A low-free-formaldehyde furan resin and its preparation method

Abstract

This application belongs to the field of furan resin modification technology, and specifically relates to a low-free-formaldehyde furan resin and its preparation method. This application uses ortho-substituted phenols, including ortho-methylphenol and ortho-allylphenol, to condense with furfural, introducing formaldehyde for hydroxymethylation. Subsequently, hydroxyl-containing acrylate monomers are introduced to participate in formaldehyde elimination under the action of a solid acid catalyst. Simultaneously, they undergo etherification with the hydroxymethyl groups of the modified furan resin segments, ultimately yielding an acryloyl-terminated modified furan resin. This resin possesses advantages such as low free formaldehyde content (not exceeding 0.5 wt%), low curing shrinkage, high crosslinking density, and high anti-corrosion performance, making it suitable as a film-forming material for electrochemical corrosion protection coatings on metal surfaces.

Description

Technical Field

[0001] This application belongs to the field of furan resin modification technology, and specifically relates to a low free formaldehyde furan resin and its preparation method. Background Technology

[0002] The new generation of furan resin is a thermosetting resin synthesized primarily from furfuryl alcohol or furfural. The presence of furan rings in its molecular chain gives it advantages such as acid resistance, alkali resistance, and high-temperature resistance. Furthermore, the raw materials for furan resin are widely available and inexpensive, making it a rapidly developing type of anti-corrosion material. Currently, the application of furan resin is mainly concentrated in casting, chemical, non-ferrous smelting, and electrolysis fields, and it is not widely used in anti-corrosion coatings and painting.

[0003] Furan resins synthesized using traditional processes often contain unreacted free formaldehyde, which releases irritating gases during paint mixing, coating, or pouring. Furthermore, furan resins require strong acidic curing agents such as benzenesulfonic acid and p-toluenesulfonic acid, and require heating to cure. These strong acidic curing agents can directly corrode metal substrates and react with alkaline substances in concrete, making them unsuitable for metal or concrete substrates. Moreover, directly cured coatings exhibit high shrinkage rates and are prone to cracking. These drawbacks limit the application of furan resins in the coatings industry. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application utilizes ortho-substituted phenols, including o-methylphenol and o-allylphenol, in a condensation reaction with furfural to introduce formaldehyde for hydroxymethylation. Subsequently, hydroxyl-containing acrylate monomers are introduced to participate in the elimination of formaldehyde under the action of a solid acid catalyst. Simultaneously, an etherification reaction is carried out with the hydroxymethyl groups of the modified furan resin segments, ultimately yielding an acryloyl-terminated modified furan resin. This resin has advantages such as low free formaldehyde content (not exceeding 0.5 wt%), low curing shrinkage, high crosslinking density, and high anti-corrosion performance, making it suitable as a film-forming substance for electrochemical corrosion protection coatings on metal surfaces.

[0005] The beneficial effects of the technical solutions proposed above in this application are: In one aspect, a modified furan resin, the raw materials of which include: furfural, substituted phenol, formaldehyde solution and acrylate monomer containing hydroxyl groups; The substituted phenols include: alkyl-substituted phenols and unsaturated alkenyl-substituted phenols; The alkyl-substituted phenols are selected from alkyl-substituted phenols with 1-4 carbon atoms; Preferably, the alkyl-substituted phenol is a methyl-substituted phenol; More preferably, the methyl-substituted phenol is o-methylphenol; The unsaturated alkenyl-substituted phenol is selected from unsaturated alkenyl-substituted phenols with 1-6 carbon atoms; Preferably, the unsaturated alkenyl-substituted phenol is an allyl-substituted phenol; More preferably, the allyl-substituted phenol is o-allylphenol; The formaldehyde solution is an aqueous solution with a formaldehyde content of 20-60 wt%. Preferably, the formaldehyde solution is an aqueous solution with a formaldehyde content of 40-60 wt%.

[0006] The hydroxyl-containing acrylate monomers include acrylates or methacrylates containing at least one hydroxyl group; Preferably, the hydroxyl-containing acrylate monomer is selected from one or more of the following: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl acrylate, 6-hydroxyhexyl methacrylate, glyceryl monoacrylate, glyceryl monomethacrylate, glyceryl diacrylate, glyceryl dimethacrylate, trimethylolpropane diacrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, and bisphenol A glycidyl methacrylate. More preferably, the hydroxyl-containing acrylate monomer comprises at least one primary hydroxyl group and one acryloyl group; More preferably, the hydroxyl-containing acrylate monomer is selected from one or more of the following: hydroxyethyl acrylate, hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl acrylate, 6-hydroxyhexyl methacrylate, glyceryl monoacrylate, and glyceryl monomethacrylate.

[0007] More preferably, the hydroxyl-containing acrylate monomer is selected from one or both of glycerol monoacrylate and glycerol monomethacrylate.

[0008] Secondly, in the above-mentioned method for preparing modified furan resin, furfural and substituted phenol first undergo a condensation reaction, then formaldehyde solution is added for hydroxymethylation, and finally hydroxyl-containing acrylate monomer is added for etherification while simultaneously eliminating free formaldehyde. The temperature of the condensation reaction is controlled at 100-130℃; The condensation reaction is enhanced with a free radical polymerization inhibitor, which is selected from: phenolic polymerization inhibitors, quinone polymerization inhibitors, aromatic amine polymerization inhibitors, or nitroxide free radical polymerization inhibitors. Preferably, the free radical polymerization inhibitor added in the condensation reaction is a phenolic polymerization inhibitor; The condensation reaction uses an alkaline catalyst, which is selected from one or more of ammonia water, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and potassium carbonate aqueous solution; Preferably, the alkaline catalyst is selected from ammonia water; Preferably, an inert gas is introduced during the condensation reaction; The reaction temperature for the hydroxymethylation reaction is 70-90℃; Preferably, vacuum distillation is performed after the hydroxymethylation reaction is completed.

[0009] The etherification reaction uses a solid acid catalytic resin as a catalyst, and the solid acid catalytic resin is selected from cation exchange resins. Preferably, the cation exchange resin is a polystyrene-based sulfonic acid resin.

[0010] Preferably, a free radical polymerization inhibitor is used during the reaction of acrylate monomers containing hydroxyl groups under the action of a solid acid catalyzing resin; Preferably, the free radical polymerization inhibitor is selected from: phenolic polymerization inhibitors, quinone polymerization inhibitors, aromatic amine polymerization inhibitors, or nitroxide free radical type polymerization inhibitors; Preferably, the free radical polymerization inhibitor is selected from nitroxide free radical type polymerization inhibitors.

[0011] Preferably, an inert gas is introduced during the reaction of the acrylate monomer containing hydroxyl groups under the action of a solid acid catalytic resin.

[0012] Preferably, the reaction temperature for adding hydroxyl-containing acrylate monomers under the action of solid acid catalytic resin is 60-100℃.

[0013] Preferably, in the substituted phenols, the molar ratio of alkyl-substituted phenols to unsaturated alkenyl-substituted phenols is (2.3-9):1; Preferably, in the substituted phenols, the molar ratio of alkyl-substituted phenols to unsaturated alkenyl-substituted phenols is (3-6):1; In a further preferred embodiment, the molar ratio of alkyl-substituted phenols to unsaturated alkenyl-substituted phenols in the substituted phenols is (3-4):1; Preferably, the molar ratio of substituted phenol to furfural is 1:(0.5-0.8); Preferably, the molar ratio of substituted phenol to formaldehyde is 1:(0.4-0.7); Preferably, the molar ratio of the substituted phenol to the hydroxyl-containing acrylate monomer is 1:(0.2-0.4).

[0014] Thirdly, the application of the modified furan resin described above in the preparation of anti-corrosion coatings for metal surfaces.

[0015] Fourthly, a furan resin-based coating comprises: the modified furan resin, pigment, filler, alcohol solvent, additives, and drier described above; The pigment is selected from one or more of titanium dioxide, iron oxide red, iron oxide yellow and carbon black; The filler is selected from one or more of talc powder, mica powder, mica iron oxide, barium sulfate, calcium carbonate, quartz powder and glass flakes; The alcohol solvent is selected from fatty alcohols with 1 to 4 carbon atoms; Preferably, the alcohol solvent is selected from one or more of ethanol, isopropanol, and n-butanol; The drying agent is selected from self-driving agents and drying aids; The main drying agent includes metal saponins containing multiple oxidation states, and the auxiliary drying agent is a metal saponin that exists in only one oxidation state. Preferably, the main drying agent is selected from organic acid metal soaps of cobalt, manganese, vanadium, and cerium; Preferably, the main drying agent is selected from manganese naphthenate; Preferably, the drying aid is selected from organic acid metal soaps of calcium, potassium, barium, and zinc; More preferably, the catalytic drying agent is selected from calcium naphthenate and zinc naphthenate.

[0016] The additives include one or more of dispersants, leveling agents, and defoamers.

[0017] Further, by weight, the furan resin-based coating comprises: 60-80 parts by weight of modified furan resin, 40-60 parts by weight of pigment, 20-40 parts by weight of filler, 40-60 parts by weight of alcohol solvent, 1-5 parts by weight of additives, and 0.05-0.2 parts by weight of drying agent.

[0018] Fifthly, the preparation method of the furan resin-based coating described above includes first dispersing pigments, fillers, dispersants, defoamers and a portion of alcohol solvents, and then preparing a pigment paste through mechanical dispersion; Modified furan resin and the remaining solvent are then added to the pigment paste, followed by leveling agent and drier. The mixture is then mechanically dispersed to obtain a furan resin-based coating.

[0019] Sixthly, the use of the furan resin-based coatings described above in corrosion protection of metal substrate surfaces.

[0020] Seventhly, a coating is obtained by applying the furan resin-based coating described above to the surface of a metal substrate, surface drying at room temperature for 1-24 hours, and then baking at 120-160°C for 15-60 minutes.

[0021] Preferably, the product is surface-dried at room temperature for 2-12 hours, followed by baking at 120-160°C for 15-60 minutes. Further optimization involves surface drying at room temperature for 2-8 hours, followed by baking at 130-160℃ for 15-60 minutes.

[0022] The beneficial effects of the technical solutions proposed above in this application are: 1. Phenolic monomers are introduced into furan resin to participate in the polycondensation reaction. The introduction of unsaturated alkenyl groups to replace phenol monomers gives the modified furan resin air-drying properties, enhances the crosslinking density of the furan resin after curing, and reduces the curing shrinkage rate. 2. Later, acrylate monomers containing hydroxyl groups are introduced to react with free formaldehyde and remove formaldehyde under the action of solid acid catalysis resin. Among them, the -(CHOH)-(CH2OH) structure with hydroxyl groups on two connected carbon atoms has the best formaldehyde removal effect. The corresponding monomers are glycerol monoacrylate or glycerol monomethacrylate. 3. The acrylate monomer contains at least one acryloyl group, which acts as an electron-deficient dienophile to undergo a Diels-Alder reaction with the diene furan ring at high temperature. It can also undergo an oxidative crosslinking reaction with allyl groups under the action of a drying agent, thereby enhancing the crosslinking density and improving the anti-corrosion effect. 4. Modified furan resin is formulated into corresponding coatings. After being coated on the metal surface and cured, it has a high low-frequency impedance modulus and mid-frequency phase angle, making it suitable for use as an electrochemical corrosion protection coating for metal surfaces. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The results are from a DSC thermal analysis of the cured furan resin-based coating of Example 8.

[0025] Figure 2 The results are from a DSC thermal analysis of the cured furan resin-based coating of Example 11.

[0026] Figure 3 The Bode plots for the electrochemical tests of furan resin-based coatings in Examples 7-12 and Comparative Examples 4-5 are shown, with logZ plotted against logFreq.

[0027] Figure 4The Bode plots for the electrochemical tests of furan resin-based coatings in Examples 7-12 and Comparative Examples 4-5 are plotted with -phase versus logFreq. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention. It should be noted that the terminology used herein is only for describing specific implementation methods and is not intended to limit the exemplary implementation methods according to the present invention.

[0029] Unless otherwise specified, the experimental conditions used in the examples are generally in accordance with conventional conditions in the art or the conditions recommended by the reagent company. Unless otherwise specified, the materials and reagents used in the examples can be purchased commercially.

[0030] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings: The terms "and / or," "or / and," and "and / or" as used herein include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that in this application, the technical solution undoubtedly includes technical solutions connected by "logical AND," and also undoubtedly includes technical solutions connected by "logical OR." For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, a technical solution that is connected by "logical OR"), as well as any and all combinations of A, B, C, and D, that is, combinations of any two or three of A, B, C, and D, and also combinations of all four of A, B, C, and D (that is, a technical solution that is connected by "logical AND").

[0031] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0032] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0033] In this application, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions composed of the listed features.

[0034] Example 1

[0035] Synthesis of modified furan resin: 86.5 g (0.8 mol) of o-cresol, 26.8 g (0.2 mol) of o-allylphenol, 1.2 g of polymerization inhibitor p-methoxyphenol, 57.7 g (0.6 mol) of furfural and 3.5 mL of 25 wt% ammonia water were added to a reaction vessel equipped with a reflux condenser. Then, stirring was started and nitrogen gas was introduced into the reaction vessel. The temperature was raised to 120 °C and the reaction was carried out for 12 hours.

[0036] After the reaction was completed, the temperature was lowered to 85°C, and 36g of 50.2wt% formaldehyde aqueous solution was added. The reaction was continued for 3 hours. Hydroxymethyl groups were introduced through polycondensation. After the reaction was completed, the temperature was lowered to 60°C and 1.33kPa (10mmHg) for vacuum distillation to remove small molecules from the reaction mixture.

[0037] After vacuum distillation, 0.05 g of polymerization inhibitor 701 (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, 4-hydroxyTEMPO), 36 g (0.25 mol) of 4-hydroxybutyl acrylate, and 0.8 g of YKCHWD-1 solid acid catalyst resin (Tianjin Yunkai) were added to the reaction vessel. The mixture was heated to 75°C and nitrogen gas was continuously introduced for 1 hour. The solid acid catalyst resin was then removed by filtration to obtain the final modified furan resin. Following the method in Part 1 of GB / T 2912.1-2009, the formaldehyde residue in the modified furan resin was tested using the acetylacetone spectrophotometric method at a wavelength of 412 nm. The formaldehyde residue in the modified furan resin prepared in Example 1 was found to be 0.47 wt%.

[0038] Example 2

[0039] 81.1 g (0.75 mol) of o-cresol, 33.6 g (0.25 mol) of o-allylphenol, 1.2 g of polymerization inhibitor p-methoxyphenol, 62.5 g (0.65 mol) of furfural, and 3.5 mL of 25 wt% ammonia water were added to a reaction vessel equipped with a reflux condenser. Then, stirring was started and nitrogen gas was introduced into the reaction vessel. The temperature was raised to 120 °C and the reaction was carried out for 12 hours.

[0040] After the reaction was completed, the temperature was lowered to 85°C, and 30g of 50.2wt% formaldehyde aqueous solution was added. The reaction was continued for 3 hours. Hydroxymethyl groups were introduced through polycondensation. After the reaction was completed, the temperature was lowered to 60°C and 1.33kPa (10mmHg) for vacuum distillation.

[0041] Structural characterization of the products of vacuum distillation 1 H-NMR (CDCl3): δ2.25 (3H, s), 3.27 (4H, d, J = 6.31 Hz), 4.48 (4H, s), 4.83 (2H, dd, J = 10.60, 2.40 Hz), 4.97 (2H, dd, J = 17.15, 2.40 Hz), 5.46 (1H,s), 5.53-5.80 (3H, m), 6.15-6.35 (4H, m), 6.73-7.00 (6H, m), 7.38 (2H,dd, J =1.75, 1.20 Hz).

[0042] After vacuum distillation, 0.05 g of polymerization inhibitor 701, 43.3 g (0.3 mol) of 4-hydroxybutyl acrylate, and 0.9 g of YKCHWD-1 solid acid catalyst resin (Tianjin Yunkai) were added to the reaction vessel. The mixture was heated to 75°C and nitrogen gas was continuously introduced for 1 hour. The solid acid catalyst resin was then removed by filtration to obtain the final modified furan resin. The formaldehyde residue of the modified furan resin prepared in Example 2 was found to be 0.39 wt% according to the method in Example 1.

[0043] Structural characterization of the modified furan resin: 1 H-NMR (CDCl3): δ 1.78 (4H, dddd, J = 7.43, 7.43, 7.25, 7.25 Hz), 1.89(4H,dddd, J = 7.43, 7.43, 7.12, 7.12 Hz), 2.24 (3H, s), 3.26 (4H, d, J = 6.31Hz), 3.39 (4H, dd, J = 7.25, 7.25 Hz), 4.32 (4H, dd, J = 7.12, 7.12 Hz), 4.53(4H, s), 4.83 (4H, dd, J= 10.60, 2.40 Hz), 5.46 (1H, s), 5.53 (1H, s), 5.70 (2H, dddd, J = 17.14, 10.60, 6.31, 6.31 Hz), 6.02 (2H, dd, J = 10.94, 1.52 Hz),6.15-6.44 (6H, m), 6.73-7.01 (8H, m), 7.38 (2H,dd, J = 1.75, 1.20 Hz).

[0044] Example 3

[0045] 81.1 g (0.75 mol) of o-cresol, 33.6 g (0.25 mol) of o-allylphenol, 1.2 g of polymerization inhibitor p-methoxyphenol, 67.3 g (0.7 mol) of furfural, and 3.5 mL of 25 wt% ammonia water were added to a reaction vessel equipped with a reflux condenser. Then, stirring was started and nitrogen gas was introduced into the reaction vessel. The temperature was raised to 120 °C and the reaction was carried out for 12 hours.

[0046] After the reaction was completed, the temperature was lowered to 85°C, and 27g of 50.2wt% formaldehyde aqueous solution was added. The reaction was continued for 3 hours. Hydroxymethyl groups were introduced through polycondensation. After the reaction was completed, the temperature was lowered to 60°C and 1.33kPa (10mmHg) for vacuum distillation.

[0047] After vacuum distillation, 0.05 g of polymerization inhibitor 701, 50.5 g (0.35 mol) of 4-hydroxybutyl acrylate, and 0.9 g of YKCHWD-1 solid acid catalyst resin (Tianjin Yunkai) were added to the reaction vessel. The mixture was heated to 75°C and nitrogen gas was continuously introduced for 1 hour. The solid acid catalyst resin was then removed by filtration to obtain the final modified furan resin. The formaldehyde residue of the modified furan resin prepared in Example 3 was found to be 0.36 wt% according to the method in Example 1.

[0048] Example 4

[0049] Based on Example 1, 4-hydroxybutyl acrylate was replaced with 40g (0.25mol) of glycerol monomethacrylate, while the amounts of other raw materials and operating procedures remained unchanged. Following the method of Example 1, the formaldehyde residue of the modified furan resin prepared in Example 4 was found to be 0.21wt%.

[0050] Example 5

[0051] Based on Example 1, 4-hydroxybutyl acrylate was replaced with 48.1 g (0.3 mol) of glycerol monomethacrylate, while the amounts of other raw materials and operating procedures remained unchanged. Following the method of Example 1, the formaldehyde residue of the modified furan resin prepared in Example 5 was found to be 0.20 wt%.

[0052] 1 H-NMR (CDCl3): δ1.83 (6H, s), 2.21 (3H, s), 3.22 (4H, d, J = 6.31 Hz), 3.51 (4H, d, J = 5.35 Hz), 4.07 (2H, dddd, J = 7.07, 7.07, 5.35, 5.35 Hz),4.50(4H,d, J = 7.07 Hz), 4.59 (4H, s), 4.87 (4H, dd, J = 10.60, 2.40 Hz), 5.41-5.81(6H, m), 6.05 (2H,d, J = 3.86 Hz), 6.20 (2H,dd, J = 3.39, 1.75 Hz), 6.29 (1H,dd, J = 3.39, 1.20 Hz), 6.37 (1H,dd, J = 3.39, 1.20 Hz)), 6.73-7.01 (6H, m),7.38 (2H,dd, J = 1.75, 1.20 Hz).

[0053] Example 6

[0054] Based on Example 1, 4-hydroxybutyl acrylate was replaced with 56.1 g (0.35 mol) of glycerol monomethacrylate, while the amounts of other raw materials and operating procedures remained unchanged. The modified furan resin prepared in Example 6 was tested using the method of Example 1 and found to have a formaldehyde residue of 0.17 wt%.

[0055] Example 7

[0056] The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Example 1, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0057] Preparation process of furan resin-based coating: First, pigments, fillers, dispersants, defoamers and the prescribed amount of ethanol solvent are added to a high-speed disperser and dispersed at a speed of 1500 r / min for 40 minutes to obtain pigment paste; Subsequently, modified furan resin was added to the pigment slurry, and the formulation amount of n-butanol solvent was added to adjust the viscosity of the coating. Finally, leveling agent and drying agent (manganese naphthenate, calcium naphthenate and zinc naphthenate) were added, and the mixture was dispersed at 1000 r / min for 20 minutes. After filtration, furan resin-based coating was obtained.

[0058] Example 8

[0059] The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Example 2, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0060] The preparation process of the furan resin-based coating is the same as in Example 7.

[0061] Example 9

[0062] The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Example 3, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0063] The preparation process of the furan resin-based coating is the same as in Example 7.

[0064] Example 10

[0065] The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Example 4, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0066] The preparation process of the furan resin-based coating is the same as in Example 7.

[0067] Example 11

[0068] The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Example 5, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0069] The preparation process of the furan resin-based coating is the same as in Example 7.

[0070] Example 12

[0071] The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Example 6, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0072] The preparation process of the furan resin-based coating is the same as in Example 7.

[0073] Comparative Example 1 Based on Example 1, 4-hydroxybutyl acrylate was not added to the reaction, while the amounts of other raw materials and operating procedures remained unchanged. Following the method of Example 1, the formaldehyde residue in the modified furan resin prepared in Comparative Example 1 was found to be 1.32 wt%.

[0074] Comparative Example 2 Based on Example 1, 4-hydroxybutyl acrylate was replaced with 18.5 g (0.25 mol) of n-butanol, while the amounts of other raw materials and operating procedures remained unchanged. Following the method of Example 1, the formaldehyde residue of the modified furan resin prepared in Comparative Example 2 was found to be 0.51 wt%.

[0075] Comparative Example 3 Based on Example 1, o-allylphenol was no longer added, and the amount of o-cresol was changed to 108.1 g (1 mol), while the amounts of other raw materials and operating procedures remained unchanged. The modified furan resin prepared in Comparative Example 3 was tested using the method of Example 1 and found to have a formaldehyde residue of 0.45 wt%.

[0076] Comparative Example 4 The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Comparative Example 2, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0077] Comparative Example 5 The furan resin-based coating, by weight, comprises: 65 parts by weight of the modified furan resin prepared in Comparative Example 3, 45 parts by weight of iron oxide red, 15 parts by weight of talc, 20 parts by weight of calcium carbonate, 30 parts by weight of ethanol, 15 parts by weight of n-butanol, 1.5 parts by weight of dispersant BYK-110, 0.6 parts by weight of leveling agent BYK-333, 0.5 parts by weight of defoamer BYK-019, 0.05 parts by weight of manganese naphthenate, 0.03 parts by weight of calcium naphthenate, and 0.02 parts by weight of zinc naphthenate.

[0078] Test section DSC thermal analysis was performed on the cured products of the furan resin-based coatings of Examples 8 and 11. The heating rate was 10°C / min, and the test atmosphere was nitrogen. The test results are as follows: Figure 1 and Figure 2 As shown, based on the DSC test results, the glass transition temperature was determined by the midpoint method using the heat flow step of the DSC curve, referring to the method in ASTM E1356-25. Thus, the glass transition temperature of the coating in Example 8 after curing was found to be 102.9℃, and the glass transition temperature of the coating in Example 11 after curing was found to be 116.4℃.

[0079] Examples 7-12: Furan resin-based coatings were applied by dip coating onto sanded and degreased tinplate test pieces (150mm×70mm×0.8mm), surface dried at room temperature for 4 hours, and then heat-cured in an oven at 150℃ for 0.5 hours to obtain a paint film with a dry film thickness of 23±3μm.

[0080] The adhesion of the paint film was tested using the cross-cut test method according to GB / T 9286-2021, with a cross-cut spacing of 1 mm; the pencil hardness of the paint film was tested according to GB / T 6739-2006; the flexibility of the paint film was tested using the cylindrical shaft bending method according to GB / T 6742-2007; the boiling water resistance of the paint film was tested according to Method B of GB / T 1733-1993; the acid and alkali resistance of the paint film were tested according to GB / T 1763-1989, and the edges of the test pieces were sealed with a paraffin-rosin mixture before the boiling water, acid, and alkali resistance tests; acid resistance was tested using a 5wt% HCl solution; and alkali resistance was tested using a 5wt% NaOH solution.

[0081] The anti-corrosion effect of the paint film was rapidly evaluated using electrochemical impedance spectroscopy (EIS). An electrochemical workstation and a three-electrode system were used for EIS testing. A corner of the paint film was sanded off to expose the metal substrate as the working electrode. An Ag / AgCl electrode was used as the reference electrode, and a graphite rod as the counter electrode. A 3.5 wt% NaCl solution was used as the electrolyte. EIS testing was performed after the open-circuit potential stabilized. The frequency range of the impedance test was selected from 10⁻² to 10⁵ Hz, with a signal amplitude of 10 mV. The low-frequency impedance modulus |Z| = 0.01 Hz at 10⁻² Hz was recorded. This low-frequency impedance modulus and the mid-frequency phase angle of the Bode plot were used to evaluate the anti-corrosion effect of the paint film. The corresponding electrochemical experimental results are recorded in Tables 3 and 4.

[0082] The test results are listed in Table 1.

[0083]

[0084] The modified furan resins prepared in Examples 1-6 used furfural as a base material. A condensation reaction was carried out with o-cresol and o-allylphenol containing unsaturated double bonds to introduce formaldehyde for hydroxymethylation. Subsequently, hydroxyl-containing acrylate monomers were introduced to participate in formaldehyde removal under the action of a solid acid catalyst. Simultaneously, etherification reactions were also carried out with the hydroxymethyl groups of the modified furan resin segments, ultimately yielding acryloyl-terminated modified furan resins. These furan resins had very low free formaldehyde content (below 0.5 wt%). In particular, Examples 4-6, which used the -(CHOH)-(CH2OH) structure in glycerol monomethacrylate, showed the best formaldehyde removal effect, achieving free formaldehyde levels below 0.25 wt%. Comparative Example 1 did not use hydroxyl-containing acrylate monomers to remove formaldehyde, resulting in a corresponding furan resin with an increased free formaldehyde content of 1.32 wt%. In addition, the acryloyl group can also act as an electron-deficient dienophile to undergo a Diels-Alder reaction with the diene furan ring, or it can undergo a cross-linking reaction with the allyl group in the furan resin under the action of a drying agent, thereby enhancing the cross-linking density and improving the anti-corrosion effect.

[0085] Analysis of the data in Table 1 shows that the coatings in Examples 7-12, based on the modified furan resin prepared in Examples 1-6, exhibited adhesion grades of 0-1, hardness grades of 2H-3H, boiling water resistance exceeding 4 hours, acid and alkali resistance exceeding 168 hours, and electrochemical impedance exceeding 10. 9 The order of magnitude. In Examples 8-9 and 11-12, due to the higher amount of hydroxy acrylate monomer, the resin crosslinking density increased, resulting in a hardness of 3H and a relatively higher electrochemical impedance, but the adhesion decreased slightly. Comparative Example 4 used the furan resin of Comparative Example 2 as a coating, replacing the hydroxyl-containing acrylate with n-butanol. Since n-butanol lacks acryloyl groups and cannot participate in subsequent crosslinking reactions, the flexibility of the cured coating was significantly improved, while the impedance modulus, adhesion, and alkali resistance decreased. This is because the acryloyl group is highly polar, which improves adhesion to the substrate. Furthermore, the double bond of the acryloyl group can undergo a Diels-Alder reaction with the furan ring and oxidatively crosslink with the allyl group under the action of a drying agent, thereby increasing the crosslinking density. Comparative Example 5 used the furan resin of Comparative Example 3 as a coating. It used o-cresol as a monomer for polycondensation with furfural alone. The molecular regularity was higher, and the corresponding coating hardness was improved, but the flexibility was significantly reduced. The impedance modulus was actually reduced. The reason may be that micro-cracks appeared in the coating, which led to a decrease in barrier performance. Chloride ions can easily diffuse in them and penetrate the coating to reach the metal substrate.

[0086] Through Bode plot ( Figure 3 , Figure 4Analysis shows that the mid-frequency phase angles of the coatings in Examples 7-12 and Comparative Example 5 are close to -90°, indicating that the coatings exhibit near-ideal capacitive behavior. As newly prepared coatings, higher absolute values ​​of the mid-frequency phase angles indicate dense cross-linking, strong hydrophobicity, low porosity, and excellent barrier properties. Chloride ions tested electrochemically have difficulty penetrating the coating to reach the metal substrate, only undergoing a displacement current process. Combined with the low-frequency impedance moduli of the coatings in Table 1, all are within 10... 9 At magnitudes above 10, the coatings of Examples 7-12 and Comparative Example 5 are expected to have excellent anti-corrosion effects. The mid-frequency phase angle of Comparative Example 4 shows a significant decrease, which, combined with the low-frequency impedance modulus, indicates that the cross-linking density of the coating in Comparative Example 4 is reduced, making it more susceptible to chloride ion penetration and causing a decline in anti-corrosion performance.

[0087] Finally, it should be noted that the above-described embodiments are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the patent application. It should be pointed out that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Furthermore, it should be understood that after reading the above teachings of this application, those skilled in the art can make various alterations or modifications to this application, and the equivalent forms obtained also fall within the scope of protection of this application. It should also be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A modified furan resin, characterized in that, The raw materials for modified furan resin include: furfural, substituted phenols, formaldehyde solution, and acrylate monomers containing hydroxyl groups; The substituted phenols include: alkyl-substituted phenols and unsaturated alkenyl-substituted phenols; The alkyl-substituted phenols are selected from alkyl-substituted phenols with 1-4 carbon atoms; The unsaturated alkenyl-substituted phenol is selected from unsaturated alkenyl-substituted phenols with 1-6 carbon atoms; The formaldehyde solution is an aqueous solution with a formaldehyde content of 20-60 wt%. The hydroxyl-containing acrylate monomers include acrylates or methacrylates containing at least one hydroxyl group.

2. A method for preparing the modified furan resin as described in claim 1, characterized in that, The reaction involves first performing a condensation reaction using furfural and substituted phenols, followed by adding formaldehyde solution for hydroxymethylation, and finally adding hydroxyl-containing acrylate monomers for etherification while simultaneously eliminating free formaldehyde. The temperature of the condensation reaction is controlled at 100-130℃; The condensation reaction is enhanced with a free radical polymerization inhibitor, which is selected from: phenolic polymerization inhibitors, quinone polymerization inhibitors, aromatic amine polymerization inhibitors, or nitroxide free radical polymerization inhibitors. The condensation reaction uses an alkaline catalyst, which is selected from one or more of ammonia water, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and potassium carbonate aqueous solution; The reaction temperature for the hydroxymethylation reaction is 70-90℃; The etherification reaction uses a solid acid catalytic resin as a catalyst, which is selected from cation exchange resins.

3. The preparation method according to claim 2, characterized in that, In substituted phenols, the molar ratio of alkyl-substituted phenols to unsaturated alkenyl-substituted phenols is (2.3-9):

1.

4. The preparation method according to claim 2, characterized in that, The molar ratio of substituted phenol to furfural is 1:(0.5-0.8); And / or, the molar ratio of substituted phenol to formaldehyde is 1:(0.4-0.7); And / or, the molar ratio of substituted phenol to hydroxyl-containing acrylate monomer is 1:(0.2-0.4).

5. The application of the modified furan resin as described in claim 1 in the preparation of anti-corrosion coatings for metal surfaces.

6. A furan resin-based coating, characterized in that, Furan resin-based coatings include: the modified furan resin as described in claim 1, pigments, fillers, alcohol solvents, additives, and driers; The pigment is selected from one or more of titanium dioxide, iron oxide red, iron oxide yellow and carbon black; The filler is selected from one or more of talc powder, mica powder, mica iron oxide, barium sulfate, calcium carbonate, quartz powder and glass flakes; The alcohol solvent is selected from fatty alcohols with 1 to 4 carbon atoms; The drying agent is selected from self-driving agents and drying aids; The main drying agent includes metal saponins containing multiple oxidation states, and the auxiliary drying agent is a metal saponin that exists in only one oxidation state. The additives include one or more of dispersants, leveling agents, and defoamers.

7. The furan resin-based coating according to claim 6, characterized in that, The furan resin-based coating, by weight, comprises: 60-80 parts by weight of modified furan resin, 40-60 parts by weight of pigment, 20-40 parts by weight of filler, 40-60 parts by weight of alcohol solvent, 1-5 parts by weight of additives, and 0.05-0.2 parts by weight of drying agent.

8. A method for preparing a furan resin-based coating as described in any one of claims 6-7, comprising first dispersing pigments, fillers, dispersants, defoamers and a portion of alcohol solvents, and then preparing a pigment slurry by mechanical dispersion; Modified furan resin and the remaining solvent are then added to the pigment paste, followed by leveling agent and drier. The mixture is then mechanically dispersed to obtain a furan resin-based coating.

9. Use of a furan resin-based coating as described in any one of claims 6-7 in corrosion protection of a metal substrate surface.

10. A coating, obtained by applying the furan resin-based coating of any one of claims 6-7 to the surface of a metal substrate, surface drying at room temperature for 1-24 hours, and then baking at 120-160°C for 15-60 minutes.

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