A high-performance double-layer polyethylene anti-corrosion powder coating, its preparation method and application

Abstract

The present invention discloses a high-performance double-layer polyethylene anti-corrosion powder coating, its preparation method and application, belonging to the field of steel pipe anti-corrosion. The coating of the present invention is composed of a bottom layer powder and a surface layer powder. By mass fraction, the raw materials of the bottom layer powder are: 15-25 parts of maleic anhydride grafted polyethylene, 3-7 parts of ABS resin, 51-76.5 parts of metallocene linear low-density polyethylene, 5-15 parts of polyolefin copolymer elastomer, 0.5-2 parts of functional additives; the raw materials of the surface layer powder are: 40-80 parts of medium and high-density polyethylene, 13-55.5 parts of linear low-density polyethylene, 4-5 parts of carbon black masterbatch, 0.5-2 parts of functional additives. The coating is composed of a bottom layer powder with an adhesive function and a surface layer powder with high mechanical properties and leveling effect, realizing the unity of high adhesion, high anti-corrosion performance and high-efficiency leveling. The adhesion of the coating is ≥60 N / cm, and the tensile strength of the coating is ≥20 MPa.

Description

Technical Field

[0001] The present invention belongs to the field of steel pipe anti-corrosion, and particularly relates to a high-performance double-layer polyethylene anti-corrosion powder coating, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Using polyethylene powder for the external wall anti-corrosion of steel pipes is a common anti-corrosion method for water conservancy and municipal steel pipes at present. Compared with thermosetting epoxy powder, polyethylene anti-corrosion has good toughness and can effectively protect steel pipes from being corroded by the buried environment. However, there are the following deficiencies when the existing polyethylene powder is used for the external wall anti-corrosion of steel pipes:

[0004] (1) From the perspective of the standards of coated steel pipes, in terms of the performance requirements for polyethylene powder in GB / T28897 or CJ / T120, it is required that the tensile strength of polyethylene > 9.8 MPa, the elongation at break > 300%, and the adhesion requirement is > 30 N / cm. The performance requirements for polyethylene powder in the standards are relatively low, so the performance of conventional polyethylene powder in the market is also relatively low;

[0005] (2) In terms of the leveling property of polyethylene powder, in order to ensure the leveling property of polyethylene powder on the outer wall of steel pipes, the melt mass flow rate (190 °C, 2.16 kg) of polyethylene powder is generally controlled at 10 - 20 g / min. Compared with other polyethylene for pipes, the above melt mass flow rate is very large, so the anti-corrosion performance of the polyethylene anti-corrosion coating is poor;

[0006] (3) In terms of the formula of polyethylene powder, in order to improve the adhesion of polyethylene powder to steel pipes, polyethylene grafted with maleic anhydride is usually added to the formula. The cross-linking side reaction of the free radical grafting reaction results in poor leveling performance of maleic anhydride grafted polyethylene. Therefore, the dosage of maleic anhydride grafted polyethylene will be appropriately reduced to ensure the leveling property of polyethylene, and reducing its dosage will lead to low adhesion of the polyethylene powder anti-corrosion coating;

[0007] (4) In terms of the preparation of the polyethylene powder anti-corrosion coating, in order to achieve the leveling of polyethylene powder on the outer wall of steel pipes, the steel pipe is generally preheated to a temperature above 250 °C, and the heat on the surface of the steel pipe is used to achieve the leveling of the polyethylene coating through a fluidized bed process or a spraying process. Due to the large wall thickness of the steel pipe, the leveling and cooling process is also the process of heat aging of the polyethylene coating. After the polyethylene anti-corrosion coating undergoes leveling, thermal oxygen aging causes the brittleness of the coating to increase.

[0008] Polyethylene itself is a material with good anti-corrosion effect. When applied to the anti-corrosion of the outer wall of steel pipes, in order to ensure processability, existing standards or technologies meet the needs of anti-corrosion processing by increasing the melt mass flow rate of polyethylene powder and sacrificing mechanical properties. Coupled with the thermal-oxidative aging that occurs during the preparation of polyethylene powder anti-corrosion coatings, the coatings have the disadvantages of high brittleness and low adhesion, resulting in poor anti-corrosion effect of polyethylene powder overall. Summary of the Invention

[0009] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a high-performance double-layer polyethylene anti-corrosion powder coating and its preparation method and application. The high-performance double-layer polyethylene anti-corrosion powder coating provided by the present invention is composed of a bottom layer powder with an adhesive function and a surface layer powder with high mechanical properties and leveling effect. The outer wall of the steel pipe is double-layer anti-corrosion by double-layer spraying or double-fluidized bed dipping. The adhesion of the coating is ≥60 N / cm, and the tensile strength of the coating is ≥20 MPa.

[0010] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0011] In the first aspect of the present invention, a high-performance double-layer polyethylene anti-corrosion powder coating is provided. It is composed of a bottom layer powder and a surface layer powder. By mass fraction, the raw material composition of the bottom layer powder is as follows: 15-25 parts of maleic anhydride grafted polyethylene, 3-7 parts of ABS resin, 51-76.5 parts of metallocene linear low-density polyethylene, 5-15 parts of polyolefin copolymer elastomer, 0.5-2 parts of functional additive; the raw material composition of the surface layer powder is as follows: 40-80 parts of medium-density polyethylene or high-density polyethylene, 13-55.5 parts of linear low-density polyethylene, 4-5 parts of carbon black masterbatch, 0.5-2 parts of functional additive.

[0012] In some embodiments of the present invention, the melt mass flow rate of the bottom layer powder at 190 °C and 2.16 kg is 3-5 g / 10 min; the tensile strength is ≥20 MPa, and the elongation at break is ≥700%.

[0013] In some embodiments of the present invention, the melt mass flow rate of the surface layer powder at 190 °C and 2.16 kg is 5-8 g / 10 min; the tensile strength is ≥25 MPa, and the elongation at break is ≥800%.

[0014] In some embodiments of the present invention, the melt mass flow rate of the maleic anhydride grafted polyethylene at 190 °C and 2.16 kg is 2-8 g / 10 min, and the maleic anhydride grafting rate is 0.5%-1.5%.

[0015] In some embodiments of the present invention, the impact strength of the ABS resin is ≥18 KJ / m 2 .

[0016] In some embodiments of the present invention, the melt mass flow rate of the metallocene linear low density polyethylene at 190 °C and 2.16 kg is 2-5 g / 10 min.

[0017] In some embodiments of the present invention, the polyolefin copolymer elastomer is an ethylene-butene copolymer or an ethylene-octene copolymer.

[0018] In some embodiments of the present invention, the density of the medium density polyethylene or high density polyethylene is 0.93-0.97 g / cm 3 , and the melt mass flow rate at 190 °C and 2.16 kg is 4-20 g / 10 min; preferably, the melt mass flow rate at 190 °C and 2.16 kg is 4-10 g / 10 min.

[0019] In some embodiments of the present invention, the melt mass flow rate of the linear low density polyethylene at 190 °C and 2.16 kg is 3-15 g / 10 min;

[0020] In some embodiments of the present invention, the content of carbon black in the carbon black masterbatch is 40%-50%.

[0021] In some embodiments of the present invention, the functional auxiliary agent is at least one of an antioxidant, an ultraviolet light stabilizer, a leveling agent, and an antifoaming agent.

[0022] In a second aspect of the present invention, there is provided a method for preparing the high-performance double-layer polyethylene anticorrosive powder coating described in the first aspect, including the following steps:

[0023] The method for preparing the bottom layer powder includes the following steps:

[0024] Mix maleic anhydride grafted polyethylene, ABS resin, metallocene linear low density polyethylene, polyolefin copolymer elastomer, and functional auxiliary agent in proportion and mix them evenly, and then carry out reactive blending and granulation at 190-210 °C with a twin-screw reactive extruder, and grind the powder to obtain the bottom layer powder;

[0025] The method for preparing the top layer powder includes the following steps:

[0026] Mix medium density, high density polyethylene, linear low density polyethylene, carbon black masterbatch, and functional auxiliary agent in proportion and mix them evenly, and then carry out reactive blending and granulation at 140-160 °C with a twin-screw reactive extruder, and grind the powder to obtain the top layer powder.

[0027] In a third aspect of the present invention, there is provided a double-layer polyethylene anticorrosive coating formed by leveling an anticorrosive coating, and the anticorrosive coating is the high-performance double-layer polyethylene anticorrosive powder coating described in the first aspect;

[0028] The thickness of the bottom layer of the double-layer polyethylene anti-corrosion coating is 0.2 - 0.4 mm, the thickness of the surface layer is 1.6 - 1.8 mm, and the total thickness ≥ 1.8 mm.

[0029] In some embodiments of the present invention, the adhesion of the double-layer polyethylene anti-corrosion coating to the steel pipe ≥ 60 N / cm.

[0030] The fourth aspect of the present invention provides a double-layer polyethylene anti-corrosion steel pipe, whose outer wall has an anti-corrosion coating, and the anti-corrosion coating is the double-layer polyethylene anti-corrosion coating described in the third aspect.

[0031] The fifth aspect of the present invention provides a method for preparing the double-layer polyethylene anti-corrosion steel pipe described in the fourth aspect, and a double-layer anti-corrosion is carried out on the outer wall of the steel pipe by using a double-layer powder spraying process or a double-powder fluidized bed process;

[0032] Preferably, the double-layer powder spraying process includes the following steps:

[0033] Heat the steel pipe to 200 - 250 °C, and use the spraying process to spray a bottom layer powder with a thickness of 0.2 - 0.4 mm on the surface of the steel pipe, and then spray a surface layer powder with a thickness of 1.6 - 1.8 mm on the surface of the bottom layer powder. Utilize the residual heat on the surface of the steel pipe or reheat to achieve the leveling of the two layers of polyethylene powder, and obtain a double-layer polyethylene anti-corrosion steel pipe with a total anti-corrosion layer thickness of more than 1.8 mm;

[0034] Preferably, the double-powder fluidized bed process includes the following steps:

[0035] Heat the steel pipe to 220 - 250 °C, then move the steel pipe onto the bottom layer powder fluidized bed, raise the fluidized bed to immerse the surface of the steel pipe into the fluidized bed, rotate the steel pipe, and use the heat on the surface of the steel pipe to thermally bond a bottom layer powder with a thickness of 0.2 - 0.4 mm on the surface of the steel pipe. Then move the steel pipe coated with the bottom layer powder onto the surface layer powder fluidized bed, raise the fluidized bed to immerse the surface of the steel pipe into the fluidized bed, continue to rotate the steel pipe, and use the heat on the surface of the steel pipe to thermally bond a surface layer powder with a thickness of 1.6 - 1.8 mm on the surface of the steel pipe. Utilize the residual heat on the surface of the steel pipe to achieve the leveling of the two layers of polyethylene powder, and obtain a double-layer polyethylene anti-corrosion steel pipe with a total anti-corrosion layer thickness of more than 1.8 mm.

[0036] The beneficial effects of the present invention are:

[0037] The present invention provides a high-performance double-layer polyethylene anti-corrosion powder coating, which is composed of a bottom-layer powder and a top-layer powder. By mass fraction, the raw material composition of the bottom-layer powder is as follows: 15-25 parts of maleic anhydride grafted polyethylene, 3-7 parts of ABS resin, 51-76.5 parts of metallocene linear low-density polyethylene, 5-15 parts of polyolefin copolymer elastomer, 0.5-2 parts of functional additives; the raw material composition of the top-layer powder is as follows: 40-80 parts of medium-density polyethylene or high-density polyethylene, 13-55.5 parts of linear low-density polyethylene, 4-5 parts of carbon black masterbatch, 0.5-2 parts of functional additives. The high-performance double-layer polyethylene anti-corrosion powder of the present invention realizes high adhesion to steel pipes through the bottom-layer powder with high adhesion, and through the top-layer polyethylene powder without maleic anhydride grafted polyethylene with high mechanical properties and excellent leveling property, double-layer compounding is carried out on the bottom-layer adhesive polyethylene with general leveling property, realizing the unity of high adhesion, high anti-corrosion performance and high-efficiency leveling, solving the contradiction between the processing performance and the inherent performance of polyethylene anti-corrosion powder, and providing a new anti-corrosion material with high adhesion and high anti-corrosion effect for the outer wall of steel pipes.

[0038] In terms of controlling the adhesion and leveling property of the powder, the adhesion to the steel pipe is adjusted by the bottom-layer powder, and the overall leveling property of the steel pipe coating is controlled by the top-layer powder. Specifically, in the bottom-layer polyethylene powder, ignoring the influence of the high dosage of maleic anhydride grafted polyethylene on leveling, by adjusting the types of materials used and introducing ABS resin, it is ensured that the bottom-layer powder has excellent adhesion performance to the steel pipe. In terms of leveling, the leveling property of the bottom-layer powder can be ignored because the thickness of the bottom-layer powder is only 0.2-0.4 mm. Even if the leveling is poor, the bottom-layer powder with poor leveling can be covered by the top-layer powder with good leveling and large thickness. In the top-layer polyethylene powder, medium-density polyethylene, high-density polyethylene and linear low-density polyethylene with excellent mechanical properties are selected and combined to endow the polyethylene with high tensile strength (up to more than 25 MPa). At the same time, because the top-layer polyethylene powder does not contain maleic anhydride grafted polyethylene, it has excellent leveling property. The present invention realizes high-strength adhesion to the steel pipe by using the excellent adhesion of the bottom-layer polyethylene powder. At the same time, by using the excellent mechanical properties and good leveling property of the top-layer polyethylene powder, through the compounding of the double-layer functional polyethylene powder, the adhesion function and the anti-corrosion function are combined. The adhesion of the polyethylene powder to the steel pipe can reach more than 60 N / cm, and the whole is bright without obvious orange peel pattern, successfully solving the contradiction problem that the leveling property and the anti-corrosion effect of polyethylene powder in the prior art cannot be unified.

[0039] Furthermore, the bottom - layer polyethylene powder of the present invention is added with ABS resin that is incompatible with polyethylene, which can promote the micro - phase separation of each component in the bottom - layer polyethylene powder, enabling polar groups such as maleic anhydride to be distributed on the surface of polyethylene. This is more conducive to the wetting of the steel pipe surface by the polyethylene powder, thereby improving the adhesion of the bottom - layer polyethylene powder to the steel pipe. And the inventor found that, compared with the formulation without adding ABS resin, when 3 - 7 parts of ABS resin are added to the bottom - layer polyethylene, the adhesion of the polyethylene powder to the steel pipe can be increased from the original 30 N / cm to more than 60 N / cm.

[0040] The preparation method of the high - performance double - layer polyethylene anti - corrosion powder coating of the present invention is simple, and its usage method is also simple, and it also has good cost performance. When the high - performance double - layer polyethylene anti - corrosion powder coating of the present invention is coated on the outer wall of the steel pipe for anti - corrosion, the thickness of the bottom - layer powder with high cost and bonding performance only needs to be 0.2 - 0.4 mm, while the thickness of the surface - layer powder with low cost, high mechanical properties and good protection effect reaches 1.6 - 1.8 mm. Therefore, it has more cost - performance advantages compared with the polyethylene powder of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0042] Figure 1 It is a schematic structural diagram of a double - layer polyethylene anti - corrosion steel pipe according to an embodiment of the present invention;

[0043] Among them, 1 is the steel pipe, 2 is the bottom - layer polyethylene powder, and 3 is the surface - layer polyethylene powder. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0045] As analyzed in the background art of the present invention, there is a contradiction between the anti - corrosion performance and processability of the polyethylene powder coating in the prior art. To solve this problem, the present invention provides a high - performance double - layer polyethylene anti - corrosion powder coating, its preparation method and application.

[0046] In a typical embodiment of the present invention, a high-performance double-layer polyethylene anti-corrosion powder coating is provided, which is composed of a bottom powder and a top powder. By mass parts, the raw material composition of the bottom powder is as follows: 15-25 parts of maleic anhydride grafted polyethylene, 3-7 parts of ABS resin, 51-76.5 parts of metallocene linear low-density polyethylene, 5-15 parts of polyolefin copolymer elastomer, and 0.5-2 parts of functional additives; the raw material composition of the top powder is as follows: 40-80 parts of medium-density polyethylene or high-density polyethylene, 13-55.5 parts of linear low-density polyethylene, 4-5 parts of carbon black masterbatch, and 0.5-2 parts of functional additives.

[0047] In some embodiments of this embodiment, the melt mass flow rate of the bottom powder at 190 °C and 2.16 kg is preferably 3-5 g / 10 min, such as 3 g / 10 min, 3.5 g / 10 min, 4 g / 10 min, 4.5 g / 10 min, 5 g / 10 min, etc., and is preferably a range value with any of the above values as the upper or lower limit; the tensile strength is preferably ≥20 MPa, such as 20 MPa, 21 MPa, 22 MPa, 23 MPa, etc., and is preferably a range value with any of the above values as the upper or lower limit; the elongation at break is preferably ≥700%, such as 700%, 750%, 800%, 1000%, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0048] In some embodiments of this embodiment, the melt mass flow rate of the top powder at 190 °C and 2.16 kg is preferably 5-8 g / 10 min, such as 5 g / 10 min, 5.5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, etc., and is preferably a range value with any of the above values as the upper or lower limit; the tensile strength is preferably ≥25 MPa, such as 27 MPa, 28 MPa, 29 MPa, 30 MPa, etc., and is preferably a range value with any of the above values as the upper or lower limit; the elongation at break is preferably ≥800%, such as 850%, 900%, 950%, 1000%, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0049] In some embodiments of this embodiment, the melt mass flow rate of the maleic anhydride grafted polyethylene at 190 °C and 2.16 kg is preferably 2-8 g / 10 min, such as 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 7 g / 10 min, 8 g / 10 min, etc., and is preferably a range value with any of the above values as the upper or lower limit. The maleic anhydride grafting rate is preferably 0.5%-1.5%, such as 0.5%, 1.0%, 1.5%, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0050] In some embodiments of this embodiment, the impact strength of the ABS resin is preferably ≥18 KJ / m 2 , such as 20 KJ / m 2 , 25 KJ / m 2 , 27 KJ / m 2 , 30 KJ / m 2 , 31 KJ / m 2 etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0051] In some embodiments of this embodiment, the melt mass flow rate of the metallocene linear low density polyethylene at 190 °C and 2.16 kg is preferably 2 - 5 g / 10 min, such as 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0052] In some embodiments of this embodiment, the polyolefin copolymer elastomer is an ethylene-butene copolymer or an ethylene-octene copolymer.

[0053] In some embodiments of this embodiment, the density of the medium density polyethylene or high density polyethylene is preferably 0.93 - 0.97 g / cm 3 , and the melt mass flow rate at 190 °C and 2.16 kg is preferably 4 - 20 g / 10 min, more preferably 4 - 10 g / 10 min, such as 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0054] In some embodiments of this embodiment, the melt mass flow rate of the linear low density polyethylene at 190 °C and 2.16 kg is preferably 3 - 15 g / 10 min, such as 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 7 g / 10 min, 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0055] In some embodiments of this embodiment, the carbon black content in the carbon black masterbatch is preferably 40% - 50%, such as 40%, 45%, 50%, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0056] In some embodiments of this embodiment, the functional aids are preferably at least one of antioxidants, UV stabilizers, leveling agents, and defoamers. In the present invention, the specific types of the functional aids such as antioxidants, UV stabilizers, leveling agents, and defoamers can be the commonly used ones in the art, and the present invention will not elaborate herein.

[0057] In another typical embodiment of the present invention, a method for preparing the above-mentioned high-performance double-layer polyethylene anticorrosive powder coating is provided, which includes the following steps:

[0058] The method for preparing the bottom layer powder includes the following steps:

[0059] Mix maleic anhydride-grafted polyethylene, ABS resin, metallocene linear low-density polyethylene, polyolefin copolymer elastomer, and functional aids in proportion and mix them evenly, then carry out reactive blending and granulation at 190-210 °C with a twin-screw reactive extruder, and grind the powder to obtain the bottom layer powder;

[0060] The method for preparing the top layer powder includes the following steps:

[0061] Mix medium-density, high-density polyethylene, linear low-density polyethylene, carbon black masterbatch, and functional aids in proportion and mix them evenly, then carry out reactive blending and granulation at 140-160 °C with a twin-screw reactive extruder, and grind the powder to obtain the top layer powder.

[0062] In some embodiments of this embodiment, the particle size of the bottom layer powder obtained after grinding is preferably 30-50 mesh, such as 30 mesh, 35 mesh, 40 mesh, 45 mesh, 50 mesh, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0063] In some embodiments of this embodiment, the particle size of the top layer powder obtained after grinding is preferably 30-50 mesh, such as 30 mesh, 35 mesh, 40 mesh, 45 mesh, 50 mesh, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0064] In another typical embodiment of the present invention, a double-layer polyethylene anticorrosive coating is provided, which is cured with an anticorrosive coating, and the anticorrosive coating is the above-mentioned high-performance double-layer polyethylene anticorrosive powder coating;

[0065] The bottom layer thickness of the double-layer polyethylene anticorrosive coating is 0.2-0.4 mm, the top layer thickness is 1.6-1.8 mm, and the total thickness ≥ 1.8 mm.

[0066] In some embodiments of this embodiment, the adhesion of the double-layer polyethylene anti-corrosion coating to the steel pipe is preferably ≥60 N / cm, such as 62 N / cm, 65 N / cm, 68 N / cm, 70 N / cm, 75 N / cm, 80 N / cm, etc., and is preferably a range value with any of the above values as the upper or lower limit.

[0067] In another typical embodiment of the present invention, a double-layer polyethylene anti-corrosion steel pipe is provided, and its outer wall has an anti-corrosion coating, and the anti-corrosion coating is the above-mentioned double-layer polyethylene anti-corrosion coating.

[0068] In another typical embodiment of the present invention, a preparation method of the above-mentioned double-layer polyethylene anti-corrosion steel pipe is provided, and the double-layer powder spraying process or the double powder fluidized bed process is used to perform double-layer anti-corrosion on the outer wall of the steel pipe.

[0069] In some embodiments of this embodiment, the double-layer powder spraying process includes the following steps:

[0070] Heat the steel pipe to 200 - 250 °C, and use the spraying process to spray a bottom layer powder with a thickness of 0.2 - 0.4 mm on the surface of the steel pipe, and then spray a surface layer powder with a thickness of 1.6 - 1.8 mm on the surface of the bottom layer powder. Utilize the residual heat on the surface of the steel pipe or reheat to achieve the leveling of the two-layer polyethylene powder, and obtain a double-layer polyethylene anti-corrosion steel pipe with a total anti-corrosion layer thickness of more than 1.8 mm.

[0071] In some embodiments of this embodiment, the double powder fluidized bed process includes the following steps:

[0072] Heat the steel pipe to 220 - 250 °C, then move the steel pipe onto the bottom layer powder fluidized bed, raise the fluidized bed to immerse the surface of the steel pipe into the fluidized bed, rotate the steel pipe, and use the heat on the surface of the steel pipe to thermally bond a bottom layer powder with a thickness of 0.2 - 0.4 mm on the surface of the steel pipe. Then move the steel pipe coated with the bottom layer powder onto the surface layer powder fluidized bed, raise the fluidized bed to immerse the surface of the steel pipe into the fluidized bed, continue to rotate the steel pipe, and use the heat on the surface of the steel pipe to thermally bond a surface layer powder with a thickness of 1.6 - 1.8 mm on the surface of the steel pipe. Utilize the residual heat on the surface of the steel pipe to achieve the leveling of the two-layer polyethylene powder, and obtain a double-layer polyethylene anti-corrosion steel pipe with a total anti-corrosion layer thickness of more than 1.8 mm.

[0073] The present invention provides a high-performance double-layer polyethylene anticorrosive powder coating, which is composed of a bottom layer powder and a top layer powder. By mass parts, the raw material composition of the bottom layer powder is as follows: 15-25 parts of maleic anhydride grafted polyethylene, 3-7 parts of ABS resin, 51-76.5 parts of metallocene linear low density polyethylene, 5-15 parts of polyolefin copolymer elastomer, 0.5-2 parts of functional additives; the raw material composition of the top layer powder is as follows: 40-80 parts of medium density polyethylene or high density polyethylene, 13-55.5 parts of linear low density polyethylene, 4-5 parts of carbon black masterbatch, 0.5-2 parts of functional additives. The high-performance double-layer polyethylene anticorrosive powder of the present invention realizes high adhesion to steel pipes through the bottom layer powder with high adhesion, and through the top layer polyethylene powder without maleic anhydride grafted polyethylene with high mechanical properties and excellent leveling property for double-layer compounding on the bottom layer adhesive polyethylene with general leveling property, achieving the unity of high adhesion, high anticorrosive performance and high efficiency leveling, solving the contradiction between the processing performance and the inherent performance of polyethylene anticorrosive powder, and providing a new anticorrosive material with high adhesion and high anticorrosive effect for the outer wall of steel pipes.

[0074] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0075] Example 1 A high-performance double-layer polyethylene anticorrosive powder coating

[0076] (1) The bottom layer polyethylene powder is composed as shown in Table 1 (by mass parts):

[0077] Table 1 Composition of the bottom layer polyethylene powder formula in Example 1

[0078]

[0079]

[0080] The information of the raw materials used in the bottom layer polyethylene powder in Example 1 is as follows:

[0081] Maleic anhydride grafted polyethylene (PE-g-MAH): M-6S, melt mass flow rate is 3.2 g / 10 min, matrix is HDPE, maleic anhydride grafting rate is 0.7%, Shandong Donghong Pipe Industry Co., Ltd.;

[0082] ABS resin: PA-757H, Charpy impact strength is 27 KJ / m 2 , Zhenjiang Qimei Chemical Co., Ltd.;

[0083] Metallocene linear low density polyethylene (mPE): VL0005, Daelim Chemical of South Korea;

[0084] Elastomer: ethylene-octene copolymer elastomer, ENGAGE 8200, Dow Chemical;

[0085] Functional additive: antioxidant 245, Beijing Jiyi Chemical Co., Ltd.

[0086] The specific steps for preparing the bottom-layer polyethylene powder are as follows:

[0087] Mix all components evenly with a mixer according to the ratio, add them to a twin-screw extruder, carry out melt blending at 210 °C, obtain modified polyethylene particles after pelletizing, then grind them with a mechanical grinder, and pass through a 50-mesh sieve to obtain the bottom-layer polyethylene powder.

[0088] (2) The surface-layer polyethylene powder is composed according to Table 2 (parts by mass):

[0089] Formulation composition of the surface-layer polyethylene powder in Example 1 in Table 2

[0090] Number HDPE LLDPE Carbon black masterbatch Functional additive 1a 50 44 5 1

[0091] The information of the raw materials used in the surface-layer polyethylene powder in Example 1 is as follows:

[0092] High-density polyethylene (HDPE): DMDA-8007, melt mass flow rate of 8 g / 10 min, Shenhua Baotou Coal Chemical Co., Ltd.;

[0093] Linear low-density polyethylene (LLDPE): Elite TM 5220G, melt mass flow rate of 3.5 g / 10 min, Dow Chemical;

[0094] Carbon black masterbatch: EM105G, carbon black content 42%, Shandong Donghong Pipe Industry Co., Ltd.;

[0095] Functional additive: a blend of antioxidant 1010 and leveling agent polyethylene wax in a mass ratio of 1:1, antioxidant 1010, Beijing Jiyi Chemical Co., Ltd., polyethylene wax Licowax PE 520, Clariant of Germany.

[0096] The specific steps for preparing the surface-layer polyethylene powder are as follows:

[0097] Mix all components evenly with a mixer according to the ratio, add them to a twin-screw extruder, carry out melt blending at 160 °C, obtain modified polyethylene particles after pelletizing, then grind them with a mechanical grinder, and pass through a 30-mesh sieve to obtain the surface-layer polyethylene powder.

[0098] (3) Testing and application of the polyethylene powder:

[0099] Test the melt flow rate, tensile strength, elongation at break, and 180° aluminum peel strength of the bottom and top layer powders according to GB / T 28897-2021. The relevant data is shown in Table 7.

[0100] Select a steel pipe with DN1220 and a wall thickness of 12 mm. After shot blasting and rust removal of the steel pipe, coat the outer wall of the steel pipe through a double-fluidized bed process. When the temperature of the steel pipe surface is 230 °C, move the steel pipe above the bottom layer polyethylene powder fluidized bed, raise the fluidized bed to dip coat the bottom layer polyethylene powder, control the coating thickness to be 0.2 - 0.4 mm, and then continue to move the steel pipe above the top layer polyethylene powder fluidized bed, raise the fluidized bed to dip coat the top layer polyethylene powder, control the total coating thickness to be 1.8 - 2.0 mm. The adhesion, test status, and leveling appearance of the coating after coating are shown in Table 8. The combination of the bottom layer powder and the top layer powder is selected from the formula numbers in Table 1 and Table 2. For example, 1D-1a means the coating is composed of the bottom layer powder 1D and the top layer powder 1a.

[0101] Example 2 A high-performance double-layer polyethylene anticorrosive powder coating

[0102] (1) The bottom layer polyethylene powder is composed as follows (parts by mass):

[0103] Table 3 Composition of the bottom layer polyethylene powder in Example 2

[0104] Number PE-g-MAH ABS resin mPE Elastomer Functional additive 2A 20 5 64 10 1

[0105] The information of the raw materials used in the bottom layer polyethylene powder in Example 2 is as follows:

[0106] Maleic anhydride grafted polyethylene (PE-g-MAH): AMPLIFY GR 209, melt mass flow rate is 2 g / 10 min, matrix is VLDPE, maleic anhydride grafting rate is 0.5% - 1%, Dow Chemical;

[0107] ABS resin: PA-749K, Charpy impact strength is 31 KJ / m 2 , Zhenjiang Qimei Chemical Co., Ltd.;

[0108] Metallocene linear low density polyethylene (mPE): Exceed TM 3518CB, ExxonMobil;

[0109] Elastomer: ethylene-octene copolymer elastomer, LUCENE TM LC670, LG Chem Korea;

[0110] Functional additive: antioxidant B215, Beijing Jiyi Chemical Co., Ltd.

[0111] The specific steps for preparing the bottom-layer polyethylene powder are as follows:

[0112] Mix all components evenly with a mixer according to the ratio, add them to a twin-screw extruder, carry out melt blending at 190 °C, obtain modified polyethylene particles after pelletizing, then grind them with a mechanical grinder, and pass through a 40-mesh sieve to obtain the bottom-layer polyethylene powder.

[0113] (2) The surface-layer polyethylene powder is composed as shown in Table 2 (parts by mass):

[0114] Table 4 Composition of the surface-layer polyethylene powder in Example 2

[0115]

[0116]

[0117] The information on the raw materials used in the surface-layer polyethylene powder in Example 2 is as follows:

[0118] Medium-density polyethylene (MDPE): 7151U, melt mass flow rate of 5 g / 10 min, Qilu Petrochemical;

[0119] Linear low-density polyethylene (LLDPE): Elite TM 5815, melt mass flow rate of 15 g / 10 min, Dow Chemical;

[0120] Carbon black masterbatch: EM105G, carbon black content 42%, Shandong Donghong Pipe Industry Co., Ltd.;

[0121] Functional additives: Blended from antioxidant 215 and leveling agent fumed silica in a mass ratio of 3:1. Antioxidant 215, Beijing Jiyi Chemical Co., Ltd., fumed silica AEROSIL R972, Degussa.

[0122] The specific steps for preparing the surface-layer polyethylene powder are as follows:

[0123] Mix all components evenly with a mixer according to the ratio, add them to a twin-screw extruder, carry out melt blending at 140 °C, obtain modified polyethylene particles after pelletizing, then grind them with a mechanical grinder, and pass through a 40-mesh sieve to obtain the surface-layer polyethylene powder.

[0124] (3) Testing and application of the polyethylene powder:

[0125] Test the melt flow rate, tensile strength, elongation at break, and 180° aluminum peel strength of the bottom-layer and surface-layer powders according to GB / T28897-2021. The relevant data are shown in Table 7.

[0126] Select a steel pipe with a nominal diameter of DN1220 and a wall thickness of 12 mm. After shot blasting and rust removal of the steel pipe, the outer wall of the steel pipe is coated by two sets of spray gun spraying processes. Adopt the mode of rotating the steel pipe and moving the spray gun for spraying. When the surface temperature of the steel pipe is 230 °C, first spray the bottom layer of polyethylene powder, control the coating thickness to be 0.2 - 0.4 mm, use the surface layer polyethylene powder spray gun, and continue to spray the surface layer polyethylene powder on the surface of the surface layer polyethylene powder, control the total coating thickness to be 1.8 - 2.0 mm. The adhesion, test status, and leveling appearance of the coating after coating are shown in Table 8. The combination of the bottom layer powder and the surface layer powder is used from the formulation numbers in Table 3 and Table 4. For example, 2A - 2a means that the coating is composed of the bottom layer powder 2A and the surface layer powder 2a.

[0127] Comparative Example 1

[0128] (1) The polyethylene bottom layer powder and the surface layer powder are selected from Example 1.

[0129] (2) Testing and application of the polyethylene powder:

[0130] Select a steel pipe with a nominal diameter of DN1220 and a wall thickness of 12 mm. After shot blasting and rust removal of the steel pipe, the outer wall of the steel pipe is coated by a double fluidized bed process. When the surface temperature of the steel pipe is 230 °C, move the steel pipe above the bottom layer polyethylene powder fluidized bed, raise the fluidized bed to dip coat the bottom layer polyethylene powder, control the coating thickness to be 0.2 - 0.4 mm, and then continue to move the steel pipe above the surface layer polyethylene powder fluidized bed, raise the fluidized bed to dip coat the surface layer polyethylene powder, control the total coating thickness to be 1.8 - 2.0 mm. Select three combinations of the bottom layer powder and the surface layer powder, namely 1A - 1A (both layers use the bottom layer powder), 1a - 1a (both layers use the surface layer powder), and 1a - 1A (the bottom layer powder uses the surface layer powder formulation of 1a, and the surface layer powder uses the bottom layer powder formulation of 1A) to carry out double - layer powder composite on the steel pipe. The peel strength and appearance of the coating after coating are shown in Table 8.

[0131] Comparative Example 2

[0132] (1) The bottom layer polyethylene powder is composed according to Table 1 (parts by mass):

[0133] Table 5 Composition of the bottom layer polyethylene powder formulation in Comparative Example 1

[0134] Number PE-g-MAH ABS resin mPE Elastomer Functional additive 3A 20 0 74.5 5 0.5 3B 20 8 66.5 5 0.5 3C 20 5 74.5 0 0.5 3D 20 5 58.5 16 0.5 3E 30 5 59.5 5 0.5 3F 10 5 79.5 5 0.5

[0135] For Comparative Example 2, the information and preparation steps of the raw materials used in the bottom layer polyethylene powder are the same as those in Example 1.

[0136] (2) The surface layer polyethylene powder uses the 1a formulation in Example 1.

[0137] (3) Testing and application of the polyethylene powder:

[0138] The melt flow rate, tensile strength, elongation at break, and 180° aluminum peel strength of the bottom layer and surface layer powders were tested according to GB / T 28897-2021. The relevant data are shown in Table 7.

[0139] Select a steel pipe with a nominal diameter of DN1220 and a wall thickness of 12 mm. After shot blasting and rust removal of the steel pipe, the outer wall of the steel pipe was coated by a double-fluidized bed process. When the temperature of the steel pipe surface was 230 °C, the steel pipe was moved above the bottom layer polyethylene powder fluidized bed, and the fluidized bed was raised to dip-coat the bottom layer polyethylene powder, controlling the coating thickness to be 0.2 - 0.4 mm. Then, the steel pipe was continuously moved above the surface layer polyethylene powder fluidized bed, and the fluidized bed was raised to dip-coat the surface layer polyethylene powder, controlling the total coating thickness to be 1.8 - 2.0 mm. The adhesion, test status, and leveling appearance of the coating after coating are shown in Table 8. The bottom layer powder and surface layer powder are used in combination according to the formulation number in Table 5 and the 1a formulation, such as 3D-1a, indicating that the coating is composed of the bottom layer powder 3D and the surface layer powder 1a.

[0140] Comparative Example 3

[0141] (1) The existing polyethylene powder formulation (according to Scheme 4 in Table 4 of the literature "Wang Zonglin, Pan Xiangdong, Ba Xumin, Research on Polyethylene Powder Coatings for Battery Boxes, Paint & Coatings Industry, 2021, 51(9), 60 - 63"), the mass fractions of each component are as follows:

[0142] Table 6 Composition of the polyethylene powder formulation in Comparative Example 3

[0143] Number PE-g-MAH PE-B PE-D 3G 15.9 50 40

[0144] The information of the raw materials used in the middle layer polyethylene powder in Comparative Example 3 is as follows:

[0145] Maleic anhydride grafted polyethylene (PE-g-MAH): SZ-07, matrix is HDPE, Huangshan Beinuo Technology Co., Ltd.;

[0146] PE-B: DNDA7150, Maoming Branch of China National Petroleum and Chemical Corporation, melt mass flow rate 50 g / 10 min;

[0147] PE-D (metallocene polyethylene): Elite TM 5815, melt mass flow rate is 15 g / 10 min, Dow Chemical;

[0148] The specific steps for the preparation of the polyethylene powder are as follows:

[0149] Mix each component evenly by a mixer according to the ratio, add it to a twin-screw extruder, carry out melt blending at 160 °C, and obtain modified polyethylene particles after pelletizing. Then, grind the particles with a mechanical grinder, and pass through a 50-mesh sieve to obtain the bottom-layer polyethylene powder.

[0150] (2) Testing and application of polyethylene powder:

[0151] Test the melt flow rate, tensile strength, elongation at break, and 180° aluminum peel strength of the bottom-layer and surface-layer powders according to GB / T28897-2021. The relevant data are shown in Table 7.

[0152] Select a steel pipe with DN1220 and a wall thickness of 12 mm. After shot blasting and rust removal of the steel pipe, coat the outer wall of the steel pipe by the fluidized bed process. When the temperature of the steel pipe surface is 230 °C, move the steel pipe above the polyethylene powder fluidized bed, raise the fluidized bed to dip-coat the bottom-layer polyethylene powder, and control the total coating thickness to be 1.8 - 2.0 mm. The adhesion of the coating after coating, the test status, and the leveling appearance are shown in Table 8.

[0153] The performance data of various powders obtained through the above examples and comparative examples are shown in Table 7, and the adhesion and leveling data of the coatings are shown in Table 8:

[0154] Table 7 Performance data of various powders in examples and comparative examples

[0155]

[0156]

[0157] Table 8 Adhesion and leveling of coatings in examples and comparative examples

[0158]

[0159]

[0160]

[0161] From the performance data of Examples 1 - 2 and Comparative Examples 1 - 3 shown in Table 7 and Table 8, it can be seen that:

[0162] In Examples 1-2 of the present invention, the adhesion of the steel pipes with double-layer polyethylene anti-corrosion is greater than 60 N / mm; in Comparative Example 1, when using the bottom powder for two layers, the surface powder for two layers of polyethylene, or first using the surface powder and then using the bottom powder for anti-corrosion of the steel pipe, problems such as qualified adhesion but poor leveling, or extremely poor adhesion occur; in Comparative Example 2, when the proportion of the bottom powder exceeds the scope of the claims of the present invention, the problem of poor coating adhesion will occur; in Comparative Example 3, when using the existing technology polyethylene for anti-corrosion of the steel pipe, the mechanical strength of the coating is poor, and the coating breaks when the adhesion test reaches 25 N. This shows that the double-layer polyethylene powder of the present invention has higher adhesion and higher mechanical strength of the coating, thus having a better protective effect on the steel pipe.

[0163] It can be seen from the comparison between Example 1 and Comparative Example 2 3A that the lack of ABS resin will lead to a decrease in the peel strength of the polyethylene powder from the metal; it can be seen from the comparison between Example 1 and Comparative Examples 2 3A and 3B that when the added amount of ABS is not within 3-7 parts, it will have an adverse effect on the adhesion of the polyethylene powder to the metal. Without addition, the strength is low, and when the addition exceeds the amount, the tensile strength of the powder will be reduced, and at the same time, the compatibility between the bottom polyethylene and the outer layer will be affected, and the problem of separation between the bottom polyethylene and the outer polyethylene will occur during the adhesion test; it can be seen from the comparison between Example 1 and Comparative Examples 2 3C and 3D that when the amount of the elastomer in the bottom polyethylene powder exceeds 5-15 parts, the tensile strength of the bottom polyethylene powder will be affected, either reduced or the adhesion to the metal will be affected; it can be seen from the comparison between Example 1 and Comparative Examples 2 3E and 3F that when the amount of maleic anhydride grafted polyethylene in the bottom polyethylene powder exceeds 15-25 parts, when the amount is low, the adhesion to the metal will be reduced to some extent, and when the amount is too high, the leveling of the bottom powder will be worse, the orange peel pattern will be very serious, and at the same time, the adhesion will not be significantly improved. Without the covering of the surface powder with good leveling, the leveling of the overall coating will become worse. For the bottom polyethylene powder involved in the present invention, by introducing 3-7 parts of ABS resin, 5-15 parts of elastomer, and using 15-25 parts of maleic anhydride grafted polyethylene in the formula, the adhesion of the bottom polyethylene powder to the metal can be relatively high, while maintaining a tensile strength greater than 20 MPa and an elongation at break greater than 700%.

[0164] It can be seen from the comparison between Examples 1 and 2 and Comparative Examples 1-3 that although the surface powder has good mechanical properties and leveling effect, since it does not contain the component maleic anhydride grafted polyethylene that has an adhesive effect on the metal, the adhesion of the surface powder to the metal is extremely small. Therefore, using the surface polyethylene powder on top of the bottom polyethylene powder can not only cover the bottom powder with poor leveling, but also provide a steel pipe with an anti-corrosion coating with high mechanical properties. The bonding performance of the bottom powder and the high mechanical properties and leveling of the outer powder are combined to complement each other's advantages, thus solving the industry problems of low adhesion and poor mechanical properties of the existing polyethylene powder.

[0165] As can be seen from Embodiment 1 and Embodiment 2 of the present invention, the double-layer anticorrosive powder of the present invention provides a high bonding effect to the steel pipe through the bottom powder, and provides excellent anticorrosive effect to the steel pipe through the surface layer powder of polyethylene without maleic anhydride graft modification. The two layers work together to achieve good anticorrosive effect on the steel pipe. It can use a double-station fluidized tank for anticorrosion, or two sets of spraying devices can be used to complete the anticorrosion of the steel pipe by spraying process. The application implementation process is relatively simple.

[0166] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-performance double-layer polyethylene anti-corrosion powder coating, characterized in that, it is composed of a bottom layer powder and a top layer powder. By mass parts, the raw material composition of the bottom layer powder is as follows: 15-25 parts of maleic anhydride grafted polyethylene, 3-7 parts of ABS resin, 51-76.5 parts of metallocene linear low-density polyethylene, 5-15 parts of polyolefin copolymer elastomer, 0.5-2 parts of functional additives; the raw material composition of the top layer powder is as follows: 40-80 parts of medium-density polyethylene or high-density polyethylene, 13-55.5 parts of linear low-density polyethylene, 4-5 parts of carbon black masterbatch, 0.5-2 parts of functional additives.

2. The high-performance double-layer polyethylene anti-corrosion powder coating according to claim 1, characterized in that, the melt mass flow rate of the bottom layer powder at 190 °C and under a load of 2.16 kg is 3-5 g / 10 min; the tensile strength ≥ 20 MPa, and the elongation at break ≥ 700%; or, the melt mass flow rate of the top layer powder at 190 °C and under a load of 2.16 kg is 5-8 g / 10 min; the tensile strength ≥ 25 MPa, and the elongation at break ≥ 800%.

3. The high-performance double-layer polyethylene anti-corrosion powder coating according to claim 1, characterized in that, the melt mass flow rate of the maleic anhydride grafted polyethylene at 190 °C and under a load of 2.16 kg is 2-8 g / 10 min, and the maleic anhydride grafting rate is 0.5%-1.5%; Or, the impact strength of the ABS resin ≥ 18 KJ / m 2 ; or, the melt mass flow rate of the metallocene linear low-density polyethylene at 190 °C and under a load of 2.16 kg is 2-5 g / 10 min; or, the polyolefin copolymer elastomer is ethylene-butene copolymer or ethylene-octene copolymer.

4. The high-performance double-layer polyethylene anti-corrosion powder coating according to claim 1, characterized in that, The density of the medium-density polyethylene or high-density polyethylene is 0.93 - 0.97 g / cm 3 , and the melt mass flow rate at 190 °C under a load of 2.16 kg is 4 - 20 g / 10 min; or, the melt mass flow rate of the linear low-density polyethylene at 190 °C and under a load of 2.16 kg is 3-15 g / 10 min; or, the carbon black content in the carbon black masterbatch is 40%-50%.

5. The high-performance double-layer polyethylene anti-corrosion powder coating according to claim 4, characterized in that, the melt mass flow rate of the medium-density polyethylene or high-density polyethylene at 190 °C and under a load of 2.16 kg is 4-10 g / 10 min.

6. The high-performance double-layer polyethylene anti-corrosion powder coating according to claim 1, characterized in that, the functional additives are at least one of antioxidant, ultraviolet light stabilizer, leveling agent, and defoaming agent.

7. A preparation method of the high-performance double-layer polyethylene anti-corrosion powder coating according to any one of claims 1-6, characterized in that, it includes the following steps: The preparation method of the bottom layer powder includes the following steps: Mix the maleic anhydride grafted polyethylene, ABS resin, metallocene linear low-density polyethylene, polyolefin copolymer elastomer, and functional additives proportionally and mix them evenly, then carry out reactive blending and pelletizing at 190-210 °C with a twin-screw reactive extruder, and grind the powder to obtain the bottom layer powder; The preparation method of the top layer powder includes the following steps: Mix medium-density polyethylene or high-density polyethylene, linear low-density polyethylene, carbon black masterbatch, and functional additives in proportion and mix them evenly. Then, use a twin-screw reactive extruder to conduct reactive blending and pelletizing at 140 - 160 °C, and grind the pellets to obtain the surface layer powder.

8. A double-layer polyethylene anti-corrosion coating formed by the leveling of anti-corrosion paint, characterized in that, the anti-corrosion paint is the high-performance double-layer polyethylene anti-corrosion powder paint described in any one of claims 1 - 6; the thickness of the bottom layer of the double-layer polyethylene anti-corrosion coating is 0.2 - 0.4 mm, the thickness of the surface layer is 1.6 - 1.8 mm, and the total thickness ≥ 1.8 mm.

9. The double-layer polyethylene anti-corrosion coating according to claim 8, characterized in that, the adhesion of the double-layer polyethylene anti-corrosion coating to the steel pipe ≥ 60 N / cm.

10. A double-layer polyethylene anti-corrosion steel pipe with an anti-corrosion coating on its outer wall, characterized in that, the anti-corrosion coating is the double-layer polyethylene anti-corrosion coating described in claim 8 or 9.

11. A preparation method of the double-layer polyethylene anti-corrosion steel pipe described in claim 10, characterized in that, a double-layer anti-corrosion treatment is carried out on the outer wall of the steel pipe by using a double-layer powder spraying process or a double-powder fluidized bed process; the double-layer powder spraying process includes the following steps: Heat the steel pipe to 200 - 250 °C, and use the spraying process to spray a bottom layer powder with a thickness of 0.2 - 0.4 mm on the surface of the steel pipe. Then, spray a surface layer powder with a thickness of 1.6 - 1.8 mm on the surface of the bottom layer powder. Utilize the residual heat on the surface of the steel pipe or reheat to achieve the leveling of the two layers of polyethylene powder, and obtain a double-layer polyethylene anti-corrosion steel pipe with an anti-corrosion layer total thickness of more than 1.8 mm; the double-powder fluidized bed process includes the following steps: Heat the steel pipe to 220 - 250 °C, then move the steel pipe onto the bottom layer powder fluidized bed, raise the fluidized bed to immerse the surface of the steel pipe into the fluidized bed, rotate the steel pipe, and use the heat on the surface of the steel pipe to thermally bond a bottom layer powder with a thickness of 0.2 - 0.4 mm on the surface of the steel pipe. Then, move the steel pipe coated with the bottom layer powder onto the surface layer powder fluidized bed, raise the fluidized bed to immerse the surface of the steel pipe into the fluidized bed, continue to rotate the steel pipe, and use the heat on the surface of the steel pipe to thermally bond a surface layer powder with a thickness of 1.6 - 1.8 mm on the surface of the steel pipe. Utilize the residual heat on the surface of the steel pipe to achieve the leveling of the two layers of polyethylene powder, and obtain a double-layer polyethylene anti-corrosion steel pipe with an anti-corrosion layer total thickness of more than 1.8 mm.

Images