Application of self-cleaning paint on building curtain wall

Application of self-cleaning paint on building curtain wall

Shenzhen Situjia Technology Co., Ltd. has been focusing on the research and development and application of water-based inorganic ceramic coatings. After more than ten years of promotion, it has been used in kitchen appliances, beauty tools, motorcycle accessories Vehicles, medical equipment and other fields are highly recognized. Jiang head office is mainly engaged in environmental protectioncurtain wall self-cleaning paint, is a professional in this industry, friends in need can inquire! 0755-22678866

Curtain wall materials such as fluorocarbon aluminum plate and glass curtain wall are widely used in building exterior wall decoration due to their advantages of strong decoration, factory production, convenient on-site installation, easy replacement and recycling, etc. more and more applications. But with the intensification of urban environmental pollution, the pollution of decorative curtain wall materials also intensifies. In order to ensure the decorative properties of the curtain wall materials, the cost of cleaning the building curtain wall is also increasing, such as the consumption of a lot of water and labor costs. At the same time, the building cleaning industry is an emerging multidisciplinary technical field, which includes the application of chemistry, physics, machinery, biology and other disciplines (such as dry ice cleaning, laser cleaning, vacuum cleaning, waterless cleaning, etc.).

With the development of science, new building materials have come out in recent years and are widely used in the exterior wall decoration of buildings, which increases the difficulty of cleaning. Conservation methods present new challenges. Nano titanium oxide coating not only has self-cleaning properties, but also can effectively block ultraviolet rays from directly acting on colored coatings such as curtain walls and billboards exposed to sunlight, slow down their fading and not easy to age for a long time, and keep buildings fresh and beautiful. The nano titanium oxide coating also decomposes harmful gases in the air to purify the ambient air. According to the statistics of foreign experts, 1000 square meters of nano-coating is equivalent to the air purification effect of 70 poplar trees. More importantly, the nano-titanium oxide self-cleaning coating has a long-term effect and can be used for 8 to 10 years after one coating.

Principle of self-cleaning paint

In 1972, the Japanese Fujishima and Honda discovered the heterogeneous photocatalysis of TiO2 semiconductors, and in 1997, R. Wang published a paper on the photo-induced hydrophilic properties of TiO2 films , these two findings constitute the technical basis for TiO2 superhydrophilic self-cleaning coatings, which utilize the photocatalytic and light-induced superhydrophilicity of TiO2 to achieve self-cleaning effects on surface films.

Nano TiO2 is a N semiconductor material, there is a forbidden band between the valence band filled with electrons and the conduction band composed of holes, when irradiated on the surface of the nano TiO2 film The energy of the ultraviolet light is greater than the forbidden band width, the electrons in the valence band of nano-TiO2 are excited, transition to the conduction band, and holes are formed in the valence band at the same time. The electrons in the conduction band react with O2 in the air to generate superoxide anion (O2-); the holes in the valence band and the surface adsorbed H2O form hydroxyl radicals (•OH). Hydroxyl radicals have strong oxidizing properties and can degrade various organic substances adsorbed on the surface of nano-TiO2 coating into H2O and CO2.

The photo-induced hydrophilicity of nano-TiO2 film is the interaction of electron-hole pairs generated by ultraviolet light excitation with the surface TiO2 crystal, forming uniformly distributed hydrophilic micro-domains on the crystal surface And hydrophobic micro-domains, each micro-domain is only a dozen nanometers wide, and a water droplet is much larger than a hydrophilic micro-domain, so it can spread continuously on the surface of the TiO2 film. The hydrophilic micro-domains formed on the surface of TiO2 film by ultraviolet light are unstable. After the light is stopped, the enrichment of O2 on the surface of TiO2 makes the hydrophilicity of the film surface gradually attenuate, and the contact angle between water and the surface gradually increases. Once again, UV light irradiates the surface, and new hydrophilic microdomains are formed again. As an ideal super-hydrophilic self-cleaning coating, it is necessary to shorten the hydrophilic response time of light irradiation as much as possible, and delay the speed of hydrophilic attenuation in the dark.

Usually the pollution on the surface of the curtain wall paint is mainly caused by the adsorption of dust and organic matter suspended in the air. This adsorption is mainly due to electrostatic adsorption and Physical adsorption due to van der Waals forces. After the self-cleaning coating is irradiated by ultraviolet light, the nano-TiO2 coating exhibits super-hydrophilic properties, forming chemically adsorbed water and physically adsorbed water on the surface of the coating. The presence of adsorbed water is beneficial to eliminating static electricity on the coating surface and eliminating electrostatic force. . The hydroxyl groups formed on the surface of the self-cleaning coating are hydrophilic. When raindrops fall on the surface of the coating, hydrogen bonds are formed between the surface hydroxyl groups and water. The force of the hydrogen bonds is much greater than the van der Waals force. On the coating surface, the dust originally adsorbed on the surface is taken away by the remaining water, while the organic adsorbate that is difficult to be taken away by water on the surface is decomposed under the photocatalysis of nano-TiO2 to form water, carbon dioxide and water that can be carried by water. Small molecular substances are removed, so as to achieve the purpose of self-cleaning on the surface of the curtain wall.

Application of self-cleaning paint on curtain wall

The self-cleaning coating itself is transparent and can be used with fluorocarbon, glass, ceramic coatings, etc. It is produced online. The self-cleaning coating is sprayed on the outer surface and cured at elevated temperature. After that, a stable coating will be formed on the surface of the curtain wall. Under normal circumstances, the coating formed is a colorless and transparent invisible coating, which will not affect the color of the underlying decorative paint. When used in combination with marble and latex paint, it can also be sprayed on site and dry at room temperature.

For example, the "Glossy" self-cleaning paint developed by KNT is a nano-TiO2 sol product. The self-cleaning paint is applied to the surface of the curtain wall by spraying during use. During the drying process, the water in the sol evaporates, and the sol particles are deposited on the surface of the curtain wall to form a nano-TiO2 film coating. Under sunlight, the coating exhibits super-hydrophilic properties, and the pollutants adsorbed on the surface can be removed by the scouring of rainwater. At the same time, the nano-TiO2 coating acts as a photocatalyst to catalyze the decomposition of various organic pollutants adsorbed on the surface of the curtain wall. thing.

In order to improve the performance of self-cleaning coatings, KNT company specially designed a transition coating for "Glossy" (as shown in Figure 1), the transition coating can use The same spray application process as self-cleaning coatings. The use of transition coating can improve the adhesion of self-cleaning coatings, prolong the service life, and more importantly, can make self-cleaning coatings fully exhibit super-hydrophilicity. It is generally considered that a water contact angle < 5° is a super-hydrophilic surface. , the contact angle of the self-cleaning coating on the surface of the transition coating is about 1°, which belongs to the superhydrophilic range. In addition, the tie coat also has a protective effect, preventing possible damage to the primer by the self-cleaning coating.

Features of self-cleaning coatings

1. Photocatalytic performance

After being irradiated by ultraviolet light, the nano-TiO2 coating is excited to form superoxide anions and hydroxyl radicals with strong oxidizing properties, which can decompose various organic organic substances adsorbed on the surface. Pollutants, oxidatively remove nitrogen oxides and sulfides, and kill microorganisms such as molds and bacteria that come into contact with the surface. If used indoors, it can significantly reduce the concentration of harmful gases such as toluene and formaldehyde, and purify indoor air.

2. Hydrophilic

The surface of the nano-TiO2 coating is excited by ultraviolet light to form hydroxyl groups, and the hydroxyl groups form hydrogen bonds with water to show super hydrophilicity. The superhydrophilic TiO2 film can rapidly wet and spread water droplets on the surface. This property allows water to preferentially occupy the surface while blocking contaminants from the surface and being carried away by excess water. At the same time, the hydrophilic film formed is very thin, so that the surface can be air-dried quickly, preventing the wet surface from being re-contaminated by dust in the air.

3. Self-cleaning performance

Self-cleaning performance is the concentrated expression of photocatalytic and super-hydrophilic properties of TiO2 coatings when applied outdoors. Compared with surfaces without self-cleaning coatings, nanometer The surface of TiO2 coating has obvious anti-fouling property and can keep the surface clean without manual cleaning. Figures 3 and 4 are the photo of the upper half coated with nano-titanium oxide coating, compared with the experimental photos on fluorocarbon and ceramic coatings. Both experiments show that nano-titanium oxide has excellent self-cleaning properties.

Factors affecting self-cleaning performance

1. Light intensity and light time

The nano self-cleaning coating is excited by ultraviolet light to produce super-hydrophilic properties. After stopping the light, the hydrophilicity decays, and the hydrophilicity disappears after a period of time. The light intensity and light time directly affect the hydrophilicity of the coating, which in turn affects the self-cleaning performance.

2. Coating structure

The coating structure includes two aspects, one is the composition of the coating, and the other is the thickness of the coating. For example, "Glossy" is composed of a transition layer and a surface layer (self-cleaning layer). The transition layer can significantly improve the adhesion of the surface layer. The thickness of the surface coating film has a great influence on the self-cleaning performance and adhesion: the coating film is thin, the hydrophilicity of the coating film becomes worse, and the hydrophilicity decays quickly in the dark; The hydrophilic retention ability in the dark is improved; if the coating is too thick, the adhesion becomes poor.

3. Other factors

There are many other factors that affect the self-cleaning performance of the coating film, such as internal factors such as the crystal form and grain size of nano-titanium oxide, and the environment in which the self-cleaning coating film is used. factors, such as pH, the type and degree of pollution of organic pollutants, etc.

 Nano TiO2 has stable chemical properties and no biological toxicity, and is an environmentally friendly building material that can be used safely. Nano TiO2 self-cleaning coatings can use natural forces such as sunlight and rain to keep the surface of decorative curtain walls clean. Its promotion and application are in line with the current development trend of energy saving and environmental protection.