A waterborne epoxy coating, its preparation method and use

Abstract

The present application belongs to the technical field of paint, and particularly relates to a water-based epoxy coating, a preparation method and application thereof. The water-based epoxy coating comprises component A and component B. Component A comprises water-based epoxy resin, additives, pigments, fillers and water. Component B comprises amine water-based epoxy curing agent, reaction regulator, additives and water. The reaction regulator comprises carboxylic acid or a derivative thereof. By introducing carboxylic acid or a derivative thereof as a reaction regulator in the curing agent component, the inherent process of water content change from wet film to dry film of the water-based coating is used as an environmental signal to trigger the curing reaction switch, so that the precise space-time control of the chemical reaction process is realized, the water-based epoxy coating has a long applicable period, the curing speed is fast, and the performance after curing is good.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a water-based epoxy coating, its preparation method, and its application. Background Technology

[0002] Waterborne epoxy coatings are gradually replacing traditional solvent-based coatings and are widely used in metal corrosion protection, industrial flooring, and automotive parts due to their advantages such as low volatile organic compound (VOC) content, safety and environmental friendliness, and strong adhesion to substrates. However, compared with solvent-based systems, waterborne epoxy coatings have a significant technical shortcoming: a short pot life (or activation period).

[0003] The pot life refers to the time it takes for a two-component coating to reach a point where its viscosity increases to the point where it cannot be applied or its performance begins to deteriorate after mixing. The fundamental reason for the short pot life of waterborne epoxy coatings is that their curing reaction, namely the ring-opening addition reaction between epoxy and amine groups, can occur in an aqueous environment. After mixing, water, as the continuous phase, promotes the diffusion and reaction of amine curing agents among the particles of the waterborne epoxy resin emulsion, leading to a rapid increase in the system viscosity, often exceeding the application limit within 1-4 hours. This not only results in material waste but also severely restricts its application in projects requiring large-scale, long-term, or intermittent application.

[0004] To address this issue, existing technologies primarily focus on the following approaches: 1) Developing low-reactivity curing agents: This involves reducing the initial activity of amine groups through molecular design. However, this often leads to slower curing speeds, affecting application efficiency, or incomplete curing at low temperatures. 2) Adding physical barrier agents: This attempts to isolate reactive components using technologies such as microencapsulation. However, this process is complex, costly, and may introduce coating defects. 3) Adjusting the formulation: Such as reducing the amount of curing agent. However, this may result in insufficient crosslinking density, sacrificing the final chemical resistance, hardness, and water resistance of the coating. None of these methods fundamentally resolve the contradiction between "extending the pot life" and "ensuring final cured performance."

[0005] Therefore, it is of great significance to develop a waterborne epoxy coating that is stable in storage, has a long construction period, cures quickly and completely after film formation, and has good performance after curing. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial solution. Specifically, the present invention provides a water-based epoxy coating that has a stable storage period, a long application period, can be quickly and completely cured after film formation, and has good performance after curing.

[0007] The inventive concept of this invention: The waterborne epoxy coating of this invention comprises component A and component B; component A comprises waterborne epoxy resin, additives, pigments, fillers, and water; component B comprises amine-based waterborne epoxy curing agent, reaction regulator, additives, and water; the reaction regulator comprises carboxylic acid or its derivatives.

[0008] This invention, based on an "environmentally responsive reaction control" mechanism, provides a waterborne epoxy coating with a long service life. Its core lies in introducing a specific carboxylic acid or its derivative as a reaction modifier into the curing agent component. In an aqueous environment (during coating storage and after mixing and application), the carboxyl group (-COOH) in the carboxylic acid molecule undergoes proton transfer with the primary and secondary amine groups (-NH2, -NH-) in the amine curing agent, forming an ammonium salt ion pair (-NH3). + … -COO - This ionization and the resulting hydrogen bond network significantly reduce the electron cloud density on the amine nitrogen atom, strongly suppressing its nucleophilic attack on the epoxy group, thus "closing" the main curing reaction pathway. At this point, the system's chemical reaction rate is extremely slow, viscosity increases slowly, and the pot life is extended several times over.

[0009] When the coating is applied to the substrate surface, the system gradually transforms from an aqueous phase to a polymer phase as moisture evaporates. During this process, the reduction in moisture hinders proton migration, leading to a local increase in the pH value of the system. Simultaneously, water molecules maintaining the hydrogen bond network are removed, weakening or even destroying the ion pairs and hydrogen bonds between carboxylic acids and amine groups. The amine groups gradually "deshield," restoring their high reactivity and rapidly undergoing cross-linking reactions with epoxy groups to form a dense three-dimensional network structure. This is the intelligent "activation" of the reactivity.

[0010] This mechanism cleverly utilizes the inherent process of water content change in water-based coatings from wet film to dry film as an environmental signal to trigger the curing reaction switch, thus achieving precise spatiotemporal control of the chemical reaction process.

[0011] Therefore, a first aspect of the present invention provides a waterborne epoxy coating.

[0012] Specifically, the waterborne epoxy coating includes component A and component B; Component A includes waterborne epoxy resin, additives, pigments, fillers, and water; Component B includes an amine-based waterborne epoxy curing agent, a reaction regulator, an additive, and water; The reaction regulator includes carboxylic acids or their derivatives.

[0013] Preferably, the reaction regulator includes at least one of formic acid, acetic acid, propionic acid, citric acid, oxalic acid, and maleic acid.

[0014] Preferably, the acetic acid is glacial acetic acid.

[0015] Preferably, the number of moles of carboxyl groups in the reaction regulator is 10-100% of the total number of theoretically active amine hydrogens in the amine-based waterborne epoxy curing agent.

[0016] Specifically, the amount of reaction regulator added is crucial. Based on the molar number of carboxyl groups (-COOH) it contains, the molar number of carboxyl groups in the reaction regulator should be 10-100% of the total molar number of theoretically active amine hydrogens (H reacting with epoxy) in the amine-based waterborne epoxy curing agent. Below 10%, the inhibition effect is not significant; above 100%, excessive acidity may affect storage stability or have potential impacts on the substrate, and excessive acid residue may interfere with the final coating film performance.

[0017] Preferably, the active hydrogen equivalent of the amine-based waterborne epoxy curing agent is 100-300 g / mol.

[0018] Preferably, the amine-based waterborne epoxy curing agent includes at least one of polyamide, modified polyamide, and phenolic amine.

[0019] Preferably, by mass percentage, component A comprises 20-35% waterborne epoxy resin, 0.8-3.6% additives, 6-20% pigments, 30-50% fillers, and 20-35% water.

[0020] Preferably, by mass percentage, component B comprises 25-50% amine-based waterborne epoxy curing agent, 5-30% reaction regulator, 7.5-31% additives, and 25-42% water.

[0021] Preferably, the additives in component A include at least one of dispersant, defoamer, wetting agent, and thickener.

[0022] Preferably, by mass percentage, component A comprises 20-35% waterborne epoxy resin, 0.2-0.6% dispersant, 0.1-0.5% defoamer, 6-20% pigment, 30-50% filler, 0-0.5% wetting agent, 0.5-2% thickener, and 20-35% water.

[0023] Preferably, the pigment includes coloring pigments and anti-rust pigments.

[0024] Preferably, by mass percentage, component A comprises 20-35% waterborne epoxy resin, 0.2-0.6% dispersant, 0.1-0.5% defoamer, 2-10% coloring pigment, 4-10% anti-rust pigment, 30-50% filler, 0-0.5% wetting agent, 0.5-2% thickener, and 20-35% water.

[0025] Preferably, in component A, the dispersant includes at least one of anionic carboxylate salts, cationic quaternary ammonium salts, and nonionic high molecular weight polymer dispersants.

[0026] Preferably, in component A, the defoamer includes at least one of silicone-based defoamers and mineral oil-based defoamers.

[0027] Preferably, in component A, the coloring pigment includes at least one of iron oxide black, iron oxide red, carbon black, and titanium dioxide.

[0028] Preferably, in component A, the anti-rust pigment includes at least one of silicon dioxide, zinc molybdate, and strontium chrome yellow.

[0029] Preferably, in component A, the filler includes at least one of talc powder, mica powder, calcined kaolin, and silica powder.

[0030] Preferably, in component A, the wetting agent includes a modified polysiloxane wetting agent.

[0031] Preferably, in component A, the thickener includes at least one of polyurethane-type thickener and alkali-swellable thickener.

[0032] Preferably, in component B, the additives include at least one of an anti-flash rust agent, a film-forming aid, an antifoaming agent, and a thickener.

[0033] Preferably, by mass percentage, component B comprises 25-50% amine-based waterborne epoxy curing agent, 5-30% reaction regulator, 0.5-1% flash rust inhibitor, 3-15% film-forming aid, 1-5% defoamer, 3-10% thickener, and 25-42% water.

[0034] Preferably, in component B, the flash rust inhibitor includes at least one of a water-based organic flash rust inhibitor and a water-based inorganic flash rust inhibitor.

[0035] Preferably, in component B, the film-forming aid includes at least one of dodecyl alcohol ester, propylene glycol, dipropylene glycol butyl ether, diethylene glycol butyl ether, and propylene glycol diacetate.

[0036] Preferably, in component B, the defoamer includes a mineral oil-based defoamer.

[0037] Preferably, in component B, the thickener includes at least one of polyurethane-type thickener and alkali-swellable thickener.

[0038] Preferably, the mass ratio of component A to component B is (5-15):1.

[0039] Preferably, the mixing ratio of components A and B, based on the molar ratio (equivalent ratio) of epoxy groups to amine hydrogen, is 1:(0.7-1.1), and a further preferred ratio is 1:0.8. By reasonably limiting the molar ratio of epoxy groups to amine hydrogen, this invention ensures complete final curing while also helping to inhibit the initial reaction and improve the water resistance of the coating film.

[0040] A second aspect of the present invention provides a method for preparing the waterborne epoxy coating described in the first aspect of the present invention.

[0041] Specifically, the preparation method of the waterborne epoxy coating includes the following steps: The raw material components of component A are mixed to obtain component A; The raw material components of component B are mixed to obtain component B; The components A and B constitute the waterborne epoxy coating.

[0042] Preferably, the preparation method of component A includes the following steps: Under stirring conditions, waterborne epoxy resin is added to water, followed by dispersant and defoamer. After uniform dispersion, coloring pigment, filler and anti-rust pigment are added, mixed evenly and then ground to obtain a slurry. Wetting agent and thickener are added to the slurry and dispersed evenly to obtain component A.

[0043] Preferably, the fineness of the slurry is no greater than 50 μm.

[0044] A third aspect of the present invention provides an application of the waterborne epoxy coating described in the first aspect of the present invention in the fields of metal corrosion protection and industrial flooring.

[0045] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: This invention introduces carboxylic acid or its derivatives into the curing agent component as a reaction regulator. It utilizes the inherent process of water content change in water-based coatings from wet film to dry film as an environmental signal to trigger the curing reaction switch, thereby achieving precise spatiotemporal control of the chemical reaction process. This results in water-based epoxy coatings having a long service life, fast curing speed, and good performance after curing.

[0046] (1) The applicable period is greatly extended: Through the “shielding” effect of carboxylic acid, the applicable period of the conventional 2-4 hours can be extended to more than 8 hours or even longer, meeting the needs of all-weather construction and reducing waste.

[0047] (2) Curing performance is not affected: After film formation, the shielding is removed, the curing reaction proceeds rapidly, and the key indicators such as crosslinking density, hardness, adhesion, and chemical corrosion resistance of the final coating all reach or even exceed the level of conventional formulations.

[0048] (3) Simple formulation and process: Only one common and inexpensive carboxylic acid component needs to be added to the existing waterborne epoxy formulation. There is no need to change the main resin and curing agent, no need for complicated encapsulation process, low production cost, and easy promotion.

[0049] (4) Wide adaptability to construction: It is especially suitable for painting occasions such as large structural components, ships, and bridges that require long-term continuous construction or repeated dipping and pausing. Detailed Implementation

[0050] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0051] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0052] The sources of the relevant raw material components in the embodiments and comparative examples of this invention are as follows: Waterborne epoxy resin: Shubang's JCW3551G; Dispersant: BYK-190 (BYK Chemicals); Defoamer: Matsuo 8807; Filler: mica powder and silica powder, with a mass ratio of mica powder to silica powder of 1:6; Wetting agent: BYK-346 (BYK Chemicals); Thickener in component A: BYK-420 from BYK Chemicals; Amine-based waterborne epoxy curing agent: L-920-50H from Dongguan Sanqi Chemical Raw Materials Co., Ltd.; Film-forming aid: Dipropylene glycol butyl ether and diethylene glycol butyl ether, mixed in a mass ratio of 1:1; Defoamer: Air Chemical's MD-20; Thickener in component B: Hesongyuan MH RHEO 0620.

[0053] Example 1 The raw material composition and dosage of the waterborne epoxy coating in Example 1 are shown in Table 1.

[0054] Table 1: Raw material components and dosage (mass percentage) of the waterborne epoxy coating in Example 1 of the present invention

[0055] In Example 1, the mass ratio of component A to component B in the waterborne epoxy coating is 6:1.

[0056] This embodiment also provides a method for preparing the above-mentioned waterborne epoxy coating, the steps of which are as follows: Under stirring conditions, waterborne epoxy resin is added to deionized water, followed by dispersant and defoamer. After uniform dispersion, coloring pigment, filler and anti-rust pigment are added, mixed evenly and then ground to obtain a slurry with a fineness of no more than 50 μm. Wetting agent and thickener are added to the slurry and dispersed evenly to obtain component A. Component B is obtained by mixing and dispersing amine-based waterborne epoxy curing agent, reaction regulator, flash rust inhibitor, film-forming aid, thickener, defoamer and deionized water. Components A and B constitute a water-based epoxy coating.

[0057] Example 2 This embodiment provides a waterborne epoxy coating with a long service life. The difference between this embodiment and Embodiment 1 is that the amount of amine waterborne epoxy curing agent in component B is 36%, the amount of reaction regulator is 5%, the mass ratio of component A to component B is 8:1, and the rest is the same as in Embodiment 1.

[0058] Example 3 This embodiment provides a waterborne epoxy coating with a long service life. The difference between this embodiment and Embodiment 1 is that the amount of amine waterborne epoxy curing agent in component B is 25%, the amount of reaction regulator is 16%, the mass ratio of component A to component B is 5:1, and the rest is the same as in Embodiment 1.

[0059] Example 4 This embodiment provides a waterborne epoxy coating with a long service life. The difference between this embodiment and Embodiment 1 is that the reaction regulator is formic acid, while the rest is the same as in Embodiment 1.

[0060] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses an amine-based waterborne epoxy curing agent to replace the reaction regulator in an equal amount, that is, no reaction regulator is added. Otherwise, it is the same as Example 1.

[0061] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses a reaction regulator to replace the amine-based waterborne epoxy curing agent in equal amounts, that is, no amine-based waterborne epoxy curing agent is added. Otherwise, it is the same as Example 1.

[0062] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses the commercially available long-life curing agent RLC2492 at a dosage of 41%, and does not contain a reaction regulator. Otherwise, it is the same as Example 1.

[0063] Performance testing In accordance with the GBT 50393-2017 Technical Standard for Corrosion Protection Engineering of Steel Oil Storage Tanks and the Sinopec Anti-corrosion and Thermal Insulation Quality Improvement Project Regulations SPMP-STD-EM2019-2021, the performance of waterborne epoxy coatings in Examples 1-4 and Comparative Examples 1-3 was tested, and the performance test results are shown in Table 2.

[0064] Table 2: Performance test results of waterborne epoxy coatings in Examples 1-4 and Comparative Examples 1-3

[0065] In Table 2, "-" indicates that the test was not conducted because the material could not be cured.

[0066] As can be seen from Table 2, the waterborne epoxy coating of the present invention has a long applicable period, which can extend the construction period, and has a fast curing speed and good performance after curing.

[0067] Comparative Example 1, which did not add a reaction regulator, resulted in a significantly reduced pot life, indicating that the reaction regulator in this invention significantly improves the pot life of the coating without affecting its performance.

[0068] Comparative Example 2 did not add epoxy curing agent, and the reaction regulator itself does not participate in the reaction curing, but only plays the role of extending the pot life, making the coating unable to cure.

[0069] Comparative Example 3 used a commercially available curing agent, which resulted in a significantly slower curing speed than in Example 1, indicating that the present invention not only improves the reaction pot life but also accelerates the curing reaction.

[0070] In summary, this invention introduces carboxylic acid or its derivatives into the curing agent component as a reaction regulator. It utilizes the inherent process of water content change in water-based coatings from wet film to dry film as an environmental signal to trigger the curing reaction switch, thereby achieving precise spatiotemporal control of the chemical reaction process. This results in water-based epoxy coatings having a long service life, fast curing speed, and good performance after curing.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A water-based epoxy coating, characterized in that, The waterborne epoxy coating comprises component A and component B; Component A includes waterborne epoxy resin, additives, pigments, fillers, and water; Component B includes an amine-based waterborne epoxy curing agent, a reaction regulator, an additive, and water; The reaction regulator includes carboxylic acids or their derivatives.

2. The waterborne epoxy coating according to claim 1, characterized in that, The reaction regulator includes at least one of formic acid, acetic acid, propionic acid, citric acid, oxalic acid, and maleic acid.

3. The waterborne epoxy coating according to claim 1, characterized in that, The number of carboxyl groups in the reaction regulator is 10-100% of the total number of theoretically active amine hydrogens in the amine-based waterborne epoxy curing agent; and / or, the active hydrogen equivalent of the amine-based waterborne epoxy curing agent is 100-300 g / mol.

4. The waterborne epoxy coating according to claim 1, characterized in that, By mass percentage, component A comprises 20-35% waterborne epoxy resin, 0.8-3.6% additives, 6-20% pigments, 30-50% fillers, and 20-35% water; And / or, by mass percentage, component B comprises 25-50% amine-based waterborne epoxy curing agent, 5-30% reaction regulator, 7.5-31% additives, and 25-42% water.

5. The waterborne epoxy coating according to claim 1, characterized in that, The additives in component A include at least one of dispersant, defoamer, wetting agent, and thickener; and / or, the pigments include coloring pigments and anti-rust pigments; and / or, the additives in component B include at least one of flash rust inhibitor, film-forming aid, defoamer, and thickener.

6. The waterborne epoxy coating according to claim 5, characterized in that, By mass percentage, component A comprises 20-35% waterborne epoxy resin, 0.2-0.6% dispersant, 0.1-0.5% defoamer, 6-20% pigment, 30-50% filler, 0-0.5% wetting agent, 0.5-2% thickener, and 20-35% water; And / or, by mass percentage, component B comprises 25-50% amine-based waterborne epoxy curing agent, 5-30% reaction regulator, 0.5-1% flash rust inhibitor, 3-15% film-forming aid, 1-5% defoamer, 3-10% thickener, and 25-42% water.

7. The waterborne epoxy coating according to claim 6, characterized in that, The film-forming aid includes at least one of dodecyl alcohol ester, propylene glycol, dipropylene glycol butyl ether, diethylene glycol butyl ether, and propylene glycol diacetate.

8. The waterborne epoxy coating according to claim 1, characterized in that, The mass ratio of component A to component B is (5-15):

1.

9. The method for preparing the waterborne epoxy coating according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: The raw material components of component A are mixed to obtain component A; The raw material components of component B are mixed to obtain component B; The components A and B constitute the waterborne epoxy coating.

10. The application of the waterborne epoxy coating according to any one of claims 1-8 in the fields of metal corrosion protection and industrial flooring.

Images