A dry water-blocking optical cable based on water-blocking microspheres and a preparation method thereof

Abstract

The application discloses a dry water-blocking optical cable based on water-blocking microspheres and a preparation method thereof. The optical cable comprises a central reinforcing member, a plurality of optical units twisted on the periphery of the central reinforcing member, a sheath layer, and water-soluble water-blocking microspheres filled in the gap between the sheath layer and the cable core and the gap between the cable core and the central reinforcing member. The optical unit can be a hollow optical fiber unit and / or a solid core optical fiber unit (for example, G.652D, G.654E, G.655, G657A, etc.), and if both types of optical fiber units are used, the optical cable is a hybrid optical cable. The water-soluble water-blocking microspheres have a core-shell structure, the core layer is water-blocking powder, and the shell layer is a water-soluble polymer material. The application uses water-soluble water-blocking microspheres to replace traditional water-blocking yarns and water-blocking powder, replacing the traditional water-blocking method which is highly polluting and energy-consuming, thereby bringing significant environmental benefits and achieving efficient water-blocking. By using microspheres with hierarchical proportioning for dense filling and cooperating with a hot melt adhesive coating or electrostatic adsorption treatment, the anti-unwinding ability of the optical cable can be significantly enhanced.

Description

Technical Field

[0001] This invention belongs to the field of optical cable technology, specifically relating to a dry water-blocking optical cable based on water-blocking microspheres and its preparation method to achieve the goal of green and environmentally friendly operation. Background Technology

[0002] Dry optical cables, due to their absence of grease filling, eliminate grease pollution and the need for grease cleaning during manufacturing and construction, offering advantages such as convenient construction and environmental friendliness. They have become an important development direction in the field of optical communication. Currently, water-blocking methods for dry optical cables are mainly divided into two categories: water-blocking yarn and water-blocking powder.

[0003] In microcables using water-blocking yarn, due to the thin wall thickness of the microcable, the water-blocking yarn forms obvious surface textures on the optical cable surface. This not only increases the cable size but also affects its roundness, thereby reducing the performance of air-blowing installation. In addition, the constraint of the water-blocking yarn on the optical unit also limits further reduction in the size of the loose tube.

[0004] When water-blocking powder is used directly as filler, it easily absorbs moisture and clumps, causing blockages in the filling device and affecting production efficiency and product quality. Furthermore, during optical cable stripping, the water-blocking powder may become airborne, posing a safety risk of being inhaled by construction workers, further increasing the environmental burden and failing to meet environmental protection requirements. Therefore, the solution of directly replacing water-blocking yarn with water-blocking powder also faces numerous problems.

[0005] Therefore, how to achieve dry water blocking while taking into account the feasibility of the preparation process and production efficiency remains a technical problem that urgently needs to be solved. Summary of the Invention

[0006] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a dry water-blocking optical cable based on water-blocking microspheres and its preparation method, aiming to solve the above-mentioned problems existing in the water-blocking methods of existing dry optical cables.

[0007] To achieve the above objectives, according to one aspect of the present invention, a dry water-blocking optical cable based on water-blocking microspheres is provided, comprising: Center reinforcement; Multiple optical units are twisted together on the outer periphery of the central reinforcing member to form a cable core; A sheath layer is fitted over the outside of the cable core, and a gap is formed between the sheath layer and the cable core; Water-soluble water-blocking microspheres are filled in the gaps between the sheath layer and the cable core, and between the cable core and the central reinforcing member; the water-soluble water-blocking microspheres have a core-shell structure, wherein the core layer is water-blocking powder and the shell layer is a water-soluble polymer material.

[0008] As a further improvement of the present invention, the optical unit includes a loose tube and an optical guide element disposed inside the loose tube; the outer surface of the loose tube is coated with a hot melt adhesive coating, or the outer surface of the loose tube is treated with electrostatic electret.

[0009] As a further improvement of the present invention, the difference between the preset twisting pitch of the optical cable and the measured pitch after untwisting is ≤10mm.

[0010] As a further improvement of the present invention, the water-soluble water-blocking microspheres are multi-size mixed microspheres, which are composed of microspheres in at least two different size ranges. The water-blocking powder is loaded into the core-shell structure at an amount of 20-60% wt.

[0011] As a further improvement of the present invention, the water-soluble water-blocking microspheres include: The first type of microspheres has a particle size of 400~500 μm and a mass percentage of 60%~70%. The second type of microspheres has a particle size of 200~300 μm and a mass percentage of 20%~30%. The third type of microspheres has a particle size of 50~100 μm and a mass percentage of 5%~10%.

[0012] As a further improvement of the present invention, the water-blocking powder includes one or more of sodium polyacrylate and acrylamide; and / or, The water-soluble polymeric material includes one or more of polyvinyl alcohol, polyethylene glycol, chitosan, and sodium alginate.

[0013] According to another aspect of the present invention, a method for preparing a dry water-blocking optical cable based on water-blocking microspheres is provided, comprising the following steps: Water-soluble water-blocking microspheres are prepared, wherein the water-soluble water-blocking microspheres have a core-shell structure, wherein the core layer is water-blocking powder and the shell layer is a water-soluble polymer material; An optical unit is fabricated, the optical unit comprising a loose tube and an optical guide element disposed inside the loose tube; Multiple optical units are twisted together around a central reinforcing member to form a cable core, and the water-soluble water-blocking microspheres are sprayed into the gaps between the cable cores after twisting. A sheath layer is extruded onto the outside of the coated cable core.

[0014] As a further improvement of the present invention, a hot melt adhesive coating is applied to the loose tube surface of the optical unit before the optical unit is stranded; when spraying the water-soluble water-blocking microspheres, compressed air with a temperature higher than the melting point of the hot melt adhesive is used as the conveying medium.

[0015] As a further improvement of the present invention, before the optical unit is stranded, the surface of the loose tube of the optical unit is subjected to electrostatic electret treatment to make it carry static charge; the water-soluble water-blocking microspheres are electrically neutral or carry opposite charges, and during spraying, the water-soluble water-blocking microspheres are adsorbed onto the surface of the loose tube under the action of electrostatic attraction.

[0016] As a further improvement of the present invention, the water-soluble water-blocking microspheres include: The first type of microspheres has a particle size of 400~500 μm and a mass percentage of 60%~70%. The second type of microspheres has a particle size of 200~300 μm and a mass percentage of 20%~30%. The third type of microspheres has a particle size of 50~100 μm and a mass percentage of 5%~10%.

[0017] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art: (1) The present invention uses water-soluble water-blocking microspheres with core-shell structure to replace traditional water-blocking yarn and water-blocking powder. The water-blocking powder is encapsulated inside the water-soluble polymer shell. During the production process, moisture absorption and clumping and equipment blockage can be avoided. During the construction process, the risk of powder flying and inhalation can be avoided. When it comes into contact with water, the shell dissolves quickly, the water-blocking powder is released in time and absorbs water and expands. The water-blocking effect is reliable and the response is rapid.

[0018] (2) This invention enhances the interfacial bonding force between the microspheres and the loose sleeve through two methods: first, a low-melting-point hot melt adhesive coating is applied to the surface of the loose sleeve, and heated compressed air is used during spraying to soften the coating, allowing the microspheres to adhere to the surface of the loose sleeve; second, the surface of the loose sleeve is subjected to electrostatic electret treatment, causing the microspheres to be adsorbed onto the surface of the loose sleeve under the action of electrostatic attraction. Both methods can effectively suppress unwinding before the sheath is extruded and further improve the water-blocking effect.

[0019] (3) The present invention uses microspheres of at least two particle size ranges for graded mixing. Compared with water-blocking powder, microspheres are larger in size and more regular in particle size, making them less prone to moisture absorption and clumping and eliminating the risk of dust. Compared with single-size microspheres, graded microspheres are interlocked by particles of different sizes. Larger-size microspheres form a filling skeleton, while smaller-size microspheres fill the gaps between large particles and the narrow dead angle gaps around the central reinforcement. Under the same filling amount, higher packing density and better spatial distribution uniformity can be obtained. The filling layer has a higher internal friction angle, which enhances the constraint effect on the optical unit.

[0020] (4) The present invention completes the microsphere filling after the cable core stranding is completed and before the sheath is extruded. The microspheres are evenly distributed in the gap between the cable cores before the sheath is extruded, avoiding the problem of inability to fill or uneven filling after the sheath is extruded. This process does not require complex modification to the existing production line, has strong compatibility, and is highly compatible with the synergistic effect of hot melt adhesive coating and graded microspheres. The overall process is closely connected and suitable for continuous large-scale production.

[0021] (5) The optical cable of the present invention uses water-blocking microspheres to fill the gaps in the cable core to replace the water-blocking yarn. At the same time, after twisting, the sheath is directly extruded, eliminating the need for binding the cable core yarn. As a result, there are no yarn patterns on the surface of the optical cable, the outer diameter can be further reduced, and the air blowing resistance is lower, significantly improving the air blowing effect. By using innovative water-blocking microsphere technology, the traditional water-blocking method, which is highly polluting and energy-intensive, is replaced, thus bringing significant environmental benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a dry water-blocking optical cable structure based on water-blocking microspheres according to an embodiment of the present invention.

[0023] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. central reinforcement; 2. optical unit; 3. water-soluble water-blocking microspheres; 4. sheath layer. Detailed Implementation

[0024] 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.

[0025] 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 are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] 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.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0029] See Figure 1 This invention provides a dry-type water-blocking optical cable based on water-blocking microspheres, comprising a central reinforcing member 1, optical units 2, water-soluble water-blocking microspheres 3, and a sheath layer 4. The optical unit 2 includes a loose tube and an optical guiding element (such as an optical fiber or optical fiber ribbon) disposed inside the loose tube. Multiple optical units 2 are twisted around the outer periphery of the central reinforcing member 1 to form a cable core; the sheath layer 4 is fitted over the cable core. The gaps between the sheath layer 4 and the cable core, and between the cable core and the central reinforcing member 1, are filled with water-soluble water-blocking microspheres 3.

[0030] Optical unit 2 can be a solid fiber unit, including a loose tube and a solid fiber disposed within the loose tube. The solid fiber can be single-mode fiber, multimode fiber, or other special fiber, such as G.652D, G.654E, G.655, or G657A. Alternatively, optical unit 2 can be a hollow fiber unit, including a loose tube and a hollow fiber disposed within the loose tube. Or, optical unit 2 can include both solid and hollow fiber units. If both types of fiber units are used simultaneously, the hollow and solid fiber units are mixed into a cable, thus forming a hybrid optical cable of hollow and solid fibers.

[0031] In a preferred embodiment, the water-soluble water-blocking microspheres 3 adopt a core-shell structure, wherein the core material is a water-blocking powder, which is not particularly limited and includes sodium polyacrylate, acrylamide, etc., which can rapidly absorb water and swell upon contact with water, thereby playing a water-blocking role; the shell material is a water-soluble polymer, which is not particularly limited and includes polyvinyl alcohol (PVA), polyethylene glycol (PEG), chitosan, or sodium alginate, etc., which have good water solubility and biocompatibility, and can dissolve or rupture upon contact with water, thereby releasing the internal water-blocking powder. More preferably, the water-blocking powder loading in the water-soluble water-blocking microspheres 3 is 20~60%wt.

[0032] It should be noted that the preparation method of the water-soluble water-blocking microspheres 3 in the embodiments of the present invention adopts the existing technology, which mainly includes mixing and dispersing water-soluble polymer materials with water-blocking powder, and then molding them by spray drying or emulsification-solvent evaporation method. When the microspheres come into contact with water, the shell layer dissolves or ruptures, releasing the water-blocking powder to exert the water-blocking effect.

[0033] This invention utilizes water-soluble water-blocking microspheres to replace traditional water-blocking yarn for dry water blocking of optical cable cores. Compared to directly using water-blocking powder, the water-soluble water-blocking microspheres of this invention encapsulate the water-blocking powder within a water-soluble polymer shell. This effectively avoids the problem of clogging of the filling device caused by moisture absorption and clumping of the water-blocking powder during optical cable production. During optical cable installation and stripping, the microspheres exist in granular form, effectively preventing the risk of water-blocking powder flying and being inhaled by construction personnel. Furthermore, the microsphere shell dissolves or ruptures rapidly upon contact with water, releasing the internal water-blocking powder in a timely manner and allowing it to absorb water and expand, resulting in reliable and rapid water blocking performance.

[0034] It should be noted that while directly removing the water-blocking yarn without other covering measures can avoid surface texture issues caused by the yarn, the optical units are at risk of untwisting after the cable core loses its covering constraint (i.e., the stranded optical units spring back, loosen, or shift, disrupting the regularity of the stranding structure). This can affect the uniformity of sheath extrusion and may lead to uneven stress or localized compression of the optical units. This invention, while achieving the aforementioned water-blocking function, uses water-soluble water-blocking microspheres filled in the gaps between the cable cores to increase the friction between the optical units through physical filling, thus also providing a certain degree of untwisting suppression.

[0035] Furthermore, to enhance the interfacial bonding between the water-soluble water-blocking microspheres 3 and the optical unit 2, in one embodiment of the present invention, a hot melt adhesive coating is pre-coated onto the surface of the loose tube of the optical unit 2. This coating is solid and non-sticky at room temperature, and does not affect the normal winding and twisting of the loose tube. When filling the gap between the cable cores with water-soluble water-blocking microspheres 3 after twisting, compressed air with a temperature higher than the melting point of the hot melt adhesive is used as the transport medium. The hot air softens or melts the hot melt adhesive coating, allowing the microspheres to contact and adhere to it during injection, thereby effectively suppressing untwisting before sheath extrusion. At the same time, the hot melt adhesive coating physically bonds the microspheres firmly to the surface of the loose tube, forming a hydrophobic interface layer, which helps to further enhance the water-blocking effect.

[0036] More preferably, the hot melt adhesive material includes, but is not limited to, polyamide, polyurethane, or EVA-based hot melt adhesives, with a melting point range of 80~120℃ and a melt index of 20~100g / 10min. The temperature of the compressed air is preferably 100~150℃.

[0037] In another embodiment of the invention, the surface of the loose tube is electrostatically electret treated by a corona discharge device to carry a static charge. After stranding into a cable, water-soluble water-blocking microspheres (electrically neutral or carrying opposite charges) are filled into the gaps between the cable cores. The microspheres are adsorbed and tightly adhered to the surface of the loose tube under electrostatic attraction, thereby increasing the friction between the microspheres and the loose tube. The microspheres are temporarily adsorbed and positioned before the sheath is extruded, effectively suppressing the de-twisting of the optical unit. At the same time, the electrostatic electret treatment ensures that the microspheres are evenly distributed in the gaps between the cable cores before the sheath is extruded, thereby improving the water-blocking effect.

[0038] More preferably, the water-soluble water-blocking microspheres 3 are multi-size mixed microspheres, that is, they are composed of microspheres with at least two particle size ranges. Compared with the direct use of water-blocking powder, microspheres, due to their larger particle size and regular particle shape, are less prone to moisture absorption and clumping during the filling process, and will not clog the filling device. Moreover, there is no risk of powder flying or inhalation during construction. In terms of anti-torsion effect, water-blocking powder particles are too small and have poor flowability, making it difficult to disperse evenly in the gaps between cable cores. They are prone to local accumulation or forming voids, and cannot form a continuous and dense filling layer. Furthermore, the powder only has loose point contact with the surface of the loose tube, and it is easy to redistribute under vibration or external force, which cannot provide a continuous and stable friction force. In contrast, microspheres form a stable particle skeleton through the interlocking of large and small particles. Small particles wedge into the gaps between large particles to create wedging, and the filling layer has a higher internal friction angle and shear strength, which can maintain the constraint force on the optical unit 2.

[0039] Specifically, the larger-diameter microspheres form the filling skeleton, providing main support and radial pressure; the smaller-diameter microspheres fill the gaps between the large particles and the narrow dead angle gaps between the outer periphery of the central reinforcement 1 and the optical unit 2, making the filling layer more dense and uniform, thereby achieving better filling density and anti-torsion effect than powder while avoiding inherent defects in powder.

[0040] More preferably, the water-soluble water-blocking microspheres 3 include microspheres with a first particle size, microspheres with a second particle size, and microspheres with a third particle size. The microspheres with the first particle size have a particle size of 400-500 μm and account for 60-70% of the total. The microspheres with the second particle size have a particle size of 200-300 μm and account for 20-30% of the total. The microspheres with the third particle size have a particle size of 50-100 μm and account for 5-10% of the total.

[0041] In a preferred embodiment, the thickness of the sheath layer 4 is 0.2-0.8 mm.

[0042] Furthermore, this embodiment of the invention also provides a method for preparing a dry water-blocking optical cable based on water-blocking microspheres, comprising the following steps: (1) Preparation of optical units and water-soluble water-blocking microspheres; 1) Optical unit fabrication The optical guide element is inserted into the extruder head, and a loose tube is extruded from the outside.

[0043] As a preferred method, a hot melt adhesive coating is applied to the surface of the loose sleeve: a layer of low-melting-point hot melt adhesive is applied online to the outer surface of the loose sleeve using a coating device located behind the extruder head, and then cooled and shaped to form a solid hot melt adhesive coating. The thickness of the hot melt adhesive coating is further preferably 10~30μm.

[0044] As another preferred method, electrostatic electret treatment is performed on the surface of the loose tube: after the loose tube is extruded and cooled, its outer surface is electrostatically electreted by a corona discharge device, so that the surface of the loose tube carries static charge and forms an electrostatically electret treated optical unit.

[0045] 2) Preparation of water-soluble water-blocking microspheres Water-soluble water-blocking microspheres employ a core-shell structure design, with a core of water-blocking powder (such as sodium polyacrylate or acrylamide) and a shell of water-soluble polymers (such as PVA or PEG). They are formed using spray drying or emulsion-solvent evaporation methods, with a water-blocking powder loading of 20–60% wt. The resulting microsphere shell dissolves or ruptures upon contact with water, releasing the internal water-blocking powder to exert its water-blocking effect.

[0046] Preferably, the water-soluble water-blocking microspheres are mixed in a multi-size gradation, wherein the first particle size is 400~500 μm, accounting for 60~70%; the second particle size is 200~300 μm, accounting for 20~30%; and the third particle size is 50~100 μm, accounting for 5~10%. The three particle sizes are thoroughly and physically mixed to form graded water-soluble water-blocking microspheres for later use.

[0047] (2) The optical unit 2 obtained in step (1) is twisted around the central reinforcing member 1 to form a cable core, and water-soluble water-blocking microspheres 3 are sprayed into the gap between the cable cores after twisting.

[0048] Specifically, during stranding, the central reinforcing member 1 is continuously laid out, and multiple optical units 2 are stranded around the central reinforcing member 1 to form the cable core. After stranding, water-soluble water-blocking microspheres 3 are injected into the gaps between the cable cores through a spraying device. The gaps between the cable cores include the gaps between the optical units 2 and the gaps between the optical units 2 and the central reinforcing member 1. During the spraying process, the larger-diameter microspheres form a filling skeleton, providing main support and radial pressure; the smaller-diameter microspheres fill the gaps between the larger particles and the narrow dead-angle gaps between the outer periphery of the central reinforcing member 1 and the optical units 2, thereby achieving dense filling from the center of the cable core to the sheath.

[0049] In one implementation, for the optical unit coated with a hot melt adhesive layer in step (1), compressed air with a temperature higher than the melting point of the hot melt adhesive is used as the transport medium to inject water-soluble water-blocking microspheres 3 into the cable core gap to achieve the water-blocking function. During this process, the hot air softens or melts the hot melt adhesive layer on the surface of the optical unit 2. The microspheres contact and adhere to the softened hot melt adhesive layer during injection, thereby generating an anti-torsion effect before the sheath is extruded. Preferably, the melting point of the hot melt adhesive is 80~120℃, and the temperature of the compressed air is 100~150℃.

[0050] As another implementation method, for the optical unit that has undergone electrostatic electret treatment in step (1), room temperature compressed air is used as the conveying medium to inject water-soluble water-blocking microspheres 3 into the gap of the cable core to achieve the water-blocking function. The water-soluble water-blocking microspheres 3 have a polarity opposite to that of the loose tube surface or are electrically neutral. When filling, the microspheres are adsorbed onto the surface of the loose tube under the action of electrostatic attraction, forming a tight contact, which increases the friction between the microspheres and the loose tube, thereby generating an effect of inhibiting untorsion before the sheath is extruded.

[0051] (3) The cable core after spraying in step (2) is passed through the extruder head to extrude the sheath layer 4 on the outside and then cooled and shaped.

[0052] Preferably, the extrusion temperature of the sheath layer 4 is 150~250℃, which is higher than the melting point of the hot melt adhesive coating (80~120℃). During the extrusion process, the heat of the sheath layer further solidifies the interface between the formed microspheres and the hot melt adhesive; during cooling and shaping, the shrinkage of the sheath layer generates radial pressure on the internal cable core, causing the microsphere filling layer to form a dense and stable structure.

[0053] The water-blocking optical cable and its preparation method of this invention use core-shell structured water-soluble water-blocking microspheres to replace traditional water-blocking yarn and water-blocking powder. This avoids the surface texture and air-blowing performance degradation problems caused by water-blocking yarn, and overcomes the risks of moisture absorption, clumping, equipment blockage, and powder inhalation associated with water-blocking powder, achieving safe and reliable dry water blocking. Simultaneously, through the synergistic effect of dense filling of graded microspheres and hot-melt adhesive coating (or electrostatic electret treatment), adhesion (or adsorption) is formed between the microspheres and the optical units, increasing the friction between the optical units, effectively suppressing de-twisting, and further improving the water-blocking effect. This invention features a compact process, strong compatibility, and suitability for industrial production, possessing significant practical value.

[0054] To better illustrate the technical solution and technical effects of the present invention, the following embodiments and comparative examples are provided: Example 1 This embodiment provides a dry water-blocking optical cable based on water-soluble water-blocking microspheres, including a central reinforcement, multiple optical units, a sheath layer, and water-soluble water-blocking microspheres.

[0055] (1) Optical unit preparation: Insert optical fiber into the extruder head and extrude loose tube on the outside to form optical unit.

[0056] (2) Preparation of water-soluble water-blocking microspheres: A core-shell structure was adopted, with the core layer being sodium polyacrylate water-blocking powder and the shell layer being polyvinyl alcohol (PVA) water-soluble polymer material. The microspheres were formed by spray drying, controlling the particle size to a single particle size of 300~500μm, with a water-blocking powder loading of 40%wt. The resulting microsphere shell dissolves in water, releasing the internal water-blocking powder to exert its water-blocking effect.

[0057] (3) Stranding and spraying: Six optical units are stranded around the central reinforcing member in an SZ configuration to form the cable core. After stranding, water-soluble water-blocking microspheres are injected into the gaps between the cable cores, including the gaps between the optical units and between the optical units and the central reinforcing member, using a spraying device under the action of compressed air.

[0058] (4) Sheath extrusion: The filled cable core is passed through the extruder head to extrude a sheath layer with a thickness of 0.5 mm, and then enters the cooling water tank for cooling and shaping.

[0059] Example 2 The difference between this embodiment and Embodiment 1 is that a hot melt adhesive coating is pre-coated on the loose tube surface of the optical unit, and heated compressed air is used as the conveying medium during spraying.

[0060] Specifically, during loose tube extrusion, a polyamide-based hot melt adhesive coating with a melting point of 100°C and a thickness of 20 μm is applied online using an annular coating device and then cooled and cured. During filling, compressed air heated to 120°C is used as the delivery medium to soften the hot melt adhesive coating, allowing the microspheres to contact and adhere to the softened hot melt adhesive layer during injection.

[0061] Example 3 The difference between this embodiment and Embodiment 1 is that the surface of the loose tube of the optical unit is subjected to electrostatic electret treatment, and the water-soluble water-blocking microspheres are electrically neutral.

[0062] Specifically, after the loose tube is extruded and cooled, it undergoes electrostatic electret treatment (30kV) using a corona discharge device, causing the surface of the loose tube to carry a static charge. During filling, room temperature compressed air is used as the transport medium, and the microspheres are adsorbed onto the surface of the loose tube under the action of electrostatic attraction, forming a tight contact.

[0063] Example 4 The difference between this embodiment and Embodiment 2 is that water-soluble water-blocking microspheres with different particle sizes are used.

[0064] Specifically, microspheres of three different particle sizes are mixed in the following proportions: 65% for the first particle size range of 400-500 μm, 25% for the second particle size range of 200-300 μm, and 10% for the third particle size range of 50-100 μm. During filling, the larger-sized microspheres form the filling skeleton, while the smaller-sized microspheres fill the gaps between the larger particles and the narrow dead-angle gaps around the central reinforcement.

[0065] Example 5 The difference between this embodiment and embodiment 3 is that water-soluble water-blocking microspheres with different particle sizes are used (with the same gradation ratio as in embodiment 4).

[0066] Example 6 The difference between this embodiment and Embodiment 1 is that water-soluble water-blocking microspheres of different particle sizes are used (with the same gradation ratio as in Embodiment 4). However, no hot melt adhesive coating is applied, and no electrostatic electret treatment is performed.

[0067] Comparative Example 1 The difference between this comparative example and Example 1 is that uncoated water-blocking powder (sodium polyacrylate, particle size 10~50μm) is used instead of water-soluble water-blocking microspheres for filling.

[0068] Comparative Example 2 This comparative example provides a microcable containing water-blocking yarn and binding yarn. The microcable includes a central reinforcing member, multiple optical units twisted around the periphery of the central reinforcing member, water-blocking yarn wrapped around the periphery of the optical units, binding yarn wrapped around the periphery of the water-blocking yarn, and an outermost sheath layer. The water-blocking yarn is used to achieve longitudinal water blocking of the cable core, and the binding yarn is used to fix the twisted structure and suppress optical unit untwisting.

[0069] The optical cables prepared in the above embodiments and comparative examples were subjected to the following performance tests: (1) Untwisting pitch: Take an optical cable sample and measure the change in the twisting pitch of the optical unit before sheath extrusion, that is, the difference between the preset twisting pitch and the measured pitch after untwisting, in order to evaluate its anti-untwisting ability.

[0070] (2) Tensile performance: According to IEC 60794-1-21, the rated tensile force is calculated based on the 1.8mm center reinforcement member, and the tensile force of the optical cable corresponding to the fiber strain of 0.05% is tested.

[0071] (3) Air blowing performance: The maximum air blowing distance of the optical cable shall be tested in a standard air blowing duct in accordance with IEC 60794-5-10.

[0072] (4) Water permeability performance: Take a 3m long optical cable sample, seal one end, apply a 1m water column static pressure from the other end, maintain for 24h, and measure the length of water that has penetrated along the cable core after the test.

[0073] The test results are shown in Table 1: Table 1 Performance test results of the examples and comparative examples

[0074] The results show that Example 1, using single-size microspheres without interface reinforcement, has a torsion pitch that is better than Comparative Example 1 without any constraints, but is still significantly larger than the example using interface reinforcement. This indicates that physical filling with microspheres alone has a certain anti-torsion effect, but the effect is limited. Examples 2 and 3, based on Example 1, add hot melt adhesive coating and electrostatic electret treatment, respectively. The torsion pitch and water penetration length are significantly reduced, and the tensile strength is significantly improved. This shows that both interface reinforcement methods can effectively suppress torsion and improve the water-blocking effect. Among them, the hot melt adhesive solution has slightly better overall performance than the electrostatic electret solution. Examples 4 and 5, based on Examples 2 and 3, introduce graded microspheres, respectively. The torsion pitch is further reduced, indicating that graded microspheres and interface reinforcement can produce a synergistic effect. Example 6 uses graded microspheres but does not perform interface reinforcement. The torsion pitch and water penetration length are better than Example 1 but worse than Examples 2 to 5. This shows that graded microspheres themselves have an improvement effect, but they need to be combined with interface reinforcement to achieve the optimal effect. Furthermore, the tensile force values ​​corresponding to 0.05% fiber strain in Examples 2 to 5 are all higher than those in Examples 1 and 6, indicating that the interface enhancement measures make the stranded structure more compact and the stress more uniform.

[0075] Comparing the various embodiments with the comparative examples, it can be seen that Comparative Example 1, which uses uncoated water-blocking powder instead of water-soluble water-blocking microspheres, has the largest untwisting pitch, the longest water seepage length, and the lowest tensile strength due to the water-blocking powder flying away and being lost without any restraint measures. Comparative Example 2 uses a traditional water-blocking yarn plus binding yarn scheme. The untwisting pitch and tensile strength are comparable to Embodiments 2 to 5 of the present invention. However, because the water-blocking yarn has a linear wrapping structure, there are overlapping gaps, and water is only absorbed locally along the wrapping path after contact with water. It cannot achieve continuous and tight sealing of the cable core gap like microsphere filling. Its water seepage length is inferior to the interface-reinforced embodiment of the present invention. Furthermore, because the binding yarn and water-blocking yarn wrapping form surface textures that increase air blowing resistance, its air blowing distance is significantly inferior to all embodiments. This shows that the present invention, by replacing the linear wrapping with microsphere filling, maintains an anti-untwisting ability comparable to the binding yarn scheme while having superior water blocking effect and air blowing performance.

[0076] In summary, this invention simplifies the process while achieving synergistic optimization of water-blocking, anti-torsion, and air-blowing performance. The overall performance of each embodiment meets or exceeds that of traditional solutions, with significantly better air-blowing distance and a compact process, making it suitable for large-scale industrial production. By using innovative water-blocking microsphere technology, it replaces traditional water-blocking methods that are highly polluting and energy-intensive, offering significant advantages in terms of green environmental protection and energy saving.

[0077] 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 dry water-blocking optical cable based on water-blocking microspheres, characterized in that, include: Center reinforcement; Multiple optical units are twisted together on the outer periphery of the central reinforcing member to form a cable core; A sheath layer is fitted over the outside of the cable core, and a gap is formed between the sheath layer and the cable core; Water-soluble water-blocking microspheres are filled in the gaps between the sheath layer and the cable core, and between the cable core and the central reinforcing member; the water-soluble water-blocking microspheres have a core-shell structure, wherein the core layer is water-blocking powder and the shell layer is a water-soluble polymer material. The optical unit includes a loose tube and an optical guide element disposed inside the loose tube; the outer surface of the loose tube is coated with a hot melt adhesive coating, or the outer surface of the loose tube is treated with electrostatic electret; the outer surface of the loose tube and the water-soluble water-blocking microspheres form an interfacial bond through the hot melt adhesive coating or the electrostatic electret treatment. The water-soluble water-blocking microspheres include: The first type of microspheres has a particle size of 400~500 μm and a mass percentage of 60%~70%. The second type of microspheres has a particle size of 200~300 μm and a mass percentage of 20%~30%. The third type of microspheres has a particle size of 50~100 μm and a mass percentage of 5%~10%.

2. The dry water-blocking optical cable based on water-blocking microspheres according to claim 1, characterized in that, The difference between the preset twist pitch and the measured twist pitch after untwisting of the optical cable is ≤10mm.

3. The dry water-blocking optical cable based on water-blocking microspheres according to claim 1, characterized in that, The water-blocking powder is loaded into the core-shell structure at an amount of 20-60% wt.

4. The dry water-blocking optical cable based on water-blocking microspheres according to any one of claims 1-3, characterized in that, The water-blocking powder includes one or more of sodium polyacrylate and acrylamide; and / or, The water-soluble polymeric material includes one or more of polyvinyl alcohol, polyethylene glycol, chitosan, and sodium alginate.

5. A method for preparing a dry water-blocking optical cable based on water-blocking microspheres, characterized in that, Includes the following steps: Water-soluble water-blocking microspheres are prepared, wherein the water-soluble water-blocking microspheres have a core-shell structure, wherein the core layer is water-blocking powder and the shell layer is a water-soluble polymer material; An optical unit is fabricated, the optical unit comprising a loose tube and an optical guide element disposed inside the loose tube; Multiple optical units are twisted together around a central reinforcing member to form a cable core, and the water-soluble water-blocking microspheres are sprayed into the gaps between the cable cores after twisting. A sheath layer is extruded onto the outside of the coated cable core; Before the optical units are stranded, a hot melt adhesive coating is applied to the loose tube surface of the optical units; When spraying the water-soluble water-blocking microspheres, compressed air with a temperature higher than the melting point of the hot melt adhesive is used as the delivery medium; or Before the optical units are stranded, the surface of the loose tube of the optical units is subjected to electrostatic electret treatment to make it carry static charge; the water-soluble water-blocking microspheres are electrically neutral or carry opposite charges, and during spraying, the water-soluble water-blocking microspheres are adsorbed onto the surface of the loose tube under the action of electrostatic attraction. The water-soluble water-blocking microspheres include: The first type of microspheres has a particle size of 400~500 μm and a mass percentage of 60%~70%. The second type of microspheres has a particle size of 200~300 μm and a mass percentage of 20%~30%. The third type of microspheres has a particle size of 50~100 μm and a mass percentage of 5%~10%.

6. The method for preparing a dry water-blocking optical cable based on water-blocking microspheres according to claim 5, characterized in that, The hot melt adhesive has a melting point of 80~120℃, and the compressed air has a temperature of 100~150℃.

7. The dry water-blocking optical cable based on water-blocking microspheres according to claim 6, characterized in that, The extrusion temperature of the sheath layer is 150~250℃.

8. The dry water-blocking optical cable based on water-blocking microspheres according to any one of claims 5-7, characterized in that, The water-blocking powder is loaded into the core-shell structure at an amount of 20-60% wt.

9. The dry water-blocking optical cable based on water-blocking microspheres according to any one of claims 5-7, characterized in that, The water-blocking powder includes one or more of sodium polyacrylate and acrylamide; and / or, The water-soluble polymeric material includes one or more of polyvinyl alcohol, polyethylene glycol, chitosan, and sodium alginate.

10. The dry water-blocking optical cable based on water-blocking microspheres according to any one of claims 5-7, characterized in that, The difference between the preset twist pitch and the measured twist pitch after untwisting of the optical cable is ≤10mm.

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