A flame-retardant insulated cable conduit and its preparation method

Abstract

This invention discloses a flame-retardant insulated cable conduit and its preparation method, relating to the technical field of PVC cable conduits. The flame-retardant insulated cable conduit comprises 80-100 parts PVC, 3-4.5 parts heat stabilizer, 5-8 parts CPE, 0.4-0.8 parts stearic acid, 1.5-2 parts titanium dioxide, 15-20 parts ultrafine calcium carbonate, and 5-8 parts composite flame retardant. The composite flame retardant is prepared by coating an inorganic flame retardant with a long-chain alkyl polyphosphate ester. By using a long-chain alkyl polyphosphate ester to modify the inorganic flame retardant, compared to ordinary inorganic flame retardants, it exhibits superior flame-retardant and smoke-suppressing effects at the same addition amount. This not only significantly reduces the amount of inorganic flame retardant added but also improves the thickness uniformity and mechanical properties of the resulting cable conduit.

Description

Technical Field

[0001] This invention relates to the technical field of PVC cable pipes, and in particular to a flame-retardant insulated cable pipe and its preparation method. Background Technology

[0002] With the rapid development of industries such as power and communications, the performance requirements for cable conduits, as an important component for cable and wire protection, are becoming increasingly stringent. Because cable conduits need to possess good mechanical strength, corrosion resistance, insulation properties, and flame retardant properties to ensure the safe operation of cables and wires in complex environments, polyvinyl chloride (PVC) has become one of the main materials for cable conduits due to its excellent electrical insulation, chemical corrosion resistance, processing performance, and cost advantages.

[0003] Because PVC molecules contain chlorine, chlorine can absorb some heat during combustion and decompose into harmful hydrogen chloride gas, which absorbs moisture and reduces the concentration of flammable gases. However, during conventional processing, various plasticizers and other additives are added, which can actually lower the oxygen index of the product. This means that conventional PVC cable pipes cannot meet the flame retardant requirements. At the same time, they also release a lot of black smoke and harmful gases during combustion, resulting in poor environmental performance.

[0004] In existing technologies, most manufacturers add flame retardants during processing to improve the flame-retardant performance of PVC cable pipes. However, traditional inorganic flame retardants, such as aluminum hydroxide and magnesium hydroxide, have low flame-retardant efficiency, requiring high dosages to meet flame-retardant requirements. This not only significantly increases material costs but also leads to increased material density and decreased flexibility. Excessive filling can also affect processing flowability, making production difficult. While adding highly efficient halogenated flame retardants can achieve good flame-retardant effects with smaller amounts, their use does not reduce smoke during cable pipe combustion and poses environmental and health risks. Therefore, developing a flame retardant that requires a small dosage, ensures the mechanical properties of PVC cable pipes, and has certain environmental benefits is of great significance and has broad application prospects for the development of PVC cable pipes. Summary of the Invention

[0005] In order to improve the flame retardant properties of PVC cable pipes, reduce the amount of smoke generated during combustion, and improve the environmental performance of PVC cable pipes, this application provides a flame retardant insulated cable pipe and its preparation method.

[0006] Firstly, the flame-retardant insulated cable conduit provided in this application adopts the following technical solution:

[0007] A flame-retardant insulated cable conduit comprises the following raw materials in parts by weight:

[0008] PVC: 80-100 parts;

[0009] Heat stabilizer: 3-4.5 parts;

[0010] CPE: 5-8 parts;

[0011] Stearic acid: 0.4-0.8 parts;

[0012] Titanium dioxide: 1.5-2 parts;

[0013] Ultrafine calcium carbonate: 15-20 parts;

[0014] Composite flame retardant: 5-8 parts;

[0015] The composite flame retardant is prepared by coating an inorganic flame retardant with a long-chain alkyl polyphosphate ester. The chemical formula of the long-chain alkyl polyphosphate ester is as follows:

[0016] ;

[0017] In long-chain alkyl polyphosphates, R1 is an ethyl group and R2 is a C8-C14 straight-chain alkyl group.

[0018] By adopting the above technical solution, the inorganic flame retardant is modified by coating it with long-chain alkyl polyphosphates. Firstly, this reduces the surface energy of the inorganic flame retardant, improving its dispersibility in PVC and enhancing its flame-retardant and smoke-suppressing effects. Secondly, the introduced polyphosphate groups, when heated during combustion, synergistically dehydrate and carbonize the PVC surface with the inorganic flame retardant. Compared to ordinary inorganic flame retardants, this results in superior flame-retardant and smoke-suppressing effects at the same dosage, improving the environmental friendliness of PVC cable conduits and reducing production costs. Furthermore, the introduced long-chain alkyl groups can create an entanglement effect with PVC segments, forming a network structure that improves the overall mechanical strength of the PVC cable conduit to some extent.

[0019] Optionally, the preparation of the composite flame retardant includes the following steps:

[0020] First, the long-chain alkyl polyphosphate was diluted to a concentration of 1% with deionized water. Then, an inorganic flame retardant was added under continuous stirring, wherein the mass ratio of the inorganic flame retardant to the diluted solution was 1:(1.5-3). The mixture was then heated to 70-75℃ and stirred continuously for 1-2 hours. After the reaction was completed, the mixture was filtered under reduced pressure while hot and the filter residue was dried under vacuum to obtain the composite flame retardant.

[0021] By adopting the above technical solution, the long-chain alkyl polyphosphate is diluted to a lower concentration using deionized water in advance. Combined with high-temperature stirring, the viscosity and reactivity of the long-chain alkyl polyphosphate can be effectively balanced. This ensures that the inorganic flame retardant can be fully dispersed in the diluted solution while improving the coating rate of the long-chain alkyl polyphosphate. This helps to prevent the inorganic flame retardant from agglomerating due to excessively high solution viscosity, which could lead to excessively large coated particle size and affect the subsequent mixing of the composite flame retardant with PVC.

[0022] Optionally, the preparation of the long-chain alkyl polyphosphate includes the following steps:

[0023] A1. Preheat phosphorus oxychloride to 10°C using an oil bath, maintain vacuum and slowly add 1,6-hexanediol dropwise while stirring rapidly and controlling the reaction temperature to not exceed 15°C. After the dropwise addition is complete, maintain the temperature and continue the reaction for 1-1.5 hours to obtain the first intermediate.

[0024] A2. Add long-chain alkyl alcohols in batches to the first intermediate, wherein the long-chain alkyl alcohols are one of the straight-chain monohydric alcohols of C8-C14, and gradually raise the temperature to 60-63°C while maintaining a vacuum. After reaching the temperature, continue the reaction for 0.5-1h. Then add ethanol in batches and raise the temperature to 85-90°C. Maintain the temperature and continue the reaction for 1-1.5h to obtain the second intermediate.

[0025] A3. The second intermediate was subjected to vacuum distillation. The resulting solid product was thoroughly washed, and the pH was adjusted to 6.5-7. After vacuum dehydration and drying, long-chain alkyl polyphosphates were obtained.

[0026] By adopting the above technical solution, the side reaction of the chlorination reaction of phosphorus oxychloride can be effectively suppressed, which is beneficial to improving the yield of long-chain alkyl polyphosphates.

[0027] Optionally, R1 in the long-chain alkyl polyphosphate is an ethyl group, and R2 is a C12 straight-chain alkyl group.

[0028] By adopting the above technical solution, when R2 of the long-chain alkyl polyphosphate is a C12 straight-chain alkyl group, the resulting composite flame retardant has excellent flame retardant and smoke suppression effects and mechanical property improvement effects. At the same time, the adverse effects on PVC melt processing are low and within an acceptable range, and the resulting PVC cable pipe has better overall performance.

[0029] Optionally, the inorganic flame retardant includes at least one of aluminum hydroxide, magnesium hydroxide, or zinc stannate.

[0030] By adopting the above technical solution, the inorganic flame retardant is not only non-toxic and environmentally friendly, but also has good flame retardant and smoke suppression effects through heat absorption and insulation effects. It does not produce harmful gases, can reduce the amount of CO generated during combustion, and can also play a certain role in filling and reinforcing. With appropriate addition, it is beneficial to work with fillers to further improve the mechanical properties of PVC cable pipes.

[0031] Optionally, the ultrafine calcium carbonate needs to undergo surface treatment before being mixed and added, including the following steps:

[0032] B1. First, use anhydrous ethanol to ultrasonically disperse ultrafine calcium carbonate into a suspension with a solid content of 20%, heat to 83-85℃, add 5% titanate coupling agent, stir continuously for 2-3 hours, filter under reduced pressure and dry under vacuum to obtain ultrafine calcium carbonate with coupling agent surface treatment.

[0033] By adopting the above technical solution, the surface treatment of ultrafine calcium carbonate with titanate coupling agent can effectively improve the surface properties of ultrafine calcium carbonate, enabling it to be fully dispersed in PVC. At the same time, it is also beneficial to further enhance the interfacial adhesion between the filler and PVC, thereby improving the mechanical properties of PVC cable pipes.

[0034] Optionally, the titanate coupling agent is a novel alkoxy-type titanate coupling agent.

[0035] By adopting the above technical solution, the new alkoxy titanate coupling agent can not only significantly improve the dispersibility, interfacial adhesion and processing performance of ultrafine calcium carbonate in PVC melt, but also introduce multiple reaction sites on the surface of ultrafine calcium carbonate, which is beneficial for subsequent grafting modification of ultrafine calcium carbonate.

[0036] Optionally, the surface treatment of the ultrafine calcium carbonate may further involve graft modification, including the following steps:

[0037] B2. Ultrafine calcium carbonate, which has been surface-treated with a coupling agent, is ultrasonically dispersed again in anhydrous ethanol into a suspension with a solid content of 20%. Then, it is heated to 75-78°C under an inert atmosphere. Methyl methacrylate and azobisisobutyronitrile are added dropwise at a mass ratio of 100:1, wherein the amount of methyl methacrylate added is twice the mass of the ultrafine calcium carbonate. The reaction is carried out under an inert atmosphere and stirred continuously for 5-6 hours. After high-speed centrifugation and filtration, it is thoroughly washed and vacuum dried to obtain surface-grafted modified ultrafine calcium carbonate.

[0038] By adopting the above technical solution, methyl methacrylate groups can be grafted onto the surface of ultrafine calcium carbonate treated with coupling agent via free radical grafting. This allows the methyl methacrylate groups to disperse uniformly with the ultrafine calcium carbonate, further reducing friction between the mixed powders and lowering the shear force and temperature required for PVC plasticization. This not only helps reduce melt flow resistance and improve the uniformity of molding dimensions, but also effectively regulates the balance between melt flowability and melt strength modulus, and solves the problem of increased melt viscosity caused by the long-chain alkyl polyphosphates in composite flame retardants.

[0039] Optionally, the heat stabilizer is a calcium-zinc stabilizer, and the titanium dioxide is rutile titanium dioxide.

[0040] By adopting the above technical solutions, calcium-zinc stabilizers are more environmentally friendly than traditional lead-salt heat stabilizers. They not only provide better stabilization and require less dosage, but also reduce the generation of black smoke or toxic gases when PVC cable pipes are burned. Rutile titanium dioxide has excellent ultraviolet shielding properties, which helps improve the appearance and weather resistance of PVC cable pipes, allowing them to maintain good performance over time and extending their service life.

[0041] Secondly, the method for preparing a flame-retardant insulated cable tube provided in this application adopts the following technical solution.

[0042] A flame-retardant insulated cable conduit includes the following steps:

[0043] First, weigh out PVC, heat stabilizer, CPE, stearic acid and titanium dioxide in the following proportions by weight. Mix them thoroughly in a high-speed mixer heated to 80-90℃ for 10-20 minutes. Then, transfer them to a low-speed mixer to cool. After cooling, add ultrafine calcium carbonate and composite flame retardant, and continue mixing at room temperature for 5-10 minutes to obtain extrusion masterbatch. Finally, melt and extrude the extrusion masterbatch to obtain a flame-retardant insulated cable pipe.

[0044] By adopting the above technical solutions, the production process is simple, the required equipment investment is small, and the cost is low, which is conducive to large-scale industrial production.

[0045] In summary, the technical solution of this application has at least one of the following beneficial effects:

[0046] 1. By using long-chain alkyl polyphosphates to coat and modify inorganic flame retardants, compared with ordinary inorganic flame retardants, they have better flame retardant and smoke suppression effects at the same addition amount. This not only greatly reduces the amount of inorganic flame retardant to be added, but also improves the thickness uniformity and mechanical properties of the resulting cable pipes.

[0047] 2. By using a specific titanate coupling agent to modify the surface of ultrafine calcium carbonate, it is beneficial to improve the dispersibility, interfacial adhesion and processing performance of ultrafine calcium carbonate in PVC melt, thereby improving the mechanical properties of PVC cable pipes.

[0048] 3. By further grafting methyl methacrylate groups onto the surface of ultrafine calcium carbonate treated with coupling agent, it is not only beneficial to reduce melt flow resistance and further improve the uniformity of molding size, but also to effectively regulate the balance between melt flowability and melt strength modulus, thus solving the problem of increased melt viscosity caused by the long-chain alkyl polyphosphates in composite flame retardants. Detailed Implementation

[0049] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0050] The PVC resin powder was purchased from SG-5 PVC resin powder in Erdos.

[0051] The ultrafine calcium carbonate was purchased from Guilin Jinshan Group, and the heavy calcium carbonate has a mesh size of 1000.

[0052] Aluminum hydroxide and magnesium hydroxide were both purchased from Zhongmei Magnesium Industry, with aluminum hydroxide graded ZM W-QYHL-3 and magnesium hydroxide graded ZM W-QYHM-MX-4.

[0053] The titanate coupling agent was purchased from Nengde New Materials, specifically the new alkoxy titanate with the brand name TCA-L38.

[0054] Preparation Example

[0055]

Preparation Example 1-1

[0056] A long-chain alkyl polyphosphate ester, with the following chemical formula:

[0057] ;

[0058] Wherein, R1 group is ethyl and R2 group is C8 straight-chain alkyl.

[0059] The above-mentioned method for preparing a long-chain alkyl polyphosphate includes the following steps:

[0060] A1. Cool phosphorus oxychloride to 10°C using an oil bath, maintain a vacuum of less than 5 mmHg, and slowly add 1,6-hexanediol, wherein the molar ratio of phosphorus oxychloride to 1,6-hexanediol is 2:1. Stir rapidly while adding the solution, and control the reaction temperature to not exceed 15°C. After the addition is complete, maintain the temperature and continue the reaction for 1 hour to obtain the first intermediate.

[0061] A2. Add a long-chain alkyl alcohol, wherein the long-chain alkyl alcohol is n-octanol, and the molar ratio of the long-chain alkyl alcohol to 1,6-hexanediol is 1:1. Maintain a vacuum of less than 5 mmHg and gradually increase the temperature to 60°C at a rate of 2°C. Then, maintain the temperature and continue the reaction for 0.5 h. Then, add anhydrous ethanol in batches and heat to 85°C, wherein the molar ratio of anhydrous ethanol to 1,6-hexanediol is 2.5:1. Maintain the temperature and continue the reaction for 1 h to obtain the second intermediate.

[0062] A3. The second intermediate was subjected to vacuum distillation in an environment with a vacuum degree of less than 5 mmHg. The resulting solid product was washed twice with hot dilute sulfuric acid and twice with hot deionized water. The pH was then adjusted to 6.5, and the product was dehydrated and dried under vacuum to obtain a long-chain alkyl polyphosphate.

[0063]

Preparation Examples 1-2

[0064] A long-chain alkyl polyphosphate, which differs from [Preparation Example 1-1] in that the R2 group is a C12 straight-chain alkyl group.

[0065] The method for preparing a long-chain alkyl polyphosphate described above differs from that in [Preparation Example 1-1] in that step A2 is different.

[0066] In this preparation example, the long-chain alkyl alcohol added in step A2 is n-dodecyl alcohol.

[0067]

Preparation Examples 1-3

[0068] A long-chain alkyl polyphosphate, which differs from [Preparation Example 1-1] in that the R2 group is a C14 straight-chain alkyl group.

[0069] The method for preparing a long-chain alkyl polyphosphate described above differs from that in [Preparation Example 1-1] in that step A2 is different.

[0070] In this preparation example, the long-chain alkyl alcohol added in step A2 is n-tetradecyl alcohol.

[0071]

Preparation Example 2-1

[0072] A composite flame-retardant material is prepared by coating an inorganic flame retardant with a long-chain alkyl polyphosphate ester as described in Preparation Example 1-1. In this preparation example, the inorganic flame retardant is aluminum hydroxide.

[0073] A method for preparing a composite flame-retardant material includes the following steps:

[0074] First, the long-chain alkyl polyphosphate was diluted to a concentration of 1% using deionized water. Then, 60 kg of the diluted solution was taken and 20 kg of inorganic combustion improver was added under continuous stirring. The mixture was then heated to 70°C and stirred continuously for 2 hours. After the reaction was completed, the mixture was filtered under reduced pressure while hot and the filter residue was dried under vacuum to obtain the composite flame retardant.

[0075]

Preparation Example 2-2

[0076] A composite flame-retardant material is prepared by coating an inorganic flame retardant with a long-chain alkyl polyphosphate ester as described in [Preparation Examples 1-2]. In this preparation example, the inorganic flame retardant is zinc stannate.

[0077] A method for preparing a composite flame-retardant material includes the following steps:

[0078] First, the long-chain alkyl polyphosphate was diluted to a concentration of 1% using deionized water. Then, 40 kg of the diluted solution was taken and 20 kg of inorganic combustion aid was added under continuous stirring. The mixture was then heated to 75°C and stirred continuously for 1 hour. After the reaction was completed, the mixture was filtered under reduced pressure while hot and the filter residue was dried under vacuum to obtain the composite flame retardant.

[0079]

Preparation Examples 2-3

[0080] A composite flame retardant, which differs from [Preparation Example 2-1] in that it uses a different long-chain alkyl polyphosphate.

[0081] In this preparation example, the long-chain alkyl polyphosphate ester specifically selected is one of the long-chain alkyl polyphosphate esters prepared in [Preparation Examples 1-2].

[0082]

Preparation Examples 2-4

[0083] A composite flame retardant, which differs from [Preparation Example 2-1] in that it uses a different long-chain alkyl polyphosphate.

[0084] In this preparation example, the long-chain alkyl polyphosphate ester specifically selected is one of the long-chain alkyl polyphosphate esters prepared in [Preparation Examples 1-3].

[0085]

Preparation Examples 2-5

[0086] A composite flame retardant, which differs from [Preparation Examples 2-3] in that it uses a different inorganic flame retardant.

[0087] In this preparation example, magnesium hydroxide is specifically selected as the inorganic flame retardant.

[0088]

Preparation Examples 2-6

[0089] A composite flame retardant, which differs from [Preparation Examples 2-3] in that it uses a different inorganic flame retardant.

[0090] In this preparation example, the agentless flame retardant is specifically a mixture of magnesium hydroxide and zinc stannate, with a specific weight ratio of 1:0.6, meaning the inorganic flame retardant includes 12.5 kg of magnesium hydroxide and 7.5 kg of zinc stannate. Example

[0091]

Example 1

[0092] A flame-retardant insulated cable conduit, comprising the following raw materials:

[0093] 100kg PVC resin powder, 4.5kg heat stabilizer, 8kg CPE, 0.4kg stearic acid, 2kg titanium dioxide, 15kg ultrafine calcium carbonate and 8kg composite flame retardant.

[0094] In this embodiment, the composite flame retardant is selected from the composite flame retardant prepared in [Preparation Example 2-1], the heat stabilizer is selected from calcium-zinc stabilizer, and the titanium dioxide is selected from rutile titanium dioxide.

[0095] A method for preparing a flame-retardant insulated cable conduit includes the following steps:

[0096] First, PVC, heat stabilizer, CPE, stearic acid, and titanium dioxide are weighed in sequence according to their weight. They are then thoroughly mixed and dried in a high-speed mixer heated to 90°C at a stirring speed of 500 r / min for 10 minutes. The mixture is then discharged into a low-speed mixer and cooled at a stirring speed of 60 r / min. After cooling, ultrafine calcium carbonate and composite flame retardant are added, and the mixture is stirred and mixed at room temperature for another 10 minutes to obtain extrusion masterbatch. Finally, the extrusion masterbatch is melted and extruded through a twin-screw extruder to obtain a flame-retardant insulated cable pipe.

[0097]

Example 2

[0098] A flame-retardant insulated cable conduit, comprising the following raw materials:

[0099] 80kg PVC resin powder, 3kg calcium-zinc stabilizer, 5kg CPE, 0.8kg stearic acid, 1.5kg titanium dioxide, 20kg ultrafine calcium carbonate, and 5kg composite flame retardant.

[0100] In this embodiment, the composite flame retardant is selected from the composite flame retardant prepared in [Preparation Example 2-2], the heat stabilizer is selected from calcium-zinc stabilizer, and the titanium dioxide is selected from rutile titanium dioxide.

[0101] In this embodiment, the ultrafine calcium carbonate undergoes surface treatment before being mixed and added, including the following steps:

[0102] B1. First, use anhydrous ethanol to ultrasonically disperse ultrafine calcium carbonate into a suspension with a solid content of 20%, heat to 83°C, add 5% by weight of titanate coupling agent of ultrafine calcium carbonate, stir continuously for 3 hours, filter under reduced pressure and dry under vacuum to obtain ultrafine calcium carbonate with coupling agent surface treatment.

[0103] A method for preparing a flame-retardant insulated cable conduit includes the following steps:

[0104] First, PVC, heat stabilizer, CPE, stearic acid, and titanium dioxide are weighed in sequence according to their weight. They are then thoroughly mixed and dried in a high-speed mixer heated to 85°C at a stirring speed of 500 r / min for 15 minutes. The mixture is then discharged into a low-speed mixer and cooled at a stirring speed of 60 r / min. After cooling, ultrafine calcium carbonate and composite flame retardant are added, and the mixture is stirred and mixed at room temperature for another 10 minutes to obtain extrusion masterbatch. Finally, the extrusion masterbatch is melted and extruded through a twin-screw extruder to obtain a flame-retardant insulated cable pipe.

[0105]

Example 3

[0106] A flame-retardant insulated cable conduit differs from [Example 1] in that it uses a different composite flame retardant.

[0107] In this embodiment, the composite flame retardant specifically selected is one of the composite flame retardants prepared in [Preparation Examples 2-3].

[0108]

Example 4

[0109] A flame-retardant insulated cable conduit differs from [Example 1] in that it uses a different composite flame retardant.

[0110] In this embodiment, the composite flame retardant specifically selected is one of the composite flame retardants prepared in [Preparation Examples 2-4].

[0111]

Example 5

[0112] A flame-retardant insulated cable conduit differs from [Example 1] in that it uses a different composite flame retardant.

[0113] In this embodiment, the composite flame retardant specifically selected is one of the composite flame retardants prepared in [Preparation Examples 2-5].

[0114]

Example 6

[0115] A flame-retardant insulated cable conduit differs from [Example 1] in that it uses a different composite flame retardant.

[0116] In this embodiment, the composite flame retardant specifically selected is one of the composite flame retardants prepared in [Preparation Examples 2-6].

[0117]

Example 7

[0118] A flame-retardant insulated cable conduit, which differs from [Example 6] in that it uses different ultrafine calcium carbonate.

[0119] In this embodiment, the ultrafine calcium carbonate undergoes surface treatment before being mixed and added, including the following steps:

[0120] B1. First, use anhydrous ethanol to ultrasonically disperse ultrafine calcium carbonate into a suspension with a solid content of 20%, heat to 85°C, add 5% by weight of titanate coupling agent of ultrafine calcium carbonate, stir continuously for 2 hours, filter under reduced pressure and dry under vacuum to obtain ultrafine calcium carbonate with coupling agent surface treatment.

[0121]

Example 8

[0122] A flame-retardant insulated cable conduit, which differs from [Example 7] in that it uses different ultrafine calcium carbonate.

[0123] In this embodiment, the ultrafine calcium carbonate undergoes surface treatment before being added in the mixture. This surface treatment also requires graft modification. The specific surface treatment includes the following steps:

[0124] B1. First, use anhydrous ethanol to ultrasonically disperse ultrafine calcium carbonate into a suspension with a solid content of 20%, heat to 85°C, add 5% by weight of titanate coupling agent of ultrafine calcium carbonate, stir continuously for 2 hours, filter under reduced pressure and dry under vacuum to obtain ultrafine calcium carbonate with coupling agent surface treatment.

[0125] B2. Ultrafine calcium carbonate, which has been surface-treated with a coupling agent, is ultrasonically dispersed again in anhydrous ethanol into a suspension with a solid content of 20%. Then, it is heated to 75°C under a nitrogen atmosphere, and methyl methacrylate and azobisisobutyronitrile are added dropwise at a mass ratio of 100:1, wherein the amount of methyl methacrylate added is twice the mass of the ultrafine calcium carbonate. The reaction is carried out under a nitrogen atmosphere and stirred continuously for 6 hours. After high-speed centrifugation and filtration, it is thoroughly washed and vacuum dried to obtain surface-grafted modified ultrafine calcium carbonate. Comparative Example

[0126] Comparative Example 1

[0127] A flame-retardant cable conduit, which differs from [Example 1] in that it does not contain a composite flame retardant.

[0128] In this comparative example, the composite flame retardant was replaced with an equal amount of aluminum hydroxide.

[0129] Comparative Example 2

[0130] A flame-retardant cable conduit differs from [Comparative Example 1] in the amount of aluminum hydroxide added, and the formula also includes 5 kg of PE wax.

[0131] In this comparative example, a flame-retardant cable conduit comprises the following raw materials:

[0132] 100kg PVC resin powder, 4.5kg calcium-zinc stabilizer, 8kg CPE, 5kg PE wax, 0.4kg stearic acid, 2kg titanium dioxide, 15kg ultrafine calcium carbonate, and 30kg aluminum hydroxide.

[0133] Performance test data

[0134] Sample preparation: PVC cable pipes were prepared according to the preparation methods of each embodiment and comparative example, wherein the pipes were produced according to the nominal size of 25 sleeves and a thickness of 1.5 mm.

[0135] 1. Flammability rating: The vertical flammability test was conducted according to Test Method B in GB / T 2408-2008 Determination of flammability of plastics by horizontal and vertical methods, and the vertical flammability rating of the cable conduits prepared in each example and comparative example was recorded.

[0136] 2. Smoke density: Flame tests were conducted according to GB / T 8323.1-2008 Plastics Smoke Generation Part 1: Guidelines for Smoke Density Test Method and GB / T 8323.2-2008 Plastics Smoke Generation Part 2: Single Chamber Method for Determination of Smoke Density Test Method. The smoke density rating (SDR) of the cable pipes prepared in each example and comparative example was recorded and certified.

[0137] 3. Thickness Uniformity: Four cross-sections are evenly selected along the length of the cable conduit, with three locations taken at each cross-section, for a total of 12 locations. The thickness of each location is measured, and the average absolute deviation from the measured thickness is calculated and recorded. Specifically, the average absolute deviation is calculated as follows:

[0138] ;

[0139] Where d1, d2, etc., are the measured thicknesses (mm) at different locations, d m The set thickness (mm) for cable conduit extrusion.

[0140] 4. High and low temperature impact resistance: The test was conducted according to Section 6.5 of "JG 3050-1998 Insulating electrical conduits and fittings for building". Heavy-duty conduits were selected for the test, and 24 test lines were used. The cracking and damage of the cable conduits were recorded.

[0141] Table 1. Partial performance test data of a flame-retardant insulated cable conduit.

[0142]

[0143] Based on Example 1 and Comparative Examples 1-2, and combined with the data in Table 1, it can be seen that by using long-chain alkyl polyphosphates to coat and modify inorganic flame retardants, the resulting composite flame retardant exhibits superior flame retardant and smoke suppression effects on PVC systems at the same addition amount compared to ordinary inorganic flame retardants. This not only significantly reduces the amount of inorganic flame retardant required, but also improves the thickness uniformity and mechanical properties of the resulting PVC cable pipes.

[0144] This may be because in Example 1 and Comparative Examples 1-2 of this application, the inorganic flame retardant mainly uses hydrated metal oxides. Since hydrated metal oxides have poor compatibility with PVC, when added in small amounts, although the effect of uneven dispersion is not very obvious, it can play a certain reinforcing role as an auxiliary filler, but its flame retardant effect is not good. However, when it is added in large quantities in order to achieve its flame retardant and smoke suppression effect, it is easy to cause adverse effects such as powder agglomeration and uneven dispersion, and it will also affect the processing performance of PVC, ultimately leading to a decrease in mechanical properties. However, this application modifies the inorganic flame retardant by coating it with long-chain alkyl polyphosphates. Firstly, this reduces the surface energy of the inorganic flame retardant and improves its dispersibility in PVC. Secondly, the introduced long-chain alkyl groups can create an entanglement effect with PVC segments, thereby forming a network structure and improving the overall impact resistance of PVC cable pipes. In addition, the introduced polyphosphate groups can decompose to generate a non-flammable liquid film of phosphoric acid when heated during combustion. This film, in turn, works with hydrated metal oxides to rapidly dehydrate and carbonize the PVC surface, further enhancing the flame retardant and smoke-suppressing effect of the inorganic flame retardant.

[0145] Based on Examples 1 and 3-4, and combined with the data in Table 1, it can be seen that as the alkyl segments in the long-chain alkyl polyphosphates become longer, the smoke density rating of the resulting PVC cable conduit can be further reduced, while its impact resistance is also improved. This indicates that the smoke suppression and mechanical improvement effects of the composite flame retardant are enhanced. However, it is undeniable that as the alkyl segments become longer, the thickness of the PVC cable conduit tends to be larger, especially when the alkyl segments are C14, where the average absolute deviation of the thickness suddenly increases compared to when the alkyl segments are C12. This may also lead to a decrease in impact resistance. This is likely because as the alkyl segments become longer, the entanglement effect between the composite flame retardant and the PVC molecular chains increases, inevitably affecting the melt viscosity of PVC and reducing its fluidity. Without the addition of additional processing aids, this can easily lead to uneven molding thickness of the product, resulting in significant differences in the mechanical properties of different areas of the PVC cable conduit.

[0146] Based on Examples 3 and 5-6 and the data in Table 1, it can be seen that when the inorganic flame retardant uses magnesium hydroxide combined with a small amount of zinc stannate, it has a better combustion-supporting and smoke-suppressing effect than the inorganic combustion aid that uses hydrated metal oxides alone, at the same addition amount.

[0147] Based on Examples 6-8 and the data in Table 1, it can be seen that surface treatment of ultrafine calcium carbonate with a titanate coupling agent can effectively improve the surface properties of ultrafine calcium carbonate, enabling it to be fully dispersed in PVC. This also helps to further enhance the interfacial adhesion between the filler and PVC, thereby improving the mechanical properties of PVC cable conduits. Furthermore, after treatment with a specific titanate coupling agent, methyl methacrylate groups can be introduced onto the surface of ultrafine calcium carbonate via free radical polymerization. With the full dispersion of ultrafine calcium carbonate, the methyl methacrylate groups grafted onto the calcium carbonate surface can reduce friction between PVC powders through intermolecular forces. This reduces the shear force and temperature required for PVC plasticization and allows the melt to exhibit more pronounced shear thinning behavior in high-shear regions, thereby reducing flow extrusion resistance and further improving the uniformity of molding dimensions.

[0148] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A flame-retardant insulated cable conduit, characterized in that, Including the following parts by weight of raw materials: PVC: 80-100 parts; Heat stabilizer: 3-4.5 parts; CPE: 5-8 parts; Stearic acid: 0.4-0.8 parts; Titanium dioxide: 1.5-2 parts; Ultrafine calcium carbonate: 15-20 parts; Composite flame retardant: 5-8 parts; The preparation of the composite flame retardant includes the following steps: First, the long-chain alkyl polyphosphate is diluted to a concentration of 1% with deionized water. Then, an inorganic flame retardant is added under continuous stirring. The inorganic flame retardant includes at least one of aluminum hydroxide, magnesium hydroxide, or zinc stannate. The mass ratio of the inorganic flame retardant to the diluted solution is 1:(1.5-3). The mixture is then heated to 70-75°C and stirred continuously for 1-2 hours. After the reaction is completed, the mixture is filtered under reduced pressure while hot and the filter residue is dried under vacuum to obtain a composite flame retardant. The preparation of the long-chain alkyl polyphosphate includes the following steps: A1. Phosphorus oxychloride is preheated to 10°C using an oil bath, and 1,6-hexanediol is slowly added dropwise while maintaining a vacuum. The molar ratio of phosphorus oxychloride to 1,6-hexanediol is 2:

1. The mixture is stirred rapidly during the dropwise addition, and the reaction temperature is controlled to not exceed 15°C. After the dropwise addition is completed, the temperature is maintained and the reaction continues for 1-1.5 hours to obtain the first intermediate. A2. Add a long-chain alkyl alcohol, which is one of the straight-chain monohydric alcohols of C8-C14, to the first intermediate in batches. The molar ratio of the long-chain alkyl alcohol to the 1,6-hexanediol is 1:

1. Maintain a vacuum and gradually raise the temperature to 60-63°C. After reaching the temperature, continue the reaction for 0.5-1 h. Then, add anhydrous ethanol in batches and raise the temperature to 85-90°C. The molar ratio of the anhydrous ethanol to the 1,6-hexanediol is 2.5:

1. Maintain the temperature and continue the reaction for 1-1.5 h to obtain the second intermediate. A3. The second intermediate was subjected to vacuum distillation. The resulting solid product was thoroughly washed with hot dilute sulfuric acid and deionized water in sequence. The pH was then adjusted to 6.5-7, and the product was dehydrated and dried under vacuum to obtain a long-chain alkyl polyphosphate.

2. The flame-retardant insulated cable conduit according to claim 1, characterized in that: The long-chain alkyl alcohol is n-dodecyl alcohol.

3. The flame-retardant insulated cable conduit according to claim 1, characterized in that: The ultrafine calcium carbonate needs to undergo surface treatment before being added in the mixture, including the following steps: B1. First, use anhydrous ethanol to ultrasonically disperse ultrafine calcium carbonate into a suspension with a solid content of 20%, heat to 83-85℃, add 5% titanate coupling agent, stir continuously for 2-3 hours, filter under reduced pressure and dry under vacuum to obtain ultrafine calcium carbonate with coupling agent surface treatment.

4. The flame-retardant insulated cable conduit according to claim 3, characterized in that: The titanate coupling agent is a novel alkoxy-type titanate coupling agent.

5. A flame-retardant insulated cable conduit according to claim 4, characterized in that: The surface treatment of the ultrafine calcium carbonate also requires grafting modification, including the following steps: B2. Ultrafine calcium carbonate, which has been surface-treated with a coupling agent, is ultrasonically dispersed again in anhydrous ethanol into a suspension with a solid content of 20%. Then, it is heated to 75-78°C under an inert atmosphere. Methyl methacrylate and azobisisobutyronitrile are added dropwise at a mass ratio of 100:1, wherein the amount of methyl methacrylate added is twice the mass of the ultrafine calcium carbonate. The reaction is carried out under an inert atmosphere and stirred continuously for 5-6 hours. After high-speed centrifugation and filtration, it is thoroughly washed and vacuum dried to obtain surface-grafted modified ultrafine calcium carbonate.

6. A method for preparing a flame-retardant insulated cable conduit, used to prepare the flame-retardant insulated cable conduit according to any one of claims 1-5, characterized in that, Includes the following steps: First, weigh out PVC, heat stabilizer, CPE, stearic acid and titanium dioxide in the following order by weight. Heat to 80-90℃ and stir thoroughly for 10-20 minutes. After cooling, add ultrafine calcium carbonate and composite flame retardant, and continue stirring at room temperature for 5-10 minutes to obtain extrusion masterbatch. Finally, melt and extrude the extrusion masterbatch to obtain a flame-retardant insulated cable pipe.

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