A method for preparing an mpp cable protection pipe

Abstract

This invention relates to the field of polymer material molding and processing technology, and particularly to a method for preparing an MPP cable protection pipe. The method includes using block copolymer polypropylene as the matrix resin to prepare an inner layer material containing grafted modified polypropylene, a middle layer material containing reinforcing fillers, and an outer layer material containing a polyolefin elastomer. The initial extrusion temperature of each layer material is determined based on the Vicat softening temperature difference between the inner and outer layers. The melt flow rate consistency of the composite pipe is determined based on the melt flow rate of each layer material to predict the interlayer bonding trend at the inner-middle layer interface and the middle-outer layer interface. Based on the interlayer bonding trend, the initial extrusion temperature or material content is adjusted, and co-extrusion molding is performed to form the composite pipe. This invention establishes a synergistic control mechanism for the thermal and rheological properties of the material, taking into account both flexibility and the tensile strength of the welded joint, enabling the pipe to adapt to drag-back construction under complex terrain conditions.

Description

Technical Field

[0001] This invention relates to the field of polymer material molding and processing technology, and in particular to a method for preparing an MPP cable protection pipe. Background Technology

[0002] MPP cable protection pipes are typically made of modified polypropylene as the main base material, with antioxidants, light stabilizers, and toughening modifiers added. These are blended and granulated to form a single-layer cable protection pipe, which is then butt-welded using a hot-melt welding machine at a melting temperature of approximately 200±10℃. They exhibit excellent corrosion resistance and abrasion resistance. However, they are prone to cracking and breakage under trenchless directional drilling conditions and in environments where cables generate prolonged heat. Therefore, there is an urgent need to develop MPP power cable protection pipes with high toughness and high strength.

[0003] Chinese Patent Publication No. CN121825101A discloses a high flame-retardant MPP cable protection pipe and its preparation method. The method involves uniformly mixing polypropylene resin, modified graphene oxide, modified maleic anhydride grafted polypropylene, lubricant, plasticizer, and antioxidant, followed by extrusion granulation using an extruder. The resulting particles are then dried and injection molded to obtain the MPP cable protection pipe. This pipe exhibits high tensile strength, excellent UV aging resistance, and good flame retardancy.

[0004] However, existing technologies still have the following problems: single-layer homogeneous structures are difficult to optimize for surface functionality in response to harsh external environments, and pipes are prone to surface powdering and aging under long-term outdoor exposure or complex geological conditions; short pipe sections produced by injection molding have numerous welding nodes, poor overall sealing, and are prone to falling off and breaking, which can shorten their service life under long-term outdoor exposure or complex geological conditions.

[0005] Therefore, there is an urgent need for a technology that can maintain the flexibility of cable conduits under trenchless conditions while effectively improving the tensile strength of their hot-melt welded joints, so that cable conduits can be adapted to pullback in complex terrain. Summary of the Invention

[0006] Therefore, the present invention provides a method for preparing MPP cable protection pipes to overcome the problems of easy surface powdering and easy breakage and detachment of pipe section welds in the existing single-layer pipe structure under complex terrain.

[0007] To achieve the above objectives, the present invention provides a method for preparing an MPP cable protection conduit, comprising: Using block copolymer polypropylene as the matrix resin, an inner layer material containing grafted modified polypropylene, a middle layer material containing reinforcing fillers, and an outer layer material containing polyolefin elastomers are prepared. The initial extrusion temperature of each layer of material is determined based on the difference in Vicat softening temperature between the inner and outer layers of material. Based on the melt mass flow rate of each layer of material, the consistency of melt mass flow rate of composite pipe is determined, so as to predict the interlayer bonding force trend of the inner and middle layer interfaces and the middle and outer layer interfaces. Based on the interlayer bonding trend, the initial extrusion temperature or material content is adjusted to perform co-extrusion molding to form composite pipes.

[0008] Furthermore, the method for preparing the inner layer material includes: 100 parts of block copolymer polypropylene, 2-10 parts of maleic anhydride grafted polypropylene, 0.2-0.5 parts of antioxidant and 0.5-1.0 parts of lubricant are added to a high-speed mixer and mixed at 800 rpm for 5 minutes at room temperature to obtain a premix. The premix is ​​then added to a twin-screw extruder and melt-extruded and granulated at a temperature range of 180-210℃ to obtain the inner layer material.

[0009] Furthermore, the method for preparing the intermediate layer material includes: First, 10-30 parts of reinforcing filler and 0.5-2.0 parts of coupling agent are activated in a high-speed mixer at 90°C for 10 minutes. Then, 100 parts of block copolymer polypropylene matrix and 0.2-0.5 parts of antioxidant are added and mixed for another 5 minutes. The mixed material is then added to a twin-screw extruder and melt-blended and granulated at 190-220°C to obtain the middle layer material.

[0010] Furthermore, the method for preparing the outer layer material includes: 100 parts of block copolymer polypropylene, 20-40 parts of polyolefin elastomer, 5-10 parts of compatibilizer, 0.2-0.5 parts of antioxidant and 0.1-0.3 parts of light stabilizer are added to a high-speed mixer and mixed evenly. The mixture is then melt-blended and granulated at a relatively low temperature of 180-200°C using a twin-screw extruder to obtain the outer layer material.

[0011] Furthermore, the process of determining the initial extrusion temperature of each layer of material includes: The initial extrusion temperature is determined based on the sum of a reference temperature value and a preset temperature range; The preset temperature range includes an upper temperature limit and a lower temperature limit; The upper limit temperature is determined based on the thermal degradation temperature of each layer of material, and the lower limit temperature is determined based on the melting temperature of each layer of material.

[0012] Furthermore, the process of determining the reference temperature value includes: Based on the Vicat softening temperature difference value. The Vicat softening temperature of the inner layer material was determined as the reference temperature value; Alternatively, the average Vicat softening temperature of the inner and outer layers of material can be used as the reference temperature value.

[0013] Furthermore, the melt mass flow rate consistency includes the melt mass flow rate consistency at the inner and middle layer interfaces, and the melt mass flow rate consistency at the middle and outer layer interfaces. The consistency of the melt mass flow rate at the inner-middle layer interface is determined based on the inner-middle layer melt index ratio; The consistency of melt mass flow rate at the middle and outer layer interfaces is determined based on the melt index ratio of the middle and outer layers; The melt flow rate of the inner and middle layers is determined based on the melt flow rate of the inner layer material and the melt flow rate of the middle layer material. The melt flow rate ratio of the middle and outer layers is determined based on the melt flow rate of the middle layer material and the melt flow rate of the outer layer material.

[0014] Furthermore, the process of predicting the interlayer bonding trend of the inner-middle layer interface and the middle-outer layer interface includes: The interlayer bonding trend includes the interlayer bonding trend of the inner-middle layer and the interlayer bonding trend of the middle-outer layer. The trend of interlayer bonding force in the inner and middle layers is determined based on the dynamic change of the consistency of the melt mass flow rate of the inner and middle layers over time. The interlayer bonding trend of the middle and outer layers is determined based on the dynamic change of the consistency of the melt mass flow rate of the middle and outer layers over time.

[0015] Furthermore, based on the decreasing trend of interfacial bonding strength in the inner and middle layers, it was determined that the amount of grafted polypropylene in the inner layer material should be reduced to improve the melt flow rate of the inner layer material. Alternatively, reduce the amount of reinforcing filler in the intermediate layer to improve the melt flow rate of the intermediate layer.

[0016] Furthermore, based on the decreasing trend of interfacial bonding force between the middle and outer layers, it was determined that the amount of reinforcing filler in the middle layer material should be reduced to improve the melt flow rate of the middle layer material. Alternatively, reduce the amount of polyolefin elastomer in the outer layer material to reduce the melt mass flow rate of the outer layer material.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: by preparing an inner layer material containing grafted modified polypropylene, the hydroxyl groups or coupling agents on the surface of the reinforcing filler in the middle layer material interact with each other, thereby enhancing the interlayer bonding strength, so that the inner layer can still maintain good dimensional stability and interface integrity under long-term cable heating conditions; by preparing a middle layer material containing reinforcing filler, chemical bonding is achieved through coupling agents, thereby building a chemical bridge between the filler and the matrix, improving the flexural modulus, ring stiffness and tensile strength, while reducing interlayer thermal stress caused by temperature changes, ensuring that the pipe does not collapse or crack in the directional drilling formation compression environment; by preparing an outer layer material containing polyolefin elastomer, the composite pipe can effectively absorb and dissipate external impact energy through the synergistic deformation mechanism of the elastomer particles even when subjected to geological compression, rock impact or drag friction during low-temperature laying and long-term operation, avoiding crack penetration through the pipe wall, thereby meeting the crack resistance requirements of trenchless construction and cable protection in extremely cold regions.

[0018] Furthermore, this invention uses block copolymer polypropylene as a common matrix, which enables the inner layer graft modification, the middle layer filler reinforcement, and the outer layer elastomer to have similar coefficients of thermal expansion and thermo-oxidative aging rates, significantly reducing interlayer thermal stress and preventing high-temperature delamination or low-temperature cracking. It can achieve gradient functional synergy from the inner wall heat resistance to the middle layer high strength load-bearing capacity and the outer layer impact resistance and weather resistance in the pipe thickness direction, thereby achieving a fused structure without clear interfaces to avoid interlayer delamination.

[0019] Furthermore, the Vicat softening temperature difference of the present invention reflects the heat resistance deformation ability of the material under heating conditions. During co-extrusion molding, the inner layer requires a higher processing temperature to obtain melt flow that matches the outer layer, while the outer layer requires a relatively lower temperature to prevent overheating degradation. When the Vicat softening temperature difference is large, the Vicat temperature of the inner layer material is used as the reference temperature value, and a differential adjustment is applied to the extrusion temperature of the outer layer to achieve viscosity matching of the two melts when they meet at the die. When the Vicat softening temperature difference is small, it indicates that the heat resistance of the two layers is similar, so the average value of the two is used as the reference to plasticize each layer under similar thermal histories.

[0020] Furthermore, this invention determines the melt index ratio of the inner and middle layers and the melt index ratio of the middle and outer layers to characterize the degree of melt viscosity matching at the co-extrusion interface of each layer, thereby predicting the diffusion and entanglement ability of molecular chains between layers, quantifying the trend of interlayer bonding force, independently judging the viscosity matching of each interface, accurately locating weak interfaces, and adjusting the extrusion temperature or material content of the corresponding layer accordingly, thereby achieving synergistic optimization of the two interfaces and ensuring that the composite pipe obtains a uniform and high-strength interlayer bond after multi-layer co-extrusion molding.

[0021] Furthermore, this invention superimposes and analyzes the dynamic monitoring curve of the consistency of the melt mass flow rate of the inner and middle layers over time with a pre-established inner and middle layer peel strength response curve. When the average rate is low, the upward trend stagnates, indicating that increasing the initial extrusion temperature of the inner layer material can increase its melt mass flow rate, or decreasing the initial extrusion temperature of the middle layer material can decrease its melt mass flow rate. When the average rate is high, the upward trend is considered to be continuously effective, indicating that the current process is correct and no adjustment is needed. When the bonding force at the inner and middle layer interface decreases, the amount of grafted polypropylene in the inner layer material is reduced to increase its melt mass flow rate, or the amount of reinforcing filler in the middle layer material is reduced to increase its melt mass flow rate, thereby causing the melt index ratio of the inner and middle layers to recover to 1, achieving good interlayer bonding force, and thus fundamentally improving the interlayer bonding strength of the inner and middle layers.

[0022] Furthermore, the dynamic monitoring curves showing the consistency of the outer and middle layer melt flow rates over time are superimposed with the pre-established inner-middle layer peel strength response curves for analysis. Based on this, graded control of the state is implemented. When the melt index ratio deviates from 1 and the rate of increase tends to stagnate, it indicates that the current temperature control measures have reached their effectiveness boundary. At this point, the initial extrusion temperature of the outer layer material is increased to increase its melt flow rate, or the initial extrusion temperature of the middle layer material is decreased to reduce its melt flow rate, causing the melt index ratio of both to converge back to 1.0. When the melt index ratio approaches 1 and the upward trend remains effective, the current process parameters are maintained unchanged. If the monitoring curves show a decreasing trend in the interfacial bonding strength between the inner and middle layers, the amount of polyolefin elastomer in the outer layer material is reduced to increase the outer layer melt flow rate, or the amount of reinforcing filler in the middle layer material is reduced to increase the middle layer melt flow rate, causing the melt index ratio between the inner and outer layers to rise back to 1, thereby achieving a fundamental improvement and long-term stability of the interlayer bonding strength.

[0023] Furthermore, this invention achieves precise closed-loop control of the interfacial bonding force of multiple layers by dynamically monitoring the melt flow rate consistency over time. This avoids interlayer rheology caused by traditional uniform temperature processes and overcomes the high cost and low efficiency of repeated adjustments and trial and error, resulting in composite pipes with excellent interfacial bonding force.

[0024] Furthermore, by enhancing interlayer bonding strength, the polypropylene molecular chains at the interfaces of each layer achieve full entanglement and stress transfer, improving the pipe's resistance to delamination under complex loads such as radial extrusion, axial tension, and uneven settlement. This avoids stress concentration and microcrack propagation caused by interface defects, extending the pipe's service life under buried, tunneled, and repeatedly thermally cycled conditions. At the same time, the optimized interlayer bonding strength gives the pipe a superior overall mechanical synergy effect, improving its interlayer peel strength, impact resistance, and long-term pressure resistance reliability. Ultimately, this achieves a comprehensive improvement in the safety life and construction convenience of MPP cable protection pipes, making them particularly suitable for the stringent requirements of cable pipes in complex environments. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation method of the MPP cable protection pipe according to an embodiment of the present invention; Figure 2 A logic diagram for determining the reference temperature value in an embodiment of the present invention; Figure 3 This is a comparison of the dynamic monitoring curves of the consistency of the inner and middle layer melt mass flow rate over time in Example 1 of the present invention and Comparative Examples 1-3. Figure 4 This is a comparison chart of the dynamic monitoring curves showing the consistency of the mass flow rate of the middle and outer layers of the melt over time in Example 1 of the present invention and Comparative Examples 1-3. Detailed Implementation

[0026] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0027] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0028] Please see Figure 1 As shown, it is a flowchart of the preparation method of the MPP cable protection pipe according to an embodiment of the present invention.

[0029] The method for preparing the MPP cable protection conduit according to the embodiments of the present invention includes: Step S1: Using block copolymer polypropylene as the matrix resin, prepare an inner layer material containing grafted modified polypropylene, a middle layer material containing reinforcing fillers, and an outer layer material containing polyolefin elastomer. Step S2: Determine the initial extrusion temperature of each layer of material based on the Vicat softening temperature difference between the inner and outer layers of material; Step S3: Based on the melt mass flow rate of each layer of material, determine the consistency of the melt mass flow rate of the composite pipe to predict the interlayer bonding force trend of the inner and middle layer interfaces and the middle and outer layer interfaces. Step S4: Based on the interlayer bonding force trend, determine and adjust the initial extrusion temperature or material content, and perform co-extrusion molding to form a composite pipe.

[0030] In this embodiment of the invention, the method for preparing the inner layer material includes: 100 parts of block copolymer polypropylene, 2-10 parts of maleic anhydride grafted polypropylene, 0.2-0.5 parts of antioxidant, and 0.5-1.0 parts of lubricant are added to a high-speed mixer and mixed at 800 rpm for 5 minutes at room temperature to obtain a premix. The premix is ​​then added to a twin-screw extruder and melt-extruded and granulated at a temperature range of 180-210℃ to obtain the inner layer material. During the melt blending process, the maleic anhydride grafted polypropylene further reacts and compatibilizes with the block copolymer polypropylene matrix, while introducing polar groups to improve the adhesion activity of the inner layer surface.

[0031] Specifically, the lubricant includes metal soaps, saturated hydrocarbons, or fatty acid amides, which are used to improve the processing fluidity of the inner layer material, promote filler dispersion, and prevent the melt from sticking to the metal surface of the equipment.

[0032] In this embodiment of the invention, the addition of maleic anhydride-grafted polypropylene to block copolymer polypropylene significantly alters the non-polar surface properties of the original polypropylene by introducing polar anhydride groups onto its molecular chain. The outer surface of a cable is typically a sheath material containing polar groups, such as cross-linked polyethylene or polyvinyl chloride. When the inner layer material contacts the outer surface of the cable, the maleic anhydride groups in the grafted polypropylene can form hydrogen bonds or dipole-dipole interactions with polar groups on the cable sheath surface, such as hydroxyl, ester, or chlorine atoms, thereby reducing interfacial tension and improving wettability. Simultaneously, the polypropylene backbone of the grafted polypropylene exhibits good compatibility and co-crystallization ability with the matrix block copolymer polypropylene, effectively creating a molecular bridge between the inner wall of the pipe and the cable sheath. One end is anchored to the cable sheath surface via polar anhydride groups, while the other end is wound or co-crystallized within the inner matrix of the pipe via polypropylene chain segments. This enhanced interfacial affinity effectively reduces sliding friction and fretting wear during cable installation and operation under thermal expansion.

[0033] In this embodiment of the invention, during the multilayer co-extrusion molding process, the polar groups of the inner layer grafted polypropylene will interact with the hydroxyl groups or coupling agents on the surface of the reinforcing filler in the middle layer material, thereby enhancing the interlayer bonding strength so that the inner layer can still maintain good dimensional stability and interface integrity under long-term cable heating conditions.

[0034] In this embodiment of the invention, the method for preparing the middle layer material includes: First, 10-30 parts of reinforcing filler and 0.5-2.0 parts of coupling agent are activated in a high-speed mixer at 90°C for 10 minutes. Then, 100 parts of block copolymer polypropylene matrix and 0.2-0.5 parts of antioxidant are added and mixed for another 5 minutes. The mixed material is then added to a twin-screw extruder and melt-blended and granulated at 190-220°C to obtain the middle layer material. The middle layer material is the main load-bearing structure of the composite pipe, used to prevent the outer heat-sensitive material from being subjected to thermal shock, thereby reducing the interlayer stress of the composite pipe when the temperature changes and preventing delamination.

[0035] Specifically, the reinforcing filler includes glass fiber, talc, or calcium carbonate.

[0036] The coupling agent includes silane coupling agents, titanate coupling agents, or aluminate coupling agents, which are used to form chemical bridges between materials, improve filler dispersion, and enhance interfacial bonding to maximize the reinforcing effect.

[0037] In this embodiment of the invention, after introducing reinforcing fillers into the intermediate layer material, a three-dimensional physical network structure is formed in the block copolymer polypropylene matrix by utilizing the high modulus and rigidity characteristics of the fillers. The filler surface is activated by a coupling agent; the hydrolyzable groups at one end of the coupling agent molecule chemically bond with the hydroxyl groups on the filler surface, while the organic functional groups at the other end physically entangle or covalently bond with the polypropylene matrix, thereby constructing a chemical bridge between the filler and the matrix to improve the uniformity of filler dispersion and inhibit agglomeration.

[0038] In this embodiment of the invention, when the composite pipe is subjected to external earth pressure, rock impact, or trenchless pullback tensile force, the uniformly dispersed high-modulus filler particles act as stress transmission centers, transferring localized concentrated stress to the surrounding polypropylene matrix through the interface, forcing the matrix to undergo shear yielding and plastic deformation, thereby significantly improving the flexural modulus, ring stiffness, and tensile strength. At the same time, the middle layer, as the main load-bearing structure of the composite pipe, effectively buffers the thermal shock of the outer heat-sensitive material under extrusion cooling or cable heating conditions with its high rigidity. Through interlayer modulus matching and thermal expansion coefficient gradient transition, the interlayer thermal stress caused by temperature changes is reduced, thereby preventing interface delamination and overall pipe structure failure, ensuring that the pipe does not collapse or rupture in the directional drilling formation extrusion environment.

[0039] In this embodiment of the invention, the method for preparing the outer layer material includes: 100 parts of block copolymer polypropylene, 20-40 parts of polyolefin elastomer, 5-10 parts of compatibilizer, 0.2-0.5 parts of antioxidant, and 0.1-0.3 parts of light stabilizer are added to a high-speed mixer and mixed evenly. The mixture is then melt-blended and granulated at a relatively low temperature of 180-200°C using a twin-screw extruder to obtain the outer layer material. The outer layer material is used to absorb and dissipate external impact energy so that the composite pipe meets the crack resistance requirements for low-temperature laying and operation.

[0040] Specifically, the polyolefin elastomer includes ethylene-octene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, or propylene-based elastomer.

[0041] Specifically, the compatibilizer includes maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyolefin elastomer, maleic anhydride-grafted polyethylene, or maleic anhydride-grafted EPDM rubber.

[0042] In this embodiment of the invention, the compatibilizer is an additive that can improve the interfacial bonding force between two or more incompatible or partially compatible polymers. In the outer layer material, it is used to reduce interfacial tension, refine the size of the dispersed phase, and enhance interfacial bonding to obtain an ideal microstructure and stable mechanical properties.

[0043] Specifically, the light stabilizer includes ultraviolet light absorbers, hindered amine light stabilizers, or quenchers, which are used to inhibit or delay the photo-oxidative degradation of polymer materials under ultraviolet irradiation, and can effectively prevent the surface of the pipe from powdering, cracking, and performance deterioration.

[0044] In this embodiment of the invention, when polyolefin elastomers are uniformly dispersed in a block copolymer polypropylene matrix as micron-sized particles, these flexible particles act as stress concentration centers. Under external impact or low-temperature loads, the polyolefin elastomer particles induce crazes and shear bands in the matrix through their large deformation. The initiation and propagation of crazes consume a large amount of energy, while the shear bands passivate the high-stress areas at the craze tips, preventing them from further developing into cracks. Simultaneously, the elastomer particles release local triaxial stress through interfacial debonding or cavitation effects, promoting the transformation of the matrix from brittle fracture to ductile fracture. Unlike conventional toughening agents, the molecular chain of the polyolefin elastomer consists of crystalline polyethylene segments and amorphous comonomer side chains. This structure allows it to maintain a rubbery state even at -40°C, and its saturated hydrocarbon backbone has no double bonds, giving the outer layer excellent thermo-oxidative stability. When the dosage is controlled at 20-40 parts and supplemented with a compatibilizer, the particle size of the dispersed phase of the polyolefin elastomer can be controlled within the ideal range of 0.3-0.8 μm, forming a large number of uniform stress dissipation units. This allows the composite pipe to effectively absorb and dissipate external impact energy through the synergistic deformation mechanism of the elastomer particles during low-temperature laying and long-term operation, even when subjected to geological compression, rock impact, or drag friction. This prevents cracks from penetrating the pipe wall, thereby meeting the crack resistance requirements for trenchless construction and cable protection in frigid regions.

[0045] In this embodiment of the invention, the antioxidants in the inner layer material, middle layer material and outer layer material include at least one of hindered phenolic primary antioxidants, phosphite auxiliary antioxidants or thioester antioxidants, which are used to inhibit the thermo-oxidative degradation of polypropylene during high-temperature processing and use, maintain material properties, and thus extend the material life.

[0046] In this embodiment of the invention, the inner layer material, the middle layer material, and the outer layer material are all based on block copolymer polypropylene as the matrix resin. The crystalline polypropylene segment provides high heat resistance, high modulus, and dimensional stability, while the amorphous polyethylene segment provides toughness and impact resistance, serving as a unified structural framework for the three-layer co-extrusion system.

[0047] In this embodiment of the invention, the three layers of materials have similar chemical compositions at the co-extrusion interface, allowing for sufficient inter-diffusion and co-crystallization between molecular chains to form a continuous transitional interface bonding layer. This avoids the interface defects and stress concentration commonly seen when composites of dissimilar resins. Furthermore, under long-term heating conditions in cables, the three layers of materials have similar coefficients of thermal expansion and thermo-oxidative aging rates. When the temperature fluctuates, each layer expands and contracts synergistically, significantly reducing interlayer thermal stress and preventing high-temperature delamination or low-temperature cracking.

[0048] In this embodiment of the invention, block copolymer polypropylene is used as a common matrix, which enables the grafting modification of the inner layer, the filler reinforcement of the middle layer, and the elastomer toughening of the outer layer to be synergistically matched within the same processing window. This eliminates the need for frequent adjustments to the extrusion process, ensuring independent optimization space for the functional modification of each layer. Furthermore, the affinity of the homogeneous matrix ensures the overall structural integrity after composite molding. This achieves a gradient functional synergy in the pipe thickness direction, from the heat-resistant affinity of the inner wall to the high-strength load-bearing capacity of the middle layer and the impact resistance and weather resistance of the outer layer. As a result, a fused structure without clear interfaces is achieved, thus avoiding interlayer delamination.

[0049] Specifically, the Vicat softening temperature difference is used to determine the initial extrusion temperature based on the degree of thermal flow matching between the inner and outer layer materials during the co-extrusion molding process.

[0050] Specifically, the process of determining the initial extrusion temperature of each layer of material includes: The initial extrusion temperature is determined based on the sum of a reference temperature value and a preset temperature range, so that the materials of each layer reach similar melt viscosity when they come together at the co-extrusion die, thereby obtaining a uniform layer thickness distribution and a stable interface bond.

[0051] The preset temperature range includes an upper temperature limit and a lower temperature limit; The upper limit temperature is determined based on the thermal degradation temperature of each layer of material. It is used to set the highest temperature limit that each layer of material cannot exceed during the extrusion process, so as to prevent the material from breaking molecular chains, decomposing or deteriorating in performance due to excessive temperature, and to ensure the thermal stability of each layer of material during the processing. The lower limit temperature is determined based on the melting temperature of each layer of material. It is used to set the minimum temperature limit that each layer of material must reach during the extrusion process, ensuring that the material is fully transformed from a solid state to a viscous flow state and has sufficient fluidity to complete co-extrusion molding and interlayer welding.

[0052] Please see Figure 2 As shown, it is a logic diagram for determining the reference temperature value in an embodiment of the present invention.

[0053] Specifically, the process of determining the reference temperature value includes: Based on the Vicat softening temperature difference being greater than or equal to the characteristic threshold, the Vicat softening temperature of the inner layer material is determined as the reference temperature value. Based on the fact that the Vicat softening temperature difference is less than the characteristic threshold, the average Vicat softening temperature of the inner layer material and the outer layer material is determined as the reference temperature value. In this embodiment of the invention, the feature threshold is a positive value.

[0054] In this embodiment of the invention, the Vicat softening temperature difference reflects the heat resistance deformation ability of the material under heating conditions. The Vicat temperature of the inner layer material is increased due to the addition of maleic anhydride-grafted polypropylene, while the Vicat temperature of the outer layer material is decreased due to the addition of polyolefin elastomer. As a result, the Vicat temperature of the inner layer is necessarily higher than that of the outer layer, and the difference between the two is always positive. Therefore, during co-extrusion molding, the inner layer needs a higher processing temperature to obtain melt flow that matches that of the outer layer, while the outer layer needs a relatively lower temperature to prevent overheating and degradation.

[0055] In this embodiment of the invention, when the Vicat softening temperature difference is large, the Vicat temperature of the inner layer material is used as the reference temperature value, and a differential downward adjustment is applied to the extrusion temperature of the outer layer to achieve viscosity matching of the two melts when they meet at the die head; when the Vicat softening temperature difference is small, it indicates that the heat resistance of the two layers is similar, so the average value of the two is used as the reference to plasticize each layer under similar thermal histories. Since the Vicat temperature of the inner layer is always higher than that of the outer layer in the material system defined by this invention, the difference is always positive.

[0056] Specifically, the melt mass flow rate consistency includes the melt mass flow rate consistency at the inner and middle layer interfaces and the melt mass flow rate consistency at the middle and outer layer interfaces; these are used to characterize the viscosity matching degree of the melts on both sides of the inner and middle layer interfaces and the middle and outer layer interfaces, respectively, thereby independently predicting the interlayer bonding trend of the two interfaces.

[0057] The consistency of the melt mass flow rate at the inner-middle layer interface is determined based on the inner-middle layer melt index ratio; The consistency of melt mass flow rate at the middle and outer layer interfaces is determined based on the melt index ratio of the middle and outer layers.

[0058] The melt flow rate ratio of the inner and middle layers is determined based on the ratio of the melt mass flow rate of the inner layer material to the melt mass flow rate of the middle layer material. It is used to characterize the degree of melt viscosity matching between the inner and middle layers at the co-extrusion interface, predict the molecular chain diffusion and entanglement ability at the interface between the inner and middle layers, and thus quantify the interlayer bonding trend of the interface.

[0059] In this embodiment of the invention, the melt flow rate ratio of the inner and middle layers reflects the degree of consistency in melt mass flow rate between the inner and middle layer materials. When the melt flow rate ratio of the inner and middle layers approaches 1, it indicates that the melt flowability of the inner and middle layers is highly consistent, the viscosity of the two at the co-extrusion interface is well matched, and the molecular chains can fully diffuse and entangle, thereby forming a high-strength interlayer bond. When the melt flow rate ratio of the inner and middle layers deviates from 1, it indicates that the consistency of the flowability of the two is reduced, and the interfacial bonding force is reduced accordingly. That is, the closer the melt flow rate ratio of the inner and middle layers is to 1, the higher the consistency of melt mass flow rate; the further the melt flow rate ratio of the inner and middle layers deviates from 1, the lower the consistency of melt mass flow rate.

[0060] The melt flow rate ratio of the middle and outer layers is determined based on the ratio of the melt mass flow rate of the middle layer material to the melt mass flow rate of the outer layer material. It is used to characterize the degree of melt viscosity matching between the middle and outer layers at the co-extrusion interface, predict the molecular chain diffusion and entanglement ability at the interface between the middle and outer layers, and thus quantify the interlayer bonding trend of the interface.

[0061] In this embodiment of the invention, the melt flow rate ratio of the middle and outer layers characterizes the consistency of the melt mass flow rate between the middle and outer layers. When the melt flow rate ratio of the middle and outer layers is close to 1, the consistency of the melt mass flow rate is high and the interfacial bonding is excellent. When the melt flow rate ratio of the middle and outer layers deviates from 1, the consistency of the melt mass flow rate is low and the interfacial bonding is deteriorated.

[0062] In this embodiment of the invention, the interfaces between the inner and middle layers, and between the middle and outer layers, are independent of each other in terms of material composition, interfacial bonding mechanism, and process control. The inner layer material contains grafted modified polypropylene, whose polar groups mainly enhance the affinity with the cable sheath and the interfacial bonding with the middle layer filler. The middle layer material contains reinforcing filler, which has high rigidity and relatively low fluidity. The outer layer material contains polyolefin elastomer, which has good flexibility and relatively high fluidity. The two adjacent layers at each interface have significant differences in chemical structure, rheological properties, and functional positioning. Therefore, the melt viscosity matching degree of the inner and middle layer interfaces, and between the middle and outer layers, is independent. That is, a reasonable melt index ratio between the inner and middle layers does not guarantee a reasonable melt index ratio between the middle and outer layers. By calculating the melt index ratios of the inner and middle layers and the middle and outer layers separately, the viscosity matching of each interface can be independently determined, the weak interface can be accurately located, and the extrusion temperature or material content of the corresponding layer can be adjusted accordingly. This achieves synergistic optimization of the two interfaces, ensuring that the composite pipe obtains a uniform and high-strength interlayer bond after multi-layer co-extrusion molding.

[0063] Specifically, the process of predicting the interlayer bonding trend of composite pipes includes: The interlayer bonding trend includes the interlayer bonding trend of the inner and middle layers and the interlayer bonding trend of the middle and outer layers, which are used to independently evaluate the bonding quality of the inner and middle layer interfaces and the middle and outer layer interfaces after co-extrusion molding.

[0064] The trend of interlayer bonding force in the inner and middle layers is determined based on the dynamic change of the consistency of the melt mass flow rate of the inner and middle layers over time. The interlayer bonding trend of the middle and outer layers is determined based on the dynamic change of the consistency of the melt mass flow rate of the middle and outer layers over time.

[0065] In this embodiment of the invention, a dynamic monitoring curve is constructed with time as the horizontal axis and the consistency of the melt flow rate of the inner and middle layers as the vertical axis to characterize the trend of the interlayer bonding force of the inner and middle layers. The curve is obtained by continuously collecting the melt flow rates of the inner and middle layers at different time points and calculating the melt index ratio of the inner and middle layers.

[0066] In this embodiment of the invention, the dynamic monitoring curve of the consistency of the inner and middle layer melt flow rate over time is superimposed and analyzed with the pre-established inner and middle layer peel strength response curve. At each time point of the curve, the changing trend of the consistency of the inner and middle layer melt flow rate is observed. When the curve shows a trend of approaching the vertical axis value 1, it indicates that the melt flowability of the inner and middle layers is gradually becoming consistent, the consistency of the inner and middle layer melt flow rate is improving, and the trend of the interlayer bonding force of the inner and middle layers is determined to be an upward trend. When the curve shows a trend of deviating from 1, it indicates that the difference in melt flowability between the inner and middle layers is increasing, the consistency of the inner and middle layer melt flow rate is decreasing, and the trend of the interlayer bonding force of the inner and middle layers is determined to be a downward trend. When the curve maintains a stable fluctuation near 1, it indicates that the consistency of the inner and middle layer melt flow rate is well maintained, and the trend of the interlayer bonding force is stable, which is excellent.

[0067] In this embodiment of the invention, the bonding trend between the middle and outer layers is determined by constructing a dynamic monitoring curve of the consistency of the melt flow rate between the middle and outer layers over time. With time as the horizontal axis and the consistency of the melt flow rate between the middle and outer layers as the vertical axis, the curve is obtained by continuously collecting the consistency of the melt flow rate between the middle and outer layers at different time points and calculating the melt index ratio between the middle and outer layers.

[0068] In this embodiment of the invention, the dynamic monitoring curve of the consistency of the melt mass flow rate of the middle and outer layers changing over time is superimposed and analyzed with the pre-established peel strength response curve of the middle and outer layers. At each time point of the curve, the changing trend of the consistency of the melt mass flow rate of the middle and outer layers is observed. When the curve shows a trend of approaching the vertical axis value 1 but does not maintain a stable fluctuation near 1, it indicates that the melt flowability of the middle and outer layers is gradually becoming consistent, the consistency of the melt mass flow rate of the middle and outer layers is improving, and the trend of the interlayer bonding force of the middle and outer layers is determined to be an upward trend. When the curve shows a trend of deviating from 1, it indicates that the difference in melt flowability between the middle and outer layers is increasing, the consistency of the melt mass flow rate of the middle and outer layers is decreasing, and the trend of the interlayer bonding force of the middle and outer layers is determined to be a downward trend. When the curve maintains a stable fluctuation near 1, it indicates that the consistency of the melt mass flow rate of the middle and outer layers remains good, and the trend of the interlayer bonding force is stable and good.

[0069] It is understandable that the peel strength response curve of the inner-middle layer interface and the peel strength response curve of the middle-outer layer interface are two independent standard curves, which need to be established and used separately.

[0070] In this embodiment of the invention, the peel strength response curve of the inner-middle layer interface is obtained by preparing a series of composite pipe samples with different inner-middle layer melt flow rate uniformities, testing the peel strength of the inner-middle layer interface under constant peel speed conditions, and fitting the inner-middle layer melt flow rate uniformity as the abscissa and peel strength as the ordinate; similarly, the peel strength response curve of the middle-outer layer interface is independently established with the middle-outer layer melt flow rate uniformity as the abscissa and the middle-outer layer interface peel strength as the ordinate.

[0071] Specifically, when the interlayer bonding force trend is upward, it is determined whether the upward trend has stalled based on the average rate at which the melt mass flow rate consistently approaches 1 within a continuous period of no less than a preset monitoring time. When the average rate is low, it is determined that the upward trend has stalled, indicating that the current process is insufficient to overcome the obstacle causing the difference in melt mass flow rate consistency, and the upward trend is unlikely to continue to rise on its own. It is determined that the melt mass flow rate of the inner layer material can be increased by increasing the initial extrusion temperature of the inner layer material, or the melt mass flow rate of the inner layer material can be decreased by decreasing the initial extrusion temperature of the middle layer material. When the average rate is high, it is determined that the upward trend is effective, that is, the current process is correct and no adjustment is required.

[0072] It is understood that the above adjustment rules apply to both the inner middle layer interface and the middle and outer layer interfaces in the embodiments of the present invention.

[0073] Specifically, when the interlayer bonding force trend is downward, it indicates that the consistency of the melt mass flow rate at the corresponding interface is deteriorating in the direction of deviating from 1. In this case, the melt mass flow rate of the single layer material can be changed by adjusting the material content.

[0074] In this embodiment of the invention, when the bonding force at the inner and middle layers interface shows a decreasing trend, the amount of grafted polypropylene in the inner layer material is reduced to increase the melt flow rate of the inner layer material, or the amount of reinforcing filler in the middle layer material is reduced to increase the melt flow rate of the middle layer material, thereby causing the melt index ratio of the inner and middle layers to rise back to 1.

[0075] In this embodiment of the invention, when the bonding force at the interface between the middle and outer layers shows a decreasing trend, it indicates that the fluidity of the middle layer is relatively lower than that of the outer layer. By reducing the amount of reinforcing filler in the middle layer material to increase the melt flow rate of the middle layer material, or by reducing the amount of polyolefin elastomer in the outer layer material to reduce the melt flow rate of the outer layer material, the melt index ratio between the middle and outer layers can be increased back to 1.

[0076] In this embodiment of the invention, when the inner and middle layer interface is in a good trend, it indicates that the melt mass flow rate consistency between the inner layer material and the middle layer material is in an excellent state, the melt viscosity of the inner layer and the middle layer at the co-extrusion interface is highly matched, the two melt layers can form a stable laminar flow interface when they meet at the die head, the molecular chains obtain sufficient cross-interface diffusion and entanglement time, the interface bonding strength reaches the expected level, and there is no need to adjust the initial extrusion temperature or material content.

[0077] In this embodiment of the invention, for the inner and middle layers, the grafted chains of maleic anhydride-grafted polypropylene in the inner layer material restrict molecular chain movement. The amount of grafted polypropylene used is negatively correlated with the inner layer melt flow rate; that is, reducing the amount of grafted polypropylene reduces the molecular chain entanglement density, thereby improving the inner layer melt fluidity and increasing the melt flow rate. Similarly, the reinforcing filler in the middle layer material hinders the flow of the polypropylene matrix molecular chains. The amount of filler used is negatively correlated with the middle layer melt flow rate; that is, reducing the amount of filler reduces flow resistance, thereby improving the middle layer melt fluidity and increasing the melt flow rate. In practice, reducing the amount of grafted polypropylene or reducing the amount of filler can increase the melt index ratio of the inner and middle layers, thus causing the inner and middle layer melt index ratio to rise back towards 1.

[0078] In this embodiment of the invention, for the middle and outer layer interface, the polyolefin elastomer in the outer layer material has high melt flowability, and its dosage is positively correlated with the outer layer melt mass flow rate. That is, reducing the dosage of polyolefin elastomer can reduce the outer layer melt flowability and decrease the outer layer melt mass flow rate. In practice, reducing the dosage of the middle layer filler or the outer layer polyolefin elastomer can both cause the middle-outer layer melt index ratio to return to 1.

[0079] Example 1 100 parts of block copolymer polypropylene, 15 parts of maleic anhydride grafted polypropylene, 0.3 parts of antioxidant 1010 and 0.5 parts of lubricant calcium stearate are added to a high-speed mixer and mixed at 800 rpm for 5 minutes at room temperature to obtain a premix. The premix is ​​then added to a twin-screw extruder and melt-extruded and granulated at a temperature range of 210°C to obtain the inner layer material.

[0080] Activate 20 parts of reinforcing filler talc powder and 0.5 parts of coupling agent KH550 in a high-speed mixer at 90°C for 10 minutes. Add 100 parts of block copolymer polypropylene matrix and 0.3 parts of antioxidant 1010, and continue mixing for 5 minutes. Add the mixed material to a twin-screw extruder, melt blend and granulate at 220°C to obtain the middle layer material.

[0081] 100 parts of block copolymer polypropylene, 30 parts of polyolefin elastomer, 15 parts of compatibilizer maleic anhydride grafted polypropylene, 0.2 parts of antioxidant 168 and 0.5 parts of light stabilizer 119 are added to a high-speed mixer and mixed evenly. The mixture is then melt-blended and granulated at a relatively low temperature of 200°C using a twin-screw extruder to obtain the outer layer material.

[0082] The temperature range for each layer is defined by using the thermal degradation temperature of each material layer as the upper limit temperature and the melting temperature of each material layer as the lower limit temperature, including: The temperature range of the inner material is 165–300℃, the temperature range of the middle material is 168–325℃, and the temperature range of the outer material is 155–290℃.

[0083] The preset characteristic threshold is set to 10℃. In this embodiment, the Vicat softening temperature of the inner layer is 152℃, the Vicat softening temperature of the middle layer is 148℃, and the Vicat softening temperature of the outer layer is 138℃. The difference between the Vicat softening temperatures of the inner and outer layers is 14℃, which is greater than the characteristic threshold. Therefore, the Vicat softening temperature of the inner layer material is determined as the reference temperature value.

[0084] Determining the initial extrusion temperature based on the temperature range and reference temperature value includes: The initial extrusion temperature of the inner layer is 195℃, the middle layer is 205℃, and the outer layer is 180℃. These three layers are melt-bonded through a co-extrusion die and extruded from the die outlet to form a tightly bonded tubular preform. The material temperature of each layer was measured at 1 second. -1 The melt mass flow rates at shear rates were 8.2 g / 10 min for the inner layer, 7.9 g / 10 min for the middle layer, and 5.1 g / 10 min for the outer layer.

[0085] The melt flow rate ratio was determined based on the melt mass flow rate of the inner and middle layers and the middle and outer layers. The melt flow rate ratio of the inner and middle layers was 1.04, which is close to 1. This indicates that the melt mass flow rates of the inner and middle layers at the co-extrusion interface are highly consistent, and the interfacial shear stress is matched, which is conducive to the formation of a stable interfacial bond. However, the melt flow rate ratio of the middle and outer layers was 1.55, which deviates from 1. This indicates that the melt mass flow rates of the middle and outer layers at the co-extrusion interface are not consistent, and the interfacial bond is weak.

[0086] Based on the consistency of the mass flow rate of the inner and middle layers of melt, a dynamic monitoring curve was made to show the change over time. With time as the horizontal axis and the consistency of the mass flow rate of the inner and middle layers of melt as the vertical axis, the dynamic monitoring curve of the consistency of the mass flow rate of the inner and middle layers of melt showed an upward trend from 0 to 30 min, and then stabilized between 1.02 and 1.06 from 30 to 120 min.

[0087] Based on the consistency of the mass flow rate of the middle and outer layers of melt, a dynamic monitoring curve was made to show the change over time. With time as the horizontal axis and the consistency of the mass flow rate of the middle and outer layers of melt as the vertical axis, the dynamic monitoring curve of the consistency of the mass flow rate of the middle and outer layers of melt showed a low-frequency oscillation between 1.45 and 1.70 in the range of 0 to 20 min, and then showed a slow downward trend in the range of 20 to 120 min.

[0088] Therefore, the high consistency of the melt mass flow rate in the inner and middle layers indicates a good trend in the interlayer bonding strength of the inner and middle layers; while the low consistency of the melt mass flow rate in the middle and outer layers indicates a decreasing trend in the interlayer bonding strength of the middle and outer layers.

[0089] In this embodiment, the outer layer polyolefin elastomer was reduced from 30 parts to 15 parts while the temperature remained constant. The adjusted melt index ratio was 1.05, approaching 1, indicating that the consistency of melt mass flow rate between the middle and outer layers at the co-extrusion interface was improved. The dynamic monitoring curve of the consistency of melt mass flow rate between the middle and outer layers over time oscillated between 1.03 and 1.06 within 0 to 30 minutes, almost a straight line, and then slowly approached 1 within 30 to 120 minutes. This indicates that the interlayer bonding strength between the middle and outer layers is good and has been significantly improved. This provides a reliable adhesion basis for the weather resistance, anti-aging and other functional properties of the outer layer, and avoids the functional layer from debonding due to the interface. Thus, while ensuring the structural integrity of the product, the synergistic effect of the reinforcing layer and the functional layer is achieved to adapt to harsh environments.

[0090] In this embodiment, antioxidant 1010 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; coupling agent KH550 is 3-aminopropyltriethoxysilane; antioxidant 168 is tri-tert-butyl-p-hydroxyphenylpropane; and light stabilizer 119 is 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)phenyltriazine.

[0091] The difference between this comparative example and Example 1 is that only 100 parts of block copolymer polypropylene, 15 parts of maleic anhydride grafted polypropylene, 0.3 parts of antioxidant 1010 and 0.5 parts of lubricant calcium stearate were added to a high-speed mixer and mixed at 800 rpm for 5 minutes at room temperature to obtain a premix. The premix was then added to a twin-screw extruder, and the initial extrusion temperature was set to 195°C. The extrusion was then melt-extruded, shaped, cooled, and traction-cut to obtain a single-layer pipe.

[0092] The difference between this comparative example and Example 1 is that the initial extrusion temperature of the three layers of material is set to the same temperature, that is, co-extrusion molding is performed at an initial extrusion temperature of 195°C to obtain the cable protection pipe.

[0093] The difference between this comparative example and Example 1 is that block copolymer polypropylene is used as the base resin to prepare the inner layer material, the middle layer material and the outer layer material. That is, maleic anhydride grafted polypropylene is not added to the inner layer material, no reinforcing filler is added to the middle layer material and no polyolefin elastomer is added to the outer layer material, so as to obtain the cable protection pipe.

[0094] The difference between this comparative example and Example 1 is that the consistency of the melt flow rate of the composite pipe based on the melt flow rate of each layer of material is omitted. That is, the interlayer bonding force trend of the inner and middle layer interfaces and the middle and outer layer interfaces is not predicted, and the initial extrusion temperature and material content are not adjusted based on the interlayer bonding force trend.

[0095] Please see Figure 3 As shown, this is a comparison of the dynamic monitoring curves of the consistency of the inner and middle layer melt mass flow rate over time in Embodiment 1 of the present invention and Comparative Examples 1-3; please refer to... Figure 4 As shown, it is a comparison of the dynamic monitoring curves of the consistency of the mass flow rate of the middle and outer layers of the melt over time in Example 1 of the present invention and Comparative Examples 1-3.

[0096] The performance of the cable protection tubing obtained in Example 1 and Comparative Examples 1-4 is shown in Table 1. Table 1 Summary of performance parameters of cable protection pipes prepared in Example 1 and Comparative Examples 1-4

[0097] The results showed that Comparative Example 1: Completely loses the middle layer reinforcement and outer layer weather resistance functions, and cannot meet the application scenarios of multilayer composite materials under complex conditions. Under high temperature loads, it is easy to deform and its heat resistance, impact resistance and UV aging resistance are all significantly insufficient.

[0098] Comparative Example 2: The optimal processing temperature range for the outer layer is 180–200℃. When extruded at the same temperature of 195℃ as the inner layer, the unsaturated bonds in the polyolefin elastomer are prone to thermal cross-linking, causing the melt flow rate to decrease over time. This further deviates the melt index ratio of the middle and outer layers from 1, resulting in poor dynamic stability. The middle layer reinforcing filler system requires a higher temperature to fully plasticize and disperse. 195℃ is at the lower limit of the middle layer range, which may lead to uneven dispersion of talc powder, higher melt viscosity, and large fluctuations in the melt flow rate measurement, affecting the accuracy of the melt index ratio calculation and compromising the convenience and flexibility of temperature measurement.

[0099] Comparative Example 3: It lost the synergistic effect that a multi-layer structure should have, completely lost its functionality, and its performance was lower than that of ordinary single-layer block copolymer polypropylene pipes. It had extremely poor heat aging and light aging resistance, and the three layers could not be effectively bonded together, making it very easy to delaminate, and its service life was greatly shortened.

[0100] Comparative Example 4: Products that abandon efficient process monitoring and prediction tools, have low interlayer bonding, and have the potential for interlayer delamination may fail after long-term use or in harsh environments.

[0101] It is evident that the preparation method of this embodiment effectively improves the controllability and stability of the PMM cable protection pipe preparation process, resulting in a composite pipe with tight interlayer bonding, excellent comprehensive performance, and adaptability to dragging under complex terrain.

[0102] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an MPP cable protection conduit, characterized in that, include: Using block copolymer polypropylene as the matrix resin, an inner layer material containing grafted modified polypropylene, a middle layer material containing reinforcing fillers, and an outer layer material containing polyolefin elastomers are prepared. The initial extrusion temperature of each layer of material is determined based on the difference in Vicat softening temperature between the inner and outer layers of material. Based on the melt mass flow rate of each layer of material, the consistency of melt mass flow rate of composite pipe is determined, so as to predict the interlayer bonding force trend of the inner and middle layer interfaces and the middle and outer layer interfaces. Based on the interlayer bonding trend, the initial extrusion temperature or material content is adjusted to perform co-extrusion molding to form composite pipes.

2. The method for preparing the MPP cable protection conduit according to claim 1, characterized in that, The method for preparing the inner layer material includes: 100 parts of block copolymer polypropylene, 2-10 parts of maleic anhydride grafted polypropylene, 0.2-0.5 parts of antioxidant and 0.5-1.0 parts of lubricant are added to a high-speed mixer and mixed at 800 rpm for 5 minutes at room temperature to obtain a premix. The premix is ​​then added to a twin-screw extruder and melt-extruded and granulated at a temperature range of 180-210℃ to obtain the inner layer material.

3. The method for preparing the MPP cable protection conduit according to claim 2, characterized in that, The method for preparing the intermediate layer material includes: First, 10-30 parts of reinforcing filler and 0.5-2.0 parts of coupling agent are activated in a high-speed mixer at 90°C for 10 minutes. Then, 100 parts of block copolymer polypropylene matrix and 0.2-0.5 parts of antioxidant are added and mixed for another 5 minutes. The mixed material is then added to a twin-screw extruder and melt-blended and granulated at 190-220°C to obtain the middle layer material.

4. The method for preparing the MPP cable protection conduit according to claim 3, characterized in that, The method for preparing the outer layer material includes: 100 parts of block copolymer polypropylene, 20-40 parts of polyolefin elastomer, 5-10 parts of compatibilizer, 0.2-0.5 parts of antioxidant and 0.1-0.3 parts of light stabilizer are added to a high-speed mixer and mixed evenly. The mixture is then melt-blended and granulated at a relatively low temperature of 180-200°C using a twin-screw extruder to obtain the outer layer material.

5. The method for preparing the MPP cable protection conduit according to claim 1, characterized in that, The process of determining the initial extrusion temperature of each layer of material includes: The initial extrusion temperature is determined based on the sum of a reference temperature value and a preset temperature range; The preset temperature range includes an upper temperature limit and a lower temperature limit; The upper limit temperature is determined based on the thermal degradation temperature of each layer of material, and the lower limit temperature is determined based on the melting temperature of each layer of material.

6. The method for preparing the MPP cable protection conduit according to claim 5, characterized in that, The process of determining the reference temperature value includes: Based on the Vicat softening temperature difference value. The Vicat softening temperature of the inner layer material was determined as the reference temperature value; Alternatively, the average Vicat softening temperature of the inner and outer layers of material can be used as the reference temperature value.

7. The method for preparing the MPP cable protection conduit according to claim 1, characterized in that, The melt mass flow rate consistency includes the melt mass flow rate consistency at the inner and middle layer interfaces, and the melt mass flow rate consistency at the middle and outer layer interfaces. The consistency of the melt mass flow rate at the inner-middle layer interface is determined based on the inner-middle layer melt index ratio; The consistency of melt mass flow rate at the middle and outer layer interfaces is determined based on the melt index ratio of the middle and outer layers; The melt flow rate of the inner and middle layers is determined based on the melt flow rate of the inner layer material and the melt flow rate of the middle layer material. The melt flow rate ratio of the middle and outer layers is determined based on the melt flow rate of the middle layer material and the melt flow rate of the outer layer material.

8. The method for preparing the MPP cable protection conduit according to claim 1, characterized in that, The process of predicting the interlayer bonding trend of the inner-middle layer interface and the middle-outer layer interface includes: The interlayer bonding trend includes the interlayer bonding trend of the inner-middle layer and the interlayer bonding trend of the middle-outer layer. The trend of interlayer bonding force in the inner and middle layers is determined based on the dynamic change of the consistency of the melt mass flow rate of the inner and middle layers over time. The interlayer bonding trend of the middle and outer layers is determined based on the dynamic change of the consistency of the melt mass flow rate of the middle and outer layers over time.

9. The method for preparing the MPP cable protection conduit according to claim 8, characterized in that, Based on the decreasing trend of interfacial bonding strength in the inner and middle layers, it was determined that reducing the amount of grafted polypropylene in the inner layer material would improve the melt flow rate of the inner layer material. Alternatively, reduce the amount of reinforcing filler in the intermediate layer to improve the melt flow rate of the intermediate layer.

10. The method for preparing the MPP cable protection conduit according to claim 9, characterized in that, Based on the decreasing trend of interfacial bonding strength between the middle and outer layers, it was determined that the amount of reinforcing filler in the middle layer material should be reduced to improve the melt flow rate of the middle layer material. Alternatively, reduce the amount of polyolefin elastomer in the outer layer material to reduce the melt mass flow rate of the outer layer material.

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