Low-shrinkage full-dry loose tube optical unit for bridging fixed water-blocking powder, preparation method thereof and optical cable

Abstract

The invention belongs to the technical field of optical communication, and particularly relates to a low-shrinkage full-dry loose tube optical unit for bridging fixed water blocking powder, a preparation method thereof and an optical cable. According to the invention, the modified copolyester material with reduced crystallinity is used as a sleeve matrix, and a reactive group is introduced to the surface of the water-blocking powder through a chemical grafting technology, so that covalent bonding of the water-blocking powder and the sleeve material is realized, and the shrinkage condition after sleeving is greatly improved; the additional attenuation of the optical fiber is obviously reduced; the water-blocking powder fixed by chemical grafting is not easy to fall off, and the water swelling rate of the water-blocking powder is obviously improved.

Description

Technical Field

[0001] This application belongs to the field of optical communication technology, and more specifically, relates to a low-shrinkage fully dry loose tube optical unit with bridging and fixed water-blocking powder, its preparation method and optical cable. Background Technology

[0002] In today's era of rapid development in optical communication networks, optical fibers and cables, as the physical carriers of information transmission, directly impact communication quality and network reliability. Fiber optic sheaths, as a core component of optical cables, protect the delicate and fragile optical fibers from mechanical stress, moisture penetration, and environmental changes. Currently, traditional sheath materials widely used in the industry, especially polybutylene terephthalate (PBT), are favored due to their semi-crystalline properties and good processing performance. However, this material faces two persistent and interconnected technical challenges in practical applications.

[0003] The post-shrinkage problem of PBT sleeves stems from the semi-crystalline nature of PBT material. During extrusion molding, the polymer molecular chains are in a disordered state at high temperatures, while during the cooling and solidification stage, the molecular chains begin to align in an orderly manner, forming crystalline regions. This process is not completed instantaneously after extrusion but continues throughout subsequent storage and use, resulting in a slow but significant shrinkage of the sleeve dimensions in both the axial and radial directions (i.e., "post-shrinkage"). Studies have shown that the post-shrinkage rate of traditional PBT sleeves can reach 0.8%-1.5% within 168 hours after extrusion. This continuous dimensional change generates sustained compressive stress on the internal optical fiber or fiber ribbon, leading to macro-bending and micro-bending losses in the fiber. This manifests as a significant increase in optical signal attenuation (additional attenuation), directly affecting the stability and reliability of transmission.

[0004] The additional attenuation caused by water-blocking powder is also a significant concern. To ensure the water-blocking performance of optical cables and prevent moisture from spreading longitudinally along the fiber, the sheath is typically filled with water-blocking powder (superabsorbent polymer, SAP). However, traditional physical filling methods result in direct and random contact between the water-blocking powder particles and the fiber surface. Under vibration, bending, and temperature changes during cable laying and operation, these hard and loose water-blocking powder particles can rub against the fiber surface and even form localized stress points, causing significant microbending loss. Industry test data shows that direct contact between water-blocking powder and the fiber can increase additional attenuation by 0.03-0.08 dB / km, and this value will further increase in low-temperature environments.

[0005] Currently, the industry has made some attempts to solve these problems. All-dry optical cable technology, by using dry water-blocking materials such as water-blocking yarn and water-blocking tape to replace traditional grease, has indeed solved the problem of difficult grease cleaning and improved splicing efficiency. Some patent literature uses a method of adsorbing and fixing water-blocking powder on the inner wall of the loose tube, reducing the problem of water-blocking powder flying and accumulation by controlling the friction coefficient of the inner surface of the loose tube within the range of 0.21-0.34. The latest patent literature even proposes forming a resin layer containing uniformly distributed water-blocking powder inside the loose tube to optimize the distribution of the water-blocking powder. However, these solutions do not fundamentally solve the problem of material shrinkage, nor do they achieve efficient bonding between the water-blocking powder and the tube material, thus failing to effectively eliminate frictional loss between the water-blocking powder and the optical fiber. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a low-shrinkage fully dry loose tube optical unit with bridging and fixed water-blocking powder, its preparation method and optical cable, aiming to solve the technical problems of severe back shrinkage of the tube material and optical cable loss caused by friction between water-blocking powder and optical fiber in the prior art fully dry loose tube optical unit.

[0007] To achieve the above objectives, in a first aspect, this application provides a low-shrinkage, fully dry loose tube optical unit with bridging and fixing water-blocking powder, including a light guide element and a loose tube housing the light guide element; The loose tube comprises an outer thermoplastic layer and an inner water-absorbing thermoplastic resin layer that is chemically bridged with the thermoplastic layer to fix water-blocking powder; the outer thermoplastic layer and the inner water-absorbing thermoplastic resin layer are prepared by a double-layer co-extrusion process. The outer thermoplastic layer is a thermoplastic modified PBT copolyester. The modified PBT copolyester is a modified copolyester obtained by introducing amorphous comonomers to participate in the copolymerization process during PBT synthesis. The amorphous comonomers participate in the copolymerization of PBT to reduce the regularity of the molecular chain structure of PBT. The extrusion raw material of the inner water-absorbing thermoplastic resin layer contains the modified PBT copolyester, monomers containing methacryloxy and epoxy groups, chemically grafted modified water-blocking powder obtained by polymerizable double-bond activated sodium polyacrylate, and a photoinitiator. In the bilayer co-extrusion process, the monomer containing methacryloyloxy and epoxy reacts with the carboxyl groups at the ends of the modified PBT copolyester chain, chemically grafting the methacryloyloxy group onto the modified PBT copolyester molecular chain in the form of a suspended chain. Then, under ultraviolet light irradiation, the photoinitiator decomposes to generate free radicals, which initiate a copolymerization reaction between the methacryloyloxy group grafted onto the modified PBT copolyester and the polymerizable double bonds on the surface of the modified water-blocking powder, forming a strong chemical bridge, resulting in a low-shrinkage, fully dry, loose sleeve with the bridged and fixed water-blocking powder.

[0008] Preferably, the amorphous comonomer is one or more selected from cyclohexanediol, dimethyl sebacate, and sebacate; and / or, In the process of copolymerizing the modified PBT copolyester, the monomers participating in the reaction, by weight, include 100 parts by weight of dimethyl terephthalate and / or terephthalic acid, 40-50 parts by weight of 1,4-butanediol, 8-15 parts by weight of cyclohexanediol, and 5-12 parts by weight of dimethyl sebacate and / or sebacate.

[0009] More preferably, the thermoplastic layer further contains a plasticizer, which is one or more of trimellitic esters, epoxy plasticizers, and adipic acid polyester plasticizers.

[0010] Preferably, the monomer containing methacryloyloxy and epoxy groups is one or more of glycidyl methacrylate, glycidyl acrylate, and methyl 3,4-epoxycyclohexyl methacrylate.

[0011] Preferably, the sodium polyacrylate water-blocking powder is modified by using a silane coupling agent containing methacryloxy group to obtain the chemically grafted modified water-blocking powder obtained by polymerizable double bond activated sodium polyacrylate.

[0012] Preferably, the mass ratio of the modified PBT copolyester, the monomer containing methacryloyloxy and epoxy groups, the chemically grafted modified water-blocking powder obtained by polymerizable double-bond activated sodium polyacrylate, and the photoinitiator in the extrusion raw material of the water-absorbing thermoplastic resin layer is (75-80):(2-5):(15-20):(0.5-1).

[0013] According to another aspect of the present invention, a method for fabricating the aforementioned all-dry loose-tube optical unit is provided, comprising the following steps: (1) Co-extrusion plasticization: The modified PBT copolyester chips and the extrusion raw materials forming the water-absorbing thermoplastic resin layer are extruded simultaneously on the outside of the bundled optical guide element through the main extruder and the sub-extruder to obtain plasticized molten tubing; (2) Online UV curing: After the extruded plasticized molten pipe is cooled in the air, it is pre-cooled in a hot water tank to obtain a semi-cured loose pipe; then the semi-cured loose pipe is passed through a shaped ultraviolet irradiation chamber. Under ultraviolet light irradiation, the photoinitiator decomposes to generate free radicals, which initiate the copolymerization reaction between the methacryloyloxy group grafted on the modified PBT copolyester and the polymerizable double bond on the surface of the modified water-blocking powder to form a strong chemical bridge. The pipe blank is sized by a vacuum sizing sleeve and cooled and cured in a cooling water tank to obtain a low-shrinkage fully dry loose pipe with the bridged fixed water-blocking powder.

[0014] Preferably, in step (1), the main extruder is melt-plasticized at 220-230°C, and the sub-extruder is melt-blended and plasticized at 210-220°C.

[0015] Preferably, the mass ratio of the modified PBT copolyester chips in step (1) to the extrusion raw material of the water-absorbing thermoplastic resin layer is 3-5:1.

[0016] More preferably, in step (1), a plasticizer is added to the chips of the modified PBT copolyester, and then the chips are extruded through a main extruder.

[0017] According to another aspect of the invention, an optical cable is provided, comprising an outer sheath and a cable core housed therein, the cable core including the aforementioned all-dry loose tube optical unit.

[0018] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: (1) Extremely low additional attenuation: This invention uses a modified copolyester material with reduced crystallinity as the sleeve matrix and introduces reactive groups on the surface of the water-blocking powder through chemical grafting technology, achieving covalent bonding between the water-blocking powder and the sleeve material, which greatly improves the post-sleeving shrinkage. Due to the significant reduction in post-sleeving shrinkage and the absence of direct contact between the water-blocking powder and the optical fiber, the additional attenuation of the optical fiber is significantly reduced. Experimental data show that in the temperature cycling test from -40℃ to +70℃, the additional attenuation of the optical cable of this invention is only 0.01-0.03 dB / km, while the additional attenuation of the optical cable filled with traditional PBT water-blocking powder reaches 0.05-0.10 dB / km, representing an improvement of 60-70%.

[0019] (2) Excellent water-blocking performance: The water-blocking powder fixed by chemical grafting in this invention is not easy to fall off, and its water absorption expansion rate can reach ≥12mm / min. The water absorption rate is maintained at 80-100 times its own weight, which can quickly prevent the longitudinal migration of water and meet the water-blocking performance requirements in Telcordia GR-20 and YD / T 901-2009 standards.

[0020] (3) Excellent mechanical properties and stability: The modified copolyester sheath maintains sufficient mechanical strength, with a tensile strength of 40-55 MPa, which is sufficient to withstand various mechanical stresses during the cabling, laying and use of the optical cable. At the same time, due to the minimal back shrinkage, the transmission performance of the optical cable is stable over a long period of time, and its service life is significantly extended.

[0021] (4) Convenience of construction: The all-dry structure avoids the cumbersome oil cleaning process in the traditional oil-coated optical cable construction, and does not require the use of cleaning agents and cleaning paper, which improves splicing efficiency and can shorten the splicing time by more than 50%. At the same time, it avoids the environmental pollution problems caused by cleaning agents.

[0022] (5) Fiber protection: The water-blocking powder is fixed to the inner wall of the sleeve by chemical bonds and will not rub against the optical fiber due to vibration, bending or temperature changes, thus fundamentally eliminating the micro-bending loss caused by the water-blocking powder. The low shrinkage characteristics of the sleeve also avoid long-term stress on the optical fiber, providing a safer protective environment for the optical fiber. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0024] The present invention provides a low-shrinkage, fully dry loose tube optical unit with bridging and fixing water-blocking powder, comprising a light guide element and a loose tube for housing the light guide element; The loose tube comprises an outer thermoplastic layer and an inner water-absorbing thermoplastic resin layer that is chemically bridged with the thermoplastic layer to fix water-blocking powder; the outer thermoplastic layer and the inner water-absorbing thermoplastic resin layer are prepared by a double-layer co-extrusion process. The outer thermoplastic layer is a thermoplastic modified PBT copolyester. The modified PBT copolyester is a modified copolyester obtained by introducing amorphous comonomers to participate in the copolymerization process during PBT synthesis. The amorphous comonomers participate in the copolymerization of PBT to reduce the regularity of the molecular chain structure of PBT. The extrusion raw material of the inner water-absorbing thermoplastic resin layer contains the modified PBT copolyester, monomers containing methacryloxy and epoxy groups, chemically grafted modified water-blocking powder obtained by polymerizable double-bond activated sodium polyacrylate, and a photoinitiator. In the bilayer co-extrusion process, the monomer containing methacryloyloxy and epoxy reacts with the carboxyl groups at the ends of the modified PBT copolyester chain, chemically grafting the methacryloyloxy group onto the modified PBT copolyester molecular chain in the form of a suspended chain. Then, under ultraviolet light irradiation, the photoinitiator decomposes to generate free radicals, which initiate a copolymerization reaction between the methacryloyloxy group grafted onto the modified PBT copolyester and the polymerizable double bonds on the surface of the modified water-blocking powder, forming a strong chemical bridge, resulting in a low-shrinkage, fully dry, loose sleeve with the bridged and fixed water-blocking powder.

[0025] The core of this invention lies in the development of a modified copolyester material as the casing matrix, and the introduction of reactive groups on the surface of the water-blocking powder through chemical grafting technology, thereby achieving covalent bonding between the water-blocking powder and the casing material.

[0026] Modified copolyester sheathing material: Based on polybutylene terephthalate (PBT), long-chain dicarboxylic acids (such as sebacic acid or dimethyl sebacic acid) and / or cyclohexanediethanol are introduced as comonomers to disrupt the regularity of the molecular chain, reduce crystallinity and crystallization rate, inhibit the crystallization process, and reduce post-shrinkage.

[0027] Chemically grafted modified water-blocking powder: Sodium polyacrylate is selected as the base water-blocking material (particle size controlled at 10-50μm). Through surface treatment technology, polymerizable double bonds (such as methacryloxy) are introduced on its surface, so that it can react with the matrix material during the extrusion process of the sleeve to form chemical bond connection, which completely changes the traditional physical filling method.

[0028] Double-layer co-extrusion process: The outer layer is extruded with modified copolyester tubing material, and the inner layer is extruded with reactive masterbatch containing online reaction capability. The reactive masterbatch is made by fully mixing modified polyester tubing material, monomers containing methacryloxy and epoxy groups such as glycidyl methacrylate (GMA), chemically grafted modified water-blocking powder obtained by polymerizing double-bond activated sodium polyacrylate, and photoinitiator in a high-speed mixer. During the co-extrusion process, the epoxy groups of GMA react with the carboxyl groups at the end of the polyester chain, chemically grafting methacryloxy groups onto the modified copolyester molecular chain in the form of suspended chains. At the same time, the melt state provides ideal mass transfer conditions for the interfacial reaction between the water-blocking powder and the matrix.

[0029] In some embodiments, the synthesis of the modified PBT copolyester sheathing material includes the following steps: Esterification / esterification stage: Add 100 parts by weight of dimethyl terephthalate (DMT) or terephthalic acid (PTA), 40-50 parts by weight of 1,4-butanediol, 8-15 parts by weight of cyclohexanediol, and 5-12 parts by weight of dimethyl sebacate or sebacate to the reactor. Simultaneously add 0.01-0.05 parts by weight of a titanate catalyst (such as tetrabutyl titanate). Under nitrogen protection, gradually raise the temperature to 180-220℃ to carry out the esterification or esterification reaction for 2-4 hours until the distillation yield of methanol or water (a byproduct of the polycondensation reaction) reaches more than 95% of the theoretical value.

[0030] Polycondensation stage: Gradually raise the system temperature to 250-260℃ and lower the pressure to below 100Pa to carry out the polycondensation reaction. The reaction time is 2-3 hours. The reaction endpoint is determined by monitoring the stirring torque. When the torque value no longer increases significantly within 10-15 minutes, reaching a plateau, it indicates that the reaction has basically reached equilibrium.

[0031] Discharge and pelletizing: The polycondensed melt is extruded through a die, cooled with water, and pelletized to obtain modified PBT copolyester base chips with an intrinsic viscosity of approximately 0.70-0.80 dL / g.

[0032] Solid-state polymerization: The base chips are subjected to solid-state polymerization at 180-200℃ under nitrogen protection, which increases the intrinsic viscosity from 0.70-0.80 dL / g to 0.85-1.05 dL / g, further improving the molecular weight and crystal stability.

[0033] In some embodiments, the water-blocking powder undergoes surface chemical modification to achieve chemical bonding with the sleeve material. The preparation steps of the chemically grafted modified water-blocking powder are as follows: Activation and modification of water-blocking powder: Disperse sodium polyacrylate water-blocking powder (particle size 10-50μm) in anhydrous ethanol to form a 10-15% suspension. Add 1-3% by weight of the water-blocking powder of a silane coupling agent containing methacryloxy group (such as KH-570, KH-571 or KH-172), and reflux at 50-80℃ for 4-6 hours to introduce polymerizable double bonds on the surface of the water-blocking powder.

[0034] Washing and drying: After the reaction is complete, the unreacted coupling agent is removed by filtration and washing with ethanol, and then dried to constant weight in a vacuum drying oven at 50-70℃ to obtain surface-activated modified water-blocking powder.

[0035] Preparation and online grafting of reactive masterbatches: Preparation of reactive masterbatch (i.e., extrusion raw material for the water-absorbing thermoplastic resin layer): 75-80 parts by weight of modified PBT polyester chips, 2-5 parts by weight of monomers containing methacryloxy and epoxy groups, 0.5-1 parts by weight of photoinitiator (such as acylphosphine oxides like Irgacure 819 and Irgacure 2100, or macromolecular photoinitiators like Omnirad 701), and 15-20 parts by weight of modified grafted water-blocking powder are thoroughly mixed in a high-speed mixer to obtain reactive masterbatch. The monomers containing methacryloxy and epoxy groups include, but are not limited to, one or more of glycidyl methacrylate (GMA), glycidyl acrylate, and 3,4-epoxycyclohexyl methacrylate.

[0036] Double-layer co-extrusion process: Main ingredient premixing: 75-80 parts by weight of modified copolyester chips and 5-10 parts by weight of plasticizer trioctyl trimellitate (based on 100 parts by weight of chips) are mixed in a high-speed mixer at 60-80°C for 5-10 minutes to ensure that the plasticizer is evenly attached and partially penetrates into the surface of the chips, thereby obtaining plasticized modified polyester chips.

[0037] The plasticizer can be one or more of trimellitic esters, epoxy plasticizers, and adipic acid polyester plasticizers. Triellitic esters include, but are not limited to, one or more of trioctyl trimellitate, triisononyl trimellitate, and triisodecyl trimellitate; epoxy plasticizers include, but are not limited to, one or more of epoxidized soybean oil, epoxidized linseed oil, epoxidized fatty acid methyl esters, epoxidized octyl stearate, and epoxidized dioctyl tetrahydrophthalate; and adipic acid polyester plasticizers include, for example, one or more of propylene glycol adipate and butylene glycol adipate.

[0038] In the preferred embodiment, trioctyl trimellitate is selected as the plasticizer. It has excellent heat resistance (can withstand processing temperatures above 220°C), low volatility and good compatibility with polyester. It can effectively reduce melt viscosity and is not easy to migrate and precipitate. It is a commonly used high-performance plasticizer in engineering plastics processing.

[0039] Co-extrusion plasticizing: Plasticized modified PBT polyester chips and reactive masterbatch are fed into the main extruder and sub-extruder at a set ratio, respectively, and simultaneously extruded outside the bundled optical guide element. The main extruder performs melt plasticizing at 220-230℃, and the sub-extruder performs melt blending plasticizing at 210-220℃. During this process, the epoxy groups of GMA react with the carboxyl groups at the ends of the copolyester chain, chemically grafting methacryloyloxy groups onto the PBT molecular chain in the form of a suspended chain.

[0040] In some embodiments, the mass ratio of modified PBT polyester chips to reactive masterbatch (extrusion material for water-absorbing thermoplastic resin layers) is 3-5:1.

[0041] In a preferred embodiment, the reactive masterbatch is vacuum dried at 80-90°C for 4-6 hours before use to prevent moisture from causing processing degradation.

[0042] Main extruder (extruding outer layer / body): The optimal processing temperature is set at 215-230℃. Due to the addition of plasticizers, the melt viscosity is reduced, so the processing temperature is significantly lower than that of conventional PBT (~250℃) to match the temperature of the sub-extruder.

[0043] Sub-extruder (extruding inner layer / functional layer): Processing temperature set to 210-220℃. This temperature is the ideal window for the grafting reaction between GMA epoxy groups and polyester terminal carboxyl groups.

[0044] In a preferred embodiment, both extruders should employ a screw configuration with moderate shear force to ensure thorough melt homogenization. In the sub-extruder, the melting and mixing sections should be designed to provide sufficient residence time and mixing intensity to promote the grafting reaction of GMA. The feed rates of the main and sub-extruders are controlled by precise metering feeders to achieve the designed inner-outer layer thickness ratio.

[0045] In a preferred embodiment, in the melt blending section and subsequent homogenization section of the sub-extruder, under sufficient melt shearing at 200-220°C, the epoxy groups of monomers containing methacryloyloxy and epoxy groups, such as GMA, undergo a ring-opening reaction with the carboxyl groups at the ends of the copolyester chain, chemically grafting the methacryloyloxy groups onto the polymer molecular chain in the form of a suspended chain. The melts output from the main and sub-extruders converge through a double-layer co-extrusion die to form a composite preform with an outer layer of modified PBT and an inner active layer containing reactive double bonds and water-blocking powder.

[0046] Shaping and cooling: The tube blank is sized by a vacuum sizing sleeve and then cooled and solidified in a cooling water tank to obtain a semi-cured loose tube in the preliminary shape.

[0047] Online UV curing: The extruded, semi-cured loose tube containing active double bonds is immediately passed through a shaped ultraviolet (UV) irradiation chamber. Under UV irradiation, the photoinitiator decomposes to generate free radicals, which initiate a copolymerization reaction between the newly grafted methacryloyloxy groups on the PBT matrix and the methacryloyloxy groups on the surface of the water-blocking powder, forming a strong chemical bridge.

[0048] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0049] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0050] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0051] Example 1 (1) The synthesis of modified copolyester sleeve material includes the following steps: Esterification / esterification stage: Add 100 parts by weight of dimethyl terephthalate (DMT), 45 parts by weight of 1,4-butanediol, 10 parts by weight of cyclohexanediol, and 8 parts by weight of dimethyl sebacate to the reactor. Simultaneously add 0.03 parts by weight of tetrabutyl titanate. Under nitrogen protection, gradually raise the temperature to 200°C to carry out the esterification or transesterification reaction for 3 hours until the methanol distillation rate reaches more than 95% of the theoretical value.

[0053] Polycondensation stage: Gradually raise the system temperature to 250-260℃ and lower the pressure to below 100Pa to carry out the polycondensation reaction. The reaction time is 2.5 hours. The reaction endpoint is determined by monitoring the stirring torque. When the torque value no longer increases significantly within 10-15 minutes, reaching a plateau, it indicates that the reaction has basically reached equilibrium.

[0054] Discharge and pelletizing: The polycondensed melt is extruded through a die, cooled with water, and pelletized to obtain modified copolyester base chips.

[0055] Solid-state polymerization: The base chips were subjected to solid-state polymerization at 190°C under nitrogen protection to increase the intrinsic viscosity to 0.95 ± 0.02 dL / g, further improving the molecular weight and crystallization stability, and obtaining modified PBT copolyester.

[0056] (2) Surface chemical modification of the water-blocking powder is performed to achieve chemical bonding between it and the sleeve material. The preparation steps of the modified grafted water-blocking powder are as follows: Activation of water-blocking powder: Disperse sodium polyacrylate water-blocking powder (particle size 10-50μm) in anhydrous ethanol to form a 12% suspension. Add 2% by weight of silane coupling agent KH-570 to the water-blocking powder and reflux at 60℃ for 5 hours to introduce polymerizable double bonds on the surface of the water-blocking powder.

[0057] Washing and drying: After the reaction is complete, the unreacted coupling agent is removed by filtration and washing with ethanol, and then dried to constant weight in a vacuum drying oven at 50°C to obtain surface-activated modified grafted water-blocking powder.

[0058] (3) Preparation of reactive masterbatch and online grafting Preparation of reactive masterbatch: 80 parts by weight of modified polyester PBT copolyester chips, 3 parts by weight of glycidyl methacrylate (GMA), 0.5 parts by weight of photoinitiator Irgacure 819, and 18 parts by weight of modified grafted water-blocking powder were thoroughly mixed in a high-speed mixer to obtain reactive masterbatch.

[0059] Double-layer co-extrusion process: Main ingredient premixing: 100 parts by weight of modified copolyester chips and 8 parts by weight of plasticizer trioctyl trimellitate are mixed in a high-speed mixer at 70°C for 8 minutes to make the plasticizer evenly adhere and partially penetrate into the surface of the chips, thus obtaining plasticized modified polyester chips.

[0060] Co-extrusion plasticizing: Plasticized modified polyester chips and reactive masterbatch are fed into the main extruder and sub-extruder respectively, and simultaneously extruded on the outside of the bundled optical guide element. The main extruder performs melt plasticizing at 215-230℃, and the sub-extruder performs melt blending plasticizing at 200-220℃. During the extrusion process, the epoxy groups of GMA react with the carboxyl groups at the ends of the copolyester chain, chemically grafting methacryloyloxy groups onto the PBT molecular chain in the form of a suspended chain.

[0061] Plasticized modified polyester chips and reactive masterbatch are fed into the main extruder and sub-extruder respectively, and simultaneously extruded outside the bundled optical guide element. The temperature of the main extruder (outer layer) should be set at 215-230℃ to ensure sufficient melting of the plasticized modified polyester chips while avoiding high-temperature thermal degradation. The temperature of the sub-extruder (inner layer) needs to be precisely controlled within the core window of 205-215℃, which is the optimal temperature range for the grafting reaction between the GMA epoxy groups and the terminal carboxyl groups of the polyester. The co-extrusion die temperature should be set between 210-220℃ to balance the melt viscosity of the two layers and promote interfacial fusion. The extrusion mass ratio of the outer layer to the inner layer is 4 / 1 (outer / inner). This ratio ensures the mechanical strength of the casing body while allowing the inner layer to contain sufficient reactive components to construct an effective water-blocking and cross-linking functional layer. Through the above gradient design of the temperature zone and the functionalized ratio of the extrusion, integrated and precise control from material reaction, structural forming to performance assurance can be achieved.

[0062] Online UV curing: After the extruded plasticized molten pipe is cooled in air, it is pre-cooled in a hot water bath to obtain a semi-cured loose tube; then it is passed through a shaped ultraviolet (UV) irradiation chamber. Under UV irradiation, the photoinitiator decomposes to generate free radicals, which initiate a copolymerization reaction between the newly grafted methacryloyloxy groups on the PBT matrix and the methacryloyloxy groups on the surface of the water-blocking powder, forming a strong chemical bridge.

[0063] Example 2 The process is the same as in Example 1, except that in the synthesis of the modified copolyester sleeve material, during the transesterification / esterification stage: 100 parts by weight of terephthalic acid (PTA), 50 parts by weight of 1,4-butanediol, 8 parts by weight of cyclohexanediol, and 12 parts by weight of sebacic acid are added to the reactor. Simultaneously, 0.05 parts by weight of tetrabutyl titanate, a titanate catalyst, is added. Under nitrogen protection, the temperature is gradually increased to 210°C to carry out the transesterification or esterification reaction for 4 hours until the water distillation reaches more than 95% of the theoretical value.

[0064] Example 3 The rest is the same as in Example 1, except that the reactive masterbatch was prepared by mixing 75 parts by weight of modified polyester chips with 5 parts by weight of glycidyl methacrylate (GMA), 1 part by weight of photoinitiator Irgacure 819, and 20 parts by weight of modified grafted water-blocking powder in a high-speed mixer to obtain the reactive masterbatch.

[0065] Comparative Example 1 The rest is the same as in Example 1, except that the modified PBT copolyester is replaced with an equal mass of polybutylene terephthalate (PBT).

[0066] Comparative Example 2 The rest is the same as in Example 1, except that the chemically grafted modified water-blocking powder is replaced with an equal mass of the basic water-blocking material, sodium polyacrylate water-blocking powder.

[0067] Table 1. Performance comparison of fully dry-tube optical cables prepared in different embodiments and comparative examples.

[0068] Table 1 shows the results obtained by testing different sections of each optical cable sample multiple times during performance evaluation, thus representing numerical ranges. As can be seen from Table 1, the crystallinity of the modified PBT copolyester sheaths in Examples 1 and 2 of this invention is 25-35% and 20-30%, respectively, significantly lower than the 40-45% of the conventional PBT sheath in Comparative Example 1. This structural characteristic is directly reflected in the post-shrinkage performance. According to the GB / T 17037.4 test standard, the dimensional change of the sheath within 24 hours after extrusion was measured: the post-shrinkage rates of Examples 1 and 2 were 0.8-1.2% and 0.5-1.0%, respectively, while that of Comparative Example 1 was as high as 1.8-2.5%. The data indicates that by introducing a third comonomer to reduce the crystallinity of the material, the post-shrinkage rate of the sheath can be effectively reduced by more than 50%.

[0069] Comparative Example 2 used the same modified copolyester matrix as Example 1, but the water-blocking powder was unmodified sodium polyacrylate, added only through physical mixing. While it passed short-term water-blocking tests, it revealed inherent defects in the traditional process, posing a potential long-term reliability risk. The "additional fiber attenuation" data for Comparative Example 2 clearly showed that although the initial value was <0.02 dB / km, it gradually increased over time, reaching 0.02-0.05 dB / km after two weeks, significantly higher than the additional attenuation value of the fiber in Example 1. This indicates that physically mixed water-blocking powder may migrate and agglomerate under long-term use or environmental stress, forming light scattering points and thus impairing optical transmission performance—a problem that traditional physical filling methods cannot solve.

[0070] Example 1 of this invention employs an innovative process of "chemically grafted modified water-blocking powder" and "co-extrusion plasticizing grafting + online UV curing." This process enables the water-blocking powder to permanently bond with the matrix through chemical bonds. The stable and excellent additional attenuation (<0.02 dB / km) and water-blocking performance in the test data directly prove that this method completely eliminates the migration of water-blocking powder, achieving a long-term harmonious coexistence of water-blocking function and optical performance. This is something that the traditional technical approach represented by Comparative Example 2 cannot achieve.

[0071] Furthermore, the optical cable of this invention exhibits particularly outstanding performance in temperature cycling. Temperature cycling tests (-40℃ to +70℃, 10 cycles) were conducted according to IEC 60794-1-22 F1 standard. The additional attenuation change of the conventional PBT resin-filled optical cable in Comparative Example 1 was 0.05-0.10 dB / km, and that of the unmodified water-blocking powder optical cable in Comparative Example 2 was 0.02-0.05 dB / km. In contrast, the optical cables of Examples 1 to 3 showed only 0.01-0.03 dB / km. This demonstrates that modifying the PBT resin to improve the post-shrinkage problem of the sheath is crucial for reducing the additional attenuation of the optical fiber.

[0072] In summary, the low-shrinkage, water-blocking powder-absorbing, fully dry-tube optical cable provided by this invention, through material modification and structural innovation, successfully solves two major technical challenges faced by traditional optical cables, providing an ideal optical cable solution for next-generation high-performance communication networks.

[0073] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A low-shrinkage, fully dry, loose-sleeve optical unit with bridging and fixing water-blocking powder, characterized in that, Includes an optical guide element and a loose tube for housing the optical guide element; The loose tube comprises an outer thermoplastic layer and an inner water-absorbing thermoplastic resin layer that is chemically bridged with the thermoplastic layer to fix water-blocking powder; the outer thermoplastic layer and the inner water-absorbing thermoplastic resin layer are prepared by a double-layer co-extrusion process. The outer thermoplastic layer is a thermoplastic modified PBT copolyester. The modified PBT copolyester is a modified copolyester obtained by introducing amorphous comonomers to participate in the copolymerization process during PBT synthesis. The amorphous comonomers participate in the copolymerization of PBT to reduce the regularity of the molecular chain structure of PBT. The extrusion raw material of the inner water-absorbing thermoplastic resin layer contains the modified PBT copolyester, monomers containing methacryloxy and epoxy groups, chemically grafted modified water-blocking powder obtained by polymerizable double-bond activated sodium polyacrylate, and a photoinitiator. In the bilayer co-extrusion process, the monomer containing methacryloyloxy and epoxy reacts with the carboxyl groups at the ends of the modified PBT copolyester chain, chemically grafting the methacryloyloxy group onto the modified PBT copolyester molecular chain in the form of a suspended chain. Then, under ultraviolet light irradiation, the photoinitiator decomposes to generate free radicals, which initiate a copolymerization reaction between the methacryloyloxy group grafted onto the modified PBT copolyester and the polymerizable double bonds on the surface of the modified water-blocking powder, forming a strong chemical bridge, resulting in a low-shrinkage, fully dry, loose sleeve with the bridged and fixed water-blocking powder.

2. The fully dry loose tube optical unit as described in claim 1, characterized in that, The amorphous comonomer is one or more selected from cyclohexanediol, dimethyl sebacate, and sebacate; and / or... In the process of copolymerizing the modified PBT copolyester, the monomers participating in the reaction, by weight, include 100 parts by weight of dimethyl terephthalate and / or terephthalic acid, 40-50 parts by weight of 1,4-butanediol, 8-15 parts by weight of cyclohexanediol, and 5-12 parts by weight of dimethyl sebacate and / or sebacate.

3. The fully dry loose-tube optical unit as described in claim 1, characterized in that, The monomer containing methacryloyloxy and epoxy groups is one or more of glycidyl methacrylate, glycidyl acrylate, and methyl methacrylate-3,4-epoxycyclohexyl methacrylate.

4. The fully dry loose-tube optical unit as described in claim 1, characterized in that, Sodium polyacrylate water-blocking powder was modified using a silane coupling agent containing methacryloxy group to obtain the chemically grafted modified water-blocking powder obtained by polymerizable double-bond activated sodium polyacrylate.

5. The fully dry loose-tube optical unit as described in claim 1, characterized in that, The mass ratio of the modified PBT copolyester, the monomer containing methacryloyloxy and epoxy groups, the chemically grafted modified water-blocking powder obtained by polymerizable double-bond activated sodium polyacrylate, and the photoinitiator in the extrusion raw material of the water-absorbing thermoplastic resin layer is (75-80): (2-5): (15-20): (0.5-1).

6. The method for fabricating a fully dry loose-tube optical unit as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Co-extrusion plasticization: The modified PBT copolyester chips and the extrusion raw materials forming the water-absorbing thermoplastic resin layer are extruded simultaneously on the outside of the bundled optical guide element through the main extruder and the sub-extruder to obtain plasticized molten tubing; (2) Online UV curing: After the extruded plasticized molten pipe is cooled in air, it is pre-cooled in a hot water tank to obtain a semi-cured loose pipe; then the semi-cured loose pipe is passed through a shaped ultraviolet irradiation chamber. Under ultraviolet light irradiation, the photoinitiator decomposes to generate free radicals, which initiate the copolymerization reaction between the methacryloyloxy group grafted on the modified PBT copolyester and the polymerizable double bond on the surface of the modified water-blocking powder to form a strong chemical bridge. The pipe blank is sized by a vacuum sizing sleeve and cooled and cured in a cooling water tank to obtain a low-shrinkage fully dry loose pipe with the bridged and fixed water-blocking powder.

7. The preparation method according to claim 6, characterized in that, In step (1), the main extruder is melt-plasticized at 220-230°C, and the sub-extruder is melt-blended and plasticized at 210-220°C.

8. The preparation method according to claim 6, characterized in that, In step (1), the mass ratio of the modified PBT copolyester chips to the extrusion raw material of the water-absorbing thermoplastic resin layer is 3-5:

1.

9. The preparation method according to claim 6, characterized in that, In step (1), a plasticizer is added to the chips of the modified PBT copolyester, and then the chips are extruded through a main extruder.

10. An optical cable, characterized in that, It includes an outer sheath and a cable core housed therein, the cable core including a fully dry loose tube optical unit as described in any one of claims 1 to 5.

Images