Method for repairing cracks of cultural relics, repairing coating and method

Abstract

The invention discloses a method for repairing cracks of cultural relics, a repairing coating and a method, and relates to the technical field of cultural relic repairing. The preparation method of the repair coating comprises the following steps: step 1, mixing isocyanate and a hydroxyl compound in an inert gas atmosphere, and reacting the isocyanate and the hydroxyl compound under a first reaction condition to generate a first intermediate product; step 2, adding a sulfhydryl compound into the first intermediate product to obtain a mixture, dropwise adding an oxidizing agent into the mixture under a second reaction condition, and reacting the mixture in the dropwise adding process to generate a second intermediate product; and 3, carrying out emulsification treatment and pH value adjustment on the second intermediate product to obtain a waterborne polyurethane dispersion liquid, and sequentially carrying out filtration and solid content adjustment on the waterborne polyurethane dispersion liquid to obtain the repair coating. The repairing coating disclosed by the invention has efficient self-repairing capability, and the repairing coating contains disulfide bonds, so that the repairing coating realizes fracture and recombination under mild conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of cultural relic restoration, and in particular to a method for repairing cracks in cultural relics, a repair coating and a method thereof. Background Art

[0002] Ceramic cultural relics are an important heritage of ancient civilizations. Repaired or undamaged ceramic cultural relics often develop microcracks due to changes in temperature and humidity, material differences or long-term stress accumulation. Ceramic microcracks are usually micron-sized (5 to 100 μm). These tiny cracks will gradually weaken the ceramic structure and eventually cause ceramic damage. In the prior art, people have proposed a variety of methods to repair microcracks to prolong and protect ceramics. For example, through image monitoring and the use of repair agents for re-sticking repair, but it requires professional equipment and a lot of manpower. Or use inorganic columnar fibers and sol impregnation for infiltration repair, and then complete the repair through drying and high-temperature sintering. Although this method has a good repair effect, it requires high-temperature sintering, which will destroy the historical information of the cultural relics. Therefore, it is not suitable for cultural relic restoration.

[0003] Chinese invention patent application CN117757030A discloses a method for preparing a dynamic disulfide bond waterborne polyurethane thermally conductive self-healing material. The dynamic disulfide bond polyurethane thermally conductive self-healing material obtained by this preparation method has a tensile repair rate of 86% before and after healing at 40°C for 2 hours.

[0004] The above-mentioned polyurethane material has its own self-healing ability, which allows it to be used in other fields such as construction, automotive industry, etc., but it cannot be used to repair cracks in cultural relics; this is because cultural relic restoration requires special consideration of factors such as material compatibility, authenticity, and the impact of the restoration process on the historical value of the cultural relics. Therefore, cultural relic restoration needs to be carried out at room temperature. However, the above-mentioned polyurethane material cannot achieve self-repair healing at room temperature. Summary of the Invention

[0005] In order to solve at least one of the problems mentioned in the above background technology, the present invention provides a method for repairing cracks in cultural relics, a repair coating and a method, by reacting an isocyanate and a hydroxyl compound to generate a first intermediate product, and then using the first intermediate product and a thiol compound under the condition of adding an oxidant to generate a second intermediate product, and the second intermediate product is subjected to a series of treatments to obtain a repair coating; the repair coating has a high-efficiency self-repairing ability, and the repair coating contains disulfide bonds, so that the repair coating can achieve breakage and recombination under mild conditions (such as room temperature).

[0006] The specific technical solutions provided by the embodiments of the present invention are as follows:

[0007] In a first aspect, a method for preparing a repair coating is provided, comprising the following steps:

[0008] Step 1: mixing an isocyanate and a hydroxyl compound under an inert gas atmosphere, and reacting the isocyanate and the hydroxyl compound under a first reaction condition to generate a first intermediate product;

[0009] Step 2: adding a thiol compound to the first intermediate product to obtain a mixture, and dropwise adding an oxidant to the mixture under second reaction conditions, wherein the mixture reacts during the dropwise addition to generate a second intermediate product;

[0010] Step 3: emulsify the second intermediate product and adjust the pH to obtain an aqueous polyurethane dispersion, and filter and adjust the solid content of the aqueous polyurethane dispersion in sequence to obtain a repair coating.

[0011] In a specific embodiment, the isocyanate is toluene diisocyanate and / or hexamethylene diisocyanate, and the hydroxyl compound is polyether diol and / or polyester diol;

[0012] The molar ratio of the isocyanate group in the isocyanate to the hydroxyl group in the hydroxy compound is (1.5-5):1.

[0013] In a specific embodiment, the thiol compound is one or more of dimercaptopropionic acid, mercaptoethanol, or ammonium tetrathiomolybdate, and the oxidant is hydrogen peroxide;

[0014] The molar ratio of the mercapto group in the mercapto compound to the isocyanate group in the isocyanate is (0.2-2):1;

[0015] The molar ratio of the hydrogen peroxide to the thiol group in the thiol compound is (0.5-1):1.

[0016] In a specific embodiment, the emulsification and pH adjustment of the second intermediate product in step three comprises the following steps:

[0017] adding deionized water dropwise to the second intermediate product under shear conditions to emulsify it and adding a neutralizing agent, triethylamine dropwise, to adjust the pH;

[0018] The shearing condition is set at a rotation speed of 3000-4000 rpm, and the temperature during the emulsification process does not exceed X, where X is set at 35-40°C.

[0019] In a specific embodiment, the step 3 of filtering the aqueous polyurethane dispersion and adjusting the solid content in sequence comprises the following steps:

[0020] Filtering the aqueous polyurethane dispersion to remove particles larger than Y to obtain a filtered aqueous polyurethane dispersion; wherein Y is 0.8 to 1 μm;

[0021] The solid content of the filtered aqueous polyurethane dispersion is adjusted to within a range of 30-35%, and then a defoamer and a leveling agent are added to the filtered aqueous polyurethane dispersion to obtain the repair coating.

[0022] In a specific embodiment, the first reaction condition is a heating temperature of 70 to 80° C. and a stirring time of 4 to 6 hours.

[0023] In a specific embodiment, the second reaction condition is a heating temperature of 55 to 60° C. and a stirring time of 1.5 to 2 h.

[0024] In a second aspect, a repair coating is provided, which is prepared by the above-mentioned preparation method of a repair coating.

[0025] In a third aspect, a method for applying a repair coating as described above in the field of repairing cracks in cultural relics is provided.

[0026] In a fourth aspect, a method for repairing cracks in cultural relics is provided, wherein the cultural relics are repaired using a repair coating according to claim 8, wherein the method comprises the following steps:

[0027] Applying the repair coating to cracks in the cultural relic to be repaired to form a self-repairing coating;

[0028] After the self-repairing coating is dried at room temperature, a protective coating is coated on the self-repairing coating.

[0029] Beneficial effects:

[0030] (1) The present application utilizes an isocyanate and a hydroxyl compound to react to generate a first intermediate product, and then utilizes the first intermediate product and a thiol compound to generate a second intermediate product under the condition of adding an oxidant, and the second intermediate product is subjected to a series of treatments to obtain a repair coating; the repair coating has a highly efficient self-repairing ability, and the repair coating contains a disulfide bond, so that the repair coating can achieve breakage-recombination under mild conditions (such as room temperature).

[0031] (2) When the repair coating is applied to repair microcracks on the surface of ceramic cultural relics, the healing efficiency of the microcracks on the surface of ceramic cultural relics is as high as 84%, and after experiencing high temperature and high humidity conditions, it still maintains a high repair healing efficiency.

[0032] (3) The restoration coating prepared in this application uses water as the dispersion medium and has a low content of organic pollutants, thereby avoiding the erosion of the cultural relic material by organic solvents (such as the risk of dissolution of ceramic glaze); disulfide bonds are generated by chain extension of thiol-containing small molecules, the synthesis process is simple, and the compatibility with polyether / polyester diols is good, thereby avoiding the interference of water-based modification with the self-repair mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 It is a flow chart of the preparation method of the present invention;

[0035] Figure 2 is a comparison chart of the healing efficiencies of Examples 1 to 3 and Comparative Examples 1 to 2 under standard conditions;

[0036] Figure 3 is a comparison chart of the refractive indices of Examples 1 to 3 and Comparative Examples 1 to 2 under standard conditions;

[0037] Figure 4 is a comparison chart of light transmittance of Examples 1 to 3 and Comparative Examples 1 to 2 under standard conditions;

[0038] Figure 5 is a comparison chart of the healing efficiency of Examples 1 to 3 and Comparative Examples 1 to 2 under high temperature and high humidity conditions;

[0039] Figure 6 is a comparison chart of the refractive indices of Examples 1 to 3 and Comparative Examples 1 to 2 under high temperature and high humidity conditions;

[0040] Figure 7 It is a comparison chart of the light transmittance of Examples 1 to 3 and Comparative Examples 1 to 2 under high temperature and high humidity conditions. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] In one embodiment, a method for preparing a repair coating is provided, comprising the following steps:

[0044] Step 1: mixing an isocyanate and a hydroxyl compound under an inert gas atmosphere, and reacting the isocyanate and the hydroxyl compound under a first reaction condition to generate a first intermediate product;

[0045] Step 2: adding a thiol compound to the first intermediate product to obtain a mixture, and dropwise adding an oxidant to the mixture under second reaction conditions, wherein the mixture reacts during the dropwise addition to generate a second intermediate product;

[0046] Step 3: emulsify the second intermediate product and adjust the pH to obtain an aqueous polyurethane dispersion, and filter and adjust the solid content of the aqueous polyurethane dispersion in sequence to obtain a repair coating.

[0047] In step 1, the isocyanate and the hydroxyl compound react to form a prepolymer (i.e., a first intermediate product), and in step 2, the thiol compound reacts with the prepolymer to form a second intermediate product having a disulfide bond. The disulfide bond is formed by oxidation of the thiol group under the promotion of an oxidant.

[0048] In a specific embodiment, the isocyanate is toluene diisocyanate and / or hexamethylene diisocyanate, and the hydroxyl compound is polyether diol and / or polyester diol;

[0049] The molar ratio of the isocyanate group in the isocyanate to the hydroxyl group in the hydroxyl compound is (1.5-5): 1. Specifically, the molar ratio of the isocyanate group in the isocyanate to the hydroxyl group in the hydroxyl compound is 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1.

[0050] An excess of isocyanate (–NCO) groups is required to ensure complete reaction of all hydroxyl (–OH) groups and sufficient prepolymer formation. Excess –NCO groups also provide reactive sites for subsequent reactions with thiol-containing small molecules, such as dimercaptopropionic acid. If the –NCO:–OH ratio is too low (less than 1.5:1), the prepolymer will not be sufficiently cross-linked, affecting the mechanical properties of the final material. If the –NCO:–OH ratio is too high (greater than 5:1), excessive isocyanate is introduced, making the material brittle and reducing its flexibility and self-healing ability.

[0051] In a specific embodiment, the thiol compound is one or more of dimercaptopropionic acid, mercaptoethanol, or ammonium tetrathiomolybdate, and the oxidant is hydrogen peroxide;

[0052] The molar ratio of the mercapto group in the mercapto compound to the isocyanate group in the isocyanate is (0.2-2):1;

[0053] The molar ratio of the hydrogen peroxide to the thiol group in the thiol compound is (0.5-1):1.

[0054] Specifically, the molar ratio of the thiol group in the thiol compound to the isocyanate group in the isocyanate is 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, or 2:1. If the ratio between the thiol group and the isocyanate group is too low (less than 0.2:1), the density of the generated disulfide bonds is insufficient, which will affect the self-healing ability. If the ratio between the thiol group and the isocyanate group is too high (greater than 2:1), it will lead to excessive cross-linking and reduce the flexibility of the material.

[0055] The molar ratio of the hydrogen peroxide to the thiol group in the thiol compound is 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1.

[0056] Hydrogen peroxide is used as an oxidant to oxidize sulfhydryl groups (–SH) to disulfide bonds (–S–S–). The amount of hydrogen peroxide added needs to be optimized based on the amount of sulfhydryl-containing compounds and the target disulfide bond density. The reaction is as follows: 2R–SH + H2O2 → R–S–S–R + 2H2O. The amount of hydrogen peroxide used in the oxidation process needs to be controlled to avoid overoxidation or side reactions. Therefore, the molar ratio of hydrogen peroxide to sulfhydryl groups (–SH) is preferably 0.5:1. To ensure complete oxidation, the amount of hydrogen peroxide used may be slightly excessive, with the molar ratio range being set to 0.6:1 to 1:1, preferably 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1. Excessive hydrogen peroxide addition can lead to side reactions (such as overoxidation) and affect material properties.

[0057] In a specific embodiment, the emulsification and pH adjustment of the second intermediate product in step three comprises the following steps:

[0058] adding deionized water dropwise to the second intermediate product under shear conditions to emulsify it and adding a neutralizing agent, triethylamine dropwise, to adjust the pH;

[0059] The shearing condition is set at a rotation speed of 3000-4000 rpm, and the temperature during the emulsification process does not exceed X, where X is set at 35-40°C.

[0060] Specifically, the shearing conditions are set at a rotation speed of 3000 rpm, 3300 rpm, 3500 rpm, 3700 rpm, or 4000 rpm. The value of x is 35°C, 36°C, 37°C, 38°C, 39°C, or 40°C. During the emulsification process, the temperature is controlled to not exceed 40°C to prevent excessive evaporation of water. The shear force and temperature are controlled during the emulsification process to obtain an aqueous polyurethane dispersion with uniform particle size.

[0061] In a specific embodiment, the step 3 of filtering the aqueous polyurethane dispersion and adjusting the solid content in sequence comprises the following steps:

[0062] Filtering the aqueous polyurethane dispersion to remove particles larger than Y to obtain a filtered aqueous polyurethane dispersion; wherein Y is 0.8 to 1 μm;

[0063] The solid content of the filtered aqueous polyurethane dispersion is adjusted to within a range of 30-35%, and then a defoamer and a leveling agent are added to the filtered aqueous polyurethane dispersion to obtain the repair coating.

[0064] Specifically, the value of Y is 0.8 μm, 0.9 μm, or 1 μm. The solid content of the filtered aqueous polyurethane dispersion is adjusted to 30%, 31%, 32%, 33%, 34%, or 35%.

[0065] In a specific embodiment, the first reaction condition is a heating temperature of 70 to 80° C. and a stirring time of 4 to 6 hours.

[0066] Specifically, the heating temperature of the first reaction condition is set to 70°C, 72°C, 74°C, 76°C, 78°C, or 80°C; the stirring time of the first reaction condition is set to 4h, 5h or 6h.

[0067] In a specific embodiment, the second reaction condition is a heating temperature of 55 to 60° C. and a stirring time of 1.5 to 2 h.

[0068] Specifically, the heating temperature of the second reaction condition is set to 55°C, 56°C, 57°C, 58°C, 59°C, or 60°C; the stirring time of the second reaction condition is 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, or 2h.

[0069] In another embodiment, a repair coating is provided, which is prepared by the above-mentioned method for preparing a repair coating.

[0070] In another embodiment, a use of the above-mentioned repair coating in the field of repairing cracks in cultural relics is provided.

[0071] In another embodiment, a method for repairing cracks in cultural relics is provided, wherein the cultural relics are repaired using a repair coating as described above, and the method comprises the following steps:

[0072] Applying the repair coating to cracks in the cultural relic to be repaired to form a self-repairing coating;

[0073] After the self-repairing coating is dried at room temperature, a protective coating is coated on the self-repairing coating.

[0074] After applying the repair paint, wait for the repair paint to dry and then apply a protective coating. Common protective coatings on the market can be used, preferably polysiloxane. The protective coating has excellent insulation, moisture resistance and chemical resistance, is transparent, has good wettability and self-leveling properties, and can quickly and comprehensively cover the surface of the cultural relics.

[0075] In this method for repairing cracks in cultural relics, a repair coating is used as the base layer to repair microcracks and enhance adhesion, preventing crack expansion. A polysiloxane surface layer, with excellent weather resistance, enhances UV resistance and high and low temperature resistance, and slows yellowing of the coating. It also provides hydrophobic protection, forming a dense, hydrophobic layer that blocks the penetration of moisture and pollutants, extending the life of the self-repairing layer. By combining the repair coating with the protective coating, this method extends the maintenance cycle of ceramic cultural relics and reduces the cost of preserving them.

[0076] Example 1

[0077] (1) Preparation of repair coating

[0078] Step 1: Under nitrogen atmosphere, toluene diisocyanate and polyether diol are mixed, wherein the molar ratio of the isocyanate group in the toluene diisocyanate to the hydroxyl group in the polyether diol is 1.5:1; the temperature is raised to 75° C. and stirred for 5 hours to react the toluene diisocyanate and the polyether diol to form a first intermediate product;

[0079] Step 2: adding dimercaptopropionic acid to the first intermediate product to obtain a mixture, wherein the molar ratio of the thiol group in the dimercaptopropionic acid to the isocyanate group in toluene diisocyanate is 0.2:1; heating the mixture and stirring the reaction for 2 hours, controlling the heating temperature to 60° C., and simultaneously adding an oxidizing agent, an aqueous hydrogen peroxide solution (30% by mass of hydrogen peroxide), to the mixture dropwise, wherein the molar ratio of the thiol group in the dimercaptopropionic acid to the hydrogen peroxide is 1:0.5, and the mixture reacts during the addition to generate a second intermediate product;

[0080] Step 3: Under the shear condition set to a speed of 3000 rpm, deionized water is added dropwise to the second intermediate product for emulsification, the temperature of the emulsification process does not exceed 40°C, and at the same time, a neutralizing agent triethylamine is added dropwise to adjust the pH value to neutral (pH≈7) to obtain an aqueous polyurethane dispersion; the aqueous polyurethane dispersion is filtered to remove substances with a particle size greater than 1 μm in the aqueous polyurethane dispersion, and the solid content of the filtered aqueous polyurethane is adjusted to 30%, and then a defoaming agent and a leveling agent are added to the filtered aqueous polyurethane dispersion to obtain a repair coating.

[0081] (2) Repair ceramic cracks

[0082] applying a repair coating to cracks in the ceramic to be repaired to form a self-repairing coating;

[0083] After the self-repairing coating is dried at room temperature, a protective coating (polysiloxane) is coated on the self-repairing coating.

[0084] Example 2

[0085] This embodiment provides a method for preparing a repair coating, comprising the following steps:

[0086] Step 1: Under nitrogen atmosphere, hexamethylene diisocyanate and polyester diol are mixed, wherein the molar ratio of the isocyanate group in the hexamethylene diisocyanate to the hydroxyl group in the polyester diol is 3:1; the temperature is raised to 70° C. and stirred for 4 hours to react the hexamethylene diisocyanate and polyester diol to form a first intermediate product;

[0087] Step 2: adding mercaptoethanol and ammonium tetrathiomolybdate to the first intermediate product to obtain a mixture, wherein the molar ratio of the mercapto groups in the mercaptoethanol and ammonium tetrathiomolybdate to the isocyanate groups in the hexamethylene diisocyanate is 1:1; heating the mixture and stirring the reaction for 1.5 hours, controlling the heating temperature to 55° C., and simultaneously adding an oxidizing agent, an aqueous hydrogen peroxide solution (30% by mass of hydrogen peroxide), to the mixture dropwise, wherein the molar ratio of the mercapto groups in the mercaptoethanol and ammonium tetrathiomolybdate to the hydrogen peroxide is 1:1, and the mixture reacts during the addition to generate a second intermediate product;

[0088] Step 3: Under the shear condition set to a speed of 4000 rpm, deionized water is added dropwise to the second intermediate product for emulsification, the temperature of the emulsification process does not exceed 35°C, and at the same time, a neutralizing agent triethylamine is added dropwise to adjust the pH value to neutral (pH≈7) to obtain an aqueous polyurethane dispersion; the aqueous polyurethane dispersion is filtered to remove substances with a particle size greater than 0.8 μm in the aqueous polyurethane dispersion, and the solid content of the filtered aqueous polyurethane is adjusted to 35%, and then a defoaming agent and a leveling agent are added to the filtered aqueous polyurethane dispersion to obtain a repair coating.

[0089] (2) Repair ceramic cracks

[0090] applying a repair coating to cracks in the ceramic to be repaired to form a self-repairing coating;

[0091] After the self-repairing coating is dried at room temperature, a protective coating (polysiloxane) is coated on the self-repairing coating.

[0092] Example 3

[0093] This embodiment provides a method for preparing a repair coating, comprising the following steps:

[0094] Step 1: Under nitrogen atmosphere, toluene diisocyanate, hexamethylene diisocyanate, polyether diol, and polyester diol are mixed, wherein the molar ratio of the isocyanate groups in toluene diisocyanate and hexamethylene diisocyanate to the hydroxyl groups in polyether diol and polyester diol is 5:1; the temperature is raised to 80° C. and stirred for 6 hours to react the toluene diisocyanate, hexamethylene diisocyanate, polyether diol, and polyester diol to generate a first intermediate product;

[0095] Step 2: adding ammonium tetrathiomolybdate to the first intermediate product to obtain a mixture, wherein the molar ratio of the thiol group in the ammonium tetrathiomolybdate to the isocyanate group in toluene diisocyanate and hexamethylene diisocyanate is 2:1; heating the mixture and stirring the reaction for 1.8 hours, controlling the heating temperature to 60° C., and simultaneously adding an oxidizing agent, an aqueous hydrogen peroxide solution (the mass percentage of hydrogen peroxide is 30%), to the mixture, wherein the molar ratio of the thiol group in the ammonium tetrathiomolybdate to the hydrogen peroxide is 1:0.8, and the mixture reacts during the addition to generate a second intermediate product;

[0096] Step 3. Under the shear condition set to a speed of 3500 rpm, deionized water is added dropwise to the second intermediate product for emulsification, the temperature of the emulsification process does not exceed 38°C, and at the same time, a neutralizing agent triethylamine is added dropwise to adjust the pH value to neutral (pH≈7) to obtain an aqueous polyurethane dispersion; the aqueous polyurethane dispersion is filtered to remove substances with a particle size greater than 0.9 μm in the aqueous polyurethane dispersion, and the solid content of the filtered aqueous polyurethane is adjusted to 32%, and then a defoaming agent and a leveling agent are added to the filtered aqueous polyurethane dispersion to obtain a repair coating.

[0097] (2) Repair ceramic cracks

[0098] applying a repair coating to cracks in the ceramic to be repaired to form a self-repairing coating;

[0099] After the self-repairing coating is dried at room temperature, a protective coating (polysiloxane) is coated on the self-repairing coating.

[0100] Comparative Example 1

[0101] Applying a commercially available water-based polyurethane material (purchased from Lanmeng Company) to the cracks in the ceramic to be repaired to form a polyurethane coating;

[0102] After the self-repairing coating is dried at room temperature, a protective coating (polysiloxane) is coated on the self-repairing coating.

[0103] Comparative Example 2

[0104] Applying a commercially available water-based polyurethane material (purchased from Xiangsheng Waterproofing Company) to the cracks in the ceramic to be repaired to form a polyurethane coating;

[0105] After the self-repairing coating is dried at room temperature, a protective coating (polysiloxane) is coated on the self-repairing coating.

[0106] In the five groups of ceramic crack repair tests in Examples 1 to 3 and Comparative Examples 1 to 2, in order to ensure the scientificity and reliability of the test results, two batches of ceramic samples were used for each test, one of which was tested under standard conditions and the other under high temperature and high humidity conditions; wherein, each batch included 5 identical ceramic samples, and the ceramic samples were numbered consecutively (such as 1, 2, 3, 4, 5). The ceramic samples used in Examples 1 to 3 and Comparative Examples 1 to 2 were the same, and the initial crack width of the ceramic samples was 50 μm (the initial cracks were artificially created by microcracks). The ceramic samples selected were smooth and homogeneous ceramic sheets with a size of 20 mm × 20 mm × 2 mm strips.

[0107] The test method is as follows:

[0108] Five ceramic samples from one batch prepared in Example 1, coated with the repair coating and protective coating, were placed under standard conditions for 24 hours. The width of the healed cracks was measured, and the healing efficiency was calculated. The refractive index and light transmittance after healing were also measured. Standard conditions refer to room temperature (25°C) and 50% relative humidity. Healing efficiency = (initial crack width - healed crack width) / initial crack width × 100%.

[0109] Another batch of five ceramic samples coated with the repair coating and protective coating prepared in Example 1 were placed under high temperature and high humidity conditions for 24 hours. The width of the healed cracks was measured, the healing efficiency was calculated, and the refractive index and light transmittance were measured after healing. The high temperature and high humidity conditions refer to a temperature of 45°C and a relative humidity of 75%.

[0110] In this embodiment, the crack width, refractive index, and light transmittance of the healed ceramic sample were measured using an optical microscope, an Abbe refractometer, and a spectrophotometer, respectively. The testing methods for Examples 2 to 3 and Comparative Examples 1 to 2 were the same as those for Example 1.

[0111] The test results are shown in Table 1:

[0112] Table 1

[0113]

[0114]

[0115] As can be seen from Table 1, the repair coatings used in Examples 1 to 3 exhibit excellent refractive index and transmittance performance. The refractive index of all example samples is stable between 1.51 and 1.53, with an average value of 1.52. This value is very close to the refractive index of glass (about 1.50 to 1.52), so it will hardly cause visual interference in actual display, and can achieve the effects of "traceless repair" and "transparent display". In contrast, the refractive index of Comparative Example 1 is relatively high, reaching 1.61 to 1.63, which is significantly higher than that of glass, and is prone to reflection or color difference; and although the refractive index of Comparative Example 2 is reduced, it is still maintained between 1.57 and 1.58, slightly higher than the examples, indicating that its material matching is still insufficient.

[0116] In terms of light transmittance, the samples in the examples measured under standard conditions ranged from 91% to 93%, with an average of 92%. This indicates that the restoration coatings in the examples barely absorb or scatter light, preserving the original clarity and color fidelity of the artifacts. Comparative Example 1, on the other hand, had a transmittance of only 82% to 86%, exhibiting significant light absorption or atomization, resulting in a dark or blurred display of the artifacts. Comparative Example 2 had a slightly better transmittance of 85% to 89%, but still lower than the examples, indicating that its optical performance still needs improvement.

[0117] In terms of weather resistance, the examples demonstrated significantly better environmental adaptability than the control examples. After exposure to high temperature and high humidity, the healing efficiency of the examples showed only a slight decrease, for example, from an average of 78% under standard conditions to 75% under high temperature and high humidity conditions, an overall decrease of approximately 3 percentage points. Furthermore, its refractive index remained unchanged under high temperature and high humidity conditions, remaining around 1.52, and its light transmittance also decreased only slightly, averaging 91%, demonstrating the material's excellent aging and moisture resistance.

[0118] Comparative Example 1 exhibited significant performance degradation in high-temperature and high-humidity environments. Healing efficiency dropped by an average of over 11 percentage points, and transmittance decreased by 3 to 4 percentage points, indicating that its material structure is susceptible to degradation or fogging in humid environments. While the refractive index of Comparative Example 2 remained stable, its healing efficiency and transmittance also decreased to varying degrees, indicating that its weather resistance still cannot meet the requirements of long-term storage and display.

[0119] The above data show that the repair coating used in the embodiment not only has excellent optical properties under standard conditions, but also maintains stable physical and chemical properties under harsh environmental conditions. This excellent weather resistance means that cultural relics no longer rely on strict temperature and humidity control environment during the preservation process. The museum can remove the constant temperature and humidity equipment accordingly, thereby significantly reducing operating costs, reducing energy consumption and equipment maintenance expenses, while improving the utilization rate of the exhibition space and enhancing the sustainability of cultural relic protection and display. The repair coating in the embodiment is superior to traditional materials in terms of optical properties and environmental adaptability. It not only meets the museum's high standards for the quality of cultural relic display, but also provides a more economical and efficient solution for the long-term protection of cultural relics, and has good application prospects and promotion value.

[0120] Although the preferred embodiment of the present invention has been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0121] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a repair coating, characterized in that: The following steps are involved: Step 1: mixing an isocyanate and a hydroxyl compound under an inert gas atmosphere, and reacting the isocyanate and the hydroxyl compound under a first reaction condition to generate a first intermediate product; Step 2: adding a thiol compound to the first intermediate product to obtain a mixture, and dropwise adding an oxidant to the mixture under second reaction conditions, wherein the mixture reacts during the dropwise addition to generate a second intermediate product; Step 3: emulsify the second intermediate product and adjust the pH to obtain an aqueous polyurethane dispersion, and filter and adjust the solid content of the aqueous polyurethane dispersion in sequence to obtain a repair coating.

2. The method for preparing a repair coating according to claim 1, wherein: The isocyanate is toluene diisocyanate and / or hexamethylene diisocyanate, and the hydroxyl compound is polyether diol and / or polyester diol; The molar ratio of the isocyanate group in the isocyanate to the hydroxyl group in the hydroxy compound is (1.5-5):

1.

3. The method for preparing a repair coating according to claim 2, wherein: The thiol compound is one or more of dimercaptopropionic acid, mercaptoethanol, or ammonium tetrathiomolybdate, and the oxidant is hydrogen peroxide; The molar ratio of the mercapto group in the mercapto compound to the isocyanate group in the isocyanate is (0.2-2):1; The molar ratio of the hydrogen peroxide to the thiol group in the thiol compound is (0.5-1):

1.

4. The method for preparing a repair coating according to any one of claims 1 to 3, characterized in that: The step 3 of emulsifying and adjusting the pH of the second intermediate product comprises the following steps: adding deionized water dropwise to the second intermediate product under shear conditions to emulsify it and adding a neutralizing agent, triethylamine dropwise, to adjust the pH; The shearing condition is set at a rotation speed of 3000-4000 rpm, and the temperature during the emulsification process does not exceed X, where X is set at 35-40°C.

5. The method for preparing a repair coating according to any one of claims 1 to 3, characterized in that: The step 3 of filtering the aqueous polyurethane dispersion and adjusting the solid content in sequence comprises the following steps: Filtering the aqueous polyurethane dispersion to remove particles larger than Y to obtain a filtered aqueous polyurethane dispersion; wherein Y is 0.8 to 1 μm; The solid content of the filtered aqueous polyurethane dispersion is adjusted to within a range of 30-35%, and then a defoamer and a leveling agent are added to the filtered aqueous polyurethane dispersion to obtain the repair coating.

6. The method for preparing a repair coating according to any one of claims 1 to 3, characterized in that: The first reaction conditions are a heating temperature of 70 to 80° C. and a stirring time of 4 to 6 hours.

7. The method for preparing a repair coating according to any one of claims 1 to 3, characterized in that: The second reaction conditions are heating temperature of 55-60° C. and stirring time of 1.5-2 h.

8. A repair coating prepared by the method for preparing a repair coating according to any one of claims 1 to 7.

9. Use of the repair coating according to claim 8 in the field of repairing cracks in cultural relics.

10. A method for repairing cracks in cultural relics, using the repair coating according to claim 8 to repair the cultural relics, characterized in that: The method comprises the following steps: Applying the repair coating to cracks in the cultural relic to be repaired to form a self-repairing coating; After the self-repairing coating is dried at room temperature, a protective coating is coated on the self-repairing coating.

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