PE composite pipe for underground coal mine and preparation method of PE composite pipe

Abstract

The invention discloses a PE composite pipe for an underground coal mine and a preparation method of the PE composite pipe. On one hand, the PE composite pipe for the underground coal mine sequentially comprises a lining layer, a reinforcing layer and an outer protection layer from inside to outside, and the raw material of the lining layer is composed of PE100-RC resin and conductive carbon black according to the mass ratio of 100: (6-12); the main raw materials of the reinforcing layer and the outer protective layer are PE100-RC resin, chopped carbon fibers are added, and specific flame-retardant components and toughening components are respectively added; the length of the short carbon fiber is 3-6mm, and the surface of the short carbon fiber is subjected to oxidation or sizing treatment. On the other hand, the invention further provides a preparation method of the PE composite pipe for the underground coal mine. The composite material can meet multiple performance requirements of high strength, static resistance, flame retardance, corrosion resistance and the like at the same time, and the mechanical performance, the safety performance and the durability are integrally improved.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and in particular to a PE composite pipe for underground coal mines and its preparation method. Background Technology

[0002] The underground environment in coal mines is complex and harsh, placing extremely stringent performance requirements on pipelines (such as drainage pipes, compressed air pipes, and grouting pipes). These pipelines not only need to withstand certain internal and external pressures, but also must simultaneously meet the antistatic requirements (surface resistivity ≤ 1×10⁻⁶) stipulated in the "Coal Mine Safety Regulations". 8 Mandatory safety standards for gas and coal dust retardancy (passing the alcohol torch test) are in place to prevent gas and coal dust explosions caused by static electricity buildup or open flames. Furthermore, the underground environment is humid and rich in corrosive media, requiring pipelines to have excellent corrosion resistance and a long service life.

[0003] Currently, commonly used pipelines in coal mines mainly include metal pipes (such as steel pipes) and plastic pipes. While metal pipes are strong, they are heavy, prone to corrosion, inconvenient to install, and prone to leaks at joints due to electrochemical corrosion. Ordinary polyethylene (PE) pipes, although corrosion-resistant and lightweight, have limited strength and modulus, and being an insulator, lack antistatic and flame-retardant properties. Existing modification methods, such as adding conductive carbon black to achieve antistatic properties or adding large amounts of flame retardants, often lead to a significant decrease in the mechanical properties of the matrix material (especially toughness and long-term hydrostatic strength), and these properties are mutually restrictive, making it difficult to achieve a balance.

[0004] In recent years, some new types of pipes have emerged on the market, such as glass fiber reinforced plastic pipes, metal wire mesh reinforced plastic pipes, and carbon fiber reinforced plastic pipes. Although these pipes have significantly improved strength, they cannot simultaneously meet the requirements of high strength, high antistatic properties, high flame retardancy, corrosion resistance, and long service life. Therefore, developing a special composite pipe for underground coal mines that can simultaneously and synergistically meet the requirements of high strength, high antistatic properties, high flame retardancy, corrosion resistance, and long service life has become an urgent need to ensure safe production in coal mines. Summary of the Invention

[0005] To address the problem mentioned in the background art that underground coal mine pipelines need to simultaneously meet multiple performance requirements such as high strength, antistatic properties, flame retardancy, and corrosion resistance, which are difficult to achieve simultaneously with existing technologies, this application provides a PE composite pipe for underground coal mines and its preparation method. This composite pipe adopts a unique three-layer co-extrusion structure design and combines a functional composite material with short-cut short fibers as the core reinforcement and conductive phase, and modified magnesium hydroxide / coated ammonium polyphosphate type II as the synergistic flame retardant system, thereby achieving an integrated improvement in mechanical properties, safety performance, and durability.

[0006] This application provides a PE composite pipe for underground coal mines, which includes an inner lining layer, a reinforcing layer and an outer protective layer from the inside to the outside. The raw material of the inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:6~12.

[0007] The reinforcing layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 18-24 parts of chopped carbon fiber, 20-30 parts of modified magnesium hydroxide, 8-14 parts of coated ammonium polyphosphate type II, 10-16 parts of nano-kaolin, 6-10 parts of maleic anhydride grafted polyolefin elastomer, 5-10 parts of ethylene-vinyl acetate copolymer with VA content of 28%, 1-2 parts of lubricant, and 0.3-0.5 parts of composite antioxidant;

[0008] The outer protective layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 8-15 parts of chopped carbon fiber, 30-45 parts of modified magnesium hydroxide, 10-15 parts of coated ammonium polyphosphate type II, 6-10 parts of maleic anhydride grafted polyolefin elastomer, 5-10 parts of ethylene-vinyl acetate copolymer with 28% VA content, 1-2 parts of lubricant, and 0.3-0.5 parts of composite antioxidant;

[0009] The chopped carbon fibers are 3-6 mm in length and have been oxidized or sized.

[0010] Optionally, the reinforcing layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 20-22 parts of chopped carbon fiber, 24-26 parts of modified magnesium hydroxide, 10-12 parts of coated ammonium polyphosphate type II, 12-14 parts of nano-kaolin, 7-8 parts of maleic anhydride grafted polyolefin elastomer, 6-9 parts of ethylene-vinyl acetate copolymer with VA content of 28%, 1.5-2 parts of lubricant, and 0.4-0.5 parts of composite antioxidant;

[0011] The outer protective layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 11-15 parts chopped carbon fiber, 35-40 parts modified magnesium hydroxide, 12-14 parts coated ammonium polyphosphate type II, 7-8 parts maleic anhydride grafted polyolefin elastomer, 6-9 parts ethylene-vinyl acetate copolymer with 28% VA content, 1.5-2 parts lubricant, and 0.4-0.5 parts composite antioxidant.

[0012] Optionally, the thickness ratio of the inner liner, the reinforcing layer, and the outer protective layer is 1:3:1.

[0013] Optionally, the raw materials for the reinforcing layer and the outer protective layer may also include silicone powder, and the amount of silicone powder added is 4 to 6 parts.

[0014] Optionally, the lubricant consists of polyethylene wax and zinc stearate in a mass ratio of 1.5:1.

[0015] Optionally, the composite antioxidant is selected from antioxidant B225.

[0016] Optionally, the raw material of the outer protective layer may also include rutile titanium dioxide, wherein the amount of rutile titanium dioxide added is 1.8 to 2.5 parts.

[0017] On the other hand, this application also provides a method for preparing the above-mentioned PE composite pipe for underground coal mines, including the following steps:

[0018] S1. According to the formulations of the reinforcing layer and the outer protective layer, the formulated amounts of PE100-RC resin, maleic anhydride grafted polyolefin elastomer, ethylene-vinyl acetate copolymer, lubricant and composite antioxidant are mixed evenly. The formulated amounts of modified magnesium hydroxide and coated ammonium polyphosphate type II are slowly added and mixed evenly to obtain the premix of the reinforcing layer and the outer protective layer.

[0019] S2. The premix of the reinforcing layer and the outer protective layer from step S1 is fed into the twin-screw extruder through the main feed port, and the remaining raw materials according to the formula of the reinforcing layer and the outer protective layer are added through the side feed port. After melting and dispersing, extrusion, cooling and pelletizing, the reinforcing layer masterbatch and the outer protective layer masterbatch are obtained respectively. The inner liner material is mixed and added into the twin-screw extruder. After melting and dispersing, extrusion, cooling and pelletizing, the inner liner masterbatch is obtained.

[0020] S3. The inner lining masterbatch, the reinforcing layer masterbatch, and the outer protective layer masterbatch are co-extruded to obtain a PE composite pipe with a three-layer structure.

[0021] Optionally, in step S2, the twin-screw extruder is a co-rotating parallel twin-screw extruder with a length-to-diameter ratio (L / D) ≥ 40, and the extrusion granulation process parameters are as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 175℃, Zone 4 180℃, Zone 5 180℃, Zone 6 175℃, Die head 170℃, and screw speed 250~300 rpm.

[0022] Optionally, in step S3, the temperatures of the six temperature zones from the feed end to the connector of the inner liner extruder are 150~160℃, 165~175℃, 175~185℃, 180~190℃, 185~195℃, and 180~185℃ respectively. The temperatures of the six temperature zones from the feed end to the connector of the reinforcing layer extruder and the outer protective layer extruder are 140~150℃, 155~165℃, 165~175℃, 170~180℃, 175~185℃, and 170~175℃ respectively. The die temperature of the three-layer co-extrusion die head is 175~180℃.

[0023] In summary, the present invention has at least one of the following beneficial technical effects:

[0024] 1. This application utilizes surface-treated chopped carbon fibers as a reinforcing phase, which not only significantly improves the ring stiffness, tensile strength, and creep resistance of the pipe, but also leverages the excellent conductivity of carbon fibers to construct a stable and permanent three-dimensional conductive network, resulting in a surface resistivity of the pipe consistently below 1×10⁻⁶. 5 Ω fundamentally solves the antistatic problem; carbon fiber and halogen-free flame retardant system (modified magnesium hydroxide and coated ammonium polyphosphate) can produce a "ceramic synergistic flame retardant effect" under flame, giving the pipe excellent flame retardant performance and meeting the core safety requirements of underground coal mines in one go.

[0025] 2. In the formulation of this application, the PE100-RC resin and maleic anhydride-grafted polyolefin elastomer of the reinforcing layer can form strong chemical and physical bonds with the surface-treated carbon fiber and flame-retardant filler, which greatly improves the interfacial compatibility of the multiphase composite system. This not only significantly improves the interlayer peel strength and avoids the risk of delamination, but also effectively transfers stress and delays crack initiation and propagation, thereby ensuring the service life and durability of the pipe under long-term hydrostatic load. In addition, the maleic anhydride-grafted polyolefin elastomer can not only improve the system compatibility, but also, in synergy with the ethylene-vinyl acetate copolymer with 28% VA content, effectively improve the toughness and crack resistance of the pipe. The introduction of nano-kaolin not only enhances the flame-retardant effect in conjunction with the flame-retardant system, but also acts as a reinforcing filler to effectively improve the strength of the pipe.

[0026] 3. This application adopts a three-layer co-extrusion structure consisting of an inner liner, a reinforcing layer, and an outer protective layer. The inner liner uses PE100-RC resin and conductive carbon black to ensure a smooth inner wall of the flow channel, low resistance, and corrosion resistance, while also possessing antistatic properties. The reinforcing layer bears the main mechanical and functional components, ensuring the strength of the tube body. The outer protective layer focuses on resisting environmental erosion and ensuring that surface performance meets standards. This design achieves a functional gradient distribution of materials, optimizing material costs while ensuring overall performance. The three-layer co-extrusion structure of this application results in a strong interface bond and high long-term reliability. Through optimized design of structure and composition, a synergistic improvement in mechanical properties, safety, and durability is achieved.

[0027] 4. The preparation method of this application adopts a two-step process of "twin-screw granulation + three-layer co-extrusion". First, functional masterbatch is prepared by twin-screw side feeding, which realizes uniform dispersion and effective protection of carbon fibers. Then, three-layer co-extrusion molding is used, which is conducive to controlling the thickness of each layer and the bonding quality. This process route is mature and stable, easy to realize industrial production, and ensures the consistency and reliability of product performance. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments.

[0029] Unless otherwise stated, the raw materials used in this application are conventional materials in this technical field and are all commercially available. Unless otherwise specified, the test methods and detection methods in the following embodiments are conventional methods, and the equipment and instruments used in the tests are all commercially available. Parts not described in detail in this specification belong to the prior art.

[0030] This application designs a PE composite pipe for underground coal mines, which includes an inner lining layer, a reinforcing layer and an outer protective layer from the inside to the outside. The raw material of the inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:6~12.

[0031] The reinforcing layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 18-24 parts of chopped carbon fiber, 20-30 parts of modified magnesium hydroxide, 8-14 parts of coated ammonium polyphosphate type II, 10-16 parts of nano-kaolin, 6-10 parts of maleic anhydride grafted polyolefin elastomer, 5-10 parts of ethylene-vinyl acetate copolymer with VA content of 28%, 1-2 parts of polyethylene wax, and 0.3-0.5 parts of composite antioxidant;

[0032] The outer protective layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 8-15 parts of chopped carbon fiber, 30-45 parts of modified magnesium hydroxide, 10-15 parts of coated ammonium polyphosphate type II, 6-10 parts of maleic anhydride grafted polyolefin elastomer, 5-10 parts of ethylene-vinyl acetate copolymer with 28% VA content, 1-2 parts of lubricant, and 0.3-0.5 parts of composite antioxidant;

[0033] The chopped carbon fibers are 3-6 mm in length and have been oxidized or sized.

[0034] Preferably, the composite antioxidant in this application is antioxidant B225.

[0035] Preferably, the raw materials for the reinforcing layer and the outer protective layer also include silicone powder, and the amount of silicone powder added is 4 to 6 parts.

[0036] Preferably, the raw material of the outer protective layer also includes rutile titanium dioxide, and the amount of rutile titanium dioxide added is 1.8 to 2.5 parts.

[0037] This application also protects the preparation method of the above-mentioned PE composite pipe for underground coal mines.

[0038] The method for preparing the above-mentioned PE composite pipe for underground coal mines according to this application includes the following steps:

[0039] S1. According to the formulations of the reinforcing layer and the outer protective layer, the formulated amounts of PE100-RC resin, maleic anhydride grafted polyolefin elastomer, ethylene-vinyl acetate copolymer, lubricant and composite antioxidant are mixed evenly. The formulated amounts of modified magnesium hydroxide and coated ammonium polyphosphate type II are slowly added and mixed evenly to obtain the premix of the reinforcing layer and the outer protective layer.

[0040] S2. The premix of the reinforcing layer and the outer protective layer from step S1 is fed into the twin-screw extruder through the main feed port, and the remaining raw materials according to the formula of the reinforcing layer and the outer protective layer are added through the side feed port. After melting and dispersing, extrusion, cooling and pelletizing, the reinforcing layer masterbatch and the outer protective layer masterbatch are obtained respectively. The inner liner material is mixed and added into the twin-screw extruder. After melting and dispersing, extrusion, cooling and pelletizing, the inner liner masterbatch is obtained.

[0041] S3. The inner lining masterbatch, the reinforcing layer masterbatch, and the outer protective layer masterbatch are co-extruded to obtain a PE composite pipe with a three-layer structure.

[0042] In terms of materials, this application creatively selects short-cut carbon fiber as a multifunctional reinforcement. Its high modulus and high strength directly improve the mechanical properties of the pipe. Its intrinsic conductivity provides the simplest and most efficient path for constructing an antistatic network, avoiding the damage to the matrix properties caused by adding conductive carbon black. Simultaneously, to meet the flame retardant requirements of coal mines, a halogen-free synergistic flame retardant system is constructed using modified magnesium hydroxide (MH) and coated ammonium polyphosphate (APP). During combustion, APP catalyzes the formation of char, while MH decomposes endothermically and generates active MgO. Both react further with the carbon fiber and its pyrolytic carbon layer, forming a robust and dense ceramic-like protective carbon layer on the material surface. This achieves highly efficient "gas-phase-condensed-ceramization" multi-mode synergistic flame retardancy, with low smoke emission and non-toxicity.

[0043] In terms of structural design, a three-layer co-extrusion technology is used to construct the functionally graded composite pipe wall. The inner lining layer uses PE100-RC and conductive carbon black to ensure the smoothness, wear resistance, and corrosion resistance of the inner wall of the transported medium, while also possessing antistatic properties. The reinforcing layer is the main load-bearing structure of the pipe wall, rich in carbon fiber and flame-retardant system, giving the pipe the required ring stiffness, burst strength, and fire safety.

[0044] The outer protective layer has a similar composition to the reinforcing layer, but focuses more on resistance to environmental aging (titanium dioxide can be added) and ensuring that the antistatic and flame-retardant properties of the outer surface directly meet the standards. The three layers are metallurgically bonded through melt co-extrusion, resulting in a strong interface.

[0045] In interface engineering, a strong "bridge" is built between the polar carbon fiber, flame-retardant filler and non-polar PE matrix by surface treatment of carbon fiber (oxidation or special sizing) and the addition of maleic anhydride grafted polyolefin elastomer (POE-g-MAH) compatibilizer in the matrix. This is the key to achieving high strength, high peel strength and long-term hydraulic resistance.

[0046] The preparation method of this application closely follows the above concept, adopts the "masterbatch method" to ensure the precise dispersion of each component, protects the length of carbon fiber through side feeding, and finally forms it through a three-layer co-extrusion process, ensuring the perfect presentation of performance from material to product.

[0047] The following are specific embodiments of this application.

[0048] All major raw materials used in the embodiments of this application are commercially available. Specifically, the crack-resistant polyethylene PE100-RC resin was purchased from Sinopec; the conductive carbon black was purchased from Wuhan Jiyesheng Chemical Co., Ltd.; the 6mm short-cut carbon fiber (monofilament diameter 7μm) with surface sizing treatment for polyethylene compatibility was custom-made and purchased from Toray New Materials (Guangdong) Co., Ltd.; the modified magnesium hydroxide was purchased from Qinghe County Ruijiang Metal Materials Co., Ltd., model SS-MH6PG, D50 particle size 1.0~2.0μm, hexagonal flake morphology; and the coated ammonium polyphosphate type II was purchased from Shanghai Huanyang Chemical Technology Co., Ltd., model Clariant Exolit. AP462, phosphorus content 29.0~31.0%, average particle size (D50) 20μm; maleic anhydride grafted polyolefin elastomer, POE-g-MAH, model Dow GR216, grafting rate 0.5~1.0%, purchased from Shanghai Tiansu Trading Co., Ltd.; ethylene-vinyl acetate copolymer EVA28-150, purchased from Dongguan Yili Plastics Co., Ltd.; lubricant, polyethylene wax, purchased from Wuhan Jiyesheng Chemical Co., Ltd., item number A00075; lubricant Zinc stearate was purchased from Shandong Qiangsen Chemical Co., Ltd.; composite antioxidant, BASF Irganox B225 (50% antioxidant 1010 content, 50% antioxidant 168 content), was purchased from Nanjing Kexulai Chemical Co., Ltd.; rutile titanium dioxide, titanium dioxide R-215, was purchased from Fuwangda Titanium Industry (Shanghai) Co., Ltd.; nano kaolin, particle size 10~100nm, was purchased from Qingdao Taiyang Sheng Chemical Co., Ltd.; silicone powder was purchased from Shanghai Jinghong Chemical Technology Co., Ltd.

[0049] The embodiments and comparative examples of this application have the following tube dimensions: outer diameter 450 mm, wall thickness 20 mm.

[0050] Example 1

[0051] The PE composite pipe used in coal mines in this embodiment includes, from the inside out, an inner lining layer, a reinforcing layer, and an outer protective layer. The outer protective layer is 6mm thick, the reinforcing layer is 10mm thick, and the inner lining layer is 4mm thick.

[0052] The inner lining is made of PE100-RC resin and conductive carbon black in a mass ratio of 100:6.

[0053] The reinforcing layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 18 parts chopped carbon fiber, 20 parts modified magnesium hydroxide, 8 parts coated ammonium polyphosphate type II, 10 parts nano kaolin, 6 parts maleic anhydride grafted polyolefin elastomer, 5 parts ethylene-vinyl acetate copolymer with VA content of 28%, 1 part polyethylene wax, and 0.3 parts composite antioxidant.

[0054] The outer protective layer comprises the following raw material components, in parts by weight: 100 parts PE100-RC resin, 8 parts chopped carbon fiber, 30 parts modified magnesium hydroxide, 10 parts coated ammonium polyphosphate type II, 6 parts maleic anhydride grafted polyolefin elastomer, 5 parts ethylene-vinyl acetate copolymer with 28% VA content, 1 part polyethylene wax, and 0.3 parts composite antioxidant.

[0055] The preparation of the PE composite pipe for underground coal mines in this embodiment includes the following steps:

[0056] S1. According to the formulations of the reinforcing layer and the outer protective layer, the formulated amounts of PE100-RC resin, maleic anhydride grafted polyolefin elastomer, ethylene-vinyl acetate copolymer, lubricant and composite antioxidant are mixed evenly. The formulated amounts of modified magnesium hydroxide and coated ammonium polyphosphate type II are slowly added and mixed evenly to obtain the premix of the reinforcing layer and the outer protective layer.

[0057] S2. The premixes of the reinforcing layer and the outer protective layer from step S1 are fed into a co-rotating parallel twin-screw extruder with a length-to-diameter ratio (L / D) of 40 through the main feed port. The remaining raw materials according to the formulas of the reinforcing layer and the outer protective layer are added through the side feed port. After melting, dispersing, extrusion, cooling, and pelletizing, the reinforcing layer masterbatch and the outer protective layer masterbatch are obtained respectively. The inner liner material is mixed and added into the twin-screw extruder. After melting, dispersing, extrusion, cooling, and pelletizing, the inner liner masterbatch is obtained. The extrusion granulation process parameters are as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 175℃, Zone 4 180℃, Zone 5 180℃, Zone 6 175℃, Die head 170℃, and screw speed 280 rpm.

[0058] S3. The inner liner masterbatch, reinforcing layer masterbatch, and outer protective layer masterbatch are co-extruded to obtain a PE composite pipe with a three-layer structure. The temperatures of the six temperature zones from the feed end to the connector of the inner liner extruder are 150℃, 165℃, 175℃, 180℃, 185℃, and 180℃ respectively. The temperatures of the six temperature zones from the feed end to the connector of the reinforcing layer extruder and the outer protective layer extruder are 140℃, 155℃, 165℃, 170℃, 175℃, and 170℃ respectively. The die temperature of the three-layer co-extrusion die head is 175℃.

[0059] Example 2

[0060] The difference between this embodiment and Embodiment 1 is that, in step S3 of the preparation process, the temperatures of the six temperature zones from the feed end to the connector of the inner liner extruder are 160°C, 175°C, 185°C, 190°C, 195°C, and 185°C, respectively; the temperatures of the six temperature zones from the feed end to the connector of the reinforcing layer extruder and the outer protective layer extruder are 150°C, 165°C, 175°C, 180°C, 185°C, and 175°C, respectively; and the die temperature of the three-layer co-extrusion die head is 180°C.

[0061] Example 3

[0062] The difference between this embodiment and Embodiment 1 is that, in step S3 of the preparation process, the temperatures of the six temperature zones from the feed end to the connector of the inner liner extruder are 155°C, 170°C, 180°C, 185°C, 190°C, and 182°C, respectively; the temperatures of the six temperature zones from the feed end to the connector of the reinforcing layer extruder and the outer protective layer extruder are 145°C, 160°C, 170°C, 175°C, 180°C, and 172°C, respectively; and the die temperature of the three-layer co-extrusion die head is 178°C.

[0063] Example 4

[0064] The difference between this embodiment and embodiment 3 lies in the ratio of the composite pipe. In this embodiment, the raw material for the inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:12.

[0065] The reinforcing layer comprises the following raw material components in parts by weight: 100 parts of PE100-RC resin, 24 parts of chopped carbon fiber, 30 parts of modified magnesium hydroxide, 14 parts of coated ammonium polyphosphate type II, 16 parts of nano-kaolin, 10 parts of maleic anhydride grafted polyolefin elastomer, 10 parts of ethylene-vinyl acetate copolymer with VA content of 28%, 2 parts of lubricant, and 0.5 parts of composite antioxidant;

[0066] The outer protective layer comprises the following raw material components, in parts by weight: 100 parts PE100-RC resin, 15 parts chopped carbon fiber, 45 parts modified magnesium hydroxide, 15 parts coated ammonium polyphosphate type II, 10 parts maleic anhydride grafted polyolefin elastomer, 10 parts ethylene-vinyl acetate copolymer with 28% VA content, 2 parts lubricant, and 0.5 parts composite antioxidant.

[0067] Example 5

[0068] The difference between this embodiment and embodiment 3 lies in the ratio of the composite pipe. In this embodiment, the inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:10.

[0069] The reinforcing layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 20 parts chopped carbon fiber, 24 parts modified magnesium hydroxide, 10 parts coated ammonium polyphosphate type II, 12 parts nano kaolin, 7 parts maleic anhydride grafted polyolefin elastomer, 6 parts ethylene-vinyl acetate copolymer with VA content of 28%, 1.5 parts lubricant, and 0.4 parts composite antioxidant;

[0070] The outer protective layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 11 parts chopped carbon fiber, 35 parts modified magnesium hydroxide, 12 parts coated ammonium polyphosphate type II, 7 parts maleic anhydride grafted polyolefin elastomer, 6 parts ethylene-vinyl acetate copolymer with 28% VA content, 1.5 parts lubricant, and 0.4 parts composite antioxidant.

[0071] Example 6

[0072] The difference between this embodiment and embodiment 3 lies in the ratio of the composite pipe. In this embodiment, the inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:8.

[0073] The reinforcing layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 22 parts chopped carbon fiber, 26 parts modified magnesium hydroxide, 12 parts coated ammonium polyphosphate type II, 14 parts nano kaolin, 8 parts maleic anhydride grafted polyolefin elastomer, 9 parts ethylene-vinyl acetate copolymer with 28% VA content, 2 parts lubricant, and 0.5 parts composite antioxidant.

[0074] The outer protective layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 15 parts chopped carbon fiber, 40 parts modified magnesium hydroxide, 14 parts coated ammonium polyphosphate type II, 8 parts maleic anhydride grafted polyolefin elastomer, 9 parts ethylene-vinyl acetate copolymer with 28% VA content, 2 parts lubricant, and 0.5 parts composite antioxidant.

[0075] Example 7

[0076] The difference between this embodiment and embodiment 3 lies in the ratio of the composite pipe. In this embodiment, the inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:9.

[0077] The reinforcing layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 21 parts chopped carbon fiber, 25 parts modified magnesium hydroxide, 11 parts coated ammonium polyphosphate type II, 13 parts nano kaolin, 7.5 parts maleic anhydride grafted polyolefin elastomer, 7.5 parts ethylene-vinyl acetate copolymer with VA content of 28%, 1.8 parts lubricant, and 0.45 parts composite antioxidant;

[0078] The outer protective layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 13 parts chopped carbon fiber, 38 parts modified magnesium hydroxide, 13 parts coated ammonium polyphosphate type II, 7.5 parts maleic anhydride grafted polyolefin elastomer, 7.5 parts ethylene-vinyl acetate copolymer with 28% VA content, 1.8 parts lubricant, and 0.45 parts composite antioxidant.

[0079] Example 8

[0080] The difference between this embodiment and embodiment 7 is that the outer protective layer is 4mm thick, the reinforcing layer is 12mm thick, and the inner lining layer is 4mm thick.

[0081] Example 9

[0082] The difference between Example 8 and Example 9 is that the lubricant is a mixture of polyethylene wax and zinc stearate in a mass ratio of 1.5:1, replacing the polyethylene wax.

[0083] Example 10

[0084] The difference between Example 1 and Example 9 is that the raw material of the outer protective layer also includes rutile titanium dioxide, and the amount of rutile titanium dioxide added is 1.8 parts.

[0085] Example 11

[0086] The difference between Example 1 and Example 9 is that the raw material of the outer protective layer also includes rutile titanium dioxide, and the amount of rutile titanium dioxide added is 2.5 parts.

[0087] Example 12

[0088] The difference between Example 1 and Example 9 is that the raw material of the outer protective layer also includes rutile titanium dioxide, and the amount of rutile titanium dioxide added is 2.2 parts.

[0089] Example 13

[0090] The difference between this embodiment and embodiment 12 is that the raw materials for the outer reinforcing layer and the outer protective layer also include silicone powder, and the amount of silicone powder added is 4 parts each.

[0091] Example 14

[0092] The difference between Example 1 and Example 12 is that the raw materials for the outer reinforcing layer and the outer protective layer also include silicone powder, and the amount of silicone powder added is 6 parts each.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 12 is that an equal amount of untreated short-cut carbon fibers of the same specifications were used to replace the treated short-cut carbon fibers.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 12 is that the maleic anhydride-grafted polyolefin elastomer was replaced with an equal amount of PE100-RC resin.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 12 is that the short-cut carbon fibers are replaced with an equal amount of glass fiber, and 10 parts of conductive carbon black are added to both the reinforcing layer and the outer protective layer formulations.

[0099] Comparative Example 4

[0100] The difference between this comparative example and Example 12 is that the modified magnesium hydroxide is replaced with an equal amount of zinc borate.

[0101] Comparative Example 5

[0102] The difference between this comparative example and Example 12 is that an equal amount of triphenyl phosphate (TPP) was used to replace the coated ammonium polyphosphate type II.

[0103] Comparative Example 6

[0104] The difference between this comparative example and Example 12 is that no nano-kaolin is added to the reinforcing layer.

[0105] Comparative Example 7

[0106] The difference between this comparative example and Example 12 is that the maleic anhydride-grafted polyolefin elastomer is replaced with an equal amount of maleic anhydride-grafted polyethylene with a grafting rate of 1.0-1.3%.

[0107] Comparative Example 8

[0108] The difference between this comparative example and Example 12 is that the die temperature of the three-layer co-extrusion die head is 170°C.

[0109] Pipe performance testing

[0110] The tensile strength, ring stiffness, burst pressure, surface resistivity, average burning time of sparks in the alcohol burner test, and oxygen index of the pipes in Examples 1-14 and Comparative Examples 1-8 were tested. A glass fiber reinforced pipe mixed with chopped glass fiber (the raw material consists of 100 parts of PE100-RC resin, 30 parts of chopped glass fiber, and 3.5 parts of maleic anhydride-grafted polyethylene, with an outer diameter of 12 mm and a wall thickness of 2 mm) was used as a control example.

[0111] Tensile strength was tested according to the method described in GB / T 8804-2003;

[0112] Ring stiffness was tested according to the method described in GB / T 9647-2015;

[0113] The burst pressure was tested according to the method described in GB / T 6111-2018;

[0114] Surface resistance was tested according to the method described in MT 181;

[0115] The burning time of the alcohol torch was tested according to the method described in MT 181;

[0116] The oxygen index was tested according to the method described in GB / T 2406.1-2008.

[0117] The results are shown in Table 1.

[0118] Table 1. Detection data of Examples 1-14 and Comparative Examples 1-8

[0119] Tensile strength Ring stiffness Explosive pressure Surface resistance Burning time Oxygen Index Example 1 361 18.6 40.7 0.8 3.6 41 Example 2 364 18.7 40.8 0.8 3.4 41 Example 3 366 18.9 41.0 0.8 3.5 42 Example 4 368 19.1 40.9 0.5 3.2 40 Example 5 373 19.6 41.3 0.7 3.9 43 Example 6 373 19.7 41.4 0.7 3.8 44 Example 7 374 19.7 41.6 0.7 3.8 44 Example 8 379 20.1 42.2 0.6 3.4 46 Example 9 380 20.3 42.2 0.4 3.4 46 Example 10 383 20.4 42.4 0.2 3.3 47 Example 11 384 20.4 42.5 0.2 3.3 47 Example 12 385 20.4 42.6 0.2 3.3 47 Example 13 385 20.4 42.7 0.2 3.3 47 Example 14 385 20.4 42.6 0.2 3.2 47 Comparative Example 1 302 17.9 37.4 3.4 3.9 45 Comparative Example 2 273 17.2 36.7 4.7 4.0 41 Comparative Example 3 237 12.2 34.2 106 5.2 39 Comparative Example 4 354 18.8 40.8 1.2 5.9 34 Comparative Example 5 378 19.9 41.5 0.9 5.4 36 Comparative Example 6 366 18.3 39.1 174 4.7 42 Comparative Example 7 344 18.9 37.5 2.2 3.9 45 Comparative Example 8 358 19.1 39.6 1.8 4.1 43 Comparison Example 232 11.6 32.4 <![CDATA[Greater than 10 7 > 17.6 21

[0120] The unit for tensile strength is MPa, and the unit for ring stiffness is KN / m. 2 The burst pressure is measured in MPa, and the surface resistivity is measured in 1×10⁻⁶ units. 5 Ω, the unit of combustion time is seconds.

[0121] As can be seen from the data in Table 1, compared with the fiberglass reinforced pipes of the prior art comparative examples, the pipes of Examples 1-14 of this application show significant improvements in mechanical properties such as strength, toughness, impact resistance, and explosion resistance, as well as safety properties such as antistatic properties and flame retardancy, achieving a comprehensive improvement in both safety and mechanical properties. Furthermore, the pipe of Example 12 of this application exhibits significantly better overall performance than the pipes of Comparative Examples 1-8. Therefore, it is evident that the PE pipes prepared in this application have properties far superior to similar pipes in the prior art, and all properties significantly exceed the requirements of existing relevant standards.

[0122] The data in Table 1, comparing the data from Examples 1 to 14, shows that after optimizing the temperature parameters of the extrusion process and the dimensional parameters of each layer of the pipe, the overall performance of the pipe can be further improved. In addition, after optimizing the component ratio of each layer of the pipe, the mechanical properties and safety performance of the pipe can also be further improved.

[0123] The data in Table 1, comparing Example 12 with Comparative Examples 1-8, shows that the sizing treatment of carbon fiber and the use of maleic anhydride-grafted polyolefin elastomer as a compatibilizer have a significant impact on the mechanical properties of the pipe. Using the scheme described in this application results in optimal raw material compatibility and significantly better mechanical properties of the pipe. Furthermore, the flame-retardant component ratio in this application also has a major impact on the performance of the pipe. Modified magnesium hydroxide (MH) and coated ammonium polyphosphate (APP) constitute a halogen-free synergistic flame-retardant system. Replacing it with other flame retardants significantly reduces the flame-retardant effect. In addition to its flame-retardant effect, the flame-retardant components in this application can also act as functional fillers to improve the mechanical properties of the pipe. The addition of kaolin is crucial, as it not only effectively increases the oxygen index but also acts as a functional filler to promote the improvement of the mechanical properties of the reinforcing layer. Additionally, among the processing parameters of this application, the die temperature of the three-layer co-extrusion die is critical, preferably above 170°C, and more preferably above 175°C. If the temperature is too low, the performance of the pipe will decrease.

[0124] Pipe aging resistance test

[0125] The pipes from Examples 1-14, Comparative Examples 1-8, and the Control Example were subjected to an ultraviolet radiation of 0.45 W / m at a temperature of 80°C, a humidity of 85%, and an ultraviolet intensity of 0.45 W / m. 2 Under these conditions, the pipes are treated for 30 days. The tensile strength, ring stiffness, and burst pressure of the pipes are then tested.

[0126] The results are shown in Table 2.

[0127] Table 2. Aging resistance test data of Examples 1-14 and Comparative Examples 1-8

[0128] Tensile strength Ring stiffness Explosive pressure Example 1 359 18.0 39.7 Example 2 361 18.1 39.9 Example 3 362 18.1 40.1 Example 4 363 18.3 40.0 Example 5 368 18.8 40.6 Example 6 367 19.0 40.8 Example 7 369 19.2 40.9 Example 8 373 19.5 41.5 Example 9 374 19.6 41.6 Example 10 377 19.7 41.8 Example 11 377 19.7 41.9 Example 12 378 19.7 42.1 Example 13 382 20.1 42.5 Example 14 383 20.2 42.5 Comparative Example 1 283 16.6 35.9 Comparative Example 2 252 15.3 34.4 Comparative Example 3 208 10.6 31.7 Comparative Example 4 351 18.6 40.2 Comparative Example 5 374 19.5 40.9 Comparative Example 6 346 17.4 36.8 Comparative Example 7 327 18.0 35.2 Comparative Example 8 349 18.4 37.8 Comparison Example 186 8.9 28.4

[0129] A comparison of the data in Table 2 and Table 1 shows that the pipes in Examples 1-14 of this application have excellent high-temperature resistance and UV aging resistance. After aging treatment, the mechanical properties of the pipes do not decrease significantly, and their aging resistance is significantly better than that of the pipes in Comparative Examples 1-8 and the control examples.

[0130] The data in Table 2, comparing the data from Examples 1-14, shows that the aging resistance of this application is significantly improved after adding silicone powder. The applicant believes that the polyethylene-based pipes of this application, under high temperature, high humidity, and ultraviolet conditions, suffer from performance aging due to component analysis in addition to the inherent aging of the material itself; adding silicone powder can significantly inhibit component analysis, thereby further improving the aging resistance of the pipes.

[0131] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A PE composite pipe for underground coal mines, comprising, from the inside out, an inner lining layer, a reinforcing layer, and an outer protective layer, characterized in that, The inner lining layer is composed of PE100-RC resin and conductive carbon black in a mass ratio of 100:6~12. The reinforcing layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 18-24 parts of chopped carbon fiber, 20-30 parts of modified magnesium hydroxide, 8-14 parts of coated ammonium polyphosphate type II, 10-16 parts of nano-kaolin, 6-10 parts of maleic anhydride grafted polyolefin elastomer, 5-10 parts of ethylene-vinyl acetate copolymer with VA content of 28%, 1-2 parts of lubricant, and 0.3-0.5 parts of composite antioxidant; The outer protective layer comprises the following raw material components, in parts by weight: 100 parts of PE100-RC resin, 8-15 parts of chopped carbon fiber, 30-45 parts of modified magnesium hydroxide, 10-15 parts of coated ammonium polyphosphate type II, 6-10 parts of maleic anhydride grafted polyolefin elastomer, 5-10 parts of ethylene-vinyl acetate copolymer with 28% VA content, 1-2 parts of lubricant, and 0.3-0.5 parts of composite antioxidant; The chopped carbon fibers are 3-6 mm in length and have been oxidized or sized.

2. The PE composite pipe for underground coal mines according to claim 1, characterized in that, The reinforcing layer comprises the following raw material components, in parts by weight: 100 parts PE100-RC resin, 20-22 parts chopped carbon fiber, 24-26 parts modified magnesium hydroxide, 10-12 parts coated ammonium polyphosphate type II, 12-14 parts nano-kaolin, 7-8 parts maleic anhydride grafted polyolefin elastomer, 6-9 parts ethylene-vinyl acetate copolymer with 28% VA content, 1.5-2 parts lubricant, and 0.4-0.5 parts composite antioxidant; The outer protective layer comprises the following raw material components in parts by weight: 100 parts PE100-RC resin, 11-15 parts chopped carbon fiber, 35-40 parts modified magnesium hydroxide, 12-14 parts coated ammonium polyphosphate type II, 7-8 parts maleic anhydride grafted polyolefin elastomer, 6-9 parts ethylene-vinyl acetate copolymer with 28% VA content, 1.5-2 parts lubricant, and 0.4-0.5 parts composite antioxidant.

3. The PE composite pipe for underground coal mines according to claim 1, characterized in that, The thickness ratio of the inner lining, reinforcing layer and outer protective layer is 1:3:

1.

4. The PE composite pipe for underground coal mines according to claim 1, characterized in that, The raw materials for the reinforcing layer and the outer protective layer also include silicone powder, and the amount of silicone powder added is 4 to 6 parts.

5. A PE composite pipe for underground coal mines according to claim 1, characterized in that, The lubricant consists of polyethylene wax and zinc stearate in a mass ratio of 1.5:

1.

6. A PE composite pipe for underground coal mines according to claim 1, characterized in that, The composite antioxidant is antioxidant B225.

7. A PE composite pipe for underground coal mines according to claim 1, characterized in that, The outer protective layer also includes rutile titanium dioxide, and the amount of rutile titanium dioxide added is 1.8 to 2.5 parts.

8. The method for preparing PE composite pipes for underground coal mines as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. According to the formulations of the reinforcing layer and the outer protective layer, the formulated amounts of PE100-RC resin, maleic anhydride grafted polyolefin elastomer, ethylene-vinyl acetate copolymer, lubricant and composite antioxidant are mixed evenly. The formulated amounts of modified magnesium hydroxide and coated ammonium polyphosphate type II are slowly added and mixed evenly to obtain the premix of the reinforcing layer and the outer protective layer. S2. The premix of the reinforcing layer and the outer protective layer from step S1 is fed into the twin-screw extruder through the main feed port, and the remaining raw materials according to the formula of the reinforcing layer and the outer protective layer are added through the side feed port. After melting and dispersing, extrusion, cooling and pelletizing, the reinforcing layer masterbatch and the outer protective layer masterbatch are obtained respectively. The inner liner material is mixed and added into the twin-screw extruder. After melting and dispersing, extrusion, cooling and pelletizing, the inner liner masterbatch is obtained. S3. The inner lining masterbatch, the reinforcing layer masterbatch, and the outer protective layer masterbatch are co-extruded to obtain a PE composite pipe with a three-layer structure.

9. The method for preparing PE composite pipes for underground coal mines according to claim 8, characterized in that, In step S2, the twin-screw extruder is a co-rotating parallel twin-screw extruder with a length-to-diameter ratio (L / D) ≥ 40, and the extrusion granulation process parameters are as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 175℃, Zone 4 180℃, Zone 5 180℃, Zone 6 175℃, Die head 170℃, and screw speed 250~300 rpm.

10. The method for preparing PE composite pipes for underground coal mines according to claim 8, characterized in that, In step S3, the temperatures of the six temperature zones from the feed end to the connector of the inner liner extruder are 150~160℃, 165~175℃, 175~185℃, 180~190℃, 185~195℃, and 180~185℃, respectively. The temperatures of the six temperature zones from the feed end to the connector of the reinforcing layer extruder and the outer protective layer extruder are 140~150℃, 155~165℃, 165~175℃, 170~180℃, 175~185℃, and 170~175℃, respectively. The die temperature of the three-layer co-extrusion die head is 175~180℃.