Application of efficient viscous compound material in oxygen barrier flame retardant material

Abstract

The invention relates to the technical field of high polymer materials and flame retardance, in particular to application of an efficient viscous compound material in oxygen barrier flame retardant materials, flame retardant polyolefin with hydroxyl is added into a high-shear twin-screw extruder, nano layered silicate and a reactive high polymer tackifier are sequentially added for reactive extrusion after melting, and the flame retardant polyolefin is obtained. And adding a micron-sized inorganic flame retardant and a carbon aid to the downstream of an extruder for blending, and finally cooling and pelletizing through an underwater pelletizing system to obtain the high-efficiency viscous compound material. According to the invention, a chemical bonding compatibilizing and toughening system is constructed through in-situ reaction of maleic anhydride grafted polypropylene and epoxy group functionalized SEBS, and complete stripping of nano-montmorillonite is realized by combining a step-by-step extrusion process, so that the problem that the mechanical property and flame retardance of a traditional high-filling flame-retardant material are difficult to consider at the same time is solved; the material has high limit oxygen index, high carbon residue rate and excellent tensile property, and the oxygen barrier layer is endowed with excellent mechanical toughness.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of high polymer materials and flame-retardant technology, and particularly relates to application of a high-efficiency adhesive compound material in an oxygen barrier flame-retardant material. BACKGROUND

[0002] Fireproof cables are widely used in emergency systems of high-rise buildings, subway tunnels, nuclear power plants and places with high population density, such as fire-fighting, monitoring, alarm and communication lines, as core components to ensure the normal operation of key lines under fire conditions.

[0003] Traditional fireproof cables usually use mica tape winding and other methods to achieve fire resistance and oxygen barrier, but the process is complex, the production efficiency is low, and the cables made have high rigidity and poor flexibility, which can easily cause damage to the fireproof layer during installation, thereby affecting the reliability. Therefore, developing a high-performance polymer-based fireproof oxygen barrier layer material that can be directly extruded and coated has become an important direction for the development of the industry.

[0004] The existing extrudable fireproof oxygen barrier layer material still faces many technical challenges. In order to meet the high-level flame retardant requirements, it is necessary to add a very high filling amount of inorganic flame retardant to the base resin such as polyolefin. Such a high filling amount can severely damage the mechanical properties of the material, resulting in a significant decrease in tensile strength and elongation at break, making the material brittle and hard, and limiting its practicality. In addition, the poor compatibility between polar inorganic fillers and non-polar polyolefin matrix leads to weak interfacial adhesion and easy aggregation of fillers, which not only affects the stability of material performance, but also makes it difficult to form a firm bond with the cable core or inner insulation. At the same time, the high filling system has poor flowability and low melt strength in the molten state, and is prone to melt rupture or "sagging" during high-speed extrusion, making it difficult to accurately control the thickness of the oxygen barrier layer and seriously affecting the production efficiency and product quality of the fireproof cable. SUMMARY

[0005] The application provides application of a high-efficiency adhesive compound material in an oxygen barrier flame-retardant material, aiming to optimize the material formula and process, improve the flame-retardant effect and mechanical properties of the cable oxygen barrier layer, reduce production costs, and meet the demand for high-efficiency and economical oxygen barrier materials for fireproof cables.

[0006] In a first aspect, the application provides a method for preparing a high-efficiency adhesive compound material, comprising the following steps:

[0007] S1: A flame-retardant polyolefin with hydroxyl groups is added to the first feed port of a high-shear twin-screw extruder. After it melts, nano-layered silicate is added through the first side feed port, and then a reactive polymer thickener is added through the second side feed port. The first stage of reactive melt extrusion is carried out at 170-200℃ and a screw speed of 300-500rpm. The material residence time in the barrel is 90-120 seconds, and a nano-composite modified masterbatch is obtained.

[0008] S2: At the downstream feed port of the extruder, micron-sized inorganic flame retardant and char-aiding agent are added to the nanocomposite modified masterbatch melt obtained in step S1 for a second stage of melt blending.

[0009] S3: The blend obtained in step S2 is cooled and pelletized using an underwater pelletizing system to obtain the high-efficiency viscous composite material.

[0010] As a further improvement of the present invention, the hydroxyl-containing flame-retardant polyolefin in step S1 is polypropylene grafted with 0.5-1.5 wt% maleic anhydride.

[0011] The reactive polymeric tackifier is an epoxy-functionalized styrene-ethylene-butene-styrene block copolymer with an epoxy value of 0.3-0.8 mol / 100g.

[0012] As a further improvement of the present invention, the nano-layered silicate in step S1 is an organomontmorillonite treated with dimethyl distearate ammonium chloride, and its initial interplanar spacing is greater than 2.5 nm as determined by X-ray diffraction.

[0013] As a further improvement of the present invention, the micron-sized inorganic flame retardant in step S2 is magnesium hydroxide with calcium stearate surface treatment, and its D90 particle size is less than 10 microns.

[0014] The charcoal aid is pentaerythritol phosphate.

[0015] Secondly, the present invention provides a highly efficient viscous compound material, which is prepared by the method described in any embodiment of the first aspect, and its material structure satisfies the following limitations:

[0016] a. Using X-ray diffraction analysis, the characteristic diffraction peaks of the nanolayered silicate disappeared in the range of 2θ = 2°-10°;

[0017] b. Observation using transmission electron microscopy shows that the nanolayered silicate is dispersed in the continuous polymer phase in a sheet structure with a thickness of less than 5 nm, and the micron-sized inorganic flame retardant particles are coated by the polymer matrix containing nanosheets.

[0018] As a further improvement of the present invention, the high-efficiency adhesive compound material, by weight, comprises the following components:

[0019] Flame-retardant polyolefins with hydroxyl groups: 50-70 parts;

[0020] Reactive polymeric thickener: 5-15 parts;

[0021] Micron-sized inorganic flame retardant: 20-40 parts;

[0022] Nanolayered silicate: 1-5 parts;

[0023] Charcoal aid: 2-8 parts.

[0024] As a further improvement of the present invention, the compound material is heated to 800°C at a rate of 10°C / min under a nitrogen atmosphere for thermogravimetric analysis (TGA), and the carbon residue at this temperature is 40-55 wt%; and the carbon residue is subjected to a compression test, and its compressive strength is greater than 0.5 MPa.

[0025] As a further improvement of the present invention, the melt flow rate of the compound material under the conditions of 190°C and 5.0 kg load is less than 1.0 g / 10 min, and its storage modulus G' is greater than its loss modulus G at an angular frequency of 0.1 rad / s, as measured by a dynamic rheometer.

[0026] Thirdly, the present invention also provides a method for applying a high-efficiency adhesive composite material to the oxygen barrier layer of fire-resistant cables, comprising the following steps:

[0027] S1: Preprocessing, including:

[0028] S101: Dry the high-efficiency viscous compound material according to any one of claims 5 to 8 in a vacuum oven at 80-90°C for 4-6 hours;

[0029] S102: The cable core to be covered, i.e., the combination of conductor and insulation layer, is heated to 90-110℃ by an infrared preheating device;

[0030] S2: Co-extrusion coating. The compound material processed in step S101 is used as the inner layer material and fed together with the outer sheath material into their respective extruders. They are simultaneously extruded and coated onto the cable core preheated in step S102 in a molten state through a dual-channel cross co-extrusion die head. A melt pump is provided between the extruder of the compound material and the co-extrusion die head to stabilize the melt output flow rate.

[0031] S3: Gradient cooling, the wrapped cable is passed through a multi-segment gradient cooling water tank in sequence, the water temperature of the first segment of the water tank is controlled at 60-70℃, and the water temperature of the second segment is controlled at 20-30℃;

[0032] S4: Online inspection and winding. The cooled cable is passed through a laser diameter gauge and an ultrasonic thickness gauge, and finally wound up by a constant tension winding device.

[0033] As a further improvement of the present invention, the process parameters in the method satisfy the following conditions:

[0034] In step S2, the extruder body temperature of the compound material is set in a zoned increasing temperature range of 150℃, 165℃, 175℃, and 185℃ from the feed inlet to the die head connection. The co-extrusion die head temperature is set to 180-185℃. The speed fluctuation rate of the melt pump is controlled within ±0.1%. The cable pulling speed is 50-100 meters / minute.

[0035] In step S3, the cable stays in the first section of the water tank for 10-15 seconds;

[0036] In step S4, the tension of the constant tension winding device is set to 5-10N.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention constructs a chemically bonded compatibilizing and toughening system through the in-situ reaction of maleic anhydride-grafted polypropylene and epoxy-functionalized SEBS. Combined with a stepwise extrusion process, it achieves complete exfoliation and dispersion of nano-montmorillonite. This allows the material to maintain excellent tensile strength and superior elongation at break while achieving extremely high limiting oxygen index and high char residue. It solves the technical problem of traditional high-filler flame retardant materials being unable to balance flame retardancy and mechanical properties, and endows the oxygen barrier layer with excellent mechanical toughness to resist external damage.

[0039] 2. The nano-montmorillonite physical network constructed in the polymer matrix in this invention enhances the viscoelastic properties of the composite material in the molten state, exhibiting an extremely low melt flow rate and a near-solid-state response with a storage modulus far greater than the loss modulus. The excellent melt strength effectively suppresses the sag phenomenon of the cable during high-speed extrusion, ensuring that the oxygen barrier layer is uniformly and stably coated on the cable core, achieving high-precision control of thickness and concentricity, and improving production efficiency and product yield.

[0040] 3. The reactive polymer tackifier used in this invention significantly improves the adhesion of the composite material to the polyolefin insulation layer such as cross-linked polyethylene through the in-situ reaction of functional groups. The interfacial peel strength is far superior to that of conventional materials. The strong adhesion ensures that the oxygen barrier layer does not delaminate and peel off between the oxygen barrier layer and the adjacent insulation layer, ensuring that the fireproof cable still has long-term structural stability and reliability under complex working conditions such as bending and vibration.

[0041] 4. Through precise design of the feeding sequence and screw functional areas, this invention creates an optimal process window for nanomaterial exfoliation, polymer reaction, and inorganic filler dispersion, resolves the contradiction between the dispersion and reaction requirements of each component, protects the equipment from excessive wear of high-hardness fillers, and ensures the stable reproduction of the excellent performance of the final product, providing solid technical support for the large-scale production of high-performance fireproof oxygen barrier materials. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method for preparing high-efficiency viscous composite materials according to the present invention;

[0043] Figure 2 This is a flow chart of the high-efficiency viscous compound material of the present invention;

[0044] Figure 3 This is a flowchart illustrating the application method of the high-efficiency viscous compound material of the present invention in oxygen barrier flame arrestor. Detailed Implementation

[0045] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with an embodiment or example that are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] 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.

[0048] Example 1, see Figure 1 Preparation of high-efficiency viscous composite materials

[0049] This embodiment describes in detail a method for preparing a high-efficiency viscous composite material.

[0050] 1. Raw material specifications and selection criteria:

[0051] (1) Hydroxyl-containing flame-retardant polyolefin (matrix resin): A commercially available maleic anhydride-grafted polypropylene (PP-g-MAH) with the brand name CEFOR-PPGMA08 was selected. Its melt index (MFR, 230℃, 2.16kg) was 10g / 10min, the maleic anhydride (MAH) grafting rate was 1.0wt%, and the acid value was 5.0mgKOH / g. The reason for choosing this material is that its anhydride groups have high reactivity in the molten state and can react in situ with the subsequently added epoxy groups, thus providing a chemical basis for constructing a strong polymer interface layer. At the same time, the moderate melt index is beneficial to the processing fluidity under high filling conditions.

[0052] (2) Reactive polymeric tackifiers (interface modifiers and toughening agents): A commercially available epoxy-functionalized SEBS with the brand name FG1901 G was selected. Its styrene content is 30wt% and its epoxy value is 0.5mol / 100g. This material was chosen not only because it provides excellent viscosity and toughness, but more importantly because the epoxy groups at the end or side chain can undergo ring-opening esterification with the anhydride groups of PP-g-MAH during melt blending to form a "PP-SEBS" chemically bonded copolymer. This can effectively eliminate the interface between components and achieve a leap from physical blending to chemical modification, thereby enhancing the toughness, interfacial bonding force and coating ability of inorganic fillers of the material.

[0053] (3) Nanolayered silicate (nano-synergistic flame retardant and mechanical reinforcement): A commercially available organomontmorillonite (OMMT) with the name FR-201 was selected. This montmorillonite was surface-organized using dimethyl distearate ammonium chloride. Its cation exchange capacity (CEC) was 95 meq / 100g. The initial (001) interplanar spacing was measured to be 2.8 nm by X-ray diffraction (XRD). The selection of organomontmorillonite with a high initial interplanar spacing is beneficial to the insertion of polymer melt chain segments, laying a key foundation for the subsequent realization of complete nanoscale exfoliation and dispersion and the construction of a "maze effect" barrier network.

[0054] (4) Micron-sized inorganic flame retardant (main flame retardant): A commercially available magnesium hydroxide (Mg(OH)2) with calcium stearate surface treatment, brand name FR-M85S, was selected. Its D50 particle size is 1.5 microns, D90 particle size is 8.5 microns, whiteness is >95%, and BET specific surface area is 8 m². 2 / g, through surface treatment, effectively reduces the surface polarity of magnesium hydroxide, significantly improves its compatibility with non-polar polyolefin matrix, thereby ensuring its uniform dispersion in the matrix and avoiding material performance degradation due to agglomeration.

[0055] (5) Charging aid (char-forming synergist): Commercial-grade pentaerythritol phosphate (PEPA) is selected. It is dehydrated and esterified at high temperature, and can react with polymer degradation products to form a dense and stable phosphorus-carbon structure carbon layer. This dense carbon layer can play a synergistic protective role with the MgO ceramic layer formed after the decomposition of Mg(OH)2, effectively isolating heat and oxygen, and significantly improving the residual carbon rate and high-temperature structural stability of the material.

[0056] 2. Formula (by weight):

[0057] Table 1 Formulation of High-Efficiency Adhesive Compound Material

[0058]

[0059]

[0060] As shown in Table 1, the formulation of this embodiment takes into account the synergistic effect between the base resin, reactive tackifier, main flame retardant and various synergists.

[0061] 3. Preparation process and equipment parameters:

[0062] The preparation process in this embodiment uses a ZSK-75Mc 18 This co-rotating twin-screw extruder has a length-to-diameter ratio of 48:1. The equipment is equipped with a high-precision loss-in-weight feeder and a melt pump. The screw assembly is carefully designed to achieve step-by-step functional processing.

[0063] Screw configuration design:

[0064] Zones 1-3 (Main feeding and conveying zone): Large lead conveying elements.

[0065] Zones 4-6 (Nanointercalation and stripping zones): Composed of multiple high-shear kneading blocks (staggered at 45°) and reverse-threaded elements, providing the necessary high shear stress field and residence time for the stripping of OMMT and the initial dispersion of SEBS.

[0066] Zones 7-8 (Reactive Extrusion Zone): Composed of a weak shear kneading block (staggered angle 30°) and a conveying element, providing adequate mixing and reaction time to promote in-situ grafting of SEBS and PP-g-MAH.

[0067] Zones 9-10 (Secondary Feeding and Dispersion Zone): Side feeding ports are provided. The screw elements are mainly large-lead conveying elements, supplemented by a small number of toothed mixing elements, to achieve rapid and uniform dispersion of inorganic fillers and avoid excessive shearing.

[0068] Zones 11-12 (homogenization and pressure building zone): Standard conveying elements and kneading blocks are combined for final homogenization and pressure building is stabilized by the melt pump in front of the die head. This finely functional zone screw design ensures that each material completes specific physical or chemical changes under the most suitable conditions, achieving a high degree of controllability and efficiency in the process.

[0069] S1: Reactive extrusion of nanocomposite modified masterbatch

[0070] PP-g-MAH is fed into the feed through the loss-in-weight weigher at a rate of 60 kg / h.

[0071] At the first side feed port of zone 4, pre-dried OMMT is fed in at a rate of 3 kg / h through a dedicated powder loss-in-weight scale.

[0072] At the second side feed port in zone 7, molten epoxy SEBS preheated to 180°C is injected at a rate of 10 kg / h through a gear melt pump with heating and insulation.

[0073] Process parameters for this stage: screw speed 400 rpm, temperature in each zone (°C):

[0074] C1 / 170, C2 / 185, C3 / 195, C4 / 200, C5 / 200, C6 / 195, C7 / 190, C8 / 190. The residence time of the material at this stage is precisely controlled at 105 seconds to ensure sufficient reaction and dispersion. This sequential feeding method allows OMMT to be preferentially and fully exfoliated in the high-shear environment of the pure polymer melt, avoiding interference from subsequent fillers. The subsequently added reactive SEBS can fully react with the matrix to form a uniform nanocomposite modified masterbatch, providing an ideal matrix environment for subsequent coating of inorganic flame retardants.

[0075] S2: Blending of inorganic flame retardants

[0076] At the downstream feed port of zone 9, 32 parts of Mg(OH)2 and 5 parts of PEPA powder, which have been pre-mixed in a high-speed mixer at 1000 rpm for 5 minutes, are added at a rate of 37 kg / h through another loss-in-weight scale.

[0077] The process parameters for this stage are C9 / 185, C10 / 180, and C11 / 175. The lower temperature setting is to avoid local overheating caused by inorganic fillers. This downstream feeding design cleverly avoids the wear of high-hardness inorganic fillers on the screw's precision kneading elements and allows for gentle mixing in the weak shear zone, protecting the formed nano-dispersion structure from damage and maximizing the overall performance of the material.

[0078] S3: Cooling and pelletizing

[0079] After homogenization in 12 zones, the blend melt is pumped into the extruder head and extruded into multiple 3mm diameter strips. These strips immediately enter the underwater pelletizing system, where the circulating water temperature is 55℃ and the cutter speed is dynamically matched with the extrusion speed. This process ultimately produces uniform cylindrical pellets with a length and diameter of 3mm. Underwater pelletizing allows for rapid and uniform cooling and shaping, resulting in pellets with regular shapes and no dust, which is beneficial for subsequent conveying, drying, and extrusion processing.

[0080] In order to objectively evaluate the advancement of the technical solution adopted in Embodiment 1 of the present invention, the following two comparative embodiments are established to compare the two dimensions of process method and key components, so as to more profoundly reveal the inventiveness of the present invention.

[0081] Compared to Example 1, the conventional one-step blending method

[0082] This comparative example aims to highlight the technical advantages of the stepwise reactive extrusion process used in this invention, which is prepared using a conventional one-step method similar to existing technologies.

[0083] Formula: exactly the same as in Example 1.

[0084] Preparation method: All components (PP-g-MAH, SEBS, OMMT, Mg(OH)2, PEPA) were premixed in a high-speed mixer for 10 minutes. Then the mixture was added at once from the main feed port of a twin-screw extruder. The extruder temperature profile was set to a smooth temperature rise profile from 170°C to 200°C, and the screw speed was 400 rpm. Except for the feeding method, the other conditions were the same as in Example 1.

[0085] Compared to Example 2, a non-reactive tackifier was used.

[0086] This comparative example aims to verify the key technical role of the "reactive polymeric tackifier" described in this invention, which replaces this key reactive component with a single-function non-reactive tackifying resin.

[0087] Formulation: Replace 10 parts of "epoxy-functionalized SEBS" in Example 1 with 10 parts of conventional hydrogenated C5 petroleum resin, with all other components and amounts exactly the same.

[0088] Preparation method: The preparation method is exactly the same as that in Example 1 to ensure consistency of process conditions.

[0089] Example 2, see Figure 2 Structural characterization and performance testing of composite materials

[0090] To visually demonstrate the significant structural and performance improvements of the preparation method (Example 1) disclosed in this invention compared to the traditional method (Comparative Example 1) and the replacement of key components (Comparative Example 2), the materials obtained in the above examples will be comprehensively characterized in terms of microstructure and tested in terms of macroscopic performance, and a detailed comparative analysis will be conducted.

[0091] 1. Microstructure characterization

[0092] XRD analysis: An advanced X-ray diffractometer was used with CuKα radiation and a scanning range of 2θ = 2°-10°.

[0093] Example 1: No characteristic diffraction peaks belonging to OMMT were observed within the scanning range, indicating that its crystal structure was completely destroyed, achieving nanoscale exfoliation and satisfying the requirements of claim 5(a).

[0094] Compared with Example 1, a broad diffuse peak was observed at 2θ≈4.5°, indicating that OMMT mainly exists as an intercalation structure with incomplete exfoliation. The presence of a large amount of inorganic filler interferes with the high shear environment required for polymer chain insertion and exfoliation.

[0095] TEM observation was performed using a field emission transmission electron microscope to observe the ultrathin sections (thickness ~80 nm).

[0096] Example 1: A large number of randomly dispersed dark linear materials (OMMT nanosheets) with a thickness of less than 5 nm are clearly visible in the field of view, forming a physical network that runs through the entire matrix. Micron-sized Mg(OH)2 particles are well wetted and coated by this nanocomposite matrix, satisfying the requirements of claim 5(b). This completely exfoliated and dispersed nanostructure and ideal coating of flame retardant particles are the microstructural basis for the material of the present invention to simultaneously obtain excellent mechanical properties, high flame retardant efficiency and high melt strength.

[0097] Compared with Example 1, a larger OMMT aggregate composed of several stacked layers can be observed, and there are obvious voids around the Mg(OH)2 particles, indicating poor interfacial bonding.

[0098] Compared with Example 2, although the dispersion of OMMT was similar to that of Example 1, there was obvious debonding at the interface between Mg(OH)2 particles and the polymer matrix, with a clear boundary. This directly demonstrates the decisive improvement effect of the chemical bonds formed by reactive SEBS on interfacial compatibility.

[0099] 2. Performance test data comparison

[0100] Table 2 Comparison of material performance test data for each embodiment

[0101]

[0102]

[0103] From Table 2, we can see that, compared to Comparative Example 1 and Comparative Example 2, Example 1 yields the following results:

[0104] Mechanical properties: The mechanical properties of Example 1 are comprehensively and significantly better than those of the two comparative examples, which strongly proves that the preparation method and component selection of the present invention, through optimization of the microstructure, have achieved a synergistic improvement in the mechanical strength and toughness of the material.

[0105] Flame retardancy and char formation: Example 1 has the highest LOI and char rate, as well as the greatest char body strength. This is attributed to the "maze effect" and ceramic skeleton formed by the exfoliated nano-montmorillonite, as well as the synergistic char formation of PEPA, which ultimately endows the material with excellent flame retardancy and structural integrity at high temperatures.

[0106] Rheological properties: The extremely low MFR and G'>G" characteristics of Example 1 confirm that a physical network structure composed of nanosheets is formed inside the material, which gives the material excellent melt strength, which is crucial for preventing melt dripping and deformation in high-temperature or cable extrusion applications.

[0107] Interface performance: The interfacial peel strength of Example 1 with cross-linked polyethylene (XLPE) is much higher than that of the control group, which directly proves the beneficial effect of the "high viscosity" of the material of the present invention, ensuring that it can be firmly bonded to the adjacent layers as a functional layer, and guaranteeing the long-term reliability of the final product.

[0108] Example 3, see Figure 3 Preparation and application of oxygen barrier layer for fireproof cables

[0109] The above structural characterization and performance test results have fully demonstrated the superiority of the high-efficiency viscous composite material prepared in Example 1. In order to transform the advantages of this material into the performance advantages of the final product and fully embody the technical solution of the present invention, this example will elaborate in detail how to prepare this high-performance material into a fireproof cable oxygen barrier layer whose structure and performance meet high standards through a set of precise industrial application methods.

[0110] 1. Production line and process flow:

[0111] Cable to be processed: A cable core with a diameter of 10mm, consisting of multiple copper conductors and a 2.0mm thick cross-linked polyethylene (XLPE) insulation layer.

[0112] Equipment: A high-precision co-extrusion production line consistent with the above description is used.

[0113] 2. Detailed application steps:

[0114] S1: Preprocessing

[0115] S101: Material drying: The granules from Example 1 are dried in a vacuum hopper with dehumidification function at 85°C with circulating hot air for 5 hours to ensure that the moisture content is below 200ppm. This step is crucial for eliminating defects such as bubbles and voids in subsequent processing and ensuring that the oxygen barrier layer is dense and uniform.

[0116] S102: Cable core preheating and surface treatment. Before entering the machine head, the cable core passes through a 2-meter-long infrared preheating channel to uniformly raise its surface temperature to 105°C. This not only eliminates moisture and stress on the surface of the cable core, but also promotes physical wetting and molecular chain diffusion between the melt and the insulation layer. This is a key process to ensure high interfacial bonding and can effectively prevent delamination or peeling of the oxygen barrier layer during use.

[0117] S2: High-precision co-extrusion coating

[0118] The process parameters for the oxygen barrier layer extruder (Φ70mm) and the sheath layer extruder (Φ90mm) are set as follows:

[0119] The temperature setting for the oxygen barrier extruder is: 150℃ (feeding section) -> 165℃ -> 175℃ -> 185℃ (compression homogenization section). This increasing temperature curve ensures that the material is fully plasticized without excessive degradation.

[0120] Temperature settings for the sheath layer extruder (low-smoke halogen-free polyolefin): 140℃->155℃->165℃->170℃.

[0121] Melt pump: By setting a constant speed, the output flow fluctuation rate of the oxygen barrier melt is controlled within ±0.1%. The use of melt pump improves the stability of melt delivery and is the core technical means to achieve uniform thickness and high cross-sectional concentricity of the oxygen barrier layer.

[0122] Co-extrusion die head: A dual-channel cross-type die head is adopted, and the die head temperature is kept constant at 183℃. By adjusting the taper and sizing length of the inner and outer dies, the thickness of the oxygen barrier layer is precisely controlled to be 1.5mm and the thickness of the outer sheath is 2.0mm.

[0123] Traction speed: precisely matched to the extrusion rate, set at 80 meters per minute.

[0124] S3: Gradient Controlled Cooling

[0125] The wrapped cable immediately enters a multi-section cooling water tank with a total length of 12 meters.

[0126] Section 1 (Slow Cooling Zone, 2 meters long): The water temperature is precisely controlled at 65°C through a heat exchanger. The cable remains in this section for approximately 1.5 seconds, allowing the temperature of the inner and outer layers of the polymer to drop slowly and evenly, releasing most of the heat of crystallization and internal stress.

[0127] The second section (strong cooling zone, 10 meters long): uses 25°C circulating water for thorough cooling, so that the cable is fully shaped before entering the next process. Through a gradient cooling process that starts slowly and then accelerates, internal stress concentration, warping deformation or surface micro-cracks caused by sudden cooling are effectively avoided, significantly improving the dimensional stability and long-term reliability of the final cable product.

[0128] S4: Online quality monitoring and constant tension winding

[0129] After cooling, the cables pass through an integrated online testing system.

[0130] Laser diameter gauge: Simultaneous dual-axis measurement, real-time monitoring of the final outer diameter.

[0131] Ultrasonic thickness gauge: It accurately measures the thickness and concentricity of the oxygen barrier layer and the sheath layer by using the time difference of ultrasonic echo.

[0132] The test data is used to form a closed-loop control system via PLC, fine-tuning the traction speed or melt pump speed to ensure that the concentricity of the oxygen barrier layer cross-section is consistently above 96%, and the thickness tolerance is within ±0.05mm. Through online closed-loop control, the production process is made intelligent and product quality is standardized, significantly improving production efficiency and yield.

[0133] Finally, the finished cable is wound smoothly onto the I-beam reel with a constant tension of 8N by a constant tension winding machine with a swing arm tension sensor. Constant tension winding can prevent the cable from being stretched and deformed, protecting the final dimensional accuracy and mechanical properties of the product from damage.

[0134] Example 4: Investigating the effect of inorganic flame retardant content on mechanical properties

[0135] This embodiment aims to verify the special enhancement effect produced by the synergistic effect of each component in the technical solution of the present invention. Based on Example 1, the amount of micron-sized inorganic flame retardant (magnesium hydroxide) is increased by about 10%, and the mechanical properties are compared and tested.

[0136] formula:

[0137] Table 3 Comparison of the formulations of Example 4 and Example 1

[0138]

[0139]

[0140] As shown in Table 3, Example 4 mainly adjusted the ratio of the main flame retardant to the matrix resin.

[0141] Preparation method: The preparation method is exactly the same as that in Example 1 to ensure consistency of process conditions.

[0142] Performance testing and analysis are shown in Table 4:

[0143] Table 4. Mechanical property test results of Example 4 and Example 1

[0144]

[0145] Table 4 presents the mechanical property test results for Example 4 and Example 1. The data clearly show that when the amount of inorganic flame retardant magnesium hydroxide added increases by 10%, the tensile strength and elongation at break of the material both increase by about 5%. This invention constructs a robust "organic-inorganic" interface layer through a reactive thickener, while the completely exfoliated nano-montmorillonite network further enhances the matrix's binding ability to the filler. Under this synergistic effect, the inorganic flame retardant particles transform from simple fillers into effective stress transfer points and reinforcements, thereby achieving an anomalous enhancement of the overall mechanical properties of the material while improving flame retardancy.

Claims

1. A method for preparing high-efficiency viscous composite materials, characterized in that, Includes the following steps: S1: A flame-retardant polyolefin with hydroxyl groups is added to the first feed port of a high-shear twin-screw extruder. After it melts, nano-layered silicate is added through the first side feed port, and then a reactive polymer thickener is added through the second side feed port. The first stage of reactive melt extrusion is carried out at 170-200℃ and a screw speed of 300-500rpm. The material residence time in the barrel is 90-120 seconds, and a nano-composite modified masterbatch is obtained. S2: At the downstream feed port of the extruder, micron-sized inorganic flame retardant and char-aiding agent are added to the nanocomposite modified masterbatch melt obtained in step S1 for a second stage of melt blending. S3: The blend obtained in step S2 is cooled and pelletized using an underwater pelletizing system to obtain the high-efficiency viscous composite material.

2. The method according to claim 1, characterized in that, The hydroxyl-containing flame-retardant polyolefin in step S1 is polypropylene grafted with 0.5-1.5 wt% maleic anhydride. The reactive polymeric tackifier is an epoxy-functionalized styrene-ethylene-butene-styrene block copolymer with an epoxy value of 0.3-0.8 mol / 100g.

3. The method according to claim 1, characterized in that, The nanolayered silicate in step S1 is an organomontmorillonite treated with dimethyl distearate ammonium chloride, and its initial interplanar spacing is greater than 2.5 nm as determined by X-ray diffraction.

4. The method according to claim 1, characterized in that, The micron-sized inorganic flame retardant in step S2 is magnesium hydroxide with calcium stearate surface treatment, and its D90 particle size is less than 10 microns. The charcoal aid is pentaerythritol phosphate.

5. A high-efficiency adhesive compound material, characterized in that, Prepared by the method according to any one of claims 1 to 4, and having the following material structure: a. Using X-ray diffraction analysis, the characteristic diffraction peaks of the nanolayered silicate disappeared in the range of 2θ = 2°-10°; b. Observation using transmission electron microscopy shows that the nanolayered silicate is dispersed in the continuous polymer phase in a sheet structure with a thickness of less than 5 nm, and the micron-sized inorganic flame retardant particles are coated by the polymer matrix containing nanosheets.

6. The high-efficiency adhesive compound material according to claim 5, by weight, comprises: Flame-retardant polyolefins with hydroxyl groups: 50-70 parts; Reactive polymeric thickener: 5-15 parts; Micron-sized inorganic flame retardant: 20-40 parts; Nanolayered silicate: 1-5 parts; Charcoal aid: 2-8 parts.

7. The high-efficiency adhesive compound material according to claim 5 or 6, characterized in that, The compound material was heated to 800°C at a rate of 10°C / min under a nitrogen atmosphere and subjected to thermogravimetric analysis (TGA). The carbon residue at this temperature was 40-55 wt%, and the carbon residue was subjected to a compression test, with a compressive strength greater than 0.5 MPa.

8. The high-efficiency adhesive compound material according to claim 5, characterized in that, The melt flow rate of the compound material under 190℃ and 5.0kg load conditions is less than 1.0g / 10min, and its storage modulus G' is greater than its loss modulus G at an angular frequency of 0.1rad / s, as measured by a dynamic rheometer.

9. A method for applying a high-efficiency adhesive composite material to the oxygen barrier layer of fire-resistant cables, characterized in that, Includes the following steps: S1: Preprocessing, including: S101: Dry the high-efficiency viscous compound material according to any one of claims 5 to 8 in a vacuum oven at 80-90°C for 4-6 hours; S102: The cable core to be covered, i.e., the combination of conductor and insulation layer, is heated to 90-110℃ by an infrared preheating device; S2: Co-extrusion coating. The compound material processed in step S101 is used as the inner layer material and fed together with the outer sheath material into their respective extruders. They are simultaneously extruded and coated onto the cable core preheated in step S102 in a molten state through a dual-channel cross co-extrusion die head. A melt pump is provided between the extruder of the compound material and the co-extrusion die head to stabilize the melt output flow rate. S3: Gradient cooling, the wrapped cable is passed through a multi-segment gradient cooling water tank in sequence, the water temperature of the first segment of the water tank is controlled at 60-70℃, and the water temperature of the second segment is controlled at 20-30℃; S4: Online inspection and winding. The cooled cable is passed through a laser diameter gauge and an ultrasonic thickness gauge, and finally wound up by a constant tension winding device.

10. The application method according to claim 9, characterized in that, The process parameters in the method satisfy the following conditions: In step S2, the extruder body temperature of the compound material is set in a zoned increasing temperature range of 150℃, 165℃, 175℃, and 185℃ from the feed inlet to the die head connection. The co-extrusion die head temperature is set to 180-185℃. The speed fluctuation rate of the melt pump is controlled within ±0.1%. The cable pulling speed is 50-100 meters / minute. In step S3, the cable stays in the first section of the water tank for 10-15 seconds; In step S4, the tension of the constant tension winding device is set to 5-10N.

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