Glass curtain wall is a beautiful and novel method of building wall decoration. It can fully reflect the imagination of the architect, show the modern style of the building, give full play to the characteristics of glass itself, and make the building look unique.
However, there is a problem of poor stain resistance in the widely used glass curtain walls. Especially in northern areas where there is a lot of dust in the atmosphere, serious air pollution, drought and little rain, glass curtain walls are easily covered with dust and dirt, with uneven color and different ripples, making light reflection uncontrollable, resulting in a messy light environment and damaging the urban landscape. .
Because the types of dirt adhered to the glass curtain wall are different, the bonding force and bonding methods are different, and the deposition time on the curtain wall is different, so the cleaning is very different, so a curtain wall cleaning agent is proposed. Series technical requirements. It is difficult to clean glass curtain walls, and a large amount of organic solvents are used, which can easily cause pollution to the surrounding environment after cleaning. The discharge of cleaning waste liquid is also a problem. Therefore, the development of coated glass with self-cleaning function has become the focus of current research.
The current status of domestic self-cleaning glass research
Research on nanotechnology giving self-cleaning function to architectural glass is in the ascendant. In my country, it is mainly concentrated on nano-photocatalyst self-cleaning glass. Its self-cleaning principle is: the photocatalyst self-cleaning glass film contains a nanomaterial (TiO2) with photocatalytic activity, which can absorb light of a certain wavelength, generate free electrons and holes, and absorb pollutants on the surface of the film. Redox decomposition occurs to remove and kill surface microorganisms to achieve the purpose of self-cleaning. Studies have shown that harmful pollutant molecules such as organic matter and ammonia compounds can be removed from the air. The basic functions of this coating are:
(1) Super hydrophilic function. The application of this functional glass can spread water completely and evenly on the glass surface, soaking the glass and pollutants at the same time. Finally, the pollutants attached to the glass will be taken away by the gravity of the water, and it can also play a certain anti-fogging role. .
(2) Photocatalytic function. Under the irradiation of ultraviolet rays, the photocatalyst will decompose organic matter but will not have any effect on inorganic matter.
Most of the existing self-cleaning glass uses TiO2 coating, and the bandgap width of TiO2 is 3.2eV. The wavelength of the excitation light must be below 385nm. Only ultraviolet rays can have a photocatalytic effect, and solar radiation energy Medium ultraviolet rays only account for 4%-6%. Therefore, under natural conditions, the self-cleaning effect of the photocatalyst is difficult to exert. Especially on rainy and cloudy days and on glass curtain walls facing north, it is difficult for photocatalytic reactions to occur.
In addition, different crystal faces of anatase TiO2 have different photocatalytic abilities. The catalytic effect of the 001 face is less than half that of the 110 face. It is also a thorny problem to control the orientation of the crystal face with high catalytic ability.
Another problem with photocatalyst self-cleaning glass is the durability of the film layer. Pilkington Company introduced that the service life of self-cleaning glass is 10 years. Domestic self-cleaning glass research reports have not yet touched on this issue. The life span of self-cleaning glass can be considered from two aspects. On the one hand, the semiconductor film material coated on the glass surface will be degraded in the photocatalytic reaction; on the other hand, the photocatalytic function of the semiconductor film will attenuate under repeated long-term exposure to ultraviolet rays. , these problems limit the feasibility of outdoor applications of photocatalysts under natural conditions.
The advent of special nano self-cleaning coatings
Recently, the Nano Powder Large Scale Preparation and Application Innovation Research Group of the Institute of Process Analysis, Chinese Academy of Sciences, has developed a special nano self-cleaning coating for glass curtain walls. coating. This research group has been conducting research on organic-inorganic hybrid films since 1995. It is the first time in China to introduce inorganic nanoparticles into organic-inorganic hybrid films. It is the first time in China to introduce inorganic nanoparticles into organic-inorganic hybrid films. The laboratory that uses hybrid films to improve various properties of substrates has successfully developed a variety of nanocomposite coatings after years of research and exploration. Due to the application of a variety of nanomaterials and nanotechnology in the preparation process of the coating, the washing resistance, adhesion, smoothness, aging resistance, surface hardness, anti-sticking, self-cleaning, antibacterial, etc. of the coating are greatly improved. Anti-mildew and other environmental purification properties.
In response to the current shortcomings in the use of glass curtain walls and market demand, this technology mainly introduces special nanoparticles and other functional units into a special coating system to give the coating stain-resistant and self-cleaning functions.
The nano-coating system isolates the glass from the outside world without affecting the transmittance of the glass, making it difficult for dust and other dirt to combine with the glass through Coulomb force.
The coating system itself forms a strong bond with the glass surface and has excellent durability. At the same time, the unique hydrophobic properties of the coating prevent rainwater containing organic matter, inorganic salts and dirt from leaving water streaks on the glass, creating a lotus leaf effect. The coating has the ability to buffer and conduct static electricity, eliminating the static adsorption of dust, which greatly improves the anti-fouling and self-cleaning performance of the glass curtain wall.
At normal pressure and room temperature, the glass is coated online using a spraying process. The equipment cost is low and it is easy to operate. There are three specific processing methods: baking (temperature around 15oC), repeatedly wiping the sprayed surface, and polishing the sprayed surface with a brush.
Relevant performance testing
Contact angle. In practice, the contact angle between the glass surface and water varies greatly. Measured by a contact angle tester, the contact angle before and after the coating film increased from 20o to 110o, indicating good hydrophobicity. Water droplets and oil droplets that come into contact with dirt entrained in the glass slide off quickly without attaching to it to form water marks, and have good self-cleaning properties.
Transmission coefficient. The glass sample coated with nano-coating was entrusted to the National Chemical Building Materials Testing Center for transmission coefficient testing in accordance with national standards (GB/T18915.1-18915.2-2002). Experiments show that the transmission coefficients before and after coating are 77.12 and 79.36 respectively. The transmission coefficient does not decrease. The coating does not affect the light transmittance of the glass.
Anti-aging. The glass sample coated with nano-coating was entrusted to the National Chemical Building Materials Testing Center for artificial accelerated aging testing in accordance with the national standard (GB/T16422.2-1999). The test conditions are: irradiation intensity 0.5W/m2, blackboard temperature 65oc_3oC, relative temperature (50_5)%, water spraying period is 18min each time, and the water-free time between two water sprays is 120min. There is no damage to the coating surface after 2000h. The total color difference E is 1.03, the discoloration is zero level, and the coating has excellent anti-aging properties.
Coating thickness. The JEOL JSM-5700 field emission electron microscope was used to test the surface morphology and thickness of the glass coating. The coating thickness was about 2um, and the glass surface was flat and smooth.
Adhesion: The coating adhesion or bonding strength is examined in accordance with GB/T9286-1998. A 20o single-edged tool is used to cross-cut the coating at an interval of 2mm. Compare it with the test result grading chart in the standard. The cross There is no peeling off in the cutting area, indicating that the coating is firmly bonded to the glass.
Acid resistance. Prepare a 5% hydrochloric acid solution (pH value = 1.5), immerse the glass sample coated with nano-coating in it, and take it out after 24 hours. The hydrophobic angle of the film remains unchanged, and the surface has no discoloration, no cracks, no blistering, no powdering, etc. Phenomenon. The coating has the ability to resist acid rain erosion.
Glass curtain walls are easily contaminated during actual use. Using nanotechnology to upgrade glass coatings and prepare coatings with self-cleaning functions is a feasible way to solve the problem of curtain wall glass being easily contaminated. No matter what kind of nanomaterials are produced by nanotechnology, only nanomaterials with excellent durability and easy for large-scale processing can be applied to real production. There are not many actual large-scale production and application examples of special nano self-cleaning coatings for glass curtain walls, and continuous exploration and improvement in production and application are needed.
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