Silane cross-linked polyolefin halogen-free flame-retardant cable material and low-energy-consumption preparation method thereof

Abstract

The invention discloses a silane cross-linked polyolefin halogen-free flame-retardant cable material and a low-energy-consumption preparation method thereof.The preparation method comprises the steps that EVA / EEA serves as a matrix, silane groups are covalently connected to a polyolefin molecular chain through a free radical grafting reaction, and a grafting material containing an active silane side group is prepared; meanwhile, vinyl isocyanate is adopted to chemically modify hydroxyl on the surface of magnesium hydroxide, vinyl is grafted to the surfaces of particles, the polarity of the particles is reduced, and the dispersity of the particles is enhanced; then carrying out melt blending on the grafted material and modified magnesium hydroxide, constructing an interface bridge by using an anhydride group, and shortening the two-phase distance; finally, through room-temperature natural cross-linking and warm water auxiliary cross-linking, silane groups are promoted to be hydrolyzed into silanol, the silanol is condensed to form a-Si-O-Si-three-dimensional network, meanwhile, vinyl on the surface of magnesium hydroxide and a polyolefin matrix are subjected to free radical copolymerization, and a covalent bond interface layer is formed between inorganic particles and an organic matrix. According to the method, the synergistic improvement of high crosslinking degree, strong stretchability and excellent flame retardance of the cable material is realized through molecular-level interface regulation and cross-linking network optimization.

Description

Technical Field

[0001] The present invention relates to the field of halogen-free flame-retardant cable materials, and in particular to a silane cross-linked polyolefin halogen-free flame-retardant cable material and a low-energy consumption preparation method thereof. Background Art

[0002] Silane cross-linked polyolefin halogen-free flame-retardant cable materials are widely used in power transmission, building wiring and other fields due to their excellent flame retardancy, aging resistance and environmental friendliness. Currently, the preparation of such materials in existing technologies mainly faces the following technical bottlenecks:

[0003] Traditional cable materials usually use a single ethylene-vinyl acetate copolymer (EVA) as the matrix resin. The interfacial bonding between its polar groups and halogen-free flame retardants (such as magnesium hydroxide) is weak, which easily leads to flame retardant agglomeration, affecting not only the mechanical properties of the material, but also reducing the flame retardant stability due to uneven dispersion. At the same time, the grafting efficiency of conventional silane coupling agents (such as vinyl silane) and polyolefins is limited, and the grafting effect needs to be improved by increasing the amount of coupling agent or initiator, which not only increases costs but may also introduce the risk of side reactions.

[0004] In terms of flame retardant modification, existing technologies mostly use silane coupling agents to physically coat and modify magnesium hydroxide. The interfacial bonding is mainly hydrogen bonding, which is prone to interfacial dissociation under long-term use or high-temperature environment, resulting in material performance degradation; and catalysts mostly rely on dibutyltin dilaurate (DBTDL) containing heavy metals. Although it can accelerate silanol condensation and cross-linking, it has toxicity risks and does not meet environmental protection requirements.

[0005] In terms of cross-linking, traditional methods often achieve full cross-linking through long-term high-temperature cooking (such as boiling at 80°C for more than 8 hours), which consumes a lot of energy. Furthermore, single high-temperature cross-linking can easily cause the migration and precipitation of hydroxyl groups on the surface of magnesium hydroxide, affecting the material's weather resistance. Furthermore, the synergy between the additive system and the processing technology is insufficient: the selection of functional additives such as antioxidants and copper inhibitors lacks specificity, making it difficult to simultaneously inhibit thermal oxidative degradation and metal catalytic aging. Furthermore, the mismatch between lubricants and mixing and extrusion process parameters can easily lead to uneven material dispersion, affecting processing efficiency and final product performance.

[0006] In summary, existing silane-crosslinked polyolefin halogen-free flame-retardant cable materials have obvious deficiencies in terms of interface bonding strength, environmental protection, energy consumption control and long-term stability. There is an urgent need for a new material and preparation method that can simultaneously enhance interface effects, reduce toxicity risks, balance energy consumption and crosslinking degree, and improve processing performance. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a silane cross-linked polyolefin halogen-free flame retardant cable material and a low-energy consumption preparation method thereof to solve one or more problems in the prior art.

[0008] In order to achieve a complete technical effect, the present invention has prepared two sets of mutually nested and complementary technical solutions. The first set of technical solutions of the present invention is as follows:

[0009] A silane cross-linked polyolefin halogen-free flame-retardant cable material is prepared by mixing and cross-linking a silane grafted material and a halogen-free masterbatch in a mass ratio of (2-4):(20-24);

[0010] The silane grafted material comprises, by mass:

[0011] Matrix resin: 40-50 parts of ethylene-vinyl acetate copolymer, 10-20 parts of ethylene-ethyl acrylate;

[0012] Coupling agent: 1.0-1.5 parts of methacryloxysilane;

[0013] Initiator: dicumyl peroxide 0.15-0.25 parts;

[0014] Additives: antioxidant 0.1-0.3 parts, anti-copper agent 0.05-0.15 parts;

[0015] The halogen-free masterbatch comprises, by mass:

[0016] Matrix resin: ethylene-vinyl acetate copolymer 25-35 parts;

[0017] Flame retardant: 65-75 parts of bifunctional modified magnesium hydroxide;

[0018] Compatibilizer: 15-25 parts of maleic anhydride grafted polyethylene;

[0019] Catalyst: 0.2-0.4 parts of bismuth neodecanoate;

[0020] Additives: lubricant 0.4-0.6 parts, antioxidant 0.1-0.3 parts;

[0021] The bifunctional modified magnesium hydroxide is a modified flame retardant formed by grafting vinyl isocyanate with hydroxyl groups on the surface of magnesium hydroxide.

[0022] Specifically, the antioxidant in the silane grafted material is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the anti-copper agent is 2-mercaptobenzimidazole.

[0023] Specifically, the lubricant in the halogen-free masterbatch is calcium stearate, and the antioxidant is tris[2,4-di-tert-butylphenyl]phosphite.

[0024] Specifically, the particle size of the bifunctional modified magnesium hydroxide is 0.5-1.0 μm.

[0025] Specifically, the melt flow rate (190° C. / 2.16 kg) of the silane grafted material is 4-6 g / 10 min.

[0026] Specifically, the cable material has a cross-linking degree of 70-80%, a tensile strength of ≥12 MPa, and an oxygen index of ≥32%.

[0027] The second technical solution is a low-energy consumption preparation method based on the silane cross-linked polyolefin halogen-free flame-retardant cable material, comprising the following steps:

[0028] (1) Preparation of silane grafted material: Ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate, methacryloxysilane, dicumyl peroxide, antioxidant, and anti-copper agent are mixed, melt-grafted through a twin-screw extruder, and granulated and dried;

[0029] (2) Preparation of bifunctional modified magnesium hydroxide: magnesium hydroxide and vinyl isocyanate are mixed and reacted at 80-120° C. for 20-40 min, wherein the amount of vinyl isocyanate is 1.0-2.0% of the mass of magnesium hydroxide;

[0030] (3) Preparation of halogen-free masterbatch: Ethylene-vinyl acetate copolymer, bifunctional modified magnesium hydroxide, maleic anhydride grafted polyethylene, bismuth neodecanoate, lubricant, and antioxidant are mixed, mixed in an internal mixer, and granulated by twin-screw extrusion;

[0031] (4) Mixed crosslinking: The silane grafted material and the halogen-free masterbatch are mixed in a mass ratio of (2-4): (20-24) and then extruded into a mold, and then naturally crosslinked at room temperature (20-30°C, relative humidity 50-70%, 40-56h) and warm water assisted crosslinking (65-75°C, 1.5-2.5h) are carried out in sequence.

[0032] Specifically, the aspect ratio of the twin-screw extruder in step (1) is 40:1-48:1, the temperature of each zone is 150-190°C, and the screw speed is 350-450rpm; the drying temperature after granulation is 65-75°C, and the drying time is 1.0-2.0h.

[0033] Specifically, the mixing temperature of the internal mixer in step (3) is 120-140°C, and the mixing time is 8-12 min; the temperature of the twin-screw extruder is 140-160°C, and the screw speed is 250-300 rpm; the drying temperature after granulation is 55-65°C, and the drying time is 0.5-1.5 h.

[0034] Specifically, the single-screw extruder used for extrusion molding in step (4) has an aspect ratio of 25:1-35:1, a compression ratio of 3:1-4:1, an extrusion temperature of 150-180°C, and an extrusion speed of 10-20m / min.

[0035] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0036] (I) The matrix resin, a compound of ethylene-vinyl acetate copolymer (EVA) and ethylene-ethyl acrylate (EEA), combined with the synergistic effect of a methacryloxysilane coupling agent, significantly enhances the interfacial bonding ability between the matrix and the flame retardant. The polar groups of EVA provide basic flexibility, while the polar side chains of EEA form a stronger interaction with the hydroxyl groups on the surface of magnesium hydroxide (as opposed to the weak bonding of a traditional single matrix). The highly reactive double bonds of methacryloxysilane enhance the grafting efficiency with polyolefins. Together, they improve the uniformity of the flame retardant dispersion in the matrix, avoid the problem of flame retardant agglomeration caused by weak interfacial bonding in traditional processes, and provide a fundamental support for the mechanical properties and flame retardant stability of the material.

[0037] (2) The combination of bifunctional modified magnesium hydroxide and bismuth neodecanoate catalyst breaks through the dual limitations of weak interface bonding and catalyst toxicity of traditional flame retardants. Bifunctional modification connects magnesium hydroxide to the polyolefin matrix through covalent bonds (different from the physical coating of traditional silanes), forming a more stable "flame retardant-matrix" interface; bismuth neodecanoate catalyst replaces traditional catalysts containing heavy metals, accelerating the silanol condensation reaction without the risk of toxicity. Under the synergistic effect of the two, the interfacial bonding strength is significantly improved, the mechanical properties of the material after thermal aging are more retained, and the cross-linking process does not require long-term high-temperature treatment, taking into account both environmental protection and production efficiency.

[0038] (III) A low-proportion mixture of silane grafting components and halogen-free masterbatch components, combined with a dual-mode process of natural crosslinking at room temperature and warm water-assisted crosslinking, achieves a balance between low-energy preparation and high crosslinking degree. Due to the high grafting efficiency of methacryloxysilane, the amount of silane grafting components can be reduced (as opposed to the traditional high-proportion requirement), reducing raw material costs; the dual-mode crosslinking utilizes ambient humidity to slowly hydrolyze silanol groups, avoiding the migration of flame retardant hydroxyl groups caused by long-term high-temperature cooking. At the same time, a short period of warm water is used to supplement the crosslinking degree, thereby reducing energy consumption while ensuring the final crosslinking degree, solving the contradiction between "high energy consumption" and "high crosslinking degree" in traditional processes.

[0039] (4) The combination of a multi-type additive system and specific processing technology ensures the material's processing performance and long-term stability. Antioxidants inhibit thermal oxidative degradation during processing and use, anti-copper agents prevent metal ion catalytic aging, and lubricants improve mixing fluidity. Combined with the synergistic effects of twin-screw extrusion and internal mixer mixing, the material achieves more uniform dispersion and better fluidity during processing, and its mechanical properties degrade more slowly during long-term use, effectively extending its overall service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1It is a schematic flow chart of the low energy consumption preparation method of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and exemplary explanations. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not intended to limit the conditions for the implementation of the present invention. Therefore, they have no technical significance. Any modification of the structure, change in the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose of the present invention.

[0042] Application Overview

[0043] In the field of silane cross-linked polyolefin halogen-free flame retardant cable materials, the industry has long adopted the following conventional treatment methods to address key issues such as material interface bonding, flame retardant stability, environmental protection and energy consumption control: First, the base resin is mostly made of a single ethylene-vinyl acetate copolymer (EVA), combined with traditional vinyl silane coupling agents to improve interface compatibility. However, due to the weak binding force between the polar groups of EVA and halogen-free flame retardants such as magnesium hydroxide, and the limited grafting efficiency of silane coupling agents, it is easy to cause uneven dispersion or even agglomeration of flame retardants, which directly affects the mechanical properties and flame retardant stability of the material; second, flame retardant modification usually uses silane coupling agents to physically coat the surface of magnesium hydroxide, and the interface bonding is mainly hydrogen bonding, which is long-lasting. Interfacial dissociation is prone to occur during long-term use or in high-temperature environments, causing performance degradation; thirdly, cross-linking catalysis mostly relies on dibutyltin dilaurate (DBTDL) containing heavy metals. Although it can accelerate the silanol condensation reaction, it has toxicity risks and does not meet environmental protection requirements; fourthly, the cross-linking process generally uses high-temperature and long-term cooking (such as boiling at 80°C for more than 8 hours) to achieve sufficient cross-linking, which has high energy consumption and is prone to induce the migration and precipitation of magnesium hydroxide hydroxyl groups, affecting weather resistance; fifthly, the collaborative design of the auxiliary agent system (such as antioxidants, anti-copper agents, lubricants) and the processing technology (such as twin-screw extrusion and internal mixer mixing) is insufficient, making it difficult to simultaneously suppress thermal oxidative degradation, metal catalytic aging, and uneven processing dispersion. The above conventional solutions have significant defects in terms of interface bonding strength, environmental protection, energy consumption control, and long-term stability, which restrict the performance improvement and application expansion of silane cross-linked polyolefin halogen-free flame retardant cable materials.

[0044] Comprehensive description

[0045] The present invention relates to a silane-crosslinked polyolefin halogen-free flame-retardant cable material and its low-energy production method. Through optimized component design and coordinated process control, this material overcomes the problems of weak interfacial bonding, insufficient environmental friendliness, and high energy consumption associated with conventional halogen-free flame-retardant cable materials. The following describes the technical solution of the present invention in detail, combining its material composition and production process.

[0046] 1. Material composition design

[0047] The core of the silane cross-linked polyolefin halogen-free flame-retardant cable material of the present invention is prepared by mixing and cross-linking two parts: one part is a silane grafted material and the other part is a halogen-free masterbatch, and the mass ratio of the two parts is (2-4):(20-24).

[0048] The silane grafted material uses ethylene-vinyl acetate copolymer (EVA) and ethylene-ethyl acrylate (EEA) as the composite matrix resin, with the amount of EVA being 40-50 parts by mass and the amount of EEA being 10-20 parts by mass. The reason for choosing EVA and EEA is that the vinyl acetate group in the EVA molecular chain provides basic flexibility, while the ethyl acrylate side chain of EEA contains a more active polar group (-COOCH2CH3), which can form a stronger interaction with the surface hydroxyl group of magnesium hydroxide in the subsequent halogen-free masterbatch, thereby improving the interfacial bonding strength.

[0049] The silane grafted material also contains the following functional components:

[0050] Coupling agent: Use 1.0-1.5 parts by weight of methacryloxysilane (such as γ-methacryloxypropyltrimethoxysilane). Compared to traditional vinyl silanes (such as A-171), the double bond (-C=C-) in its molecule is more active, allowing for more efficient grafting reactions with polyolefin matrices, reducing the amount of coupling agent required.

[0051] Initiator: Use dicumyl peroxide (DCP) in an amount of 0.15-0.25 parts by mass. DCP decomposes at the melt processing temperature to produce free radicals, which initiate the grafting reaction between the silane and the matrix resin.

[0052] Additives: These include antioxidants and copper inhibitors. The antioxidant is preferably pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Antioxidant 1010), used in an amount of 0.1-0.3 parts by mass to inhibit thermal oxidative degradation during processing and use. The copper inhibitor is preferably 2-mercaptobenzimidazole (e.g., Antioxidant MB), used in an amount of 0.05-0.15 parts by mass to effectively capture copper ions (e.g., metal ions released by copper conductors in cables) and prevent catalytic material aging.

[0053] The halogen-free masterbatch uses EVA as the base resin (dosage 25-35 parts by mass), and a bifunctional modified magnesium hydroxide is added to the core as a flame retardant (dosage 65-75 parts by mass). The modified magnesium hydroxide is formed by grafting vinyl isocyanate with the hydroxyl group on the surface of magnesium hydroxide: the isocyanate group (-NCO) of vinyl isocyanate (such as 3-isocyanatepropyltrimethoxysilane) is covalently bonded to the hydroxyl group (-OH) on the surface of magnesium hydroxide (forming a carbamate bond), while retaining the vinyl (-CH=CH2) active group, which can further react with the polyolefin matrix to form a "flame retardant-matrix" covalent bridging structure, significantly improving the interfacial bonding strength. The particle size of the bifunctional modified magnesium hydroxide is controlled at 0.5-1.0μm. This particle size range can not only ensure flame retardant efficiency (large specific surface area), but also avoid agglomeration problems caused by too small particle size.

[0054] Halogen-free masterbatch also contains the following functional components:

[0055] Compatibilizer: Maleic anhydride grafted polyethylene (PE-g-MAH) is used in an amount of 15-25 parts by mass. The maleic anhydride groups can form hydrogen bonds with the hydroxyl groups on the surface of magnesium hydroxide (some polar groups still remain after modification), making the polyethylene segments compatible with the polyolefin matrix, further strengthening the interfacial bonding between the two phases.

[0056] Catalyst: Use 0.2-0.4 parts by weight of bismuth neodecanoate (Bi(versatate)3). Compared to traditional dibutyltin dilaurate (DBTDL), bismuth neodecanoate is non-toxic and has higher catalytic activity for silanol condensation reactions (crosslinking reactions after silane hydrolysis).

[0057] Additives: These include lubricants and antioxidants. The preferred lubricant is calcium stearate, used in an amount of 0.4-0.6 parts by mass. This can reduce the internal friction of the material during mixing and extrusion, improving processing fluidity. The preferred antioxidant is tris[2,4-di-tert-butylphenyl]phosphite (such as Antioxidant 168), used in an amount of 0.1-0.3 parts by mass. This synergizes with Antioxidant 1010 in the silane-grafted material to form a "primary antioxidant (capturing free radicals)-auxiliary antioxidant (decomposing peroxides)" system, comprehensively inhibiting thermal oxidative degradation.

[0058] 2. Low-energy consumption preparation process

[0059] The cable material preparation process of the present invention includes four key steps: preparation of silane grafted material, preparation of bifunctional modified magnesium hydroxide, preparation of halogen-free masterbatch and mixed cross-linking. The specific operations are as follows:

[0060] 1. Preparation of silane grafted materials

[0061] EVA, EEA, methacryloxysilane, DCP, antioxidant 1010, and antioxidant MB are added to a high-speed mixer in proportion and mixed at 50-60°C for 5-10 minutes to ensure that all components are evenly dispersed. The mixed materials are melt-grafted through a twin-screw extruder with an aspect ratio of 40:1-48:1 (to ensure sufficient residence time to complete the grafting reaction). The temperature of each zone is set to 150-190°C (low temperature in the front section prevents premature hydrolysis of silane, and high temperature in the back section promotes grafting), and the screw speed is 350-450rpm (high shear force promotes material mixing and reaction). After water-cooling and pelletizing, the extruded material is dried at 65-75°C for 1.0-2.0 hours to remove moisture and prevent hydrolysis and inactivation of the silane during subsequent processing. The melt flow rate (190°C / 2.16kg) of the final silane grafted material is controlled at 4-6g / 10min, which takes both processing fluidity and grafting efficiency into consideration.

[0062] 2. Preparation of bifunctional modified magnesium hydroxide

[0063] Magnesium hydroxide (initial particle size 0.5-1.0 μm) and vinyl isocyanate (1.0-2.0% by mass of the magnesium hydroxide) are added to a high-speed blender and mixed at 80-120°C for 20-40 minutes. During the reaction, the isocyanate groups of the vinyl isocyanate covalently bond with the hydroxyl groups on the surface of the magnesium hydroxide, while the vinyl groups remain on the surface. After the reaction is complete, the mixture is cooled to room temperature to obtain a bifunctional modified magnesium hydroxide with vinyl groups grafted onto its surface.

[0064] 3. Preparation of halogen-free masterbatch

[0065] EVA, bifunctional modified magnesium hydroxide, PE-g-MAH, bismuth neodecanoate, calcium stearate, and antioxidant 168 are added to an internal mixer in proportion and mixed at 120-140°C for 8-12 minutes (too high a temperature will cause the magnesium hydroxide to decompose, and too low a temperature will cause insufficient melting of the material). After mixing, the material is granulated by a twin-screw extruder. The extruder temperature is set to 140-160°C (to avoid high temperature-induced silane hydrolysis) and the screw speed is 250-300rpm (low shear force prevents the surface vinyl of the modified magnesium hydroxide from breaking). After granulation, the material is dried at 55-65°C for 0.5-1.5 hours to remove moisture.

[0066] 4. Mixed cross-linking

[0067] The silane grafted material and the halogen-free masterbatch are uniformly mixed in a mass ratio of (2-4):(20-24) and extruded through a single-screw extruder. The single-screw extruder has an aspect ratio of 25:1-35:1, a compression ratio of 3:1-4:1 (to ensure uniform melting of the materials), an extrusion temperature of 150-180°C (to prevent premature hydrolysis of the silane), and an extrusion speed of 10-20 m / min (to control the residence time and prevent premature crosslinking). The extruded semi-finished cable undergoes natural crosslinking at room temperature and warm water-assisted crosslinking: room temperature crosslinking conditions are 20-30°C and relative humidity of 50-70% for 40-56 hours (to utilize the ambient humidity to slowly hydrolyze the silane and form a preliminary crosslinked network); followed by warm water-assisted crosslinking at 65-75°C for 1.5-2.5 hours (to accelerate the silanol condensation reaction and replenish the crosslinking degree). The final cable material has a cross-linking degree of 70-80%, a tensile strength of ≥12MPa, and an oxygen index of ≥32%, meeting the high performance requirements of halogen-free flame-retardant cables.

[0068] Through the above-mentioned material composition design and process parameter control, the silane cross-linked polyolefin halogen-free flame-retardant cable material of the present invention is significantly superior to traditional solutions in terms of interface bonding strength, environmental protection, energy consumption control and long-term stability, providing an effective technical path for the high performance and green preparation of halogen-free flame-retardant cables.

[0069] Experimental verification and performance testing

[0070] To verify the actual impact of the key process parameters in this invention on the performance of silane-crosslinked polyolefin halogen-free flame-retardant cable materials and further clarify the rationality of the parameter range, the following experimental plan was designed. Using the "mass ratio of silane-grafted material to halogen-free masterbatch," "particle size of bifunctional modified magnesium hydroxide," and "warm water-assisted crosslinking time" as variables, the experiment compared the material properties under different parameter combinations to verify the technical effectiveness of the parameter range of this invention.

[0071] 1. Experimental Design

[0072] Test standard:

[0073] Cross-linking degree: Determined by xylene extraction method in accordance with GB / T 2951.12-2008 "General test methods for insulation and sheathing materials of electric and optical cables - Part 12: General test methods - Thermal aging test method" (cross-linking degree = (mass after extraction / mass before extraction) × 100%).

[0074] Tensile strength: tested in accordance with GB / T 1040.3-2006 “Plastics — Determination of tensile properties — Part 3: Test conditions for film and sheeting” using a universal testing machine (specimen size: 150 mm × 10 mm × 2 mm, tensile rate: 50 mm / min);

[0075] Oxygen index: According to GB / T 2406.2-2009 “Determination of combustion behavior of plastics by oxygen index method Part 2: Room temperature test”, the test is carried out using an oxygen index meter (sample size 150mm×6.5mm×3mm).

[0076] Variable selection:

[0077] The mass ratio of silane grafted material to halogen-free masterbatch (denoted as variable A);

[0078] Particle size of bifunctional modified magnesium hydroxide (denoted as variable B, unit: μm);

[0079] Warm water assisted crosslinking time (recorded as variable C, unit: h).

[0080] Experimental group settings:

[0081] A total of 10 experiments were designed, including:

[0082] Conventional group (groups 1-5): variables A, B, and C were all within the ranges defined by the present invention (A: 2-4; 20-24; B: 0.5-1.0 μm; C: 1.5-2.5 h);

[0083] Out-of-range group (Groups 6-9): Variable A, B, or C exceeds the defined range of the present invention;

[0084] Blank control group (10 groups): using existing technology (single EVA matrix, traditional vinyl silane coupling agent, high temperature cooking cross-linking process).

[0085] Except for the variables, the other material components (EVA, EEA, methacryloxysilane, bifunctional modified magnesium hydroxide, etc.), proportions and environmental parameters (room temperature cross-linking conditions 25°C / humidity 60%) were consistent in all experimental groups.

[0086] 2. Experimental Data and Results Analysis

[0087] Table 1. Performance test results of experimental group

[0088]

[0089]

[0090] Comprehensive scoring rules: cross-linking degree (weight 40%), tensile strength (weight 30%), oxygen index (weight 30%). The scoring formula is:

[0091] Comprehensive score = (cross-linking degree / 80×40) + (tensile strength / 14×30) + (oxygen index / 35×30) (Note: 80%, 14MPa, and 35% are reference values ​​for the upper limit of performance of the conventional group).

[0092] 3. Experimental Conclusion

[0093] From the experimental data we can see that:

[0094] The cross-linking degree (71.23-77.31%), tensile strength (12.15-13.86 MPa), and oxygen index (32.41-34.92%) of the conventional group (groups 1-5) were significantly better than those of the out-of-range group (groups 6-9) and the blank control group (group 10), verifying the rationality of the limited ranges of variables A, B, and C (A: 2-4: 20-24; B: 0.5-1.0 μm; C: 1.5-2.5 h) of the present invention.

[0095] The dependent variables of the out-of-range group (groups 6-9) exceeded the specified range (such as A was too low / too high, resulting in a decrease in interfacial bonding strength, and B was too small / too large, resulting in flame retardant agglomeration). Although their cross-linking degree (61.95-67.42%), tensile strength (9.98-11.05MPa), and oxygen index (27.83-30.12%) were better than those of the blank control group, the key performance indicators all showed varying degrees of attenuation, further illustrating the necessity of parameter range.

[0096] The blank control group (Group 10) used the traditional process (single matrix, physical coating flame retardant, high temperature cooking cross-linking), and its cross-linking degree (55.24%), tensile strength (9.51 MPa), and oxygen index (25.36%) were all the lowest, verifying the significant effect of the preparation method of the present invention in improving material performance.

[0097] Among the conventional groups, Group 3 (A=3:22, B=0.7μm, C=2.0h) had the highest comprehensive score (91.3), but it was not the first or last group, reflecting the nonlinear relationship between material properties and variables (such as the best flame retardant dispersion when B=0.7μm, and the most significant synergistic effect between silane grafted material and halogen-free masterbatch when A=3:22), which is consistent with the complexity of the reaction mechanism of multi-component materials.

[0098] In summary, this experiment verified the practical significance of the key parameter ranges in the present invention and the technical advantages of the preparation method through quantitative data, providing experimental support for the industrial application of the material.

[0099] Molecular-level analysis of experimental data and performance trend mechanisms

[0100] In the experimental data, the comprehensive score of the conventional group (groups 1-5) was significantly better than that of the out-of-range group (groups 6-9) and the blank control group (group 10). The root cause of the performance difference can be explained from the microscopic level such as intermolecular interaction, interface structure and cross-linking network formation mechanism.

[0101] 1. Influence of variable A (mass ratio of silane grafted material to halogen-free masterbatch)

[0102] The mass ratio (A) of the silane grafted material to the halogen-free masterbatch directly determines the degree of matching of the "reactive groups" in the system. The core component of the silane grafted material is a polyolefin molecular chain containing a silane group (-Si-OCH3), and the surface of the bifunctional modified magnesium hydroxide in the halogen-free masterbatch is grafted with a vinyl group (-CH=CH2). When A is within the conventional range (2-4:20-24), the silane groups of the silane grafted material and the vinyl groups of the halogen-free masterbatch form covalent bonds (-Si-O-Si- and -CC- bonds) through free radical reactions during the melt mixing process, significantly enhancing the interfacial bonding force (covalent bond energy of approximately 300-400kJ / mol, much higher than the 20-40kJ / mol of traditional hydrogen bonds).

[0103] Taking Group 3 (A=3:22) as an example, the ratio of silane grafted material to halogen-free masterbatch is just enough to make the reactive groups of the two (-Si-OCH3 and -CH=CH2) reach a stoichiometric balance, and the interfacial covalent bond density is the highest, so the cross-linking degree (77.31%) and tensile strength (13.86MPa) are optimal. When A is lower than the conventional range (such as Group 6, 1.5:19), the silane grafting material is insufficient, the number of reactive -Si-OCH3 groups is reduced, the unreacted magnesium hydroxide vinyl (-CH=CH2) cannot form effective crosslinking, "dangling bond" defects appear at the interface, and the crosslinking degree and tensile strength decrease; when A is higher than the conventional range (such as Group 7, 4.5:25), the silane grafting material is excessive, the unreacted -Si-OCH3 groups are hydrolyzed into silanols (-Si-OH), and these silanols form "weak bonds" (low hydrogen bond energy between -Si-OH) in the crosslinked network, resulting in local relaxation of the crosslinked network, and a decrease in the oxygen index (relatively reduced proportion of flame retardant) and overall performance.

[0104] 2. Influence of variable B (particle size of bifunctional modified magnesium hydroxide)

[0105] The particle size (B) of the bifunctional modified magnesium hydroxide affects the material properties through "interface area" and "surface group distribution". When B is in the conventional range (0.5-1.0 μm), the specific surface area (surface area per unit mass) of the magnesium hydroxide is balanced with the number of vinyl groups (-CH=CH2) grafted on the surface: when the particle size is 0.7 μm (Group 3), the specific surface area is about 12 m 2 / g (theoretical value), the surface vinyl density is about 1.2×10 18 pcs / m 2 , which can not only ensure that there are enough covalent bonding sites with the silane grafted material, but also avoid agglomeration caused by too small particle size (small particle size particles have high surface energy and are easy to agglomerate through van der Waals forces).

[0106] When B is smaller than the normal range (such as group 8, 0.4 μm), the specific surface area of ​​magnesium hydroxide increases to 15 m 2 / g, but the proportion of unmodified hydroxyl groups (-OH) on the surface increased (about 30% of the hydroxyl groups did not react with vinyl isocyanate), and these hydroxyl groups formed aggregates through hydrogen bonds (-OH...-OH), destroying the continuity of the matrix. The tensile strength (10.24MPa) and oxygen index (28.45%) decreased significantly; when B was greater than the conventional range (such as group 9, 1.1μm), the specific surface area dropped to 9m 2 / g, and the surface vinyl density is only 0.8×10 18 pcs / m 2 , the covalent bonding sites with the silane grafted material are reduced, the interfacial bonding force is weakened, and the crosslinking degree (61.95%) and oxygen index (27.83%) are further reduced.

[0107] 3. Influence of variable C (warm water assisted cross-linking time)

[0108] The warm water-assisted crosslinking time (C) determines the completion of the silanol condensation reaction. The -Si-OCH3 groups in the silane-grafted material hydrolyze into silanols (-Si-OH) in warm water (65-75°C). Subsequently, the silanols react with each other through condensation to form a -Si-O-Si- crosslinked network. When C is within the conventional range (1.5-2.5 hours), the condensation reaction proceeds to 70-80% (theoretical conversion rate), achieving a moderate crosslinking network density, ensuring material strength while avoiding brittleness caused by excessive crosslinking.

[0109] Group 3 (C = 2.0h) achieved an approximately 78% condensation reaction conversion rate, resulting in a uniform and defect-free crosslinking network, resulting in an optimal crosslinking degree (77.31%) and tensile strength (13.86MPa). When C was too short (e.g., Group 1, 1.5h), the condensation reaction was only 60% complete, resulting in an incomplete crosslinking network (presence of unreacted -Si-OH groups), a lower crosslinking degree (71.23%) and tensile strength (12.15MPa). When C was too long (e.g., Group 5, 2.5h), the condensation reaction approached 90%, and the crosslinking network was locally overly dense (excessive accumulation of -Si-O-Si- bonds), causing stress concentration within the material and a decrease in tensile strength (12.53MPa).

[0110] 4. Molecular Mechanism Defects in the Blank Control Group

[0111] The blank control group (Group 10) used the traditional process (single EVA matrix, physical coating of magnesium hydroxide, high-temperature cooking and cross-linking). Its performance disadvantages were due to the following molecular level problems:

[0112] Weak interfacial bonding: Traditional silane coupling agents only bond to magnesium hydroxide through physical hydrogen bonds (-Si-OH…-OH-magnesium hydroxide), which have low bond energy and are easily dissociated at high temperatures, resulting in significantly lower crosslinking degree (55.24%) and tensile strength (9.51 MPa) than the conventional group;

[0113] Poor dispersibility of flame retardant: a large number of hydroxyl groups (-OH) on the surface of unmodified magnesium hydroxide are exposed, forming agglomerates (average particle size 2-3 μm) through hydrogen bonds, and the oxygen index (25.36%) is reduced due to the reduction of effective flame retardant area;

[0114] Cross-linked network defects: High-temperature cooking (8h) causes excessive condensation of silanol (-Si-OH), forming a "hard and brittle" cross-linked network (the cross-linking degree is only 55.24% because some silane groups decompose and fail at high temperatures), with the worst overall performance.

[0115] in conclusion

[0116] The performance trend of the experimental data is essentially the result of the synergistic effect of intermolecular interactions (covalent bonds, hydrogen bonds, van der Waals forces) and interface structure (group distribution, specific surface area). The parameter range (A, B, C) of the conventional group just balances the three key molecular-level factors of "reactive group matching", "interface area and dispersion", and "cross-linking network integrity", resulting in optimal performance; while the out-of-range group weakens a key factor due to parameter deviation, ultimately resulting in decreased performance. This pattern verifies the scientific nature of the parameter range of the present invention and the technical advantages of the preparation method.

[0117] Example

[0118] Example 1

[0119] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0120] 1. Preparation of silane grafted materials

[0121] Weigh 45 parts by mass of EVA (ethylene-vinyl acetate copolymer), 15 parts by mass of EEA (ethylene ethyl acrylate), 1.2 parts by mass of methacryloxysilane (γ-methacryloxypropyltrimethoxysilane), 0.2 parts by mass of DCP (dicumyl peroxide), 0.2 parts by mass of antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and 0.1 parts by mass of anti-copper agent MB (2-mercaptobenzimidazole) into a high-speed mixer and mix at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio of 44:1). The temperatures in each zone are set at 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed is 400 rpm. The extruded material was water-cooled and pelletized, and then dried at 70° C. for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190° C. / 2.16 kg).

[0122] 2. Preparation of bifunctional modified magnesium hydroxide

[0123] Magnesium hydroxide with an initial particle size of 0.5 μm and 1.5% of its mass of vinyl isocyanate (3-isocyanatepropyltrimethoxysilane) were added into a high-speed stirrer and mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted on the surface.

[0124] 3. Preparation of halogen-free masterbatch

[0125] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.5 μm), 20 parts by mass of PE-g-MAH (maleic anhydride grafted polyethylene), 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 (tris[2,4-di-tert-butylphenyl]phosphite) were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized using a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0126] 4. Mixed cross-linking

[0127] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 2:20 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally crosslinked at 25°C and 60% relative humidity for 48 hours, followed by auxiliary crosslinking in warm water at 65°C for 1.5 hours to produce the cable material.

[0128] Example 2

[0129] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0130] 1. Preparation of silane grafted materials

[0131] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0132] 2. Preparation of bifunctional modified magnesium hydroxide

[0133] Magnesium hydroxide with an initial particle size of 0.6 μm and 1.5% of its mass of vinyl isocyanate were weighed and added into a high-speed stirrer, and mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted on its surface.

[0134] 3. Preparation of halogen-free masterbatch

[0135] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.6 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0136] 4. Mixed cross-linking

[0137] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 2.5:22 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally crosslinked at 25°C and 60% relative humidity for 48 hours, followed by auxiliary crosslinking in warm water at 65°C for 2 hours to produce the cable material.

[0138] Example 3

[0139] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0140] 1. Preparation of silane grafted materials

[0141] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0142] 2. Preparation of bifunctional modified magnesium hydroxide

[0143] Magnesium hydroxide with an initial particle size of 0.7 μm and 1.5% of vinyl isocyanate by mass were weighed and added into a high-speed stirrer. The mixture was mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted onto its surface.

[0144] 3. Preparation of halogen-free masterbatch

[0145] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.7 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0146] 4. Mixed cross-linking

[0147] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 3:22 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally crosslinked for 48 hours at 25°C and 60% relative humidity, followed by auxiliary crosslinking in warm water at 65°C for 2 hours to produce the cable material.

[0148] Example 4

[0149] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0150] 1. Preparation of silane grafted materials

[0151] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0152] 2. Preparation of bifunctional modified magnesium hydroxide

[0153] Magnesium hydroxide with an initial particle size of 0.8 μm and 1.5% of its mass of vinyl isocyanate were weighed and added into a high-speed stirrer, and mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted on its surface.

[0154] 3. Preparation of halogen-free masterbatch

[0155] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.8 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized using a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, and a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0156] 4. Mixed cross-linking

[0157] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 3.5:23 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally cross-linked for 48 hours at 25°C and 60% relative humidity, followed by auxiliary cross-linking in warm water at 65°C for 2.5 hours to produce the cable material.

[0158] Example 5

[0159] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0160] 1. Preparation of silane grafted materials

[0161] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0162] 2. Preparation of bifunctional modified magnesium hydroxide

[0163] Magnesium hydroxide with an initial particle size of 1.0 μm and 1.5% of its mass of vinyl isocyanate were weighed and added into a high-speed stirrer, and mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted on its surface.

[0164] 3. Preparation of halogen-free masterbatch

[0165] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 1.0 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized using a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0166] 4. Mixed cross-linking

[0167] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 4:24 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally cross-linked for 48 hours at 25°C and 60% relative humidity, followed by auxiliary cross-linking in warm water at 65°C for 2.5 hours to produce the cable material.

[0168] Example 6

[0169] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0170] 1. Preparation of silane grafted materials

[0171] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0172] 2. Preparation of bifunctional modified magnesium hydroxide

[0173] Magnesium hydroxide with an initial particle size of 0.6 μm and 1.5% of its mass of vinyl isocyanate were weighed and added into a high-speed stirrer, and mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted on its surface.

[0174] 3. Preparation of halogen-free masterbatch

[0175] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.6 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0176] 4. Mixed cross-linking

[0177] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 1.5:19 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally crosslinked at 25°C and 60% relative humidity for 48 hours, followed by auxiliary crosslinking in warm water at 65°C for 2 hours to produce the cable material.

[0178] Example 7

[0179] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0180] 1. Preparation of silane grafted materials

[0181] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0182] 2. Preparation of bifunctional modified magnesium hydroxide

[0183] Magnesium hydroxide with an initial particle size of 0.7 μm and 1.5% of vinyl isocyanate by mass were weighed and added into a high-speed stirrer. The mixture was mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted onto its surface.

[0184] 3. Preparation of halogen-free masterbatch

[0185] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.7 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0186] 4. Mixed cross-linking

[0187] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 4.5:25 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded cable semi-finished product was naturally crosslinked at 25°C and 60% relative humidity for 48 hours, followed by auxiliary crosslinking in warm water at 65°C for 2 hours to produce the cable material.

[0188] Example 8

[0189] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0190] 1. Preparation of silane grafted materials

[0191] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0192] 2. Preparation of bifunctional modified magnesium hydroxide

[0193] Magnesium hydroxide with an initial particle size of 0.4 μm and 1.5% of vinyl isocyanate by mass were weighed and added into a high-speed stirrer. The mixture was mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted onto its surface.

[0194] 3. Preparation of halogen-free masterbatch

[0195] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 0.4 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0196] 4. Mixed cross-linking

[0197] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 3:22 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally crosslinked for 48 hours at 25°C and 60% relative humidity, followed by auxiliary crosslinking in warm water at 65°C for 2 hours to produce the cable material.

[0198] Embodiment 9

[0199] Preparation method of silane cross-linked polyolefin halogen-free flame retardant cable material

[0200] 1. Preparation of silane grafted materials

[0201] Weigh 45 parts by mass of EVA, 15 parts by mass of EEA, 1.2 parts by mass of methacryloxysilane, 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0202] 2. Preparation of bifunctional modified magnesium hydroxide

[0203] Magnesium hydroxide with an initial particle size of 1.1 μm and 1.5% of vinyl isocyanate by mass were weighed and added into a high-speed stirrer. The mixture was mixed and reacted at 100° C. for 30 minutes to obtain bifunctional modified magnesium hydroxide with vinyl groups grafted onto its surface.

[0204] 3. Preparation of halogen-free masterbatch

[0205] 30 parts by mass of EVA, 70 parts by mass of bifunctional modified magnesium hydroxide (particle size 1.1 μm), 20 parts by mass of PE-g-MAH, 0.3 parts by mass of bismuth neodecanoate, 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. After pelletization, the material was dried at 60°C for 1 hour.

[0206] 4. Mixed cross-linking

[0207] The silane-grafted material and halogen-free masterbatch were mixed in a mass ratio of 3:22 and extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. The extruded semi-finished cable was naturally crosslinked for 48 hours at 25°C and 60% relative humidity, followed by auxiliary crosslinking in warm water at 65°C for 2 hours to produce the cable material.

[0208] Example 10 (blank control group)

[0209] Preparation method of traditional halogen-free flame retardant cable material

[0210] 1. Preparation of silane grafted materials

[0211] Weigh 60 parts by mass of EVA (single matrix, no EEA), 1.0 part by mass of vinyl silane (A-171, traditional coupling agent), 0.2 parts by mass of DCP, 0.2 parts by mass of antioxidant 1010, and 0.1 parts by mass of anti-copper agent MB, put them into a high-speed mixer, and mix them at 55°C for 8 minutes until uniform. The mixture is melt-grafted through a twin-screw extruder (aspect ratio 44:1), with the temperatures of each zone being 155°C, 165°C, 175°C, 185°C, and 190°C, respectively, and the screw speed being 400 rpm. After water-cooling and pelletizing, the extruded material is dried at 70°C for 1.5 hours to obtain a silane-grafted material (melt flow rate 5.2 g / 10 min, 190°C / 2.16 kg).

[0212] 2. Magnesium hydroxide pretreatment (unmodified)

[0213] Magnesium hydroxide with an initial particle size of 1.5 μm (without bifunctional modification) was weighed and directly put into a high-speed blender and mixed at 100° C. for 10 minutes (only water was removed without chemical modification).

[0214] 3. Preparation of halogen-free masterbatch

[0215] 30 parts by mass of EVA, 70 parts by mass of unmodified magnesium hydroxide (particle size 1.5 μm), 10 parts by mass of polyethylene (PE, without compatibilizer), 0.2 parts by mass of dibutyltin dilaurate (DBTDL, a conventional catalyst), 0.5 parts by mass of calcium stearate, and 0.2 parts by mass of Antioxidant 168 were placed in an internal mixer and mixed at 130°C for 10 minutes. The mixed material was pelletized in a twin-screw extruder (aspect ratio 44:1) at extrusion temperatures of 145°C, 150°C, 155°C, and 160°C, respectively, at a screw speed of 280 rpm. The pelletized material was dried at 60°C for 1 hour.

[0216] 4. Mixed cross-linking

[0217] The silane-grafted material and halogen-free masterbatch were mixed uniformly at a conventional mass ratio of 1:10. The mixture was then extruded through a single-screw extruder (length-to-diameter ratio 30:1, compression ratio 3.5:1) at temperatures of 155°C, 165°C, and 175°C, respectively, at a speed of 15 m / min. After extrusion, the semi-finished cable was directly cross-linked by high-temperature cooking (95°C hot water cooking for 8 hours) without natural cross-linking at room temperature, resulting in the cable material.

[0218] Specific working process

[0219] EVA and EEA are evenly dispersed in a high-speed mixer. Methacryloxysilane decomposes with DCP, generating free radicals that attack the polyolefin molecular chains. Silane groups (-Si-OCH3) are covalently grafted onto the EVA / EEA molecular chains, forming a grafted material containing reactive silane pendant groups. At this point, the silane groups in the grafted material are "suspended" on the polyolefin backbone, awaiting subsequent cross-linking reactions.

[0220] The bifunctional modified magnesium hydroxide collides with vinyl isocyanate in a high-speed blender. The isocyanate group (-NCO) undergoes a nucleophilic addition reaction with the hydroxyl group (-OH) on the surface of the magnesium hydroxide to form a urea bond (-NH-CO-O-), covalently attaching the vinyl group (-CH=CH2) to the surface of the magnesium hydroxide particles. In this process, the surface properties of the magnesium hydroxide change from being dominated by polar hydroxyl groups to being dominated by non-polar vinyl groups. The particles that were originally prone to agglomeration are dispersed more evenly due to the reduced surface energy.

[0221] When the grafted material and modified magnesium hydroxide are melt-blended in an internal mixer, the anhydride group (-CO-O-CO-) of PE-g-MAH, the silane group of the grafted material, and the vinyl group of magnesium hydroxide undergo intermolecular entanglement to form a "bridge" structure: one end of the anhydride group is embedded in the polyolefin matrix, and the other end is adsorbed on the surface of magnesium hydroxide, forcing the two phases originally separated due to polarity differences to be brought closer to the nanometer level.

[0222] After extrusion, the semi-finished cable is exposed to room temperature. The trace moisture in the air begins to slowly hydrolyze the silane groups (-Si-OCH3→-Si-OH) of the grafted material, but the reaction rate is limited. When exposed to warm water, the hydrolysis reaction accelerates, and the concentration of silanols (-Si-OH) rapidly increases. Adjacent silanols condense to remove water molecules, forming -Si-O-Si- covalent bonds, which cross-link the discrete polyolefin molecular chains into a three-dimensional network. Simultaneously, the vinyl groups (-CH=CH2) on the surface of the magnesium hydroxide, under the action of residual free radicals, undergo free radical copolymerization with the unsaturated bonds (-CH=CH2) of the polyolefin backbone, "stitching" a covalent bond interface layer between the inorganic particles and the organic matrix.

[0223] Ultimately, the three-dimensional cross-linked network provides mechanical support through -Si-O-Si- bonds, the magnesium hydroxide particles disperse external stress to the entire network through interfacial covalent bonds, and the synergistic effect of the vinyl and anhydride groups inhibits particle agglomeration, ensuring that the flame retardant is evenly distributed in the matrix in a single particle state. This series of dynamic processes jointly constructs a cable material with high cross-linking degree, strong tensile strength and excellent flame retardancy.

[0224] The various technical features described in the above exemplary embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above exemplary embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A silane cross-linked polyolefin halogen-free flame retardant cable material, characterized by: It is prepared by mixing and cross-linking silane grafted material and halogen-free masterbatch in a mass ratio of (2-4): (20-24); The silane grafted material comprises, by mass: Matrix resin: 40-50 parts of ethylene-vinyl acetate copolymer, 10-20 parts of ethylene-ethyl acrylate; Coupling agent: 1.0-1.5 parts of methacryloxysilane; Initiator: dicumyl peroxide 0.15-0.25 parts; Additives: antioxidant 0.1-0.3 parts, anti-copper agent 0.05-0.15 parts; The halogen-free masterbatch comprises, by mass: Matrix resin: ethylene-vinyl acetate copolymer 25-35 parts; Flame retardant: 65-75 parts of bifunctional modified magnesium hydroxide; Compatibilizer: 15-25 parts of maleic anhydride grafted polyethylene; Catalyst: 0.2-0.4 parts of bismuth neodecanoate; Additives: lubricant 0.4-0.6 parts, antioxidant 0.1-0.3 parts; The bifunctional modified magnesium hydroxide is a modified flame retardant formed by grafting vinyl isocyanate with hydroxyl groups on the surface of magnesium hydroxide.

2. The silane cross-linked polyolefin halogen-free flame-retardant cable material according to claim 1, characterized in that: The antioxidant in the silane grafted material is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the anti-copper agent is 2-mercaptobenzimidazole.

3. The silane cross-linked polyolefin halogen-free flame-retardant cable material according to claim 1, characterized in that: The lubricant in the halogen-free masterbatch is calcium stearate, and the antioxidant is tris[2,4-di-tert-butylphenyl]phosphite.

4. The silane cross-linked polyolefin halogen-free flame-retardant cable material according to claim 1, characterized in that: The particle size of the bifunctional modified magnesium hydroxide is 0.5-1.0 μm.

5. The silane cross-linked polyolefin halogen-free flame-retardant cable material according to claim 1, characterized in that: The melt flow rate (190° C. / 2.16 kg) of the silane grafted material is 4-6 g / 10 min.

6. The silane cross-linked polyolefin halogen-free flame-retardant cable material according to claim 1, characterized in that: The cable material has a cross-linking degree of 70-80%, a tensile strength of ≥12 MPa, and an oxygen index of ≥32%.

7. A low-energy preparation method based on the silane cross-linked polyolefin halogen-free flame-retardant cable material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Preparation of silane grafted material: Ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate, methacryloxysilane, dicumyl peroxide, antioxidant, and anti-copper agent are mixed, melt-grafted through a twin-screw extruder, and granulated and dried; (2) Preparation of bifunctional modified magnesium hydroxide: magnesium hydroxide and vinyl isocyanate are mixed and reacted at 80-120° C. for 20-40 min, wherein the amount of vinyl isocyanate is 1.0-2.0% of the mass of magnesium hydroxide; (3) Preparation of halogen-free masterbatch: Ethylene-vinyl acetate copolymer, bifunctional modified magnesium hydroxide, maleic anhydride grafted polyethylene, bismuth neodecanoate, lubricant, and antioxidant are mixed, mixed in an internal mixer, and granulated by twin-screw extrusion; (4) Mixed crosslinking: The silane grafted material and the halogen-free masterbatch are mixed in a mass ratio of (2-4): (20-24) and then extruded into a mold, and then naturally crosslinked at room temperature (20-30°C, relative humidity 50-70%, 40-56h) and warm water assisted crosslinking (65-75°C, 1.5-2.5h) are carried out in sequence.

8. A low-energy consumption preparation method according to claim 7, characterized in that: The aspect ratio of the twin-screw extruder in step (1) is 40:1-48:1, the temperature of each zone is 150-190° C., and the screw speed is 350-450 rpm; the drying temperature after granulation is 65-75° C., and the drying time is 1.0-2.0 h.

9. A low-energy consumption preparation method according to claim 7, characterized in that: The mixing temperature of the internal mixer in step (3) is 120-140° C., and the mixing time is 8-12 min; the temperature of the twin-screw extruder is 140-160° C., and the screw speed is 250-300 rpm; the drying temperature after granulation is 55-65° C., and the drying time is 0.5-1.5 h.

10. A low-energy preparation method according to claim 7, characterized in that: The single-screw extruder used for the extrusion molding in step (4) has an aspect ratio of 25:1-35:1, a compression ratio of 3:1-4:1, an extrusion temperature of 150-180°C, and an extrusion speed of 10-20m / min.

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