A method for preparing a low-smoke halogen-free flame-retardant cable sheath material

Abstract

This invention relates to a method for preparing a low-smoke, halogen-free flame-retardant cable sheath material, belonging to the field of cable material technology. The invention involves preparing a flame retardant and blending it with polyethylene to obtain the cable sheath material. The phosphorus-silicon-boron cross-linked network present in the flame retardant forms a protective layer during combustion, reducing smoke emission while providing flame retardancy. Low-smoke, halogen-free flame retardancy is achieved through the synergistic effect of phosphorus-silicon-boron. The flame retardant connects phosphorus-oxygen groups and silicon-oxygen groups via benzene rings, buffering polarity abrupt changes. Furthermore, the flame retardant exhibits low polarity overall, enhancing its compatibility with the polyethylene matrix, resulting in a more uniform distribution of the flame retardant within the matrix, superior interfacial bonding, and significantly improved mechanical properties. The long-chain siloxane coating structure in the flame retardant forms a water-repellent layer on the material surface, providing a hydrophobic effect and ensuring that the dielectric properties of the material are not affected in humid environments, thus guaranteeing the stability and safety of power transmission.

Description

Technical Field

[0001] This invention belongs to the field of cable material technology, specifically, it relates to a method for preparing a low-smoke, halogen-free, flame-retardant cable sheath material. Background Technology

[0002] Low-smoke halogen-free flame-retardant cable sheath materials have become key materials in fields such as rail transit, construction, and new energy because they produce less smoke and release no toxic gases such as hydrogen halides when burning.

[0003] While traditional inorganic flame retardants are highly effective in suppressing flame propagation, they rely on high-filler, highly polar metal hydroxides. This polarity mismatch between the metal hydroxide and the low-polarity matrix resin makes it difficult for the flame retardant to disperse uniformly in the polymer matrix, resulting in weak interfacial bonding between the flame retardant and the polymer matrix. This weakens the material's mechanical properties and severely limits its practical application in demanding environments. Phosphorus-silicon-boron composite systems have become a key research focus due to their comprehensive advantages of high efficiency, smoke suppression, and anti-dripping properties. However, phosphorus-silicon-boron composite flame retardants often experience separation during lamination due to polarity mismatch, leading to voids in the formed dense char layer and eventual failure. Furthermore, the components of phosphorus-silicon-boron composite flame retardants contain many polar groups, which differ significantly from the non-polarity of the polyolefin matrix, resulting in uneven dispersion of the flame retardant in the matrix and a tendency for phase separation. Therefore, modifying phosphorus-silicon-boron composite flame retardants has become an effective approach for preparing high-performance cable sheath materials.

[0004] Based on this, the present invention will provide a method for preparing a low-smoke halogen-free flame-retardant cable sheath material. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a low-smoke, halogen-free, flame-retardant cable sheath material, in order to solve the problems mentioned in the background art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a low-smoke halogen-free flame-retardant cable sheath material includes the following steps:

[0008] Step 1: Add 3,4-dihydroxystyrene, phosphorus oxychloride, acid-binding agent, magnesium chloride and acetonitrile to a three-necked flask, attach a condenser and thermometer, turn on magnetic stirring, and react at 55-65℃ for 2-3 hours. After cooling to room temperature, filter out the solid. Remove the solvent from the remaining filtrate by rotary evaporation, wash with water, and then elute by column chromatography to obtain the phosphorus-containing flame retardant unit.

[0009] The second step involves adding phosphorus-containing flame retardant units, trimethoxysilane, platinum catalyst, and toluene to a three-necked flask under nitrogen protection, attaching a condenser and thermometer, turning on magnetic stirring, reacting at 70–90°C for 4–8 hours, cooling to room temperature, and then filtering. The filtrate is then eluted by rotary evaporation and column chromatography to obtain the flame retardant precursor.

[0010] The third step involves adding the flame retardant precursor, boric acid, hydrochloric acid, and tetrahydrofuran into a three-necked flask, attaching a condenser and a thermometer, turning on the magnetic stirrer, and reacting at 60–80°C for 8–12 hours. After the reaction is complete, the mixture is rotary evaporated and washed with ethanol and acetone before drying to obtain the flame retardant.

[0011] Step 4: Add high-density polyethylene, low-density polyethylene, flame retardant, lubricant and antioxidant into a mixer and mix at 150-170°C for 5-15 minutes. Then transfer to a screw extruder for melt extrusion and granulation to obtain low-smoke halogen-free flame-retardant cable sheath material.

[0012] Furthermore, the acid-binding agent in the first step is at least one of triethylamine, 4-dimethylaminopyridine, and N,N-diisopropylethylamine.

[0013] Furthermore, in the first step, the mass fractions of 3,4-dihydroxystyrene, phosphorus oxychloride, acid binder, magnesium chloride, and acetonitrile are 13–16: 18.5–21.5: 25–30: 0.9–2.8: 200–240.

[0014] Furthermore, the platinum catalyst in the second step is at least one of the Speier catalyst and the Karstedt catalyst.

[0015] Furthermore, in the second step, the mass ratio of phosphorus-containing flame retardant unit, trimethoxysilane, platinum catalyst, and toluene is 17–25: 12–18: 0.5–2.5: 120–140.

[0016] Furthermore, in the third step, the mass fraction of hydrochloric acid is 30-38%.

[0017] Furthermore, in the third step, the mass ratio of the flame retardant precursor, boric acid, hydrochloric acid, and tetrahydrofuran is 22–35: 12–13.6: 2.24–2.38: 160–200.

[0018] Furthermore, in the fourth step, the lubricant is at least one of polyethylene wax or oxidized polyethylene wax.

[0019] Furthermore, in the fourth step, the antioxidant is at least one of antioxidant 300, antioxidant 1010, and antioxidant 3114.

[0020] Furthermore, in the fourth step, the mass ratio of high-density polyethylene, low-density polyethylene, flame retardant, lubricant and antioxidant is 65-75:25-35:15-20:1-3:1-3.

[0021] Furthermore, the temperature of melt extrusion in the fourth step is 150–180°C.

[0022] A low-smoke halogen-free flame-retardant cable sheath material is prepared by any of the above preparation steps.

[0023] The beneficial effects of this invention are:

[0024] This invention uses 3,4-dihydroxystyrene and phosphorus oxychloride as raw materials to carry out a phosphoric acid esterification reaction to obtain phosphorus-containing flame retardant units. Then, it uses the phosphorus-containing flame retardant units and trimethoxysilane as raw materials to carry out a hydrosilylation reaction to obtain a flame retardant precursor. Next, it uses the flame retardant precursor and boric acid as raw materials to carry out a hydrolysis condensation reaction to obtain a flame retardant. Finally, it uses high-density polyethylene, low-density polyethylene, flame retardant, lubricant and antioxidant to carry out blending and granulation to obtain a low-smoke halogen-free flame retardant cable sheath material.

[0025] This invention utilizes a phosphorus-silicon-boron crosslinked network formed by hydrolysis and condensation of a flame retardant. By leveraging the synergistic effect of phosphorus-silicon-boron, it enables low-smoke, halogen-free flame-retardant cable sheath materials to achieve highly efficient flame retardancy. During combustion, the phosphorus system promotes char formation, the silicon system stabilizes the char layer, and the boron system enhances the density of the char layer, thereby forming a hard, continuous protective ceramic layer. This protective layer possesses extremely high thermal stability, effectively isolating heat and oxygen, and protecting the internal materials. Simultaneously, the formed barrier char layer significantly inhibits the formation of flammable volatiles, thus significantly reducing smoke production. Furthermore, the material is halogen-free, avoiding the large amounts of dense smoke and toxic corrosive gases produced during the combustion of halogen-based flame retardants. It simultaneously achieves low smoke, flame retardancy, heat resistance, and environmental friendliness.

[0026] The flame retardant of this invention features a structure in which siloxane encapsulates borate and phosphate groups, resulting in an overall low polarity, similar to that of the polyethylene matrix. This leads to better compatibility between the flame retardant and the low-polarity polyethylene matrix, resulting in more uniform dispersion and superior interfacial bonding. Simultaneously, the benzene ring structure in the flame retardant connects the highly polar phosphooxy groups with the non-polar siloxo groups, acting as a polarity bridge. This avoids polarity mismatch issues arising from direct connection, buffers abrupt polarity changes, and forms a stable molecular structure. This ensures that both fully exert their flame-retardant mechanism while also making the internal bonding of the flame retardant molecules tighter, thereby significantly improving the mechanical properties of the low-smoke halogen-free flame-retardant cable sheath material.

[0027] The siloxane coating structure of the flame retardant of this invention forms a water-repellent layer on the material surface, preventing moisture from penetrating the interior of the sheath and achieving a hydrophobic effect. This greatly improves the storage stability and processing stability of the flame retardant, avoids premature decomposition due to high temperature and high humidity environments, and ensures that the dielectric properties of the material are not affected in humid environments, thus guaranteeing the stability and safety of power transmission. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application.

[0029] The raw materials used in this invention are not particularly restricted in terms of their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0030] Example 1:

[0031] A method for preparing a low-smoke halogen-free flame-retardant cable sheath material includes the following steps:

[0032] Step 1: Add 13g of 3,4-dihydroxystyrene, 18.5g of phosphorus oxychloride, 25g of triethylamine, 0.9g of magnesium chloride and 200g of acetonitrile to a three-necked flask, attach a condenser and a thermometer, turn on the magnetic stirrer, and react at 55℃ for 3h. After cooling to room temperature, filter out the solid. Remove the solvent from the remaining filtrate by rotary evaporation, wash with water, and then elute by column chromatography to obtain the phosphorus-containing flame retardant unit.

[0033] The second step involves adding 17g of phosphorus-containing flame retardant unit, 12g of trimethoxysilane, 0.5g of Speier catalyst and 120g of toluene to a three-necked flask under nitrogen protection. A condenser and thermometer are attached, and magnetic stirring is turned on. The mixture is reacted at 70°C for 4 hours and then cooled to room temperature. After filtration, the filtrate is eluted by rotary evaporation and column chromatography to obtain the flame retardant precursor.

[0034] The third step involves adding 22g of flame retardant precursor, 12g of boric acid, 2.24g of hydrochloric acid with a mass fraction of 38% and 160g of tetrahydrofuran into a three-necked flask, attaching a condenser and a thermometer, turning on magnetic stirring, and reacting at 60℃ for 12 hours. After the reaction is completed, the mixture is rotary evaporated and washed with ethanol and acetone before drying to obtain the flame retardant.

[0035] Step 4: Add 65g of high-density polyethylene, 35g of low-density polyethylene, 15g of flame retardant, 1g of polyethylene wax and 1g of antioxidant 300 to a mixer and mix at 150°C for 15 minutes. Then transfer to a screw extruder and melt extrude and granulate at 150°C to obtain low-smoke halogen-free flame-retardant cable sheath material.

[0036] A low-smoke halogen-free flame-retardant cable sheath material is prepared by the above-described preparation steps.

[0037] Example 2:

[0038] A method for preparing a low-smoke halogen-free flame-retardant cable sheath material includes the following steps:

[0039] Step 1: Add 16g of 3,4-dihydroxystyrene, 20g of phosphorus oxychloride, 27.5g of 4-dimethylaminopyridine, 1.85g of magnesium chloride and 220g of acetonitrile to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at 60℃ for 2.5h. After cooling to room temperature, filter out the solid. Remove the solvent from the remaining filtrate by rotary evaporation, wash with water, and then elute by column chromatography to obtain the phosphorus-containing flame retardant unit.

[0040] The second step involves adding 21g of phosphorus-containing flame retardant unit, 15g of trimethoxysilane, 1.5g of Karstedt catalyst, and 130g of toluene to a three-necked flask under nitrogen protection. A condenser and thermometer are attached, and magnetic stirring is turned on. The mixture is reacted at 120°C for 10 hours and then cooled to room temperature. After filtration, the filtrate is eluted by rotary evaporation and column chromatography to obtain the flame retardant precursor.

[0041] The third step involves adding 28.5g of flame retardant precursor, 12.8g of boric acid, 2.36g of hydrochloric acid with a mass fraction of 34%, and 180g of tetrahydrofuran into a three-necked flask, attaching a condenser and a thermometer, turning on magnetic stirring, and reacting at 70℃ for 10 hours. After the reaction is complete, the mixture is rotary evaporated and washed with ethanol and acetone before drying to obtain the flame retardant.

[0042] Step 4: Add 70g of high-density polyethylene, 30g of low-density polyethylene, 17.5g of flame retardant, 2g of oxidized polyethylene wax and 2g of antioxidant 1010 to a mixer and mix at 160°C for 10 minutes. Then transfer to a screw extruder and melt extrude and granulate at 165°C to obtain low-smoke halogen-free flame-retardant cable sheath material.

[0043] A low-smoke halogen-free flame-retardant cable sheath material is prepared by the above-described preparation steps.

[0044] Example 3:

[0045] A method for preparing a low-smoke halogen-free flame-retardant cable sheath material includes the following steps:

[0046] Step 1: Add 16g of 3,4-dihydroxystyrene, 21.5g of phosphorus oxychloride, 30g of N,N-diisopropylethylamine, 2.8g of magnesium chloride and 240g of acetonitrile to a three-necked flask, attach a condenser and a thermometer, turn on magnetic stirring, and react at 65℃ for 2h. After cooling to room temperature, filter out the solid. Remove the solvent from the remaining filtrate by rotary evaporation, wash with water, and then elute by column chromatography to obtain the phosphorus-containing flame retardant unit.

[0047] The second step involves adding 25g of phosphorus-containing flame retardant unit, 18g of trimethoxysilane, 2.5g of Speier catalyst and 140g of toluene to a three-necked flask under nitrogen protection. A condenser and thermometer are attached, and magnetic stirring is turned on. The mixture is reacted at 130°C for 8 hours and then cooled to room temperature. After filtration, the filtrate is eluted by rotary evaporation and column chromatography to obtain the flame retardant precursor.

[0048] The third step involves adding 35g of flame retardant precursor, 13.6g of boric acid, 2.38g of hydrochloric acid with a mass fraction of 30% and 200g of tetrahydrofuran into a three-necked flask, attaching a condenser and a thermometer, turning on magnetic stirring, and reacting at 80℃ for 8 hours. After the reaction is completed, the mixture is rotary evaporated and washed with ethanol and acetone before drying to obtain the flame retardant.

[0049] Step 4: Add 75g of high-density polyethylene, 25g of low-density polyethylene, 20g of flame retardant, 3g of polyethylene wax and 3g of antioxidant 3114 to a mixer and mix at 170°C for 5 minutes. Then transfer to a screw extruder and melt extrude at 180°C and granulate to obtain low-smoke halogen-free flame-retardant cable sheath material.

[0050] A low-smoke halogen-free flame-retardant cable sheath material is prepared by the above-described preparation steps.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 2 is that the flame retardant is replaced with a commercially available phosphate ester flame retardant, while the other raw materials and preparation steps remain unchanged.

[0053] Experimental Example 1

[0054] The materials in Examples 1-3 and Comparative Example 1 were subjected to performance tests. The flame retardancy rating of each group of cable sheath materials was tested according to GB / T19666-2019 "General Rules for Flame Retardant and Fire Resistant Wires, Cables or Optical Cables". The tensile strength of each group of cable sheath materials was tested according to GB / T2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Cables". The surface water contact angle of each group of cable sheath materials was tested according to GB / T32129-2015 "Halogen-Free Low-Smoke Flame Retardant Cable Materials for Wires and Cables". The test results are shown in Table 1.

[0055] Table 1

[0056]

[0057] As can be seen from Table 1, Examples 1-3 have higher flame retardant ratings, tensile strengths, and surface contact angles compared to Comparative Example 1. This indicates that the flame retardant, mechanical, and hydrophobic properties of Examples 1-3 are all superior to those of Comparative Example 1. Combined with Comparative Example 1, it can be seen that the self-made flame retardant can effectively improve the flame retardant, mechanical, and hydrophobic properties of cable sheath materials.

[0058] The descriptions of the above embodiments are merely illustrative of the methods and core ideas of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a low-smoke, halogen-free, flame-retardant cable sheath material, characterized in that, Includes the following steps: Preparation of flame retardant: Phosphoric acid flame retardant unit is obtained by phosphorylation reaction of 3,4-dihydroxystyrene and phosphorus oxychloride under the action of acid binder. Then, flame retardant precursor is obtained by hydrosilylation reaction of phosphoric acid flame retardant unit and trimethoxysilane under the action of platinum catalyst. Finally, flame retardant is obtained by hydrolysis condensation reaction of flame retardant precursor and boric acid. Preparation of low-smoke halogen-free flame-retardant cable sheath material: The low-smoke halogen-free flame-retardant cable sheath material is obtained by blending high-density polyethylene, low-density polyethylene, flame retardant, lubricant and antioxidant, followed by melt extrusion and granulation. In the step of preparing the flame retardant, the mass ratio of 3,4-dihydroxystyrene, phosphorus oxychloride, and acid binder is 13-16:18.5-21.5:25-30; the mass ratio of phosphorus-containing flame retardant unit, trimethoxysilane, and platinum catalyst is 17-25:12-18:0.5-2.5; and the mass ratio of flame retardant precursor and boric acid is 22-35:12-13.

6.

2. The method for preparing a low-smoke halogen-free flame-retardant cable sheath material according to claim 1, characterized in that, The acid-binding agent is at least one of triethylamine, 4-dimethylaminopyridine, and N,N-diisopropylethylamine.

3. The method for preparing a low-smoke halogen-free flame-retardant cable sheath material according to claim 1, characterized in that, The platinum catalyst is at least one of the Speier catalyst and the Karstedt catalyst.

4. The method for preparing a low-smoke halogen-free flame-retardant cable sheath material according to claim 1, characterized in that, The lubricant is at least one of polyethylene wax and oxidized polyethylene wax.

5. The method for preparing a low-smoke halogen-free flame-retardant cable sheath material according to claim 1, characterized in that, The antioxidant is at least one of antioxidant 300, antioxidant 1010, and antioxidant 3114.

6. The method for preparing a low-smoke halogen-free flame-retardant cable sheath material according to claim 1, characterized in that, The mass ratio of high-density polyethylene, low-density polyethylene, flame retardant, lubricant, and antioxidant is 65-75: 25-35: 15-20: 1-3: 1-3.

7. The method for preparing a low-smoke halogen-free flame-retardant cable sheath material according to claim 1, characterized in that, The temperature for melt extrusion is 150–180℃.

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