A low-temperature curing modified resin for water-based coatings and preparation method thereof

Abstract

The present invention relates to a low-temperature curing modified resin for water-based coatings and a preparation method thereof, the preparation method comprising the following steps: S1, weighing bisphenol A and trifluoroacetic acid, adding hexamethylenetetramine, heating and reflux stirring reaction, and obtaining formaldehyde bisphenol A; S2, weighing formaldehyde bisphenol A and anhydrous ethanol, mixing, adding 2-amino-5-hydroxypyrimidine, reflux reaction, and obtaining hydroxypyrimidinyl bisphenol A; S3, weighing hydroxypyrimidinyl bisphenol A and halogenated epoxypropane mixing and stirring reaction, and obtaining modified bisphenol A epoxy resin. The epoxy resin modified by the present invention does not require a very high temperature, and can achieve better curing even at room temperature, and compared with traditional low-temperature curing epoxy resins, after curing, it not only has higher hardness, but also has better high temperature resistance and adhesion.

Description

Technical Field

[0001] The invention relates to the field of water-based coatings, and in particular to a low-temperature curing modified resin for water-based coatings and a preparation method thereof. Background Art

[0002] As people's living standards continue to improve, their pursuit of beauty becomes stronger and stronger. Various daily necessities are painted with colorful decorative paints according to their needs to meet the design requirements of different styles. However, with the continuous expansion of application areas, people have put forward more requirements on the functional characteristics of coatings, which are no longer just traditional decoration and beautification, but more on safety and health. However, since most of the current coatings are organic solvent-based coatings, solvent-based coatings contain a large amount of VOCs, which will evaporate into the air during the process of painting, drying and storage, resulting in a decrease in indoor air quality, causing harm to the human body, and also causing environmental pollution.

[0003] Compared with traditional solvent-based paints, water-based paints use water as a diluent, do not contain high volatile organic compounds, do not produce harmful gases, odors and other environmental pollution problems, and do not contain harmful heavy metals and toxic solvents. It is safer to use and handle, so it has gradually been favored by the market in recent years. The main raw material of water-based paint is water-based resin. Water-based resin is a resin system that uses water instead of organic solvents as a dispersion medium. The resin and water are fused to form a solution. After the water evaporates, a resin film material is formed. Water-based epoxy resin is a stable dispersion system prepared by dispersing epoxy resin in the form of particles or droplets in a dispersion medium with water as a continuous phase. Water-based epoxy resin has the advantages of good corrosion resistance, chemical resistance, low VOC content, and easy construction. However, water-based epoxy resin usually requires high temperature conditions to complete curing. The curing speed at room temperature is too slow, and even the mechanical properties of the cured product are poor, which leads to greater restrictions on its use in daily use. Therefore, it is extremely important to develop a water-based epoxy resin that still has high performance after low-temperature curing. Summary of the invention

[0004] In view of the problems existing in the prior art, the object of the present invention is to provide a low-temperature curing modified resin for water-based coatings and a preparation method thereof.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] In a first aspect, the present invention discloses a method for preparing a low-temperature curing modified resin for water-based coatings, comprising the following steps:

[0007] S1, weigh bisphenol A and trifluoroacetic acid, mix, fully stir until uniform, introduce nitrogen as protective gas, add hexamethylenetetramine, after all are added, heat up and reflux and stir, after the reaction is finished, cool naturally to room temperature, then pour into hydrochloric acid and stir, then after extraction and washing, remove the solvent under reduced pressure to obtain formaldehyde bisphenol A (OHC-BPA);

[0008] S2, weighing formaldehyde bisphenol A and anhydrous ethanol, mixing, fully stirring, adding 2-amino-5-hydroxypyrimidine, reflux reaction after all the addition, after the reaction is completed, naturally cooling to room temperature, discharging in pure water, filtering and collecting precipitates, and vacuum drying to obtain hydroxypyrimidinyl bisphenol A (OH-Py-BPA);

[0009] S3, weighing hydroxypyrimidinyl bisphenol A and halogenated propylene oxide, mixing, introducing nitrogen as protective gas, stirring thoroughly, adding a catalyst, heating to react, then cooling and adding sodium hydroxide solution, continuing to stir and react, after the reaction is completed, extracting and washing the reaction solution, and removing the solvent under reduced pressure to obtain a modified bisphenol A epoxy resin (Mod-BPAER).

[0010] Preferably, in S1, the mass volume ratio of bisphenol A, hexamethylenetetramine and trifluoroacetic acid is (0.9-1.4) g: (6.2-8.6) g: (40-60) mL.

[0011] Preferably, in S1, the reaction temperature is 80-90° C. and the reaction time is 3-6 h.

[0012] Preferably, in S1, the concentration of hydrochloric acid is 1-3 mol / L, and the volume ratio of hydrochloric acid to trifluoroacetic acid is 2-4:1.

[0013] Preferably, in S1, after adding hydrochloric acid, stirring is continued at room temperature for 2-4 hours.

[0014] Preferably, in S1, the extraction is performed using dichloromethane, and the organic phase is collected by extraction; and the washing is performed using pure water for at least three times.

[0015] Preferably, in S2, the mass volume ratio of formaldehyded bisphenol A, 2-amino-5-hydroxypyrimidine and anhydrous ethanol is 1 g: (1.1-1.6) g: (20-40) mL.

[0016] Preferably, in S2, the reaction temperature is 80-90°C and the reaction time is 6-10h.

[0017] Preferably, in S2, during the process of discharging in pure water, the volume ratio of pure water to anhydrous ethanol is 2-3:1.

[0018] Preferably, in S3, the halogenated epoxypropane is epichlorohydrin or epibromohydrin; and the mass ratio of hydroxypyrimidinyl bisphenol A to the halogenated epoxypropane is 1.2-1.8:15-20.

[0019] Preferably, in S3, the catalyst is tetrabutylammonium bromide or hexadecyltrimethylammonium bromide, and the amount of the catalyst added is 1%-3% of the mass of the hydroxypyrimidinyl bisphenol A.

[0020] Preferably, in S3, the temperature of the temperature-raising reaction is 110-140° C., and the reaction time is 4-6 hours; the temperature is lowered to 60-80° C., and the sodium hydroxide solution is added and the reaction is continued for 1-2 hours.

[0021] Preferably, in S3, the mass fraction of the sodium hydroxide solution is 15%-25%, and the mass ratio of the sodium hydroxide solution to the halogenated epoxypropane is 5-8:30.

[0022] Preferably, in S3, the extraction is performed using saturated saline solution, and the organic phase is collected; and the washing is performed using pure water for at least three times.

[0023] In a second aspect, the present invention discloses a low-temperature curing modified resin for water-based coatings, which is prepared by the above-mentioned preparation method.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention prepares a novel modified resin, which is a modified bisphenol A epoxy resin, which is prepared by etherification reaction of hydroxypyrimidinyl bisphenol A and halogenated epoxy propane. The epoxy resin modified by the present invention does not require a very high temperature, and can achieve good curing even at room temperature. Compared with traditional low-temperature curing epoxy resins, after curing, it not only has higher hardness and high temperature resistance, but also has better storage stability and adhesion.

[0026] 2. In the process of preparing the modified bisphenol A epoxy resin of the present invention, the formaldehyded bisphenol A is first prepared by the Duff formaldehyde reaction of bisphenol A and hexamethylenetetramine, and then the formaldehyded bisphenol A and 2-amino-5-hydroxypyrimidine containing an amino group undergo an amine-aldehyde condensation reaction to prepare hydroxypyrimidinyl bisphenol A. Finally, the hydroxypyrimidinyl bisphenol A is subjected to an etherification reaction under the action of a halopropylene oxide to graft an epoxy group to the hydroxyl group in the molecule, thereby obtaining the modified bisphenol A epoxy resin.

[0027] 3. The modified bisphenol A epoxy resin prepared by the present invention is tested after curing at low temperature and found that it not only has higher surface hardness than traditional bisphenol A epoxy resin, but also has better high temperature resistance and adhesion. The reason may be that in the process of preparing the modified bisphenol A epoxy resin, more hydroxyl groups are introduced due to the participation of 2-amino-5-hydroxypyrimidine in the reaction. After the etherification reaction, more epoxy groups are obtained than conventional bisphenol A. In addition, pyrimidine groups are introduced, which may also be the reason for the improvement of its performance. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0029] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0030] The raw materials and reagents used in the present invention are all purchased from the market and are of analytical grade.

[0031] The present invention will be further described below in conjunction with the following examples.

[0032] Example 1

[0033] A method for preparing a low-temperature curing modified resin for water-based coatings comprises the following steps:

[0034] S1. Duff aldehydation reaction:

[0035] Weigh bisphenol A (BPA) and trifluoroacetic acid (TFA), mix them, stir them until they are uniform, introduce nitrogen as a protective gas, add hexamethylenetetramine (HMTA) several times and slowly, control the temperature of the system not to exceed 60°C during the addition process, the mass volume ratio of bisphenol A, hexamethylenetetramine and trifluoroacetic acid is 1.2g:7.4g:50mL, after all are added, reflux and stir for 4h at 85°C, after the reaction is completed, cool naturally to room temperature, and then gradually and slowly pour into 2mol / L hydrochloric acid, the volume ratio of hydrochloric acid to trifluoroacetic acid is 3:1, stir at room temperature for 3h, then use dichloromethane to extract, collect the organic phase, wash the organic phase with pure water at least three times, and then remove the solvent under reduced pressure to obtain formaldehyde bisphenol A (OHC-BPA);

[0036] S2, amine-aldehyde condensation reaction:

[0037] Weigh aldehyde bisphenol A (OHC-BPA) and anhydrous ethanol, mix well, and gradually add 2-amino-5-hydroxypyrimidine (C 5 H 6 N 2 O), the mass volume ratio of formyl bisphenol A, 2-amino-5-hydroxypyrimidine and anhydrous ethanol is 1g:1.4g:30mL. After all are added, reflux and stir for 8h at 85°C. After the reaction is completed, the temperature is naturally cooled to room temperature, and then the reaction solution is poured into pure water with a volume of 3 times that of anhydrous ethanol to discharge the material, filter and collect the precipitate, and vacuum dry to obtain hydroxypyrimidinyl bisphenol A (OH-Py-BPA);

[0038] S3, etherification reaction:

[0039] Weigh hydroxypyrimidinyl bisphenol A (OH-Py-BPA) and epichlorohydrin (ECH) and mix them in a mass ratio of 1.5:18. Pass nitrogen as protective gas. After sufficient stirring, add tetrabutylammonium bromide in an amount of 2% of the mass of hydroxypyrimidinyl bisphenol A. Heat to 120° C. and stir for 5 hours. Then cool to 70° C. and gradually drop 20% sodium hydroxide solution in a mass ratio of 6.5:30. After the dropwise addition is completed, stir again for 1.5 hours. The reaction is terminated. The reaction solution is first extracted with saturated brine, and the organic phase is collected. The organic phase is then washed with pure water for at least three times. Finally, the solvent is removed under reduced pressure to obtain a modified bisphenol A epoxy resin (Mod-BPAER).

[0040] Example 2

[0041] A method for preparing a low-temperature curing modified resin for water-based coatings comprises the following steps:

[0042] S1. Duff aldehydation reaction:

[0043] Weigh bisphenol A (BPA) and trifluoroacetic acid (TFA), mix them, stir them until they are uniform, introduce nitrogen as a protective gas, add hexamethylenetetramine (HMTA) several times and slowly, control the temperature of the system not to exceed 60°C during the addition process, the mass volume ratio of bisphenol A, hexamethylenetetramine and trifluoroacetic acid is 0.9g:6.2g:40mL, after all are added, reflux and stir for 3h at 80°C, after the reaction is completed, cool naturally to room temperature, and then gradually and slowly pour into 1mol / L hydrochloric acid, the volume ratio of hydrochloric acid to trifluoroacetic acid is 2:1, stir at room temperature for 2h, then use dichloromethane to extract, collect the organic phase, wash the organic phase with pure water at least three times, and then remove the solvent under reduced pressure to obtain formaldehyde bisphenol A (OHC-BPA);

[0044] S2, amine-aldehyde condensation reaction:

[0045] Weigh aldehyde bisphenol A (OHC-BPA) and anhydrous ethanol, mix well, and gradually add 2-amino-5-hydroxypyrimidine (C 5 H 6 N 2 O), the mass volume ratio of formyl bisphenol A, 2-amino-5-hydroxypyrimidine and anhydrous ethanol is 1g:1.1g:20mL. After all are added, reflux and stir for 6h at 80°C. After the reaction is completed, the temperature is naturally cooled to room temperature, and then the reaction solution is poured into pure water with a volume of 2 times that of anhydrous ethanol to discharge the material, filter and collect the precipitate, and vacuum dry to obtain hydroxypyrimidinyl bisphenol A (OH-Py-BPA);

[0046] S3, etherification reaction:

[0047] Weigh hydroxypyrimidinyl bisphenol A (OH-Py-BPA) and epibromopropane, the mass ratio of hydroxypyrimidinyl bisphenol A to epibromopropane is 1.2:15, introduce nitrogen as protective gas, stir thoroughly, add hexadecyltrimethylammonium bromide, the addition amount is 1% of the mass of hydroxypyrimidinyl bisphenol A, heat to 110°C, stir to react for 4h, then cool to 60°C, gradually dropwise add 15% sodium hydroxide solution, the mass ratio of sodium hydroxide solution to halogenated epoxypropane is 5:30, stir again for 1h after the addition is completed, the reaction is terminated, the reaction solution is first extracted with saturated brine, the organic phase is collected, and then the organic phase is washed with pure water for at least three times, and finally the solvent is removed under reduced pressure to obtain modified bisphenol A epoxy resin (Mod-BPAER).

[0048] Example 3

[0049] A method for preparing a low-temperature curing modified resin for water-based coatings comprises the following steps:

[0050] S1. Duff aldehydation reaction:

[0051] Weigh bisphenol A (BPA) and trifluoroacetic acid (TFA), mix them, stir them until they are uniform, introduce nitrogen as a protective gas, add hexamethylenetetramine (HMTA) several times and slowly, control the temperature of the system not to exceed 60°C during the addition process, the mass volume ratio of bisphenol A, hexamethylenetetramine and trifluoroacetic acid is 1.4g:8.6g:60mL, after all are added, reflux and stir for 6h at 90°C, after the reaction is completed, cool naturally to room temperature, and then gradually and slowly pour into 3mol / L hydrochloric acid, the volume ratio of hydrochloric acid to trifluoroacetic acid is 4:1, stir at room temperature for 4h, then use dichloromethane to extract, collect the organic phase, wash the organic phase with pure water at least three times, and then remove the solvent under reduced pressure to obtain formaldehyde bisphenol A (OHC-BPA);

[0052] S2, amine-aldehyde condensation reaction:

[0053] Weigh aldehyde bisphenol A (OHC-BPA) and anhydrous ethanol, mix well, and gradually add 2-amino-5-hydroxypyrimidine (C 5 H 6 N 2 O), the mass volume ratio of formyl bisphenol A, 2-amino-5-hydroxypyrimidine and anhydrous ethanol is 1g:1.6g:40mL, after all are added, reflux and stir for 10h at 90°C, after the reaction is completed, cool naturally to room temperature, and then pour the reaction solution into pure water with a volume of 3 times that of anhydrous ethanol, filter and collect the precipitate, and vacuum dry to obtain hydroxypyrimidinyl bisphenol A (OH-Py-BPA);

[0054] S3, etherification reaction:

[0055] Weigh hydroxypyrimidinyl bisphenol A (OH-Py-BPA) and epibromopropane, the mass ratio of hydroxypyrimidinyl bisphenol A to epibromopropane is 1.8:20, introduce nitrogen as protective gas, stir thoroughly, add tetrabutylammonium bromide, the addition amount is 3% of the mass of hydroxypyrimidinyl bisphenol A, heat to 140°C, stir to react for 6 hours, then cool to 80°C, gradually dropwise add 25% sodium hydroxide solution, the mass ratio of sodium hydroxide solution to halogenated epoxypropane is 8:30, stir again for 2 hours after the addition is completed, the reaction is terminated, the reaction solution is first extracted with saturated brine, the organic phase is collected, and then the organic phase is washed with pure water for at least three times, and finally the solvent is removed under reduced pressure to obtain modified bisphenol A epoxy resin (Mod-BPAER).

[0056] Comparative Example 1

[0057] An epoxy resin is a conventional bisphenol A epoxy resin, and the preparation method comprises:

[0058] Weigh bisphenol A and epichlorohydrin and mix them in a mass ratio of 1.5:18. Pass nitrogen as protective gas. After sufficient stirring, add tetrabutylammonium bromide in an amount of 2% of the mass of bisphenol A. Heat to 120°C and stir to react for 5 hours. Then cool to 70°C and gradually drop 20% sodium hydroxide solution in a mass ratio of 6.5:30 to halogenated epoxypropane. After the dropwise addition is completed, stir again for 1.5 hours. The reaction is completed. The reaction solution is first extracted with saturated brine, the organic phase is collected, and then the organic phase is washed with pure water for at least three times. Finally, the solvent is removed under reduced pressure to obtain bisphenol A epoxy resin (BPAER).

[0059] Comparative Example 2

[0060] A modified bisphenol A epoxy resin, the preparation method is different from that of Example 1 in that step S2 is omitted and the rest of the process remains unchanged. The preparation method comprises:

[0061] S1. Preparation of formaldehyde-modified bisphenol A, the same as in Example 1.

[0062] S2. Weigh the formaldehyded bisphenol A and epichlorohydrin, mix them in a mass ratio of 1.5:18, introduce nitrogen as protective gas, and after sufficient stirring, add tetrabutylammonium bromide in an amount of 2% of the mass of the formaldehyded bisphenol A, raise the temperature to 120°C, stir and react for 5 hours, then cool to 70°C, gradually dropwise add a 20% sodium hydroxide solution in a mass ratio of 6.5:30 to the sodium hydroxide solution, and stir again for 1.5 hours after the addition is complete. The reaction is terminated, and the reaction solution is first extracted with saturated brine, the organic phase is collected, and then the organic phase is washed with pure water for at least three times, and finally the solvent is removed under reduced pressure to obtain a modified bisphenol A epoxy resin.

[0063] Comparative Example 3

[0064] A modified bisphenol A epoxy resin, the preparation method of which is different from that of Example 1 in that 2-amino-5-hydroxypyrimidine is replaced with p-aminophenol, and the rest of the process remains unchanged. The preparation method comprises:

[0065] S1. Preparation of formaldehyde-modified bisphenol A, the same as in Example 1.

[0066] S2, weighing formaldehyde bisphenol A and anhydrous ethanol, mixing, fully stirring, gradually adding p-aminophenol under stirring, the mass volume ratio of formaldehyde bisphenol A, p-aminophenol and anhydrous ethanol is 1g:1.4g:30mL, after all are added, reflux stirring at 85°C for 8h, after the reaction is completed, naturally cool to room temperature, then pour the reaction solution into pure water with a volume of 3 times that of anhydrous ethanol, filter and collect the precipitate, and vacuum dry to obtain phenolized bisphenol A;

[0067] S3, preparing modified bisphenol A epoxy resin, replacing hydroxypyrimidinyl bisphenol A with phenolized bisphenol A, and the rest is the same as Example 1.

[0068] In order to more clearly illustrate the content of the present invention, the resins prepared in Example 1 and Comparative Examples 1-3 were first emulsified in water and then subjected to low-temperature curing treatment, and the properties of the cured products were tested. The low-temperature curing agent used in the low-temperature curing process was a water-based epoxy resin curing agent CYDHD-220.

[0069] The specific processing and detection process includes:

[0070] 1. Treatment of water-based paint:

[0071] (1) Preparation of aqueous emulsifier:

[0072] The epoxy resin (one of Example 1 and Comparative Examples 1-3) and polyethylene glycol PEG-400 were mixed in a mass ratio of 1:10, heated to 100° C., stirred evenly, and then potassium persulfate was added. The mixture was heated to 180° C. and heated for 2 hours to obtain an aqueous emulsifier.

[0073] (2) Preparation of water-based epoxy resin emulsion:

[0074] An epoxy resin (one of Example 1 and Comparative Examples 1-3, corresponding to step (1)), an aqueous emulsifier and deionized water are mixed in a mass ratio of 5:1:4, and stirred at a speed of 2000 r / min until uniform, to obtain an aqueous epoxy resin emulsion;

[0075] (3) Waterborne epoxy resin curing:

[0076] The water-based epoxy resin emulsion and the water-based epoxy resin curing agent CYDHD-220 were mixed in a mass ratio of 5:1. After mixing evenly, the mixture was sprayed on a stainless steel plate with a spraying thickness of 75 μm. The mixture was dried at room temperature (25°C) for 24 hours to complete the curing.

[0077] 2. Paint detection:

[0078] Hardness is tested according to the pencil method of GB / T6739-1996; adhesion is tested according to the method of GB / T 1720-1979 and judged by passing the grade; high temperature resistance is tested according to the method of GB / T 1735-2009, after being treated at 200℃ for 2h, observing whether the paint film is cracked or falls off; storage stability is tested according to the method of GB / T 6753.3-1986, sealed and stored at 50℃ for 30 days, and the viscosity change value is tested.

[0079] Table 1 Performance test of different coatings

[0080]

[0081]

[0082] It can be seen from the test results in Table 1 that the water-based coating prepared using the resin of Example 1 of the present invention has higher hardness and high temperature resistance than other comparative examples after being cured at a lower temperature (25°C) for 24 hours, and also has excellent adhesion and storage stability.

[0083] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0084] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a low-temperature curing modified resin for water-based coatings, characterized in that: The following steps are involved: S1, weigh bisphenol A and trifluoroacetic acid, mix them, stir them until they are uniform, introduce nitrogen as a protective gas, add hexamethylenetetramine, and after all of them are added, heat up and reflux with stirring. After the reaction is completed, cool them naturally to room temperature, pour them into hydrochloric acid and stir, and then extract and wash them, and then remove the solvent under reduced pressure to obtain formaldehyde bisphenol A; S2, weighing formaldehyde bisphenol A and anhydrous ethanol, mixing, fully stirring, adding 2-amino-5-hydroxypyrimidine, reflux reaction after all the addition, and naturally cooling to room temperature after the reaction is completed, discharging in pure water, filtering and collecting the precipitate, and vacuum drying to obtain hydroxypyrimidinyl bisphenol A; S3, weighing hydroxypyrimidinyl bisphenol A and halogenated epoxypropane, mixing, introducing nitrogen as protective gas, stirring thoroughly, adding a catalyst, heating to react, then cooling and adding sodium hydroxide solution, continuing to stir to react, after the reaction is completed, extracting and washing the reaction solution, and removing the solvent under reduced pressure to obtain a modified bisphenol A epoxy resin; In S1, the mass volume ratio of bisphenol A, hexamethylenetetramine and trifluoroacetic acid is (0.9-1.4) g: (6.2-8.6) g: (40-60) mL; In S2, the mass volume ratio of formaldehyded bisphenol A, 2-amino-5-hydroxypyrimidine and anhydrous ethanol is 1 g: (1.1-1.6) g: (20-40) mL; In S3, the halogenated epoxypropane is epichlorohydrin or epibromohydrin, the mass ratio of hydroxypyrimidinyl bisphenol A to halogenated epoxypropane is 1.2-1.8:15-20; the catalyst is tetrabutylammonium bromide or hexadecyltrimethylammonium bromide, and the added amount of the catalyst is 1%-3% of the mass of the hydroxypyrimidinyl bisphenol A.

2. The method for preparing a low-temperature curing modified resin for water-based coatings according to claim 1, characterized in that: In the S1, the reaction temperature is 80-90°C and the reaction time is 3-6h.

3. The method for preparing a low-temperature curing modified resin for water-based coatings according to claim 1, characterized in that: In the S1, the concentration of hydrochloric acid is 1-3 mol / L, and the volume ratio of hydrochloric acid to trifluoroacetic acid is 2-4:1; after adding hydrochloric acid, stirring is continued at room temperature for 2-4 hours.

4. The method for preparing a low-temperature curing modified resin for water-based coatings according to claim 1, characterized in that: In S2, the reaction temperature is 80-90°C and the reaction time is 6-10h.

5. The method for preparing a low-temperature curing modified resin for water-based coatings according to claim 1, characterized in that: In S3, the temperature of the temperature-raising reaction is 110-140° C., and the reaction time is 4-6 hours; the temperature is lowered to 60-80° C., and after adding the sodium hydroxide solution, the reaction is continued for 1-2 hours.

6. The method for preparing a low-temperature curing modified resin for water-based coatings according to claim 1, characterized in that: In S3, the mass fraction of the sodium hydroxide solution is 15%-25%, and the mass ratio of the sodium hydroxide solution to the halogenated epoxypropane is 5-8:

30.

7. A low-temperature curing modified resin for water-based coatings, prepared by the preparation method according to claim 1.

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