Aliphatic epoxy resin composite coating and preparation method and application thereof

Abstract

This invention discloses an alicyclic epoxy resin composite coating for the protection of bronze artifacts and its preparation method. The coating is based on alicyclic epoxy resin, with 4-methylhexahydrophthalic anhydride as a curing agent, ZIF-8 as a curing accelerator, and polyethylene glycol as a removable modifier, prepared according to a specific ratio. ZIF-8 catalyzes the curing reaction through tertiary amine groups, reducing the activation energy from 130.7 kJ / mol to approximately 60 kJ / mol, achieving low-temperature, high-efficiency curing. After immersion in 3.5% NaCl solution for 30 days, the corrosion current density of the coating is only 8.3 × 10⁻⁶. ‑7 Acm ‑2 It has excellent protective performance. Polyethylene glycol gives the coating good affinity to ethanol, and it can be gently removed after swelling, meeting the requirements of reversible protection. Low-temperature curing gives the coating good visible light transmittance without changing the appearance of the cultural relics. The coating is easy to prepare, the raw materials are readily available, and the process is compatible with traditional methods. It is suitable for long-term reversible protection of metal cultural relics such as bronzes and has good promotion value.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and relates to materials for the protection of cultural relics, specifically to an alicyclic epoxy resin composite coating, its preparation method, and its application. Background Technology

[0002] Metal artifacts such as bronzes are susceptible to corrosion from moisture, oxygen, and chloride ions in the environment during long-term preservation, thus requiring the use of organic coatings for protection. Currently, acrylic resins (such as Paraaloid B72), commonly used in artifact preservation, offer good workability and reversibility (removable), but their long-term corrosion resistance is insufficient. Epoxy resins, especially bisphenol A type epoxy resins (such as E51), while possessing excellent protective properties, are difficult to remove and prone to yellowing under ultraviolet light, failing to meet the core principles of artifact preservation: "reversible treatment" and "preservation of original appearance." Alicyclic epoxy resins (such as ERL-4221) exhibit excellent weather resistance and anti-yellowing ability due to their saturated cyclic structure, but they suffer from three key drawbacks: 1) the alicyclic epoxy groups have weak electrophilicity, resulting in poor reactivity with acid anhydride curing agents and difficulty in curing; 2) the formed cross-linked network is dense and chemically inert, making it difficult to dissolve and remove with conventional solvents. Therefore, there is an urgent need to develop a modified alicyclic epoxy resin coating to overcome its above-mentioned shortcomings and ultimately achieve a comprehensive balance between corrosion resistance, removability and appearance transparency. Summary of the Invention

[0003] To address the shortcomings of the existing technologies, the present invention aims to provide an alicyclic epoxy resin composite coating, its preparation method, and its application. This coating can be cured efficiently, has high corrosion resistance, excellent removability, and high transparency, and its preparation process is simple and easy to promote.

[0004] This invention is achieved through the following technical solution: A method for preparing an alicyclic epoxy resin composite coating includes the following steps: S1. Mix and disperse 4-methylhexahydrophthalic anhydride with ZIF-8 powder to obtain mixture A; S2. Add the alicyclic epoxy resin monomer to mixture A and stir until the mixture is homogeneous to obtain mixture B; S3. Add polyethylene glycol to mixture B and stir until the mixture is homogeneous to obtain the Z / P-CEP curing system; S4. Mix the curing system obtained in step S3 with an organic solvent, stir until completely dissolved, prepare a coating solution, apply it to the substrate surface, and after curing, form an alicyclic epoxy resin composite coating. The mass ratio of the alicyclic epoxy resin monomer to 4-methylhexahydrophthalic anhydride is (0.65~0.70):(0.48~0.52). The amount of polyethylene glycol added accounts for 10-15 wt% of the total mass of the Z / P-CEP curing system; the amount of ZIF-8 added accounts for 0.2-0.5 wt% of the total mass of the Z / P-CEP curing system. The mass ratio of the Z / P-CEP curing system to the organic solvent is 1:(1.2~1.8).

[0005] The present invention also has the following technical effects: Preferably, the curing conditions described in step S3 are curing at 65~75°C for 40~50 hours.

[0006] Preferably, the dispersion in step S1 is ultrasonic dispersion at a power of 200~300 W for 20~40 min.

[0007] Preferably, the stirring in step S2 is manual stirring in the same direction for 5 to 10 minutes.

[0008] Preferably, the stirring described in steps S3 and S4 is performed by using a magnetic stirrer at a speed of 600 r / min for 30 to 50 minutes.

[0009] The present invention also protects an alicyclic epoxy resin composite coating prepared according to the above method, with a thickness of 30~50 μm.

[0010] This invention also protects the application of the above-mentioned alicyclic epoxy resin composite coating in the protection of bronze or metal artifacts.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The alicyclic epoxy resin composite coating of this invention exhibits excellent comprehensive performance and significant application advantages: ZIF-8 catalysis reduces the curing activation energy from 130.7 kJ / mol to approximately 60 kJ / mol, significantly improving reaction efficiency and lowering curing temperature and time requirements; relying on the dense cross-linked network of epoxy resin, the structure is stable and dense, possessing extremely strong corrosion resistance. After immersion in 3.5% NaCl solution for 30 days, the corrosion current density is only 8.3 × 10⁻⁶. -7 A·cm -2 It has excellent anti-corrosion and protective properties; the introduction of PEG functional components makes the coating have good affinity for ethanol, and it can swell naturally after being soaked in solvent. It can be gently peeled off with a high removal rate, meeting the reversible requirements of cultural relic protection; the low-temperature curing process ensures high light transmittance and does not affect the original appearance of cultural relics. The raw materials of this invention are readily available, the preparation is simple, the overall performance is excellent, the coating process is compatible with traditional methods, and it is easy to promote and apply in the practice of cultural relic protection. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of the preparation process of the Z / P-CEP composite coating of the present invention; Figure 2 The X-ray diffraction (XRD) pattern of ZIF-8 used in the embodiments; Figure 3 The Fourier transform infrared (FTIR) spectrum of the ZIF-8 used in the embodiments; Figure 4 These are comparative photos of the macroscopic states of the three curing systems, CEP, Z / CEP, and Z / P-CEP, after curing under the same conditions in Example 1. Figure 5 These are the DSC curves and activation energy calculation fitting diagrams of the three systems CEP, Z / CEP, and Z / P-CEP in Example 1; Figure 6 Curing degree-temperature-time relationship surface plot of the Z / P-CEP system prepared in Example 1; Figure 7 These are photos of the Z / P-CEP composite coating after curing at different temperatures, showing its high transparency after curing at 70℃.

[0013] Figure 8 The UV-Vis transmittance spectra of the Z / P-CEP composite coating prepared in Example 1 after curing at different temperatures are shown. Figure 9 This is a comparison chart of the removability of three coatings, E51, Z / P-CEP and B72, prepared in Example 1, Comparative Example 1 and Comparative Example 2. Figure 10 This is a comparison of the Tafel polarization curves and corrosion current density changes of the three coatings (E51, Z / P-CEP, and B72) prepared in Example 1, Comparative Example 1, and Comparative Example 2 after immersion in 3.5% NaCl solution for different times. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0015] The alicyclic epoxy resins used in the following examples are: 3,4-epoxycyclohexylcarboxylic acid-3,4-epoxycyclohexylmethyl ester (ERL-4221), bis(3,4-epoxycyclohexylmethyl) ether (brand name: ERL-4206), and bis(3,4-epoxycyclohexylmethyl) adipic acid (RE-26), with a purity of 97%. The polyethylene glycol used is PEG-400, with an average molecular weight of 400; The zinc acetate dihydrate used had a purity of 99%, dimethylimidazole had a purity of 98%, and 4-methylhexahydrophthalic anhydride had a purity of 98%. The metal-organic framework ZIF-8 used was synthesized via a known method: zinc acetate and 2-methylimidazole were dissolved in methanol at a molar ratio of 1:6, stirred at room temperature for 24 hours, and then centrifuged, washed with methanol, and dried at 70°C. Its XRD and FTIR spectra are shown below. Figure 2 and Figure 3 As shown, the structure is correct. In practical applications, commercially available ZIF-8 products can also be used.

[0016] Example 1 This embodiment provides a composite coating made of alicyclic epoxy resin, and its preparation process flow diagram is shown below. Figure 1 As shown, the preparation method includes the following steps: Preparation of the curing system: First, 0.003g of ZIF-8 powder was added to 0.5g of 4-MHHPA and ultrasonically dispersed at 200 W for 30 minutes to make it uniform, thus obtaining the CEP premix; then, 0.681g of ERL-4221 was added and manually stirred in the same direction for 10 minutes to mix evenly, thus obtaining the Z / CEP premix; then, 0.15g of polyethylene glycol 400 (PEG 400) was added to the premix and stirred with a magnetic stirrer at 600 r / min for 30 minutes until the system was uniform, thus obtaining the final Z / P-CEP curing system; Coating preparation and application: Take 1.331g of the above Z / P-CEP curing system, add 2g of ethyl acetate (EA) as solvent, and stir with a magnetic stirrer at 600 r / min for 30 min until completely dissolved to prepare a coating solution; use a brush to evenly coat the solution onto the surface of the bronze test piece that has been sanded, ultrasonically cleaned with acetone and ethanol, and dried; place the coated test piece horizontally in a 70℃ forced-air drying oven and cure for 46 hours, then allow it to cool naturally to room temperature to obtain a Z / P-CEP composite coating with a film thickness of approximately 40μm.

[0017] Example 2 This embodiment provides an alicyclic epoxy resin composite coating, the preparation method of which includes the following steps: Preparation of the curing system: First, 0.0061 g of ZIF-8 powder was added to 0.52 g of 4-MHHPA and ultrasonically dispersed at 300 W for 40 minutes to obtain a homogeneous CEP premix. Next, 0.7 g of RE-26 was added and manually stirred in the same direction for 10 minutes to obtain a homogeneous Z / CEP premix. Then, 0.1839 g of polyethylene glycol 400 (PEG 400) was added to the premix and stirred with a magnetic stirrer at 600 r / min for 50 minutes until the system was homogeneous, thus obtaining the final Z / P-CEP curing system. Coating preparation and application: Take 1.2g of the above Z / P-CEP curing system, add 2.16g of ethyl acetate (EA) as solvent, and stir with a magnetic stirrer at 600 r / min for 50 min until completely dissolved to prepare a coating solution; use a brush to evenly coat the solution onto the surface of the bronze test piece that has been sanded, ultrasonically cleaned with acetone and ethanol, and dried; place the coated test piece horizontally in a 75℃ forced-air drying oven and cure for 40 hours, then allow it to cool naturally to room temperature to obtain a Z / P-CEP composite coating with a film thickness of approximately 30μm.

[0018] Example 3 This embodiment provides an alicyclic epoxy resin composite coating, the preparation method of which includes the following steps: Preparation of the curing system: First, 0.0024 g of ZIF-8 powder was added to 0.48 g of 4-MHHPA and ultrasonically dispersed for 20 minutes at 200 W to obtain a homogeneous CEP premix. Next, 0.7 g of ERL-4206 was added and manually stirred in the same direction for 8 minutes to obtain a homogeneous Z / CEP premix. Then, 0.118 g of polyethylene glycol 400 (PEG 400) was added to the premix and stirred with a magnetic stirrer at 600 r / min for 40 minutes until the system was homogeneous, thus obtaining the final Z / P-CEP curing system. Coating preparation and application: Take 1.667 g of the above Z / P-CEP curing system, add 2 g of ethyl acetate (EA) as solvent, and stir with a magnetic stirrer at 600 r / min for 40 min until completely dissolved to prepare a coating solution; use a brush to evenly coat the solution onto the surface of the bronze test piece that has been sanded, ultrasonically cleaned with acetone and ethanol, and dried; place the coated test piece horizontally in a 65℃ forced-air drying oven and cure for 50 hours, then allow it to cool naturally to room temperature to obtain a Z / P-CEP composite coating with a film thickness of approximately 50 μm.

[0019] Comparative Example 1: Weigh 0.63g of conventional E51 epoxy coating epoxy resin and 0.5g of 4-MHHPA anhydride curing agent, and add 0.003g of 2-methylimidazole as a curing accelerator. Dissolve in 2g of ethyl acetate, brush onto a similarly treated bronze sample, and cure at 70℃ for 36 hours.

[0020] Comparative Example 2: Weigh 0.25g of commercially available Paralloid B72 acrylic coating solid resin and add 4.75g of ethyl acetate to prepare a 5 wt% solution. After magnetic stirring for 1 hour, brush the solution onto a bronze sample and allow it to dry at room temperature to form a film.

[0021] Performance Testing and Result Analysis Referring to the accompanying drawings, the coatings of Example 1, Comparative Example 1, and Comparative Example 2 were tested: Curing behavior and process optimization: Figure 4 The macroscopic comparison photos of the three curing systems CEP, Z / CEP, and Z / P-CEP prepared in Example 1 after curing under the same conditions visually demonstrate the curing-promoting effect of ZIF-8.

[0022] Figure 5 The DSC curves and activation energy calculation fitting plots of the three systems CEP, Z / CEP, and Z / P-CEP in Example 1 are shown to demonstrate the effect of ZIF-8 in reducing the curing activation energy. Differential scanning calorimetry (DSC) tests were performed using a NETZSCH DSC 200PC thermal analyzer. Epoxy resin liquid samples (5-10 mg) with mixed curing agents were placed in aluminum crucibles, with an empty crucible as a reference, and tested at 5, 10, 15, 20, and 25 °C·min. -1 The heating rate was tested.

[0023] As attached Figure 5 As shown, DSC tests and activation energy calculations indicate that after the addition of ZIF-8, the activation energy of the curing system significantly decreased from 130.7 kJ / mol (CEP) to approximately 60 kJ / mol (Z / CEP and Z / P-CEP), demonstrating the highly efficient catalytic effect of ZIF-8.

[0024] Figure 6 The curing degree-temperature-time surface plot of the Z / P-CEP system prepared in Example 1 is obtained by numerical solution of the curing kinetic equations established by the Starink and Malek methods, and is used to simulate and guide the curing process. (See attached image) Figure 6 The curing kinetics analysis and process surface diagrams clarified the temperature-time process window required for the Z / P-CEP system to achieve 90% curing degree, providing guidance for actual curing operations.

[0025] Appearance and transparency: Figure 7 These are photographs of the Z / P-CEP composite coating prepared in Example 1 after curing at different temperatures, as shown in the attached images. Figure 7 As shown, the Z / P-CEP coating, after curing at an optimized process of 70℃, has a complete appearance and high transparency. Figure 8 The UV-Vis transmittance spectra of the Z / P-CEP composite coating prepared in Example 1 after curing at different temperatures are shown in the attached figure. Figure 8 As shown, the average transmittance in the visible light region (400-800 nm) is as high as 90.2%, ensuring the visibility of the original appearance of the cultural relics.

[0026] Removability: Figure 9 This is a comparison chart of the removability of the three coatings—E51, Z / P-CEP, and B72—prepared in Example 1, Comparative Example 1, and Comparative Example 2, used to demonstrate the high removability of the Z / P-CEP coating. (See attached chart.) Figure 9 As shown, through mass method testing, the removal rate of the Z / P-CEP coating reached as high as 87.5%. This performance is far superior to the 33.2% of the traditional E51 epoxy coating and is close to that of the B72 acrylic coating (94.1%), which has excellent removability, thus meeting the principle of reversibility in cultural relic protection.

[0027] Electrochemical corrosion resistance: Figure 10 The images show Tafel polarization curves and corrosion current density changes of the three coatings (E51, Z / P-CEP, and B72) prepared in Example 1, Comparative Example 1, and Comparative Example 2 after immersion in 3.5% NaCl solution for different times, to demonstrate the high corrosion resistance of the Z / P-CEP coating.

[0028] Tafel polarization was measured using a Corrtest CS350 electrochemical workstation in a three-electrode system. The working electrode was a coated bronze sample, and the electrolyte was a 0.5 mol / L Na₂SO₄ solution. Tafel polarization was measured at a scan rate of 10 mV / s, and electrochemical impedance spectroscopy was performed with a 10 mV amplitude signal applied in the frequency range of 10⁻²–10⁵ Hz.

[0029] The working electrode is prepared as follows: (1) Connecting wires: Adhere a copper wire to a non-working surface of the bronze sample (10 mm × 10 mm) with conductive adhesive. Place the working surface of the sample with the wire connected down into the center of the bottom of the mold, ensuring that the wire is led out from the top of the mold, and use a clamp to temporarily fix the wire outside the mold.

[0030] (2) Inlay: Mix the cold-mounted epoxy resin with the curing agent, stir thoroughly in a disposable beaker, and stir slowly along the beaker wall to reduce air bubbles. Slowly pour the mixed epoxy resin along the inner wall of the mold until the sample is completely submerged and there is enough encapsulation thickness. Then use a vacuum drying oven to remove air bubbles mixed in the resin.

[0031] (3) Static curing: Place the mold horizontally in a dust-free and stable place and wait for curing. Then remove the epoxy resin insert from the mold.

[0032] (4) Surface polishing: Use coarse sandpaper to polish the front end of the insert until the electrode material is fully exposed, then use finer sandpaper to polish until it is smooth and flat, and finally rinse with plenty of deionized water and dry in an oven.

[0033] (5) Coating preparation: The alicyclic epoxy coating is brushed onto the working surface of the electrode and cured in an oven to form a film; B72 is dissolved in ethyl acetate and brushed onto the working surface of the electrode, and dried at room temperature to form a film.

[0034] As attached Figure 10 As shown, the corrosion resistance of the coating in 3.5% NaCl solution was tested using Tafel polarization curves. After immersion for 30 days, the corrosion current density of Z / P-CEP was 8.3 × 10⁻⁶. -7 A·cm -2 B72 is 2.7 × 10 -5 A·cm -2 E51 is 7.3 × 10 -9 A·cm -2 The results show that the corrosion resistance of Z / P-CEP is far superior to that of B72. Although it is slightly lower than that of E51, it is already at an excellent level of protection, fully meeting the requirements for long-term protection, and solving the problem of E51's inability to be removed.

[0035] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; any deductions or substitutions made by those skilled in the art without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing an alicyclic epoxy resin composite coating, characterized in that, Includes the following steps: S1. Mix and disperse 4-methylhexahydrophthalic anhydride with ZIF-8 powder to obtain mixture A; S2. Add the alicyclic epoxy resin monomer to mixture A and stir until the mixture is homogeneous to obtain mixture B; S3. Add polyethylene glycol to mixture B and stir until the mixture is homogeneous to obtain the Z / P-CEP curing system; S4. Mix the curing system obtained in step S3 with an organic solvent, stir until completely dissolved, prepare a coating solution, apply it to the substrate surface, and after curing, form an alicyclic epoxy resin composite coating. The mass ratio of the alicyclic epoxy resin monomer to 4-methylhexahydrophthalic anhydride is (0.65~0.70):(0.48~0.52). The amount of polyethylene glycol added accounts for 10-15 wt% of the total mass of the Z / P-CEP curing system; the amount of ZIF-8 added accounts for 0.2-0.5 wt% of the total mass of the Z / P-CEP curing system. The mass ratio of the Z / P-CEP curing system to the organic solvent is 1:(1.2~1.8).

2. The method for preparing the alicyclic epoxy resin composite coating according to claim 1, characterized in that, The curing conditions described in step S3 are curing at 65~75℃ for 40~50 hours.

3. The method for preparing the alicyclic epoxy resin composite coating according to claim 1, characterized in that, The dispersion described in step S1 is ultrasonic dispersion at a power of 200~300 W for 20~40 min.

4. The method for preparing the alicyclic epoxy resin composite coating according to claim 1, characterized in that, The stirring described in step S2 is manual stirring in the same direction for 5 to 10 minutes.

5. The method for preparing the alicyclic epoxy resin composite coating according to claim 1, characterized in that, The stirring described in steps S3 and S4 is to use a magnetic stirrer to stir at a speed of 600 r / min for 30 to 50 minutes.

6. An alicyclic epoxy resin composite coating prepared by the method according to any one of claims 1 to 5, characterized in that, The thickness is 30~50 μm.

7. The application of the alicyclic epoxy resin composite coating according to claim 6 in the protection of bronze or metal artifacts.

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