Pretreatment layer for improving binding force of matrix and heat-resistant resin, preparation method and application

Abstract

The invention discloses a preparation method of a pretreatment layer for improving binding force of a matrix and heat-resistant resin, which comprises the following steps: (1) dissolving a polymer rich in hydroxyl and amino in an acetic acid aqueous solution to obtain a polymer solution, adding the polymer solution into ethanol, and adding a nitrate solution into the ethanol to obtain a uniform electro-deposition solution; and (2) a metal matrix is placed in the electro-deposition solution obtained in the step (1) for electro-deposition, the metal matrix obtained after electro-deposition is soaked in an organic acid solution, and then a pretreatment layer is obtained after drying. The prepared pretreatment layer can remarkably improve the binding force of the heat-resistant resin and the metal matrix, so that the heat-resistant resin is firmly combined on the surface of the metal matrix, the thermal stress of the prepared protective coating in the high-temperature curing or service environment is remarkably improved, and the pretreatment layer is particularly suitable for preparing the protective coating resistant to the high-temperature and high-pressure water environment.

Description

Technical Field

[0001] This invention relates to the field of metal pretreatment technology, specifically to a pretreatment layer and its preparation method for improving the bonding strength between a matrix and a heat-resistant resin. Background Technology

[0002] In clean and green energy sources such as geothermal water and nuclear power plants, the structural metals operate under harsh temperature and pressure conditions. To date, the main components of hydrothermal resistant coatings developed by researchers are still heat-resistant resins. However, these resins are difficult to adhere to the surface of metal substrates, and the substrate is highly susceptible to corrosion after damage in hydrothermal environments.

[0003] Metal pretreatment layers can effectively solve these problems. Traditional pretreatment techniques include chromate passivation and inorganic phosphate passivation. Hexavalent chromium electroplating typically uses chromate passivation solutions, resulting in coatings with high oxidation resistance, corrosion resistance, and good self-healing capabilities. However, hexavalent chromium is highly carcinogenic and poses serious harm to human health and the environment. With increasing environmental awareness, the use of hexavalent chromium has been restricted, and manufacturers are increasingly adopting more environmentally friendly and energy-efficient production methods. Researchers have also developed low-chromium passivation solutions, using trivalent chromium, which has relatively lower toxicity and wastewater pollution, to replace hexavalent chromium. This mitigates the harmful effects to some extent and barely meets current environmental regulations, but it still falls short of increasingly stringent environmental standards. Furthermore, trivalent chromium oxidizes to hexavalent chromium under high temperatures and in the presence of oxidants, posing significant potential risks during passivation and metal use, thus failing to fundamentally solve the problem.

[0004] In China's metal pretreatment industry, phosphating remains the dominant method. While traditional phosphating technology is mature, its environmental pollution is increasing. The extensive use of phosphating agents leads to severe phosphorus-rich pollution, causing rampant aquatic plant growth and the proliferation of bacteria in lakes. Phosphorus pollution is also a killer of aquatic life; the large-scale proliferation of bacteria competes for oxygen in lakes, causing the death of oxygen-dependent organisms. Phosphating agents also contain large amounts of heavy metals and potent carcinogens (such as chromium, nickel, cobalt, and sodium nitrite) that are strictly controlled by the state. The use of phosphating baths also generates a large amount of phosphating slag byproducts. The treatment of phosphating slag, which is strictly controlled by environmental protection departments, is difficult and costly, and some regional governments have imposed limits on the total amount of phosphating slag that can be treated.

[0005] Green pretreatment layer technologies such as silanization and in-situ LDH pretreatment layers have poor adhesion to heat-resistant resins. However, it is difficult to achieve a silanization agent with a solvent that is entirely water; the mixture of organic solvents makes it difficult to meet environmental protection standards. Furthermore, silane solutions are not easily stable in the long term due to their own hydrolysis and condensation, and are prone to failure, thus increasing costs and causing a certain degree of environmental pollution.

[0006] Chinese patent document CN111235576A discloses a method for constructing a micro-nano porous organic acid pretreatment layer on a metal surface. The pretreatment reagent is prepared by chemical grafting an organic acid with a hydroxyl-rich polymer. The metal substrate is then immersed in the pretreatment reagent for a period of time, followed by drying and curing, resulting in an organic acid pretreatment layer with excellent bonding and a micro-nano porous structure. However, the composite pretreatment layer prepared using hydroxyl-rich polyvinyl alcohol is prone to carbonization or degradation in high-temperature water environments.

[0007] Therefore, it is very important to develop a pretreatment layer that has good bonding with heat-resistant resin and can withstand long-term exposure to high-temperature and high-pressure water environments. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing a pretreatment layer that enhances the bonding strength between the substrate and the heat-resistant resin. The resulting pretreatment layer significantly improves the bonding strength between the heat-resistant resin and the metal substrate, ensuring that the heat-resistant resin is firmly bonded to the surface of the metal substrate. This significantly improves the thermal stress resistance of the prepared protective coating under high-temperature curing or service environments, making it particularly suitable for preparing protective coatings resistant to high-temperature and high-pressure water environments.

[0009] A method for preparing a pretreatment layer to improve the adhesion between a matrix and a heat-resistant resin includes the following steps: (1) Dissolve the polymer rich in hydroxyl and amino groups in an aqueous acetic acid solution to obtain a polymer solution. Add the polymer solution to ethanol and add nitrate solution to obtain a uniform electrodeposition solution. (2) The metal substrate is placed in the electrodeposition solution obtained in step (1) for electrodeposition. The electrodeposited metal substrate is then immersed in an organic acid solution and dried to obtain a pretreatment layer that improves the bonding strength between the substrate and the heat-resistant resin.

[0010] In this invention, electrodeposition technology is used to co-deposit a polymer rich in hydroxyl and amino groups with a nitrate electrolyte on the surface of a metal substrate, forming an organic polymer film with a three-dimensional network structure and rich in a large number of active functional groups (-NH2, -OH). The film is then immersed in an organic acid solution. On one hand, the organic acid solution protonates the amino groups in the organic polymer film, making them positively charged (-NH3). +On the other hand, the carboxyl groups of organic acids can form stronger coordination bonds or hydrogen bonds with organic polymer films and metal substrates, thereby enhancing the adhesion between the pretreated layer after organic acid treatment and the metal substrate.

[0011] Meanwhile, the pretreatment layer, with its micro-nano porous three-dimensional network structure, provides a huge specific surface area for subsequent resin penetration, achieving microscale physical-mechanical interlocking. The functional groups (-OH, -NH2, -COOH) on the surface of the pretreatment layer can undergo covalent bonding reactions with the active groups (such as thiol and hydroxyl groups) of the subsequent heat-resistant resin during curing, significantly improving the adhesion between the heat-resistant resin and the metal matrix. This ensures the heat-resistant resin is firmly bonded to the metal matrix surface, significantly enhancing the prepared protective coating's resistance to thermal stress under high-temperature curing or service environments, thus achieving extremely durable and strong adhesion.

[0012] Preferably, in step (1), the polymer rich in hydroxyl and amino groups is one or more of chitosan, carboxymethyl chitosan, and aminocellulose.

[0013] Preferably, in step (1), the concentration of the polymer solution rich in hydroxyl and amino groups is 0.01~0.05 g / mL.

[0014] Preferably, in step (1), the mass ratio of the polymer rich in hydroxyl and amino groups to nitrate in the electrodeposition solution is 3~6:15~18.

[0015] Preferably, in step (2), the metal matrix is ​​an alloy containing one or more of iron, aluminum, zinc, copper, and magnesium.

[0016] Preferably, in step (2), the electrodeposition conditions are a temperature of 25 °C, an applied cathode potential of -1.0 to -2.0 V, and an electrodeposition time of 1 to 15 min.

[0017] Preferably, in step (2), the organic acid is phytic acid, tannic acid, or hydroxyethylidene diphosphonic acid.

[0018] In this invention, the organic acids used are all polydentate ligands, whose molecular structures are rich in multiple polar functional groups (such as phosphate groups, catechol groups, and phosphonic acid groups) that can provide lone pair electrons. These functional groups can simultaneously react with metal ions (such as Fe). 2+ / 3+ Al 3+ Ca 2+The organic components coordinate with each other, forming multiple coordination bonds to construct stable five- or six-membered ring chelates, resulting in an insoluble, dense organometallic composite film with a binding force far stronger than physical adsorption. Simultaneously, the organic components on the film surface (such as the alkyl chains of phytic acid) exhibit good compatibility and reactivity with the subsequent heat-resistant resin, forming a strong bond through hydrogen bonding, covalent bonding, and other interactions, greatly enhancing the adhesion between the coating and the metal substrate.

[0019] In addition, functional groups that have not fully reacted after chelation (such as -OH, -PO(OH)) can serve as active sites to further react with functional groups (such as amino groups) in the heat-resistant resin, achieving chemical bonding rather than just physical adhesion. This makes the heat-resistant resin more resistant to high temperature and humid environments when bonded to the metal matrix.

[0020] More preferably, the polymer rich in hydroxyl and amino groups is chitosan, and the organic acid is phytic acid.

[0021] In this invention, in step (2), when the polymer film is chitosan and the organic acid solution is phytic acid, a porous nano-network structure and nanoparticles are generated after reacting at 25 °C for 60 s. The porous structure can form a mechanical hook-lock with the resin to enhance the bonding force with the coating. The mechanism is shown in the following formula: Preferably, in step (2), the drying temperature is 40~60 ℃ and the time is 120~180 min.

[0022] The present invention also provides a pretreatment layer for improving the bonding strength between the matrix and the heat-resistant resin prepared by the above preparation method.

[0023] The present invention also provides the application of the above-mentioned pretreatment layer for improving the bonding strength between the matrix and the heat-resistant resin in the preparation of a protective coating resistant to high temperature and high pressure water environment.

[0024] Preferably, the method for preparing the protective coating resistant to high temperature and high pressure water environment is as follows: the above-mentioned pretreatment layer is immersed in a corrosion inhibitor solution, dried to obtain a pretreatment layer loaded with corrosion inhibitor, and then a heat-resistant resin is electrostatically sprayed onto the pretreatment layer loaded with corrosion inhibitor, and cured at high temperature to obtain a protective coating resistant to high temperature and high pressure water environment.

[0025] Preferably, the corrosion inhibitor is sodium silicate and / or sodium molybdate.

[0026] In this invention, the adsorption mechanism of the corrosion inhibitor in the pretreatment layer is shown in the following formula: Where R and R' represent connected chitosan monomer structures.

[0027] Preferably, the drying conditions are 20~80 ℃ and 120~180 min.

[0028] Preferably, the heat-resistant resin is at least one of polyphenylene sulfide, polyetheretherketone, and polytetrafluoroethylene.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with traditional metal surface coating systems, the pretreatment layer with micron-level rough structure prepared by this invention has excellent protective performance, strong environmental protection, achieves organic solvent-free processing, has good bonding force with heat-resistant resin, and has excellent hydrolysis resistance in high temperature and high pressure water environment. Attached Figure Description

[0030] Figure 1 This is a transmission electron microscope (TEM) image of the pretreatment layer prepared in Example 1 that improves the bonding strength between the matrix and the heat-resistant resin.

[0031] Figure 2 This is a transmission electron microscope (TEM) image of a chitosan pretreatment layer used alone.

[0032] Figure 3 Images of the MS / PPS coating, MS / CS / PPS coating, and MS / CS-PA / PPS coating prepared in Example 1 after immersion in 3.5% NaCl solution for 15 days are shown, where a~c are images of the MS / PPS coating, MS / CS / PPS coating, and MS / CS-PA / PPS coating, respectively. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the following embodiments.

[0034] All raw materials used in this invention are commercially available.

[0035] Example 1 (1) At room temperature, dissolve 0.5 g chitosan (CS) in 50 mL of water, add 500 μL of acetic acid, stir for 30 min and set aside. Take 20 mL of chitosan solution and add it to 50 mL of ethanol, then add 50 mL of sodium nitrate aqueous solution (0.2 M), stir at room temperature for 2 h to obtain a homogeneous electrodeposition solution for later use.

[0036] (2) Add the uniform electrodeposition solution obtained in step (1) to the three-electrode tank. Use the polished and degreased Q235B low-carbon steel substrate as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. Control the potential at -1.2V, the deposition time at 300 s, and the deposition temperature at 30 ℃. After deposition, rinse with deionized water and dry with nitrogen. Immerse the electrodeposited Q235B low-carbon steel substrate in 0.01 M phytic acid (PA) solution. After 45 s, rinse with deionized water and dry with nitrogen. Dry at 60 ℃ for 120 min to obtain a pretreatment layer that improves the bonding strength between the substrate and the heat-resistant resin. Its transmission electron microscopy image is shown below. Figure 1 As shown, it exhibits a distinctly rough and porous state.

[0037] Figure 2 To directly use chitosan solution of the same concentration and under the same conditions, the morphology of carbon steel pretreated with phytic acid was compared. It can be seen that the surface is relatively... Figure 1 Compared to other areas, it is relatively flat.

[0038] Sample Analysis: Adhesion and Corrosion Resistance Tests of Polyphenylene Sulfide under Different Treatment Groups The pretreated layer obtained above was immersed in a corrosion inhibitor solution (0.1 M sodium molybdate aqueous solution) and dried at 80 °C for 120 min to obtain a pretreated layer loaded with corrosion inhibitor. Subsequently, polyphenylene sulfide was electrostatically sprayed onto the pretreated layer loaded with corrosion inhibitor, and cured at 320 °C for 60 min to obtain a protective coating resistant to high-temperature and high-pressure water environments, namely MS / CS-PA / PPS. Organic acids alone can easily corrode metals, so this is not considered here.

[0039] In the above pretreatment layer preparation process, only the chitosan-treated pretreatment layer and the direct Q235B low-carbon steel substrate were added. Protective coatings, MS / CS / PPS and MS / PPS, were prepared according to the above method. The adhesion test results for paints and varnishes, referring to GB / T9286—2021 cross-cut adhesion test, are shown in Table 1.

[0040] Table 1: Adhesion test results of polyphenylene sulfide for different treatment groups As shown in Table 1, the adhesion rating from 0 to 2 represents a gradual decrease in adhesion. MS / CS-PA / PPS exhibits excellent adhesion, while MS / PPS shows poor adhesion.

[0041] Figure 3Images of the MS / PPS coating, MS / CS / PPS coating, and MS / CS-PA / PPS coating prepared in Example 1 after immersion in 3.5% NaCl solution for 15 days are shown, where a~c are images corresponding to the MS / PPS coating, MS / CS / PPS coating, and MS / CS-PA / PPS coating, respectively. Figure 3 As shown, the pretreatment layer with both chitosan and phytic acid added, after the preparation of the polyphenylene sulfide coating, can remain uncorroded for 15 days in a 3.5% NaCl solution at 120 °C and 0.15 mPa. Compared with the polyphenylene sulfide coating without any treatment and with only chitosan added, the pretreatment layer of Example 1 exhibits excellent corrosion resistance under high temperature and high pressure hydrothermal conditions.

[0042] Example 2 (1) At room temperature, dissolve 1 g of chitosan (CS) in 50 mL of water, add 500 μL of acetic acid, stir for 30 min and set aside. Take 15 mL of chitosan solution and add it to 50 mL of ethanol, then add 50 mL of sodium nitrate aqueous solution (0.2 M), stir at room temperature for 2 h to obtain a homogeneous electrodeposition solution for later use.

[0043] (2) Add the uniform electrodeposition solution obtained in step (1) to the three-electrode tank. Use the polished and degreased Q235B low carbon steel substrate as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. Control the potential at -1.1V, the deposition time at 200 s, and the deposition temperature at 30 ℃. After deposition, rinse with deionized water and dry with nitrogen. Immerse the electrodeposited Q235B low carbon steel substrate in 0.01 M phytic acid (PA) solution. After 30 s, rinse with deionized water and dry with nitrogen. Dry at 60 ℃ for 120 min to obtain a pretreatment layer that improves the bonding strength between the substrate and the heat-resistant resin.

[0044] Sample analysis: Adhesion and corrosion resistance tests were performed according to the method in Example 1. Table 2: Adhesion test results of polyphenylene sulfide for different treatment groups As shown in Table 2, the adhesion rating from small to large indicates that the adhesion gradually deteriorates. MS / CS-PA / PPS exhibits excellent adhesion, while MS / PPS exhibits poor adhesion.

[0045] After being coated with polyphenylene sulfide, the resulting MS / CS-PA / PPS coating can remain uncorroded for 12 days in a 3.5% NaCl solution at 120 °C and 0.15 mPa.

[0046] Example 3 (1) At room temperature, dissolve 0.5 g of carboxymethyl chitosan (CMCS) in 50 mL of water, add 200 μL of acetic acid, stir for 30 min and set aside. Take 15 mL of carboxymethyl chitosan solution and add it to 50 mL of ethanol, then add 50 mL of sodium nitrate aqueous solution (0.2 M), stir at room temperature for 2 h to obtain a homogeneous electrodeposition solution for later use.

[0047] (2) Add the uniform electrodeposition solution obtained in step (1) to the three-electrode tank. Use the polished and degreased 316L stainless steel substrate as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. Control the potential at -1.2 V, the deposition time at 300 s, and the deposition temperature at 30 ℃. After deposition, rinse with deionized water and dry with nitrogen. Immerse the electrodeposited 316L stainless steel substrate in 0.01 M phytic acid (PA) solution. After 60 s, rinse with deionized water and dry with nitrogen. Dry at 60 ℃ for 120 min to obtain a pretreatment layer that improves the bonding strength between the substrate and the heat-resistant resin.

[0048] Sample analysis: Adhesion and corrosion resistance tests were performed according to the method in Example 1. Table 3: Adhesion test results of polyphenylene sulfide for different treatment groups As shown in Table 3, the adhesion rating from small to large represents a gradual decrease in adhesion. Among them, 316L / CMCS-PA / PPS exhibits excellent adhesion, while 316L / PPS exhibits poor adhesion.

[0049] After being coated with polyphenylene sulfide, the resulting 316L / CMCS-PA / PPS coating can remain uncorroded for 12 days in a 3.5% NaCl solution at 120 °C and 0.15 mPa.

[0050] Example 4 (1) At room temperature, dissolve 0.5 g of carboxymethyl chitosan in 50 mL of water, add 200 μL of acetic acid, stir for 30 min and set aside. Take 15 mL of carboxymethyl chitosan solution and add it to 50 mL of ethanol, then add 50 mL of sodium nitrate aqueous solution (0.2 M), stir at room temperature for 2 h to obtain a homogeneous electrodeposition solution for later use.

[0051] (2) Add the uniform electrodeposition solution obtained in step (1) to the three-electrode tank. Use the polished and degreased 316L stainless steel substrate as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. Control the potential at -1.2 V, the deposition time at 300 s, and the deposition temperature at 30 ℃. After deposition, rinse with deionized water and dry with nitrogen. Immerse the electrodeposited 316L stainless steel substrate in 0.01 M tannic acid (TA) solution. After 60 s, rinse with deionized water and dry with nitrogen. Dry at 60 ℃ for 120 min to obtain a pretreatment layer that improves the bonding strength between the substrate and the heat-resistant resin.

[0052] Sample analysis: Adhesion and corrosion resistance tests were performed according to the method in Example 1. Table 4: Adhesion test results of polyphenylene sulfide for different treatment groups As shown in Table 4, the adhesion rating from small to large represents a gradual decrease in adhesion. Among them, 316L / CS-TA / PPS exhibits excellent adhesion, while 316L / PPS exhibits poor adhesion.

[0053] After being coated with polyphenylene sulfide, the resulting 316L / CS-TA / PPS coating can remain uncorroded for 12 days in a 3.5% NaCl solution at 120 °C and 0.15 mPa.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a pretreatment layer to improve the bonding strength between a matrix and a heat-resistant resin, characterized in that, Includes the following steps: (1) Dissolve the polymer rich in hydroxyl and amino groups in an aqueous acetic acid solution to obtain a polymer solution. Add the polymer solution to ethanol and add nitrate solution to obtain a uniform electrodeposition solution. (2) The metal substrate is placed in the electrodeposition solution obtained in step (1) for electrodeposition. The electrodeposited metal substrate is then immersed in an organic acid solution and dried to obtain a pretreatment layer that improves the bonding strength between the substrate and the heat-resistant resin.

2. The method for preparing the pretreatment layer to improve the bonding strength between the matrix and the heat-resistant resin according to claim 1, characterized in that, In step (1), the polymer rich in hydroxyl and amino groups is one or more of chitosan, carboxymethyl chitosan, and aminocellulose.

3. The method for preparing the pretreatment layer to improve the bonding strength between the matrix and the heat-resistant resin according to claim 1, characterized in that, In step (1), the concentration of the polymer solution rich in hydroxyl and amino groups is 0.01~0.05 g / mL.

4. The method for preparing the pretreatment layer for improving the bonding strength between the matrix and the heat-resistant resin according to claim 1, characterized in that, In step (1), the mass ratio of the polymer rich in hydroxyl and amino groups to nitrate in the electrodeposition solution is 3~6:15~18.

5. The method for preparing the pretreatment layer for improving the bonding strength between the matrix and the heat-resistant resin according to claim 1, characterized in that, In step (2), the electrodeposition conditions are a temperature of 25 °C, an applied cathode potential of -1.0 to -2.0 V, and an electrodeposition time of 1 to 15 min.

6. The method for preparing the pretreatment layer for improving the bonding strength between the matrix and the heat-resistant resin according to claim 1, characterized in that, In step (2), the organic acid is phytic acid, tannic acid, or hydroxyethylidene diphosphonic acid.

7. A pretreatment layer for improving the bonding strength between the matrix and the heat-resistant resin, prepared by any one of claims 1 to 6.

8. The application of the pretreatment layer according to claim 7, which improves the bonding strength between the substrate and the heat-resistant resin, in the preparation of a protective coating resistant to high temperature and high pressure water environments.

9. The application according to claim 8, characterized in that, The method for preparing the protective coating resistant to high temperature and high pressure water environment is as follows: the pretreatment layer described in claim 7 is immersed in a corrosion inhibitor solution, dried to obtain a pretreatment layer loaded with corrosion inhibitor, and then a heat-resistant resin is electrostatically sprayed onto the pretreatment layer loaded with corrosion inhibitor, and cured at high temperature to obtain a protective coating resistant to high temperature and high pressure water environment.

10. The application according to claim 9, characterized in that, The corrosion inhibitor is sodium silicate and / or sodium molybdate; The heat-resistant resin is at least one of polyphenylene sulfide, polyether ether ketone, and polytetrafluoroethylene.

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