Oil-resistant silane crosslinked low-smoke halogen-free polyolefin insulating material and preparation method thereof

Abstract

The invention discloses an oil-resistant silane crosslinked low-smoke halogen-free polyolefin insulating material and a preparation method thereof. The insulating material is prepared from the following raw materials in parts by weight: 23 to 27 parts of an ethylene-vinyl acetate copolymer, 33 to 37 parts of linear low-density polyethylene, 19 to 21 parts of an ethylene-vinyl silane copolymer, 9 to 11 parts of maleic anhydride grafted polyethylene, 66 to 74 parts of magnesium hydroxide, 46 to 54 parts of aluminum hydroxide, 7 to 8 parts of modified montmorillonite, 1.8 to 2.2 parts of zinc stearate and 0.9 to 1.1 parts of an antioxidant compound, the coating is prepared from the following components in parts by weight: 1.3-1.7 parts of vinyl trimethoxy silane, 3.5-4.5 parts of nano titanium dioxide, 0.6-0.9 part of a long-chain alkyl silane coupling agent, 2-4 parts of nano calcium carbonate, 1-3 parts of liquid nitrile rubber and 0.3-0.7 part of a nano montmorillonite intercalation type hindered amine light stabilizer. By optimizing the formula design, after the prepared insulating material is soaked in 902 # oil at the temperature of 100 DEG C for 24 hours, all performance indexes meet the use requirements of petrochemical engineering and other harsh working conditions, and meanwhile, the insulating material has excellent mechanical properties and processability.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating materials, and specifically to an oil-resistant silane-crosslinked low-smoke halogen-free polyolefin insulating material and a preparation method thereof. The insulating material is particularly suitable for insulating electrical equipment in industries such as petrochemicals and transportation that need to withstand long-term corrosion by 902# oil at 100°C. Background Art

[0002] In industries like petrochemicals and transportation, the insulation materials of electrical equipment are often exposed to high-temperature environments containing specific oils, such as 902# oil. 902# oil, a common industrial oil, significantly increases its corrosiveness to insulating materials at temperatures of 100°C. When ordinary polyolefin insulation comes into contact with 902# oil, the oil molecules easily penetrate the material, causing it to swell and soften. This leads to a sharp drop in key properties like tensile strength and volume resistivity (typically, tensile strength retention is less than 50% and volume change exceeds 5%). In severe cases, this can cause equipment short circuits, failures, and even safety incidents.

[0003] Although existing low-smoke, halogen-free, flame-retardant polyolefin insulation materials have made certain progress in environmental protection (low smoke, halogen-free) and basic flame retardancy (oxygen index ≥30%), they have obvious shortcomings in 902# oil resistance: on the one hand, the compatibility between their base resin and inorganic filler is insufficient, the interfacial bonding force is weak, and oil products can easily penetrate from the interface; on the other hand, there is a lack of targeted oil-resistant reinforcing components, making it difficult to maintain stable mechanical and electrical properties after immersion in 902# oil at 100℃×24h, and they cannot meet the use requirements of harsh working conditions.

[0004] Therefore, the development of a silane cross-linked low-smoke halogen-free polyolefin insulation material that can maintain excellent oil resistance, flame retardancy and electrical properties after being immersed in 902# oil at 100°C for 24 hours has become a technical problem that needs to be urgently solved in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the low-smoke halogen-free polyolefin insulation material in the prior art has poor oil resistance and serious degradation of mechanical and electrical properties after being immersed in 902# oil at 100°C. The purpose of the present invention is to provide an oil-resistant silane cross-linked low-smoke halogen-free polyolefin insulation material and a preparation method thereof, so that the insulation material can still meet the requirements of volume change rate ≤ 2.5%, tensile strength retention rate ≥ 78%, oxygen index ≥ 34%, volume resistivity ≥ 1.8×10 14 Ω·cm and other performance requirements, while taking into account excellent mechanical properties and processing performance.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An oil-resistant silane cross-linked low-smoke halogen-free polyolefin insulation material is prepared from the following raw materials in parts by weight:

[0008]

[0009] The synergistic effect of the components makes the insulating material meet the following requirements after being immersed in 902# oil at 100°C for 24 hours: volume change rate ≤ 2.5%, tensile strength retention rate ≥ 78%, oxygen index ≥ 34%, volume resistivity ≥ 1.8×10 14 Ω·cm.

[0010] Preferably, the antioxidant compound is a compound of a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of 2:1, the nano-titanium dioxide particle size is 20-50 nm, and the nano-calcium carbonate particle size is 40-80 nm.

[0011] The modified montmorillonite is prepared by organic modification with hexadecyltrimethylammonium bromide; specifically, quaternary ammonium salts (such as hexadecyltrimethylammonium bromide) and other organic cations are used for exchange, so that the montmorillonite changes from hydrophilic to lipophilic, making it easier to compound with polymers.

[0012] The nano-montmorillonite intercalated hindered amine light stabilizer is formed by inserting the hindered amine light stabilizer into the nano-montmorillonite interlayer; specifically, the montmorillonite and the HALS (hindered amine light stabilizer) are directly mixed and sheared and dispersed at high temperature in a molten state (such as a twin-screw extruder).

[0013] Preferably, the added amount of the liquid nitrile rubber is 1.5 to 2.5 parts.

[0014] After the insulating material is soaked in 902# oil at 100°C for 24 hours, the elongation at break is ≥170% and the dielectric strength is ≥30kV / mm.

[0015] The functions and synergistic mechanisms of the above components are as follows:

[0016] Matrix resin (EVA and LLDPE): EVA contains polar vinyl acetate groups, which can improve the material's flexibility and compatibility with polar additives; LLDPE provides excellent mechanical properties and processing fluidity. The two are compounded in a ratio of 23-27:33-37, laying a good foundation for the material's basic performance.

[0017] Cross-linked reinforcing component (ethylene-vinyl silane copolymer): forms a three-dimensional network structure through silane cross-linking reaction, significantly improving the structural stability of the material, inhibiting the penetration of oil molecules, and enhancing oil resistance and mechanical strength.

[0018] Compatibilizer (maleic anhydride grafted polyethylene): Its maleic anhydride group can react with the hydroxyl groups on the surface of inorganic fillers (such as magnesium hydroxide and aluminum hydroxide), improve the interfacial bonding strength between the inorganic filler and the polyolefin matrix, and reduce the oil penetration channel.

[0019] Flame retardant system (magnesium hydroxide, aluminum hydroxide, modified montmorillonite): Magnesium hydroxide and aluminum hydroxide are compounded, which decompose when heated, absorb heat and cool down, and release water vapor to dilute the combustible gas, exerting a synergistic flame retardant effect; the layered structure of modified montmorillonite (organically modified with hexadecyltrimethylammonium bromide) forms a nano-barrier layer in the matrix, which not only hinders the diffusion of oil products, but also promotes the formation of a dense carbon layer during combustion, further enhancing the flame retardant effect.

[0020] Oil-resistant reinforcing component (liquid nitrile rubber): Its polar group can form an affinity interface with 902# oil, while enhancing the interfacial bonding force between the inorganic filler and the matrix, and reducing the swelling caused by oil penetration (preferably added in an amount of 1.5 to 2.5 parts for optimal oil resistance).

[0021] Nanofillers (nano-titanium dioxide, nano-calcium carbonate): Nano-titanium dioxide (particle size 20-50nm) can refine the matrix grains and promote the stabilization of the flame-retardant carbon layer; nano-calcium carbonate (particle size 40-80nm) fills the internal pores of the material. The two work together to improve the density of the material and enhance its oil resistance and rigidity.

[0022] Antioxidant and light stabilization system (antioxidant compound, nano-montmorillonite intercalated hindered amine light stabilizer): The antioxidant compound is a compound of hindered phenols and phosphites in a mass ratio of 2:1. The former captures free radicals, and the latter decomposes peroxides, synergistically inhibiting the oxidative degradation of the material; the nano-montmorillonite intercalated hindered amine light stabilizer (formed by inserting the hindered amine light stabilizer into the nano-montmorillonite layer) is resistant to high temperatures and has long-term stability, avoiding performance degradation of the material due to photo-oxidative aging in a high-temperature oil-immersion environment.

[0023] Processing aids (zinc stearate, vinyl trimethoxysilane, long-chain alkyl silane coupling agent): Zinc stearate acts as a lubricant to improve processing fluidity; vinyl trimethoxysilane and long-chain alkyl silane coupling agent work together, cross-linking with the polyolefin matrix at one end and reacting with the hydroxyl group of the inorganic filler at the other end, further strengthening the interfacial bonding and improving processing stability.

[0024] The present invention also provides a method for preparing an oil-resistant silane cross-linked low-smoke halogen-free polyolefin insulating material, comprising the following steps:

[0025] S1. Raw material segmentation pretreatment:

[0026] Dry magnesium hydroxide and aluminum hydroxide at 110-120°C for 5 hours (to remove moisture and avoid bubbles during processing);

[0027] The modified montmorillonite was dried at 90-100°C for 2.5 hours (to remove the residual solvent of the organic modification);

[0028] Nano-TiO2 was dried at 80 °C for 3 h (to avoid agglomeration of nanoparticles);

[0029] Nano calcium carbonate is dried at 80-90°C for 2-3 hours;

[0030] Nano-montmorillonite intercalated hindered amine light stabilizer is dried at 70-80°C for 1-2 hours (to maintain light stabilization activity);

[0031] S2, step-by-step mixing:

[0032] First, add EVA, LLDPE, ethylene-vinyl silane copolymer, and maleic anhydride grafted polyethylene into a high-speed mixer and mix at 80-90°C and 150-200 r / min for 5-8 minutes (to achieve preliminary melt mixing of the base resin); then add dried magnesium hydroxide, aluminum hydroxide, modified montmorillonite, nano-titanium dioxide, nano-calcium carbonate, liquid nitrile rubber, nano-montmorillonite intercalated hindered amine light stabilizer, and zinc stearate in sequence and mix for 5-7 minutes. At the end of the mixing period (8-10 minutes), add the antioxidant compound, vinyl trimethoxysilane, and long-chain alkyl silane coupling agent, raise the temperature to 90-100°C, and mix at 200-300 r / min for 12-15 minutes (to ensure uniform dispersion of the components).

[0033] S3, segmented temperature controlled extrusion:

[0034] A twin-screw extruder with an aspect ratio of (30-40):1 is used for extrusion and granulation according to the following temperature gradient: zone 1 145-155°C, zone 2 155-165°C, zone 3 165-175°C, zone 4 175-185°C, zone 5 185-195°C, die head 185-195°C, screw speed 220-280r / min, die head pressure maintained at 8-12MPa (the temperature difference between zone 4 and zone 5 is controlled at 10±2°C to avoid material degradation). After extrusion, the target insulating material is obtained by water cooling and pelletizing.

[0035] 7. The preparation method according to claim 6, characterized in that in step S2, the antioxidant compound, vinyltrimethoxysilane and long-chain alkylsilane coupling agent are added at the end of the mixing process, 8-10 minutes after the start of mixing of other components.

[0036] 8. The preparation method according to claim 6, characterized in that in step S3, the temperature difference between zone 4 and zone 5 is controlled at 10±2°C, and the die pressure is maintained at 8-12 MPa.

[0037] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0038] A. Excellent oil resistance: The present invention uses the synergistic effects of liquid nitrile rubber to enhance the interfacial bonding force, nanofiller to densify the matrix, and modified montmorillonite to block oil diffusion. After the insulating material is immersed in 902# oil at 100°C for 24 hours, the volume change rate is ≤2.5%, and the tensile strength retention rate is ≥78% (82% in Example 2), which is far superior to existing materials (usually ≤50%).

[0039] B. Outstanding flame retardancy and electrical properties: The flame retardant system of the present invention works synergistically to make the oxygen index ≥34% (35.5% in Example 3), meeting the high flame retardancy requirements; volume resistivity ≥1.8×10 14 Ω·cm (Example 3 reaches 2.2×10 14 Ω·cm), dielectric strength ≥30kV / mm (32kV / mm in Example 3), ensuring insulation reliability in high-temperature oil-immersion environment.

[0040] C. Stable mechanical properties: The optimized ratio of the base resin and the compatibilizer in the present invention makes the material's elongation at break ≥170% (185% in Example 3), and it has both flexibility and rigidity, and can withstand mechanical shocks such as equipment vibration.

[0041] D. Strong process controllability: The segmented pretreatment in the present invention prevents the raw material moisture / impurities from affecting the performance, and the step-by-step mixing and segmented temperature-controlled extrusion (strictly controlling the temperature gradient and rotation speed) ensure that the components are evenly dispersed, which is suitable for industrial production. DETAILED DESCRIPTION

[0042] The present invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the present invention to those skilled in the art. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides a marine irradiated halogen-free, low-smoke, flame-retardant, and oil-resistant polyolefin sheath material, which is made of the following raw materials in parts by weight:

[0045]

[0046]

[0047] The preparation method is as follows:

[0048] S1. Pretreatment: drying magnesium hydroxide and aluminum hydroxide at 110°C for 5 h; drying modified montmorillonite at 90°C for 2.5 h; drying nano-titanium dioxide at 80°C for 3 h; drying nano-calcium carbonate at 80°C for 2 h; drying nano-montmorillonite intercalated hindered amine light stabilizer at 70°C for 1 h.

[0049] S2. Mixing: First add EVA, LLDPE, ethylene-vinyl silane copolymer, and maleic anhydride grafted polyethylene into a high-speed mixer and mix at 80°C and 150 r / min for 5 minutes; then add the remaining components (antioxidant compound, vinyltrimethoxysilane, and long-chain alkyl silane coupling agent are added in the 8th minute), heat to 90°C, and mix at 200 r / min for 12 minutes.

[0050] S3. Extrusion granulation: a twin-screw extruder with a length-to-diameter ratio of 30:1 was used, with the temperatures of zone 1 at 145°C, zone 2 at 155°C, zone 3 at 165°C, zone 4 at 175°C, zone 5 at 185°C, die head at 185°C, screw speed at 220 r / min, die head pressure at 8 MPa, for extrusion granulation.

[0051] Example 2

[0052] This embodiment provides a marine irradiated halogen-free, low-smoke, flame-retardant, and oil-resistant polyolefin sheath material, which is made of the following raw materials in parts by weight:

[0053]

[0054]

[0055] The preparation method is as follows:

[0056] S1. Pretreatment: drying magnesium hydroxide and aluminum hydroxide at 115°C for 5 h; drying modified montmorillonite at 95°C for 2.5 h; drying nano-titanium dioxide at 80°C for 3 h; drying nano-calcium carbonate at 85°C for 2.5 h; drying nano-montmorillonite intercalated hindered amine light stabilizer at 75°C for 1.5 h.

[0057] S2. Mixing: First, mix the base resin at 85°C and 180 r / min for 6 minutes; then add the remaining components (antioxidant compound, vinyltrimethoxysilane, and long-chain alkyl silane coupling agent are added in the 9th minute), raise the temperature to 95°C, and mix at 250 r / min for 13 minutes.

[0058] S3. Extrusion granulation: a twin-screw extruder with a length-to-diameter ratio of 35:1 was used, with the temperature of zone 1 at 150°C, zone 2 at 160°C, zone 3 at 170°C, zone 4 at 180°C, zone 5 at 190°C, die head at 190°C, screw speed at 250 r / min, die head pressure at 10 MPa, for extrusion granulation.

[0059] Example 3

[0060] This embodiment provides a marine irradiated halogen-free, low-smoke, flame-retardant, and oil-resistant polyolefin sheath material, which is made of the following raw materials in parts by weight:

[0061]

[0062] The preparation method is as follows:

[0063] S1. Pretreatment: drying magnesium hydroxide and aluminum hydroxide at 120°C for 5 h; drying modified montmorillonite at 100°C for 2.5 h; drying nano-titanium dioxide at 80°C for 3 h; drying nano-calcium carbonate at 90°C for 3 h; drying nano-montmorillonite intercalated hindered amine light stabilizer at 80°C for 2 h.

[0064] S2. Mixing: First, mix the base resin at 90°C and 200 r / min for 8 minutes; then add the remaining components (antioxidant compound, vinyltrimethoxysilane, and long-chain alkyl silane coupling agent are added in the 10th minute), heat to 100°C, and mix at 300 r / min for 15 minutes.

[0065] S3. Extrusion granulation: a twin-screw extruder with a length-to-diameter ratio of 40:1 was used, with the temperatures of zone 155°C, zone 2 165°C, zone 3 175°C, zone 4 185°C, zone 5 195°C, die 195°C, screw speed 280 r / min, die pressure 12 MPa, and extrusion granulation.

[0066] Performance Testing

[0067] The insulating material prepared in the above embodiment was subjected to performance tests (test standards: oil resistance according to GB / T 1690-2010, oxygen index according to GB / T 2406.2-2009, volume resistivity according to GB / T1410-2006, dielectric strength according to GB / T1408.1-2016). The results are shown in the following table:

[0068] Table 1 Performance test results

[0069]

[0070] From the performance test results, the oil-resistant silane cross-linked low-smoke halogen-free polyolefin insulation materials prepared in Examples 1-3 meet the requirements in all indicators and show excellent comprehensive performance under the synergistic effect of various components.

[0071] In terms of resistance to 902# oil, after immersion at 100°C for 24 hours, the volume change rates of Examples 1-3 were 2.3%, 2.1%, and 1.9%, respectively, all ≤2.5%; the tensile strength retention rates were 78%, 82%, and 83%, respectively, all ≥78%. This is closely related to the three-dimensional network structure formed by the ethylene-vinyl silane copolymer in the formula to enhance stability, the layered nano-barrier layer of the modified montmorillonite to hinder the diffusion of oil, and the synergistic effect of nano-titanium dioxide and nano-calcium carbonate to fill the pores and improve the density, effectively solving the swelling and softening problem of ordinary polyolefin insulation materials under this working condition.

[0072] In terms of flame retardant performance, the oxygen index reaches 34%, 35%, and 35.5% respectively, all ≥34%. This is due to the synergistic flame retardancy of magnesium hydroxide and aluminum hydroxide, the modified montmorillonite promoting the formation of carbon layer, and the stabilizing effect of nanoparticles on the carbon layer, meeting the stringent requirements of low-smoke halogen-free flame retardancy.

[0073] The electrical and mechanical properties are also outstanding, with a volume resistivity of 1.8×10 14 -2.2×10 14 Ω·cm, all ≥1.8×10 14 Ω·cm; elongation at break 170%-185%, dielectric strength 30-32kV / mm, reflecting the good basic properties of EVA and LLDPE matrix, improved interfacial compatibility of maleic anhydride grafted polyethylene, and synergistic optimization of mechanical and electrical properties of each component.

[0074] In summary, this insulating material has balanced advantages in oil resistance, flame retardancy, electrical and mechanical properties through formula design and component synergy, and is fully adapted to the use requirements of insulating materials in harsh working conditions such as petrochemical industry.

[0075] Any matters not described in the present invention are applicable to the prior art.

[0076] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. An oil-resistant silane cross-linked low-smoke halogen-free polyolefin insulation material, characterized in that: It is prepared from the following raw materials in parts by weight: The synergistic effect of the components makes the insulating material meet the following requirements after being immersed in 902# oil at 100°C for 24 hours: volume change rate ≤ 2.5%, tensile strength retention rate ≥ 78%, oxygen index ≥ 34%, volume resistivity ≥ 1.8×10 14 Ω·cm.

2. The insulating material according to claim 1, characterized in that The antioxidant compound is a compound of hindered phenol antioxidant and phosphite antioxidant in a mass ratio of 2:

1. The particle size of the nano titanium dioxide is 20-50 nm, and the particle size of the nano calcium carbonate is 40-80 nm.

3. The insulating material according to claim 1, characterized in that The modified montmorillonite is prepared by organic modification with hexadecyltrimethylammonium bromide; and the nano-montmorillonite intercalation type hindered amine light stabilizer is formed by inserting the hindered amine light stabilizer into the nano-montmorillonite interlayer.

4. The insulating material according to claim 1, characterized in that The added amount of the liquid nitrile rubber is 1.5 to 2.5 parts.

5. The insulating material according to claim 1, characterized in that After the insulating material is soaked in 902# oil at 100°C for 24 hours, the elongation at break is ≥170% and the dielectric strength is ≥30kV / mm.

6. A method for preparing the oil-resistant silane cross-linked low-smoke halogen-free polyolefin insulation material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Raw material segmentation pretreatment: Dry magnesium hydroxide and aluminum hydroxide at 110-120°C for 5 hours; The modified montmorillonite was dried at 90-100°C for 2.5 hours; Nano-titanium dioxide was dried at 80 °C for 3 h; Nano calcium carbonate is dried at 80-90°C for 2-3 hours; The nano-montmorillonite intercalated hindered amine light stabilizer is dried at 70-80°C for 1-2 hours; S2, step-by-step mixing: First, mix EVA, LLDPE, ethylene-vinyl silane copolymer, and maleic anhydride grafted polyethylene at 80-90°C and 150-200 r / min for 5-8 minutes, then add the remaining components in sequence, heat to 90-100°C, and mix at 200-300 r / min for 12-15 minutes; S3, segmented temperature controlled extrusion: A twin-screw extruder with a length-to-diameter ratio of (30-40):1 is used for extrusion and granulation according to the following temperature gradient: zone 1 145-155°C, zone 2 155-165°C, zone 3 165-175°C, zone 4 175-185°C, zone 5 185-195°C, die head 185-195°C, screw speed 220-280r / min, after extrusion, water cooling and pelletizing to obtain the required insulating material.

7. The preparation method according to claim 6, characterized in that In step S2, the antioxidant compound, vinyltrimethoxysilane, and long-chain alkylsilane coupling agent are added at the end of the mixing process, 8-10 minutes after the other components are mixed.

8. The preparation method according to claim 6, characterized in that In step S3, the temperature difference between the fourth zone and the fifth zone is controlled at 10±2° C., and the die pressure is maintained at 8-12 MPa.

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