Water-based cardanol-based epoxy resin curing agent as well as preparation method and application thereof

Abstract

The invention discloses a water-based cardanol-based epoxy resin curing agent as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, uniformly mixing cardanol and a catalyst, then adding hydrogen peroxide into the mixed solution, and stirring and reacting at 45-95 DEG C to obtain epoxidized cardanol; the method comprises the following steps: reacting a micromolecule polyamine solution with polyether polyol glycidyl ether to obtain hydrophilic polyamine; and adding the obtained epoxidized cardanol into hydrophilic polyamine, stirring and reacting at 45-95 DEG C for 3-5 hours, and adding water to adjust the solid content, thereby obtaining the water-based cardanol-based modified epoxy resin curing agent. The process is simple, energy-saving and environment-friendly. When the coating is applied, the hardness of a coating film is 1-3 H, the impact resistance is 25 kg.cm or above, the acid resistance lasts for 8 days or above, the alkali resistance and brine resistance lasts for 30 days or above, and the salt fog resistance lasts for 720 hours or above.

Description

Technical Field

[0001] The present invention relates to the technical field of waterborne epoxy resin curing agents, and particularly relates to a waterborne cashew phenol-based epoxy resin curing agent, a preparation method thereof, and an application thereof. Background Art

[0002] Metal corrosion widely occurs in various fields of the national economy, bringing serious harm to the national economy and personal and property safety. Therefore, the protection against corrosion is very important, especially in heavy anti-corrosion fields such as coastal areas and ships. The epoxy coating is widely used in the anti-corrosion field due to its excellent acid resistance, alkali resistance, and salt spray resistance.

[0003] The film-forming substances of epoxy coatings mainly consist of resins and curing agents, and the performance of the curing agent plays a decisive role in the performance of the coating. Traditional curing agents are all solvent-based curing agents, which will volatilize a large amount of organic substances during use, causing harm to the environment and the human body. While waterborne epoxy curing agents use water as a solvent, and the volatile organic substances are almost zero. However, due to the introduction of hydrophilic groups, the anti-corrosion performance of the film formed by the curing of waterborne epoxy curing agents is often inferior to that of solvent-based curing agents. Therefore, it is of great and urgent practical significance to develop a waterborne epoxy curing agent with high anti-corrosion performance.

[0004] Introducing a hydrophobic chain segment on small molecule polyamines to block the entry of corrosive media into the coating, and at the same time improving the compatibility between the curing agent and the epoxy emulsion can effectively solve the above problems. Chinese invention patent CN101333286A discloses a cashew phenol-modified amine epoxy curing agent. A formaldehyde solution is dropped into a mixed solution of cashew phenol and small molecule polyamines, and through the Mannich base reaction, dehydration and condensation form a phenolic amine curing agent. The phenolic amine generated by the reaction has a large number of amine active hydrogens and phenolic hydroxyl groups, greatly enhancing the reaction activity of the curing agent. The presence of phenolic hydroxyl groups will also promote the curing reaction, reduce the curing temperature, and shorten the curing time. At the same time, the hydrophobic long carbon chain enhances the hydrophobicity and flexibility of the cured film. However, due to the extremely strong hydrophobicity of the prepared phenolic amine, its compatibility with the waterborne epoxy emulsion is poor, and there is a problem of curing agent precipitation during use. Moreover, during its reaction process, it is necessary to add a formaldehyde solution, which poses a huge challenge to environmental protection and safety.

[0005] Chinese invention patent application CN108822281B discloses an aqueous epoxy resin curing agent and its preparation method. The aqueous epoxy resin curing agent first uses an organic acid to neutralize the amino group to form a salt to form a hydrophilic group, and then allows a hydrophilic polyamine to react with the epoxy resin to graft the epoxy resin structure, improving the compatibility with the epoxy resin while increasing the molecular weight of the small molecule polyamine and reducing its toxicity. The prepared curing agent has a simple process, is well dispersed in water, and has good compatibility with the epoxy emulsion. However, due to the addition of an organic acid in the preparation process, the corrosion resistance of the paint film is limited; at the same time, due to the large excess of small molecule polyamine required in the reaction process, a large amount of free small molecule polyamine will also affect the appearance and performance of the coating film.

[0006] Chinese invention patent application CN106883379A discloses an aqueous epoxy resin curing agent, its preparation method, an aqueous epoxy asphalt containing the curing agent, its preparation method and application. The aqueous epoxy resin curing agent first reacts a small molecule polyamine with a polyether polyol glycidyl ether to generate a hydrophilic polyamine, and then reacts the hydrophilic polyamine with the epoxy resin to graft the epoxy structure, improving the compatibility of the curing agent with the epoxy emulsion. The prepared curing agent is well dispersed in water, has good compatibility with the epoxy emulsion, has good emulsifying properties, and does not contain organic acids. However, the prepared curing agent consumes a large amount of amine active hydrogen, its reaction activity decreases, and the crosslinking density is low, making it difficult to meet the anti-corrosion requirements in the heavy anti-corrosion field.

[0007] Chinese invention patent application CN110938209A discloses a preparation method and application of a cardanol-based aqueous epoxy resin curing agent. The curing agent first condenses the epoxy resin with the polyether polyol to obtain an emulsifier containing epoxy groups, and then dehydrates and condenses cardanol, formaldehyde, and a small molecule polyamine to generate a phenolic aldehyde amine by Mannich base reaction, and then reacts the emulsifier containing epoxy groups with the phenolic aldehyde amine to generate a cardanol-based aqueous epoxy resin curing agent. The curing agent introduces the hydrophilic structure of the polyether polyol to improve the water solubility of the curing agent, enabling it to be well compatible with the epoxy emulsion and solving the problem of precipitation of the phenolic aldehyde amine curing agent. At the same time, due to the introduction of cardanol having a hydrophobic long carbon chain, the hydrophobicity and flexibility of the cured film are also enhanced. However, in the reaction process, a formaldehyde solution needs to be added, which poses a huge challenge to environmental protection and safety. Summary of the Invention

[0008] The object of the present invention is to provide an aqueous cardanol-based epoxy resin curing agent and its preparation method in view of the problems of poor compatibility between the existing aqueous epoxy curing agent and the aqueous epoxy coating and limited corrosion resistance of the paint. The curing agent can be well dispersed in water and will not precipitate when used in combination with the aqueous epoxy emulsion. At the same time, the coating prepared by using the curing agent has excellent comprehensive properties, especially excellent acid resistance, alkali resistance, salt water resistance and salt spray resistance.

[0009] Another object of the present invention is to provide the application of the waterborne cardanol-based epoxy resin curing agent in the preparation of metal anti-corrosion coatings.

[0010] In order to achieve the object of the present invention, the present invention provides the following technical solutions:

[0011] A waterborne cardanol-based epoxy resin curing agent and its preparation method, characterized by comprising the following steps:

[0012] (1) Mix cardanol and a catalyst evenly, and then slowly dropwise add hydrogen peroxide to the mixed solution, and stir and react at 45°C to 95°C for 3 to 5 hours to obtain epoxidized cardanol; the catalyst is one or more of concentrated sulfuric acid, formic acid, glacial acetic acid, solid acid IR120H, and p-toluenesulfonic acid;

[0013] (2) Then add and react with polyether polyol glycidyl ether to the small molecule polyamine solution to obtain a hydrophilic polyamine; stir at 45°C to 95°C for 3 to 5 hours to obtain a hydrophilic polyamine;

[0014] (3) Add the epoxidized cardanol obtained in step (1) to the hydrophilic polyamine obtained in step (2), stir and react at 45°C to 95°C for 3 to 5 hours, and add water to adjust the solid content to obtain a waterborne cardanol-based modified epoxy resin curing agent.

[0015] To further achieve the object of the present invention, preferably, in step (1), the mass ratio of the catalyst, cardanol, and hydrogen peroxide is 1:(3 to 6):(3 to 12). The catalyst is one or more of organic acids and inorganic acids, preferably one or more of concentrated sulfuric acid, formic acid, glacial acetic acid, solid acid IR120H, and p-toluenesulfonic acid.

[0016] Preferably, in step (2), the small molecule polyamine is one or more of diethylenetriamine, triethylenetetramine, isophorone diamine, cyclohexanedimethanamine, m-xylenediamine, and polyetheramine D230; the polyether polyol glycidyl ether is polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether. In step (1), the mass ratio of the catalyst, cardanol, and hydrogen peroxide is 1:(3 to 6):(3 to 12); the reaction temperature is 45°C to 95°C; the reaction time is 3 hours to 5 hours.

[0017] Preferably, the molecular weight of the polyether polyol glycidyl ether is 400 to 5000. In step (2), the small molecule polyamine is one or more of diethylenetriamine, triethylenetetramine, isophorone diamine, cyclohexanedimethanamine, m-xylenediamine, and polyetheramine D230.

[0018] Preferably, in step (2), the reaction between the small molecule polyamine solution and the polyether polyol glycidyl ether is a stirring reaction, with a temperature of 45°C to 95°C and a time of 3 to 5 h. The polyether polyol glycidyl ether is a polyether polyol glycidyl ether with a molecular weight of 400 to 5000, and the polyether polyol glycidyl ether is polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.

[0019] Preferably, in step (2), the mass ratio of the small molecule polyamine to the polyether polyol glycidyl ether is (1 to 5):1; the reaction temperature is 45°C to 95°C; the reaction time is 3 h to 5 h.

[0020] Preferably, in step (3), the mass ratio of the hydrophilic polyamine to the epoxidized cashew phenol is (2 to 6):1.

[0021] Preferably, in step (3), adding water to adjust the solid content means adding deionized water to adjust the solid content to 45% to 65%, and then stirring for 20 min to 30 min and cooling to room temperature. In step (3), the reaction temperature is 45°C to 95°C; the reaction time is 3 h to 5 h.

[0022] An aqueous cashew phenol-based epoxy resin curing agent is prepared by the above preparation method.

[0023] An application of an aqueous cashew phenol-based epoxy resin curing agent in the preparation of a metal anti-corrosion coating.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) The present invention uses the reaction of double bond epoxidation to prepare a multi-functional long carbon chain epoxidized cashew phenol, which not only introduces a long carbon chain with excellent hydrophobic properties but also improves the functionality of the curing agent, thereby increasing the cross-linking density and hydrophobicity of the cured coating, and greatly improving the anti-corrosion performance of the coating from two aspects of isolating the corrosive medium and blocking the ion channels; at the same time, different from the traditional Mannich base reaction, this reaction does not require the addition of formaldehyde, and the obtained product is safer and more environmentally friendly.

[0026] (2) In the preparation method of the present invention, the long carbon chain epoxidized cashew phenol and the hydrophilic polyether polyol glycidyl ether chain segments are formulated to regulate the amphiphilicity of the curing agent, effectively solving the compatibility problem between the curing agent and the aqueous epoxy resin and improving the film performance; at the same time, the polyether polyol glycidyl ether has a flexible chain segment, which can effectively solve the problem that the cured product of a general epoxy curing agent is too brittle. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the synthesis principle of the aqueous cashew phenol epoxy curing agent.

[0028] Figure 2 Apparent diagram of the paint film applied to tinplate for Comparative Example 1 and Comparative Example 2.

[0029] Figure 3 Adhesion test diagram of Example 3 and Comparative Example 3 applied to tinplate.

[0030] Figure 4 Side view of the acid resistance performance of Example 4 and Comparative Example 3 applied to tinplate. Specific implementation mode

[0031] To better understand the present invention, the present invention will be further described below in conjunction with embodiments. However, the scope claimed by the present invention is not limited to the scope expressed by the embodiments.

[0032] Cardanol itself is a natural product, which is green, environmentally friendly, cheap and easily available, and has many reactive sites. It is a chemical raw material with high industrial added value. As Figure 1 shown, the mechanism for preparing the waterborne cardanol-based epoxy resin curing agent of the present invention is as follows: The present invention discovers that when the catalyst is one or more of concentrated sulfuric acid, formic acid, glacial acetic acid, solid acid IR120H, and p-toluenesulfonic acid, cardanol, hydrogen peroxide and the catalyst can react to obtain epoxidized cardanol; specifically, cardanol and the catalyst are mixed evenly, and then hydrogen peroxide is added to the mixed solution, and the reaction is stirred at 45°C to 95°C for 3 to 5 hours. Based on the reaction mechanism, the dosages of the catalyst, cardanol, and hydrogen peroxide in the present invention can be obtained through experiments in combination with the purpose of the invention. Preferably, the mass ratio of the catalyst, cardanol, and hydrogen peroxide is 1:(3 to 6):(3 to 12). The epoxidized cardanol reacts with hydrophilic polyamines to introduce cardanol containing phenolic hydroxyl groups and long carbon chain side chains, which can significantly improve the corrosion resistance of the coating. Preferably, the mass ratio of the hydrophilic polyamine to the epoxidized cardanol is (2 to 6):1; the phenolic hydroxyl groups it has can react with the substrate to improve the adhesion of the coating; at the same time, during the process of curing the curing agent and the epoxy emulsion into a film, the phenolic hydroxyl groups can form hydrogen bonds with the oxygen atoms of the epoxy groups to promote ring opening, acting as an epoxy accelerator, which can greatly reduce the curing temperature and shorten the curing time. The benzene ring structure of cardanol can improve the hardness of the coating, as well as acid and heat resistance. In addition, the long carbon chain side chains on cardanol can provide good hydrophobicity and flexibility, preventing corrosive media from entering the coating through water molecules while improving the flexibility of the coating and solving the problem of large brittleness of the coating.

[0033] The present invention improves the hydrophilicity of the curing agent by introducing polyether polyol glycidyl ether onto small molecule polyamines, enabling it to be well compatible with the epoxy emulsion without precipitation. Without adding organic acids, it will not affect the corrosion resistance of the coating film. At the same time, the long-chain polyether polyol segments will also improve the flexibility of the curing agent. In the present invention, the preparation of the hydrophilic polyamine is a conventional measure in the art. The hydrophilic polyamine is obtained by reacting a small molecule polyamine solution with polyether polyol glycidyl ether. Preferably, the small molecule polyamine is one or more of diethylenetriamine, triethylenetetramine, isophorone diamine, cyclohexanedimethanamine, m-xylenediamine, polyetheramine D230; the reaction of the small molecule polyamine solution with polyether polyol glycidyl ether is preferably a stirring reaction, with a temperature of 45°C to 95°C and a time of 3 to 5 hours; the molecular weight of the polyether polyol glycidyl ether is preferably 400 to 5000; the polyether polyol glycidyl ether is preferably polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether. The mass ratio of the small molecule polyamine to the polyether polyol glycidyl ether is preferably (1 to 5):1.

[0034] According to the purpose of the present invention, the solid content is adjusted by adding deionized water to adjust the solid content to 45% to 65%, and then stirred for 20 min to 30 min and cooled to room temperature.

[0035] It should be noted that the traditional method for modifying the cashew phenol curing agent mainly focuses on the ortho position of the phenolic hydroxyl group, and phenol, aldehyde, and amine are dehydrated and condensed through the Mannich base reaction to form phenolic aldehyde amine. Inevitably, formaldehyde solution needs to be added during the reaction process, which poses a huge challenge to environmental protection and safety. The waterborne cashew phenol-based modified epoxy resin curing agent of the present invention mainly oxidizes the unsaturated double bonds in the side chain into epoxy groups, and then reacts with the hydrophilic modified polyamine to form a curing agent, which can effectively avoid the use of formaldehyde. At the same time, since cashew phenol itself is a mixture, the proportion of cashew phenol with more than two double bonds in the side chain is more than 60%. The curing agent formed after the reaction of the epoxidized cashew phenol with the polyamine has a branched structure, which can more effectively avoid the steric hindrance effect, has more reactive sites, a larger functionality in reacting with the epoxy emulsion, thereby increasing the crosslinking density of the coating, blocking the ion channels of the corrosive medium, and further improving the corrosion resistance of the coating.

[0036] The anti-corrosion performance of the coating of the present invention is improved from two aspects: blocking corrosive media and sealing the ion channels of corrosive media. At the same time, the special structure of cardanol also improves the properties of the coating such as hardness, adhesion, and flexibility. It is a waterborne epoxy resin curing agent with excellent comprehensive performance. The coating prepared by compounding this curing agent with epoxy emulsion has excellent mechanical properties. For example, the pencil hardness is between H and 3H, the adhesion reaches grade 0, and the impact resistance is above 25 kg·cm. It can effectively adhere to the metal substrate and protect the substrate against mechanical damage. In particular, the coating obtained by using the curing agent of the present invention has good corrosion resistance. The acid resistance duration is more than 14 days, the alkali and brine resistance durations are both more than 30 days, and the salt spray resistance duration is more than 720 hours, which can meet the anti-corrosion requirements of metal equipment in heavy anti-corrosion fields such as offshore platforms and heavy salt areas.

[0037] The testing methods for the coatings obtained in each embodiment of the present invention are tested according to the following standards.

[0038] Hardness: GB / T 6379-2022;

[0039] Impact resistance: GB / T 1732-93;

[0040] Adhesion: GB / T 9286-2021;

[0041] Salt water resistance performance: GB / T 9274-1988;

[0042] Acid and alkali resistance performance: GB / T 9274-1988;

[0043] Salt spray resistance performance: GB / T 1771-2007;

[0044] Example 1:

[0045] (1) Preparation of waterborne cardanol-based epoxy resin curing agent

[0046] Put 50 g of cardanol, 7 g of glacial acetic acid, and 1.5 g of p-toluenesulfonic acid into a four-necked flask and mix evenly. Slowly heat up to 60 °C, and use a peristaltic pump to dropwise add 80.92 g of 30% hydrogen peroxide solution. React at 75 °C for 4 h to obtain epoxidized cardanol.

[0047] Put 40.8 g of diethylenetriamine into a four-necked flask and mix evenly. Slowly heat up to 45 °C, and use a peristaltic pump to dropwise add 20 g of polyethylene glycol diglycidyl ether. React at 85 °C for 3 h to obtain a hydrophilic modified polyamine.

[0048] Slowly drop 30 g of epoxidized cardanol into the hydrophilic polyamine. React at 55 °C for 3 h, and then use a peristaltic pump to dropwise add 49 g of deionized water to adjust the solid content to 65% to obtain a waterborne cardanol-based epoxy resin curing agent.

[0049] (2) Preparation of Epoxy Varnish

[0050] Take 10 g of the prepared 2092 epoxy emulsion, 2 g of waterborne cashew phenol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer, and mix them evenly to obtain epoxy varnish.

[0051] Example 2:

[0052] (1) Preparation of Waterborne Cashew Phenol-Based Modified Epoxy Resin Curing Agent

[0053] Put 50 g of cashew phenol, 9.36 g of sulfuric acid, and 1.75 g of solid acid IR120H into a four-necked flask and mix evenly. Slowly heat up to 50 °C, and use a peristaltic pump to dropwise add 69.36 g of 30% hydrogen peroxide solution. React at 65 °C for 5 h to obtain epoxidized cashew phenol.

[0054] Put 40.8 g of m-phenylenediamine into a four-necked flask and mix evenly. Slowly heat up to 65 °C, and use a peristaltic pump to dropwise add 40 g of polypropylene glycol diglycidyl ether. React at 55 °C for 3 h to obtain a hydrophilic modified polyamine.

[0055] Slowly drop 20 g of epoxidized cashew phenol into the hydrophilic polyamine. React at 75 °C for 4 h, and then use a peristaltic pump to dropwise add 57 g of deionized water to adjust the solid content to 60% to obtain a waterborne cashew phenol-based epoxy resin curing agent.

[0056] (2) Preparation of Epoxy Varnish

[0057] Take 10 g of the prepared 2092 epoxy emulsion, 2.25 g of waterborne cashew phenol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer, and mix them evenly to obtain epoxy varnish.

[0058] Example 3:

[0059] (1) Preparation of Waterborne Cashew Phenol-Based Epoxy Resin Curing Agent

[0060] Put 50 g of cashew phenol, 11.7 g of formic acid, and 1.2 g of solid acid IR120H into a four-necked flask and mix evenly. Slowly heat up to 60 °C, and use a peristaltic pump to dropwise add 57.8 g of 30% hydrogen peroxide solution. React at 75 °C for 4 h to obtain epoxidized cashew phenol.

[0061] Put 40.8 g of polyetheramine D230 into a four-necked flask and mix evenly. Slowly heat up to 65 °C, and use a peristaltic pump to dropwise add 30 g of polyethylene glycol diglycidyl ether. React at 65 °C for 4 h to obtain a hydrophilic modified polyamine.

[0062] Slowly add 40 g of epoxidized cashew phenol dropwise to the hydrophilic polyamine, react at 65 °C for 3 h, then use a peristaltic pump to add 110.8 g of deionized water drop by drop to adjust the solid content to 50%, and obtain an aqueous cashew phenol-based epoxy resin curing agent.

[0063] (2) Preparation of epoxy varnish

[0064] Take 10 g of the prepared 2092 epoxy emulsion, 2.5 g of the aqueous cashew phenol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer, mix them evenly to obtain epoxy varnish.

[0065] Example 4:

[0066] (1) Preparation of aqueous cashew phenol-based epoxy resin curing agent

[0067] Place 50 g of cashew phenol, 13.8 g of formic acid, and 2 g of p-toluenesulfonic acid in a four-necked flask and mix evenly. Slowly heat up to 50 °C, and use a peristaltic pump to add 86.7 g of 30% hydrogen peroxide solution drop by drop. React at 85 °C for 5 h to obtain epoxidized cashew phenol.

[0068] Place 51 g of isophorone diamine in a four-necked flask and mix evenly. Slowly heat up to 75 °C, and use a peristaltic pump to add 10 g of polyethylene glycol diglycidyl ether drop by drop. React at 75 °C for 4 h to obtain a hydrophilic modified polyamine.

[0069] Slowly add 20 g of epoxidized cashew phenol dropwise to the hydrophilic polyamine, react at 75 °C for 5 h, then use a peristaltic pump to add 54 g of deionized water drop by drop to adjust the solid content to 60%, and obtain an aqueous cashew phenol-based epoxy resin curing agent.

[0070] (2) Preparation of epoxy varnish

[0071] Take 10 g of the prepared 2092 epoxy emulsion, 2.25 g of the aqueous cashew phenol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer, mix them evenly to obtain epoxy varnish.

[0072] Example 5:

[0073] (1) Preparation of aqueous cashew phenol-based epoxy resin curing agent

[0074] Place 50 g of cashew phenol, 12.48 g of glacial acetic acid, and 1 g of p-toluenesulfonic acid in a four-necked flask and mix evenly. Slowly heat up to 60 °C, and use a peristaltic pump to add 92.48 g of 30% hydrogen peroxide solution drop by drop. React at 75 °C for 4 h to obtain epoxidized cashew phenol.

[0075] Place 40.8 g of cyclohexanediamine diamine in a four-necked flask and mix evenly. Slowly heat up to 55 °C, and use a peristaltic pump to dropwise add 20 g of polyethylpropylene glycol diglycidyl ether. React at 65 °C for 3 h to obtain a hydrophilic modified polyamine.

[0076] Slowly drop 20 g of epoxidized cashew phenol into the hydrophilic polyamine. React at 65 °C for 3 h, then use a peristaltic pump to dropwise add 65.5 g of deionized water to adjust the solid content to 45%, and obtain an aqueous cashew phenol-based epoxy resin curing agent.

[0077] (2) Preparation of epoxy varnish

[0078] Take 10 g of the prepared 2092 epoxy emulsion, 2.75 g of the aqueous cashew phenol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoaming agent and mix evenly to obtain an epoxy varnish.

[0079] Example 6:

[0080] (1) Preparation of aqueous cashew phenol-based epoxy resin curing agent

[0081] Place 50 g of cashew phenol, 14 g of sulfuric acid, and 1.4 g of p-toluenesulfonic acid in a four-necked flask and mix evenly. Slowly heat up to 50 °C, and use a peristaltic pump to dropwise add 75.14 g of 30% hydrogen peroxide solution. React at 55 °C for 5 h to obtain epoxidized cashew phenol.

[0082] Place 40.8 g of triethylenetetramine in a four-necked flask and mix evenly. Slowly heat up to 55 °C, and use a peristaltic pump to dropwise add 40 g of polyethylene glycol diglycidyl ether. React at 85 °C for 4 h to obtain a hydrophilic modified polyamine.

[0083] Slowly drop 30 g of epoxidized cashew phenol into the hydrophilic polyamine. React at 65 °C for 4 h, then use a peristaltic pump to dropwise add 90 g of deionized water to adjust the solid content to 55%, and obtain an aqueous cashew phenol-based epoxy resin curing agent.

[0084] (2) Preparation of epoxy varnish

[0085] Take 10 g of the prepared 2092 epoxy emulsion, 2 g of the aqueous cashew phenol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoaming agent and mix evenly to obtain an epoxy varnish.

[0086] Comparative Example 1: (Without polyether polyol glycidyl ether with hydrophilic chain segment)

[0087] (1) Preparation of aqueous cashew phenol-based epoxy resin curing agent

[0088] Mix 50 g of cardanol, 7.8 g of formic acid, and 1 g of p-toluenesulfonic acid evenly in a four-necked flask. Slowly heat up to 50 °C, and use a peristaltic pump to dropwise add 57.8 g of 30% hydrogen peroxide solution. React at 65 °C for 3 h to obtain epoxidized cardanol.

[0089] Slowly drop 20 g of epoxidized cardanol into triethylenetetramine. React at 65 °C for 3 h, reduce the pressure, and then use a peristaltic pump to dropwise add 53 g of deionized water to adjust the solid content to 60% to obtain an aqueous cardanol-based epoxy resin curing agent.

[0090] (2) Preparation of epoxy varnish

[0091] Take 10 g of the prepared 2092 epoxy emulsion, 2.25 g of the aqueous cardanol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer, and mix them evenly to obtain epoxy varnish.

[0092] Comparative Example 2: (Without cardanol)

[0093] (1) Preparation of aqueous cardanol-based epoxy resin curing agent

[0094] Place 40.8 g of isophorone diamine in a four-necked flask and mix evenly. Slowly heat up to 65 °C, and use a peristaltic pump to dropwise add 20 g of polyethylene glycol diglycidyl ether. React at 65 °C for 3 h to obtain a hydrophilic modified polyamine. Then use a peristaltic pump to dropwise add 40 g of deionized water to adjust the solid content to 60% to obtain an aqueous cardanol-based epoxy resin curing agent.

[0095] (2) Preparation of epoxy varnish

[0096] Take 10 g of the prepared 2092 epoxy emulsion, 2.25 g of the aqueous cardanol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer, and mix them evenly to obtain epoxy varnish.

[0097] Comparative Example 3: (Synthesize an aqueous cardanol-based epoxy resin curing agent at the ortho position of the phenolic hydroxyl group of cardanol by Mannich base reaction)

[0098] (1) Preparation of aqueous cardanol-based epoxy resin curing agent

[0099] Place 40.8 g of isophorone diamine in a four-necked flask and mix evenly. Slowly heat up to 65 °C, and use a peristaltic pump to dropwise add 20 g of polyethylene glycol diglycidyl ether. React at 65 °C for 3 h to obtain a hydrophilic modified polyamine.

[0100] 30 g of hydrophilically modified polyamine, 30 g of cardanol, and 25 g of ethanol were placed in a four-necked flask and mixed evenly. The temperature was slowly raised to 65 °C, and 10 g of formaldehyde was added dropwise using a peristaltic pump. The reaction was carried out at 90 °C for 3 h, and the solvent was removed by vacuum distillation. Then, 53 g of deionized water was added dropwise using a peristaltic pump to adjust the solid content to 60%, and an aqueous cardanol-based epoxy resin curing agent was obtained.

[0101] (2) Preparation of epoxy varnish

[0102] 10 g of the prepared 2092 epoxy emulsion, 2.25 g of the aqueous cardanol-based epoxy resin curing agent, and 0.1 g of AKN3386 defoamer were mixed evenly to obtain an epoxy varnish.

[0103] The epoxy varnishes obtained in the above Examples 1-6 were applied to tinplate for film coating. The dry film thickness was about 50 μm, and the film performance was tested after drying at room temperature for 7 days. The test results are shown in Table 1.

[0104] Table 1 Film performance of epoxy emulsion cured film

[0105]

[0106] From the results in Table 1, there are problems with the deviation of the comprehensive performance of the coatings in the comparative examples. The highest hardness in the comparative examples is H, and the hardness of Comparative Example 2 is only HB. The adhesion is below level 0, and the impact resistance is below 25 kg·cm. In particular, it is difficult to achieve the balance of comprehensive performance in the comparative examples. For example, although the hardness of Comparative Examples 3 and 1 reaches H, the adhesion is only 1 and 2 respectively, not reaching level 0, and there is an obvious gap in the corrosion resistance performance compared with the examples of the present invention. In Examples 1-6 of the present invention, the obtained coatings show excellent acid resistance, alkali resistance and salt resistance. There are also obvious differences in the performance of all aspects between Comparative Example 2 and Comparative Examples 1 and 3, and the gap is even greater compared with Examples 1-6. Specifically, hydrophilic polyether polyol glycidyl ether segments are introduced in Examples 1-6, and the side-chain double bonds of cardanol are epoxidized to form a branched structure. The hardness of the coatings is above H, the impact resistance is above 25 kg·cm, the adhesion is at level 0, and there is no problem of brittle coatings. The corrosion resistance of Example 1, which has the worst corrosion resistance among the examples, is also better than that of the comparative examples. Its acid resistance is above 8 days, alkali resistance is above 20 days, salt water resistance is above 30 days, and salt spray resistance is above 20 days, and it also has excellent protective performance for tinplate. This is mainly due to the special structure of cardanol. The benzene ring structure provides good hardness and impact resistance for the coating, the presence of phenolic hydroxyl groups provides excellent adhesion for the coating and promotes the curing of the coating, and the long carbon chain side chains provide good hydrophobicity for the coating. The branched structure improves the crosslinking density of the coating, and improves the anti-corrosion performance from two aspects: blocking the corrosion medium and closing the ion channels of the corrosion medium. The introduction of hydrophilic segments ensures that the waterborne cardanol-based modified epoxy resin curing agent can be well compatible with the waterborne epoxy emulsion without precipitation. Coatings are the simplest and most effective method to protect metals and wood from corrosion, and the main function of coatings is basically to protect easily corroded materials. While meeting the requirements of film transparency, hardness, impact resistance and excellent adhesion, the present invention greatly improves the corrosion resistance of the coating and can be effectively used for the varnish protection of metals and wood.

[0107] Figure 2The left side in the middle is the coating appearance obtained by compounding Example 1 with 2092 epoxy emulsion. In Example 1, no hydrophilic segment polyether polyol glycidyl ether is added. Although it can also form a branched structure while introducing cardanol, its hydrophobicity is too strong. When compounded with water-based epoxy emulsion, it has poor compatibility and will separate the curing agent into phases, resulting in uneven coating and shrinkage holes. This will affect the overall performance of the entire coating. The corrosive medium can also pass through the coating through the shrinkage holes of the coating and contact the substrate, thereby corroding the substrate. In Example 2, no cardanol is added, and small molecule polyamines are directly reacted with polyether polyol glycidyl ether. Although the obtained curing agent is well compatible with the water-based epoxy emulsion, since the small molecule polyamine needs to be greatly excessive during the reaction, there will be many free small molecule amines. The free small molecule amines will react rapidly with the latex particles on the surface, blocking the curing agent from further entering the interior of the latex particles, resulting in incomplete curing of the coating, such as Figure 2 Shown on the right.

[0108] Free small molecule amines will also react with carbon dioxide and water in the air, affecting the various properties of the coating. In Comparative Example 3, the traditional Mannich base reaction was used to introduce the cardanol structure into the curing agent. Compared with Examples 1-6, it can be seen that the water-based cardanol-modified epoxy resin curing agent generated by the Mannich base reaction has good performance in hardness, adhesion, impact resistance, etc. because it also has the structure of cardanol. However, there is still a significant gap in comprehensive performance compared with the examples, as can be seen in detail. Figure 3 and Figure 4 . Figure 3 The adhesion of the paint film of Example 3 and Comparative Example 3 is compared. Since the epoxy group reacts with the amino group to generate a hydroxyl group, the adhesion of the coating is improved. Therefore, the adhesion of the curing agent generated by the Mannich base reaction is lower than that of Examples 1-6, and it is a linear structure. Compared with Examples 1-6 with a branched structure, its cross-linking density is lower, and the obtained coating is acid-resistant for 7 days, alkali-resistant for 15 days, salt water-resistant for 20 days, and salt spray-resistant for 20 days, which are all worse than Examples 1-6.

[0109] Figure 4 The acid resistance of Example 4 is compared with that of Comparative Example 3. It can be seen that after the coating prepared in Comparative Example 3 was immersed in a 5% sulfuric acid solution for 14 days, only slight corrosion occurred at the coating defects; while after the Comparative Example 3 was immersed in a 5% sulfuric acid solution for 7 days, the sulfuric acid solution had penetrated into the coating and corroded the tinplate. In addition, the addition of formaldehyde solution during the synthesis process will also affect environmental protection and safety.

[0110] In the present invention, the unsaturated double bonds in the side chain of cardanol are oxidized to epoxy groups to form a branched structure, and then reacted with a hydrophilic modified polyamine to form a curing agent. While introducing a hydrophilic chain segment to improve the compatibility with the waterborne epoxy emulsion, cardanol is introduced and a branched structure is formed. The hydrophobic cardanol can effectively block the entry of corrosive media into the coating; and the branched structure can effectively reduce the steric hindrance effect, enhance the reaction activity, increase the functionality of the epoxy emulsion reaction and the crosslinking density of the coating, and block the ion channels of the corrosive media. While ensuring that the coating has excellent hardness, adhesion and impact resistance, the corrosion resistance of the coating is improved from two aspects of blocking the corrosive media and blocking the ion channels of the corrosive media, which is a waterborne epoxy resin curing agent with excellent comprehensive performance.

[0111] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an aqueous cardanol-based epoxy resin curing agent, characterized in that It includes the following steps: (1) Mix cardanol and a catalyst evenly, then add hydrogen peroxide to the mixed solution, and stir and react at 45°C to 95°C for 3 to 5 hours to obtain epoxidized cardanol; the catalyst is one or more of concentrated sulfuric acid, formic acid, glacial acetic acid, solid acid IR120H, and p-toluenesulfonic acid; (2) React a small molecule polyamine solution with a polyether polyol glycidyl ether to obtain a hydrophilic polyamine; (3) Add the epoxidized cardanol obtained in step (1) to the hydrophilic polyamine obtained in step (2), stir and react at 45°C to 95°C for 3 hours to 5 hours, and add water to adjust the solid content to obtain an aqueous cardanol-based modified epoxy resin curing agent.

2. The preparation method of the waterborne cardanol-based epoxy resin curing agent according to claim 1, characterized in that, In step (1), the mass ratio of the catalyst, cardanol, and hydrogen peroxide is 1:(3 to 6):(3 to 12).

3. The waterborne cashew phenol-based epoxy resin curing agent according to claim 1 and its preparation method are characterized in that, In step (2), the small molecule polyamine is one or more of diethylenetriamine, triethylenetetramine, isophoronediamine, cyclohexanedimethanamine, m-xylenediamine, and polyetheramine D230; the polyether polyol glycidyl ether is polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.

4. The preparation method of the aqueous cardanol-based epoxy resin curing agent according to claim 3, characterized in that, The polyether polyol glycidyl ether has a molecular weight of 400 to 5000.

5. The preparation method of the waterborne cardanol-based epoxy resin curing agent according to claim 1, wherein In step (2), the reaction of the small molecule polyamine solution with the polyether polyol glycidyl ether is a stirring reaction, the temperature is 45°C to 95°C, and the time is 3 to 5 hours.

6. The preparation method of the aqueous cardanol-based epoxy resin curing agent according to claim 1, wherein The mass ratio of the small molecule polyamine to the polyether polyol glycidyl ether is (1 to 5):

1.

7. The preparation method of the waterborne cardanol-based epoxy resin curing agent according to claim 1, characterized in that, The mass ratio of the hydrophilic polyamine to the epoxidized cardanol is (2 to 6):

1.

8. The preparation method of the waterborne cardanol-based epoxy resin curing agent according to claim 1, wherein In step (3), adding water to adjust the solid content means adding deionized water to adjust the solid content to 45% to 65%, then stirring for 20 minutes to 30 minutes, and cooling to room temperature.

9. An aqueous cashew phenol-based epoxy resin curing agent, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. Use of the aqueous cardanol-based epoxy resin curing agent according to claim 9 in the preparation of metal anticorrosive coatings.

Images