Multilayer co-extruded cable based on low-smoke halogen-free flame-retardant composite layer and method for manufacturing same

Abstract

The application relates to the technical field of cables, in particular to a multilayer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, which comprises, from inside to outside, a conductor layer, a double-layer insulation layer, a reinforcing buffer layer and a composite sheath layer; wherein the double-layer insulation layer comprises an inner layer and an outer layer; the inner layer takes ethylene-octene copolymer as a core layer and grafted polyether ester elastomer of norbornene diacid anhydride as a shell layer, and is endowed with high elasticity, impact resistance and insulation layer cracking inhibition; modified nano montmorillonite is dispersed into a nano sheet barrier to delay heat diffusion and realize low smoke and halogen-free; the outer layer is composed of an ethylene-methyl acrylate matrix and aluminum salt of di-tert-butyl phosphinic acid, the aluminum salt of di-tert-butyl phosphinic acid is decomposed into aluminum phosphate at high temperature to form a carbon layer to insulate oxygen and heat, and phosphorus-containing free radicals capture active free radicals to interrupt flame propagation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable, in particular to a multi-layer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer and a preparation method thereof. BACKGROUND

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

[0003] However, the traditional low-smoke halogen-free cable realizes flame retardation by adding aluminum hydroxide, magnesium hydroxide and other halogen-free flame retardants, but high filling amount leads to too strong rigidity and insufficient flexibility of the material, which is easy to crack due to stress concentration during laying or running, especially in large size cable or armored structure, therefore, we propose a multi-layer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer and a preparation method thereof. SUMMARY

[0004] The purpose of the present application is to provide a multi-layer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, to solve the problem that the traditional low-smoke halogen-free cable realizes flame retardation by adding aluminum hydroxide, magnesium hydroxide and other halogen-free flame retardants, but high filling amount leads to too strong rigidity and insufficient flexibility of the material, which is easy to crack due to stress concentration during laying or running.

[0005] To achieve the above purpose, the present application provides a multi-layer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer, which is composed of a conductor layer, a double-layer insulation layer, a reinforced buffer layer and a composite sheath layer from inside to outside.

[0006] The double-layer insulation layer is composed of an inner layer and an outer layer;

[0007] 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 norbornene diacid anhydride, and modified nano montmorillonite is dispersed in the shell layer, and the mass ratio of the core layer and the shell layer is 1:0.4-0.7;

[0008] The outer layer is an elastomer modified halogen-free flame-retardant layer composed of ethylene-methyl acrylate matrix and aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio is 1:0.3-0.5.

[0009] As a preferred, the preparation method of the inner layer of the double-layer insulation layer is as follows:

[0010] Pre-disperse 1-3% modified nano-montmorillonite and 1-3% grafted norbornene anhydride polyether ester elastomer in a high-speed mixer at 800-1200 rpm for 10-15 min; then add ethylene-octene copolymer for pre-mixing;

[0011] Add the pre-mixed ethylene-octene copolymer and grafted norbornene anhydride polyether ester elastomer with dispersed modified nano-montmorillonite into a twin-screw extruder, with 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.

[0012] The ethylene-octene copolymer core layer provides high elasticity and flexibility, effectively relieving the bending stress of the cable; the shell layer uses grafted norbornene anhydride polyether ester elastomer, whose anhydride groups decompose at high temperatures to release active intermediates (such as carboxylate ions or free radicals), which can react with functional groups such as hydroxyl and amino groups in the polyether ester elastomer to form a three-dimensional cross-linked structure, thereby promoting the formation of carbon layer and significantly improving the flame retardant efficiency; in addition, the modified montmorillonite interacts with the polar groups (such as ester groups) of the polyether ester elastomer through the surface hydroxyl groups, achieving intercalation and dispersion, and its lamellar structure can prolong the escape path of pyrolysis gas and reduce the burning rate.

[0013] As a preferred embodiment, the preparation method of the double-layer insulation layer outer layer is as follows:

[0014] Pre-disperse aluminum di-tert-butyl phosphinate and vinyltrimethoxysilane in a high-speed mixer at 800-1000 rpm for 10-15 min;

[0015] Then add ethylene-methyl acrylate matrix and dilauryl thiodipropionate for melt blending through a twin-screw extruder, with an extrusion temperature of 160-210°C and a screw speed of 250-300 rpm, to obtain the outer layer of the double-layer insulation layer.

[0016] The outer layer of the elastomer-modified halogen-free flame-retardant layer achieves the unity of high flame retardant 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 under bending or vibration environment; aluminum di-tert-butyl phosphinate, as a halogen-free flame retardant, significantly reduces the flame spread rate through endothermic decomposition and gas dilution mechanism during combustion, while inhibiting the release of smoke and toxic gases, meeting the environmental protection requirements of low smoke and halogen-free.

[0017] At high temperatures, aluminum di-tert-butyl phosphinate decomposes into aluminum phosphate and phosphorus-containing radicals; aluminum phosphate, as an inorganic residue, forms a dense and continuous carbon layer on the surface of the material, effectively isolating oxygen and blocking heat transfer; phosphorus-containing radicals (such as PO 2-) Through the gas phase flame retardant mechanism, combined with active free radicals (such as -OH, -H) in the combustion chain reaction, stable water or hydrocarbon molecules are generated, thereby interrupting the combustion reaction.

[0018] Preferably, the composite sheath layer is composed of an inner layer and an outer layer; wherein the inner layer is a ternary ethylene-propylene rubber modified polyolefin, and the outer layer is an outer layer irradiation cross-linked polyamide.

[0019] The inner layer of the composite sheath layer uses a ternary ethylene-propylene rubber 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 uses irradiation cross-linked polyamide, which gives the sheath layer high wear resistance, high temperature resistance and chemical corrosion resistance through a high-density cross-linked network.

[0020] The inner layer uses a ternary ethylene-propylene rubber modified polyolefin, which disperses stress through its long-chain structure and combines the hydrolysis resistance of polyolefin to form a dynamic buffer layer that effectively inhibits crack initiation; the outer layer uses irradiation cross-linked polyamide, which uses electron beam or gamma rays to initiate molecular chain cross-linking to form a three-dimensional network structure, significantly improving the thermal stability and mechanical strength of the material; the cross-linked polyamide molecular chain movement is limited, and the creep resistance and deformation resistance are enhanced, and its dense structure effectively blocks the penetration of water, acid and alkali and other media, protecting the inner layer material; in addition, the rigid protection of the outer layer and the flexible support of the inner layer form a gradient structure of "rigidity and flexibility", which disperses external impact energy and avoids stress concentration leading to cracking or peeling of the sheath layer.

[0021] On the other hand, the present application provides a preparation method of a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer, for making the multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer as described above, comprising the following steps:

[0022] S1.1, immerse the tinned copper conductor in a graphene ethanol dispersion solution with a concentration of 0.5-1%, uniformly coat it through an immersion coater at a speed of 2-3 m / min, and after drying with hot air at 50-80℃, perform tight pressing and twisting to obtain a conductor layer with a plating layer thickness of 5-10 μm;

[0023] S1.2, use a double-layer co-extrusion mold to synchronously extrude the inner layer and the outer layer of the double-layer insulation layer to obtain a double-layer insulation layer wrapping the conductor layer;

[0024] S1.3, heat the silica gel strip added with nano boron nitride to 120-130℃, as a reinforcing buffer layer, and wrap it around the double-layer insulation layer through a spiral winding machine at a pitch of 3-5 times the outer diameter of the cable;

[0025] S1.4, use a clothes hanger type co-extrusion mold to extrude the inner layer and the outer layer of the composite sheath layer to obtain a composite sheath layer wrapping the reinforcing buffer layer, thereby obtaining a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer.

[0026] As preferred, in S1.2, the temperature gradient of the double-layer co-extrusion die is: inner layer 160-170℃, outer layer 180-190℃.

[0027] As preferred, in S1.3, the thickness of the silica gel strip is 0.5-1.0mm, and the winding tension of the silica gel strip is 5-8N.

[0028] As preferred, in S1.3, the addition amount of nano-boron nitride is 3%-5% of the mass of the silica gel strip.

[0029] As preferred, in S1.4, the temperature gradient of the clothes hanger type co-extrusion die is: inner layer 170-180℃, outer layer 230-240℃.

[0030] As preferred, in S1.4, the thickness of the inner layer is 0.3-0.5mm, and the thickness of the outer layer is 0.2-0.4mm.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] 1. In the multilayer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer and the preparation method thereof, the inner layer of the double-layer insulation layer adopts a core-shell structure nano composite resin, wherein the core layer is ethylene-octene copolymer, which gives the material high elasticity and impact resistance, effectively inhibiting the cracking of the insulation layer; the shell layer forms a chemical crosslinking network by grafting norbornene diacid anhydride polyether ester elastomer, and the modified nano montmorillonite is uniformly dispersed into a nanosheet barrier, delaying the diffusion of heat and smoke, and realizing the low-smoke halogen-free effect; the modified nano montmorillonite enhances the rigidity of the shell layer and improves the tensile strength through decomposition endothermic, release of flame-retardant gas and formation of a dense carbon layer, and its high specific surface area.

[0033] 2. In the multilayer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer and the preparation method thereof, the outer layer elastomer modified halogen-free flame-retardant layer takes ethylene-methyl acrylate as the matrix, providing excellent flexibility and weather resistance; aluminum salt of di-tert-butyl phosphinic acid as a halogen-free flame retardant decomposes to generate aluminum phosphate at high temperature, forming a dense carbon layer to insulate oxygen and heat, and the phosphorus-containing free radical captures active free radicals to interrupt flame propagation, while the inert gas generated by decomposition dilutes the combustible gas, reducing smoke toxicity. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the multilayer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer.

[0035] In the drawings, the reference signs are:

[0036] 1. Conductor layer; 2. Double-layer insulation layer; 3. Reinforced buffer layer; 4. Composite sheath layer. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0038] The present application provides a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer, which has a structure from inside to outside as follows: a conductor layer 1, a double-layer insulation layer 2, a reinforcing buffer layer 3, and a composite sheath layer 4.

[0039] The double-layer insulation layer 2 is composed of an inner layer and an outer layer.

[0040] The inner layer adopts a core-shell structure nano-composite resin, wherein the core layer is an 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, and the mass ratio of the core layer to the shell layer is 1:0.4-0.7.

[0041] The outer layer is an elastomer-modified halogen-free flame-retardant layer composed of an ethylene-methyl acrylate matrix and an aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio thereof is 1:0.3-0.5.

[0042] The preparation method of the inner layer of the double-layer insulation layer 2 is as follows:

[0043] Modified nano-montmorillonite with a mass fraction of 1%-3% of the polyether ester elastomer and the polyether ester elastomer grafted with norbornene dianhydride 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.

[0044] The pre-mixed ethylene-octene copolymer and the polyether ester elastomer grafted with norbornene dianhydride with dispersed modified nano-montmorillonite are added into a double-screw extruder, the extrusion temperature is 150-200℃, and the screw rotation speed is 300-400 rpm, to obtain the inner layer of the double-layer insulation layer 2.

[0045] The specific steps of grafting norbornene dianhydride on the polyether ester elastomer are as follows:

[0046] The polyether ester elastomer and dimethylbenzene are added into a reaction kettle, heated to 130-150℃, and stirred until the polyether ester elastomer is completely dissolved; 3-5% of norbornene dianhydride and 0.5-1% of dicumyl peroxide based on the mass of the polyether ester elastomer are added, and stirred at a speed of 100-150 rpm at 160-180℃ for 2-3 h.

[0047] 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, washed to remove unreacted monomers and impurities, and finally dried under vacuum at 60-80°C to a constant weight to obtain a grafted norbornene diacid anhydride polyether ester elastomer.

[0048] The preparation method of the outer layer of the double-layer insulation layer 2 is as follows:

[0049] The aluminum salt of di-tert-butyl hypophosphite and vinyl trimethoxysilane are pre-dispersed in a high-speed mixer at a speed of 800-1000 rpm for 10-15 min;

[0050] Then, the ethylene-methyl acrylate matrix and dilauryl thiodipropionate are added and melt blended through a twin-screw extruder, with an extrusion temperature of 160-210°C and a screw speed of 250-300 rpm, to obtain the outer layer of the double-layer insulation layer 2.

[0051] 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 performance, therefore the following modification method is adopted:

[0052] The nano-montmorillonite is mixed with deionized water at a mass ratio of 1:10, stirred for 24 hours to form a uniform suspension, and the pH is adjusted to 3-4 to obtain a montmorillonite suspension;

[0053] The cetyltrimethylammonium bromide is dissolved in deionized water at a mass ratio of 1:20, heated to 60-70°C to dissolve, and an intercalation agent solution is obtained; the intercalation agent solution is slowly added to the montmorillonite suspension and stirred vigorously for 4-6 hours;

[0054] After the reaction is completed, the unreacted intercalation agent is removed by centrifugation multiple times; and the modified nano-montmorillonite is dried under vacuum at 60-80°C for 12 hours.

[0055] Example 1: A multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, comprising the following steps:

[0056] S1.1, immerse the tinned copper conductor in a graphene ethanol dispersion solution with a concentration of 1%, uniformly coat it through an immersion coater at a speed of 3 m / min, dry it with hot air at 80°C, and then tightly twist it to obtain a conductor layer 1 with a plating thickness of 6 μm;

[0057] S1.2, use a double-layer co-extrusion mold to synchronously extrude an inner layer core-shell structure nano-composite resin (160°C) and an outer layer elastomer modified halogen-free flame-retardant layer (180°C) to obtain a double-layer insulation layer 2 wrapping the conductor layer 1;

[0058] S1.3, heat the silica gel strip with 5% nano boron nitride to 120℃, as the reinforced buffer layer 3, wrapped outside the double-layer insulation layer 2 by the spiral winding machine with 8N tension, 5 times the cable outer diameter pitch, the thickness of the silica gel strip is 1.0mm;

[0059] S1.4, use the clothes hanger type co-extrusion die, extrude the inner layer of ethylene-propylene rubber modified polyolefin (180℃) with a thickness of 0.5mm and the outer layer of irradiation crosslinked polyamide (230℃) with a thickness of 0.4mm to obtain the composite sheath layer 4, which wraps the reinforced buffer layer 3, to obtain the multi-layer co-extrusion cable based on low smoke halogen-free flame-retardant composite layer.

[0060] The double-layer insulation layer 2 is composed of an inner layer and an outer layer;

[0061] 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 norbornene diacid 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; the outer layer is an elastomer modified halogen-free flame-retardant layer composed of ethylene-methyl acrylate matrix and aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio is 1:0.3.

[0062] Example 2: a multi-layer co-extrusion cable based on low smoke halogen-free flame-retardant composite layer and a preparation method thereof, comprising the following steps:

[0063] S1.1, dip the tinned copper conductor into a graphene ethanol dispersion solution with a concentration of 1%, uniformly coat by the dip coater at a speed of 3m / min, after drying by hot air at 80℃, perform tight pressure stranding to obtain the conductor layer 1 with a plated layer thickness of 6μm;

[0064] S1.2, use a double-layer co-extrusion die to synchronously extrude the inner layer of core-shell structure nano composite resin (160℃) and the outer layer of elastomer modified halogen-free flame-retardant layer (180℃) to obtain the double-layer insulation layer 2, which wraps the conductor layer 1;

[0065] S1.3, heat the silica gel strip with 5% nano boron nitride to 120℃, as the reinforced buffer layer 3, wrapped outside the double-layer insulation layer 2 by the spiral winding machine with 8N tension, 5 times the cable outer diameter pitch, the thickness of the silica gel strip is 1.0mm;

[0066] S1.4, use the clothes hanger type co-extrusion die, extrude the inner layer of ethylene-propylene rubber modified polyolefin (180℃) with a thickness of 0.5mm and the outer layer of irradiation crosslinked polyamide (230℃) with a thickness of 0.4mm to obtain the composite sheath layer 4, which wraps the reinforced buffer layer 3, to obtain the multi-layer co-extrusion cable based on low smoke halogen-free flame-retardant composite layer.

[0067] The double-layer insulation layer 2 is composed of an inner layer and an outer layer;

[0068] The inner layer adopts a core-shell structure nanocomposite resin, wherein the core layer is ethylene-octene copolymer, the shell layer is polyether ester elastomer grafted with norbornene dianhydride, and modified nanometer montmorillonite is dispersed in the shell layer, and 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 composed of ethylene-methyl acrylate matrix and aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio is 1:0.3.

[0069] Example 3: A multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, comprising the following steps:

[0070] S1.1, immerse the tinned copper conductor in a graphene ethanol dispersion solution with a concentration of 1%, uniformly coat by an immersion coater at a speed of 3 m / min, after drying by hot air at 80°C, perform tight pressing and twisting to obtain a conductor layer 1 with a plating layer thickness of 6 μm;

[0071] S1.2, use a double-layer co-extrusion die to synchronously extrude an inner layer core-shell structure nanocomposite resin (160°C) and an outer layer elastomer modified halogen-free flame-retardant layer (180°C) to obtain a double-layer insulation layer 2 wrapping the conductor layer 1;

[0072] S1.3, heat a silica gel strip with an added amount of 5% nanometer boron nitride to 120°C as a reinforcing buffer layer 3, wrap the double-layer insulation layer 2 outside by a spiral winding machine at a tension of 8N and a pitch of 5 times the outer diameter of the cable, and the thickness of the silica gel strip is 1.0 mm;

[0073] S1.4, use a clothes hanger type co-extrusion die to extrude an inner layer ethylene-propylene-diene rubber modified polyolefin (180°C) with a thickness of 0.5 mm and an outer layer irradiation cross-linked polyamide (230°C) with a thickness of 0.4 mm to obtain a composite sheath layer 4 wrapping the reinforcing buffer layer 3 outside to obtain a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer.

[0074] The double-layer insulation layer 2 is composed of an inner layer and an outer layer;

[0075] The inner layer adopts a core-shell structure nanocomposite resin, wherein the core layer is ethylene-octene copolymer, the shell layer is polyether ester elastomer grafted with norbornene dianhydride, and modified nanometer montmorillonite is dispersed in the shell layer, and 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 composed of ethylene-methyl acrylate matrix and aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio is 1:0.3.

[0076] Example 4: A multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, comprising the following steps:

[0077] S1.1, immerse the tinned copper conductor in a graphene ethanol dispersion solution with a concentration of 1%, uniformly coated by an immersion coater at a speed of 3 m / min, dried by hot air at 80°C, and then tightly twisted to obtain a conductor layer 1 with a plating layer thickness of 6 μm;

[0078] S1.2, use a double-layer co-extrusion die to synchronously extrude an inner layer of core-shell structure nanocomposite resin (160°C) and an outer layer of elastomer modified halogen-free flame retardant layer (180°C) to obtain a double-layer insulation layer 2 wrapping the conductor layer 1;

[0079] S1.3, heat the silica gel strip with a nano-boron nitride addition of 5% to 120°C as a reinforced buffer layer 3, wrap it outside the double-layer insulation layer 2 by a spiral winding machine at a tension of 8N and a pitch of 5 times the outer diameter of the cable, and the thickness of the silica gel strip is 1.0 mm;

[0080] S1.4, use a clothes hanger type co-extrusion die to extrude an inner layer of ethylene-propylene rubber modified polyolefin (180°C) with a thickness of 0.5 mm and an outer layer of irradiation cross-linked polyamide (230°C) with a thickness of 0.4 mm to obtain a composite sheath layer 4 wrapping the reinforced buffer layer 3, thereby obtaining a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer.

[0081] The double-layer insulation layer 2 is composed of an inner layer and an outer layer;

[0082] The inner layer adopts a core-shell structure nanocomposite resin, wherein the core layer is an ethylene-octene copolymer, the shell layer is a polyether ester elastomer grafted with norbornene diacid anhydride, and modified nano-montmorillonite is dispersed in the shell layer, and the mass ratio of the core layer to the shell layer is 1:0.5; the outer layer is an elastomer modified halogen-free flame retardant layer composed of an ethylene-methyl acrylate matrix and an aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio is 1:0.4.

[0083] Example 5: a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer and a preparation method thereof, comprising the following steps:

[0084] S1.1, immerse the tinned copper conductor in a graphene ethanol dispersion solution with a concentration of 1%, uniformly coated by an immersion coater at a speed of 3 m / min, dried by hot air at 80°C, and then tightly twisted to obtain a conductor layer 1 with a plating layer thickness of 6 μm;

[0085] S1.2, use a double-layer co-extrusion die to synchronously extrude an inner layer of core-shell structure nanocomposite resin (160°C) and an outer layer of elastomer modified halogen-free flame retardant layer (180°C) to obtain a double-layer insulation layer 2 wrapping the conductor layer 1;

[0086] S1.3, heating the silica gel strip with 5% nano-boron nitride to 120℃ as the enhanced buffer layer 3, winding on the outer layer of the double-layer insulation layer 2 by the spiral winding machine with a tension of 8N, a pitch of 5 times the cable outer diameter, and the thickness of the silica gel strip is 1.0mm;

[0087] S1.4, using a clothes hanger type co-extrusion die, extruding an inner layer of ethylene-propylene rubber modified polyolefin with a thickness of 0.5mm (180℃) and an outer layer of irradiation cross-linked polyamide with a thickness of 0.4mm (230℃) to obtain a composite sheath layer 4, wrapping the enhanced buffer layer 3 to obtain a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer.

[0088] The double-layer insulation layer 2 is composed of an inner layer and an outer layer;

[0089] 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 norbornene diacid anhydride, and modified nano-montmorillonite is dispersed in the shell layer, and the mass ratio of the core layer and the shell layer is 1:0.5; the outer layer is an elastomer modified halogen-free flame-retardant layer composed of ethylene-methyl acrylate matrix and aluminum salt of di-tert-butyl phosphinic acid, and the mass ratio is 1:0.5.

[0090] Comparative Example 1: using the method of Example 4, directly using ethylene-octene copolymer and polyether ester elastomer mixture without using the inner layer core-shell structure nano-composite resin as the inner layer insulation layer.

[0091] Comparative Example 2: using the method of Example 4, no modified nano-montmorillonite is added in the shell layer of the inner layer core-shell structure nano-composite resin.

[0092] Comparative Example 3: using the method of Example 4, replacing the aluminum salt of di-tert-butyl phosphinic acid with decabromodiphenyl ethane in the outer layer of the elastomer modified halogen-free flame-retardant layer.

[0093] During the preparation of the multi-layer co-extrusion cable based on the low-smoke halogen-free flame-retardant composite layer, the double-layer insulation layer composed of the inner layer core-shell structure nano-composite resin and the outer layer of the elastomer modified halogen-free flame-retardant layer is added, and the performance index test items and test standards of the obtained multi-layer co-extrusion cable based on the low-smoke halogen-free flame-retardant composite layer are as follows:

[0094] According to GB / T2951 standard, cut dumbbell-shaped samples (thickness 1-2mm, gauge length 25mm) from the cable, the distance between the grips of the testing machine is 50mm, the tensile rate is 250mm / min; measure the initial thickness and width of the sample, calculate the cross-sectional area; clamp the sample in the grips of the testing machine, start the testing machine until the sample breaks, record the maximum force value (F) and the gauge length at break (L1); calculate the tensile strength (MPa) = F / cross-sectional area, elongation at break (%) = [(L1-initial gauge length) / initial gauge length] x 100%; higher tensile strength indicates that the cable material has strong tensile fracture resistance, suitable for scenarios that need to bear mechanical stress; higher elongation at break indicates that the material has excellent ductility and can withstand large deformation (such as bending, stretching) without breaking.

[0095] According to GB / T9330-2020 standard, take 3 one-meter-long cables, remove the outer sheath (if armored, keep it); bend the cable 360° unidirectionally with different mandrel diameters, observe whether cracks appear on the surface, record the minimum bending radius (multiple of the cable outer diameter (D)); lower minimum bending radius indicates that the cable is soft, suitable for narrow spaces or scenarios that need to be bent frequently.

[0096] According to GB / T 18380-2008 standard, bundle the cables according to the specified number (such as 6), vertically hang them in the combustion chamber; use a propane burner, the flame height is 750mm, apply the flame for 20 minutes; observe the total heat release and carbonization height of the bundled cables within 600 seconds, lower cumulative heat release and carbonization height indicates that the cable has excellent flame retardant performance, slow spread during combustion, low smoke production, and less toxic gas release.

[0097] The low-smoke halogen-free flame-retardant composite layer-based multilayer co-extrusion cables prepared in Examples 1-5 and Comparative Examples 1-3 were tested according to the above standards, and the data obtained are shown in Table 1:

[0098] Table 1 Performance data of cables of Examples 1-5 and Comparative Examples 1-3

[0099]

[0100] As can be seen from Examples 1-3, in the low-smoke halogen-free flame-retardant composite layer-based multilayer co-extrusion cable, when the other components remain unchanged and the mass ratio of the core layer to the shell layer of the inner layer core-shell structure nanocomposite resin gradually increases, the mechanical properties, flexibility and flame retardant properties of the cable are continuously improved.

[0101] The flexible long chains of the core layer ethylene-octene copolymer endow the material with high elasticity and impact resistance, capable of absorbing mechanical stress and inhibiting crack propagation; the shell layer forms a chemical crosslinking network through grafting polyether ester elastomer of nadic anhydride, enhancing the interfacial adhesion and limiting the movement of molecular chains, thereby improving the heat resistance; the dispersed modified nano-montmorillonite in the shell layer forms a physical barrier through intercalation effect, blocking the transmission of oxygen and heat, delaying the combustion process; even if the proportion of the shell layer is reduced, the crosslinking network can still effectively improve the tensile strength, and the sheet barrier effect of the modified nano-montmorillonite maintains the flame retardant performance.

[0102] The modified nano-montmorillonite in the shell layer absorbs heat and releases inert gases such as water vapor and carbon dioxide at high temperatures, diluting the concentration of combustible gases, and its sheet structure promotes the formation of a carbonized layer, together with the shell layer crosslinking network, to build a "gas- condensed phase" dual-effect flame retardant mechanism, significantly reducing the carbonization height; the high flexibility of the core layer ethylene-octene copolymer reduces the rigidity of the material, reducing the minimum bending radius of the cable and adapting to complex wiring requirements; the core-shell interface is further dispersed through the polarity matching and chemical bonding of the anhydride group, avoiding interlayer peeling and ensuring the stability of mechanical properties.

[0103] Further, as can be seen from the comparison of Examples 3-5, in a multi-layer co-extrusion cable based on a low-smoke halogen-free flame-retardant composite layer, when the mass ratio of the ethylene-methyl acrylate matrix of the outer layer elastomer modified halogen-free flame-retardant layer to aluminum salt of di-tert-butyl phosphinic acid gradually increases while other components remain unchanged, the mechanical properties, flexibility, and flame retardant performance of the cable are continuously improved.

[0104] At high temperatures, aluminum salt of di-tert-butyl phosphinic acid decomposes into aluminum phosphate and phosphorus-containing radicals; the former forms a dense carbon layer on the surface of the material, blocking the transmission of oxygen and heat; the latter captures active radicals (such as -OH) in the combustion chain reaction, interrupting flame propagation, reducing the total heat release within 600 seconds, and significantly reducing the carbonization height; the ethylene-methyl acrylate matrix maintains flexibility through its elastomer properties, while dilauryl thiodipropionate as a compatibilizer further improves the dispersibility of aluminum salt of di-tert-butyl phosphinic acid in the ethylene-methyl acrylate matrix, avoiding mechanical property degradation caused by flame retardant aggregation.

[0105] The increase in the ethylene-methyl acrylate matrix significantly improves the elastic network of the material through the physical crosslinking effect of its long-chain carboxylate structure, thereby endowing it with high elongation at break; at the same time, the hydrogen bonding between the matrix and the decomposition products of aluminum salt of di-tert-butyl phosphinic acid enhances the interfacial adhesion, further improving the tensile strength; in addition, the flexibility dominant characteristic of the ethylene-methyl acrylate matrix allows the minimum bending radius of the cable to be reduced, thereby better adapting to complex wiring requirements.

[0106] According to the above test experiments, Example 4 is the optimal embodiment.

[0107] It can be seen from the comparison of Example 4 and Comparative Example 1, Comparative Example 2 that: in the core-shell structure, the shell layer polyether ester elastomer forms chemical bonding with the core layer ethylene-octene copolymer through grafted nadic anhydride, which significantly enhances the interfacial bonding force between the two phases, thereby improving the overall performance of the material; in contrast, when simply blended, the ethylene-octene copolymer and the polyether ester elastomer are only physically mixed, the interfacial compatibility is poor, and phase separation easily occurs, leading to a decrease in interlayer adhesion and a low stress transfer efficiency, which in turn deteriorates 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; when simply blended, the two phases are unevenly distributed, and the hard area of the elastomer forms a stress concentration point with the soft phase of the ethylene-octene copolymer, exacerbating local crack initiation; in addition, the uncrosslinked shell layer cannot limit the sliding of molecular chains, resulting in a decrease in the material's creep resistance and easy deformation failure during long-term use.

[0108] The modified nano-montmorillonite dispersed in the shell layer of the core-shell structure forms a lamellar barrier through intercalation effect, inhibits crack propagation and improves rigidity; the blending system lacks nano-filler, and there is no physical barrier structure inside the material, resulting in a decrease in elongation at break and insufficient heat resistance; at the same time, the lack of endothermic decomposition of montmorillonite and the strengthening effect of carbon layer during combustion leads to a decrease in flame retardant performance.

[0109] It can be seen from the comparison of Example 4 and Comparative Example 3 that: in the outer elastomer modified halogen-free flame retardant layer, decabromodiphenyl ethane is used to replace aluminum salt of di-tert-butyl phosphinic acid, which significantly reduces the flame retardant performance of the cable; aluminum salt of di-tert-butyl phosphinic acid is a phosphorus-based flame retardant, and its flame-retardant mechanism mainly forms a dense carbon layer through condensed-phase flame retardation to isolate heat and oxygen, and release tert-butyl free radicals to capture flame free radicals, thereby inhibiting combustion; decabromodiphenyl ethane is a bromine-based flame retardant, and its flame-retardant mechanism relies on gas-phase flame retardation to inhibit fire by releasing bromine radicals; in addition, decabromodiphenyl ethane has poor compatibility with the ethylene-methyl acrylate matrix, and easily agglomerates, leading to interfacial defects, a decrease in tensile strength, and a destruction of carbon layer continuity, thereby affecting the heat release rate.

[0110] In summary, in the preparation process of the multi-layer co-extrusion cable based on low-smoke halogen-free flame-retardant composite layer, the addition of the inner layer core-shell structure nanocomposite resin and the outer layer elastomer modified halogen-free flame-retardant layer can significantly improve the performance of the cable; the inner layer core-shell structure provides high elasticity through the ethylene-octene copolymer core layer to relieve bending stress concentration; the polyether ester elastomer shell layer grafted with fumaric anhydride and the modified nanometer montmorillonite form a three-dimensional reinforcing network to improve the tensile strength and solve the contradiction of "rigid and brittle" of traditional halogen-free materials; the outer layer elastomer modified layer takes ethylene-methyl acrylate as the matrix to further improve the tensile strength and elongation at break, and ensure the flexibility of the cable under complex stress; the inner layer core-shell structure catalyzes the formation of carbon through the shell anhydride group, and the modified nanometer montmorillonite blocks heat transfer to improve the oxygen index; the mixed salt decomposition product of the outer layer elastomer modified layer captures the combustion free radicals to inhibit flame propagation, and the microencapsulated red phosphorus delays heat release, so that the total heat release within 600s is reduced, and the length of the bundle combustion carbonization is shortened.

[0111] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only preferred examples of the present application and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. Multi-layer co-extruded cable based on low-smoke halogen-free flame retardant composite layer, characterized in that: Its structure, from inside to outside, is 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 nanocomposite 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. 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 the low-smoke halogen-free flame retardant composite layer according to claim 1, 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 weight of the polyether ester elastomer with modified nano-montmorillonite and polyether ester elastomer grafted with nadic anhydride in a high-speed mixer at 800-1200 rpm for 10-15 minutes; then add ethylene-octene copolymer and pre-mix; 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 the low-smoke halogen-free flame retardant composite layer according to claim 1, characterized in that: The outer layer of the double-layer insulation layer (2) is prepared as follows: Pre-disperse aluminum di-tert-butylphosphinate and vinyltrimethoxysilane in a high-speed mixer at 800-1000 rpm for 10-15 minutes; Then, ethylene-methyl acrylate matrix and dilauryl thiodipropionate are added and melt-blended through a twin-screw extruder at an extrusion temperature of 160-210° C. and a screw speed of 250-300 rpm to obtain the outer layer of the double-layer insulation layer (2).

4. The multi-layer co-extruded cable based on the 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 modified polyolefin, and the outer layer is radiation cross-linked polyamide.

5. A method for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer, for preparing a multi-layer co-extruded cable based on a low-smoke halogen-free flame-retardant composite layer according to 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%, uniformly coating the conductor with a dip coater at a speed of 2-3 m / min, drying the conductor with hot air at 50-80°C, and then pressing and twisting the conductor to obtain a conductor layer (1) with 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) to obtain the double-layer insulation layer (2), which wraps the conductor layer (1); S1.3, heating the silica gel strip added with nano boron nitride to 120-130°C as a reinforcement buffer layer (3), and winding it around the double insulation layer (2) with a pitch of 3-5 times the outer diameter of the cable using 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 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 the above-mentioned 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 thickness of the inner layer is 0.3-0.5 mm, and the thickness of the outer layer is 0.2-0.4 mm.

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