Interior and exterior wall coatings have become the mainstream of interior and exterior wall decoration. With the improvement of people's living standards, higher requirements are put forward for interior and exterior wall coatings, and it is increasingly necessary to develop a decorative and functional interior and exterior wall coating. With the rapid development of science and technology, nano-materials and nano-technology have sprung up, becoming the most dynamic research objects in the field of new materials, which has an important impact on future economic and social development. At the same time, with the deepening of research, nanotechnology has penetrated into many fields. The application of nanotechnology provides new opportunities for transforming traditional industries and injecting high-tech content. The application of nanotechnology in coatings is the perfect combination of the two. Nanotechnology has opened up a new way for people to develop new coatings.
Nanotechnology is a science and technology to study the motion law and interaction of the system composed of substances with the size between 0. 1 ~ 100nm, as well as the possible technical problems in practical application. Nanotechnology mainly includes: nano-system physics, nano-materials, nano-chemistry, nano-processing, nano-biology, nano-mechanics and so on. The application of nanotechnology in interior and exterior wall coatings mainly includes nano-processing and nano-materials. Nano-processing means that emulsion is directly processed into nano-emulsion, and nano-materials are produced by different means or general materials are modified to make them have the properties of nano-materials. The application of nano-materials in coatings can be divided into two situations: first, nano-particles are dispersed in traditional organic coatings to form nano-composite coatings; The second is a nano-coating material composed entirely of nanoparticles. The first kind of nano-composite coatings mainly modify traditional coatings by adding nano-particles. The process is relatively simple and the industrial feasibility is good. The second method is difficult to achieve a breakthrough in industrialization in the short term due to technical and cost problems.
Application of 1 nano-materials in interior and exterior wall coatings
Nano-materials are divided into two levels, namely nano-ultrafine particles and nano-solid materials. Nano-ultrafine particles refer to ultrafine particles with a particle size of 1 ~ 100 nm. Nano-solid refers to solid materials made of nano-ultrafine particles. Nano-materials have special properties, such as surface effect, small size effect, optical effect, quantum size effect, macro quantum size effect and so on. This paper introduces how to apply these properties of nano-materials to interior and exterior wall coatings.
Optical Properties and Applications of (1) Nanomaterials
Nanoparticles have different absorption, reflection and scattering effects on light with different wavelengths because of their small particle size and high surface dispersibility. The particle size of nano-particles is much smaller than the wavelength of visible light (400 ~ 750 nm), which has the function of transmission, thus ensuring the high transparency of nano-composite coatings. Nano-materials with different particle sizes have different scattering and reflection effects on light, and can produce color-changing effect with different angles of incident light. Nano-materials with particle size less than 300 nanometers have visible light reflection and scattering ability. They are transparent in the visible region, but they have strong absorption and scattering ability to ultraviolet light. Of course, the absorption capacity is also related to the structure of the material. Combined with the surface catalytic characteristics of nano-materials, nano-silica, titanium dioxide, zinc oxide and other filling coatings are endowed with disinfection and self-cleaning functions. The coat used for external wall can improve weather resistance and pollution resistance. Some nano-materials with particle size less than 100nm can absorb and scatter radioactive α and γ rays, improve the radiation protection ability of coatings, and play a role in radon prevention in interior wall coatings.
(2) Surface activity and application of nanomaterials.
Nano-materials have high surface activity because of their huge surface area and particle size close to macromolecular level.
The huge surface area of highly active nano-materials forms a strong interaction with film-forming substances and solvents. Nano-SiO2 _ 2 and silicate-based nano-modified bentonite can greatly improve the rheological properties of coatings, improve their opening performance, anti-sedimentation, good thixotropy and construction performance, and prevent sagging. With the particle size entering the nanometer scale, the active center on the surface of the material increases, which improves its chemical catalysis and photocatalytic reaction ability, and endows the coating with self-cleaning ability under the action of ultraviolet rays and oxygen. The surface active center can be combined with the functional groups of film-forming substances through secondary chemical bonds, which greatly increases the rigidity and strength of the coating, thus improving the scratch resistance of the coating. Nanomaterials with high surface energy can obtain hydrophobic and oleophobic properties at the same time through surface modification. This material can significantly improve the anti-pollution ability of coatings when used in interior and exterior wall coatings.
(3) Small volume effect and application of nanomaterials.
Nano-pigments and fillers can greatly reduce the free volume between pigments and film-forming substances in coatings and enhance the binding force between film-forming substances and nano-fillers, thus greatly improving the filling rate, improving the mechanical strength of coatings, reducing capillary phenomenon and improving the shielding effect of coatings. The application of nano-materials in primer can strengthen the adhesion between primer and base, and the fine particles of primer penetrate into the base to make it a whole, and its mechanical strength is self-evident. The strength and filling effect of nano pigments and fillers on primer is helpful to improve the interface bonding between primer and coating. Similarly, nano-materials play the role of surface filling and modification in topcoat, improving the luster of topcoat and reducing the resistance. Adding nano-silica into exterior wall coatings can improve the scrubbing resistance of coatings. Nano-calcium carbonate can improve the strength and hardness of polyurethane.
Nano-materials and nano-technology currently used for interior and exterior wall coatings
Application of (1) nano-silica in interior and exterior wall coatings
The aggregate of nano-silica is amorphous white powder, and the surface molecular state is three-dimensional network structure. This structure gives the coating excellent thixotropy and dispersion stability. Nano-silica has strong ultraviolet absorption and infrared reflection characteristics, which can improve the aging resistance of coatings. If the surface of silica is treated, the surface of silica nanoparticles can have hydrophilic groups and lipophilic groups, which improves the original wetting characteristics of silica nanoparticles.
After adding a small amount of nano-silica into the interior and exterior wall coatings of buildings, the ultraviolet aging resistance of the coatings is improved from 250 hours to over 600 hours, the scrubbing resistance is improved from 1000 times to over 10000 times, and the drying time is greatly reduced. At the same time, the problems of poor suspension stability, poor thixotropy and low finish are well solved. The opening effect of interior and exterior wall coatings with nano-silica is obviously improved, and the coating is not layered, sag-proof, good in construction, especially greatly improved in pollution resistance, and has excellent self-cleaning and adhesion. In addition, because the absorption rate of nano-silica to ultraviolet light within 400nm is more than 70%, the intensity of ultraviolet light absorption and ultraviolet light irradiation is relatively weak, which can obviously improve the aging resistance of the coating.
Addition amount of nano-silica: generally, the addition amount of nano-silica is 0. 1% ~ 1%, and the maximum is 5%.
(2) The application of nanometer titanium dioxide in interior and exterior wall coatings.
The optical effect of nano-TiO _ 2 changes with the change of particle size. In particular, the ruby red nano-TiO _ 2 changes with the angle, and it also has the function of absorbing ultraviolet rays. The weather resistance of latex paint can also be improved to a new level by adding proper amount of nano-titanium dioxide into building exterior wall coatings. At the same time, the aging resistance of latex paint is greatly improved.
Addition amount of nanometer titanium dioxide: the particle size of nanometer titanium dioxide is generally 10 ~ 50 nm, and its addition amount is controlled below 1%.
(3) Application of nano-calcium carbonate in interior and exterior wall coatings
As a filler, calcium carbonate is widely used in interior and exterior wall coatings. As a high-quality filler and white pigment, nano-calcium carbonate has the characteristics of rich resources, good color and high grade. It can be used for interior and exterior wall coatings, endowing the coatings with good thixotropy and leveling, and improving the mechanical strength of the coatings.
It should be noted that although the price of nano-calcium carbonate is not very high, it is still much higher than that of calcium carbonate. If a large amount of nano-calcium carbonate is used, it is not only uneconomical, but also may have a negative impact on the coating. For example, excessive dosage or poor dispersion of nanoparticles will lead to the deterioration of mechanical strength of coatings.
(4) Application of nano-zinc oxide in interior and exterior wall coatings
Nano-zinc oxide has unparalleled new properties and new uses, which can make the coating have the functions of shielding ultraviolet rays, absorbing infrared rays, sterilizing and antivirus. Used in interior and exterior wall coatings together with other nano-materials. In addition, nano-zinc oxide also has the function of thickening, which contributes to the stability of pigment dispersion.
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