Halogen-free low smoke flame-retardant polyolefin insulation material crosslinked by irradiation at 125 ℃ and its preparation process

Abstract

The application discloses 125 DEG C irradiation crosslinking halogen-free low-smoke flame-retardant polyolefin insulating material and a preparation process thereof, which is composed of the following components in parts by weight: ethylene-vinyl acetate copolymer 50-80 parts, linear low-density polyethylene 10-20 parts, polyolefin elastomer 5-15 parts, magnesium hydroxide 45-60 parts, aluminum hypophosphite 4-6 parts, melamine cyanurate 1-3 parts, compatilizer 5-10 parts, antioxidant 1-3 parts, triallyl isocyanurate 0.5-1.5 parts, modified attapulgite 5-10 parts, plasticizer 5-8 parts, and the production comprises the following steps: S1, pre-mixing all raw materials except crosslinking agent at high speed; S2, feeding the pre-mixed material into a banbury mixer for mixing; S3, melt extrusion and hot cutting granulation; S4, extruding and coating on a conductor through an extruder to form an insulating layer; and S5, irradiation crosslinking by an electron accelerator, so that the high-temperature dimensional stability is excellent, and the problems of low upper limit of heat resistance, easy softening and deformation at high temperature and by-product defects existing in chemical crosslinking are solved.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to 125°C irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulation material and its preparation process. Background Technology

[0002] With the development of modern industry and urban infrastructure, the use of traditional polyolefin cable insulation materials in high-temperature environments has been significantly limited. The long-term operating temperature of conventional polyethylene (PE) or ethylene-vinyl acetate copolymer (EVA) based insulation materials typically does not exceed 90°C. Under overload or short-circuit conditions, they are prone to softening, deformation, and even melting and dripping, posing significant safety hazards. To improve heat resistance, existing technologies generally employ chemical crosslinking or radiation crosslinking methods to enhance their thermal dimensional stability.

[0003] However, chemical crosslinking often requires the addition of peroxide initiators, which release small molecule byproducts during processing, affecting insulation resistance and potentially causing micropore defects. While electron beam irradiation crosslinking is a clean physical process, if an efficient sensitization system is lacking, the crosslinking density will be insufficient, making it difficult to meet the application requirements of 125°C and above.

[0004] Furthermore, while traditional halogenated flame retardant systems (such as decabromodiphenyl ether and hexabromocyclododecane combined with antimony trioxide) have good flame retardant effects, they release large amounts of toxic and corrosive gases during fires, seriously threatening personnel escape and equipment safety. Therefore, halogen-free flame retardants have become the mainstream development direction. Currently, the mainstream approach uses magnesium hydroxide (MDH) or aluminum hydroxide (ATH) as the main flame retardant, but their filler content usually needs to reach 50-60 parts by weight or more to achieve effective flame retardancy, resulting in a significant decrease in the mechanical properties of the material, especially in terms of reduced elongation at break and poor processing fluidity.

[0005] Although existing studies have attempted to introduce phosphorus- and nitrogen-based synergistic flame retardants to reduce the amount of inorganic fillers, such as the combination of hypophosphite and melamine compounds, problems such as large fluctuations in flame retardant efficiency and weak interfacial bonding still exist due to poor compatibility and uneven dispersion among the components. Furthermore, existing formulations rarely include systematic optimization designs for irradiation crosslinking efficiency, resulting in low crosslinking degrees and failure to meet thermal elongation performance standards.

[0006] In summary, achieving the technical goals of maintaining excellent flexibility and processability while ensuring a long-term operating temperature of 125℃, an oxygen index of ≥30%, an elongation of ≤100% under thermal stretching load, and permanent deformation of ≤25% remains a key challenge that urgently needs to be addressed in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a 125°C irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulation material and its preparation process, in order to solve the problems mentioned in the background art.

[0008] To achieve the aforementioned objective, the present invention provides the following technical solution: a 125°C irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulating material, composed of the following components in parts by weight: 50-80 parts of ethylene-vinyl acetate copolymer (EVA), 10-20 parts of linear low-density polyethylene (LLDPE), 5-15 parts of polyolefin elastomer (POE), 45-60 parts of magnesium hydroxide, 4-6 parts of aluminum hypophosphite, 1-3 parts of melamine cyanurate, 5-10 parts of compatibilizer, 1-3 parts of antioxidant, 0.5-1.5 parts of triallyl isocyanurate (TAC), 5-10 parts of modified attapulgite, and 5-8 parts of plasticizer.

[0009] Preferably, the vinyl acetate (VA) content in the EVA is 28%-45%, and the melt index is 0.5-6.0 g / 10 min.

[0010] Preferably, the modified attapulgite is obtained by calcining natural attapulgite at 500-600℃ for 3-5 hours, then activating it sequentially with 4% sodium hydroxide solution and 14% hydrochloric acid, washing it with deionized water until neutral and drying it, and finally surface modifying it with 2-4wt% γ-aminopropyltriethoxysilane (KH-550).

[0011] Preferably, it also includes 0.2-0.8 parts of trimethylpropane trimethacrylate (TMPTMA) as an auxiliary crosslinking sensitizer.

[0012] Preferably, the compatibilizer is at least one of maleic anhydride-grafted polyethylene (MAH-g-PE) or maleic anhydride-grafted POE.

[0013] Preferably, the plasticizer is any one of tributyl citrate, DOA, or pentaerythritol ester. A process for preparing a 125℃ irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulation material includes the following steps: S1: Premix all raw materials except crosslinking agent at high speed; S2: Put the premixed material into an internal mixer and mix at 145-170℃ for 6-8 minutes; S3: Masterbatch is obtained by melt extrusion and hot cutting granulation using a twin-screw extruder; S4: After drying the masterbatch, it is extruded onto the conductor through an extruder to form an insulating layer; S5: The extruded wire core is sent to an electron accelerator for irradiation crosslinking, with an irradiation dose of 12-14 Mrad.

[0014] Preferably, the electron beam energy in S5 is 2.5-3.5 MeV, and irradiation is performed using a unidirectional or bidirectional scanning method.

[0015] Preferably, the length-to-diameter ratio (L / D) of the twin-screw extruder in S3 is 20-25, and the compression ratio is 1:1.2-1:1.5.

[0016] Preferably, the antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 0.8:1-1.2:1.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a multifunctional crosslinking sensitization system based on triallyl isocyanurate (TAC) and supplemented with trimethylpropane trimethacrylate (TMPTMA), combined with an electron beam irradiation crosslinking process. Under electron beam action, the multifunctional monomers rapidly generate active free radicals, efficiently promoting the crosslinking reaction between the polyolefin backbone chains. This significantly increases the crosslinking density and gel content of the matrix even with moderate irradiation doses. Compared to traditional chemical crosslinking methods, this approach eliminates the need for peroxide initiators, avoids the release of small molecule byproducts during processing, and prevents problems such as decreased insulation resistance and internal micropore defects, resulting in more stable electrical insulation properties. Through the formed three-dimensional crosslinked network, the material can operate at a long-term temperature of up to 125°C. Under high-temperature loads, both thermal elongation and permanent deformation meet standard requirements, demonstrating excellent high-temperature dimensional stability. This solves the problems of low heat resistance limits, easy softening and deformation at high temperatures in ordinary polyolefin insulation materials, and byproduct defects inherent in chemical crosslinking. 2. This invention constructs a ternary synergistic flame retardant system with magnesium hydroxide as the main flame retardant and aluminum hypophosphite and melamine cyanurate as synergists: magnesium hydroxide decomposes upon heating, absorbing a large amount of heat and releasing water vapor to dilute combustible gases; aluminum hypophosphite can promote the formation of a dense and continuous char layer in the condensed phase to block heat and oxygen transfer; and melamine cyanurate can capture combustion free radicals in the gas phase to block chain reactions. The three work synergistically from multiple dimensions of the gas and solid phases, significantly improving flame retardant performance. At the same time, the physical barrier and filler carrier effect of modified attapulgite improves the dispersion uniformity of the flame retardant in the matrix. Under the premise of ensuring that the oxygen index meets the standard and fully meeting the requirements of halogen-free and low smoke, it avoids the disadvantage of requiring an extremely high filling amount for a single inorganic flame retardant, resulting in more stable flame retardant performance. It solves the problems of material deterioration caused by excessive filling amount in traditional halogen-free formulations, poor compatibility of phosphorus-nitrogen compound systems, and large fluctuations in flame retardant effect. Attached Figure Description

[0018] Figure 1 A flowchart illustrating the preparation process of the insulating material of the present invention is shown. Detailed Implementation

[0019] The technical solutions of 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.

[0020] according to Figure 1 As shown, this invention provides a technical solution: a 125℃ irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulation material, composed of the following components in parts by weight: 50-80 parts of ethylene-vinyl acetate copolymer (EVA), where EVA, as the main matrix resin, contains polar vinyl acetate segments, which can effectively promote the dispersion of inorganic flame retardants and improve compatibility with other polymer components; 10-20 parts of linear low-density polyethylene (LLDPE), where LLDPE is used to adjust hardness and crystallization behavior, enhancing material rigidity; 5-15 parts of polyolefin elastomer (POE), where POE imparts excellent elasticity and low-temperature toughness to the material, preventing embrittlement after irradiation; 45-60 parts of magnesium hydroxide; and hypophosphite. The flame retardant system consists of 4-6 parts aluminum, 1-3 parts melamine cyanurate, and a phosphorus-nitrogen-metal ternary synergistic mechanism with magnesium hydroxide as the main component and aluminum hypophosphite and melamine cyanurate as synergists. When magnesium hydroxide is heated and decomposed, it absorbs a large amount of heat and releases water vapor to dilute the combustible gas. Aluminum hypophosphite can form a dense carbon layer in the condensed phase to inhibit heat transfer, while melamine cyanurate plays a flame retardant role by capturing free radicals in the gas phase. The three components work synergistically to significantly improve the overall flame retardant performance, making the oxygen index stably reach more than 30%. The system also includes 5-10 parts compatibilizer, 1-3 parts antioxidant, 0.5-1.5 parts triallyl isocyanurate (TAC), 5-10 parts modified attapulgite, and 5-8 parts plasticizer. The vinyl acetate (VA) content in EVA is 28%-45%, and the melt index is 0.5-6.0 g / 10 min; Modified attapulgite is obtained by calcining natural attapulgite at 500-600℃ for 3-5 hours, followed by activation treatment with 4% sodium hydroxide solution and 14% hydrochloric acid, washing with deionized water until neutral and drying, and finally surface modification with 2-4wt% γ-aminopropyltriethoxysilane (KH-550). Attapulgite surface-treated with silane coupling agent (KH-550) is selected as the modified filler. This mineral has a rod-shaped nanostructure and a large specific surface area. After calcination and acid-base activation, its pores are well developed. After modification with coupling agent, its interfacial bonding force with polyolefin matrix can be significantly enhanced. This not only helps to improve mechanical properties, but also serves as a carrier for flame retardant additives and improves the uniformity of flame retardant distribution. It also includes 0.2-0.8 parts of trimethylpropane trimethacrylate (TMPTMA) as an auxiliary crosslinking sensitizer. The crosslinking system uses TAC as the main crosslinking sensitizer, preferably supplemented with a small amount of trimethylpropane trimethacrylate (TMPTMA). Both are multifunctional monomers that readily generate free radicals under electron beam irradiation, promoting the crosslinking reaction between polyolefin backbones, significantly increasing gel content and crosslinking density, thereby ensuring the dimensional stability of the material at 125°C. The compatibilizer is at least one of maleic anhydride-grafted polyethylene (MAH-g-PE) or maleic anhydride-grafted POE; The plasticizer is any one of tributyl citrate, DOA, or pentaerythritol ester. A process for preparing a 125℃ irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulation material includes the following steps: S1: Premix all raw materials except crosslinking agent at high speed; S2: Put the premixed material into an internal mixer and mix at 145-170℃ for 6-8 minutes; S3: Masterbatch is obtained by melt extrusion and hot cutting granulation using a twin-screw extruder; S4: After drying the masterbatch, it is extruded onto the conductor through an extruder to form an insulating layer; S5: The extruded wire core is sent into an electron accelerator for irradiation crosslinking, with an irradiation dose of 12-14 Mrad. In S5, the electron beam energy is 2.5-3.5 MeV, and irradiation is performed using unidirectional or bidirectional scanning. The S3 twin-screw extruder has a length-to-diameter ratio (L / D) of 20-25 and a compression ratio of 1:1.2-1:1.5. The antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 0.8:1-1.2:1.

[0021] Working principle: Example 1: Weigh the raw materials according to the following parts by weight: 70 parts EVA (VA content 32%, melt index MI=2.5g / 10min), 15 parts LLDPE, 10 parts POE, 55 parts magnesium hydroxide, 5 parts aluminum hypophosphite, 2 parts melamine cyanurate, 8 parts maleic anhydride grafted polyethylene (MAH-g-PE), 2 parts antioxidant 168 and antioxidant 1010 compounded in a 1:1 mass ratio, 1 part TAC, 9 parts attapulgite surface treated with silane coupling agent KH-550, and 6 parts tributyl citrate.

[0022] The preparation steps are as follows: S1: Add all raw materials except TAC to a high-speed mixer and mix at room temperature for 5 minutes to ensure uniform dispersion; S2: Put the mixture into an internal mixer and mix at 150°C for 7 minutes; S3: After the mixing is completed, the material is discharged and melt-extruded through a twin-screw extruder with L / D=22 and a compression ratio of 1:1.3. The material is then pelletized by the die head and air-cooled to obtain masterbatch. S4: Dry the obtained masterbatch in a 60℃ forced-air drying oven for 4 hours; S5: Use a Φ65 single screw extruder to extrude the dried masterbatch onto a copper conductor to form an insulating layer with a thickness of 1.0 mm. The extrusion temperature is set as follows: Zone 1 90℃, Zone 2 110℃, Zone 3 125℃, Zone 4 140℃, and both the die head and the die head are 145℃. S6: The extruded wire core immediately enters the electron accelerator irradiation area and is irradiated unidirectionally using an electron beam with an energy of 3.0 MeV, with a total dose of 13 Mrad.

[0023] The obtained samples were subjected to performance tests, and the results are listed in the table below and compared with the comparative example.

[0024] Performance items Test Standards Example 1 Comparative Example 1 (without TAC) Comparative Example 2 (without aluminum hypophosphite) Tensile strength (MPa) GB / T 2951.11 14.2 11.8 12.5 Elongation at break (%) GB / T 2951.11 235 260 190 Oxygen index (%) GB / T 2406.2 31.5 28.0 27.2 Heat extension (200℃, 15min) GB / T 2951.31 Elongation: 92%, Permanent Deformation: 21% Elongation: 168%, Permanent Deformation: 45% Elongation: 155%, Permanent Deformation: 38% Volume resistivity (Ω·cm) GB / T 3048.5 1.3×10¹³ 1.1×10¹³ 1.0×10¹³ Dielectric strength (kV / mm) GB / T 1408.1 23.6 21.0 20.5 As can be seen from the table, Example 1 outperforms the comparative example in all key indicators. The lack of TAC leads to insufficient crosslinking and severely deteriorates the thermal extension performance; while the absence of aluminum hypophosphite significantly weakens the flame retardant synergy, reduces the oxygen index, and also results in poor thermal extension performance. Example 2

[0025] The amount of EVA was adjusted to 60 parts, and the amount of LLDPE was increased to 20 parts, while the remaining components and process parameters were the same as in Example 1. The tensile strength of the resulting material increased slightly to 15.0 MPa, the elongation at break was 210%, the thermal elongation test results showed an elongation of 96% and a permanent deformation of 23%, indicating that appropriately increasing the amount of LLDPE can improve rigidity without significantly sacrificing ductility. Example 3

[0026] When TAC was replaced with an equal amount of TAIC (tallyl isocyanurate), and other conditions remained unchanged, the gel content was slightly lower, and the thermal elongation reached 105%, which is close to the upper limit. This indicates that TAC has better sensitization efficiency in this system.

[0027] All embodiments demonstrate good processing stability and repeatability, indicating that the technical solution of the present invention has good universality and industrialization prospects.

[0028] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] 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 halogen-free, low-smoke, flame-retardant polyolefin insulating material irradiated at 125℃, characterized in that: It is composed of the following components in parts by weight: 50-80 parts of ethylene-vinyl acetate copolymer (EVA), 10-20 parts of linear low-density polyethylene (LLDPE), 5-15 parts of polyolefin elastomer (POE), 45-60 parts of magnesium hydroxide, 4-6 parts of aluminum hypophosphite, 1-3 parts of melamine cyanurate, 5-10 parts of compatibilizer, 1-3 parts of antioxidant, 0.5-1.5 parts of triallyl isocyanurate (TAC), 5-10 parts of modified attapulgite, and 5-8 parts of plasticizer.

2. The 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulating material according to claim 1, characterized in that: The EVA contains 28%-45% vinyl acetate (VA) and has a melt index of 0.5-6.0 g / 10 min.

3. The 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulating material according to claim 1, characterized in that: The modified attapulgite is obtained by calcining natural attapulgite at 500-600℃ for 3-5 hours, then activating it sequentially with 4% sodium hydroxide solution and 14% hydrochloric acid, washing it with deionized water until neutral and drying it, and finally surface modifying it with 2-4wt% γ-aminopropyltriethoxysilane (KH-550).

4. The 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulating material according to claim 1, characterized in that: It also includes 0.2-0.8 parts of trimethylpropane trimethacrylate (TMPTMA) as an auxiliary crosslinking sensitizer.

5. The 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulating material according to claim 1, characterized in that: The compatibilizer is at least one of maleic anhydride-grafted polyethylene (MAH-g-PE) or maleic anhydride-grafted POE.

6. The 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulating material according to claim 1, characterized in that: The plasticizer is any one of tributyl citrate, DOA, or pentaerythritol ester.

7. A preparation process for a 125℃ irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulating material, applied to the 125℃ irradiated crosslinked halogen-free, low-smoke, flame-retardant polyolefin insulating material according to any one of claims 1-6, characterized in that: Includes the following steps: S1: Premix all raw materials except the crosslinking agent at high speed; S2: Put the premixed material into the internal mixer and mix at 145-170℃ for 6-8 minutes; S3: Masterbatch is obtained by melt extrusion and hot cutting granulation using a twin-screw extruder; S4: After drying the masterbatch, it is extruded onto the conductor through an extruder to form an insulating layer; S5: The extruded wire core is sent to an electron accelerator for irradiation crosslinking, with an irradiation dose of 12-14 Mrad.

8. The preparation process of the 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulation material according to claim 7, characterized in that: The electron beam energy in S5 is 2.5-3.5 MeV, and irradiation is performed using a unidirectional or bidirectional scanning method.

9. The preparation process of the 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulation material according to claim 7, characterized in that: The twin-screw extruder in S3 has a length-to-diameter ratio (L / D) of 20-25 and a compression ratio of 1:1.2-1:1.

5.

10. The 125℃ irradiated crosslinked halogen-free low-smoke flame-retardant polyolefin insulating material according to claim 1, characterized in that: The antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 0.8:1-1.2:1.

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