Flame-retardant insulated cable tube and preparation method thereof

Abstract

The invention discloses a flame-retardant insulated cable tube and a preparation method thereof, and relates to the technical field of PVC (polyvinyl chloride) cable tubes, the flame-retardant insulated cable tube comprises 80-100 parts of PVC, 3-4.5 parts of heat stabilizer, 5-8 parts of CPE (chlorinated polyethylene), 0.4-0.8 part of stearic acid, 1.5-2 parts of titanium dioxide, 15-20 parts of superfine calcium carbonate and 5-8 parts of composite flame retardant. Wherein the composite flame retardant is prepared by coating an inorganic flame retardant with long-chain alkyl polyphosphate. The long-chain alkyl polyphosphate is adopted to carry out coating modification on the inorganic flame retardant, so that compared with a common inorganic flame retardant, the flame retardant has more excellent flame retardant effect and smoke suppression effect under the same addition amount, the addition amount of the inorganic flame retardant can be greatly reduced, and the thickness uniformity and the mechanical property of the prepared cable tube are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of PVC cable pipes, and in particular to a flame-retardant and insulating cable pipe and a preparation method thereof. Background Art

[0002] With the rapid development of industries such as electric power and communication, cable pipes, as important components for protecting cables and wires, have increasingly higher performance requirements. Since cable pipes need to have good mechanical strength, corrosion resistance, insulation performance, and flame-retardant performance to ensure the safe operation of cables and wires in complex environments, polyvinyl chloride has become one of the main materials for cable pipes due to its excellent electrical insulation, chemical corrosion resistance, processing performance, and cost advantages.

[0003] Since the PVC molecule contains chlorine element, the chlorine element can absorb part of the heat during the combustion process and will decompose into harmful hydrogen chloride gas to reduce the concentration of combustible gas. However, in the conventional processing process, a variety of plasticizers and other additives are added, which will instead cause the oxygen index of the product to decrease, resulting in the inability of conventional PVC cable pipes to meet the flame-retardant requirements. At the same time, a large amount of black smoke and harmful gases will be released during combustion, and the environmental protection performance is poor.

[0004] In the prior art, most manufacturers will add flame retardants during the processing to improve the flame-retardant performance of PVC cable pipes. However, the flame-retardant efficiency of traditional inorganic flame retardants is relatively low. For example, aluminum hydroxide and magnesium hydroxide, etc., require a high addition amount to make the cable pipes meet the flame-retardant requirements. This not only greatly increases the material cost, but also causes the material density to increase and the flexibility to decrease. Excessive filling will also affect the processing fluidity and is difficult to process and produce. And adding highly efficient halogen-containing flame retardants, although a small amount can be added to achieve good flame-retardant effects, the use of halogen-containing flame retardants cannot reduce the smoke volume during the combustion of cable pipes, and there are also environmental protection and health risks. Therefore, developing a flame retardant with a small addition amount, which can ensure the mechanical properties of PVC cable pipes and has certain environmental protection value, is of great significance and broad application prospects for the development of PVC cable pipes. Summary of the Invention

[0005] In order to improve the flame-retardant performance of PVC cable pipes, while reducing the smoke volume generated during combustion and improving the environmental protection performance of PVC cable pipes, the present application provides a flame-retardant and insulating cable pipe and a preparation method thereof.

[0006] In the first aspect, a flame-retardant and insulating cable pipe provided by the present application adopts the following technical solution: A flame-retardant and insulating cable pipe, comprising the following raw materials in parts by weight: 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 composite flame retardant is prepared by coating an inorganic flame retardant with a long-chain alkyl polyphosphate, and the chemical formula of the long-chain alkyl polyphosphate is as follows: ; R in long chain alkyl polyphosphate 1 Ethyl, R 2 It is a C8-C14 straight chain alkyl group.

[0007] By adopting the above technical solution, the inorganic flame retardant is coated and modified with a long-chain alkyl polyphosphate, which can reduce the surface energy of the inorganic flame retardant and improve its dispersibility in PVC, which is beneficial to improving the flame retardant effect and smoke suppression effect of the inorganic flame retardant. Secondly, the introduced polyphosphate group can cooperate with the inorganic flame retardant to quickly dehydrate and carbonize the PVC surface when burning and heated. Compared with ordinary inorganic flame retardants, it has better flame retardant and smoke suppression effects at the same addition amount, which is beneficial to improve the environmental protection of PVC cable pipes and reduce production costs. In addition, the introduced long-chain alkyl can produce an entanglement effect with the PVC chain segment, thereby forming a network structure, which is beneficial to improve the overall mechanical strength of the PVC cable pipe to a certain extent.

[0008] Optionally, the preparation of the composite flame retardant comprises the following steps: First, use deionized water to dilute the long-chain alkyl polyphosphate to a 1% dilution solution, and then add an inorganic flame retardant under continuous stirring, wherein the mass ratio of the inorganic flame retardant to the diluted solution is 1: (1.5-3), and then heat to 70-75°C and continue stirring to react for 1-2 hours. After the reaction, reduce the pressure while hot and vacuum dry the filter residue to obtain a composite flame retardant.

[0009] By adopting the above technical scheme, the long-chain alkyl polyphosphate is diluted to a lower concentration with deionized water in advance, and high-temperature stirring is combined, which can effectively balance the viscosity and reactivity of the long-chain alkyl polyphosphate, thereby ensuring that the inorganic flame retardant can be fully dispersed in the diluted solution while improving the coverage rate of the long-chain alkyl polyphosphate, which is beneficial to prevent the situation where the inorganic flame retardant agglomerates due to the high viscosity of the solution, resulting in excessively large coated particle size and affecting the subsequent mixing of the composite flame retardant and PVC.

[0010] Optionally, the preparation of the long-chain alkyl polyphosphate comprises the following steps: A1. Pre-cool phosphorus oxychloride to 10°C using an oil bath, maintain a vacuum and slowly add 1,6-hexanediol dropwise. While adding the drops, stir rapidly and control the reaction temperature not to exceed 15°C. After the addition is completed, maintain the temperature and continue the reaction for 1 - 1.5 h to obtain a first intermediate. A2. Add long-chain alkyl alcohol to the first intermediate in batches. The long-chain alkyl alcohol is one of the straight-chain monohydric alcohols with C8 - C14 carbon atoms. Maintain a vacuum and gradually heat up to 60 - 63°C. After reaching the temperature, continue the reaction for 0.5 - 1 h. Then add ethanol in batches and heat up to 85 - 90°C. Maintain the temperature and continue the reaction for 1 - 1.5 h to obtain a second intermediate. A3. Take the second intermediate for vacuum distillation. Thoroughly wash the obtained solid product, then adjust the pH to 6.5 - 7, and obtain long-chain alkyl polyphosphate after vacuum dehydration and drying.

[0011] By adopting the above technical solution, the side reaction of the chlorination reaction of phosphorus oxychloride can be effectively inhibited, which is beneficial to improving the yield of long-chain alkyl polyphosphate.

[0012] Optionally, R in the long-chain alkyl polyphosphate 1 is ethyl, and R 2 is a straight-chain alkyl group with C12 carbon atoms.

[0013] By adopting the above technical solution, when R of the long-chain alkyl polyphosphate 2 is a straight-chain alkyl group with C12 carbon atoms, the prepared composite flame retardant has relatively excellent flame retardant and smoke suppression effects and mechanical property improvement effects. At the same time, the adverse effects caused by the processing of PVC melt are relatively low and within an acceptable range, and the comprehensive performance of the prepared PVC cable pipe is better.

[0014] Optionally, the inorganic flame retardant includes at least one of aluminum hydroxide, magnesium hydroxide, or zinc stannate.

[0015] By adopting the above technical solution, the above inorganic flame retardant is not only non-toxic and environmentally friendly, but also has good flame retardant and smoke suppression effects through endothermic effect and isolation effect. It will not generate harmful gases, can also reduce the generation amount of CO during the combustion process, and at the same time can play a certain role in reinforcing the filler. At an appropriate addition amount, it is beneficial to further improve the mechanical properties of the PVC cable pipe in cooperation with the filler.

[0016] Optionally, the ultrafine calcium carbonate needs to be surface-treated before being added in mixture, and it includes the following steps: B1. First, use absolute ethanol to ultrasonically disperse the ultrafine calcium carbonate into a suspension with a solid content of 20%. Heat it to 83 - 85°C, add 5% titanate coupling agent, continuously stir and react for 2 - 3 h, carry out vacuum filtration under reduced pressure and vacuum drying to obtain ultrafine calcium carbonate with surface treatment by the coupling agent.

[0017] By adopting the above technical solution, using a titanate coupling agent to perform surface treatment on ultrafine calcium carbonate 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.

[0018] Optionally, the titanate coupling agent is selected as a neoalkoxy type titanate coupling agent.

[0019] By adopting the above technical solution, the neoalkoxy type titanate coupling agent can not only significantly improve the dispersibility, interfacial adhesion and processing performance of ultrafine calcium carbonate in the PVC melt, but also introduce multiple reaction sites on the surface of ultrafine calcium carbonate, which is beneficial to further graft modification of ultrafine calcium carbonate in the future.

[0020] Optionally, the surface treatment of the ultrafine calcium carbonate also needs to go through graft modification, which includes the following steps: B2. Use anhydrous ethanol to ultrasonically disperse the ultrafine calcium carbonate surface-treated with the coupling agent again into a suspension with a solid content of 20%, then heat it to 75 - 78 °C under an inert atmosphere, and simultaneously dropwise add methyl methacrylate and azobisisobutyronitrile according to a mass ratio of 100:1, where the addition amount of methyl methacrylate is 2 times the mass of the ultrafine calcium carbonate. Maintain the inert atmosphere and continuously stir and react for 5 - 6 h. After high-speed centrifugation and filtration, wash it thoroughly and dry it under vacuum to obtain ultrafine calcium carbonate with surface graft modification treatment.

[0021] By adopting the above technical solution, the methyl methacrylate group can be grafted onto the surface of the coupling agent-treated ultrafine calcium carbonate through free radical grafting. Then, with the uniform dispersion of the ultrafine calcium carbonate, the methyl methacrylate group can further reduce the friction between the mixed powders, lower the shear force and temperature required for PVC plasticization. This is not only beneficial to reducing the melt flow resistance and further improving the dimensional uniformity of molding, but also can effectively adjust the balance between the melt fluidity and the melt strength modulus, and solve the problem of increased melt viscosity caused by the long-chain alkyl groups in the long-chain alkyl polyphosphate of the composite flame retardant. Optionally, the heat stabilizer is a calcium-zinc stabilizer, and the titanium dioxide is rutile titanium dioxide.

[0022] By adopting the above technical solution, compared with traditional lead salt heat stabilizers, calcium-zinc stabilizers are environmentally friendly. They not only have good stabilizing effects and less addition amount, but also can reduce the generation of black smoke or toxic gases when PVC cable pipes burn. Rutile titanium dioxide has excellent shielding effects on ultraviolet rays, which is beneficial to improving the appearance and weather resistance of PVC cable pipes, enabling PVC cable pipes to maintain good performance over time and extending the service life of PVC cable pipes.

[0023] In a second aspect, a method for preparing a flame-retardant and insulating cable pipe provided by the present application adopts the following technical solution.

[0024] A method for preparing a flame-retardant and insulating cable pipe includes the following steps: First, weigh PVC, heat stabilizer, CPE, stearic acid, and titanium dioxide in sequence according to parts by weight, fully stir and mix them in a high-speed mixer heated to 80 - 90 °C for 10 - 20 min, then discharge them into a low-speed mixer for cooling. After cooling, add ultrafine calcium carbonate and a composite flame retardant, and continue to stir and mix at room temperature for 5 - 10 min to obtain an extrusion masterbatch. Finally, melt and extrude the extrusion masterbatch to form a flame-retardant and insulating cable pipe.

[0025] By adopting the above technical solution, the production process is simple, the required equipment investment is less, the cost is low, which is conducive to large-scale industrial production.

[0026] To sum up, the technical solution of the present application has at least any one of the following beneficial effects: 1. By coating and modifying the inorganic flame retardant with long-chain alkyl polyphosphate, compared with ordinary inorganic flame retardants, it has more excellent flame retardant and smoke suppression effects under the same addition amount. It can not only greatly reduce the addition amount of the inorganic flame retardant, but also improve the thickness uniformity and mechanical properties of the cable pipe prepared.

[0027] 2. By surface-modifying ultrafine calcium carbonate with a specific titanate coupling agent, it is beneficial to improve the dispersibility, interfacial adhesion, and processing performance of ultrafine calcium carbonate in the PVC melt, thereby improving the mechanical properties of the PVC cable pipe.

[0028] 3. By further grafting methyl methacrylate groups onto the surface of the ultrafine calcium carbonate treated with the coupling agent, it is not only beneficial to reduce the melt flow resistance and further improve the forming size uniformity, but also can effectively adjust the balance between the melt fluidity and the melt strength modulus, and solve the problem of increased melt viscosity caused by the long-chain alkyl of the long-chain alkyl polyphosphate in the composite flame retardant. Specific Embodiments

[0029] The present application will be further described in detail below with reference to preparation examples, examples, and comparative examples.

[0030] The PVC resin powder was purchased as SG-5 PVC resin powder from Ordos.

[0031] The ultrafine calcium carbonate was purchased as heavy calcium carbonate with a mesh number of 1000 from Guilin Jinshan Group.

[0032] Both aluminum hydroxide and magnesium hydroxide were purchased from Zhongmei Magnesium Industry. Among them, the grade of aluminum hydroxide is ZM W-QYHL-3, and the grade of magnesium hydroxide is ZM W-QYHM-MX-4.

[0033] The titanate coupling agent was purchased from Nengde New Materials, a new alkoxy type titanate with the grade of TCA-L38. Preparation Example

[0034]

Preparation Example 1-1

[0035] The preparation method of the above-mentioned long-chain alkyl polyphosphate ester includes the following steps: A1. Use an oil bath to cool phosphorus oxychloride to 10°C, keep the vacuum degree less than 5 mmHg and slowly dropwise add 1,6-hexanediol. The molar ratio of phosphorus oxychloride to 1,6-hexanediol is 2:1. While dropping, stir rapidly, and during this period, control the reaction temperature not to exceed 15°C. After the dropping is completed, keep the temperature and continue the reaction for 1 h to obtain the first intermediate; A2. Batchwise add long-chain alkyl alcohol to the first intermediate. The long-chain alkyl alcohol is n-octanol. The molar ratio of long-chain alkyl alcohol to 1,6-hexanediol is 1:1. Keep the vacuum degree less than 5 mmHg and gradually heat up to 60°C at a rate of 2°C, then keep the temperature and continue the reaction for 0.5 h. Then, batchwise add anhydrous ethanol and heat to 85°C. The molar ratio of anhydrous ethanol to 1,6-hexanediol is 2.5:1. Keep the temperature and continue the reaction for 1 h to obtain the second intermediate; A3. Take the second intermediate and perform vacuum distillation in an environment with a vacuum degree less than 5 mmHg. Wash the obtained solid product twice with hot dilute sulfuric acid and twice with hot deionized water, then adjust the pH to 6.5, and obtain the long-chain alkyl polyphosphate ester after vacuum dehydration and drying.

[0036]

Preparation Example 1-2

Preparation Example 1-1

[0037] The preparation method of the above-mentioned long-chain alkyl polyphosphate ester, different from

Preparation Example 1-1

[0038] In this preparation example, the long-chain alkyl alcohol added in step A2 is n-dodecanol.

[0039]

Preparation Example 1-3

Preparation Example 1-1

[0040] The preparation method of the above long-chain alkyl polyphosphate is different from

Preparation Example 1-1

[0041] In this preparation example, the long-chain alkyl alcohol added in step A2 is n-tetradecanol.

[0042]

Preparation Example 2-1

Preparation Example 1-1

[0043] A preparation method of a composite flame retardant material includes the following steps: First, dilute the long-chain alkyl polyphosphate with deionized water to a dilution solution with a concentration of 1%, then take 60 kg of the dilution solution and add 20 kg of an inorganic combustion aid under continuous stirring, then heat to 70 °C and continuously stir and react for 2 h. After completion, filter while hot under reduced pressure and vacuum-dry the filter residue to obtain a composite flame retardant.

[0044]

Preparation Example 2-2

Preparation Example 1-2

[0045] A preparation method of a composite flame retardant material includes the following steps: First, dilute the long-chain alkyl polyphosphate with deionized water to a dilution solution with a concentration of 1%, then take 40 kg of the dilution solution and add 20 kg of an inorganic combustion aid under continuous stirring, then heat to 75 °C and continuously stir and react for 1 h. After completion, filter while hot under reduced pressure and vacuum-dry the filter residue to obtain a composite flame retardant.

[0046]

Preparation Example 2-3

Preparation Example 2-1

[0047] In this preparation example, the long-chain alkyl polyphosphate specifically selects a long-chain alkyl polyphosphate prepared in

Preparation Example 1-2

[0048]

Preparation Example 2-4

Preparation Example 2-1

[0049] In this preparation example, the long-chain alkyl polyphosphate is specifically selected from one of the long-chain alkyl polyphosphates prepared in [Preparation Examples 1-3].

[0050]

Preparation Example 2-5

[0051] In this preparation example, the inorganic flame retardant is specifically selected as magnesium hydroxide.

[0052]

Preparation Example 2-6

[0053] In this preparation example, the inorganic flame retardant is specifically selected as a mixture of two kinds, magnesium hydroxide and zinc stannate. The specific mixing weight ratio of magnesium hydroxide to zinc stannate is 1:0.6, that is, the inorganic flame retardant includes 12.5 kg of magnesium hydroxide and 7.5 kg of zinc stannate. Examples

[0054]

Example 1

[0055] In this example, the composite flame retardant is selected from one of the composite flame retardants prepared in [Preparation Example 2-1], the heat stabilizer is selected as calcium-zinc stabilizer, and the titanium dioxide is selected as rutile titanium dioxide.

[0056] A preparation method of a flame-retardant and insulating cable pipe, comprising the following steps: First, weigh PVC, heat stabilizer, CPE, stearic acid, and titanium dioxide in parts by weight in sequence, and fully stir, dry, and mix them in a high-speed mixer heated to 90 °C at a stirring speed of 500 r / min for 10 min, then discharge them into a low-speed mixer and cool at a stirring speed of 60 r / min. After cooling, add ultrafine calcium carbonate and composite flame retardant, and continue to stir and mix at room temperature for 10 min to obtain an extrusion masterbatch. Finally, melt and extrude the extrusion masterbatch through a twin-screw extruder to obtain a flame-retardant and insulating cable pipe.

[0057]

Example 2

[0058] In this embodiment, the composite flame retardant is selected from a composite flame retardant prepared in

Preparation Example 2-2

[0059] In this embodiment, the ultrafine calcium carbonate is surface-treated before being mixed and added, and the following steps are included: B1. First, use absolute ethanol to ultrasonically disperse the ultrafine calcium carbonate into a suspension with a solid content of 20%, heat it to 83 °C, add a titanate coupling agent accounting for 5% of the mass of the ultrafine calcium carbonate, continuously stir and react for 3 h, carry out vacuum filtration under reduced pressure, and then vacuum-dry to obtain ultrafine calcium carbonate surface-treated with the coupling agent.

[0060] A preparation method of a flame-retardant insulating cable pipe includes the following steps: First, weigh PVC, heat stabilizer, CPE, stearic acid, and titanium dioxide in parts by weight in sequence, fully stir, dry, and mix in a high-speed mixer heated to 85 °C at a stirring speed of 500 r / min for 15 min, then discharge it into a low-speed mixer and cool it at a stirring speed of 60 r / min. After cooling, add ultrafine calcium carbonate and the composite flame retardant, and continue to stir and mix at room temperature for 10 min to obtain an extrusion masterbatch. Finally, melt and extrude the extrusion masterbatch through a twin-screw extruder to obtain a flame-retardant insulating cable pipe.

[0061]

Example 3

Example 1

[0062] In this embodiment, the composite flame retardant is specifically selected from a composite flame retardant prepared in

Preparation Example 2-3

[0063]

Example 4

Example 1

[0064] In this embodiment, the composite flame retardant is specifically selected from a composite flame retardant prepared in

Preparation Example 2-4

[0065]

Example 5

Example 1

[0066] In this embodiment, the composite flame retardant is specifically selected from a composite flame retardant prepared in

Preparation Example 2-5

[0067]

Example 6

Example 1

[0068] In this embodiment, the composite flame retardant is specifically selected as a composite flame retardant prepared in [Preparation Example 2-6].

[0069]

Example 7

[0070] In this embodiment, the ultrafine calcium carbonate is surface-treated before being mixed and added, and the following steps are included: B1. First, use absolute ethanol to ultrasonically disperse the ultrafine calcium carbonate into a suspension with a solid content of 20%, heat it to 85 °C, add a titanate coupling agent accounting for 5% of the mass of the ultrafine calcium carbonate, continuously stir and react for 2 h, carry out vacuum filtration under reduced pressure and then vacuum dry to obtain ultrafine calcium carbonate surface-treated with the coupling agent.

[0071]

Example 8

[0072] In this embodiment, the ultrafine calcium carbonate is surface-treated before being mixed and added, and the surface treatment of the ultrafine calcium carbonate also needs to undergo graft modification. The specific surface treatment includes the following steps: B1. First, use absolute ethanol to ultrasonically disperse the ultrafine calcium carbonate into a suspension with a solid content of 20%, heat it to 85 °C, add a titanate coupling agent accounting for 5% of the mass of the ultrafine calcium carbonate, continuously stir and react for 2 h, carry out vacuum filtration under reduced pressure and then vacuum dry to obtain ultrafine calcium carbonate surface-treated with the coupling agent; B2. Use absolute ethanol again to ultrasonically disperse the ultrafine calcium carbonate surface-treated with the coupling agent into a suspension with a solid content of 20%, then heat it to 75 °C under a nitrogen atmosphere, and simultaneously dropwise add methyl methacrylate and azobisisobutyronitrile according to a mass ratio of 100:1, wherein the addition amount of methyl methacrylate is 2 times the mass part of the ultrafine calcium carbonate, maintain the nitrogen atmosphere and continuously stir and react for 6 h, carry out high-speed centrifugal filtration, fully wash and then vacuum dry to obtain ultrafine calcium carbonate with surface graft modification treatment. Comparative Example

[0073]

Comparative Example 1

[0074] In this comparative example, the composite flame retardant is replaced with aluminum hydroxide in equal amounts.

[0075]

Comparative Example 2

[0076] In this comparative example, a flame-retardant cable pipe comprises the following raw materials: 100 kg of PVC resin powder, 4.5 kg of calcium-zinc stabilizer, 8 kg of CPE, 5 kg of PE wax, 0.4 kg of stearic acid, 2 kg of titanium dioxide, 15 kg of ultrafine calcium carbonate, and 30 kg of aluminum hydroxide. Performance test data

[0077] Preparation of samples to be tested: The corresponding PVC cable pipes were prepared according to the preparation methods of the examples and comparative examples, and were produced according to the nominal size of 25 sleeves and a thickness of 1.5 mm.

[0078] 1. Combustion rating: Test according to test method B (vertical burning test) in "GB / T 2408-2008 Plastics - Determination of burning behavior - Horizontal and vertical methods", and record the vertical burning ratings of the cable pipes prepared in the examples and comparative examples.

[0079] 2. Smoke density: Conduct a flaming test according to "GB / T 8323.1-2008 Plastics - Smoke generation - Part 1: Guide for smoke density test methods" and "GB / T 8323.2-2008 Plastics - Smoke generation - Part 2: Test method for determination of smoke density in a single chamber method", record the smoke density rating (SDR) of the cable pipes prepared in the examples and comparative examples, and obtain evidence.

[0080] 3. Thickness uniformity: Uniformly take 4 cross-sections along the length direction of the cable pipe, take 3 positions on each cross-section, a total of 12 positions, and measure their thicknesses, calculate and record the average absolute deviation of the 12 thicknesses from the average thickness. Specifically, the calculation method of the average absolute deviation is: ; where d 1 、d 2 etc. are the measured thicknesses (mm) at different positions, and d m is the set thickness (mm) when the cable pipe is extruded.

[0081] 4. High and low temperature impact resistance: Test according to Section 6.5 in "JG 3050-1998 Insulated electrical casing and fittings for building use", where the heavy-duty casing type is selected for testing, the number of test pieces is 24, and record the cracking and damage conditions of the cable pipes.

[0082] Table 1 Partial performance test data of a flame-retardant insulated cable pipe

[0083] According to 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 polyphosphate to coat and modify the inorganic flame retardant, the obtained composite flame retardant has more excellent flame retardant effect and smoke suppression effect on the PVC system compared with the ordinary inorganic flame retardant under the same addition amount. It can not only greatly reduce the addition amount of the inorganic flame retardant, but also improve the thickness uniformity and mechanical properties of the prepared PVC cable pipe.

[0084] This may be because in Example 1 and Comparative Examples 1-2 of this application, the inorganic flame retardant mainly selects hydrated metal oxides. Also, because the compatibility between hydrated metal oxides and PVC is poor, when added in a small amount, although the effect of uneven dispersion is not very obvious and it can act as an auxiliary filler to play a certain reinforcing role, its flame retardant effect is not good. However, when it is added in a large amount to achieve its flame retardant and smoke suppression effect, it is easy to cause adverse effects such as powder agglomeration and uneven dispersion, and at the same time, it will also affect the processing performance of PVC, ultimately leading to a decrease in mechanical properties. However, in this application, by using long-chain alkyl polyphosphate to coat and modify the inorganic flame retardant, on the one hand, it can reduce the surface energy of the inorganic flame retardant and improve its dispersion in PVC. Secondly, the introduced long-chain alkyl can produce a tangling effect with the PVC chain segments, and then a network structure can be formed to improve the overall impact resistance of the PVC cable pipe. In addition, when the introduced polyphosphate group is heated by combustion, it can decompose to generate a non-combustible liquid film of phosphoric acid, and then cooperate with the hydrated metal oxide to quickly dehydrate and carbonize the PVC surface, which can further improve the flame retardant and smoke suppression effect of the inorganic flame retardant.

[0085] According to Example 1 and Examples 3-4 and combined with the data in Table 1, it can be seen that as the alkyl chain segment in the long-chain alkyl polyphosphate becomes longer, the smoke density grade of the prepared PVC cable pipe can be further reduced, and at the same time, its impact resistance is also improved, that is, the smoke suppression effect and mechanical improvement effect of the composite flame retardant are improved. However, it cannot be ignored that as the alkyl chain segment becomes longer, the thickness size of the PVC cable pipe becomes larger. Especially when the alkyl chain segment is C14, the average absolute deviation of the thickness size suddenly increases compared with when the alkyl chain segment is C12, and at the same time, it may cause a problem of decreased impact resistance. This may be because as the alkyl chain segment becomes longer, the tangling effect between the molecular chain segments of the composite flame retardant and PVC becomes greater, which will inevitably affect the melt viscosity of PVC and reduce its fluidity. Without adding additional processing aids, it is easy to cause uneven forming thickness of the product, and then the mechanical properties of different regions of the PVC cable pipe will vary greatly.

[0086] According to Example 3 and Examples 5-6 and combined with the data in Table 1, it can be seen that when the inorganic flame retardant uses magnesium hydroxide compounded with a small amount of zinc stannate, compared with the inorganic combustion aid that solely uses hydrated metal oxides, under the same addition amount, its combustion aid and smoke suppression effect are better.

[0087] According to Examples 6-8 and combined with the data in Table 1, it can be seen that using a titanate coupling agent to perform surface treatment on ultrafine calcium carbonate 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. In addition, after treatment with a specific titanate coupling agent, methyl methacrylate groups can be introduced onto the surface of ultrafine calcium carbonate through free radical polymerization. With the full dispersion of ultrafine calcium carbonate, the methyl methacrylate groups grafted on the surface of calcium carbonate can reduce the friction between PVC powder particles through intermolecular forces, which can not only reduce the shear force and temperature required for PVC plasticization, but also make the melt exhibit a more obvious shear thinning behavior in the high shear region, thereby reducing the flow extrusion resistance and being beneficial to further improving the uniformity of the forming size.

[0088] This specific implementation manner is only an interpretation of the present application, and it is not a limitation of the present application. After reading this specification, those skilled in the art can make modifications that do not contribute creatively to this specific implementation manner as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A flame retardant insulated cable tube, characterized in that: It includes the following raw materials in parts by weight: PVC: 80-100 parts; Heat stabilizer: 3-4.5 parts; CPE: 5-8 copies; 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 composite flame retardant is prepared by coating an inorganic flame retardant with a long-chain alkyl polyphosphate, and the chemical formula of the long-chain alkyl polyphosphate is as follows: ； In the long-chain alkyl polyphosphate, R1 is an ethyl group, and R2 is a C8-C14 straight-chain alkyl group.

2. The flame-retardant insulated cable tube according to claim 1, characterized in that: The preparation of the composite flame retardant comprises the following steps: First, use deionized water to dilute the long-chain alkyl polyphosphate to a 1% dilution solution, and then add an inorganic flame retardant under continuous stirring, wherein the mass ratio of the inorganic flame retardant to the diluted solution is 1: (1.5-3), and then heat to 70-75°C and continue stirring to react for 1-2 hours. After the reaction, reduce the pressure while hot and vacuum dry the filter residue to obtain a composite flame retardant.

3. The flame-retardant insulated cable tube according to claim 2, characterized in that: The preparation of the long-chain alkyl polyphosphate comprises the following steps: A1. Pre-cool phosphorus oxychloride to 10°C using an oil bath, maintain vacuum and slowly drop 1,6-hexanediol, stir rapidly while dropping, and control the reaction temperature not to exceed 15°C. After the dropwise addition is completed, maintain the temperature and continue the reaction for 1-1.5 hours to obtain a first intermediate; A2, adding a long-chain alkyl alcohol in batches to the first intermediate, wherein the long-chain alkyl alcohol is one of the C8-C14 straight-chain monohydric alcohols, and gradually heating to 60-63° C. while maintaining vacuum, and continuing to react for 0.5-1 h after reaching the temperature, and then adding ethanol in batches and heating to 85-90° C., maintaining the temperature and continuing to react for 1-1.5 h to obtain a second intermediate; A3. The second intermediate is subjected to reduced pressure distillation, the solid product is fully washed, the pH is adjusted to 6.5-7, and the long-chain alkyl polyphosphate is obtained after vacuum dehydration and drying.

4. The flame-retardant insulated cable tube according to claim 3, characterized in that: In the long-chain alkyl polyphosphate, R1 is an ethyl group, and R2 is a C12 straight-chain alkyl group.

5. The flame-retardant insulated cable tube according to claim 1, characterized in that: The inorganic flame retardant includes at least one of aluminum hydroxide, magnesium hydroxide or zinc stannate.

6. The flame-retardant insulated cable tube according to claim 1, characterized in that: The ultrafine calcium carbonate needs to be surface treated before mixing and adding, which includes the following steps: B1. Ultrasonic dispersion of ultrafine calcium carbonate into a suspension with a solid content of 20% using anhydrous ethanol, heat to 83-85°C, add 5% titanate coupling agent, continue stirring and reacting for 2-3 hours, reduce pressure, filter and vacuum dry to obtain ultrafine calcium carbonate surface treated with coupling agent.

7. The flame-retardant insulated cable tube according to claim 6, characterized in that: The titanate coupling agent is a neoalkoxy type titanate coupling agent.

8. The flame-retardant insulated cable tube according to claim 7, characterized in that: The surface treatment of the ultrafine calcium carbonate also needs to be grafted and modified, which includes the following steps: B2. Ultrasonic dispersion of the ultrafine calcium carbonate surface-treated with a coupling agent into a suspension with a solid content of 20% is performed again using anhydrous ethanol, and then heated to 75-78° C. in an inert atmosphere, and methyl methacrylate and azobisisobutyronitrile are simultaneously 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 inert atmosphere is maintained and the reaction is continuously stirred for 5-6 hours. After high-speed centrifugal filtration, the mixture is fully washed and vacuum dried to obtain ultrafine calcium carbonate with surface grafting modification.

9. A method for preparing a flame-retardant insulated cable tube, used for preparing a flame-retardant insulated cable tube as claimed in any one of claims 1 to 8, characterized in that: The following steps are involved: First, PVC, heat stabilizer, CPE, stearic acid and titanium dioxide are weighed in order according to weight, heated to 80-90°C and fully stirred and mixed for 10-20 minutes, and then ultrafine calcium carbonate and composite flame retardant are added after cooling, and stirring and mixing is continued at room temperature for 5-10 minutes to obtain an extrusion masterbatch, and finally the extrusion masterbatch is melt-extruded to obtain a flame-retardant insulating cable tube.

Images