Highly-transparent bio-based polyurethane fluoride-free antifouling coating as well as preparation method and application thereof

Abstract

The invention discloses a highly-transparent bio-based polyurethane fluoride-free antifouling coating and a preparation method and application thereof.The highly-transparent bio-based polyurethane fluoride-free antifouling coating is prepared by taking tannic acid (TA) as biological polyol, hexamethylene diisocyanate trimer (HDIT) as a cross-linking agent and monohydroxy polydimethylsiloxane (PDMS-OH) as a low-surface-tension material through thermocuring cross-linking, so that the highly-transparent bio-based polyurethane fluoride-free antifouling coating is prepared. And the tannic acid-based polyurethane fluoride-free antifouling coating is prepared. The coating shows up to 99% of optical transparency, has an ultraviolet shielding effect, and has excellent self-cleaning, anti-doodling and anti-artificial fingerprint pollution capabilities, and water, hexadecane, vegetable oil and pump oil easily slide off from the surface without traces. And even if the coating is repeatedly written and erased for 500 times, the coating still keeps excellent anti-graffiti performance. Due to the excellent adhesive force of the TA, the TA can be applied to various base materials. When the coating is bent and folded, the coating is still kept complete, the coating does not crack or peel off, and the coating has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to a highly transparent bio - based polyurethane fluorine - free antifouling coating, its preparation method and application, belonging to the technical field of polymer materials. Background Art

[0002] Polyurethane antifouling coatings are functional coatings prepared by polymer modification. The low surface energy of such coatings enables aqueous and oily liquids to easily slide off the surface without leaving marks. Polyurethane antifouling coatings also possess excellent properties such as self - cleaning and graffiti - proofing, and have wide applications in many fields, such as the self - cleaning of glass windows in high - rise buildings, medical utensils, solar panels, and graffiti - proof protection of public infrastructure, showing broad application potential. Currently, the preparation of polyurethane antifouling coatings still faces many challenges. To reduce the surface energy, fluorine - containing substances are usually used for modification, but such substances are expensive, and long - chain perfluorinated compounds are biotoxic and cumulative, which may pose potential threats to human health and the ecological environment. Secondly, traditional polyurethane coatings rely on polyols derived from fossil fuels. The over - exploitation of fossil fuels not only accelerates resource depletion but also has a significant negative impact on social economy and ecological environment, restricting their long - term application in the context of sustainable development. Therefore, developing an environmentally friendly, low - cost and efficient polyurethane antifouling coating has become an urgent problem to be solved, and also provides an important research opportunity for the design of bio - based coatings based on polyurethane.

[0003] Tannic acid (TA) is a natural polyphenolic compound widely present in the plant kingdom, especially common in plant tissues such as bark, leaves, fruits, and seeds. The phenolic hydroxyl groups of tannic acid can capture free radicals and terminate the oxidation chain reaction through hydrogen atom transfer or electron transfer. Its antioxidant ability is well - known in the fields of food, medicine, and material protection. Tannic acid interacts with other molecules (such as polyurethane, PDMS) through hydrogen bonds, π - π stacking, and ester bonds to form a stable network structure, enhancing the mechanical properties and adhesion of the coating.

[0004] Polydimethylsiloxane (PDMS) is a silicone - based organic silicon polymer whose molecular structure consists of alternating Si - O repeating units, which gives the polymer a high degree of rotational freedom. This allows the freely rotating methyl groups to migrate to the surface, generating a large amount of steric repulsion force. At room temperature, its surface tension is about 20 mN m -1 . In addition, compared with the C - O bond, the Si - O bond has a higher dissociation energy, making the PDMS molecular chain not easily broken, and having excellent thermal stability and chemical stability. PDMS also has good biocompatibility, moderate price, environmental friendliness and other characteristics.

[0005] In the literature (Jingtian Chen, Huanxian Yang, Yong Qian, et al. Translucent Lignin-Based Omniphobic Polyurethane Coating with Antismudge and UV-Blocking Dual Functionalities[J]. ACS Sustainable Chem. Eng. 2023, 11, 2613-2622.), pine kraft lignin was used as the polyol. After purification by processes such as alkali dissolution, filtration, acidification, and washing with deionized water, it was used. Hexamethylene diisocyanate trimer was used as the crosslinking agent, and a small amount of polydimethylsiloxane capped with monomethanol was used as the antifouling agent to prepare a polydimethylsiloxane-modified lignin-based polyurethane coating (lig-PU-PDMS). The prepared coating is a semi-transparent coating, showing dark brown, which limits its development in practical applications. Moreover, the previous polyol raw material lignin needs to be purified, and the process is complex and cumbersome. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, such as complex preparation, high cost, and insufficient transparency of antifouling coatings. The purpose of the present invention is to propose a simple method for preparing an antifouling coating, using inexpensive raw materials, following sustainable development, and being conducive to industrial production.

[0007] The present invention provides a highly transparent bio-based polyurethane fluorine-free antifouling coating, its preparation method and application. The bio-polyol raw material tannic acid can be directly used without further modification, providing an innovative direction for the development of green functional coatings.

[0008] The present invention provides a highly transparent bio-based polyurethane fluorine-free antifouling coating, its preparation method and application. The selected low surface tension material monohydroxy polydimethylsiloxane has excellent thermal stability and chemical stability, and also has good biocompatibility, moderate price, environmental friendliness, etc., meeting the long-term application under the background of sustainable development.

[0009] The purpose of the present invention is achieved through the following technical solutions.

[0010] A preparation method of a highly transparent bio-based polyurethane fluorine-free antifouling coating, comprising the following steps:

[0011] (1) Dissolve hexamethylene diisocyanate trimer (HDIT), monohydroxy polydimethylsiloxane (PDMS-OH) and dibutyltin dilaurate (DBTDL) in a solvent, and heat at 75 °C to 90 °C for 1 to 3 hours to obtain a prepolymer solution PDMS-HDIT;

[0012] (2) Dissolve tannic acid (TA) in a solvent to obtain a TA solution. Add the TA solution to the prepolymer solution PDMS-HDIT and heat it in the range of 75 °C to 90 °C for 1 to 3 hours to obtain a coating solution.

[0013] (3) Dilute the coating solution prepared above. Use the drop-coating method to drop the diluted solution on a glass slide and let it spread naturally. Then place it in the range of 120 °C to 140 °C for curing for 2 to 4 hours to obtain the bio-based polyurethane fluorine-free antifouling coating.

[0014] Further, the solvent in step (1) is one of DMF, methyl ethyl ketone, and propylene glycol methyl ether acetate.

[0015] Further, the solvent in step (2) is one of DMF, methyl ethyl ketone, and propylene glycol methyl ether acetate.

[0016] Further, in the coating solution in step (2), the mass ratio of TA to HDIT is 1.0 to 5.0 wt%.

[0017] Further, in step (3), DMF is used to dilute the coating solution, and the dilution ratio is 1:(1 - 3).

[0018] A highly transparent bio-based polyurethane fluorine-free antifouling coating obtained by the above preparation method has an optical transparency as high as 99%.

[0019] Due to the poor compatibility between PDMS-OH and HDIT, in order to avoid macroscopic phase separation, the present invention uses PDMS-OH and excessive HDIT to carry out a pre-reaction through the isocyanate-hydroxy reaction to generate PDMS-HDIT, ensuring that all PDMS-OH participate in the reaction, thereby avoiding macroscopic phase separation and ensuring the high transparency of the coating.

[0020] The application of the above-mentioned highly transparent bio-based polyurethane fluorine-free antifouling coating in the preparation of substrates such as high-transparency glass, screens, ceramics, and wooden wares.

[0021] The highly transparent bio-based polyurethane fluorine-free antifouling coating prepared by the present invention has excellent self-cleaning, anti-graffiti and anti-fingerprint contamination capabilities. The self-cleaning performance of the coating is based on the dynamic liquid-repellent property of the PDMS flexible chain and the surface synergistic effect of tannic acid, forming a liquid-like surface antifouling coating, reducing the adhesion force of water droplets and dust, and enabling the removal of pollutants under slight water flow or inclination. The polyphenol structure of tannic acid enhances the coating stability through a hydrogen bond network, ensuring the durability of the self-cleaning effect. Through the surface enrichment of the PDMS flexible polymer chain, a liquid-like dynamic interface is formed, which not only avoids the vulnerability of the rough structure of the superhydrophobic and superoleophobic coating, but also avoids the risk of lubricant loss in the smooth liquid-infused porous surface. It can not only effectively remove pollutants, but also inhibit the attachment of microorganisms, and is suitable for application scenarios requiring high transparency and biocompatibility.

[0022] The bio-based polyurethane fluorine-free antifouling coating described in the present invention exhibits an optical transparency of up to 99% and has an ultraviolet shielding effect. It has excellent self-cleaning, anti-graffiti and anti-fingerprint contamination capabilities. Water, hexadecane, vegetable oil and pump oil slide off the surface easily without leaving a trace. Even after 500 times of repeated writing and erasing, the coating still maintains its excellent anti-graffiti performance. Due to the excellent adhesion of TA, it can be applied to a variety of substrates. When bending and folding occur, the coating remains intact, and no cracks or peeling are observed in the coating, showing broad application prospects.

[0023] Compared with the existing technologies, the present invention has the following advantages:

[0024] (1) The bio-based polyurethane fluorine-free antifouling coating of the present invention uses the bio-based raw material tannic acid as a polyol. Tannic acid can be used directly without further modification, and the raw material price is low. Aiming at its natural renewable property, green reaction activity and multifunctional biological characteristics, it breaks through the bottleneck of traditional coatings using fossil resources and promotes sustainable development.

[0025] (2) The bio-based polyurethane fluorine-free antifouling coating of the present invention uses monohydroxy polydimethylsiloxane as the low surface energy material of the polyurethane coating. Not only based on its excellent hydrophobicity and durability given by chemical bonds, but also due to its environmental friendliness and biocompatibility, it effectively avoids the ecological risks of traditional fluorocarbon materials.

[0026] (3) In the preparation method of the present invention, the PDMS flexible polymer chain is introduced into the commercial resin matrix polyurethane, and a coating with liquid-like characteristics is formed through crosslinking and curing. It not only retains the low adhesion and dynamic wettability of the liquid-like surface, but also improves the mechanical strength of the coating through the crosslinking network, broadening the application scope.

[0027] (4) The bio-based polyurethane fluorine-free antifouling coating of the present invention has high transparency, is applicable to various substrates such as screens, woodware, glass, plastic plates, metals, stones, ceramics, etc., and has excellent antifouling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the synthesis route of PDMS-HDIT.

[0029] Figure 2 is the synthesis route for preparing the coating solution from TA and HDIT.

[0030] Figure 3 is a schematic diagram of the preparation process of the highly transparent bio-based polyurethane fluorine-free antifouling coating.

[0031] Figure 4 is the infrared spectrum of the coating in Example 1.

[0032] Figure 5 is the XPS analysis of the coating in Example 1.

[0033] Figure 6 is the contact angle (a) and rolling angle (b) of the coating in Example 1 with water and hexadecane.

[0034] Figure 7 is the ultraviolet transmittance of the coating in Example 1.

[0035] Figure 8 is the dynamic screenshot of the sliding of typical liquids on a coated glass slide (Example 1) and a blank glass slide.

[0036] Figure 9 is the test effect diagram of the self-cleaning performance of the coating in Example 1.

[0037] Figure 10 is the ink shrinkage image of the coating in Example 1 after 100, 200, 300, 400, and 500 writing and erasing cycles.

[0038] Figure 11 is the test effect diagram of the mechanical properties of the coating in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some representative embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0040] The reaction routes for preparing the prepolymer solution PDMS-HDIT in the following Examples 1 to 5 are as Figure 1As shown, the reaction route for preparing the coating solution is as Figure 2 shown.

[0041] Figure 3 It is a schematic diagram of the preparation process of a highly transparent bio-based polyurethane non-fluorinated antifouling coating. A small amount of low surface tension material PDMS-OH needs to be introduced into the antifouling coating to improve its antifouling performance. To prevent macroscopic phase separation, PDMS-OH first undergoes a pre-reaction with an excess of HDIT to form stable covalent urethane bonds, ensuring that PDMS-OH is firmly grafted onto the HDIT polyurethane network and achieving complete reaction of PDMS-OH. The pre-reacted PDMS-HDIT is further reacted with TA. The multi-hydroxyl structure of TA can efficiently crosslink with isocyanate to form a polyurethane network. The obtained coating solution is thermally cured on the substrate to form an antifouling coating with a high degree of crosslinking. The high degree of crosslinking not only enhances the mechanical strength and wear resistance of the coating but also improves its chemical corrosion resistance, enabling the coating to maintain a stable antifouling effect.

[0042] Example 1

[0043] This example provides a highly transparent bio-based polyurethane non-fluorinated antifouling coating, and the preparation method includes the following steps:

[0044] (1) Dissolve 200 mg of HDIT, 2.7 mg of PDMS-OH, and 10 mg of DBTDL in 1.0 mL of butanone, and heat at 75 °C for 1 hour to obtain a prepolymer solution PDMS-HDIT;

[0045] (2) Dissolve 350 mg of TA in 10 mL of DMF to prepare a TA solution with a concentration of 0.035 g / mL. Add 2 mL of the TA solution to the prepolymer solution PDMS-HDIT, and heat at 75 °C for 1 hour to obtain a coating solution, and prepare a coating solution with a PDMS-OH mass fraction of 1.0 wt%. The mass fraction is the ratio of PDMS-OH to the total mass of TA and HDIT;

[0046] (3) Dilute the above-prepared coating solution with DMF, and the dilution ratio is 1:1. Use the drop-coating method to drop the diluted solution on a glass slide and let it spread naturally, and then cure it at 120 °C for 2 hours. The preparation process of the antifouling coating is as Figure 3 shown, and the corresponding cured coating is named TA-g-PDMS 1.0 .

[0047] Example 2

[0048] This example provides a highly transparent bio-based polyurethane non-fluorinated antifouling coating, and the preparation method includes the following steps:

[0049] (1) Dissolve 100 mg of HDIT, 2.7 mg of PDMS-OH, and 10 mg of DBTDL in 1.0 mL of methyl ethyl ketone, and heat at 75 °C for 1 hour to obtain a prepolymer solution PDMS-HDIT;

[0050] (2) Dissolve 350 mg of TA in 10 mL of DMF to prepare a TA solution with a concentration of 0.035 g / mL. Add 1 mL of the TA solution to the prepolymer solution PDMS-HDIT, and heat at 75 °C for 1 hour to obtain a coating solution, and prepare a coating solution with a PDMS-OH mass fraction of 2.0 wt%, where the mass fraction is the ratio of PDMS-OH to the total mass of TA and HDIT.

[0051] (3) Dilute the above-prepared coating solution with DMF at a dilution ratio of 1:1. Use the drop-coating method to drop the diluted solution on a glass slide, let it spread naturally, and then cure it at 120 °C for 2 hours. The preparation process of the antifouling coating is as Figure 3 shown, and the corresponding cured coating is named TA-g-PDMS 2.0 .

[0052] Example 3

[0053] This example provides a highly transparent bio-based polyurethane fluorine-free antifouling coating, and the preparation method includes the following steps:

[0054] (1) Dissolve 100 mg of HDIT, 4.1 mg of PDMS-OH, and 10 mg of DBTDL in 1.0 mL of methyl ethyl ketone, and heat at 75 °C for 1 hour to obtain a prepolymer solution PDMS-HDIT;

[0055] (2) Dissolve 350 mg of TA in 10 mL of DMF to prepare a TA solution with a concentration of 0.035 g / mL. Add 1 mL of the TA solution to the prepolymer solution PDMS-HDIT, and heat at 75 °C for 1 hour to obtain a coating solution, and prepare a coating solution with a PDMS-OH mass fraction of 3.0 wt%, where the mass fraction is the ratio of PDMS-OH to the total mass of TA and HDIT;

[0056] (3) Dilute the above-prepared coating solution with DMF at a dilution ratio of 1:1. Use the drop-coating method to drop the diluted solution on a glass slide, let it spread naturally, and then cure it at 120 °C for 2 hours. The preparation process of the antifouling coating is as Figure 3 shown, and the corresponding cured coating is named TA-g-PDMS 3.0 .

[0057] Example 4

[0058] This example provides a highly transparent bio-based polyurethane fluorine-free antifouling coating, and the preparation method includes the following steps:

[0059] (1) Dissolve 100 mg of HDIT, 5.4 mg of PDMS-OH and 10 mg of DBTDL in 1.0 mL of methyl ethyl ketone, and heat at 75 °C for 1 hour to obtain a prepolymer solution PDMS-HDIT;

[0060] (2) Dissolve 350 mg of TA in 10 mL of DMF to prepare a TA solution with a concentration of 0.035 g / mL. Add 1 mL of the TA solution to the prepolymer solution PDMS-HDIT, and heat at 75 °C for 1 hour to obtain a coating solution, and prepare a coating solution with a PDMS-OH mass fraction of 4.0 wt%, where the mass fraction is the ratio of PDMS-OH to the total mass of TA and HDIT.

[0061] (3) Dilute the above-prepared coating solution with DMF at a dilution ratio of 1:1. Use the drop-coating method to drop the diluted solution on a glass slide, let it spread naturally, and then cure it at 120 °C for 2 hours. The preparation process of the antifouling coating is as Figure 3 shown, and the corresponding cured coating is named TA-g-PDMS 4.0 .

[0062] Example 5

[0063] This example provides a highly transparent bio-based polyurethane fluorine-free antifouling coating, and the preparation method includes the following steps:

[0064] (1) Dissolve 100 mg of HDIT, 6.8 mg of PDMS-OH and 10 mg of DBTDL in 1.0 mL of methyl ethyl ketone, and heat at 75 °C for 1 hour to obtain a prepolymer solution PDMS-HDIT;

[0065] (2) Dissolve 350 mg of TA in 10 mL of DMF to prepare a TA solution with a concentration of 0.035 g / mL. Add 1 mL of the TA solution to the prepolymer solution PDMS-HDIT, and heat at 75 °C for 1 hour to obtain a coating solution, and prepare a coating solution with a PDMS-OH mass fraction of 5.0 wt%, where the mass fraction is the ratio of PDMS-OH to the total mass of TA and HDIT.

[0066] (3) Dilute the above-prepared coating solution with DMF at a dilution ratio of 1:1. Use the drop-coating method to drop the diluted solution on a glass slide, let it spread naturally, and then cure it at 120 °C for 2 hours. The preparation process of the antifouling coating is as Figure 3 shown, and the corresponding cured coating is named TA-g-PDMS 5.0。

[0067] Performance testing and result analysis;

[0068] The following performance tests were conducted on the polyurethane antifouling coating prepared in Example 1 as the experimental object.

[0069] 1. Infrared spectroscopy test

[0070] The reaction between the isocyanate group of hexamethylene diisocyanate trimer (HDIT) and the hydroxyl group of monohydroxy polydimethylsiloxane (PDMS-OH) was monitored by infrared spectroscopy. As shown in (a) of Figure 4 , the characteristic peaks at 1261 cm -1 and 803 cm -1 proved the existence of Si-CH3, and the characteristic peak at 1025 cm -1 indicated the existence of Si-O-Si. These absorption peaks proved the successful introduction of monohydroxy polydimethylsiloxane (PDMS-OH). The PDMS-HDIT obtained from the pre-reaction was further reacted with tannic acid (TA), and the resulting infrared spectrum is shown in (b) of Figure 4 . The absorption peak at 1683 cm -1 was attributed to the vibration of polyurethane C=O, indicating the successful preparation of the polyurethane coating. The isocyanate peak at 2270 cm -1 did not completely disappear, and the isocyanate group still existed, and it might react with impurities and moisture in the air during the subsequent curing process.

[0071] 2. X-ray photoelectron spectroscopy test

[0072] X-ray photoelectron spectroscopy was used to further verify the chemical element composition of the TA-g-PDMS 1.0 coating. As shown in Figure 5 , the characteristic peaks of Si 2s and Si 2p were detected, and the silicon content was 6.61%. The XPS results confirmed the presence of a large amount of PDMS on the surface of the TA-g-PDMS 1.0 coating. PDMS migrated from the inside of the coating to the surface during the curing process, causing the silicon element to enrich on the surface. PDMS can reduce the surface energy of the coating and provide antifouling effect for the coating.

[0073] 3. Contact angle and rolling angle test

[0074] The test liquids are water and hexadecane. Ensure the surface of the coated sample is clean. Fix the sample on the test bench and adjust its position so that it is in the middle of the camera. The droplet volume for the static contact angle test is 5.0 μL. Measure the contact angle three times at different positions on the sample and take the average value. The volume of water for the rolling angle test is 30.0 μL, and the volume of hexadecane is 15.0 μL. Measure the rolling angle three times at different positions on the sample and take the average value. The results are as Figure 6 shown. The contact angles of water and hexadecane for the coating without PDMS are both very low. Hexadecane will wet and contaminate the surface, and neither of these two liquids can slide on this coating. After introducing PDMS-OH, it can be found that for the TA-g-PDMS 1.0 coating, the contact angles and rolling angles of water and hexadecane on the surface change significantly. Both water and hexadecane can slide down the coating surface without leaving a trace, further proving that the introduction of PDMS can provide anti-fouling performance for the coating. Further increasing the content of PDMS-OH, the contact angles of water and hexadecane increase gently with the increase of PDMS content, and the rolling angle decreases with the increase of PDMS content.

[0075] 4. Coating transparency test

[0076] Using a blank glass slide as the background, measure the optical transmittance of the coating. Measure the optical transmittance three times at different positions on the sample. As Figure 7 shown, the optical transparency of the glass slide with the coating is as high as 99% at 550 nm. The QR code placed behind the glass slide with the coating is clearly visible. Compared with the coating without PDMS, the coating containing PDMS has higher transparency. This difference may be that the surface morphology of the coating affects the scattering of light. A smooth surface allows light to pass through with minimal scattering, while a rough surface leads to enhanced scattering and reduced transparency. The low surface energy of PDMS causes it to migrate to the surface during film formation, thus producing a smoother surface and increasing transparency by reducing light scattering. On the contrary, the coating without PDMS has a rougher surface, resulting in more light scattering.

[0077] 5. Self-cleaning test of the coating

[0078] Test the sliding behavior of four liquids on the glass slide with the coating and the blank glass slide. The four liquids are water (dyed blue with blue ink), hexadecane (dyed red with oil red), olive oil, and pump oil. Drop the four liquids on the inclined surface of the glass slide and observe the sliding behavior of the droplets. The results are as Figure 8 shown. The sliding times of the four liquids are different, but all of them slide down without leaving a trace on the glass slide with the TA-g-PDMS 1.0 coating, while obvious traces appear when the four liquids slide down on the blank glass slide. Pump oil is very difficult to clean in daily life. It takes 24 seconds to slide down on the blank glass slide, but on the glass slide containing TA-g-PDMS 1.0It only takes 13 seconds for the coating to slide off the glass slide without leaving a sliding mark. This is because the introduction of PDMS provides the coating with a low surface energy, so the coating has excellent anti-fouling performance. Methyl red powder is used to simulate pollutants. The powder is dispersed on the surface of the inclined glass slide with the coating, and the sliding behavior of the powder after being rinsed with water (dyed blue) is observed. As Figure 9 shown, the methyl red powder slides off with the sliding water droplets, leaving no residue of water and methyl red powder on the coating surface. This is based on the dynamic liquid-repellent property of the PDMS flexible chain and the surface synergistic effect of tannic acid, forming a liquid-like surface anti-fouling coating, reducing the adhesion force of the methyl red powder, and making it slide off with the sliding water droplets, which confirms that the coating has self-cleaning performance.

[0079] 6. Anti-graffiti performance test of the coating

[0080] Multiple writing and erasing cycles are carried out on the TA-g-PDMS coating to evaluate its long-term ink resistance. Use an oil-based marker to write on the coating, and then wipe it with a lint-free lens paper. This is one cycle. As Figure 10 shown, after 100, 200, 300, 400, and 500 cycles, the ink on the coating still continuously shrinks into discrete droplets, and the ink marks can be easily removed after wiping with a lint-free lens paper. The coating can still maintain its excellent ink resistance after repeated writing and erasing, showing good durability.

[0081] 7. Mechanical property test of the coating

[0082] In addition to the glass substrate, the coating prepared by the present invention can also be extended to the field of metal surface treatment, such as tinplate and aluminum sheets. The anti-graffiti performance of the coating on tinplate and aluminum sheets is tested. As Figure 11 shown in (a) of, it is observed that obvious ink marks will still be left on the tinplate and aluminum sheets without the coating after wiping the ink with a lint-free lens paper, while on the tinplate and aluminum sheets with the coating, the ink will shrink, and the ink marks can be easily removed after wiping with a lint-free lens paper. The anti-graffiti effect is the same as that of the glass slide, indicating that the coating has a certain universality. The coating often bends and folds during use. When bending and folding occur, the coating still remains intact, without cracks or peeling. Use an oil-based marker to apply marks at the folds of the bent and folded parts. The ink shrinks significantly, and the ink marks can be easily removed after wiping with a lint-free lens paper, as Figure 11 shown in (b) of. Immerse the folded tinplate in olive oil, and it is found that the olive oil easily slides off the tinplate after taking it out, as Figure 11 shown in (c) of, indicating that the coating still has good self-cleaning ability after undergoing deformation. These results show that the coating has good mechanical strength and adhesion.

Claims

1. A method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating, characterized in that: The following steps are involved: (1) dissolving hexamethylene diisocyanate trimer HDIT, monohydroxy polydimethylsiloxane PDMS-OH and dibutyltin dilaurate DBTDL in a solvent, heating and reacting to obtain a prepolymer solution PDMS-HDIT; (2) dissolving tannic acid TA in a solvent to obtain a TA solution, adding the TA solution to the prepolymer solution PDMS-HDIT, heating for reaction, and obtaining a coating solution; (3) diluting the obtained coating solution, dropping the diluted solution on a glass slide by a drop coating method, spreading it naturally, and curing it to obtain the bio-based polyurethane fluorine-free antifouling coating.

2. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: The solvent in step (1) is one of DMF, butanone and propylene glycol methyl ether acetate.

3. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: The solvent in step (2) is one of DMF, butanone and propylene glycol methyl ether acetate.

4. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: The temperature of the heating reaction in step (1) is 75° C. to 90° C., and the reaction time is 1 to 3 hours.

5. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: In the coating solution described in step (2), the mass ratio of TA to HDIT is 1.0 to 5.0 wt %.

6. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: The temperature of the heating reaction in step (2) is 75°C to 90°C, and the reaction time is 1 to 3 hours.

7. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: In step (3), the coating solution is diluted with DMF at a dilution ratio of 1:(1-3).

8. The method for preparing a highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 1, characterized in that: The curing in step (3) is performed at 120°C to 140°C for 2 to 4 hours.

9. A highly transparent bio-based polyurethane fluorine-free antifouling coating prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The optical transparency of the coating is up to 99%.

10. Use of the highly transparent bio-based polyurethane fluorine-free antifouling coating according to claim 9 in the preparation of high-transmittance glass, screens, ceramics, and wooden substrates.

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