Anticorrosive coating for plastic-coated composite steel pipe and preparation method thereof

Abstract

This invention discloses an anti-corrosion coating for plastic-coated composite steel pipes and its preparation method, relating to the field of coating preparation technology. The coating comprises the following raw materials in parts by weight: 48-52 parts of E-12 epoxy resin, 12-16 parts of E-20 epoxy resin, 15-17 parts of low-temperature curing agent, 0.6-1.0 parts of leveling agent, 0.2-0.4 parts of defoamer, 8-10 parts of precipitated barium sulfate, 2-4 parts of mica powder, and 0.2-0.4 parts of fumed silica. The low-temperature curing agent used in this invention is obtained by mixing aromatic amine compounds, fatty acid esters, and imidazole-containing compounds in a certain mass ratio. By combining the low-temperature curing agent with other raw materials, the roller coating temperature of the anti-corrosion coating on the inner wall of the plastic-coated composite steel pipe is reduced to 150-160℃, and curing can be completed quickly at 160-165℃, reducing the processing temperature. The coating exhibits high storage stability and good anti-corrosion performance.

Description

Technical Field

[0001] This invention relates to the field of coating preparation technology, specifically to an anti-corrosion coating for plastic-coated composite steel pipes and its preparation method. Background Technology

[0002] The existing anti-corrosion treatment of the inner wall of spiral welded plastic-coated composite steel pipes mainly uses epoxy resin powder coating. Traditional epoxy powder systems generally have high melting and softening temperatures, with a conventional processing temperature of about 200℃, requiring prolonged high-temperature heating during production. This high-temperature process not only has high energy consumption, large heat loss, long production cycle, and low overall processing efficiency, but also easily causes thermal aging loss of raw materials. At the same time, the coating melts and spreads unevenly under high-temperature conditions, making it difficult to control the uniformity of the finished film thickness and the appearance stability.

[0003] To ensure the comprehensive performance of the inner wall anti-corrosion coating in terms of high temperature resistance and resistance to media corrosion, the industry often chooses aromatic amine curing agents with excellent thermal stability. However, conventional aromatic amine curing systems have high reaction activation energy and high curing start temperature, which further increases the overall processing temperature, making it difficult to achieve low-temperature energy-saving production.

[0004] At the same time, pure epoxy resin melt has high surface tension and high melt viscosity, poor wettability and spreadability on metal substrates, and insufficient leveling during roller coating of steel pipe inner wall, which easily leads to uneven coating, obvious roller coating marks and other drawbacks, increasing the difficulty of inner wall forming and processing.

[0005] Therefore, in response to the technical bottleneck of high-temperature processing of epoxy powder coating on the inner wall of existing plastic-coated steel pipes, it is of great engineering application value and practical significance to develop an anti-corrosion epoxy powder coating with low melting temperature, low-temperature curing capability, adaptability to inner wall roller coating construction, energy saving and consumption reduction, and excellent comprehensive coating performance. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an anti-corrosion coating for plastic-coated composite steel pipes and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions: A corrosion-resistant coating for plastic-coated composite steel pipes comprises the following raw materials in parts by weight: 48-52 parts of E-12 epoxy resin, 12-16 parts of E-20 epoxy resin, 15-17 parts of low-temperature curing agent, 0.6-1.0 parts of leveling agent, 0.2-0.4 parts of defoamer, 8-10 parts of precipitated barium sulfate, 2-4 parts of mica powder, and 0.2-0.4 parts of fumed silica.

[0008] A method for preparing an anti-corrosion coating for plastic-coated composite steel pipes includes the following steps: E-12 epoxy resin, E-20 epoxy resin, leveling agent, defoamer, precipitated barium sulfate, mica powder, and fumed silica are mixed and stirred for 20-30 minutes. A low-temperature curing agent is added, and stirring is continued for 5-10 minutes. After melt extrusion, cooling, crushing, and sieving, an anti-corrosion coating for plastic-coated composite steel pipes is obtained.

[0009] Furthermore, the mixing speed is 500-600 rpm; during the melt extrusion process, the temperature in zone one is 85-95℃, the temperature in zone two is 95-105℃, the die temperature is 90-100℃, the screw speed is 250-350 rpm, and the feeding speed is 80-120 rpm; an 80-100 mesh sieve is used for sieving.

[0010] Furthermore, the low-temperature curing agent is obtained by mixing aromatic amine compounds, fatty acid esters and imidazole-containing compounds in a mass ratio of (10-12):(2-2.5):(4-6).

[0011] Furthermore, the preparation method of the imidazole-containing compound includes the following steps: Step (1): After mixing and stirring imidazole, DMF and epichlorohydrin, add sodium hydroxide solution, continue stirring, heat, add sodium hydroxide solution again, stir, cool, and rotary evaporate to obtain product 1; Step (2): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, adjust pH, add sodium dithionite, heat and stir, cool, filter, extract filtrate, combine organic phases, dry, filter, and rotary evaporate to obtain product 2; Step (3): After mixing and stirring product 2 and DMF, add product 1, continue stirring, heat and stir to react, cool, rotary evaporate, and dry to obtain the imidazole-containing compound.

[0012] Furthermore, the preparation method of the imidazole-containing compound includes the following specific steps: Step (1): Mix imidazole, DMF and epichlorohydrin, stir for 5-10 min, add sodium hydroxide solution, continue stirring for 2-3 h, heat to 40-45℃, add sodium hydroxide solution again, stir for 1.5-2 h, cool, and rotary evaporate to obtain product 1; Furthermore, the ratio of the amounts of imidazole, DMF, epichlorohydrin, and sodium hydroxide solution is (4-5) g: (20-25) mL: (5.5-6.0) g: (10-15) mL; the mass fraction of the sodium hydroxide solution is 30-35%, and the sodium hydroxide solution is added in two portions, with the volume ratio of the first and second additions being 0.5: (1-1.5).

[0013] In step (1), imidazole reacts with epichlorohydrin in a ring-opening and then ring-closing reaction to obtain imidazole containing an epoxy group, i.e., product 1.

[0014] Step (2): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, stir for 10-15 min, adjust pH to 8-8.5, add sodium dithionite, heat to 35-45℃ and stir for 4-5 h, cool, filter, extract the filtrate, combine the organic phases, dry, filter, and rotary evaporate to obtain product 2. Furthermore, the ratio of 2-chloro-5-nitrotrifluorotoluene, methanol aqueous solution, and sodium dithionite is (12-13) g: (50-60) mL: (14-16) g; the methanol aqueous solution is obtained by mixing methanol and water in a volume ratio of (7-8): (2-3).

[0015] In step (2), the nitro group in 2-chloro-5-nitrotrifluorotoluene is reduced to an amino group to obtain product 2.

[0016] Step (3): Mix product 2 and DMF, stir for 5-10 min, add product 1, continue stirring for 20-25 min, heat to 50-55℃, stir and react for 5-6 h, cool, rotary evaporate, and dry to obtain the imidazole-containing compound.

[0017] Furthermore, the ratio of product 2, DMF, and product 1 is (11-12) g : (60-70) mL : (16.5-17.5) g.

[0018] In step (3), the amino group in product 2 reacts with the epoxy group in product 1 to undergo a ring-opening reaction, resulting in a product containing a tertiary amine group and a hydroxyl group, i.e., an imidazole compound.

[0019] Furthermore, the fatty acid ester is obtained by mixing pentaerythritol tetrastearate, tristearate glyceryl ester, and hexadecanoate in a mass ratio of (2-2.5):(1-1.5):(1-2).

[0020] Furthermore, the aromatic amine compound is obtained by mixing product a with diaminodiphenylmethane in a mass ratio of (1-1.5):2.

[0021] Furthermore, the preparation method of product a is as follows: After mixing and stirring 2-methoxy-4-nitroaniline and an aqueous ethanol solution, the pH was adjusted, sodium dithionite was added, the mixture was heated and stirred, cooled, filtered, the filtrate was extracted, dried, filtered, and rotary evaporated to obtain product a.

[0022] Furthermore, the specific method for preparing product a is as follows: Mix 2-methoxy-4-nitroaniline and an aqueous ethanol solution, stir for 10-15 min, adjust the pH to 8.5-9, add sodium dithionite, heat to 45-50℃ and stir for 4-5 h, cool, filter, extract the filtrate, dry, filter, and rotary evaporate to obtain product a.

[0023] Furthermore, the ratio of 2-methoxy-4-nitroaniline, aqueous ethanol solution, and sodium dithionite is (9-10) g: (45-50) mL: (13-14) g; the aqueous ethanol solution is obtained by mixing anhydrous ethanol and water in a volume ratio of (6-8): (2-4).

[0024] This invention discloses an anti-corrosion coating for plastic-coated composite steel pipes and its preparation method. The coating is made by mixing and stirring raw materials such as E-12 epoxy resin, E-20 epoxy resin, low-temperature curing agent, leveling agent, defoamer, precipitated barium sulfate, mica powder, and fumed silica, followed by melt extrusion, cooling, crushing, and sieving.

[0025] It has the following beneficial effects: The low-temperature curing agent used in this invention is obtained by mixing an aromatic amine compound, a fatty acid ester, and an imidazole-containing compound. The aromatic amine compound is obtained by mixing diaminodiphenylmethane and product a, where product a is obtained by reacting 2-methoxy-4-nitroaniline. The imidazole-containing compound is synthesized by reacting imidazole, epichlorohydrin, and 2-chloro-5-nitrotrifluorotoluene.

[0026] In the imidazole-containing compounds used in this invention, the steric hindrance effect of the groups attached to the imidazole and the electron-withdrawing effect of the trifluoromethyl and chlorine atoms can synergistically inhibit the room-temperature reactivity of imidazole, preventing premature curing of the coating and resulting in powder agglomeration, thus further improving the storage stability of the coating. The hydroxyl groups in the imidazole-containing compound molecules can enhance the compatibility between the low-temperature curing agent and the epoxy resin, improving the dispersion uniformity of the coating. The weakly polar trifluoromethyl and chlorine atoms in the imidazole-containing compound, the ester groups in the fatty acid ester, and the ether bonds contained in product a of the aromatic amine compound can break the original dense and strong hydrogen bond network structure of the epoxy resin through weak hydrogen bonding and competitive binding. At the same time, the flexible alkane long chains in the fatty acid ester insert into the epoxy resin molecular chains, playing an internal lubricating role. The imidazole-containing compound, fatty acid ester, and aromatic amine compound can synergistically reduce the coating's reactivity. The melting and softening temperature of the material system allows epoxy resin coatings to be roller-coated at a relatively low temperature (150-160℃), thereby reducing the processing temperature of the coating on the inner wall of the plastic-coated composite steel pipe and improving the uniformity and stability of the coating. The tertiary amine group containing imidazole compounds can also catalyze the active amino group of aromatic amine compounds to cure epoxy resin during the high-temperature curing stage, synergistically lowering the curing temperature and accelerating the curing speed with imidazole, thus improving production and processing efficiency, allowing the coating to be cured quickly at 160-165℃. The trifluoromethyl group and long alkane chain in the imidazole compound in the low-temperature curing agent used in this invention, due to their good hydrophobicity, can not only reduce the viscosity of the system during melting, but also work with raw materials such as precipitated barium sulfate and mica powder to enable the epoxy resin coating to exert its good anti-corrosion ability.

[0027] The anti-corrosion coating for plastic-coated composite steel pipes prepared by this invention has a simple preparation method, greatly reduces energy consumption, and is suitable for industrial production. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 An imidazole-containing compound, the preparation method of which includes the following steps: Step (1): Mix imidazole, DMF, and epichlorohydrin, stir at room temperature for 5 min, add sodium hydroxide solution, continue stirring at room temperature for 2 h, heat to 40℃, add sodium hydroxide solution again, stir at 40℃ for 1.5 h, cool to room temperature, and rotary evaporate at 40℃ to obtain product 1; the ratio of imidazole, DMF, epichlorohydrin, and sodium hydroxide solution is 4 g: 20 mL: 5.5 g: 10 mL; the mass fraction of sodium hydroxide solution is 30%, and the sodium hydroxide solution is added in two parts, with the volume ratio of the first and second additions being 0.5:1.

[0030] Step (2): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, stir at room temperature for 10 min, adjust pH to 8 with 5% sodium bicarbonate solution, add sodium dithionite, heat to 35℃ and stir for 4 h, cool to room temperature, filter, extract the filtrate three times with 85 mL ethyl acetate at room temperature, combine the organic phases, dry with anhydrous sodium sulfate, filter, and rotary evaporate at 40℃ to obtain product 2; the ratio of 2-chloro-5-nitrotrifluorotoluene, methanol aqueous solution and sodium dithionite is 12 g: 50 mL: 14 g; the methanol aqueous solution is obtained by mixing methanol and water in a volume ratio of 7:3.

[0031] Step (3): Mix product 2 and DMF, stir at room temperature for 5 min, add product 1, continue stirring at room temperature for 20 min, heat to 50℃, stir and react for 5 h, cool to room temperature, rotary evaporate at 42℃, and dry at 80℃ for 8 h to obtain the imidazole-containing compound; the ratio of product 2, DMF and product 1 is 11 g: 60 mL: 16.5 g.

[0032] Example 2 An imidazole-containing compound, the preparation method of which includes the following steps: Step (1): Mix imidazole, DMF, and epichlorohydrin, stir at room temperature for 5 min, add sodium hydroxide solution, continue stirring at room temperature for 2 h, heat to 40℃, add sodium hydroxide solution again, stir at 40℃ for 1.5 h, cool to room temperature, and rotary evaporate at 40℃ to obtain product 1; the ratio of imidazole, DMF, epichlorohydrin, and sodium hydroxide solution is 4 g: 20 mL: 5.5 g: 10 mL; the mass fraction of sodium hydroxide solution is 32%, and the sodium hydroxide solution is added in two parts, with the volume ratio of the first and second additions being 0.5: 1.2.

[0033] Step (2): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, stir at room temperature for 13 min, adjust pH to 8.2 with 5% sodium bicarbonate solution, add sodium dithionite, heat to 40℃ and stir for 4.5 h, cool to room temperature, filter, extract the filtrate three times with 85 mL ethyl acetate at room temperature, combine the organic phases, dry with anhydrous sodium sulfate, filter, and rotary evaporate at 40℃ to obtain product 2; the ratio of 2-chloro-5-nitrotrifluorotoluene, methanol aqueous solution and sodium dithionite is 12.5 g: 55 mL: 15 g; the methanol aqueous solution is obtained by mixing methanol and water in a volume ratio of 7.5: 2.5.

[0034] Step (3): Mix product 2 and DMF, stir at room temperature for 8 min, add product 1, continue stirring at room temperature for 23 min, heat to 53℃, stir and react for 5.5 h, cool to room temperature, rotary evaporate at 42℃, and dry at 80℃ for 8 h to obtain the imidazole-containing compound; the ratio of product 2, DMF and product 1 is 11.5 g: 65 mL: 17.0 g.

[0035] Example 3 An imidazole-containing compound, the preparation method of which includes the following steps: Step (1): Mix imidazole, DMF, and epichlorohydrin, stir at room temperature for 10 min, add sodium hydroxide solution, continue stirring at room temperature for 3 h, heat to 45℃, add sodium hydroxide solution again, stir at 45℃ for 2 h, cool to room temperature, and rotary evaporate at 40℃ to obtain product 1; the ratio of imidazole, DMF, epichlorohydrin, and sodium hydroxide solution is 5 g: 25 mL: 6.0 g: 15 mL; the mass fraction of sodium hydroxide solution is 35%, and the sodium hydroxide solution is added in two parts, with the volume ratio of the first and second additions being 0.5: 1.5.

[0036] Step (2): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, stir at room temperature for 15 min, adjust pH to 8.5 with 5% sodium bicarbonate solution, add sodium dithionite, heat to 45℃ and stir for 5 h, cool to room temperature, filter, extract the filtrate three times with 85 mL ethyl acetate at room temperature, combine the organic phases, dry with anhydrous sodium sulfate, filter, and rotary evaporate at 40℃ to obtain product 2; the ratio of 2-chloro-5-nitrotrifluorotoluene, methanol aqueous solution and sodium dithionite is 13 g: 60 mL: 16 g; the methanol aqueous solution is obtained by mixing methanol and water in a volume ratio of 8:2.

[0037] Step (3): Mix product 2 and DMF, stir at room temperature for 10 min, add product 1, continue stirring at room temperature for 25 min, heat to 55℃, stir and react for 6 h, cool to room temperature, rotary evaporate at 42℃, and dry at 80℃ for 8 h to obtain the imidazole-containing compound; the ratio of product 2, DMF and product 1 is 12 g: 70 mL: 17.5 g.

[0038] Example 4 A corrosion-resistant coating for plastic-coated composite steel pipes comprises the following raw materials in parts by weight: 48 parts of E-12 epoxy resin (supplier: Qingdao Baichen New Material Technology Co., Ltd., specification 25kg), 12 parts of E-20 epoxy resin (supplier: Qingdao Baichen New Material Technology Co., Ltd., specification 25kg), 15 parts of low-temperature curing agent, 0.6 parts of leveling agent (supplier: Shanghai Ziyi Chemical Co., Ltd., model ZY-1099), 0.2 parts of defoamer (supplier: Beijing Zhubao New Technology Co., Ltd., model DZ-1130), 8 parts of precipitated barium sulfate (supplier: Shijiazhuang Xunhua Mineral Products Co., Ltd., specification 25kg), 2 parts of mica powder (supplier: Shijiazhuang Xunhua Mineral Products Co., Ltd., 325 mesh), and 0.2 parts of fumed silica (supplier: Hangzhou Jiuli Biomaterials Co., Ltd., model JL-SP15).

[0039] A method for preparing an anti-corrosion coating for plastic-coated composite steel pipes includes the following steps: E-12 epoxy resin, E-20 epoxy resin, leveling agent, defoamer, precipitated barium sulfate, mica powder, and fumed silica were mixed and stirred at 500 rpm at room temperature for 20 minutes. A low-temperature curing agent was added, and stirring was continued at 500 rpm at room temperature for 5 minutes. After melt extrusion, cooling, crushing, and sieving, an anti-corrosion coating for plastic-coated composite steel pipes was obtained. During the melt extrusion process, the temperature of zone one was 85℃, the temperature of zone two was 95℃, the die temperature was 90℃, the screw speed was 250 rpm, and the feeding speed was 80 rpm. An 80-mesh sieve was used for sieving.

[0040] The low-temperature curing agent was obtained by mixing aromatic amine compound, fatty acid ester and imidazole-containing compound obtained in Example 1 in a mass ratio of 10:2:4; the fatty acid ester was obtained by mixing pentaerythritol tetrastearate, tristearate glyceryl ester and hexadecyl hexadecanoate in a mass ratio of 2:1:1; the aromatic amine compound was obtained by mixing product a and diaminodiphenylmethane in a mass ratio of 1:2.

[0041] The preparation method of product a is as follows: 2-Methoxy-4-nitroaniline and an aqueous ethanol solution were mixed and stirred for 10 min. The pH was adjusted to 8.5 with a 5% sodium hydroxide solution. Sodium dithionite was added, and the mixture was heated to 45°C and stirred for 4 h. After cooling to room temperature, the mixture was filtered, and the filtrate was extracted four times with 75 mL of ethyl acetate. The filtrate was dried with anhydrous sodium sulfate, filtered, and rotary evaporated at 40°C to obtain product a. The ratio of 2-methoxy-4-nitroaniline, aqueous ethanol solution, and sodium dithionite was 9 g: 45 mL: 13 g. The aqueous ethanol solution was prepared by mixing anhydrous ethanol and water in a volume ratio of 6:4.

[0042] Example 5 A corrosion-resistant coating for plastic-coated composite steel pipes comprises the following raw materials in parts by weight: 50 parts of E-12 epoxy resin (supplier: Qingdao Baichen New Material Technology Co., Ltd., specification 25kg), 14 parts of E-20 epoxy resin (supplier: Qingdao Baichen New Material Technology Co., Ltd., specification 25kg), 16 parts of low-temperature curing agent, 0.8 parts of leveling agent (supplier: Shanghai Ziyi Chemical Co., Ltd., model ZY-1099), 0.3 parts of defoamer (supplier: Beijing Zhubao New Technology Co., Ltd., model DZ-1130), 9 parts of precipitated barium sulfate (supplier: Shijiazhuang Xunhua Mineral Products Co., Ltd., specification 25kg), 3 parts of mica powder (supplier: Shijiazhuang Xunhua Mineral Products Co., Ltd., 325 mesh), and 0.3 parts of fumed silica (supplier: Hangzhou Jiuli Biomaterials Co., Ltd., model JL-SP15).

[0043] A method for preparing an anti-corrosion coating for plastic-coated composite steel pipes includes the following steps: E-12 epoxy resin, E-20 epoxy resin, leveling agent, defoamer, precipitated barium sulfate, mica powder, and fumed silica were mixed and stirred at room temperature for 25 minutes at 550 rpm. A low-temperature curing agent was added, and stirring was continued at room temperature for 8 minutes at 550 rpm. After melt extrusion, cooling, crushing, and sieving, an anti-corrosion coating for plastic-coated composite steel pipes was obtained. During the melt extrusion process, the temperature of zone one was 90℃, the temperature of zone two was 100℃, the die temperature was 95℃, the screw speed was 300 rpm, and the feeding speed was 100 rpm. A 90-mesh sieve was used for sieving.

[0044] The low-temperature curing agent was obtained by mixing aromatic amine compound, fatty acid ester and imidazole-containing compound obtained in Example 2 in a mass ratio of 11:2.3:5; the fatty acid ester was obtained by mixing pentaerythritol tetrastearate, tristearate, and hexadecyl palmitate in a mass ratio of 2.3:1.3:1.5; the aromatic amine compound was obtained by mixing product a and diaminodiphenylmethane in a mass ratio of 1.3:2.

[0045] The preparation method of product a is as follows: 2-Methoxy-4-nitroaniline and an aqueous ethanol solution were mixed and stirred for 13 min. The pH was adjusted to 8.8 with a 5% sodium hydroxide solution. Sodium dithionite was added, and the mixture was heated to 48°C and stirred for 4.5 h. After cooling to room temperature, the mixture was filtered, and the filtrate was extracted four times with 75 mL of ethyl acetate. The filtrate was dried with anhydrous sodium sulfate, filtered, and rotary evaporated at 40°C to obtain product a. The ratio of 2-methoxy-4-nitroaniline, aqueous ethanol solution, and sodium dithionite was 9.5 g: 47 mL: 13.5 g. The aqueous ethanol solution was prepared by mixing anhydrous ethanol and water in a volume ratio of 7:3.

[0046] Example 6 A corrosion-resistant coating for plastic-coated composite steel pipes comprises the following raw materials in parts by weight: 52 parts of E-12 epoxy resin (supplier: Qingdao Baichen New Material Technology Co., Ltd., specification 25kg), 16 parts of E-20 epoxy resin (supplier: Qingdao Baichen New Material Technology Co., Ltd., specification 25kg), 17 parts of low-temperature curing agent, 1.0 part of leveling agent (supplier: Shanghai Ziyi Chemical Co., Ltd., model ZY-1099), 0.4 parts of defoamer (supplier: Beijing Zhubao New Technology Co., Ltd., model DZ-1130), 10 parts of precipitated barium sulfate (supplier: Shijiazhuang Xunhua Mineral Products Co., Ltd., specification 25kg), 4 parts of mica powder (supplier: Shijiazhuang Xunhua Mineral Products Co., Ltd., 325 mesh), and 0.4 parts of fumed silica (supplier: Hangzhou Jiuli Biomaterials Co., Ltd., model JL-SP15).

[0047] A method for preparing an anti-corrosion coating for plastic-coated composite steel pipes includes the following steps: E-12 epoxy resin, E-20 epoxy resin, leveling agent, defoamer, precipitated barium sulfate, mica powder, and fumed silica were mixed and stirred at room temperature for 30 minutes at 600 rpm. A low-temperature curing agent was added, and stirring was continued at room temperature for 10 minutes at 600 rpm. After melt extrusion, cooling, crushing, and sieving, an anti-corrosion coating for plastic-coated composite steel pipes was obtained. During the melt extrusion process, the temperature of zone 1 was 95℃, the temperature of zone 2 was 105℃, the die temperature was 100℃, the screw speed was 350 rpm, and the feeding speed was 120 rpm. A 100-mesh sieve was used for sieving.

[0048] The low-temperature curing agent was obtained by mixing aromatic amine compound, fatty acid ester and imidazole-containing compound obtained in Example 3 in a mass ratio of 12:2.5:6; the fatty acid ester was obtained by mixing pentaerythritol tetrastearate, tristearate glyceryl ester and hexadecyl hexadecanoate in a mass ratio of 2.5:1.5:2; the aromatic amine compound was obtained by mixing product a and diaminodiphenylmethane in a mass ratio of 1.5:2.

[0049] The preparation method of product a is as follows: 2-Methoxy-4-nitroaniline and an aqueous ethanol solution were mixed and stirred for 15 min. The pH was adjusted to 9 with a 5% sodium hydroxide solution. Sodium dithionite was added, and the mixture was heated to 50°C and stirred for 5 h. After cooling to room temperature, the mixture was filtered, and the filtrate was extracted four times with 75 mL of ethyl acetate. The filtrate was dried with anhydrous sodium sulfate, filtered, and rotary evaporated at 40°C to obtain product a. The ratio of 2-methoxy-4-nitroaniline, aqueous ethanol solution, and sodium dithionite was 10 g: 50 mL: 14 g. The aqueous ethanol solution was prepared by mixing anhydrous ethanol and water in a volume ratio of 8:2.

[0050] Comparative Example 1 Compared with Example 6, the imidazole-containing compound was replaced with imidazole-containing compound-1, and the rest was exactly the same as in Example 6, to obtain an anti-corrosion coating for plastic-coated composite steel pipes; The preparation method of imidazole compound-1 includes the following steps: Step (1): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, stir at room temperature for 15 min, adjust pH to 8.5 with 5% sodium bicarbonate solution, add sodium dithionite, heat to 45℃ and stir for 5 h, cool to room temperature, filter, extract the filtrate three times with 85 mL ethyl acetate at room temperature, combine the organic phases, dry with anhydrous sodium sulfate, filter, and rotary evaporate at 40℃ to obtain product 2; the ratio of 2-chloro-5-nitrotrifluorotoluene, methanol aqueous solution and sodium dithionite is 13 g: 60 mL: 16 g; the methanol aqueous solution is obtained by mixing methanol and water in a volume ratio of 8:2.

[0051] Step (2): Mix product 2, DMF, and epichlorohydrin, stir at room temperature for 10 min, add sodium hydroxide solution, continue stirring at room temperature for 3 h, heat to 45℃, add sodium hydroxide solution again, stir at 45℃ for 2 h, cool to room temperature, and rotary evaporate at 40℃ to obtain product 1-1; the ratio of product 2, DMF, epichlorohydrin, and sodium hydroxide solution is 5 g: 25 mL: 6.0 g: 15 mL; the mass fraction of sodium hydroxide solution is 35%, and the sodium hydroxide solution is added in two parts, with the volume ratio of the first and second additions being 0.5: 1.5.

[0052] Step (3): Mix imidazole and DMF, stir at room temperature for 10 min, add product 1-1, continue stirring at room temperature for 25 min, heat to 55℃, stir and react for 6 h, cool to room temperature, rotary evaporate at 42℃, and dry at 80℃ for 8 h to obtain imidazole-containing compound-1. The ratio of imidazole, DMF and product 1-1 is 12 g: 70 mL: 17.5 g.

[0053] Comparative Example 2 Compared with Example 6, the 2-chloro-5-nitrotrifluorotoluene in the preparation process of the imidazole compound was replaced with o-nitrotoluene, and the rest was exactly the same as in Example 6, to obtain the anti-corrosion coating for plastic-coated composite steel pipes.

[0054] Comparative Example 3 Compared with Example 6, the imidazole-containing compound was replaced with Product 1, and everything else was exactly the same as in Example 6, to obtain an anti-corrosion coating for plastic-coated composite steel pipes.

[0055] Comparative Example 4 Compared with Example 6, the low-temperature curing agent was replaced with low-temperature curing agent-1, which was a mixture of aromatic amine compound and fatty acid ester in a mass ratio of 15:5.5. The rest was exactly the same as in Example 6, and a corrosion-resistant coating for plastic-coated composite steel pipe was prepared.

[0056] Comparative Example 5 Compared with Example 6, the low-temperature curing agent was replaced with low-temperature curing agent-2, which was a mixture of aromatic amine compound and imidazole compound in a mass ratio of 13:7.5. The rest was exactly the same as in Example 6, and a corrosion-resistant coating for plastic-coated composite steel pipe was prepared.

[0057] Comparative Example 6 Compared with Example 6, the low-temperature curing agent was replaced with low-temperature curing agent-3, which was a mixture of fatty acid ester and imidazole compound in a mass ratio of 8.5:12. The rest was exactly the same as in Example 6, and a corrosion-resistant coating for plastic-coated composite steel pipe was prepared.

[0058] The anti-corrosion coatings for plastic-coated composite steel pipes prepared in Examples 4-6 and Comparative Examples 1-6 of the present invention were further tested below, and the test results are shown below.

[0059] Storage stability: The paint was sealed and stored at 25°C and 50% humidity for 6 months, and the presence of lumps or clusters was observed.

[0060] Curing time: The coating was applied to the inner wall of the plastic-coated composite steel pipe at 150℃ (preheated to 80℃ in advance) and then cured at 165℃. The coating thickness was controlled to be 300μm, and the time for complete curing was measured.

[0061] Corrosion resistance: The coating was prepared according to the curing time method mentioned above. The coating was then immersed in a 25°C salt water solution (5% sodium chloride solution by mass) for 72 hours. The coating surface was then observed for blistering, cracking, and rust.

[0062] The results are recorded in Table 1; Table 1: Test Results According to the data in Table 1, the anti-corrosion coatings for plastic-coated composite steel pipes prepared in Examples 4-6 of this invention have good storage stability, curing speed and anti-corrosion performance.

[0063] Comparing Example 6 with Comparative Example 1, it can be seen that replacing the imidazole-containing compound with imidazole-containing compound-1 shows that the room temperature reactivity of imidazole in the imidazole-containing compound used in this invention is effectively suppressed, which can avoid the occurrence of clumping and agglomeration during storage, and can also play a catalytic curing role during high temperature curing, thereby helping to improve the anti-corrosion performance of the coating.

[0064] Comparing Example 6 with Comparative Example 2, it can be seen that replacing 2-chloro-5-nitrotrifluorotoluene with o-nitrotoluene in the preparation process of imidazole-containing compounds shows that the room temperature reactivity of imidazole in the imidazole-containing compounds prepared by using 2-chloro-5-nitrotrifluorotoluene in this invention is effectively suppressed, which can better avoid the occurrence of clumping and agglomeration during storage, and can also play a better catalytic curing role in the high temperature curing process, thereby helping to improve the anti-corrosion performance of the coating.

[0065] Comparing Example 6 with Comparative Example 3, it can be seen that replacing the imidazole-containing compound with Product 1 shows that the room temperature reactivity of imidazole in the imidazole-containing compound used in this invention is effectively suppressed, which can avoid the occurrence of clumping and agglomeration during storage, and can also play a catalytic curing role during high-temperature curing, thereby helping to improve the anti-corrosion performance of the coating.

[0066] Comparing Example 6 with Comparative Example 4, it can be seen that replacing the low-temperature curing agent with low-temperature curing agent-1, which is a mixture of aromatic amine compound and fatty acid ester in a mass ratio of 15:5.5, indicates that the low-temperature curing agent obtained by mixing aromatic amine compound, fatty acid ester and imidazole compound in a specific ratio in this invention can better improve the storage stability of the coating, accelerate the curing speed of the coating, and improve the anti-corrosion performance of the coating.

[0067] Comparing Example 6 with Comparative Example 5, it can be seen that replacing the low-temperature curing agent with low-temperature curing agent-2, which is a mixture of aromatic amine compound and imidazole compound in a mass ratio of 13:7.5, indicates that the low-temperature curing agent obtained by mixing aromatic amine compound, fatty acid ester and imidazole compound in a specific ratio in this invention can accelerate the curing speed of the coating and improve the anti-corrosion performance of the coating.

[0068] Comparing Example 6 with Comparative Example 6, it can be seen that replacing the low-temperature curing agent with low-temperature curing agent-3, which is a mixture of fatty acid ester and imidazole-containing compound in a mass ratio of 8.5:12, indicates that the low-temperature curing agent obtained by mixing aromatic amine compound, fatty acid ester and imidazole-containing compound in a specific ratio in this invention is more conducive to accelerating the curing speed of the coating and improving the anti-corrosion performance of the coating.

[0069] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A corrosion-resistant coating for plastic-coated composite steel pipes, characterized in that: The raw materials include the following parts by weight: 48-52 parts of E-12 epoxy resin, 12-16 parts of E-20 epoxy resin, 15-17 parts of low-temperature curing agent, 0.6-1.0 parts of leveling agent, 0.2-0.4 parts of defoamer, 8-10 parts of precipitated barium sulfate, 2-4 parts of mica powder, and 0.2-0.4 parts of fumed silica; The low-temperature curing agent is obtained by mixing aromatic amine compounds, fatty acid esters and imidazole-containing compounds in a mass ratio of (10-12):(2-2.5):(4-6).

2. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 1, characterized in that: The preparation method of the imidazole-containing compound includes the following steps: Step (1): After mixing and stirring imidazole, DMF and epichlorohydrin, add sodium hydroxide solution, continue stirring, heat, add sodium hydroxide solution again, stir, cool, and rotary evaporate to obtain product 1; Step (2): Mix 2-chloro-5-nitrotrifluorotoluene and methanol aqueous solution, adjust pH, add sodium dithionite, heat and stir, cool, filter, extract filtrate, combine organic phases, dry, filter, and rotary evaporate to obtain product 2; Step (3): After mixing and stirring product 2 and DMF, add product 1, continue stirring, heat and stir to react, cool, rotary evaporate, and dry to obtain the imidazole-containing compound.

3. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 2, characterized in that: In step (1), the ratio of the amount of imidazole, DMF, epichlorohydrin and sodium hydroxide solution is (4-5) g: (20-25) mL: (5.5-6.0) g: (10-15) mL.

4. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 2, characterized in that: In step (2), the ratio of the amounts of 2-chloro-5-nitrotrifluorotoluene, methanol aqueous solution, and sodium dithionite is (12-13) g: (50-60) mL: (14-16) g.

5. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 2, characterized in that: In step (3), the ratio of the amount of product 2, DMF and product 1 is (11-12) g: (60-70) mL: (16.5-17.5) g.

6. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 1, characterized in that: The fatty acid ester is obtained by mixing pentaerythritol tetrastearate, tristearate glyceryl ester, and hexadecanoate in a mass ratio of (2-2.5):(1-1.5):(1-2).

7. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 1, characterized in that: The aromatic amine compound is obtained by mixing product a with diaminodiphenylmethane in a mass ratio of (1-1.5):

2.

8. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 7, characterized in that: The preparation method of product a is as follows: After mixing and stirring 2-methoxy-4-nitroaniline and an aqueous ethanol solution, the pH was adjusted, sodium dithionite was added, the mixture was heated and stirred, cooled, filtered, the filtrate was extracted, dried, filtered, and rotary evaporated to obtain product a.

9. The anti-corrosion coating for plastic-coated composite steel pipes according to claim 8, characterized in that: The ratio of the amounts of 2-methoxy-4-nitroaniline, ethanol aqueous solution, and sodium dithionite is (9-10) g: (45-50) mL: (13-14) g.

10. A method for preparing an anti-corrosion coating for plastic-coated composite steel pipes according to any one of claims 1-9, characterized in that: Includes the following steps: E-12 epoxy resin, E-20 epoxy resin, leveling agent, defoamer, precipitated barium sulfate, mica powder, and fumed silica are mixed and stirred for 20-30 minutes. A low-temperature curing agent is added, and stirring is continued for 5-10 minutes. After melt extrusion, cooling, crushing, and sieving, an anti-corrosion coating for plastic-coated composite steel pipes is obtained.

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