixing, and the discharge temperature in step S7 is 8-25°C lower than that of the third stage internal mixing.

8. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 1, characterized in that, In steps S4, S5 and S7, the stable value of torque is the average torque when the torque fluctuation amplitude does not exceed 5% of the average torque within 60 seconds after the torque peak occurs in the corresponding step. In step S4, the torque during the first stage of internal mixing decreases from its peak value to a stable value by 20% to 38%. In step S5, during the second stage of internal mixing, the torque decreases from its peak value to a stable value by 12% to 28%. In step S7, the torque decreases from its peak value to its stable value during homogenization by 6% to 16%. The torque decrease rate decreases sequentially during the first stage of intensive mixing, the second stage of intensive mixing, and the homogenization process.

9. The method for preparing the radiation-resistant, high flame-retardant special optical cable according to claim 8, characterized in that, In step S4, the time required for the torque to reach a stable value during the first stage of internal mixing is the first stabilization time, which is 180 to 420 seconds. In step S5, the time required for the torque to reach a stable value during the second stage of internal mixing is the second stabilization time, which is 100 to 260 seconds. In step S7, the time required for the torque to reach a stable value during homogenization is the third stabilization time, which is 60 to 180 seconds. The first stabilization time, the second stabilization time, and the third stabilization time are successively shortened; The torque reduction in the second stage of internal mixing is 0.50 to 0.78 of the torque reduction in the first stage of internal mixing. The ratio of the torque reduction during homogenization to the torque reduction during the second stage of internal mixing is 0.45 to 0.

82. The ratio of the second settling time to the first settling time is 0.45 to 0.75; The ratio of the third stable time to the second stable time is 0.40 to 0.80; The ratio of the torque decrease during the second stage of intensive mixing to the torque decrease during the first stage of intensive mixing is greater than the ratio of the second stabilization time to the first stabilization time.

10. A radiation-resistant, high flame-retardant special optical cable, characterized in that, It includes the cable core, a water-blocking layer covering the outside of the cable core, an inner sheath covering the outside of the water-blocking layer, and a radiation-resistant and highly flame-retardant outer sheath covering the outside of the inner sheath. The radiation-proof and flame-retardant outer sheath layer is formed by extrusion cross-linking of the radiation-proof and flame-retardant optical cable sheath material prepared by the preparation method described in any one of claims 1 to 9; The cable core includes optical fiber units and reinforcing components; The inner sheath layer is formed by extrusion of low-smoke halogen-free flame-retardant sheath material; The thickness of the inner sheath layer is 0.4–1.2 mm, and the thickness of the radiation-proof and highly flame-retardant outer sheath layer is 1.0–3.5 mm. A fiberglass tape, mica tape, or low-smoke halogen-free flame-retardant wrapping tape is provided between the inner sheath layer and the radiation-proof, high-flame-retardant outer sheath layer, and the overlap rate of the fiberglass tape, mica tape, or low-smoke halogen-free flame-retardant wrapping tape is 15% to 35%. The thermal elongation of the cross-linked radiation-proof and flame-retardant outer sheath is 38% to 68% of that of the uncross-linked radiation-proof and flame-retardant outer sheath. The oxygen index of the cross-linked radiation-proof and flame-retardant outer sheath is 0.6 to 2.2 higher than that of the uncross-linked radiation-proof and flame-retardant outer sheath. After a vertical combustion test, the radiation shielding efficiency of the residual outer sheath layer is no less than 82% of the radiation shielding efficiency of the radiation shielding high flame retardant outer sheath layer before combustion.

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