A silane crosslinked polyethylene pipe and a method for producing the same

Abstract

This invention relates to a silane cross-linked polyethylene pipe and its preparation method, belonging to the technical field of polyethylene pipes. The silane cross-linked polyethylene pipe provided by this invention, by mass percentage, comprises the following components: 0.8-2.5% silane, 0.3-0.6% antioxidant, 0.3-0.6% UV resistant agent, 0.01-0.05% organotin catalyst, 0.1-0.3% compound lubricant, 2-5% nano-montmorillonite, 0.1-0.5% free radical initiator, and the balance being high-density polyethylene; the compound lubricant includes calcium stearate and pentaerythritol tetrastearate; the nano-montmorillonite has a diameter-to-thickness ratio of 500-1000. The pipe provided by this invention has excellent chlorine and UV resistance and high strength, passing the highest level of chlorine and UV resistance testing by the US NSF and obtaining Australian PEX125 certification, meeting market demands for higher pressure ratings, stronger aging resistance, greater flow capacity, and longer outdoor service life.

Description

Technical Field

[0001] This invention relates to the field of polyethylene pipe technology, and in particular to a silane cross-linked polyethylene pipe and its preparation method. Background Technology

[0002] With the emergence of applications such as high-rise buildings and outdoor heating, both domestic and international markets have increasingly stringent application requirements for cross-linked polyethylene (PEX) pipes, mainly focusing on three key dimensions: first, higher pressure rating compatibility to address issues such as pressure superposition in high-rise buildings and pressure loss during long-distance transportation; second, stronger aging resistance, especially in environments with chlorinated water and outdoor ultraviolet radiation, enhancing safety and stability; and third, greater throughput and longer outdoor service life to meet high-flow water demands and resist corrosion from complex outdoor climates. A comprehensive improvement in the performance of PEX pipes is a common goal across the entire industry.

[0003] In recent years, the global PEX pipe market has maintained a relatively stable technological landscape, with mainstream products concentrated in the PEX80 and PEX100 pressure ratings. These two ratings, thanks to their mature technology and stable performance, have long been suitable for the needs of conventional buildings and general heating systems, dominating the market. However, with the expansion of high-end applications, high-performance PEX pipe products exceeding the pressure resistance limit of PEX100 and reaching PEX125 levels remain unavailable, with no mature mass-produced products yet. Meanwhile, market demand for PEX125 level applications has emerged. For example, in high-rise buildings, the increased hydrostatic pressure due to floor height places higher demands on the pipes' pressure resistance limits; in industrial or commercial building water supply and heating systems with significant water hammer effects, instantaneous pressure surges also severely test the pipes' pressure resistance. These scenarios urgently require PEX125 level pipes to fill the performance gap.

[0004] Therefore, there is an urgent need to develop a pipe material that meets the PEX125 standard to meet the market's application requirements for high pressure resistance and weather resistance of pipes, and to promote product upgrading and technological progress in the plastic pipe industry. This is of great significance for industrialization. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a silane cross-linked polyethylene pipe and its preparation method. The pipe provided by this invention has high chlorine resistance, UV resistance, and high strength, and can meet the current market requirements for high-pressure resistant pipe materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a silane cross-linked polyethylene pipe, wherein the raw materials for preparing the silane cross-linked polyethylene pipe, by mass percentage, comprise the following components: 0.8-2.5% silane, 0.3-0.6% antioxidant, 0.3-0.6% UV resistant agent, 0.01-0.05% organotin catalyst, 0.1-0.3% compound lubricant, 2-5% nano-montmorillonite, 0.1-0.5% free radical initiator, balance high-density polyethylene; The compound lubricant includes calcium stearate and pentaerythritol tetrastearate; The aspect ratio of the nano-montmorillonite is 500-1000.

[0007] This invention utilizes multiple strategies, including cross-linking reinforcement, protective enhancement, and nano-reinforcement, to obtain cross-linked polyethylene pipes with high pressure resistance, weather resistance, aging resistance, and easy processing. High-density polyethylene (HDPE) provides the basic mechanical strength, and its molecular chains provide the backbone for silane crosslinking. A specific amount of silane acts as the crosslinking functional agent, containing unsaturated bonds that can be grafted onto the polyethylene chains and hydrolyzable alkoxy groups. This allows it to graft onto the HDPE molecular chains, hydrolyze and condense to form Si-O-Si crosslinks, constructing a three-dimensional network structure. During processing, a free radical initiator decomposes to generate free radicals, initiating dehydrogenation of the HDPE molecular chains to form active sites, promoting silane molecule grafting, and laying the foundation for subsequent crosslinking reactions. An organotin catalyst accelerates the hydrolysis and condensation after silane grafting, improving the uniformity of crosslinking and reaction efficiency, and avoiding performance defects caused by insufficient or excessive crosslinking.

[0008] Using specific compound lubricants effectively reduces friction within the material and between the material and equipment during processing, improving pressure resistance. Furthermore, these specific compound lubricants enhance the degree of cross-linking, promote grafting reactions, reduce processing defects, ensure structural integrity, and comprehensively construct a strengthened cross-linked network structure. Using a single lubricant may result in uneven distribution, incomplete cross-linked networks, or insufficient cross-linking. Using inappropriate lubricant combinations can also weaken the cross-linking effect, capture free radicals, reduce cross-linking reaction efficiency, and affect the overall mechanical properties of the material.

[0009] Antioxidants can inhibit the oxidative degradation of HDPE during long-term outdoor use, reduce molecular chain breakage, and protect the cross-linked structure from oxidative damage; UV-resistant additives extend the service life of the material, absorb or shield ultraviolet rays, and inhibit polymer degradation and cross-linked structure aging caused by ultraviolet radiation. The two together form a synergistic protection system.

[0010] Meanwhile, this invention also employs nano-montmorillonite with a specific ratio and aspect ratio, which not only enhances the material's compressive strength but also physically blocks ultraviolet rays due to its layered structure, synergistically improving the protective effect with anti-UV additives. On the other hand, the high aspect ratio nano-montmorillonite has a huge specific surface area and high aspect ratio. The nano-layered structure is dispersed in the matrix and can generate strong interfacial interactions with the polyethylene molecular chains, effectively restricting the movement of polymer chain segments, thereby significantly improving the tensile modulus, flexural modulus, and hardness of the material, achieving higher compressive strength. Synergistic reinforcement with the silane-high-density polyethylene crosslinking network can improve the material's rigidity, heat resistance, and resistance to environmental stress cracking.

[0011] This invention optimizes the formulation system, crosslinking method, and nano-reinforcement of silane crosslinked polyethylene materials. By reconstructing the material's formulation system, it endows the pipes with properties such as chlorine resistance, UV resistance, and high strength. It can pass the highest level of chlorine and UV resistance tests by the US NSF and also pass the Australian PEX 125 level certification, meeting the current market's high demand for pipe performance.

[0012] Preferably, the high-density polyethylene conforms to PEX 100 grade. The present invention preferably uses high-density polyethylene material with good pressure resistance as the matrix, including but not limited to HE3495-LS.

[0013] Preferably, the silane includes at least one of vinyltriethoxysilane (VTES) and vinyltri(2-methoxyethoxy)silane (VTMOEO).

[0014] Preferably, the anti-UV additive includes at least one of ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS).

[0015] More preferably, the UV-resistant additive includes at least one of UV950L, UV-328, UV570, UV-622, UV-3346, reactive UVA, and reactive HALS.

[0016] More preferably, the UV-resistant additive comprises reactive UVA and reactive HALS in a mass ratio of (0.8-1.2):(0.8-1.2).

[0017] As a preferred embodiment of the present invention, the reactive UVA is a benzotriazole reactive UVA, such as at least one of 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, 1-(2'-hydroxy-5'-methacryloyloxyethylphenyl)-2H-benzotriazole, and 2-[2'-hydroxy-3'-(2-acryloyloxyethyl)-5'-methylphenyl]-2H-benzotriazole; the reactive HALS is an acryloyloxy-containing reactive HALS, such as at least one of 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine, and 1-acryloyl-4-acryloyloxy-2,2,6,6-tetramethylpiperidine.

[0018] Preferably, the free radical initiator includes at least one of dicumyl peroxide (DCP) and di-tert-butyl peroxide (DTBP).

[0019] As a preferred embodiment of the present invention, the mass ratio of the free radical initiator to the UV-resistant auxiliary agent is (0.8-1.2):(1.8-2.2).

[0020] The present invention preferably uses the above-mentioned specific reactive anti-UV additive combination, which, under the action of free radical initiator, can be better grafted onto the molecular chain of HDPE, avoid migration and precipitation, better block the degradation effect of ultraviolet rays on the cross-linking network, significantly improve the long-term anti-UV effect of the pipe, further extend the service life and weather resistance, and better meet the high usage requirements of high-rise buildings and outdoor heating for pipes.

[0021] Preferably, the compound lubricant comprises calcium stearate and pentaerythritol tetrastearate in a mass ratio of (0.8-1.2):(0.8-1.2).

[0022] Using the lubricant in the above specific ratio is beneficial to the formation of a uniform and dense silane cross-linked network and a defect-free molded structure, thereby improving structural stability.

[0023] Preferably, the organotin catalyst includes at least one of dibutyltin dilaurate and stannous octoate.

[0024] Preferably, the antioxidant includes a primary antioxidant and a secondary antioxidant; the primary antioxidant includes at least one of antioxidant AO-80, antioxidant 1790, and antioxidant 1098, and the secondary antioxidant includes at least one of antioxidant 626, antioxidant 168, and antioxidant DSTDP.

[0025] More preferably, the antioxidant comprises antioxidant AO-80 and antioxidant 168 in a mass ratio of (0.8-1.2):(0.8-1.2).

[0026] Secondly, the present invention provides a method for preparing the above-mentioned silane cross-linked polyethylene pipe, comprising the following steps: S1. The raw materials are mixed evenly, and then a plastic pipe is prepared by single screw extrusion process. The plastic pipe is then vacuum sizing and cooled to obtain the shaped pipe. S2. The molded pipe is subjected to steam pressurization treatment to obtain the silane cross-linked polyethylene pipe.

[0027] Preferably, the pressurization pressure is 0.4-0.6 MPa, and the steam temperature is 115-125 °C; Preferably, the extrusion temperatures for the single-screw process are: Zone 1: 145-155℃, Zone 2: 155-165℃, Zone 3: 165-175℃, Zone 4: 175-185℃, Zone 5: 180-190℃, Zone 6: 185-195℃, and Zone 7: 190-200℃; the die head temperature is 195-205℃. Excessive temperature in any zone will produce pre-crosslinking impurities, while insufficient temperature will result in substandard crosslinking, affecting the pipe's performance.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a silane cross-linked polyethylene pipe. Through multiple strategies of cross-linking reinforcement, protection, and nano-reinforcement, the material formulation system, cross-linking method, and nano-reinforcement are optimized. By reconstructing the formulation system of the cross-linked polyethylene material, the pipe is endowed with properties such as chlorine resistance, UV resistance, and high strength. It can pass the highest level of chlorine and UV resistance tests by the US NSF and can also pass the Australian PEX125 level certification, meeting the current market's high demand for pipe performance and having high application value. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the appearance of the silane cross-linked polyethylene pipe in an embodiment of the present invention. Detailed Implementation

[0030] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0031] Examples 1-10 and Comparative Examples 1-9 Examples 1-10 are embodiments of a silane cross-linked polyethylene pipe of the present invention, with the appearance as follows: Figure 1 As shown.

[0032] The raw material formulations for the preparation of silane cross-linked polyethylene pipes in Examples 1-10 are shown in Table 1; the raw material formulations for the preparation of silane cross-linked polyethylene pipes in Comparative Examples 1-9 are shown in Table 2; the formulations in Tables 1 and 2 are all expressed as mass percentages. Specifically, the reactive UVA uses 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole (Chengfeng), and the reactive HALS uses 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine (Shanghai Yuanye); the nano-montmorillonite with different aspect ratios is the SMP series product from Zhejiang Fenghong.

[0033] The preparation methods of the silane crosslinked polyethylene pipes described in Examples 1-10 and Comparative Examples 1-9 all include the following steps: S1. The raw materials are mechanically mixed evenly according to the mass percentages in Tables 1 and 2. A single-screw extruder is used to extrude the plastic pipe through a die. The pipe is then drawn by a traction machine and subjected to vacuum sizing and cooling to obtain the shaped pipe. The barrel temperature of the single-screw extruder is set as follows: Zone 1: 145~155 ℃; Zone 2: 155~165 ℃; Zone 3: 165~175 ℃; Zone 4: 175~185 ℃; Zone 5: 180~190 ℃; Zone 6: 185~195 ℃; Zone 7: 190~200 ℃; Head temperature: 195~205 ℃; S2. Place the pipe in a high-temperature and high-pressure steam chamber and treat it at a steam temperature of 120 ℃ and a pressure of 0.5 MPa for 3.5 h to complete the hydrolysis and cross-linking, and obtain the silane cross-linked polyethylene pipe.

[0034] Table 1 Table 2 Example of effect To investigate the performance of the silane cross-linked polyethylene pipe provided by the present invention, the following performance tests were conducted on the silane cross-linked polyethylene pipes in the examples and comparative examples: 1) Degree of crosslinking: Tested according to ISO 10147; 2) Chlorine resistance and UV resistance: Refer to ASTM F876 "Standard Specifification for Crosslinked Polyethylene (PEX) Tubing" for testing, which requires a chlorine resistance level of 5 and a UV resistance level of 3. 3) Hydrostatic strength: Refer to AS 2492 "Cross-linked polyethylene (PE-X) pipes for pressure applications", which requires compliance with PEX 125 level; 4) UV-resistant additive grafting rate: Using solvent extraction, the grafted sample was accurately weighed (W1). A reagent that is a good solvent for the UV-resistant additive but a poor solvent for the polymer matrix was used for reflux extraction in a Soxhlet extractor until all ungrafted additives were completely removed. The extracted sample was dried to constant weight and accurately weighed again (W2). The grafting rate was calculated as (W1-W2) / W1×100%. The test results are shown in Table 3 below.

[0035] Table 3 In Table 3, a chlorine resistance rating of 5 indicates that the pipe will not degrade or fail in water containing 4 ppm chlorine at 60 ℃, with a decrease in chlorine resistance and a lower chlorine resistance rating; a UV resistance rating of 3 indicates that the pipe can be safely exposed to the outdoor natural environment for 6 months without performance failure, with a decrease in UV resistance and a lower UV resistance rating.

[0036] As shown in Table 3: The silane cross-linked polyethylene pipe provided by this invention has excellent chlorine resistance and UV resistance, meeting the 5306 grade of ASTM F876; at the same time, its pressure resistance meets the PEX125 grade specified in AS 2492, and its overall performance is significantly better than that of the comparative example.

[0037] Comparative Examples 1 and 2 showed significant deterioration in all performance aspects under unsuitable component ratios. In Comparative Example 3, replacing calcium stearate in the compound lubricant with zinc stearate resulted in zinc stearate capturing free radicals, thus affecting crosslinking efficiency and significantly reducing the degree of crosslinking, severely weakening the pipe's weather resistance and mechanical properties. In Comparative Example 4, replacing pentaerythritol tetrastearate in the compound lubricant with oleamide may cause phase separation interference in this system, leading to uneven distribution of crosslinking degree inside and outside the pipe and a decrease in crosslinking point density, directly affecting various performance aspects. Comparative Example 5 used a single hard... Although calcium fatty acid has little impact on the overall degree of crosslinking, it is more prone to uneven crosslinking, increasing the risk of local stress cracking and making the pipe more prone to rupture and leakage under hydrostatic strength test conditions. In Comparative Example 6, when pentaerythritol tetrastearate was used alone, the compatibility was poor, resulting in uneven component migration, easier surface deterioration, decreased weather resistance, and poorer resistance to chlorine and UV. In Comparative Examples 7, 8, and 9, when nano-montmorillonite was not used, the diameter-to-thickness ratio of montmorillonite was insufficient, or other fillers were used, the weather resistance and mechanical properties of the pipes were affected to varying degrees.

[0038] In summary, the silane cross-linked polyethylene pipe provided by this invention effectively improves the performance of existing cross-linked polyethylene pipes from multiple aspects through a multi-pronged strategy of strengthening the cross-linking network, optimizing auxiliary additives, and nano-reinforcement. By reconstructing the material formulation system, it endows the pipe with superior chlorine resistance, UV resistance, and high strength. The silane cross-linked polyethylene pipe provided by this invention can pass the highest level of chlorine and UV resistance tests by the US NSF and can pass the Australian PEX 125 level certification, meeting the current market's high demand for pipe performance and possessing high application value.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silane cross-linked polyethylene pipe, characterized in that, The raw materials for preparing the silane cross-linked polyethylene pipe, by weight percentage, include the following components: 0.8-2.5% silane, 0.3-0.6% antioxidant, 0.3-0.6% UV resistant agent, 0.01-0.05% organotin catalyst, 0.1-0.3% compound lubricant, 2-5% nano-montmorillonite, 0.1-0.5% free radical initiator, balance high-density polyethylene; The compound lubricant includes calcium stearate and pentaerythritol tetrastearate; The aspect ratio of the nano-montmorillonite is 500-1000.

2. The silane cross-linked polyethylene pipe as described in claim 1, characterized in that, The silane includes at least one of vinyltriethoxysilane and vinyltri(2-methoxyethoxy)silane.

3. The silane cross-linked polyethylene pipe as described in claim 1, characterized in that, The UV-resistant additives include at least one of ultraviolet absorbers and hindered amine light stabilizers.

4. The silane cross-linked polyethylene pipe as described in claim 3, characterized in that, The UV-resistant additives include a reactive UV absorber and a reactive hindered amine light stabilizer in a mass ratio of (0.8-1.2):(0.8-1.2).

5. The silane cross-linked polyethylene pipe as described in claim 1, characterized in that, The free radical initiator includes at least one of dicumyl peroxide and di-tert-butyl peroxide.

6. The silane cross-linked polyethylene pipe as described in claim 4 or 5, characterized in that, The mass ratio of the free radical initiator to the UV-resistant auxiliary agent is (0.8-1.2):(1.8-2.2).

7. The silane cross-linked polyethylene pipe as described in claim 1, characterized in that, The compound lubricant comprises calcium stearate and pentaerythritol tetrastearate in a mass ratio of (0.8-1.2):(0.8-1.2).

8. The silane cross-linked polyethylene pipe as described in claim 1, characterized in that, The organotin catalyst includes at least one of dibutyltin dilaurate and stannous octoate.

9. The method for preparing silane cross-linked polyethylene pipes as described in claims 1-8, characterized in that, Includes the following steps: S1. The raw materials are mixed evenly, and then a plastic pipe is prepared by single screw extrusion process. The plastic pipe is then vacuum sizing and cooled to obtain the shaped pipe. S2. The molded pipe is subjected to steam pressurization treatment to obtain the silane cross-linked polyethylene pipe.

10. The method for preparing a silane cross-linked polyethylene pipe as described in claim 9, characterized in that, The extrusion temperatures for the single-screw extrusion process are as follows: Zone 1: 145-155℃, Zone 2: 155-165℃, Zone 3: 165-175℃, Zone 4: 175-185℃, Zone 5: 180-190℃, Zone 6: 185-195℃, Zone 7: 190-200℃; and the die head temperature is 195-205℃.

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