Low-density low-smoke halogen-free flame-retardant optical cable and preparation method thereof

Abstract

The application discloses a kind of low-density low-smoke halogen-free flame-retardant optical cable and preparation method thereof, belong to optical cable technical field, optical cable includes optical unit, and sheath layer is arranged in the outer periphery of optical unit;Wherein, sheath layer is prepared using polyphenyl sulfone as base material, and sheath layer has uniformly distributed closed pore, the aperture of closed pore is 10~100 μm, and the porosity of closed pore is 20~50%.The low-density low-smoke halogen-free flame-retardant optical cable of the application selects PPSU with excellent flame-retardant property as the base material of sheath layer, so that the sheath layer itself has flame-retardant property, without additional addition of metal hydroxide flame retardant for flame-retardant, avoid the problem of heavy, precipitation in long-term use and the mechanical property of sheath layer is reduced etc.

Description

Technical Field

[0001] This invention belongs to the field of optical cable technology, specifically relating to a low-density, low-smoke, halogen-free flame-retardant optical cable and its preparation method. Background Technology

[0002] Flame-retardant optical cables, as important safety cables in communication lines, are widely used in data centers, building cabling, subways, tunnels, nuclear power plants, mines, and densely populated public areas where fire safety requirements are high. Furthermore, with the continuous expansion of communication network coverage and the increasing number of special application scenarios, the performance requirements for flame-retardant optical cables are constantly increasing.

[0003] Existing flame-retardant optical cables primarily improve their flame-retardant properties by incorporating flame retardants into the cable sheath material. These flame retardants mainly utilize metal hydroxides, such as magnesium hydroxide or aluminum hydroxide. The flame retardants undergo an endothermic decomposition reaction at high temperatures, absorbing heat and producing water vapor and metal oxides. The evaporation of the water vapor carries away some heat, and the metal oxides deposit on the material surface, forming a dense protective layer that prevents heat transfer and avoids contact between the internal materials of the optical cable and oxygen, thus achieving flame retardancy.

[0004] While existing metal hydroxides offer good flame retardant properties, they also have several adverse effects on the overall performance of optical cables. Compared to optical cable sheath materials, metal hydroxides have a higher overall density. Common flame-retardant metal hydroxides include magnesium hydroxide and aluminum hydroxide, with magnesium hydroxide having a density of approximately 2.36 g / cm³. 3 Aluminum hydroxide has a density of approximately 2.42 g / cm³. 3 Common polyolefin sheathing materials have a density of 0.9~0.95 g / cm³. 3 The density of the fiber optic cable sheath is much lower than that of metal hydroxides. As the flame-retardant performance of optical cables gradually increases, the amount of metal hydroxide added also increases, leading to a higher density of the cable sheath layer. This significantly increases the overall weight of the cable, raising transportation, installation, and support structure costs. Secondly, since metal hydroxides and polyolefin sheath materials are physically blended, the flame retardant is prone to migration and precipitation during long-term use, causing the flame-retardant performance of the optical cable to gradually decline over time. Furthermore, adding metal hydroxides to polyolefin sheath materials also degrades the mechanical properties of the sheath material, resulting in a decrease in elongation at break and increased brittleness. Summary of the Invention

[0005] In response to one or more of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a low-density, low-smoke, halogen-free flame-retardant optical cable to solve the problem that the polyolefin sheath material in the existing flame-retardant optical cable is incompatible with metal hydroxides, which leads to a decrease in the breaking elongation of the optical cable sheath, an increase in brittleness, and easy precipitation during long-term use, resulting in a decrease in the flame-retardant performance of the optical cable.

[0006] To achieve the above objectives, the present invention provides a low-density, low-smoke, halogen-free flame-retardant optical cable, comprising: An optical unit, and a sheath layer disposed on the outer periphery of the optical unit; The sheath layer is made of polyphenylene sulfone as the matrix material. The sheath layer has uniformly distributed closed pores with a pore size of 10~100μm and a porosity of 20%~50%.

[0007] As a further improvement of the present invention, the sheath layer is a foamed material, and the density of the sheath layer is 0.9~1.05 g / cm³. 3 .

[0008] As a further improvement of the present invention, the sheath layer is formed by physical foaming.

[0009] As a further improvement of the present invention, a smoke suppressant and a char-forming synergist are also added to the sheath layer.

[0010] As a further improvement of the present invention, the sheath material comprises the following components: polyphenylene sulfone, foaming nucleating agent, physical foaming agent, molybdenum compound, ammonium polyphosphate and pentaerythritol.

[0011] As a further improvement of the present invention, the sheath layer material comprises the following components by weight: 70-95 parts polyphenylene sulfone, 0.5-5 parts foaming nucleating agent, 0.5-5 parts physical foaming agent, 0.1-1 parts molybdenum compound, 0.1-1 parts ammonium polyphosphate and 0.1-1 parts pentaerythritol.

[0012] As a further improvement of the present invention, the physical foaming agent is supercritical nitrogen.

[0013] This invention also includes a method for preparing a low-density, low-smoke, halogen-free flame-retardant optical cable, comprising the following steps: S1. Dry PPSU and talc separately, weigh PPSU, talc and molybdenum compound in proportion and mix them to obtain a mixture. S2. Extrude the mixture into granules to obtain the sheath layer molding masterbatch; S3. The sheath layer molding masterbatch is fed into an extruder for extrusion molding, and supercritical nitrogen is injected into the melt to obtain a polymer and gas homogeneous system with high pressure. S4, the traction optical unit, passes the optical unit through the extrusion die, introduces the polymer and gas homogeneous system into the extrusion die, and adds ammonium polyphosphate and pentaerythritol into the extrusion die to obtain a low-density, low-smoke, halogen-free flame-retardant optical cable by extrusion molding.

[0014] As a further improvement of the present invention, in step S3: a mixture of ethanol and supercritical nitrogen is injected into the melt.

[0015] As a further improvement of the present invention, the talc powder in S1 has a particle size of 0.5~5μm, and the talc powder is surface treated with a silane coupling agent.

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

[0017] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include: (1) The low-density, low-smoke, halogen-free flame-retardant optical cable of the present invention uses PPSU, which has excellent flame-retardant properties, as the base material of the sheath layer, so that the sheath layer itself has flame-retardant properties. There is no need to add metal hydroxide flame retardants for flame retardancy, which avoids the problems of heavy weight, precipitation during long-term use, and decline in mechanical properties of the sheath layer caused by adding flame retardants to the sheath layer. In addition, the present invention prepares the sheath layer as a porous material with a uniform closed-cell structure, which can further reduce the weight of the sheath layer and facilitate the transportation and installation of the optical cable. Moreover, the closed-cell structure in the sheath layer can form a tightly arranged air chamber between the sheath layer and the internal optical unit when the optical cable is burning. The air chamber can isolate the internal optical unit from the external environment, reduce the conduction of external heat to the internal optical unit, and effectively protect the internal optical fiber.

[0018] (2) The preparation method of the low-density, low-smoke, halogen-free flame-retardant optical cable of the present invention uses PPSU as the matrix material of the sheath layer, so that the sheath layer has flame-retardant properties without adding flame retardants. Secondly, in view of the problem that ammonium polyphosphate and pentaerythritol are easily decomposed when the extrusion temperature of PPSU is too high, the present invention adjusts the sheath layer molding process, first extruding to obtain a high-pressure polymer and gas homogeneous system, completing the melting of PPSU and gas injection, and then adding ammonium polyphosphate and pentaerythritol to the extrusion mold. After adding ammonium polyphosphate and pentaerythritol, it is directly foamed to form the sheath layer, ensuring the effectiveness of the char-forming synergist. By using this method, a low-density, low-smoke, halogen-free flame-retardant optical cable with good flame-retardant properties and light weight can be obtained. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the method for preparing low-density, low-smoke, halogen-free flame-retardant optical cables in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0021] In the description of this invention, it should be understood that, unless otherwise stated, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] Furthermore, unless otherwise stated, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0025] Example: The low-density, low-smoke, halogen-free flame-retardant optical cable in a preferred embodiment of the present invention includes an optical unit and a sheath layer disposed on the outer periphery of the optical unit; wherein, the sheath layer is made of polyphenylene sulfone as the matrix material, and the sheath layer has uniformly distributed closed pores, and the pore diameter of the closed pores is 10~100μm, and the porosity of the closed pores is 20%~50%.

[0026] The low-density, low-smoke, halogen-free flame-retardant optical cable of this invention uses polyphenylene sulfone (PPSU) as the matrix material for the sheath layer. The main chain of PPSU contains dense benzene rings and sulfone groups. The benzene rings give PPSU rigidity, and the sulfone groups require a large amount of energy to break, which gives the sheath formed by the PPSU matrix extremely high thermal stability. Secondly, when PPSU burns, the internal benzene rings rearrange and cross-link to form a dense carbonized layer on the surface of the sheath layer, isolating the interior of the sheath layer from the outside air, thereby interrupting combustion. By selecting PPSU, which has excellent inherent flame-retardant properties, as the matrix material for the sheath layer, this invention enables the sheath layer to possess flame-retardant properties on its own, eliminating the need for additional metal hydroxide flame retardants. This avoids the problems caused by adding flame retardants to the sheath layer, such as increased weight, precipitation during long-term use, and decreased mechanical properties of the sheath layer. In addition, by preparing the sheath layer as a porous material with a uniform closed-cell structure, the present invention can further reduce the weight of the sheath layer, which facilitates the transportation and installation of optical cables. Moreover, the closed-cell structure in the sheath layer can form a tightly arranged air chamber between the sheath layer and the internal optical unit when the optical cable is burning. The air chamber can isolate the internal optical unit from the external environment, reduce the conduction of external heat to the internal optical unit, and effectively protect the internal optical fiber.

[0027] It is worth noting that the sheath layer made of PPSU in this invention has excellent flame retardant properties, low smoke and non-toxicity in fire, and biocompatibility, fatigue resistance, oil resistance and radiation resistance. This makes the low-density, low-smoke, halogen-free flame-retardant optical cable of this invention suitable for environments such as data centers, aerospace, rail transportation, deep sea environment, nuclear power plant, petrochemical wells, and biomedicine. It is a low-density, low-smoke, halogen-free flame-retardant optical cable with broad application prospects.

[0028] Alternatively, the sheath layer in this invention is made of foamed material, and the density of the sheath layer is between 0.9 and 1.05 g / cm³. 3 PPSU has a density of 1.29 g / cm³. 3 To reduce the weight of the optical cable and adjust its weight to be close to that of seawater, thus facilitating its use in submarine cable applications, this invention controls the porosity of the closed pores within the sheath layer to adjust the sheath layer density to 0.9~1.05 g / cm³. 3 This is to further reduce the weight of the optical cable and increase its applicability.

[0029] Optionally, the sheath layer in this invention is formed using a physical foaming method. Currently, foaming materials are mainly used for polyolefin materials, primarily polyethylene, polypropylene, or polyvinyl chloride; in addition, there are polystyrene and polyurethane, etc., which broadly cover the application scenarios of foaming materials. The foaming of polyolefin materials mainly employs physical and chemical foaming processes. However, the PPSU in this invention is used in optical cable extrusion processes, with processing extrusion temperatures typically between 340 and 360°C. Conventional chemical foaming agents, such as sodium bicarbonate, decompose at temperatures between 130 and 230°C, and azodicarbonamide at temperatures between 195 and 210°C. This mismatch in processing temperatures can lead to premature decomposition or uncontrolled decomposition of the chemical foaming agent. Furthermore, the optical cable sheath layer has high requirements for roundness, with a non-roundness typically below 5%. Therefore, existing chemical foaming methods are not suitable for the sheath layer in this invention. Based on this, this invention employs a physical foaming method to form the sheath layer, avoiding the problem of uncontrolled foaming caused by premature decomposition of the chemical foaming agent.

[0030] Optionally, the sheath layer of this invention also contains a smoke suppressant and a char-forming synergist. In evaluating the flame-retardant performance of optical cables, in addition to considering the cable's own high-temperature resistance, the smoke density during a fire must also be considered. Although PPSU has good high-temperature resistance, it cannot effectively suppress smoke. Therefore, this invention adds a smoke suppressant to the sheath layer to suppress the smoke generated during sheath combustion. Furthermore, this invention adds a char-forming synergist to the sheath layer to promote the formation of a dense char layer structure in PPSU, further preventing the spread of external flames into the optical cable. It is worth noting that the closed-cell structure within the sheath layer of this invention forms chambers during optical cable combustion. These chambers can store some smoke, reducing the degree of smoke escape and further reducing the smoke density during optical cable combustion.

[0031] Further, as an optional embodiment of the present invention, the sheath layer material of the present invention includes the following components: polyphenylene sulfone, a foaming nucleating agent, a physical foaming agent, a molybdenum compound, ammonium polyphosphate, and pentaerythritol. Specifically, the polyphenylene sulfone in the present invention is the matrix material of the sheath layer, which itself possesses excellent heat resistance, mechanical strength, and self-extinguishing properties, providing the basic physical and chemical properties for the sheath layer. The foaming nucleating agent and the physical foaming agent work synergistically. The foaming nucleating agent is used to provide micro-interfaces, assisting the physical foaming agent in forming a uniform and dense closed-cell structure within the sheath layer; ammonium polyphosphate decomposes and releases phosphoric acid or polyphosphoric acid when heated, which is used to catalyze the char formation reaction and assist the sheath layer in forming a carbon layer structure; pentaerythritol undergoes esterification under the action of the acid released by ammonium polyphosphate, thereby forming a carbon-rich melt to form a dense carbon layer; the molybdenum compound can catalyze the cross-linking char formation reaction, improve the density and strength of the carbon layer, and the molybdenum compound can significantly reduce the amount of smoke and the release of toxic gases during combustion.

[0032] More specifically, the sheath layer material comprises, by weight, the following components: 70-95 parts polyphenylene sulfone, 0.5-5 parts foaming nucleating agent, 0.5-5 parts physical foaming agent, 0.1-1 parts molybdenum compound, 0.1-1 parts ammonium polyphosphate, and 0.1-1 parts pentaerythritol. By controlling the composition of the sheath layer in this invention, the apparent density of the molded sheath layer is achieved to be 0.9-1.05 g / cm³. 3 Its limiting oxygen index is ≥38%, vertical flammability rating is V-0, and long-term operating temperature is ≥160℃; and the formed optical cable, according to the IEC61034 test standard, has a light transmittance of ≥80% when burning; according to the IEC 60754-2 standard test, the halogen acid gas content is 0, the pH value is ≥5.0, and the conductivity is ≤10μS / cm, meeting the requirements for low smoke and halogen-free environmental protection; in addition, based on the foamed sheath layer, its tensile strength is ≥50MPa and the elongation at break is ≥50%, meeting the requirements for optical cable laying and use.

[0033] Optionally, the polyphenylene sulfone used in this invention has a density of 1.29 g / cm³. 3 The glass transition temperature is 220℃, the limiting oxygen index is ≥38%, the vertical flammability rating is V-0, the long-term service temperature is ≥160℃, and the melt flow rate (MFR, 365℃ / 5kg) is 10~30g / 10min.

[0034] The foaming nucleating agent in this invention can be one or more of talc, titanium dioxide, mica or calcium carbonate, with an average particle size of 0.5~5μm.

[0035] The physical foaming agent in this invention is supercritical nitrogen or supercritical carbon dioxide. It is worth noting that both supercritical nitrogen and supercritical carbon dioxide in this invention are gases, and in the actual addition process, they are mainly injected into the melt material of the sheath layer under high pressure, with the injection amount controlled according to the component ratio of the physical foaming agent.

[0036] The molybdenum compound in this invention is one or more of molybdenum trioxide, ammonium octamolate, and ammonium dimolate.

[0037] In this invention, the ammonium polyphosphate is crystalline type II ammonium polyphosphate with a degree of polymerization ≥1000, a decomposition temperature ≥280℃, a nitrogen content ≥14%, and a phosphorus content ≥31%. The particle size of the ammonium polyphosphate is not greater than 10 micrometers, preferably not greater than 5 micrometers.

[0038] In this invention, pentaerythritol has a purity of ≥98%, a hydroxyl functionality of 4, and a particle size of no more than 10 micrometers, preferably no more than 5 μm.

[0039] More preferably, the physical foaming agent in this invention is supercritical nitrogen. Supercritical carbon dioxide and supercritical nitrogen are commonly used physical foaming agents in the field, but their use in preparing foamed materials from PPSU is relatively rare. Studies have found that the solubility of supercritical carbon dioxide in PPSU is very limited, resulting in a foaming expansion ratio of only 1.10 to 2.45 for PPSU. To achieve the desired porosity and density, more gas needs to be injected during the sheath preparation process. However, the extrusion of optical cable sheaths differs from conventional foamed sheets. In the continuous extrusion process of the sheath, physical foaming agents face problems such as short residence time within the sheath, complex temperature field, and high melt pressure. This makes supercritical carbon dioxide unsuitable for the extrusion preparation of PPSU-based sheaths. In contrast, supercritical nitrogen has a slower diffusion rate than supercritical carbon dioxide, resulting in more stable cell growth during sheath extrusion, making it suitable for sheath extrusion preparation.

[0040] Furthermore, such as Figure 1 As shown, the present invention also includes a method for preparing a low-density, low-smoke, halogen-free flame-retardant optical cable, which includes the following steps: PPSU and talc are dried separately. PPSU, talc and molybdenum compound are weighed in proportion and mixed to obtain a mixture. The mixture is extruded and granulated to obtain the sheath layer molding masterbatch; The sheath layer molding masterbatch is fed into an extruder for extrusion molding, and supercritical nitrogen is injected into the melt to obtain a polymer and gas homogeneous system with high pressure. The optical unit is pulled through the extrusion die, and the homogeneous system of polymer and gas is introduced into the extrusion die. Ammonium polyphosphate and pentaerythritol are added in the extrusion die by side feeding, and low-density, low-smoke, halogen-free flame-retardant optical cable is obtained by extrusion molding.

[0041] The method for preparing low-density, low-smoke, halogen-free flame-retardant optical cables in this invention utilizes PPSU as the matrix material for the sheath layer, enabling the sheath layer to possess flame-retardant properties without the addition of flame retardants. Secondly, addressing the issue of easy decomposition of ammonium polyphosphate and pentaerythritol when the extrusion temperature of PPSU is too high, this invention adjusts the sheath layer molding process. First, a high-pressure polymer and gas homogeneous system is obtained through extrusion molding, completing the melting of PPSU and gas injection. Then, ammonium polyphosphate and pentaerythritol are added to the extrusion mold. After adding ammonium polyphosphate and pentaerythritol, the sheath layer is directly foamed, ensuring the effectiveness of the char-forming synergist. Using this method, a low-density, low-smoke, halogen-free flame-retardant optical cable with good flame-retardant properties and lightweight structure can be obtained.

[0042] Furthermore, as an optional embodiment of the present invention, ethanol is blended with supercritical nitrogen and then fed into an extruder. When supercritical nitrogen is used as a foaming agent, its diffusion rate is relatively slow, allowing for stable cell growth within the sheath layer and more stable bubble formation. However, this results in a lower PPSU foaming expansion ratio, meaning that while stable foaming of the sheath layer can be achieved, the foaming efficiency is low. Therefore, the present invention blends ethanol with supercritical nitrogen and then feeds it into the extruder. During sheath layer foaming, nitrogen rapidly precipitates and becomes the nucleus of the bubbles, while the more polar ethanol remains at the interface between the PPSU matrix and the bubbles, thereby reducing interfacial tension, promoting nitrogen molecule diffusion, stabilizing the cell walls, and inhibiting bubble coalescence. By blending ethanol with supercritical nitrogen, the foaming ratio of the sheath layer can be effectively increased, reducing the weight of the optical cable. On the other hand, most of the ethanol will escape from the surface of the sheath layer, with only trace amounts remaining within the sheath layer, having virtually no impact on the overall performance of the optical cable.

[0043] Furthermore, as an optional embodiment of the present invention, the talc powder in the present invention has a particle size of 0.5~5μm, and the talc powder is talc powder surface-treated with a silane coupling agent. Talc powder is an inorganic particle, and as a heterogeneous nucleating agent, it has poor compatibility with PPSU. Bubbles at the location of talc powder tend to coalesce, resulting in the inability to form effective closed pores within the sheath layer. However, talc powder treated with a silane coupling agent has better compatibility with PPSU, and the talc powder can be uniformly dispersed within the PPSU, which helps to uniformly distribute bubbles within the sheath layer and can significantly improve the density and pore size uniformity of the bubbles.

[0044] Example 1: Twelve G652 optical fibers are selected, twisted together, and fed into a loose tube. The eight-core loose tube is twisted around the central reinforcing member. Water-blocking tape is wrapped around the outside of the twisted structure, and the water-blocking tape is wrapped with yarn to obtain the cable core. 100 parts of polyethylene resin are selected as the sheath layer matrix material, and the sheath layer is extruded and formed around the outside of the cable core to obtain the optical cable.

[0045] Example 2: Twelve G652 optical fibers are selected, twisted together, and fed into a loose tube. The eight-core loose tube is twisted around the central reinforcing member. Water-blocking tape is wrapped around the outside of the twisted structure, and the water-blocking tape is wrapped with yarn to obtain the cable core. 100 parts of PPSU resin are selected as the sheath layer matrix material, and the sheath layer is extruded and formed around the outside of the cable core to obtain the optical cable.

[0046] Example 3: Twelve G652 optical fibers are stranded together and fed into a loose tube. The eight-core loose tube is stranded around the central reinforcing member. Water-blocking tape is wrapped around the outside of the stranded structure, and the water-blocking tape is wrapped with yarn to obtain the cable core. 98.6 parts of PPSU resin are selected as the sheath layer matrix material, and 1 part of talc, 0.2 parts of ammonium polyphosphate, and 0.2 parts of pentaerythritol are added. Supercritical nitrogen gas is introduced into the molten PPSU resin, and the pressure in the extrusion die is maintained at 15~30MPa. The sheath layer is extruded and formed around the cable core to obtain the optical cable.

[0047] Example 4: Twelve G652 optical fibers were stranded together and fed into a loose tube. The eight-core loose tube was then stranded around the central reinforcing member. Water-blocking tape was wrapped around the outside of the stranded structure, and the water-blocking tape was then wrapped with yarn to obtain the cable core. 98.4 parts of PPSU resin were selected as the sheath layer matrix material, and 1 part of talc, 0.2 parts of molybdenum compound, 0.2 parts of ammonium polyphosphate, and 0.2 parts of pentaerythritol were added. Supercritical nitrogen gas was introduced into the molten PPSU resin, and the pressure inside the extrusion die was maintained at 15~30MPa. The sheath layer was extruded and formed around the cable core to obtain the optical cable.

[0048] Example 5: Twelve G652 optical fibers were stranded together and fed into a loose tube. The eight-core loose tube was then stranded around the central reinforcing member. Water-blocking tape was wrapped around the outside of the stranded structure, and the water-blocking tape was then wrapped with yarn to obtain the cable core. 98.4 parts of PPSU resin were selected as the sheath layer matrix material, and 1 part of talc, 0.2 parts of molybdenum compound, 0.2 parts of ammonium polyphosphate, and 0.2 parts of pentaerythritol were added. A mixture of supercritical nitrogen and ethanol was introduced into the molten PPSU resin, and the pressure inside the extrusion die was maintained at 15~30MPa. The sheath layer was extruded and formed around the cable core to obtain the optical cable.

[0049] The flame retardant properties, density, and tensile properties of the optical cables prepared in the above embodiments were tested, and the specific parameters are shown in Table 1 below: Table 1

[0050] Based on the comparison of Examples 1 and 2, it can be seen that the optical cable in this invention possesses good high-temperature resistance and flame retardant properties due to the inherent characteristics of the PPSU matrix. Based on the comparison of Examples 2 and 3, it can be seen that by preparing the sheath layer as a porous foamed structure material, the overall weight of the optical cable can be reduced, and the flame retardant properties of the optical cable can be further improved. Based on the comparison of Examples 3 and 4, it can be seen that by adding molybdenum compounds into the sheath layer, the smoke density during optical cable combustion can be further reduced. Based on the comparison of Examples 4 and 5, it can be seen that by filling the PPSU with a mixture of supercritical nitrogen and ethanol, the foaming rate of the sheath layer can be increased, further reducing the density of the optical cable, thereby obtaining the low-density, low-smoke, halogen-free optical cable with excellent flame retardant properties in this invention.

[0051] Those skilled in the art will readily understand 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 within the scope of protection of the present invention.

Claims

1. A low-density, low-smoke, halogen-free flame-retardant optical cable, characterized in that, include: An optical unit, and a sheath layer disposed on the outer periphery of the optical unit; The sheath layer is made of polyphenylene sulfone as the matrix material. The sheath layer has uniformly distributed closed pores with a pore size of 10~100μm and a porosity of 20%~50%.

2. The low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 1, characterized in that, The sheath layer is made of foamed material, and the density of the sheath layer is between 0.9 and 1.05 g / cm³. 3 .

3. The low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 2, characterized in that, The sheath layer is formed using a physical foaming method.

4. The low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 1, characterized in that, The sheath layer also contains smoke suppressants and char-forming synergists.

5. The low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 1, characterized in that, The sheath material comprises the following components: polyphenylene sulfone, foaming nucleating agent, physical foaming agent, molybdenum compound, ammonium polyphosphate, and pentaerythritol.

6. The low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 5, characterized in that, The sheath material comprises the following components by weight: 70-95 parts polyphenylene sulfone, 0.5-5 parts foaming nucleating agent, 0.5-5 parts physical foaming agent, 0.1-1 parts molybdenum compound, 0.1-1 parts ammonium polyphosphate and 0.1-1 parts pentaerythritol.

7. The low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 5, characterized in that, The physical foaming agent is supercritical nitrogen.

8. A method for preparing a low-density, low-smoke, halogen-free flame-retardant optical cable, characterized in that, Includes the following steps: S1. Dry PPSU and talc separately, weigh PPSU, talc and molybdenum compound in proportion and mix them to obtain a mixture. S2. Extrude the mixture into granules to obtain the sheath layer molding masterbatch; S3. The sheath layer molding masterbatch is fed into an extruder for extrusion molding, and supercritical nitrogen is injected into the melt to obtain a polymer and gas homogeneous system with high pressure. S4, the traction optical unit, passes the optical unit through the extrusion die, introduces the polymer and gas homogeneous system into the extrusion die, and adds ammonium polyphosphate and pentaerythritol into the extrusion die to obtain a low-density, low-smoke, halogen-free flame-retardant optical cable by extrusion molding.

9. The method for preparing low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 8, characterized in that, In step S3: a mixture of ethanol and supercritical nitrogen is injected into the melt.

10. The method for preparing a low-density, low-smoke, halogen-free flame-retardant optical cable according to claim 8, characterized in that, The talc powder in S1 has a particle size of 0.5~5μm and is surface-treated with a silane coupling agent.

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