Preparation process of a waterproof coating for road bridges

Abstract

The present invention relates to the technical field of coatings, and discloses a preparation process of a waterproof coating for road bridges. In the present invention, polyester polyol, isocyanate monomer, 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid, etc. are reacted, and then water, nanocellulose, copper salt, neutralizing agent, pigment, etc. are added to obtain a waterproof coating for road bridges. Copper ions respectively form coordination with the pyridine-2-carboxylic acid of polyurethane and the hydroxyl groups of nanocellulose, acting as a cross-linking agent to perform ionic cross-linking between polyurethane and nanocellulose, improving the interfacial bonding performance of polyurethane and nanocellulose, enabling nanocellulose to play a better reinforcing role, and the coating film having higher pencil hardness, impact resistance and mechanical properties. At the same time, the waterproof and corrosion protection performance is improved, and it has good practical applications in fields such as road bridges.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and specifically to a preparation process of a waterproof coating for road bridges. Background Art

[0002] Coatings are widely used in aspects such as road bridges, automobiles and ships, mechanical equipment, etc., playing roles such as waterproofing, corrosion prevention, and beautification. Waterborne polyurethane uses water as a solvent, does not contain toxic volatile solvents, is green and environmentally friendly, and is widely used. Traditional polyester-based waterborne polyurethane has poor water resistance, is prone to hydrolysis when absorbing water, resulting in deterioration of the mechanical properties, corrosion prevention and other properties of the paint film. Currently, the modification methods for polyurethane coatings include crosslinking modification, filling modification, etc.

[0003] Nano microcrystalline cellulose is cheap and easy to obtain, has high mechanical strength, is green and environmentally friendly, and is widely used in materials such as coatings, inks, plastics, etc. The Chinese patent with the publication number CN108610721B discloses a flame-retardant modified polyurethane curing agent and its preparation method and a two-component polyurethane coating. The composite microspheres are obtained by mixing the microcrystalline cellulose solution and nano magnesium hydroxide, and then mixed and modified with 4,4-diphenylmethane diisocyanate, improving the hardness and flame retardancy of the polyurethane coating film of the curing agent. However, this patent does not improve the waterproofing, corrosion prevention and other properties of the polyurethane coating, which is not conducive to the practical application of the polyurethane coating in road bridges and other aspects. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a preparation process of a waterproof coating for road bridges, solving the problems of poor waterproofing and corrosion prevention performance and poor mechanical properties of the polyurethane coating.

[0005] A preparation process of a waterproof coating for road bridges: Add polyester polyol to a reaction vessel, after drying and dehydrating, add isocyanate monomer and dibutyltin dilaurate, introduce nitrogen, heat to 70 - 80 °C, react for 2 - 2.5 h, lower the temperature to 40 - 45 °C, add acetone, 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid, react for 40 - 60 min, add water, nano cellulose, copper salt, stir for 6 - 10 h, and finally add neutralizing agent triethylamine, pigment, dispersant, defoaming agent, and shear and disperse to obtain a waterproof coating for road bridges.

[0006] Preferably, the molar ratio n(-OH):n(-NCO) of polyester polyol to isocyanate monomer is 1:(2.6 - 2.8).

[0007] Preferably, the molar ratio of isocyanate monomer to 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid is 1:(1 - 1.1).

[0008] Preferably, the isocyanate monomer is any one of toluene-2,4-diisocyanate, isophorone diisocyanate, and 4,4'-diphenylmethane diisocyanate.

[0009] Preferably, the mass of the nanocellulose is 10-25% of the total mass of the polyester polyol, the isocyanate monomer, and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

[0010] Preferably, the mass of the copper salt is 0.5-1.4% of the total mass of the polyester polyol, the isocyanate monomer, and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

[0011] Preferably, the copper salt is cuprous chloride or copper nitrate.

[0012] Preferably, the preparation process of 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid is as follows:

[0013] (1) Add water, propionic acid, and methyl 4-aminopyridine-2-carboxylate to the reaction vessel, add a tetrahydrofuran solution of ethylene oxide at 0-5°C, control the molar ratio of methyl 4-aminopyridine-2-carboxylate to ethylene oxide to be 1:(2.4-3), then react at 10-15°C for 18-30 h, distill off tetrahydrofuran and low-boiling substances under reduced pressure, extract the aqueous phase with ethyl acetate, and distill the ethyl acetate phase under reduced pressure and dry to obtain methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate.

[0014] (2) Add methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate and an aqueous sodium hydroxide solution with a concentration of 2.8-4 mol / L to methanol, heat to 85-90°C, carry out a condensation reflux reaction for 5-8 h, distill off methanol under reduced pressure, add hydrochloric acid dropwise to the aqueous phase to precipitate a large amount of precipitate, filter, and dry to obtain 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. The reaction formula is:

[0015] .

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] In the present invention, methyl 4-aminopyridine-2-carboxylate and ethylene oxide are subjected to a ring-opening addition reaction, and then the ester group is hydrolyzed to obtain 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid, which is used as an aqueous carboxylic acid chain extender for polyurethane. It undergoes a polymerization chain extension reaction with a polyester polyol and an isocyanate monomer to obtain an aqueous polyurethane, and finally is compounded with nanocellulose, a copper salt, a pigment, etc. to obtain a waterproof coating for road bridges.

[0018] The aqueous polyurethane coating emulsion of the present invention does not delaminate and has excellent storage stability. At the same time, the added copper ions form coordination with pyridine-2-carboxylic acid of polyurethane and hydroxyl groups of nanocellulose respectively, so that the copper ions act as a crosslinking agent to ionically crosslink polyurethane and nanocellulose, improving the interfacial bonding performance between polyurethane and nanocellulose, enabling nanocellulose to play a better reinforcing role, and the coating film having higher pencil hardness, impact resistance and mechanical properties.

[0019] The polyurethane and nanocellulose of the present invention are ionically crosslinked to form a dense molecular chain crosslinking network, which can inhibit the entry of corrosive media such as water molecules, acids, alkalis and salts into the interior of the polyurethane film, so that the film exhibits higher water resistance and salt spray resistance and has better waterproof and anti-corrosion properties. It has good practical applications in fields such as road bridges. Specific embodiments

[0020] The following combines specific embodiments to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work fall within the scope of protection of the present invention.

[0021] Nanocellulose, with a content of 99.9%, was purchased from Hubei Watson Chemical Technology Co., Ltd. Polyester polyol, model Evonik Dynacoll 7130, was purchased from Wuhan Jinqu New Materials Co., Ltd.

[0022] Example 1:

[0023] (1) Add 30 mL of water, 2.3 mL of propionic acid, and 50 mmol of methyl 4-aminopyridine-2-carboxylate to a reaction vessel. Add a 75 mL tetrahydrofuran solution containing 120 mmol of ethylene oxide at 5 °C, and then react at 10 °C for 30 h. Distill off tetrahydrofuran and low-boiling substances under reduced pressure. Extract the aqueous phase with ethyl acetate, and distill the ethyl acetate phase under reduced pressure and dry to obtain methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate.

[0024] (2) Add 8 g of methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate and 75 mL of a 3.5 mol / L sodium hydroxide aqueous solution to 100 mL of methanol. Heat to 85 °C and reflux for 7 h. Distill off methanol under reduced pressure. Dropwise add concentrated hydrochloric acid to the aqueous phase to precipitate a large amount of precipitate. Filter and dry to obtain 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

[0025] (3) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content is 0.1 mol) into the reaction vessel. After drying and dehydration, add 0.28 mol of toluene - 2,4 - diisocyanate and 0.3 g of dibutyltin dilaurate. Introduce nitrogen, heat to 75 °C, react for 2.5 h, then cool the temperature to 45 °C, add 30 mL of acetone and 0.308 mol of 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid, react for 60 min, add 400 mL of water, nanocellulose, and cuprous chloride. Control the mass of nanocellulose to be 10% of the total mass of polyester polyol, toluene - 2,4 - diisocyanate, and 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid. The mass of cuprous chloride is 0.5% of the total mass of polyester polyol, toluene - 2,4 - diisocyanate, and 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid. Stir for 6 h, and finally add 42 mL of neutralizer triethylamine, 46 g of pigment titanium dioxide, 2.7 g of dispersant, and 1.3 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge.

[0026] Example 2:

[0027] (1) Add 40 mL of water, 2.2 mL of propionic acid, and 50 mmol of methyl 4 - aminopyridine - 2 - carboxylate into the reaction vessel. Add 75 mL of a tetrahydrofuran solution containing 130 mmol of ethylene oxide at 5 °C, and then react at 15 °C for 24 h. Distill off tetrahydrofuran and low - boiling substances under reduced pressure. Extract the aqueous phase with ethyl acetate, and distill the ethyl acetate phase under reduced pressure and dry to obtain methyl 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylate.

[0028] (2) Add 8 g of methyl 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylate and 65 mL of a 4 mol / L aqueous sodium hydroxide solution into 100 mL of methanol. Heat to 85 °C and perform reflux condensation reaction for 8 h. Distill off methanol under reduced pressure. Dropwise add concentrated hydrochloric acid to the aqueous phase, a large amount of precipitate will form. Filter and dry to obtain 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid.

[0029] (3) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content 0.1 mol) to the reaction vessel. After drying and dehydration, add 0.26 mol of 4,4'-diphenylmethane diisocyanate, 0.32 g of dibutyltin dilaurate. Introduce nitrogen, heat to 70 °C, react for 2.5 h, cool the temperature to 40 °C, add 40 mL of acetone, 0.26 mol of 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid, react for 40 min, add 400 mL of water, nanocellulose, copper nitrate. Control the mass of nanocellulose to be 15% of the total mass of polyester polyol, 4,4'-diphenylmethane diisocyanate and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. The mass of copper nitrate is 0.8% of the total mass of polyester polyol, 4,4'-diphenylmethane diisocyanate and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. Stir for 10 h, and finally add 36 mL of neutralizer triethylamine, 56 g of pigment titanium dioxide, 3.4 g of dispersant, 1.3 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge.

[0030] Example 3:

[0031] (1) Add 40 mL of water, 2.5 mL of propionic acid, 50 mmol of methyl 4-aminopyridine-2-carboxylate to the reaction vessel. Add a 60 mL tetrahydrofuran solution containing 150 mmol of ethylene oxide at 0 °C, and then react at 15 °C for 18 h. Distill off tetrahydrofuran and low-boiling substances under reduced pressure. Extract the aqueous phase with ethyl acetate, and distill the ethyl acetate phase under reduced pressure and dry to obtain methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate.

[0032] (2) Add 8 g of methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate and 90 mL of 2.8 mol / L sodium hydroxide aqueous solution to 80 mL of methanol. Heat to 90 °C and reflux for 5 h. Distill off methanol under reduced pressure. Dropwise add concentrated hydrochloric acid to the aqueous phase, a large amount of precipitate will form. Filter and dry to obtain 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

[0033] (3) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content is 0.1 mol) into the reaction vessel. After drying and dehydration, add 0.274 mol of isophorone diisocyanate, 0.3 g of dibutyltin dilaurate, introduce nitrogen gas, heat to 80 °C, react for 2 h, cool the temperature to 45 °C, add 40 mL of acetone, 0.28 mol of 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid, react for 60 min, add 500 mL of water, nanocellulose, copper chloride. Control the mass of nanocellulose to be 20% of the total mass of polyester polyol, isophorone diisocyanate and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. The mass of copper chloride is 1.1% of the total mass of polyester polyol, isophorone diisocyanate and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. Stir for 10 h, and finally add 40 mL of neutralizer triethylamine, 40 - 56 g of pigment titanium dioxide, 2.2 - 3.4 g of dispersant, 1.3 - 1.6 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge

[0034] Example 4:

[0035] (1) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content is 0.1 mol) into the reaction vessel. After drying and dehydration, add 0.27 mol of isophorone diisocyanate, 0.3 g of dibutyltin dilaurate, introduce nitrogen gas, heat to 80 °C, react for 2 h, cool the temperature to 45 °C, add 40 mL of acetone, 0.278 mol of 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid (prepared by Example 1), react for 60 min, add 450 mL of water, nanocellulose, copper chloride. Control the mass of nanocellulose to be 25% of the total mass of polyester polyol, isophorone diisocyanate and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. The mass of copper chloride is 1.4% of the total mass of polyester polyol, isophorone diisocyanate and 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid. Stir for 10 h, and finally add 40 mL of neutralizer triethylamine, 44 g of pigment titanium dioxide, 2.6 g of dispersant, 1.6 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge

[0036] Comparative Example 1:

[0037] (1) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content 0.1 mol) into the reaction vessel. After drying and dehydration, add 0.28 mol of toluene - 2,4 - diisocyanate, 0.3 g of dibutyltin dilaurate. Introduce nitrogen, heat to 75 °C, react for 2.5 h, then cool the temperature to 45 °C, add 30 mL of acetone, 0.308 mol of 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid (prepared in Example 1), react for 60 min, add 400 mL of water, and nanocellulose. Control the mass of nanocellulose to be 10% of the total mass of polyester polyol, toluene - 2,4 - diisocyanate, and 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid. Stir for 6 h, and finally add 42 mL of neutralizer triethylamine, 46 g of pigment titanium dioxide, 2.7 g of dispersant, 1.3 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge.

[0038] Comparative Example 2:

[0039] (1) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content 0.1 mol) into the reaction vessel. After drying and dehydration, add 0.28 mol of toluene - 2,4 - diisocyanate, 0.3 g of dibutyltin dilaurate. Introduce nitrogen, heat to 75 °C, react for 2.5 h, then cool the temperature to 45 °C, add 30 mL of acetone, 0.308 mol of methyl 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylate (prepared in Example 1), react for 60 min, add 400 mL of water, and nanocellulose. Control the mass of nanocellulose to be 10% of the total mass of polyester polyol, toluene - 2,4 - diisocyanate, and methyl 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylate. Stir for 6 h, and finally add 46 g of pigment titanium dioxide, 2.7 g of dispersant, 1.3 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge.

[0040] Comparative Example 3:

[0041] (1) Add polyester polyol (molecular weight 2000, total hydroxyl -OH content is 0.1 mol) into the reaction vessel. After drying and dehydration, add 0.28 mol of toluene - 2,4 - diisocyanate, 0.3 g of dibutyltin dilaurate. Introduce nitrogen gas, heat to 75 °C, react for 2.5 h, then cool the temperature to 45 °C, add 30 mL of acetone, 0.308 mol of 2,2 - dimethylolpropionic acid, react for 60 min, add 400 mL of water, nanocellulose, and cuprous chloride. Control the mass of nanocellulose to be 10% of the total mass of polyester polyol, toluene - 2,4 - diisocyanate, and 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid. The mass of cuprous chloride is 0.5% of the total mass of polyester polyol, toluene - 2,4 - diisocyanate, and 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid. Stir for 6 h, and finally add 42 mL of neutralizing agent triethylamine, 46 g of pigment titanium dioxide, 2.7 g of dispersant, and 1.3 g of defoamer, and perform shear dispersion to obtain the waterproof coating for road and bridge

[0042] The storage stability of the coating is tested according to the standard of GB / T 6753.3 - 1986, and the storage time is 6 months. The pencil hardness of the paint film is tested according to the standard of GB / T 6739 - 2022, and the curing condition is baking at 80 °C for 5 h. The impact resistance is tested according to the standard of GB / T 1732 - 2020. The water resistance is tested according to the standard of GB / T 1733 - 1993. The salt spray resistance performance is tested according to the standard of GB / T 1771 - 2007

[0043] Table 1

[0044] ,

[0045] In Examples 1 - 4, 4 - N,N - bis(2 - hydroxyethyl)aminopyridine - 2 - carboxylic acid containing carboxyl group is used as the hydrophilic chain extender. The obtained waterborne polyurethane has good dispersibility in water, the emulsion does not delaminate, and has excellent storage stability. At the same time, cuprous ions and nanocellulose are added. Cuprous ions form coordination with the pyridine - 2 - carboxylic acid of polyurethane ( ), and the hydroxyl groups of nanocellulose, thus acting as a cross - linker to perform ionic cross - linking between polyurethane and nanocellulose, improving the interfacial bonding performance between polyurethane and nanocellulose, enabling nanocellulose to play a better reinforcing role. The paint film of the coating has higher pencil hardness, impact resistance, and mechanical properties. And through ionic cross - linking, polyurethane and nanocellulose form a tight molecular chain cross - linked network, which can inhibit water molecules and corrosive media such as acids, alkalis, and salts from entering the interior of the polyurethane paint film, so that the paint film shows higher water resistance and salt spray resistance performance, and has better waterproof and anti - corrosion performance

[0046] Compared with Example 1, copper ions were not added in Comparative Example 1, and it was impossible to carry out ionic crosslinking between waterborne polyurethane and nanocellulose, resulting in lower interfacial bonding performance between polyurethane and nanocellulose, lower pencil hardness, impact resistance and mechanical properties of the paint film, and poor water resistance and salt spray resistance.

[0047] In Comparative Example 2, methyl 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylate was used as the chain extender. Since it does not contain a carboxyl group, waterborne polyurethane cannot be obtained, resulting in poor dispersibility in water, easy stratification of the coating, and poor storage stability. And it does not contain the pyridine-2-carboxylic acid structure, making it difficult to coordinate and ionically crosslink with the hydroxyl groups of nanocellulose and copper ions, resulting in poor pencil hardness, impact resistance, water resistance and salt spray resistance of the paint film.

[0048] In Comparative Example 3, conventional 2,2-dimethylolpropionic acid was used as the chain extender. The obtained waterborne polyurethane does not contain the pyridine-2-carboxylic acid structure, and has a low coordination effect with the hydroxyl groups of nanocellulose and copper ions, and weak ionic crosslinking performance, resulting in poor pencil hardness, impact resistance, water resistance and salt spray resistance of the paint film.

Claims

1. A preparation process of a waterproof coating for roads and bridges, characterized in that: The preparation process comprises the following steps: adding polyester polyol into a reaction container, adding isocyanate monomer and dibutyltin dilaurate after drying and dehydration, introducing nitrogen, heating to 70-80° C., reacting for 2-2.5 h, lowering the temperature to 40-45° C., adding acetone and 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylic acid, reacting for 40-60 min, adding water, nanocellulose and copper salt, stirring for 6-10 h, and finally adding a neutralizer, a pigment, a dispersant and a defoaming agent, shearing and dispersing, and obtaining a waterproof coating for roads and bridges.

2. The preparation process of the waterproof coating for roads and bridges according to claim 1, characterized in that: The molar ratio of the hydroxyl group of the polyester polyol to the isocyanate group of the isocyanate monomer is n(-OH):n(-NCO) is 1:(2.6-2.8).

3. The preparation process of the waterproof coating for roads and bridges according to claim 1, characterized in that: The molar ratio of the isocyanate monomer to 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylic acid is 1:(1-1.1).

4. The preparation process of the waterproof coating for roads and bridges according to claim 2 or 3, characterized in that: The isocyanate monomer is any one of toluene-2,4-diisocyanate, isophorone diisocyanate, and 4,4'-diphenylmethane diisocyanate.

5. The preparation process of the waterproof coating for roads and bridges according to claim 1, characterized in that: The mass of the nanocellulose is 10-25% of the total mass of the polyester polyol, the isocyanate monomer and the 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

6. The preparation process of the waterproof coating for roads and bridges according to claim 1, characterized in that: The mass of the copper salt is 0.5-1.4% of the total mass of the polyester polyol, the isocyanate monomer and the 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

7. The preparation process of the waterproof coating for roads and bridges according to claim 1, characterized in that: The copper salt is cuprous chloride or copper nitrate.

8. The preparation process of the waterproof coating for roads and bridges according to claim 5 or 6, characterized in that: The preparation process of the 4-N,N-bis(2-hydroxyethyl)aminopyridine-2-carboxylic acid is as follows: (1) Add water, propionic acid, and methyl 4-aminopyridine-2-carboxylate to a reaction vessel, add a tetrahydrofuran solution of ethylene oxide at 0-5°C, then react at 10-15°C for 18-30 hours, distill under reduced pressure, extract, and dry to obtain methyl 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylate; (2) Add 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylic acid methyl ester and aqueous sodium hydroxide solution to methanol, heat to 85-90°C, condense and reflux for 5-8 hours, distill under reduced pressure, add hydrochloric acid dropwise to the aqueous phase to precipitate, filter, and dry to obtain 4-N,N-di(2-hydroxyethyl)aminopyridine-2-carboxylic acid.

9. The preparation process of the waterproof coating for roads and bridges according to claim 8, characterized in that: The molar ratio of 4-aminopyridine-2-carboxylic acid methyl ester to ethylene oxide in (1) is 1:(2.4-3).

10. The preparation process of the waterproof coating for roads and bridges according to claim 8, characterized in that: The concentration of the sodium hydroxide aqueous solution in (2) is 2.8-4 mol / L.