High-flame-retardant-grade air-blowing micro cable and preparation method thereof

Abstract

The invention discloses a high-flame-retardant-grade air-blowing micro-cable, which belongs to the technical field of optical cable manufacturing and comprises a cable core, an inner protective layer and an outer protective layer, the inner protective layer and the outer protective layer are respectively arranged on the periphery of the cable core, and an oxygen barrier is formed through the extremely high oxygen index of the inner protective layer, so that oxygen is prevented from entering the optical cable, and the combustion speed in the optical cable is slowed down; the high elongation at break of the outer sheath provides necessary mechanical properties for the optical cable, and ensures that the optical cable does not crack in the use process. Meanwhile, a carbon shell formed after combustion of the inner protective layer and the outer protective layer continuously blocks transmission of oxygen and heat, and the flame-retardant effect of the optical cable is further improved. According to the high-flame-retardant-grade air-blowing micro-cable and the preparation method thereof, the high-flame-retardant-grade air-blowing micro-cable is simple in structure and convenient to produce, can provide enough physical and mechanical properties for the optical cable while achieving a higher-grade flame-retardant effect, and has a better application prospect and popularization value.

Description

Technical Field

[0001] The invention belongs to the technical field of optical cable manufacturing, and specifically relates to a high flame retardant grade air-blown microcable and a preparation method thereof. Background Art

[0002] In modern urban construction, communication optical cables are the "nerve veins" of information transmission, and their safety and reliability are of vital importance. Flame-retardant gas-blown microcables are often used in the construction of communication networks in densely populated areas such as urban trunk roads, commercial areas, and residential areas due to their good flame retardant properties and flexible installation methods.

[0003] At present, the development of optical cables is gradually moving towards large core counts to maximize pipeline resources, and large core count optical cables need to achieve high fiber core density at the same time. Therefore, the outer diameter of the optical cable is limited, and a compact structure design needs to be used as much as possible. The internal structure of the optical cable cannot be too complicated, and the sheath thickness is also limited; for air-blown micro cables, it is also necessary to meet its passability and flexibility during the air-blowing installation process. The existing high-flame-retardant grade optical cables generally have thicker outer sheaths, and the common sheath wall thickness is nominally 2mm and above. In addition, mica tapes, metal armor layers, etc. will also be added as supporting components to assist the flame-retardant material to form a dense carbon shell after combustion, so as to play the role of oxygen isolation and flame retardancy, ensuring the flame retardant effect of the optical cable, but its structure is relatively complex and its size is large, which cannot meet the design requirements of large-core air-blown micro cables. Summary of the invention

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

[0005] To achieve the above object, one aspect of the present invention provides a high flame retardant grade air-blown microcable, which comprises a cable core and an inner sheath and an outer sheath sequentially arranged on the outer periphery of the cable core;

[0006] The inner protective layer is used to isolate oxygen, its oxygen index is greater than 45%, and it can form a carbon layer after combustion;

[0007] The outer protective layer serves as a physical protective layer, has an elongation at break of ≥125%, an oxygen index of ≥35%, and can form a carbon layer after combustion.

[0008] As a further improvement of the present invention, the inner protective layer material composition includes 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 composition includes a second base material, a second flame retardant, a plasticizer, an anti-ultraviolet agent 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 anti-ultraviolet agent 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 accelerator with a content of 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 ≥0.9 mm, the wall thickness of the outer protective layer is ≥0.5 mm, and the total thickness of the inner protective layer and the outer protective layer does not exceed 1.85 mm.

[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 grade air-blown microcable, comprising the following steps:

[0015] (1) preparing a cable core;

[0016] (2) Extruding the outer periphery of the cable core using an extruder and cooling and shaping to form an inner sheath;

[0017] (3) Extruding the outer periphery of the inner sheath through an extruder and cooling and shaping to form an outer sheath, thereby completing the preparation of a high flame retardant grade air-blown microcable.

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

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

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

[0021] In general, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0022] (1) The high flame retardant grade air-blown microcable of the present invention is provided with an inner sheath and an outer sheath respectively on the outer periphery of the cable core, so that the inner sheath has an extremely high oxygen index to form an oxygen barrier, thereby preventing oxygen from entering the interior of the optical cable, thereby slowing down the burning speed inside the optical cable; the outer sheath has a high elongation at break to provide the optical cable with the necessary mechanical properties, thereby ensuring that the optical cable will not crack during use; at the same time, the carbon shell formed after the inner sheath and the outer sheath are burned continues to block the transfer of oxygen and heat, thereby further improving the flame retardant effect of the optical cable.

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

[0024] (3) The high flame retardant grade air-blown microcable of the present invention is characterized by closely fitting the inner sheath to the cable core and bonding the inner sheath to the outer sheath to minimize the gap between the inner sheath and the cable core and between the inner sheath and the outer sheath, thereby preventing oxygen from entering and improving the flame retardant effect. At the same time, it is prevented that the outer sheath is peeled off during use, which causes the gap to increase.

[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. While being able to achieve a high level of flame retardant effect, they can also provide sufficient physical and mechanical properties for the optical cable, and have good application prospects and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use 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 paying creative work.

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

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

[0029] In all the drawings, the same reference numerals represent the same technical features, specifically: 1. optical fiber sleeve; 2. filling rope; 3. open cable; 4. inner sheath; 5. outer sheath; 6. reinforcement; 7. water-blocking yarn. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can be combined with each other as long as they do not conflict with each other.

[0031] In the description of the present invention, it should be understood that 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 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0032] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0033] Example:

[0034] See also Figure 1-2 The high flame retardant grade air-blown microcable in the preferred embodiment of the present invention comprises a cable core and an inner sheath 4 and an outer sheath 5 which are sequentially coated on the outside of the cable core. The outer sheath 5 can form a carbon layer during combustion to form a carbon barrier to isolate oxygen and heat, thereby slowing down the burning speed, while providing the mechanical properties required by the optical cable. At the same time, the inner sheath 4 as a flame retardant layer has an extremely high oxygen index to form an oxygen barrier to prevent oxygen from entering the interior of the optical cable, thereby slowing down the burning speed and further improving the flame retardant effect of the optical cable.

[0035] Specifically, the cable core includes a plurality of optical fiber sleeves 1 twisted and arranged on the periphery of the strength member 6. Figure 1 As shown in, or at least one optical fiber sleeve 1 and at least one filling rope 2 are twisted and arranged on the periphery of the reinforcement member 6, and further preferably a flame retardant filling rope, such as Figure 2 as shown in .

[0036] The optical fiber sleeve 1 includes a sleeve and an optical fiber disposed in the sleeve, and the sleeve is filled with grease to protect the optical fiber from moisture and insulate it. In actual production, in order to avoid the increase in heat released during combustion due to excessive grease content, it is necessary to reasonably control the oil ratio (the cross-sectional ratio of the internal space of the optical fiber sleeve after the optical fiber is removed to the outer diameter of the optical cable) so as to control the grease content to restrict the maximum heat release after the sheath is burned through.

[0037] Preferably, at least one water-blocking yarn 7 is provided between the strength member 6 and the optical fiber sleeve 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 sheath 4 of the present invention is flame-retardant by isolating oxygen, forming an oxygen-isolating barrier and an oxygen-isolating layer to prevent oxygen from entering the interior of the optical cable to slow down the burning speed. It has a high oxygen index and can form a carbon shell after burning to continue to isolate the internal optical cable from oxygen.

[0039] Preferably, the oxygen index of the inner protective layer 4 is greater than 45%, and further preferably, the oxygen index of the inner protective layer 4 is greater than or equal to 48%; in order to increase the oxygen index of the inner protective layer 4, the present application achieves this by controlling the content of the flame retardant, so that the flame retardant can capture active free radicals such as -H and -OH in the combustion process, cut off the free radical chain reaction of the polymer combustion, and thus achieve flame retardancy; at the same time, the flame retardant can also decompose to release non-combustible gases, thereby achieving the effect of diluting the concentration of combustible gas or combustion-supporting gas (such as oxygen) to achieve flame retardancy.

[0040] Preferably, the components of the material of the inner protective layer 4 mainly include a first base material, a first flame retardant, a synergistic flame retardant and other additives; wherein, the first base material content of the inner protective layer 4 is 50% to 60%, and its components usually select 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 compatibility with flame retardants.

[0041] The content of the first flame retardant in the preferred embodiment of the present invention 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, so that a dense protective layer can be formed on the surface of the substrate without a support, forming a carbon shell, and then inhibiting the thermal decomposition of the substrate by blocking the transfer of oxygen and heat, which can fundamentally reduce the generation of combustible small molecules and reduce the release of heat and toxic gases.

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

[0043] The content of the synergistic flame retardant in the preferred embodiment of the present invention is about 1% to 5%. Generally, silicon-based or phosphorus-based flame retardant synergists are selected to further enhance the flame retardant effect by capturing free radicals or promoting carbonization. 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 ≥0.9 mm. The thicker the wall thickness of the inner sheath 4 is, the better the overall flame retardant effect of the optical cable is. 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 has sufficient elongation at break and breaking strength as a physical protective layer, so that the optical cable can meet normal construction and use requirements; at the same time, the oxygen index of the outer sheath 5 is preferably ≥35%, and further preferably ≥38%, so that it has certain flame retardant properties and can form a charcoal 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. The present invention increases the elongation at break of the outer sheath 5 by adding a plasticizer to the outer sheath material.

[0047] Preferably, the components of the outer protective layer 5 material mainly include a second base material, a second flame retardant, a plasticizer, an anti-ultraviolet agent, a carbonization accelerator and other additives; the content of the second base material is 50% to 60%, and it can be made of PE or PP that is the same as the base material of the inner protective layer 4, or it can be made of weather-resistant or high-strength materials to enhance the anti-ultraviolet ability and mechanical properties of the outer protective layer 5, such as high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE), and combined with a small amount of ultraviolet stabilizer.

[0048] The second flame retardant content in the preferred embodiment of the present invention is about 10% to 20%, which may specifically be a mixture of magnesium hydroxide and aluminum hydroxide. In actual production, the flame retardant property and mechanical property of the outer protective layer 5 need to be balanced when selecting the second flame retardant content.

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

[0050] The content of the anti-ultraviolet agent in the preferred embodiment of the present invention is about 2% to 5%. Generally, a high-efficiency ultraviolet absorber or light stabilizer is selected to improve the anti-ultraviolet ability of the outer sheath 5, protect the material from ultraviolet aging, and ensure that the optical cable will not crack during use.

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

[0052] In the preferred embodiment of the present invention, the total content of other additives in the material composition of the outer protective layer 5 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 can be understood that, under the premise that the overall diameter of the optical cable is certain, increasing the thickness of the inner sheath 4 and reducing the thickness of the outer sheath 5 can improve the overall flame retardant properties 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 peeling and breaking.

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

[0055] In addition, in order to further improve the flame retardancy of the optical cable as a whole, it is preferred that the cable core and the inner sheath 4, and the inner sheath 4 and the outer sheath 5 are tightly fitted, so that the gaps between the layers are smaller, oxygen is less likely to enter, and the flame retardant effect is better.

[0056] In order to achieve a close fit between the inner sheath 4 and the outer sheath 5, it is preferred that the inner sheath 4 and the outer sheath 5 are bonded, and further preferably the peel strength is ≥ 0.5N / mm to ensure the bonding effect and avoid the outer sheath from peeling off during production and use, resulting in a gap between the inner sheath 4 and the outer sheath 5 or an increase in the gap, which deteriorates the flame retardant properties of the optical cable.

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

[0058] (1) preparing a cable core;

[0059] A plurality of optical fiber sleeves 1 are twisted around the outer periphery of the strength member 6, or at least one optical fiber sleeve 1 and at least one filling rope 2 are twisted around the outer periphery of the strength member 6 to form a cable core, and a water-blocking yarn 7 is preferably wound inside the cable core.

[0060] (2) Extruding the outer periphery of the cable core by an extruder, and cooling and shaping to form an inner sheath 4;

[0061] It should be noted that in the extrusion process, due to the high oxygen index of the inner protective layer 4, if conventional components and parameters are used, it may lead to problems such as increased screw wear, significantly increased extrusion pressure, and reduced material fluidity. Therefore, the screw used in the present invention is a flame-retardant screw specially made of wear-resistant alloy, which has higher hardness and wear resistance than ordinary screws, and can effectively reduce wear during the processing of high oxygen index materials.

[0062] In addition, since too deep a groove depth of the screw may cause excessive shearing of the material, increase screw wear and extrusion pressure, while too shallow a groove depth may affect the plasticization and extrusion stability of the material, the present invention optimizes the design of the screw groove depth according to the characteristics of the highly flame retardant material to meet the processing requirements of the highly flame retardant material, so as to ensure uniform distribution and effective transfer of the material in the screw.

[0063] Accordingly, since the processing of highly 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 a larger torque at a lower speed and will not get stuck due to insufficient torque, resulting in the flame-retardant material being unable to be extruded smoothly, ensuring that the extruder has better adaptability and stability when processing highly flame-retardant materials.

[0064] Furthermore, in order to ensure that the inner sheath 4 and the cable core fit closely, an A-type mold or a semi-extrusion mold is preferably used during extrusion. Since the inner sheath 4 material in the present invention contains a flame retardant with a low melt index, in order to avoid bamboo-shaped fluctuations in the outer diameter of the sheath that may occur during the extrusion process, an A-type mold with a smaller extrusion pressure at the die head is further preferred to make the outer diameter more stable.

[0065] (3) Extrusion molding is performed on the outer periphery of the inner sheath 4 by an extruder, and the outer sheath 5 is formed by cooling and shaping, thereby completing the preparation of the high flame retardant grade air-blown microcable.

[0066] When the outer protective layer 5 is extruded, it is also preferred 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 under high temperature state is extruded and bonded with the inner protective layer 4.

[0067] Embodiment 1:

[0068] The cable core is formed by twisting 6 optical fiber sleeves, such as Figure 2 As shown in the figure, each optical fiber sleeve has 24 cores, a total of 144 cores, the outer diameter of the sleeve is 1.46mm~1.52mm, the inner diameter of the sleeve is 1.16mm~1.25mm, and the wall thickness of the sleeve is 0.11~0.16; a water-blocking yarn 7 is placed around the outer periphery of the cable core, and an open cable 3 is set, and the diameter of the optical cable is 8.0mm±0.2mm.

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

[0070] Embodiment 2:

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

[0072] Embodiment 3:

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

[0074] Comparative Example 1:

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

[0076] Comparative Example 2:

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

[0078] The optical cable was prepared by using the structural parameters of the optical cable in the above embodiment, and a nozzle was used to spray fire on the lower edge of the optical cable. The nozzle supply time was 20 minutes. The results are shown in the following table:

[0079]

[0080] According to the above table, the shorter the flame propagation length, the less the part of the optical cable burns, and the less heat and smoke released by the combustion. In addition, when the internal oxygen protection index in Examples 1 to 3 is within the design requirements of the present invention, all of its indicators are within the flame retardant requirements of the Cca combustion grade index, and the flame retardant effect of the optical cable is better; and the higher the internal oxygen protection index, the thicker the wall thickness, and the better the overall flame retardant effect of the optical cable. If the internal oxygen protection index in Comparative Examples 1 and 2 is not within the design requirements of the present invention, many of its indicators cannot meet the flame retardant requirements, and the optical cable is completely burned, and the flame retardant effect is poor.

[0081] The high flame retardant grade air-blown microcable and preparation method thereof in the present invention have a simple structure and are easy to produce. While being able to achieve a high level of flame retardant effect, they can also provide sufficient physical and mechanical properties for the optical cable, and have good application prospects and promotion value.

[0082] It will be easily understood by those skilled in the art that the above description is only 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 protection scope of the present invention.

Claims

1. A high flame retardant grade air-blown microcable, characterized in that: It comprises a cable core and an inner sheath and an outer sheath sequentially arranged on the outer periphery of the cable core; The inner protective layer is used to isolate oxygen, its oxygen index is greater than 45%, and it can form a carbon layer after combustion; The outer protective layer serves as a physical protective layer, has an elongation at break of ≥125%, an oxygen index of ≥35%, and can form a carbon layer after combustion.

2. The high flame retardant grade air-blown microcable according to claim 1, characterized in that: The inner protective layer material composition includes 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%.

3. The high flame retardant grade air-blown microcable according to claim 1, characterized in that: The outer protective layer material composition includes a second base material, a second flame retardant, a plasticizer, an anti-ultraviolet agent 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 anti-ultraviolet agent is 2% to 5%, and the total content of other additives does not exceed 5%.

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

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

6. The high flame retardant grade air-blown microcable according to claim 1, characterized in that: The inner sheath is tightly fitted to the cable core, and the inner sheath is bonded to the outer sheath.

7. The high flame retardant grade air-blown microcable according to claim 6, characterized in that: The peel strength between the inner protective layer and the outer protective layer is ≥0.5N / mm.

8. A method for preparing a high flame retardant grade air-blown microcable, characterized in that: The steps include: (1) preparing a cable core; (2) Extruding the outer periphery of the cable core using an extruder and cooling and shaping to form an inner sheath; (3) Extruding the outer periphery of the inner sheath through an extruder and cooling and shaping to form an outer sheath, thereby completing the preparation of a high flame retardant grade air-blown microcable.

9. The method for preparing a high flame retardant grade air-blown microcable according to claim 8, characterized in that: The screw in the extruder is a flame-retardant screw specially made of wear-resistant alloy.

10. The method for preparing a high flame retardant grade air-blown microcable according to claim 8, characterized in that: The mold in the extruder of step (2) and step (3) is an A-type mold or a semi-extrusion mold to increase the extrusion pressure.

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