Flexible high strength insulation cable material, method of manufacture and power cable

Abstract

The application relates to the technical field of cables, and discloses a flexible high-strength insulated cable material, a preparation method and a power cable. The material formula comprises ethylene-propylene rubber, ethylene-octene copolymer, magnesium hydroxide, solid maleic anhydride, zinc methacrylate, alpha-methyl styrene dimer, dicumyl peroxide and compound antioxidants. During the processing, maleic anhydride is heated to open a ring and in-situ consumes free water on the surface of magnesium hydroxide, thereby improving powder dispersion; the alpha-methyl styrene dimer acts as a chain transfer agent to inhibit long-chain homopolymerization of zinc methacrylate and avoid the formation of hard and brittle crosslinking points in the matrix; and the polar grafting end and the hydroxyl group on the surface of magnesium hydroxide construct a reversible coordination network containing metal ion bonds. The application solves the problems of dehydration difficulty and crosslinking brittleness of high-filled flame-retardant materials, so that the material can dissipate strain energy through ion node slipping when being stretched or bent, and has high flame retardancy, high tensile strength and excellent flexibility.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a flexible high-strength insulated cable material, its preparation method, and a power cable. Background Technology

[0002] With the increasing sophistication of cable safety standards, halogen-free, low-smoke, flame-retardant cables have become widely used. In insulation materials based on EPDM rubber and polyolefin elastomers, large amounts of inorganic flame-retardant powders such as magnesium hydroxide are typically added to achieve the specified flame-retardant rating. However, the large dosage of inorganic powder significantly alters the material's processing characteristics and microstructure. Because magnesium hydroxide powder has a highly polar surface and readily adsorbs large amounts of free water, dehydration during the mixing process is extremely difficult, easily leading to particle agglomeration in the matrix. This not only causes a sharp increase in the mixing viscosity of the system but also makes it difficult for the inorganic flame retardant to achieve uniform dispersion within the resin matrix.

[0003] To compensate for the disruption of matrix continuity and loss of mechanical properties caused by the large amount of inorganic powder filling, existing technologies often introduce unsaturated metal compounds such as methacrylates into the formulation for crosslinking modification. However, in actual free radical-induced crosslinking processes, these unsaturated modifiers, due to their high reactivity, are prone to continuous long-chain homopolymerization reactions, leading to the formation of large-sized, hard, brittle crosslinking nodes within the polymer matrix. This locally large, rigid structure causes the cable insulation layer to harden and become brittle after curing, causing the material to lose its original flexibility.

[0004] Traditional covalent cross-linked networks are highly rigid and have a fixed structure. When the cable insulation material in a highly filled state is subjected to external forces of tension or bending, the internally solidified cross-linked network cannot effectively dissipate strain energy through physical deformation, making stress concentration and microcracks prone to occur at the stressed areas. This results in a significant decrease in the overall tensile strength and bending fracture resistance of highly filled halogen-free flame-retardant cables during actual laying and use, making it difficult to meet the dual requirements of cable flexibility and high strength under complex working conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a flexible high-strength insulated cable material, a preparation method, and a power cable. It solves the problems of existing high-filler halogen-free flame-retardant cable materials, which suffer from difficulties in processing and dehydration due to inorganic powder agglomeration, and the problems of large-sized rigid brittle points easily formed by cross-linking modification, resulting in poor material flexibility and reduced tensile and bending fracture resistance.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a flexible high-strength insulated cable material, which adopts the following technical solution:

[0008] A flexible, high-strength insulating cable material comprises the following components by weight: 50-70 parts of ethylene propylene diene monomer (EPDM) rubber; 30-50 parts of ethylene-octene copolymer; 100-150 parts of magnesium hydroxide; 1.0-3.0 parts of solid maleic anhydride; 5-15 parts of zinc methacrylate; 0.5-1.5 parts of α-methylstyrene dimer; 1.0-2.5 parts of dicumyl peroxide; and 0.5-2.0 parts of compounded antioxidant.

[0009] By adopting the above technical solution, during the heating process of the mixing process, solid maleic anhydride melts upon heating, and its anhydride rings directly react with the free water adhering to the surface of magnesium hydroxide powder to form maleic acid. This process consumes the moisture brought in by the powder in situ, thereby reducing the polarity of the magnesium hydroxide surface, weakening the tendency of particle agglomeration, and thus improving the dispersion state of inorganic powder in the polymer matrix.

[0010] When the system temperature reaches the decomposition temperature of dicumyl peroxide, the alkoxy radicals generated by homolytic cleavage abstract hydrogen atoms from the backbone of ethylene propylene diene monomer (EPDM) rubber and ethylene-octene copolymer, generating polymer macromolecular radicals with addition activity. These macromolecular radicals then initiate a double-bond addition reaction of zinc methacrylate within the system. The α-methylstyrene dimer added to the formulation acts as a chain transfer agent, providing a relatively stable chain transfer center and suppressing the continuous initiation rate of zinc methacrylate by the macromolecular radicals. This ensures that zinc methacrylate is grafted onto the polymer backbone primarily in the form of monomers or low-molecular-weight oligomers, avoiding the formation of localized hard and brittle crosslinking points during long-chain homopolymerization.

[0011] The polar zinc ion terminals of zinc methacrylate grafted onto the main chain and the carboxyl terminals of maleic acid coordinate and hydrogen bond with the hydroxyl groups on the surface of magnesium hydroxide, forming a complex interface network composed of coordinate bonds, ionic bonds, and hydrogen bonds. Metal ionic bonds possess the physical property of reversible dissociation. When the cable is subjected to external force for stretching or bending, the internal ionic nodes dissipate strain energy through slippage, improving overall flexibility while ensuring high tensile strength of the material.

[0012] Preferably, the EPDM rubber specifically comprises an ethylene-propylene-diolefin copolymer with 5-ethylidene-2-norbornene as the third monomer, wherein the ethylene mass fraction is 65% to 75%, the 5-ethylidene-2-norbornene mass fraction is 4% to 6%, and the Mooney viscosity at 125°C is 40 to 60.

[0013] By adopting the above technical solution and selecting EPDM rubber with the above mass ratio, a basic crystalline state and covalent crosslinking active sites are provided for the matrix, enabling the cable material to obtain the weather resistance and deformation recovery characteristics required for conventional applications.

[0014] Preferably, the ethylene-octene copolymer has a 1-octene mass fraction of 20% to 30%, a melt flow rate of 1.0 g / 10 min to 5.0 g / 10 min at 190°C and 2.16 kg, and a crystallinity of less than 20%.

[0015] By employing the above technical solution, controlling the mass fraction of 1-octene keeps the polymer crystallinity at a low level, retaining more free volume in the amorphous regions within the internal structure. This provides physical space for the high-filling-weight magnesium hydroxide powder; combined with this melt flow rate range, it ensures that the material maintains sufficient melt strength during the extrusion coating stage, preventing core eccentricity.

[0016] Preferably, the solid maleic anhydride has a melting point of 52℃~55℃, is a solid powder at room temperature, and has a purity ≥99.5%; the magnesium hydroxide has an average particle size D50 of 1.0μm~2.5μm, a purity ≥99.0%, and a specific surface area of ​​5m². 2 / g~15m 2 / g of flame-retardant magnesium hydroxide powder.

[0017] By adopting the above technical solution, the melting point of maleic anhydride is slightly lower than the initial mixing temperature, ensuring that it melts into a liquid phase and coats the powder surface in the initial stage of mixing with a large amount of inorganic powder. The magnesium hydroxide with the above particle size and specific surface area can provide an endothermic decomposition area that meets the flame retardant requirements, while avoiding a sharp increase in the processing viscosity of the system caused by an excessively large specific surface area.

[0018] Preferably, the zinc content of the zinc methacrylate is 26% to 30% by mass, and the specific surface area is >20 m2 / g; the purity of the α-methylstyrene dimer is ≥97.0%, and the boiling point is 310℃ to 313℃.

[0019] By adopting the above technical solution, zinc methacrylate with a high specific surface area is more easily and uniformly dispersed within the matrix during compounding. The boiling point of α-methylstyrene dimer is much higher than the material processing and vulcanization temperature, and it is not easily volatilized during the heated extrusion process, ensuring a continuous regulating effect on the free radical chain transfer reaction.

[0020] Preferably, the compound antioxidant is composed of antioxidant 1010 and antioxidant 168, and the mass ratio of antioxidant 1010 to antioxidant 168 is 1 to 2:1.

[0021] By adopting the above technical solution, hindered phenolic and phosphite antioxidants produce a synergistic effect at this ratio, which can promptly terminate the peroxide free radicals generated during processing and protect the polymer backbone from thermal degradation and chain breakage under high temperature melting and extrusion conditions.

[0022] Secondly, this invention provides a method for preparing a flexible high-strength insulated cable material, employing the following technical solution:

[0023] A method for preparing a flexible high-strength insulated cable material includes the following steps:

[0024] (1) Preparation of formulation: Prepare EPDM rubber, ethylene-octene copolymer, magnesium hydroxide, maleic anhydride, zinc methacrylate, α-methylstyrene dimer, dicumyl peroxide and compound antioxidant;

[0025] (2) Masterbatch mixing: EPDM rubber, ethylene-octene copolymer, magnesium hydroxide and maleic anhydride are put into an internal mixer for the first stage of mixing; then zinc methacrylate and compound antioxidant are added, and the second stage of mixing is carried out under slight negative pressure; after discharge, the rubber is cooled to room temperature to obtain the compounded rubber.

[0026] (3) Premixing: After cooling, the compounded rubber is added to a two-roll mill with dicumyl peroxide and α-methylstyrene dimer. After being mixed evenly, it is sheeted and granulated to obtain crosslinkable masterbatch for cable materials.

[0027] By adopting the above technical solution, the process combining segmented feeding and micro-negative pressure control matched the reaction conditions of each component. The first stage of feeding ensured that maleic anhydride and moisture in the material came into full contact and underwent a ring-opening reaction; the micro-negative pressure environment in the second stage removed water vapor and low-molecular-weight volatiles generated during the reaction from the system, reducing porosity defects inside the compound. The crosslinking initiation system was introduced later in the open mill at a lower temperature, eliminating the risk of early crosslinking (dead rubber) caused by the high-temperature shearing of the internal mixer, ensuring that the material was extruded smoothly and completed dynamic crosslinking and shaping in the continuous vulcanizing tube.

[0028] Preferably, step (2) specifically includes: the temperature of the first stage of mixing is 130℃~140℃, the rotation speed is 40rpm~60rpm, and the time is 3~8min; the second stage of intensive mixing maintains the same temperature, the vacuum system is turned on to make the pressure reach -0.05MPa~-0.09MPa, and intensive mixing continues for 5~10min.

[0029] By adopting the above technical solution, a mixing temperature of 130℃~140℃ softens the matrix resin to a low-viscosity melt state that is easily sheared and dispersed, while also meeting the temperature requirements for the ring-opening reaction of maleic anhydride. Negative pressure operation promotes the dehydration reaction in the positive direction, further reducing the micropores formed inside the rubber compound due to moisture vaporization.

[0030] Preferably, in step (3), the temperature of the open mill is controlled at 90℃~100℃ and the turning time is 5~10min.

[0031] By adopting the above technical solution, the open mixing temperature of 90℃~100℃ is lower than the rapid decomposition temperature of dicumyl peroxide, and the uniform mixing of the initiator is achieved within the safe processing range.

[0032] Thirdly, the present invention provides a power cable, which adopts the following technical solution:

[0033] An electric cable includes an inner conductor core and an insulation layer covering the periphery of the conductor core, the insulation layer being formed by extrusion vulcanization of the flexible high-strength insulated cable material described in the first aspect.

[0034] By adopting the above technical solution, a uniform organic-inorganic hybrid cross-linked network is formed inside the cable insulation layer. When exposed to an external fire source, magnesium hydroxide decomposes under heat and generates an inorganic magnesium oxide barrier layer; the polar cross-linking nodes within the insulation layer restrict the thermal slippage of polymer chains, reduce the generation of combustion droplets, and improve the cable's flame retardant safety level and mechanical tensile strength.

[0035] This invention provides a flexible high-strength insulated cable material, a preparation method, and a power cable. It has the following beneficial effects:

[0036] 1. This invention utilizes the thermal melting and ring-opening reaction of solid maleic anhydride during the heating stage of the mixing process to consume the free water adhering to the surface of high-filled magnesium hydroxide in situ. This reduces the polarity of the inorganic powder surface and decreases the agglomeration of powder particles, allowing magnesium hydroxide to be uniformly dispersed in the EPDM rubber and ethylene-octene copolymer matrix. This solves the problems of difficult dehydration and excessively high mixing viscosity in high-filled inorganic flame retardant systems.

[0037] 2. This invention introduces α-methylstyrene dimer as a chain transfer agent, which can regulate the double bond addition process of zinc methacrylate. Furthermore, by providing competitive chain transfer centers, it can inhibit the long-chain homopolymerization reaction of zinc methacrylate, causing it to be grafted onto the polymer backbone mainly in the form of monomers or low molecular weight oligomers. This avoids the formation of large-sized hard and brittle crosslinking nodes inside the matrix, thereby maintaining the low-temperature flexibility of the cable while increasing the crosslinking density of the system.

[0038] 3. This invention utilizes the coordination and hydrogen bonding between the polar zinc ion ends of zinc methacrylate and the carboxyl ends of maleic acid grafted onto the polymer backbone and the hydroxyl groups on the surface of magnesium hydroxide. When the cable is subjected to external tensile or bending forces, the metal ion nodes can dissipate strain energy through moderate slippage. This allows the cable insulation material to retain both high tensile strength and excellent resistance to bending and breakage while accommodating a large amount of inorganic flame retardant. Attached Figure Description

[0039] Figure 1Example 2 of the present invention, and Comparative Examples 2 and 4, were performed at 1400 cm. -1 ~1800cm -1 Local comparison images of infrared spectra within the specified bands;

[0040] Figure 2 This is a two-dimensional mapping distribution diagram of apparent gel content and swelling ratio for embodiments and comparative examples of the present invention;

[0041] Figure 3 Figure 2 shows the dynamic thermomechanical analysis curves of Embodiment 2, Comparative Examples 1 and 4 of the present invention. Figure 3 shows the curve of energy storage modulus as a function of temperature, and Figure 4 shows the curve of loss tangent as a function of temperature.

[0042] Figure 4 Figure 1 shows a comparison of the room temperature mechanical properties of the embodiments and comparative examples of the present invention. Figure 2(a) shows the typical stress-strain evolution curves of comparative examples 1 to 3 and example 2 in tensile testing. Figure 3(b) shows the macroscopic bending modulus distribution of all experimental objects measured under three-point bending test.

[0043] Figure 5 This is a scatter plot showing the number of microcracks and the maximum crack width in low-temperature winding tests of embodiments and comparative examples of the present invention;

[0044] Figure 6 The scatter plot shows the correlation between water absorption rate and AC breakdown voltage for embodiments and comparative examples of the present invention.

[0045] Figure 7 Figure 1 shows the halogen-free flame retardant performance test characteristics of the embodiments and comparative examples of the present invention. Figure 2 shows the distribution of the upper limit of limiting oxygen index of each formulation and Figure 3 shows the total flaming time span of each test object in the UL94 vertical burning test. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0048] Ethylene propylene diene monomer (EPDM) rubber: An ethylene-propylene-diolefin copolymer with 5-ethylidene-2-norbornene as the third monomer, CAS number 25038-36-2, wherein the ethylene mass fraction is 65%–75%, the 5-ethylidene-2-norbornene mass fraction is 4%–6%, the Mooney viscosity ML(1+4) at 125℃ is 40–60, and the density is 0.86 g / cm³. 3 ~0.88g / cm 3 .

[0049] Ethylene-octene copolymer (POE): CAS No. 26221-73-8, wherein the mass fraction of 1-octene is 20%–30%, the melt flow rate is 1.0 g / 10 min–5.0 g / 10 min (test conditions: 190℃, 2.16 kg), and the density is 0.865 g / cm³. 3 ~0.875g / cm 3 The crystallinity is less than 20%.

[0050] Magnesium hydroxide: Industrial-grade flame-retardant magnesium hydroxide powder, CAS number 1309-42-8, with an average particle size D50 of 1.0μm~2.5μm, purity greater than or equal to 99.0%, and specific surface area of ​​5m². 2 / g~15m 2 / g.

[0051] Zinc methacrylate (ZDMA): CAS No. 13189-00-9, molecular formula C8H 10 O4Zn is a white, extremely fine powder at room temperature, with a zinc content of 26%–30% by mass and a specific surface area greater than 20m². 2 / g.

[0052] α-Methylstyrene dimer (AMSD): Chemical name is 2,4-diphenyl-4-methyl-1-pentene, CAS number is 6362-80-7, molecular formula is C 18 H 20 The purity is greater than or equal to 97.0%, and the density is 0.98 g / cm³. 3 Its boiling point is 310℃~313℃.

[0053] Dicumyl peroxide (DCP): chemical name is di(2-phenyl-2-propyl)peroxide, CAS number is 80-43-3, melting point is 39℃~41℃, active oxygen mass fraction is greater than or equal to 5.8%, and half-life temperature (0.1 hours) is 154℃.

[0054] Maleic anhydride (MAH): Commercially available industrial-grade solid maleic anhydride, CAS number 108-31-6, is a white flake or crystalline powder at room temperature, with a melting point of 52℃~55℃ and a purity of ≥99.5%.

[0055] Example 1:

[0056] This embodiment provides a flexible high-strength insulated cable material and a method for preparing a power cable, including the following steps:

[0057] (1) Preparation of formulation: By weight, take 70 parts of ethylene propylene diene monomer (EPDM), 30 parts of ethylene-octene copolymer (POE), 100 parts of magnesium hydroxide, 1.0 part of maleic anhydride (MAH), 5 parts of zinc methacrylate (ZDMA), 0.5 parts of α-methylstyrene dimer (AMSD), 1.0 part of dicumyl peroxide (DCP), and 0.5 parts of compound antioxidant (the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1).

[0058] (2) Masterbatch mixing: Add the above-mentioned parts of EPDM, POE, magnesium hydroxide and MAH into a mixer and mix at 130°C and 40 rpm for 3 min; maintain 130°C, add ZDMA and compound antioxidant, turn on the vacuum system to -0.05MPa and continue mixing for 5 min; after debinding, cool naturally to room temperature;

[0059] (3) Premixing: Add DCP and AMSD to the cooled rubber compound in a 90°C open mill, knead for 5 minutes until uniform, then sheet and granulate to obtain crosslinkable masterbatch for cable materials;

[0060] Example 2:

[0061] This embodiment provides a flexible high-strength insulated cable material and a method for preparing a power cable, including the following steps:

[0062] (1) Preparation of the formula: By weight, take 60 parts of ethylene propylene diene monomer (EPDM), 40 parts of ethylene-octene copolymer (POE), 120 parts of magnesium hydroxide, 1.5 parts of maleic anhydride (MAH), 10 parts of zinc methacrylate (ZDMA), 0.8 parts of α-methylstyrene dimer (AMSD), 1.5 parts of dicumyl peroxide (DCP), and 1.0 part of compound antioxidant (the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1).

[0063] (2) Masterbatch mixing: The above-mentioned parts of EPDM, POE, magnesium hydroxide and MAH are put into an internal mixer and mixed at 135°C and 50 rpm for 5 min; maintain 135°C, add ZDMA and compound antioxidant, turn on the vacuum system to -0.07MPa and continue mixing for 8 min; after debinding, cool to room temperature;

[0064] (3) Premixing: Add DCP and AMSD to the cooled rubber compound in a 95°C open mill, knead for 8 minutes until uniform, then sheet and granulate to obtain crosslinkable masterbatch for cable materials;

[0065] Example 3:

[0066] This embodiment provides a flexible high-strength insulated cable material and a method for preparing a power cable, including the following steps:

[0067] (1) Preparation of formulation: By weight, take 50 parts of ethylene propylene diene monomer (EPDM), 50 parts of ethylene-octene copolymer (POE), 150 parts of magnesium hydroxide, 3.0 parts of maleic anhydride (MAH), 15 parts of zinc methacrylate (ZDMA), 1.5 parts of α-methylstyrene dimer (AMSD), 2.5 parts of dicumyl peroxide (DCP), and 2.0 parts of compound antioxidant (the mass ratio of antioxidant 1010 to antioxidant 168 is 2:1).

[0068] (2) Masterbatch mixing: The above-mentioned parts of EPDM, POE, magnesium hydroxide and MAH are put into an internal mixer and mixed at 140°C and 60 rpm for 8 min; maintain 140°C, add ZDMA and compound antioxidant, turn on the vacuum system to -0.09MPa and continue mixing for 10 min; after debinding, cool to room temperature;

[0069] (3) Premixing: Add DCP and AMSD to the cooled rubber compound in a 100°C open mill, knead for 10 minutes until uniform, then sheet and granulate to obtain crosslinkable masterbatch for cable materials;

[0070] Example 4:

[0071] This embodiment provides a flexible high-strength insulated cable material and a method for preparing a power cable, including the following steps:

[0072] (1) Preparation of the formula: By weight, take 65 parts of ethylene propylene diene monomer (EPDM), 35 parts of ethylene-octene copolymer (POE), 130 parts of magnesium hydroxide, 2.0 parts of maleic anhydride (MAH), 12 parts of zinc methacrylate (ZDMA), 1.0 parts of α-methylstyrene dimer (AMSD), 2.0 parts of dicumyl peroxide (DCP), and 1.5 parts of compound antioxidant (the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1).

[0073] (2) Masterbatch mixing: The above-mentioned parts of EPDM, POE, magnesium hydroxide and MAH are put into an internal mixer and mixed at 138°C and 55 rpm for 6 min; maintain 138°C, add ZDMA and compound antioxidant, turn on the vacuum system to -0.08MPa and continue mixing for 9 min; after debinding, cool to room temperature;

[0074] (3) Premixing: Add DCP and AMSD to the cooled rubber compound in a 98°C open mill, knead for 8 minutes until uniform, then sheet and granulate to obtain crosslinkable masterbatch for cable materials;

[0075] Example 5:

[0076] This embodiment provides a flexible high-strength insulated cable material and a method for preparing a power cable, including the following steps:

[0077] (1) Preparation of the formula: By weight, take 55 parts of ethylene propylene diene monomer (EPDM), 45 parts of ethylene-octene copolymer (POE), 110 parts of magnesium hydroxide, 1.2 parts of maleic anhydride (MAH), 8 parts of zinc methacrylate (ZDMA), 0.6 parts of α-methylstyrene dimer (AMSD), 1.2 parts of dicumyl peroxide (DCP), and 0.8 parts of compound antioxidant (the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1).

[0078] (2) Masterbatch mixing: The above-mentioned parts of EPDM, POE, magnesium hydroxide and MAH are put into an internal mixer and mixed at 132°C and 45 rpm for 4 min; maintain 132°C, add ZDMA and compound antioxidant, turn on the vacuum system to -0.06MPa and continue mixing for 6 min; after debinding, cool to room temperature;

[0079] (3) Premixing: Add DCP and AMSD to the cooled rubber compound in a 92°C open mill, knead for 6 minutes until uniform, then sheet and granulate to obtain crosslinkable masterbatch for cable materials;

[0080] (4) Extrusion vulcanization: The crosslinkable masterbatch of cable material is fed into a single screw extruder, the die temperature is set to 112°C, and it is extruded around the conductor core (tin-plated copper conductor); then it enters a 175°C continuous vulcanization tube and stays for 5 minutes for dynamic crosslinking, and the finished power cable is obtained by water cooling.

[0081] Comparative Example 1:

[0082] Compared with Example 2, the difference is that maleic anhydride (MAH), zinc methacrylate (ZDMA), and α-methylstyrene dimer (AMSD) are all replaced with an equal weight of the conventional silane coupling agent vinyltrimethoxysilane, and no vacuum operation is performed during the first stage of internal mixing; otherwise, they are the same.

[0083] Comparative Example 2:

[0084] The difference from Example 2 is that solid maleic anhydride (MAH) was not added; otherwise, they are the same.

[0085] Comparative Example 3:

[0086] The difference from Example 2 is that α-methylstyrene dimer (AMSD) was not added; otherwise, they are the same.

[0087] Comparative Example 4:

[0088] The difference from Example 2 is that zinc methacrylate (ZDMA) was not added; otherwise, they are the same.

[0089] Comparative Example 5:

[0090] Compared with Example 2, the difference is that in step (2) masterbatch mixing, 1.5 parts of solid maleic anhydride (MAH) are replaced with an equal weight of liquid glacial acetic acid, and the rest are the same.

[0091] Test Example 1:

[0092] 1. Sample setup: The crosslinkable masterbatches prepared in Example 2, Comparative Example 2 and Comparative Example 4 were selected as test subjects.

[0093] 2. Test steps:

[0094] 2.1 To eliminate the interference of unreacted small molecules and free additives on the spectral signal, the masterbatch of each group was freeze-pulverized into powder under liquid nitrogen environment, and then extracted by continuous reflux for 24 hours in a Soxhlet extractor using acetone as solvent.

[0095] 2.2 After extraction, the remaining solid mixture was dried in a vacuum drying oven at 80°C for 12 hours until constant weight was obtained, yielding the purified cross-linked network and inorganic filler composite sample.

[0096] 2.3 Take a small amount of the dried sample powder and mix it with the dried potassium bromide (KBr) powder at a mass ratio of 1:100 and grind it thoroughly in an agate mortar. Use a tablet press to press it into transparent sheets under a pressure of 10 MPa.

[0097] 2.4. Place the compressed tablet in the sample chamber of the Fourier transform infrared spectrometer for transmission mode scanning. Set the spectral resolution to 4 cm⁻¹. -1 The scanning range is 4000cm. -1 ~400cm -1 The cumulative number of scans was 32, and background baseline interference from ambient water vapor and carbon dioxide was deducted.

[0098] 2.5. Export the test data, perform baseline calibration and normalization on the spectrum, and extract the wavenumber positions and relative absorbance values ​​corresponding to the characteristic functional groups. The results are as follows: Figure 1 As shown:

[0099] Table 1: Numerical Extraction of Infrared Spectral Characteristic Absorption Peaks of Example 2, Comparative Examples 2 and 4

[0100]

[0101] According to Table 1 and Figure 1 The data shows that the absorption characteristics in the infrared band directly reflect the chemical evolution of the phase interfaces within the system. Specifically, at 3690 cm⁻¹... -1 The sharp peaks nearby correspond to the stretching vibrations of unreacted hydroxyl groups (Mg-OH) on the magnesium hydroxide surface. In Comparative Example 2, because no solid maleic anhydride was introduced, the relative absorbance of Mg-OH was at a relatively high level of 0.784, indicating that the physically bound water and hydration layer on the filler surface are difficult to eliminate spontaneously at conventional mixing temperatures. In previous formulation adjustments, such residual moisture at the interface was often the direct cause of microporous defects in the extruded insulation layer. In Example 2 and Comparative Example 4, the absorbance at this location decreased to 0.312 and 0.347, respectively. This substantial decrease in absorption intensity confirms that solid maleic anhydride with a melting point of 52°C melts during the system heating phase. Its anhydride rings open upon contact with moisture on the filler surface, and the resulting maleic acid consumes the Mg-OH groups in situ. This acid-base neutralization reaction removes interfacial moisture, freeing up physical space for the subsequent coordination assembly of active groups.

[0102] After confirming that the moisture on the interface has been effectively removed, 1550cm -1 ~1600cm -1 Carboxylate (COO) in the range - The asymmetric stretching vibration peaks further reflect the coordination network state of the system. Magnesium maleate, formed by the single reaction of maleic anhydride and magnesium hydroxide, typically exhibits its ionic bond characteristic peak at 1582.1 cm⁻¹. -1 The peaks are near the same location and relatively narrow, consistent with the spectral characteristics of Comparative Example 4. In Comparative Example 2, which lacks maleic anhydride pretreatment, the interaction between zinc methacrylate and the filler is limited, resulting in a shift of the absorption peak to 1554.7 cm⁻¹. -1The binding force is relatively weak. In Example 2, the absorption peak in this region shifted to 1568.4 cm⁻¹. -1 The half-height and full width have also been expanded to 42.6cm. -1 The broadening of this spectral band indicates that the system contains not only single chemical bonds. Under the influence of micro-negative pressure exhaust and a strong shear field, the polar sites activated by maleic anhydride and the zinc carboxylate groups of zinc methacrylate form a complex network including dipole interactions, multiple hydrogen bonds, and secondary coordination bonds. Referring to Example 2 in Table 1, at 1637.2 cm⁻¹... -1 The carbon-carbon double bond characteristic peaks retained at the site, and this interfacial physical cross-linking based on the superposition of multiple interactions constitutes the microstructure basis for the energy consumption of ion slippage and recombination when the material is under pressure or tension, explaining the intrinsic reason why this highly filled system can take into account both mechanical strength and flexibility.

[0103] Test Example 2:

[0104] 1. Sample setup: The masterbatches prepared in Examples 2 and 4, as well as Comparative Examples 1 and 3, were selected as test subjects.

[0105] 2. Test steps:

[0106] 2.1. Shred the masterbatch into small particles with a side length not exceeding 2mm to increase the solvent contact area.

[0107] 2.2 Accurately weigh approximately 0.5g (denoted as m0) of the sample particles, wrap them in a pre-weighed (denoted as m1) and solvent-cleaned 120-mesh stainless steel wire mesh bag, fold the bag opening and seal it tightly with a stapler to prevent the particles from leaking out during the test.

[0108] 2.3 Place the mesh bag containing the sample into the extraction tube of a Soxhlet extractor, and add 200 mL of analytical grade toluene to the bottom-side round-bottom flask. Extract continuously by reflux at 110°C in an oil bath for 24 hours to elute uncrosslinked polymer chains and low-molecular-weight free additives from the network.

[0109] 2.4 After the extraction stage is completed, remove the mesh bag and quickly blot the free toluene solvent adhering to the surface of the mesh bag with filter paper. Immediately place it into a sealed weighing bottle that has been zeroed and record the total mass after full swelling (denoted as m2).

[0110] 2.5. Transfer the wire mesh bag into a vacuum drying oven, set the temperature to 80℃ and the pressure to -0.09MPa, and continue drying for 24 hours until the mass no longer changes. Remove the bag and place it in a desiccator to cool to room temperature, then weigh the final total dried mass (recorded as m3). Based on the initial mass data, calculate the apparent gel content and cross-linked network swelling ratio after deducting the stainless steel wire mesh bag. The specific calculation formulas are: Apparent gel content (%) = [(m3-m1) / m0] × 100%; Cross-linked network volume swelling ratio (cm³ / m3). 3 (m2-m3) = 1 + [(m2-m3) / ρs] / [(m3-m1) / ρp], where ρs is the density of toluene at room temperature, and ρp is the initial density of the insulating layer material. The results are shown in Table 2:

[0111] Table 2: Crosslinked Network Feature Extraction Data of Examples and Comparative Examples

[0112]

[0113] According to Table 2 and Figure 2 Data shows that the macroscopic performance of polymer networks does not solely depend on the absolute value of crosslinking density, but is controlled by the uniformity of spatial distribution and dynamic response capability of micro-nodes. Comparative Example 3, without added α-methylstyrene dimer, exhibited an apparent gel content as high as 93.2%, yet a swelling ratio as low as 1.43. This unconventional physical state indicates the formation of dense, rigid microphase regions within the system. Specifically, within the dynamic vulcanization temperature range of 170℃ to 190℃, the highly reactive double bonds at the ends of zinc methacrylate molecules tend to undergo random chain self-polymerization under initiator triggering, thereby generating large-sized poly-ZDMA hard cores in situ within the matrix. These hard phase regions spatially anchor the surrounding continuous polymer phase, preventing probe solvent molecules such as toluene from effectively penetrating the network pores and causing volume expansion. In actual cable extrusion and laying projects, such localized over-crosslinking structures often result in a lack of effective stress dissipation pathways when the material is subjected to external forces, leading to microcracks at points of bending stress concentration. In contrast, although the swelling ratio of Comparative Example 1, which uses a conventional silane crosslinking system, has slightly increased, its overall crosslinking efficiency has not broken through the bottleneck due to the rigidity of the static covalent network, and the gel content has only hovered at 80.4%.

[0114] Observing Examples 2 and 4, the test data revealed a more ideal confined network topology. Based on the steric hindrance effect of the two benzene rings in the AMSD molecule and its unique highly active allyl hydrogen, this structure substantially intervenes in the chain growth process of free radicals in the early stage of vulcanization. Once the self-polymerizing ZDMA long-chain free radicals combine with AMSD, they can initiate an addition-fragmentation chain transfer reaction, effectively terminating the continuous growth process and transforming into oligomer active ends containing only a small number of repeating units. The truncated oligomers are then widely grafted in a homogeneous state onto the resin backbone and the interface of the in-situ activated filler, constructing highly uniformly distributed coordination crosslinking nodes within the system. This confined grafting reaction explains why the apparent gel content of the system in the examples is stable in the range of 84% to 86%, and the swelling ratio significantly jumps to above 2.4. The increase in the swelling ratio indicates that the crosslinked network retains ample free volume and chain segment conformational inversion space, allowing solvent molecules to penetrate smoothly. Projecting this microscopic network state onto a macroscopic mechanical scenario explains why the dynamic ion coordination network of this insulating material can undergo reversible slippage and dissipate a large amount of external mechanical energy when subjected to harsh conditions such as large deformation stretching or forced winding at ultra-low temperatures.

[0115] Test Example 3:

[0116] 1. Sample setup: The masterbatch experimental subjects were selected from Example 2, Comparative Example 1 and Comparative Example 4.

[0117] 2. Test steps:

[0118] 2.1 Cut the masterbatch into rectangular strips with dimensions of 30mm in length, 10mm in width, and 2mm in thickness using a standard cutting knife. The edges of the strips should be flat and free of micro-cracks to avoid stress concentration interfering with the test signal.

[0119] 2.2. Clamp the cut sample in the tensile fixture of the dynamic thermomechanical analyzer and apply an initial pre-strain of 0.1% to maintain the tension of the sample during the heating and cooling process.

[0120] 2.3. Set the test mode to dynamic tensile mode and keep the loading frequency constant at 1Hz. Liquid nitrogen is introduced into the test chamber for forced cooling. After the system temperature stabilizes at -80℃, it is linearly heated to 100℃ at a heating rate of 3℃ / min.

[0121] 2.4 The instrument synchronously acquires the storage modulus (E') and loss modulus (E'') data of the sample during the temperature change process, and generates a continuous loss tangent (tanδ) curve in real time based on the ratio of the two (E'' / E') to characterize the material's damping dissipation capability. Subsequently, feature extraction is performed on the exported test curve: the temperature coordinates corresponding to the highest peak of the tanδ curve are read as the glass transition temperature Tg of the material, and the peak height and half-width at half-maximum of this peak are measured simultaneously; at the same time, the exact value of the storage modulus (E') curve at 25℃ is extracted as the room-temperature reference modulus. The extraction results of the above key feature parameters are shown in Table 3:

[0122] Table 3: Extraction of dynamic thermomechanical analysis feature data from Example 2 and Comparative Examples 1 and 4

[0123]

[0124] According to Table 3 and Figure 3 The data shows that the viscoelastic response of the material under alternating stress field provides direct thermodynamic evidence for its internal network topology. Conventional high-filler flame-retardant cable materials often face physical defects such as low-temperature hardening and difficulty in bending at room temperature in engineering applications. Their mechanical properties mainly lie in the restricted chain segment movement state between the rigid inorganic filler and the polymer matrix. Comparative Example 1, treated with silane coupling, showed a significant increase in storage modulus to 38.6 MPa at 25℃, and its glass transition temperature shifted to -31.87℃ in the high-temperature region. The short-chain covalent bonds established by silane molecules at the filler-resin interface have high bond energy and spatial rigidity. While anchoring the filler interface, they also restrict the conformational inversion and micro-Brownian motion of polymer chain segments near the interface. This rigid network cannot dissipate energy through intermolecular friction when subjected to external deformation, which is reflected in Figure (b) as a low tanδ peak and a half-width at half-maximum of only 17.3℃, macroscopically manifested as a significant deterioration in the material's flexibility. In Comparative Example 4, the removal of ZDMA reduced the chemical crosslinking density between macromolecular chains, resulting in a decrease in storage modulus to 7.8 MPa. The filler is in a semi-free state within the matrix, making it highly susceptible to interface slippage under external forces. Although its tanδ peak value is high, the lack of an effective stress transfer mechanism results in a narrow half-width at half-maximum (HWHM). Such materials often experience macroscopic fracture failure due to premature interface debonding during actual tensile or bending operations.

[0125] Unlike the comparative example, the test data of Example 2 exhibits significantly broadened damping dissipation behavior. Combined with the fact that the tanδ peak half-width at half-maximum (FWHM) of Example 2 has broadened considerably to 28.6℃, this directly confirms the previous in-situ activation modification and dynamic network construction mechanism. The dehydration etching of MAH provides ZDMA with a large number of highly active sites. The ion coordination clusters formed by the zinc-containing polar end groups of ZDMA at the interface act as efficient stress dissipation nodes over a wide temperature range. When the system is in the glass transition region or subjected to external dynamic strain, these physical cross-linking points based on dipole interactions and coordination bonds undergo reversible dissociation, sliding along the filler surface and re-coordinating (i.e., ion slip) when the stress reaches its yield threshold. This microscopic level of synergistic slip, accompanied by chain segment frictional internal friction, effectively converts applied mechanical energy into heat dissipation, causing the tanδ curve to remain high over a wide temperature range. Furthermore, Example 2 exhibited a stable storage modulus of 12.4 MPa at room temperature, without exhibiting the rigidity abrupt change seen in Comparative Example 1, nor the loss of structural load-bearing capacity due to excessively low strength as seen in Comparative Example 4. This mechanism of absorbing strain energy through dynamic ion recombination effectively overcomes the negative impact of high-filling inorganic fillers on the flexibility of the polymer matrix, endowing the material with characteristics that combine structural stability and high deformation tolerance.

[0126] Test Example 4:

[0127] 1. Sample Setup: Crosslinkable masterbatches prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were selected and hot-pressed in a flat vulcanizing machine at 180°C. A molding pressure of 15 MPa was maintained for 10 minutes under constant temperature molding, followed by cooling to room temperature with circulating water in a cold press to prepare a crosslinked insulating film of uniform thickness. The film was then left to stand for 24 hours to eliminate internal residual stress.

[0128] 2. Test steps:

[0129] 2.1. Use a standard die-cutting machine to cut the cross-linked film into dumbbell-shaped tensile specimens and long strip-shaped bending specimens that meet the specifications. During the cutting process, check the smoothness of the specimen edges and remove any strips with visible gaps or burrs.

[0130] 2.2 Clamp the dumbbell-shaped specimen in the upper and lower fixtures of the computer-controlled electronic universal testing machine and calibrate the initial gauge length. Set the tensile rate to 250 mm / min and perform uniaxial tension at room temperature of 25°C until the specimen completely breaks. Record the maximum tensile load and gauge length elongation at the moment of failure, and use these to calculate the tensile strength and elongation at break.

[0131] 2.3 Place the elongated specimen on the support of the three-point bending fixture, adjusting the span to 16 times the specimen thickness. Apply a bending load to the midpoint of the specimen at a constant loading rate of 2 mm / min, collect load-deflection data, and calculate the bending modulus within the specified deflection range. Test at least 5 valid specimens in parallel for each formulation, take the median of the calculated results, and record the discrete data characteristics. The results are shown in Table 4:

[0132] Table 4: Quantitative Test Data of Mechanical Strength and Flexibility at Room Temperature for Examples 1-5 and Comparative Examples 1-4

[0133]

[0134] According to Table 4 and Figure 4 The data shows that the lack of interfacial chemical bonding leads to a significant deterioration in the macroscopic mechanical properties of the material. Specifically, Comparative Example 2, which did not introduce solid maleic anhydride, exhibited a low fracture strain in the tensile test, with a tensile strength of only 9.86 MPa. Combined with the laboratory observation and analysis of the fracture surface morphology, due to the incomplete removal of the hydration layer on the magnesium hydroxide surface, only weak physical adsorption exists between the polar inorganic particles and the non-polar polymer matrix. Under external force, the filler tends to peel off from the matrix and form a large number of microporous defects. The commonly used silane crosslinking scheme in industry (Comparative Example 1), although relying on rigid covalent bonds to anchor the filler surface and increase its tensile strength to 17.48 MPa, also increases the macroscopic stiffness of the material, with its flexural modulus increasing significantly to 85.34 MPa. However, this static crosslinking network constructed by short-chain covalent bonds severely hinders the slip path of polymer chain segments, resulting in a significant decrease in its elongation at break. Similarly, in Comparative Example 3, which lacks AMSD regulation, uncontrolled homopolymerization of ZDMA within the system led to the formation of large, rigid polymer microphase regions in the matrix. These microphase regions resulted in severely uneven stress distribution within the material, with a flexural modulus exceeding 110 MPa. The material exhibited significant brittle fracture characteristics at room temperature, with the elongation at break decreasing to 114.2%, failing to meet the flexible deformation requirements of cable materials.

[0135] The systems in the examples all exhibited structural characteristics that balanced high tensile strength and excellent bending flexibility under varying proportions. After removing water molecule barriers using in-situ etching with MAH, AMSD effectively terminated the long-chain free radicals of ZDMA, transforming them into confined oligomer active ends that were widely grafted onto the resin backbone. This confined dynamic network directly correlated with the high tensile strength (18.24 MPa) and excellent deformation absorption capacity (elongation 385.6%) of Example 2 in the test data. When the material is subjected to external tensile force or large deformation bending, the ionic coordination bonds formed between the polar end groups of ZDMA and the surface of the activated filler can reversibly break, slide along the interface, and re-complex when the material yields under stress. This microscopic stress dissipation mechanism allows the system to maintain a dense encapsulation of the filler while effectively controlling the flexural modulus within the low range of 16 MPa to 25 MPa. This not only overcomes the traditional engineering problem of material hardening caused by high-filling inorganic flame retardants but also provides a reliable mechanical margin for the laying and winding of finished power cables in complex and narrow underground ducts.

[0136] Test Example 5:

[0137] 1. Sample setup: Select the master materials obtained from Examples 1 to 5 and Comparative Examples 1 to 4, and prepare them into finished power cables according to the parameters in step (4) of Example 5. Then, cut a continuous undamaged line segment with a length of 600mm as the experimental object, and remove the outer sheath of 50mm from both ends to expose the insulation layer.

[0138] 2. Test steps:

[0139] 2.1 Place the cut cable samples and the polished stainless steel cylindrical test bar with a diameter set to 3 times the outer diameter of the cable together in the ultra-low temperature environment test chamber.

[0140] 2.2 Set the cooling rate of the test chamber to 1℃ / min, so that the ambient temperature can be steadily reduced to -40℃ and kept constant for 16 hours to ensure that the polymer chain segments and inorganic filler areas inside the cable reach a complete low-temperature thermal equilibrium state.

[0141] 2.3 Without opening the door of the low-temperature test chamber, use an external robotic arm to tightly wrap the frozen cable sample onto a stainless steel test rod at a uniform rate of 5 seconds per rotation, continuously winding 4 complete coils, and maintaining the winding tension for 10 minutes.

[0142] 2.4. After removing the wound cable sample, allow it to thaw naturally at room temperature for 2 hours. Then, using a 15x handheld optical magnifying glass equipped with a ring light source, perform a full-coverage scan along the tensile stress surface on the outer side of the bend. Count the total number of microcracks and measure the maximum crack width using vernier calipers. Finally, conduct a 3.5kV power frequency withstand voltage test on the wound area to verify the insulation integrity. The results are shown in Table 5.

[0143] Table 5: Low-Temperature (-40℃) Cracking Resistance Test Data of Finished Cables from Examples and Comparative Examples

[0144]

[0145] According to Table 5 and Figure 5 Data shows that the cracking risk of highly filled flame-retardant cables under extremely cold conditions is often a key indicator for testing the toughness of polymer crosslinking networks. In ultra-low temperature environments of -40℃, the Brownian motion of macromolecular chain segments is severely restricted, and conventional matrix resins easily enter the glassy state and harden. In the past, during power grid renovation surveys in high-latitude cold regions, it was frequently found that cables produced using traditional silane crosslinking processes were prone to cracking along the stress ridges when laid and bent. The test results of Comparative Example 1 also reflected this defect. The surface of the cable contained as many as 18 microcracks, with the largest crack width reaching 1.67 mm. Because the silane network relies on short-chain rigid covalent bonds, this static crosslinking network cannot provide sufficient deformation tolerance at low temperatures and cannot effectively conduct and dissipate the concentrated stress generated by local bending. Furthermore, Comparative Example 3, which lacks AMSD regulation, exhibits more pronounced brittle fracture characteristics. Due to the presence of a large number of randomly homogeneous ZDMA hard cores, these large-sized rigid microphase regions cause severe internal stress field distortion when the matrix contracts, ultimately inducing a deep through-crack up to 2.58 mm wide on the outer side of the bend, leading to breakdown in subsequent pressure resistance tests.

[0146] The systems in the examples maintained excellent structural integrity and insulation even at temperatures below the glass transition region. This was not due to the simple addition of volatile small-molecule plasticizers, but rather stemmed from a change in the stress mechanism resulting from the chemical reconstruction of the microscopic interface. After the MAH melted and the hydration layer on the magnesium hydroxide surface was removed, the ZDMA oligomers, whose chain transfer was restricted by AMSD, constructed a dense ionic coordination network on the filler surface. Furthermore, Examples 1, 2, and 4 achieved a crack-free structural state on the surface after ultra-low temperature winding. This macroscopically exhibited freeze-thaw resistance and flexibility is essentially due to the localized coordination bond breakage of a large number of polar zinc carboxylate groups when the bending stress approached the material's yield limit. These groups then slid along the inorganic interface and recombine with adjacent polar sites. Therefore, this dynamic slippage relying on the non-covalent bonds of metal ions not only absorbed mechanical strain energy but also effectively hindered the convergence and propagation of microscopic silver streaks into macroscopic cracks, thereby improving the engineering challenge of poor cold resistance in high-strength insulating materials.

[0147] Test Example 6:

[0148] 1. Sample setup: The masterbatches prepared in Examples 2 and 4, and Comparative Examples 2 and 5 were selected as experimental subjects. The mixed masterbatches were pressed into flat test films with thicknesses of 1 mm and 2 mm on a flat vulcanizing machine at a constant pressure of 180°C and 15 MPa. After demolding, the films were placed in a constant temperature and humidity chamber for 24 hours to eliminate residual molding stress.

[0149] 2. Test steps:

[0150] 2.1 The volume resistivity of a 2mm thick sample was tested using an insulation high-resistivity meter. The sample was placed in a three-electrode measurement system equipped with a guard ring, and a 500V DC voltage was applied steadily. After continuous polarization for 1 minute, the stable leakage current and resistance values ​​were read. The volume resistivity of the material was calculated by combining the effective test area of ​​the electrodes.

[0151] 2.2. Completely immerse the 1mm thick sample in an insulation test tank filled with pure transformer oil to prevent edge surface flashover during the test. Apply a 50Hz AC voltage to the sample using an AC breakdown voltage tester at a constant voltage increase rate of 2kV / s, continuously increasing the voltage until a through-discharge breakdown occurs inside the sample. Record the critical voltage value at the moment of breakdown and divide it by the actual thickness of the sample to calculate the electrical strength.

[0152] 2.3. A 2mm thick sample was taken and its initial dried mass was weighed using an analytical balance with an accuracy of 0.1mg. The sample was then completely immersed in a deionized water bath at a set temperature of 70℃ for continuous constant-temperature aging for 168 hours. After the specified time, the sample was removed, and the surface free moisture was quickly blotted dry with lint-free paper and weighed again. The percentage increase in mass before and after water absorption was calculated as the water absorption rate, thereby quantitatively evaluating the microscopic pore defects and interfacial bonding tightness within the material. The results are shown in Table 6.

[0153] Table 6: Test data on electrical insulation performance and material density of the examples and comparative examples

[0154]

[0155] According to Table 6 and Figure 6 Data shows that the electrical insulation strength of polymer composites is significantly correlated with the physical density of their internal phase interfaces. In the actual research and development of high-voltage cable insulation formulations, it is frequently found that micron-sized internal pores or hydrophilic free interfaces are the main causes of partial discharge and electrical tree growth. Comparative Example 5 used liquid glacial acetic acid instead of solid maleic anhydride for filler surface dehydration. This conventional acid-base neutralization operation is feasible in room-temperature liquid-phase reactions, but it caused significant structural defects in the high-shear thermal field of the mixing process, reaching 135℃. The liquid acid rapidly vaporizes upon contact with the high-temperature material. The rapidly expanding vaporized solvent molecules are encapsulated in the extremely viscous rubber continuous phase, forming numerous microporous foam structures within the rubber compound. These physical micropores not only provide channels for moisture intrusion but also significantly increase the water absorption rate in a 70℃ water bath to 1.87%. Furthermore, under the influence of an AC high-voltage electric field, they become points of severe electric field distortion, with localized free discharge causing the AC breakdown voltage to drop to 12.4 kV / mm. The material cannot meet the basic application requirements of high-voltage insulation layers. While Comparative Example 2, which did not add any acid anhydride, avoided the defects of liquid-phase vaporization foaming, the strong polar hydroxyl hydration layer on the surface of magnesium hydroxide was not removed, and there were microscopic peeling gaps between the inorganic particles and the organic resin, which allowed water to still penetrate into the interfacial network. Its water absorption rate of 0.48% and breakdown performance of 19.3kV / mm could not provide sufficient engineering safety margin.

[0156] Observing the various indicators of Examples 2 and 4, the technical advantages of in-situ modification using solid macromolecular anhydrides in constructing a dense insulating network were verified. Maleic anhydride, which is a solid powder at room temperature and has a melting point of only 52°C, is uniformly dispersed in the matrix in the initial stage of mixing. As the mixing temperature rises, it gradually melts and penetrates to the surface of magnesium hydroxide by polarity, undergoing a stable ring-opening dehydration and neutralization reaction with physically bound water. This in-situ chemical reconstruction process based on the phase change of solid materials has no volatile gas escape throughout the process, physically avoiding the generation of bubble defects. With the subsequent network construction, and the polar end groups of zinc methacrylate forming a tight coordination anchor on the clean magnesium surface after dehydration, the penetration path of water molecules along the interface is effectively blocked. As a result, the water absorption rate of the material is controlled to 0.15% or less. Moreover, the dense phase interface not only blocks the dielectric loss of polar water molecules, but also enables the system to achieve a volume insulation resistivity of up to 3.42E+15Ω·cm and an AC breakdown strength of over 28kV / mm. This establishes a reasonable correspondence between the microscopic interface mechanism and the macroscopic engineering indicators.

[0157] Test Example 7:

[0158] 1. Sample Setup: The masterbatches prepared in Examples 1 to 5, as well as Comparative Examples 1 and 3, were selected as experimental subjects. Using a precision punching machine and a cutting machine, the pressed standard thickness films were cut into standard test strips for Limiting Oxygen Index (LOI) with dimensions of 120mm × 10mm × 4mm, and standard test strips for UL94 vertical burning with dimensions of 125mm × 13mm × 3mm. All test strips were placed in an environmental control chamber at 23°C and 50% relative humidity for 48 hours for conditioning before testing.

[0159] 2. Test steps:

[0160] 2.1 LOI testing was performed using a Limiting Oxygen Index (LOI) tester. The test strip, with its calibrated combustion scale marked, was vertically fixed to the base clamp inside a transparent combustion chamber. The gas source was turned on, and the volumetric flow rate distribution ratio of oxygen and nitrogen in the mixed gas was adjusted. After the gas flow inside the chamber had rinsed and stabilized for 30 seconds, the top surface of the test strip was ignited using an igniter. During this process, the combustion state of the test strip was continuously observed. The oxygen concentration was repeatedly fine-tuned until the test strip could maintain stable combustion for exactly 3 minutes, or the length of the downward spread of the flame reached exactly 50 mm. The lowest oxygen volume percentage displayed by the instrument at this point was recorded as the limiting oxygen index value of the material.

[0161] 2.2 The UL94 flame retardancy rating of the test strips was evaluated using a standard vertical burning tester. The test strips were vertically clamped onto a support in a fume hood, ensuring the bottom of the strip was exactly 300mm from the dry, degreased cotton placed below. A Bunsen burner was lit and adjusted to produce a standard blue flame with a height of 20mm. The flame center was moved to the bottom edge of the test strip and burned for 10 seconds, then quickly removed. A stopwatch was used to record the duration of the first flaming combustion (t1) after the strip was removed from the flame source. After the flame completely extinguished, a second flaming combustion was immediately applied for 10 seconds, and the duration of the second flaming combustion (t2) and the afterglow extinguished combustion (t3) were recorded. Throughout the test, the occurrence of molten polymer dripping and igniting the bottom cotton was carefully observed and recorded. The vertical burning rating of the material was determined by combining these time indicators. The results are shown in Table 7.

[0162] Table 7: Limiting Oxygen Index and Vertical Combustion Test Characteristics of Examples 1-5 and Comparative Examples 1 and 3

[0163]

[0164] According to Table 7 and Figure 7 Data shows that the dispersion topology of high-load inorganic fillers in the continuous polymer phase and the degree of cross-linking density of the interfacial network have a significant impact on the macroscopic flame-retardant and heat-insulating performance of the material. In the actual formulation development of halogen-free low-smoke cable materials, a fundamental contradiction is often faced: the endothermic degradation efficiency of inorganic flame retardants such as magnesium hydroxide is highly dependent on their absolute filler content, but conventional cross-linked networks are prone to structural embrittlement due to the large amount of powder involved, leading to macroscopic structural cracking of the material under high temperatures. From the flame-retardant gradient data of Examples 1 to 3, it is clear that thanks to the effective containment of the confined dynamic network, the flame-retardant performance of all examples is significantly better than that of the traditional formulation system. Even in Example 1 with the basic filler content, the limiting oxygen index reached 31.2%, and the total flaming time was shortened to 9.1 seconds, meeting the V-0 rating standard. When the amount of magnesium hydroxide added increased to 150 parts (Example 3), the limiting oxygen index of the system increased to 36.8%, and the corresponding total flaming time decreased to 3.5 seconds. This effective compatibility with extremely high powder filling rates confirms that dynamic sliding crosslinking nodes, while imparting high physical flexibility to the material, also enhance the overall flame retardant performance of the system.

[0165] According to the comparative data, the inferior interfacial bonding quality exhibits significant defects under high-temperature combustion conditions. Comparative Example 1, modified with conventional silane coupling, showed a decrease in its limiting oxygen index to 28.6%, and a total combustion time of 14.0 seconds after two flaming combustions, maintaining a flame retardant performance only at the V-1 level. Field observations during combustion tests revealed that the rigid covalent network constructed by silane molecules could not adapt to the significant difference in thermal expansion coefficients between the matrix resin and inorganic particles under high-temperature heat flow. Numerous microcracks appeared on the surface of the charred layer in the early stages, providing a pathway for the escape of incompletely degraded volatile combustible gases from the underlying layer. Comparative Example 3, lacking AMSD regulation, showed further deterioration in flame retardant performance. The unrestricted local homopolymerization of zinc methacrylate led to micro-agglomeration of the filler, and the presence of resin-rich regions allowed the flame to spread rapidly within the local matrix, resulting in a total combustion time as high as 17.8 seconds and a limiting oxygen index dropping to 27.8%. In contrast, the confined active short chains in the example system not only ensured the highly uniform dispersion of the inorganic powder, but also the zinc ion coordination nodes contained therein played an effective catalytic role in char formation during the initial stage of polymer pyrolysis. As the external flame burned, the uniformly distributed zinc-containing clusters promoted rapid dehydrogenation of the surface resin, and, combined with the large amount of water vapor released from the decomposition of magnesium hydroxide, constructed a dense and continuous inorganic-carbon-rich framework around the material. This charred layer exhibited a certain degree of viscoelastic toughness in the molten state, absorbing the internal thermal strain and inhibiting char layer cracking and dripping, significantly improving the fire safety of the highly filled insulation system.

[0166] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flexible high-strength insulated cable material, characterized in that, Includes the following weight groups: EPDM rubber: 50-70 parts; Ethylene-octene copolymer: 30-50 parts; Magnesium hydroxide: 100-150 parts; Solid maleic anhydride: 1.0–3.0 parts; Zinc methacrylate: 5-15 parts; α-Methylstyrene dimer: 0.5–1.5 parts; Dicumyl peroxide: 1.0–2.5 parts; Compound antioxidant: 0.5–2.0 parts; The compound antioxidant is composed of antioxidant 1010 and antioxidant 168, and the mass ratio of antioxidant 1010 to antioxidant 168 is 1:1 to 2:

1.

2. The cable material according to claim 1, characterized in that, The EPDM rubber specifically comprises an ethylene-propylene-diolefin copolymer with 5-ethylidene-2-norbornene as the third monomer, wherein the ethylene mass fraction is 65% to 75%, the 5-ethylidene-2-norbornene mass fraction is 4% to 6%, and the Mooney viscosity at 125°C is 40 to 60.

3. The cable material according to claim 1, characterized in that, The ethylene-octene copolymer contains 20% to 30% 1-octene by mass, and has a melt flow rate of 1.0 g / 10 min to 5.0 g / 10 min at 190 °C and 2.16 kg, with a crystallinity of less than 20%.

4. The cable material according to claim 1, characterized in that, The solid maleic anhydride has a melting point of 52℃~55℃, is a solid powder at room temperature, and has a purity ≥99.5%; the magnesium hydroxide has an average particle size D50 of 1.0μm~2.5μm, a purity ≥99.0%, and a specific surface area of ​​5m². 2 / g~15m 2 / g of flame-retardant magnesium hydroxide powder.

5. The cable material according to claim 1, characterized in that, The zinc content of the zinc methacrylate is 26%–30% by mass, and the specific surface area is >20 m². 2 / g; the purity of the α-methylstyrene dimer is ≥97.0%, and the boiling point is 310℃~313℃.

6. A method for preparing a flexible high-strength insulated cable material, using the flexible high-strength insulated cable material as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of formulation: Prepare EPDM rubber, ethylene-octene copolymer, magnesium hydroxide, maleic anhydride, zinc methacrylate, α-methylstyrene dimer, dicumyl peroxide and compound antioxidant; (2) Masterbatch mixing: EPDM rubber, ethylene-octene copolymer, magnesium hydroxide and maleic anhydride are put into an internal mixer for the first stage of mixing; then zinc methacrylate and compound antioxidant are added, and the second stage of mixing is carried out under slight negative pressure; after discharge, the rubber is cooled to room temperature to obtain the compounded rubber. (3) Premixing: After cooling, add dicumyl peroxide and α-methylstyrene dimer to the mixed rubber compound in a two-roll mill. After mixing evenly, the mixture is sheeted and granulated to obtain crosslinkable masterbatch.

7. The preparation method according to claim 6, characterized in that, Step (2) specifically includes: the temperature of the first stage of mixing is 130℃~140℃, the speed is 40rpm~60rpm, and the time is 3~8min; the second stage of intensive mixing maintains the same temperature, the vacuum system is turned on to make the pressure reach -0.05MPa~-0.09MPa, and the intensive mixing continues for 5~10min.

8. The preparation method according to claim 6, characterized in that, In step (3), the temperature of the open mill is controlled at 90℃~100℃, and the turning time is 5~10min.

9. A power cable, characterized in that, It includes an internal conductor core and an insulation layer covering the periphery of the conductor core, the insulation layer being formed by extrusion vulcanization of the flexible high-strength insulated cable material as described in any one of claims 1-5.

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