Preparation method and application of resorcinol-formaldehyde resin and epoxy resin composite coating

Abstract

The invention discloses a resorcinol-formaldehyde resin and epoxy resin composite coating as well as a preparation method and application thereof. The composite coating is prepared by mixing resorcinol-formaldehyde resin serving as a functional filler with epoxy resin, the composite coating is applied to the surface of Q235 carbon steel as a bifunctional anti-corrosion and anti-fouling composite coating, and has remarkable corrosion resistance and biological fouling resistance. And after the material is soaked in a 3.5 wt% NaCl solution for 28 days, the impedance of the material still reaches up to 6 * 10 < 6 > omega.cm <-2 >. Besides, the RF / EP composite coating generates active substances (. OH and. O2 <->) through photo-induced electron-hole pairs and generates H2O2 through an oxidation-reduction reaction, so that adhesion of bacteria (such as escherichia coli and staphylococcus aureus) and algae (chlorella) is effectively inhibited, and the RF / EP composite coating shows excellent biological pollution resistance.

Description

Technical Field

[0001] The present invention relates to a composite coating, and particularly to a resorcinol-formaldehyde resin and epoxy resin composite coating, its preparation method and application. Background Art

[0002] Carbon steel, as an important metal material, is widely used in industries such as ship equipment and marine infrastructure. However, the complex corrosion factors in the marine environment, including high salinity (about 3.5%), abundant oxygen content, marine microorganisms, and the combined action of waves and solar radiation, lead to serious corrosion problems. Traditional epoxy resin coatings have been widely used in marine anti-corrosion research due to their chemical stability, excellent adhesion, and electrical insulation. However, due to solvent volatilization and microporous defects during the coating curing process, their long-term protection ability is still limited.

[0003] In addition, traditional epoxy resin coatings cannot exhibit anti-biofouling performance, and the long-term attachment of microorganisms also seriously affects the anti-corrosion protection performance of the coatings. The present invention aims to develop a new composite coating that not only has excellent anti-corrosion performance but also has high anti-biofouling performance to overcome the deficiencies of the prior art and provide more efficient and durable protection for marine equipment. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a resorcinol-formaldehyde resin and epoxy resin composite coating with anti-corrosion and anti-biofouling performance. Secondly, a preparation method of the composite coating is provided, as well as its application in the fields of anti-corrosion and anti-biofouling.

[0005] Technical Solution: The resorcinol-formaldehyde resin and epoxy resin composite coating described in the present invention is obtained by mixing resorcinol-formaldehyde resin as a functional filler with epoxy resin and a curing agent; the mass ratio of the resorcinol-formaldehyde resin to the epoxy resin is 0.004 - 0.008:3.

[0006] Preferably, the mass ratio of the resorcinol-formaldehyde resin to the epoxy resin is 0.006:3.

[0007] Preferably, the mass ratio of the epoxy resin to the curing agent is 5:1.

[0008] The preparation method of the above composite coating includes the following steps:

[0009] (1) Add resorcinol, formaldehyde, and ammonia water to deionized water, stir, and then carry out a hydrothermal reaction to generate a resorcinol-formaldehyde resin solution;

[0010] (2) Wash the resorcinol-formaldehyde resin solution and then dry it to obtain resorcinol-formaldehyde resin;

[0011] (3) Mix the resorcinol-formaldehyde resin, epoxy resin and curing agent according to the mass ratio, add a small amount of defoamer and absolute ethanol, and stir evenly.

[0012] (4) Uniformly coat the obtained mixed solution on the surface of the Q235 carbon steel substrate by spin coating, and form a composite coating through room temperature curing.

[0013] Preferably, in step (1), the hydrothermal reaction temperature is 250 °C and the time is 24 hours.

[0014] Preferably, in step (2), the drying temperature is 60 °C and the time is 12 hours.

[0015] Preferably, in step (3), the stirring rate is 800 - 1200 revolutions per minute and the time is 15 minutes.

[0016] Application of the above-mentioned resorcinol-formaldehyde resin and epoxy resin composite coating in the fields of anti-corrosion and anti-biofouling.

[0017] Preferably, the composite coating is used to coat the surface of a metal substrate to form a coating with a thickness of 100 - 110 μm.

[0018] Preferably, the coating process includes high-speed rotary coating for 5 minutes (rotation speed 1500 revolutions per minute).

[0019] Principle of the invention: In the present invention, resorcinol-formaldehyde resin is used as a functional filler. Through compounding with epoxy resin, a "labyrinth effect" is formed in the coating, effectively extending the diffusion path of corrosive ions, thereby significantly improving the anti-corrosion performance of the coating. At the same time, the introduction of resorcinol-formaldehyde resin improves the mechanical strength and adhesion performance of the coating, further enhancing the stability and durability of the coating. In addition, resorcinol-formaldehyde resin has certain photocatalytic activity and can generate reactive oxygen species (·OH, ·O2 - and H2O2) under light irradiation conditions to achieve the function of anti-biofouling.

[0020] Advantageous effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) The composite coating of the present invention has excellent anti-corrosion performance, and its EIS impedance radius is 1.56×10 9 Ω·cm 2 , which is improved by 2 orders of magnitude compared with the pure epoxy resin coating; (2) The coating of the present invention has excellent anti-biofouling ability. Under light irradiation conditions, the antibacterial rates against Escherichia coli and Staphylococcus aureus reach 98% and 93% respectively; at the same time, it also has a certain inhibitory effect on the attachment of Chlorella vulgaris. Description of the drawings

[0021] Figure 1Structural and performance characterizations of all examples and all comparative examples. Figure a is the X-ray diffraction analysis spectrum (XRD) of RF in Example 1, Figure b is the Fourier transform infrared analysis spectrum (FT-IR) of RF in Example 1, Figure c is the scanning electron microscope image of RF in Example 1, Figure d is the scanning electron microscope image of Comparative Example 1, Figures e - f are the scanning electron microscope images of Example 1, Figure g is the adhesion stress image of all examples, Figure h is the confocal microscope image of Example 1, Figure i is the water contact angle image of all examples, Figure j is the stress-strain curve of Example 1 and Comparative Example 1, Figure k is the friction and wear test image of Example 1, and Figure l is the thermogravimetric curve of Example 1 and Comparative Example 1;

[0022] Figure 2 Nyquist diagrams, Bode diagrams, and phase angle diagrams of all examples and all comparative examples under the condition of 3.5 wt% sodium chloride solution. Figures a, d, and g are Nyquist diagrams, Figures b, e, and h are Bode diagrams, and Figures c, f, and i are phase angle diagrams;

[0023] Figure 3 Corrosion optical photographs of coatings of all examples and all comparative examples;

[0024] Figure 4 Anti-biofouling performance characterizations of Example 1 and Comparative Example 1. Figure a is the H2O2 production curve of Example 1, Comparative Example 1, and pure water, Figure b is the H2O2 production diagram of Example 1 under different atmospheres, Figure c is the ESR spectrum analysis diagram of Example 1, Figure d is the digital antibacterial test photographs of Example 1, Comparative Example 1, and the blank control group, Figure e is the antibacterial rate image of Example 1 and Comparative Example 1, and Figure g is the scanning electron microscope image of algal attachment of Example 1, Comparative Example 1, and the blank control group;

[0025] Figure 5 Photoelectrochemical performance characterizations of RF in Example 1. Among them, Figure a is the ultraviolet-visible diffuse reflection spectrum and the estimated band gap value, b is the VB-XPS spectrum, c is the VB-XPS energy level, and d is the transient photocurrent response. Detailed implementation manners

[0026] The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

[0027] Example 1

[0028] (1) Preparation of resorcinol-formaldehyde resin: Dissolve 792 mg of resorcinol, 1080 μL of formaldehyde, and 460 μL of ammonia water in 60 mL of deionized water. After stirring at room temperature, transfer it to a stainless steel autoclave and heat at 250 °C for 24 hours. After cooling to room temperature, wash it thoroughly with deionized water and absolute ethanol, and dry it in vacuum at 60 °C for 12 hours to obtain resorcinol-formaldehyde resin (labeled as RF).

[0029] (2) Preparation of resorcinol-formaldehyde resin-epoxy resin composite coating: Disperse 6 mg of RF powder in 3 g of epoxy resin, add 0.6 g of curing agent (the ratio of epoxy resin to curing agent is 5:1), and add a small amount of defoamer and anhydrous ethanol. Stir at room temperature for 15 minutes, then spin-coat on the surface of Q235 carbon steel with a spin coater at 1500 rpm, and cure at room temperature for 24 hours to obtain a composite coating with a thickness of 100 - 110 μm, marked as RF / EP-6.

[0030] Example 2

[0031] Compared with Example 1, adjust the dosage of resorcinol-formaldehyde resin:

[0032] (1) Preparation of resorcinol-formaldehyde resin: Dissolve 792 mg of resorcinol, 1080 μL of formaldehyde and 460 μL of ammonia water in 60 mL of deionized water, stir at room temperature and then transfer to a stainless steel reaction kettle, and heat at 250 °C for 24 hours. After cooling to room temperature, wash thoroughly with deionized water and anhydrous ethanol, and vacuum dry at 60 °C for 12 hours to obtain resorcinol-formaldehyde resin (marked as RF).

[0033] (2) Preparation of resorcinol-formaldehyde resin-epoxy resin composite coating: Disperse 4 mg of RF powder in 3 g of epoxy resin, add 0.6 g of curing agent (the ratio of epoxy resin to curing agent is 5:1), and add a small amount of defoamer and anhydrous ethanol. Stir at room temperature for 15 minutes, then spin-coat on the surface of Q235 carbon steel with a spin coater at 1500 rpm, and cure at room temperature for 24 hours to obtain a composite coating with a thickness of 100 - 110 μm, marked as RF / EP-4.

[0034] Example 3

[0035] Compared with Example 1, adjust the dosage of resorcinol-formaldehyde resin:

[0036] (1) Preparation of resorcinol-formaldehyde resin: Dissolve 792 mg of resorcinol, 1080 μL of formaldehyde and 460 μL of ammonia water in 60 mL of deionized water, stir at room temperature and then transfer to a stainless steel reaction kettle, and heat at 250 °C for 24 hours. After cooling to room temperature, wash thoroughly with deionized water and anhydrous ethanol, and vacuum dry at 60 °C for 12 hours to obtain resorcinol-formaldehyde resin (marked as RF).

[0037] (2) Preparation of resorcinol-formaldehyde resin-epoxy resin composite coating: Disperse 8 mg of RF powder in 3 g of epoxy resin, add 0.6 g of curing agent (the ratio of epoxy resin to curing agent is 5:1), and add a small amount of defoamer and absolute ethanol. Stir at room temperature for 15 minutes, then spin-coat it on the surface of Q235 carbon steel with a spin coater at 1500 rpm, and cure at room temperature for 24 hours to obtain a composite coating with a thickness of 100-110 μm, marked as RF / EP-8.

[0038] Comparative Example 1

[0039] Preparation of pure epoxy resin coating:

[0040] Take 3 g of epoxy resin and 0.6 g of curing agent, mix them in a ratio of 5:1, add a small amount of defoamer and absolute ethanol, stir at room temperature for 15 minutes, then spin-coat it on the surface of Q235 carbon steel with a spin coater at 1500 rpm, and cure at room temperature for 24 hours to obtain a pure-phase epoxy resin coating with a thickness of 100-110 μm, marked as EP.

[0041] As Figure 1 shown, in the X-ray diffraction (XRD) pattern of Figure a, the RF peak at 2θ≈23° shows a broad diffraction signal, corresponding to the graphite carbon (002) plane caused by the π-stacking interaction between the electron donor and acceptor units. In Figure b, the Fourier transform infrared spectroscopy (FT-IR) of the RF resin clearly shows the characteristic bands of resorcinol, linker, and residue. The characteristic υ -1 oscillation peak of methanol or resorcinol can be observed at 3353 cm O-H , while the characteristic υ -1 oscillation peak of resorcinol and methanol can be found at 1096 cm C-O . In addition, the υ -1 and υ C-H at 2921 and 1610 cm C＝CThe oscillation peaks are respectively attributed to the methylene linker and the aromatic ring. Figure c shows the scanning electron microscope (SEM) image of the RF resin, which has a spherical morphology with an average diameter and a distribution size of about 500 nm. Figure d shows the SEM image of the EP coating, which will form holes, cracks and other defects during the curing process. Figures e - f show the SEM images of the RF / EP-6 coating. The surface defects of the RF / EP-6 composite coating are significantly reduced. The RF spherical particles are clearly and evenly dispersed, and the particles are blocked and porous, generating an effective "labyrinth effect", making it difficult for the corrosion factors to contact the metal substrate. Figure g demonstrates the adhesion ability of each coating. It can be seen that the bonding strength of the RF / EP-6 composite coating is increased by 33.2% compared with the pure EP coating. Figure h shows that after adding the RF resin, the surface roughness of the composite coating increases. This is because the RF resin is spherical and can fill the original defects of the EP coating, increasing the effective area of interface light absorption by forming irregular protrusions on the surface of the composite coating. Figure i illustrates the results of contact angle measurement. The measurement shows hydrophilicity for several coatings. The RF / EP-6 composite coating exhibits a good contact angle value of 80°, which can be attributed to its high adhesion and low surface roughness. The stress - strain curve (Figure j) shows that the tensile strength of EP is 10.41 MPa and the elongation at break is 2.86%. With the addition of RF, the tensile strength of the RF / EP-6 composite coating is increased to 11.76 MPa, while the elongation at break remains at a level close to 2.8%. This indicates that reinforcement has been carried out in the existing cross - linked network. The introduction of RF not only does not affect the original cross - linked sites, but also fills the original defects and increases the cross - link density of the system. Figure 1 k shows that the RF / EP-6 composite coating has high wear resistance. The thermal stability of the coating is evaluated by thermogravimetric analysis (TGA), and the corresponding curve is shown in Figure 1 l. The thermal decomposition mainly occurs between 100 °C and 450 °C. Due to the desorption of small - molecule organic substances, there is a slight mass loss between 100 °C and 300 °C. Between 300 °C and 450 °C, obvious decomposition and polymer network cracking occur, mainly involving bisphenol A. The highest decomposition temperature of the composite coating is about 310 °C, indicating that adding the RF resin can improve the thermal stability of EP.

[0042] As Figure 2 shown, to evaluate the long - term corrosion resistance of all examples and comparative examples in 3.5 wt% sodium chloride solution, electrochemical impedance spectroscopy (EIS) measurements were carried out at different immersion times (1, 14, and 28 days). The results show that as the immersion time increases (up to 28 days), the overall trend is downward, indicating that the coating is gradually attacked by the corrosive medium during the immersion process and the coating resistance gradually decreases. After the RF / EP-6 composite coating is immersed for 28 days, its impedance is still as high as 6×10 6 Ω·cm -2, with excellent corrosion resistance.

[0043] As Figure 3 shown, in order to verify the corrosion resistance of all examples and comparative examples in practical applications, a salt spray test was adopted. The RF / EP-6 composite coating has excellent corrosion resistance.

[0044] As Figure 4 shown, Figure a uses the test of photocatalytic generation of H2O2 to study the photocatalytic performance of the prepared coating. The RF / EP-6 coating can generate 36 μM H2O2, which is attributed to its unique π-conjugated and π-stacked benzoquinone donor-resorcinol pair structure, which can catalyze the oxidation of H2O and the reduction of O2 by the charges generated by light, thus generating H2O2. In order to verify that there are two pathways for the generation of H2O2 by water oxidation and oxygen reduction in the presence of RF, we studied the photocatalytic generation of H2O2 by the prepared RF / EP coating by changing the environmental conditions (Figure b). In an N2 environment, the detected H2O2 was negligible. Combining with the air condition, this indicates that the main pathway for the photocatalytic generation of H2O2 by the RF / EP-6 coating involves oxygen reduction, highlighting the role of dissolved oxygen. In order to further determine that the main reaction in the photocatalytic generation of H2O2 by the RF / EP-6 composite coating is the ORR reaction, electron spin resonance (ESR) free radical detection was also carried out (Figure c). As shown in Figure d, the number of colonies of the two bacteria attached to the prepared coating is decreasing, which is the result of comparison with the control group. Here, the bacteriostatic rate of the prepared coating was also calculated using the control group, and the results are shown in Figure e. After adding simulated light, the bacteriostatic rates of the EP coating against Escherichia coli and Staphylococcus aureus are 69% and 64% respectively. This is because the amino groups in the EP coating have antibacterial properties, and some of the amino groups do not participate in the curing reaction, which can eliminate some bacteria. In contrast, the RF / EP-6 composite coating has higher bacteriostatic rates against Escherichia coli and Staphylococcus aureus, which are 98% and 93% respectively. First, under light illumination conditions, the RF / EP-6 composite coating can generate electron-hole pairs, which combine with the adsorbed water and oxygen to generate reactive species (-OH and -O2 -) Thus, it changes the bacterial osmotic barrier, destroys bacterial proteases, amino acids and nucleic acids, and ultimately leads to bacterial death. Figures f - h show that compared with the control group, fewer Chlorella vulgaris are attached to the surface of the EP coating because Chlorella vulgaris tends to attach to hydrophobic surfaces, while the EP coating is hydrophilic, which can slightly resist the attachment of Chlorella vulgaris. Compared with the EP coating, adding RF resin can significantly reduce the attachment density of Chlorella vulgaris on the RF / EP - 6 composite coating. This is because the RF / EP - 6 composite coating will generate reactive substances and H2O2 under the action of light, water and oxygen, thus destroying the cell wall and affecting the growth of algae. In addition, the RF / EP - 6 composite coating can also reduce the adhesion of bacteria and inhibit the formation of biofilms, thereby making the coating resistant to Chlorella vulgaris. The results of the anti - algae experiment are consistent with the trend of the antibacterial experiment results, confirming the excellent antifouling performance of the RF / EP - 6 composite coating.

[0045] As Figure 5 shown, ultraviolet - visible absorption spectroscopy and photochemical photoelectrochemical tests were used to evaluate the optical absorption properties of all examples and all comparative examples. The results show that RF has good light absorption and photogenerated charge separation efficiency, indicating that more photogenerated charges can be generated at the cathode of carbon steel, promoting its good corrosion resistance.

Claims

1. A resorcinol-formaldehyde resin and epoxy resin composite coating, characterized in that: The composite coating is obtained by mixing resorcinol-formaldehyde resin as a functional filler with epoxy resin and a curing agent; the mass ratio of the resorcinol-formaldehyde resin to the epoxy resin is 0.004-0.008:

3.

2. The composite coating according to claim 1, characterized in that: The mass ratio of the epoxy resin to the curing agent is 5:

1.

3. The composite coating according to claim 1, characterized in that: The thickness of the composite coating is 100-110 μm.

4. A method for preparing the composite coating according to claim 1, characterized in that: The following steps are involved: a. adding resorcinol, formaldehyde and ammonia water into deionized water, stirring and then performing a hydrothermal reaction to generate a resorcinol-formaldehyde resin solution; b. washing the resorcinol-formaldehyde resin solution and then drying it to obtain a resorcinol-formaldehyde resin; c. Mix the resorcinol-formaldehyde resin, epoxy resin and curing agent according to the mass ratio, add a small amount of defoamer and anhydrous ethanol, and stir evenly; d. The obtained mixed solution is evenly coated on the surface of the Q235 carbon steel substrate by spin coating process, and cured at room temperature to form a composite coating.

5. The method according to claim 4, characterized in that: In step a, the mass ratio of resorcinol, formaldehyde, ammonia water and deionized water is 0.792:1.08:0.46:60; the temperature of the hydrothermal reaction is 250° C. and the time is 24 hours.

6. The method according to claim 4, characterized in that: In step b, the drying temperature is 60° C. and the drying time is 12 hours.

7. The method according to claim 4, characterized in that: In step c, the spin coating has a rotation speed of 1500 rpm and a time of 3 to 5 minutes.

8. An application of the composite coating according to claim 1 in corrosion resistance and antifouling, characterized in that: The composite coating is applied to the surface of a Q235 carbon steel substrate, which can significantly improve the corrosion resistance and anti-biological contamination ability of the substrate.

9. The use according to claim 8, characterized in that: After the coating was immersed in 3.5wt% NaCl solution for 28 days, its impedance remained at 6×10 6 Ω·cm -2 and above; and can effectively inhibit the attachment of bacteria such as Escherichia coli and Staphylococcus aureus and algae such as Chlorella.

Images