Composite pipe and preparation method thereof

Abstract

The invention discloses a composite pipe and a preparation method thereof, and relates to the technical field of water supply pipes. The composite pipe sequentially comprises an outer layer, a middle layer and an inner layer from outside to inside, raw materials of the outer layer comprise polypropylene random copolymer and composite rubber, and the mass ratio of the polypropylene random copolymer to the composite rubber is (3-9): 1; the composite rubber comprises ethylene propylene rubber, isoprene rubber and nano silicon dioxide, the mass ratio of the ethylene propylene rubber to the isoprene rubber in the composite rubber is (2.3-4): 1, and the mass ratio of the nano silicon dioxide to the composite rubber is (2-3): 10; the raw material of the middle layer is a propenyl block copolymer; the raw materials of the inner layer comprise heat-resistant polyethylene and glass fibers. The composite pipe provided by the invention has excellent mechanical strength and impact resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of water supply pipes, and particularly to a composite pipe and a preparation method thereof. Background Art

[0002] The prior art discloses a polypropylene-polyethylene composite pipe. The outer layer is a polypropylene pipe extruded and formed from a random copolymer polypropylene (PPR) or block copolymer polypropylene (PPB) material, and the inner layer is an inner layer extruded and formed from a peroxide cross-linked polyethylene (PE-Xa) material or a heat-resistant polyethylene (PERT) material. The outer polypropylene pipe layer and the inner polyethylene pipe layer form a composite pipe through a hot melt adhesive layer between the two pipe layers.

[0003] Random copolymer polypropylene (PPR) has excellent optical properties, processability, and mechanical strength balance, and plays an important role in pipeline applications. However, due to the disadvantages of poor impact performance and poor extensibility of PPR in low-temperature environments, its application in environments below zero degrees has been greatly hindered. Moreover, the content of ethylene in block polypropylene (PPB) is relatively high, reaching more than 15%, which improves its impact resistance but reduces its heat resistance and long-term creep resistance, thereby affecting the service life of the pipe. At the same time, although heat-resistant polyethylene (PERT) pipes have good thermal stability, are environmentally friendly and non-toxic, and have good impact resistance, their strength is low, the hot melt connection effect is poor, and they are prone to leakage. Peroxide cross-linked polyethylene (PE-Xa) pipes use high-density polyethylene as the main raw material, and use organic peroxides as cross-linking agents to extrude and cross-link the pipes by a plunger extruder. The production speed is slow, it is not easy to co-extrude and produce pipes with polypropylene materials, and it cannot be hot melt connected. Generally, mechanical connection is used, which increases the use cost. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a composite pipe and a preparation method thereof. The composite pipe of the present invention has excellent mechanical strength and impact resistance.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides a composite pipe, which sequentially includes an outer layer, an intermediate layer, and an inner layer from the outside to the inside. The raw materials of the outer layer include random copolymer polypropylene and composite rubber, and the mass ratio of the random copolymer polypropylene to the composite rubber is (3-9):1; the composite rubber includes ethylene propylene diene monomer (EPM), isoprene rubber (IR), and nano-silica, and the mass ratio of ethylene propylene diene monomer to isoprene rubber in the composite rubber is (2.3-4):1; the mass ratio of the nano-silica to the composite rubber is (2-3):10; The raw material of the middle layer is propylene-based block copolymer (OBC); the raw materials of the inner layer include heat-resistant polyethylene and glass fiber.

[0006] In the raw materials of the outer layer of the present invention, by adding ethylene propylene diene monomer rubber (EPDM), isoprene rubber, and nano-silica in combination, it is beneficial to improve the toughness of the outer layer, so that the composite pipe has excellent impact resistance in a low-temperature environment. Using propylene-based block copolymer as a hot melt adhesive in the raw materials of the middle layer can reduce the interfacial tension between polyethylene and polypropylene, and it has high compatibility with both polyethylene and polypropylene materials, playing the role of a connecting bridge, which is beneficial to enhancing the bonding strength between the outer layer and the inner layer. Adding glass fiber to heat-resistant polyethylene in the raw materials of the inner layer is beneficial to improving the strength of the inner layer, so that the composite pipe has high mechanical strength. Therefore, through the mutual cooperation of the outer layer, the middle layer, and the inner layer, the composite pipe has both excellent mechanical strength and impact resistance at the same time.

[0007] By controlling the content of ethylene propylene diene monomer rubber (EPDM), isoprene rubber, and nano-silica in the composite rubber and the mass ratio of random copolymer polypropylene and the composite rubber within the above ranges in the present invention, it is beneficial to further improve the strength and toughness of the composite pipe.

[0008] In the present invention, the composite rubber (EPM phase encapsulating the IR domain) is dispersed in the PPR matrix. When the IR content in the composite rubber is too high or too low, it will cause the particle spacing of the composite rubber to become larger, weaken the PPR matrix-rubber interface or reduce the contribution of the loss factor, resulting in a decline in mechanical properties. Therefore, by controlling the content of EPM and IR in the composite rubber within the above ranges, it is beneficial to improve the mechanical properties of the composite pipe.

[0009] Preferably, the mass ratio of ethylene propylene diene monomer rubber (EPDM) and isoprene rubber in the composite rubber is any one or the range value of both of 2.3:1, 2.5:1, 3:1, 3.5:1, 4:1.

[0010] Preferably, the mass ratio of heat-resistant polyethylene and glass fiber is (2.3 - 4):1.

[0011] More preferably, the mass ratio of heat-resistant polyethylene and glass fiber is any one or the range value of both of 2.3:1, 2.5:1, 3:1, 3.5:1, 4:1.

[0012] Preferably, the mass ratio of random copolymer polypropylene and the composite rubber is any one or the range value of both of 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1.

[0013] Preferably, the thickness of the middle layer is 0.5 - 1 mm.

[0014] Preferably, the thickness ratio of the intermediate layer to the composite pipe is (0.12~0.16):1.

[0015] Preferably, the thickness ratio of the outer layer to the inner layer is (1~2):1. Preferably 2:1.

[0016] Preferably, the weight-average molecular weight (Mw) of the random copolymerized polypropylene is 55×10 4 ~65×10 4 , and the molecular weight detection method is matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOFMS).

[0017] Preferably, the mass fraction of ethylene in the ethylene-propylene rubber is 50~60%, and the detection method for the mass fraction of ethylene is gas chromatography (external standard method for quantitative analysis).

[0018] Preferably, the weight-average molecular weight of the ethylene-propylene rubber is 25×10 4 ~30×10 4 , and the molecular weight detection method is matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOFMS).

[0019] Preferably, the weight-average molecular weight of the isoprene rubber is 85×10 4 ~95×10 4 , and the molecular weight detection method is matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOFMS).

[0020] Preferably, the nano-silica is fumed nano-silica with a surface area of 170~200 m 2 / g.

[0021] Preferably, the average particle size of the nano-silica is 10~15 nm.

[0022] Preferably, the weight-average molecular weight of the propylene-based block copolymer is 8×10 4 ~16×10 4 , and the molecular weight detection method is matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOFMS).

[0023] Preferably, the heat-resistant polyethylene is a high-density type II heat-resistant polyethylene copolymerized with hexene.

[0024] Preferably, the melt index of the heat-resistant polyethylene under the test conditions of 190℃ / 5.0 kg is 0.5~0.8 g / 10min.

[0025] Preferably, the weight-average molecular weight of the heat-resistant polyethylene is 15×10 4 ~25×10 4, the molecular weight detection method is matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOFMS).

[0026] Preferably, the melting point of the heat-resistant polyethylene is 120~150°C.

[0027] Preferably, the glass fiber is an alkali-free glass fiber, and the sodium oxide content in the alkali-free glass fiber is 0.1~0.5%.

[0028] Preferably, the short cut length of the glass fiber is 8~15 mm.

[0029] When the length of the glass fiber is less than 8 mm, the mechanical property advantage in the axial direction of the glass fiber cannot be exerted in the resin; when the length of the glass fiber is greater than 15 mm, it is difficult to blend the glass fiber and the resin evenly, and mechanical weak points are formed in the microstructure. Therefore, by controlling the length of the glass fiber in the present invention, it is beneficial to improve the mechanical properties of the inner layer.

[0030] Preferably, the diameter of the glass fiber is 10~13 μm.

[0031] Preferably, the glass fiber is modified by a silane coupling agent, and the method is as follows: after burning the glass fiber to 380~400°C, it is infiltrated in an ethanol solution containing a silane coupling agent for 1~2 h to obtain the modified glass fiber.

[0032] Preferably, the silane coupling agent includes vinyltrimethoxysilane or aminosilane.

[0033] In the second aspect, the present invention also provides a method for preparing a composite pipe, including the following steps: (1) Mix ethylene propylene diene monomer rubber, isoprene rubber, and nano-silica evenly to obtain a composite rubber, then extrude and pelletize the composite rubber to obtain composite rubber pellets, and finally mix the random copolymer polypropylene and the composite rubber pellets evenly to obtain an outer layer mixture; (2) Mix the glass fiber or the modified glass fiber and the heat-resistant polyethylene evenly to obtain an inner layer mixture; (3) Extrude and mold the outer layer mixture and the inner layer mixture respectively in a twin-screw extruder, extrude and mold the propylene-based block copolymer in the middle layer in a single-screw extruder, and after three-layer co-extrusion at the die head, cool and shape to obtain the composite pipe.

[0034] Preferably, in the step (1), the composite rubber is mixed by a mixer, the temperature of the mixer is 100~110°C, and the mixing time is 15~20 min.

[0035] Preferably, in the step (1), the random copolymer polypropylene and the composite rubber pellets are mixed by a blender, the rotation speed of the blender is 30 - 40 rpm / min, and the mixing time is 10 - 15 min.

[0036] Preferably, in the step (2), the glass fiber or the modified glass fiber and the heat-resistant polyethylene are mixed by a blender, the rotation speed of the blender is 30 - 40 rpm / min, and the mixing time is 8 - 10 min.

[0037] Preferably, the parameters of the twin-screw extruder in the step (3) are as follows: the temperatures of the 4 sections in the barrel area are: the first section is 170 ± 5 °C, the second section is 175 ± 5 °C, the third section is 180 ± 5 °C, and the fourth section is 185 ± 5 °C; the temperatures of the 7 sections of the die head in the die head area of the twin-screw extruder are: the first section is 195 ± 10 °C, the second section is 185 ± 5 °C, the third section is 190 ± 5 °C, the fourth section is 195 ± 5 °C, the fifth section is 200 ± 5 °C, the sixth section is 205 ± 5 °C, and the seventh section is 210 ± 5 °C. The rotation speed of the twin-screw extruder is 80 - 120 r / min, and the traction speed is 8 - 10 m / min.

[0038] Preferably, the parameters of the single-screw extruder in the step (3) are as follows: the extrusion temperature of the first section is 205 - 215 °C, the extrusion temperature of the second section is 195 - 205 °C, the extrusion temperature of the third section is 185 - 190 °C, the die temperature is 200 °C, the rotation speed of the screw is 80 - 100 r / min, and the traction speed is 800 - 1000 cm / min.

[0039] Preferably, in the step (3), the composite pipe is sized under the conditions of a vacuum of 0.012 - 0.04 MPa and a water temperature of 20 - 25 °C, and is cooled in a water tank at 18 - 23 °C.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: In the raw materials of the outer layer of the present invention, by adding ethylene propylene diene monomer rubber, isoprene rubber, and nano-silica in combination, it is beneficial to improve the toughness of the outer layer, so that the composite pipe has excellent impact resistance in a low-temperature environment. In the raw materials of the middle layer, an acrylate block copolymer is used as a hot melt adhesive, which can reduce the interfacial tension between polyethylene and polypropylene, and has high compatibility with both polyethylene and polypropylene materials, playing the role of a connecting bridge and being beneficial to improving the bonding strength between the outer layer and the inner layer. In the raw materials of the inner layer, glass fiber is added to the heat-resistant polyethylene, which is beneficial to improving the strength of the inner layer, so that the composite pipe has high mechanical strength. Therefore, through the mutual cooperation of the outer layer, the middle layer, and the inner layer, the composite pipe simultaneously has excellent mechanical strength and impact resistance. Description of the Drawings

[0041] Figure 1 It is a schematic structural diagram of the composite pipe of the present invention. Specific Embodiments

[0042] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the protection scope and implementation manner of the present invention are not limited thereto.

[0043] The materials, reagents, etc. used in the following embodiments are commercially available reagents and materials unless otherwise specified.

[0044] Example 1 This embodiment discloses a composite pipe, as Figure 1 shown, which sequentially includes an outer layer 1, an intermediate layer 2, and an inner layer 3 from outside to inside. The total thickness of the composite pipe is 4.2 mm, and the diameter of the composite pipe is 25 mm, that is, the national standard PPR S2.5 D25×4.2.

[0045] The thickness ratio of the intermediate layer 2 to the composite pipe is 0.14:1, that is, the thickness of the intermediate layer 2 is 0.6 mm; the thickness ratio of the outer layer 1 to the inner layer 3 is 2:1, that is, the thickness of the outer layer 1 is 2.4 mm, and the thickness of the inner layer 3 is 1.2 mm.

[0046] The raw materials of the outer layer include random copolymerized polypropylene and composite rubber, and the mass ratio of the random copolymerized polypropylene to the composite rubber is 9:1; the composite rubber includes ethylene propylene diene monomer rubber, isoprene rubber, and nano-silica, and the mass ratio of ethylene propylene diene monomer rubber to isoprene rubber in the composite rubber is 7:3, and the mass ratio of nano-silica to the composite rubber is 3:10.

[0047] The random copolymerized polypropylene is purchased from Daqing Petrochemical, China, with the model of PA14D-2, and the weight average molecular weight Mw is 56.3×10 4 .

[0048] The ethylene propylene diene monomer rubber is purchased from Jilin Petrochemical, China, with the model of J-0050, the mass fraction of ethylene is 51.6%, and Mw is 27.2×10 4 .

[0049] The isoprene rubber is purchased from Shanghai Duokang Co., Ltd., with the model of 2200, and the weight average molecular weight Mw is 92×10 4 .

[0050] The nano-silica is fumed nano-silica, purchased from the hydrophobic modification of AEROSIL®R974, with the model of A200, hydrophobic type, and the surface area is 200 m 2 / g.

[0051] The raw material of the middle layer is a propylene-based block copolymer; the propylene-based block copolymer is purchased from Dow Chemical of the United States, with a brand name of D5545 and a weight average molecular weight Mw of 10×10 4 .

[0052] The raw materials of the inner layer include heat-resistant polyethylene and alkali-free glass fiber, and the mass ratio of the heat-resistant polyethylene to the alkali-free glass fiber is 7:3.

[0053] The heat-resistant polyethylene was purchased from Total of France, model XRT70, with a weight average molecular weight Mw of 20×10 4 , the melt index is 0.70g / 10min.

[0054] The alkali-free glass fiber was purchased from Sichuan Fiberglass Group Co., Ltd., with a short cut length of 12 mm and a sodium oxide content of 0.45%.

[0055] The alkali-free glass fiber is modified by a silane coupling agent in the following manner: the alkali-free glass fiber is burned to 400° C., and then immersed in an ethanol solution containing a silane coupling agent for 1 hour to obtain the modified alkali-free glass fiber; wherein the mass percentage of the silane coupling agent in the ethanol solution containing the silane coupling agent is 2%.

[0056] The silane coupling agent is vinyl trimethoxy silane, purchased from Momentive, model number A-171.

[0057] This embodiment also discloses a method for preparing a composite pipe, comprising the following steps: (1) EPDM rubber, isoprene rubber and nano-silica were added to an internal mixer (XSM-2 / 10-80, Shanghai Kechuang Rubber & Plastic Machinery Co., Ltd.) and mixed. The mixture was stirred at 110°C for 20 min to obtain a composite rubber. The composite rubber was then extruded and granulated to obtain composite rubber pellets. Finally, random copolymer polypropylene and the composite rubber pellets were added to a mixer and mixed evenly to obtain an outer layer mixture. The mixer speed was 30 rpm / min and the stirring time was 15 min.

[0058] (2) Adding the modified alkali-free glass fiber and heat-resistant polyethylene into a mixer and mixing them evenly to obtain an inner layer mixed material; wherein the speed of the mixer is 40 rpm / min, and the mixing time is 10 min.

[0059] (3) The outer layer mixed material and the inner layer mixed material are extruded into shapes in a twin-screw extruder respectively, and the propylene-based block copolymer of the middle layer is extruded into shapes in a single-screw extruder. After three-layer co-extrusion is performed in a die head, the three layers are sized under the conditions of a vacuum of 0.012 MPa and a water temperature of 25° C., and the tube is cooled in a water tank at 18° C. to obtain the composite tube.

[0060] Among them, the parameters of the single-screw extruder are as follows: the extrusion temperature of the first stage is 205-215 °C, the extrusion temperature of the second stage is 195-205 °C, the extrusion temperature of the third stage is 185-190 °C, the die temperature is 200 °C, the rotation speed of the screw is 80-100 r / min, and the traction speed is 800-1000 cm / min.

[0061] The parameters of the twin-screw extruder are as follows: the temperatures of the 4 sections in the barrel area are: the first section is 170±5 °C, the second section is 175±5 °C, the third section is 180±5 °C, and the fourth section is 185±5 °C; the temperatures of the 7 sections of the die head in the die head area of the twin-screw extruder are: the first section is 195±10 °C, the second section is 185±5 °C, the third section is 190±5 °C, the fourth section is 195±5 °C, the fifth section is 200±5 °C, the sixth section is 205±5 °C, and the seventh section is 210±5 °C. The rotation speed of the twin-screw extruder is 80-120 r / min, and the traction speed is 8-10 m / min.

[0062] Example 2 A composite pipe includes an outer layer 1, an intermediate layer 2, and an inner layer 3 from outside to inside in sequence. The total thickness of the composite pipe is 4.2 mm, and the diameter of the composite pipe is 25 mm, which is the national standard PPR S2.5 D25×4.2.

[0063] The thickness ratio of the intermediate layer 2 to the composite pipe is 0.14:1, that is, the thickness of the intermediate layer 2 is 0.6 mm; the thickness ratio of the outer layer 1 to the inner layer 3 is 1:1, that is, the thickness of the outer layer 1 is 1.8 mm, and the thickness of the inner layer 3 is 1.8 mm.

[0064] The raw materials of the outer layer include random copolymer polypropylene and composite rubber, and the mass ratio of the random copolymer polypropylene to the composite rubber is 6:1; the composite rubber includes ethylene propylene diene monomer rubber, isoprene rubber, and nano-silica. The mass ratio of ethylene propylene diene monomer rubber to isoprene rubber in the composite rubber is 3:1, and the mass ratio of nano-silica to the composite rubber is 3:10.

[0065] The random copolymer polypropylene is purchased from Yanshan Petrochemical, with the model of 4220 and a weight average molecular weight of 65×10 4 .

[0066] The ethylene propylene diene monomer rubber is purchased from Jilin Petrochemical of China, with the model of J-3080, the mass fraction of ethylene is 50.5%, and the weight average molecular weight is 25.1×10 4 .

[0067] The isoprene rubber is purchased from Fushun Yikes, with the model of IR80 and a weight average molecular weight of 88×10 4 .

[0068] The nano-silica is fumed nano-silica, purchased from Hubei Huifu Nano Materials, with the model number of hydrophobic HB-139 and a surface area of 190m 2 / g.

[0069] The raw material of the intermediate layer is propylene block copolymer; the propylene block copolymer is purchased from Dow Chemical of the United States, with the model number of D5535 and a weight-average molecular weight of 9×10 4 .

[0070] The raw materials of the inner layer include heat-resistant polyethylene and alkali-free glass fiber, and the mass ratio of the heat-resistant polyethylene to the alkali-free glass fiber is 7:3.

[0071] The heat-resistant polyethylene is purchased from LG of South Korea, with the model number of SP988 and a weight-average molecular weight of 25×10 4 , and the melt index is 0.6 g / 10min.

[0072] The alkali-free glass fiber is purchased from Jushi Group, with the model number of 534A, a chopped length of 13mm, and a sodium oxide content of 0.4%.

[0073] The alkali-free glass fiber is modified by a silane coupling agent, and the method is as follows: after the alkali-free glass fiber is calcined to 400°C, it is infiltrated in an ethanol solution containing a silane coupling agent for 1h to obtain the modified alkali-free glass fiber; among them, the mass percentage of the silane coupling agent in the ethanol solution containing the silane coupling agent is 2%.

[0074] The silane coupling agent is vinyltrimethoxysilane, purchased from Momentive, with the model number of A-171.

[0075] The preparation method of a composite pipe is the same as that of Example 1.

[0076] Example 3 A composite pipe, different from Example 1 in that the mass ratio of ethylene propylene diene monomer rubber to isoprene rubber in the composite rubber is 4:1.

[0077] Example 4 A composite pipe, different from Example 1 in that the mass ratio of the nano-silica to the composite rubber is 2:10.

[0078] Example 5 A composite pipe, different from Example 1 in that the mass ratio of random copolymer polypropylene to composite rubber in the raw materials of the outer layer is 3:1.

[0079] Example 6 A composite pipe, different from Example 1 in that the mass ratio of heat-resistant polyethylene to alkali-free glass fiber in the raw materials of the inner layer is 3:1.

[0080] Example 7 A composite pipe, which is different from that in Example 1 in that the mass ratio of heat-resistant polyethylene to alkali-free glass fiber in the raw material of the inner layer is 4:1.

[0081] Comparative Example 1 A composite pipe, which is different from that in Example 1 in that no composite rubber is added to the raw material of the outer layer.

[0082] Comparative Example 2 A composite pipe, which is different from that in Example 1 in that no ethylene propylene diene monomer rubber is added to the composite rubber.

[0083] Comparative Example 3 A composite pipe, which is different from that in Example 1 in that no isoprene rubber is added to the composite rubber.

[0084] Comparative Example 4 A composite pipe, which is different from that in Example 1 in that no nano-silica is added to the composite rubber.

[0085] Comparative Example 5 A composite pipe, which is different from that in Example 1 in that no alkali-free glass fiber is added to the raw material of the inner layer.

[0086] Comparative Example 6 A composite pipe, which is different from that in Example 1 in that the mass ratio of nano-silica to composite rubber is 1:10.

[0087] Comparative Example 7 A composite pipe, which is different from that in Example 1 in that the mass ratio of nano-silica to composite rubber is 4:10.

[0088] Comparative Example 8 A composite pipe, which is different from that in Example 1 in that the mass ratio of random copolymer polypropylene to composite rubber in the raw material of the outer layer is 2:1.

[0089] Comparative Example 9 A composite pipe, which is different from that in Example 1 in that the mass ratio of random copolymer polypropylene to composite rubber in the raw material of the outer layer is 10:1.

[0090] Comparative Example 10 A composite pipe, which is different from that in Example 1 in that ethylene propylene diene monomer rubber with equal mass is used to replace ethylene propylene diene monomer rubber, and the ethylene propylene diene monomer rubber is purchased from Dow Chemical Company in the United States, with the model of 4725P.

[0091] Comparative Example 11 A composite pipe, which is different from that in Example 1 in that mesoporous silica of equal mass is used to replace nano-silica. The mesoporous silica is at the micron level and is purchased from Ruijiang Metal Materials Co., Ltd., Qinghe County, Xingtai City, Hebei Province.

[0092] Comparative Example 12 A composite pipe, which is different from that in Example 1 in that an equal mass of polyolefin elastomer (POE) is used to replace the propylene-based block copolymer. The polyolefin elastomer (POE) is purchased from Dow Chemical Company, USA, and the grade is 8150.

[0093] Performance testing 1. Tensile property test: Samples are prepared according to the standard method of GB / T8804.1-2003, and the sample shape is Type 1. The standard tensile test is carried out using a universal mechanical testing machine at room temperature (23°C). The test speed is 50 mm / min. The results are the average values of 5 samples.

[0094] 2. Impact height experiment: After being placed in a low temperature (-20°C) and room temperature (23°C) environment for 1 h, a R10 hammer head with a weight of 1 kg is dropped from a certain height to impact the composite pipe. Observe and record the highest height at which the composite pipe does not break after being impacted. After a total of 10 groups of experiments, the recorded data are averaged.

[0095] 3. Low-temperature falling weight impact strength: According to the standard of 《GB / T14152-2001》, the prepared composite pipes are tested at 0°C, with a hammer weight of 1 kg, a height of 0.8 m, and a DN25 hammer head (chamfered cylinder). A total of 100 composite pipes are tested. Among them, the composite pipe that does not break is considered to pass, and the composite pipe that breaks is considered to fail. The anti-low-temperature impact performance of the composite pipe is characterized by the passing rate (%).

[0096] The above test results are shown in Table 1.

[0097] Table 1 It can be seen from Table 1 that the composite pipe of the present invention has excellent mechanical strength and impact resistance.

[0098] From the comparison between Comparative Example 1 and Example 1, it can be obtained that in Comparative Example 1, no composite rubber is added to the raw materials of the outer layer. Although the tensile strength of the composite pipe increases, the impact performance of the composite pipe is significantly lower than that of Example 1. This shows that by adding composite rubber to the raw materials of the outer layer of the present invention, the composite pipe can simultaneously have excellent mechanical strength and impact resistance.

[0099] Comparing Comparative Examples 2 to 4 with Example 1 respectively, it can be seen that in Comparative Examples 2 to 3, no ethylene propylene diene monomer (EPDM) rubber or isoprene rubber is added to the composite rubber. Although the tensile strength of the composite pipe is increased, the impact resistance of the composite pipe is decreased; in Comparative Example 4, no nano-silica is added to the composite rubber, and both the strength and toughness of the composite pipe are decreased. This shows that the compounding of EPDM rubber, isoprene rubber, and nano-silica is beneficial to improving the toughness of the composite pipe, improving its low-temperature brittleness, and at the same time, is also beneficial to increasing the mechanical strength of the composite pipe.

[0100] Comparing Comparative Example 5 with Example 1, it can be seen that in Comparative Example 5, no glass fiber is added to the raw materials of the inner layer, and both the strength and toughness of the composite pipe are affected. This shows that adding glass fiber to the inner layer is beneficial to simultaneously increasing the mechanical strength and impact resistance of the composite pipe.

[0101] Comparing Comparative Examples 6 to 7 with Example 1 respectively, it can be seen that when the content of nano-silica in the composite rubber is too high, nano-silica is extremely easy to agglomerate in the matrix, resulting in the composite rubber becoming brittle and losing good elasticity, and the toughness of the composite pipe is decreased; when the content of nano-silica in the composite rubber is too low, it cannot cooperate well with rubber toughening, resulting in the decrease of the toughness of the composite pipe. Therefore, by controlling the content of nano-silica in the composite rubber in the present invention, it is beneficial to simultaneously increase the strength and toughness of the composite pipe.

[0102] Comparing Comparative Examples 8 to 9 with Example 1 respectively, it can be seen that in Comparative Example 8, the mass ratio of random copolymer polypropylene to composite rubber is too small, and the strength of the composite pipe is significantly decreased; in Comparative Example 9, the mass ratio of random copolymer polypropylene to composite rubber is too large, and both the strength and toughness of the composite pipe are decreased. Therefore, by controlling the mass ratio of random copolymer polypropylene to composite rubber within the range of (3 to 9):1 in the present invention, it is beneficial to simultaneously increase the strength and toughness of the composite pipe.

[0103] Comparing Comparative Examples 10 to 11 with Example 1 respectively, it can be seen that in Comparative Example 10, equal mass of ethylene propylene terpolymer rubber is used to replace ethylene propylene diene monomer rubber. Although the toughness of the composite pipe does not decrease, the strength of the composite pipe will decrease; in Comparative Example 11, micron-sized mesoporous silica is used to replace nano-silica, and both the strength and toughness of the composite pipe are decreased. This shows that not any compounding of rubber or any filler can simultaneously increase the strength and toughness of the composite pipe.

[0104] Comparing Comparative Example 12 with Example 1, it can be seen that in Comparative Example 12, POE of equal mass was used to replace the propylene-based block copolymer. The strength of the composite pipe decreased significantly compared with that of Example 1, and the toughness was also affected. This shows that only when the propylene-based block copolymer is used as the hot melt adhesive in the raw materials of the intermediate layer can the polyethylene and polypropylene materials have high compatibility, thereby enhancing the bonding strength between the outer layer and the inner layer, and thus improving the strength and toughness of the composite pipe at the same time.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite pipe, characterized in that, It sequentially includes an outer layer, a middle layer, and an inner layer from outside to inside. The raw materials of the outer layer include random copolymer polypropylene and composite rubber, and the mass ratio of the random copolymer polypropylene to the composite rubber is (3 - 9):

1. The composite rubber includes ethylene propylene diene monomer rubber, isoprene rubber, and nano-silica. The mass ratio of the ethylene propylene diene monomer rubber to the isoprene rubber in the composite rubber is (2.3 - 4):1, and the mass ratio of the nano-silica to the composite rubber is (2 - 3):

10. The raw material of the middle layer is a propylene-based block copolymer; the raw materials of the inner layer include heat-resistant polyethylene and glass fiber.

2. The composite pipe according to claim 1, characterized in that, The mass ratio of the heat-resistant polyethylene to the glass fiber is (2.3 - 4):

1.

3. The composite pipe according to claim 1, wherein, The thickness ratio of the middle layer to the composite pipe is (0.12 - 0.16):1; and / or, the thickness ratio of the outer layer to the inner layer is (1 - 2):

1.

4. The composite pipe according to claim 1, characterized in that, The weight-average molecular weight of the random copolymerized polypropylene is 55×10 4 ~65×10 4 ; and / or, the weight-average molecular weight of the propylene-based block copolymer is 8×10 4 ~16×10 4 .

5. The composite pipe according to claim 1, characterized in that, The mass fraction of ethylene in the binary ethylene-propylene rubber is 50-60%; and / or, the weight-average molecular weight of the binary ethylene-propylene rubber is 25×10 4 ~30×10 4 .

6. The composite pipe according to claim 1, wherein The surface area of the nano-silica is 170~200 m 2 / g; and / or, the average particle size of the nano-silica is 10~15 nm.

7. The composite pipe according to claim 1, characterized in that, The melt index of the heat-resistant polyethylene under the test conditions of 190 °C / 5.0 kg is 0.5 to 0.8 g / 10 min; and / or, the weight-average molecular weight of the heat-resistant polyethylene is 15×10 4 ~25×10 4 .

8. The composite pipe according to claim 1, characterized in that, The glass fiber is alkali-free glass fiber, and the sodium oxide content in the alkali-free glass fiber is 0.1 - 0.5%; and / or, the short cut length of the glass fiber is 8 - 15 mm.

9. The composite pipe according to claim 1, wherein, The glass fiber is modified by a silane coupling agent, and the method is as follows: After burning the glass fiber to 380 - 400 °C, it is infiltrated in an ethanol solution containing a silane coupling agent to obtain the modified glass fiber.

10. A method for preparing a composite tube according to any one of claims 1 to 9, characterized in that, It includes the following steps: (1) Mix ethylene propylene diene monomer rubber, isoprene rubber, and nano-silica evenly to obtain composite rubber, then extrude and granulate the composite rubber to obtain composite rubber pellets, and finally mix the random copolymer polypropylene and the composite rubber pellets evenly to obtain the outer layer mixed ingredients. (2) Mix glass fiber or modified glass fiber and heat-resistant polyethylene evenly to obtain the inner layer mixed ingredients. (3) Extrude and mold the outer layer mixed ingredients and the inner layer mixed ingredients in a twin-screw extruder respectively, extrude and mold the propylene-based block copolymer of the middle layer in a single-screw extruder, and after three-layer co-extrusion at the die head, cool and shape it to obtain the composite pipe.

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