Preparation method of low-smoke halogen-free fireproof cold-resistant cable

Abstract

The invention discloses a preparation method of a low-smoke halogen-free fireproof cold-resistant cable, which comprises the following steps: S1, extruding an insulating material through a first plastic extruding machine, wrapping the insulating material on a conductor to form an insulating layer, and forming a wire core by the conductor and the insulating layer; s2, twisting the plurality of wire cores to obtain a twisted wire core; and S3, extruding a sheath material through a second plastic extruding machine, wrapping the sheath material on the stranded wire core to form an outer sheath layer, irradiating the cable by adopting an electron irradiation accelerator, and performing cross-linking molding on the outer sheath layer to obtain a finished cable, the sheath material is made of a low-smoke halogen-free flame-retardant material resistant to the temperature of-55 DEG C, and the low-smoke halogen-free flame-retardant material resistant to the temperature of-55 DEG C is composed of the following raw materials: a polyvinyl elastomer, ethylene propylene rubber, hydrogenated nitrile butadiene rubber, methyl vinyl phenyl silicone rubber, hydrogenated base oil, an inorganic flame retardant, methyl-2, 4-dicarbamic acid dimethyl methylphosphonate and a processing aid. And a composite antioxidant. The cable is resistant to low temperature and can meet the requirements of fixed laying and use at the temperature of-55 DEG C.

Description

Technical Field

[0001] The invention relates to the technical field of cable manufacturing, and in particular to a method for preparing a low-smoke, halogen-free, fire-proof and cold-resistant cable. Background Art

[0002] With the widespread application of low-smoke halogen-free flame-retardant materials, low-smoke halogen-free flame-retardant cables have been widely used in petrochemical, nuclear power, solar photovoltaic and other industries. However, in some high-latitude areas, the winter temperature is low and long, and the lowest extreme temperature can reach -50℃ and below. Even in some cold uninhabited areas, due to the needs of new construction projects, it is necessary to consider not only low smoke, halogen-free, flame retardant, but also special working conditions such as ultra-low temperature resistance and oil resistance. However, there is a conflict between the cold resistance index and the flame retardant and oil resistance performance. How to balance these indicators poses new challenges to the cable material formula design and cable structure design. Because some special materials such as fluoroplastics, polyurethane, silicone rubber, polyetheretherketone and other materials are expensive, such as fluoroplastics, polyetheretherketone, silicone rubber, etc., and some are difficult to achieve low smoke halogen-free flame retardant such as polyurethane. Therefore, it is particularly urgent to develop a cable that meets the requirements of low smoke halogen-free flame retardant and low temperature resistance and has the economic value of large-scale use.

[0003] The sheath of the cable plays a key role in ensuring the performance of the cable in the specific use environment. The temperature resistance level of conventional low-smoke halogen-free flame-retardant polyolefin materials is -40℃, and the impact of each degree drop in low temperature on performance is very obvious, for example:

[0004] (1) Material brittleness and reduced conductivity: In low temperature environments, the insulation and sheath materials in wires and cables will become brittle and lose their original softness due to long-term exposure to low temperatures, which reduces the reliability and safety of wires and cables. At the same time, low temperatures will increase the resistance of certain conductive materials, thereby reducing the conductivity of wires and cables. Some metal conductors may become more rigid at low temperatures, affecting the transmission of current.

[0005] (2) Deterioration of insulation performance and fire resistance: In low temperature environments, the insulation performance of insulating materials may decline, resulting in insulation damage between wires and cables, posing potential risks to personal safety. In addition, the flame retardant properties of certain sheath materials and insulating materials may decrease at low temperatures, which may easily cause fires in the event of a failure or short circuit.

[0006] (3) Structural mismatch and change in discharge characteristics: For certain types of cables, such as ethylene propylene rubber (EPR) cables in cold environments, differences in the elastic modulus and free space volume of the EPR insulation layer and the stress control tube (SCT) lead to structural defects between the two, inducing the occurrence of partial discharge inside the terminal. Under low temperature conditions, the starting voltage and extinction voltage of partial discharge are both reduced by more than 40% compared with normal temperature, the breakdown probability is significantly increased, and the discharge spectrum has obvious shape characteristics Changes.

[0007] From the above, it can be seen that the material used for the sheath in the cable is crucial in low temperature environments. Summary of the invention

[0008] The invention provides a method for preparing a low-smoke, halogen-free, fire-proof and cold-resistant cable. The cable of the invention has a low temperature resistance that can meet the requirements of fixed installation and use at a minimum temperature of -55°C.

[0009] The technical solutions to the above technical problems are as follows:

[0010] The preparation method of the low-smoke halogen-free fireproof and cold-resistant cable comprises the following steps:

[0011] S1, extruding an insulating material through a first extruder and wrapping it on a conductor to form an insulating layer, wherein the conductor and the insulating layer constitute a wire core;

[0012] S2, twisting a plurality of wire cores to obtain a twisted wire core;

[0013] S3, extruding the sheath material through a second extruder and wrapping it on the twisted wire core to form an outer sheath layer, and irradiating the cable with an electron irradiation accelerator to cross-link the outer sheath layer to obtain a finished cable;

[0014] The sheath material is low-smoke, halogen-free, flame-retardant and cold-resistant material at -55°C. The low-smoke, halogen-free, flame-retardant and cold-resistant material at -55°C is composed of the following raw materials in mass fraction: 7-18% polyethylene elastomer, 5-10% ethylene-propylene rubber, 5-15% hydrogenated nitrile butadiene rubber, 5-15% methyl vinyl phenyl silicone rubber, 5-10% hydrogenated base oil, 35-45% inorganic flame retardant, 10-15% methyl-2,4-diaminomethylphosphonic acid dimethyl ester, 1-2% processing aid, and 1-3% composite antioxidant.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] First, the present invention uses hydrogenated nitrile butadiene rubber as an adhesive between methyl vinyl phenyl silicone rubber and polyethylene elastomer and ethylene propylene rubber to fuse the resins together well. Due to the presence of phenyl in methyl vinyl phenyl silicone rubber, there is a large steric hindrance, which causes phase separation after mixing with non-polar polyethylene elastomer and ethylene propylene rubber, and it cannot be well fused. By selecting hydrogenated nitrile butadiene rubber as a fusion aid, the butadiene segment on its chain can be well compatible with polyethylene elastomer and ethylene propylene rubber, and the cyanide group with strong electronegativity has good miscibility with the benzene ring structure. Through such blending, the resin can be delicate, smooth and shiny after extrusion, without alligator skin, silver streaks and the like, and can also improve cold resistance, reduce material hardness, and improve resistance to low-temperature embrittlement.

[0017] Second, the selection of methyl-2,4-diaminomethylphosphonic acid dimethyl ester as a flame retardant can promote the early degradation of the base resin and form a continuous and dense carbon layer, which plays a good barrier role, reduces the release of combustible gas inside the carbon layer, and reduces the intensity of gas phase combustion. At the same time, the carbon layer protects the further degradation of the internal matrix and the generation of combustible volatiles, reducing the raw materials required for combustion. In addition, the combustibles participate in carbonization and remain in the condensed phase, effectively reducing the raw materials for generating smoke and heat. At the same time, aluminum hydroxide dehydrates to generate aluminum oxide, which will fill the middle of the carbon layer, effectively supporting the strength of the carbon layer, so that it can be firmly adhered to the cable surface.

[0018] In summary, the cable of the present invention has the characteristics of smooth and round appearance, excellent flame retardant performance, good cold resistance, and good oil resistance. At the same time, the present invention also meets the requirements of low-smoke halogen-free flame retardant bundled A, B and C. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a cross-sectional structural diagram of the low-smoke, halogen-free, fire-proof and cold-resistant cable in the present invention.

[0020] Figure 2 This is a schematic diagram of the sheath extrusion equipment for low-smoke, halogen-free, fire-resistant and cold-resistant cables.

[0021] Figure 3 It is a top view of the talcum powder storage mechanism.

[0022] Markings in the attached drawings:

[0023] Conductor 1, insulation layer 2, lining layer 3, shielding layer 4, inner sheath layer 5, steel wire armor layer 6, outer sheath layer 7, pay-off frame 11, second extruder 12, cooling water tank 13, blow dryer 14, spark machine 15, take-up frame 16, talcum powder storage mechanism 17, input hole 17a, output hole 17b, first protection component 17c, main hopper 18, stirring shaft 19, stirring blade 19a, first auxiliary hopper 20, through hole 20a, second protection component 20b, second auxiliary hopper 21, cover plate 22. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] like Figures 1 to 3 As shown, the present invention provides a method for preparing a low-smoke, halogen-free, fire-proof and cold-resistant cable, and the method for preparing a low-smoke, halogen-free, fire-proof and cold-resistant cable comprises the following steps:

[0026] S1, extruding an insulating material through a first extruder and wrapping it on a conductor 1 to form an insulating layer 2, and the conductor 1 and the insulating layer 2 form a wire core; in this embodiment, the conductor 1 is a tinned stranded copper conductor. The preparation process of the tinned stranded copper conductor is as follows: the copper rod is drawn into bare copper wire by a wire drawing machine, the bare copper wire is electroplated or hot-dip tinned to form a uniform metal tin coating on the surface of the copper wire, and the tinned copper wire is twisted into a cable by a stranding machine to form a finished tinned stranded copper conductor.

[0027] The insulating material is cross-linked polyethylene insulating material, which is extruded onto the tinned copper conductor by an extruder to form an insulating layer 2, ensuring that there is no gap between the conductor 1 and the insulating layer 2.

[0028] S2, untwisting and twisting the plurality of wire cores through a cabling machine to obtain a twisted wire core;

[0029] S3, extrude the sheath material through a second extruder and wrap it on the twisted wire core to form an outer sheath layer 7, and use an electron irradiation accelerator to irradiate the cable to obtain a finished cable after the outer sheath layer is cross-linked and formed; in this step, use an electron accelerator with an energy of 1.8 to 2.5 MeV (preferably 2.0 MeV), a beam current of 10 to 40 mA (preferably 25 mA), and a scanning width of 120 cm to irradiate the cable.

[0030] In this embodiment, preferably, an inner lining layer 3, a shielding layer 4, an inner sheath layer 5, and a steel wire armor layer 6 are further provided between the insulating layer 2 and the outer sheath layer 7. The specific production process is as follows: the inner lining material is extruded onto the twisted wire core by a third extruder 12 to obtain a semi-finished cable core, and the inner lining material wrapped around the twisted wire core is cooled to form the inner lining layer 3. Extrusion is adopted when extruding the inner lining material, and a layer of talcum powder is evenly applied on the twisted wire core by a talcum powder machine to prevent the insulating layer 2 from adhering to the inner lining material when the inner lining material is extruded.

[0031] The inner lining layer 3 is extruded in an extrusion manner. Compared with the traditional method of adding filling ropes and wrapping the inner lining layer, the gaps between the wire cores are filled more densely, which is more conducive to the realization of bundled flame retardant properties and can achieve moisture-proof function. It can be used in some coastal or humid environments.

[0032] In addition, the inner lining layer 3 is extruded by vacuuming to make the inner lining layer 3 and the insulating layer 2 fit tightly, which can effectively prevent the cable core from getting damp and water from entering, and can also effectively prevent air from entering during combustion to improve the fire retardant performance.

[0033] Tinned copper wire is braided on the inner lining layer 3 by a braiding machine to form a shielding layer 4. The sheath material is extruded on the shielding layer 4 by a molding machine, and the sheath material extruded on the shielding layer 4 forms an inner sheath layer 5 after cooling. Galvanized steel wire is arranged on the inner sheath layer 5 in a braided manner by a braiding armoring machine to form a steel wire armor layer 6. The sheath material is extruded and wrapped on the steel wire armor layer 6 by an extruder, and the sheath material extruded on the steel wire armor layer 6 forms an outer sheath layer 7 after cooling. The cable is irradiated by an electron irradiation accelerator to cross-link the inner sheath layer 5 and the outer sheath layer 7 respectively.

[0034] When extruding the inner liner layer 3, the inner jacket layer 5, and the outer jacket layer 7, a medium compression ratio screw is used, and the compression ratio is 1.4-2.0. In this embodiment, the compression ratio is 1.8, and the screw aspect ratio is selected as 25:1. The extrusion temperatures of the third extruder 12 from the first to the ninth zone of the barrel are: 90±10 (barrel zone 1, feeding section), 100±10 (barrel zone 2, feeding section), 120±10 (barrel zone 3, plasticizing section), 130±10 (barrel zone 4, plasticizing section), 140±10 (barrel zone 5, plasticizing section), 150±10 (barrel zone 6, plasticizing section), 160±10 (barrel zone 7, plasticizing section), 170±10 (barrel zone 8, homogenizing section), 170±10℃ (barrel zone 9, homogenizing section), the pushing pressure of the screw in the third extruder 12 is 18-25MPa, and the extrusion speed is 5-120m / min.

[0035] like Figures 2 to 3As shown, when extruding the inner liner 3, the structure of the sheath extrusion equipment used is: including a pay-off frame 11, a third extruder 12, a cooling water tank 13, a blow dryer 14, a spark machine 15, a take-up frame 16, and a talcum powder storage mechanism 17. The following is a detailed description of the various parts of the sheath extrusion equipment and their relationship:

[0036] like Figures 2 to 3 As shown, the pay-off stand 11 is used to release the twisted wire core, that is, the twisted wire core is stored on the pay-off stand 11 in a winding manner. The third extruder 12 extrude the lining material on the twisted wire core to form the lining layer 3, and the third extruder 12 is located downstream of the pay-off stand 11; the cooling water tank 13 cools the lining layer 3, and the cooling water tank 13 is located downstream of the third extruder 12. The blow dryer 14 blows air on the surface of the lining layer 3 to convert the surface of the lining layer 3 cooled by water from a wet state to a dry state, and the blow dryer 14 is located downstream of the cooling water tank 13. The spark machine 15 is used to test whether the lining layer 3 will be broken down under the corresponding electric field, and the spark machine 15 is located downstream of the blow dryer 14. After the lining layer 3 is extruded on the twisted wire core, a semi-finished cable core is obtained, and the semi-finished cable core is wound and taken up by the take-up stand 16, and the take-up stand 16 is located downstream of the spark machine 15.

[0037] like Figures 2 to 3 As shown, talcum powder is contained in the talcum powder storage mechanism 17, and the talcum powder storage mechanism 17 is located between the pay-off frame 11 and the third extruder 12. The talcum powder storage mechanism 17 is provided with an input hole 17a and an output hole 17b for the twisted wire core to pass through. The twisted wire core passes through the input hole 17a and the output hole 17b in sequence. When the twisted wire core passes through the inside of the talcum powder storage mechanism 17, it passes through the talcum powder at the same time, so that the talcum powder is attached to the surface of the insulating layer 2. When the third extruder 12 extrude the inner lining layer 3 on the twisted wire core, the high temperature and high pressure of the third extruder 12 can be avoided to cause the inner lining layer 3 and the insulating layer 2 to adhere together.

[0038] like Figures 2 to 3 As shown, the talcum powder storage mechanism 17 also includes a first protective component 17c for isolating the twisted wire core from the wall surface of the input hole 17a. The first protective component 17c is annular and cooperates with the input hole 17a. The isolation function of the first protective component 17c prevents the twisted wire core from rubbing against the input hole 17a when passing through the input hole 17a, and prevents the wall surface of the input hole 17a from scraping the insulating layer 2, so that the roundness of the insulating layer 2 is maintained. In this embodiment, the first protective component 17c preferably uses a sponge, which has the characteristic of being soft.

[0039] like Figures 2 to 3As shown, the talcum powder storage mechanism 17 includes a main hopper 18, a stirring shaft 19, a stirring blade 19a, and a driver. The main hopper 18 is used to store talcum powder, and the input hole 17a and the output hole 17b are respectively arranged at the two ends of the main hopper 18; the stirring shaft 19 is located in the middle and lower part of the main hopper 18, and the two ends of the stirring shaft 19 are rotatably supported on the main hopper 18 respectively. When the stirring blade 19a works, the talcum powder forms a tumbling state, and the stirring blade 19a is fixed to the stirring shaft 19. The driver (not shown in the figure) drives the stirring shaft 19 to rotate, and the driver is connected to the stirring shaft 19. The driver can be composed of a motor, a reducer and a belt transmission mechanism, or the driver is composed of a motor, a reducer and a gear transmission mechanism.

[0040] like Figures 2 to 3 As shown, the driver drives the stirring shaft 19 to rotate, causing the stirring blades 19a to rotate. The stirring blades 19a cause the talcum powder to tumble, which can make more talcum powder adhere to the surface of the insulating layer 2. At the same time, the talcum powder attached to the surface of the insulating layer 2 will also be more uniform.

[0041] like Figures 2 to 3 As shown, the talcum powder storage mechanism 17 also includes a first auxiliary hopper 20 for receiving powder overflowing from the input hole 17a. The first auxiliary hopper 20 is arranged on the side of the main hopper 18 where the input hole 17a is arranged. Since the talcum powder in the main hopper 18 is in a tumbling state driven by the stirring blade 19a, the talcum powder may overflow to the outside of the main hopper 18 through the input hole 17a. Therefore, in this embodiment, the talcum powder overflowing from the input hole 17a is stored by the first auxiliary hopper 20 to avoid polluting the working environment.

[0042] like Figures 2 to 3 As shown, in this embodiment, the height position of the opening of the first auxiliary hopper 20 is equal to the height position of the opening of the main hopper 18. Therefore, a through hole 20a for the twisted wire core to pass through is provided on the first auxiliary hopper 20. At the same time, the talcum powder storage mechanism 17 also includes a second protective component 20b for isolating the twisted wire core from the wall of the through hole 20a. The second protective component 20b is annular and cooperates with the through hole 20a.

[0043] like Figures 2 to 3 As shown, the isolation effect of the second protective component 20b prevents the twisted wire core from rubbing against the hole wall of the through hole 20a when passing through the through hole 20a, and prevents the hole wall of the through hole 20a from scraping the insulating layer 2, thereby maintaining the roundness of the insulating layer 2. In this embodiment, the second protective component 20b is preferably sponge.

[0044] like Figures 2 to 3As shown, the talcum powder storage mechanism 17 also includes a second auxiliary hopper 21 for receiving powder overflowing from the output hole 17b. The second auxiliary hopper 21 is arranged on the other side of the main hopper 18 where the output hole 17b is arranged. Since the insulating layer with talcum powder on the surface cannot contact with protective components such as sponges, nor can it contact with the wall surface of the output hole 17b, in this embodiment, on the one hand, the opening of the second auxiliary hopper 22 is located below the output hole 17b, and on the other hand, the inner hole of the output hole 17b is set to be at least 2 times larger than the outer diameter of the twisted wire core to avoid scraping of the twisted wire core against the wall surface of the output hole 17b due to factors such as shaking.

[0045] like Figures 2 to 3 As shown, the talcum powder is in a tumbling state driven by the mixing blades 20. Since the talcum powder itself is in a powdery state, it is easy to fly to the outside of the main hopper 18 during the tumbling process, causing pollution to the working environment. Therefore, the talcum powder storage mechanism 17 in this embodiment also includes a cover plate 22, one end of which is hinged to the main hopper 18, and the opening of the main hopper 18 is blocked by the cover plate 22 to prevent the talcum powder from flying around.

[0046] In this embodiment, the sheath material adopts low-smoke halogen-free flame retardant and cold-resistant material at -55°C. The low-smoke halogen-free flame retardant and cold-resistant material at -55°C is composed of the following raw materials in mass fraction: 12% polyethylene elastomer, 8% ethylene propylene rubber, 11% hydrogenated nitrile butadiene rubber, 8% methyl vinyl phenyl silicone rubber, 6% hydrogenated base oil, 40% inorganic flame retardant, 11% methyl-2,4-diaminomethylphosphonic acid dimethyl ester, 2% processing aid, and 2% composite antioxidant.

[0047] The density of the polyethylene-based elastomer is 0.883 g / cm3, the melt index is 2.0 g / 10 min, and the Mooney viscosity of the EPDM rubber is 70 MU. The acrylonitrile content of the hydrogenated nitrile butadiene rubber is 30-35%, the butadiene content is 65-70%, the viscosity is 40-45 at 100°C using the Mooney viscosity ML (1+4) test method, and the degree of hydrogenation is ≥99%. The molar fraction of phenyl in the methyl vinyl phenyl silicone rubber (Ph-si-rubber for short) is 0.05-0.1%. The density of the hydrogenated base oil is 0.84 g / cm 3 Its kinematic viscosity at 40°C is 30-35 mm 2 / s. The inorganic flame retardant is aluminum hydroxide, the diameter D50 of the powder particles is 0.5-1 μm, the methyl-2,4-diaminomethylphosphonic acid dimethyl ester is industrial pure, and the effective content is ≥99%. The processing aid is composed of a cross-linking sensitizer and a lubricant, the weight proportion of the cross-linking sensitizer is 1-2 parts, and the weight proportion of the lubricant is 4-6 parts.

[0048] The composite antioxidant comprises: 2-4 parts of a main antioxidant and 1-3 parts of an auxiliary antioxidant, wherein the main antioxidant is a composition consisting of the following substances: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (1010), β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl (1076), N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl]hydrazine (1024), di(2-methyl-5-tert-butyl-4-hydroxyphenyl) sulfide, and 4,4'-thiobis(6-tert-butyl-3-methylphenol) (300); and the auxiliary antioxidant is didodecyl thiodipropionate and / or di(octadecyl)thiodipropionate.

[0049] The preparation process of low smoke halogen-free flame retardant and cold-resistant -55℃ material is as follows:

[0050] The polyethylene elastomer, ethylene propylene rubber, hydrogenated nitrile rubber, methyl vinyl phenyl silicone rubber, hydrogenated base oil, inorganic flame retardant, methyl-2,4-diaminomethylphosphonic acid dimethyl ester, processing aid, and composite antioxidant according to the above ratio are put into a pressure mixer, and the pressure of the mixer is controlled to be 2.5-3MPa. The mixer is mixed at 160-180℃ to mix the various components evenly to form a mixed soft colloid; the obtained mixed soft colloid is put into a twin-screw extruder for extrusion to obtain a granular material. The granular material is a low-smoke, halogen-free, flame-retardant and cold-resistant material at -55℃.

[0051] The temperature in each zone of the above-mentioned twin-screw extruder is: 130-145 ℃ (feeding section) in the first zone, 130-145 ℃ (feeding section) in the second zone, 130-145 ℃ (plasticizing section) in the third zone, 130-145 ℃ (plasticizing section) in the fourth zone, 130-145 ℃ (plasticizing section) in the fifth zone, 130-145 ℃ (plasticizing section) in the sixth zone, 130-145 ℃ (plasticizing section) in the seventh zone, 130-145 ℃ (plasticizing section) in the eighth zone, 130-145 ℃ (homogenizing section) in the ninth zone, 140-155 ℃ in the die head, and the vacuum pump pressure is set at 0.1-0.2ATM.

[0052] In the present embodiment, the temperature of the twin-screw extruder is: 130° C. (feeding section) in the first zone, 132° C. (feeding section) in the second zone, 134° C. (plasticizing section) in the third zone, 136° C. (plasticizing section) in the fourth zone, 138° C. (plasticizing section) in the fifth zone, 140° C. (plasticizing section) in the sixth zone, 142° C. (plasticizing section) in the seventh zone, 144° C. (homogenizing section) in the eighth zone, 145° C. (homogenizing section) in the ninth zone, 150° C. at the die head, and the vacuum pump pressure is set to 0.15ATM.

[0053] The low-smoke halogen-free fireproof and cold-resistant cable made of the low-smoke halogen-free flame-retardant and cold-resistant -55°C sheath layer 7 in Example 1 was subjected to relevant test experiments with the low-smoke halogen-free flame-retardant and cold-resistant cables currently sold on the market. The test and comparison results are shown in Table 1 below.

[0054] Table 1 Test experiment comparison results

[0055]

[0056]

[0057] (1), as shown in Table 1, it can be seen from the comparison index ① in Table 1 that the volume resistivity index of the commercially available low-smoke halogen-free flame retardant and cold-resistant -55°C is significantly lower than that of the product in Example 1.

[0058] (2) From the comparison indicators ① and ② in Table 1, it can be seen that the insulation resistance of the commercially available low-smoke, halogen-free, flame-retardant and cold-resistant materials is two orders of magnitude lower. When used for single-insulation or unshielded cables, low insulation resistance will bring great hidden dangers to the safe operation of the cables, which may cause the cables to overheat, break down and catch fire, causing safety accidents. At the same time, the low-temperature performance of the commercially available cables at the extreme low temperature of -55℃ is relatively poor in bending and impact resistance, which can easily cause the cables to crack when encountering extreme environments.

[0059] (3) From the comparison index ③ in Table 1, it can be seen that the low-smoke halogen-free flame-retardant and cold-resistant materials on the market are difficult to pass the bundled flame retardant test. This is because there is a conflict between cold resistance and flame retardancy. How to balance the two indicators is very important.

[0060] (4) From the comparison index ④ in Table 1, it can be seen that the mechanical property retention rate of the product in Example 1 after being immersed in mineral oil (70±2℃×4h) is as high as 90%, while the mechanical property retention rate of the commercially available low-smoke halogen-free flame-retardant and cold-resistant cable material is only 50%, which is lower than the material oil resistance limit requirement of 60% and is unqualified. In particular, it cannot be used on oil refining and oil production equipment and other petrochemical projects.

[0061] Example 2

[0062] The difference between Example 2 and Example 1 is that the ratio of low-smoke halogen-free flame retardant and cold-resistant -55°C is as follows:

[0063] In this embodiment, the low-smoke halogen-free flame retardant and cold-resistant -55°C material is composed of the following raw materials in parts by weight: 10% polyethylene elastomer, 10% ethylene propylene rubber, 12% hydrogenated nitrile rubber, 6% methyl vinyl phenyl silicone rubber, 5% hydrogenated base oil, 41% inorganic flame retardant, 13% methyl-2,4-diaminomethylphosphonic acid dimethyl ester, 1% processing aid, and 2% composite antioxidant.

[0064] In addition, in this embodiment, during the preparation of the low-smoke halogen-free flame retardant and cold-resistant -55°C material, the temperature of the twin-screw extruder is not exactly the same as that in Example 1, specifically: the first zone 131°C (feeding section), the second zone 133°C (feeding section), the third zone 134°C (plasticizing section), the fourth zone 135°C (plasticizing section), the fifth zone 137°C (plasticizing section), the sixth zone 140°C (plasticizing section), the seventh zone 141°C (plasticizing section), the eighth zone 143°C (homogenizing section), the ninth zone 145°C (homogenizing section), the die head 148°C, and the vacuum pump pressure is set to 0.2ATM.

[0065] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are used to illustrate the technical solution of the present invention, rather than limiting it, let alone limiting the protection scope of the present invention. Although the invention has been described in detail with reference to the above embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solution from the protection scope of the claims.

Claims

1. A method for preparing a low-smoke, halogen-free, fire-proof and cold-resistant cable, characterized in that: The following steps are involved: S1, extruding an insulating material through a first extruder and wrapping the insulating material on a conductor (1) to form an insulating layer (2), wherein the conductor (1) and the insulating layer (2) constitute a wire core; S2, twisting a plurality of wire cores to obtain a twisted wire core; S3, extruding the sheath material through a second extruder and wrapping it on the twisted wire core to form an outer sheath layer (7), and irradiating the cable with an electron irradiation accelerator to crosslink the outer sheath layer (7) to obtain a semi-finished cable; The sheath material is low-smoke, halogen-free, flame-retardant and cold-resistant material at -55°C. The low-smoke, halogen-free, flame-retardant and cold-resistant material at -55°C is composed of the following raw materials in mass fraction: 7-18% polyethylene elastomer, 5-10% ethylene-propylene rubber, 5-15% hydrogenated nitrile butadiene rubber, 5-15% methyl vinyl phenyl silicone rubber, 5-10% hydrogenated base oil, 35-45% inorganic flame retardant, 10-15% methyl-2,4-diaminomethylphosphonic acid dimethyl ester, 1-2% processing aid, and 1-3% composite antioxidant.

2. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The polyethylene-based elastomer has a density of 0.883 g / cm3 and a melt index of 2.0 g / 10 min.

3. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The Mooney viscosity of the EPDM rubber is 70MU.

4. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The hydrogenated nitrile rubber has an acrylonitrile content of 30-35%, a viscosity of 40-45 at 100° C. using the Mooney viscosity ML (1+4) test method, and a hydrogenation degree of ≥99%.

5. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The molar fraction of phenyl in the methyl vinyl phenyl silicone rubber is 0.05-0.1%.

6. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The density of the hydrogenated base oil is 0.84 g / cm 3 Its kinematic viscosity at 40°C is 30-35mm 2 / s.

7. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The inorganic flame retardant is aluminum hydroxide, and the diameter D50 of the powder particles is 0.5-1 μm.

8. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The methyl-2,4-diaminoformic acid methylphosphonic acid dimethyl ester is industrially pure, and the effective content is ≥99%.

9. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The processing aid is composed of a cross-linking sensitizer and a lubricant, wherein the weight portion of the cross-linking sensitizer is 1-2 parts, and the weight portion of the lubricant is 4-6 parts.

10. The method for preparing the low-smoke, halogen-free, fire-proof and cold-resistant cable according to claim 1, characterized in that: The composite antioxidant comprises: 2-4 parts of a primary antioxidant and 1-3 parts of an auxiliary antioxidant, wherein: The primary antioxidant is a composition consisting of the following substances: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (1010), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (1076), N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine (1024), di(2-methyl-5-tert-butyl-4-hydroxyphenyl)sulfide, 4,4'-thiobis(6-tert-butyl-3-methylphenol) (300); The auxiliary antioxidant is didodecyl thiodipropionate and / or dioctadecyl thiodipropionate.

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