High-temperature-resistant acid and alkali corrosion resistant optical fiber and preparation method thereof

Abstract

The present application relates to power transmission cable technical field, specifically, it relates to a kind of high-temperature acid and alkali corrosion resistant optical fiber and preparation method thereof.From inside to outside, it includes quartz glass fiber core layer, high-temperature resistant composite coating and corrosion resistant sheath layer;High-temperature resistant composite coating includes: nanometer boron nitride sheet layer, nanometer silicon dioxide particles, aromatic diamine monomer and polyamide acid solution;Corrosion resistant sheath layer includes: fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, triallyl isocyanurate and perfluoroether rubber raw rubber.In the present application, the thermal conductivity and thermal stability are improved by the inner layer coated polyimide-based composite material and nanometer boron nitride sheet layer, which can effectively diffuse local hot spots, prevent coating from failure due to high-temperature aging, carbonization, so as to avoid the damage of optical fiber.

Description

Technical Field

[0001] This invention relates to the field of power transmission optical cable technology, and more specifically, to a high-temperature acid and alkali resistant optical fiber and its preparation method. Background Technology

[0002] In fiber optic composite cables, the electrical conductor is responsible for transmitting energy (electricity), while the optical fiber is responsible for transmitting information and sensing status (data). The introduction of optical fiber transforms traditional "blind" power cables into intelligent cables that are perceptible, controllable, and highly reliable, making them a key component in the modernization of energy and information infrastructure towards intelligence.

[0003] In practical applications of optical fiber composite cables, optical fibers are often deployed alongside electrical conductors under complex conditions such as high temperatures and strong corrosion, including chemical industrial parks, underground utility tunnels, and high-temperature power tunnels. However, existing optical fiber coatings and cladding materials mostly use conventional polymer systems, which are prone to aging, embrittlement, and even melting under long-term high-temperature environments (such as above 85°C), leading to increased transmission loss and decreased mechanical strength. Especially during power transmission, under conditions of current-induced thermal effects or localized temperature rises caused by external heat sources, the long-term stability of optical fibers faces severe challenges, potentially causing data transmission interruptions or sensing function failures.

[0004] Furthermore, although optical fibers themselves possess high chemical inertness, their protective coatings and coloring layers often lack sufficient resistance to acidic and alkaline corrosive media. In chemical plants, coastal high-salt and humid environments, or areas with industrial wastewater leakage, acidic or alkaline substances gradually erode the protective structure of the optical fiber surface, leading to microcracks, coating peeling, and even fiber breakage. Such damage not only affects the quality of optical signal transmission but also causes data deviations or blind spots in fiber-optic distributed sensing systems (such as temperature and strain monitoring), thereby impacting the intelligent functions of optical-electric composite cables. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that damage to optical fibers caused by high temperature and acid / alkali corrosion in existing optical-electric composite cables affects the functionality of the cables.

[0006] The purpose of this invention is to provide a high-temperature resistant acid and alkali corrosion-resistant optical fiber and its preparation method. By using a polyimide-based composite material and nano-boron nitride sheets to coat the inner layer, the thermal conductivity and thermal stability are improved, which can effectively diffuse local hot spots and prevent the coating from failing due to high-temperature aging and carbonization, thereby avoiding damage to the optical fiber.

[0007] To achieve the above objectives, one of the objectives of this invention is to provide a high-temperature resistant acid and alkali corrosion resistant optical fiber, which comprises, from the inside out, a quartz glass fiber core layer, a high-temperature resistant composite coating layer, and a corrosion resistant sheath layer. The high-temperature resistant composite coating comprises the following raw materials in the indicated mass percentages: The composition consists of 5-8% boron nitride nanosheets, 10-15% nano silica particles, and 3-5% aromatic diamine monomers, with the remainder being a polyamic acid solution. The corrosion-resistant sheath layer comprises the following raw materials in the following mass percentages: The composition consists of 5-10% fumed silica, 4-6% epoxy group-containing silane coupling agent, 2-4% peroxide vulcanizing agent, and 1-2% triallyl isocyanurate, with the balance being perfluoroether rubber raw rubber.

[0008] As a further improvement to this technical solution, the aromatic diamine monomer contains a reactive amino group in its molecular structure, and contains at least one side chain amino group or an amino group that is easily exposed after curing.

[0009] As a further improvement to this technical solution, the solid content of the polyamic acid solution is 15-20%.

[0010] As a further improvement to this technical solution, the epoxy-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0011] This invention includes the following raw materials: The composition includes quartz glass, polyamic acid solution, nano-boron nitride sheets, nano-silica particles, aromatic diamine monomers, perfluoroether rubber raw material, fumed silica, epoxy-containing silane coupling agent, peroxide vulcanizing agent, and triallyl isocyanurate. Specifically: the nano-boron nitride sheets and nano-silica particles together construct a high-temperature resistant reinforcing network. The high thermal conductivity of boron nitride rapidly dissipates localized heat, while the steric hindrance effect of silica enhances the coating's density, synergistically inhibiting the thermal degradation of the polymer matrix. The active amino groups in the aromatic diamine monomer molecules are partially exposed on the coating surface during imidization, providing reaction sites for interfacial bonding. The perfluorovinyl ether active sites introduced into the raw rubber molecular chain of the perfluoroether rubber can react with amino groups; the epoxy group-containing silane coupling agent acts as a bridging molecule, with one end forming a covalent bond with the active amino group on the coating surface through an epoxy group, and the other end combining with fumed silica and the rubber matrix through silanol groups; the peroxide vulcanizing agent decomposes under high temperature and high pressure to generate free radicals, which initiate the formation of a crosslinked network of perfluoroether rubber. The polyamic acid solution is converted into polyimide during the step-heat imidization process, forming a high-temperature resistant skeleton structure; the fumed silica serves as a reinforcing filler, improving the mechanical strength and creep resistance of the sheath layer; the triallyl isocyanurate promotes the improvement of the rubber vulcanization network, increasing the crosslinking density and chemical resistance.

[0012] A second objective of this invention is to provide a method for preparing the above-mentioned high-temperature acid and alkali resistant optical fiber, comprising the following steps: Step S1: Use optical fiber preforms to draw fibers in a high-temperature drawing tower to form a quartz glass fiber core layer; Step S2: The nano-silica particles and nano-boron nitride sheets are sheared and dispersed in a polyamic acid solution to form a preliminary dispersion. Then, the aromatic diamine monomer is added to the preliminary dispersion and stirred continuously at room temperature to fully dissolve and mix evenly to form a coating slurry. Before the quartz glass fiber core layer formed by drawing has cooled, the above-mentioned coating slurry is applied through a coating mold. The coated quartz glass fiber core layer completes the imidization reaction through a step-by-step heating process to form a high-temperature resistant composite coating. Step S3: After the fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, crosslinking agent and perfluoroether rubber raw rubber are mixed evenly in an internal mixer, they are fed into the feed port of an extruder and heated and sheared by the extruder to obtain a uniform and viscous melt. Then, the melt is extruded through an extrusion die over the high-temperature resistant composite coating that has been imidized and cooled, and after preliminary shaping treatment, a corrosion-resistant sheath layer is obtained. Step S4: Insert the optical fiber with the corrosion-resistant sheath layer on its surface into the continuous high-temperature vulcanization pipeline for vulcanization; The final optical fiber is then wound up and stored using a traction wheel.

[0013] As a further improvement to this technical solution, in step S2, the stepped heating process involves the quartz glass fiber core layer first undergoing a preheating treatment, and then the quartz glass fiber core layer entering a programmable temperature curing oven, where it undergoes a stepped heating process under nitrogen protection to complete the imidization reaction from polyamic acid to polyimide.

[0014] As a further improvement to this technical solution, the temperature during the preheating treatment is 80-120℃.

[0015] As a further improvement to this technical solution, in step S3, the melt is passed through a 100-200 mesh filter and then extruded from the annular gap between the die core and the die sleeve, and coated with a high-temperature resistant composite coating at the exit of the die.

[0016] As a further improvement to this technical solution, in step S3, the preliminary shaping process is to use a temperature-controlled guide roller to keep the melt coated on the surface of the high-temperature resistant composite coating in shape and maintain its temperature.

[0017] As a further improvement to this technical solution, in step S4, vulcanization is carried out at a temperature of 190-210℃ under a normal pressure nitrogen protective atmosphere.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: In this high-temperature resistant acid and alkali corrosion optical fiber and its preparation method, a high-temperature resistant reinforcing skeleton is first constructed by introducing nano-silica particles and nano-boron nitride sheets as the matrix. The nano-silica improves the density of the coating through steric hindrance, while the high thermal conductivity of the boron nitride sheets can quickly dissipate local heat and synergistically inhibit the thermal degradation and creep of the polymer matrix at high temperatures. Furthermore, an aromatic diamine monomer is added. The benzimidazole ring and side chain active amino groups in the monomer are partially retained on the coating surface during the imidization curing process, providing highly reactive sites for subsequent interfacial bonding. Furthermore, a corrosion-resistant sheath layer is constructed using perfluoroether rubber raw material. The perfluorovinyl ether active sites introduced into its molecular chain, along with fumed silica filler and silane coupling agent containing epoxy groups, achieve initial dispersion and composite during the mixing process. In the subsequent high-temperature and high-pressure vulcanization stage, while the peroxide vulcanizing agent triggers the formation of the rubber crosslinking network, the epoxy groups in the silane coupling agent undergo ring-opening addition reactions with the active amino groups exposed in the inner coating layer, forming a strong covalent bond bridge at the interface between the two layers. This transforms physical adhesion into chemical bonding, solving the interlayer delamination problem caused by thermal expansion coefficient mismatch or medium penetration, and ultimately obtaining an optical fiber structure with excellent heat resistance, chemical corrosion resistance, and long-term service stability. Attached Figure Description

[0019] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram showing the attenuation changes of optical fibers with different mass percentages of aromatic diamine monomers. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] One of the objectives of this invention is to provide a high-temperature resistant acid and alkali corrosion resistant optical fiber, which comprises, from the inside out, a quartz glass fiber core layer, a high-temperature resistant composite coating layer, and a corrosion resistant sheath layer. The high-temperature resistant composite coating comprises the following raw materials in the following mass proportions: The composition consists of 5-8% boron nitride nanosheets, 10-15% nano silica particles, and 3-5% aromatic diamine monomers, with the remainder being a polyamic acid solution. The corrosion-resistant sheath layer comprises the following raw materials in the following mass proportions: The composition consists of 5-10% fumed silica, 4-6% epoxy group-containing silane coupling agent, 2-4% peroxide vulcanizing agent, and 1-2% triallyl isocyanurate (TAIC), with the balance being perfluoroether rubber raw rubber (which has active sites that can react with amino groups introduced into its molecular chain, such as perfluorovinyl ether).

[0022] Furthermore, the aromatic diamine monomer contains reactive amino groups in its molecular structure, and at least one side-chain amino group or an amino group that is easily exposed after curing. In this invention, 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) or 4,4'-diaminodiphenyl sulfone (DDS) are preferred, as they can provide additional reactive sites after curing, thereby enhancing interlayer coordination and long service life.

[0023] Furthermore, the solid content of the polyamic acid solution is 15-20%, and in this invention, the epoxy group-containing silane coupling agent is selected as γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0024] Please see Figure 1 As shown, the present invention also provides a method for preparing the above-mentioned high-temperature acid and alkali resistant optical fiber, comprising the following steps: Step S1: Use an optical fiber preform to draw fibers in a high-temperature drawing tower to form a quartz glass fiber core layer.

[0025] Step S2: The nano-silica particles and nano-boron nitride sheets are dispersed in a polyamic acid solution by high-speed shearing to form a preliminary dispersion. Then, the aromatic diamine monomer is added to the preliminary dispersion and stirred continuously at room temperature to fully dissolve and mix evenly, forming a reactive nano-coating slurry.

[0026] Before the quartz glass fiber core layer formed by drawing has cooled, the above-mentioned coating slurry is immediately applied through a coating mold. The coated quartz glass fiber core layer completes the imidization reaction through a stepped heating process to form a high-temperature resistant composite coating. During this process, some of the added diamine monomers participate in the chain extension reaction, while some of their terminal active amino groups are retained and exposed on the surface of the cured coating.

[0027] The stepped heating process involves first preheating the quartz glass fiber core layer at 80-120℃ to remove most of the solvent. Then, the quartz glass fiber core layer enters a programmed temperature curing oven and undergoes stepped heating (e.g., 150℃ / 1h → 250℃ / 1h → 280℃ / 0.5h) under nitrogen protection to complete the imidization reaction from polyamic acid to polyimide. Step S3: After the fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, crosslinking agent and perfluoroether rubber raw rubber are mixed evenly in a mixer, the mixture is fed into the feed port of an extruder and heated and sheared by the extruder to obtain a uniform and viscous melt.

[0028] The melt is then extruded through an extrusion die over the high-temperature resistant composite coating that has undergone imidization and cooling, and after preliminary shaping, a corrosion-resistant sheath layer is obtained. Specifically, the melt is passed through a 100-200 mesh filter (to remove any possible trace impurities or undispersed lumps of adhesive material), and extruded from the annular gap between the die core and the die sleeve, directly and tightly coating the high-temperature resistant composite coating of the uniformly advancing optical fiber at the die exit.

[0029] Furthermore, the initial shaping process involves using temperature-controlled guide rollers or a small amount of air cooling to maintain the shape and appropriate temperature of the melt coated on the surface of the high-temperature resistant composite coating, preventing it from deforming due to gravity or surface tension, thus preparing it for subsequent vulcanization.

[0030] Step S4: Immediately insert the optical fiber with the corrosion-resistant sheath layer on its surface into the continuous high-temperature vulcanization pipeline for vulcanization. The vulcanization is carried out at a temperature of 190-210℃ under a normal pressure (or slightly positive pressure) nitrogen protective atmosphere.

[0031] This process is crucial: First, the epoxy-containing silane coupling agent in the sheath layer acts as a "bridging molecule." Under heating conditions, its epoxy groups preferentially undergo ring-opening addition reactions with the active amino groups exposed on the primary coating surface, forming strong CN covalent bonds and completing interfacial chemical bonding. Subsequently, free radicals generated from the decomposition of the perfluoroether rubber initiate a crosslinking reaction in the perfluoroether rubber. Triallyl isocyanurate, acting as a co-crosslinking agent, participates in and optimizes the crosslinking network structure, forming a three-dimensional network structure. The other end of the silane coupling agent is tightly bonded to the perfluoroether rubber matrix and fumed silica filler through chemical or physical interactions. Thus, chemical bonding is achieved at the interface between the two layers, rather than traditional physical adhesion.

[0032] The final optical fiber is then wound up and stored using a traction wheel.

[0033] The following specific embodiments will further illustrate the high-temperature acid and alkali corrosion resistant optical fiber and its preparation method provided by the present invention. Example

[0034] Step S1: Use an optical fiber preform to draw fibers in a high-temperature drawing tower to form a quartz glass fiber core layer.

[0035] Step S2: The nano-silica particles and nano-boron nitride sheets are dispersed in a polyamic acid solution by high-speed shearing to form a preliminary dispersion. Then, the aromatic diamine monomer is added to the preliminary dispersion and stirred continuously at room temperature to fully dissolve and mix evenly, forming a reactive nano-coating slurry.

[0036] Before the quartz glass fiber core layer formed by drawing has cooled, the above-mentioned coating slurry is immediately applied through a coating mold. The coated quartz glass fiber core layer completes the imidization reaction through a step-by-step heating process to form a high-temperature resistant composite coating.

[0037] The stepped heating process involves the quartz glass fiber core layer first undergoing a preheating treatment at 80℃, followed by the quartz glass fiber core layer entering a programmed temperature curing oven. Under nitrogen protection, it undergoes a stepped heating process of 150℃ / 1h → 250℃ / 1h → 280℃ / 0.5h to complete the imidization reaction from polyamic acid to polyimide.

[0038] Step S3: Fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, triallyl isocyanurate and perfluoroether rubber raw rubber are mixed evenly in a mixer and then fed into the feed port of an extruder. The mixture is heated and sheared by the extruder to obtain a uniform and viscous melt.

[0039] The melt is then extruded through an extrusion die onto the high-temperature resistant composite coating that has undergone imidization and cooling, and after preliminary shaping treatment, a corrosion-resistant sheath layer is obtained. Specifically, the melt is passed through a 100-mesh filter and extruded from the annular gap between the die core and the die sleeve, directly and tightly covering the high-temperature resistant composite coating of the optical fiber that is moving at a uniform speed at the exit of the die.

[0040] Furthermore, the initial shaping process involves using temperature-controlled guide rollers to maintain the shape and appropriate temperature of the melt coated on the surface of the high-temperature resistant composite coating.

[0041] Step S4: The optical fiber with the corrosion-resistant sheath layer on its surface is immediately put into the continuous high-temperature vulcanization pipeline for vulcanization, and the vulcanization is carried out at a temperature of 190°C and under a normal pressure nitrogen protective atmosphere.

[0042] The final optical fiber is then wound up and stored using a traction wheel.

[0043] It is worth noting that, in this embodiment, the mass percentages of each raw material in the high-temperature resistant composite coating are as follows: The composition consists of 5% boron nitride nanosheets, 15% nano silica particles, and 3% aromatic diamine monomer, with the remainder being a polyamic acid solution. The mass percentages of each raw material in the corrosion-resistant sheath layer are as follows: The composition consists of 10% fumed silica, 4% epoxy group-containing silane coupling agent, 4% peroxide vulcanizing agent, and 1% triallyl isocyanurate, with the balance being perfluoroether rubber raw material.

[0044] Furthermore, the aromatic diamine monomer is 2-(4-aminophenyl)-5-aminobenzimidazole (BIA); the solid content of the polyamic acid solution is 20%, and the epoxy group-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. Example

[0045] Step S1: Use an optical fiber preform to draw fibers in a high-temperature drawing tower to form a quartz glass fiber core layer.

[0046] Step S2: The nano-silica particles and nano-boron nitride sheets are dispersed in a polyamic acid solution by high-speed shearing to form a preliminary dispersion. Then, the aromatic diamine monomer is added to the preliminary dispersion and stirred continuously at room temperature to fully dissolve and mix evenly, forming a reactive nano-coating slurry.

[0047] Before the quartz glass fiber core layer formed by drawing has cooled, the above-mentioned coating slurry is immediately applied through a coating mold. The coated quartz glass fiber core layer completes the imidization reaction through a step-by-step heating process to form a high-temperature resistant composite coating.

[0048] The stepped heating process involves first preheating the quartz glass fiber core layer to 100℃, then placing it in a programmed temperature curing oven under nitrogen protection. The process involves a stepped heating sequence of 160℃ / 1h → 240℃ / 1.5h → 270℃ / 1h to complete the imidization reaction from polyamic acid to polyimide. Step S3: Fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, triallyl isocyanurate and perfluoroether rubber raw rubber are mixed evenly in a mixer and then fed into the feed port of an extruder. The mixture is heated and sheared by the extruder to obtain a uniform and viscous melt.

[0049] The melt is then extruded through an extrusion die over the high-temperature resistant composite coating that has undergone imidization and cooling, and undergoes preliminary shaping treatment to obtain a corrosion-resistant sheath layer. Specifically, the melt is passed through a 150-mesh filter and extruded from the annular gap between the die core and the die sleeve, directly and tightly coating the uniformly advancing high-temperature resistant composite coating of the optical fiber at the die exit.

[0050] Furthermore, the initial shaping process involves using temperature-controlled guide rollers to maintain the shape and appropriate temperature of the melt coated on the surface of the high-temperature resistant composite coating.

[0051] Step S4: Immediately insert the optical fiber with the corrosion-resistant sheath layer on its surface into the continuous high-temperature vulcanization pipeline for vulcanization. The vulcanization is carried out at a temperature of 200°C and under a normal pressure nitrogen protective atmosphere.

[0052] The final optical fiber is then wound up and stored using a traction wheel.

[0053] It is worth noting that, in this embodiment, the mass percentages of each raw material in the high-temperature resistant composite coating are as follows: The composition consists of 7% boron nitride nanosheets, 12% nano silica particles, and 4% aromatic diamine monomers, with the remainder being a polyamic acid solution. The mass percentages of each raw material in the corrosion-resistant sheath layer are as follows: The composition consists of 8% fumed silica, 5% epoxy group-containing silane coupling agent, 3% peroxide vulcanizing agent, and 2% triallyl isocyanurate, with the balance being perfluoroether rubber raw material.

[0054] Furthermore, the aromatic diamine monomer is 4,4'-diaminodiphenyl sulfone (DDS); the solid content of the polyamic acid solution is 18%, and the epoxy group-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. Example

[0055] Step S1: Use an optical fiber preform to draw fibers in a high-temperature drawing tower to form a quartz glass fiber core layer.

[0056] Step S2: The nano-silica particles and nano-boron nitride sheets are dispersed in a polyamic acid solution by high-speed shearing to form a preliminary dispersion. Then, the aromatic diamine monomer is added to the preliminary dispersion and stirred continuously at room temperature to fully dissolve and mix evenly, forming a reactive nano-coating slurry.

[0057] Before the quartz glass fiber core layer formed by drawing has cooled, the above-mentioned coating slurry is immediately applied through a coating mold. The coated quartz glass fiber core layer completes the imidization reaction through a step-by-step heating process to form a high-temperature resistant composite coating.

[0058] The stepped heating process involves the quartz glass fiber core layer first undergoing a preheating treatment at 120℃, followed by the quartz glass fiber core layer entering a programmed temperature curing oven. Under nitrogen protection, it undergoes a stepped heating process of 140℃ / 1.5h → 260℃ / 1h → 290℃ / 0.5h to complete the imidization reaction from polyamic acid to polyimide.

[0059] Step S3: Fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, triallyl isocyanurate and perfluoroether rubber raw rubber are mixed evenly in a mixer and then fed into the feed port of an extruder. The mixture is heated and sheared by the extruder to obtain a uniform and viscous melt.

[0060] The melt is then extruded through an extrusion die over the high-temperature resistant composite coating that has undergone imidization and cooling, and undergoes preliminary shaping to obtain a corrosion-resistant sheath layer. Specifically, the melt is passed through a 200-mesh filter and extruded from the annular gap between the die core and the die sleeve, directly and tightly coating the uniformly advancing high-temperature resistant composite coating of the optical fiber at the die exit.

[0061] Furthermore, the initial shaping process involves using temperature-controlled guide rollers to maintain the shape and appropriate temperature of the melt coated on the surface of the high-temperature resistant composite coating.

[0062] Step S4: Immediately insert the optical fiber with the corrosion-resistant sheath layer on its surface into the continuous high-temperature vulcanization pipeline for vulcanization. The vulcanization is carried out at a temperature of 210°C and under a normal pressure nitrogen protective atmosphere.

[0063] The final optical fiber is then wound up and stored using a traction wheel.

[0064] It is worth noting that, in this embodiment, the mass percentages of each raw material in the high-temperature resistant composite coating are as follows: The composition consists of 8% boron nitride nanosheets, 10% nano silica particles, and 5% aromatic diamine monomer, with the remainder being a polyamic acid solution. The mass percentages of each raw material in the corrosion-resistant sheath layer are as follows: The composition consists of 5% fumed silica, 6% epoxy group-containing silane coupling agent, 2% peroxide vulcanizing agent, and 2% triallyl isocyanurate, with the balance being perfluoroether rubber raw rubber.

[0065] Furthermore, the aromatic diamine monomer is 2-(4-aminophenyl)-5-aminobenzimidazole (BIA); the solid content of the polyamic acid solution is 15%, and the epoxy group-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0066] Comparative Example Quartz glass fiber core was prepared using the same fiber preform and drawing process as in Example 1, and a standard acrylate coating (approximately 62.5 μm thick) was immediately coated on its surface and cured under ultraviolet light to obtain a control fiber with only a standard single-layer protective coating.

[0067] Optical fibers were prepared according to Examples 1-3 and comparative examples, and then the prepared optical fibers were tested for high-temperature performance and acid and alkali corrosion resistance.

[0068] The high-temperature performance test process involved cutting a 1-meter-long optical fiber sample and placing it in a high-temperature cycling test chamber. One end of the sample was connected to an optical time domain reflectometer (OTDR), and the other end was connected to a stable light source. The test chamber temperature program was set as follows: from 25°C to 200°C, held for 4 hours, and then lowered to 25°C, which constituted one cycle. This was repeated for 10 cycles. The attenuation change of the optical fiber at a wavelength of 1550nm at the extreme points of high and low temperatures in each cycle was recorded (unit: dB / km), and the measured data were recorded in Table 1.

[0069] The acid and alkali corrosion resistance test process was as follows: 500 mL each of sulfuric acid solution (pH=2) and sodium hydroxide solution (pH=12) were prepared; three 1-meter-long optical fiber samples were cut and immersed in the above two corrosive solutions and deionized water (control); the containers were placed in an 85℃ constant temperature water bath and left to soak for 240 hours; the samples were removed, rinsed with deionized water and dried; the attenuation value of the optical fiber after immersion was measured at a wavelength of 1550nm using an OTDR and compared with the attenuation value before immersion, and the attenuation change was calculated (unit: dB / km). The measured data were recorded in Table 1.

[0070] Table 1. Attenuation changes in high-temperature performance and acid / alkali corrosion resistance of optical fibers in Examples 1-3. Attenuation change during high-temperature performance testing (dB / km) 0.07 0.06 0.07 0.35 Change in acid and alkali corrosion resistance attenuation value (dB / km) 0.15 0.14 0.14 Fiber optic cable damaged As shown in Table 1, the optical fiber samples prepared by this invention (Examples 1-3) maintained extremely low optical attenuation changes under harsh conditions such as high-temperature cycling and acid-alkali corrosion, and their performance was significantly better than that of the comparative optical fiber with only a standard single-layer coating. The comparative optical fiber exhibited significantly higher attenuation at high temperatures and completely failed in acid-alkali corrosion environments. This fully demonstrates the key role of the multilayer composite structure and interfacial chemical bonding process of this invention in improving the long-term reliability of optical fibers in extreme environments. This invention effectively solves the technical problem of easy failure of traditional optical fiber coatings in high-temperature and corrosive environments, and significantly improves the long-term reliability of optoelectronic composite cables in complex environments such as smart grids and industrial IoT.

[0071] In this invention, a high-temperature resistant reinforcing framework is first constructed by introducing nano-silica particles and nano-boron nitride sheets using a polyamic acid solution as the matrix. The nano-silica improves the density of the coating through steric hindrance, while the highly thermally conductive boron nitride sheets can quickly dissipate local heat and synergistically inhibit the thermal degradation and creep of the polymer matrix at high temperatures. Furthermore, aromatic diamine monomers with special structures, such as 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), are added. The benzimidazole ring and active amino groups in the BIA molecule are partially retained on the coating surface during imidization curing, providing highly reactive sites for subsequent interfacial bonding. Furthermore, a corrosion-resistant sheath layer is constructed using perfluoroether rubber raw material. The perfluorovinyl ether active sites introduced into its molecular chain, along with fumed silica filler and silane coupling agent containing epoxy groups, achieve initial dispersion and composite during the mixing process. In the subsequent high-temperature and high-pressure vulcanization stage, while the peroxide vulcanizing agent triggers the formation of the rubber crosslinking network, the epoxy groups in the silane coupling agent undergo ring-opening addition reactions with the active amino groups exposed in the inner coating layer, forming a strong covalent bond bridge at the interface between the two layers. This transforms physical adhesion into chemical bonding, solving the interlayer delamination problem caused by thermal expansion coefficient mismatch or medium penetration, and ultimately obtaining an optical fiber structure with excellent heat resistance, chemical corrosion resistance, and long-term service stability.

[0072] Experimental Example 1 In the preparation process of this invention, the perfluoroether rubber raw rubber undergoes two types of reactions: bulk vulcanization crosslinking and interfacial chemical bonding. The bulk vulcanization crosslinking process involves the homolytic cracking of peroxides under heating, generating active free radicals that abstract hydrogen atoms. These generated alkoxy radicals then attack specific hydrogen atom sites on the perfluoroether rubber molecular chain, generating rubber macromolecular free radicals. Two rubber macromolecular free radicals combine to form stable CC crosslinking bonds, connecting linear molecules into a network. The co-crosslinking agent participates in and improves this network through its multiple double bond structure. That is, by forming CC bonds, linear rubber molecules are transformed into a three-dimensional crosslinked network, endowing the sheath layer with high elasticity and strength.

[0073] The interfacial chemical bonding reaction process is as follows: In the formula, It is an active amino group. The epoxy group of the silane coupling agent, with its exposed active amino group acting as a nucleophile, attacks the epoxy group of the silane coupling agent to yield an oxygen anion intermediate. This oxygen anion intermediate then extracts a proton from the environment. The silane coupling agent completes a ring-opening addition reaction, ultimately forming a stable CN bond and introducing a hydroxyl group into the molecule. The other end of the silane coupling agent undergoes hydrolytic condensation with the fumed silica (SiO2) filler via its silanoxy group, forming a Si-O-Si covalent bond, which then physically entangles with the rubber matrix, thus completing the "bridging." This results in a strong CN covalent bond being constructed at the two-layer interface.

[0074] In this invention, replacing the perfluoroether rubber raw material with other types of rubber will have a significant negative impact on the attenuation variation of the optical fiber in several ways, especially in harsh environments such as high temperature, high humidity, or corrosive conditions. This impact mainly stems from the inherent defects of the substitute rubber in terms of heat resistance, chemical stability, adhesion to the inner coating, and mechanical properties.

[0075] To verify that perfluoroether rubber raw material in the corrosion-resistant sheath layer is one of the important components of the high-temperature acid and alkali corrosion resistant optical fiber and its preparation method provided in this invention, which can produce optical fibers with low attenuation changes.

[0076] This experimental example is based on Example 1 above, except that the perfluoroether rubber raw material is changed. In the corrosion-resistant sheath layer, the perfluoroether rubber raw material is replaced with ordinary silicone rubber, fluororubber, or EPDM rubber. Then, the optical fiber is fabricated, and the test is carried out according to the test methods given in the above examples. The test results are shown in Table 2.

[0077] Table 2. Influence of different components on the change in fiber attenuation Attenuation change during high-temperature performance testing (dB / km) 0.07 0.54 0.27 1.02 Change in acid and alkali corrosion resistance attenuation value (dB / km) 0.15 0.65 0.36 1.20 As shown in Table 2, when the rubber component in the corrosion-resistant sheath is replaced by perfluoroether rubber raw rubber with ordinary silicone rubber, fluororubber or EPDM rubber, the change in optical fiber attenuation increases significantly. Therefore, it can be concluded that perfluoroether rubber raw rubber in the corrosion-resistant sheath is one of the important components that enables the preparation of optical fibers with low attenuation changes in the high-temperature acid and alkali corrosion resistant optical fiber and its preparation method provided by this invention.

[0078] Experimental Example 2 In this invention, the aromatic diamine monomer accounts for 3-5% of the mass of the high-temperature resistant composite coating. If this percentage deviates from this optimal range, it will lead to a series of performance defects. Too low a diamine monomer content means that after imidization curing, the amount of reactive amino groups available for reaction on the coating surface (…) Insufficient density. During subsequent vulcanization, the epoxy silane coupling agent in the sheath layer cannot find enough reaction sites for ring-opening addition reactions, which will lead to failure of interfacial chemical bonding, a significant reduction in interlayer peel strength, and easy occurrence of interlayer peel under thermal cycling or mechanical stress, causing the optical fiber to lose protection; Excessive diamine content leads to overly rigid and densely packed polyimide molecular chains. This significantly increases the coating's brittleness and reduces its flexibility. When the optical fiber is bent or the temperature changes, the rigid coating cannot release stress through deformation, making it highly susceptible to microcracks. These cracks not only directly increase the scattering loss of the optical signal but also become rapid channels for corrosive media to penetrate the fiber core.

[0079] To verify this, the 3-5% mass ratio of aromatic diamine monomer in the high-temperature resistant composite coating is one of the key factors enabling the high-temperature acid and alkali corrosion resistant optical fiber and its preparation method provided by this invention to produce optical fibers with low attenuation changes.

[0080] This experimental example, based on Example 2 above, only changed the mass percentage of aromatic diamine monomers in the high-temperature resistant composite coating. The mass percentage of aromatic diamine monomers was set to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. Then, optical fibers were fabricated, and the resulting optical fibers were tested according to the acid and alkali corrosion resistance test methods given in the above examples. The test results are as follows: Figure 2 As shown.

[0081] according to Figure 2 It can be seen that when the mass percentage of aromatic diamine monomer in the high-temperature resistant composite coating is 1%, 2%, 6%, 7%, 8%, 9%, or 10%, i.e., not 3-5%, the attenuation change value of the prepared optical fiber is significantly greater than that of the optical fiber prepared when the mass percentage of aromatic diamine monomer in the high-temperature resistant composite coating is 3%, 4%, or 5%. Therefore, it can be shown that a mass percentage of 3-5% of aromatic diamine monomer in the high-temperature resistant composite coating is one of the important factors that enable the high-temperature acid and alkali corrosion resistant optical fiber and its preparation method provided by this invention to prepare optical fibers with low attenuation change.

[0082] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing optical fibers resistant to high-temperature acid and alkali corrosion, characterized in that, Includes the following steps: Step S1: Use optical fiber preforms to draw fibers in a high-temperature drawing tower to form a quartz glass fiber core layer; Step S2: The nano-silica particles and nano-boron nitride sheets are sheared and dispersed in a polyamic acid solution to form a preliminary dispersion. Then, the aromatic diamine monomer is added to the preliminary dispersion and stirred continuously at room temperature to fully dissolve and mix evenly to form a coating slurry. Before the quartz glass fiber core layer formed by drawing has cooled, the above-mentioned coating slurry is applied through a coating mold. The coated quartz glass fiber core layer completes the imidization reaction through a step-by-step heating process to form a high-temperature resistant composite coating. Step S3: Fumed silica, epoxy group-containing silane coupling agent, peroxide vulcanizing agent, triallyl isocyanurate and perfluoroether rubber raw rubber are mixed evenly in an internal mixer and then fed into the feed port of an extruder. The mixture is heated and sheared by the extruder to obtain a uniform and viscous melt. Then, the melt is extruded through an extrusion die over the high-temperature resistant composite coating that has been imidized and cooled, and after preliminary shaping treatment, a corrosion-resistant sheath layer is obtained. Step S4: Insert the optical fiber with the corrosion-resistant sheath layer on its surface into the continuous high-temperature vulcanization pipeline for vulcanization; The final optical fiber is wound up and stored using a traction wheel; The high-temperature resistant composite coating comprises the following raw materials in the following mass percentages: The composition consists of 5-8% boron nitride nanosheets, 10-15% nano silica particles, and 3-5% aromatic diamine monomers, with the remainder being a polyamic acid solution. The corrosion-resistant sheath layer comprises the following raw materials in the following mass percentages: The composition consists of 5-10% fumed silica, 4-6% epoxy group-containing silane coupling agent, 2-4% peroxide vulcanizing agent, and 1-2% triallyl isocyanurate, with the balance being perfluoroether rubber raw rubber.

2. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S2, the aromatic diamine monomer contains a reactive amino group in its molecular structure, and at least one side chain amino group or an amino group that is easily exposed after curing.

3. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S2, the solid content of the polyamic acid solution is 15-20%.

4. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S3, the epoxy group-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

5. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S2, the stepped heating process involves the quartz glass fiber core layer first undergoing a preheating treatment, and then the quartz glass fiber core layer entering a programmable temperature curing oven, where it undergoes a stepped heating process under nitrogen protection to complete the imidization reaction from polyamic acid to polyimide.

6. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 5, characterized in that: The preheating temperature is 80-120℃.

7. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S3, the melt is passed through a 100-200 mesh filter and then extruded from the annular gap between the die core and the die sleeve, and coated with a high-temperature resistant composite coating at the exit of the die.

8. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S3, the preliminary shaping process involves using a temperature-controlled guide roller to maintain the shape and temperature of the melt coated on the surface of the high-temperature resistant composite coating.

9. The method for preparing high-temperature acid and alkali resistant optical fiber according to claim 1, characterized in that: In step S4, vulcanization is carried out at a temperature of 190-210℃ under a normal pressure nitrogen protective atmosphere.

10. A high-temperature acid and alkali resistant optical fiber prepared by the preparation method according to any one of claims 1-9, characterized in that, Including the following raw materials: The composition includes quartz glass, polyamic acid solution, nano-boron nitride sheets, nano-silica particles, aromatic diamine monomers, perfluoroether rubber raw material, fumed silica, epoxy-containing silane coupling agent, peroxide vulcanizing agent, and triallyl isocyanurate. Specifically: the nano-boron nitride sheets and nano-silica particles together construct a high-temperature resistant reinforcing network. The high thermal conductivity of boron nitride rapidly dissipates localized heat, while the steric hindrance effect of silica enhances the coating's density, synergistically inhibiting the thermal degradation of the polymer matrix. The active amino groups in the aromatic diamine monomer molecules are partially exposed on the coating surface during imidization, providing reaction sites for interfacial bonding. The perfluorovinyl ether active sites introduced into the raw rubber molecular chain of the perfluoroether rubber can react with amino groups; the epoxy group-containing silane coupling agent acts as a bridging molecule, with one end forming a covalent bond with the active amino group on the coating surface through an epoxy group, and the other end combining with fumed silica and the rubber matrix through silanol groups; the peroxide vulcanizing agent decomposes under high temperature and high pressure to generate free radicals, which initiate the formation of a crosslinked network of perfluoroether rubber. The polyamic acid solution is converted into polyimide during the step-heat imidization process, forming a high-temperature resistant skeleton structure; the fumed silica serves as a reinforcing filler, improving the mechanical strength and creep resistance of the sheath layer; the triallyl isocyanurate promotes the improvement of the rubber vulcanization network, increasing the crosslinking density and chemical resistance.

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