Waterproof coating for wall surface and preparation method thereof

Abstract

The application relates to a waterproof coating for a wall surface and a preparation method thereof, and belongs to the technical field of coatings. The waterproof coating is prepared from the following components: 50-53 parts by weight of epoxy resin, 75-81 parts by weight of a curing agent and 8.5-11.5 parts by weight of a waterproof filler. The waterproof filler is prepared by the following steps: reacting epoxidized nanosilica with a nucleophilic reagent p-aminophenyl POSS, ring-opening and polymerization of N acid anhydride and modification of isocyanate ethyl. The waterproof coating suitable for being coated on a wall surface is prepared by taking epoxy resin as a film-forming material and adding the waterproof filler to build a waterproof system. The waterproof coating can have ideal waterproof effect without an auxiliary agent, effectively blocks the invasion of water, and has low water absorption of a coating layer.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a waterproof coating for walls and its preparation method. Background Technology

[0002] In modern construction engineering, walls typically require coating treatment to form a protective functional film on their surface. Applying paint to walls not only improves the building's appearance but also creates a stable, continuous protective layer on the wall surface, providing a degree of protection for the wall structure and reducing the adverse effects of external factors. Among these coatings, polymer coatings with synthetic resins as the main film-forming substance are gradually becoming important materials in wall coating systems. These polymer coatings form a polymer coating after curing, offering high versatility and wide applicability, thus gaining widespread adoption in the field of building wall protection.

[0003] Waterproofing performance is a crucial indicator for evaluating the effectiveness of polymer coatings. By establishing a water-resistant coating structure on the wall surface, polymer coatings can reduce the possibility of moisture penetrating the wall substrate, thus providing waterproof protection. However, based on the current usage of wall waterproofing coatings, their waterproofing performance still has room for improvement. Water absorption rate is a key indicator reflecting the water-resistant coating's ability to block water, and some existing wall waterproofing coatings perform poorly in this aspect, exhibiting high water absorption rates and only moderate waterproofing effects, failing to meet the urgent need for high waterproofing performance in building walls. Therefore, technological improvements to wall waterproofing coatings are urgently needed. Summary of the Invention

[0004] Based on the problems and shortcomings of existing technologies, the purpose of this invention is to provide a waterproof coating for walls and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions: I. A waterproof coating for walls, prepared from the following components: 50-53 parts by weight of epoxy resin, 75-81 parts by weight of curing agent and 8.5-11.5 parts by weight of waterproof filler; The waterproof filler is prepared by the following steps: Step (1): Add 0.5-0.75 parts by weight of epoxidized nano silica, 2-5 parts by weight of p-aminophenyl POSS and 0.4-0.45 parts by weight of p-toluenesulfonic acid to 28-50 parts by weight of dimethylformamide, stir, filter out the solid phase, wash, dry and obtain the first product; Step (2): Add 0.85-1.4 parts by weight of the first product and 1.5-2 parts by weight of N anhydride to 45-75 parts by weight of dimethylformamide, stir, filter out the solid phase, wash, dry, and obtain the second product; Step (3): Add 1.2-2.5 parts by weight of the second product and 3-7 parts by weight of ethyl isocyanate to 60-150 parts by weight of toluene, stir, filter out the solid phase, wash and dry.

[0006] As a preferred technical solution of the present invention, in step (1), the epoxidized nano silica is prepared by surface modification of nano silica with an epoxy silane coupling agent.

[0007] As a preferred technical solution of the present invention, in step (1), the stirring refers to stirring at 72-86°C for 7-13 hours under a nitrogen atmosphere.

[0008] As a preferred embodiment of the present invention, in step (2), the N-anhydride is prepared by the following steps: Step A: Mix 125-155 parts by weight of 1,4-dioxane aqueous solution, 16-18 parts by weight of triethylamine and 3-7 parts by weight of N-phenylglycine to obtain the first solution; Step B: Mix 35-45 parts by weight of 1,4-dioxane and 18-21 parts by weight of di-tert-butyl dicarbonate to obtain a second solution; Step C: Add 53-66 parts by weight of the second solution dropwise to 144-180 parts by weight of the first solution. After the addition is complete, stir at room temperature for 10-18 hours to obtain material A. After post-processing, obtain the intermediate. Step D: Add 4-6.5 parts by weight of intermediate and 5-6 parts by weight of phosphorus trichloride to 130-150 parts by weight of dichloromethane, stir, and obtain material B, which will then undergo post-processing.

[0009] Preferably, in step A, the concentration of the 1,4-dioxane aqueous solution is 40-46 wt%.

[0010] Preferably, in step A, the mixing refers to stirring and mixing at room temperature for 5-10 minutes.

[0011] Preferably, in step B, the mixing refers to stirring and mixing at room temperature for 5-10 minutes.

[0012] Preferably, in step C, the post-treatment refers to adding n-hexane at 15-20 wt% of material A, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the lower layer, adjusting the pH of the acetic acid solution to 2.8-3, adding ethyl acetate at 25-30 wt%, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the upper layer, adding saturated sodium chloride aqueous solution at 25-30 wt%, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the upper layer, adding deionized water at 20-25 wt%, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the upper layer, and then rotary evaporating.

[0013] Preferably, in step D, the stirring refers to stirring at 0-5°C under a nitrogen atmosphere for 1.5-3 hours and then stirring at room temperature for 20-25 hours.

[0014] Preferably, in step D, the post-treatment refers to adding n-hexane at 20-25 wt% of the material B, filtering out the liquid phase, allowing it to evaporate naturally at room temperature to 25-30% of the initial volume, filtering out the solid phase, washing, and drying.

[0015] As a preferred technical solution of the present invention, in step (2), the stirring refers to stirring at 62-67°C for 8-15 hours under a nitrogen atmosphere.

[0016] As a preferred technical solution of the present invention, in step (3), the stirring refers to stirring at room temperature under a nitrogen atmosphere for 6-7 hours.

[0017] II. A method for preparing a waterproof coating for walls, comprising the following steps: Add curing agent and waterproof filler to epoxy resin, homogenize, and then degas under vacuum.

[0018] The beneficial effects of this invention are: (1) This invention uses epoxy resin as a film-forming substance and adds waterproof filler to construct a waterproof system, thus preparing a waterproof coating suitable for application on walls. It can achieve a relatively ideal waterproof effect without the need for additives. The waterproof coating can effectively block the intrusion of water, and the coating has a low water absorption rate. It is suitable for use in daily living environments and high-end scenarios with high requirements for protective performance. Overall, it has considerable application value. After curing, epoxy resin can form a continuous coating and play a basic waterproof barrier role. The addition of waterproof filler improves the structure and properties of the coating, greatly enhancing the waterproof effect on the inherent basis.

[0019] (2) The waterproof filler of this invention combines inorganic particles, p-aminophenyl POSS, N-anhydride, and ethyl isocyanate to form a composite structure. Each component performs its function to improve the structure and properties of the coating and synergistically enhance the waterproofing effect. The inorganic particles are selected as nano-silica, which effectively enhances the density of the coating and reduces the water absorption rate. After epoxidation treatment, it can react with the nucleophilic reagent p-aminophenyl POSS. Relying on its unique cage-like three-dimensional structure, after the reaction, it can reduce the aggregation between nanomaterials on the one hand, and generate significant space occupation on the other hand, enhancing the barrier effect and increasing the resistance to water diffusion. In addition, p-aminophenyl POSS, as an eight-arm amino compound, can provide an amino group, enabling N-anhydride to open the ring and polymerize. N-anhydride is prepared with slight modifications according to existing technology. It is obtained by first synthesizing an intermediate from N-phenylglycine and di-tert-butyl dicarbonate and then closing the ring. Unlike general anhydrides, it reacts with the amino group to produce... The resulting RNCOOH is unstable and will rapidly and spontaneously disappear, releasing CO2 and generating secondary amine groups. The secondary amine groups further open the ring with N-anhydride, gradually forming a polymer molecular chain. The resulting polymer molecular chain is mainly composed of repeating rigid planar benzene rings, which reduces the free volume and improves the impermeability. The remaining secondary amine groups react with ethyl isocyanate to modify the end of the polymer molecular chain, thereby regulating the end-capping. The alkane reduces the surface energy, inhibits water penetration, and weakens the adsorption of water. This invention uses ethyl isocyanate, which has a short ethyl chain, reducing the surface energy while having less disturbance to the inherent structure. When the carbon chain is extended to propyl or butyl ester, the longer carbon chain will interfere with hydrogen bonding, molecular forces, π-stacking, etc., which will increase the free volume, increase the tendency of water diffusion, and reduce the waterproof performance. With butyl ester, it is even worse than no modification. Although methyl isocyanate has a shorter carbon chain, it lacks industrial application prospects due to factors such as toxicity and safety. Detailed Implementation

[0020] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0021] Unless otherwise specified, the raw materials, reagents, and apparatus used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0022] Preparation Example 1 Epoxidized nano-silica was prepared by surface modification of nano-silica with an epoxy silane coupling agent, specifically as follows: 1) Weigh 0.5g of nano silica (Sigma-Aldrich Trading Co., Ltd., No. 637238), add 100mL of ethanol and 40mL of deionized water, and sonicate at 40kHz for 30min at room temperature to obtain a suspension. 2) Weigh 1.5 mL of silane coupling agent A-187, add 8 mL of ethanol and 2 mL of deionized water, adjust the pH to 4.7 with acetic acid, stir at room temperature for 5 min to obtain the hydrolysate; 3) At room temperature, the hydrolysate was added dropwise to the suspension while stirring at a rate of 4 drops / s. After the addition was complete, a reflux condenser was installed, and the suspension was transferred to an 80°C oil bath and stirred for 60 min. The suspension was then removed, centrifuged at 10,000 rpm for 10 min, the precipitate was collected, washed with ethanol, and dried at 60°C to constant weight.

[0023] Example 1 A waterproof coating for walls is prepared from the following components: 50 parts by weight of epoxy resin (Baling Petrochemical CYDW-100), 75 parts by weight of curing agent (Baling Petrochemical CYDHD-220), and 8.5 parts by weight of waterproof filler. The specific preparation method is as follows: at room temperature, the curing agent and waterproof filler are added to the epoxy resin, homogenized at 500 rpm for 2 minutes, and then degassed under vacuum (vacuum degree -0.09 MPa) for 5 minutes. After being applied to the wall, it is cured at room temperature for 7 days.

[0024] The waterproof filler is prepared by the following steps: Step (1): Add 0.5g of epoxidized nano silica (provided by Preparation Example 1), 2g of p-aminophenyl POSS and 0.4g of p-toluenesulfonic acid to 28g of dimethylformamide, stir at 72°C for 7h under nitrogen atmosphere, filter out the solid phase, wash with deionized water, and dry at 70°C to constant weight to obtain the first product; Step (2): Add 0.85g of the first product and 1.5g of N anhydride to 45g of dimethylformamide, stir at 62°C for 8h under nitrogen atmosphere, filter out the solid phase, wash with deionized water, and dry at 70°C to constant weight to obtain the second product; Step (3): Add 1.2g of the second product and 3g of ethyl isocyanate to 60g of toluene, stir at room temperature under nitrogen atmosphere for 6h, filter out the solid phase, wash with acetone, and dry at 95℃ to constant weight.

[0025] In step (2), the N-anhydride is prepared by the following steps: Step A: Mix 125g of 1,4-dioxane aqueous solution (40wt%), 16g of triethylamine and 3g of N-phenylglycine at room temperature for 5min to obtain the first solution; Step B: Mix 35g of 1,4-dioxane and 18g of di-tert-butyl dicarbonate at room temperature for 5 minutes to obtain the second solution; Step C: Under nitrogen atmosphere, at room temperature, 53g of second solution is added dropwise to 144g of first solution with stirring at a rate of 3 drops / s. After the addition is complete, the mixture is stirred at room temperature for 10 hours to obtain material A. After post-processing, an intermediate is obtained. Step D: Add 4g of intermediate and 5g of phosphorus trichloride to 130g of dichloromethane, stir at 0℃ under nitrogen atmosphere for 1.5h and then stir at room temperature for 20h to obtain material B, which is then processed.

[0026] In step C, the post-treatment refers to adding n-hexane at 15 wt% of material A, shaking for 5 min, letting stand for 5 min to separate the layers, retaining the lower layer, adjusting the pH to 2.8 with acetic acid aqueous solution (25 wt%), adding ethyl acetate at 25 wt%, shaking for 5 min, letting stand for 5 min to separate the layers, retaining the upper layer, adding saturated sodium chloride aqueous solution (25°C) at 25 wt%, shaking for 5 min, letting stand for 5 min to separate the layers, retaining the upper layer, adding deionized water at 20 wt%, shaking for 5 min, letting stand for 5 min to separate the layers, retaining the upper layer, and rotary evaporating in a 20 kPa water bath at 40°C until no ethyl acetate is detected.

[0027] In step D, the post-processing refers to adding n-hexane at 20 wt% of material B, filtering out the liquid phase, allowing it to evaporate naturally at room temperature to 25% of the initial volume, filtering out the solid phase, washing with n-hexane at 7°C, and drying at 40°C to constant weight.

[0028] Example 2 A waterproof coating for walls is prepared from the following components: 53 parts by weight of epoxy resin (Baling Petrochemical CYDW-100), 81 parts by weight of curing agent (Baling Petrochemical CYDHD-220), and 11.5 parts by weight of waterproof filler. The specific preparation method is as follows: at room temperature, the curing agent and waterproof filler are added to the epoxy resin, homogenized at 500 rpm for 2 minutes, and then degassed under vacuum (vacuum degree -0.09 MPa) for 5 minutes. After being applied to the wall, it is cured at room temperature for 7 days.

[0029] The waterproof filler is prepared by the following steps: Step (1): Add 0.75g of epoxidized nano silica (provided by Preparation Example 1), 5g of p-aminophenyl POSS and 0.45g of p-toluenesulfonic acid to 50g of dimethylformamide, stir at 86°C for 13h under nitrogen atmosphere, filter out the solid phase, wash with deionized water, and dry at 70°C to constant weight to obtain the first product; Step (2): Add 1.4g of the first product and 2g of N anhydride to 75g of dimethylformamide, stir at 67°C for 15h under nitrogen atmosphere, filter out the solid phase, wash with deionized water, and dry at 70°C to constant weight to obtain the second product. Step (3): Add 2.5g of the second product and 7g of ethyl isocyanate to 150g of toluene, stir at room temperature under nitrogen atmosphere for 7h, filter out the solid phase, wash with acetone, and dry at 95℃ to constant weight.

[0030] In step (2), the N-anhydride is prepared by the following steps: Step A: Mix 155g of 1,4-dioxane aqueous solution (46wt%), 18g of triethylamine and 7g of N-phenylglycine at room temperature for 10min to obtain the first solution; Step B: Mix 45g of 1,4-dioxane and 21g of di-tert-butyl dicarbonate at room temperature for 10 minutes to obtain the second solution; Step C: Under nitrogen atmosphere, at room temperature, 66g of second solution is added dropwise to 180g of first solution with stirring at a rate of 3 drops / s. After the addition is complete, the mixture is stirred at room temperature for 18 hours to obtain material A. After post-processing, an intermediate is obtained. Step D: Add 6.5g of intermediate and 6g of phosphorus trichloride to 150g of dichloromethane, stir at 5°C for 3h under nitrogen atmosphere, and then stir at room temperature for 25h to obtain material B, which is then processed.

[0031] In step C, the post-treatment refers to adding n-hexane at 20 wt% of material A, shaking for 10 min, letting stand for 10 min to separate the layers, retaining the lower layer, adjusting the pH to 3 with acetic acid aqueous solution (25 wt%), adding ethyl acetate at 30 wt%, shaking for 10 min, letting stand for 10 min to separate the layers, retaining the upper layer, adding saturated sodium chloride aqueous solution (25°C) at 30 wt%, shaking for 10 min, letting stand for 10 min to separate the layers, retaining the upper layer, adding deionized water at 25 wt%, shaking for 10 min, letting stand for 10 min to separate the layers, retaining the upper layer, and rotary evaporating in a 20 kPa water bath at 40°C until no ethyl acetate is detected.

[0032] In step D, the post-processing refers to adding n-hexane at 25 wt% of material B, filtering out the liquid phase, allowing it to evaporate naturally at room temperature to 30% of the initial volume, filtering out the solid phase, washing with n-hexane at 7°C, and drying at 40°C to constant weight.

[0033] Example 3 A waterproof coating for walls is prepared from the following components: 50 parts by weight of epoxy resin (Baling Petrochemical CYDW-100), 78 parts by weight of curing agent (Baling Petrochemical CYDHD-220), and 10 parts by weight of waterproof filler. The specific preparation method is as follows: at room temperature, the curing agent and waterproof filler are added to the epoxy resin, homogenized at 500 rpm for 2 minutes, and then degassed under vacuum (vacuum degree -0.09 MPa) for 5 minutes. After being applied to the wall, it is cured at room temperature for 7 days.

[0034] The waterproof filler is prepared by the following steps: Step (1): Add 0.5g of epoxidized nano silica (provided by Preparation Example 1), 2.5g of p-aminophenyl POSS and 0.4g of p-toluenesulfonic acid to 40g of dimethylformamide, stir at 75°C for 8h under nitrogen atmosphere, filter out the solid phase, wash with deionized water, and dry at 70°C to constant weight to obtain the first product; Step (2): Add 0.9g of the first product and 2g of N anhydride to 70g of dimethylformamide, stir at 65°C for 12h under nitrogen atmosphere, filter out the solid phase, wash with deionized water, and dry at 70°C to constant weight to obtain the second product; Step (3): Add 1.5g of the second product and 4.5g of ethyl isocyanate to 135g of toluene, stir at room temperature under nitrogen atmosphere for 6h, filter out the solid phase, wash with acetone, and dry at 95℃ to constant weight.

[0035] In step (2), the N-anhydride is prepared by the following steps: Step A: Mix 140g of 1,4-dioxane aqueous solution (42wt%), 16g of triethylamine and 5g of N-phenylglycine at room temperature for 10min to obtain the first solution; Step B: Mix 45g of 1,4-dioxane and 20g of di-tert-butyl dicarbonate at room temperature for 10 minutes to obtain the second solution; Step C: Under nitrogen atmosphere, at room temperature, 65g of second solution is added dropwise to 161g of first solution with stirring at a rate of 3 drops / s. After the addition is complete, the mixture is stirred at room temperature for 14 hours to obtain material A. After post-processing, an intermediate is obtained. Step D: Add 6g of intermediate and 5.5g of phosphorus trichloride to 140g of dichloromethane, stir at 2°C for 2h under nitrogen atmosphere, and then stir at room temperature for 22h to obtain material B, which is then processed.

[0036] In step C, the post-treatment refers to adding n-hexane at 20 wt% of material A, shaking for 10 min, letting stand for 5 min to separate the layers, retaining the lower layer, adjusting the pH to 2.9 with acetic acid aqueous solution (25 wt%), adding ethyl acetate at 30 wt%, shaking for 10 min, letting stand for 5 min to separate the layers, retaining the upper layer, adding saturated sodium chloride aqueous solution (25°C) at 25 wt%, shaking for 10 min, letting stand for 5 min to separate the layers, retaining the upper layer, adding deionized water at 25 wt%, shaking for 10 min, letting stand for 5 min to separate the layers, retaining the upper layer, and rotary evaporating in a 20 kPa water bath at 40°C until no ethyl acetate is detected.

[0037] In step D, the post-processing refers to adding n-hexane at 25 wt% of material B, filtering out the liquid phase, allowing it to evaporate naturally at room temperature to 30% of the initial volume, filtering out the solid phase, washing with n-hexane at 7°C, and drying at 40°C to constant weight.

[0038] Comparative Example 1 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the waterproof filler, that is, step (3) was not required in this comparative example. The rest was completely the same as in Example 3.

[0039] Comparative Example 2 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the waterproof filler, that is, in step (3) of this comparative example, 4.5g of ethyl isocyanate was replaced with 4.5g of propyl isocyanate. The rest was completely consistent with Example 3.

[0040] Comparative Example 3 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the waterproof filler, that is, in step (3) of this comparative example, 4.5g of ethyl isocyanate was replaced with 4.5g of butyl isocyanate. The rest was completely the same as in Example 3.

[0041] Comparative Example 4 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the waterproof filler, that is, steps (2) and (3) were not required in this comparative example. The rest was completely the same as in Example 3.

[0042] Comparative Example 5 The waterproof coating for walls was prepared in accordance with the method of Example 3, except for the waterproof filler. Specifically, 10 parts by weight of the waterproof filler in the waterproof coating for walls prepared in this comparative example were replaced with 10 parts by weight of epoxidized nano silica (provided by Preparation Example 1). The rest was completely consistent with Example 3.

[0043] Comparative Example 6 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the waterproof filler. That is, step (3) was not required in this comparative example. Step (2) was changed to add 1.5g of the first product and 4.5g of ethyl isocyanate to 135g of toluene, stir at room temperature under nitrogen atmosphere for 6h, filter out the solid phase, wash with acetone, and dry at 95°C to constant weight. The rest was completely consistent with Example 3.

[0044] Comparative Example 7 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the waterproof filler. In this comparative example, step (1) was not required. Step (2) was changed to add 0.9g of aminated nano silica (prepared by replacing 1.5mL of silane coupling agent A-187 in Preparation Example 1 with 1.5mL of silane coupling agent KH-540) and 2g of N anhydride to 70g of dimethylformamide. The mixture was stirred at 65°C for 12h under a nitrogen atmosphere, the solid phase was filtered out, washed with deionized water, and dried at 70°C to constant weight to obtain the second product. The rest was completely consistent with Example 3.

[0045] Comparative Example 8 The waterproof coating for walls was prepared in accordance with the method of Example 3. The difference was in the composition of the waterproof coating for walls. In this comparative example, there was no waterproof filler. Otherwise, it was completely the same as Example 3.

[0046] Test Example 1 The water absorption rate of the waterproof coatings for walls prepared in Examples 1-3 and Comparative Examples 1-8 was determined, with reference standard HG / T 3344-2012. The base plate was tinplate, the coating thickness was 150 micrometers (obtained by curing at room temperature for 7 days), the water temperature was set at (23±2)℃, and the curing time was 24h.

[0047] Table 1. Water absorption rate determination of Test Example 1 As can be seen from Table 1 above, the waterproof coatings for walls prepared in Examples 1-3 have a lower water absorption rate than those in Comparative Examples 1-8.

[0048] In summary, this invention uses epoxy resin as the film-forming substance and adds waterproof fillers to construct a waterproof system, thus preparing a waterproof coating suitable for application on walls. It can achieve a relatively ideal waterproof effect without the need for additives, effectively blocking the intrusion of water, and the coating has a low water absorption rate.

[0049] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention, and are not actually limited thereto. In short, if those skilled in the art are inspired by this description and design similar embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A waterproof coating for walls, characterized in that: It is prepared from the following components: 50-53 parts by weight of epoxy resin, 75-81 parts by weight of curing agent and 8.5-11.5 parts by weight of waterproof filler; The waterproof filler is prepared by the following steps: Step (1): Add 0.5-0.75 parts by weight of epoxidized nano silica, 2-5 parts by weight of p-aminophenyl POSS and 0.4-0.45 parts by weight of p-toluenesulfonic acid to 28-50 parts by weight of dimethylformamide, stir, filter out the solid phase, wash, dry and obtain the first product; Step (2): Add 0.85-1.4 parts by weight of the first product and 1.5-2 parts by weight of N anhydride to 45-75 parts by weight of dimethylformamide, stir, filter out the solid phase, wash, dry, and obtain the second product; Step (3): Add 1.2-2.5 parts by weight of the second product and 3-7 parts by weight of ethyl isocyanate to 60-150 parts by weight of toluene, stir, filter out the solid phase, wash, and dry; In step (2), the N-anhydride is prepared by the following steps: Step A: Mix 125-155 parts by weight of 1,4-dioxane aqueous solution, 16-18 parts by weight of triethylamine and 3-7 parts by weight of N-phenylglycine to obtain the first solution; Step B: Mix 35-45 parts by weight of 1,4-dioxane and 18-21 parts by weight of di-tert-butyl dicarbonate to obtain a second solution; Step C: Add 53-66 parts by weight of the second solution dropwise to 144-180 parts by weight of the first solution. After the addition is complete, stir at room temperature for 10-18 hours to obtain material A. After post-processing, obtain the intermediate. Step D: Add 4-6.5 parts by weight of intermediate and 5-6 parts by weight of phosphorus trichloride to 130-150 parts by weight of dichloromethane, stir, and obtain material B, which will then undergo post-processing.

2. The waterproof coating for walls according to claim 1, characterized in that: In step (1), the epoxidized nano silica is prepared by surface modification of nano silica with an epoxy silane coupling agent.

3. The waterproof coating for walls according to claim 1, characterized in that: In step (1), the stirring refers to stirring at 72-86℃ for 7-13 hours under a nitrogen atmosphere.

4. A waterproof coating for walls according to claim 1, characterized in that: In step A, the concentration of the 1,4-dioxane aqueous solution is 40-46 wt%.

5. A waterproof coating for walls according to claim 1, characterized in that: In step C, the post-treatment refers to adding n-hexane at 15-20 wt% of material A, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the lower layer, adjusting the pH of the acetic acid solution to 2.8-3, adding ethyl acetate at 25-30 wt%, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the upper layer, adding saturated sodium chloride aqueous solution at 25-30 wt%, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the upper layer, adding deionized water at 20-25 wt%, shaking for 5-10 min, letting it stand for 5-10 min to separate the layers, retaining the upper layer, and then rotary evaporating.

6. A waterproof coating for walls according to claim 1, characterized in that: In step D, the post-processing refers to adding n-hexane at 20-25 wt% of material B, filtering out the liquid phase, allowing it to evaporate naturally at room temperature to 25-30% of the initial volume, filtering out the solid phase, washing, and drying.

7. A waterproof coating for walls according to claim 1, characterized in that: In step (2), the stirring refers to stirring at 62-67℃ for 8-15 hours under a nitrogen atmosphere.

8. A waterproof coating for walls according to claim 1, characterized in that: In step (3), the stirring refers to stirring at room temperature under a nitrogen atmosphere for 6-7 hours.

9. A method for preparing a waterproof coating for walls according to any one of claims 1-8, characterized in that: Includes the following steps: Add curing agent and waterproof filler to epoxy resin, homogenize, and then degas under vacuum.

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