Multi-layer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer and preparation method of multi-layer co-extrusion cable

Abstract

The invention relates to the technical field of cables, in particular to a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method of the multi-layer co-extrusion cable based on the low-smoke halogen-free flame-retardant composite layer, and the multi-layer co-extrusion cable structurally comprises a conductor layer, a double-layer insulating layer, a reinforced buffer layer and a composite sheath layer from inside to outside in sequence; wherein the double-layer insulating layer comprises an inner layer and an outer layer; the inner layer takes an ethylene-octylene copolymer as a core layer and takes a norbornene dianhydride grafted polyether ester elastomer as a shell layer, so that the material is endowed with high elasticity and impact resistance, and the cracking of the insulating layer is inhibited; the modified nano montmorillonite is dispersed into a nano lamellar barrier, so that heat diffusion is delayed, and low smoke and zero halogen are realized; the outer layer is composed of an ethylene-methyl acrylate matrix and di-tert-butyl phosphinic acid aluminum salt, the di-tert-butyl phosphinic acid aluminum salt is decomposed at high temperature to generate aluminum phosphate, a carbon layer is formed to isolate oxygen heat, and phosphorus-containing free radicals capture active free radicals to interrupt flame propagation.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and more specifically, to a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof. Background Art

[0002] With the acceleration of the process of modern industry and urbanization, as the core carrier for energy transmission and signal transfer, the requirements for the safety, reliability, and environmental protection of cables are becoming increasingly stringent; traditional cables (such as polyvinyl chloride insulated cables) will release a large amount of toxic hydrogen halide gas and thick smoke when burning, causing serious harm to people and equipment, so they are gradually replaced by low-smoke halogen-free flame-retardant cables.

[0003] However, traditional low-smoke halogen-free cables achieve flame retardancy by adding halogen-free flame retardants such as aluminum hydroxide and magnesium hydroxide, but the high filling amount results in too strong rigidity and insufficient flexibility of the material, and it is easy to crack due to stress concentration during laying or operation, especially prominent in large-size cables or armored structures. In view of this, we propose a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, so as to solve the problem that traditional low-smoke halogen-free cables achieve flame retardancy by adding halogen-free flame retardants such as aluminum hydroxide and magnesium hydroxide, but the high filling amount results in too strong rigidity and insufficient flexibility of the material, and it is easy to crack due to stress concentration during laying or operation as mentioned in the above background art.

[0005] To achieve the above purpose, the present invention provides a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer, and its structure from the inside to the outside is successively a conductor layer, a double-layer insulation layer, a reinforcing buffer layer, and a composite sheath layer; The double-layer insulation layer is composed of an inner layer and an outer layer; The inner layer adopts a core-shell structure nano-composite resin, where the core layer is ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene dicarboxylic anhydride, and modified nano-montmorillonite is dispersed in the shell layer, and the mass ratio of the core layer to the shell layer is 1:0.4 - 0.7; The outer layer is an elastomer-modified halogen-free flame-retardant layer, which is composed of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate, and its mass ratio is 1:0.3 - 0.5.

[0006] Preferably, the preparation method of the inner layer of the double-layer insulation layer is as follows: Pre-disperse 1% - 3% of the modified nano-montmorillonite by mass of the polyether ester elastomer and the polyether ester elastomer grafted with norbornene dicarboxylic anhydride in a high-speed mixer at a speed of 800 - 1200 rpm for 10 - 15 min; then add ethylene-octene copolymer for pre-mixing; The pre-mixed ethylene-octene copolymer and the polyether ester elastomer grafted with maleic anhydride and dispersed with modified nano-montmorillonite are added into a twin-screw extruder. The extrusion temperature is 150 - 200 °C, and the screw speed is 300 - 400 rpm to obtain the inner layer of the double-layer insulation layer.

[0007] The inner core layer uses an ethylene-octene copolymer core layer to provide high elasticity and flexibility, effectively relieving the bending stress of the cable; the shell layer uses a polyether ester elastomer grafted with maleic anhydride. Its anhydride groups undergo thermal decomposition at high temperatures, releasing active intermediates (such as carboxylate ions or free radicals). These intermediates can react with functional groups such as hydroxyl groups and amino groups in the polyether ester elastomer to form a three-dimensional cross-linked structure, thus promoting the formation of a carbon layer and significantly improving the flame retardancy efficiency. In addition, the modified montmorillonite is intercalated and dispersed through the interaction between its surface hydroxyl groups and the polar groups (such as ester groups) of the polyether ester elastomer. Its lamellar structure can extend the escape path of pyrolysis gases and reduce the combustion rate.

[0008] Preferably, the preparation method of the outer layer of the double-layer insulation layer is as follows: Aluminum di-tert-butyl phosphinate and vinyltrimethoxysilane are pre-dispersed in a high-speed mixer at a speed of 800 - 1000 rpm for 10 - 15 min; Then ethylene-methyl acrylate matrix and dilauryl thiodipropionate are added, and melt blending is carried out through a twin-screw extruder. The extrusion temperature is 160 - 210 °C, and the screw speed is 250 - 300 rpm to obtain the outer layer of the double-layer insulation layer.

[0009] The outer elastomer-modified halogen-free flame retardant layer realizes the unity of high flame retardancy efficiency and environmental protection characteristics through the synergistic effect of the ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate; the ethylene-methyl acrylate matrix has excellent flexibility, weather resistance, and processing performance, ensuring the stability of the insulation layer of the cable in a bending or vibrating environment; aluminum di-tert-butyl phosphinate, as a halogen-free flame retardant, significantly reduces the flame spread rate during combustion through endothermic decomposition and gas dilution mechanisms, while suppressing the release of soot and toxic gases, meeting the environmental protection requirements of low smoke and halogen-free.

[0010] At high temperatures, aluminum di-tert-butyl phosphinate decomposes to form aluminum phosphate and phosphorus-containing free radicals; aluminum phosphate, as an inorganic residue, forms a dense and continuous carbon layer on the material surface, effectively isolating oxygen and blocking heat transfer; phosphorus-containing free radicals (such as PO 2- ) combine with active free radicals (such as -OH, -H) in the combustion chain reaction through a gas-phase flame retardancy mechanism to form stable water or hydrocarbon molecules, thus interrupting the combustion reaction.

[0011] Preferably, the composite sheath layer is composed of an inner layer and an outer layer; the inner layer is a ternary ethylene-propylene rubber modified polyolefin, and the outer layer is an outer layer of irradiated cross-linked polyamide.

[0012] The inner layer of the composite sheath layer is made of ethylene propylene diene monomer (EPDM) modified polyolefin, which has excellent flexibility, impact resistance and weather resistance, and can effectively buffer external mechanical stress and resist environmental erosion such as ultraviolet rays and ozone. The outer layer is made of irradiated cross-linked polyamide, which endows the sheath layer with high wear resistance, high temperature resistance and chemical corrosion resistance through a high-density cross-linked network.

[0013] The inner layer uses EPDM modified polyolefin to disperse stress through its long-chain structure and combines with the hydrolysis resistance characteristics of polyolefin to form a dynamic buffer layer, effectively inhibiting crack initiation. The outer layer is irradiated cross-linked polyamide, which uses electron beam or γ-ray to initiate molecular chain cross-linking to form a three-dimensional network structure, significantly improving the thermal stability and mechanical strength of the material. After cross-linking, the movement of polyamide molecular chains is restricted, and the creep resistance and deformation resistance are enhanced. At the same time, its dense structure effectively blocks the penetration of media such as moisture, acids and alkalis, protecting the inner layer material. In addition, the rigid protection of the outer layer and the flexible support of the inner layer form a "rigid-flexible combination" gradient structure, dispersing external impact energy and avoiding cracking or peeling of the sheath layer caused by stress concentration.

[0014] On the other hand, the present invention provides a preparation method of a multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer for manufacturing the above-mentioned multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer, including the following steps: S1.1. Immerse the tinned copper conductor in a graphene ethanol dispersion with a concentration of 0.5-1%, and uniformly coat it at a speed of 2-3 m / min through a dip coater. After drying with hot air at 50-80 °C, perform compact stranding to obtain a conductor layer with a coating thickness of 5-10 μm. S1.2. Use a double-layer co-extrusion die to simultaneously extrude the inner layer and the outer layer of the double-layer insulation layer to obtain a double-layer insulation layer, which wraps the conductor layer. S1.3. Heat the silica gel strip added with nano boron nitride to 120-130 °C as an enhanced buffer layer, and wind it around the double-layer insulation layer through a spiral winding machine with a pitch of 3-5 times the cable outer diameter. S1.4. Use a coat-hanger type co-extrusion die to extrude the inner layer and the outer layer of the composite sheath layer to obtain a composite sheath layer, which wraps the enhanced buffer layer to obtain a multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer.

[0015] Preferably, in the S1.2, the temperature gradient of the double-layer co-extrusion die is: the inner layer is 160-170 °C, and the outer layer is 180-190 °C.

[0016] Preferably, in the S1.3, the thickness of the silica gel strip is 0.5-1.0 mm, and the winding tension of the silica gel strip is 5-8 N.

[0017] Preferably, in S1.3, the added amount of nano-boron nitride is 3%-5% of the mass of the silicone strip.

[0018] Preferably, in S1.4, the temperature gradient of the coat-hanger type co-extrusion die is: 170-180°C for the inner layer and 230-240°C for the outer layer.

[0019] Preferably, in S1.4, the inner layer thickness is 0.3-0.5 mm, and the outer layer thickness is 0.2-0.4 mm.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. In the multi-layer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer and its preparation method, the inner layer of the double-layer insulation layer adopts a core-shell structured nano-composite resin, wherein the core layer is an ethylene-octene copolymer, which gives the material high elasticity and impact resistance and effectively inhibits the cracking of the insulation layer; the shell layer is formed by a chemically cross-linked network of polyether ester elastomer grafted with naphthalene anhydride, and the modified nano-montmorillonite is evenly dispersed into a nano-sheet barrier to delay the diffusion of heat and smoke and achieve a low-smoke halogen-free effect; the modified nano-montmorillonite absorbs heat by decomposition, releases flame-retardant gas and forms a dense carbon layer, and its high specific surface area enhances the rigidity of the shell layer and improves the tensile strength.

[0021] 2. In the multi-layer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer and its preparation method, the outer elastomer modified halogen-free flame-retardant layer is based on ethylene-methyl acrylate, which provides excellent flexibility and weather resistance; di-tert-butylphosphinate aluminum salt is used as a halogen-free flame retardant, which decomposes at high temperature to generate aluminum phosphate, forming a dense carbon layer to isolate oxygen and heat, and phosphorus-containing free radicals capture active free radicals to interrupt flame propagation. At the same time, the inert gas generated by decomposition dilutes the combustible gas and reduces smoke toxicity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer.

[0023] The reference numerals in the accompanying drawings are: 1. Conductor layer; 2. Double insulation layer; 3. Reinforced buffer layer; 4. Composite sheath layer. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention provides a multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer, whose structure from the inside to the outside is successively a conductor layer 1, a double-layer insulation layer 2, a reinforcing buffer layer 3, and a composite sheath layer 4; The double-layer insulation layer 2 consists of an inner layer and an outer layer; The inner layer adopts a core-shell structure nano-composite resin, where the core layer is an ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene dicarboxylic anhydride, and modified nano-montmorillonite is dispersed in the shell layer. The mass ratio of the core layer to the shell layer is 1:0.4 - 0.7; The outer layer is an elastomer-modified halogen-free flame-retardant layer, which consists of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate, and their mass ratio is 1:0.3 - 0.5.

[0026] The preparation method of the inner layer of the double-layer insulation layer 2 is as follows: 1% - 3% of the modified nano-montmorillonite by the mass of the polyether ester elastomer and the polyether ester elastomer grafted with norbornene dicarboxylic anhydride are pre-dispersed in a high-speed mixer at a speed of 800 - 1200 rpm for 10 - 15 min; then the ethylene-octene copolymer is added for pre-mixing; The pre-mixed ethylene-octene copolymer and the polyether ester elastomer grafted with norbornene dicarboxylic anhydride dispersed with modified nano-montmorillonite are added into a twin-screw extruder. The extrusion temperature is 150 - 200 °C, and the screw speed is 300 - 400 rpm to obtain the inner layer of the double-layer insulation layer 2.

[0027] The specific steps for grafting norbornene dicarboxylic anhydride onto the polyether ester elastomer are as follows: The polyether ester elastomer and xylene are added into a reaction kettle, heated to 130 - 150 °C, and stirred until the polyether ester elastomer is completely dissolved; 3 - 5% of norbornene dicarboxylic anhydride by the mass of the polyether ester elastomer and 0.5 - 1% of diisopropylbenzene peroxide are added, and stirred and reacted at 160 - 180 °C at a speed of 100 - 150 rpm for 2 - 3 h; After the reaction is completed, the reaction solution is cooled to room temperature, poured into a large amount of ethanol for precipitation; the precipitate is filtered and washed to remove unreacted monomers and impurities, and finally vacuum dried at 60 - 80 °C to constant weight to obtain the polyether ester elastomer grafted with norbornene dicarboxylic anhydride.

[0028] The preparation method of the outer layer of the double-layer insulation layer 2 is as follows: Aluminum di-tert-butyl phosphinate and vinyltrimethoxysilane are pre-dispersed in a high-speed mixer at a speed of 800 - 1000 rpm for 10 - 15 min; Then the ethylene-methyl acrylate matrix and dilauryl thiodipropionate are added, and melt-blended through a twin-screw extruder. The extrusion temperature is 160 - 210 °C, and the screw speed is 250 - 300 rpm to obtain the outer layer of the double-layer insulation layer 2.

[0029] Because the nano-montmorillonite is pre-dispersed with the grafted elastomer, if ordinary nano-montmorillonite is used, it is easy to cause agglomeration and affect the performance. Therefore, the following method is used for modification: Mix nano-montmorillonite and deionized water at a mass ratio of 1:10, stir for 24 hours to form a uniform suspension, and adjust the pH to 3-4 to obtain a montmorillonite suspension; Dissolve cetyltrimethylammonium bromide in deionized water and mix at a mass ratio of 1:20, heat to 60-70 °C to dissolve to obtain an intercalating agent solution; slowly add the intercalating agent solution to the montmorillonite suspension and stir vigorously for 4-6 hours; After the reaction is completed, centrifuge multiple times to remove the unreacted intercalating agent; vacuum dry at 60-80 °C for 12 hours to obtain modified nano-montmorillonite.

[0030] Example 1: A multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer and its preparation method, including the following steps: S1.1. Immerse the tinned copper conductor in a graphene ethanol dispersion with a concentration of 1%, uniformly coat it at a speed of 3 m / min through a dip coater, and after drying with hot air at 80 °C, perform tight compression stranding to obtain a conductor layer 1 with a coating thickness of 6 μm; S1.2. Use a double-layer co-extrusion die to simultaneously extrude an inner core-shell structure nano-composite resin (160 °C) and an outer elastomer-modified halogen-free flame-retardant layer (180 °C) to obtain a double-layer insulation layer 2, which wraps the conductor layer 1; S1.3. Heat a silica gel strip with 5% nano-boron nitride added to 120 °C as the enhanced buffer layer 3, and wind it around the double-layer insulation layer 2 through a spiral winding machine with a tension of 8 N and a pitch of 5 times the cable outer diameter. The thickness of the silica gel strip is 1.0 mm; S1.4. Use a coat-hanger type co-extrusion die to extrude an inner ethylene-propylene-diene monomer (EPDM)-modified polyolefin (180 °C) with a thickness of 0.5 mm and an outer irradiated cross-linked polyamide (230 °C) with a thickness of 0.4 mm to obtain a composite sheath layer 4, which wraps the enhanced buffer layer 3 to obtain a multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer.

[0031] The double-layer insulation layer 2 consists of an inner layer and an outer layer; Among them, the inner layer uses a core-shell structure nano-composite resin, where the core layer is an ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with maleic anhydride, and modified nano-montmorillonite is dispersed in the shell layer. The mass ratio of the core layer to the shell layer is 1:0.4; the outer layer is an elastomer-modified halogen-free flame-retardant layer, which consists of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate salt, and their mass ratio is 1:0.3.

[0032] Example 2: A multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer and its preparation method, including the following steps: S1.1. Immerse the tinned copper conductor in a 1% graphene ethanol dispersion liquid, uniformly coat it at a speed of 3 m / min through a dip coater, and after drying with hot air at 80 °C, perform compact stranding to obtain the conductor layer 1 with a coating thickness of 6 μm. S1.2. Use a double-layer co-extrusion die to simultaneously extrude the inner core-shell structure nano-composite resin (160 °C) and the outer elastomer-modified halogen-free flame retardant layer (180 °C) to obtain the double-layer insulation layer 2, which wraps the conductor layer 1. S1.3. Heat the silica gel strip with 5% nano-boron nitride added to 120 °C as the enhanced buffer layer 3, and wind it around the double-layer insulation layer 2 through a spiral winding machine with a tension of 8 N and a pitch of 5 times the cable outer diameter. The thickness of the silica gel strip is 1.0 mm. S1.4. Use a coat-hanger type co-extrusion die to extrude the inner ethylene propylene diene monomer (EPDM) modified polyolefin (180 °C) with a thickness of 0.5 mm and the outer irradiated cross-linked polyamide (230 °C) with a thickness of 0.4 mm to obtain the composite sheath layer 4, which wraps the enhanced buffer layer 3 to obtain the multi-layer co-extruded cable based on the low-smoke halogen-free flame retardant composite layer.

[0033] The double-layer insulation layer 2 consists of an inner layer and an outer layer. Among them, the inner layer uses a core-shell structure nano-composite resin, where the core layer is ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene dianhydride, and modified nano-montmorillonite is dispersed in the shell layer. The mass ratio of the core layer to the shell layer is 1:0.5. The outer layer is an elastomer-modified halogen-free flame retardant layer, which consists of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate salt, and their mass ratio is 1:0.3.

[0034] Example 3: A multi-layer co-extruded cable based on a low-smoke halogen-free flame retardant composite layer and its preparation method, including the following steps: S1.1. Immerse the tinned copper conductor in a 1% graphene ethanol dispersion liquid, uniformly coat it at a speed of 3 m / min through a dip coater, and after drying with hot air at 80 °C, perform compact stranding to obtain the conductor layer 1 with a coating thickness of 6 μm. S1.2. Use a double-layer co-extrusion die to simultaneously extrude the inner core-shell structure nano-composite resin (160 °C) and the outer elastomer-modified halogen-free flame retardant layer (180 °C) to obtain the double-layer insulation layer 2, which wraps the conductor layer 1. S1.3. Heat the silica gel strip with 5% nano-boron nitride added to 120 °C as the enhanced buffer layer 3, and wind it around the double-layer insulation layer 2 through a spiral winding machine with a tension of 8 N and a pitch of 5 times the cable outer diameter. The thickness of the silica gel strip is 1.0 mm. S1.4. Use a hanger coextrusion die to extrude an inner layer of ethylene propylene diene monomer (EPDM) modified polyolefin with a thickness of 0.5 mm (at 180 °C) and an outer layer of irradiated crosslinked polyamide with a thickness of 0.4 mm (at 230 °C) to obtain a composite sheath layer 4. Wrap the enhanced buffer layer 3 to obtain a multi-layer coextruded cable based on a low-smoke and halogen-free flame retardant composite layer.

[0035] The double-layer insulation layer 2 consists of an inner layer and an outer layer. Among them, the inner layer uses a core-shell structured nano-composite resin, where the core layer is an ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene dicarboxylic anhydride, and modified nano-montmorillonite is dispersed in the shell layer. The mass ratio of the core layer to the shell layer is 1:0.7. The outer layer is an elastomer-modified halogen-free flame retardant layer, which consists of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate, and their mass ratio is 1:0.3.

[0036] Example 4: A multi-layer coextruded cable based on a low-smoke and halogen-free flame retardant composite layer and its preparation method, including the following steps: S1.1. Immerse the tinned copper conductor in a graphene ethanol dispersion with a concentration of 1%, uniformly coat it at a speed of 3 m / min through a dip coater, and after drying with hot air at 80 °C, perform compact stranding to obtain a conductor layer 1 with a coating thickness of 6 μm. S1.2. Use a double-layer coextrusion die to simultaneously extrude an inner layer of core-shell structured nano-composite resin (at 160 °C) and an outer layer of elastomer-modified halogen-free flame retardant layer (at 180 °C) to obtain a double-layer insulation layer 2, which wraps the conductor layer 1. S1.3. Heat a silica gel strip with 5% nano-boron nitride added to 120 °C as the enhanced buffer layer 3, and wind it around the double-layer insulation layer 2 with a tension of 8 N and a pitch of 5 times the cable outer diameter through a spiral winding machine. The thickness of the silica gel strip is 1.0 mm. S1.4. Use a hanger coextrusion die to extrude an inner layer of ethylene propylene diene monomer (EPDM) modified polyolefin with a thickness of 0.5 mm (at 180 °C) and an outer layer of irradiated crosslinked polyamide with a thickness of 0.4 mm (at 230 °C) to obtain a composite sheath layer 4. Wrap the enhanced buffer layer 3 to obtain a multi-layer coextruded cable based on a low-smoke and halogen-free flame retardant composite layer.

[0037] The double-layer insulation layer 2 consists of an inner layer and an outer layer. Among them, the inner layer uses a core-shell structured nano-composite resin, where the core layer is an ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene dicarboxylic anhydride, and modified nano-montmorillonite is dispersed in the shell layer. The mass ratio of the core layer to the shell layer is 1:0.5. The outer layer is an elastomer-modified halogen-free flame retardant layer, which consists of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate, and their mass ratio is 1:0.4.

[0038] Example 5: A multi-layer co-extruded cable based on a low-smoke and halogen-free flame-retardant composite layer and its preparation method, including the following steps: S1.1. Immerse the tinned copper conductor in a graphene ethanol dispersion with a concentration of 1%, and evenly coat it at a speed of 3 m / min through a dip coater. After drying with hot air at 80 °C, perform compact stranding to obtain the conductor layer 1 with a coating thickness of 6 μm. S1.2. Use a double-layer co-extrusion die to simultaneously extrude the inner core-shell structure nano-composite resin (160 °C) and the outer elastomer-modified halogen-free flame-retardant layer (180 °C) to obtain the double-layer insulation layer 2, which wraps the conductor layer 1. S1.3. Heat the silica gel strip with 5% nano-boron nitride added to 120 °C as the enhanced buffer layer 3, and wind it around the double-layer insulation layer 2 through a spiral winding machine with a tension of 8 N and a pitch of 5 times the cable outer diameter. The thickness of the silica gel strip is 1.0 mm. S1.4. Use a coat-hanger type co-extrusion die to extrude the inner ethylene-propylene-diene monomer (EPDM)-modified polyolefin (180 °C) with a thickness of 0.5 mm and the outer irradiated cross-linked polyamide (230 °C) with a thickness of 0.4 mm to obtain the composite sheath layer 4, which wraps the enhanced buffer layer 3 to obtain the multi-layer co-extruded cable based on the low-smoke and halogen-free flame-retardant composite layer.

[0039] The double-layer insulation layer 2 consists of an inner layer and an outer layer. Among them, the inner layer uses a core-shell structure nano-composite resin, where the core layer is ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene dicarboxylic anhydride, and modified nano-montmorillonite is dispersed in the shell layer. The mass ratio of the core layer to the shell layer is 1:0.5; the outer layer is an elastomer-modified halogen-free flame-retardant layer, which consists of an ethylene-methyl acrylate matrix and aluminum di-tert-butyl phosphinate, and their mass ratio is 1:0.5.

[0040] Comparative Example 1: Using the method of Example 4, directly mix ethylene-octene copolymer and polyether ester elastomer without using the inner core-shell structure nano-composite resin as the inner insulation layer.

[0041] Comparative Example 2: Using the method of Example 4, no modified nano-montmorillonite is added to the shell layer of the inner core-shell structure nano-composite resin.

[0042] Comparative Example 3: Using the method of Example 4, in the outer elastomer-modified halogen-free flame-retardant layer, replace aluminum di-tert-butyl phosphinate with decabromodiphenyl ethane.

[0043] During the preparation process of the multi-layer co-extruded cable based on the low-smoke and halogen-free flame-retardant composite layer, a double-layer insulation layer composed of an inner core-shell structure nano-composite resin and an outer elastomer-modified halogen-free flame-retardant layer is added. The performance index inspection items and inspection standards of the obtained multi-layer co-extruded cable based on the low-smoke and halogen-free flame-retardant composite layer are as follows: According to the GB / T2951 standard, dumbbell-shaped specimens (with a thickness of 1 - 2 mm and a gauge length of 25 mm) are cut from the cable. The distance between the clamps of the testing machine is 50 mm, and the tensile rate is 250 mm / min. Measure the initial thickness and width of the specimen, and calculate the cross-sectional area. Clamp the specimen in the clamps of the testing machine, start the testing machine until the specimen breaks, and record the maximum force value (F) and the gauge length (L1) at break. Calculate the tensile strength (MPa) = F / cross-sectional area according to the formula, and the elongation at break (%) = [(L1 - initial gauge length) / initial gauge length] × 100%. A higher tensile strength indicates that the cable material has a strong ability to resist tensile fracture and is suitable for scenarios that need to withstand mechanical stress. A higher elongation at break indicates that the material has excellent ductility and can withstand large deformations (such as bending and stretching) without cracking.

[0044] According to the GB / T9330 - 2020 standard, take 3 cables with a length of 1 meter and remove the outer sheath (retain the armor if any). Bend the cables 360° unidirectionally with different mandrel diameters, observe whether cracks appear on the surface, and record the minimum bending radius (multiple of the cable outer diameter (D)) at which no cracking occurs. A lower minimum bending radius indicates that the cable is flexible and suitable for narrow spaces or scenarios that require frequent bending.

[0045] According to the GB / T 18380 - 2008 standard, bundle the cables into a bunch according to the specified number (such as 6 cables) and hang them vertically in the combustion chamber. Use a propane burner with a flame height of 750 mm and apply the flame for 20 minutes. Observe the total heat release and char height of the bundled cables within 600 seconds. A lower cumulative heat release and char height indicate that the cable has excellent flame retardancy, slow spread rate, low smoke production, and low release of toxic gases during combustion.

[0046] Through the above standards, the multi-layer co-extruded cables based on the low-smoke and halogen-free flame-retardant composite layer prepared in Examples 1 - 5 and Comparative Examples 1 - 3 are tested, and the obtained data are shown in Table 1: Table 1 Performance data of the cables in Examples 1 - 5 and Comparative Examples 1 - 3 It can be seen from Examples 1 - 3 that in the multi-layer co-extruded cables based on the low-smoke and halogen-free flame-retardant composite layer, when other components remain unchanged and the mass ratio of the core layer to the shell layer of the inner core-shell structured nano-composite resin gradually increases, the mechanical properties, flexibility, and flame retardancy of the cables are continuously improved.

[0047] The flexible long chains of the core layer ethylene-octene copolymer endow the material with high elasticity and impact resistance, enabling it to absorb mechanical stress and inhibit crack propagation. The shell layer forms a chemical cross-linking network through grafted polyether ester elastomer of norbornene anhydride, enhancing the interfacial adhesion force and restricting the movement of molecular chains, thereby improving the heat resistance. The dispersed modified nano-montmorillonite in the shell layer forms a physical barrier through the intercalation effect, blocking the transmission of oxygen and heat and delaying the combustion process. Even when the proportion of the shell layer decreases, its cross-linking network can still effectively improve the tensile strength, while the lamellar barrier effect of the modified nano-montmorillonite maintains the flame retardant performance.

[0048] In the shell layer, the modified nano-montmorillonite decomposes endothermically at high temperatures and releases inert gases such as water vapor and carbon dioxide, diluting the concentration of combustible gases. At the same time, its lamellar structure promotes the formation of a char layer, jointly constructing a "gas phase - condensed phase" dual-effect flame retardant mechanism with the shell layer cross-linking network, significantly reducing the char height. The high flexibility of the core layer ethylene-octene copolymer reduces the material rigidity, enabling the minimum bending radius of the cable to decrease and adapting to complex wiring requirements. The core-shell interface further disperses stress through the polar matching and chemical bonding of acid anhydride groups, avoiding interlayer peeling and ensuring the stability of mechanical properties.

[0049] Furthermore, by comparing Examples 3 - 5, it can be seen that in a multi-layer co-extruded cable based on a low-smoke and halogen-free flame retardant composite layer, when other components remain unchanged and the mass ratio of the ethylene-methyl acrylate matrix to aluminum di-tert-butyl phosphinate in the outer elastomer-modified halogen-free flame retardant layer gradually increases, the mechanical properties, flexibility, and flame retardant performance of the cable continuously improve.

[0050] At high temperatures, aluminum di-tert-butyl phosphinate decomposes to form aluminum phosphate and phosphorus-containing free radicals. The former forms a dense char layer on the material surface, isolating the transmission of oxygen and heat. The latter captures active free radicals (such as -OH) in the combustion chain reaction, interrupting the flame propagation, reducing the total heat release within 600 seconds, and significantly decreasing the char height. The ethylene-methyl acrylate matrix maintains flexibility through its elastomer properties, while dilauryl thiodipropionate, as a compatibilizer, further improves the dispersion of aluminum di-tert-butyl phosphinate in the ethylene-methyl acrylate matrix, avoiding the deterioration of mechanical properties caused by the agglomeration of the flame retardant.

[0051] The increase in the ethylene-methyl acrylate matrix significantly enhances the elastic network of the material through the physical cross-linking effect of its long-chain carboxylate structure, thereby endowing it with a high elongation at break. At the same time, the hydrogen bond interaction between the matrix and the decomposition products of aluminum di-tert-butyl phosphinate enhances the interfacial bonding force, further improving the tensile strength. In addition, the dominant flexibility characteristic of the ethylene-methyl acrylate matrix enables the minimum bending radius of the cable to decrease, thus better adapting to complex wiring requirements.

[0052] According to the above test experiments, Example 4 is taken as the optimal example; It can be seen from the comparison between Example 4 and Comparative Example 1 and Comparative Example 2 that: in the core-shell structure, the shell layer polyether ester elastomer forms a chemical bond with the core layer ethylene-octene copolymer by grafting norbornene dianhydride, significantly enhancing the interfacial bonding force between the two phases, thereby improving the comprehensive properties of the material; in contrast, when simply blended, the ethylene-octene copolymer and the polyether ester elastomer are only physically mixed, with poor interfacial compatibility, prone to phase separation, resulting in a decrease in interlayer adhesion and low stress transfer efficiency, and further deteriorating the tensile strength and impact resistance; in the core-shell structure, the ethylene-octene copolymer core layer acts as a flexible matrix to absorb mechanical stress, effectively avoiding stress concentration; while in simple blending, the two phases are unevenly distributed, and stress concentration points are formed at the hard regions of the elastomer and the soft phase of the ethylene-octene copolymer, exacerbating the initiation of local cracks; in addition, the uncrosslinked shell layer cannot restrict the slip of molecular chains, resulting in a decrease in the creep resistance of the material and easy deformation and failure during long-term use.

[0053] The modified nano-montmorillonite dispersed in the shell layer of the core-shell structure forms a lamellar barrier through the intercalation effect, inhibiting crack propagation and enhancing rigidity; while the blend system lacks nano-fillers, there is no physical barrier structure inside the material, the elongation at break decreases, and the heat resistance is insufficient; at the same time, the lack of the endothermic decomposition and carbon layer strengthening effect of montmorillonite during combustion leads to a decrease in flame retardancy.

[0054] It can be seen from the comparison between Example 4 and Comparative Example 3 that: in the outer elastomer modified halogen-free flame retardant layer, replacing aluminum di-tert-butyl phosphinate with decabromodiphenylethane significantly reduces the flame retardancy of the cable; aluminum di-tert-butyl phosphinate is a phosphorus-based flame retardant, and its flame retardant mechanism mainly forms a dense carbon layer through condensed-phase flame retardancy, isolating heat and oxygen, and releasing tert-butyl free radicals to capture flame free radicals, thereby inhibiting combustion; decabromodiphenylethane is a bromine-based flame retardant, and its flame retardant mechanism relies on gas-phase flame retardancy, inhibiting the flame by releasing bromine free radicals; in addition, the compatibility between decabromodiphenylethane and the ethylene-methyl acrylate matrix is poor, prone to agglomeration, resulting in interfacial defects, a decrease in tensile strength, and the destruction of the carbon layer continuity, thus affecting the heat release rate.

[0055] In summary, during the preparation of the multi-layer co-extruded cable based on the low-smoke halogen-free flame-retardant composite layer, adding the inner core-shell structured nano-composite resin and the outer elastomer-modified halogen-free flame-retardant layer can significantly improve the performance of the cable; the inner core-shell structure provides high elasticity through the ethylene-octene copolymer core layer to relieve the bending stress concentration; the polyether ester elastomer shell layer grafted with norbornene dicarboxylic anhydride forms a three-dimensional reinforcement network with the modified nano-montmorillonite to enhance the tensile strength and solve the contradiction of the traditional halogen-free material being "rigid and brittle"; the outer elastomer-modified layer uses ethylene-methyl acrylate as the matrix to further enhance the tensile strength and elongation at break to ensure the flexibility of the cable under complex stresses; the inner core-shell structure catalyzes carbonization through the anhydride groups in the shell layer and the modified nano-montmorillonite blocks heat transfer to increase the oxygen index; the decomposition products of the mixed salts in the outer elastomer-modified layer capture combustion free radicals to inhibit flame propagation, combined with microencapsulated red phosphorus to delay heat release, reducing the total heat release within 600 s and shortening the carbonization length of the bundle combustion.

[0056] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only the preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. Multilayer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer, characterized in that: The structure thereof comprises, from the inside to the outside, a conductor layer (1), a double-layer insulation layer (2), a reinforced buffer layer (3) and a composite sheath layer (4); The double insulating layer (2) consists of an inner layer and an outer layer; The inner layer adopts a core-shell structure nano-composite resin, wherein the core layer is ethylene-octene copolymer, the shell layer is polyether ester elastomer grafted with nadic anhydride, and modified nano-montmorillonite is dispersed in the shell layer, and the mass ratio of the core layer to the shell layer is 1:0.4-0.7; The outer layer is an elastomer-modified halogen-free flame-retardant layer, which is composed of an ethylene-methyl acrylate matrix and di-tert-butylphosphinate aluminum salt, with a mass ratio of 1:0.3-0.

5.

2. The multi-layer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer according to claim 1 is characterized in that: The preparation method of the inner layer of the double-layer insulation layer (2) is as follows: Pre-disperse 1%-3% of the modified nano-montmorillonite by weight of the polyether ester elastomer and the polyether ester elastomer grafted with nadic anhydride in a high-speed mixer at a speed of 800-1200 rpm for 10-15 minutes; then add ethylene-octene copolymer for pre-mixing; The pre-mixed ethylene-octene copolymer and the polyether ester elastomer grafted with nadic anhydride dispersed with modified nano-montmorillonite are added into a twin-screw extruder at an extrusion temperature of 150-200° C. and a screw speed of 300-400 rpm to obtain the inner layer of the double-layer insulation layer (2).

3. The multi-layer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer according to claim 1, characterized in that: The preparation method of the outer layer of the double-layer insulation layer (2) is as follows: Pre-disperse aluminum di-tert-butylphosphinate and vinyltrimethoxysilane in a high-speed mixer at a speed of 800-1000 rpm for 10-15 minutes; Then, ethylene-methyl acrylate matrix and dilauryl thiodipropionate are added and melt-blended by a twin-screw extruder at an extrusion temperature of 160-210° C. and a screw speed of 250-300 rpm to obtain a double-layer insulation layer (2) outer layer.

4. The multi-layer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer according to claim 1, characterized in that: The composite sheath layer (4) consists of an inner layer and an outer layer; the inner layer is EPDM rubber-modified polyolefin, and the outer layer is radiation-crosslinked polyamide.

5. A method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer, which is used to prepare a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer as described in any one of claims 1 to 4, characterized in that: The preparation method of the multi-layer co-extruded cable based on the low-smoke halogen-free flame-retardant composite layer is as follows: S1.1, immersing the tinned copper conductor in a graphene ethanol dispersion having a concentration of 0.5-1%, coating the conductor uniformly at a speed of 2-3 m / min using a dip coating machine, drying the conductor with hot air at 50-80°C, and then pressing and twisting the conductor to obtain a conductor layer (1) having a coating thickness of 5-10 μm; S1.2, using a double-layer co-extrusion die, synchronously extruding the inner layer and the outer layer of the double-layer insulation layer (2), obtaining the double-layer insulation layer (2), and wrapping the conductor layer (1); S1.3, heating the silica gel strip added with nano boron nitride to 120-130°C as a reinforced buffer layer (3), and winding it around the double insulating layer (2) with a pitch of 3-5 times the outer diameter of the cable by a spiral winding machine; S1.

4. Use a hanger-type co-extrusion die to extrude the inner layer and the outer layer of the composite sheath layer (4) to obtain the composite sheath layer (4), which is then wrapped around the reinforced buffer layer (3) to obtain a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer.

6. The method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer according to claim 5, characterized in that: In S1.2, the temperature gradient of the double-layer co-extrusion die is: 160-170°C for the inner layer and 180-190°C for the outer layer.

7. The method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer according to claim 5, characterized in that: In S1.3, the thickness of the silicone strip is 0.5-1.0 mm, and the winding tension of the silicone strip is 5-8N.

8. The method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer according to claim 5, characterized in that: In S1.3, the added amount of nano boron nitride is 3%-5% of the mass of the silicone strip.

9. The method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer according to claim 5, characterized in that: In S1.4, the temperature gradient of the coat-hanger co-extrusion die is: 170-180° C. for the inner layer and 230-240° C. for the outer layer.

10. The method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer according to claim 5, characterized in that: In the S1.4, the inner layer thickness is 0.3-0.5 mm, and the outer layer thickness is 0.2-0.4 mm.

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