Flame-retardant 8-shaped optical cable and preparation method thereof

Abstract

The invention discloses a flame-retardant 8-shaped optical cable and a preparation method thereof, and belongs to the technical field of optical cable preparation, the flame-retardant 8-shaped optical cable comprises a self-supporting part and an optical cable part, and the self-supporting part is connected with the optical cable part through a connecting piece; the optical cable part comprises a central reinforcing piece and a plurality of optical units which are twisted on the periphery of the central reinforcing piece; and the outer sheath wraps the periphery of the plurality of optical unit stranded structures, the outer sheath comprises a first flame-retardant layer and a second flame-retardant layer, the first flame-retardant layer comprises a bio-based thermoplastic polyurethane flame-retardant material, and the second flame-retardant layer comprises a low-smoke halogen-free flame-retardant material. According to the flame-retardant 8-shaped optical cable, the bio-based thermoplastic polyurethane flame-retardant material is adopted as the protective layer structure, a compact, continuous and high-strength carbon layer can be formed on the periphery of the optical unit at a high temperature, the carbon layer can isolate oxygen and heat to achieve physical flame retardance, the bio-based material is renewable, dependence on petroleum resources is reduced, and the flame-retardant 8-shaped optical cable is suitable for industrial production. And the manufacturing cost of the optical cable is reduced on the premise of meeting the flame-retardant requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of optical cable preparation, and particularly relates to a flame-retardant figure-8 optical cable and a preparation method thereof. Background Art

[0002] The figure-8 self-supporting optical cable is suitable for long-distance and inter-office communications. It consists of a self-supporting component and a sheath structure that houses the optical fibers. The self-supporting component and the sheath structure are connected by a suspension wire. Due to the presence of the self-supporting component, the figure-8 self-supporting optical cable is suitable for overhead installation. By directly hanging the self-supporting component on a utility pole or other supporting structure, the figure-8 self-supporting optical cable can be laid.

[0003] Due to its aerial layout, the figure-8 self-supporting optical cable is ideal for network deployment in complex environments such as mountainous, forested, and mining areas. Conventional figure-8 self-supporting optical cables use ordinary polyethylene sheaths, which are not flame-retardant. In these complex environments, optical cable combustion can cause fires. Furthermore, mountainous, forested, and mining areas are sparsely populated, making fires difficult to extinguish immediately, which can cause even greater losses. Summary of the Invention

[0004] In response to one or more of the above-mentioned defects or improvement needs in the prior art, the present invention provides a flame-retardant figure-8 optical cable to solve the problem that the existing figure-8 self-supporting optical cable is not flame-retardant. To achieve the above object, the present invention provides a flame-retardant figure-8 optical cable, which includes a self-supporting portion and an optical cable portion, wherein the self-supporting portion and the optical cable portion are connected by a connector; the optical cable portion includes: center reinforcement; a plurality of optical units, wherein the plurality of optical units are twisted and arranged on the periphery of the central reinforcement member; An outer sheath, the outer sheath is wrapped around the periphery of the twisted structure of the multiple optical units; the outer sheath includes a first flame retardant layer and a second flame retardant layer, the first flame retardant layer is arranged on the periphery of the twisted structure of the optical unit, and the second flame retardant layer is arranged on the periphery of the first flame retardant layer, the first flame retardant layer contains a bio-based thermoplastic polyurethane flame retardant material, and the second flame retardant layer contains a low-smoke halogen-free flame retardant material.

[0005] As a further improvement of the present invention, the raw materials for preparing the bio-based thermoplastic polyurethane flame retardant material include, by weight: 60-70 parts of bio-based polyol, 20-30 parts of bio-based isocyanate, 3-5 parts of chain extender, 5-10 parts of plasticizer, 1-2 parts of lubricant, 3-5 parts of filler, 0.5-1 part of antioxidant, 0.5-1 part of ultraviolet absorber and 5-10 parts of flame retardant.

[0006] As a further improvement of the present invention, the bio-based thermoplastic polyurethane flame retardant material includes phytic acid, chitosan or lignin.

[0007] As a further improvement of the present invention, an adhesive layer is further provided between the first flame retardant layer and the second flame retardant layer, and the adhesive layer includes ethylene-acrylic acid copolymer.

[0008] As a further improvement of the present invention, a tensile layer is provided between the sheath layer and the twisted structures of the plurality of optical units. The tensile layer is wrapped around the periphery of the twisted structures of the plurality of optical units and is formed by twisting a plurality of tensile fibers.

[0009] As a further improvement of the present invention, the plurality of tensile strength fibers are formed by twisting ultra-high molecular weight polyethylene fibers and glass fibers.

[0010] As a further improvement of the present invention, the glass fiber is a porous glass fiber, and water-blocking powder is attached to the glass fiber.

[0011] The present invention also includes a method for preparing a flame-retardant figure-8 optical cable, which comprises the following steps: pulling a central reinforcement member, and twisting a plurality of optical units along the periphery of the central reinforcement member; A three-layer co-extrusion process is used to sequentially form a first flame retardant layer, an adhesive layer, and a second flame retardant layer on the periphery of the optical unit twisted structure; After cooling and forming, a flame-retardant figure-8 optical cable is obtained.

[0012] As a further improvement of the present invention, the raw materials for preparing the first flame retardant layer include, by weight: 60-70 parts of bio-based polyol, 20-30 parts of bio-based isocyanate, 3-5 parts of chain extender, 5-10 parts of plasticizer, 1-2 parts of lubricant, 3-5 parts of filler, 0.5-1 part of antioxidant, 0.5-1 part of ultraviolet absorber, 5-10 parts of flame retardant and 40-50 parts of phytic acid; The extrusion molding of the first flame retardant layer comprises the following steps: drying the bio-based polyol and the bio-based isocyanate, respectively adding the bio-based polyol, the bio-based isocyanate, a chain extender, a plasticizer, a lubricant, a filler, an antioxidant, an ultraviolet absorber, a flame retardant, and phytic acid into a reaction extruder, and extruding and granulating the mixture to obtain bio-based thermoplastic polyurethane flame retardant material particles; The bio-based thermoplastic polyurethane flame retardant material is added into the extruder and extruded to obtain the first flame retardant layer.

[0013] As a further improvement of the present invention, the filler is silicon dioxide, and the silicon dioxide needs to be mixed with the silane coupling agent under high-speed shearing for more than 30 minutes before being added.

[0014] As a further improvement of the present invention, the extruder of the first flame retardant layer is a twin-screw extruder, the screw speed of the twin-screw extruder is 80-120 rpm, and the extruded melt pressure is ≥15 MPa.

[0015] As a further improvement of the present invention, the three-layer co-extrusion process extrude the base materials of the first flame retardant layer, the adhesive layer and the second flame retardant layer respectively through three extrusion heads, and then open three flow channel openings on the extrusion die to sequentially extrude the first flame retardant layer, the adhesive layer and the second flame retardant layer on the periphery of the optical unit twisted structure; the temperature of the extrusion die is 180~190℃.

[0016] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0017] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art: (1) The flame-retardant figure-8 optical cable of the present invention is formed by setting the outer sheath as a double-layer sheath structure of a first flame-retardant layer and a second flame-retardant layer. The first flame-retardant layer is formed of a bio-based thermoplastic polyurethane flame-retardant material. The bio-based material can produce strong dehydration catalysts such as phosphoric acid and polyphosphoric acid when decomposed by heat. The strong dehydration catalyst can catalyze the dehydration and cross-linking reactions of the hydroxyl groups and ester groups of the polyurethane matrix, thereby promoting the formation of a dense, continuous and high-strength carbon layer in the first flame-retardant layer. The carbon layer can isolate oxygen and heat to achieve physical flame retardancy. Moreover, the bio-based material is lower in cost than conventional sheath materials, and its source is wide and renewable, which can reduce dependence on petroleum resources. The polyurethane material has good weather resistance and is resistant to ultraviolet rays, oxidation and moisture. The bio-based thermoplastic polyurethane flame-retardant material can reduce the manufacturing cost of the optical cable while meeting the flame retardant requirements.

[0018] (2) The flame-retardant figure-8 optical cable of the present invention is provided with an adhesive layer between the first flame-retardant layer and the second flame-retardant layer. The adhesive layer contains an ethylene-acrylic acid copolymer. The ethylene-acrylic acid copolymer contains both polar functional groups and non-polar functional groups, which are compatible with the bio-based thermoplastic polyurethane flame-retardant material and the low-smoke halogen-free flame-retardant material, respectively, so as to bond the two incompatible materials into one, avoid delamination and cracking during the sheath production process, obtain an outer sheath structure with good consistency, and improve the service life of the flame-retardant figure-8 optical cable.

[0019] (3) The flame-retardant figure-8 optical cable of the present invention is coated with tensile fibers on the periphery of the optical unit. The tensile fibers are formed by twisting ultra-high molecular weight polyethylene fibers and glass fibers. The glass fibers are porous glass fibers, and water-blocking powder is attached to the porous glass fibers. The ultra-high molecular weight polyethylene fibers can greatly improve the impact resistance of the flame-retardant figure-8 optical cable; the combined structure of the porous glass fibers and the water-blocking powder can form an effective water-blocking structure inside the first flame-retardant layer, preventing the biomass base in the first flame-retardant layer from contacting with moisture, thereby ensuring the flame-retardant performance of the first flame-retardant layer. In addition, when the biomass base generates a carbon layer structure, it means that the optical cable is in a high-temperature environment. The porous glass fiber has good thermal insulation ability, which can reduce the heat transferred from the outside to the optical unit, avoiding damage to the optical unit, so that the flame-retardant figure-8 optical cable can be used normally in a high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Schematic diagram of the overall structure of the flame-retardant figure-8 optical cable in an embodiment of the present invention.

[0020] In all the drawings, the same reference numerals represent the same technical features, specifically: 1. Central reinforcement; 2. Optical unit; 3. Tensile layer; 4. First flame retardant layer; 5. Adhesive layer; 6. Second flame retardant layer; 7. Connector; 8. Self-supporting part. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0022] In the description of the present invention, it should be understood that, unless otherwise specified, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the present invention.

[0023] Furthermore, unless otherwise specified, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specified.

[0024] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0025] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0026] Example: See also Figure 1 The flame-retardant 8-shaped optical cable in the preferred embodiment of the present invention includes a self-supporting portion 8 and an optical cable portion, which are connected by a connector 7. The optical cable portion includes a central reinforcement member 1, and a plurality of optical units 2, which are twisted and arranged on the periphery of the central reinforcement member 1; and an outer sheath, which is wrapped around the periphery of the twisted structure of the plurality of optical units 2 to protect the optical units 2. The outer sheath includes a first flame-retardant layer 4 and a second flame-retardant layer 6, the first flame-retardant layer 4 is sleeved on the periphery of the twisted structure of the optical units 2, and the second flame-retardant layer 6 is sleeved on the periphery of the first flame-retardant layer 4, and the first flame-retardant layer 4 contains a bio-based thermoplastic polyurethane flame-retardant material, and the second flame-retardant layer 6 contains a low-smoke halogen-free flame-retardant material.

[0027] The flame-retardant figure-8 optical cable of the present invention is a double-layer sheath structure of a first flame-retardant layer 4 and a second flame-retardant layer 6. The first flame-retardant layer 4 is formed of a bio-based thermoplastic polyurethane flame-retardant material. The bio-based material can produce strong dehydration catalysts such as phosphoric acid and polyphosphoric acid when decomposed by heat. The strong dehydration catalyst can catalyze the dehydration and cross-linking reaction of the hydroxyl group and ester group of the polyurethane matrix, thereby promoting the formation of a dense, continuous and high-strength carbon layer in the first flame-retardant layer 4. The carbon layer can isolate oxygen and heat to achieve physical flame retardancy. In addition, the cost of the bio-based material is lower than that of conventional sheath materials. Lower, its source is wide and renewable, which can reduce dependence on petroleum resources. Polyurethane material has good weather resistance, certain resistance to ultraviolet rays, oxidation and moisture, and bio-based thermoplastic polyurethane flame retardant material can save the manufacturing cost of optical cable while meeting the flame retardant requirements; in addition, the second flame retardant layer 6 adopts low-smoke halogen-free flame retardant material, which itself has good flame retardant effect, and can form protection on the outer layer of the first flame retardant layer 4, avoiding biomass-based materials from absorbing water in contact with the external environment, avoiding deformation of the optical cable during manufacturing and use, and ensuring the stable use of the flame retardant 8-shaped optical cable.

[0028] Furthermore, the self-supporting part 8 in the present invention is a cylindrical structure, the center of the self-supporting part 8 is a load-bearing element formed by twisting multiple strands of steel wire, the outer periphery of the multiple strands of steel wire is a sheath layer, the material of the sheath layer and the connecting part 7 is the same as the material of the second flame retardant layer 6, and the self-supporting part 8, the connecting part 7 and the optical cable part form an integrated structure.

[0029] Furthermore, as an optional embodiment of the present invention, the raw materials for preparing the bio-based thermoplastic polyurethane flame retardant material include, by weight: 60-70 parts of bio-based polyol, 20-30 parts of bio-based isocyanate, 3-5 parts of chain extender, 5-10 parts of plasticizer, 1-2 parts of lubricant, 3-5 parts of filler, 0.5-1 part of antioxidant, 0.5-1 part of ultraviolet absorber and 5-10 parts of flame retardant.

[0030] Specifically, bio-based polyols are preferably castor oil-based polyols with a hydroxyl value of 200-300 mg KOH / g, to provide a biomass base; the bio-based isocyanate is preferably Mitsui Chemicals bio-based isocyanate PDI curing agent or L-lysine diisocyanate, to provide cross-linking density and weather resistance; the chain extender is preferably 1,4-butanediol or ethylene glycol, to adjust the fluidity of the molecular chain and the sheath material; the plasticizer is preferably triethyl citrate, whose bio-based content is ≥90%, and can reduce the viscosity of the sheath material, facilitating the extrusion of the outer sheath; the lubricant is preferably stearic acid or polyethylene wax, which can reduce extrusion friction and prevent mold sticking; the filler can be nano-silica, the silica particle size is preferably 20~50nm, and it is surface treated with a silane coupling agent to improve mechanical properties and increase dispersibility; the antioxidant is preferably hindered phenols to prevent material aging; the UV absorber can be benzotriazoles to absorb UV rays and improve overall weather resistance; the flame retardant can be hexa-DOPO benzoxazine cyclotriphosphazene flame retardant.

[0031] Preferably, the raw materials for preparing the bio-based thermoplastic polyurethane flame retardant material also include 0.1 to 0.5 parts by weight of a catalyst, preferably 0.1 to 0.3 parts by weight of dibutyltin dilaurate and 0.1 to 0.2 parts by weight of an organic bismuth catalyst, the dibutyltin dilaurate is used to increase the reaction rate of the bio-based thermoplastic polyurethane flame retardant material, and the organic bismuth catalyst is used to improve processing stability.

[0032] Preferably, the bio-based polyol further includes lignin polyol in an amount of 5 to 10% by mass of castor oil-based polyol. Lignin polyol can appropriately improve the thermal stability and rigidity of the bio-based thermoplastic polyurethane flame retardant material.

[0033] Alternatively, the bio-based thermoplastic polyurethane flame retardant material in the present invention also includes one or more of phytic acid, chitosan or lignin. The above-mentioned phytic acid, chitosan and lignin can form a dense carbon layer structure on the periphery of the optical unit 2 when the optical cable is heated, so as to achieve a good flame retardant effect. Phytic acid, chitosan and lignin can produce strong dehydration catalysts such as phosphoric acid and polyphosphoric acid when thermally decomposed. These catalysts can react with the hydroxyl group, ester group and the like in the polyurethane matrix to produce a dehydration cross-linking reaction to promote the formation of a dense, continuous and high-strength carbon layer to achieve the purpose of flame retardancy. Preferably, phytic acid, chitosan or lignin are 40 to 50 parts by weight, so that a dense carbon layer structure can be formed in the event of a fire, to provide flame retardancy.

[0034] Furthermore, as an optional embodiment of the present invention, an adhesive layer 5 is provided between the first flame-retardant layer 4 and the second flame-retardant layer 6. The adhesive layer 5 comprises an ethylene-acrylic acid copolymer. Bio-based thermoplastic polyurethane flame-retardant materials contain polar segments, while low-smoke halogen-free flame-retardant materials contain non-polar segments. These two materials present compatibility issues, and simultaneous extrusion of the first and second flame-retardant layers 4 and 6 can easily lead to interfacial delamination, causing delamination and cracking of the optical cable outer sheath. Therefore, an adhesive layer 5 is provided between the first and second flame-retardant layers 4 and 6. The ethylene-acrylic acid copolymer possesses both polar functional groups (acrylic acid units) and non-polar functional groups (ethylene units), which bond to the first and second flame-retardant layers 4 and 6, respectively. The three layers form a good interface, resulting in a unified outer sheath.

[0035] Furthermore, as an optional embodiment of the present invention, a tensile layer 3 is further provided between the sheath layer and the twisted structure of the optical unit 2 in the present invention. The tensile layer 3 is wrapped around the periphery of the twisted structure of multiple optical units 2, and the tensile layer 3 is formed by twisting multiple tensile fibers. The main use scenario of the flame-retardant 8-shaped optical cable is outdoors. In addition to paying attention to the flame retardant performance of the optical cable, it is also necessary to ensure that the optical cable has good tensile properties. Therefore, a tensile layer 3 structure is provided on the periphery of the optical unit 2. The tensile fiber itself has good tensile properties, and the twisted structure will not significantly affect the bending performance of the optical cable, which is convenient for the construction and use of the optical cable.

[0036] Optionally, a water-blocking tape is further provided on the periphery of the twisted structure of the optical unit 2, and the water-blocking tape is wrapped around the periphery of the twisted structure of the optical unit 2 to wrap the twisted structure of the optical unit 2 into a cylindrical structure, which is convenient for twisting and wrapping the tensile fiber.

[0037] Further preferably, the plurality of tensile-resistant fibers are formed by twisting ultra-high molecular weight polyethylene fibers and glass fibers. Ultra-high molecular weight polyethylene refers to linear structural polyethylene with a relative molecular mass of more than 1.5 million. It has relatively good tensile strength and low density. It is light in weight and high in strength. It can effectively disperse and absorb energy and has good impact resistance. The elongation at break is 3% to 4%, which can absorb more impact energy, greatly improve the impact resistance of the flame-retardant figure-8 optical cable, and effectively protect the internal optical unit 2. Glass fiber has a certain rigidity and has tensile and high temperature resistance. By twisting ultra-high molecular weight polyethylene fibers with glass fibers, the tensile-resistant fibers have tensile, compressive and temperature resistance properties.

[0038] Optionally, the ultra-high molecular weight polyethylene fibers and glass fibers in the tensile fibers are formed in an SZ twisted form.

[0039] Further preferably, the glass fiber is a porous glass fiber, and water-blocking powder is attached to the porous glass fiber. In addition to being combined with ultra-high molecular weight polyethylene fibers to form a tensile, compressive and temperature-resistant structure, the glass fiber itself has good thermal insulation properties. The structure of the porous glass fiber and the water-blocking powder enables the glass fiber to have thermal insulation and water-blocking capabilities. The inner side of the first flame retardant layer 4 in the outer sheath is connected to the tensile layer 3, and the outer side is connected to the second flame retardant layer 6. The bio-based structure in the first flame retardant layer 4 is hydrophilic and easily absorbs moisture to cause material hydrolysis, affecting the protective performance of the outer sheath of the optical cable and the overall sealing performance of the optical cable. During the preparation and use of the optical cable, the second flame retardant layer 6 is co-extruded with the first flame retardant layer 4. The second flame retardant layer 6 can form effective protection on the outside of the first flame retardant layer 4 to prevent external water vapor from contacting the first flame retardant layer 4 during extrusion molding and use, thereby ensuring the flame retardant performance and molding performance of the first flame retardant layer 4. However, the inner layer of the first flame-retardant layer 4 cannot effectively block moisture contact. Therefore, the present invention provides a tensile layer 3 within the inner layer of the first flame-retardant layer 4. The combined structure of porous glass fiber and water-blocking powder can form an effective water-blocking structure within the first flame-retardant layer 4, preventing the biomass base in the first flame-retardant layer 4 from contacting moisture, thereby ensuring the flame-retardant performance of the first flame-retardant layer 4. In addition, when the biomass base forms a carbon layer structure, it means that the optical cable is in a high-temperature environment. The porous glass fiber has good thermal insulation capabilities, which can reduce the heat transferred from the outside to the optical unit 2, preventing damage to the optical unit 2, and allowing the flame-retardant figure-8 optical cable to be used normally in high-temperature environments.

[0040] As an optional embodiment of the present invention, the optical unit 2 in the present invention includes a loose tube, and a plurality of ribbon optical fibers are placed in the loose tube.

[0041] Optionally, a plurality of light units 2 and at least one filling rope are twisted and arranged on the periphery of the central reinforcement member 1 .

[0042] Optionally, a water-blocking paste is further coated between the twisted structure of the plurality of optical units 2 and the central reinforcement member 1 .

[0043] Furthermore, the flame-retardant figure-8 optical cable of the present invention also includes a method for preparing the flame-retardant figure-8 optical cable, which comprises the following steps: Pulling the central reinforcement member 1, and twisting a plurality of optical units 2 along the periphery of the central reinforcement member 1; A three-layer co-extrusion process is used to sequentially form a first flame retardant layer 4, an adhesive layer 5, and a second flame retardant layer 6 on the periphery of the twisted structure of the optical unit 2; After cooling and forming, a flame-retardant figure-8 optical cable is obtained.

[0044] Furthermore, as an optional embodiment of the present invention, the three-layer co-extrusion process in this application is similar to the conventional two-layer co-extrusion, and the extrudates of the first flame retardant layer 4, the adhesive layer 5 and the second flame retardant layer 6 are extruded respectively through three extrusion heads, and then three flow channel openings are opened on the extrusion die, and the first flame retardant layer 4, the adhesive layer 5 and the second flame retardant layer 6 are extruded in sequence on the periphery of the twisted structure of the optical unit 2. The present invention adopts the form of a three-layer co-extrusion process to form a sheath layer in one step, which can reduce the overall thickness of the sheath layer and save the use of sheath materials; the one-time molding method simplifies the outer sheath extrusion molding process and improves the production speed of the flame-retardant 8-shaped optical cable; in addition, the three-layer co-extrusion method avoids the first flame retardant layer 4 from contacting with moisture from the external environment during the separate extrusion molding stage and the stage when the first flame retardant layer 4 is coated on the periphery of the optical unit 2, thereby reducing the probability of defective products caused by moisture in the bio-based thermoplastic polyurethane flame retardant material and improving the yield rate of the flame-retardant 8-shaped optical cable.

[0045] Further, as an optional embodiment of the present invention, the raw materials for preparing the first flame retardant layer 4 include, by weight: 60-70 parts of bio-based polyol, 20-30 parts of bio-based isocyanate, 3-5 parts of chain extender, 5-10 parts of plasticizer, 1-2 parts of lubricant, 3-5 parts of filler, 0.5-1 part of antioxidant, 0.5-1 part of ultraviolet absorber, 5-10 parts of flame retardant and 40-50 parts of phytic acid; the extrusion molding of the first flame retardant layer 4 includes the following steps: drying the bio-based polyol and the bio-based isocyanate, respectively adding the bio-based polyol, the bio-based isocyanate, a chain extender, a plasticizer, a lubricant, a filler, an antioxidant, an ultraviolet absorber, a flame retardant, and phytic acid into a reaction extruder, and extruding and granulating the mixture to obtain bio-based thermoplastic polyurethane flame retardant material particles; Bio-based thermoplastic polyurethane flame retardant material particles are added to an extruder and extruded to obtain a first flame retardant layer 4 .

[0046] Preferably, the bio-based polyol needs to be vacuum dried at 70°C-85°C for more than 4 hours to ensure that the moisture content of the bio-based polyol is ≤0.05%, so as to avoid the bio-based polyol and bio-based isocyanate reacting to generate bubbles, causing subsequent problems such as bulging or damage of the first flame retardant layer 4.

[0047] Preferably, the filler is silica, and the silica needs to be mixed with the silane coupling agent under high shear for more than 30 minutes before being added, and then blended with the bio-based polyol, and finally added to the extruder.

[0048] Preferably, the extruder in the first flame-retardant layer 4 is a twin-screw extruder, the screw speed is 80-120 rpm, and the extruded melt pressure is ≥15 MPa.

[0049] Preferably, the extrusion barrel temperature of the first flame retardant layer 4 is controlled in layers, which includes barrel zone 1, barrel zone 2, and barrel zone 3 along the material extrusion direction, wherein the temperature of barrel zone 1 is 180~190℃, the temperature of barrel zone 2 is 190~200℃, and the temperature of barrel zone 3 is 200~220℃.

[0050] The first flame retardant layer 4 obtained by the extrusion molding process of the present invention has a tensile strength of ≥15 MPa, an elongation at break ≥300%, and a tear strength ≥50 N / mm; UV aging (QUV 1000 hours, strength retention rate ≥80%), at 85°C / 85% RH for 500 hours, no cracking or powdering; vertical burning rating: UL 94 V0 level, and an oxygen index ≥30%.

[0051] Preferably, the temperature of the extrusion die is 180-190°C. The extrusion temperature of a conventional extrusion die is between 200-230°C. The extrusion die temperature in the present invention is slightly lower than the conventional extrusion temperature. On the one hand, it meets the extrusion temperature of the low-smoke halogen-free flame retardant material and the ethylene-acrylic acid copolymer, and on the other hand, it can prevent the interface delamination of the first flame retardant layer 4, the adhesive layer 5, and the second flame retardant layer 6, and avoid damage to the adhesive layer 5.

[0052] Preferably, after pulling the central reinforcement 1 and twisting multiple optical units 2 along the periphery of the central reinforcement 1, it also includes: winding tensile fibers around the periphery of the twisted structure of multiple optical units 2, and the tensile fibers are wrapped around the periphery of the twisted structure of multiple optical units 2 in the form of SZ twisting.

[0053] Optionally, a flame-retardant figure-8 optical cable is prepared by the flame-retardant figure-8 optical cable preparation method of the present invention, as follows: An FRP rod is selected as the central reinforcement 1 with a diameter of 5.1 mm. A 6-core ribbon cable is selected as the optical unit 2. Six optical units 2 are wrapped around the periphery of the central reinforcement 1. The loose tube of the optical unit 2 is made of PBT. The diameter of the optical unit 2 is 4.9 mm, and the twisting pitch of the optical unit 2 is 290 mm. Water-blocking paste is applied on the twisted structure of the optical unit 2 and the central reinforcement 1. Tensile fiber is wrapped around the periphery of the twisted structure of the optical unit 2. The tensile fiber is twisted and coated on the periphery of the twisted structure of the optical unit 2. The twisting form is S-direction twisting or Z-direction twisting. A three-layer co-extrusion process is used to form an outer sheath around the tensile fiber, and the sheath is cooled and formed to obtain a flame-retardant figure-8 optical cable.

[0054] The first flame-retardant layer (4) is made from 60 parts castor oil polyol, 20 parts bio-based isocyanate PDI curing agent, 3 parts 1,4-butanediol, 6 parts triethyl citrate, 1 part stearic acid, 4 parts nano-silica, 0.1 part hindered phenol, 0.5 part benzotriazole, 5 parts hexa-DOPO benzoxazine cyclotriphosphazene flame retardant, 40 parts phytic acid, 0.2 parts dibutyltin dilaurate, and 0.2 parts organic bismuth catalyst. The extruded thickness of the first flame-retardant layer (4) is 1.2 mm. The extruded thickness of the ethylene-acrylic acid copolymer is 0.1-0.2 mm, and the extruded thickness of the low-smoke, halogen-free flame-retardant polyethylene is 0.5 mm.

[0055] The performance indicators of the flame retardant 8 optical cable of the present invention are tested as follows:

[0056] The flame-retardant figure-8 optical cable of the present invention forms flame-retardant protection on the outside of the optical cable by using low-smoke halogen-free flame-retardant material, and arranges a bio-based polyurethane flame-retardant structural layer on the inner layer of the optical cable to form a double-layer flame-retardant structure, thereby greatly improving the flame retardant performance of the optical cable. The inner layer adopts a bio-based flame-retardant structure, which reduces the overall production and manufacturing cost of the optical cable; at the same time, the inner layer of the optical cable is provided with ultra-high molecular weight polyethylene fiber as an armor structure, which greatly improves the impact resistance of the optical cable.

[0057] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flame-retardant figure-8 optical cable, comprising a self-supporting portion and an optical cable portion, wherein the self-supporting portion and the optical cable portion are connected by a connector; characterized in that: The optical cable portion comprises: center reinforcement; a plurality of optical units, wherein the plurality of optical units are twisted and arranged on the periphery of the central reinforcement member; An outer sheath, the outer sheath is wrapped around the periphery of the twisted structure of the multiple optical units; the outer sheath includes a first flame retardant layer and a second flame retardant layer, the first flame retardant layer is arranged on the periphery of the twisted structure of the optical unit, and the second flame retardant layer is arranged on the periphery of the first flame retardant layer, the first flame retardant layer contains a bio-based thermoplastic polyurethane flame retardant material, and the second flame retardant layer contains a low-smoke halogen-free flame retardant material.

2. The flame-retardant figure-8 optical cable according to claim 1, characterized in that: The raw materials for preparing the bio-based thermoplastic polyurethane flame retardant material include, by weight, 60-70 parts of bio-based polyol, 20-30 parts of bio-based isocyanate, 3-5 parts of chain extender, 5-10 parts of plasticizer, 1-2 parts of lubricant, 3-5 parts of filler, 0.5-1 part of antioxidant, 0.5-1 part of ultraviolet absorber and 5-10 parts of flame retardant.

3. The flame-retardant figure-8 optical cable according to claim 2, characterized in that: The bio-based thermoplastic polyurethane flame retardant material further includes phytic acid, chitosan or lignin.

4. The flame-retardant figure-8 optical cable according to claim 1, characterized in that: An adhesive layer is further provided between the first flame retardant layer and the second flame retardant layer, and the adhesive layer comprises ethylene-acrylic acid copolymer.

5. The flame-retardant figure-8 optical cable according to claim 1, characterized in that: A tensile layer is further provided between the sheath layer and the plurality of optical unit twisted structures. The tensile layer is wrapped around the periphery of the plurality of optical unit twisted structures and is formed by twisting a plurality of tensile fibers.

6. The flame-retardant figure-8 optical cable according to claim 5, characterized in that: The plurality of tensile strength fibers are formed by twisting ultra-high molecular weight polyethylene fibers and glass fibers.

7. The flame-retardant figure-8 optical cable according to claim 6, characterized in that: The glass fiber is porous glass fiber, and water-blocking powder is attached to the glass fiber.

8. A method for preparing a flame-retardant figure-8 optical cable, characterized in that: The steps include: pulling a central reinforcement member, and twisting a plurality of optical units along the periphery of the central reinforcement member; A three-layer co-extrusion process is used to sequentially form a first flame retardant layer, an adhesive layer, and a second flame retardant layer on the periphery of the optical unit twisted structure; After cooling and forming, a flame-retardant figure-8 optical cable is obtained.

9. The method for preparing the flame-retardant figure-8 optical cable according to claim 8, characterized in that: The raw materials for preparing the first flame retardant layer include, by weight, 60-70 parts of bio-based polyol, 20-30 parts of bio-based isocyanate, 3-5 parts of chain extender, 5-10 parts of plasticizer, 1-2 parts of lubricant, 3-5 parts of filler, 0.5-1 part of antioxidant, 0.5-1 part of ultraviolet absorber, 5-10 parts of flame retardant and 40-50 parts of phytic acid; The extrusion molding of the first flame retardant layer comprises the following steps: drying the bio-based polyol and the bio-based isocyanate, respectively adding the bio-based polyol, the bio-based isocyanate, a chain extender, a plasticizer, a lubricant, a filler, an antioxidant, an ultraviolet absorber, a flame retardant, and phytic acid into a reaction extruder, and extruding and granulating the mixture to obtain bio-based thermoplastic polyurethane flame retardant material particles; Bio-based thermoplastic polyurethane flame retardant material particles are added into an extruder and extruded to obtain a first flame retardant layer.

10. The method for preparing the flame-retardant figure-8 optical cable according to claim 8, characterized in that: The three-layer co-extrusion process uses three extruder heads to extrude the base materials of the first flame retardant layer, the adhesive layer, and the second flame retardant layer respectively, and then opens three flow channel openings on the extrusion die to sequentially extrude the first flame retardant layer, the adhesive layer, and the second flame retardant layer on the periphery of the optical unit twisted structure; the temperature of the extrusion die is 180~190℃.

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