Flame-retardant cable insulation layer and preparation method thereof

Abstract

The invention provides a flame-retardant cable insulation layer and a preparation method thereof, and relates to the technical field of flame-retardant material preparation, and the flame-retardant cable insulation layer comprises the following components by mass: 50-70% of halogen-free flame-retardant crosslinked polyethylene, 5-20% of SBS, 5-25% of an intercalated metal oxide, 10-25% of epoxy silane, 2-10% of graphene oxide, 2-5% of an impact modifier, 2-5% of an auxiliary agent, and 2-10% of a charring agent. The intercalation metal oxide and the graphene oxide are simultaneously added into the flame-retardant cable insulating layer, so that the oxidation resistance and the flame retardance of the material can be effectively improved, and the flame-retardant cable can reach the B1-level flame-retardant standard.

Description

Technical Field

[0001] The present invention relates to the technical field of flame - retardant material preparation, and particularly to a flame - retardant cable insulating layer and a preparation method thereof. Background Art

[0002] The flame - retardant cable insulating layer is an important part of the cable industry, and its performance directly affects the safety and reliability of the cable. However, there are still many problems in the flame - retardant cable insulating layer in the prior art in terms of flame - retardant performance, antioxidant property, lifespan, and weather resistance. These problems seriously restrict the development of the cable industry. This article will analyze in detail the problems existing in the flame - retardant cable insulating layer in the prior art from the following aspects: (1) Poor flame - retardant performance: Flame - retardant performance refers to the ability of a material to prevent or slow down the spread of fire when exposed to fire or high temperature. Existing flame - retardant cable insulating layers generally use halogen compounds as flame retardants. These halogen compounds will release toxic and harmful hydrogen halide gases during combustion, causing serious harm to the environment and human health. In addition, the flame - retardant effect of these halogen compounds is greatly affected by factors such as temperature and humidity, making the flame - retardant performance unstable. In order to improve the flame - retardant performance, researchers have tried to use halogen - free flame retardants to replace halogen compounds, such as aluminum hydroxide, magnesium hydroxide, etc. However, halogen - free flame retardants usually have a high addition amount, which may reduce the electrical and mechanical properties of the cable insulating layer. Therefore, how to improve the flame - retardant efficiency to the B1 level while maintaining the electrical and mechanical properties of the cable insulating layer is an urgent problem to be solved in the existing flame - retardant cable insulating layer.

[0003] (2) Poor antioxidant property: Antioxidant property refers to the ability of a material to resist oxidation in an oxidative environment. Existing flame - retardant cable insulating layers mostly use polyethylene as the matrix material. The oxidation stability of polyethylene is poor and it is easy to undergo oxidative degradation under conditions such as high temperature and light, generating harmful substances such as aldehydes, ketones, and acids. These oxidation products will cause a decline in material performance and shorten the service life of the cable. In order to improve the antioxidant property, researchers have tried to add antioxidants, such as phosphites, phenolic compounds, etc., to the polyethylene matrix. However, the compatibility between the antioxidant and polyethylene is poor, and it is difficult to play an ideal antioxidant role. In addition, factors such as the addition amount and distribution uniformity of the antioxidant will also affect the antioxidant property. Therefore, how to improve the compatibility and antioxidant effect of the antioxidant is the key to improving the antioxidant property of the flame - retardant cable insulating layer.

[0004] (3) Poor weather resistance: Weather resistance refers to the ability of materials to resist the effects of aging, corrosion, etc. under natural environmental conditions. During the outdoor application of existing flame-retardant cable insulation layers, they are easily affected by environmental factors such as ultraviolet rays, ozone, and moisture, resulting in a decline in material properties. To improve weather resistance, researchers have tried to add additives such as ultraviolet absorbers and anti-ozone agents. However, the compatibility of these additives with the polyethylene matrix is poor, making it difficult to achieve an ideal weather resistance effect. In addition, factors such as the addition amount and distribution uniformity of the additives also affect weather resistance. Therefore, how to improve the compatibility and weather resistance of the additives to enhance the weather resistance of the flame-retardant cable insulation layer is an urgent problem to be solved for existing flame-retardant cable insulation layers.

[0005] (4) Short lifespan: Short lifespan is another serious problem existing in existing flame-retardant cable insulation layers. Due to factors such as poor flame retardancy, poor antioxidant property, and poor weather resistance, the performance of existing flame-retardant cable insulation layers is prone to decay during long-term use, leading to cable failures and even fire accidents. To increase the lifespan, researchers have tried to improve the comprehensive properties of the materials by improving the formulation and optimizing the process. However, these methods often fail to fundamentally solve the problem of short lifespan. Therefore, how to improve the antioxidant property, weather resistance, and anti-aging property of the flame-retardant cable insulation layer to extend its service life is an urgent problem to be solved for existing flame-retardant cable insulation layers.

[0006] In response to the above problems existing in existing flame-retardant cable insulation layers, researchers have been exploring new flame retardants, antioxidants, weather resistance improvers, etc. to solve these problems. In addition, they have also tried to improve the comprehensive properties of the materials by improving the formulation and optimizing the process. However, these methods often fail to fundamentally solve the above problems.

[0007] In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] The purpose of the present invention is to provide a flame-retardant cable insulation layer and its preparation method. By simultaneously adding intercalated metal oxides and graphene oxide to the flame-retardant cable insulation layer, the antioxidant property and flame retardancy of the material can be effectively improved, enabling the flame retardancy level of the cable insulation layer to reach B1 level. It also increases the lifespan of the material. An impact-resistant modifier with a core-shell structure is used, which can not only enhance the impact resistance of the insulating material but also significantly improve the material's resistance to environmental factors.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions: The present invention provides a flame-retardant cable insulating layer, which comprises the following components by mass percentage: 50-70% of halogen-free flame-retardant cross-linked polyethylene, 5-20% of SBS, 5-25% of intercalated metal oxide, 10-25% of epoxy group silane, 2-10% of graphene oxide, 2-5% of impact modifier, 2-5% of auxiliary agent and 2-10% of charring agent.

[0010] Further, on the basis of the above technical solution of the present invention, the intercalated metal oxide is a magnesium-aluminum intercalated metal oxide; The magnesium-aluminum intercalated metal oxide has a main body layer board and anions located between the main body layer boards, and the main body layer board is composed of hydroxides of magnesium and aluminum; The anion is any one of phosphate ion, borate ion, sulfate ion or molybdate ion.

[0011] Further, on the basis of the above technical solution of the present invention, the epoxy group silane includes one or more of 3-glycidyltrimethoxysilane, 3-glycidyltriethoxysilane, 3-glycidyltriisopropoxysilane, 2,3-glycidylmethoxysilane, 2,3-glycidylethoxysilane.

[0012] Further, on the basis of the above technical solution of the present invention, the impact modifier is a core-shell structure impact modifier, including at least one of MBS impact modifier or ACR impact modifier; And / or, the auxiliary agent includes one or more of aromatic oil, silicone oil, microcrystalline wax.

[0013] Further, on the basis of the above technical solution of the present invention, the charring agent includes one or more of ammonium phosphate, pentaerythritol, melamine, borate, silicate.

[0014] The present invention also provides a preparation method of the flame-retardant cable insulating layer as described above, which comprises the following steps: S1: Pretreat graphene oxide and intercalated metal oxide respectively; S2: Place epoxy group silane, pretreated graphene oxide and pretreated intercalated metal oxide in a solvent, adjust the pH value, and stir to obtain a mixed material; S3: After drying the mixed material, carry out ball milling to obtain a mixture powder; S4: Stir halogen-free flame-retardant cross-linked polyethylene, SBS, auxiliary agent and impact modifier, then add the mixture powder and charring agent, and continue to stir to obtain a mixed slurry; S5: Melt and extrude the mixed slurry, and shape it through a mold to prepare the flame-retardant cable insulating layer.

[0015] Further, on the basis of the above technical solution of the present invention, in step S1, the pretreatment of graphene oxide includes: Placing graphene oxide under ultraviolet light for photo-oxidation, the light intensity of the ultraviolet light is 10 - 100 mW / cm 2 , and the light irradiation time is 30 - 60 min; And / or, in step S1, the pretreatment of the intercalated metal oxide includes: Placing the intercalated metal oxide in an oven at 50 - 60 °C for drying for 4 - 6 h; And / or, in step S2, the solvent is one of ethanol, acetone or water; And / or, in step S2, the temperature of the stirring is 30 - 60 °C, the stirring time is 1 - 2 h, and the stirring rate is 200 - 500 r / min; And / or, in step S2, adjusting the pH value to 4 - 5; And / or, in step S2, the addition amount of epoxy silane ≥ the total addition amount of the pretreated graphene oxide and the pretreated intercalated metal oxide.

[0016] Further, on the basis of the above technical solution of the present invention, in step S3, the ball milling includes the following conditions: The ball milling time is 2 - 4 h, the ball milling speed is 50 - 100 r / min, the mass ratio of the balls to the mixed material is (5 - 10):1, and zirconia balls are selected; And / or, the drying temperature is 50 - 80 °C, and the time is 12 - 24 h; And / or, the particle size of the mixture powder is 1 - 100 μm; And / or, in step S4, the temperature of the stirring is 130 - 150 °C, the stirring time is 1 - 2 h, and the stirring rate is 200 - 500 r / min; And / or, in step S4, after adding the mixture powder and the charring agent, continue to stir for 3 - 5 h.

[0017] Further, on the basis of the above technical solution of the present invention, the particle sizes of the halogen-free flame-retardant cross-linked polyethylene and SBS are both 1 - 3 mm; And / or, the particle sizes of the charring agent and the impact modifier are both 200 - 500 μm.

[0018] Further, on the basis of the above technical solution of the present invention, in step S5, the conditions of the melt extrusion include: the heating temperature is 140 - 180 °C; the die head extrusion temperature is 170 - 200 °C.

[0019] A flame-retardant cable insulating layer and a preparation method thereof provided by the present invention have the following beneficial effects: 1. In the flame-retardant cable insulation layer of the present invention, intercalated metal oxides and graphene oxide are added simultaneously. This is because graphene oxide has a very high specific surface area and good thermal stability. When it is compounded with magnesium-aluminum intercalated oxides, it can effectively improve the antioxidant property and flame retardancy of the material, and the flame retardancy level of the material can reach Class B1. The higher flame retardancy and antioxidant property improve the lifespan of the material. When the composite material is exposed to high temperature or flame, graphene oxide and intercalated metal oxides can act together to form a porous carbonized layer, which has high thermal stability and flame retardancy and can protect the material from direct damage by the flame. The barrier property of graphene oxide can prevent the diffusion of oxygen and combustible gases, while the decomposition of intercalated metal oxides can release water vapor, which can absorb heat and inhibit flame propagation. Moreover, the two-dimensional structure of graphene oxide can form a network structure in the composite material, and this structure can effectively disperse thermal stress and improve the thermal stability of the material.

[0020] 2. The present invention uses epoxy-based silane as an intermediate medium to connect graphene oxide and intercalated metal oxides. Epoxy-based silane can bind to both graphene oxide and metal oxides simultaneously, playing a bridging role and enabling them to be evenly distributed in the mixture. In addition, the silicon-oxygen bond in epoxy-based silane can form a stable chemical bond with metal ions in metal oxides, thereby enhancing the interaction between graphene oxide and metal oxides and improving the overall performance of the mixture.

[0021] 3. The present invention uses an impact modifier with a core-shell structure, which can not only enhance the impact resistance of the insulation material, making it more tough and not easily broken when subjected to external forces, but also significantly improve the material's resistance to environmental factors such as ultraviolet radiation, temperature changes, and humidity effects, thereby greatly extending the service life of the cable and ensuring the stable operation of the cable system in harsh environments.

[0022] 4. The flame-retardant cable insulation layer provided by the present invention is completely halogen-free. This not only endows the cable insulation layer with excellent flame retardancy and meets the Class B1 flame retardancy standard, but more importantly, it is environmentally friendly and meets the current society's demand for green and environmentally friendly materials. Since it does not contain halogens, this material will not produce toxic halogenated gases during combustion, which greatly reduces the harm to the environment and human health. Through the application of this material, the safety and environmental friendliness of cable products can be effectively improved, contributing new strength to the development of the cable industry. Detailed implementation mode

[0023] To make the objectives, technical solutions and advantages of the present invention clearer, the following will describe the technical solutions in the embodiments of the present invention clearly and completely in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the said embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0024] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0025] According to the first aspect of the present invention, there is provided a flame-retardant cable insulating layer, which includes the following components by mass percentage: 50-70% of halogen-free flame-retardant cross-linked polyethylene (such as 52%, 55%, 60%, 62%, 65%, 67%, etc.), 5-20% of SBS (styrene-butadiene-styrene block copolymer) (such as 7%, 10%, 15%, 17%, etc.), 5-25% of intercalated metal oxide (such as 10%, 15%, 20%, etc.), 10-25% of epoxy group silane (such as 15%, 20%, 21%, 22%, 23%, 24%, etc.), 2-10% of graphene oxide (such as 5%, 7%, 9%, etc.), 2-5% of impact modifier (such as 3%, 4%, 5%, etc.), 2-5% of auxiliary agent (such as 3%, 4%, 5%, etc.) and 2-10% of charring agent (such as 5%, 7%, 9%, etc.).

[0026] Specifically, the flame-retardant cable insulating layer provided by the present invention is completely free of halogen elements, which not only endows the cable insulating layer with excellent flame-retardant performance and reaches the B1-level flame-retardant standard, but more importantly, it is environmentally friendly and meets the requirements of today's society for green and environmental protection materials. Since it does not contain halogen, this material will not produce toxic halogenated gases during the combustion process, which greatly reduces the harm to the environment and human health. Through the application of this material, the safety and environmental protection of cable products can be effectively improved, contributing new strength to the development of the cable industry.

[0027] As an optional implementation manner of the present invention, the intercalated metal oxide is a magnesium-aluminum intercalated metal oxide; Specifically, in the flame-retardant cable insulating layer of the present invention, magnesium-aluminum intercalated metal oxide and graphene oxide are added simultaneously. This is because graphene oxide has a very high specific surface area and good thermal stability. When it is compounded with magnesium-aluminum intercalated oxide, it can effectively improve the antioxidant property and flame retardancy of the material, making it meet the B1-level flame retardant standard. When the composite material is subjected to high temperature or flame, graphene oxide and intercalated metal oxide can act together to form a porous carbonized layer, which has high thermal stability and flame retardancy and can protect the material from direct attack by the flame. The barrier property of graphene oxide can prevent the diffusion of oxygen and combustible gases, while the decomposition of intercalated metal oxide can release water vapor, which can absorb heat and inhibit flame propagation. Moreover, the two-dimensional structure of graphene oxide can form a network structure in the composite material, and this structure can effectively disperse thermal stress and improve the thermal stability of the material.

[0028] However, the surface properties of graphene oxide and intercalated metal oxide are different. Graphene oxide has strong hydrophilicity, while intercalated metal oxide has strong hydrophobicity, which makes it difficult for the two to be uniformly mixed. Secondly, the tiny structure of intercalated metal oxide is prone to agglomeration, which may lead to uneven distribution on graphene oxide, thus affecting the performance of the mixture. Therefore, in order to overcome these problems, epoxy group silane is used as an intermediate medium to connect graphene oxide and intercalated metal oxide. Epoxy group silane can bind to both graphene oxide and metal oxide simultaneously, playing a bridging role and enabling the two to be uniformly distributed in the mixture. In addition, the silicon-oxygen bond in epoxy group silane can form stable chemical bonds with metal ions in metal oxide, thereby enhancing the interaction between graphene oxide and metal oxide and improving the overall performance of the mixture.

[0029] Preferably, the magnesium-aluminum intercalated metal oxide has a main layer board and anions located between the main layer boards, and the main layer board is composed of hydroxides of magnesium and aluminum; Preferably, the anion is any one of phosphate ion, borate ion, sulfate ion or molybdate ion.

[0030] Specifically, the purpose of inserting phosphate ion, borate ion, sulfate ion or molybdate ion between magnesium-aluminum intercalated metal oxides in the present invention is as follows: Phosphate ion can form stable phosphates with metal ions. Such compounds usually have good thermal stability and flame retardancy. The phosphate compound combines with magnesium-aluminum intercalated oxide to form a new type of layered composite material, which has high thermal stability and flame retardant performance. Because phosphate itself has good flame retardant effect and can decompose into phosphoric acid, phosphate and phosphoric acid ester at high temperature, these products contribute to the formation of a carbonized layer and prevent the propagation of flame. In addition, the addition of phosphate can also improve the mechanical strength and chemical corrosion resistance of magnesium-aluminum intercalated oxide.

[0031] Borate ions: Borate ions can form stable borates with metal ions. These compounds can release non-combustible gases, such as water vapor and boric acid gas, at high temperatures, which helps to inhibit the spread of flames.

[0032] Sulfate ions: Sulfate ions can form stable sulfates with metal ions. These compounds are not easily decomposed at high temperatures, which helps to improve the flame retardancy of materials.

[0033] Silicate ions: Silicate ions can form stable silicates with metal ions. These compounds can remain stable at high temperatures and are not easily combustible, thus providing good flame retardant effects.

[0034] Molybdate ions: Molybdate ions can form stable molybdates with metal ions. These compounds have high thermal stability and can promote the formation of a protective oxide layer at high temperatures, thus playing a flame retardant role.

[0035] As an alternative embodiment of the present invention, the epoxy group silane includes one or more of 3-glycidyltrimethoxysilane, 3-glycidyltriethoxysilane, 3-glycidyltriisopropoxysilane, 2,3-glycidylmethoxysilane, and 2,3-glycidylethoxysilane.

[0036] Specifically, the epoxy group silane is added in the present invention because the structure of the epoxy group silane contains both siloxane bonds that can provide strong binding force and epoxy groups with high reactivity. This unique structure enables the epoxy group silane to react with oxygen-containing groups such as carboxyl groups on the surface of graphene oxide. At the same time, the silanol formed after hydrolysis of the siloxane bond can react with the hydroxyl groups on the surface of the intercalated metal oxide, thereby effectively connecting graphene oxide and the intercalated metal oxide. Through this bridging effect of the epoxy group silane, the resulting composite material can not only obtain better flame retardant performance, but also possess excellent stability, antioxidant property, and mechanical properties.

[0037] As an alternative embodiment of the present invention, the impact modifier is a core-shell structure impact modifier, including at least one of MBS impact modifier or ACR impact modifier.

[0038] The MBS impact modifier is a terpolymer obtained by emulsion graft polymerization of methyl methacrylate (M), butadiene (B) and styrene (S). It has a typical "core-shell" multi-layer structure in terms of particle microstructure. The core is a rubber phase of polybutadiene, a rubber phase with a diameter of about 100 nm, and the outside is a shell layer composed of styrene and methyl methacrylate. Each layer has its unique function. The center of the particle is the rubber phase. When the matrix material is subjected to external impact, the rubber core induces crazes, disperses and absorbs the impact energy, preventing brittle fracture of the material. The outer styrene layer and methyl methacrylate layer have excellent compatibility with the halogen-free flame-retardant crosslinked polyethylene and can generate good adhesion with the halogen-free flame-retardant crosslinked polyethylene. Due to the above special structure of the MBS resin, it has good toughness below -40°C, sufficient rigidity at 80-90°C, and can improve the impact resistance, weather resistance and processing fluidity of the halogen-free flame-retardant crosslinked polyethylene after blending.

[0039] The ACR impact modifier is an acrylate copolymer with a core-shell structure, which is formed by coagulating and drying composite latex particles with a core-shell structure, and is a white free-flowing powder. Among them, the composite latex particles generally have a crosslinked acrylate rubber-like polymer with a low glass transition temperature as the "core" and an acrylate plastic-like polymer as the "shell". The rubber in the core layer is the part that truly plays the role of impact modification. The crosslinked rubber particles are distributed in the modified plastic matrix in the form of dispersed particles. When subjected to external force, a large number of crazes are generated around the particles and quickly spread to form many shear bands, absorbing a large amount of impact energy, thus greatly promoting and improving the impact resistance of the halogen-free flame-retardant crosslinked polyethylene and reducing the reject rate.

[0040] Based on its own structural characteristics, the ACR impact modifier has many excellent properties. The products prepared with it can not only have higher strength, but also significantly improve the heat distortion, melt fluidity and weather resistance of the halogen-free flame-retardant crosslinked polyethylene.

[0041] As an optional embodiment of the present invention, the auxiliary agent typically and non-limitingly includes one or more of aromatic oil, silicone oil, and microcrystalline wax.

[0042] As an optional embodiment of the present invention, the charring agent includes one or more of ammonium phosphate, pentaerythritol, melamine, borate, and silicate.

[0043] According to the second aspect of the present invention, the present invention provides a method for preparing a flame-retardant cable insulating layer as described above, comprising the following steps: S1: Pretreat graphene oxide and intercalated metal oxide respectively; S2: Place the epoxy group silane, pretreated graphene oxide, and pretreated intercalated metal oxide in a solvent, adjust the pH value, and stir to obtain a mixed material; S3: After drying the mixed material, perform ball milling to obtain a mixture powder; S4: Stir the halogen-free flame retardant crosslinked polyethylene, SBS, additives, and impact modifier, then add the mixture powder and charring agent, and continue to stir to obtain a mixed slurry; S5: Melt-extrude the mixed slurry and shape it through a mold to produce a flame retardant cable insulation layer.

[0044] As an optional implementation mode of the present invention, in step S1, the pretreatment of graphene oxide includes: Place the graphene oxide under ultraviolet light for photooxidation, and the light intensity of the ultraviolet light is 10 - 100 mW / cm 2 , and the light irradiation time is 30 - 60 min; Specifically, the purpose of irradiating graphene oxide with ultraviolet light is to increase its surface oxidation degree and the density of oxygen-containing functional groups, thereby promoting the reaction between the epoxy group in graphene oxide and the epoxy group in the epoxy group silane; the light intensity needs to be sufficient to drive the oxidation reaction, but should not be too high to avoid overheating or damaging the structure of graphene oxide; the light irradiation time needs to be long enough to ensure that the oxidation reaction proceeds fully, but should not be too long to avoid unnecessary energy consumption or over-oxidation of the material.

[0045] And / or, in step S1, the pretreatment of the intercalated metal oxide includes: Place the intercalated metal oxide in an oven at 50 - 60 °C (such as 53 °C, 55 °C, 57 °C, 59 °C, etc.) for drying for 4 - 6 h to ensure the stability of the intercalated metal oxide during the mixing process.

[0046] As an optional implementation mode of the present invention, in step S2, the solvent is one of ethanol, acetone, or water, and the addition amount of the solvent can be adjusted according to the total amount of reactants to ensure that the reactants are fully dissolved; And / or, in step S2, the temperature of the stirring is 30 - 60 °C (such as 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, etc.), the stirring time is 1 - 2 h, and the stirring rate is 200 - 500 r / min (such as 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, etc.); And / or, in step S2, use 1 mol / L sulfuric acid and 1 mol / L sodium hydroxide to adjust the pH value to 4 - 5. Under slightly acidic conditions, the hydrolysis of the silicon-oxygen bond in the epoxy group silane can be promoted; And / or, in step S2, the addition amount of epoxy group silane ≥ the total addition amount of the pretreated graphene oxide and the pretreated intercalated metal oxide.

[0047] Specifically, under the above reaction conditions, the hydrolysis reaction of epoxy group silane and its interaction with graphene oxide and magnesium-aluminum intercalated metal oxide can be effectively promoted. Under this reaction condition, the silicon-oxygen bond in epoxy group silane will generate silanol under hydrolysis, and these silanol groups can react with the hydroxyl groups on the surface of the intercalated metal oxide to form stable chemical bonds. At the same time, the epoxy groups of epoxy group silane have high reactivity, and they can undergo ring-opening polymerization reactions with oxygen-containing functional groups such as carboxyl groups on the surface of graphene oxide, thereby establishing a chemical connection between graphene oxide and epoxy group silane. Through this dual reaction mechanism, epoxy group silane can not only connect graphene oxide and intercalated metal oxide as a bridge, but also enhance the overall stability and performance of the composite material.

[0048] Furthermore, in order to ensure the bridging effect of epoxy group silane, it is necessary to make the added mass of epoxy group silane greater than or equal to the total added mass of the pretreated graphene oxide and the pretreated intercalated metal oxide. Sufficient epoxy group silane can ensure that both graphene oxide sheets and intercalated metal oxides can be effectively covered and connected, thus forming a continuous and stable network structure. Moreover, the hydrolyzed epoxy groups and silanol groups in the excess epoxy group silane can form chemical bonds with the main materials in the flame-retardant cable insulation layer, namely halogen-free flame-retardant crosslinked polyethylene and SBS, thereby improving the compatibility between components and further enhancing the mechanical properties of the material. At the same time, due to the fact that epoxy group silane itself has certain flame-retardant properties, the excess epoxy group silane can further improve the flame retardancy of the material and reduce the flame propagation speed and smoke density during combustion. However, it should also be noted to avoid adding too much epoxy group silane. Excessive addition (such as the mass percentage of epoxy group silane added to the material being greater than 25%) may lead to an increase in the viscosity of the composite material, a decrease in processing performance, and affect the mechanical properties of the product, etc.

[0049] As an alternative embodiment of the present invention, in step S3, the ball milling includes the following conditions: The ball milling time is 2 - 4 h, the ball milling speed is 50 - 100 r / min (such as 60 r / min, 70 r / min, 80 r / min, 90 r / min, etc.), the mass ratio of balls to the mixed material is (5 - 10):1, and zirconia balls are selected; And / or, the drying temperature is 50 - 80 °C and the time is 12 - 24 h; And / or, the particle size of the mixture powder is 1 - 100 μm (such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, etc.).

[0050] Specifically, ball-milling the dried mixed materials can ensure the uniform mixing of graphene oxide, intercalated metal oxides, and epoxy group silanes at the molecular level, thereby significantly improving the performance of the final composite material. It can also act on the mixed materials through strong mechanical forces. This mechanical force can effectively reduce the particle size, increase its surface area, and further enhance the interaction and contact interface between the materials.

[0051] Furthermore, since halogen-free flame-retardant crosslinked polyethylene and the like are large-particle substances while the particle size of the mixture powder is small, special consideration needs to be given to the mixing uniformity of the two during the preparation process. To ensure that the mixture can be fully and uniformly fused. These large-particle substances are effectively refined and uniformly dispersed in the mixture powder during the mixing process, thus avoiding stratification or agglomeration phenomena caused by differences in particle size. This mixing not only ensures the uniformity of the cable insulation layer at the microstructural level but also improves the overall performance of the material, providing a reliable material guarantee for the development of the cable industry.

[0052] As an alternative embodiment of the present invention, in step S4, the stirring temperature is 130 - 150 °C, the stirring time is 1 - 2 h, and the stirring rate is 200 - 500 r / min (such as 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, etc.); And / or, in step S4, after adding the mixture powder and the charring agent, continue stirring for 3 - 5 h.

[0053] As an alternative embodiment of the present invention, the particle sizes of both the halogen-free flame-retardant crosslinked polyethylene and SBS are 1 - 3 mm (such as 1.5 mm, 2 mm, 2.5 mm, etc.); And / or, the particle sizes of both the charring agent and the impact modifier are 200 - 500 μm (such as 300 μm, 350 μm, 400 μm, 450 μm, etc.).

[0054] Specifically, in the present invention, the particle size of the halogen-free flame-retardant cross-linked polyethylene of 1-3 mm helps to form a uniform distribution of flame-retardant properties in the composite material, thereby improving the flame-retardant efficiency of the material. The particle size of the charring agent and the impact modifier of 200-500 μm helps to optimize their dispersion in the composite material, improve the impact resistance, and reduce impact damage. The setting of a reasonable particle size range not only makes the composite material easier to mix and form during the processing, improves the production efficiency and the quality of the finished product, but also can balance and enhance the flame retardancy, stability, antioxidant property and mechanical properties of the composite material to meet the performance requirements of different application scenarios.

[0055] As an optional implementation manner of the present invention, in step S5, the conditions for melt extrusion include: the heating temperature is 140-180 °C; the die head extrusion temperature is 170-200 °C; In step S5, the mold can be selected according to the requirements in actual operation, and typically and non-limitingly includes a pressing mold, a roll pressing mold, etc.

[0056] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0057] In the examples provided by the present invention, all the raw materials for preparing the flame-retardant cable insulation layer are commercially available products.

[0058] Example 1 According to mass percentages, the contents of each component are configured as follows: 50% of halogen-free flame-retardant cross-linked polyethylene, 5% of SBS, 15% of magnesium-aluminum intercalated metal oxide (the interlayer anion is phosphate ion), 20% of 3-glycidyltrimethoxysilane, 2% of graphene oxide, 2% of MBS impact modifier, 3% of microcrystalline wax, and 3% of ammonium phosphate.

[0059] S1: Pretreat graphene oxide and magnesium-aluminum intercalated metal oxide respectively: Place graphene oxide under ultraviolet light for photo-oxidation, the light intensity of the ultraviolet light is 70 mW / cm 2 , and the light irradiation time is 40 min; Place the magnesium-aluminum intercalated metal oxide in an oven at 55 °C for drying for 5 h.

[0060] S2: Place 3-glycidyltrimethoxysilane, the pretreated graphene oxide, and the pretreated magnesium-aluminum intercalated metal oxide in ethanol, adjust the pH value to 5, and stir at a stirring rate of 300 r / min at a temperature of 50 °C for 2 h to obtain a mixed material; S3: Dry the mixed material at a temperature of 70 °C for 20 h, and then perform ball milling to obtain a mixture powder (average particle size is 85 μm); Among them, the ball milling time is 3 h, the ball milling speed is 70 r / min, the mass ratio of balls to the mixed materials is 7:1, and zirconia balls are selected; S4: Mix halogen-free flame-retardant crosslinked polyethylene (particle size 2 mm), SBS (particle size 2 m), microcrystalline wax, and MBS impact modifier (particle size 300 μm) at 140 °C with a stirring rate of 400 r / min for 2 h. Then add the mixture powder and ammonium phosphate (particle size 300 μm) and continue stirring for 4 h to obtain a mixed slurry; S5: Melt-extrude the mixed slurry in a melt extruder at a heating temperature of 160 °C and a die head extrusion temperature of 180 °C, and shape it through a die to obtain a flame-retardant cable insulation layer.

[0061] Example 2 Configure the content of each component by mass percentage: halogen-free flame-retardant crosslinked polyethylene 50%, SBS 10%, magnesium-aluminum intercalated metal oxide (interlayer anion is borate ion) 10%, 3-glycidyltriethoxysilane 17%, graphene oxide 5%, ACR impact modifier 2%, silicone oil 2%, and pentaerythritol 4%.

[0062] S1: Pretreat graphene oxide and magnesium-aluminum intercalated metal oxide respectively: Expose graphene oxide to ultraviolet light for photooxidation. The light intensity of the ultraviolet light is 50 mW / cm 2 , and the illumination time is 60 min; Dry magnesium-aluminum intercalated metal oxide in an oven at 60 °C for 4 h.

[0063] S2: Place 3-glycidyltriethoxysilane, pretreated graphene oxide, and pretreated magnesium-aluminum intercalated metal oxide in acetone, adjust the pH value to 4, and stir at 60 °C with a stirring rate of 500 r / min for 1 h to obtain a mixed material; S3: Dry the mixed material at 80 °C for 12 h and then perform ball milling to obtain a mixture powder (average particle size 70 μm); Among them, the ball milling time is 4 h, the ball milling speed is 50 r / min, the mass ratio of balls to the mixed materials is 5:1, and zirconia balls are selected; S4: Mix halogen-free flame-retardant crosslinked polyethylene (particle size 2.5 mm), SBS (particle size 2 mm), silicone oil, and ACR impact modifier (particle size 500 μm) at 150 °C with a stirring rate of 300 r / min for 2 h. Then add the mixture powder and pentaerythritol (particle size 400 μm) and continue stirring for 5 h to obtain a mixed slurry; S5: Melt and extrude the mixed slurry in a melt extruder at a heating temperature of 160 °C; the head extrusion temperature is 180 °C, and it is shaped through a die to obtain a flame-retardant cable insulation layer.

[0064] Example 3 Configure the content of each component by mass percentage: 50% of halogen-free flame-retardant cross-linked polyethylene, 5% of SBS, 13% of magnesium-aluminum intercalated metal oxide (the interlayer anion is molybdate ion), 21% of 2,3-epoxypropyl methoxysilane, 5% of graphene oxide, 2% of MBS impact modifier, 2% of aromatic oil, and 2% of melamine.

[0065] S1: Pretreat graphene oxide and magnesium-aluminum intercalated metal oxide respectively: Place graphene oxide under ultraviolet light for photo-oxidation, the light intensity of ultraviolet light is 100 mW / cm 2 , and the light irradiation time is 30 min; Place magnesium-aluminum intercalated metal oxide in an oven at 50 °C for drying for 6 h.

[0066] S2: Place 2,3-epoxypropyl methoxysilane, pretreated graphene oxide, and pretreated magnesium-aluminum intercalated metal oxide in water, adjust the pH value to 5, and stir at a stirring rate of 400 r / min at a temperature of 50 °C for 2 h to obtain a mixed material; S3: Dry the mixed material at a temperature of 60 °C for 18 h, and then carry out ball milling to obtain a mixture powder (average particle size is 80 μm); Among them, the ball milling time is 3 h, the ball milling speed is 80 r / min, the mass ratio of the ball to the mixed material is 6:1, and zirconia balls are selected; S4: Place halogen-free flame-retardant cross-linked polyethylene (particle size is 1.5 mm), SBS (particle size is 2 mm), aromatic oil, and MBS impact modifier (particle size is 400 μm) at a temperature of 130 °C, and stir at a stirring rate of 300 r / min for 2 h, then add the mixture powder and melamine (particle size is 300 μm), and continue to stir for 4 h to obtain a mixed slurry; S5: Melt and extrude the mixed slurry in a melt extruder at a heating temperature of 160 °C; the head extrusion temperature is 180 °C, and it is shaped through a die to obtain a flame-retardant cable insulation layer.

[0067] Comparative Example 1 The main difference between this comparative example and Example 1 is that graphene oxide is not added, specifically: By mass percentage, configure the content of each component: halogen-free flame-retardant cross-linked polyethylene 50%, SBS 5%, magnesium-aluminum intercalated metal oxide (the interlayer anion is phosphate ion) 17%, 3-glycidyltrimethoxysilane 20%, MBS impact modifier 2%, microcrystalline wax 3% and ammonium phosphate 3%.

[0068] All the remaining operation steps and technical parameters are the same as those in Example 1.

[0069] Comparative Example 2 The main difference between this comparative example and Example 1 is that a compound without an epoxy group, γ-aminopropyltriethoxysilane, is added, and all the remaining operation steps and technical parameters are the same as those in Example 1.

[0070] Comparative Example 3 The main difference between this comparative example and Example 1 is that no epoxy group-containing silane is added. Specifically: By mass percentage, configure the content of each component: halogen-free flame-retardant cross-linked polyethylene 60%, SBS 15%, magnesium-aluminum intercalated metal oxide (the interlayer anion is phosphate ion) 15%, graphene oxide 2%, MBS impact modifier 2%, microcrystalline wax 3% and ammonium phosphate 3%.

[0071] All the remaining operation steps and technical parameters are the same as those in Example 1.

[0072] Comparative Example 4 The main difference between this comparative example and Example 1 is that the mass percentage of the added epoxy group-containing silane is greater than 25%. Specifically: By mass percentage, configure the content of each component: halogen-free flame-retardant cross-linked polyethylene 43%, SBS 5%, magnesium-aluminum intercalated metal oxide (the interlayer anion is phosphate ion) 15%, 3-glycidyltrimethoxysilane 27%, graphene oxide 2%, MBS impact modifier 2%, microcrystalline wax 3% and ammonium phosphate 3%.

[0073] All the remaining operation steps and technical parameters are the same as those in Example 1.

[0074] Performance test: In Examples 1-3 and Comparative Examples 1-4, the performance detection standards are as follows: Flame retardancy test: Refer to GB8624-2012 "Classification of the burning behavior of building materials and products"; Among them, the flame retardancy grades are: Class A - non-combustible materials, Class B1 - difficult-to-combust materials, Class B2 - combustible materials, Class B3 - flammable materials.

[0075] Antioxidant experiment: Refer to "ISO 4589-2:2015"; The aging test conditions set by the present invention are a temperature of 70 °C and an oxygen atmosphere. If the performance remains unchanged for more than 500 hours under this condition, it is considered to have good antioxidant properties.

[0076] Mechanical properties: Refer to 《ISO 179-1:2010》.

[0077] Effect data The performance of the flame-retardant cable insulation layers prepared in Examples 1-3 and Comparative Examples 1-4 is shown in Table 1: Table 1 Comparison table of the performance of the flame-retardant cable insulation layers prepared in Examples 1-3 and Comparative Examples 1-4 According to Table 1, when comparing Example 1 with Comparative Example 1, since graphene oxide was not added in Comparative Example 1 and could not be compounded with the magnesium-aluminum intercalated oxide, the antioxidant and flame-retardant properties of the material were reduced, and the mechanical properties of the material were also affected.

[0078] According to Table 1, when comparing Example 1 with Comparative Example 2, since γ-aminopropyltriethoxysilane was added in Comparative Example 2 and it does not contain epoxy groups, graphene oxide and the magnesium-aluminum intercalated metal oxide both reacted with the silanol hydrolyzed from γ-aminopropyltriethoxysilane, and no bridging was formed between graphene oxide and the magnesium-aluminum intercalated metal oxide, resulting in a reduction in the compounding effect, and the antioxidant and flame-retardant properties of the material were reduced, and the mechanical properties of the material were also affected.

[0079] According to Table 1, when comparing Example 1 with Comparative Example 3, since epoxy group silane was not added in Comparative Example 3, graphene oxide and the magnesium-aluminum intercalated metal oxide could not form a bridge, and due to the different surface properties of graphene oxide and the intercalated metal oxide, the uniformity of the two was affected, resulting in a reduction in the antioxidant and flame-retardant properties of the material, and the mechanical properties of the material were also affected.

[0080] According to Table 1, when comparing Example 1 with Comparative Example 4, since too much epoxy group silane was added in Comparative Example 4, the viscosity of the material increased, thereby affecting the mechanical properties of the material.

[0081] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flame-retardant cable insulating layer, characterized in that, By mass percentage, it includes the following components: 50 - 70% of halogen-free flame-retardant cross-linked polyethylene, 5 - 20% of SBS, 5 - 25% of intercalated metal oxide, 10 - 25% of epoxy group silane, 2 - 10% of graphene oxide, 2 - 5% of impact modifier, 2 - 5% of additives, and 2 - 10% of charring agent.

2. The flame-retardant cable insulating layer according to claim 1, wherein The intercalated metal oxide is a magnesium-aluminum intercalated metal oxide; The magnesium-aluminum intercalated metal oxide has a main body layer board and anions located between the main body layer boards, and the main body layer board is composed of hydroxides of magnesium and aluminum; The anion is any one of phosphate ions, borate ions, sulfate ions, or molybdate ions.

3. The flame-retardant cable insulating layer according to claim 1, characterized in that, The epoxy group silane includes one or more of 3-glycidyltrimethoxysilane, 3-glycidyltriethoxysilane, 3-glycidyltriisopropoxysilane, 2,3-glycidylmethoxysilane, and 2,3-glycidylethoxysilane.

4. The flame-retardant cable insulating layer according to claim 1, wherein The impact modifier is a core-shell structure impact modifier, including at least one of MBS impact modifier or ACR impact modifier; And / or, the additives include one or more of aromatic oil, silicone oil, and microcrystalline wax.

5. The flame-retardant cable insulating layer according to claim 1, wherein The charring agent includes one or more of ammonium phosphate, pentaerythritol, melamine, borate, and silicate.

6. A method for preparing a flame-retardant cable insulating layer according to any one of claims 1-5, characterized in that, It includes the following steps: S1: Pretreat graphene oxide and intercalated metal oxide respectively; S2: Place epoxy group silane, pretreated graphene oxide, and pretreated intercalated metal oxide in a solvent, adjust the pH value, and stir to obtain a mixed material; S3: After drying the mixed material, perform ball milling to obtain a mixture powder; S4: Stir halogen-free flame-retardant cross-linked polyethylene, SBS, additives, and impact modifier, then add the mixture powder and charring agent, and continue to stir to obtain a mixed slurry; S5: Melt-extrude the mixed slurry and shape it through a mold to produce a flame-retardant cable insulation layer.

7. The preparation method of the flame-retardant cable insulating layer according to claim 6, characterized in that, In step S1, the pretreatment of graphene oxide includes: The graphene oxide is subjected to photo-oxidation under ultraviolet light, and the light intensity of the ultraviolet light is 10-100 mW / cm 2 , and the light irradiation time is 30-60 min; And / or, in step S1, the pretreatment of intercalated metal oxide includes: Place the intercalated metal oxide in an oven at 50 - 60 °C for drying for 4 - 6 h; And / or, in step S2, the solvent is one of ethanol, acetone, or water; And / or, in step S2, the stirring temperature is 30 - 60 °C, the stirring time is 1 - 2 h, and the stirring rate is 200 - 500 r / min; And / or, in step S2, adjust the pH value to 4 - 5; And / or, in step S2, the addition amount of epoxy group silane ≥ the total addition amount of pretreated graphene oxide and pretreated intercalated metal oxide.

8. The preparation method of the flame-retardant cable insulating layer according to claim 6, wherein, In step S3, the ball milling includes the following conditions: The ball milling time is 2 - 4 h, the ball milling speed is 50 - 100 r / min, the mass ratio of balls to the mixed material is (5 - 10):1, and zirconia balls are selected; And / or, the drying temperature is 50 - 80 °C, and the time is 12 - 24 h; And / or, the particle size of the mixture powder is 1 - 100 μm; And / or, in step S4, the temperature of stirring is 130 - 150 °C, the stirring time is 1 - 2 h, and the stirring rate is 200 - 500 r / min; And / or, in step S4, after adding the mixture powder and the charring agent, continue to stir for 3 - 5 h.

9. The flame-retardant cable insulating layer according to claim 6, characterized in that, The particle sizes of the halogen-free flame-retardant crosslinked polyethylene and SBS are both 1 - 3 mm; And / or, the particle sizes of the charring agent and the impact modifier are both 200 - 500 μm.

10. The preparation method of the flame-retardant cable insulating layer according to claim 6, characterized in that, In step S5, the conditions for melt extrusion include: the heating temperature is 140 - 180 °C; the die head extrusion temperature is 170 - 200 °C.

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