Preparation method of full-dry type large-core-number flame-retardant micro cable and product thereof

Abstract

The invention belongs to the related field of optical communication transmission technology, and discloses a preparation method of a full-dry type large-core-number flame-retardant micro cable and a product thereof, in a yarn binding process, a plurality of optical fibers are twisted into an optical fiber bundle, and yarn binding is performed by adopting first flame-retardant water-blocking yarn; in the cabling process, a plurality of optical fiber bundles are stranded into a fiber core, second flame-retardant water-blocking yarn is adopted to perform yarn binding, a water-blocking tape is longitudinally wrapped, water-blocking powder is added, and third flame-retardant water-blocking yarn is adopted to perform yarn binding. And in the two sets of extrusion molding procedures, the sleeve is formed, and no fiber paste is added. According to the invention, performance parameters such as cable diameter, core number density and the like of a fiber core type optical cable product can be further improved, and a total cross-section flame-retardant design is realized while a triple dry type water-blocking barrier is formed; on the basis, the technical problems that in the prior art, the roundness of the optical fiber bundle is insufficient, attenuation exceeds the standard and the like can be effectively solved, and therefore the method is particularly suitable for being applied to preparation of micro-cables with the target cable diameter being 5.0 mm or below and the overall comprehensive performance being enhanced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical communication transmission technology, and more particularly relates to a preparation method of a full-dry large-core flame-retardant microcable and a product thereof. BACKGROUND

[0002] The traditional optical cable structure generally comprises, from the inside to the outside, a central reinforcing core, a plurality of optical fiber units distributed around the central reinforcing core, an armor such as made of aluminum material, and an outer sheath layer at the outermost layer, wherein each optical fiber unit comprises a sleeve and a plurality of optical fibers placed therein, and all the optical fiber units are wound around the central reinforcing core in a circular form, thereby forming a cable core in the form of a cylinder.

[0003] The process for manufacturing such a traditional optical cable generally involves coloring, double sleeving, cabling, and sheathing processes, which are relatively complex and have high material costs. For example, the cable core requires a central reinforcing core, and the amount of material used for double sleeving is large. In addition, there are problems such as low optical fiber density of the optical cable, large thickness of the sheath and armor.

[0004] Therefore, the inventors proposed a new optical cable with a fiber core type double-layer twisted structure in an earlier patent CN202411963477X, in which 12 optical fibers are arranged in a circular form, and a forward and reverse winding yarn is performed outside the optical fibers. The 12 optical fibers after the yarn are formed into a bundle of optical fibers. Then, the 12 bundles of optical fibers are twisted into a bundle of optical fibers. The bundle of optical fibers is then wrapped with a sleeve by a double-sleeving process through an extrusion device, and a fiber paste is added to the sleeve during the extrusion process. Finally, an aluminum tape is wrapped outside the sleeve, extruded through a machine head, and finally a small-diameter large-core optical cable is formed. This scheme can reduce the cable diameter and increase the optical fiber density to a certain extent, and significantly reduce the amount of other materials such as sleeve, sheath, and armor.

[0005] However, further research shows that the above-mentioned prior art still has the following defects or deficiencies: Firstly, since the wet fiber paste filling method is used in the above-mentioned scheme, it is easy to cause pollution of the cable pipeline, and there is a contradiction between the flame retardation and water resistance key indicators, especially in terms of water resistance performance, which cannot meet the required level; Secondly, when the target cable diameter is ≤5.0mm microcable, the current preparation process needs to be further strengthened in terms of product parameters such as core diameter size, core density, and dynamic bending radius; Thirdly, it is found in actual tests that during the yarn process of the single bundle of optical fibers, it is often difficult to fully guarantee the formation of a cylindrical form of 3 inner optical fibers and 9 outer optical fibers, which has the disadvantage that when the bundle of optical fibers is twisted, there is a probability that the optical fibers will jump out, causing single or multiple optical fibers to be alone on the outside, which cannot fully guarantee the roundness of the bundle of optical fibers, and thus may cause uneven stress on the optical fibers, ultimately affecting the transmission of signals. Fourth, it is also found in the actual test that in the cabling process of the multi-fiber bundle, compared with the outer 9 optical fibers, the inner 3 optical fibers of each fiber bundle can bear part of the axial torque, while the inner straight optical fiber will directly bear the force, which accordingly causes the attenuation of the inner layer optical fiber to be greater than that of the outer layer optical fiber in the final product, which will ultimately affect the signal transmission.

[0006] Therefore, it is necessary to continue to study and improve the prior art in order to better solve the above technical problems and obtain a micro-cable product with a target cable diameter of 5.0 mm or less and enhanced overall performance. SUMMARY

[0007] In view of one or more of the above defects or improvement needs of the prior art, the present application provides a preparation method of a full-dry large-core number flame-retardant micro-cable and a product thereof, wherein the cable diameter and core number density and other performance parameters of the fiber core type optical cable product are further improved by researching and designing the entire preparation process, especially the operation requirements and key parameters and working mechanism of the key processes such as yarn twisting, cabling and two-set extrusion, and at the same time forming a triple dry water-blocking barrier and achieving full cross-section flame-retardant design. On this basis, the technical problems of insufficient roundness of the optical fiber bundle and excessive attenuation in the current process can be effectively solved, and therefore the present application is particularly suitable for micro-cable preparation application occasions with a target cable diameter of 5.0 mm or less and enhanced overall performance.

[0008] To achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of a full-dry large-core number flame-retardant micro-cable is provided, which is prepared by coloring, yarn twisting, cabling, two-set extrusion and sheathing procedures in sequence, wherein: In the yarn twisting procedure, a plurality of optical fibers are arranged in layers and coaxially in close proximity, and twisted into a single fiber bundle, and then subjected to yarn twisting treatment; in this process, a first flame-retardant and water-blocking yarn is used to perform first yarn twisting treatment; In the cabling procedure, a plurality of the fiber bundles are further arranged in layers and coaxially in close proximity, and twisted into a single fiber bundle unit, thereby forming a fiber core; in this process, a second flame-retardant and water-blocking yarn is used to perform second yarn twisting treatment on the outside of the fiber bundle unit, and after the second yarn twisting treatment is completed, a layer of water-blocking tape is wrapped in a longitudinal manner on the outside of the second flame-retardant and water-blocking yarn, and then a third flame-retardant and water-blocking yarn is used to perform third yarn twisting treatment on the outside of the water-blocking tape; in addition, water-blocking powder is added from above the longitudinal wrapping interface when the water-blocking tape is longitudinally wrapped; In the two-set extrusion procedure, a sleeve is extruded on the outer layer of the fiber bundle unit after the above-mentioned operation, and in this process, no fiber paste is added; In the sheathing process, when the sleeve passes through the mold, hot melt water-blocking glue is poured into the inside of the mold in the circumferential direction, and the hot melt water-blocking glue is uniformly coated and solidified on the outer surface of the water-blocking tape, and finally an outer sheath layer with flame retardation is formed on the outermost layer.

[0009] As a further preferred, in the stranding process, the optical fiber bundle preferably contains 12 optical fibers with a core diameter of 200 μm, wherein the inner layer is formed by 3 optical fibers, the outer layer is formed by 9 optical fibers, and the positive and negative spiral stranding is performed with a single-stranding pitch of 800 mm ± 10 mm, thereby forming a quasi-cylindrical structure. Correspondingly, in the cabling process, the optical fiber bundle unit preferably contains 12 optical fiber bundles, wherein the inner layer is formed by 3 optical fiber bundles, the outer layer is formed by 9 optical fiber bundles, and the positive and negative spiral stranding is performed on the optical fiber bundles of the inner layer with a single-stranding pitch of 1200 mm ± 10 mm, and the positive and negative spiral stranding is performed on the optical fiber bundles of the outer layer with a single-stranding pitch of 1000 mm ± 10 mm, thereby forming a quasi-cylindrical structure.

[0010] As a further preferred, in the stranding process, the diameter error of a single optical fiber is preferably controlled within ± 5 μm, and the payout tension of a single optical fiber is periodically detected and controlled to be 0.8 N ± 0.05 N.

[0011] As a further preferred, in the cabling process, with respect to each optical fiber bundle, the water-blocking powder is preferably uniformly sprayed with a filling density of 5 g / m 3 ~ 10 g / m 3 ; In addition, the water-blocking powder is a pH-neutral flowing powder, and is modified by a flame retardant coating. Its main water-blocking indexes are designed as follows: water absorption ratio with respect to deionized water ≥ 300 g / g, water absorption ratio with respect to 0.9% NaCl solution ≥ 70 g / g, particle size passing rate through a 200-mesh screen ≥ 98%, moisture content ≤ 8.0%, chloride ion content < 50 ppm; and its main flame-retardation indexes are designed as follows: limiting oxygen index ≥ 26%.

[0012] As a further preferred, the stranding tension of the first stranding treatment is preferably set to be 15 N ± 2 N, and the stranding density is ≥ 10 turns / pitch; the stranding tension of the second stranding treatment is preferably set to be 20 N ± 2 N, and the stranding pitch is set to be 30 mm ± 3 mm; and the stranding tension of the third stranding treatment is preferably set to be 30 N ± 2 N, and the stranding pitch is set to be 50 mm ± 3 mm.

[0013] As further preferred, the first, second and third flame-retardant and water-resistant yarns are preferably made of flame-retardant base materials made of Fenlon fiber materials, and are water-resistant treated on the surface; the water-resistant tape is preferably an ultra-thin water-resistant tape with a thickness of ≤0.05 mm.

[0014] As further preferred, in the two-set extrusion process, PBT particles are blended with flame retardants, and then the temperature of the melting zone is set to 240℃±5℃, and the head pressure is 12MPa±1MPa, thereby forming the sleeve by extrusion.

[0015] As further preferred, the inner side of the sleeve is preferably attached with a layer of nano-hydrophobic modified polyacrylamide coating by electrostatic spraying process, and forms a molecular level barrier.

[0016] As further preferred, in the two-set extrusion process, the outer side of the sleeve can be armored with a stainless steel tape as needed.

[0017] As further preferred, in the sheath process, the outer sheath layer is preferably made of a halogen-free composite based on polyolefin, and is compounded by adding nano-aluminum hydroxide and phosphorus-nitrogen intumescent flame retardant, wherein the particle size of the aluminum hydroxide is 25%-30% of the particle size and is treated with a surface silane coupling agent.

[0018] According to another aspect of the present application, a corresponding full-dry large-core number flame-retardant micro-cable product is also provided.

[0019] As further preferred, the total cable diameter of the micro-cable product is ≤5.0 mm.

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages: (1) In terms of water resistance, the present application performs multiple stranding processes with flame-retardant and water-resistant yarns around the optical fiber bundle, and cooperates with water-resistant tape + intumescent hot melt water-resistant glue, etc., to form a three-layer dry water-resistant barrier, thereby achieving excellent water resistance without using any fiber paste; In addition, by designing nano-hydrophobic modified polyacrylamide powder on the inner side of the sleeve, a molecular level water-resistant barrier can be formed; by adding water-resistant powder during fiber core stranding, filling and water-resistant protection between all voids can be achieved, and the risk of metal component corrosion is eliminated; the cooperation of the above multiple water-resistant means can achieve three-dimensional, multi-level and multi-functional water-resistant protection, ensuring that the micro-cable of the present application has no water penetration under 1 meter water column, 1000 meters length and 72 hours test; (2) In terms of flame retardant index, the above-mentioned water-blocking functional element processed by the application can provide good flame retardant performance, and through the improved design of the sleeve, the armor and the outer sheath and other structural layers, all combustible materials in the whole microcable are cancelled, and a full cross-section flame-retardant design is formed; In particular, it should be pointed out that the water-blocking powder filled in the fiber core gap can be modified by flame retardant coating, and the limiting oxygen index (LOI) can be increased from 18% to more than 26%, so that it is no longer just a filler when it meets fire, but an active participant in the flame-retardant heat shield, effectively delaying the heat transfer to the cable core; In addition, the outer sheath layer in the application can use a halogen-free compound based on polyolefin, and by compounding nano aluminum hydroxide with phosphorus-nitrogen intumescent flame retardant, the limiting oxygen index can be as high as more than 32%, which can not only capture free radicals to interrupt gas phase combustion at high temperature, but also form a dense and uniform expanded carbon layer with high carbon layer strength and good thermal stability, which can maintain integrity at 800℃ for more than 30 minutes; (3) In terms of optical cable product parameters, the application can completely cancel the central reinforcing core and other components by adopting a fiber core type double-layer twisted structure, and improvements have been made in terms of compressing the sleeve wall thickness and simplifying the outer sheath layer size; In addition, the application also makes targeted improvements to the size of the optical fiber itself, the twisting parameters of the optical fiber / optical fiber bundle, and other aspects, and uses stainless steel belts instead of conventional aluminum belts and cancels the peripheral steel wire armor, which can inherit and upgrade the structure of the fiber core type optical cable, further reduce the core diameter, improve the core density, and improve the dynamic bending radius, and the 144-core microcable product has a core diameter of ≤4.5mm; (4) In terms of solving technical pain points, the application controls the optical fiber diameter error and the optical fiber mounting line tension, and actual tests show that it can effectively avoid the jumping phenomenon of the optical fiber during twisting, ensure the uniform stress of the optical fiber during twisting, and thus greatly avoid the problem of insufficient roundness of the optical fiber bundle; In addition, the water-blocking powder added in the cabling process of the application also helps to increase the friction coefficient between the optical fiber bundles, especially the inner and outer optical fiber bundles, so that relative displacement between them is less likely to occur, thereby ensuring the stress consistency of the optical fiber bundle during twisting, and thus effectively reducing the phenomenon that the attenuation of the inner optical fiber is greater than that of the outer optical fiber; (5) In terms of process simplification and green environmental protection, the process window of the application is fixed, and existing production equipment can be fully utilized for modification, production efficiency is improved, and product yield is improved; In addition, the process method of the application is particularly suitable for the core vertical shaft of super high-rise buildings, the mixed power and communication channel of data centers, and the overlapping area of fireproof and water resistance requirements at the landing end of submarine optical cables. The all-dry product structure eliminates the pollution of oil paste, improves the splicing efficiency by about 30%, and reduces the comprehensive material cost by more than 25% compared with the scheme of using imported high-performance flame-retardant oil paste. While providing military-grade protection reliability, it also shows cost and maintenance advantages, and is particularly suitable for micro-cable preparation application occasions with a target cable diameter of 5.0 mm or less and overall comprehensive performance enhancement. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is the overall process flow chart of the preparation method of the all-dry flame-retardant micro-cable with a large number of cores according to the application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0023] In the description of the application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application.

[0024] In addition, the terms "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0025] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrated; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, it can be the internal communication of two elements or the interaction relationship of two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature. The first and second features can be in direct contact, or the first and second features can be in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0027] Figure 1 It is the overall process flow chart of the preparation method of the full-dry large-core flame-retardant microcable according to the present application, which will be explained more specifically below with reference to Figure 1 The present application.

[0028] In the preparation method of the full-dry large-core flame-retardant microcable according to the present application, the microcable is prepared by the processes of coloring, stranding, cabling, two sets of extrusion and sheath, etc. in turn, wherein: Step one, coloring process.

[0029] In this step, various conventional methods can be used to color the optical fibers respectively. The purpose of coloring is to add a layer of protection mechanism to the optical fibers, and at the same time, to distinguish the multiple optical fibers in the same tube, so as to facilitate fiber fusion and information transmission.

[0030] Step two, stranding process.

[0031] In this step, multiple optical fibers are arranged coaxially and tightly in layers, and are stranded into a single fiber bundle, and then stranding treatment is carried out; in this process, the first flame-retardant and water-retardant yarn is used to perform the first stranding treatment.

[0032] More specifically, taking the 144-core micro-cable with a target cable diameter of ≤4.5 mm as an example, wherein each optical fiber adopts a cable diameter of 200 μm (standard optical fiber is 250 μm), 3 optical fibers are coaxially layered and closely arranged into an inner layer, 9 optical fibers are coaxially layered and closely arranged into an outer layer, and a unidirectional stranding pitch of 800 mm±10 mm is adopted to perform positive and reverse helical stranding, thereby forming a single optical fiber bundle in a cylindrical structure; Next, preferably, a flame-retardant and water-repellent yarn made of a flame-retardant base material made of a finlon fiber material and simultaneously subjected to water-repellent treatment on the surface is used to replace the traditional binding yarn, and the first binding process is performed on the optical fiber bundle; in this process, according to one preferred embodiment of the present application, the binding tension of the first binding process is set to 15 N±2 N, and the binding density is ≥10 turns / pitch.

[0033] It should be noted that in the above binding process, the diameter error of the single optical fiber is preferably controlled within ±5 μm, and the payout tension of the single optical fiber is periodically detected and controlled to 0.8 N±0.05 N.

[0034] The reason for this design is that in actual working conditions, it is found that the single optical fiber bundle cannot fully guarantee the formation of a cylindrical structure during the binding process, which has the disadvantage that the optical fibers on the outside of the optical fiber bundle have a probability of jumping out during stranding, causing single or multiple optical fibers to be alone on the outside, which cannot fully guarantee the roundness of the optical fiber bundle, and may eventually affect the transmission of signals.

[0035] After actual testing, the project team of the present application found that the main reason for the above is: a, the diameter of the optical fiber is not uniform, causing the overall circumference diameter to be greater than the designed diameter; b, the payout tension of the single optical fiber is large; Correspondingly, the specific solving means proposed by the present application is: on the one hand, the error range of the diameter of the optical fiber is controlled within ±5 μm; on the other hand, the payout tension of the optical fiber rack is periodically corrected, for example, once every shift (8 hours), and the payout tension of the single optical fiber is set to 0.8 N±0.05 N; in this way, the jumping phenomenon of the optical fiber during stranding can be effectively avoided, the stress of the optical fiber during stranding is uniform, and the problem of insufficient roundness of the optical fiber bundle is largely avoided.

[0036] Step three, cabling process.

[0037] In this step, the multiple fiber bundles continue to be layered and coaxially closely arranged, and are further twisted into a single fiber bundle unit, thereby forming a fiber core; in this process, a second fire-retardant and water-resistant yarn is used to perform secondary binding on the outside of the fiber bundle unit, and after the secondary binding is completed, a layer of water-resistant tape is wrapped in a longitudinal manner on the outside of the second fire-retardant and water-resistant yarn, and then a third fire-retardant and water-resistant yarn is used to perform tertiary binding on the outside of the water-resistant tape; in addition, water-resistant powder is added from above the longitudinal wrapping interface during the longitudinal wrapping of the water-resistant tape.

[0038] More specifically, the number of the fiber bundles is 12, of which 3 fiber bundles are coaxially layered and closely arranged as an inner layer, and 9 fiber bundles are coaxially layered and closely arranged as an outer layer, and the fiber bundles of the inner layer are positively and negatively spirally twisted with a one-way twisting pitch of 1200 mm ± 10 mm, and the fiber bundles of the outer layer are positively and negatively spirally twisted with a one-way twisting pitch of 1000 mm ± 10 mm, thereby forming a single fiber bundle unit, i.e., a fiber core, in a cylindrical structure. Then, a fire-retardant and water-resistant yarn made of a fire-retardant base material made of Fenlon fiber material and having a water-proof surface treatment is used to replace the traditional binding yarn, and secondary binding is performed on the outside of the fiber bundle unit, i.e., the fiber core; in this process, according to another preferred embodiment of the present application, the binding tension of the secondary binding is set to 20 N ± 2 N, and the binding pitch is set to 30 mm ± 3 mm. Then, after the secondary binding is completed, a layer of water-resistant tape is wrapped in a longitudinal manner on the outside of the second fire-retardant and water-resistant yarn, and then a third fire-retardant and water-resistant yarn is used to perform tertiary binding on the outside of the water-resistant tape; in this process, according to another preferred embodiment of the present application, the binding tension of the tertiary binding is set to 30 N ± 2 N, and the binding pitch is set to 50 mm ± 3 mm.

[0039] The water-resistant tape is wrapped in a longitudinal manner on the outside of all the completed bindings, and the water-resistant tape is an ultra-thin water-resistant tape with a thickness of ≤0.05 mm. In addition, during the longitudinal wrapping of the water-resistant tape, the water-resistant powder is uniformly sprayed at a filling density of 5 g / m 3 ~ 10 g / m 3 for each fiber bundle.

[0040] Through the above design, the fire-retardant and water-resistant yarn can be used to perform multiple bindings around the fiber bundles during the binding and cabling processes, and the water-resistant tape and the expandable hot-melt water-resistant glue can be used in cooperation to form a triple dry water-resistant barrier, thereby achieving excellent water-resistant performance without using any fiber paste.

[0041] According to a preferred embodiment of the present application, the water-blocking powder is a pH-neutral flowing powder and is modified by a flame-retardant coating; its main water-blocking indexes are designed as follows: water absorption ratio relative to deionized water ≥ 300 g / g, water absorption ratio relative to 0.9% NaCl solution ≥ 70 g / g, particle size passing rate of 200 mesh screen ≥ 98%, moisture content ≤ 8.0%, and chloride ion content < 50 ppm; and its main flame-retardant indexes are designed as follows: limiting oxygen index ≥ 26%.

[0042] As analyzed in the "BACKGROUND", when the multi-fiber bundle is being stranded, the stress on the inner and outer fiber bundles is often inconsistent, and the attenuation of the inner fiber is more likely to exceed the standard than that of the outer fiber in the final product. Through actual testing, the project team of the present application found that the main reason for the above is that the outer layer forms a spring-like arrangement, and when the whole fiber bundle is stressed (for example, during the laying process of the fiber bundle), the outer fiber bundle has a certain relaxation state to bear part of the torque, while the inner fiber bundle is directly stressed.

[0043] In view of this technical pain point, the above water-blocking powder of the present application not only can fill and protect the space between all the fiber cores, but also can increase the friction coefficient between the fiber bundles, especially between the inner and outer fiber bundles, so that the relative displacement between them is less likely to occur, thereby ensuring the consistency of the stress on the fiber bundle during the stranding process, and further effectively reducing the phenomenon that the attenuation of the inner fiber is more likely to exceed the standard than that of the outer fiber.

[0044] Step four, two sets of extrusion processes.

[0045] In this step, a sleeve is extruded on the outer layer of the fiber bundle unit after the above operation, and no fiber paste is added during this process.

[0046] More specifically, according to another preferred embodiment of the present application, polybutylene terephthalate (PBT) particles can be blended with a flame retardant, and then the melt zone temperature is set to 240℃±5℃ and the die pressure is 12MPa±1MPa, thereby extruding the sleeve.

[0047] In addition, a metal strip can be added to the outer layer of the second extrusion according to specific needs, and the metal strip is replaced by a stainless steel strip instead of a conventional aluminum strip, thereby having the functions of flame retardation and lateral pressure resistance.

[0048] According to another preferred embodiment of the present application, the inner side of the sleeve can preferably also be attached with a layer of nano-hydrophobic modified polyacrylamide coating by an electrostatic spraying process, and form a molecular-level barrier. This means can cooperate with the above various waterproof means to achieve three-dimensional, multi-level and multi-functional waterproof protection.

[0049] Step five, sheath process.

[0050] In this step, when the sleeve passes through the mold, hot melt water-blocking glue is poured into the inside of the mold in a circumferential direction, and the hot melt water-blocking glue is uniformly coated and solidified on the outer surface of the water-blocking tape, and finally an outer sheath layer of flame-retardant is processed on the outermost layer.

[0051] According to another preferred embodiment of the present application, the outer sheath layer is preferably made of a halogen-free composite based on polyolefin, and is compounded by adding nano-aluminum hydroxide and phosphorus-nitrogen intumescent flame retardant, wherein the particle size of the aluminum hydroxide is 25%-30% of the particle size and is treated by a surface silane coupling agent. The limiting oxygen index of this outer sheath layer material can be as high as more than 32%, which not only efficiently captures free radicals to interrupt gas phase combustion at high temperatures, but also forms a dense and uniform intumescent carbon layer with high carbon layer strength and good thermal stability, which can maintain integrity for more than 30 minutes at 800°C; in addition, this outer sheath layer material is also easy to combine with the hot melt water-blocking glue, thereby providing reliable protection in terms of flame retardancy and water resistance.

[0052] In summary, in view of the technical problems of large cable diameter, prominent flame-retardant-water-resistant contradiction, and failure to solve the problems of fiber jump-out under ≤5 mm micro-cable large core number, and inner-outer layer attenuation difference in the prior art which generally adopts a central reinforcing core, a wet fiber paste, and aluminum tape armor, the present application can realize 144 cores in 4.5 mm by using the overall systematic comprehensive scheme of "fiber core type double-layer non-reinforcing core + three-layer flame-retardant-water-resistant yarn - ultra-thin water-blocking tape - flame-retardant powder synergistic dry water-blocking + nano-hydrophobic coating - hot melt water-blocking glue - halogen-free intumescent flame-retardant sheath full cross-section flame-retardant", which takes into account 1 m water column 72 h zero penetration, LOI≥32, and attenuation≤0.22 dB / km, and therefore has outstanding substantial features and significant progress, and has good practical value and application prospect.

[0053] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a fully dry, high-core-count flame-retardant microcable, wherein the microcable is prepared sequentially through coloring, yarn binding, cabling, two sets of extrusion, and sheathing processes, characterized in that: In the yarn binding process, multiple optical fibers are coaxially arranged in layers and tightly twisted together into a single fiber bundle, and then yarn binding is performed; during this process, the first flame-retardant and water-blocking yarn is used to perform the first yarn binding process. In the cabling process, multiple fiber bundles are further arranged coaxially and tightly in layers, and then twisted into a single fiber bundle unit to form a fiber core. During this process, a second flame-retardant and water-blocking yarn is used to perform a secondary binding process on the outside of the fiber bundle unit. After the secondary binding process is completed, a layer of water-blocking tape is wrapped longitudinally on the outside of the second flame-retardant and water-blocking yarn. Then, a third flame-retardant and water-blocking yarn is used to perform a third binding process on the outside of the water-blocking tape. In addition, water-blocking powder is added from above the longitudinal binding interface when the water-blocking tape is wrapped longitudinally. In the second extrusion process, the outer layer of the fiber bundle unit after the above operations is completed is extruded to form a sleeve, and no fiber paste is added during this process. In the sheathing process, when the sleeve passes through the mold, hot melt water-blocking adhesive is poured into the inner circumferential side of the mold, and the hot melt water-blocking adhesive is evenly coated and cured on the outer surface of the water-blocking strip. Finally, a flame-retardant outer sheath layer is formed on the outermost layer.

2. The preparation method according to claim 1, characterized in that, In the yarn binding process, the optical fiber bundle preferably contains 12 optical fibers with a core diameter of 200μm, wherein 3 optical fibers are combined to form an inner layer and 9 optical fibers are combined to form an outer layer, and a unidirectional stranding pitch of 800mm±10mm is used to perform forward and reverse helical stranding, thereby forming a cylindrical structure. Correspondingly, in the cabling process, the fiber bundle unit preferably includes 12 fiber bundles, wherein 3 fiber bundles are combined to form an inner layer and 9 fiber bundles are combined to form an outer layer. The fiber bundles of the inner layer are twisted in both directions with a unidirectional twisting pitch of 1200mm±10mm, and the fiber bundles of the outer layer are twisted in both directions with a unidirectional twisting pitch of 1000mm±10mm, thereby forming a cylindrical structure.

3. The preparation method according to claim 1 or 2, characterized in that, In the yarn binding process, it is preferable to control the diameter error of a single optical fiber within ±5μm, and to periodically detect the tension of the single optical fiber and control it to 0.8N±0.05N.

4. The preparation method according to claim 3, characterized in that, In the cabling process, the preferred spraying rate is 5 g / m for each fiber bundle. 3 ~10g / m 3 The water-blocking powder is sprayed evenly using a filling density; Furthermore, the water-blocking powder is a pH-neutral flowing powder and is modified by coating with a flame retardant. Its main water-blocking properties are designed as follows: water absorption ratio relative to deionized water ≥ 300g / g, water absorption ratio relative to 0.9% NaCl solution ≥ 70g / g, particle size passing rate through a 200-mesh sieve ≥ 98%, moisture content ≤ 8.0%, and chloride ion content < 50ppm. Its main flame-retardant properties are designed as follows: limiting oxygen index ≥ 26%.

5. The preparation method according to any one of claims 1-4, characterized in that, The yarn tension for the first yarn binding process is preferably set to 15N±2N, and the yarn binding density is ≥10 turns / pitch; the yarn tension for the second yarn binding process is preferably set to 20N±2N, and the yarn binding pitch is set to 30mm±3mm; the yarn tension for the third yarn binding process is preferably set to 30N±2N, and the yarn binding pitch is set to 50mm±3mm.

6. The preparation method according to any one of claims 1-5, characterized in that, The first, second, and third flame-retardant and water-blocking yarns are preferably made of fenron fiber material to form a flame-retardant substrate, and are waterproofed on the surface; the water-blocking tape is preferably an ultra-thin water-blocking tape with a thickness of ≤0.05mm.

7. The preparation method according to any one of claims 1-6, characterized in that, In the two extrusion processes, polybutylene terephthalate (PBT) particles are preferably blended with flame retardant, and then the melting zone temperature is set to 240℃±5℃ and the die head pressure is 12MPa±1MPa, thereby forming the sleeve by extrusion. In addition, the inner side of the sleeve is preferably coated with a nano-sized hydrophobic modified polyacrylamide coating by electrostatic spraying process to form a molecular-level barrier.

8. The preparation method according to any one of claims 1-7, characterized in that, In the sheathing process, the outer sheath layer is preferably made of a halogen-free composite material based on polyolefin, and is compounded with nano aluminum hydroxide and phosphorus-nitrogen intumescent flame retardant, wherein the aluminum hydroxide has a particle size of 25% to 30% and is treated with a surface silane coupling agent.

9. A fully dry, high-core-count flame-retardant microcable product, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The all-dry, high-core-count flame-retardant microcable product as described in claim 9, characterized in that, The total cable diameter of the microcable product is ≤5.0mm.

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