Anti-graffiti polyurethane paint, coating, preparation method and application thereof

Abstract

The present invention belongs to the technical field of polyurethane coatings and coatings, and specifically relates to an anti-graffiti polyurethane coating, coating, preparation method, and application thereof. The anti-graffiti polyurethane coating comprises the following components, by weight: 15-30 parts of bismercaptan, 5-30 parts of polythiol, 0.20-0.6 parts of a catalyst, and 20-55 parts of an isocyanate; the bismercaptan has a molecular weight of 154.32; and the polythiol has a molecular weight of 260.53. The present invention produces polyurethane by reacting bismercaptan, polythiol, and isocyanate. This significantly improves the adhesion and anti-graffiti properties of the polyurethane on synthetic leather / leather surfaces, is easy to industrialize, and has broad application prospects and market value.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyurethane coatings and coatings, and in particular relates to an anti-graffiti polyurethane coating, a coating, and a preparation method and application thereof. Background Art

[0002] Coating is an essential and critical process in the manufacturing of leather and synthetic leather. Coating not only imparts an aesthetically pleasing appearance to leather and synthetic leather, but also significantly enhances its functionality, such as abrasion resistance, chemical resistance, water resistance, breathability, and hand feel. The functionality of a coating depends on the bond strength—in other words, adhesion—between the coating material and the substrate (synthetic or leather). Inadequate adhesion between the coating and the substrate can lead to peeling, shedding, blistering, and damage from friction or bending, resulting in cosmetic damage and functional failure, directly impacting product lifespan. Good adhesion ensures that the coating provides an intact, comfortable feel and lasting performance over long-term use.

[0003] Polyurethane coatings are applied during the manufacturing of leather and synthetic leather. However, traditional organic solvent-based polyurethane coatings are subject to complex preparation processes and high volatile organic compound (VOC) emissions, posing risks to the environment, human health, and substrate performance. Existing technologies utilize water as a dispersant instead of organic solvents to prepare novel polyurethane systems, such as waterborne polyurethanes. However, these systems suffer from poor water resistance, low adhesion, moisture absorption, and easy detachment after repeated friction. This is particularly true when contaminated by graffiti, stains, or corrosive substances, leading to coating damage. Summary of the Invention

[0004] The present invention aims to provide an anti-graffiti polyurethane coating, a coating, a preparation method, and an application thereof, thereby overcoming the deficiencies of the prior art. The present invention prepares polyurethane by reacting dithiol mercaptan, polythiol, and isocyanate, significantly improving the adhesion and anti-graffiti properties of polyurethane on the surface of synthetic leather / leather, and is easy to industrialize and produce, thereby having broad application prospects and market value.

[0005] The overall inventive concept adopted by the present invention is:

[0006] This invention aims to address the problems of polyurethane coatings in existing synthetic leather and leather products, such as easy detachment, difficulty in cleaning, and poor stain resistance. This is particularly problematic when dealing with common contaminants such as coffee, markers, and ketchup, which traditional coatings struggle to effectively protect against and quickly remove. While water-based polyurethanes are environmentally friendly, they have a loose film structure, are highly absorbent, and offer limited stain resistance. Solvent-based systems, while offering some performance, also have VOC emissions, hindering green production.

[0007] The present invention provides a solvent-free anti-graffiti polyurethane coating and coating system. This coating, based on dithiolthiol and polythiol as the main reaction components, reacts with a multifunctional isocyanate in the presence of a catalyst to form a polyurethane network with a high crosslink density. The thiol groups preferentially react with -NCO groups to form thiocarbamate structures (-NH-C(=S)-O-), which are more chemically stable and impermeable than conventional carbamate bonds. Furthermore, by adjusting the molar ratio of dithiolthiol to polythiol, a good balance between rigid crosslinks and flexible segments can be achieved, imparting excellent mechanical properties and crack resistance to the coating. The coating can be applied to leather or synthetic leather substrates by blade coating, spraying, or dipping. It then undergoes staged thermal curing (e.g., thermal curing at 65°C for 35 hours followed by 20-30 hours at room temperature) to form a dense, stable polyurethane coating. The thermal curing process promotes complete crosslinking of the three-dimensional network, eliminates residual stress, and improves the coating's adhesion and flexibility.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] In a first aspect, the present invention provides an anti-graffiti polyurethane coating, comprising the following components in parts by weight:

[0010] 15-30 parts of bismercaptomercaptan, 5-30 parts of polythiol, 0.20-0.6 parts of catalyst, 20-55 parts of isocyanate;

[0011] The molecular weight of the polythiol is 260.53-488.66.

[0012] In some other embodiments, the composition is composed of the following components, by weight: 16-30 parts of bismercaptan, 6-26.3 parts of polythiol, 0.22-0.52 parts of catalyst, and 23.1-53.9 parts of isocyanate;

[0013] The molecular weight of the bis-mercaptothiol is 154.32;

[0014] The molecular weight of the polythiol is 260.53-398.56;

[0015] The molar ratio of the bis-mercaptothiol to the polythiol is (1-8): (1-4).

[0016] In some other embodiments, the composition is composed of the following components in parts by weight:

[0017] 30 parts of bismercaptomercaptan, 12 parts of polythiol, 0.42 parts of catalyst, 44.1 parts of isocyanate;

[0018] The molecular weight of the bis-mercaptothiol is 154.32;

[0019] The molecular weight of the polythiol is 260.53;

[0020] The molar ratio of the bismercaptan to the polythiol is 6:4.

[0021] In some other embodiments, the catalyst is one or more of triethylenediamine, triethylamine, NN-dimethylethanolamine, trimethylbenzylamine, NN-dimethylcyclohexylamine, dibutyltin dilaurate, and succinic acid;

[0022] The isocyanate is one or more of diphenylmethane diisocyanate, isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, vinyl diisocyanate, tetramethylene 1,4-diisocyanate, dodecyl 1,2-diisocyanate and 3,3-dichloro-4,4-biphenyl diisocyanate.

[0023] In a second aspect, the present invention provides a method for preparing the anti-graffiti polyurethane coating according to the first aspect, comprising the following steps:

[0024] The dimercaptan and the polythiol are mixed, a catalyst is added, and the mixture is heated; and then isocyanate is added and reacted to obtain the product.

[0025] In some other embodiments, the mixing molar ratio of the bis-mercaptothiol and the polythiol is (1-8): (1-4);

[0026] The heating is performed at 60-70° C. for 3-6 minutes;

[0027] The reaction is carried out at 60-70°C for 2-4 hours.

[0028] The reaction mechanism of anti-graffiti polyurethane coatings involves nucleophilic addition reactions and the formation of a crosslinked network. Specifically, dithiol mercaptan provides dithiol groups to form linear segments; polythiol provides three -SH groups as crosslinking points; the mixing ratio of dithiol mercaptan and polythiol balances crosslink density and flexibility. Organotin catalysts accelerate the reaction of -SH with -NCO. Heating conditions activate the proton dissociation of the thiol (-SH) to form a more nucleophilic thiolate (-S⁻). The specific reaction process is as follows: R-SH + -R'- N=C=O → RSC(=O)-NH-R'

[0029] The core of this reaction mechanism is the nucleophilic addition of thiol (-SH) to isocyanate (-NCO), forming a thiol crosslinked network. By manipulating the catalyst, temperature, and functionality ratio, coating properties (such as the wear and water resistance of anti-crow coatings) can be optimized.

[0030] In a third aspect, the present invention provides an anti-graffiti polyurethane coating made from the anti-graffiti polyurethane coating described in the first aspect.

[0031] In a fourth aspect, the present invention provides a method for preparing an anti-graffiti polyurethane coating, comprising coating the anti-graffiti polyurethane coating described in the first aspect on a substrate and subjecting the coating to staged curing.

[0032] In some other embodiments, the coating method is one of blade coating, spray coating and dip coating;

[0033] The staged curing is first curing at 60-70° C. for 3-5 hours and then standing at room temperature for 20-30 hours.

[0034] In a fifth aspect, the present invention provides use of the anti-graffiti polyurethane coating described in the third aspect in synthetic leather and leather.

[0035] Beneficial effects of the present invention:

[0036] The coating prepared by the present invention has the following excellent properties:

[0037] (1) Excellent anti-graffiti performance: After the leather surface is contaminated by oil-based pens, ballpoint pens, coffee, etc., it can be easily wiped off with a wet towel without leaving any residual image; (2) Good adhesion and wear resistance: The coating remains intact after 6500 cycles of wear under the TABER test; (3) Thermal stability and low Tg properties coexist: The glass transition temperature (Tg) is about 35℃, and it exhibits high elasticity and soft feel at room temperature;

[0038] (4) Excellent environmental friendliness and industrial adaptability: The entire formula is solvent-free and suitable for green manufacturing processes. It can directly replace traditional solvent-based coating materials on synthetic leather production lines. In summary, the present invention has constructed a polyurethane coating system that combines anti-graffiti, high adhesion strength, good flexibility, and excellent environmental friendliness. It is suitable for surface functionalization of various flexible substrates such as high-end synthetic leather, genuine leather, and elastic films, and has good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0040] Figure 1 The following are pictures of the polyurethane coating prepared in Example 1 of the present invention before and after wear, where A is before wear and B is after wear;

[0041] Figure 2 is a differential scanning calorimetry spectrum of the polyurethane coating prepared in Example 1 of the present invention;

[0042] Figure 3 This is an infrared scanning image of the polyurethane coating prepared in Example 1 of the present invention;

[0043] Figure 4 These are pictures of the polyurethane coating surface prepared in Example 1 of the present invention before and after graffiti is erased, where A is before graffiti is erased and B is after graffiti is erased;

[0044] Figure 5 These are pictures of the surface of the polyurethane coating prepared in Example 2 of the present invention before and after graffiti is erased, where A is before graffiti is erased and B is after graffiti is erased. DETAILED DESCRIPTION

[0045] Those skilled in the art will appreciate that the following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the invention. Unless otherwise specified, the examples were performed under conventional conditions or manufacturer's recommended conditions. Components used without manufacturer's indication are commercially available conventional products.

[0046] Example 1.

[0047] 30g of bismercaptothiol (molecular weight 154.32) and 12g of polythiol (molecular weight 260.53) were mixed (molar ratio 6:4), and 0.42g of dibutyltin dilaurate catalyst was added. The mixture was heated at 65°C for 5 minutes. 44.1g of HDI was then added and mixed into a reactor. The mixture was reacted at 65°C for 2.5 hours to produce a polyurethane coating. The polyurethane coating was then applied to the leather surface using a stainless steel scraper (scraping speed 15cm / s, scraping angle 50°, coating thickness 100μm). A step-curing method was used: reacting at 65°C for 4 hours, followed by stabilization at room temperature for 24 hours to produce the polyurethane coating.

[0048] Example 2

[0049] A mixture of 16g ​​of bismercaptomercaptan (molecular weight 154.32) and 6g of polythiol (molecular weight 260.53) (molar ratio 8:3) was added, followed by the addition of 0.22g of dibutyltin dilaurate catalyst. The mixture was heated at 65°C for 5 minutes, followed by the addition of 23.1g of HDI. The mixture was then added to a reactor and reacted at 65°C for 2.5 hours to produce a polyurethane coating. The polyurethane coating was then applied to the leather surface using a stainless steel scraper (constant speed of 15cm / s, angle of 45°, coating thickness 100μm). A step-curing process was employed: a 4-hour reaction at 65°C followed by a 24-hour stabilization at room temperature to produce the polyurethane coating.

[0050] Example 3

[0051] A 1:1 molar ratio of 25g of bismercaptan (molecular weight 154.32) and 26.3g of polythiol (molecular weight 260.53) was mixed, followed by the addition of 0.513g of dibutyltin dilaurate catalyst. The mixture was heated at 65°C for 5 minutes, followed by the addition of 53.865g of HDI. The mixture was then added to a reactor and allowed to react at 65°C for 2-4 hours (specifically, 2.5 hours) to produce a polyurethane coating. The polyurethane coating was then sprayed onto the leather surface (at a uniform spray speed of 0.5m / s, a spray pressure of 100MPa, and a coating thickness of 100μm). A step-curing process was employed, initially reacting at 65°C for 4 hours, followed by a 24-hour undisturbed reaction at room temperature to produce the polyurethane coating.

[0052] Comparative Example 1

[0053] 25g of bismercaptomercaptan (molecular weight 154.32) was added to 0.513g of dibutyltin dilaurate catalyst and heated at 65°C for 5 minutes. 53.865g of HDI was then added, mixed, and added to a reactor. The mixture was reacted at 65°C for 2-4 hours (specifically, 2.5 hours) to produce a polyurethane coating. The polyurethane coating was sprayed onto the leather surface (at a uniform spray speed of 0.5m / s, a spray pressure of 100MPa, and a coating thickness of 100μm). A step-curing process was used: reacting at 65°C for 4 hours, followed by a 24-hour stabilization at room temperature to produce the polyurethane coating.

[0054] Comparative Example 2

[0055] 26.3g of polythiol (molecular weight 260.53) was added to 0.513g of dibutyltin dilaurate catalyst and heated at 65°C for 5 minutes. 53.865g of HDI was then added, mixed, and added to a reactor. The mixture was reacted at 65°C for 2-4 hours (specifically, 2.5 hours) to produce a polyurethane coating. The polyurethane coating was sprayed onto the leather surface (at a uniform spray speed of 0.5m / s, a spray pressure of 100MPa, and a coating thickness of 100μm). A step-curing process was used: reacting at 65°C for 4 hours, followed by a 24-hour stand at room temperature to produce the polyurethane coating.

[0056] Comparative Example 3

[0057] 24.586g of polythiol GL1800 and 29.44g of HDI were mixed and added to a reactor. 0.54g of dibutyltin dilaurate catalyst was added dropwise, and the mixture was reacted at 65°C for 3 hours to produce a polyurethane coating. The polyurethane coating was then applied to the leather surface using a stainless steel scraper (constant speed of 15cm / s, angle of 50°, coating thickness of 100μm). A step-curing method was used: first reacting at 65°C for 4 hours, then allowing the mixture to stand at room temperature for 24 hours to produce the polyurethane coating.

[0058] Performance Testing

[0059] 1. Wear resistance test:

[0060] The polyurethane coating prepared in Example 1 was tested for wear resistance at room temperature using a TABER wear tester (manufacturer: Hongtu High-Tech Development Zone, Nancheng District, Dongguan City, Guangdong Province, model: GT7012-T). The results are as follows: Figure 1 As shown, A is before wear and B is after wear.

[0061] Figure 1 The bright ring area in Figure B is the area formed after the polyurethane coating is polished 6500 times. The hole in the middle is formed when polishing. Figure 1 The A in the figure is fixed on the TABER wear tester. Figure 1 As shown in Figures A and B, the polyurethane coatings before and after polishing are smooth and uniform. This is due to the two -SH groups provided by the bismercaptothiol, which react with HDI to form linear thiolcarbamate segments, providing the coating with a basic backbone. The thiol groups contained in the polythiol form a three-dimensional crosslinked network with HDI, significantly increasing the crosslink density. A mixture of bismercaptothiol and polythiol in a molar ratio of 6:4 achieves a balance between linear segments (toughness) and crosslinks (rigidity), avoiding the brittleness of pure polythiol or the softness of pure bismercapto. The increased crosslink density inhibits molecular chain slippage, thereby improving wear resistance.

[0062] 2. Differential Scanning Calorimetry

[0063] The polyurethane coating prepared in Example 1 was subjected to differential scanning calorimetry testing at a temperature of -50-220°C, a nitrogen atmosphere, and a heating rate of 10°C / min. The results are shown in FIG. Figure 2 As shown. Figure 2 The cured coating has a glass transition temperature (Tg) of 35.38°C, indicating that the material transitions from a glassy state to a highly elastic state near room temperature. Low-Tg coatings remain flexible at low temperatures and are therefore suitable for dynamic substrates.

[0064] 3. Infrared scanning test

[0065] The polyurethane coating prepared in Example 1 was subjected to infrared scanning test, and the results were as follows: Figure 3 As shown. Figure 3 It can be seen that at 1700cm -1 Thiocarbamate appears at 1730 cm -1 ), the sulfide bond (C=S) causes the absorption peak to shift slightly to a lower wave number. At 3350cm -1 The stretching vibration of carbamate (-NH) appeared at the cation, confirming the successful reaction of thiol with HDI.

[0066] 4. Anti-graffiti performance test

[0067] The anti-graffiti performance test of the polyurethane coatings prepared in Examples 1 and 2 was conducted. The specific process is as follows:

[0068] Graffiti with ketchup, coffee, oil-based marker, and ballpoint pen were placed on the surface of the polyurethane coating, and the graffiti was wiped off with a wet towel after being left there for one night. Figure 4 、 5 As shown. Among them, Figure 4 These are pictures of the polyurethane coating surface prepared in Example 1 before and after graffiti erasure, where A is before graffiti erasure and B is after graffiti erasure; Figure 5 These are pictures of the polyurethane coating surface prepared in Example 2 before and after graffiti erasure, where A is before graffiti erasure and B is after graffiti erasure.

[0069] from Figure 4 and Figure 5 A comparison revealed that the polyurethane coatings prepared in Examples 1 and 2 exhibited excellent anti-graffiti effectiveness against both ketchup and coffee. However, Example 1 exhibited significantly better anti-graffiti effectiveness against oil-based markers and ballpoint pens than Example 2. This is because the polythiol (40%) in the 6:4 ratio provides multifunctional crosslinking points (three -SH groups), forming a dense and uniform three-dimensional network. The bisthiothiol (60%) acts as a flexible spacer, balancing crosslink brittleness and avoiding localized stress concentration. This results in a denser coating surface, making it difficult for graffiti substances (such as inks and pigments) to penetrate. In contrast, the 8:3 ratio, due to the low polythiol ratio, results in insufficient crosslinking points and a loose network, allowing graffiti to easily penetrate micropores. Furthermore, an excessive amount of bisthiol groups may result in an excess of linear segments, reducing surface hardness.

[0070] 5. Other performances are shown in Table 1

[0071] Table 1 Other properties

[0072]

[0073] As can be seen from Table 1, the performance of Example 2 with a thiol ratio of 8:3 is weaker than that of Example 1 because the 8:3 ratio results in a lower crosslink density, which is determined by the functionality and ratio of the polythiol (a 6:4 system has denser crosslinks than an 8:3 system).

[0074] The performance of Example 3 is inferior to that of Example 1 because the 1:1 ratio of thiol systems (especially high-functionality polythiol) can lead to excessively high crosslink density, making the material brittle. The poor flexibility of thiourethane bonds further exacerbates brittleness; this increased brittleness leads to poor long-term water resistance.

[0075] The performance of Comparative Example 1 is inferior to that of Example 1 because the polymer is primarily linear. The dihydroxythiol has only two -SH groups, which react with HDI to form linear urethane segments lacking crosslinking points. The material is soft but weak, and has poor abrasion and solvent resistance.

[0076] The performance of Comparative Example 2 is worse than that of Example 1 because the reaction of polythiol and HDI generates an ultra-high cross-linking density network, which makes the material brittle (low impact strength). The excessively dense cross-linking points may cause microscopic stress concentration and easily generate microcracks.

[0077] The performance of Comparative Example 3 is inferior to that of Example 1 because the steric structure of GL1800 hinders contact between the -SH group and the -NCO group of HDI during the reaction between GL1800 and HDI, reducing the reaction rate. The high molecular weight causes the -SH group to be embedded within the chain segments, preventing complete reaction. While organotin catalysts are effective for small-molecule thiols, their catalytic efficiency may be reduced for high-molecular-weight polythiols.

[0078] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An anti-graffiti polyurethane coating, characterized in that: By weight, it is composed of the following components: 15-30 parts of bismercaptomercaptan, 5-30 parts of polythiol, 0.20-0.6 parts of catalyst, 20-55 parts of isocyanate; The molecular weight of the bis-mercaptothiol is 154.32; The molecular weight of the polythiol is 260.53-488.66; The molar ratio of the bis-mercaptothiol to the polythiol is (1-8): (1-4); Bis-mercaptothiol provides two -SH groups to form linear segments, which react with HDI to generate linear thiocarbamate segments, giving the coating a basic skeleton. Polythiol provides three -SH groups as crosslinking points, forming a three-dimensional crosslinked network with HDI. The mixture of bis-mercaptothiol and polythiol balances the toughness of the linear segments and the rigidity of the crosslinking points. The preparation method of the anti-graffiti polyurethane coating comprises the following steps: mixing dithiol mercaptan and polythiol, adding a catalyst and heating; and then adding isocyanate and reacting to obtain the coating.

2. The anti-graffiti polyurethane coating according to claim 1, characterized in that: The invention is composed of the following components in parts by weight: 16-30 parts of bismercaptan, 6-26.3 parts of polythiol, 0.22-0.52 parts of catalyst and 23.1-53.9 parts of isocyanate.

3. The anti-graffiti polyurethane coating according to claim 1, characterized in that: By weight, it is composed of the following components: 30 parts of bismercaptomercaptan, 12 parts of polythiol, 0.42 parts of catalyst, 44.1 parts of isocyanate; The molecular weight of the polythiol is 260.

53.

4. The anti-graffiti polyurethane coating according to claim 1, characterized in that: The catalyst is one or more of triethylenediamine, triethylamine, NN-dimethylethanolamine, trimethylbenzylamine, NN-dimethylcyclohexylamine, dibutyltin dilaurate and succinic acid; The isocyanate is one or more of diphenylmethane diisocyanate, isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, vinyl diisocyanate, tetramethylene 1,4-diisocyanate, dodecyl 1,2-diisocyanate and 3,3-dichloro-4,4-biphenyl diisocyanate.

5. A method for preparing the anti-graffiti polyurethane coating according to any one of claims 1 to 4, characterized in that: The following steps are involved: The dimercaptan and the polythiol are mixed, a catalyst is added, and the mixture is heated; and then isocyanate is added and reacted to obtain the product.

6. The method for preparing the anti-graffiti polyurethane coating according to claim 5, characterized in that: The mixing molar ratio of the bis-mercaptothiol and the polythiol is (1-8): (1-4); The heating is performed at 60-70° C. for 3-6 minutes; The reaction is carried out at 60-70°C for 2-4 hours.

7. An anti-graffiti polyurethane coating made from the anti-graffiti polyurethane coating according to any one of claims 1 to 4.

8. A method for preparing an anti-graffiti polyurethane coating, characterized in that: The anti-graffiti polyurethane coating according to any one of claims 1 to 4 is coated on a substrate and cured in stages to obtain the anti-graffiti polyurethane coating.

9. The method for preparing the anti-graffiti polyurethane coating according to claim 8, characterized in that: The coating method is one of scraping, spraying and dipping; The staged curing is first curing at 60-70° C. for 3-5 hours and then standing at room temperature for 20-30 hours.

10. Use of the anti-graffiti polyurethane coating according to claim 7 in synthetic leather and leather.

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