Halogen-free low-smoke flame-retardant polyolefin insulating material for nuclear-grade cable and preparation method of halogen-free low-smoke flame-retardant polyolefin insulating material

Abstract

The invention discloses a halogen-free low-smoke flame-retardant polyolefin insulating material for a nuclear-grade cable. The halogen-free low-smoke flame-retardant polyolefin insulating material comprises the following raw material components in parts by weight: 30-50 parts of an ethylene-vinyl acetate copolymer, 10-30 parts of a polyolefin plastomer, 10-30 parts of polyethylene, 5-15 parts of a grafting material, 150-180 parts of a flame retardant, 10-20 parts of a flame-retardant synergist, 1-3 parts of a lubricant, 3-5 parts of an antioxidant, 1-2 parts of a light stabilizer and 1-2 parts of a silane coupling agent. Wherein the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is 14%; the polyolefin plastomer is metallocene catalyzed ethylene-octene copolymer POP, the mass fraction of comonomer octene is 15%-20%, the density range is 0.9 g / cm < 3 >-0.92 g / cm < 3 >, and the melting point is greater than 90 DEG C; the polyethylene is one or a mixture of two of ultralow-density polyethylene, low-density polyethylene and linear low-density polyethylene. The preparation method of the insulating material comprises the following steps: putting the raw materials into an internal mixer for mixing, feeding into a double-screw extruder through a double-cone feeding system, and finally extruding and granulating by a single-screw extruder.

Description

Technical Field

[0001] The invention relates to a halogen-free, low-smoke, flame-retardant polyolefin insulating material for nuclear-grade cables and a preparation method thereof, belonging to the technical field of cables. Background Art

[0002] A large amount of ionizing radiation will be generated during the operation of nuclear power plants, including α rays, β rays, γ rays and neutron rays, etc. These rays have high energy and will change the molecular structure of polymer materials, such as chemical bond breaking and cross-linking, which will reduce the performance of the materials, causing hardening, embrittlement, discoloration, etc. At the same time, the temperature in some areas of the nuclear power plant is very high, and there is a heat and oxygen environment. Under the double effect of high temperature and oxygen, the thermal motion of the material molecules intensifies, which will accelerate the aging process of the material, making the insulation and mechanical properties of the cable worse, and may cause cable short circuit and other faults, affecting the normal operation of the nuclear power plant. Therefore, in order to ensure its safe and reliable operation and avoid serious consequences such as nuclear accidents caused by cable damage, the insulation material for nuclear-grade cables should have excellent resistance to long-term thermal oxygen aging, radiation resistance and electrical insulation. Summary of the invention

[0003] The first object of the present invention is to provide a halogen-free, low-smoke, flame-retardant polyolefin insulating material for nuclear-grade cables. The insulated wire prepared by the insulating material can maintain excellent flame retardant properties and electrical insulation properties under radiation under conventional working conditions (resistance to a cumulative dose of 60Co-γ rays of 500kGy / room temperature) and accident working conditions (DBA and AG, resistance to a cumulative dose of 60Co-γ rays of 850kGy / room temperature), with a total cumulative dose of 1350kGy, and under long-term high-temperature thermal oxidation aging, and the wire will not crack even when bent at 20 times the outer diameter.

[0004] The second object of the present invention is to provide a halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables, which can also achieve the purpose of resisting nuclear radiation by using commonly used flame retardants, flame retardant synergists, antioxidants, etc.

[0005] The third object of the present invention is to provide a method for preparing a halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables, which is produced by first mixing and then mixing with a twin-screw extruder to ensure that various additives can be evenly dispersed, avoiding the problem of aggregation and causing local defects.

[0006] To achieve the above object, the technical solution of the present invention is a halogen-free low-smoke flame-retardant polyolefin insulation material for nuclear-grade cables, the raw material components and the weight proportions of each component are respectively:

[0007]

[0008] in,

[0009] The mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is 14%.

[0010] ——The applicant has found through research that, in ethylene-vinyl acetate copolymer EVA, the smaller the mass fraction of vinyl acetate is, the better the regularity of the molecular structure is, the higher the crystallinity is, the more difficult it is for electrons to find a conduction path, and the better the insulation performance and low-temperature resistance are.

[0011] The polyolefin plastomer is a metallocene-catalyzed ethylene-octene copolymer POP, the mass fraction of the comonomer octene is (15-20)%, and the density range is (0.9-0.92) g / cm 3 , melting point>90℃.

[0012] ——The applicant has found through research that compared with polyolefin elastomer POE, polyolefin plastic POP exhibits better electrical insulation performance at high temperatures, and its melting point is generally between 90 and 100°C. However, due to its low melting point, generally below 80°C, polyolefin elastomer POE begins to soften under 90°C water immersion conditions, and its internal molecular structure changes, crystallinity decreases, and insulation performance decreases. In addition, during the synthesis process, polyolefin plastic POP is catalyzed by metallocene, and its physical and mechanical properties are better.

[0013] The polyethylene is one or a mixture of two of ultra-low density polyethylene, low density polyethylene and linear low density polyethylene.

[0014] More preferably, the polyethylene is a mixture of ultra-low density polyethylene and linear low density polyethylene in a mass ratio of 1:(1-2).

[0015] ——The applicant has found through research that ultra-low density polyethylene (ULDPE) has good compatibility with other polyolefin resins. Due to its low crystallinity, it has the ability to accommodate inorganic fillers similar to ethylene-vinyl acetate copolymer (EVA), but its melting point is significantly lower than that of linear low-density polyethylene, between 90 and 100°C. Therefore, under high temperature conditions, its insulation performance is not as good as that of linear low-density polyethylene. The melting point of linear low-density polyethylene is higher than that of low-density polyethylene, generally between 120 and 125°C. Its insulation performance is still relatively excellent under high temperature conditions, but its filling capacity is poor. Therefore, the selection of ultra-low density polyethylene and linear low-density polyethylene for compounding can play a role in performance complementarity to a certain extent.

[0016] The grafted material is one of maleic anhydride grafted PE, maleic anhydride grafted POP, and maleic anhydride grafted EVA.

[0017] Further preferably, the grafted material is maleic anhydride grafted polyethylene, the carrier is linear low-density polyethylene, the maleic anhydride grafting rate is 1.1%, and the melt index is 0.3g / 10min. Its main function is to act as a "bridge" between the polymer and the filler, increase the bonding force of the phase interface, and thus improve the tensile properties of the material. In addition, compared with EVA and POP grafted materials, PE grafted materials have better high temperature resistance.

[0018] The flame retardant is one or a mixture of aluminum hydroxide, magnesium hydroxide, antimony trioxide and melamine cyanurate.

[0019] More preferably, the flame retardant is a mixture of aluminum hydroxide, magnesium hydroxide and antimony trioxide in a mass ratio of (1-3):(1-2):1.

[0020] ——The applicant has found through research that the flame retardant effect of aluminum hydroxide, magnesium hydroxide and antimony trioxide is better, especially for the vertical combustion performance of a single wire. Among them, the decomposition temperature of aluminum hydroxide is lower. After exceeding 200°C, it begins to dehydrate, absorb heat, and dilute the combustible gas, and the crystal water is more than that of magnesium hydroxide. Therefore, in the early stage of combustion, the flame retardant effect of aluminum hydroxide is better; but in the middle and late stages, the flame retardant effect of magnesium hydroxide is better than that of aluminum hydroxide. In addition to dehydration, heat absorption, and dilution of combustible gases, its carbonization effect is better than that of aluminum hydroxide. This is mainly because the residual metal oxides after the decomposition of magnesium oxide will react with zinc borate to form a eutectic reaction, which will enhance the strength of the combustion residue while flame retardant. Antimony trioxide, in addition to mainly playing the role of gas phase flame retardant, can capture highly active free radicals generated by combustion, reduce the concentration of free radicals in the flame area, interrupt the combustion reaction, and promote the formation of a carbonized layer, further enhancing the flame retardant performance. At the same time, antimony trioxide is also a material with excellent nuclear radiation resistance. It can not only reduce the damage of nuclear radiation to the main structure of polymer materials, but also improve the problem of poor carbonization of materials after irradiation by electron accelerators. The reason why melamine cyanurate was not selected is that on the one hand, the nitrogen oxides and hydrogen cyanide produced by its high-temperature decomposition will affect the toxicity index of the insulating material, and on the other hand, it will increase the conductivity of the insulating material, affecting the electrical insulation performance at high temperatures.

[0021] The flame retardant synergist is one of zinc borate, carbon nanotubes and hydrotalcite.

[0022] More preferably, the flame retardant synergist is zinc borate.

[0023] ——The applicant has found through research that zinc borate has both flame retardant and nuclear radiation resistance properties. On the one hand, it undergoes thermal decomposition at high temperatures, releasing crystal water, reducing the temperature of the combustion surface and diluting the oxygen in the air. At the same time, the decomposition forms a B2O3 glassy film that covers the polymer, playing a role in heat insulation and oxygen barrier. On the other hand, the boron atoms in zinc borate have a good effect on absorbing neutrons. In a nuclear radiation environment, boron atoms can effectively capture neutrons, thereby reducing the damage of neutrons to the material matrix, just like setting up a "protective wall" in front of the material to intercept neutrons. The reason why carbon nanotubes or hydrotalcite were not selected is mainly because carbon nanotubes have a certain conductivity, which will affect the electrical insulation performance of the material, and hydrotalcite is a nano-level flame retardant. When added in large quantities, it is easy to agglomerate and have poor interface bonding problems, affecting the physical and mechanical properties of the material.

[0024] The lubricant is one or a mixture of two of polyethylene wax, PPA, zinc stearate, oleic acid amide and EBS.

[0025] More preferably, the lubricant is a mixture of polyethylene wax and zinc stearate in a mass ratio of 1:1, and the combination of the two plays the role of both internal and external lubrication.

[0026] The antioxidants are at least two of 1010, 168, DLTP, KY405, 412S and 1024.

[0027] More preferably, the antioxidant is a mixture of 1010, 412S, DLTP and 1024 in a mass ratio of (1-2):(1-2):(1-3):1.

[0028] ——The applicant has found through research that 412S is a high temperature resistant long-term antioxidant, which is beneficial to the resistance of polyolefin materials to long-term high temperature thermal oxidation aging. In addition, antioxidants will inhibit the occurrence of secondary cross-linking reactions of polyolefin materials in radiation environments to a certain extent.

[0029] The light stabilizer is one or a mixture of two of a hindered amine light stabilizer and a benzotriazole ultraviolet absorber.

[0030] The hindered amine light stabilizer may be UV-944 or UV-770 (ie, UV-770DF, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate), and the benzotriazole ultraviolet absorber may be UV-329 or UV-326.

[0031] More preferably, the light stabilizer is a mixture of a triazole ultraviolet absorber (UV-329) and a hindered amine light stabilizer (UV-770) in a mass ratio of 1:1.

[0032] ——The applicant has found through research that the combination of light stabilizers and antioxidants can complement each other in the process of inhibiting or delaying the light aging and heat aging of polymer materials, producing a synergistic effect. Light stabilizers can capture and inactivate peroxide free radicals generated by antioxidants, thereby preventing them from further decomposing and generating free radicals, while antioxidants can capture these free radicals to form stable compounds, thereby protecting polymer materials from oxidation and light aging. At the same time, light stabilizers can inhibit the secondary cross-linking reaction caused by nuclear radiation to a certain extent.

[0033] The preparation method of the above-mentioned halogen-free low-smoke flame-retardant polyolefin insulation material for nuclear-grade cables comprises the following steps:

[0034] The raw materials are weighed by mass and put into the internal mixer for mixing. When the material temperature reaches 150-155°C, the material is discharged, passed through a double-cone feeding system to a twin-screw extruder, and finally enters a single-screw extrusion granulation, air-cooled and packaged to obtain the finished material.

[0035] The temperature of the double-cone feeding system is set to 90-100°C, the temperature of zones 1 to 7 of the twin-screw extruder is set to 90-100°C from zone 1 to zone 2, and 80-90°C from zone 3 to zone 7; the temperature of the single-screw extruder is set to 110-115°C from zone 1, 120-125°C from zone 2, 125-130°C from zone 3, 130-135°C from the die head, and 130-135°C from the hot cutting die surface.

[0036] The raw material components and weight proportions of the halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables are preferably:

[0037]

[0038]

[0039] The raw material components and weight proportions of the halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables are preferably:

[0040] The raw material components and weight proportions of the halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables are optimally as follows:

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The raw materials used in the invention are simple, widely available, and reasonably proportioned, and the synergistic effect between the components is significant, so that good processing performance and excellent physical and chemical properties can be obtained, and the requirements of industrial mass production can be met.

[0043] The invention introduces flame retardants, flame retardant synergists, antioxidants and light stabilizers into the polyolefin substrate, so that the polyolefin material can still maintain excellent electrical insulation performance, flame retardant performance and bending crack resistance performance after long-term high-temperature aging and nuclear radiation damage. DETAILED DESCRIPTION

[0044] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0045] The raw materials in the examples are all commercially available.

[0046] The raw material information in each implementation is shown in Table 1 below.

[0047] Table 1:

[0048]

[0049] In each example, the composition of the halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables is shown in the following table, wherein parts represent parts by weight.

[0050] Table 2 below is the formulation of Examples 1 to 11. Table 3 below is the formulation of Comparative Examples 1 to 11.

[0051] The preparation methods of the insulating materials of Examples 1 to 11 and Comparative Examples 1 to 11 are all:

[0052] The raw materials are weighed by mass and put into the internal mixer for mixing. When the material temperature reaches 150-155°C, the material is discharged, passed through a double-cone feeding system to a twin-screw extruder, and finally enters a single-screw extrusion granulation, air-cooled and packaged to obtain the finished material.

[0053] The double-cone feeding temperature is set to 90-100°C, the temperature of zones 1 to 7 of the twin-screw extruder is set to 90-100°C from zone 1 to zone 2, and 80-90°C from zone 3 to zone 7; the temperature of the single-screw extruder is set to 110-115°C from zone 1, 120-125°C from zone 2, 125-130°C from zone 3, 130-135°C from the die head, and 130-135°C from the hot cutting die surface.

[0054] The test results of the above-mentioned Examples 1 to 11 after irradiation are shown in Table 4. The test results of the above-mentioned Comparative Examples 1 to 11 after irradiation are shown in Table 5 (the reference standard is the same as that of the examples).

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061] It can be seen from the test data of Examples 1, 2 and Comparative Example 1 that as the amount of polyolefin plastomer POP increases, the low-temperature resistance, mechanical properties, electrical insulation properties at high temperatures, and nuclear radiation resistance are improved, mainly because the molecular chain of the polyolefin plastomer POP is relatively regular and has a higher degree of crystallinity, so that its molecular structure can more effectively transfer stress when subjected to external force, thereby exhibiting better mechanical properties; the polyolefin plastomer POP molecular chain has good flexibility, and the molecular chain can still maintain a certain degree of activity in a low-temperature environment, while the EVA molecular chain contains polar acetate groups, the molecular chain has a strong force, the molecular chain activity is more restricted at low temperatures, and the flexibility decreases significantly, so the amount of polyolefin plastomer POP increases, and the low-temperature resistance is improved; the polyolefin plastomer POP is mainly composed of carbon-hydrogen bonds, and its carbon-carbon bonds and carbon-hydrogen bonds are relatively stable in a nuclear radiation environment, and the presence of vinyl acetate groups in the EVA molecules makes the ester bonds more easily broken under the action of nuclear radiation.

[0062] It can be seen from the test data of Example 3 and Comparative Examples 2 and 3 that too much or too little maleic anhydride grafted polyethylene material has a significant impact on the mechanical properties. This is mainly because too little is difficult to fully improve the interaction between the polyolefin resin and other materials. When subjected to external force, interface separation is likely to occur inside the material, affecting the mechanical properties; while too much will lead to agglomeration problems between the molecular chains of the material, causing stress concentration, making it easy for the material to crack at the agglomeration during the force process, resulting in a decrease in mechanical properties.

[0063] From the test data of Examples 2, 4, 5, 6 and Comparative Examples 4 and 5, it can be seen that ① the amount of antimony trioxide is reduced, the nuclear radiation resistance of the material is reduced, and after nuclear radiation, the mechanical properties, flame retardant properties and electrical insulation properties of the material are all reduced. This is mainly because antimony trioxide can absorb and scatter radiation energy in the material. When the material is subjected to nuclear radiation, antimony trioxide can reduce the damage of radiation to the main structure of the material through its own physical and chemical properties. After the amount is reduced, the effect of resisting radiation energy is reduced, resulting in performance degradation; ② the amount of antimony trioxide is reduced, and the vertical combustion performance of a single insulated wire core is reduced. This is mainly because antimony trioxide can capture highly active free radicals generated by combustion in the gas phase, reduce the concentration of free radicals in the flame area, and thus interrupt the combustion reaction.

[0064] It can be seen from the test data of Examples 4, 7 and Comparative Examples 6, 7, and 8 that as the amount of zinc borate decreases, the radiation resistance of the material deteriorates. This is mainly because zinc borate is a neutron capture agent. When the amount is reduced, the material will be more susceptible to direct impact from neutron radiation. Neutrons will interact with atoms in the material, destroying the chemical bonds and crystal structure of the material, resulting in a decrease in the performance of the material, thereby reducing the radiation resistance of the material.

[0065] From the test data of Examples 3, 8, 9, 10, 11 and Comparative Example 9, it can be seen that when the amount of antioxidant is reduced, the crosslinking degree is improved, and the electrical properties are slightly improved, but the material's resistance to nuclear radiation is reduced to a certain extent. This shows that the antioxidant can inhibit the influence of nuclear radiation degradation to a certain extent; however, when the amount of antioxidant is too large, the crosslinking degree of the material decreases greatly under the same irradiation dose, which will have a reverse effect on the mechanical properties and low temperature resistance. When the amount of antioxidant 412S is reduced, the material's resistance to high temperature and long-term aging performance deteriorates significantly, especially the rate of change of the material's electrical properties and mechanical properties decreases significantly, which shows that antioxidant 412S can still maintain good antioxidant activity under high temperature conditions.

[0066] It can be seen from the test data of Example 3 and Comparative Examples 10 and 11 that as the amount of light stabilizer is reduced, the material's resistance to thermal oxidation aging and radiation resistance both decrease, which is mainly reflected in the rate of change of mechanical properties. This is mainly because the light stabilizer can capture free radicals generated by thermal oxidation and inhibit the chain reaction of oxidation. At the same time, the light stabilizer can absorb or dissipate radiation energy and reduce the generation of free radicals. After the amount is reduced, this inhibitory effect becomes weaker, the chemical bonds of the material are easily destroyed, and the performance is reduced.

[0067] The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables of Examples 4 and 7 of the present invention has better comprehensive performance of raw materials. The 2.5 square insulated wire prepared by using this material still has good electrical insulation performance and flame retardant performance after high-temperature aging at 165°C×21 days and 60Co-γ ray radiation (cumulative dose of 1350kGy / room temperature), and the wire remains intact without cracks after bending.

[0068] By comparing the insulating materials of the embodiments of the present invention and the comparative examples, it is found that antimony trioxide, zinc borate, antioxidant, light stabilizer and other materials all have certain anti-nuclear radiation performance, and after compounding, the anti-nuclear radiation performance is better.

[0069] The above embodiments of the present invention are only for explaining the principle and efficacy of the present invention, and are not intended to limit the present invention. Any person familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by a person with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables, characterized in that The weight parts of the raw material components and each component are respectively: in, The mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer is 14%; The polyolefin plastomer is a metallocene-catalyzed ethylene-octene copolymer POP, the mass fraction of the comonomer octene is 15% to 20%, and the density range is 0.9g / cm 3 ~0.92g / cm 3 , melting point>90℃; The polyethylene is one or a mixture of two of ultra-low density polyethylene, low density polyethylene and linear low density polyethylene.

2. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1, characterized in that The grafted material is one of maleic anhydride grafted PE, maleic anhydride grafted POP, and maleic anhydride grafted EVA; The flame retardant is one or a mixture of aluminum hydroxide, magnesium hydroxide and antimony trioxide; The flame retardant synergist is one of zinc borate, carbon nanotubes and hydrotalcite; The lubricant is one or a mixture of two of polyethylene wax, PPA, zinc stearate, oleamide, and EBS; The antioxidant is at least two of 1010, 168, DLTP, KY405, 412S, and 1024; The light stabilizer is one or a mixture of two of a hindered amine light stabilizer and a benzotriazole ultraviolet absorber.

3. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1 or 2, characterized in that The polyethylene is a mixture of ultra-low density polyethylene and linear low density polyethylene in a mass ratio of 1: (1-2).

4. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1 or 2, characterized in that The grafted material is maleic anhydride grafted polyethylene, the carrier is linear low-density polyethylene, the maleic anhydride grafting rate is 1.1%, and the melt index is 0.3g / 10min.

5. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1 or 2, characterized in that The flame retardant is a mixture of aluminum hydroxide, magnesium hydroxide and antimony trioxide in a mass ratio of (1-3):(1-2):1; and the flame retardant synergist is zinc borate.

6. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1 or 2, characterized in that The lubricant is a mixture of polyethylene wax and zinc stearate in a mass ratio of 1:

1.

7. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1 or 2, characterized in that The antioxidant is a mixture of 1010, 412S, DLTP and 1024 in a mass ratio of (1-2):(1-2):(1-3):

1.

8. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 2, characterized in that the hindered amine light stabilizer is UV-944 or UV-770; and the benzotriazole ultraviolet absorber is UV-329 or UV-326.

9. The halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables according to claim 1 or 2, characterized in that The light stabilizer is a mixture of UV-329 and UV-770 in a mass ratio of 1:

1.

10. A method for preparing a halogen-free, low-smoke, flame-retardant polyolefin insulation material for nuclear-grade cables, characterized by the steps of: Weigh any raw material of claims 1 to 9 by weight and put it into an internal mixer for mixing. When the material temperature reaches 150 to 155° C., discharge the material, pass through a double-cone feeding system to a twin-screw extruder, and finally enter a single-screw extruder for extrusion granulation, air-cooling and packaging to obtain a finished product. The temperature of the double cone feeding system is set at 90-100°C; The temperature of the twin-screw extruder from zone 1 to zone 7 is set to 90-100°C from zone 1 to zone 2 and 80-90°C from zone 3 to zone 7; The temperature of the single screw extruder is set to 110-115°C in zone 1, 120-125°C in zone 2, 125-130°C in zone 3, 130-135°C in the die head, and 130-135°C in the hot cutting die surface.

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