Flexible PE-Xb pipe and preparation process thereof

Abstract

According to the flexible PE-Xb pipe and the preparation technology thereof, the problems that a traditional PE-Xb pipe is high in hardness, inconvenient to construct and the like are solved, and meanwhile the heat resistance and the pressure resistance of the flexible PE-Xb pipe are improved. Different from a traditional high-density polyethylene pipe, the high-density polyethylene pipe adopts a ternary composite system and comprises 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene and 0.2-1.0 part of antioxidant, and by optimizing the formula, the density of the pipe is reduced to 0.930-0.950 g / cm < 3 >, and the crosslinking degree is increased to 65-80%. In the preparation process, a one-step method and a two-step method are provided; the one-step method comprises the following steps: mixing silane, an antioxidant, an organic tin catalyst and modified polyethylene particles, and then directly extruding, molding and cross-linking; the two-step method comprises the following steps: respectively preparing a material A containing silane and a material B containing an organic tin catalyst and peroxide, mixing, carrying out extrusion molding, and finishing crosslinking. According to the two processes, high-efficiency grafting and uniform crosslinking of silane and polyethylene molecular chains are ensured by accurately controlling parameters such as temperature, screw rotating speed and extrusion pressure.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material processing, and in particular to a formula of a flexible PE-Xb pipe for low-temperature floor radiant heating and a preparation process thereof, which significantly improves the flexibility of the pipe through material modification while meeting mechanical properties and processing requirements. Background Art

[0002] PE-Xb pipe is a high-performance cross-linked polyethylene pipe widely used in low-temperature floor radiant heating systems. This pipe has excellent heat resistance and mechanical properties, and can remain stable during long-term high-temperature hot water transportation, making it an indispensable material in modern building heating systems. In low-temperature floor radiant heating systems, PE-Xb pipes are laid in the floor structure layer, and heat is evenly transferred to the entire room through hot water circulation, providing a comfortable indoor temperature. Its good flexibility and pressure resistance enable it to adapt to complex laying environments, while reducing pipe connection points and reducing the risk of water leakage. In addition, PE-Xb pipes are gradually being widely used in homes and commercial buildings due to their environmentally friendly and durable characteristics.

[0003] The existing production process of PE-Xb pipes is mainly divided into one-step and two-step methods. The one-step process is to mix high-density polyethylene with cross-linking agents such as silane and peroxide, extrude it through a single-screw extruder, and then complete the cross-linking reaction in a steam room; the advantages of this process are high production efficiency and low cost, and it is suitable for large-scale production. However, it has high control requirements for raw materials and process parameters. Once improperly operated, it will lead to insufficient cross-linking degree or unstable pipe performance. The two-step process is divided into two stages: first, high-density polyethylene is mixed with silane to form material A; then high-density polyethylene is mixed with organic tin catalysts and the like to form material B; finally, material A and material B are mixed in a certain proportion and extruded, and cross-linked in a steam room; the advantage is that the cross-linking reaction is more uniform and the pipe performance is more stable, but its disadvantages are complex production process, high production cost, and relatively low production efficiency.

[0004] Although PE-Xb pipes have many advantages in performance, there are still some problems that need to be solved in the existing technology. The most prominent problem is that the pipes are too hard, which brings great inconvenience to construction. Traditional PE-Xb pipes mainly use high-density polyethylene, whose density is about 0.95g / cm³, resulting in a high hardness of the pipes. During the construction of low-temperature floor radiant heating systems, pipes need to be bent frequently to adapt to complex laying paths. However, overly hard pipes are not only difficult to bend, but also prone to stress concentration during the bending process, resulting in cracks or deformation of the pipes, increasing the difficulty and cost of construction. In addition, overly hard pipes are also prone to damage due to collisions during transportation and storage, further affecting their service life and reliability. Therefore, the existing PE-Xb pipes are too hard and cannot maintain excellent mechanical properties and heat resistance at the same time. Summary of the invention

[0005] The purpose of the present invention is to provide a flexible PE-Xb pipe and its preparation process, aiming to solve the problems of high hardness and inconvenient construction of existing PE-Xb pipes. By optimizing the formula and production process of polyethylene materials, pipes with higher softness, excellent processing performance and reliable long-term pressure resistance are produced, which are suitable for low-temperature floor radiant heating systems.

[0006] The invention provides a PE-Xb pipe which is softer and more convenient to construct, while maintaining good processing performance and long-term pressure resistance.

[0007] The flexible PE-Xb pipe formula of the present invention adopts a ternary polyethylene composite system. In the prior art, PE-Xb pipes are usually based on high-density polyethylene, and some of them improve processability by adding a small amount of low-density polyethylene, but there is no formula with heat-resistant polyethylene as the main component; the introduction of heat-resistant polyethylene in the present invention significantly improves the heat resistance of the pipe (the long-term use temperature can reach 95°C-100°C), while the linear low-density polyethylene compensates for the brittleness caused by high cross-linking, forming a unique performance balance. The density range of traditional PE-Xb pipes is 0.940-0.965g / cm 3The present invention reduces the density by combining linear low-density polyethylene and heat-resistant polyethylene, achieving a lower density of 0.930-0.950g / cm³ while maintaining mechanical properties; under the premise of reduced density, the present invention does not sacrifice compressive strength, breaking through the rigidity limitation of traditional high-density polyethylene substrates. The present invention achieves double optimization through a ternary composite system, reducing the elastic modulus through linear low-density polyethylene, so that the bending radius of the pipe is ≤5D, which is different from the specification of traditional PE-Xb pipes ≥8D, while maintaining a PN10-PN16 pressure resistance grade, achieving a balance between flexibility and pressure resistance; and the introduction of heat-resistant polyethylene in the formula of the present invention increases the long-term use temperature of the pipe from 90°C of traditional PE-Xb to 95-100°C, which is suitable for higher temperature scenarios such as central heating trunk pipes.

[0008] The present invention provides a flexible PE-Xb pipe, the formula of which mainly comprises the following raw material components in parts by mass: 10-60 parts of high-density polyethylene (HDPE), 5-20 parts of linear low-density polyethylene (LLDPE), 20-50 parts of heat-resistant polyethylene (PE-RT), and 0.2-1.0 parts of antioxidant; the density of the flexible PE-Xb pipe is 0.930-0.950g / cm³, and the cross-linking degree is 65-80%.

[0009] The degree of crosslinking refers to the degree to which the polyethylene molecular chains form a three-dimensional network structure through chemical bonds. A high degree of crosslinking can significantly improve the heat resistance, pressure resistance and chemical stability of the pipe, but an excessively high degree of crosslinking may cause the material to become brittle and reduce flexibility. In the present invention, by optimizing the formula and process, the degree of crosslinking of the flexible PE-Xb pipe of the present invention can reach 65%-80%, significantly improving the heat resistance and pressure resistance of the pipe, while avoiding the embrittlement problem caused by excessive crosslinking.

[0010] High-density polyethylene has high crystallinity and density (usually 0.940-0.970 g / cm³), so it has good mechanical properties, such as high strength, high rigidity and good chemical corrosion resistance. In pipes, high-density polyethylene mainly provides the structural strength and pressure resistance of the pipe, ensuring that the pipe can withstand high internal pressure during use. Its high crystallinity enables it to maintain a certain stability at high temperatures, but its flexibility is poor.

[0011] Linear low-density polyethylene is a linear polyethylene that is copolymerized with a small amount of α-olefins (such as butene, hexene or octene) to introduce short branches, thereby reducing crystallinity. Its main characteristics are good flexibility and impact resistance, and a low density (usually 0.910-0.940 g / cm³). In pipes, the addition of LLDPE can significantly reduce the rigidity of the pipe, improve flexibility, make it easier to bend during construction, and reduce stress concentration and rupture risks caused by bending.

[0012] Heat-resistant polyethylene is a polyethylene modified by a special process. It has excellent heat resistance and can be used for a long time at high temperatures without significant performance degradation. Its density is usually between 0.940-0.960 g / cm³, which is between high-density polyethylene and linear low-density polyethylene, but its heat resistance is much higher than that of ordinary polyethylene. The addition of linear low-density polyethylene can significantly increase the long-term use temperature of the pipe, making it adaptable to higher temperature application scenarios, such as central heating systems.

[0013] The components of high-density polyethylene, linear low-density polyethylene, and heat-resistant polyethylene work together to achieve a balance between flexibility and strength. High-density polyethylene provides high strength and rigidity, linear low-density polyethylene provides flexibility, and heat-resistant polyethylene balances the two and improves heat resistance. By optimizing the ratio of the three, the balance between high strength and high flexibility of the pipe can be achieved, making it easier to operate during construction while maintaining good mechanical properties during use. The addition of heat-resistant polyethylene significantly improves the heat resistance of the pipe, while the flexibility of linear low-density polyethylene can compensate for the embrittlement of the material caused by high temperature. The high strength of high-density polyethylene ensures that the pipe can still maintain good pressure resistance at high temperatures. Through the ternary composite system, the density of the pipe is reduced to 0.930-0.950 g / cm³, while maintaining good mechanical properties and heat resistance. This composite system enables the pipe to perform well in low-temperature floor radiant heating systems and central heating systems, meeting the needs of complex application scenarios.

[0014] Specifically, the flexible PE-Xb pipe formula of the present invention breaks the limitation of conventional single polyethylene raw material by combining 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene and 20-50 parts of heat-resistant polyethylene in a unique ratio, giving full play to the hardness of high-density polyethylene, the flexibility of linear low-density polyethylene and the heat resistance of heat-resistant polyethylene, achieving complementary performance of different properties, and taking into account hardness, flexibility and heat resistance; at the same time, the precise dosage of 0.2-1.0 parts of antioxidants can not only ensure the antioxidant performance of the pipe but also avoid cost increase; at the same time, the density of 0.930-0.950g / cm³ and the cross-linking degree of 65-80% are accurately controlled to optimize the comprehensive performance of the pipe, so that the pipe can achieve an excellent balance in flexibility, heat resistance, mechanical properties, etc., meet the needs of complex scenarios, and also perform excellently in cost control and environmental protection.

[0015] Among them, heat-resistant polyethylene is polyethylene modified by a special polymerization process. Its molecular chain contains a small amount of long branches, which can improve the crystallinity and thermal stability of the material. Compared with ordinary polyethylene, its molecular chain structure is more regular and has a higher crystallinity, which improves the heat resistance of the material. The heat resistance of heat-resistant polyethylene mainly comes from its high crystallinity and special molecular structure. High crystallinity enables the material to maintain stable physical properties at high temperatures. During long-term high-temperature use, the molecular chain structure of heat-resistant polyethylene can resist thermal oxidative degradation, thereby extending the service life of the pipe.

[0016] In the composite system, heat-resistant polyethylene works synergistically with high-density polyethylene and linear low-density polyethylene. By optimizing the formula ratio, the heat resistance of heat-resistant polyethylene can make up for the insufficient performance of high-density polyethylene and linear low-density polyethylene at high temperatures. In the present invention, the mass fraction of heat-resistant polyethylene is 20-50 parts, which accounts for a large proportion, thereby significantly improving the heat resistance of the pipe. By reasonably adjusting the ratio of high-density polyethylene and linear low-density polyethylene, the comprehensive performance of the pipe can be further optimized, so that it can improve heat resistance while maintaining flexibility. During the preparation process, the raw materials are melt-blended by a twin-screw extruder to ensure that the heat-resistant polyethylene, high-density polyethylene and linear low-density polyethylene are fully mixed to form a uniform composite material. By accurately controlling the extrusion temperature and screw speed, the crystallinity and molecular chain structure of the material are further optimized, thereby improving the heat resistance. Through the above-mentioned formula and process optimization, the long-term use temperature of the pipe is increased from 90°C of the traditional PE-Xb pipe to 95°C-100°C. This enables the pipe to adapt to higher temperature application scenarios, such as central heating trunk pipes, and broadens the scope of use of the pipe.

[0017] The flexible PE-Xb pipe preparation process of the present invention is a raw material processing link. A specific proportion of high-density polyethylene, linear low-density polyethylene, heat-resistant polyethylene and antioxidant are mixed and modified, and a variety of polyethylenes, especially heat-resistant polyethylene, are introduced to form a unique ternary composite system, which not only reduces the material density, but also adjusts the melt flow rate. While reducing the density, the mechanical properties of the material are maintained or even improved, breaking the inherent connection between density and performance in traditional concepts, and laying a foundation for subsequent processing and pipe performance improvement; a one-step or two-step process is adopted, and the cross-linking process is optimized; in the one-step method, silane, antioxidant, organic tin and other components are directly mixed and extruded with modified polyethylene particles to complete cross-linking, and efficient cross-linking is achieved by accurately controlling the proportion of each component and extrusion process parameters, such as extrusion temperature, screw speed, etc.; in the two-step method, material A and material B are prepared respectively, and then mixed and extruded for cross-linking, which optimizes the cross-linking uniformity, makes the cross-linking degree of the pipe reach 65-80%, significantly enhances the heat resistance and pressure resistance of the pipe, and avoids the problem of pipe embrittlement caused by high cross-linking degree. Through raw material mixing modification and cross-linking process optimization, this preparation process produces pipes with higher softness, which greatly improves the construction performance; while maintaining good flexibility, the pressure resistance level and long-term use temperature are both improved, achieving a comprehensive improvement in flexibility, pressure resistance and heat resistance, and meeting the needs of more complex application scenarios.

[0018] The invention provides a preparation process of a flexible PE-Xb pipe, which specifically comprises the following steps: 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene and 0.2-1.0 parts of an antioxidant are mixed and modified in proportion, the material density is reduced to 0.930-0.950 g / cm³, and the melt flow rate is adjusted to 4-9 g / 10 min to form modified polyethylene particles; a one-step or two-step process is adopted to produce the modified polyethylene particles, silane and a catalyst in a formula ratio, and the modified polyethylene particles are mixed and extruded to complete cross-linking to obtain the flexible PE-Xb pipe.

[0019] Specifically, the present invention improves the crosslinking degree of flexible PE-Xb pipes to 65-80% by optimizing the process such as silane addition amount, catalyst ratio, and cooking condition control. The high crosslinking degree significantly enhances the heat resistance and pressure resistance, and the flexible compensation of linear low-density polyethylene and heat-resistant polyethylene does not cause the pipe to become brittle. In the preparation process of the flexible PE-Xb pipe of the present invention, silane, organic tin catalyst and modified polyethylene particles are mixed and extruded online in the one-step method, and the extrusion temperature, screw speed and cooking time are controlled; in the two-step method, material A (silane modified polyethylene particles) and material B (organic tin + peroxide modified polyethylene particles) are mixed and extruded in proportion to optimize the crosslinking uniformity; the modified polyethylene particles are produced by the one-step or two-step process, and the refined combination of process parameters such as screw speed and temperature partition is adapted to the ternary polyethylene composite system.

[0020] Preferably, the preparation process of the flexible PE-Xb pipe provided by the present invention specifically comprises the following steps: S1 Modification of polyethylene materials: 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene, and 0.2-1.0 parts of antioxidant are mixed evenly in proportion; twin-screw granulation equipment is used for granulation to ensure that polyethylenes with different molecular weights and different branched structures are completely melted and mixed together to form uniform modified polyethylene particles, and modified polyethylene particles with a density of 0.930-0.950g / cm³ and a melt flow rate of 4-9g / 10min are prepared to improve the homogeneity and processing performance of the material; by reducing the density, the rigidity of the pipe is reduced, and sufficient mechanical strength is maintained. The melt flow rate is used to ensure that the material has good fluidity during the processing process, which is convenient for extrusion molding and avoids processing defects caused by excessive fluidity; by introducing linear low-density polyethylene and heat-resistant polyethylene, the density of the pipe is reduced and the flexibility is improved, making the pipe easier to bend during the construction of the low-temperature floor radiant heating system, reducing the construction difficulty and cost, and reducing the risk of rupture caused by the pipe being too hard.

[0021] At the same time, the present invention provides two process options for preparing flexible PE-Xb pipes from modified polyethylene particles, namely a one-step process and a two-step process, to meet different production needs. The one-step process is simple and efficient, suitable for large-scale production; the two-step process further improves the performance of the pipe by optimizing the uniformity of cross-linking, while reducing the production complexity and cost.

[0022] S2-1 one-step process: silane, antioxidant, organotin and other ingredients are mixed with modified polyethylene particles, extruded through a single-screw extruder, cross-linked and prepared into flexible PE-Xb pipes; silane acts as a cross-linking agent, and chemically reacts with polyethylene molecular chains to form a three-dimensional network structure, significantly improving the heat resistance and pressure resistance of the pipe; the organotin catalyst accelerates the cross-linking reaction of silane, shortens the cross-linking time and improves production efficiency; the antioxidant further protects the stability of the material during processing and use to prevent oxidative degradation; the single-screw extruder ensures that silane is evenly grafted onto the polyethylene molecular chain to form a stable cross-linked structure by precisely controlling the extrusion temperature and screw speed; the cross-linking reaction is carried out in a steam room, and the hydrolysis and cross-linking reaction of silane are promoted by high temperature and humidity conditions to complete the final performance optimization of the pipe.

[0023] S2-2 two-step process: prepare material A (modified polyethylene particles and silane) and material B (modified polyethylene particles and organic tin, peroxide) separately, extrude and mix them to produce pipes, and then cross-link them to prepare flexible PE-Xb pipes; material A is mixed by a twin-screw machine to ensure that silane is evenly dispersed in the polyethylene matrix, providing a basis for the subsequent cross-linking reaction; the organic tin catalyst in material B accelerates the cross-linking reaction, and the peroxide initiator further promotes cross-linking to ensure the uniformity and efficiency of the cross-linking reaction; during mixed extrusion, material A and material B are mixed in a ratio of 7:3 to 9:1 and then extruded, and the uniformity of the cross-linking reaction and the molding quality of the pipe are ensured by controlling the extrusion pressure and temperature zoning; the cross-linking process is similar to the one-step method, and the final cross-linking reaction of the pipe is completed by cross-linking in a steam room at 80-95°C for 4-8 hours; the two-step method further optimizes the uniformity of the cross-linking reaction and improves the performance of the pipe by separating the steps of adding silane and catalyst.

[0024] Furthermore, in the preparation process of the flexible PE-Xb pipe provided by the present invention, the modification of the polyethylene material specifically comprises the following steps: S11 Raw material preparation: weigh 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene, and 0.2-1.0 parts of antioxidant in proportion and mix them evenly; ensure that each component can be evenly dispersed during subsequent processing to avoid performance differences caused by uneven local components and improve the overall performance and consistency of the material.

[0025] S12 premixing granulation: The above raw material mixture is melt-blended and granulated at a temperature of 160-200℃ and a screw speed of 200-400rpm through a twin-screw extruder granulator to form modified polyethylene particles with a density of 0.930-0.940g / cm³ and a melt flow rate of 4-8g / 10min; the reasonable setting of temperature and screw speed ensures the uniform mixing and melting of different polyethylene materials, and improves the quality and performance consistency of the modified particles; the control of density and melt flow rate ensures the adaptability of the modified polyethylene particles in subsequent processing and the performance optimization of the final pipe.

[0026] Among them, the temperature in the application of the twin-screw extruder granulator is controlled at 160-200℃ to ensure that the polyethylene material can be fully melted and to avoid thermal degradation of the polyethylene material at too high a temperature, which leads to molecular chain breakage and reduces the mechanical properties of the material. The appropriate temperature is conducive to the uniform mixing of different polyethylene materials and ensures the performance consistency of the modified particles. The screw speed is 200-400rpm, which provides sufficient shear force to fully mix polyethylenes with different molecular weights and branched structures to form uniform modified particles. The appropriate speed can balance the mixing effect and production efficiency, avoiding uneven mixing due to too low a speed or excessive shearing of the material due to too high a speed or even local overheating. While ensuring the mixing effect, material degradation is avoided to ensure production efficiency; the density of modified polyethylene particles is 0.930-0.940g / cm³. By optimizing the formula and process, the density of the pipe is reduced, the rigidity is reduced, and sufficient mechanical strength is maintained. Low density helps to improve flexibility, making the pipe more suitable for the construction needs of low-temperature floor radiant heating systems; the melt flow rate of 4-8g / 10min reflects the fluidity of the material. By controlling the melt flow rate, it is ensured that the material has good processing performance in the subsequent extrusion molding process. The appropriate melt flow rate can not only ensure the smooth extrusion of the material, but also avoid processing defects such as uneven pipe wall thickness caused by excessive fluidity.

[0027] The modification of the polyethylene material of the present invention uses a twin-screw extruder to melt blend high-density polyethylene, linear low-density polyethylene and heat-resistant polyethylene at 160-200°C and a screw speed of 200-400rpm to prepare modified particles, adapt to the ternary polyethylene composite system, achieve a balance between flexibility and strength, and improve the homogeneity of the material; this process not only improves the homogeneity and processing performance of the material, but also optimizes the comprehensive performance of the pipe through the design of the ternary composite system, and realizes the high performance of the flexible PE-Xb pipe. The twin-screw extruder has efficient shear force and mixing ability, ensuring that the three polyethylene materials with different molecular weights and branched structures of high-density polyethylene, linear low-density polyethylene and heat-resistant polyethylene are fully mixed; the screw design and mixing elements can make the materials fully mixed in a molten state, avoid local uneven components, thereby improving the homogeneity of the material, improving production efficiency, and reducing production costs.

[0028] The modified particles prepared by melt blending in a twin-screw extruder are the basic materials for subsequent pipe production. These modified polyethylene particles have uniform component distribution and specific physical properties, providing stable raw materials for subsequent extrusion molding and cross-linking reactions. The density and melt flow rate of the modified particles are precisely controlled to ensure good fluidity of the material in the subsequent extrusion molding process and avoid processing defects caused by insufficient or excessive fluidity. The homogeneity and performance consistency of the modified particles directly affect the quality of the final pipe. By optimizing the formula and process parameters, the modified polyethylene particles of the present invention can ensure that the pipe has excellent flexibility, heat resistance and pressure resistance during use.

[0029] The present invention optimizes the steaming and cross-linking conditions, controls the temperature of the steam room and the steaming time, combines an organic tin catalyst to accelerate the cross-linking reaction, shortens the time through catalyst optimization, and improves efficiency.

[0030] Furthermore, in the preparation process of the flexible PE-Xb pipe provided by the present invention, the one-step process specifically comprises the following steps: S31 formula preparation: silane, antioxidant, organic tin catalyst and other ingredients are mixed according to the one-step process formula ratio; the amount of silane added is 0.5-2% of the total weight of the modified polyethylene particles. Silane, as a cross-linking agent, plays a key role in subsequent reactions. The addition of an appropriate amount of silane can be grafted onto the polyethylene molecular chain through free radical reaction during the pipe production process, thereby initiating a cross-linking reaction; if the amount added is too little, the degree of cross-linking is insufficient, and the heat resistance, pressure resistance and other properties of the pipe cannot be effectively improved; if the amount added is too much, it will lead to excessive cross-linking, the pipe will become brittle, and the flexibility will decrease; the amount of antioxidant added is 0.2-1.0% of the total weight of the modified polyethylene particles. The antioxidant is mainly used to prevent polyethylene Polyethylene is oxidized during processing and use. In the high temperature environment of extrusion and cross-linking, polyethylene is prone to oxidation reaction, resulting in degradation of material properties. Antioxidants can capture free radicals, inhibit the oxidation process, ensure the stability and durability of the pipe, and extend its service life. The addition amount of the organic tin catalyst is 0.05-0.5% of the total weight of the modified polyethylene particles. The organic tin catalyst can accelerate the cross-linking reaction. Within the appropriate addition amount range, the activation energy of the cross-linking reaction can be reduced, so that the cross-linking reaction of silane and polyethylene molecular chains occurs quickly and fully under relatively mild conditions. However, if the addition amount is too low, the cross-linking reaction speed is slow and the production efficiency is low; if the addition amount is too high, the reaction will be out of control, affecting the quality of the pipe.

[0031] S32 extrusion process: the modified polyethylene particles are mixed evenly with the above-mentioned formula ingredients through an online feeding system to ensure that the ingredients are evenly distributed during the pipe production process. This helps to ensure the consistency of the subsequent cross-linking reaction, avoid areas with large performance differences in the pipe, and ensure the overall quality of the pipe is stable; the mixture is extruded and grafted through a single-screw extruder at a temperature of 160-220°C. Within this temperature range, the modified polyethylene particles can be fully melted and have good fluidity, which is convenient for extrusion molding. At the same time, high temperature conditions provide energy for the grafting reaction of silane and polyethylene molecular chains, promote free radical reactions, and gradually graft silane onto polyethylene molecular chains, laying the foundation for subsequent cross-linking reactions; the extrusion pressure is 10-20MPa. The appropriate extrusion pressure ensures that the mixture can pass through the single-screw extruder smoothly and It is formed into a pipe in a mold. The extrusion pressure helps to compact the material, make the internal structure of the pipe tight, reduce internal defects, and improve the physical properties of the pipe. At the same time, the pressure can also promote the interaction between the components, which is beneficial to the cross-linking reaction. It is extruded into a pipe through a mold and cut into the required length after cooling and shaping. The extrusion process includes extrusion grafting, molding, cooling and shaping, and cutting. The screw shearing action of the single-screw extruder cooperates with the high temperature environment to promote the grafting of silane molecules onto the polyethylene molecular chain. The extruded material is formed into a pipe through a mold. Cooling and shaping makes the pipe maintain a stable shape. Cutting to the required length meets the size requirements for actual use.

[0032] S33 cross-linking process: the extruded pipe is placed in a steam room, saturated steam is introduced, the temperature is controlled at 80-95℃, and the cross-linking reaction is completed for 4-8 hours. Under this temperature and time conditions, the cross-linking reaction in the pipe can be fully carried out. The saturated steam provides a good reaction environment, which accelerates the reaction between the cross-linking agent and the polyethylene molecular chain, so that the cross-linking degree of the pipe reaches 65-80%. The appropriate temperature can not only ensure the rate of the cross-linking reaction, but also will not cause the performance of the pipe to deteriorate due to excessive temperature; sufficient steaming time ensures that the cross-linking reaction is complete, so that the pipe obtains good heat resistance, pressure resistance and other properties; dry to remove surface moisture, dry to remove surface moisture, prevent moisture from having an adverse effect on the performance of the pipe, avoid reducing the insulation performance of the pipe or causing corrosion of the pipe during storage; cool to room temperature to stabilize the pipe, which is convenient for subsequent storage and transportation, and obtain flexible PE-Xb pipe.

[0033] In the preparation process of the flexible PE-Xb pipe of the present invention, the two-step process prepares material A (containing silane) and material B (containing an organic tin catalyst and a peroxide initiator) in stages, and mixes the two materials in proportion, extrudes and cross-links them, thereby achieving precise control of the cross-linking reaction and uniformity optimization. This method not only improves the cross-linking degree of the pipe, enhances the heat resistance and pressure resistance, but also avoids the problem of pipe embrittlement caused by excessive cross-linking. At the same time, the two-step method further improves the stability and consistency of the pipe performance by separating the addition steps of silane and catalyst, and is particularly suitable for the production of flexible PE-Xb pipes with high performance requirements, taking into account both product quality and production efficiency.

[0034] Furthermore, in the preparation process of the flexible PE-Xb pipe provided by the present invention, the two-step process specifically comprises the following steps: Preparation of S41 A material: 50% of the total weight of modified polyethylene particles is taken as the base material. This ratio setting provides a suitable material basis for the subsequent cross-linking reaction; silane is added and mixed according to the formula ratio of the two-step process, and the silane is 0.5-2% of the total weight of the modified polyethylene particles. An appropriate amount of silane can form sufficient cross-linking points in the cross-linking reaction, improve the cross-linking degree of the pipe, and enhance the heat resistance and pressure resistance of the pipe. However, if too little is added, insufficient cross-linking will affect the performance, and too much will cause excessive cross-linking and make the pipe brittle; the mixed material passes through a twin-screw machine at a temperature of 180-220°C. This temperature range can fully melt the modified polyethylene particles, enhance their fluidity, and facilitate uniform mixing with silane; the screw speed of 200-400rpm provides suitable shear force for melt blending, promotes uniform dispersion of silane in polyethylene, forms A material of uniform quality, and lays the foundation for the uniformity of the subsequent cross-linking reaction.

[0035] Preparation of S42 B material: Take 50% of the total weight of modified polyethylene particles as the base material, add organic tin catalyst, peroxide initiator and other ingredients and mix them according to the formula ratio of the two-step process, the organic tin catalyst is 0.05-0.5% of the total weight of the modified polyethylene particles, which reduces the activation energy of the cross-linking reaction and accelerates the cross-linking reaction; the peroxide is 0.1-1% of the total weight of the modified polyethylene particles, as an initiator, it produces free radicals when heated or otherwise stimulated, and initiates the cross-linking reaction between the polyethylene molecular chain and the silane, and the two cooperate to control the progress and degree of the cross-linking reaction; the mixed material is granulated at a temperature of 170-200°C in a twin-screw machine, which can not only melt and granulate the material, but also ensure that the peroxide and organic tin catalyst remain stable in the process and do not over-react in advance, thereby ensuring the quality of B material and the controllability of subsequent cross-linking reactions.

[0036] S43 mixed extrusion: After mixing material A and material B in a mass ratio of 9:1 to 7:3, within this ratio range, silane, organotin catalyst and peroxide can be evenly distributed in the pipe, ensuring that the cross-linking reaction proceeds evenly; the mixed material is sent to a single-screw extruder for extrusion grafting, with an extrusion pressure of 10-20MPa, and the pipe is extruded through a die, and cut after cooling and shaping; ensure that the mixed material flows smoothly in the single-screw extruder and is extruded into a pipe through a die. The pressure helps to compact the material, reduce the internal voids of the pipe, and improve the density and physical properties of the pipe; the extrusion grafting process allows silane to react with the polyethylene molecular chain under the action of screw shear and high temperature to initially form a cross-linking structure; cooling and shaping allows the pipe to maintain a stable shape and is cut into a suitable length to meet actual use requirements.

[0037] S44 cross-linking process: cross-linking in a steam room, 80-95℃ for 4-8 hours. The temperature and time conditions can fully carry out the cross-linking reaction in the pipe, ensuring that the degree of cross-linking reaches 65-80%, so that the pipe has good heat resistance, pressure resistance and other properties. After the cross-linking reaction is completed, the flexible PE-Xb pipe is obtained by drying; after the cross-linking reaction is completed, the pipe is dried to remove surface moisture to prevent moisture from affecting the insulation performance and corrosion resistance of the pipe. The drying process ensures the stability of the pipe quality and facilitates subsequent storage and transportation.

[0038] In the preparation process of the flexible PE-Xb pipe of the present invention, the extrusion grafting process of the single screw extruder ensures the physical state and chemical reaction conditions of the mixture at different stages by accurately controlling the temperature partition, screw speed and extrusion pressure. This parameter optimization enables the silane molecules to be efficiently grafted onto the polyethylene molecular chain through free radical reaction under the action of screw shear and high temperature, thereby forming a stable three-dimensional cross-linked structure inside the pipe. This process not only improves the cross-linking degree and mechanical properties of the pipe, but also ensures its flexibility and heat resistance, providing key technical support for the production of high-performance flexible PE-Xb pipes.

[0039] Furthermore, in the preparation process of the flexible PE-Xb pipe provided by the present invention, the single screw extruder extrusion grafting process specifically includes the following parameters: after the mixed material is fed into the single screw extruder, the temperature is controlled by zone, the feeding section is 160-180°C, so that the mixed material is initially softened and has a certain fluidity, which facilitates the material to smoothly enter the screw groove. At the same time, this temperature will not cause the material to melt prematurely, avoid clogging or agglomeration of the material in the feeding section, and ensure the continuity and stability of the feeding; the melting section is 180-200°C, the material is further heated, and the modified polyethylene particles are The temperature of the homogenization section is 200-220℃. The high temperature of the homogenization section can make the melt further mixed evenly under the shearing action of the screw, eliminating the temperature difference and concentration difference in the melt. The higher temperature can also promote the free radical reaction between the silane molecules and the polyethylene molecular chains, so that the silane molecules are more fully grafted onto the polyethylene molecular chains, improving The grafting rate can improve the cross-linking degree and performance of the pipe. The screw speed is 200-400rpm. The appropriate screw speed provides the necessary shear force. On the one hand, the shear force can further disperse the materials in the melt, so that additives such as silane, antioxidants, and organic tin catalysts are more evenly distributed in the polyethylene melt to ensure the consistency of pipe performance. On the other hand, the shearing effect of the screw can promote the collision between silane molecules and polyethylene molecular chains, increase the chance of free radical reaction, accelerate the process of silane molecules grafting onto polyethylene molecular chains, and improve production efficiency. The extrusion pressure is 10-20MPa, so that the molten material, under the push of the screw, overcomes the resistance of the die head, die, etc., and is smoothly extruded through the die to form a pipe. The pressure can compact the material, reduce the gaps and defects inside the pipe, and improve the density and strength of the pipe. At the same time, under a certain pressure, the contact between the silane molecules and the polyethylene molecular chains is closer, which is conducive to the free radical reaction, promotes the grafting and cross-linking reaction of silane, and improves the comprehensive performance of the pipe; under the action of screw shear and high temperature, the silane molecules are grafted onto the polyethylene molecular chain through free radical reaction.

[0040] In summary, the present invention has the following beneficial effects: 1. Different from the high hardness and large bending radius (≥8D) of traditional PE-Xb pipes, the present invention introduces linear low-density polyethylene and heat-resistant polyethylene to form a ternary polyethylene composite system including high-density polyethylene, linear low-density polyethylene, and heat-resistant polyethylene, optimizes the pipe density to 0.930-0.950g / cm³, and significantly reduces the bending radius to ≤5D, which not only makes the pipe easier to bend during construction, reduces the construction difficulty and cost, but also reduces the risk of rupture caused by excessively hard pipes, and improves construction efficiency and safety; 2. The invention increases the long-term use temperature of the pipe to 95-100°C by introducing heat-resistant polyethylene, significantly enhancing the heat resistance of the pipe. Different from the traditional PE-Xb pipe, which has a long-term use temperature of only 90°C, the pipe can be adapted to higher temperature application scenarios, such as central heating trunk pipes, broadening the use scope of the pipe and meeting the requirements of modern building heating systems for high-temperature operating environments; 3. The present invention optimizes the formula and cross-linking process to reduce the density of the pipe while maintaining the PN10-PN16 pressure resistance level, avoiding the problem of traditional PE-Xb pipes easily sacrificing compressive strength when improving flexibility, ensuring the reliability and stability of the pipe under complex working conditions, and meeting the strict requirements of the low-temperature floor radiant heating system on the pressure resistance of the pipe; 4. Different from the limitations of the traditional one-step and two-step processes, the present invention provides two flexible production processes, one-step and two-step. The one-step process is simple and efficient, suitable for large-scale production; the two-step process further improves the performance of the pipe by optimizing the cross-linking uniformity, while reducing the production complexity and cost; this process flexibility provides more options for production enterprises, and can adjust the production process according to actual needs, thereby improving production efficiency and product quality; 5. The present invention achieves a crosslinking degree of 65-80% for the pipe by precisely controlling silane, catalyst and crosslinking conditions. This high crosslinking degree significantly enhances the heat resistance and pressure resistance of the pipe, while avoiding the problem of insufficient crosslinking degree or embrittlement of the pipe caused by high crosslinking degree in the traditional crosslinking process, thus ensuring the stability and durability of the pipe during long-term use; 6. Different from the problems of long cross-linking reaction time and low efficiency in traditional processes, the present invention accelerates the cross-linking reaction by using an organic tin catalyst, significantly shortens the production time, and improves the production efficiency. The optimized steaming and cross-linking conditions further improve the efficiency of the cross-linking reaction and reduce the production cost. At the same time, the present invention improves the flexibility of the pipe, making it less likely to break or deform during the construction process, thereby reducing the risk of damage during the construction process. During transportation and storage, the pipe also reduces the risk of damage caused by collision due to enhanced flexibility, thereby extending the service life and reducing maintenance costs. 7. The present invention improves the performance of the pipe by optimizing the formula and process, while avoiding unnecessary material waste and energy consumption. By accurately controlling the amount of antioxidants, etc., it not only ensures the physical properties of the pipe but also avoids cost increases. This optimization not only improves the market competitiveness of the product, but also has good environmental performance and cost-effectiveness, and solves the problems of high material waste and energy consumption in traditional preparation processes. DETAILED DESCRIPTION

[0041] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0042] Example 1

[0043] S1 Polyethylene material modification: 30 parts of Beijing Yanshan 2300XM high-density polyethylene, 15 parts of SABIC218WJ linear low-density polyethylene, 20 parts of Quanzhou Petrochemical 3606 heat-resistant polyethylene and 0.5 parts of antioxidant were mixed evenly, and melt-blended using a twin-screw extruder granulator at 170°C and a screw speed of 250rpm to prepare modified polyethylene particles with a density of 0.935g / cm³ and a melt flow rate of 4g / 10min; S2 one-step extrusion molding and cross-linking: After the modified polyethylene particles are evenly mixed with 1.5 parts of silane and 0.3 parts of organic tin catalyst, they are fed into a single-screw extruder through an online feeding system. The temperature of the single-screw extruder is controlled by zoning, feeding section: 165°C, melting section: 185°C, homogenization section: 210°C, screw speed: 300rpm, extrusion pressure: 18MPa; the mixture is extruded into a pipe through a mold, and cut into the required length after cooling and shaping; S3 cross-linking process: The extruded pipe is placed in a steam room and steamed in saturated steam at 92°C for 5 hours to complete the cross-linking reaction. After drying, a flexible PE-Xb pipe is obtained.

[0044] Example 2

[0045] S1 Polyethylene material modification: 40 parts of high-density polyethylene, 10 parts of linear low-density polyethylene, 30 parts of heat-resistant polyethylene and 0.8 parts of antioxidant were mixed evenly, and then melt-blended using a twin-screw extruder granulator at 190°C and a screw speed of 350rpm to prepare modified polyethylene particles with a density of 0.935g / cm³ and a melt flow rate of 5g / 10min; S2 Preparation of A and B materials: Take 50% of the total weight of the modified polyethylene particles, add 1.2% of silane, and melt-blend them through a twin-screw machine at 210°C and a screw speed of 300rpm to form A material; take the remaining modified polyethylene particles, add 0.2% of organic tin catalyst and 0.6% of peroxide, and granulate them through a twin-screw machine at 190°C and a screw speed of 280rpm to form B material; S3 mixed extrusion: material A and material B are mixed in a mass ratio of 7:3, and then fed into a single screw extruder. The extrusion pressure is controlled to be 16 MPa, and the extruder is formed into a pipe through a die. After cooling and shaping, the pipe is cut into the required length; S4 cross-linking process: The extruded pipe was placed in a steam room and steamed in saturated steam at 95°C for 4 hours to complete the cross-linking reaction, and a flexible PE-Xb pipe was obtained after drying.

[0046] Example 3

[0047] S1 raw material preparation: using 55 parts of high-density polyethylene, 18 parts of linear low-density polyethylene, 12 parts of heat-resistant polyethylene and 0.7 parts of antioxidant as raw materials, the modified polyethylene particles with a density of 0.935 g / cm³ and a melt flow rate of 7 g / 10 min were prepared by the method in Example 1; S2 mixed extrusion: After mixing the above raw materials with 1.2% silane, extrude and shape them through a single screw extruder at 195°C and a screw speed of 270rpm. The extrusion pressure is 16MPa, and the mixture is cut into the required length after cooling and shaping. S3 cross-linking process: the extruded pipe is placed in saturated steam at 92°C and boiled for 7 hours to complete the cross-linking reaction, and the pipe is obtained after drying.

[0048] Comparative Example 1 S1 Raw material preparation: Use 100 parts of medium-density polyethylene with a density of 0.935g / cm³ and 0.5 parts of antioxidant as raw materials; S2 extrusion molding: After mixing the above raw materials, extrude them through a single screw extruder at 190°C and a screw speed of 200rpm. The extrusion pressure is 12MPa, and after cooling and shaping, they are cut into the required length; S3 cross-linking process: The extruded pipe is placed in a steam room and steamed in saturated steam at 85°C for 6 hours to complete the cross-linking reaction, and the pipe is obtained after drying.

[0049] Comparative Example 2 S1 Raw material preparation: weigh 50 parts of high-density polyethylene and 0.5 parts of antioxidant as raw materials according to the following mass parts; S2 mixed extrusion: the above raw materials are mixed with 1% silane and 0.2% organotin catalyst, and then extruded by a single screw extruder at 200°C and a screw speed of 250rpm. The extrusion pressure is 15MPa, and the mixture is cut into the required length after cooling and shaping. S3 cross-linking process: The extruded pipe is placed in a steam room and steamed in saturated steam at 90°C for 6 hours to complete the cross-linking reaction. After drying, the traditional PE-Xb pipe is obtained.

[0050] Comparative Example 3 S1 Raw material preparation: Use 60 parts of high-density polyethylene and 0.6 parts of antioxidant as raw materials; S2 Preparation of A and B materials: Take 50% of the total weight of the raw materials, add 1.0% of silane, and melt-blend them through a twin-screw extruder at 200°C and a screw speed of 280rpm to form A material; take the remaining raw materials, add 0.3% of organic tin catalyst and 0.5% of peroxide, and granulate them through a twin-screw extruder at 180°C and a screw speed of 260rpm to form B material; S3 mixed extrusion: material A and material B are mixed in a mass ratio of 6:4, and then fed into a single screw extruder. The extrusion pressure is controlled to be 17 MPa, and the extruder is formed into a pipe through a die. After cooling and shaping, the pipe is cut into the required length; S4 cross-linking process: The extruded pipe is placed in saturated steam at 90°C and cooked for 5 hours to complete the cross-linking reaction. After drying, the traditional PE-Xb pipe is obtained.

[0051] The flexible PE-Xb pipes prepared in Examples 1-3 and the conventional PE-Xb pipes prepared in Comparative Examples 1-3 were subjected to performance tests, including density detection, melt flow rate, crosslinking degree, hydrostatic test and flexibility test.

[0052] 1. Density detection Testing method: Use the density gradient column method and test according to ISO1183 "Plastics - Determination of density". Cut the pipe sample into small pieces, put them into the density gradient column, record its equilibrium position and calculate the density.

[0053] 2. Melt flow rate detection Testing method: Use a melt flow rate meter to test according to ISO1133 "Plastics - Determination of melt mass flow rate and melt volume flow rate by capillary viscometer" standard, and measure the melt flow rate of the pipe sample at 230°C and 2.16kg load.

[0054] 3. Cross-linking degree detection Detection method: The solvent extraction method is used according to the DIN53799 "Plastics - Determination of the degree of crosslinking". The sample is immersed in xylene for 24 hours, and the degree of crosslinking is calculated by weighing the mass before and after extraction.

[0055] 4. Thermal stability test Testing method: The thermal stability of polyethylene pipes is evaluated through the oxidation induction period test. The test is carried out in accordance with GB / T17391-1998 "Test method for thermal stability of polyethylene pipes and fittings". The thermal stability of PE-Xb pipes is evaluated by measuring the time it takes for the sample to start auto-catalytic oxidation reaction under high temperature oxygen conditions.

[0056] 5. Hydrostatic test method: According to GB / T18992 "Cross-linked Polyethylene (PE-X) Pipe System for Hot and Cold Water", the pipes are subjected to cold water long-term hydrostatic test and hot water long-term hydrostatic test respectively. The specific test steps include: During the cold water long-term hydrostatic test, a pipe sample with a length of (300±20) mm and flat and defect-free ends is cut, installed in a hydrostatic test machine and sealed, filled with distilled water or deionized water to exhaust the air, placed in a (20±2)℃ constant temperature water bath to stabilize the sample temperature for 1-2 hours, and slowly apply the specified test pressure within 1-5 minutes. During the test, the pressure fluctuation is controlled within the set value ±2%, and the temperature fluctuation is ±2℃. The pressure and The temperature data is collected and the sample is observed. The test lasts for no less than 1000 hours. If there is no failure such as leakage or rupture, it is judged to have passed. For long-term hot water hydrostatic testing, select a suitable pipe sample, install and seal it, fill it with water and exhaust it, put it in a constant temperature water bath or oven at a specified temperature for 2-4 hours to make the temperature uniform and stable, apply the corresponding test pressure according to the standard and temperature correction factor within 1-5 minutes, ensure that the pressure fluctuation is within ±2% and the temperature fluctuation is ±2℃ during the test, observe the appearance of the sample every 30 minutes to 1 hour, and conduct tests ranging from 1000 to 8760 hours according to requirements. If there is no failure, it is judged to have passed. After the test, slowly release the pressure and take out the sample to observe the overall condition.

[0057] 6. High temperature hot water hydrostatic test Test method: Evaluate the long-term pressure resistance of pipes under high temperature and high pressure conditions. Test according to ISO1167:2019 "Thermoplastic pipes-Determination of internal pressure resistance". During the test, install the pipe sample in a hydrostatic test system, exhaust the air and place it in a constant temperature water bath at 95°C or 100°C. Slowly apply the specified pressure and keep the pressure fluctuation within ±2% and the temperature fluctuation within ±2°C. The test time is set according to demand, usually 1000 hours, 2000 hours or longer. During the test, record the pressure and temperature data, and observe whether the sample leaks or ruptures to verify the reliability of the pipe under extreme conditions.

[0058] 7. Flexibility test Testing method: Repeated bending test is carried out according to GB / T8802-2001 "Determination of Vicat softening temperature of thermoplastic pipes and fittings". The pipe sample is bent repeatedly at the specified temperature, the number of cracks or breaks is recorded, and the bending radius is calculated.

[0059] 8. Summary of results Table 1 Summary of performance test results of each group of PE-Xb pipes

[0060] Data Analysis: In the density test, the pipe density of Examples 1-3 is 0.935g / cm³, which meets the design requirements (0.930-0.950g / cm³), indicating that the pipe density is successfully reduced by the ternary composite system (HDPE, LLDPE, PE-RT) while maintaining good mechanical properties; the melt flow rate of Examples 1-3 is 6g / 10min, which is within the design range (4-9g / 10min), indicating that the material has good fluidity during processing and is suitable for extrusion molding; it shows that the flexible PE-Xb pipe of the present invention has successfully achieved a balance between low density and good processing performance by optimizing the formula, providing favorable conditions for subsequent extrusion molding and cross-linking reaction.

[0061] In the cross-linking degree detection, the cross-linking degrees of the flexible PE-Xb pipes of Examples 1-3 all reached 80%, indicating that efficient cross-linking was successfully achieved by optimizing the formula (such as the amount of silane and organic tin catalyst) and process (such as extrusion temperature and cross-linking time); the cross-linking degrees of the traditional PE-Xb pipes of Comparative Examples 1-3 were 75%, 70% and 65%, respectively, which were significantly lower than those of the embodiments, among which Comparative Example 1 did not use a composite system, and the amount of cross-linking agent used in Comparative Examples 2 and 3 was relatively low, resulting in insufficient cross-linking; the high cross-linking degree of the flexible PE-Xb pipe of the present invention significantly improves the heat resistance and pressure resistance of the pipe, while avoiding the embrittlement problem caused by excessive cross-linking.

[0062] In the thermal stability test, the oxidation induction periods of the flexible PE-Xb pipes of Examples 1-3 were 35, 32 and 30 minutes, respectively, indicating that the pipes had good thermal stability and antioxidant properties; the oxidation induction periods of Comparative Examples 1-3 were 25, 20 and 18 minutes, respectively, which were significantly lower than those of the embodiments, wherein the comparative examples did not use heat-resistant polyethylene and the amount of cross-linking agent was insufficient, resulting in poor thermal stability of the pipes; this indicates that the introduction of heat-resistant polyethylene in the flexible PE-Xb pipe of the present invention and the optimized cross-linking process significantly improve the thermal stability of the pipe, making it more suitable for high-temperature application scenarios.

[0063] In the hydrostatic test, the flexible PE-Xb pipes of Examples 1-3 in the cold water hydrostatic test (20°C, 10MPa) all passed the test for ≥800 hours, indicating that the pipes have excellent pressure resistance at room temperature; the test time of Comparative Examples 1-3 is ≤700 hours, indicating that the pressure resistance of the traditional formula and process is poor. The test time of the flexible PE-Xb pipes of Examples 1-3 in the hot water hydrostatic test (80°C, 10MPa) is ≥1000 hours, ≥1200 hours and ≥1000 hours, respectively, indicating that the pipes can still maintain good pressure resistance under high temperature conditions; while the test time of Comparative Examples 1-3 is ≤600 hours, indicating that the pressure resistance of traditional pipes at high temperatures is insufficient; it shows that the flexible PE-Xb pipes of the present invention have excellent pressure resistance at both room temperature and high temperature conditions by optimizing the formula and process, and are suitable for complex application scenarios such as floor heating.

[0064] In the high-temperature hot water hydrostatic test, the flexible PE-Xb pipes of Examples 1-3 were tested for 1500 hours, 1400 hours and 1300 hours at 95°C, respectively, showing excellent high-temperature pressure resistance performance; at 100°C, the test times of Examples 1, 2 and 3 were 1200 hours, 1100 hours and 1000 hours, respectively, still showing good high-temperature pressure resistance performance, but slightly lower than the performance at 95°C, indicating that the pipes still have a certain durability at higher temperatures, but the performance has declined. The conventional PE-Xb pipes of Comparative Examples 1-3 were tested for 800 hours, 900 hours and 850 hours at 95°C, respectively, which are significantly lower than the examples; at 100°C, the test times of Comparative Examples 1, 2 and 3 were 600 hours, 700 hours and 650 hours, respectively, further indicating that the durability of conventional formulas and processes under high temperature and high pressure conditions is insufficient. The pipes of Examples 1-3 prepared by the present invention performed well in high-temperature hot water hydrostatic tests at 95°C and 100°C, and can withstand long-term high temperature and high pressure. They are suitable for use in scenarios with higher requirements such as central heating main pipes. The pipes of Comparative Examples 1-3 have poor pressure resistance under high temperature conditions. The long-term pressure resistance, thermal stability and reliability of the pipes under high temperature and high pressure conditions are fully verified, providing a scientific basis for the use of pipes in complex application scenarios.

[0065] In the flexibility test, the bending radius of the flexible PE-Xb pipes of Examples 1-3 is ≤5D, and there is no crack after repeated bending 1000 times at -20°C, indicating that the pipes have excellent flexibility and low-temperature performance; the bending radius of the traditional pipes of Comparative Examples 1-3 is ≥8D, and cracks appear after repeated bending 500-600 times at low temperature, indicating that the flexibility of the traditional pipes is poor and the construction is difficult; it shows that the introduction of linear low-density polyethylene in the flexible PE-Xb pipe formula of the present invention significantly reduces the bending radius of the pipe, improves the flexibility, and makes it more suitable for complex laying environments.

[0066] In summary, the flexible PE-Xb pipe of the present invention successfully reduces the density of the pipe and improves its flexibility through the ternary composite system, and at the same time, the introduction of heat-resistant polyethylene significantly enhances the thermal stability; by precisely controlling the amount of silane and organotin catalyst, as well as the extrusion and cross-linking conditions, a high degree of cross-linking is achieved, which significantly improves the heat resistance and pressure resistance of the pipe; the use of an appropriate proportion of antioxidants ensures the antioxidant properties of the pipe during processing and use. The flexible PE-Xb pipe of the embodiment of the present invention is significantly superior to the comparative example in terms of density, degree of cross-linking, thermal stability, pressure resistance and flexibility, and is suitable for complex environments such as low-temperature floor radiant heating systems and central heating trunk pipes, and has good flexibility, pressure resistance and thermal stability. However, the comparative example does not use a composite system or the amount of cross-linking agent is insufficient, resulting in insufficient performance and cannot meet the needs of complex application scenarios. It is more suitable for traditional application scenarios and has obvious deficiencies in flexibility and thermal stability. Through the above data analysis, it can be seen that the flexible PE-Xb pipe of the present invention is significantly superior to traditional pipes in performance, successfully solves the problems of high hardness, poor flexibility, insufficient thermal stability, etc. of traditional PE-Xb pipes, and has broad application prospects.

Claims

1. A flexible PE-Xb pipe, characterized in that: The formula mainly includes the following raw material components in parts by weight: 10-60 parts of high-density polyethylene (HDPE), 5-20 parts of linear low-density polyethylene (LLDPE), 20-50 parts of heat-resistant polyethylene (PE-RT), and 0.2-1.0 parts of antioxidant; the density of the flexible PE-Xb pipe is 0.930-0.950g / cm³, and the degree of cross-linking is 65-80%.

2. A process for preparing a flexible PE-Xb pipe, characterized in that: The specific steps include: 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene, and 0.2-1.0 parts of antioxidant are mixed and modified in proportion to reduce the material density to 0.930-0.950g / cm³, and the melt flow rate is adjusted to 4-9g / 10min to form modified polyethylene particles; one-step or two-step process is adopted to produce, the modified polyethylene particles are mixed with silane and catalyst according to the formula ratio and extruded to complete cross-linking to obtain flexible PE-Xb pipes.

3. The preparation process of the flexible PE-Xb pipe according to claim 2 is characterized in that: The specific steps include: S1 Modification of polyethylene materials: 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene, and 0.2-1.0 parts of antioxidant are mixed evenly in proportion; twin-screw granulation equipment is used for granulation to ensure that polyethylenes with different molecular weights and different branched structures are completely melt-mixed into one, and a density of 0.930-0.950 g / cm is prepared. 3 , modified polyethylene particles having a melt flow rate of 4-9 g / 10 min; S2-1 one-step process: Silane, antioxidant, organotin and other ingredients are mixed with modified polyethylene particles, extruded through a single screw extruder, cross-linked, and flexible PE-Xb pipes are prepared; S2-2 two-step process: prepare material A and material B separately, wherein material A is composed of modified polyethylene particles and silane, and material B is composed of modified polyethylene particles, organic tin and peroxide. After mixing, they are extruded to produce pipes, and then cross-linked to prepare flexible PE-Xb pipes.

4. The preparation process of the flexible PE-Xb pipe according to claim 2 is characterized in that: The modification of the polyethylene material specifically comprises the following steps: S11 Raw material preparation: weigh 10-60 parts of high-density polyethylene, 5-20 parts of linear low-density polyethylene, 20-50 parts of heat-resistant polyethylene, and 0.2-1.0 parts of antioxidant according to proportion, and mix them evenly; S12 premixing and granulation: The raw material mixture is melt-blended and granulated by a twin-screw extruder at a temperature of 160-200°C and a screw speed of 200-400rpm to form modified polyethylene particles with a density of 0.930-0.940g / cm³ and a melt flow rate of 4-8g / 10min.

5. The preparation process of the flexible PE-Xb pipe according to claim 2, characterized in that: The one-step process specifically comprises the following steps: S31 formula preparation: silane, antioxidant, organotin catalyst and other ingredients are mixed according to the one-step process formula ratio; the amount of silane added is 0.5-2% of the total weight of the modified polyethylene particles, the amount of antioxidant added is 0.2-1.0% of the total weight of the modified polyethylene particles, and the amount of organotin catalyst added is 0.05-0.5% of the total weight of the modified polyethylene particles; S32 extrusion process: the modified polyethylene particles are mixed evenly with the above formula ingredients through an online feeding system, the mixture is extruded and grafted through a single screw extruder at a temperature of 160-220°C and an extrusion pressure of 10-20MPa, and is extruded through a die to form a pipe, which is then cut into the required length after cooling and shaping; S33 cross-linking process: place the extruded pipe in a steam room, introduce saturated steam, control the temperature at 80-95°C, and cook for 4-8 hours to complete the cross-linking reaction. After drying to remove surface moisture, cool to room temperature to obtain a flexible PE-Xb pipe.

6. The process for preparing the flexible PE-Xb pipe according to claim 2, characterized in that: The two-step process specifically comprises the following steps: S41 Preparation of material A: 50% of the total weight of modified polyethylene particles is taken as the base material, and silane is added and mixed according to the formula ratio of the two-step process, wherein the silane is 0.5-2% of the total weight of the modified polyethylene particles; the mixed material is melt-blended by a twin-screw machine at a temperature of 180-220° C. and a screw speed of 200-400 rpm to form material A; S42 Preparation of material B: Take 50% of the total weight of modified polyethylene particles as the base material, add organic tin catalyst, peroxide initiator and other ingredients and mix them according to the formula ratio of the two-step process, the organic tin catalyst is 0.05-0.5% of the total weight of the modified polyethylene particles, and the peroxide is 0.1-1% of the total weight of the modified polyethylene particles; the mixed material is granulated at a temperature of 170-200°C in a twin-screw machine to form material B; S43 mixed extrusion: after mixing material A and material B in a mass ratio of 9:1 to 7:3, the mixed material is fed into a single screw extruder for extrusion grafting at an extrusion pressure of 10-20 MPa, extruded through a die to form a pipe, and cut after cooling and shaping; S44 cross-linking process: cross-linking in a steam room, treated at 80-95℃ for 4-8 hours, and dried after the cross-linking reaction is completed to obtain a flexible PE-Xb pipe.

7. The process for preparing the flexible PE-Xb pipe according to claim 5 or 6, characterized in that: The single-screw extruder extrusion grafting process specifically includes the following parameters: after the mixed material is fed into the single-screw extruder, the temperature is controlled by zone, the feeding section is 160-180°C, the melting section is 180-200°C, the homogenization section is 200-220°C, the screw speed is 200-400rpm, the extrusion pressure is 10-20MPa, and under the action of screw shear and high temperature, the silane molecules are grafted onto the polyethylene molecular chain through free radical reaction.

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