Low-smoke halogen-free irradiation crosslinking polyolefin cable sheath material and granulation process thereof

Abstract

The invention relates to the technical field of high polymer materials, and discloses a low-smoke halogen-free irradiation crosslinking polyolefin cable sheath material and a granulation process thereof, the raw materials comprise an ethylene-vinyl acetate copolymer, an ethylene-octylene copolymer, an epoxy group-containing terpolymer and functionalized composite powder, the powder system superfine aluminum hydroxide is subjected to high-temperature grafting through vinyl silane, after cooling, an active coating layer is constructed by zinc methacrylate, active magnesium oxide and a lubricant, and the process adopts matrix resin main feeding, powder side feeding and low-temperature low-shear extrusion, and is subjected to air-cooled die surface hot cutting and electron beam irradiation crosslinking forming. The covalent bond and ionic bond synergistic enhancement mechanism is utilized, the contradiction between mechanical property loss and processing rheological property deterioration is solved under the high filling amount of 137-160 parts, the active components are effectively prevented from being scorched in the early stage, and the material is endowed with excellent tensile strength, elongation at break and surface quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular materials, in particular to a low-smoke halogen-free irradiation crosslinking polyolefin cable sheath material and a granulation process thereof. BACKGROUND

[0002] With the improvement of safety and environmental protection requirements in the cable industry, low-smoke halogen-free flame-retardant materials have become the mainstream choice for cable sheath materials because they produce low smoke and no toxic and corrosive gases during combustion. In order to achieve the flame-retardant level required by the industry standard, a large amount of inorganic flame retardant such as aluminum hydroxide or magnesium hydroxide is usually added to the polyolefin matrix. Although this high-filled system meets the flame-retardant requirements, the inorganic filler and the organic resin matrix differ in physical and chemical properties, making it difficult to balance the overall performance of the material.

[0003] Inorganic flame retardants belong to polar materials, while polyolefins belong to non-polar materials, and the interface compatibility between the two is poor. When the filling amount of the flame retardant reaches a high proportion, the continuous phase of the resin matrix is destroyed, and a weak interface layer is easily formed between the filler and the matrix. In the prior art, silane coupling agents are often used to treat the surface of the filler to improve the dispersibility, but this single chemical bonding is not enough to maintain the overall toughness of the material at a high filling amount. The cured crosslinked network restricts the movement of the molecular chain, causing the stress to be unable to effectively transfer and dissipate between the rigid filler and the matrix when the material is stretched by external force, resulting in a decrease in elongation at break and difficulty in meeting the anti-cracking requirements in complex installation environments.

[0004] In addition, high-proportion powder filling leads to an increase in melt viscosity, and an increase in flow resistance of the material in the extruder. During the granulation or extrusion process, friction between the material and the inner wall of the equipment and the screw will generate shear heat. This heat process will cause the surface of the extruded product to be rough or have appearance defects, and limit the use of active functional additives. Some active monomers or metal salt additives added to improve strength are prone to early thermal polymerization or scorching in a high-temperature and high-shear environment, resulting in pre-crosslinking particles due to a narrow processing process window, affecting the finished product quality and production stability of the cable sheath material. Therefore, how to solve the contradiction between the mechanical property loss and the deterioration of the processing rheology caused by high filling amount while ensuring high flame-retardant grade is a technical problem to be solved in the current field. SUMMARY

[0005] The technical problem solved by the present application is that existing low-smoke halogen-free flame-retardant cable materials usually need to add a high proportion of inorganic flame retardants to meet the flame-retardant requirements, but the high filling amount leads to an increase in the viscosity of the matrix resin, poor processing flowability, and poor interface compatibility between the inorganic filler and the organic matrix, resulting in a decrease in tensile strength and elongation at break, making it difficult to balance high flame retardancy, processing flowability, and physical and mechanical properties.

[0006] To solve the above problems, the present application provides the following technical solutions: In the first aspect, the present application provides a low-smoke halogen-free irradiation cross-linked polyolefin cable sheath material, which adopts the following technical solutions: A low-smoke halogen-free irradiation cross-linked polyolefin cable sheath material is made of raw materials including the following components by weight: ethylene-vinyl acetate copolymer 70-80 parts; ethylene-octene copolymer 20-30 parts; ethylene-methyl acrylate-glycidyl methacrylate terpolymer 3-6 parts; hindered phenolic antioxidant 0.8-1.2 parts; functionalized composite powder 137-160 parts; wherein the hindered phenolic antioxidant is antioxidant 1010, and the functionalized composite powder is prepared from ultra-fine aluminum hydroxide, vinyl silane, zinc methacrylate, active magnesium oxide, and lubricating dispersant, and the lubricating dispersant is stearic acid.

[0007] By adopting the above technical solutions, the present application utilizes the ethylene-vinyl acetate copolymer to provide the base polarity and filler containment, the ethylene-octene copolymer to provide toughness, and the ethylene-methyl acrylate-glycidyl methacrylate terpolymer to utilize the epoxy group to compatibilize the interface. Through a specific preparation process, the present application constructs a layered coating structure of inner chemical bonding and outer physical adsorption on the surface of the functionalized composite powder, and realizes the performance balance under high filling amount in cooperation with the resin matrix.

[0008] The specific action mechanism and beneficial effects are as follows: Constructing the layered coating structure: the vinyl silane preferentially reacts with the hydroxyl group on the surface of the ultra-fine aluminum hydroxide under high temperature conditions to form an inner layer of chemical bonding, reduces the surface polarity of the powder, and introduces reactive vinyl groups; the zinc methacrylate and the active magnesium oxide are coated on the outside of the modified layer in the form of physical adsorption with the aid of the lubricating dispersant. The active magnesium oxide adsorbs free acid in this process and assists the dispersion of the zinc methacrylate, preventing metal salt agglomeration.

[0009] In-situ synergistic cross-linking reinforcement: during the irradiation cross-linking process, the functional groups on the surface of the powder participate in the high molecular cross-linking reaction.

[0010] Silane coupling effect: the vinyl end of the vinyl silane is grafted with the macromolecular chain of the polyolefin matrix under the initiation of radiation, chemically anchoring the inorganic particles in the polymer network.

[0011] Ionic bond cross-linking effect: the zinc methacrylate contains unsaturated double bonds and ionic bonds. The double bonds are opened by electron beam irradiation to participate in the free radical reaction of the resin matrix to form grafting points; at the same time, the zinc ions aggregate in the polymer matrix to form physical cross-linking centers.

[0012] The double cross-linking network of covalent bond and ionic bond improves the tensile strength of the material; the slippage of ionic bond during force deformation dissipates energy, so that the material maintains high elongation at break at a high filling amount of 137-160 parts.

[0013] Improved processing rheology: the outer layer lubricating dispersant and the metal salt layer reduce the friction coefficient between powders, combined with the particle size characteristics of ultra-fine aluminum hydroxide, reduce the shear heat of the melt during the double screw extrusion process, avoid local scorching of the material, and improve the extrusion appearance.

[0014] Preferably, the weight parts of each component for preparing the functionalized composite powder are: ultra-fine aluminum hydroxide 130-145 parts; vinyl silane 1.5-2.0 parts; zinc methacrylate 4-7 parts; active magnesium oxide 1-3 parts; lubricating dispersant 1.2-2.3 parts.

[0015] By adopting the above technical solution, the proportion of each component is limited to ensure that the coating layer is complete and has an appropriate thickness. The amount of vinyl silane ensures the surface coverage, and the zinc methacrylate content in this range provides sufficient cross-linking density increment and prevents processing scorching caused by excessive metal salt.

[0016] Preferably, the functionalized composite powder is prepared by the following steps: putting ultra-fine aluminum hydroxide into a mixer, adjusting the stirring speed to 1000-1200 rpm and heating the material temperature to 90-95℃, keeping the temperature constant for 5-8 minutes to obtain preheated ultra-fine aluminum hydroxide; adding vinyl silane to the preheated ultra-fine aluminum hydroxide, keeping the temperature at 90-95℃ and the stirring speed at 1000-1200 rpm to continue mixing for 5-8 minutes to obtain a modified intermediate; adjusting the cooling water flux of the mixer jacket to reduce the temperature of the modified intermediate to 75-80℃, and reducing the stirring speed to 400-600 rpm to obtain a cooled modified intermediate; adding zinc methacrylate, active magnesium oxide and lubricating dispersant to the cooled modified intermediate, keeping the temperature at 75-80℃ and the stirring speed at 400-600 rpm to mix for 3-5 minutes.

[0017] By adopting the above technical solution, the step-by-step temperature and speed changing process is the key to building a layered structure: High temperature grafting stage: 90-95℃ high temperature combined with high speed shearing removes the physical adsorbed water on the surface of aluminum hydroxide and increases the number of active hydroxyl groups on the surface, while providing reaction activation energy to promote the de-alcohol condensation reaction between vinyl silane and the hydroxyl groups on the surface of the powder: ; Thus a firm inner hydrophobic film is formed.

[0018] Low temperature coating stage: zinc methacrylate belongs to heat-sensitive organic metal salt, high temperature and high shear can easily cause its double bond to early thermal polymerization. Reduce the temperature to 75-80 DEG C and reduce the speed, use the physical wetting effect to make it uniformly wrapped in the modified intermediate outer layer, form a coating layer with reactivity, and wait for the irradiation process to initiate the reaction.

[0019] Preferably, in the process of preparing the functionalized composite powder, the vinyl silane is added to the mixer in a spraying manner.

[0020] In the second aspect, the application provides a granulation process of low-smoke halogen-free irradiation cross-linked polyolefin cable sheath material, which adopts the following technical scheme: A granulation process of low-smoke halogen-free irradiation cross-linked polyolefin cable sheath material, comprising the following steps: The ethylene-vinyl acetate copolymer, the ethylene-octene copolymer, the ethylene-methyl acrylate-glycidyl methacrylate terpolymer and the hindered phenolic antioxidant are weighed and premixed to obtain a base resin premix; The base resin premix is added to the main feeding port of the double-screw extruder, and the functionalized composite powder is added to the side feeding port of the double-screw extruder; The temperature of zone one to zone three of the double-screw extruder is set to 110-120 DEG C, the temperature of zone four to zone five is set to 120-125 DEG C, the melt mixing temperature of zone six to zone nine is set to 125-135 DEG C, and the die head temperature is set to 120-125 DEG C, and the material is extruded through the die head to obtain a molten glue strip; The molten glue strip is granulated by air-cooled die face hot cutting, the granulation water temperature is controlled to be 40-50 DEG C, and after granulation, centrifugal dewatering and drying are performed to obtain uncrosslinked cable material particles.

[0021] By adopting the above technical scheme, the application adopts the process strategy of combining "base pre-plasticization and side filling" with "low temperature and low heat history" for a high filling system (137-160 parts of powder): Side feeding process principle: the resin matrix is first completely melted and plasticized to form a low-viscosity polymer melt by using the screw segment between the main feeding port and the side feeding port. When the functionalized composite powder enters from the side feeding port, it can be quickly wetted and coated by the melt. Compared with the traditional main feeding port mixing feeding, this method effectively reduces the dry friction between the high filling powder and the inner wall of the barrel, reduces the screw wear and equipment torque load, and improves the dispersion uniformity of the powder in the resin.

[0022] Low temperature extrusion control: strictly control the highest melt mixing temperature not more than 135℃. This is due to the zinc methacrylate contained in the system has a high reactivity, and the ultra-fine aluminum hydroxide has a risk of dehydration at high temperature. The temperature range matches the side feeding to shorten the thermal history of the material, effectively preventing the early thermal polymerization of zinc methacrylate in the granulation stage (i.e. scorching phenomenon), ensuring the subsequent processing performance of the material.

[0023] Air-cooled die face hot cutting: for the characteristics of high filling material melt strength low, easy to break, the use of die face hot cutting makes the material extrusion immediately cut off and cool down, avoiding long distance traction, solving the problem of granulation difficulty of high filling low smoke halogen-free material.

[0024] Preferably, the length-diameter ratio of the twin-screw extruder is 48:1-52:1, and the side feeding port is located at 15D-20D of the twin-screw extruder; in the twin-screw extruder, the functionalized composite powder is dispersed in the resin matrix under the conveying of the low shear screw combination.

[0025] By adopting the above technical scheme, the length-diameter ratio of 48:1-52:1 prolongs the residence time of the material in the barrel, so that plasticization can be completed at a lower screw speed without relying on strong shear brought by high speed. The side feeding port is arranged at 15D-20D, which ensures that the base resin is in a completely molten state when it reaches this position, providing a good melt coating environment for the powder.

[0026] The use of low shear screw combination is the key control point of the process: by reducing the number of kneading blocks and optimizing the arrangement of screw elements, the screw mainly plays a distribution mixing role rather than a dispersion mixing role. This flexible shear mode maximizes the reduction of shear heat generation, avoids the opening of zinc methacrylate double bond due to local overheating to produce pre-crosslinking particles, and ensures the smooth surface of the extruded product without pitting.

[0027] Preferably, after obtaining the uncrosslinked cable material particles, a crosslinking step is further included: extruding the uncrosslinked cable material particles on a single screw extruder to coat the conductor, and then placing it under an electron accelerator for irradiation treatment to obtain a low smoke halogen-free irradiation crosslinked polyolefin cable sheath material; the temperature of the extrusion coating is 130-150℃; the irradiation voltage of the irradiation treatment is 1.5-2.5MeV, and the absorbed dose is 100-140kGy.

[0028] By adopting the above technical scheme, irradiation treatment initiates multiple chemical reactions in the system, building the final performance network: Under the action of 1.5-2.5 MeV high-energy electron beams, the polymer matrix generates free radicals. The vinyl silane on the surface of the functionalized composite powder utilizes its vinyl group to graft with the macromolecular chain of the resin to realize chemical anchoring of the inorganic-organic interface; meanwhile, the double bond of zinc methacrylate participates in the grafting reaction, and its metal ions gather in the matrix to form ion crosslinking clusters.

[0029] Controlling the absorbed dose to be 100-140 kGy can form a mixed crosslinking network of "covalent bond-ion bond" with a suitable density, which can endow the material with high temperature resistance, solvent resistance and high strength while retaining the toughness contribution of the ion bond.

[0030] By adopting the above technical scheme, the liquid silane is atomized into micron-sized droplets by spray feeding, the contact area with the powder surface is increased, the self-polymerization phenomenon caused by excessive local concentration is avoided, the formation of a uniform monomolecular or oligomer layer covering on the surface of the ultrafine aluminum hydroxide is promoted, and the coupling efficiency is improved.

[0031] The application provides a low-smoke halogen-free irradiation crosslinking polyolefin cable sheath material and a granulation process thereof. 1. The functionalized composite powder with double crosslinking structure of covalent bond and ion bond solves the technical problem of the decrease of the mechanical properties of the material under high filling system. The vinyl silane realizes the chemical anchoring of the ultrafine aluminum hydroxide and the polyolefin matrix, and improves the interfacial bonding strength; the ion bond introduced by the zinc methacrylate improves the tensile strength of the material, and utilizes the dissociation and recombination characteristics of the ion clusters when the material is deformed under stress to dissipate energy, so that the material can still have excellent tensile strength and elongation at break under a high filling amount of 137 to 160 parts.

[0032] 2. The synergistic effect of the stepwise temperature modification process and the side feeding granulation technology effectively improves the processing rheological properties of the high filling material. The lubricating and dispersing layer formed on the outer layer of the functionalized composite powder reduces the friction coefficient between the powders, and cooperates with the matrix pre-plasticization, side filling and low shear extrusion process to reduce the shear heat generation of the melt in the processing process, avoids the early scorching of the heat-sensitive zinc methacrylate, and ensures the flatness and fineness of the extruded rubber particles and the cable sheath surface.

[0033] 3. The epoxy group of the ethylene methyl acrylate glycidyl methacrylate terpolymer is used for interfacial compatibilization, and the acid adsorption effect of the active magnesium oxide is used to improve the thermal stability and aging resistance of the system. The compound system promotes the uniform dispersion of the inorganic flame retardant in the matrix, and absorbs the acidic substances separated in the processing process through the active magnesium oxide, prevents the catalytic degradation of the polymer matrix, DETAILED DESCRIPTION The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments and comparative examples of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0034] Preparation Example 1-3: Preparation Example 1: The present preparation example provides a functional composite powder A for a low-filled high-flow formula, comprising the following steps: Put 130 parts by weight of ultra-fine aluminum hydroxide into a high-speed mixer with a heating jacket, adjust the stirring speed to 1000 rpm and heat the material temperature to 90℃, keep constant temperature for 5 minutes to remove physically adsorbed water and activate the surface; Uniformly add 1.5 parts by weight of vinyl silane to the ultra-fine aluminum hydroxide under high-temperature and high-speed stirring in a spraying manner, continue to mix for 5 minutes at 90℃ and 1000 rpm, and use in-situ hydrolysis condensation reaction to close the hydroxyl groups on the powder surface to obtain a hydrophobic modified intermediate; Adjust the cooling water flux of the mixer jacket to reduce the temperature of the hydrophobic modified intermediate to 75℃, and reduce the stirring speed to 400 rpm; Add 4 parts by weight of zinc methacrylate, 1 part by weight of active magnesium oxide and 1.2 parts by weight of lubricating dispersant (specifically stearic acid) to the cooled hydrophobic modified intermediate; Keep low-speed mixing at 75℃ and 400 rpm for 3 minutes to make the organic metal salt components physically adsorbed on the outer layer of the particles by electrostatic action, and discharge to obtain the functional composite powder A.

[0035] Preparation Example 2: The present preparation example provides a functional composite powder B for a comprehensive performance balanced formula, comprising the following steps: Put 138 parts by weight of ultra-fine aluminum hydroxide into a high-speed mixer with a heating jacket, adjust the stirring speed to 1100 rpm and heat the material temperature to 92℃, keep constant temperature for 6 minutes to remove physically adsorbed water and activate the surface; Uniformly add 1.8 parts by weight of vinyl silane to the ultra-fine aluminum hydroxide under high-temperature and high-speed stirring in a spraying manner, continue to mix for 6 minutes at 92℃ and 1100 rpm, and use in-situ hydrolysis condensation reaction to close the hydroxyl groups on the powder surface to obtain a hydrophobic modified intermediate; Adjust the cooling water flux of the mixer jacket to reduce the temperature of the hydrophobic modified intermediate to 78℃, and reduce the stirring speed to 500 rpm; 5.5 parts by weight of zinc methacrylate, 2 parts by weight of active magnesium oxide and 1.8 parts by weight of a lubricating dispersant (specifically stearic acid) were added to the hydrophobically modified intermediate after cooling; The organic metal salt component was physically adsorbed on the outer layer of the particles by electrostatic action by keeping the low-speed mixing at 78℃ and 500 rpm for 4 minutes, and the functionalized composite powder B was obtained by discharging.

[0036] Preparation Example 3: The present preparation example provides a functionalized composite powder C for a high-filled high-toughness formula, comprising the following steps: 145 parts by weight of ultra-fine aluminum hydroxide was put into a high-speed mixer with a heating jacket, the stirring speed was adjusted to 1200 rpm, and the material temperature was heated to 95℃, and kept at constant temperature for 8 minutes to remove physically adsorbed water and activate the surface; 2.0 parts by weight of vinyl silane was uniformly added to the ultra-fine aluminum hydroxide under high-temperature and high-speed stirring in a spray manner, and the mixing was continued at 95℃ and 1200 rpm for 8 minutes to close the hydroxyl groups on the surface of the powder by in-situ hydrolysis and condensation reaction, to obtain a hydrophobically modified intermediate; The temperature of the hydrophobically modified intermediate was reduced to 80℃ by adjusting the cooling water flux of the mixer jacket, and the stirring speed was reduced to 600 rpm; 7 parts by weight of zinc methacrylate, 3 parts by weight of active magnesium oxide and 2.3 parts by weight of a lubricating dispersant (specifically stearic acid) were added to the hydrophobically modified intermediate after cooling; The organic metal salt component was physically adsorbed on the outer layer of the particles by electrostatic action by keeping the low-speed mixing at 80℃ and 600 rpm for 5 minutes, and the functionalized composite powder C was obtained by discharging.

[0037] Examples 1-3: Example 1: The present example provides a low-smoke halogen-free irradiation crosslinked polyolefin cable sheath material and its granulation process, comprising the following steps: S1, 80 parts of ethylene-vinyl acetate copolymer, 20 parts of ethylene-octene copolymer, 3 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer and 0.8 parts of hindered phenolic antioxidant (specifically antioxidant 1010) were weighed according to the weight fraction, and the above raw materials were pre-mixed in a tumbling mixer for 5 minutes to obtain a base resin premix; S2, the base resin premix was added to the main feeding port of the double screw extruder with a length-diameter ratio of 48:1, and the functionalized composite powder A obtained in Preparation Example 1 was added to the side feeding port located at 15D of the extruder; S3, set the temperature distribution of the twin-screw extruder, control the temperature of zone 1 to 3 to be 110℃, the temperature of zone 4 to 5 to be 120℃, the melt mixing temperature of zone 6 to 9 to be 125℃, and the temperature of the die head to be 120℃, under the transportation of the low-shear screw combination, make the functionalized composite powder A uniformly dispersed in the low-temperature molten resin matrix, and extrude the molten glue strip through the die head; S4, adopt the air-cooled die face hot cutting method to cut the molten glue strip into particles, control the cutting water temperature to be 40℃, immediately centrifugalize and dehydrate after cutting, and dry in the fluidized bed at 60℃ for 2 hours, to obtain the uncrosslinked cable material particles; S5, extrude the uncrosslinked cable material particles on the single-screw extruder at 130℃ to coat outside the conductor, then place it under the electron accelerator, and perform irradiation treatment at 1.5MeV voltage and 120kGy absorbed dose to initiate the grafting reaction of the vinyl and zinc methacrylate double bonds, to prepare the low-smoke halogen-free irradiation crosslinked polyolefin cable sheath material.

[0038] Example 2: The embodiment provides a low-smoke halogen-free irradiation crosslinked polyolefin cable sheath material and a granulation process thereof, which comprises the following steps: S1, take 75 parts of ethylene-vinyl acetate copolymer, 25 parts of ethylene-octene copolymer, 4.5 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, and 1.0 part of hindered phenolic antioxidant (specifically antioxidant 1010) according to weight fraction, pre-mix the above raw materials in a tumbling mixer for 6 minutes to obtain a matrix resin premix; S2, add the matrix resin premix to the main feeding port of the twin-screw extruder with a length-diameter ratio of 50:1, and add the functionalized composite powder B obtained in Preparation Example 2 to the side feeding port located at 18D of the extruder; S3, set the temperature distribution of the twin-screw extruder, control the temperature of zone 1 to 3 to be 115℃, the temperature of zone 4 to 5 to be 122℃, the melt mixing temperature of zone 6 to 9 to be 130℃, and the temperature of the die head to be 122℃, under the transportation of the low-shear screw combination, make the functionalized composite powder B uniformly dispersed in the low-temperature molten resin matrix, and extrude the molten glue strip through the die head; S4, adopt the air-cooled die face hot cutting method to cut the molten glue strip into particles, control the cutting water temperature to be 45℃, immediately centrifugalize and dehydrate after cutting, and dry in the fluidized bed at 60℃ for 2 hours, to obtain the uncrosslinked cable material particles; S5, extrude the uncrosslinked cable material particles on the single-screw extruder at 140℃ to coat outside the conductor, then place it under the electron accelerator, and perform irradiation treatment at 2.0MeV voltage and 120kGy absorbed dose to initiate the grafting reaction of the vinyl and zinc methacrylate double bonds, to prepare the low-smoke halogen-free irradiation crosslinked polyolefin cable sheath material.

[0039] Example 3: The embodiment provides a low-smoke halogen-free irradiation crosslinking polyolefin cable sheath material and a granulation process thereof, and comprises the following steps: S1, 70 parts of ethylene-vinyl acetate copolymer, 30 parts of ethylene-octene copolymer, 6 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer and 1.2 parts of hindered phenolic antioxidant (specifically antioxidant 1010) are weighed according to the weight fraction, and the above raw materials are pre-mixed in a tumbling mixer for 8 minutes to obtain a base resin premix; S2, the base resin premix is added to the main feeding port of the double-screw extruder with a length-diameter ratio of 52:1, and the functionalized composite powder C obtained in the preparation example 3 is added to the side feeding port located at the 20D of the extruder; S3, the temperature distribution of the double-screw extruder is set, the temperature of the first zone to the third zone is controlled to be 120 DEG C, the temperature of the fourth zone to the fifth zone is controlled to be 125 DEG C, the melt mixing temperature of the sixth zone to the ninth zone is controlled to be 135 DEG C, and the head temperature is controlled to be 125 DEG C, under the conveying of the low-shear screw combination, the functionalized composite powder C is uniformly dispersed in the low-temperature molten resin matrix, and the molten glue strip is obtained through the head extrusion; S4, the molten glue strip is granulated by adopting the air-cooled die face hot cutting mode, the water temperature of the granulation is controlled to be 50 DEG C, the granulation is immediately centrifuged and dehydrated, and then dried in a fluidized bed at 60 DEG C for 2 hours to obtain uncrosslinked cable material particles; S5, the uncrosslinked cable material particles are extruded on a single-screw extruder at 150 DEG C to coat the conductor, and then placed under an electron accelerator for irradiation treatment at a voltage of 2.5 MeV and an absorbed dose of 140 kGy, to initiate the grafting reaction of the ethylene group and the zinc methacrylic double bond, thereby preparing a low-smoke halogen-free irradiation crosslinking polyolefin cable sheath material.

[0040] Comparative examples 1-4: Comparative example 1: Compared with example 2, the difference lies in that the step-by-step pretreatment step of the functionalized composite powder in the preparation example is omitted. The specific operation is as follows: the ultra-fine aluminum hydroxide, vinyl silane, zinc methacrylate and active magnesium oxide without any treatment are directly mixed with the base resin and the antioxidant in the mixing machine at room temperature, and then all are added to the extruder through the main feeding port for granulation, and the remaining process parameters are the same.

[0041] Comparative example 2: Compared with example 2, the difference lies in that the ethylene-methyl acrylate-glycidyl methacrylate terpolymer is not contained. The component is removed in the formula, and the fraction of ethylene-vinyl acetate copolymer is correspondingly increased to make up the total amount, and the remaining parts are the same.

[0042] Comparative example 3: The difference compared with Example 2 is that the zinc methacrylate is not contained. This component is removed from the formulation and replaced with an equal amount of inert filler (such as calcium carbonate) or a conventional irradiation sensitizer (such as trimethylolpropane trimethacrylate, 1.0 part), and the rest is the same.

[0043] Comparative Example 4: The difference compared with Example 2 is that the process temperature for extrusion granulation is set too high. Specifically, the melt mixing temperature of the six to nine zones of the twin-screw extruder is set to 160°C, and the die temperature is set to 150°C, and the rest is the same.

[0044] Test Examples 1-5: Test Example 1: The uncrosslinked cable material particles prepared from Example 1-3, Comparative Example 1 and Comparative Example 4, respectively, are taken as test samples, and dried in a vacuum oven at 60°C for 4 hours.

[0045] According to GB / T 3682.1-2018 “Plastics - Determination of the melt mass-flow rate and melt volume-flow rate of thermoplastics - Part 1 : Standard method”, a melt flow rate instrument is used for testing, with a test temperature of 190°C and a nominal load of 2.16 kg. After the barrel is kept at a constant temperature, the sample is added, preheated for 4 minutes, and the sample is cut every 15 seconds. The continuous bubble-free sample is weighed and the melt mass flow rate is calculated.

[0046] Subsequently, the dried particles are added to a single-screw extruder with a length-diameter ratio of 25:1, and the barrel temperature is set from the feeding port to the die as 130°C, 140°C, 150°C, and 150°C, respectively, with a rotation speed of 60 rpm. The extruded thin strip is 1 mm thick. After stable extrusion for 10 minutes, the extruded strip sample is taken, and the surface flatness, glossiness and gel particle conditions are observed under standard light source.

[0047] The appearance evaluation standard is set to three levels: A level for fine, smooth and glossy surface, with neat edges; B level for surface with slight particle feeling, with general glossiness; and C level for rough surface, with melt rupture or a large number of dead material particles.

[0048] Table 1. Melt flow rate and extrusion appearance evaluation results of each component sample

[0049] Note: “A-” means between A and B levels, with acceptable surface flatness but slightly lower glossiness.

[0050] Conclusion: According to the data in Table 1, the melt mass flow rate values of Examples 1-3 were in the range of 2.92 to 5.23 g / 10 min, and the extrusion appearance rating was A or A-. It was shown that in the system containing epoxy functional groups and zinc methacrylate, the use of vinyl silane to treat the surface of aluminum hydroxide blocked the contact of the filler surface hydroxyl group with the epoxy group, and with an extrusion process below 145°C, the zinc methacrylate was in an inactive state, and the system maintained the thermoplastic processing ability during the granulation and secondary extrusion stages. The melt mass flow rate value of Comparative Example 1 dropped to 0.15 g / 10 min, and the appearance rating was C. Since the step-by-step treatment was not used, the aluminum hydroxide surface hydroxyl group was directly exposed, and ring-opening addition reaction occurred between the epoxy group and the aluminum hydroxide surface hydroxyl group during the extrusion stage, and the molecular chain was chemically crosslinked to form a gel. The melt mass flow rate value of Comparative Example 4 was 0.42 g / 10 min, and melt fracture occurred. Since the extrusion temperature was set to 160°C, the thermal energy activated the Lewis acid catalytic activity of the zinc ion, which promoted the premature crosslinking of the epoxy group and zinc methacrylate, limiting the movement of the molecular chain.

[0051] Test Example 2: The irradiation crosslinked sheets prepared from Examples 1-3, Comparative Example 1 and Comparative Example 3 were conditioned in an environment of 23±2°C for 24 hours.

[0052] According to GB / T 2951.11-2008 "Cables and optical cables - Insulation and sheath materials - General test methods - Part 11: General test methods - Measurement of thickness and outer dimensions - Mechanical property tests", the sheets were punched into 2-type dumbbell-shaped test pieces using a punching machine.

[0053] Tensile testing was performed using a universal material testing machine equipped with a high-precision extensometer, with a tensile speed of 250 mm / min, and the maximum load and gauge elongation at the time of sample breakage were recorded, and the tensile strength (MPa) and elongation at break (%) were calculated. Five parallel samples were tested for each group of samples, and the arithmetic mean was taken after removing the maximum and minimum values.

[0054] Table 2. Mechanical property test results of the material after irradiation crosslinking

[0055] Conclusion: According to the data in Table 2, the elongation at break of Examples 1 to 3 is distributed between 205% to 278%, and the tensile strength is increased from 13.4 MPa to 16.5 MPa with the increase of filler amount and crosslinking degree. Compared with Comparative Example 1, the elongation at break (243%) of Example 2 is higher than that of Comparative Example 1 (165%) while the tensile strength (15.8 MPa) is higher than that of Comparative Example 1 (14.1 MPa). Comparative Example 1 uses conventional trimethylolpropane trimethacrylate as a crosslinking coagent, and the covalent bond network structure formed thereby is rigid and has weak energy dissipation capacity. The zinc methacrylate introduced in the examples aggregates with carboxylate ions in the matrix to form ionic clusters, and the ionic bonds dissociate to dissipate energy during tensile stress, and recombine before unloading or breaking, which endows the material with toughness. Compared with Comparative Example 3, the mechanical indicators of Example 2 are obviously improved. Comparative Example 3 removes zinc methacrylate, and the system lacks active nodes bridging the polymer chains and ionic reinforcing phases, and the tensile strength is 9.8 MPa, and the interfacial bonding force decreases, and the elongation at break decreases to 132%. Zinc methacrylate plays a role in constructing the crosslinking network skeleton and providing physical crosslinking points in the system.

[0056] Test Example 3: The insulating wire core samples prepared in Examples 1-3 and Comparative Example 2 were taken, and the conductor was removed after cutting to length.

[0057] According to GB / T 2951.31-2008 "Cable and optical cable insulation and sheath materials General test methods Part 31: Special test methods for polyvinyl chloride compounds High temperature pressure test Anti-cracking test", the test temperature was set to 110±2℃, the loading time was 4 hours, the knife edge force value was calculated according to the formula F=k×2δ (wherein k is 0.6), and after the test, the sample was naturally cooled to room temperature under load, the insulation thickness at the indentation was measured and the indentation depth percentage was calculated.

[0058] Another set of dumbbell piece samples was taken, and according to GB / T 2951.21-2008 "Cable and optical cable insulation and sheath materials General test methods Part 21: Special test methods for elastomer compounds Ozone resistance test Hot extension test Mineral oil immersion test", the oven temperature was set to 200±3℃, the hanging load was 20N / cm 2 , the load was maintained for 15 minutes, the elongation under load was measured, and the permanent deformation rate was measured after the load was removed and the sample was allowed to recover at room temperature for 5 minutes.

[0059] Table 3. High temperature pressure and hot extension performance test results

[0060] Conclusion: According to the data in Table 3, the indentation depth of Examples 1 to 3 at 110°C was controlled between 7.5% and 14.2%, exhibiting excellent high-temperature dimensional stability. Comparative Example 2 showed an indentation depth of 78.4%, resulting in severe deformation. Although Comparative Example 2 contained zinc methacrylate and underwent irradiation crosslinking, it lacked the ethylene-methyl acrylate-glycidyl methacrylate terpolymer. At 110°C, the ionic clusters formed by zinc methacrylate underwent thermal relaxation and slippage, and the carbon-carbon backbone crosslinking formed solely by irradiation was insufficient to resist continuous mechanical creep. The examples retained epoxy functional groups. During the high-temperature pressure test, thermal energy activated the Lewis acid catalytic activity of zinc ions, promoting in-situ esterification of the epoxy groups with carboxylate groups, converting the slipping ionic bonds into thermally stable covalent bonds, thus limiting the relative displacement of the molecular chains. In the 200°C thermal elongation data, the thermal elongation rate of the examples was lower than that of Comparative Example 2, indicating a higher effective network density at high temperatures, corroborating the contribution of the thermal locking mechanism to the crosslinking density.

[0061] Test Example 4: Take dumbbell-shaped tensile specimens prepared in Examples 1-3, Comparative Example 1 and Comparative Example 3, and in accordance with GB / T 2951.12-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 12: General Test Methods - Thermal Aging Test Methods", suspend the specimens vertically in the center area of ​​a naturally ventilated aging oven, keeping the specimen spacing greater than 20 mm.

[0062] The aging temperature was set at 135±2℃ for 168 hours. After aging, the sample was removed and allowed to cool at ambient temperature for 16 hours. Following the tensile test procedure in Test Example 2, the maximum load and gauge length elongation of the aged sample were measured. The tensile strength and elongation at break after aging were calculated, and the rate of change of tensile strength and the retention rate of elongation at break were calculated according to the formula.

[0063] Table 4. Performance test results of air oven aging (135℃×168h)

[0064] Note: In the tensile strength change rate, "+" indicates that the value increases and "-" indicates that the value decreases.

[0065] in conclusion: According to the data in Table 4, after aging at 135°C for 168 hours, Examples 1 to 3 exhibited elongation at break retention rates between 87.3% and 93.8%, and tensile strength increased by 1.9% to 4.2%, demonstrating post-curing characteristics in the early stages of aging. Comparative Example 1 showed an elongation at break retention rate reduced to 69.1%, and Comparative Example 3 showed a reduction to 64.4% with a 9.2% decrease in tensile strength.

[0066] In the examples, vinylsilane forms a hydrophobic layer on the surface of aluminum hydroxide, reducing interfacial separation between the inorganic filler and the organic matrix at high temperatures and blocking oxygen penetration along the phase interface. Under aging at 135°C, the residual zinc methacrylate catalyzes the esterification of epoxy groups, resulting in chemical bonds with higher thermal stability than physical entanglement. This secondary crosslinking compensates for the performance loss caused by the oxidative breakage of the polymer backbone. Comparative Example 1 lacks interfacial pretreatment, leading to interfacial bonding failure under thermal stress and a decrease in elongation at break. Comparative Example 3 lacks zinc methacrylate, resulting in a lack of ion-covalent interpenetrating network and the ability of metal ions to capture oxidation products, causing oxidative degradation of the matrix resin and resulting in strength reduction.

[0067] Test Example 5: Uncrosslinked particles prepared in Examples 1-3 were preheated for 3 minutes at 135°C and 10MPa pressure on a flat vulcanizing machine and then hot-pressed for 5 minutes to form sheets. Subsequently, they were placed under an electron accelerator for crosslinking treatment according to the irradiation process corresponding to each example.

[0068] According to GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test", the sheet was cut into 80mm×10mm×4mm samples, conditioned in an environment of 23℃ and 50% relative humidity for 88 hours, vertically fixed in a combustion chamber, the mixed flow rate of oxygen and nitrogen was adjusted, the top of the sample was ignited, and the lowest oxygen concentration when the sample just maintained combustion for 3 minutes or the combustion length reached 50mm was recorded, and the limiting oxygen index was calculated.

[0069] Another sheet was cut into 125mm×13mm×3.2mm samples. A vertical burning test was conducted according to GB / T 2408-2008 "Determination of the flammability of plastics - Horizontal and Vertical Methods". After applying a flame to the sample for 10 seconds, the flame was removed and the afterflame time t1 was recorded. After the flame was extinguished, the flame was applied again for 10 seconds and the afterflame time t2 was recorded, as well as whether molten droplets ignited the degreased cotton. Five samples were tested in each group. The flammability rating was evaluated based on the total afterflame time and the molten droplet situation.

[0070] Table 5. Flame retardant performance test results

[0071] Note: The total afterflame time is the average of the cumulative time after two ignitions of a single spline.

[0072] in conclusion: According to the data in Table 5, the limiting oxygen index of Examples 1 to 3 ranged from 36.4% to 41.2%, and the vertical flammability rating was V-0 for all of them. No combustion drippings were observed during the testing process. The data showed an increasing trend with the increase of flame retardant content in the formulation.

[0073] The formulation in this example maintains its flame-retardant properties after the introduction of organic modified components and crosslinking aids. The aluminum hydroxide filled in the matrix decomposes upon heating, releasing water of crystallization, absorbing heat, and diluting the concentration of combustible gases, thus exerting a physical flame-retardant effect. Zinc methacrylate in the system participates in char formation at high combustion temperatures; zinc ions catalyze the dehydrogenation and carbonization of the polymer matrix, forming a dense char layer with the alumina produced from the decomposition of aluminum hydroxide, isolating oxygen and heat transfer. Simultaneously, the ion-covalent interpenetrating network restricts the melt's fluidity at high temperatures, preventing droplet formation and achieving a V-0 flame-retardant rating.

Claims

1. A low-smoke, halogen-free irradiated cross-linked polyolefin cable sheath material, characterized in that, Made from the following ingredients in parts by weight: 70-80 parts of ethylene-vinyl acetate copolymer; 20-30 parts of ethylene-octene copolymer; 3-6 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer; 0.8-1.2 parts of hindered phenolic antioxidants; 137-160 parts of functionalized composite powder; The hindered phenolic antioxidant is antioxidant 1010, and the functionalized composite powder is prepared from ultrafine aluminum hydroxide, vinyl silane, zinc methacrylate, active magnesium oxide and a lubricating dispersant, wherein the lubricating dispersant is stearic acid.

2. The low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 1, characterized in that, The weight parts of each component used to prepare the functionalized composite powder are as follows: 130-145 parts of ultrafine aluminum hydroxide; Vinylsilane 1.5-2.0 parts; 4-7 parts zinc methacrylate; 1-3 parts of active magnesium oxide; 1.2-2.3 parts of lubricating dispersant.

3. The low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 2, characterized in that, The functionalized composite powder is prepared through the following steps: Add ultrafine aluminum hydroxide into a mixer, adjust the stirring speed to 1000-1200 rpm and heat the material to 90-95℃, keep the temperature constant for 5-8 minutes to obtain preheated ultrafine aluminum hydroxide; Vinylsilane was added to the preheated ultrafine aluminum hydroxide, and the mixture was kept at 90-95°C and 1000-1200 rpm for 5-8 minutes to obtain the modified intermediate. Adjust the cooling water flow rate of the mixer jacket to reduce the temperature of the modified intermediate to 75-80℃ and reduce the stirring speed to 400-600rpm to obtain a cooled modified intermediate. Add zinc methacrylate, active magnesium oxide and lubricating dispersant to the cooling modified intermediate, and mix for 3-5 minutes at 75-80℃ and 400-600 rpm.

4. The low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 3, characterized in that, In the process of preparing the functionalized composite powder, the vinylsilane is added to the mixer by spraying.

5. A granulation process for a low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material as described in any one of claims 1-4, characterized in that, Includes the following steps: Weigh out ethylene-vinyl acetate copolymer, ethylene-octene copolymer, ethylene-methyl acrylate-glycidyl methacrylate terpolymer and hindered phenolic antioxidant and premix them to obtain matrix resin premix; The matrix resin premix is ​​added to the main feed port of the twin-screw extruder, and the functionalized composite powder is added to the side feed port of the twin-screw extruder at the same time. The temperature of the twin-screw extruder is set to 110-120℃ for zones one to three, 120-125℃ for zones four to five, 125-135℃ for the melt mixing temperature of zones six to nine, and 120-125℃ for the die head. The material is extruded through the die head to obtain molten rubber strips. The molten rubber strip is granulated using an air-cooled die-cutting method, with the granulation water temperature controlled at 40-50℃. After granulation, the material is centrifuged, dehydrated, and dried to obtain uncrosslinked cable material granules.

6. The granulation process for a low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 5, characterized in that, The length-to-diameter ratio of the twin-screw extruder is 48:1-52:1, and the side feed port is located at 15D-20D of the twin-screw extruder.

7. The granulation process for a low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 5, characterized in that, The premixing time for preparing the matrix resin premix is ​​5-8 minutes.

8. The granulation process for a low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 5, characterized in that, In the twin-screw extruder, the functionalized composite powder is dispersed in the resin matrix under the conveying of a low-shear screw assembly.

9. The granulation process for a low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 5, characterized in that, After obtaining the uncrosslinked cable material particles, a crosslinking molding step is also included: The uncrosslinked cable material particles are extruded onto the conductor using a single-screw extruder, and then subjected to irradiation treatment under an electron accelerator to obtain a low-smoke halogen-free irradiated crosslinked polyolefin cable sheath material.

10. The granulation process for a low-smoke halogen-free irradiated cross-linked polyolefin cable sheath material according to claim 9, characterized in that, The extrusion coating temperature is 130-150℃; the irradiation voltage of the irradiation treatment is 1.5-2.5MeV, and the absorbed dose is 100-140kGy.

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