An ACP double-layer pipe and a preparation method thereof

Abstract

The present application relates to the technical field of co-extrusion double-layer pipe, and discloses an ACP double-layer pipe and a preparation method thereof, which comprises an outer layer and an inner layer; the preparation raw materials of the inner layer comprise, in terms of weight fractions, CPVC 20-25 parts, AGR 20-25 parts, PVC 40-50 parts, a first stabilizer 2-5 parts, a first filler 1-5 parts and a first lubricant 0.2-0.5 parts. The present application introduces AGR into the inner layer raw material system, and utilizes the excellent toughening characteristics of AGR, so that the double-layer pipe can maintain or even exceed the ring stiffness, pressure resistance grade and impact strength of the conventional thick-wall pipe, and the mechanical properties are excellent; at the same time, the raw material cost can be reduced and the pipe weight can be reduced, and under the condition that the outer diameter of the pipe remains unchanged, the inner diameter of the pipe can be increased, so that a larger flow cross section is provided for water supply and drainage transportation, and the water flow and cable passing efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of co-extruded double-layer pipe technology, and particularly to an ACP double-layer pipe and its preparation method. Background Technology

[0002] Co-extruded double-layer pipes are produced using a two-layer co-extrusion process. Two extruders feed molten plastics composed of two different raw materials into the same co-extrusion die, where they are extruded in a single, molten state to form a solid-walled pipe with the inner and outer layers fused together. Co-extruded double-layer pipes used in power, telecommunications, and water supply and drainage applications typically use PVC (polyvinyl chloride) or CPVC (chlorinated polyvinyl chloride) as raw materials.

[0003] However, this type of pipe has the following disadvantages: 1. Double-layer pipes require a thicker wall to maintain their impact resistance and other mechanical properties, which not only increases manufacturing costs and pipe weight but also reduces the inner diameter, affecting the efficiency of water supply and drainage and cable installation; 2. The raw materials for the inner layer are usually fed into the extruder in powder form. Powder has poor melt plasticization stability, and uneven material distribution is likely to occur during extrusion, leading to fluctuations in the inner layer wall thickness and ultimately resulting in uneven overall pipe wall thickness. Thinner sections of the pipe will reduce ring stiffness, impact resistance, and pressure resistance, making them prone to cracking and breakage under pressure or external impact; thicker sections will... 1. Increased local weight, causing deviations in the inner and outer diameters of the pipe, affecting the precision of pipe assembly; 2. Low gloss and high friction coefficient of the inner wall surface of the pipe, leading to increased fluid transport resistance and reduced water flow under water supply and drainage conditions. At the same time, the inner wall of the pipe is more prone to scale buildup, exacerbating the risk of pipe scaling and blockage; 3. Difficulty in welding the pipes together, resulting in lower strength at the joint than the pipe body itself. Under external pressure, internal pressure, or external disturbances, the joint is prone to cracking, leading to a reduction in the overall pressure-bearing capacity and reliability of the pipeline; 4. Incompatibility between the inner and outer materials, resulting in insufficient weld strength between the inner and outer layers of the pipe. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an ACP double-layer pipe and its preparation method, which aims to solve the technical problems of existing PVC double-layer co-extruded pipes, such as overall thick pipe wall, poor uniformity of wall thickness distribution, low gloss of inner wall surface, high coefficient of friction of inner wall, and difficulty in welding the pipe.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides an ACP double-layer pipe, comprising an outer layer and an inner layer; the raw materials for preparing the inner layer, by weight, include: 20-25 parts of CPVC, 20-25 parts of AGR, 40-50 parts of PVC, 2-5 parts of a first stabilizer, 1-5 parts of a first filler, and 0.2-0.5 parts of a first lubricant.

[0006] In the aforementioned ACP double-layer pipe, the raw materials for preparing the outer layer, by weight, include: 40-50 parts of PVC, 20-25 parts of CPVC, 2-5 parts of the second stabilizer, 1-5 parts of the second filler, and 0.2-0.5 parts of the second lubricant.

[0007] In the aforementioned ACP double-layer pipe, the raw materials for preparing the outer layer, by weight, further include: 10-25 parts of modifier; the modifier is a mixture of AGR, MBS, ABS high-rubber powder, ACR and a third filler.

[0008] In the aforementioned ACP double-layer pipe, the weight ratio of AGR, MBS, ABS high-rubber powder, ACR and the third filler is (5-7):(0.4-0.6):(2.2-2.8):(0.4-0.6):(0.4-0.6).

[0009] In the aforementioned ACP double-layer pipe, the third filler is at least one of ultrafine wollastonite powder and light calcium carbonate.

[0010] In the aforementioned ACP double-layer pipe, the ratio of the total weight of the raw materials used to prepare the inner layer to the total weight of the raw materials used to prepare the outer layer is (1-2):(8-9).

[0011] A second aspect of the present invention provides a method for preparing the above-described ACP double-layer pipe, comprising the following steps: S10. Weigh the raw materials for the preparation of the inner layer according to the ratio, and subject the raw materials for the preparation of the inner layer to high-speed mixing and low-speed mixing in sequence. Then, granulate the mixed raw materials to obtain granules. S20. The granules are fed into the inner extruder, and the raw materials for the preparation of the outer layer are fed into the outer extruder according to the ratio. The ACP double-layer pipe is extruded through the double-layer co-extrusion die.

[0012] In the preparation method of the ACP double-layer pipe, in step S10, after the raw material is mixed at high speed until the temperature rises to 85-95°C, the raw material is transferred to a low-speed mixer for mixing until the temperature of the raw material drops to 55-60°C, and then the mixing is stopped.

[0013] In the preparation method of the ACP double-layer pipe, the extrusion temperature of the inner layer extruder in step S20 is set sequentially as follows: Zone 1 150-160℃, Zone 2 145-155℃, Zone 3 145-155℃, Zone 4 145-155℃; the extrusion temperature of the outer layer extruder is set sequentially as follows: Zone 1 175-185℃, Zone 2 170-180℃, Zone 3 165-175℃, Zone 4 150-160℃, Zone 5 155-165℃.

[0014] In the preparation method of the ACP double-layer pipe, in step S20, the double-layer co-extrusion die is set on the confluence die, and the extrusion temperature of the double-layer co-extrusion die is set sequentially as follows: zone 1 165~175℃, zone 2 165~175℃, zone 3 145~155℃, zone 4 190~200℃; the extrusion temperature of the confluence die is 155~165℃.

[0015] Beneficial effects: The first aspect of this invention provides an ACP double-layer pipe. By introducing AGR into the inner layer material system and utilizing the excellent toughening properties of AGR, the double-layer pipe can maintain or even exceed the ring stiffness, pressure resistance, and impact strength of traditional thick-walled pipes without increasing the inner layer wall thickness, exhibiting excellent mechanical properties. At the same time, it can reduce raw material costs and pipe weight, and increase the inner diameter of the pipe while keeping the outer diameter unchanged, thereby providing a larger flow cross-section for water supply and drainage, which is beneficial for improving water flow rate and cable laying efficiency.

[0016] In addition, the polar acrylate groups contained in the AGR molecular chain give the material good surface smoothing properties, improve the demolding performance of the melt, thereby reducing the forming defects of the inner wall of the pipe, improving the gloss of the inner wall of the pipe and reducing the surface roughness of the inner wall, effectively reducing the frictional resistance along the flow of fluid in the pipe.

[0017] The second aspect of this invention provides a method for preparing ACP double-layer pipes. By sequentially subjecting the raw materials for the inner layer to high-speed and low-speed mixing before granulation, sufficient pre-dispersion of the components in the inner layer can be achieved, resulting in uniformly composed granules. Compared to directly feeding powder into an extruder, using granule feeding avoids the defects of uneven melt flow distribution, effectively suppresses fluctuations in the inner layer wall thickness of the pipe, ensures uniform overall wall thickness of the ACP double-layer pipe, avoids the reduction in ring stiffness and pressure resistance caused by local thinning of the pipe wall, and also improves the assembly accuracy of the pipe. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of the ACP double-layer pipe provided by the present invention.

[0019] Figure 2This is a physical image of the ACP double-layer pipe provided by this invention. Detailed Implementation

[0020] This invention provides an ACP double-layer pipe and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0021] like Figure 2 As shown, the first aspect of the present invention provides an ACP double-layer pipe, which is an acrylate-blended chlorinated polyvinyl chloride co-extruded pipe, comprising an outer layer and an inner layer, and can be used in applications such as pressure sewage discharge, drainage, power supply, and communication.

[0022] The raw materials for preparing the inner layer, by weight, include: 20-25 parts of CPVC, 20-25 parts of AGR, 40-50 parts of PVC, 2-5 parts of the first stabilizer, 1-5 parts of the first filler, and 0.2-0.5 parts of the first lubricant.

[0023] In the structure of co-extruded double-layer pipes, the inner layer is the core component that bears pressure and provides mechanical strength, and it is also the key structure for achieving the pipe's impact resistance. The properties of the inner layer material directly determine whether the pipe can maintain long-term stable operation under harsh working conditions. Therefore, in existing co-extruded double-layer pipes, mechanical strength is often provided by increasing the thickness of the inner layer. However, increasing the pipe wall thickness reduces the inner diameter of the double-layer pipe and increases its weight.

[0024] To address this issue, and to reduce the wall thickness of co-extruded double-layer pipes without compromising their mechanical properties and pressure resistance, AGR (acrylic acid copolymer polyvinyl chloride) is introduced into the inner layer raw material system provided in this invention. AGR is an acrylic acid copolymer polyvinyl chloride resin with excellent melt flow properties. The acrylate copolymer component introduced into its molecular chain effectively reduces the melt viscosity of the CPVC / PVC blend system, improves the plasticization uniformity of the inner layer material during extrusion, and avoids significant fluctuations in the inner layer wall thickness. Simultaneously, the acrylate segments in the AGR structure possess excellent low-temperature toughening properties and exhibit good interfacial compatibility with CPVC and PVC matrix resins, forming uniformly distributed elastic micro-regions in the blend system. When the pipe is subjected to external impact, these elastic micro-regions act as stress concentration points, effectively absorbing and dissipating impact energy, thereby significantly improving the pipe's impact resistance and crack propagation resistance. Therefore, without increasing the inner layer wall thickness, the double-layer pipe can still maintain or even exceed the ring stiffness and pressure resistance of traditional thick-walled pipes, exhibiting excellent mechanical properties.

[0025] In addition, the polar acrylate groups contained in the AGR molecular chain can give the material good surface smoothing properties. During the extrusion molding process, the interfacial tension between the inner melt and the mold flow channel surface is reduced, thereby improving the demolding performance of the melt, reducing the surface defects of the inner wall of the pipe after extrusion molding, and ultimately significantly improving the gloss of the inner wall surface of the pipe and reducing the surface roughness, thereby reducing the frictional resistance along the flow of fluid in the pipe.

[0026] To reduce the melt viscosity of CPVC / PVC blends and improve processing fluidity, a relatively high amount of lubricant is added to the raw materials used in the preparation of existing co-extruded double-layer pipes. However, when the amount of lubricant added is too high, excess lubricant migrates within the material and precipitates on the surface. Furthermore, when heated to high temperatures, the lubricant melts and spreads at the joint surface of the pipe, physically hindering the diffusion and entanglement of PVC / CPVC macromolecular chains at the welding interface. This makes it difficult to weld the pipes together, typically requiring adhesive bonding, resulting in a joint strength lower than the overall strength of the pipe.

[0027] In response, by strictly controlling the amount of the first lubricant in the inner layer preparation raw materials provided by the present invention to a relatively low level of 0.2 to 0.5 parts, the amount of free lubricant available for migration and precipitation inside the pipe is limited. Even if the pipes are joined by welding, it is insufficient to form a continuous weak boundary layer at the joint surface. This ensures that the pipes can be joined by welding (e.g., using high-frequency welding process). The heat generated during the welding process can cause the matrix resin at the joint surface to melt uniformly from the inside to the outside. After cooling, a uniform and dense weld can be formed, so that the strength of the joint part can be the same as the strength of other areas of the pipe, which greatly improves the overall pressure bearing capacity and long-term reliability of the pipeline.

[0028] It should be noted that although the amount of the first lubricant is strictly controlled at a low level, AGR is also introduced into the inner layer raw material system of the present invention, which can effectively compensate for the problem of insufficient processing fluidity that may be caused by the reduction of lubricant amount.

[0029] As an example, in the raw materials for preparing the inner layer, the first lubricant can be polyethylene wax; the first stabilizer can be calcium-zinc stabilizer; and the first filler can be light calcium carbonate.

[0030] To improve the compatibility of the inner and outer layer materials and ensure the weld strength between the inner and outer layers, preventing delamination during the service life of the ACP double-layer pipe, in a preferred embodiment, the outer layer preparation materials, by weight, include: 40-50 parts PVC, 20-25 parts CPVC, 2-5 parts second stabilizer, 1-5 parts second filler, and 0.2-0.5 parts second lubricant. In this embodiment, both the outer layer preparation materials and the inner layer matrix resin use PVC and CPVC as base materials, and the base resin systems of the inner and outer layers are completely corresponding. This allows for sufficient penetration and entanglement of molecules at the melt interface of the inner and outer layers during the melt co-extrusion stage, thereby improving the weld strength between the double-layer structure and effectively preventing delamination and peeling of the inner and outer layers during long-term use of the ACP double-layer pipe.

[0031] To ensure that the free lubricant content of the entire double-layer pipe is at an extremely low level, and that the double-layer co-extruded pipe can be assembled by welding, this invention also controls the amount of the second lubricant in the raw materials for preparing the outer layer, controlling the amount of the second lubricant to 0.2 to 0.5 parts, thereby ensuring that the free lubricant content of the entire double-layer pipe is at an extremely low level. When welding the pipe, a uniform and dense weld can be formed in both the inner and outer layers.

[0032] As an example, in the raw materials for preparing the outer layer, the second lubricant can be polyethylene wax; the second stabilizer can be calcium-zinc stabilizer; and the second filler can be light calcium carbonate.

[0033] In order to further improve the comprehensive mechanical properties of the outer layer of the pipe, while taking into account the processing performance and economy of the ACP double-layer pipe, and avoiding the limitations of a single modifier in terms of performance or process, in a preferred embodiment, the raw materials for preparing the outer layer further include, by weight, 10 to 25 parts of modifier; the modifier is a mixture of AGR, MBS, ABS high-rubber powder, ACR and a third filler.

[0034] Specifically, AGR, as the core toughening component in the modifier system, has good interfacial compatibility between its acrylate copolymer segments and the CPVC / PVC matrix resin. It can form uniformly dispersed elastic micro-regions in the outer layer blend system. When the outer layer of the pipe is subjected to external impact, these elastic micro-regions can act as stress concentration points to absorb and dissipate impact energy, thereby improving the impact strength of the outer layer. MBS is a methyl methacrylate-butadiene-styrene copolymer with a typical core-shell structure. Its core is a rubber phase (polybutadiene), and its outer shell is a rigid resin phase (methyl methacrylate-styrene). The rubber phase imparts excellent low-temperature impact resistance to the outer layer of the pipe, effectively compensating for the defects of single toughening agents with fluctuating toughening efficiency within complex service temperature ranges, ensuring that the pipe maintains stable impact resistance over a wide temperature range. ABS high-rubber powder is a high-rubber-content ABS resin powder. In synergy with MBS, it can further broaden the effective toughening temperature range of the outer layer of the pipe, enabling the double-layer pipe to maintain good impact toughness over a wider temperature range. ACR is an acrylate copolymer. As a polymer processing aid, it promotes the gelation process of CPVC / PVC blends, improves melt strength and elongation, and enhances the flow uniformity and plasticization quality of the outer layer material during extrusion molding. This reduces surface defects on the pipe outer wall, delays the erosion of the pipe outer wall by external corrosive media, and extends the service life of ACR double-layer pipes. The third filler reduces the raw material cost of the compound modifier and provides the outer layer of the pipe with a certain degree of rigidity reinforcement and dimensional stability.

[0035] The synergistic effect of the various components of the aforementioned modifier allows it to improve the overall mechanical properties of the outer layer while also considering processing performance and economy. This invention found that when the amount of modifier added is less than 10 parts, the impact toughening effect on the outer layer of the pipe is not significant; however, when the total amount of the modifier added exceeds 25 parts by weight, excessive elastomer components (especially the rubber phase in AGR and ABS high-rubber powder) will accumulate and percolate in the CPVC / PVC continuous phase, leading to excessive dilution of the continuous phase structure of the matrix resin. Although this can further improve the toughness of the outer layer of the pipe to some extent, it will significantly reduce the yield stress and flexural modulus of the outer matrix. Simultaneously, since the Vicat softening temperature of the rubber phase itself is much lower than that of the CPVC / PVC matrix resin, excessive introduction will cause a significant decrease in the Vicat softening temperature of the outer layer of the pipe, thereby deteriorating its creep resistance and heat deformation resistance under high-temperature conditions, affecting the dimensional stability of the ACP double-layer pipe during long-term use.

[0036] In order to achieve the optimal balance between improving impact resistance, ensuring processing rheological stability and controlling raw material costs, in a preferred embodiment, the AGR, MBS, ABS high-resin powder, ACR and the third filler are mixed in the following weight ratios: (5-7):(0.4-0.6):(2.2-2.8):(0.4-0.6):(0.4-0.6).

[0037] In this formulation, AGR, as the main toughening component, has the highest proportion, ensuring sufficient impact toughening effect on the outer layer of the pipe. If the AGR content is too low, the improvement in the impact strength of the outer layer of the pipe will be limited, making it difficult to meet the mechanical performance requirements of the pipe under harsh working conditions. If the AGR content is too high, it will easily lead to excessively low melt viscosity in the outer layer, affecting the stability of extrusion molding. The amount of ABS high-rubber powder is second only to AGR, forming a complementary toughening effect with AGR, effectively broadening the toughening temperature range of the outer layer of the pipe within the above formulation range. The proportions of MBS and ACR in the modifier are both at a low level, ensuring that MBS plays a supplementary role in low-temperature impact toughening, while ACR effectively improves the processing fluidity and plasticization uniformity of the melt. The amount of the third filler within the above formulation range can play a role in rigid reinforcement and cost reduction, while not affecting the toughness and surface quality of the outer layer of the pipe due to excessive filler.

[0038] The components work synergistically in the aforementioned specific ratio to fully leverage the toughening effect of AGR, the temperature-range complementarity of ABS, the interfacial compatibilization of MBS, the plasticizing promotion of ACR, and the rigid support and cost reduction effects of fillers. This formulation design achieves an optimal balance between improving impact resistance, ensuring processing rheological stability, and controlling raw material costs, avoiding the performance or process limitations of a single modifier. The overall effect is significantly better than simply adding the components together.

[0039] For example, the third filler can be at least one of ultrafine wollastonite powder and light calcium carbonate. Specifically, ultrafine wollastonite powder has a unique needle-like or fibrous crystal structure with a large aspect ratio, which can form a reinforcing network in CPVC / PVC blend systems, improving the mechanical properties of the outer layer of the pipe; at the same time, wollastonite powder has stable chemical properties and good weather resistance, and will not affect the long-term aging resistance of the outer layer of the pipe. Light calcium carbonate has the characteristics of fine particle size and uniform distribution, which can effectively improve the hardness, rigidity and heat resistance of rigid PVC products; at the same time, it can also improve the fluidity of the outer melt and improve the surface smoothness of the outer wall of the pipe.

[0040] To ensure that the ACP double-layer pipe meets the requirements for pressure resistance and impact resistance while also having a large inner diameter, in a preferred embodiment, the ratio of the total weight of the inner layer preparation materials to the total weight of the outer layer preparation materials is (1-2):(8-9). Within this ratio range, the inner layer of the pipe, relying on the toughening effect of AGR itself, can meet the requirements for pressure resistance and impact resistance with a low proportion of raw materials, which helps to effectively expand the flow aperture inside the pipe and reduce its weight. The outer layer of the pipe, as the external protective body of the double-layer pipe, has a large proportion of raw materials used in its preparation, which can form a sufficient protective layer to resist soil compression, external impact, and outdoor aging. Furthermore, the high heat capacity of the outer layer melt during co-extrusion and merging can promote the full entanglement of the inner and outer layer resin molecules, improve the interlayer fusion strength, and prevent the inner and outer layers of the pipe from delaminating. However, when the ratio of the total weight of the outer layer preparation materials to the total weight of the inner layer preparation materials is greater than 9, the outer layer wall thickness is too thick, which will increase the brittleness of the outer layer and make the pipe prone to cracking at low temperatures or under impact.

[0041] like Figure 1 As shown, a second aspect of the present invention provides a method for preparing the above-described ACP double-layer pipe, comprising the following steps: S10. Weigh the raw materials for the preparation of the inner layer according to the ratio, and subject the raw materials for the preparation of the inner layer to high-speed mixing and low-speed mixing in sequence. Then, granulate the mixed raw materials to obtain granules. S20. The granules are fed into the inner extruder, and the raw materials for the preparation of the outer layer are fed into the outer extruder according to the ratio. The ACP double-layer pipe is extruded through the double-layer co-extrusion die.

[0042] In the preparation method of the ACP double-layer pipe, by sequentially subjecting the raw materials for the inner layer to high-speed and low-speed mixing before granulation, sufficient pre-dispersion of each component in the inner layer can be achieved, resulting in uniformly composed granules. Compared to directly feeding powder into the extruder, using granule feeding avoids the defects of uneven melt flow distribution, effectively suppresses fluctuations in the inner layer wall thickness of the pipe, ensures uniform overall wall thickness of the ACP double-layer pipe, avoids the reduction in ring stiffness and pressure resistance caused by local thinning of the pipe wall, and also improves the assembly accuracy of the pipe.

[0043] In addition, the uniformly plasticized granules can fully utilize the effect of AGR in reducing interfacial tension during extrusion, which significantly improves the gloss of the inner wall surface of the formed pipe and lowers the coefficient of friction, thereby reducing fluid transport resistance and the risk of dirt deposition.

[0044] In the inner layer raw material system provided by this invention, CPVC, PVC, and AGR all contain the same polyvinyl chloride main chain structure, and there are no significant differences in polarity or interfacial tension among them. Therefore, in step S10 of the preparation method, an excessively high mixing temperature is not required to ensure sufficient pre-dispersion of the inner layer components. This not only reduces production energy consumption but also shortens the material cooling time and improves production efficiency. Specifically, in step S10, after high-speed mixing until the raw material temperature reaches 85-95°C, the raw material is transferred to a low-speed mixer for further mixing until the raw material temperature drops to 55-60°C, at which point mixing is stopped. The granulation temperatures are set sequentially as follows: Zone 1: 160-165°C, Zone 2: 155-160°C, Zone 3: 155-160°C, Zone 4: 155-160°C, and Zone 5: 155-160°C.

[0045] To ensure interlayer fusion strength and prevent delamination and peeling of the inner and outer layers during long-term use of the ACP double-layer pipe, in a preferred embodiment, the extrusion temperatures of the inner layer extruder in step S20 are sequentially set as follows: Zone 1 150–160°C, Zone 2 145–155°C, Zone 3 145–155°C, and Zone 4 145–155°C; the extrusion temperatures of the outer layer extruder are sequentially set as follows: Zone 1 175–185°C, Zone 2 170–180°C, Zone 3 165–175°C, Zone 4 150–160°C, and Zone 5 155–165°C. In this embodiment, the inner layer extrusion temperature is significantly lower than that of the outer layer, which ensures that the viscosities of the inner and outer melts are similar when co-extruded and merged, thereby achieving sufficient interfacial molecular chain diffusion and entanglement, and ensuring interlayer fusion strength.

[0046] Furthermore, in step S20, the double-layer co-extrusion die is placed on the merging die. The extrusion temperature of the merging die is 155–165°C, which is relatively mild. This temperature is conducive to the stable merging of the inner and outer melts at similar viscosities during merging, promoting the full diffusion and entanglement of PVC / CPVC macromolecular chains at the interface, thereby ensuring interlayer fusion strength and preventing delamination. The extrusion temperatures of the double-layer co-extrusion die are set sequentially as follows: Zone 1 165–175°C, Zone 2 165–175°C, Zone 3 145–155°C, and Zone 4 190–200°C. The double-layer co-extrusion die maintains a temperature of 165-175°C in zones 1 and 2, which ensures that the combined double-layer melt maintains good fluidity in the initial stage of entering the die to uniformly fill the flow channel. Zone 3 is cooled to 145-155°C, which allows the surface of the melt to be moderately cooled to increase the strength of the preform and prevent the ACP double-layer pipe from sagging due to its own weight at the exit, resulting in uneven wall thickness. Zone 4 is heated to 190-200°C, which can reduce the elastic recovery of the melt at the die exit section, accurately control the outer diameter of the pipe, and improve the gloss of the inner wall surface, thereby comprehensively improving the dimensional accuracy and appearance quality of the ACP pipe.

[0047] The present invention will be further illustrated by the following examples and comparative examples.

[0048] Example 1 This embodiment provides an ACP double-layer pipe, including an outer layer and an inner layer; by weight, the raw materials for preparing the inner layer include: 22 parts CPVC, 22 parts AGR, 45 parts PVC, 3 parts first stabilizer (calcium-zinc stabilizer), 3 parts first filler (light calcium carbonate), and 0.3 parts first lubricant (polyethylene wax).

[0049] The raw materials for preparing the outer layer, by weight, include: 45 parts PVC, 22 parts CPVC, 3 parts second stabilizer (calcium-zinc stabilizer), 3 parts second filler (light calcium carbonate), 0.3 parts second lubricant (polyethylene wax), and 20 parts modifier.

[0050] The modifier is a mixture of AGR, MBS, ABS high-resin powder, ACR and a third filler; the third filler is ultrafine wollastonite powder; the weight ratio of AGR, MBS, ABS high-resin powder, ACR and the third filler is 6:0.5:2.5:0.5:0.5.

[0051] The ratio of the total weight of the raw materials used to prepare the inner layer to the total weight of the raw materials used to prepare the outer layer is 1.5:8.5.

[0052] This embodiment also provides a method for preparing ACP double-layer pipe, which includes the following steps: S10. Weigh the raw materials for the preparation of the inner layer according to the ratio, and subject the raw materials for the preparation of the inner layer to high-speed mixing and low-speed mixing in sequence. Then, granulate the mixed raw materials to obtain granules. S20. The granules are fed into the inner extruder, and the raw materials for the preparation of the outer layer are fed into the outer extruder according to the ratio. The ACP double-layer pipe is extruded through the double-layer co-extrusion die.

[0053] In step S10, after the raw material is heated to 90°C by high-speed mixing, it is transferred to a low-speed mixer for further mixing until the raw material temperature drops to 56°C, at which point mixing is stopped. The granulation temperatures are set sequentially as follows: Zone 1 165°C, Zone 2 160°C, Zone 3 160°C, Zone 4 160°C, and Zone 5 160°C.

[0054] In step S20, the extrusion temperatures of the inner extruder are set sequentially as follows: Zone 1 155℃, Zone 2 150℃, Zone 3 150℃, Zone 4 150℃; the extrusion temperatures of the outer extruder are set sequentially as follows: Zone 1 180℃, Zone 2 175℃, Zone 3 170℃, Zone 4 155℃, Zone 5 160℃.

[0055] In step S20, the double-layer co-extrusion die is placed on the confluence die, and the extrusion temperatures of the double-layer co-extrusion die are set sequentially as follows: Zone 1 170℃, Zone 2 170℃, Zone 3 150℃, Zone 4 195℃; the extrusion temperature of the confluence die is 160℃.

[0056] Example 2 This embodiment provides an ACP double-layer pipe, including an outer layer and an inner layer; by weight, the raw materials for preparing the inner layer include: 20 parts CPVC, 20 parts AGR, 40 parts PVC, 2 parts first stabilizer (calcium-zinc stabilizer), 1 part first filler (light calcium carbonate), and 0.2 parts first lubricant (polyethylene wax).

[0057] The raw materials for preparing the outer layer, by weight, include: 40 parts PVC, 20 parts CPVC, 2 parts second stabilizer (calcium-zinc stabilizer), 1 part second filler (light calcium carbonate), 0.2 parts second lubricant (polyethylene wax), and 10 parts modifier.

[0058] The modifier is a mixture of AGR, MBS, ABS high-resin powder, ACR and a third filler; the third filler is ultrafine wollastonite powder; the weight ratio of AGR, MBS, ABS high-resin powder, ACR and the third filler is 6:0.5:2.5:0.5:0.5.

[0059] The ratio of the total weight of the raw materials used to prepare the inner layer to the total weight of the raw materials used to prepare the outer layer is 2:8.

[0060] In step S10, after the raw material is heated to 85°C by high-speed mixing, the raw material is transferred to a low-speed mixer for mixing until the raw material temperature drops to 55°C, at which point mixing is stopped.

[0061] In step S20, the extrusion temperatures of the inner extruder are set sequentially as follows: Zone 1 150℃, Zone 2 145℃, Zone 3 145℃, Zone 4 145℃; the extrusion temperatures of the outer extruder are set sequentially as follows: Zone 1 175℃, Zone 2 170℃, Zone 3 165℃, Zone 4 150℃, Zone 5 155℃. The granulation temperatures are set sequentially as follows: Zone 1 165℃, Zone 2 160℃, Zone 3 160℃, Zone 4 160℃, Zone 5 160℃.

[0062] In step S20, the double-layer co-extrusion die is placed on the confluence die, and the extrusion temperatures of the double-layer co-extrusion die are set sequentially as follows: Zone 1 165℃, Zone 2 165℃, Zone 3 145℃, Zone 4 190℃; the extrusion temperature of the confluence die is 155℃.

[0063] Example 3 This embodiment provides an ACP double-layer pipe, including an outer layer and an inner layer; by weight, the raw materials for preparing the inner layer include: 25 parts CPVC, 25 parts AGR, 50 parts PVC, 5 parts first stabilizer (calcium-zinc stabilizer), 5 parts first filler (light calcium carbonate), and 0.5 parts first lubricant (polyethylene wax).

[0064] The raw materials for preparing the outer layer, by weight, include: 50 parts PVC, 25 parts CPVC, 5 parts second stabilizer (calcium-zinc stabilizer), 5 parts second filler (light calcium carbonate), 0.5 parts second lubricant (polyethylene wax), and 25 parts modifier.

[0065] The modifier is a mixture of AGR, MBS, ABS high-resin powder, ACR and a third filler; the third filler is ultrafine wollastonite powder; the weight ratio of AGR, MBS, ABS high-resin powder, ACR and the third filler is 6:0.5:2.5:0.5:0.5.

[0066] The ratio of the total weight of the raw materials used to prepare the inner layer to the total weight of the raw materials used to prepare the outer layer is 1:9.

[0067] In step S10, after the raw material is heated to 95°C by high-speed mixing, it is transferred to a low-speed mixer for further mixing until the raw material temperature drops to 60°C, at which point mixing is stopped. The granulation temperatures are set sequentially as follows: Zone 1 165°C, Zone 2 160°C, Zone 3 160°C, Zone 4 160°C, and Zone 5 160°C.

[0068] In step S20, the extrusion temperatures of the inner extruder are set sequentially as follows: Zone 1 160℃, Zone 2 155℃, Zone 3 155℃, Zone 4 155℃; the extrusion temperatures of the outer extruder are set sequentially as follows: Zone 1 185℃, Zone 2 180℃, Zone 3 175℃, Zone 4 160℃, Zone 5 165℃.

[0069] In step S20, the double-layer co-extrusion die is placed on the confluence die, and the extrusion temperatures of the double-layer co-extrusion die are set sequentially as follows: Zone 1 175℃, Zone 2 175℃, Zone 3 155℃, Zone 4 200℃; the extrusion temperature of the confluence die is 165℃.

[0070] Comparative Example 1 This comparative example provides an ACP double-layer pipe, including an outer layer and an inner layer. The difference between this ACP double-layer pipe and Example 1 is that the only difference is the raw materials used to prepare the inner layer. Specifically, by weight, the raw materials used to prepare the inner layer include: 22 parts of CPVC, 67 parts of PVC, 3 parts of the first stabilizer (calcium-zinc stabilizer), 3 parts of the first filler (light calcium carbonate), and 0.3 parts of the first lubricant (polyethylene wax).

[0071] Comparative Example 2 This comparative example provides an ACP double-layer pipe, including an outer layer and an inner layer; the raw materials for preparing the outer layer and the inner layer are the same as those provided in Example 1.

[0072] This comparative example also provides a method for preparing ACP double-layer pipe, which is used to prepare the ACP double-layer pipe provided in this comparative example. The difference between this preparation method and the preparation method provided in Example 1 is that the raw materials for preparing the inner layer do not undergo high-speed and low-speed mixing and granulation processes, but are directly fed into the inner layer extruder.

[0073] Comparative Example 3 This comparative example provides an ACP double-layer pipe, including an outer layer and an inner layer; the difference between this ACP double-layer pipe and Example 1 is that the amount of the first lubricant in the preparation raw materials of the inner layer is increased from 0.3 parts to 1 part.

[0074] Comparative Example 4 This comparative example provides an ACP double-layer pipe, comprising an outer layer and an inner layer. The difference between this ACP double-layer pipe and Example 1 is that the amount of the second lubricant in the preparation materials of the outer layer is increased from 0.3 parts to 1 part. Note: The purpose of this comparative example is primarily to investigate the effect of excessive outer layer lubricant usage preventing welding assembly.

[0075] Comparative Example 5 This comparative example provides an ACP double-layer pipe, including an outer layer and an inner layer; the difference between this ACP double-layer pipe and Example 1 is only that in the preparation raw materials of the outer layer, the weight ratio of AGR, MBS, ABS high-rubber powder, ACR and the third filler is 1:0.5:2.5:0.5:0.5.

[0076] Comparative Example 6 This comparative example provides an ACP double-layer pipe, comprising an outer layer and an inner layer. The difference between this ACP double-layer pipe and Example 1 is only that the amount of modifier used in the preparation of the outer layer is reduced to 19 parts, and ultrafine wollastonite filler is not used in the modifier. The weight ratio of AGR, MBS, ABS high-rubber powder, and ACR is 6:0.5:2.5:0.5.

[0077] Comparative Example 7 This comparative example provides an ACP double-layer pipe, including an outer layer and an inner layer; the only difference between this ACP double-layer pipe and Example 1 is that the ratio of the total weight of the raw materials used to prepare the inner layer to the total weight of the raw materials used to prepare the outer layer is 0.5:9.5.

[0078] Comparative Example 8 This comparative example provides an ACP double-layer pipe, including an outer layer and an inner layer; the only difference between this ACP double-layer pipe and Example 1 is that the ratio of the total weight of the raw materials used to prepare the inner layer to the total weight of the raw materials used to prepare the outer layer is 3:7.

[0079] It should be noted that Comparative Example 1 and Comparative Examples 3 to 8 also provide a method for preparing the corresponding ACP double-layer pipe, and the preparation method is the same as the preparation method provided in Example 1.

[0080] The performance of the ACP double-layer pipes provided in the above embodiments and comparative examples was tested using the following methods: (1) Inner layer thickness and outer layer thickness test In accordance with GB / T 8806-2008 "Determination of Dimensions of Plastic Components in Plastic Piping Systems", a wall thickness micrometer was used to measure the pipe cross-section. The specific procedure was as follows: the pipe was cut perpendicular to its axis to obtain a cross-sectional sample; on the pipe cross-section, the thickness of the inner and outer layers was measured using an optical microscope or a wall thickness micrometer. To assess the uniformity of the pipe wall thickness distribution, at least eight measurement points were selected at equal intervals along the circumference of the pipe. The inner and outer layer thicknesses at each point were measured, and the maximum deviation and average value of each measurement were calculated. The ratio of the maximum deviation to the average value was used as the evaluation index for the pipe wall thickness non-uniformity. When the pipe wall thickness non-uniformity exceeded 10%, it was determined that the pipe wall thickness distribution was non-uniform.

[0081] (2) The static friction coefficient of the inner wall of the pipe shall be tested in accordance with the provisions of JT / T 496-2018 "High-density polyethylene silicon core plastic pipe for underground communication pipelines of highway".

[0082] (3) In accordance with the provisions of GB / T 14153-1993 "General Rules for Drop Impact Test of Rigid Plastics", the overall impact strength of the pipe is tested by a drop impact tester at a height of 5m.

[0083] The test results are shown in Tables 1 and 2 below. Table 1:

[0084] Table 2:

[0085] Note: In Tables 1 and 2 above, Comparative Example 9 is a control example of increasing the thickness of the ACP double-layer tube wall (by controlling the thickness by controlling the amount of inner and outer layer raw materials). In Comparative Example 1, the inner and outer layer raw materials are the same as those provided in Example 1, and the preparation method is the same as that provided in Example 1.

[0086] As can be seen from the test results in Tables 1 and 2, the ACP double-layer pipes prepared in Examples 1 to 3 of the present invention exhibit excellent comprehensive performance. Examples 2 and 3 are at the upper and lower limits of the protection scope of this patent, and their performance is still better than that of the comparative examples. This indicates that the ACP double-layer pipes provided by the present invention have low inner wall surface roughness and high gloss, and the overall wall thickness of the pipe is uniform. Without significantly increasing the wall thickness of the pipe, the mechanical properties such as impact resistance are excellent.

[0087] Comparing Comparative Example 1 with Example 1, it was found that the static friction coefficient of the inner wall of the ACP double-layer pipe provided by Comparative Example 1 increased, and the pipe was not impact-resistant. At the same time, the pipe wall thickness was uneven. This is because the inner layer of the ACP double-layer pipe provided by Comparative Example 1 did not use AGR as the raw material, thus missing the toughening effect of AGR on the CPVC / PVC system and the synergistic effect of reducing melt viscosity. This resulted in a decrease in the melt flowability of the inner layer and a worse uniformity of the pipe wall thickness. At the same time, the friction coefficient of the inner wall increased due to the lack of the smoothing effect of the acrylate polar groups, and the overall impact resistance decreased significantly.

[0088] Comparing Comparative Example 2 with Example 1, it was found that the static friction coefficient of the inner wall of the ACP double-layer pipe provided by Comparative Example 2 increased, and the pipe was not resistant to impact. At the same time, the pipe wall thickness was uneven. This is because the inner layer raw material of Comparative Example 2 was not mixed and granulated at high / low speed, but was directly fed into the extruder as powder. The components were not pre-dispersed evenly, which led to an imbalance in melt flow distribution, uneven pipe wall thickness distribution, and an increase in inner wall surface defects, which increased the friction coefficient and decreased impact resistance.

[0089] Comparing Comparative Example 3 with Example 1, it was found that the static friction coefficient of the inner wall of the ACP double-layer pipe provided by Comparative Example 3 was slightly increased, and the pipe was not impact-resistant. This was due to the increased amount of inner layer lubricant in the raw materials used to prepare the inner layer of Comparative Example 3. Comparing Comparative Example 4 with Example 1, it was found that the ACP double-layer pipe provided by Comparative Example 4 was not impact-resistant. This was due to the increased amount of lubricant in the raw materials used to prepare the outer layer of Comparative Example 4.

[0090] Comparing Comparative Example 5 with Example 1, it was found that the ACP double-layer pipe provided by Comparative Example 5 was not impact resistant. This was because the amount of AGR in the outer layer modifier of Comparative Example 5 was reduced from 6 parts to 1 part, resulting in insufficient number of elastic micro-regions, which significantly weakened the impact toughening effect of the outer layer and reduced the overall drop hammer impact strength. At the same time, the increased viscosity of the outer layer melt caused the pipe wall thickness uniformity to deteriorate.

[0091] Comparing Comparative Example 6 with Example 1, it was found that the ACP double-layer pipe provided by Comparative Example 6 was not impact resistant. This was because ultrafine wollastonite filler was not used in the outer layer modifier of Comparative Example 6.

[0092] Comparing Comparative Example 7 with Example 1, it was found that the inner layer of the ACP double-layer pipe provided by Comparative Example 7 was thinner and the outer layer was thicker, and the pipe was not impact resistant. This was because the proportion of raw materials used in the preparation of the inner layer was reduced, and the thinner inner layer would lead to a decrease in the overall impact resistance of the pipe.

[0093] Comparing Comparative Example 8 with Example 1, it was found that the inner layer of the ACP double-layer pipe provided by Comparative Example 8 was thicker and the outer layer was thinner. This was because the proportion of raw materials used in the preparation of the outer layer was reduced. Furthermore, the thinner outer layer would lead to increased brittleness of the outer layer, resulting in a decrease in the impact resistance of the pipe.

[0094] In addition, the pipes obtained in Example 1, Comparative Example 3, and Comparative Example 4 were butt-welded using high-frequency welding. After welding, strength tests were performed on the welded joint and the pipe body (non-welded parts), respectively. The specific test methods are as follows: Referring to GB / T 8804.2-2003 "Determination of Tensile Properties of Thermoplastic Pipes - Part 2: Rigid Polyvinyl Chloride (PVC-U) Pipes", dumbbell-shaped tensile specimens were cut from both the welded joint and the pipe body. Tensile tests were performed on a universal testing machine at a specified speed, and the tensile strength and fracture location of the specimens were recorded. The strength retention rate of the welded joint was evaluated by comparing the tensile strength of the welded joint and the pipe body. The test results are shown in Table 3 below.

[0095] As shown in Table 3:

[0096] As can be seen from the test results in Table 3 above, the strength retention rate of the ACP double-layer pipe welded joint prepared in Example 1 of the present invention is much higher than that of Comparative Example 3 and Comparative Example 4. This indicates that by reducing the amount of lubricant in the raw materials, the amount of free lubricant precipitated inside the pipe can be significantly reduced, the isolation layer at the welding interface can be eliminated, and the mechanical strength and weld bonding reliability of the pipe welded joint can be significantly improved.

[0097] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. An ACP double-layer pipe, comprising an outer layer and an inner layer; characterized in that, The raw materials for preparing the inner layer, by weight, include: 20-25 parts of CPVC, 20-25 parts of AGR, 40-50 parts of PVC, 2-5 parts of the first stabilizer, 1-5 parts of the first filler, and 0.2-0.5 parts of the first lubricant.

2. The ACP double-layer pipe according to claim 1, characterized in that, The raw materials for preparing the outer layer, by weight, include: 40-50 parts of PVC, 20-25 parts of CPVC, 2-5 parts of the second stabilizer, 1-5 parts of the second filler, and 0.2-0.5 parts of the second lubricant.

3. The ACP double-layer pipe according to claim 2, characterized in that, The raw materials for preparing the outer layer, by weight, also include: 10-25 parts of modifier; the modifier is a mixture of AGR, MBS, ABS high-adhesion powder, ACR and a third filler.

4. The ACP double-layer pipe according to claim 3, characterized in that, The weight ratio of AGR, MBS, ABS high-rubber powder, ACR and the third filler is (5-7):(0.4-0.6):(2.2-2.8):(0.4-0.6):(0.4-0.6).

5. The ACP double-layer pipe according to claim 3, characterized in that, The third filler is at least one of ultrafine wollastonite powder and light calcium carbonate.

6. The ACP double-layer pipe according to claim 1 or 2, characterized in that, The ratio of the total weight of the raw materials for the inner layer to the total weight of the raw materials for the outer layer is (1-2):(8-9).

7. A method for preparing an ACP double-layer pipe as described in any one of claims 1-6, characterized in that, Includes the following steps: S10. Weigh the raw materials for the preparation of the inner layer according to the ratio, and subject the raw materials for the preparation of the inner layer to high-speed mixing and low-speed mixing in sequence. Then, granulate the mixed raw materials to obtain granules. S20. The granules are fed into the inner extruder, and the raw materials for the preparation of the outer layer are fed into the outer extruder according to the ratio. The ACP double-layer pipe is extruded through the double-layer co-extrusion die.

8. The method for preparing ACP double-layer pipe according to claim 7, characterized in that, In step S10, after the raw material is heated to 85-95°C by high-speed mixing, the raw material is transferred to a low-speed mixer for mixing until the raw material temperature drops to 55-60°C, at which point mixing is stopped.

9. The method for preparing ACP double-layer pipe according to claim 7, characterized in that, In step S20, the extrusion temperatures of the inner extruder are set sequentially as follows: Zone 1 150-160℃, Zone 2 145-155℃, Zone 3 145-155℃, and Zone 4 145-155℃; the extrusion temperatures of the outer extruder are set sequentially as follows: Zone 1 175-185℃, Zone 2 170-180℃, Zone 3 165-175℃, Zone 4 150-160℃, and Zone 5 155-165℃.

10. The method for preparing ACP double-layer tubing according to claim 7, characterized in that, In step S20, the double-layer co-extrusion die is placed on the confluence die, and the extrusion temperatures of the double-layer co-extrusion die are set sequentially as follows: Zone 1 165~175℃, Zone 2 165~175℃, Zone 3 145~155℃, Zone 4 190~200℃; the extrusion temperature of the confluence die is 155~165℃.

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