High-efficiency flame-retardant heat-resistant aluminum-plastic composite pipe and preparation method thereof

Abstract

This invention discloses a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe and its preparation method, belonging to the field of composite pipe technology. This invention adds a specific ratio of expandable graphite, ammonium polyphosphate, and magnesium hydroxide as a composite flame retardant to the system, producing a highly efficient synergistic flame-retardant effect. The addition of specific expandable graphite forms a denser, continuous expandable char layer, further promoting flame retardancy. Furthermore, the cross-linked polyethylene prepared by this invention exhibits superior stability and is less prone to softening and deformation at high temperatures. Both the cross-linked polyethylene and the catalyst masterbatch formulations incorporate a highly efficient antioxidant system, effectively preventing thermo-oxidative aging during high-temperature processing and ensuring the pipe's resistance to oxygen degradation during long-term use, thereby contributing to improved flame-retardant performance.

Description

Technical Field

[0001] This invention relates to the field of composite pipe technology, and more specifically, to a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe and its preparation method. Background Technology

[0002] Aluminum-plastic composite pipe is a five-layer composite pipe, typically consisting of inner and outer layers of non-metallic materials such as polyethylene or cross-linked polyethylene, a middle aluminum strip layer, and adhesives bonding the layers together. This type of pipe combines the strength of metallic pipes with the corrosion resistance and ease of installation of non-metallic pipes, and is widely used in building hot water supply systems.

[0003] However, traditional aluminum-plastic composite pipes mostly use ordinary cross-linked polyethylene (XLPE) for both the inner and outer layers. XLPE has poor flame retardant properties and is prone to combustion under fire conditions, releasing large amounts of heat and toxic fumes, and producing molten drips, posing significant safety hazards. To improve the flame retardant rating, a large amount of flame retardant is usually added, but this affects the degree of cross-linking of XLPE, leading to a decline in its physical properties, such as reduced compressive strength and uneven cross-linking. This makes it difficult to simultaneously meet the requirements of a high flame retardant rating (such as Class B in EN13501-1:2009) and a high degree of cross-linking (>65%). Summary of the Invention

[0004] Based on this, in order to solve one of the above-mentioned technical problems, the present invention provides a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe and its preparation method, the specific technical solution of which is as follows:

[0005] A high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe, wherein the aluminum-plastic composite pipe comprises, from the inside out, a first cross-linked polyethylene layer, a first adhesive layer, an aluminum strip layer, a second adhesive layer, and a second cross-linked polyethylene layer; wherein, by weight ratio, the second cross-linked polyethylene layer comprises the following raw materials: 70-80 parts of cross-linked polyethylene, 3-5 parts of catalyst masterbatch, 10-25 parts of composite flame retardant, and 0.5-1 parts of antioxidant; The composite flame retardant is obtained by mixing expandable graphite, ammonium polyphosphate and magnesium hydroxide in a mass ratio of (5~10):(5~10):(5~15).

[0006] Further, the cross-linked polyethylene comprises the following raw materials in parts by weight: 90-100 parts high-density polyethylene, 0-10 parts low-density polyethylene, 1-3 parts silane coupling agent, 0.05-1 part initiator, and 0.5-5 parts antioxidant.

[0007] Furthermore, the catalyst masterbatch comprises the following raw materials in parts by weight: 100 parts high-density polyethylene, 3-10 parts catalyst, and 0.5-5 parts antioxidant.

[0008] Furthermore, in the cross-linked polyethylene, the silane coupling agent is one or both of vinyltrimethoxysilane and vinyltriethoxysilane.

[0009] Furthermore, in the cross-linked polyethylene, the initiator is at least one of dicumyl peroxide, benzoyl tert-butyl peroxide, and bis-tert-butyl dicumyl peroxide.

[0010] Further, in the cross-linked polyethylene, the antioxidant is at least one of pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl)phosphite, and dodecyl thiodipropionate.

[0011] Furthermore, in the catalyst masterbatch, the catalyst is at least one of dibutyltin dilaurate and dioctyltin dilaurate.

[0012] Furthermore, in the catalyst masterbatch, the antioxidant is at least one selected from pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl)phosphite, and dodecyl thiodipropionate.

[0013] Furthermore, the gradation of the expandable graphite is as follows: expandable graphite with a particle size of less than 0.3 μm accounts for 60-80%, expandable graphite with a particle size of 0.5-0.9 μm accounts for 15-25%, and expandable graphite with a particle size of 1-20 μm accounts for 1-10%.

[0014] In addition, the present invention also provides a method for preparing a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe, comprising the following steps: S1. Based on the raw materials for preparing cross-linked polyethylene, cross-linked polyethylene is prepared; S2. Based on the raw materials used in the preparation of catalyst masterbatch, catalyst masterbatch is prepared; S3. After mixing cross-linked polyethylene, catalyst masterbatch, composite flame retardant and antioxidant, the mixture is melt-blended and then injected into the molding die of plastic pipe to obtain the inner and outer pipes required for aluminum-plastic pipe; S4. After the aluminum strip is rolled into an aluminum tube, the joint of the aluminum tube is welded using welding equipment. Then, the aluminum tube is cut into the required length using shearing equipment. After that, it is polished by a polishing machine to obtain the shaped aluminum tube. Then, glue is evenly applied to the inner and outer surfaces of the shaped aluminum tube. S5. The injection-molded inner tube is adhered to the inner surface of the aluminum tube with glue, and then the injection-molded outer tube is covered to the outer surface of the aluminum tube with glue. The inner tube and outer tube are co-extruded with the aluminum tube to form an aluminum-plastic composite pipe. After cooling, an aluminum-plastic composite pipe is obtained.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention adds a specific ratio of expandable graphite, ammonium polyphosphate, and magnesium hydroxide as a composite flame retardant to the system of this invention. This effectively utilizes the multiple flame retardant mechanisms of expandable graphite forming a dense carbon layer upon heating, ammonium polyphosphate promoting char formation and gas-phase flame retardancy, and magnesium hydroxide decomposing and absorbing heat and diluting oxygen, resulting in a highly efficient synergistic flame retardant effect, significantly improving the fire safety level of pipelines, and effectively delaying the spread of flames.

[0016] 2. The present invention incorporates specific expandable graphite. Expandable graphite with different gradations can form a denser and more continuous expanded carbon layer, thereby more effectively isolating heat and oxygen. Furthermore, the reasonable particle size distribution is also beneficial to improving the dispersibility of the flame retardant in the polymer matrix, allowing it to fully exert its flame retardant effect.

[0017] 3. The specially formulated cross-linked polyethylene of this invention has a three-dimensional network structure, which has better stability, is not easily softened and deformed at high temperatures, extends service life, and can have a stronger bond with the first adhesive layer and the second adhesive layer, reducing the risk of interlayer separation. The formulations of cross-linked polyethylene and catalyst masterbatch both contain a highly efficient antioxidant system, which effectively prevents thermo-oxidative aging during high-temperature processing, protects the pipeline from oxygen degradation during long-term use, and thus helps to improve thermal stability and flame retardant performance. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] An embodiment of the present invention provides a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe, wherein the aluminum-plastic composite pipe comprises, from the inside out, a first cross-linked polyethylene layer, a first adhesive layer, an aluminum strip layer, a second adhesive layer, and a second cross-linked polyethylene layer; wherein, by weight ratio, the second cross-linked polyethylene layer comprises the following raw materials: 70-80 parts of cross-linked polyethylene, 3-5 parts of catalyst masterbatch, 10-25 parts of composite flame retardant, and 0.5-1 parts of antioxidant; The composite flame retardant is obtained by mixing expandable graphite, ammonium polyphosphate and magnesium hydroxide in a mass ratio of (5~10):(5~10):(5~15).

[0021] In one embodiment, the crosslinked polyethylene comprises the following raw materials in parts by weight: 90-100 parts high-density polyethylene, 0-10 parts low-density polyethylene, 1-3 parts silane coupling agent, 0.05-1 part initiator, and 0.5-5 parts antioxidant.

[0022] In one embodiment, the catalyst masterbatch comprises the following raw materials in parts by weight: 100 parts high-density polyethylene, 3 to 10 parts catalyst, and 0.5 to 5 parts antioxidant.

[0023] In one embodiment, the silane coupling agent in the crosslinked polyethylene is one or both of vinyltrimethoxysilane and vinyltriethoxysilane.

[0024] In one embodiment, the initiator in the crosslinked polyethylene is at least one of dicumyl peroxide, benzoyl tert-butyl peroxide, and bis-tert-butyl dicumyl peroxide.

[0025] In one embodiment, the antioxidant in the crosslinked polyethylene is at least one of pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl)phosphite, and dodecyl thiodipropionate.

[0026] In one embodiment, the catalyst masterbatch contains at least one of dibutyltin dilaurate and dioctyltin dilaurate.

[0027] In one embodiment, the antioxidant in the catalyst masterbatch is at least one selected from pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl)phosphite, and dodecyl thiodipropionate.

[0028] In one embodiment, the gradation of the expandable graphite is as follows: 60-80% of the expandable graphite has a particle size of less than 0.3 μm, 15-25% of the expandable graphite has a particle size of 0.5-0.9 μm, and 1-10% of the expandable graphite has a particle size of 1-20 μm.

[0029] In one embodiment, the expandable graphite has an expansion ratio of 80-100 mg / g below 100°C, an expansion ratio of 100-300 mg / g between 100-300°C, and an expansion ratio of more than 300 mg / g above 300°C.

[0030] In addition, the present invention also provides a method for preparing a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe, comprising the following steps: S1. Based on the raw materials for preparing cross-linked polyethylene, cross-linked polyethylene is prepared; S2. Based on the raw materials used in the preparation of catalyst masterbatch, catalyst masterbatch is prepared; S3. After mixing cross-linked polyethylene, catalyst masterbatch, composite flame retardant and antioxidant, the mixture is melt-blended and then injected into the molding die of plastic pipe to obtain the inner and outer pipes required for aluminum-plastic pipe; S4. After the aluminum strip is rolled into an aluminum tube, the joint of the aluminum tube is welded using welding equipment. Then, the aluminum tube is cut into the required length using shearing equipment. After that, it is polished by a polishing machine to obtain the shaped aluminum tube. Then, glue is evenly applied to the inner and outer surfaces of the shaped aluminum tube. S5. The injection-molded inner tube is adhered to the inner surface of the aluminum tube with glue, and then the injection-molded outer tube is covered to the outer surface of the aluminum tube with glue. The inner tube and outer tube are co-extruded with the aluminum tube to form an aluminum-plastic composite pipe. After cooling, an aluminum-plastic composite pipe is obtained.

[0031] In one embodiment, the cross-linked polyethylene is prepared by mixing 0-100 parts of high-density polyethylene, 0-10 parts of low-density polyethylene, 1-3 parts of silane coupling agent, 0.05-1 part of initiator and 0.5-5 parts of antioxidant for 5-10 minutes, melting and extruding at a temperature of 150-190°C with a screw speed of 100-300 r / min, cooling, and pelletizing to obtain cross-linked polyethylene.

[0032] In one embodiment, the catalyst masterbatch is prepared by mixing 100 parts of high-density polyethylene, 3-10 parts of catalyst and 0.5-5 parts of antioxidant for 5-10 minutes, melting and extruding at a temperature of 150-180°C, with the screw speed at 100-300 r / min, cooling, and pelletizing to obtain the catalyst masterbatch.

[0033] In one embodiment, in step S3, the temperature of the melt blending is 150~190°C.

[0034] In one embodiment, the inner tube is a first cross-linked polyethylene layer.

[0035] In one embodiment, the adhesive forms a first adhesive layer and a second adhesive layer. In one embodiment, the aluminum tube is an aluminum strip layer.

[0036] In one embodiment, the outer tube is a second cross-linked polyethylene layer.

[0037] In one embodiment, the thickness of the first cross-linked polyethylene layer is 2 mm to 3 mm.

[0038] In one embodiment, the thickness of the aluminum strip layer is 0.2 mm to 0.3 mm.

[0039] In one embodiment, the thickness of the second cross-linked polyethylene layer is 2 mm to 3 mm.

[0040] The above solution, by optimizing the composition of the first cross-linked polyethylene layer and the second cross-linked polyethylene layer and adding a composite flame retardant, can impart high heat resistance and flame retardancy to the aluminum-plastic composite pipe.

[0041] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0042] Examples 1-5: The difference between Examples 1 to 5 lies in the different raw materials and proportions used to prepare cross-linked polyethylene; otherwise, they are the same, as shown in Table 1.

[0043] The preparation method of cross-linked polyethylene includes the following steps: mixing high-density polyethylene, low-density polyethylene, silane coupling agent, initiator and antioxidant for 10 min, melt extruding at a temperature of 150~190℃ with a screw speed of 100 r / min, cooling, pelletizing to obtain cross-linked polyethylene.

[0044] Comparative Examples 1-3: Compared with Example 5, Comparative Examples 1-3 differ in that the raw materials and ratios for preparing cross-linked polyethylene are different, while other aspects are the same, as shown in Comparative Table 1.

[0045] Table 1: Raw materials for the preparation of cross-linked polyethylene

[0046] The cross-linked polyethylene samples prepared in Examples 1-5 and the cross-linked polyethylene samples prepared in Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Table 2 below.

[0047] The degree of crosslinking is referenced to GB / T18474-2001; the yield strength is referenced to GB / T18992; the condition of crosslinked polyethylene materials is obtained by sampling and testing records by those skilled in the art, and a microscope may be used when necessary.

[0048] Table 2: Properties of Crosslinked Polyethylene

[0049] The data analysis in Table 2 shows that by adding different amounts of the component lecithin to prepare cross-linked polyethylene, while ensuring the degree of cross-linking and yield strength, the quality of cross-linking should also be guaranteed. The cross-linked polyethylene with different degrees of cross-linking mentioned above was selected for use in the preparation of aluminum-plastic composite pipes.

[0050] Examples 6-8: The difference between Examples 6 to 8 lies in the ratio of the raw materials used for preparation; everything else is the same, as shown in Table 3. Examples 6-8 describe the preparation method of high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipes, including the following steps: S1. Based on the raw materials for preparing cross-linked polyethylene, cross-linked polyethylene is prepared; The preparation method of cross-linked polyethylene is the same as that of Examples 1 to 5. The cross-linked polyethylene prepared in Example 5 is selected for the preparation of aluminum-plastic composite pipes. S2. Based on the raw materials used in the preparation of catalyst masterbatch, catalyst masterbatch is prepared; The catalyst masterbatch is prepared by mixing 100 parts of high-density polyethylene, 3 parts of dibutyltin dilaurate and 0.5 parts of pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenylpropionate) for 10 min, melting and extruding at a temperature of 150~180℃ with a screw speed of 100 r / min, cooling, and pelletizing to obtain the catalyst masterbatch. S3. After mixing cross-linked polyethylene, catalyst masterbatch, composite flame retardant and antioxidant, melt blending is carried out at a temperature of 150~190℃, and then injected into the molding mold of plastic pipe to obtain the inner and outer pipes required for aluminum-plastic pipe; The composite flame retardant is obtained by mixing expandable graphite, ammonium polyphosphate, and magnesium hydroxide; and the gradation of the expandable graphite is as follows: 70% expandable graphite with a particle size of less than 0.3 μm, 20% expandable graphite with a particle size of 0.5~0.9 μm, and 10% expandable graphite with a particle size of 1~20 μm. S4. After the aluminum strip is rolled into an aluminum tube, the joint of the aluminum tube is welded using welding equipment. Then, the aluminum tube is cut into the required length using shearing equipment. After that, it is polished by a polishing machine to obtain the shaped aluminum tube. Then, glue is evenly applied to the inner and outer surfaces of the shaped aluminum tube. S5. The injection-molded inner tube is adhered to the inner surface of the aluminum tube with glue, and then the injection-molded outer tube is covered to the outer surface of the aluminum tube with glue. The inner tube and outer tube are co-extruded with the aluminum tube to form an aluminum-plastic composite pipe. After cooling, an aluminum-plastic composite pipe is obtained.

[0051] Comparative Example 4: The difference between Comparative Example 4 and Example 8 is that the catalyst masterbatch was replaced with dibutyltin dilaurate in Comparative Example 4, while the rest was the same as in Example 8.

[0052] Comparative Example 5: The difference between Comparative Example 5 and Example 8 is that Comparative Example 5 adds a single expandable graphite as a flame retardant, while the rest is the same as Example 8.

[0053] Comparative Example 6: The difference between Comparative Example 6 and Example 8 is that the gradation of expandable graphite in Comparative Example 6 is different, while the rest is the same as in Example 8. The gradation of expandable graphite in Comparative Example 6 is as follows: expandable graphite with a particle size of 20 μm accounts for 100%.

[0054] Comparative Example 7: The difference between Comparative Example 7 and Example 8 is that Comparative Example 7 adds a single ammonium polyphosphate as a flame retardant, while the rest is the same as Example 8.

[0055] Comparative Example 8: The difference between Comparative Example 8 and Example 8 is that Comparative Example 8 adds a single magnesium hydroxide as a flame retardant, while the rest is the same as Example 8.

[0056] Comparative Example 9: The difference between Comparative Example 9 and Example 8 is that no composite flame retardant was added in Comparative Example 9, but otherwise it is the same as Example 8.

[0057] Table 3: Raw materials (parts by weight) for the preparation of the first and second cross-linked polyethylene layers.

[0058] The aluminum-plastic composite pipe samples prepared in Examples 6-8 and the aluminum-plastic composite pipe samples prepared in Comparative Examples 4-9 were subjected to performance tests, and the results are shown in Table 4 below.

[0059] The samples were placed in a thermogravimetric analyzer for thermogravimetric analysis in a nitrogen atmosphere. The heating rate was 10℃ / min, and the maximum test temperature was 600℃ to test the temperature resistance. The oxygen index was tested according to GB / T2406.1-2008 standard, and the vertical burning performance was tested according to UL94 method.

[0060] Table 4: Performance Test Results of Aluminum-Plastic Composite Pipes

[0061] Analysis of the data in Table 4 shows that, through component optimization, this invention achieves an aluminum-plastic composite pipe with excellent thermal stability and significant flame retardant performance. Compared to Example 8, Comparative Example 4, which used dibutyltin dilaurate to replace the catalyst masterbatch, exhibited a lower thermal decomposition temperature and oxygen index, indicating that directly using the catalyst affects the dispersion of the system, the crosslinking, and the compatibility of the flame retardant and its functional groups. Comparative Example 5, which added a single expandable graphite as a flame retardant, while possessing some flame retardancy, lacked gas-phase flame retardancy and endothermic dilution effects, resulting in inferior flame retardant performance compared to Example 8. Comparative Example 7, which added a single ammonium polyphosphate as a flame retardant, lacked char layer reinforcement and endothermic effects, resulting in poor thermal stability and inferior flame retardant performance compared to Example 8. Comparative Example 8, which added a single magnesium hydroxide as a flame retardant, while possessing endothermic properties, lacked char formation and gas-phase flame retardancy, resulting in significantly worse flame retardancy than Example 8. This demonstrates that the present invention, using a composite system of expandable graphite, ammonium polyphosphate, and magnesium hydroxide as a flame retardant, not only effectively improves thermal stability but also exhibits a certain synergistic effect on flame retardancy. The expanded graphite in Comparative Example 6 has a different gradation. The carbon layer formed by the large-particle-size expanded graphite is not as dense as that in Example 8, and it also affects its dispersibility in the system, thus affecting the flame retardant effect and the decrease in oxygen index. This shows that the optimization of the expanded graphite gradation in this invention has a promoting effect on the flame retardant liquid. No composite flame retardant was added in Comparative Example 9. Without the addition of flame retardant, the material is flammable and cannot meet the safety requirements. Therefore, no flame retardant rating is evaluated.

[0062] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high efficiency flame retardant heat resistant type of aluminium plastic composite pipe, characterized by, The aluminum-plastic composite pipe comprises, from the inside out, a first cross-linked polyethylene layer, a first adhesive layer, an aluminum strip layer, a second adhesive layer, and a second cross-linked polyethylene layer; wherein, by weight, the second cross-linked polyethylene layer comprises the following raw materials: 70-80 parts of cross-linked polyethylene, 3-5 parts of catalyst masterbatch, 10-25 parts of composite flame retardant, and 0.5-1 parts of antioxidant. ​ The composite flame retardant is obtained by mixing expandable graphite, ammonium polyphosphate and magnesium hydroxide in a mass ratio of (5~10):(5~10):(5~15).

2. The aluminum-plastic composite pipe according to claim 1, characterized by The cross-linked polyethylene comprises the following raw materials in parts by weight: 90-100 parts high-density polyethylene, 0-10 parts low-density polyethylene, 1-3 parts silane coupling agent, 0.05-1 part initiator, and 0.5-5 parts antioxidant.

3. The aluminum-plastic composite pipe according to claim 1, wherein The catalyst masterbatch comprises the following raw materials in parts by weight: 100 parts high-density polyethylene, 3-10 parts catalyst, and 0.5-5 parts antioxidant.

4. The aluminum-plastic composite pipe according to claim 2, characterized in that, In the cross-linked polyethylene, the silane coupling agent is one or both of vinyltrimethoxysilane and vinyltriethoxysilane.

5. The aluminum-plastic composite pipe according to claim 2, characterized in that, In the cross-linked polyethylene, the initiator is at least one of dicumyl peroxide, benzoyl tert-butyl peroxide, and bis-tert-butyl dicumyl peroxide.

6. The aluminum-plastic composite pipe according to claim 2, characterized in that, In the cross-linked polyethylene, the antioxidant is at least one of pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl)phosphite, and disododecyl thiodipropionate.

7. The aluminum-plastic composite pipe according to claim 3, characterized in that, In the catalyst masterbatch, the catalyst is at least one of dibutyltin dilaurate and dioctyltin dilaurate.

8. The aluminum-plastic composite pipe according to claim 3, characterized in that, In the catalyst masterbatch, the antioxidant is at least one selected from pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl)phosphite, and dodecyl thiodipropionate.

9. The aluminum-plastic composite pipe according to claim 1, characterized in that, The gradation of the expandable graphite is as follows: 60-80% of the expandable graphite has a particle size of less than 0.3 μm, 15-25% of the expandable graphite has a particle size of 0.5-0.9 μm, and 1-10% of the expandable graphite has a particle size of 1-20 μm.

10. A method for preparing a high-efficiency flame-retardant and heat-resistant aluminum-plastic composite pipe, characterized in that, The preparation method is used to prepare the aluminum-plastic composite pipe according to any one of claims 1 to 9, and the preparation method includes the following steps: S1. Based on the raw materials for preparing cross-linked polyethylene, cross-linked polyethylene is prepared; S2. Based on the raw materials used in the preparation of catalyst masterbatch, catalyst masterbatch is prepared; S3. After mixing cross-linked polyethylene, catalyst masterbatch, composite flame retardant and antioxidant, the mixture is melt-blended and then injected into the molding die of plastic pipe to obtain the inner and outer pipes required for aluminum-plastic pipe; S4. After the aluminum strip is rolled into an aluminum tube, the joint of the aluminum tube is welded using welding equipment. Then, the aluminum tube is cut into the required length using shearing equipment. After that, it is polished by a polishing machine to obtain the shaped aluminum tube. Then, glue is evenly applied to the inner and outer surfaces of the shaped aluminum tube. S5. The injection-molded inner tube is adhered to the inner surface of the aluminum tube with glue, and then the injection-molded outer tube is covered to the outer surface of the aluminum tube with glue. The inner tube and outer tube are co-extruded with the aluminum tube to form an aluminum-plastic composite pipe. After cooling, an aluminum-plastic composite pipe is obtained.

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