Preparation method of epoxy epoxy silica / epoxy resin photocurable coating

Abstract

This invention relates to a green process for preparing epoxy cyclic silica / epoxy resin composite films, suitable for multiple applications such as marine anti-corrosion coatings and thermal insulation coatings for building materials. The film is prepared by photopolymerization of epoxy cyclic silica and epoxy resin in the presence of a cationic photoinitiator. Compared to traditional solvent-based coatings that release harmful volatile organic compounds (VOCs), this invention uses green photopolymerization technology, which not only effectively reduces energy consumption and improves production efficiency, but also achieves anti-corrosion, thermal insulation, and environmentally friendly effects without the need for added organic solvents. The added modified epoxy cyclic silica (FSi-OH) significantly improves the dispersibility of epoxy resin and inorganic substances while enhancing crosslinking reactions and substrate adhesion. The introduction of FSi-OH creates an air physical barrier between the coating and the solution, lengthening the corrosion ion penetration path and increasing the material's service life. The coating's thermal insulation performance under xenon lamp irradiation was also evaluated. Therefore, the green photopolymerization technology that uses epoxy epoxide silicon dioxide FSi-OH as an additive not only provides efficient corrosion protection but also achieves a cooling effect, demonstrating superior thermal insulation performance.

Description

[Technical Field]

[0001] This invention relates to the preparation of a novel green photopolymerizable composite film containing silica inorganic materials. The film is based on epoxy resin, with different proportions of epoxy cyclic silica FSi-OH added to the epoxy resin. The addition of FSi-OH inorganic materials to the polymer significantly improves the dispersibility, barrier properties, and adhesion to the substrate of the composite film, making it suitable for applications in corrosion resistance and heat insulation. [Previous Technology]

[0002] Metal corrosion is an unavoidable phenomenon that causes significant losses to the modern economy and poses safety hazards. Corrosion occurs when metals come into contact with corrosive agents in the environment and undergo chemical reactions. Therefore, how to effectively prevent metal materials from coming into contact with corrosive agents has become an important research topic. Currently, the six common metal protection technologies include: (1) sacrificial anode; (2) anti-corrosion material; (3) metal coating; (4) impressed voltage protection; (5) inorganic and organic coating; and (6) metal passivation. Depending on the coating material, coatings can be divided into inorganic coatings (such as ceramic coatings) and organic coatings (such as polymer coatings), both of which have been widely used in many fields.

[0003] To improve coating performance and applicability, inorganic materials such as silicon dioxide, titanium dioxide, zinc oxide, hollow glass spheres, graphene, disulfides, and coffee grounds are added to organic coatings, enabling their application in antibacterial, antifouling, and anti-corrosion applications. This study synthesized an epoxy-cyclic silicon dioxide additive (FSi-OH) by surface modification of 3-glycidoxypropyltrimethoxysilane (GPTMS) and hydroxyl-containing silicon dioxide using a sol-gel method. The epoxy-cyclic silicon dioxide retains the original properties of silicon dioxide and has numerous epoxy functional groups on the spherical shell surface. This not only increases its dispersibility with epoxy resins but also allows for cross-linking reactions with epoxy resins through ring-opening reactions, thereby improving the adhesion, hydrophobicity, and corrosion resistance of the composite coating.

[0004] Currently, most organic coatings are thermosetting solvent-based, which consumes a lot of energy and produces toxic substances and VOCs during the curing process. Given the current emphasis on net-zero carbon emissions and environmental awareness, traditional thermosetting will be a focus of future attention. Therefore, this study proposes a green photopolymerization technology, using rapid and efficient room temperature polymerization to significantly reduce and effectively utilize energy consumption and shorten process time. In the future, mature ultraviolet curing technology has the potential to replace solvent-based coatings and become a novel trend.

[0005] Photopolymerization technology generally refers to the process where unsaturated monomers are converted from a liquid to a solid state by energy generated under ultraviolet light, visible light, or electron beam irradiation. The main components of a photocuring system are oligomers (55-65 wt%), reactive monomers (25-35 wt%), photoinitiators (0.5-4 wt%), and additives (0.1-10 wt%). The reaction mechanism involves the photoinitiator capturing light radiation energy, generating reactive fragments through this energy, and transferring the energy to the oligomers and reactive monomers, causing a phase change process of reactive polymerization. Appropriate additives can be added as needed. Photoinitiators can be classified into cationic polymerization (CP) and free radical polymerization (FRP) photocuring systems based on their structure and energy transfer mechanism. The CP system, which requires epoxy resin monomers, is the photocuring system used in this invention. The CP mechanism involves the photoinitiator absorbing light energy, causing the molecule to transition from the ground state to the excited state, undergoing a photolysis reaction to produce Lewis acid or Bronsted acid, which then undergoes a ring-opening reaction with the epoxy groups on the epoxy resin. [Summary of the Invention]

[0006] This invention patent relates to a method for preparing an epoxy cyclic silica / epoxy resin photocurable coating, comprising the following steps: (a) preparing a photopolymer, which is a photopolymer composed of modified epoxy cyclic silica (FSi-OH), epoxy resin and a cationic initiator, the photopolymer comprising: (i) modified epoxy cyclic silica, wherein the modified epoxy cyclic silica accounts for 1 wt% to 5 wt% of the photopolymer; (ii) epoxy resin, which contains at least two epoxy groups, and the epoxy resin accounts for 95 wt% to 97 wt% of the photopolymer; and (iii) a cationic initiator, wherein the cationic initiator accounts for 0.5 wt% to 4 wt% of the photopolymer; (b) (c) Photopolymer stirring: The photopolymer is stirred at room temperature to make it uniform; (d) Photopolymer coating: The photopolymer is coated onto the surface of the object using a doctor blade coating method, and the coating thickness of the photopolymer is 30 μm to 150 μm; and (e) Photopolymerization reaction: The photopolymer on the surface of the object is subjected to photopolymerization reaction by exposure to ultraviolet light or ultraviolet to visible light, and after the photopolymerization reaction, the photopolymer is cured into a composite film, which is used as an anti-corrosion and heat-insulating coating. The modified epoxy cyclic silica has multiple epoxy functional groups. Furthermore, silica (Si-OH) with a particle size of nanometers is added to the formulation of the photopolymer, as shown in chemical formula I: (I)

[0007] The chemical structure of the modified epoxy silicon dioxide is as shown in chemical formula II: (II)

[0008] The epoxy resin is a bisphenol A epoxy resin, as shown in chemical formula III: (III)

[0009] Among them, the cationic initiator is trimethylarylhexafluorophosphate thioonium salt, such as chemical formula IV: (IV)

[0010] The solid content of the cationic initiator is 40 wt%. The photopolymer is stirred at room temperature for 24 hours to ensure uniformity. The photopolymer is coated onto the surface of the object using a doctor blade at a speed of 100 mm / min. The photopolymerization reaction uses ultraviolet light or ultraviolet to visible light in multiple wavelength ranges from 250 nm to 450 nm, or uses a single wavelength of ultraviolet light at 365 nm (20 mW / cm²). The photopolymerization reaction is carried out by exposing the photopolymer on the surface of the object to ultraviolet light or ultraviolet to visible light for 30 minutes.

[0011] The purpose of this invention is to introduce epoxy-containing silicon dioxide into the overall formulation, and to propose a novel green photopolymerization technology to prepare composite films, which differs from traditional thermosetting methods. The photopolymerization process can shorten the reaction time and effectively reduce the use of organic solvents to reduce VOC emissions, thereby obtaining composite films simply and quickly. The content of added inorganic materials is as follows: in the experimental examples of this invention, 3 wt% of inorganic materials is sufficient to achieve good dispersibility, thermal stability, adhesion, corrosion resistance, and thermal insulation, which is different from traditional technologies and is innovative, unique, and practically beneficial.

Implementation Method

[0012] First, please refer to Figure 1, which shows a schematic diagram of the method for preparing an epoxy cyclic silica / epoxy resin photocurable coating of the present invention. This invention patent is a method for preparing an epoxy cyclic silica / epoxy resin photocurable coating, comprising the following steps: (a) preparing a photopolymer, which is a photopolymer composed of modified epoxy cyclic silica (FSi-OH), epoxy resin, and a cationic initiator. The photopolymer comprises: (i) modified epoxy cyclic silica, wherein the modified epoxy cyclic silica accounts for 1 wt% to 5 wt% of the photopolymer; (ii) an epoxy resin containing at least two epoxy groups, wherein the epoxy resin accounts for 95 wt% to 97 wt% of the photopolymer; and (iii) a cationic initiator, wherein the cationic initiator accounts for 0.5 wt% to 4 wt% of the photopolymer; (b) (c) Photopolymer stirring: The photopolymer is stirred at room temperature to make it uniform; (d) Photopolymer coating: The photopolymer is coated onto the surface of the object using a doctor blade coating method, and the coating thickness of the photopolymer is 30 μm to 150 μm; and (e) Photopolymerization reaction: The photopolymer on the surface of the object is subjected to photopolymerization reaction by exposure to ultraviolet light or ultraviolet to visible light, and after the photopolymerization reaction, the photopolymer is cured into a composite film, which is used as an anti-corrosion and heat-insulating coating. The modified epoxy cyclic silica has multiple epoxy functional groups. Furthermore, silica (Si-OH) with a particle size of nanometers is added to the formulation of the photopolymer, as shown in chemical formula I: (I)

[0013] The chemical structure of the modified epoxy silicon dioxide is as shown in chemical formula II: (II)

[0014] The epoxy resin is a bisphenol A epoxy resin, such as chemical formula III: (III)

[0015] The cationic initiator is trimethylarylhexafluorophosphate thioonium salt, such as chemical formula IV: (IV)

[0016] The solid content of the cationic initiator is 40 wt%. The photopolymer is stirred at room temperature for 24 hours to ensure uniformity. The photopolymer is coated onto the surface of the object using a doctor blade at a speed of 100 mm / min. The photopolymerization reaction uses ultraviolet light or ultraviolet to visible light in multiple wavelength ranges from 250 nm to 450 nm, or uses a single wavelength of ultraviolet light at 365 nm (20 mW / cm²). The photopolymerization reaction is carried out by exposing the photopolymer on the surface of the object to ultraviolet light or ultraviolet to visible light for 30 minutes.

[0017] The object to be coated is a galvanized steel sheet. The pretreatment method of the test sample is as follows: first, cut the galvanized steel sheet into 2.5 cm * 2.5 cm sizes, then clean it with surfactant and acetone by ultrasonic vibration for 15 minutes, then put the galvanized steel sheet into a prepared 1 wt% dilute nitric acid solution and acid wash for 30 seconds. After that, rinse it with acetone and store it in a sample bottle containing acetone.

[0018] The preparation of the anti-corrosion and heat insulation coating involves dripping a photopolymer coating onto the object to be coated, which is the previously treated galvanized steel sheet. The coating is then applied using a scraper at a speed of 100 mm / min to control the thickness to 50 μm. Finally, the coating is cured by irradiating it with a 365 nm ultraviolet lamp for 30 minutes. This completes the anti-corrosion and heat insulation coating process.

[0019] Silica (Si-OH) with a particle size of nanometers (I) / epoxy epoxy silica (FSi-OH) with a particle size of nanometers (II), conventional bisphenol A type epoxy resin (III) and cationic photoinitiator (IV) are mixed and prepared in different proportions to form photopolymer coatings. The solid content of (IV) is 40 wt% and its usage is fixed at 2 wt% of the total weight. In addition, the formulation experiments of (I) / (II) and (III) are shown in Table 1 and Table 2. They are mixed with each other in different proportions, 5 ml of acetone is added as a solvent, and the mixture is stirred with a magnet for 24 hours. Then the solvent is removed and the mixture is left to stand for one day to complete the Si-OH / Epoxy and FSi-OH / Epoxy coatings.

[0020] Table 1. Experimental Examples a of Si-OH, BE-188, and Photoinitiator in this Patent code name Si-OH BE188 Epoxy 0.00 100 Si-OH-3 3.00 97.00 a contains 2 wt% photoinitiator

[0021] Table 2. Experimental Examples a of FSi-OH, BE-188, and Photoinitiator in this Patent code name FSi-OH BE188 Epoxy 0.00 100 FSi-OH-3 3.00 97.00 FSi-OH-4 4.00 96.00 FSi-OH-5 5.00 95.00 a contains 2 wt% photoinitiator

[0022] The analysis of corrosion resistance by polarization curves is shown in Figure 2: polarization curves of steel plate, Si-OH / Epoxy and FSi-OH / Epoxy series. The results of the polarization curve plot (Tafel plot) are summarized in Table 3. From the polarization curves, the maximum corrosion voltage and the minimum corrosion current density can be obtained. The corrosion protection rate is calculated according to (Equation 1), the polarization resistance is calculated according to (Equation 2), and the coating porosity is calculated according to (Equation 3). In epoxy resin, 3, 4, and 5 wt% FSi-OH and 3 wt% Si-OH were added as control groups, respectively. Table 3 shows that the 3 wt% FSi-OH group exhibited the best corrosion resistance, with a maximum corrosion voltage (E corr = -1173.0 mV) and a minimum corrosion current density (I corr = 1.3 x 10⁻⁷ A cm⁻²), achieving a corrosion protection rate (PI = 99.87%), compared to only 96.80% for the control group. Therefore, adding epoxy silica FSi-OH powder significantly improves corrosion resistance, especially FSi-OH-3, which is the most effective. With increasing FSi-OH powder concentration, FSi-OH agglomeration intensifies, and the increased concentration also darkens the solution color, preventing complete penetration during light exposure. This results in only surface drying of the film, with the interior remaining uncured, thus gradually decreasing corrosion resistance. The improved corrosion resistance mainly comes from the hydrophobicity of the epoxy groups in the epoxy silica itself, which lengthens the path for the electrolyte to penetrate into the substrate, increases the reaction with epoxy, improves the crosslinking density, and makes the composite film more compact.

[0023] (Equation 1)

[0024] (Equation 2)

[0025] (Equation 3)

[0026] Table 3. Corrosion resistance analysis of steel plates with different proportions of Si-OH / Epoxy and FSi-OH / Epoxy after 30 minutes of irradiation. a. Corrosion voltage. b. Corrosion current. c. Corrosion rate. d. Polarization resistance. e. Coating porosity. f. Protection percentage.

[0027] Electrochemical Impedance Spectroscopy (EIS): EIS analysis was performed after immersion in 3.5wt% NaCl electrolyte for 1, 7, and 28 days to evaluate the effect of the coating on the ionic resistance of electrolyte diffusion and corrosion protection performance. Figure 3 (abc) Nyquist plot shows that the larger the impedance arc radius, the better the corrosion resistance. In the initial immersion stage, the impedance arc radius of the composite coating was significantly larger than that of the steel plate itself. Among them, the 3wt% FSi-OH / Epoxy coating had the largest impedance arc radius after immersion for 28 days, indicating that the coating has excellent corrosion resistance. In the phase angle plot, the characteristic peaks appearing in the high-frequency region (10 1-10 6) indicate the barrier between the coating and the electrolyte; the characteristic peaks appearing in the mid-to-low frequency region (10 -3-10 1) indicate that corrosive substances diffuse to the substrate and undergo chemical reactions; however, there are no characteristic peaks in the mid-to-low frequency region, indicating that the coating can effectively block the intrusion of corrosive substances and is difficult to undergo corrosion reactions. In the Bode plot, the impedance modulus at low frequencies (|Z| 0.01 Hz) is used to evaluate the corrosion resistance of the coating; a higher order of magnitude indicates better corrosion resistance. In Figure 3 (ghi), the 3wt% FSi-OH / Epoxy coating exhibits a significantly higher impedance modulus at low frequencies (|Z| 0.01 Hz) than other samples, notably maintaining a modulus of 1.30 × 10⁷ Ω at low frequencies (|Z| 0.01 Hz) after 28 days of immersion. In contrast, the 3wt% Si-OH / Epoxy coating initially showed a modulus of 1.20 × 10⁷ Ω at low frequencies (|Z| 0.01 Hz), decreasing to 1.2 × 10⁴ Ω after 28 days of immersion. This indicates that GPTMS modification of Si-OH significantly improves dispersibility, and the addition of inorganic substances also greatly enhances corrosion resistance. This is attributed to the hydrophobicity of the epoxy groups in the epoxy silica, which provides an additional physical barrier to the coating, lengthening the electrolyte erosion path. Figure 3 (def) shows the phase diagram. Initially, all composite coatings have a phase angle of 90°, which decreases over time, indicating the presence of pores in the coatings. After 28 days of immersion in the steel plate and Epoxy, a time constant was observed in the low-to-mid frequency region, with the phase angle dropping to above 20°. This indicates that corrosive substances (Na+, O2, H2O, and Cl-) penetrate the substrate interface through the coating pores, causing delamination. Notably, the 3 wt% FSi-OH / Epoxy coating has a phase angle close to 90°, indicating excellent corrosion resistance even after prolonged immersion in the electrolyte. The absence of a time constant in the low-to-mid frequency region suggests good adhesion between the coating and the steel plate. All EIS analyses described above used the equivalent circuit diagram in Figure 4.

[0028] The thermal insulation performance test is shown in Figure 5, which illustrates the simulated structure of an uncoated (left) and coated (right) steel plate (middle). The middle section consists of an acrylic plate covered with aluminum foil, with a hollow cube at the top and bottom. The steel plate is placed on top, with the coated side facing outwards. Figure 6 shows the temperature monitored using a handheld infrared thermal imager. The thermal insulation performance of coated (FSi-OH-3) and uncoated steel plates under xenon lamp (210 mW / cm²) irradiation for 10 and 30 minutes was evaluated (Table 4). After 30 minutes of irradiation, the temperature of the bottom surface of the coated steel plate was 43 °C, while the temperature facing outwards reached 61 °C. Furthermore, the bottom surface of the uncoated steel plate was 48 °C, and the temperature facing outwards was 36 °C. It can be observed that with the coating, after 10 or 30 minutes of irradiation, the temperature difference between the inward and outward sides was 17 and 18 °C, respectively, demonstrating excellent thermal insulation. However, the uncoated sample not only lacked thermal insulation, but its inward temperature was even higher than its outward temperature. Therefore, the photopolymer composite film with epoxy epoxide silicon dioxide FSi-OH as an additive not only provides efficient corrosion protection, but also has good heat insulation effect.

[0029] Table 4. Temperature of upper (a, c) and lower (b, d) layers of coated and uncoated steel plates at 10 and 30 minutes. 10 minutes 30 minutes BK facing outwards (°C) 37 36 BK facing inwards (°C) 45 48 FSi-OH-3 facing outwards (°C) 59 61 FSi-OH-3 facing inward (°C) 42 43 [Simplified Explanation of the Diagram]

[0030] Figure 1 shows a schematic diagram of the method for preparing the epoxy epoxide / epoxy resin photocurable coating of the present invention. Figure 2 shows the polarization curves of steel plates and different proportions of Si-OH / Epoxy and FSi-OH / Epoxy after 30 minutes of illumination in 3.5wt% NaCl solution. Figure 3 shows the AC impedance test spectra of steel plates, Epoxy, 3 wt% Si-OH / Epoxy and 3 wt% FSi-OH / Epoxy samples after immersion in 3.5wt% NaCl for 1, 7 and 30 days. (a) (d) (g) are the Nyquist plot, phase diagram and Bode plot after 1 day of immersion; (b) (e) (h) are the Nyquist plot, phase diagram and Bode plot after 7 days of immersion; (c) (f) (i) are the Nyquist plot, phase diagram and Bode plot after 28 days of immersion. Figure 4 shows the equivalent circuit used to fit EIS data. Figure 5 shows a schematic diagram of the simulated structure of an uncoated (left) and coated (right) steel plate, with an aluminum foil-wrapped acrylic plate in the middle, featuring a hollow cube with the steel plate on top and the coated side facing outwards. Figure 6 shows the temperature of the upper (a, c) and lower (b, d) layers of the steel plate monitored by FLIR at 30 minutes.

Claims

1. A method for preparing an epoxy epoxide / epoxy resin photocurable coating, comprising the following steps: (a) Preparing a photopolymer, which is a photopolymer composed of modified epoxy cyclic silica, epoxy resin and a cationic initiator, the photopolymer comprising: (i) modified epoxy cyclic silica, the modified epoxy cyclic silica comprising 1 wt% to 5 wt% of the photopolymer; (ii) epoxy resin comprising at least two epoxy groups, the epoxy resin comprising 95 wt% to 97 wt% of the photopolymer; and (iii) a cationic initiator comprising 0.5 wt% to 4 wt% of the photopolymer; (b) Stirring the photopolymer, stirring the photopolymer at room temperature to make it homogeneous; (c) Coating the photopolymer, coating the photopolymer onto the surface of the object to be coated by a doctor blade coating method, the coating thickness of the photopolymer being 30 μm to 150 μm; (d) Photopolymerization reaction, wherein the photopolymer on the surface of the coated object undergoes photopolymerization reaction by exposure to ultraviolet light or ultraviolet to visible light, and the photopolymer is cured into a composite film after photopolymerization reaction, the composite film serving as an anti-corrosion and heat-insulating coating.

2. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The modified epoxy epoxide has multiple epoxy functional groups.

3. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The chemical structure of the modified epoxy silicon dioxide is shown in chemical formula II: (II).

4. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The epoxy resin is a bisphenol A epoxy resin, as shown in chemical formula III: (III).

5. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The cationic initiator is trimethylarylhexafluorophosphate thioonium salt, such as chemical formula IV:(IV).

6. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The solid content of this cationic initiator is 40 wt%.

7. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The photopolymer was stirred at room temperature for 24 hours to make it homogenous.

8. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The photopolymer coating is applied to the surface of the object by a doctor blade coating method, with the doctor blade moving at a speed of 100 mm / min.

9. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The photopolymerization reaction uses ultraviolet light or ultraviolet to visible light as a multi-band wavelength, the wavelength range of which is between 250 nm and 450 nm, or the photopolymerization reaction uses ultraviolet light as a single wavelength, the wavelength of which is 365 nm (20 mW / cm2).

10. The method for preparing an epoxy epoxy silica / epoxy resin photocurable coating as described in claim 1, wherein, The photopolymerization reaction occurs when the photopolymer on the surface of the coated object is exposed to ultraviolet light or ultraviolet to visible light for 30 minutes.

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