High-filling super-curing floating coating in field of rail transit

Abstract

The invention relates to the technical field of coatings, and discloses a high-filling super-curing floating coating in the field of rail transit, and the floating coating comprises nano titanium dioxide-based hydroxyl-terminated hyperbranched polyester, medium molecular weight acrylic resin, a blocked high-functionality polyisocyanate cross-linking agent, a dispersing agent and the like. A coating obtained by adopting a super-curing system of nano titanium dioxide-based hydroxyl-terminated hyperbranched polyester and an isocyanate crosslinking agent is high in crosslinking density and good in toughness, coating resistance such as water resistance and moisture resistance is remarkably improved, a higher-level protection effect on putty is achieved, particularly, the water resistance can reach 48 h, and the water resistance can reach 48 h. Meanwhile, the floating coating is quick to dry and easy to construct, has high gloss, fullness and leveling property, can be widely applied to the field of rail transit by matching with high-performance putty and finish paint, and realizes periodic performance guarantee of the whole life.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to a highly filled super-cured mid-coat in the field of rail transportation. Background Art

[0002] In the rail transit sector, midcoat coatings are a key step in construction. Midcoat is a coating between primer / putty and topcoat. Its primary function is to fill minor surface defects in the primer / putty, increase coating thickness to enhance overall protective and decorative properties, strengthen adhesion between the primer / putty and the topcoat, make the topcoat smoother, and improve the coating's wear, corrosion, and weather resistance, thereby extending the service life of rail transit equipment. Based on the development needs of the rail transit industry, the performance requirements for midcoat coatings have also increased. The super-cured midcoat coating of this patented invention has made a significant contribution to the concept of full life cycle protection in the rail transit industry. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In response to the shortcomings of the existing technology, the present invention provides a highly filled super-cured mid-coat for the rail transit field, which is matched with putty and topcoat and is applied to the rail transit industry. It has a highly filling effect on the putty surface, enhances the adhesion of the coating, and improves the durability of the coating.

[0005] (2) Technical solution

[0006] A highly filled super-cured mid-coat for the rail transit field, wherein the highly filled super-cured mid-coat is prepared by mixing a main agent and a curing agent in a mass ratio of 90.8-93:7-9.2;

[0007] The mid-coat is a two-component coating;

[0008] The main agent includes polymer resin, additives, fillers and cosolvents;

[0009] Preferably, the polymer resin comprises a medium molecular weight acrylic resin polymer, the amount of which is 14.5-18.2% of the total mass of the coating, and the monomer composition of the medium molecular weight acrylic resin polymer is any of styrene, acrylic acid, methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, isobornyl methacrylate, versatate glycidyl ester, glycidyl methacrylate, and glycidyl acrylate.

[0010] Preferably, the polymer resin comprises nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester, the amount of which is 9.2-12.1% of the total mass of the coating, and the preparation method thereof comprises the following steps:

[0011] (1) Add magnesium powder to tetrahydrofuran solvent, stir and heat for 20-30 minutes, slowly raise the temperature to 55-65℃, then add tetrahydrofuran solution of p-chlorostyrene, stir and react for 2-3 hours, control the temperature to 10-20℃, add tetrahydrofuran solution of cyanuric chloride, wherein the molar ratio of magnesium powder, p-chlorostyrene and cyanuric chloride is 1-1.2:1:0.9-1.2, stir and react for 3-5 hours, after the reaction is completed, add toluene and 12% by mass of Aqueous hydrochloric acid solution is prepared, the organic phase is separated, washed with deionized water, and the organic phase is concentrated to obtain 2-chloro-4,6-diphenylethylene-1,3,5-triazine. In this reaction, magnesium powder, p-chlorostyrene, and cyanuric chloride are used as raw materials, and a Grignard reaction is performed to obtain 2-chloro-4,6-diphenylethylene-1,3,5-triazine, that is, a styrene structure is introduced into the product, which not only contains a UV-resistant benzene ring structure, but also has a diene structure, which is an active group for the subsequent reaction. The reaction route is:

[0012] ;

[0013] (2) Add 2-chloro-4,6-diphenylethylene-1,3,5-triazine and resorcinol to chlorobenzene solvent, stir and disperse, then add aluminum chloride, wherein the molar ratio of 2-chloro-4,6-diphenylethylene-1,3,5-triazine, resorcinol and aluminum chloride is 1:0.8-1:0.05-0.08, heat and stir to dissolve, control the temperature to 70-80°C, react for 5-8h, after the reaction is completed, steam distill, cool, filter and dry to obtain 2-(2′,4′-hydroxyphenyl) -4,6-distyryl-1,3,5-triazine. In this reaction, under the action of aluminum chloride, 2-chloro-4,6-distyryl-1,3,5-triazine and resorcinol undergo a Friedel-Craft reaction to obtain 2-(2',4'-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine. The product obtained by this reaction contains a triazine ultraviolet absorption structure, which can convert the absorbed ultraviolet energy into harmless energy through the opening and closing of intramolecular hydrogen bonds. The reaction route is:

[0014] ;

[0015] (3) Sodium hydroxide is added to N,N-dimethylformamide solvent, heated and stirred to dissolve, and then 2-(2′,4′-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine is added thereto, and the temperature is raised to 65-75°C. 2-bromoisocyanate is added thereto and reacted for 40-60 minutes, wherein the molar ratio of sodium hydroxide, 2-(2′,4′-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine, and 2-bromoisocyanate is 1-1.4:1:1-1.2. After the reaction is completed, the mixture is cooled, vacuum filtered, dissolved in dichloromethane, and recrystallized to obtain compound A. In this reaction, 2-(2′,4′-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine and 2-bromoisocyanate are subjected to a substitution reaction to obtain compound A. An isocyanate active structure is introduced into compound A for the subsequent reaction. The reaction route is:

[0016] ;

[0017] (4) Add nano-titanium dioxide to toluene solvent and ultrasonically disperse for 5 minutes, then add compound A and dibutyltin dilaurate, wherein the molar ratio of nano-titanium dioxide to compound A is 1:4-6, continue ultrasonic dispersion for 10 minutes, react at 80-90°C under nitrogen protection for 5-7 hours, filter, extract with toluene, and dry to obtain compound B. In this reaction, the hydroxyl groups on the surface of nano-titanium dioxide and the isocyanate groups in compound A are used to carry out in-situ polymerization to obtain compound B. At this time, compound A can not only disperse the easily agglomerated nano-titanium dioxide and improve the comprehensive performance of nano-titanium dioxide, but also can cooperate with nano-titanium dioxide to improve the anti-ultraviolet effect of the material. The reaction route is:

[0018] ,in It is nano titanium dioxide;

[0019] (5) Add diethanolamine to ethanol solvent, introduce nitrogen, heat to 65-75°C, add compound B, wherein the molar ratio of diethanolamine to compound B is 2-2.4:1, react for 20-28 hours, and after the reaction is completed, distill under reduced pressure, wash with deionized water, and dry to obtain nano-titanium dioxide-based tetrahydroxy triazine. In this reaction, the alkenyl structure contained in compound B is reacted with diethanolamine through Michael addition reaction to obtain nano-titanium dioxide-based tetrahydroxy triazine, that is, a tetrahydroxy structure is introduced into the product for the next reaction. The reaction route is:

[0020] ;

[0021] (6) Add 2,2-dihydroxypropionic acid and nano-titanium dioxide-based tetrahydroxytriazine to N,N-dimethylformamide solvent, stir and disperse, then add N,N′-dicyclohexylcarbodiimide, wherein the molar ratio of 2,2-dihydroxypropionic acid, nano-titanium dioxide-based tetrahydroxytriazine and N,N′-dicyclohexylcarbodiimide is 12-12.5:1:12-13, react in an ice water bath for 3-5 hours, after the reaction is completed, centrifuge, wash with deionized water, and dry to obtain nano-dimethylformamide. Titanium dioxide-based hydroxyl-terminated hyperbranched polyester. In this reaction, nano-titanium dioxide-based tetrahydroxytriazine is used as the core molecule, 2,2-dihydroxypropionic acid is used as the polymerization monomer, and N,N′-dicyclohexylcarbodiimide is used as the dehydrating agent. A one-step method is adopted to synthesize a second-generation nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester with a regular structure. The molecular chain is not easy to entangle, and its end contains an active hydroxyl structure so that secondary reactions can continue to occur during the preparation of the coating, thereby increasing the crosslinking density of the coating and thus improving the overall performance of the coating.

[0022] Preferably, the curing agent is a blocked high-functionality polyisocyanate crosslinking agent portion, containing a high-functionality macromolecule that releases isocyanate groups after unblocking, the functionality of the curing agent after unblocking is 2-9, and the unblocking temperature is 90-120°C.

[0023] Preferably, the cosolvent is any one of ethanol, butanol, isopropanol, isobutanol, xylene, toluene, ethyl acetate, butyl acetate, methyl formate, methyl acetate, and butyl benzoate, and its usage is 18-30%.

[0024] Preferably, the additive is a wetting agent, a defoaming agent, a dispersant, an adhesion promoter, and an anti-settling agent; the adhesion promoter is any one of γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), γ-methacryloxypropyltrimethoxysilane (KH-570), vinyltrimethoxysilane (A-171), and γ-mercaptopropyltrimethoxysilane (KH-590).

[0025] Preferably, the filler is titanium dioxide, heavy calcium, or barium sulfate.

[0026] Further preferably, the highly filled super-cured mid-coat in the rail transit field is used to improve the coating's resistance, enhance adhesion, and adjust leveling properties, and its application fields include but are not limited to the rail transit field, the industrial anti-corrosion field, etc.

[0027] Preferably, the mid-coat can be applied to the substrate by an electrostatic spraying method and can be cured under heating conditions at a curing temperature of 100-120°C.

[0028] (3) Beneficial technical effects

[0029] The nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester used in the present invention has a hydroxyl structure on its surface and is therefore very prone to secondary aggregation, which is not conducive to its dispersion in the material and affects the comprehensive performance of the material. The present invention utilizes the isocyanate group contained in compound A to disperse the nano-titanium dioxide. On the one hand, the dispersion effect of the nano-titanium dioxide can be improved. On the other hand, the nano-titanium dioxide can form an organic-inorganic synergistic anti-ultraviolet structure with the anti-ultraviolet structure triazine structure and benzene ring structure. Introducing the nano-titanium dioxide into the coating can improve the material's anti-ultraviolet ability and thus increase the service life of the coating. On another hand, the nano-titanium dioxide can serve as a stress concentration point in the coating material and synergistically improve the mechanical properties of the coating with the branched structure.

[0030] The nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester used in the present invention contains a relatively large number of branched structures. On the one hand, the branched structures can cross-link with each other to increase the density of the material and improve the resistance and mechanical properties of the coating. On the other hand, when the nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester is added to the coating, it further reacts with the isocyanate groups contained in the multifunctional isocyanate curing agent to produce secondary cross-linking, giving the coating a higher cross-linking density, that is, a higher coating density. This can not only further enhance the resistance of the coating formed by the coating, but also a large number of polar groups such as carbamate and hydroxyl groups can generate hydrogen bonds and other forces with polar groups on the surface of the substrate material, further improving the adhesion and mechanical properties. In practical applications, the coating far exceeds industry standards and has a long service life.

[0031] The medium-molecular-weight acrylic polymer with a specific monomer structure, which is preferably introduced in this invention, can molecularly fill the putty surface during the crosslinking process, improving the appearance and leveling of the mid-coat. This improved filling effect (promoting the coating's filling of putty pores and / or defects) further enhances the coating's adhesion. The combination of a hyperbranched polyester and a curing agent, along with the structural design of a medium-molecular-weight acrylic resin, results in a superior appearance, increased durability, and stronger adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of a medium molecular weight acrylic polymer filled coating. DETAILED DESCRIPTION

[0033] As used herein, unless otherwise expressly stated, numerical values, ranges, amounts, or percentages used in the specification and claims should be considered to vary in all instances by the term "about," even if the term is not expressly indicated. Therefore, unless otherwise indicated, the numerical parameters listed in the specification and claims herein are approximate and may vary depending on the properties to be obtained by the present invention.

[0034] Dispersants, wetting agents, and anti-settling agents were purchased from Digo Additives;

[0035] Defoamer was purchased from BYK;

[0036] Titanium dioxide, talc, and barium sulfate were purchased from DuPont;

[0037] Solvents were purchased from Dow Chemical;

[0038] The curing agent was purchased from Wanhua Chemical;

[0039] Adhesion promoters were γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane, all of which were purchased from Momentive.

[0040] The medium molecular weight acrylic resin polymer 1 is hereinafter referred to as acrylic resin 1, and the medium molecular weight acrylic resin polymer 2 is hereinafter referred to as acrylic resin 2.

[0041] Acrylic resin 1 is a medium molecular weight acrylic resin polymer with a molecular weight of 80,000-150,000, and its monomer composition is a combination of styrene (accounting for 40% of the total monomer mass), methyl methacrylate (accounting for 30% of the total monomer mass), acrylic acid (accounting for 10% of the total monomer mass), and hydroxypropyl methacrylate (accounting for 10% of the total monomer mass).

[0042] Acrylic resin 2 is a medium molecular weight acrylic resin polymer with a molecular weight of 100,000-500,000, and its monomer composition is a combination of methyl methacrylate (accounting for 35% of the total monomer mass), hydroxypropyl methacrylate (accounting for 25% of the total monomer mass), isobornyl methacrylate (accounting for 10% of the total monomer mass), acrylic acid (accounting for 10% of the total monomer mass), versatate glycidyl ester (accounting for 5% of the total monomer mass), glycidyl methacrylate (accounting for 5% of the total monomer mass), and glycidyl acrylate (accounting for 10% of the total monomer mass).

[0043] Example 1

[0044] (1) Add 0.4 mol of magnesium powder to tetrahydrofuran solvent, stir and heat for 30 min, slowly raise the temperature to 65 ° C, add a tetrahydrofuran solution containing 0.4 mol of p-chlorostyrene, stir and react for 3 h, control the temperature at 10 ° C, add a tetrahydrofuran solution containing 0.36 mol of cyanuric chloride, stir and react for 5 h, after the reaction is completed, add toluene and a 12% by mass hydrochloric acid aqueous solution, stir and mix evenly, separate the organic phase, wash with deionized water, and concentrate the organic phase to obtain 2-chloro-4,6-diphenylethylene-1,3,5-triazine.

[0045] (2) Add 0.5 mol of 2-chloro-4,6-diphenylethylene-1,3,5-triazine and 0.5 mol of resorcinol to chlorobenzene solvent, stir and disperse, then add 0.025 mol of aluminum trichloride, heat and stir to dissolve, control the temperature to 80°C, react for 5 hours, and after the reaction is completed, steam distill, cool, filter, and dry to obtain 2-(2′,4′-hydroxyphenyl)-4,6-diphenylethylene-1,3,5-triazine.

[0046] (3) Add 0.5 mol of sodium hydroxide to N,N-dimethylformamide solvent, heat and stir to dissolve, then add 0.5 mol of 2-(2′,4′-hydroxyphenyl)-4,6-diphenylethylene-1,3,5-triazine, heat to 65°C, add 0.6 mol of 2-ethyl bromoisocyanate and react for 60 minutes. After the reaction is completed, cool, vacuum filter, dissolve in dichloromethane, and recrystallize to obtain compound A.

[0047] (4) Add 0.08 mol of nano-titanium dioxide to toluene solvent and ultrasonically disperse for 5 minutes. Then add 0.48 mol of compound A and 3 drops of dibutyltin dilaurate and continue ultrasonically dispersing for 10 minutes. Under nitrogen protection, react at 90°C for 7 hours. After the reaction is completed, filter, extract with toluene, and dry to obtain compound B.

[0048] (5) 0.4 mol of diethanolamine was added to the ethanol solvent, nitrogen was introduced, the temperature was raised to 75°C, 0.2 mol of compound B was added thereto, and the reaction was carried out for 20 hours. After the reaction was completed, the mixture was distilled under reduced pressure, washed with deionized water, and dried to obtain nano-titanium dioxide-based tetrahydroxytriazine.

[0049] (6) 1.25 mol of 2,2-dihydroxypropionic acid and 0.1 mol of nano-titanium dioxide-based tetrahydroxytriazine were added to N,N-dimethylformamide solvent and stirred for dispersion. Then, 1.2 mol of N,N′-dicyclohexylcarbodiimide was added thereto and reacted in an ice-water bath for 3 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain nano-titanium dioxide-based terminal hydroxyl hyperbranched polyester.

[0050] Example 2

[0051] (1) Add 0.48 mol of magnesium powder to tetrahydrofuran solvent, stir and heat for 20 min, slowly raise the temperature to 55 ° C, add a tetrahydrofuran solution containing 0.4 mol of p-chlorostyrene, stir and react for 2 h, control the temperature to 20 ° C, add a tetrahydrofuran solution containing 0.48 mol of cyanuric chloride, stir and react for 3 h, after the reaction is completed, add toluene and a 12% by mass hydrochloric acid aqueous solution, stir and mix evenly, separate the organic phase, wash with deionized water, and concentrate the organic phase to obtain 2-chloro-4,6-diphenylethylene-1,3,5-triazine.

[0052] (2) Add 0.5 mol of 2-chloro-4,6-diphenylethylene-1,3,5-triazine and 0.4 mol of resorcinol to chlorobenzene solvent, stir and disperse, then add 0.04 mol of aluminum trichloride, heat and stir to dissolve, control the temperature to 70°C, react for 8 hours, and after the reaction is completed, steam distill, cool, filter, and dry to obtain 2-(2′,4′-hydroxyphenyl)-4,6-diphenylethylene-1,3,5-triazine.

[0053] (3) Add 0.7 mol of sodium hydroxide to N,N-dimethylformamide solvent, heat and stir to dissolve, then add 0.5 mol of 2-(2′,4′-hydroxyphenyl)-4,6-diphenylethylene-1,3,5-triazine, heat to 75°C, add 0.5 mol of 2-ethyl bromoisocyanate and react for 40 minutes. After the reaction is completed, cool, vacuum filter, dissolve in dichloromethane, and recrystallize to obtain compound A.

[0054] (4) Add 0.08 mol of nano-titanium dioxide to toluene solvent and ultrasonically disperse for 5 minutes. Then add 0.32 mol of compound A and 5 drops of dibutyltin dilaurate and continue ultrasonically dispersing for 10 minutes. Under nitrogen protection, react at 80°C for 5 hours. After the reaction is completed, filter, extract with toluene, and dry to obtain compound B.

[0055] (5) 0.48 mol of diethanolamine was added to the ethanol solvent, nitrogen was introduced, the temperature was raised to 65 °C, 0.2 mol of compound B was added thereto, and the reaction was carried out for 28 h. After the reaction was completed, the mixture was distilled under reduced pressure, washed with deionized water, and dried to obtain nano-titanium dioxide-based tetrahydroxytriazine.

[0056] (6) 1.2 mol of 2,2-dihydroxypropionic acid and 0.1 mol of nano-titanium dioxide-based tetrahydroxytriazine were added to N,N-dimethylformamide solvent and stirred for dispersion. Then, 1.3 mol of N,N′-dicyclohexylcarbodiimide was added thereto and reacted in an ice-water bath for 5 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain nano-titanium dioxide-based terminal hydroxyl hyperbranched polyester.

[0057] Example 3-5:

[0058] The raw materials were mixed uniformly according to the following weight order to prepare Examples 3-5 of the coating composition according to the present invention.

[0059] Material Name Example 3 Example 4 Example 5 Nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester of Example 1 22.9 24.9 26.9 Acrylic resin 1 19.6 19.6 19.6 Acrylic resin 2 20 20 20 dispersants 1 1 1 defoaming agent 0.3 0.3 0.3 Titanium dioxide 48 48 48 talcum powder 17 17 17 barium sulfate 20 20 20 Wetting agent 0.5 0.5 0.5 Isobutanol solvent 40 40 40 Ethyl acetate solvent 40 40 40 anti-settling agent 6 6 6 Butyl benzoate solvent 2.7 2.7 2.7 curing agent 20 20 20

[0060] Example 6-7:

[0061] The raw materials were mixed uniformly according to the following weight order, and Examples 6-7 of the coating composition according to the present invention were prepared by parallel experiments and comparison with Example 4.

[0062] Material Name Example 4 Example 6 Example 7 Nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester of Example 1 24.9 24.9 24.9 Acrylic resin 1 19.6 17.6 21.6 Acrylic resin 2 20 20 20 dispersants 1 1 1 defoaming agent 0.3 0.3 0.3 Titanium dioxide 48 48 48 talcum powder 17 17 17 barium sulfate 20 20 20 Wetting agent 0.5 0.5 0.5 Isobutanol solvent 40 40 40 Ethyl acetate solvent 40 40 40 anti-settling agent 6 6 6 Butyl benzoate solvent 2.7 2.7 2.7 curing agent 20 20 20

[0063] Example 8-9:

[0064] The raw materials were mixed uniformly according to the following weight order, and Examples 8-9 of the coating composition according to the present invention were prepared by parallel experiments and comparative example 4.

[0065] Material Name Example 4 Example 8 Example 9 Nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester of Example 1 24.9 24.9 24.9 Acrylic resin 1 19.6 19.6 19.6 Acrylic resin 2 20 20 20 dispersants 1 1 1 defoaming agent 0.3 0.3 0.3 Titanium dioxide 48 48 48 talcum powder 17 17 17 barium sulfate 20 20 20 Wetting agent 0.5 0.5 0.5 Isobutanol solvent 40 40 40 Ethyl acetate solvent 40 40 40 anti-settling agent 6 6 6 Butyl benzoate solvent 3 2.7 2.7 2.7 curing agent 20 18 22

[0066] Examples 10-14:

[0067] The raw materials were mixed uniformly according to the following weight order to prepare Examples 10-14 of the coating composition according to the present invention.

[0068] Material Name Example 10 Example 11 Example 12 Example 13 Example 14 Nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester of Example 2 24.9 24.9 24.9 24.9 24.9 Acrylic resin 1 19.6 19.6 19.6 19.6 19.6 Acrylic resin 2 20 20 20 20 20 dispersants 1 1 1 1 1 defoaming agent 0.3 0.3 0.3 0.3 0.3 Titanium dioxide 48 48 48 48 48 talcum powder 17 17 17 17 17 barium sulfate 20 20 20 20 20 Wetting agent 0.5 0.5 0.5 0.5 0.5 Isobutanol solvent 40 40 40 40 40 Ethyl acetate solvent 40 40 40 40 40 anti-settling agent 6 6 6 6 6 Butyl benzoate solvent 2.7 2.7 2.7 2.7 2.7 γ-Aminopropyltriethoxysilane 2 0 0 0 0 γ-Glycidyloxypropyltrimethoxysilane 0 2 0 0 0 γ-Methacryloxypropyltrimethoxysilane 0 0 2 0 0 Vinyltrimethoxysilane 0 0 0 2 0 γ-Mercaptopropyltrimethoxysilane 0 0 0 0 2 curing agent 20 20 20 20 20

[0069] Performance Testing

[0070] The mid-coat coating composition obtained as above was applied to the surface of the homemade putty, and the specific parameters were as follows: the construction environment was maintained at a temperature of 25°C and a humidity of 50-60%; an air spray gun was used for spraying; the coating thickness was ultimately controlled at 50 μm, and the sprayed coating was flash-dried at ambient temperature for 30 min, then baked at 100°C for 20 min, and the cured coating was subjected to the following performance tests.

[0071] 1. Appearance: Use a BYK orange peel meter to test the surface appearance of the midcoat. Refer to the BYK orange peel meter operating manual for standard operation. Mainly record long wave Lw, short wave Sw, and distinctness of image Doi.

[0072] 2. Impact Resistance Test: Conduct the test at 23±2°C and 50±5% relative humidity. Place the painted test panel flat on an anvil, paint film facing upward. The impacted portion of the panel must be at least 15 mm from the edge, and the edge of each impact point must be at least 15 mm apart. A weight is fixed to a certain height on the slide using a control device. Pressing the control button causes the weight to fall freely onto the punch. Lift the weight and remove the test panel. Record the height at which the weight falls on the panel. Perform the impact test three times on the same panel. Observe the paint film with a 4x magnifying glass to determine if there are any cracks, wrinkles, or peeling.

[0073] 3. Cupping Test: Conduct the test at 23±2°C and 50±5% relative humidity. Secure the test panel between a retaining ring and a stretch die. Apply no additional pressure, with the coating facing the die. Ensure the hemispherical tip of the punch is in contact with the uncoated side of the test panel. Push the hemispherical tip of the punch toward the test panel at a constant speed of 0.1-0.3 mm per second until the specified depth, defined as the distance the punch has traveled from zero, is reached. Inspect the test panel for cracking and detachment of the coating from the substrate using corrected normal vision or, if necessary, a microscope or 10x magnifying glass.

[0074] 4. Adhesion test: Place the sample on a hard, flat surface to prevent any deformation of the sample during the test. Hold the cutting tool perpendicular to the sample surface and apply uniform force to the cutting tool. Use an appropriate spacing guide device to make the specified number of cuts on the coating at a uniform cutting rate. Make the same number of parallel cuts that intersect the original cuts at an angle to form a grid pattern. Use a soft brush to gently sweep back and forth several times along each diagonal line of the grid pattern. Cut an adhesive tape about 75mm long and place the center point of the tape above the grid, parallel to one set of cut lines. Within 5 minutes of applying the tape, hold the dangling end of the tape and tear it off smoothly within 0.5-1s at an angle as close to 60° as possible. Carefully inspect the cut area of the test coating with a visual magnifier and rate the test results.

[0075] 5. Solvent Wipe Test: Test the solvent resistance of the sample using a Taber 5750 Linear Abraser. Wipe a 120mm long area on the sample surface. Fix a cotton pad soaked in butanone (no droplets should fall when squeezed manually) to the test end of the abraser. Visually inspect the coating in the middle 8cm area of the test panel under diffused sunlight to see if any damage is present, exposing the substrate.

[0076] 6. Water Resistance Test: Refer to GB / T 5209 standard and immerse the specimen in a constant-temperature water bath at 40°C. Remove the specimen every two hours, wipe the surface dry, and inspect for defects such as blistering, discoloration, and smudges. Add sufficient deionized water to the bath to keep three-quarters of the specimen immersed in the water, then begin circulating or aerating the water in the bath. Adjust the water temperature to 40±1°C. For intermediate inspections during the test cycle, remove the specimen from the bath, blot dry with filter paper, immediately inspect for signs of damage, and then immediately return it to the bath. At the end of the specified period, remove the specimen from the bath, blot dry with filter paper, and inspect for signs of damage.

[0077] The performance test results of Examples 3-8 are shown in the following table:

[0078] Test items Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Appearance-Lw 22.8 23.4 23.8 25.5 22.0 23.8 Appearance-Sw 19.6 20.2 20.7 22.9 19.9 20.7 Doi 88.6 88.2 87.2 85.7 89.2 86.9 Impact resistance 40 70 80 45 90 70 Cupping test 3.5 4.5 5 4 5 5 Cross-cut test 2 3 5 3 4 2 Solvent resistant wipe 50 40 30 40 30 20 Water resistance 48 48 48 48 24 24

[0079] The performance test results of Examples 9-14 are shown in the following table:

[0080] Test items Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Appearance-Lw 23.9 22.9 23.1 23.3 23.8 23.4 Appearance-Sw 20.7 20.2 20.4 20.5 20.5 20.6 Doi 88.2 88.7 88.5 88.6 88.2 88.5 Impact resistance 90 70 70 70 70 70 Cupping test 4.5 4.5 4.5 4.5 4.5 4.5 Cross-cut test 3 3 1 1 1 1 Solvent resistant wipe 30 30 30 30 30 30 Water resistance 48 48 48 48 48 48

[0081] As can be seen from the table, as the amount of nano-titanium dioxide-based end-hydroxyl hyperbranched polyester increases, its overall performance improves. As the amount of curing agent increases, the density is further increased, and its overall performance increases. For the mid-coat protected by this patent, its main function is to connect the putty and the topcoat. The filling effect of the mid-coat on the putty layer can be seen from the appearance of the mid-coat. In the examples listed in this patent, the comprehensive performance of the appearance test results is excellent. The present invention has excellent filling performance.

[0082] While particular aspects of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the invention. It is therefore intended that the appended claims cover all such changes and modifications as fall within the scope of the invention.

Claims

1. A highly filled super-cured mid-coat for rail transit, characterized in that: The highly filled super-cured mid-coat is made by mixing a main agent and a curing agent in a mass ratio of 90.8-93:7-9.2; The mid-coat is a two-component coating; The main agent includes polymer resin, additives, fillers and cosolvents.

2. The highly filled super-cured mid-coat for rail transit according to claim 1, characterized in that: The polymer resin comprises a medium molecular weight acrylic resin polymer, the amount of which is 14.5-18.2% of the total mass of the coating, and the monomers constituting the medium molecular weight acrylic resin polymer are any of styrene, acrylic acid, methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, isobornyl methacrylate, versatate glycidyl ester, glycidyl methacrylate, and glycidyl acrylate.

3. The highly filled super-cured mid-coat for rail transit according to claim 1, characterized in that: The polymer resin comprises nano-titanium dioxide-based hydroxyl-terminated hyperbranched polyester, the amount of which is 9.2-12.1% of the total mass of the coating, and the preparation method thereof comprises the following steps: (1) Add magnesium powder to tetrahydrofuran solvent, stir and heat for 20-30 minutes, slowly raise the temperature to 55-65°C, then add tetrahydrofuran solution of p-chlorostyrene, stir and react for 2-3 hours, control the temperature to 10-20°C, add tetrahydrofuran solution of cyanuric chloride, wherein the molar ratio of magnesium powder, p-chlorostyrene and cyanuric chloride is 1-1.2:1:0.9-1.2, stir and react for 3-5 hours, after the reaction is completed, add toluene and 12% by mass hydrochloric acid aqueous solution, separate the organic phase, wash with deionized water, and concentrate the organic phase to obtain 2-chloro-4,6-diphenylethylene-1,3,5-triazine; (2) Add 2-chloro-4,6-distyryl-1,3,5-triazine and resorcinol to chlorobenzene solvent, stir and disperse, then add aluminum chloride, wherein the molar ratio of 2-chloro-4,6-distyryl-1,3,5-triazine, resorcinol and aluminum chloride is 1:0.8-1:0.05-0.08, heat and stir to dissolve, control the temperature to 70-80°C, react for 5-8h, after the reaction is completed, steam distill, cool, filter and dry to obtain 2-(2′,4′-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine; (3) Sodium hydroxide is added to N,N-dimethylformamide solvent, heated and stirred to dissolve, and then 2-(2′,4′-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine is added thereto, and the temperature is raised to 65-75°C. 2-bromoisocyanate is added thereto and reacted for 40-60 minutes, wherein the molar ratio of sodium hydroxide, 2-(2′,4′-hydroxyphenyl)-4,6-distyryl-1,3,5-triazine, and 2-bromoisocyanate is 1-1.4:1:1-1.

2. After the reaction is completed, the mixture is cooled, vacuum filtered, dissolved in dichloromethane, and recrystallized to obtain compound A; (4) Add nano-titanium dioxide to toluene solvent and ultrasonically disperse for 5 minutes, then add compound A and dibutyltin dilaurate, wherein the molar ratio of nano-titanium dioxide to compound A is 1:4-6, and continue ultrasonically dispersing for 10 minutes. Under nitrogen protection, react at 80-90°C for 5-7 hours. After the reaction is completed, filter, extract with toluene, and dry to obtain compound B; (5) Add diethanolamine to ethanol solvent, introduce nitrogen, raise the temperature to 65-75°C, add compound B, wherein the molar ratio of diethanolamine to compound B is 2-2.4:1, react for 20-28 hours, and after the reaction is completed, distill under reduced pressure, wash with deionized water, and dry to obtain nano-titanium dioxide-based tetrahydroxytriazine; (6) Add 2,2-dihydroxypropionic acid and nano-titanium dioxide-based tetrahydroxytriazine to N,N-dimethylformamide solvent, stir and disperse, then add N,N′-dicyclohexylcarbodiimide, wherein the molar ratio of 2,2-dihydroxypropionic acid, nano-titanium dioxide-based tetrahydroxytriazine and N,N′-dicyclohexylcarbodiimide is 12-12.5:1:12-13, react in an ice-water bath for 3-5 hours, after the reaction is completed, centrifuge, wash with deionized water, and dry to obtain nano-titanium dioxide-based terminal hydroxyl hyperbranched polyester.

4. The highly filled super-cured mid-coat for rail transit according to claim 1, characterized in that: The curing agent is a blocked high-functionality polyisocyanate crosslinking agent, which contains high-functionality macromolecules that release isocyanate groups after unblocking. The functionality of the curing agent after unblocking is 2-9, and the unblocking temperature is 90-120°C.

5. The highly filled super-cured mid-coat for rail transit according to claim 1, characterized in that: The cosolvent is any one of ethanol, butanol, isopropanol, isobutanol, xylene, toluene, ethyl acetate, butyl acetate, methyl formate, methyl acetate, and butyl benzoate, and its usage is 18-30%.

6. The highly filled super-cured mid-coat for rail transit according to claim 1, characterized in that: The additives are a wetting agent, a defoaming agent, a dispersant, an adhesion promoter, and an anti-settling agent; the adhesion promoter is any one of γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), γ-methacryloxypropyltrimethoxysilane (KH-570), vinyltrimethoxysilane (A-171), and γ-mercaptopropyltrimethoxysilane (KH-590).

7. The highly filled super-cured mid-coat for rail transportation according to claim 1, characterized in that: The filler is one or more of titanium dioxide, heavy calcium and barium sulfate.

8. The highly filled super-cured mid-coat for rail transit according to any one of claims 1 to 7, characterized in that: The mid-coat can be applied to the substrate by an electrostatic spraying method and can be cured under heating conditions at a curing temperature of 100-120° C. The application fields include but are not limited to the rail transportation field, the industrial anti-corrosion field, etc.

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