Plastic-coated steel pipe and preparation method thereof

Abstract

The invention relates to the technical field of plastic-coated steel pipes, and provides a plastic-coated steel pipe and a preparation method thereof. The plastic-coated steel pipe comprises a steel pipe body and an anti-corrosion layer arranged on the outer surface of the steel pipe body, and the anti-corrosion layer comprises a sintered epoxy layer, an adhesive layer and a polyethylene layer which are sequentially arranged from inside to outside; the polyethylene layer comprises the following raw material components in parts by mass: 100-110 parts of high-density polyethylene, 20-28 parts of zinc oxide, 6-10 parts of a lubricant, 1-4 parts of an antioxidant and 6-8 parts of an auxiliary agent; the auxiliaries comprise poly (p-phenylene terephthalamide) fibers and polyethylene glycol terephthalate powder. Through the technical scheme, the problem of poor chemical corrosion resistance of the plastic-coated steel pipe in the related technology is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic-coated steel pipes, and in particular to a plastic-coated steel pipe and a preparation method thereof. Background Art

[0002] In the field of industrial fluid transportation, plastic-coated steel pipes, as a typical representative of steel-plastic composite pipes, can take into account the high strength of steel and the corrosion resistance of plastic anti-corrosion layers, but they still face multiple technical bottlenecks in extreme chemical environments. The polyethylene layer of existing plastic-coated steel pipes is prone to swelling, interface peeling or molecular chain degradation in media such as strong acids, strong alkalis, and organic solvents, resulting in protection failure. For example, when the high-density polyethylene in the raw material of the polyethylene layer is in contact with aromatic solvents for a long time, the molecular chain diffusion will cause the polyethylene layer to soften; and the ester bond hydrolysis reaction of the epoxy resin layer in a high-temperature alkaline environment will significantly shorten its service life.

[0003] The complexity of soil corrosion further exacerbates the service risk of the polyethylene layer of plastic-coated steel pipes. Buried pipelines not only need to deal with differences in physical and chemical factors such as soil conductivity, water content, and pH value, but also need to resist erosion by microorganisms and stray currents. In the chemical, petroleum and other fields, plastic-coated steel pipes often suffer from brittle fractures due to the synergistic effect of tensile stress and corrosive media caused by the corrosion of the polyethylene layer. In the field of marine engineering, high concentrations of chloride ions in seawater, microorganisms, and alternating dry and wet conditions in tidal zones significantly accelerate the aging and corrosion of the polyethylene layer.

[0004] In summary, the existing plastic-coated steel pipes are insufficiently resistant to chemical corrosion, and it is of vital importance to develop a plastic-coated steel pipe with improved chemical corrosion resistance. Summary of the invention

[0005] The present invention provides a plastic-coated steel pipe and a preparation method thereof, which solves the problem of poor chemical corrosion resistance of the plastic-coated steel pipe in the related art.

[0006] The technical solution of the present invention is as follows: The present invention provides a plastic-coated steel pipe, comprising a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged in sequence from the inside to the outside; The raw materials of the polyethylene layer include the following components in parts by weight: 100-110 parts of high-density polyethylene, 20-28 parts of zinc oxide, 6-10 parts of lubricant, 1-4 parts of antioxidant, 6-8 parts of additives; The auxiliary agent comprises poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder.

[0007] When lubricant is added to the polyethylene layer of the plastic-coated steel pipe of the present invention, the lubricant molecules can be inserted between the polyethylene molecular chains. Since the intermolecular force is relatively weak, the mutual friction and entanglement between the polyethylene molecular chains are reduced, and the internal friction between the polymer molecules is reduced, so that the polyethylene molecular chains are smoother in relative motion, thereby reducing the viscosity of the material and improving the fluidity of the polyethylene layer during processing. In addition, the addition of lubricant can also improve the interface lubrication between the polymer and the surface of the processing equipment. When the plastic-coated steel pipe is extruded, the lubricant will form a lubricating film on the surface of the polymer and the equipment, thereby reducing the adhesion between the polymer and the surface of the equipment, making the flow of the material in the equipment smoother, reducing the accumulation and hanging of the material on the surface of the equipment, and ensuring the continuity and stability of the processing process.

[0008] During the processing of the plastic-coated steel pipe, such as the extrusion stage, polyethylene will be affected by factors such as high temperature and mechanical shear force, and it is easy to induce an oxidation reaction. Therefore, the present invention adds an antioxidant to the polyethylene layer of the plastic-coated steel pipe. The antioxidant can quickly play a role in the processing process and inhibit the oxidation of polyethylene caused by high temperature and mechanical action. During the extrusion process, when the polyethylene material passes through the high-temperature barrel under the push of the screw, the antioxidant can timely capture the free radicals generated by the high temperature, prevent the breakage and degradation of the polyethylene molecular chain, and avoid the degradation of the material performance caused by oxidation, thereby ensuring the smooth progress of the processing, improving production efficiency, and reducing product defects caused by oxidation during the processing.

[0009] As a further technical solution, the particle size of the polyethylene terephthalate powder is 800 meshes.

[0010] In the present invention, high-density polyethylene is used as the basic material of the polyethylene layer of the plastic-coated steel pipe. It has highly regular linear molecular chains, which promotes the formation of a higher degree of crystallinity. The high degree of crystallinity enables the polyethylene layer to have good strength, toughness and wear resistance. In the plastic-coated steel pipe, the high-density polyethylene provides basic physical protection for the steel pipe, enabling it to effectively resist external physical effects such as friction and impact.

[0011] As a further technical solution, the raw materials of the sintered epoxy layer include the following components in parts by mass: 50-60 parts of epoxy resin, 20-30 parts of ethylene-vinyl acetate copolymer, 10-20 parts of petroleum resin, 20-30 parts of titanium hydride, 2-5 parts of benzoin, and 1-4 parts of adipic acid dihydrazide.

[0012] As a further technical solution, the raw materials of the adhesive layer include the following components in parts by mass: 15-45 parts of ethylene acrylic resin, 8-14 parts of polyvinyl butyral, 10-20 parts of polyisobutylene, and 1-3 parts of dioctyl phthalate.

[0013] As a further technical solution, the mass ratio of the poly(p-phenylene terephthalamide) fiber to the polyethylene terephthalate powder is 7-9:1.

[0014] In the present invention, the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder can be 7:1, 7.1:1, 7.2:1, 7.3:1, 7.4:1, 7.5:1, 7.6:1, 7.7:1, 7.8:1, 7.9:1, 8:1, 8.1:1, 8.2:1, 8.3:1, 8.4:1, 8.5:1, 8.6:1, 8.7:1, 8.8:1, 8.9:1, 9:1, and preferably 8:1.

[0015] In the polyethylene layer of the plastic-coated steel pipe of the present invention, if the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder is higher or lower than 7-9:1, the chemical corrosion resistance of the plastic-coated steel pipe will decrease. When the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder is 7-9:1, the chemical corrosion resistance of the plastic-coated steel pipe can be greatly improved. Ethylene interacts with each other to form a denser microstructure, in which the rigid chain segments of poly(p-phenylene terephthalamide) fibers play a skeletal support role in the polyethylene matrix, making the molecular arrangement more orderly and reducing the gaps between molecules. Poly(ethylene terephthalate) powder, with its film-forming property, fills in the gaps formed by polyethylene and poly(p-phenylene terephthalamide) fibers, further densifying the microstructure and effectively blocking the penetration of chemical substances, thereby improving the chemical corrosion resistance of the plastic-coated steel pipe.

[0016] As a further technical solution, the zinc oxide is modified zinc oxide; The raw materials of the modified zinc oxide include zinc oxide, a silane coupling agent and 5-carboxylic acid benzotriazole.

[0017] As a further technical solution, the silane coupling agent includes one of KH550, KH560, and KH570, preferably KH550.

[0018] In the polyethylene layer of the plastic-coated steel pipe of the present invention, the raw materials of the modified zinc oxide include zinc oxide, silane coupling agent and 5-carboxylic acid benzotriazole. Zinc oxide itself is an inorganic compound with excellent ultraviolet absorption performance, but its compatibility with organic polymer material polyethylene is poor. The molecular structure of the silane coupling agent contains two groups of different properties: one end is an active group that can chemically react with the surface of inorganic matter; the other end is an organic group that can physically or chemically react with organic matter. In the preparation process of modified zinc oxide, one end of the silane coupling agent chemically reacts with the hydroxyl group on the surface of zinc oxide to form a chemical bond, thereby grafting the silane coupling agent to the surface of zinc oxide, and the other end of the silane coupling agent is connected to 5-carboxylic acid benzotriazole to obtain modified zinc oxide. The modification process changes the surface properties of zinc oxide, changing its hydrophilicity to hydrophilicity. It becomes organophilic, which greatly enhances the compatibility of zinc oxide with the polyethylene matrix. When the modified zinc oxide is added to the polyethylene layer, it can be better dispersed between the polyethylene molecules to form a more uniform microstructure, thereby improving the UV resistance of the polyethylene layer. Moreover, after being exposed to ultraviolet radiation, the photogenerated electrons generated inside the zinc oxide will be affected by the "withdrawal effect" of the unsaturated groups in 5-carboxylic acid benzotriazole and transferred from zinc oxide to 5-carboxylic acid benzotriazole, thereby improving the absorption of ultraviolet rays by zinc oxide and thus improving the UV resistance of the plastic-coated steel pipe.

[0019] As a further technical solution, the preparation method of the modified zinc oxide comprises the following steps: A1. Add zinc oxide to ethanol, disperse evenly by ultrasonication, add silane coupling agent, stir, and dry to obtain silane-modified zinc oxide; A2. Add 5-carboxylic acid benzotriazole into ethanol for a first mixing, then add the silane-modified zinc oxide for a second mixing, concentrate, and dry to obtain the modified zinc oxide.

[0020] As a further technical solution, the mass volume ratio of the zinc oxide to the ethanol in A1 is 1g:8~10mL.

[0021] As a further technical solution, the mass volume ratio of the 5-carboxylic acid benzotriazole to the ethanol in A2 is 1 g:15~20 mL.

[0022] As a further technical solution, the mass ratio of the zinc oxide to the silane coupling agent is 1:0.8~1; The mass ratio of the zinc oxide to the 5-carboxylic acid benzotriazole is 1:0.7-0.9.

[0023] In the polyethylene layer of the plastic-coated steel pipe of the present invention, in the process of preparing modified zinc oxide, when the mass ratio of zinc oxide to silane coupling agent is 1:0.8~1, the silane coupling agent molecules can form a uniform modified layer on the surface of zinc oxide. If the content of the silane coupling agent is too low, the modification is insufficient, the compatibility of zinc oxide and polyethylene is poor, and agglomeration is likely to occur in the polyethylene layer, affecting the performance of the polyethylene layer; if the content is too high, too much silane coupling agent will cause side reactions such as self-polymerization in the system, which not only wastes raw materials, but also destroys the microstructure of the polyethylene layer and reduces the physical properties of the polyethylene layer. Performance, when the mass ratio of zinc oxide to 5-carboxylic acid benzotriazole is 1:0.7~0.9, the two can achieve good synergistic effect in anti-ultraviolet performance, 5-carboxylic acid benzotriazole and zinc oxide cooperate with each other to broaden the absorption range of ultraviolet rays and improve the overall anti-ultraviolet efficiency. If the content of 5-carboxylic acid benzotriazole is too low, it cannot fully make up for the deficiency of zinc oxide in ultraviolet absorption, and the anti-ultraviolet performance of the polyethylene layer is not significantly improved; if the content is too high, it will affect other properties of the polyethylene layer, such as thermal stability, processing performance, etc., resulting in a decrease in the performance of the polyethylene layer.

[0024] As a further technical solution, during the stirring, the temperature is 55-65° C., the time is 10-12 hours, and the rotation speed is 7000-8000 rpm.

[0025] In the polyethylene layer of the plastic-coated steel pipe of the present invention, during the process of preparing the modified zinc oxide, the temperature is in the range of 55-65°C. In this temperature range, the reaction activity of the silane coupling agent molecules with the hydroxyl groups on the surface of the zinc oxide is greatly improved, which promotes a more efficient chemical reaction between the two to form a stable chemical bond, thereby realizing the surface modification of the zinc oxide. The stirring speed is maintained at 7000-8000 rpm, which can ensure that the reactants are fully mixed in the system, promote the silane coupling agent to be evenly dispersed in the ethanol solution containing zinc oxide, and greatly increase the collision probability between the silane coupling agent and the zinc oxide particles.

[0026] As a further technical solution, during the first mixing, the temperature is 25-35° C. and the time is 3-4 hours.

[0027] As a further technical solution, during the second mixing, the temperature is 20-30° C. and the time is 20-24 hours.

[0028] As a further technical solution, the lubricant includes one or more of zinc stearate, calcium stearate, and polyethylene wax.

[0029] In the polyethylene layer of the plastic-coated steel pipe of the present invention, the lubricant can be any one or more of conventional lubricants, and can be one or more of magnesium stearate, barium stearate, oxidized polyethylene wax, zinc stearate, calcium stearate, polyethylene wax, preferably one or more of zinc stearate, calcium stearate, polyethylene wax.

[0030] As a further technical solution, the antioxidant includes one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0031] In the polyethylene layer of the plastic-coated steel pipe of the present invention, the antioxidant may be any one or more of conventional antioxidants, and may be one or more of antioxidant 1098, antioxidant 3114, antioxidant 626, antioxidant 126, antioxidant 1010, antioxidant 1076, and antioxidant 168, and preferably one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0032] The present invention also provides a method for preparing a plastic-coated steel pipe, which is used to prepare the plastic-coated steel pipe, comprising the following steps: S1, blending, extruding, and crushing the raw materials of the sintered epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain an adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, press and laminate, and obtain the plastic-coated steel pipe.

[0033] The working principle and beneficial effects of the present invention are: The present invention uses poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder as additives in the polyethylene anti-corrosion layer of the plastic-coated steel pipe, thereby improving the chemical corrosion resistance of the plastic-coated steel pipe. In the prior art, natural plant fibers are generally used to improve chemical corrosion resistance. However, the presence of polyhydroxy chemical structures in natural plant fibers causes the natural plant fibers to easily agglomerate. In the present invention, poly(p-phenylene terephthalamide) fiber is firstly used to avoid this problem. Poly(p-phenylene terephthalamide) fiber forms a stable "molecular reinforcement skeleton" in the polyethylene layer by virtue of its regular and rigid molecular chain structure and strong hydrogen bonding between molecular chains. When the plastic-coated steel pipe is eroded by chemical substances, the "skeleton" can effectively block the penetration of chemical substance molecules, while hydrogen bonds promote the arrangement of polyethylene molecules. More tightly ordered, greatly reducing the gaps that chemical substances can invade, adding polyethylene terephthalate powder and poly(p-phenylene terephthalamide) fiber to cooperate at the same time, polyethylene terephthalate powder has good compatibility with polyethylene, can be evenly distributed in the polyethylene matrix, fill the poly(p-phenylene terephthalamide) fiber, polyethylene molecules between small gaps, further block the diffusion path of chemical substances, and enhance the overall structural strength of the polyethylene layer, and the ester group in the molecular structure of polyethylene terephthalate powder can resist the attack of some chemical substances, making the polyethylene layer more stable in the chemical environment, therefore, poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder are added to the polyethylene layer together to effectively resist the penetration and erosion of chemical substances, significantly improving chemical corrosion resistance. The plastic-coated steel pipe prepared by the present invention is more conducive to application in scenes with complex chemical environments such as chemical industry and sewage treatment, has stronger adaptability and corrosion resistance, reduces pipeline damage and leakage caused by corrosion, reduces maintenance costs, and extends the service life of the pipeline. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the following embodiments and comparative examples, the model of high-density polyethylene is HE2550, the particle size of zinc oxide is 20 nm, the length of poly(p-phenylene terephthalamide) fiber is 3 mm, the thickness is 1.5D, the model is kevlar 1414, the model of polyethylene terephthalate powder is WB-8828, the particle size is 800 mesh, the model of epoxy resin is SM601, the model of ethylene-vinyl acetate copolymer is EVA910, the model of petroleum resin is C9 petroleum resin, the model of ethylene acrylic acid resin is EAA3440, the model of polyvinyl butyral is B60H, the model of polyisobutylene is HRD850, the length of poplar fiber is 149 μm, and the aspect ratio is 3.22.

[0036] Example 1 A plastic-coated steel pipe comprises a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged from the inside to the outside, and the raw materials of the polyethylene layer comprise the following components in parts by weight: 110 parts of high-density polyethylene, 28 parts of zinc oxide, 10 parts of zinc stearate, 4 parts of antioxidant 1010, 8 parts of auxiliary agent; The auxiliary agent includes poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder in a mass ratio of 11:1; The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 60 parts of epoxy resin, 30 parts of ethylene-vinyl acetate copolymer, 20 parts of petroleum resin, 30 parts of titanium hydride, 5 parts of benzoin, and 4 parts of adipic acid dihydrazide; The raw materials of the adhesive layer include the following components in parts by mass: 45 parts of ethylene acrylic resin, 14 parts of polyvinyl butyral, 20 parts of polyisobutylene, and 3 parts of dioctyl phthalate; The method for preparing the plastic-coated steel pipe comprises the following steps: S1, blending, extruding, and crushing the raw materials of the sintered epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, pressurize and compound, and obtain a plastic-coated steel pipe.

[0037] Example 2 A plastic-coated steel pipe comprises a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged from the inside to the outside, and the raw materials of the polyethylene layer comprise the following components in parts by weight: 100 parts of high-density polyethylene, 20 parts of zinc oxide, 2 parts of zinc stearate, 2 parts of calcium stearate, 2 parts of polyethylene wax, 0.5 parts of antioxidant 1076, 0.5 parts of antioxidant 168, 6 parts of additives; The auxiliary agent includes poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder in a mass ratio of 5:1; The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 50 parts of epoxy resin, 20 parts of ethylene-vinyl acetate copolymer, 10 parts of petroleum resin, 20 parts of titanium hydride, 2 parts of benzoin, and 1 part of adipic acid dihydrazide.

[0038] The raw materials of the adhesive layer include the following components in parts by mass: 15 parts of ethylene acrylic resin, 8 parts of polyvinyl butyral, 10 parts of polyisobutylene, and 1 part of dioctyl phthalate; The method for preparing the plastic-coated steel pipe comprises the following steps: S1, blending, extruding, and crushing the raw materials of the sintered epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, pressurize and compound, and obtain a plastic-coated steel pipe.

[0039] Example 3 A plastic-coated steel pipe comprises a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged from the inside to the outside, and the raw materials of the polyethylene layer comprise the following components in parts by weight: 105 parts of high-density polyethylene, 24 parts of zinc oxide, 8 parts of polyethylene wax, 2 parts of antioxidant 168, and 7 parts of additives; The auxiliary agent includes poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder in a mass ratio of 10:1; The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 55 parts of epoxy resin, 25 parts of ethylene-vinyl acetate copolymer, 15 parts of petroleum resin, 25 parts of titanium hydride, 4 parts of benzoin, and 2 parts of adipic acid dihydrazide; The raw materials of the adhesive layer include the following components in parts by mass: 35 parts of ethylene acrylic resin, 9 parts of polyvinyl butyral, 15 parts of polyisobutylene, and 2 parts of dioctyl phthalate; The method for preparing the plastic-coated steel pipe comprises the following steps: S1, blending, extruding, and crushing the raw materials of the sintered epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, pressurize and compound, and obtain a plastic-coated steel pipe.

[0040] Example 4 The only difference between this embodiment and embodiment 3 is that the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder in this embodiment is 6:1.

[0041] Example 5 The only difference between this embodiment and embodiment 3 is that the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder in this embodiment is 7:1.

[0042] Example 6 The only difference between this embodiment and embodiment 3 is that the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder in this embodiment is 8:1.

[0043] Example 7 The only difference between this embodiment and embodiment 3 is that the mass ratio of poly(p-phenylene terephthalamide) fiber to polyethylene terephthalate powder in this embodiment is 9:1.

[0044] Example 8 The difference between this embodiment and embodiment 6 is that the zinc oxide in this embodiment is replaced by modified zinc oxide of equal mass, and the preparation method of the modified zinc oxide comprises the following steps: A1. Add zinc oxide to ethanol (the mass volume ratio of zinc oxide to ethanol is 1 g:10 mL), add KH550 (the mass ratio of zinc oxide to KH550 is 1:1) after uniform ultrasonic dispersion, stir at 8000 rpm for 10 h at 65 °C, and dry to obtain KH550-modified zinc oxide; A2. Add 5-carboxylic acid benzotriazole to ethanol (the mass volume ratio of 5-carboxylic acid benzotriazole to ethanol is 1 g:20 mL), mix at 35°C for 4 hours, then add zinc oxide modified by KH550, mix at 30°C for 20 hours, concentrate, and dry to obtain modified zinc oxide, wherein the mass ratio of zinc oxide to 5-carboxylic acid benzotriazole is 1:0.7.

[0045] Example 9 The difference between this embodiment and embodiment 6 is that the zinc oxide in this embodiment is replaced by modified zinc oxide of equal mass, and the preparation method of the modified zinc oxide comprises the following steps: A1. Add zinc oxide to ethanol (the mass volume ratio of zinc oxide to ethanol is 1 g:8 mL), add KH550 (the mass ratio of zinc oxide to KH550 is 1:0.8) after ultrasonic dispersion, stir at 7000 rpm for 12 h at 55 °C, and dry to obtain KH550-modified zinc oxide; A2. Add 5-carboxylic acid benzotriazole to ethanol (the mass volume of 5-carboxylic acid benzotriazole and ethanol is 1 g:15 mL), mix at 25°C for 3 hours, then add zinc oxide modified by KH550, mix at 20°C for 24 hours, concentrate, and dry to obtain modified zinc oxide, wherein the mass ratio of zinc oxide to 5-carboxylic acid benzotriazole is 1:0.9.

[0046] Comparative Example 1 The difference between this comparative example and Example 3 is that the auxiliary agent in this comparative example is replaced by poly(p-phenylene terephthalamide) fiber of equal mass.

[0047] Comparative Example 2 The only difference between this comparative example and Example 3 is that the auxiliary agent in this comparative example is replaced by polyethylene terephthalate powder of the same mass.

[0048] Comparative Example 3 The only difference between this comparative example and Example 3 is that this comparative example does not contain an auxiliary agent.

[0049] Comparative Example 4 The difference between this comparative example and Example 3 is that the auxiliary agent in this comparative example is replaced by poplar fiber of equal mass.

[0050] Experimental Example 1 The polyethylene layer of the plastic-coated steel pipes prepared in Examples 1 to 7 and Comparative Examples 1 to 4 was tested for impact strength according to the method specified in GB / T 1843-2008 "Determination of Izod Impact Strength of Plastics", with the notch being type A, and then the samples were immersed in 30wt% sulfuric acid for 48h and then tested for impact strength again, with the sample size being 80mm×10mm and the thickness being 4mm. The test results are shown in Table 1.

[0051] Table 1 Impact strength test results

[0052] As can be seen from Table 1, in the present invention, the impact strength of the plastic-coated steel pipes prepared in Examples 1 to 7 after acid treatment decreases less than that of Comparative Examples 1 to 4, indicating that the poly(p-phenylene terephthalamide) fiber and the polyethylene terephthalate powder act synergistically to improve the chemical corrosion resistance of the plastic-coated steel pipe.

[0053] Experimental Example 2 The polyethylene layer of the plastic-coated steel pipes prepared in Examples 6 and 8-9 was tested for impact strength according to the method specified in GB / T 1843-2008 "Determination of Izod Impact Strength of Plastics", with the notch being type A. The samples were then UV treated according to the method specified in GB / T 16585-1996 "Artificial Weathering (Fluorescent UV Lamp) Test Method for Vulcanized Rubber", and the impact strength was tested again under the UV condition of 0.89 W / m 2 , temperature is 50℃, time is 480h, cycle time is 4h, UV exposure time is 4h, condensation time is 4h, sample size is 80mm×10mm, thickness is 4mm. The test results are shown in Table 2.

[0054] Table 2 Impact strength test results

[0055] It can be seen from Table 2 that the impact strength of the plastic-coated steel pipes prepared in Examples 8 to 9 of the present invention after UV treatment decreases less than that in Example 6. Therefore, in the present invention, zinc oxide is modified using silane coupling agent and 5-carboxylic acid benzotriazole to improve the UV resistance of the plastic-coated steel pipe.

[0056] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A plastic coated steel pipe, characterized in that: It comprises a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged in sequence from the inside to the outside; The raw materials of the polyethylene layer include the following components in parts by weight: 100-110 parts of high-density polyethylene, 20-28 parts of zinc oxide, 6-10 parts of lubricant, 1-4 parts of antioxidant, 6-8 parts of additives; The auxiliary agent comprises poly(p-phenylene terephthalamide) fiber and polyethylene terephthalate powder.

2. A plastic coated steel pipe according to claim 1, characterized in that: The mass ratio of the poly(p-phenylene terephthalamide) fiber to the polyethylene terephthalate powder is 7-9:

1.

3. The plastic-coated steel pipe according to claim 1, characterized in that: The zinc oxide is modified zinc oxide; The raw materials of the modified zinc oxide include zinc oxide, a silane coupling agent and 5-carboxylic acid benzotriazole.

4. The plastic-coated steel pipe according to claim 3, characterized in that: The preparation method of the modified zinc oxide comprises the following steps: A1. Add zinc oxide to ethanol, disperse evenly by ultrasonication, add silane coupling agent, stir, and dry to obtain silane-modified zinc oxide; A2. Add 5-carboxylic acid benzotriazole into ethanol for a first mixing, then add the silane-modified zinc oxide for a second mixing, concentrate, and dry to obtain the modified zinc oxide.

5. The plastic-coated steel pipe according to claim 4, characterized in that: The mass ratio of the zinc oxide to the silane coupling agent is 1:0.8-1; The mass ratio of the zinc oxide to the 5-carboxylic acid benzotriazole is 1:0.7-0.

9.

6. The plastic-coated steel pipe according to claim 4, characterized in that: During the stirring, the temperature is 55-65° C., the time is 10-12 hours, and the rotation speed is 7000-8000 rpm.

7. The plastic-coated steel pipe according to claim 4, characterized in that: During the first mixing, the temperature is 25-35° C. and the time is 3-4 hours.

8. The plastic-coated steel pipe according to claim 4, characterized in that: During the second mixing, the temperature is 20-30° C. and the time is 20-24 hours.

9. The plastic-coated steel pipe according to claim 1, characterized in that: The lubricant includes one or more of zinc stearate, calcium stearate, and polyethylene wax; The antioxidant includes one or more of antioxidant 1010 , antioxidant 1076 , and antioxidant 168 .

10. A method for preparing a plastic-coated steel pipe, used for preparing a plastic-coated steel pipe as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: S1, blending, extruding, and crushing the raw materials of the sintered epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain an adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, press and laminate, and obtain the plastic-coated steel pipe.

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