Anti-doodling polyurethane coating, coating and preparation method and application of anti-doodling polyurethane coating

Abstract

The invention belongs to the technical field of polyurethane coatings and coatings, and particularly relates to an anti-doodling polyurethane coating, a coating as well as a preparation method and application of the anti-doodling polyurethane coating, and the anti-doodling polyurethane coating comprises the following components in parts by weight: 15-30 parts of dimercaptomercaptan, 5-30 parts of polymercaptan, 0.20-0.6 part of a catalyst and 20-55 parts of isocyanate. The molecular weight of the dimercapto mercaptan is 154.32; and the molecular weight of the polymercaptan is 260.53. Polyurethane is prepared through reaction of dimercaptomercaptan, polymercaptan and isocyanate, the adhesion performance and anti-doodling performance of polyurethane on the surface of synthetic leather / leather are remarkably improved, industrial production is easy, and wide application prospects and market value are achieved.

Description

Technical Field

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

[0002] Coating is an essential key process in the manufacturing process of leather and synthetic leather. The coating can not only endow leather and synthetic leather with a beautiful appearance, but also significantly improve their functionality, such as abrasion resistance, chemical resistance, waterproofness, breathability, and hand feeling. The functionality of the coating depends on the bonding strength between the coating material and the substrate (synthetic leather or leather), that is, adhesion. If the adhesion between the coating and the substrate is insufficient, the coating is prone to peeling, falling off, blistering, damage due to friction or bending, etc., resulting in damage to the product appearance and failure of functions, directly affecting the product life. Good adhesion can ensure that the coating provides a complete and comfortable hand feeling and durable performance during long-term use.

[0003] Polyurethane coating is a coating material applied in the manufacturing process of leather and synthetic leather. However, in traditional organic solvent-based polyurethane coatings, there are problems such as complex preparation processes and emissions of volatile organic compounds (VOCs), which are harmful to the environment, human health, and substrate properties. In the prior art, although water is used instead of organic solvents as a dispersant to prepare a new polyurethane system such as waterborne polyurethane, it has poor water resistance, low adhesion, is prone to moisture absorption, and is easy to fall off after repeated friction, especially when it has been contaminated by various graffiti or stains, corroded by corrosive substances, etc., resulting in damage to the coating. Summary of the Invention

[0004] The purpose of the present invention is to provide an anti-graffiti polyurethane coating, a coating, and a preparation method and application thereof, so as to overcome the deficiencies of the prior art. In the present invention, polyurethane is prepared by reacting bis-mercapto thiol, polythiol, and isocyanate, which significantly improves the adhesion performance and anti-graffiti property of polyurethane on the surface of synthetic leather / leather, is easy to industrialize, and has broad application prospects and market value.

[0005] The overall inventive concept adopted by the present invention is: The present invention aims to solve the problems that the polyurethane coating on existing synthetic leather and leather products is easy to fall off, difficult to clean, and has poor stain resistance, especially when dealing with common pollution sources such as coffee, oil-based pens, and ketchup, it is difficult for traditional coatings to achieve effective protection and rapid removal. Although waterborne polyurethane is environmentally friendly, its film structure is loose, water absorption is strong, and its anti-fouling ability is insufficient; while the solvent-based system has certain properties, but there are VOC emission problems, which are not conducive to green production.

[0006] The present invention provides a solvent-free anti-graffiti polyurethane coating and a coating system. The coating uses bis(mercaptomethyl) sulfide and polythiol as the main reaction components, which react with polyfunctional isocyanate in the presence of a catalyst to form a polyurethane network with a high crosslinking density. The mercapto group can preferentially form a thiocarbamate structure (-NH-C(=S)-O-) with the -NCO group during the reaction, and this structure has better chemical stability and anti-permeability than ordinary urethane bonds. At the same time, by adjusting the molar ratio of bis(mercaptomethyl) sulfide to polythiol, a good balance can be achieved between rigid crosslinking and flexible segments, endowing the coating with good mechanical properties and crack resistance. The coating can be applied to the surface of leather or synthetic leather substrates by scraping, spraying or dipping, and a dense and stable polyurethane coating film can be formed by staged thermal curing (for example, thermal curing at 65 °C for 35 hours and then standing at room temperature for 20 - 30 hours). The thermal curing process helps to promote the complete crosslinking of the three-dimensional network, and at the same time eliminates residual stress, improving the adhesion and flexibility of the coating.

[0007] To achieve the above object, the technical solution of the present invention is as follows: In the first aspect, the present invention provides an anti-graffiti polyurethane coating, which is composed of the following components by weight: 15 - 30 parts of bis(mercaptomethyl) sulfide, 5 - 30 parts of polythiol, 0.20 - 0.6 part of catalyst, 20 - 55 parts of isocyanate; The molecular weight of the polythiol is 260.53 - 488.66.

[0008] In some other embodiments, it is composed of the following components by weight: 16 - 30 parts of bis(mercaptomethyl) sulfide, 6 - 26.3 parts of polythiol, 0.22 - 0.52 part of catalyst, 23.1 - 53.9 parts of isocyanate; The molecular weight of the bis(mercaptomethyl) sulfide is 154.32; The molecular weight of the polythiol is 260.53 - 398.56; The molar ratio of the bis(mercaptomethyl) sulfide to the polythiol is (1 - 8):(1 - 4).

[0009] In some other embodiments, it is composed of the following components by weight: 30 parts of bis(mercaptomethyl) sulfide, 12 parts of polythiol, 0.42 part of catalyst, 44.1 parts of isocyanate; The molecular weight of the bis(mercaptomethyl) sulfide is 154.32; The molecular weight of the polythiol is 260.53; The molar ratio of the bis(mercaptomethyl) sulfide to the polythiol is 6:4.

[0010] In some other embodiments, the catalyst is one or more of triethylenediamine, triethylamine, N-N-dimethylethanolamine, trimethylbenzylamine, N-N-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.

[0011] In a second aspect, the present invention provides a method for preparing the anti-graffiti polyurethane coating described in the first aspect, comprising the following steps: Mix the bis-mercapto thiol and polythiol, add the catalyst and then heat; then add the isocyanate and react to obtain the product.

[0012] In some other embodiments, the mixing molar ratio of the bis-mercapto thiol to the polythiol is (1-8):(1-4); The heating is carried out at 60-70 °C for 3-6 minutes; The reaction is carried out at 60-70 °C for 2-4 hours.

[0013] The reaction mechanism of the anti-graffiti polyurethane coating involves nucleophilic addition reaction and the formation of a crosslinked network. Specifically: the bis-mercapto thiol provides two mercapto groups to form a linear segment; the polythiol provides three -SH groups as crosslinking points; the mixing ratio of the bis-mercapto thiol and the polythiol balances the crosslinking density and flexibility. The organotin catalyst accelerates the reaction of -SH with -NCO, and the heating condition activates the proton dissociation of thiol (-SH) to generate a more nucleophilic thiolate (-S⁻). The specific reaction process is as follows: R-SH + -R'-N=C=O → R-S-C(=O)-NH-R' The core of this reaction mechanism is the attack of thiol (-SH) on isocyanate (-NCO) to achieve the nucleophilic addition of thiol to isocyanate and form a thiocarbamate crosslinked network. By regulating the catalyst, temperature, and functionality ratio, the coating properties (such as the abrasion resistance and water resistance of the anti-graffiti coating) can be optimized.

[0014] In a third aspect, the present invention provides an anti-graffiti polyurethane coating made of the anti-graffiti polyurethane coating described in the first aspect.

[0015] In a fourth aspect, the present invention provides a method for preparing an anti-graffiti polyurethane coating, which is obtained by coating the anti-graffiti polyurethane coating described in the first aspect on a substrate and subjecting it to staged curing.

[0016] In some other embodiments, the coating method is one of knife coating, spraying, and dip coating; The step curing is to first cure at 60 - 70 °C for 3 - 5 h, and then leave it to stand at room temperature for 20 - 30 h.

[0017] In a fifth aspect, the present invention provides the application of the anti - graffiti polyurethane coating described in the third aspect in synthetic leather and leather.

[0018] Advantages of the present invention: The coating prepared by the present invention has the following excellent properties: (1) Excellent anti - graffiti performance: After the leather surface is contaminated with oil - based pens, ballpoint pens, coffee, etc., it can be easily wiped off with a wet towel without leaving a residue; (2) Good adhesion and abrasion resistance: The coating remains intact after 6500 rounds of abrasion under TABER test; (3) Coexistence of thermal stability and low Tg characteristics: The glass transition temperature (Tg) is about 35 °C, showing high elasticity and a compliant feel at room temperature; (4) Excellent environmental protection and industrial adaptability: The whole formulation does not contain solvents, is suitable for green manufacturing processes, and can directly replace traditional solvent - based coating materials on synthetic leather production lines. In summary, the present invention constructs a polyurethane coating system that simultaneously has anti - graffiti properties, high adhesion strength, good flexibility, and excellent environmental protection, and is suitable for surface functionalization of various flexible substrates such as high - end synthetic leather, genuine leather, and elastic membranes, and has good industrialization prospects. Description of the Drawings

[0019] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0020] Figure 1 It is a physical picture of the polyurethane coating prepared in Example 1 of the present invention before and after abrasion. Among them, A is before abrasion, and B is after abrasion; Figure 2 It is a differential scanning calorimetry spectrum of the polyurethane coating prepared in Example 1 of the present invention; Figure 3 It is an infrared scan of the polyurethane coating prepared in Example 1 of the present invention; Figure 4 It is a picture of the polyurethane coating surface prepared in Example 1 of the present invention before and after graffiti erasure. Among them, A is before graffiti erasure, and B is after graffiti erasure; Figure 5 It is a picture of the polyurethane coating surface prepared in Example 2 of the present invention before and after graffiti erasure. Among them, A is before graffiti erasure, and B is after graffiti erasure. Detailed Embodiments

[0021] Those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention. For the examples where specific conditions are not indicated, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the components whose manufacturers are not indicated, they are all conventional products available commercially.

[0022] Example 1. After mixing 30 g of dimercaptothiol (molecular weight 154.32) and 12 g of polythiol (molecular weight 260.53) (molar ratio 6:4), 0.42 g of dibutyltin dilaurate catalyst was added, and then heated at 65 °C for 5 min. Then 44.1 g of HDI was added. After mixing, it was added into a reaction kettle and reacted at 65 °C for 2.5 h to obtain a polyurethane coating. The polyurethane coating was scraped on the leather surface with a stainless steel scraper (scraping speed 15 cm / s at a uniform speed, scraping angle 50°, coating thickness 100 μm). Stepwise curing was adopted, that is, first reacted at 65 °C for 4 h, and then left standing at room temperature for 24 h to obtain a polyurethane coating.

[0023] Example 2 After mixing 16 g of dimercaptothiol (molecular weight 154.32) and 6 g of polythiol (molecular weight 260.53) (molar ratio 8:3), 0.22 g of dibutyltin dilaurate catalyst was added, and then heated at 65 °C for 5 min. Then 23.1 g of HDI was added. After mixing, it was added into a reaction kettle and reacted at 65 °C for 2.5 h to obtain a polyurethane coating. The polyurethane coating was scraped on the leather surface with a stainless steel scraper (scraping speed 15 cm / s at a uniform speed, scraping angle 45°, coating thickness 100 μm). Stepwise curing was adopted, that is, first reacted at 65 °C for 4 h, and then left standing at room temperature for 24 h to obtain a polyurethane coating.

[0024] Example 3 After mixing 25 g of dimercaptothiol (molecular weight 154.32) and 26.3 g of polythiol (molecular weight 260.53) (molar ratio 1:1), 0.513 g of dibutyltin dilaurate catalyst was added, and then heated at 65 °C for 5 min. Then 53.865 g of HDI was added. After mixing, it was added into a reaction kettle and reacted at 65 °C for 2 - 4 h (specific time 2.5 h) to obtain a polyurethane coating. The polyurethane coating was sprayed on the leather surface (spraying speed 0.5 m / s at a uniform speed, spraying pressure 100 MPa, coating thickness 100 μm). Stepwise curing was adopted, that is, first reacted at 65 °C for 4 h, and then left standing at room temperature for 24 h to obtain a polyurethane coating.

[0025] Comparative Example 1 After adding 25 g of dimercaptothiol (molecular weight 154.32) and 0.513 g of dibutyltin dilaurate catalyst, heat at 65 °C for 5 min, then add 53.865 g of HDI. After mixing, add it to the reaction kettle and react at 65 °C for 2 - 4 hours (specific time 2.5 h) to obtain the polyurethane coating. Spray the polyurethane coating on the leather surface (spraying speed is uniform at 0.5 m / s, spraying pressure is 100 MPa, coating thickness is 100 μm). Adopt step curing, that is, react at 65 °C for 4 h first, and then stand at room temperature for 24 h to obtain the polyurethane coating.

[0026] Comparative Example 2 After adding 26.3 g of polythiol (molecular weight 260.53) and 0.513 g of dibutyltin dilaurate catalyst, heat at 65 °C for 5 min, then add 53.865 g of HDI. After mixing, add it to the reaction kettle and react at 65 °C for 2 - 4 hours (specific time is 2.5 h) to obtain the polyurethane coating. Spray the polyurethane coating on the leather surface (spraying speed is uniform at 0.5 m / s, spraying pressure is 100 MPa, coating thickness is 100 μm). Adopt step curing, that is, react at 65 °C for 4 h first, and then stand at room temperature for 24 h to obtain the polyurethane coating.

[0027] Comparative Example 3 After mixing 24.586 g of polythiol GL1800 and 29.44 g of HDI, add them to the reaction kettle, dropwise add 0.54 g of dibutyltin dilaurate catalyst, and react at 65 °C for 3 hours to obtain the polyurethane coating. Use a stainless steel spatula to scrape the polyurethane coating on the leather surface (scraping speed is uniform at 15 cm / s, scraping angle is 50°, coating thickness is 100 μm). Adopt step curing, that is, react at 65 °C for 4 h first, and then stand at room temperature for 24 h to obtain the polyurethane coating.

[0028] Performance Test 1. Abrasion resistance test: Under room temperature conditions, use a TABER abrasion resistance tester (manufacturer: Hongtu High-tech Development Zone, Nancheng District, Dongguan City, Guangdong Province; model: GT7012-T) to conduct an abrasion resistance test on the polyurethane coating prepared in Example 1. The results are as Figure 1 shown, where A is before abrasion and B is after abrasion.

[0029] Figure 1 In Figure B of Figure 1 the bright circular area is the area formed after grinding the polyurethane coating 6500 times. The hole in the middle is caused by fixing A in Figure 1As can be seen from A and B in [reference], the polyurethane coatings before and after grinding are smooth and uniform. This is because the bis-mercapto thiol provides two -SH groups, which react with HDI to form linear thiocarbamate chain segments, giving the coating a basic skeleton. The thiol groups contained in the polythiol form a three-dimensional crosslinked network with HDI, significantly increasing the crosslinking density. After the bis-mercapto thiol and polythiol are mixed at a molar ratio of 6:4, the linear chain segments (toughness) and crosslinking points (rigidity) are balanced, avoiding excessive brittleness of pure polythiol or excessive softness of pure bis-mercapto thiol; the increased crosslinking density inhibits the slippage of molecular chains, thereby improving the wear resistance.

[0030] 2. Differential Scanning Calorimetry Test The polyurethane coating prepared in Example 1 was tested by differential scanning calorimetry. The test temperature was -50 - 220 °C, the atmosphere was nitrogen, and the heating rate was 10 °C / min. The results are as Figure 2 shown. As can be seen from Figure 2 this, the glass transition temperature Tg of the cured coating is 35.38 °C, indicating that the material changes from the glassy state to the high elastic state near room temperature. The low Tg coating remains flexible at low temperatures and is suitable for dynamic substrates.

[0031] 3. Infrared Scanning Test The polyurethane coating prepared in Example 1 was tested by infrared scanning. The results are as Figure 3 shown. As can be seen from Figure 3 this, the thiocarbamate appearing at 1700 cm -1 is different from ordinary polyurethane (C=O at 1730 cm -1 ). The thiocarbonyl bond (C=S) shifts the absorption peak slightly to lower wavenumbers. The stretching vibration of carbamate (-NH) appears at 3350 cm -1 , confirming the successful reaction of thiol with HDI.

[0032] 4. Anti-Graffiti Performance Test The anti-graffiti performance of the polyurethane coatings prepared in Examples 1 and 2 was tested. The specific process is as follows: Ketchup, coffee, oil-based marker, and ballpoint pen were respectively scribbled on the surface of the polyurethane coating. After standing overnight, the scribbles were wiped with a wet towel. The results are as Figure 4 , 5 shown. Among them, Figure 4 are the pictures of the scribbles on the surface of the polyurethane coating prepared in Example 1 before and after being wiped off. Among them, A is before the scribbles are wiped off, and B is after the scribbles are wiped off; Figure 5 are the pictures of the scribbles on the surface of the polyurethane coating prepared in Example 2 before and after being wiped off. Among them, A is before the scribbles are wiped off, and B is after the scribbles are wiped off.

[0033] As can be seen from Figure 4 and Figure 5It was found by comparison that the polyurethane coatings prepared in Example 1 and Example 2 had good anti-graffiti effects on ketchup and coffee; however, the anti-graffiti effect of Example 1 on oil-based markers and ballpoint pens was significantly better than that of Example 2. This is because the polythiol (40%) in the 6:4 ratio system provides multi-functional crosslinking points (3 -SH), forming a high-density and uniform three-dimensional network. The bis-mercapto thiol (60%) acts as a flexible spacer to balance the crosslinking brittleness and avoid local stress concentration. The coating surface is denser, and it is difficult for graffiti substances (such as inks and pigments) to penetrate. In the 8:3 system, due to the too low proportion of polythiol, there are insufficient crosslinking points, the network is loose, and graffiti is easy to penetrate into the micropores. And the excessive amount of bis-mercapto may lead to too many linear segments, reducing the surface hardness. 5. Other properties are shown in Table 1 Table 1 Other properties

[0034] It can be seen from Table 1 that 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 crosslinking density, and the crosslinking density is determined by the functionality and ratio of polythiol (the 6:4 system has a denser crosslinking than 8:3).

[0035] The performance of Example 3 is worse than that of Example 1 because the thiol system with a 1:1 ratio (especially the high-functional polythiol) may lead to too high a crosslinking density, making the material brittle. The thio-carbamate bond has poor flexibility, further exacerbating the brittleness; with high brittleness, the long-term water resistance is poor.

[0036] The performance of Comparative Example 1 is worse than that of Example 1 because it is mainly composed of linear polymers, and the bis-hydroxy thiol has only 2 -SH, reacting with HDI to form linear urethane segments, lacking crosslinking points. The material is soft but has low strength, poor wear resistance and solvent resistance.

[0037] The performance of Comparative Example 2 is worse than that of Example 1 because the reaction of polythiol with HDI forms an ultra-high crosslinking density network, resulting in high brittleness of the material (low impact strength), and the over-dense crosslinking points may cause micro-stress concentration, easily generating micro-cracks.

[0038] The performance of Comparative Example 3 is worse than that of Example 1 because in the reaction of GL1800 with HDI, the spatial structure of GL1800 hinders the contact between -SH and the -NCO group of HDI, reducing the reaction rate. The high molecular weight causes -SH to be embedded inside the chain segments and cannot react completely. The organotin catalyst is effective for small molecule thiols, but the catalytic efficiency for high molecular weight polythiols may decrease.

[0039] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope 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 dithiol mercaptan, 5-30 parts of polythiol, 0.20-0.6 parts of catalyst, 20-55 parts of isocyanate; The molecular weight of the polythiol is 260.53-488.

66.

2. The anti-graffiti polyurethane coating according to claim 1, characterized in that: The composition is composed of the following components by weight: 16-30 parts of dithiol mercaptan, 6-26.3 parts of polythiol, 0.22-0.52 parts of catalyst, and 23.1-53.9 parts of isocyanate; The molecular weight of the dithiol mercaptan is 154.32; The molecular weight of the polythiol is 260.53-398.56; The molar ratio of the dithiothiol mercaptan to the polythiol is (1-8):(1-4).

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 dithiothiol mercaptan, 12 parts of polymercaptan, 0.42 parts of catalyst, 44.1 parts of isocyanate; The molecular weight of the dithiol mercaptan is 154.32; The molecular weight of the polythiol is 260.53; The molar ratio of the dithiothiol mercaptan to the polythiol is 6:

4.

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: After dithiothiol mercaptan and 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 dithiothiocarbyl mercaptan to 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 firstly 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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