A high flame-retardant air-blown microcable and its preparation method

Abstract

This invention discloses a high flame-retardant air-blown microcable, belonging to the field of optical cable manufacturing technology. It includes a cable core and an inner sheath and an outer sheath sequentially disposed around the outer periphery of the cable core. By separately setting the inner and outer sheaths around the outer periphery of the cable core, the inner sheath's extremely high oxygen index forms an oxygen barrier, preventing oxygen from entering the optical cable and thus slowing down the combustion rate inside the cable. The outer sheath's high elongation at break provides the necessary mechanical properties for the optical cable, ensuring that the cable will not crack during use. Simultaneously, the charred shell formed after the inner and outer sheaths burn further blocks the transfer of oxygen and heat, further improving the flame-retardant effect of the optical cable. The high flame-retardant air-blown microcable and its preparation method of this invention have a simple structure, are easy to produce, and can achieve a high level of flame retardancy while providing sufficient physical and mechanical properties for the optical cable, showing good application prospects and promotional value.

Description

Technical Field

[0001] This invention belongs to the field of optical cable manufacturing technology, specifically relating to a high flame-retardant air-blown microcable and its preparation method. Background Technology

[0002] In modern urban construction, optical fiber cables serve as the "nerve vessels" of information transmission, and their safety and reliability are of paramount importance. Flame-retardant microcables, due to their excellent flame-retardant properties and flexible installation methods, are frequently used in communication network construction in densely populated areas such as urban main roads, commercial districts, and residential areas.

[0003] Currently, the development of optical cables is gradually moving towards larger core counts to maximize pipeline resources. Larger core count cables also require high fiber density, thus limiting the cable's outer diameter and necessitating a compact structural design. The internal structure of the cable cannot be overly complex, and the sheath thickness is also limited. For air-blown microcables, the cable must also meet the requirements for maneuverability and flexibility during air-blown installation. Existing high flame-retardant optical cables generally have thicker outer sheaths, typically with a nominal wall thickness of 2mm or more. In addition, mica tape and metal armor layers are added as supporting components to assist the flame retardant in forming a dense carbon shell after combustion, thus providing oxygen isolation and flame retardancy, ensuring the cable's flame-retardant effect. However, these methods are structurally complex and large in size, failing to meet the design requirements of large-core-count air-blown microcables. Summary of the Invention

[0004] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a high flame retardant grade air-blown microcable and its preparation method, which can meet the flame retardant and mechanical properties required for flame retardant optical cables while simplifying the optical cable structure.

[0005] To achieve the above objectives, one aspect of the present invention provides a high flame retardant air-blown microcable, which includes a cable core and an inner sheath and an outer sheath sequentially disposed around the outer periphery of the cable core.

[0006] The inner protective layer is used to isolate oxygen, has an oxygen index >45%, and is able to form a char layer after combustion.

[0007] The outer protective layer serves as a physical protective layer, with an elongation at break of ≥125%, an oxygen index of ≥35%, and the ability to form a char layer after combustion.

[0008] As a further improvement of the present invention, the inner protective layer material comprises a first base material, a first flame retardant, a synergistic flame retardant, and other additives; wherein the content of the first base material is 50% to 60%, the content of the first flame retardant is 30% to 40%, the content of the synergistic flame retardant is 1% to 5%, and the total content of other additives does not exceed 5%.

[0009] As a further improvement of the present invention, the outer protective layer material comprises a second base material, a second flame retardant, a plasticizer, a UV stabilizer, and other additives; wherein the content of the second base material is 50% to 60%, the content of the second flame retardant is 10% to 20%, the content of the plasticizer is 5% to 10%, the content of the UV stabilizer is 2% to 5%, and the total content of other additives does not exceed 5%.

[0010] As a further improvement of the present invention, the outer protective layer material also includes a carbonization promoter, the content of which is 2% to 5%, to promote the formation of a carbon layer on the surface of the outer protective layer.

[0011] As a further improvement of the present invention, the wall thickness of the inner protective layer is ≥0.9mm, the wall thickness of the outer protective layer is ≥0.5mm, and the total thickness of the inner protective layer and the outer protective layer does not exceed 1.85mm.

[0012] As a further improvement of the present invention, the inner sheath is tightly fitted to the cable core, and the inner sheath is bonded to the outer sheath.

[0013] As a further improvement of the present invention, the peel strength between the inner protective layer and the outer protective layer is ≥0.5N / mm.

[0014] Another aspect of the present invention provides a method for preparing a high flame-retardant air-blown microcable, comprising the following steps:

[0015] (1) Preparation of cable core;

[0016] (2) The inner sheath is formed by extruding the outer periphery of the cable core using an extruder and cooling it to solidify.

[0017] (3) The outer sheath is formed by extruding the inner sheath through an extruder and cooling it to form the outer sheath, thus completing the preparation of the high flame retardant air-blown microcable.

[0018] As a further improvement of the present invention, the screw in the extruder is a flame-retardant screw made of a wear-resistant alloy.

[0019] As a further improvement of the present invention, the mold in the extruder in steps (2) and (3) is an A-type mold or a semi-extrusion mold to increase the extrusion pressure.

[0020] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0021] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include:

[0022] (1) The high flame retardant air-blown microcable of the present invention provides an inner sheath and an outer sheath on the outer periphery of the cable core. The inner sheath has an extremely high oxygen index, which forms an oxygen barrier to prevent oxygen from entering the optical cable and thus slow down the burning rate inside the optical cable. The outer sheath has a high elongation at break, which provides the necessary mechanical properties for the optical cable and ensures that the optical cable will not crack during use. At the same time, the carbon shell formed after the inner and outer sheaths burns continues to block the transfer of oxygen and heat, further improving the flame retardant effect of the optical cable.

[0023] (2) The high flame retardant grade air-blown microcable of the present invention enhances the flame retardant effect of the inner sheath by adding a synergistic flame retardant to the inner sheath material, thereby synergistically capturing free radicals or promoting carbonization; and by adding a carbonization promoter to the outer sheath material, it promotes the formation of a carbon layer on the surface of the outer sheath material during combustion.

[0024] (3) The high flame retardant air-blown microcable of the present invention is made by tightly bonding the inner sheath to the cable core and bonding the inner sheath to the outer sheath, so as to minimize the gap between the inner sheath and the cable core and between the inner sheath and the outer sheath, prevent oxygen from entering, improve the flame retardant effect, and at the same time avoid the gap from increasing due to the outer sheath peeling off during use.

[0025] (4) The high flame retardant grade air-blown microcable and its preparation method of the present invention have a simple structure and are easy to produce. They can achieve a high level of flame retardant effect while also providing sufficient physical and mechanical properties for optical cables. They have good application prospects and promotion value. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the overall structure of a high flame-retardant air-blown microcable in a specific embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the overall structure of a high flame-retardant air-blown microcable in another specific embodiment of the present invention;

[0029] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. Optical fiber sheath; 2. Filler rope; 3. Cable opening rope; 4. Inner sheath; 5. Outer sheath; 6. Reinforcing member; 7. Water-blocking yarn. Detailed Implementation

[0030] 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.

[0031] In the description of this invention, it should be understood that 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 do not 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 limitations on this invention.

[0032] Furthermore, 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 technical features indicated. 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.

[0033] Example:

[0034] Please see Figures 1-2 In a preferred embodiment of the present invention, the high flame-retardant air-blown microcable includes a cable core and an inner sheath 4 and an outer sheath 5 sequentially covering the cable core. The outer sheath 5 provides the mechanical properties required for the optical cable and also forms a char layer during combustion, constituting a char barrier to isolate oxygen and heat, thereby slowing down the combustion rate. Simultaneously, the inner sheath 4, as a flame-retardant layer, has an extremely high oxygen index, forming an oxygen barrier to prevent oxygen from entering the optical cable, thus slowing down the combustion rate and further improving the flame-retardant effect of the optical cable.

[0035] Specifically, the cable core includes multiple fiber optic sleeves 1 stranded around the outer periphery of the reinforcing member 6, such as... Figure 1 As shown, or at least one optical fiber sleeve 1 and at least one filler rope 2 are stranded around the outer periphery of the reinforcing member 6, more preferably flame-retardant filler rope, such as Figure 2 As shown in the image.

[0036] The optical fiber sheath 1 includes a sheath and an optical fiber housed within it. The sheath is filled with grease to protect the optical fiber from moisture and provide insulation. In actual production, to avoid excessive grease content potentially increasing heat release during combustion, the grease ratio (the ratio of the internal space of the sheath after removing the optical fiber to the cross-sectional area of ​​the optical cable's outer diameter) needs to be carefully controlled. This control of grease content helps limit the maximum heat release after the sheath burns through.

[0037] Preferably, at least one water-blocking yarn 7 is provided between the reinforcing member 6 and the optical fiber sheath 1, and at least one cable-opening rope 3 is provided between the cable core and the inner sheath 4 to assist in cable opening during laying and subsequent maintenance.

[0038] Furthermore, the inner protective layer 4 of the present invention is flame-retardant by isolating oxygen, forming an oxygen barrier and an oxygen barrier layer to prevent oxygen from entering the optical cable interior, thereby slowing down the burning rate. It has a high oxygen index and can form a carbon shell after combustion, continuing to provide oxygen protection for the internal optical cable.

[0039] Preferably, the oxygen index of the inner protective layer 4 is >45%, and more preferably, the oxygen index of the inner protective layer 4 is ≥48%. In order to improve the oxygen index of the inner protective layer 4, this application achieves this by controlling the content of flame retardant, so as to capture active free radicals such as -H and -OH in the combustion process through the flame retardant, cut off the free radical chain reaction of polymer combustion, and thus achieve flame retardancy. At the same time, the flame retardant can also release non-flammable gas through decomposition, thereby achieving the effect of diluting the concentration of combustible gas or combustion-supporting gas (such as oxygen) and thus achieving flame retardancy.

[0040] Preferably, the inner protective layer 4 mainly comprises a first base material, a first flame retardant, a synergistic flame retardant, and other additives; wherein, the content of the first base material of the inner protective layer 4 is 50% to 60%, and its composition is usually polyethylene (PE) or polypropylene (PP) as the base polymer, which has low cost and good processing performance; in order to improve the flame retardant performance, modified PE or modified PP, such as ethylene-vinyl acetate copolymer (EVA), can also be selected to increase the compatibility with flame retardants.

[0041] In a preferred embodiment of the present invention, the content of the first flame retardant is 30% to 40% to achieve the required oxygen index. It can be understood that the flame retardant promotes the aromatization and carbonization of the base material, enabling the formation of a dense protective layer on the surface of the substrate without support, forming a carbon shell. This inhibits the thermal decomposition of the substrate by blocking the transfer of oxygen and heat, thereby fundamentally reducing the generation of combustible small molecules and thus reducing the release of heat and toxic gases.

[0042] Preferably, the first flame retardant is mainly a mixture of magnesium hydroxide and aluminum hydroxide, and the specific mixing ratio is adjusted according to the specific flame retardant effect required and cost considerations.

[0043] In the preferred embodiments of this invention, the content of the synergistic flame retardant is approximately 1% to 5%, generally using silicon-based or phosphorus-based flame retardant synergists. These synergistic agents work together to capture free radicals or promote charring, thereby further enhancing the flame retardant effect. Other additives generally include antioxidants, processing aids, etc., and their total content does not exceed 5%.

[0044] Preferably, the wall thickness of the inner sheath 4 is ≥0.9mm. The thicker the inner sheath 4 is, the better the overall flame retardant effect of the optical cable. In actual production, the thickness of the inner sheath 4 can be increased as much as possible while meeting the overall optical cable diameter requirements.

[0045] Furthermore, the outer sheath 5 of the present invention, as a physical protective layer, has sufficient elongation at break and tensile strength, enabling the optical cable to meet normal construction and usage requirements; at the same time, it is preferred that the oxygen index of the outer sheath 5 is ≥35%, and more preferably ≥38%, so that it has certain flame retardant properties and can form a char layer after combustion to isolate oxygen and heat, thereby slowing down the combustion rate.

[0046] Preferably, the elongation at break of the outer sheath 5 is ≥125% to ensure that the cable sheath does not break during construction and to adapt to high and low temperature performance. This invention increases the elongation at break of the outer sheath 5 by adding a plasticizer to the outer sheath material.

[0047] Preferably, the outer sheath 5 material mainly comprises a second base material, a second flame retardant, a plasticizer, a UV stabilizer, a carbonization accelerator, and other additives; wherein the content of the second base material is 50% to 60%, which can be the same PE or PP as the base material of the inner sheath 4, or it can be a weather-resistant or high-strength material to enhance the UV resistance and mechanical properties of the outer sheath 5, such as high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE), and combined with a small amount of UV stabilizer.

[0048] In a preferred embodiment of the present invention, the content of the second flame retardant is about 10% to 20%, and it can specifically be a mixture of magnesium hydroxide and aluminum hydroxide. In actual production, the flame retardant content of the outer protective layer 5 needs to be balanced with its mechanical properties when selecting the content of the second flame retardant.

[0049] Accordingly, in the preferred embodiment of the present invention, the content of plasticizer is about 5% to 10% to improve the processing fluidity and flexibility of the material. Specifically, phthalate or environmentally friendly plasticizers can be selected.

[0050] In the preferred embodiment of the present invention, the content of the UV-resistant agent is about 2% to 5%. Generally, a highly efficient UV absorber or light stabilizer is selected to improve the UV resistance of the outer sheath 5, protect the material from UV aging, and ensure that the optical cable will not crack during use.

[0051] In a preferred embodiment of the present invention, the content of the carbonization promoter is about 2% to 5%, specifically a phosphorus- or silicon-containing compound, so as to promote the formation of a carbon layer on the surface of the outer protective layer 5 material during combustion and isolate oxygen.

[0052] In a preferred embodiment of the present invention, the total content of other additives in the outer protective layer 5 material generally does not exceed 5%, including pigments, anti-aging agents, lubricants, etc.

[0053] Preferably, the wall thickness of the outer sheath 5 is ≥0.5mm. It is understood that, given a fixed overall diameter of the optical cable, increasing the thickness of the inner sheath 4 and decreasing the thickness of the outer sheath 5 can improve the overall flame retardant performance of the optical cable. However, since the outer sheath 5 bears the various mechanical properties required by the optical cable, if the wall thickness of the outer sheath 5 is less than 0.5mm, there may be a risk of material stripping and tearing.

[0054] Preferably, in order to meet the small size requirements of the air-blown microcable, the total wall thickness of the inner sheath 4 and the outer sheath 5 does not exceed 1.85mm, and their respective thicknesses are selected within the above range according to specific requirements.

[0055] In addition, to further improve the overall flame retardancy of the optical cable, it is preferable to have a tight fit between the cable core and the inner sheath 4, and between the inner sheath 4 and the outer sheath 5, so that the gaps between the layers are smaller, making it more difficult for oxygen to enter, and the flame retardant effect is better.

[0056] To achieve a tight fit between the inner sheath 4 and the outer sheath 5, it is preferable to bond the inner sheath 4 and the outer sheath 5 together, and further preferably, the peel strength should be ≥0.5N / mm to ensure the bonding effect and prevent the outer sheath from coming off during production and use, which would cause gaps or increase in the gaps between the inner sheath 4 and the outer sheath 5, thus deteriorating the flame retardant performance of the optical cable.

[0057] Furthermore, the present invention also relates to a method for preparing a high flame-retardant grade air-blown microcable, specifically including the following steps:

[0058] (1) Preparation of cable core;

[0059] Multiple optical fiber sheaths 1 are twisted around the outer periphery of the reinforcing member 6, or at least one optical fiber sheath 1 is twisted with at least one filler rope 2 around the outer periphery of the reinforcing member 6 to form a cable core, and preferably water-blocking yarn 7 is wound inside the cable core.

[0060] (2) The inner sheath 4 is formed by extruding the outer periphery of the cable core using an extruder and cooling and shaping it.

[0061] It is important to note that in the extrusion process, due to the high oxygen index of the inner protective layer 4, using conventional components and parameters may lead to problems such as accelerated screw wear, significantly increased extrusion pressure, and reduced material flowability. Therefore, the screw used in this invention is a flame-retardant screw specially made of wear-resistant alloy, which has higher hardness and wear resistance than ordinary screws, effectively reducing wear during the processing of high oxygen index materials.

[0062] In addition, excessively deep grooves in the screw may lead to excessive shearing of the material, increasing screw wear and extrusion pressure, while shallow grooves may affect the plasticization and extrusion stability of the material. Therefore, in order to meet the processing requirements of high flame retardant materials, this invention optimizes the screw groove depth according to the characteristics of high flame retardant materials to ensure uniform distribution and effective transfer of material in the screw.

[0063] Accordingly, since the processing of high flame retardant materials requires higher torque and more stable speed control, the gear ratio and transmission efficiency of the gearbox need to be adjusted so that the screw can provide greater torque at lower speeds, preventing jamming due to insufficient torque and thus ensuring that the extruder has better adaptability and stability when processing high flame retardant materials.

[0064] Furthermore, in order to ensure a tighter fit between the inner sheath 4 and the cable core, it is preferable to use an A-type die or a semi-extrusion die during extrusion. Since the inner sheath 4 material in this invention contains a flame retardant with a low melt index, in order to avoid possible bamboo-shaped fluctuations in the outer diameter of the sheath during extrusion, it is even more preferable to use an A-type die with a lower extrusion pressure, so that the outer diameter is more stable.

[0065] (3) The outer sheath 5 is formed by extruding the inner sheath 4 through an extruder and cooling and shaping it, thus completing the preparation of the high flame retardant air-blown microcable.

[0066] When extruding the outer protective layer 5, it is preferable to use an A-type mold or a semi-extrusion mold so that the outer protective layer 5 is tightly extruded and formed on the outer periphery of the inner protective layer 4, so that the outer protective layer material and the inner protective layer 4 are extruded and bonded under high temperature.

[0067] Example 1:

[0068] The cable core is formed by twisting together 6 optical fiber sheaths, such as Figure 2 As shown, each optical fiber sheath has 24 cores, for a total of 144 cores. The outer diameter of the sheath is 1.46mm to 1.52mm, the inner diameter is 1.16mm to 1.25mm, and the wall thickness is 0.11 to 0.16mm. A water-blocking yarn 7 is wrapped around the outer circumference of the cable core, and a cable opening rope 3 is installed. The diameter of the optical cable is 8.0mm ± 0.2mm.

[0069] The inner protective layer 4 has a limiting oxygen index of 55% and a wall thickness of 0.9 mm to 1.0 mm; the outer protective layer 5 has a limiting oxygen index of 43%, an elongation at break of 135%, and a wall thickness of 0.7 mm to 0.8 mm.

[0070] Example 2:

[0071] The cable core configuration is the same as in Example 1, with the inner sheath 4 having a limiting oxygen index of 55% and a wall thickness of 1.1mm to 1.2mm; the outer sheath 5 having a limiting oxygen index of 43%, an elongation at break of 135%, and a wall thickness of 0.5mm to 0.6mm.

[0072] Example 3:

[0073] The cable core configuration is the same as in Example 1, with the inner sheath 4 having a limiting oxygen index of 48% and a wall thickness of 0.9mm to 1.0mm; and the outer sheath 5 having a limiting oxygen index of 43%, an elongation at break of 135%, and a wall thickness of 0.7mm to 0.8mm.

[0074] Comparative Example 1:

[0075] The cable core configuration is the same as in Example 1, with the inner sheath 4 having a limiting oxygen index of 45% and a wall thickness of 0.9mm to 1.0mm; the outer sheath 5 having a limiting oxygen index of 45%, an elongation at break of 170%, and a wall thickness of 0.7mm to 0.8mm.

[0076] Comparative Example 2:

[0077] The cable core configuration is the same as in Example 1, with the inner sheath 4 having a limiting oxygen index of 45% and a wall thickness of 0.9mm to 1.0mm; the outer sheath 5 having a limiting oxygen index of 43%, an elongation at break of 135%, and a wall thickness of 0.7mm to 0.8mm.

[0078] The optical cable was fabricated using the structural parameters of the optical cable in the above embodiments, and the lower edge of the optical cable was sprayed with fire using a nozzle for 20 minutes. The results are shown in the table below:

[0079]

[0080] As shown in the table above, the shorter the flame spread length, the less of the optical cable is burned, and the less heat and smoke is released during combustion. Furthermore, in Examples 1-3, when the internal oxygen protection index is within the design requirements of this invention, all its indicators are within the flame-retardant requirements of the Cca flammability rating, indicating a good flame-retardant effect on the optical cable. Moreover, the higher the internal oxygen protection index and the thicker the wall, the better the overall flame-retardant effect of the optical cable. However, in Comparative Examples 1 and 2, the internal oxygen protection index is not within the design requirements of this invention, and many of its indicators fail to meet the flame-retardant requirements, with the entire optical cable burned, resulting in a poor flame-retardant effect.

[0081] The high flame-retardant air-blown microcable and its preparation method in this invention have a simple structure and are easy to produce. They can achieve a high level of flame retardancy while also providing sufficient physical and mechanical properties for optical cables, and have good application prospects and promotion value.

[0082] 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 high flame-retardant air-blown microcable, characterized in that, It includes a cable core and an inner sheath and an outer sheath sequentially disposed around the outer periphery of the cable core; The inner protective layer is used to isolate oxygen, has an oxygen index >45%, and is able to form a char layer after combustion. The inner protective layer is formed by extruding the inner protective layer material using a type A mold and a specially made flame-retardant screw made of wear-resistant alloy. The inner protective layer material comprises a first base material, a first flame retardant, a synergistic flame retardant, and other additives; wherein the content of the first base material is 50%~60%, the content of the first flame retardant is 30%~40%, the content of the synergistic flame retardant is 1%~5%, and the total content of other additives does not exceed 5%; wherein the first flame retardant is a mixture of magnesium hydroxide and aluminum hydroxide, and the synergistic flame retardant is a silicon-based or phosphorus-based synergistic flame retardant; The outer sheath serves as a physical protective layer, with an elongation at break of ≥125%, an oxygen index of ≥35%, and the ability to form a char layer after combustion; the inner sheath is tightly bonded to the cable core, and the inner sheath is bonded to the outer sheath.

2. The high flame-retardant air-blown microcable according to claim 1, characterized in that, The outer protective layer material comprises a second base material, a second flame retardant, a plasticizer, a UV stabilizer, and other additives; wherein the content of the second base material is 50% to 60%, the content of the second flame retardant is 10% to 20%, the content of the plasticizer is 5% to 10%, the content of the UV stabilizer is 2% to 5%, and the total content of other additives does not exceed 5%.

3. The high flame-retardant air-blown microcable according to claim 2, characterized in that, The outer protective layer material also includes a carbonization accelerator, which has a content of 2% to 5%, to promote the formation of a carbon layer on the surface of the outer protective layer.

4. The high flame-retardant air-blown microcable according to any one of claims 1 to 3, characterized in that, The inner protective layer has a wall thickness of ≥0.9mm, the outer protective layer has a wall thickness of ≥0.5mm, and the total thickness of the inner and outer protective layers does not exceed 1.85mm.

5. The high flame-retardant air-blown microcable according to claim 1, characterized in that, The peel strength between the inner sheath and the outer sheath is ≥0.5 N / mm.

6. A method for preparing a high flame-retardant air-blown microcable, characterized in that, Includes the following steps: (1) Preparation of cable core; (2) The inner sheath is formed by extruding the outer periphery of the cable core using an extruder and cooling it to set. (3) The outer sheath is formed by extruding the inner sheath through an extruder and cooling and shaping it to complete the preparation of the high flame retardant air-blown microcable.

7. The method for preparing a high flame-retardant air-blown microcable according to claim 6, characterized in that, The screw inside the extruder is a flame-retardant screw made of a specially designed wear-resistant alloy.

8. The method for preparing a high flame-retardant air-blown microcable according to claim 6, characterized in that, The molds in the extruder in steps (2) and (3) are type A molds or semi-extrusion molds to increase the extrusion pressure.

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