Photocatalytic self-cleaning water-based paint and preparation method thereof

Abstract

The invention relates to a photocatalytic self-cleaning water-based paint and a preparation method thereof, which are applied to the field of paint compositions, and the photocatalytic self-cleaning water-based paint realizes self-decomposition of organic dirt and self-inactivation of pathogenic microorganisms by doping a nano-photocatalyst into a water-based system and utilizing a photocatalytic reaction triggered by light energy, and can purify pollutants in air, so that the photocatalytic self-cleaning water-based paint has the advantages of environmental protection and environmental protection. The formula of the coating is optimized, so that the photocatalyst is uniformly dispersed and stably exists in the coating, the coating not only has efficient action under ultraviolet light, but also has certain activity under visible light conditions, and in addition, the coating is a water-based system, is low in VOCs emission, safe and environment-friendly, and has a good application prospect. The self-cleaning antibacterial air purifying coating is suitable for construction and use in a manned environment, creatively integrates self-cleaning, antibacterial and air purifying functions into a whole so as to solve the problems that in the prior art, outer walls and public environment surfaces are difficult to clean and maintain, and a traditional coating lacks active purifying and antibacterial capabilities, and has important practical application value.

Description

Technical Field

[0001] The present invention relates to a coating, and particularly to a photocatalytic self-cleaning aqueous coating applied in the field of coating compositions and a preparation method thereof. Background Art

[0002] The outer walls and curtain walls of buildings are exposed to the atmosphere for a long time and are prone to attaching organic stains such as dust and oil stains, which not only affect the appearance but also increase the maintenance cost. Traditional exterior wall coatings usually require regular cleaning, consuming a lot of manpower and material resources. Moreover, the walls and surfaces of public places such as hospitals need to be kept clean more strictly to reduce the breeding and spread of pathogenic microorganisms. However, traditional methods mainly rely on manual cleaning and chemical disinfectants, and cannot achieve continuous active cleaning and sterilization of pollutants on the coating surface.

[0003] Photocatalytic materials (such as titanium dioxide TiO2) can generate strongly oxidizing free radicals under ultraviolet light irradiation, which can oxidize and decompose organic substances into harmless substances such as carbon dioxide and water. This property has been applied to the research and development of self-cleaning coatings. For example, TiO2-based photocatalytic coatings decompose dirt when exposed to light, weaken its adhesion to the surface, and make it easier for rainwater to wash away the dirt through the hydrophilic effect, so that the coating has the function of "decomposing dirt by light and self-cleaning by rainwater". Some building exterior wall glasses and panels have adopted photocatalytic coatings to achieve long-term self-cleaning and can keep the surface clean without manual cleaning under sunlight irradiation and rainwater action. However, many early photocatalytic self-cleaning technologies are limited to the need for ultraviolet light activation and are mainly based on solvent-based coating systems, and have deficiencies in environmental friendliness and indoor applications.

[0004] Nanoscale titanium dioxide photocatalysts have been widely studied for antibacterial and air purification coatings due to their high specific surface area and high activity. Under light excitation, the photocatalytic free radicals generated on the surface of TiO2 can not only decompose organic stains but also destroy the cell walls and proteins of microorganisms such as bacteria and viruses, making them lose their activity. Research shows that TiO2 photocatalytic coatings have the potential to be used as self-disinfecting surfaces in hospital environments. For example, doping nitrogen into TiO2 can activate the coating with visible light commonly used in hospitals, so that bacteria can be killed even under indoor lighting conditions. However, there are still technical challenges in achieving the above functions, including: how to stably and uniformly disperse the photocatalyst in the aqueous coating, avoid the photocatalytic degradation and side effects of the photocatalyst on the organic coating base material, and improve the activity of the photocatalyst under visible light.

[0005] In summary, there is an urgent need for an environmentally friendly waterborne photocatalytic self-cleaning coating that can automatically decompose surface stains and kill pathogenic microorganisms under daily light conditions (including natural light and indoor light), play a role in long-term self-cleaning and air purification, reduce maintenance costs and the use of chemical cleaners, which is of great significance for maintaining the cleanliness and beauty of building facades and ensuring the hygiene of public facilities such as hospitals. Summary of the Invention

[0006] Aiming at the above-mentioned existing technologies, the technical problem to be solved by the present invention is that traditional exterior wall coatings cannot actively clean and sterilize pollutants on the coating surface, resulting in difficulties in cleaning and maintaining the exterior walls and public environmental surfaces.

[0007] To solve the above problems, the present invention provides a photocatalytic self-cleaning waterborne coating, which includes a waterborne film-forming base material, a nano-photocatalyst and additives. The waterborne film-forming base material adopts at least one of waterborne acrylic emulsion, polyurethane dispersion or waterborne epoxy resin. The nano-photocatalyst adopts nano-titanium dioxide, and its particle size is 5-50 nanometers. The additives include a dispersant, a wetting agent, a leveling agent, an antifoaming agent and a photosensitizer. The mass ratio of the waterborne film-forming base material to the nano-photocatalyst is 100:1-10.

[0008] As a further supplement to the present application, the nano-photocatalyst is subjected to enhanced modification treatment. The enhanced modification treatment operation includes any one of the following two operations: doping a non-metallic element in the nano-photocatalyst or loading metal nanoparticles in the nano-photocatalyst. The non-metallic element includes nitrogen element, and the metal nanoparticles include one of Ag ions or Cu ions.

[0009] As a further supplement to the present application, the nano-photocatalyst is subjected to coating modification treatment. The operation of the coating modification treatment includes coating the nano-photocatalyst with one of silica or alumina.

[0010] As a further supplement to the present application, the nano-photocatalyst is surface-treated with a silane coupling agent so that silane molecules are adsorbed on the surface of the nano-photocatalyst.

[0011] A preparation method of a photocatalytic self-cleaning waterborne coating includes the following steps: Under the condition of high-speed stirring, add a nano-photocatalyst and additives to a waterborne film-forming base material according to a mass ratio, and stir and disperse for 30-40 minutes to obtain a photocatalytic coating slurry, wherein the waterborne film-forming base material adopts a waterborne acrylic emulsion.

[0012] A preparation method of a photocatalytic self-cleaning waterborne coating, comprising the following steps: mixing a nano-photocatalyst, a waterborne film-forming base material and an auxiliary agent according to a mass ratio, ultrasonically dispersing for 10-20 minutes, then adding a curing agent to the mixture and continuing to disperse for 10-20 minutes to obtain a photocatalytic coating slurry, wherein the waterborne film-forming base material is a waterborne epoxy resin and the curing agent is a waterborne amine curing agent emulsion.

[0013] In summary, the beneficial effects of this application are as follows:

[0014] (1) Excellent self-cleaning performance: The use of a nano-photocatalyst (such as the synergy of nitrogen-doped TiO2 and metallic silver) realizes the self-cleaning and antibacterial functions under visible light conditions, breaking through the limitations of traditional ultraviolet activation. Under the irradiation of light sources such as sunlight, the nano-photocatalyst on the coating formed by this paint decomposes the attached organic stains (such as dust, oil stains, biofilms, etc.) into inorganic small molecules, significantly reducing the adhesion force between the dirt and the substrate. With the flushing of rainwater or clean water, the dirt can be removed. Therefore, after applying this paint to the exterior wall, it can remain clean for a long time and reduce the frequency of manual cleaning.

[0015] (2) Broad-spectrum antibacterial and disinfection: The coating formed by this paint continuously generates highly oxidizing active free radicals under ultraviolet or visible light irradiation, which can kill pathogenic microorganisms such as bacteria, fungi, and viruses on the coating surface, helping to reduce the pathogen residues in environments such as hospitals and prevent the risk of infection.

[0016] (3) Air purification and deodorization: The nano-photocatalyst not only acts on the stains on the solid surface but also can oxidize and decompose volatile organic compounds (VOCs) and harmful gases (such as formaldehyde, benzene series, NOx, SOx, etc.) in the air. The coating formed by this paint can decompose the air pollutants passing through its surface into harmless substances (such as converting NOx into nitrate ions) under light irradiation, thus playing a role in purifying the air and deodorizing, which is of positive significance for indoor environments such as laboratories and the exterior walls of buildings facing the street.

[0017] (4) Environmentally friendly and safe: This invention is a waterborne paint, which does not contain organic solvents and heavy metal components, has extremely low VOC emissions, meets the requirements of green environmental protection, is friendly to construction workers and the environment during construction and use, and is especially suitable for places with high environmental protection and safety requirements such as medical and health care and food processing.

[0018] (5) Durable and stable: Through the modification of the photocatalyst and the optimized paint formula, the coating has good stability and weather resistance. The photocatalyst exists in the coating for a long time and maintains its activity, and is not easy to lose from the coating; the coating itself has excellent ultraviolet aging resistance and can be used outdoors for a long time without powdering, has good industrial application prospects, can improve the service life of the surface of buildings and facilities, and reduce the maintenance cost. Description of the Drawings

[0019] Figure 1 This is a schematic diagram of the working mechanism of this application. Detailed implementation modes

[0020] The following will make a detailed description of two implementation modes of this application with reference to the accompanying drawings.

[0021] The first implementation mode:

[0022] The present invention provides a photocatalytic self-cleaning waterborne coating. Please refer to Figure 1 , which includes a waterborne film-forming base material, a nano-photocatalyst, and additives. The waterborne film-forming base material adopts at least one of various materials such as waterborne acrylic emulsion, polyurethane dispersion, or waterborne epoxy resin. The nano-photocatalyst adopts nano-titanium dioxide, and its particle size is 5 - 50 nanometers. The additives include a dispersant, a wetting agent, a leveling agent, an antifoaming agent, and a photosensitizer. The additives can improve the stable dispersion effect of the nano-photocatalyst in the waterborne system and form a uniform coating film. The mass ratio of the waterborne film-forming base material to the nano-photocatalyst is 100:1 - 10.

[0023] To improve the visible light response and antibacterial effect, the nano-photocatalyst can be subjected to enhanced modification treatment. The enhanced modification treatment operation includes any one of the following two operations: doping non-metallic elements in the nano-photocatalyst or loading metal nanoparticles in the nano-photocatalyst. The non-metallic elements include nitrogen element, and the nitrogen doping content is that the atomic ratio of N to Ti is 1 - 5 at.%. Its preparation method can adopt a plasma technology-assisted doping process. The metal nanoparticles include one of Ag ions or Cu ions, and the loading amount of the metal nanoparticles is 0.1 - 1 wt%. The in-situ reduction method can be used to load the metal nanoparticles. Compared with the traditional solid-phase doping or wet chemical impregnation method, this process can make the metal particle size more uniform (<10 nm) and the dispersion more stable, without post-treatment high-temperature calcination, thus protecting the organic components in the waterborne system. Through the above treatment, the photocatalyst can be activated by visible light and the efficiency of generating antibacterial free radicals can be enhanced.

[0024] The working mechanism of the nano-photocatalyst: As Figure 1 shown, under illumination (such as sunlight or indoor lighting), the nano-photocatalyst particles are activated, and the generated photo-generated carriers form highly active hydroxyl radicals and superoxide anions. These active species can oxidize and decompose the organic stains on the coating surface and destroy the cell structures of microorganisms such as bacteria and viruses, making them lose their activity. After photocatalytic degradation, the organic pollutants are converted into small molecules such as carbon dioxide and water, and the pathogenic microorganisms are inactivated.

[0025] To prevent the nanophotocatalyst from having an adverse effect on the organic base material during its operation, the nanophotocatalyst can be subjected to a coating modification treatment. The operation of the coating modification treatment includes coating the nanophotocatalyst with one of silica or alumina, and the thickness of the coating layer is 1 - 3 nm.

[0026] The surface of the nanophotocatalyst can also be treated with a silane coupling agent. The principle is to utilize the polar group and lipophilic property of the silane coupling agent. In the chemical reaction that occurs between it and the surface of titanium dioxide, the silane molecules are firmly adsorbed on the surface of titanium dioxide. The silane coupling agent forms chemical bonds with the surface of titanium dioxide through groups such as hydroxyl or amino groups it contains, and at the same time, through its lipophilic property, it adsorbs with organic substances in the surrounding environment to form a protective layer on the surface of titanium dioxide, effectively preventing surface oxidation and deterioration, thereby improving the stability and adhesion of titanium dioxide.

[0027] By means of inorganic coating (such as silica coating) and surface treatment technology, the stable dispersion of the photocatalyst in the aqueous system and its compatibility with the coating base material are improved, and the degradation of the substrate is prevented.

[0028] For exterior wall use, the following is a preparation and usage method of this photocatalytic self - cleaning water - borne coating:

[0029] Preparation process: Select an aqueous acrylic emulsion as the aqueous film - forming base material. The solid content in the aqueous acrylic emulsion is 50%, the glass transition temperature is about 10°C, and it has excellent weather resistance. Select nanometer titanium dioxide as the nanophotocatalyst, such as anatase TiO₂, with an average particle size of about 20 nm. Under high - speed stirring conditions, add nanometer titanium dioxide photocatalyst with a mass of 5% of the mass of the aqueous film - forming base material to the aqueous acrylic emulsion. Conventional additives such as a dispersant (such as ammonium polyacrylate salt) with a mass of 0.2%, a leveling agent with a mass of 0.3%, and an antifoaming agent with a mass of 0.2% can also be added as required. Stir and disperse for 30 minutes to make the nanometer titanium dioxide evenly dispersed in the emulsion, obtaining a milky - white photocatalytic coating slurry.

[0030] Usage and testing method: Apply the coating to a clean concrete exterior wall panel specimen by spraying. The wet film thickness is about 100 microns, and it is left to dry at room temperature for 7 days to form a tough coating. The obtained coating appearance is white and translucent, with a thickness of about 50 microns. Obtain several specimens in the above - mentioned manner;

[0031] To test the self-cleaning performance of the coating, a layer of simulated dirt mixed with engine oil and carbon black was evenly applied on the coating surface. Then, several specimens with the coating and several comparative specimens without the coating were placed outdoors under natural sunlight exposure. After one week of outdoor exposure, both types of specimens were rinsed with clean water. It could be seen that obvious black stains still remained on the surface of the comparative specimens without the coating, while the stains on the surface of the specimens with the coating had been basically decomposed and washed away, and the surface returned to cleanliness. This demonstrated that the coating had significant self-cleaning ability in natural light and rain environments: light decomposed the organic stains and rain washed them away. At the same time, it was measured that the mass change of the coating before and after exposure was very small, indicating that the coating itself was stable and there was no obvious photo-degradation phenomenon.

[0032] The following table shows the comparison of experimental data of this coating and other products applied to the exterior wall of a building.

[0033] Index This product at 0h This product at 15000h Other products at 0h Other products at 15000h Color difference ΔE 0.0 1.2 0.0 6.5 Gloss retention rate % (measured at 60°) 100% 98% 100% 55% Adhesion (tensile force required to pull off the coating) 2.8MPa 2.7MPa 2.8MPa 1.8MPa Coating thickness change 0μm –3μm 0μm –18μm Surface hardness (pencil hardness) 4H 4H 4H 2H

[0034] As can be seen from the above table, for the coating before use and the coating after 15,000 h of use, in terms of color difference, the change of this product was only 1.2 after 15,000 h, which was hardly noticeable to the naked eye, while that of other products reached 6.5, showing obvious fading. The gloss retention rate of this product was 98% after 15,000 h, and the surface was still smooth. The gloss of other products was almost halved. The adhesion retention rate of this product was about 96%, while that of other products decreased to 64%, making them easy to peel off. In terms of the change in coating thickness, this product had almost no loss, while other products were significantly eroded by UV and rain, and the thickness was reduced by about 18 μm. In terms of surface hardness, this product maintained a pencil hardness of 4H, while the hardness of other products decreased to 2H, making the surface soft and easy to scratch.

[0035] Further performance tests showed that after 8 hours of sunlight irradiation, the coating could achieve a degradation removal rate of more than 85% for organic pollutants (such as organic substances like benzo[a]pyrene in simulated atmosphere) attached to its surface; it also had a certain degradation effect on nitrogen oxides in the air. Simulated tests showed that the daily average purification amount of NO2 per square meter of the coating surface was about 0.04 grams, which was equivalent to the air purification ability of 68 poplar trees per 10,000 square meters of the coating.

[0036] Quantitative test under visible light conditions: The degradation rate of methyl orange (MO) reached 85% within 30 min under visible light irradiation by UV–Vis quantitative monitoring; under visible light of 400–700 nm, the antibacterial rate against E. coli was ≥99%. Through the above data, the performance advantages of the modified TiO2 of the present invention in indoor / weak light environments can be further demonstrated.

[0037] The second implementation method:

[0038] This embodiment is for indoor wall antibacterial use, and provides another preparation and use method of this photocatalytic self-cleaning waterborne coating:

[0039] Preparation process: Select an aqueous epoxy resin emulsion (the main agent is a modified epoxy dispersion, which needs to be mixed and cured with a curing agent) as the aqueous film-forming base material. The nano-photocatalyst used is nitrogen-doped titanium dioxide N-TiO2, with a particle size of about 15 nm and visible light response characteristics. In addition, to enhance the antibacterial performance, TiO2 loaded with nano-silver is also used. The specific preparation method is as follows: Mix 5 parts of N-TiO2 powder, 0.05 parts of TiO2 powder loaded with nano-silver and 100 parts of the aqueous epoxy main agent emulsion by mass ratio, ultrasonically disperse for 10 minutes, and then add 5 parts of the aqueous amine curing agent emulsion and stir evenly;

[0040] Use and test method: The obtained coating is applied to the surface of the disinfected gypsum board by brushing within 30 minutes, with a film thickness of about 60 microns. It is left at room temperature for 24 hours to complete curing. By adopting the above method, several specimens coated with this antibacterial coating are obtained.

[0041] To evaluate the antibacterial effect of the coating, Escherichia coli (E. coli) is selected as the test strain. A certain concentration of Escherichia coli suspension is inoculated on the surfaces of several specimens coated with the antibacterial coating of the present invention as the experimental group, and the same material surface without coating is used as the control group. The two groups of specimens are respectively placed in a sealed test chamber equipped with a fluorescent lamp (emitting a simulated indoor lighting spectrum, containing a small amount of UV component) and irradiated for 4 hours. Then, the surviving bacteria on the surface are sampled and cultured for counting;

[0042] The results show that the number of residual bacteria per square centimeter of the control group specimens is more than 105, while the number of culturable bacteria per square centimeter of the experimental group with this coating is less than 10. Even under indoor visible light containing only a weak UV component, this coating also shows good antibacterial activity. This is attributed to the fact that the nitrogen-doped TiO2 in the coating can also generate a certain amount of oxidation radicals under visible light excitation, and at the same time, nano-silver has a broad-spectrum antibacterial effect and shows a synergistic effect with photocatalysis.

[0043] Further tests show that for common pathogenic microorganisms such as Staphylococcus aureus (including drug-resistant MRSA strains) and Aspergillus niger, the growth and reproduction of these microorganisms can be effectively inhibited by this coating under light conditions. After the coating is wiped many times and irradiated for a long time, the antibacterial performance does not decrease significantly, indicating that the photocatalyst exists stably in the coating and the long-term antibacterial performance is reliable.

[0044] The above embodiments prove the photocatalytic self-cleaning waterborne coating: its self-cleaning and antibacterial functions have good performance in the actual application environment. At the same time, as a waterborne environmental protection coating, it is easy to construct and has high safety. During industrial scale-up production, the existing coating production equipment can be used to pre-disperse the nano-photocatalyst, and then add the waterborne film-forming base material to mix and prepare the product. It is expected that the coating has broad application prospects in aspects such as self-cleaning and mildew prevention of building exterior walls, and sterilization and air purification of interior walls in medical institutions.

[0045] Combined with the current actual needs, the above embodiments adopted in this application do not limit the protection scope thereto. Within the scope of knowledge possessed by those skilled in the art, various changes made without departing from the concept of this application still fall within the protection scope of the present invention.

Claims

1. A photocatalytic self-cleaning waterborne coating, characterized in that: It includes a waterborne film-forming base material, a nano-photocatalyst, and additives. The waterborne film-forming base material is at least one of waterborne acrylic emulsion, polyurethane dispersion, or waterborne epoxy resin. The nano-photocatalyst is nano-titanium dioxide with a particle size of 5 - 50 nanometers. The additives include a dispersant, a wetting agent, a leveling agent, an antifoaming agent, and a photosensitizer. The mass ratio of the waterborne film-forming base material to the nano-photocatalyst is 100:1 - 10.

2. The photocatalytic self-cleaning waterborne coating according to claim 1, wherein: The nano-photocatalyst is subjected to enhanced modification treatment. The enhanced modification treatment operation includes any one of the following two operations: doping a non-metallic element in the nano-photocatalyst or loading metal nanoparticles in the nano-photocatalyst. The non-metallic element includes nitrogen, and the nitrogen doping content is an atomic ratio of N to Ti of 1 - 5 at.%, prepared by a plasma-assisted doping process. The metal nanoparticles include one of Ag ions or Cu ions, and the loading amount of the metal nanoparticles is 0.1 - 1 wt%, and the metal nanoparticles are loaded by an in-situ reduction method.

3. The photocatalytic self-cleaning waterborne coating according to claim 1, characterized in that: The nano-photocatalyst is subjected to coating modification treatment. The operation of the coating modification treatment includes coating the nano-photocatalyst with one of silica or alumina, and the thickness of the coating layer is 1 - 3 nm.

4. The photocatalytic self-cleaning waterborne coating according to claim 1, wherein: The nano-photocatalyst is surface-treated with a silane coupling agent so that silane molecules are adsorbed on the surface of the nano-photocatalyst.

5. A preparation method of a photocatalytic self-cleaning waterborne coating, characterized in that: It includes the following steps: Under the condition of high-speed stirring, the nano-photocatalyst and additives are added to the waterborne film-forming base material according to the mass ratio, and stirred and dispersed for 30 - 40 minutes to obtain a photocatalytic coating slurry, where the waterborne film-forming base material is waterborne acrylic emulsion.

6. A preparation method of a photocatalytic self-cleaning waterborne coating, characterized in that: It includes the following steps: The nano-photocatalyst, the waterborne film-forming base material, and the additives are mixed according to the mass ratio, ultrasonically dispersed for 10 - 20 minutes, and then a curing agent is added to the mixture and continuously dispersed for 10 - 20 minutes to obtain a photocatalytic coating slurry, where the waterborne film-forming base material is waterborne epoxy resin and the curing agent is a waterborne amine curing agent emulsion.

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