Method for producing curing agent for aqueous epoxy coating formulations

Abstract

The invention relates to a method for producing a hardener for aqueous epoxy coating formulations, said method comprising a step of carbonating an aqueous dispersion of a water-insoluble hardener comprising amine and / or amide functional groups, and the use of said hardener for applying an aqueous epoxy coating on a substrate.

Description

Technical Field

[0001] This application claims priority to application number 22305920.5 filed in Europe on June 24, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The invention relates to a process for producing a hardener for waterborne epoxy coating formulations and to the use of the hardener for applying waterborne epoxy coatings on substrates. Background Art

[0003] Epoxy resins as coating bases have been commercialized many years ago. Historically, most high-performance epoxy coatings are based on solvent-based formulations. Although they provide excellent performance, they have the disadvantage of relatively high VOC (volatile organic compound) content. Therefore, waterborne epoxy coating formulations with significantly lower VOC levels have been developed compared to solvent-based epoxy coating formulations. These generally use compounds containing multiple amine groups to cure epoxy resins. However, the coating formulations obtained by mixing one or more epoxy resins with one or more amine-containing compounds are generally unstable and should be applied to the substrate as soon as possible to form a single continuous phase. Therefore, they have a so-called limited pot life.

[0004] US 4526721 solves this problem by providing a process for producing a curing agent for epoxy resins, comprising the steps of dissolving an amidoamine or an imidazoline in water and contacting the solution thus obtained with carbon dioxide. The process is specific to water-soluble amine curing agents.

[0005] However, the latest generation of waterborne epoxy formulations are based on hydrophobic, water-insoluble amine or amide curing agents. Such formulations provide coatings with improved chemical resistance and corrosion protection compared to formulations containing hydrophilic, water-soluble amine curing agents. Applicants have discovered that carbonating dispersions of water-insoluble amines or amides can also provide waterborne epoxy coating formulations with curing agents with improved pot life. Furthermore, if the resulting coating is properly cured, it will exhibit high chemical resistance and corrosion protection characteristics. Summary of the invention

[0006] Therefore, a first object of the present invention is a process for producing a waterborne curing agent for waterborne epoxy coating formulations, said process comprising the step of carbonating an aqueous dispersion of a water-insoluble curing agent comprising amine and / or amide functional groups.

[0007] For a two-component epoxy coating system, an epoxy resin (often referred to as Part A) is mixed with a curing agent (often referred to as Part B or hardener). The curing agent chemically reacts with the epoxy resin to produce a high-performance coating with excellent mechanical and chemical resistance.

[0008] For waterborne epoxy coating systems, the curing agent can be soluble or insoluble in water. Water-soluble curing agents are completely miscible with water, forming a homogeneous mixture. It consists of one phase.

[0009] Water-insoluble curing agents are heterogeneous mixtures of curing agents in water, such as colloidal suspensions and emulsions. They include at least two phases. Non-limiting examples are (i) colloidal suspensions of solid particles of curing agent dispersed in water; (ii) droplets of curing agent dispersed in water, wherein the liquid curing agent is immiscible with the surrounding aqueous phase. Typical (non-limiting) sizes of colloidal particles / droplets range from about 50 nm to about 5 μm.

[0010] In the framework of the present invention, the waterborne epoxy formulation comprises an aqueous continuous phase and a solid dispersed phase. In addition to water, the aqueous phase may comprise one or more solvents and / or dissolved curing agents. The dispersed phase comprises the epoxy resin preparation and may comprise curing agent particles. The one or more solvents are typically selected from acetone and glycol ethers, more particularly ethylene glycol ethers and propylene glycol ethers. The waterborne epoxy formulation may comprise other ingredients, like pigments, defoamers ...

[0011] The waterborne epoxy formulation of the invention is obtained by mixing a waterborne epoxy dispersion with an aqueous curing agent dispersion or solution and finally with a solvent as mentioned above. An advantage of the invention is that once the two components are mixed, the pot life of the formulation is increased compared to formulations also based on insoluble amine curing agent dispersions but not pretreated by carbonation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Other features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which:

[0013] - Figure 1 is a graph showing the Brookfield viscosity of waterborne epoxy coating formulations with and without CO2 treatment as a function of pot life;

[0014] - Figure 2 is a graph showing the gloss of dried coatings applied to painted opaque chart as a function of pot life. DETAILED DESCRIPTION

[0015] The aqueous epoxy dispersion comprises epoxy resin particles, water and finally a solvent as described above, but the amount of the solvent does not exceed 10% by weight, preferably does not exceed 5%. The amount of epoxy resin particles in the dispersion is generally between 50% and 60% by weight. The epoxy resin is generally of the bisphenol A type, but other epoxy resins (e.g. bisphenol F or phenolic resins) can also be used. The epoxy resin may contain a built-in surfactant or emulsifier. Alternatively or additionally, the aqueous epoxy dispersion may contain a surfactant or an emulsifier. Such aqueous epoxy dispersions are commercially available and are those that give good results in the framework of the present invention under the trade name EPIKOTE TM Resin 6520-WH-53. These commercial dispersions can be used as is or diluted with water and / or solvents prior to use.

[0016] Aqueous dispersions of water-insoluble curing agents comprise curing agent particles dispersed in a liquid phase comprising water and eventually a solvent as described above, but the amount of solvent does not exceed 10%, preferably does not exceed 5%, by weight.

[0017] The curing agent used in the present invention is a compound containing amine and / or amide functional groups that can react with the epoxy functional groups of the epoxy resin. The curing agent can be a polyamide, a polyamidoamine or a polyamine. If chemical resistance and stain resistance and anticorrosion protection are key characteristics of the final coating, polyamines are preferred. More preferably, polyamines with an amine value from 100 to 350 are used. The amine value is measured by titrating a known mass of the polyamine with hydrochloric acid and is expressed as mg KOH / g.

[0018] Preferred polyamines are those consisting of modified polyamine adducts, preferably containing aliphatic polyamine moieties, more preferably containing primary and / or secondary unhindered amine groups like triethylenetetramine or N,N'-bis(3-aminopropyl)ethylenediamine moieties. In a preferred embodiment, the aliphatic polyamine moieties are reacted with bisphenol A diglycidyl ether to increase epoxy compatibility. In yet further preferred embodiments, the amine functional groups can be reacted with EO / PO and / or with fatty acids to make the polyamine water dispersible.

[0019] According to the invention, the curing agent is water-insoluble at least at room temperature before its carbonation. In a preferred embodiment, the curing agent becomes at least partially water-soluble (and thus less opaque) at room temperature after carbonation. This has the advantage of improving compatibility with waterborne epoxy resins and enhancing the film properties of the cured coating.

[0020] As in the case of epoxy resins, the curing agent may contain a built-in surfactant (or emulsifier).Alternatively or additionally, the aqueous dispersion of the curing agent may contain a surfactant in its liquid phase.

[0021] The aqueous curing agent dispersion comprises solid particles of the curing agent dispersed in an aqueous phase, typically in an amount of 50% to 60% by weight of the particles in the aqueous dispersion. It may contain a solvent as described above, such as ethylene glycol ether or propylene glycol ether, typically in an amount of up to 10% by weight.

[0022] Aqueous curing agent dispersions as described above are commercially available, for example under the trade name EPIKURE TM 6870-W-53 (amine value 250) or Those sold as VEH 2188w / 55WA (amine number 135). These can be used as is or diluted with water and / or solvents before use.

[0023] The carbonation step is carried out by contacting the aqueous curing agent dispersion with liquid, solid or gaseous carbon dioxide, the latter being preferred. It can be carried out over a wide temperature range, for example from 0°C to 100°C, preferably between 10°C and 40°C, more preferably at room temperature. It can be carried out over a wide pressure range, but is preferably carried out at atmospheric pressure, more preferably by bubbling CO2 gas in the curing agent dispersion at room temperature.

[0024] Typically, the duration of carbonation is such that a large number of amine / amide groups of the end-capping curing agent are achieved. This is usually well indicated by the evolution of pH. Therefore, it may be advantageous to measure pH at the beginning and end of the carbonation step, and it is preferably monitored during the entire carbonation step. In a preferred embodiment, the carbonation step is terminated when the pH of the dispersion is stable and close to a target value, which preferably makes the pot life long enough and the film properties comparable to when there is no carbonation.

[0025] The present invention also relates to the use of the aqueous curing agent obtained as described above in a waterborne epoxy coating formulation. More specifically, a second object of the present invention is a method for providing a substrate with a waterborne epoxy coating, the method comprising the following steps:

[0026] - producing a carbonated aqueous curing agent as described above;

[0027] - mixing the aqueous curing agent with an aqueous epoxy dispersion to obtain a waterborne epoxy coating formulation (mixing step);

[0028] - applying the waterborne epoxy coating formulation to a substrate (applying step);

[0029] - Curing the waterborne epoxy coating formulation on the substrate (curing step).

[0030] The waterborne epoxy dispersion and waterborne epoxy formulation of the present invention are as described above.

[0031] In a preferred embodiment, the waterborne epoxy formulation comprises a solvent selected from acetone and glycol ethers, more particularly ethylene glycol ethers and propylene glycol ethers. The solvent may be introduced as a separate ingredient during the mixing step and / or may be added via the waterborne curing agent and / or via the waterborne epoxy dispersion.

[0032] Any substrates can be used in the method of the invention. However, their properties may be constrained by the temperature used in the curing step. Thus, metal, glass, enamel ... substrates give good results within the framework of the invention.

[0033] In a preferred embodiment of the invention, the aqueous curing agent is substantially free of CO2 bubbles before being used in the mixing step. This can be achieved, for example, by aging the carbonated curing agent under conditions where excess CO2 (not reacted with the amine) can leave the system.

[0034] In the mixing step, the amount of aqueous curing agent relative to the amount of aqueous epoxy dispersion is adapted to the target stoichiometric ratio between amine / amide hydrogen and epoxy functional groups. In practice, this is calculated using the equivalent weight of the epoxy resin and the amine / amide hydrogen equivalent weight of the curing agent. The epoxy equivalent weight (EEW) is defined as the number of grams of epoxy resin required to give 1 mole of epoxy groups. The amine / amide hydrogen equivalent weight (AHEW) of the curing agent is the number of grams of curing agent required to give 1 mole of amine / amide hydrogen.

[0035] In the process of the invention, the duration between the mixing step and the application step can be extended to 24 hours (compared to only a few hours in the prior art) without compromising the coating ability and quality. More precisely: the mixture remains applyable after this period (i.e. it remains sufficiently fluid), and the coatings made from the mixture still have a good visual appearance (such as film gloss), as well as good mechanical and chemical resistance properties, provided they are properly cured. In other words: the invention allows the benefits of a two-component coating system with a significantly extended pot life, without having to compromise the final mechanical properties and chemical resistance of the coating.

[0036] The method of applying the coating formulation to the surface is not critical. It can be done by using a brush and / or roller, spraying, etc., preferably on a pre-treated surface free of oil, grease, dust, previous paint, etc.

[0037] On the other hand, the curing step is a key element of the method of the present invention. That is, it has the purpose of unblocking the amine / amide functional groups of the curing agent so that they can react with the epoxy functional groups of the epoxy resin and form a coating. For some formulations and / or depending on the desired properties of the final coating, room temperature curing may be sufficient. However, in order to obtain a chemically resistant coating, the temperature during this step is preferably at least 50°C, preferably at least 60°C. Depending on the chemical nature of the curing agent, a temperature of up to 95°C may be required, and even up to 120°C. However, especially when the curing agent becomes at least partially water-soluble after carbonation, a temperature between 50°C and 90°C, preferably between 60°C and 80°C may be sufficient. The duration of the curing step should be adjusted so that the curing is sufficient, i.e., a coating with the desired mechanical and chemical resistance is provided. This usually requires less than one hour.

[0038] In a preferred embodiment of the invention, curing is performed at a temperature above room temperature while the coating is still wet. This facilitates the deblocking of the amine / amide functional groups and allows the process to be accelerated and / or the curing temperature to be lowered, which is valuable from an industrial point of view.

[0039] The present invention is illustrated by the following examples, which relate to some preferred embodiments of the invention.

[0040] Examples

[0041] Example 1

[0042] The materials detailed in Table 1 below were used to prepare the waterborne epoxy coating formulations detailed in Table 2 below.

[0043] Table 1

[0044]

[0045] Table 2 - Waterborne (WB) Epoxy Coating Formulation 1

[0046]

[0047] For Part A, the solvent (DPnB) was added to the resin and stirred for 2 days to ensure good distribution of the solvent to the epoxy particles containing the resin.

[0048] For the pot life test, Part B was added to Part A and stirred vigorously with a spatula to ensure homogenization, the entire formulation was contained in a beaker. To monitor pot life performance, two types of measurements were performed periodically (typically 1 hour):

[0049] - Brookfield viscosity measurement of mixed coating formulations. A Brookfield spindle (RV04) was immersed in the formulation and the (apparent) viscosity was measured at a spindle speed of 10 rpm.

[0050] - Wet Film Application. Wet films of the WB epoxy coating formulations were applied to various substrates (see below) and dried and cured at ambient temperature.

[0051] Example 2

[0052] The weight of each material used in the WB epoxy coating was the same as in Example 1, with the hardener in Part B being replaced by a CO2 treated hardener as described below.

[0053] Treating the hardener with carbon dioxide (Part B)

[0054] A 50 g mass of Epikure (hardener) was weighed in a beaker. The pH was measured and determined to be 10.7 (at 21.7° C.). The hardener was CO2 sparged via a gas dispersion tube connected to a CO2 cylinder for 25 minutes. The pH was remeasured and determined to be 7.1, indicating a significant reaction between the amine and the CO2.

[0055] result

[0056] Brookfield viscosity measurements (10 rpm) of the formulations (Part B treated with CO2 - Example 2: squares; and Part B not treated with CO2 - Example 1: diamonds) were taken as an additional Figure 1 Function of the applicable period shown in .

[0057] Most strikingly, the formulations prepared using the CO2 treated hardener had much lower viscosity and less viscosity increase as a function of pot life than the formulations prepared using the as-received hardener. Note that for the pot life = 22h of the formulation using the CO2 treated hardener, the Brookfield viscosity (10 rpm) was measured to be 1900 mPa.s (not shown in the figure).

[0058] General visual appearance of coating on opaque card

[0059] For Example 1, the initial drying conditions in the environment are recorded as temperature T=20.9° C. and relative humidity RH=65%.

[0060] For Example 2, the initial drying conditions in the environment were recorded as temperature T = 21.7°C and relative humidity RH = 66%.

[0061] For each example / composition, coatings were prepared after different "pot lives", i.e. after different time intervals from mixing the 2 components (Part A and Part B) and applying the coating. The general appearance of the coatings was obtained 1 week after application (cured at ambient).

[0062] For Example 1, at short pot life (t=30 min), the film appearance was excellent, resulting in a clear film with a good, glossy visual appearance. However, after 2 hours pot life, degradation of the glossy appearance of the film was observed. At 3 hours pot life, the film appearance was very poor, showing cracks and opaque areas. This became worse as the pot life increased to 4 hours and above.

[0063] For Example 2, the visual appearance of all films was excellent regardless of pot life, resulting in clear films with a good, glossy visual appearance. At the longest pot life (=22 h), the film clarity dropped only slightly.

[0064] Coating gloss measurement

[0065] use 3-GLOSS 20°-60°-85° glossmeter (calibrated, Brant industrie) was used to measure the gloss of the dry coating applied on a lacquered opaque card (PA2810-250). The glossmeter is capable of measuring the gloss at 3 different levels (20°-60°-85°) simultaneously.

[0066] After curing for 3 weeks at ambient temperature, the gloss of the film was measured. Figure 2 Plotted as a function of the pot life.

[0067] For the formulation of Example 2, excellent gloss values ​​at 60° (98% to typically 96%) were observed over a pot life from 0 to 5 h, these values ​​being significantly better than those measured for the formulation of Example 1 (except for the very short pot life). Note that for Example 2 pot life = 22 h, the gloss value (60°) was 81% (not shown in the figure).

[0068] Chemical resistance

[0069] The coatings tested were applied to aluminum substrates with a wet film thickness of 100 μm, resulting in a dry film thickness of typically 25 μm. All films were cured at ambient temperature for a period of approximately 6 weeks prior to solvent resistance testing. In addition, some of the dry films (which had been cured at ambient for 6 weeks) were placed in a high temperature oven (95°C or 120°C depending on the test) and maintained at this curing temperature for a period of 90 minutes.

[0070] Solvent resistance is tested using the "double rub" method. According to this test procedure, a cotton swab (cotton stick) is immersed in a specific solvent to be used (e.g., ethanol, acetone, MEK). The coating is then subjected to 25 "double rubs" by placing the absorbed cotton swab on the coating and performing a "back and forth" motion at each "double rub". After 25 double rubs, the coating is visually inspected. If the coating has been damaged to the extent that the underlying substrate is exposed, the test result is considered to be "failed". However, if the substrate is not exposed (i.e., the continuous coating that is rubbed is retained), the test result is considered to be "passed". In the case of a "pass" of 25 double rubs using MEK, the test is extended to find the maximum number of MEK double rubs until the substrate is exposed.

[0071] A summary of the results obtained is given in Table 3 below.

[0072] Table 3

[0073]

[0074] Example 3: Chemical resistance versus curing conditions

[0075] Treating the hardener with carbon dioxide (Part B)

[0076] A 50 g mass of Epikure hardener was weighed in a beaker. The pH was measured and determined to be 10.7. The hardener was CO2 sparged via a gas dispersion tube connected to a CO2 cylinder for 40 minutes. The pH was remeasured and determined to be 7.2, indicating a significant reaction between the amine and the CO2.

[0077] Preparations

[0078] For Part A, 200 g of a "stock" solution containing 119.6 g of EPI-REZ was prepared in advance. TM Resin, 7.4g solvent DPnB and 24g water. The solvent (DPnB) was pre-added to the resin and water and stirred overnight to ensure good distribution between the solvent and the epoxy particles containing the resin. The weight of each material used in the WB epoxy coating is given in Table 4 below.

[0079] Table 4 - Waterborne (WB) Epoxy Coating Formulation 2

[0080]

[0081] Coatings with short and very long pot life

[0082] For pot life testing, add Part B to Part A and stir vigorously with a spatula to ensure homogenization. Place the entire formulation in a 100 mL Erlenmeyer beaker.

[0083] Four different application conditions were tested:

[0084] 1. Coating applied after a "short" pot life (<1 hour) and cured for 24 hours under ambient conditions

[0085] 2. The coating was applied after a "short" pot life (<1 hour) and then immediately cured at T = 95°C for 90 minutes, followed by 24 hours at ambient conditions

[0086] 3. Coating applied after 24 hours "very long" pot life and cured for an additional 24 hours at ambient conditions.

[0087] 4. Coating applied after 24 hours "very long" pot life, immediately thereafter cured at T = 95°C for 90 minutes, and then left at ambient conditions for 24 hours

[0088] Note: For the specific case of very long pot life (24h), the formulation was covered with parafilm to avoid evaporation.

[0089] Solvent resistance, visual appearance, and film gloss were determined using the methods described previously.

[0090] result

[0091] All coatings prepared under the above conditions had excellent visual appearance, and even after 24 hours, the formulations remained fluid enough to apply the coating. Thus, the effective pot life of the formulations prepared using the CO2-treated hardener was at least 24 hours.

[0092] The coatings were subjected to 25 double rubs with various solvents to test their solvent resistance. A summary of the solvent resistance results is given in Table 5 below.

[0093] Table 5

[0094]

[0095] Additional Tests and Results 1

[0096] Formulations very similar to Formulations 1 and 2 detailed above were tested at a "short" pot life (15 minutes) with the results described below.

[0097] - WB epoxy formulation using hardener as is (no CO2 injection) cured at ambient for 15 minutes, then at T=80°C for 15 minutes, then at ambient for 13 days; it showed very good chemical resistance: 225 + / - 50 double rubs with MEK

[0098] - WB epoxy resin using CO2 treated hardener was cured at ambient for 15 minutes, then at T=80°C for 15 minutes, then at ambient for 13 days; it showed very good chemical resistance: 206 + / - 50 double rubs with MEK

[0099] - WB epoxy formulation using hardener as is (no CO2 injection) simply left at ambient for 13 days (no temperature cure) showed good chemical resistance: 131 + / - 13 double rubs with MEK

[0100] Both formulations (with and without CO2 treatment of the hardener) were then kept for an additional 24 hours. The WB epoxy resin using the as-is hardener (without CO2) was a gel after this period and could not be applied as a coating. On the other hand, the WB epoxy resin using the CO2 treated hardener remained fluid and could be applied as a coating after 24 hours. This "aged" formulation / sample was tested, with the results described below.

[0101] - After curing at ambient for 15 minutes, then at T=80°C for 15 minutes, then at ambient for 13 days: it showed good chemical resistance: 144 + / - 40 double rubs with MEK

[0102] - After simply leaving it at ambient for 13 days: It showed very poor chemical resistance: only 18 + / - 2 double rubs with MEK.

[0103] Additional Tests and Results 2

[0104] Formulations very similar to Formulations 1 and 2 detailed above were tested at a "short" pot life (15 minutes) with the results described below.

[0105] - WB epoxy formulation using hardener as is (no CO2 injection) was cured at ambient for 15 minutes, then at T=70°C for 30 minutes, then at ambient for 7 days; it showed good chemical resistance: 144 + / - 24 double rubs with MEK

[0106] - WB epoxy resin using CO2 treated hardener was cured at ambient for 15 minutes, then at T=70°C for 30 minutes, then at ambient for 7 days; it showed good chemical resistance: 131 + / - 31 double rubs with MEK

[0107] Both formulations (with and without CO2 treatment of the hardener) were then kept for an additional 24 hours. The WB epoxy resin using the as-is hardener (without CO2) was a gel after this period and could not be applied as a coating. On the other hand, the WB epoxy resin using the CO2 treated hardener remained fluid and could be applied as a coating after 24 hours. This "aged" formulation / sample was tested, with the results described below.

[0108] - After curing at ambient for 15 minutes, then at T=70°C for 30 minutes, then at ambient for 7 days: it showed good chemical resistance: 131 + / - 24 double rubs with MEK

[0109] - After simply leaving it at ambient for 7 days: It showed very poor chemical resistance: only 15 + / - 3 double rubs with MEK.

[0110] Additional Tests and Results 3

[0111] A formulation similar to Formulation 2 detailed above was prepared. However, this time the hardener was treated with CO2 and kept in a sealed flask for a period of 19 days before preparing the waterborne epoxy formulation. The above formulation was tested under "short" pot life (15 minutes), with the results described below.

[0112] - WB epoxy with CO2 treated hardener (19 days) cured at ambient for 15 minutes, then at T=70°C for 30 minutes, then at ambient for 7 days; showed good chemical resistance: 113 + / - 14 double rubs with MEK

[0113] The formulation using the CO2 treated hardener (19 days) was then kept for an additional 24 hours. It remained fluid and could be applied as a coating after 24 hours. This "aged" formulation / sample was tested with the results described below.

[0114] - After curing at ambient for 15 minutes, then at T=70°C for 30 minutes, then at ambient for 7 days: it showed good chemical resistance: 119 + / - 24 double rubs with MEK

[0115] - After simply leaving it at ambient for 7 days: It showed very poor chemical resistance: only 15 + / - 3 double rubs with MEK.

[0116] Example 4

[0117] A waterborne epoxy coating formulation 3 as detailed in Table 7 below was prepared using a preparation method similar to that described above with the materials detailed in Table 6 below.

[0118] Table 6

[0119]

[0120] Table 7 - Waterborne (WB) Epoxy Coating Formulation 3

[0121]

[0122] Wet films of the WB epoxy coating formulations were applied to various substrates and cured as follows: (a) dried / cured at ambient temperature for 15 minutes under a fume hood, then (b) cured in a laboratory oven at T = 80 ° C for 15 minutes. After high temperature curing, the coatings were placed at ambient temperature. The coating visual appearance and film gloss were evaluated following the methods described in the previous examples. Gloss measurements were made on the films 4 days after application and curing. The chemical resistance of the coatings was measured 9 days after application and curing. The chemical resistance of the coatings was determined by the maximum number of MEK double rubs until the substrate was exposed, as described previously.

[0123] result

[0124] The film appearance was excellent at pot life times of t=10 minutes to 2 hours, resulting in a clear film with a good, glossy visual appearance. Also during this time period, it was noted that the formulation remained fluid and easy to apply. At 3 hours of pot life, the final visual appearance of the film was also good; however, it was noted that the formulation showed a significant increase in viscosity, as determined by simple stirring. After four and a half hours of pot life, the film quality declined significantly, and the texture was extremely rough. During the pot life, the formulation itself became very viscous and uneven ("lumpy"). At six hours of pot life, the formulation became so viscous that additional water needed to be added to dilute it. The final film quality was very poor.

[0125] Starting from excellent gloss values ​​(20°) of 85%-86% for short pot lives of 1-2 hours, the gloss starts to deteriorate (82%) at 3h pot life and then drops sharply to values ​​of <50% for longer pot lives.

[0126] MEK solvent resistance for short pot life (0-2h) determined as 100 + / - 16 double rubs with MEK

[0127] Example 5

[0128] A waterborne epoxy coating formulation 4 detailed in Table 8 below was prepared using a method similar to that described above, except that Part B was prepared as follows:

[0129] A stock solution containing 5 g of hardener pre-dispersed in 5 g of water was prepared in advance. The pH of this dispersion was determined to be 9.3. The hardener dispersion was then treated with CO2 by gently bubbling CO2 through a gas dispersion tube immersed in the sample, while mixing using a magnetic stirrer. After 20 minutes of CO2 sparging, the pH of the sample was remeasured and found to be 7.1, indicating a significant reaction between the CO2 and the hardener amine. It was noted that as a result of the CO2 treatment, the initially opaque and white dispersion became less opaque and yellow in color, indicating a reduction in the dispersion particle size. The sample was then hermetically sealed with a lid and left overnight to separate out any foam / bubbles created by the bubbling.

[0130] Table 8 - Waterborne Epoxy Coating Formulation 4

[0131]

[0132] Wet film application and curing were as described above for Example 4, and coating visual appearance and film gloss were also evaluated as described above for Example 4. In addition, some coatings were prepared at very short pot life (0 h) and very long pot life (25 h) and cured at ambient for a period of 9 days (no elevated temperature cure).

[0133] result

[0134] At pot life times of t = 10 minutes to 5 hours, the film appearance was excellent, resulting in a clear film with a good, glossy visual appearance. Also during this period, the formulation remained fluid and easy to apply. Even for the coatings prepared after a pot life of 25 hours, the final visual appearance of the film was very good. Similarly, the formulation remained fluid, albeit more viscous than for a short pot life. Furthermore, the gloss values ​​measured for the coatings at a pot life of 25 h were very good (78% at 20°, 96% at 60°, and 90% at 85°, respectively).

[0135] For pot life of 0 to 5 hours, MEK solvent resistance was determined to be 92 + / - 13 double rubs with MEK, close to the value for the reference film at short pot life (0-2 hours) in Example 4. For the 25 hour pot life coating, MEK solvent resistance was 160 + / - 70 double rubs.

[0136] Finally, for the additional coatings that were simply cured at ambient for a 9 day period (no elevated temperature cure) at both very short pot life (0 h) and very long pot life (26 h), MEK solvent resistance was very poor (< 25 double rubs).

[0137] Example 6: Chemical resistance test under low temperature curing conditions

[0138] The chemical resistance of WB epoxy coating formulation 5 given in Table 9 below was evaluated, including a version in which Part B was used as is and two versions in which Part B was treated by CO2 blasting:

[0139] 1. Soon after CO2 sparging (1 hour), mix CO2 sparged Part B with Part A;

[0140] 2. Cover the CO2 blasted Part B with parafilm pierced with three small pinholes and leave overnight to eliminate any "excess" CO2. The sample becomes completely transparent, indicating that the hardener dispersion is dissolved.

[0141] Table 9: Waterborne Epoxy Coating Formulation 5

[0142]

[0143] Wet film application and curing.

[0144] Wet films of the WB epoxy coating formulations were applied to various substrates and cured. All film coatings were initially dried / cured in a fume hood at ambient temperature for 15 minutes. The coatings were then divided into four separate groups and then subjected to high temperature curing in a laboratory oven under one of the following conditions:

[0145] (i) T = 60 ° C for 15 minutes (ii) T = 60 ° C for 30 minutes (iii) T = 70 ° C for 15 minutes (iv) T = 70 ° C for 30 minutes. After high temperature curing, the coatings were left at ambient temperature. Some coatings were applied within 1 hour after mixing parts A and B, i.e. before the end of the pot life, while other coatings were applied after more than 24 hours of pot life.

[0146] MEK solvent resistance test on coating samples

[0147] The tested coatings were applied to aluminum substrates with a wet film thickness of 100 μm, resulting in a dry film thickness of typically 25 μm. After initial curing (15 minutes in ambient followed by 15 or 30 minutes at specific curing conditions of 60°C or 70°C), the coatings were stored for a further 7 days at ambient conditions before testing for solvent resistance.

[0148] MEK solvent resistance results

[0149] Solvent resistance was tested using the "double rub" method described above.

[0150] The results of each cure for cure conditions (i) to (iv) are summarized in Tables 10 to 13 below.

[0151] Table 10: MEK resistance for curing condition (i) T = 60 ° C for 15 minutes

[0152]

[0153] Table 11: MEK resistance for curing condition (ii) T = 60 °C for 30 minutes

[0154]

[0155] Table 12: MEK resistance for curing condition (i) T = 70 ° C for 15 minutes

[0156]

[0157] Table 13: MEK resistance for curing condition (i) T = 70 ° C for 30 minutes

[0158]

[0159] For coatings prepared at short pot lives (<1 hour), coatings prepared with the CO2 treated hardeners achieved MEK double rubs of the substrate that were on average equal to or greater than those of the reference system under the same cure conditions.

[0160] Coatings prepared using CO2 treated hardeners have very long extended pot lives (>24 hours) and also have good solvent resistance.

[0161] Should the disclosure of any patents, patent applications, and publications incorporated herein by reference conflict with the description of the present application to the extent that a term is unclear, the present description shall take precedence.

Claims

1. A process for producing a waterborne curing agent for use in waterborne epoxy coating formulations, the process comprising the step of carbonating an aqueous dispersion of a water-insoluble curing agent comprising amine and / or amide functional groups.

2. The method of claim 1, wherein: The curing agent is a polyamide, polyamidoamine or a polyamine.

3. The method of claim 2, wherein: The curing agent is a polyamine, preferably a polyamine having an amine number of 100 to 350.

4. The method of claim 3, wherein: The polyamine consists of a modified polyamine adduct, preferably comprising aliphatic polyamine moieties, more preferably comprising primary and / or secondary unhindered amine groups like triethylenetetramine or N,N'-bis(3-aminopropyl)ethylenediamine moieties.

5. The method of claim 4, wherein: The polyamine comprises an aliphatic polyamine portion reacted with bisphenol A diglycidyl ether and / or an amine functional group reacted with EO / PO and / or with a fatty acid.

6. The method according to any one of claims 1 to 5, wherein: The curing agent comprises a built-in surfactant and / or the aqueous dispersion of the water-insoluble curing agent comprises a surfactant in its liquid phase.

7. The method according to any one of claims 1 to 6, wherein: The carbonation step is carried out by contacting the dispersion of the water-insoluble solidifying agent with liquid, solid or gaseous carbon dioxide, the latter being preferred.

8. The method of claim 7, wherein: The carbonation step is carried out at atmospheric pressure by bubbling CO2 gas through the dispersion of the water-insoluble solidifying agent at room temperature.

9. The method according to any one of claims 1 to 8, wherein: When the pH of the dispersion is stable and close to the target value, the carbonation step is terminated.

10. Use of an aqueous curing agent obtained by the process according to any one of claims 1 to 9 in a waterborne epoxy coating formulation.

11. A method for providing a substrate with a waterborne epoxy coating, the method comprising the steps of: - producing an aqueous curing agent by the method according to any one of claims 1 to 9; - mixing the aqueous curing agent with an aqueous epoxy dispersion to obtain a waterborne epoxy coating formulation (mixing step); - applying the waterborne epoxy coating formulation to a substrate (applying step); - Curing the waterborne epoxy coating formulation on the substrate (curing step).

12. The method of claim 11, wherein: The solvent is introduced as a separate ingredient into the waterborne epoxy coating formulation during the mixing step and / or via the waterborne curing agent and / or via the waterborne epoxy dispersion.

13. The method of claim 12, wherein: The solvent is selected from acetone and glycol ethers, more particularly ethylene glycol ethers and propylene glycol ethers.

14. The method according to any one of claims 11 to 13, wherein: Prior to using the aqueous curing agent in the mixing step, it is made substantially free of CO2 bubbles.

15. The method according to any one of claims 11 to 14, wherein: The curing step is carried out at a temperature between 50 and 90°C, preferably between 60 and 80°C.

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