Silica sol used in nanocomposite coatings
Nano particles are used in coatings to obtain coatings with anti-radiation, aging resistance and high peel strength or with some special functions, called nano composite coatings. According to the fineness of the coating, nanocomposite coatings can be subdivided into nano-modified coatings and nano-structured coatings. The existing coatings can be modified by using nano-particle anti-ultraviolet properties to improve certain properties of the coatings. Such coatings should be called Nano modified coatings. However, the fineness of coatings prepared by some special processes is in the order of magnitude, and this category is called nanostructured coatings. According to the function and purpose of the coating, nano composite coatings can be divided into nano anti-aging coatings, nano antibacterial coatings, and nano stealth coatings.
Nano SiO2 has the optical characteristics of ultraviolet absorption and infrared reflection. The absorption rate of ultraviolet rays within the wavelength of 400 nm can reach more than 70%, and the reflection of infrared rays outside the wavelength of 800 nm can also reach more than 70%. Because there are a large number of unsaturated residual bonds in its molecular structure and different states of hydroxyl groups bond with certain groups of the resin, the thermal and chemical stability of the material can be greatly improved. In addition, due to its insufficient surface coordination, it exhibits strong activity and can adsorb pigment particles such as pigments, greatly reducing the attenuation of pigments caused by UV irradiation, thereby reducing the "chattering" of the coating film. The addition of nano-SiO2 can improve the whiteness. Adding nano-SiO2 to architectural coatings can significantly improve the can-opening effect of the coating. The coating does not delaminate, has thixotropy, anti-sagging, and has good construction performance, especially the anti-fouling property of the coating is greatly improved, and it has excellent self-cleaning Sex and adhesion. When the coating film is dried, the nano-SiO2 quickly forms a network structure, which improves the aging resistance and strength of the coating film.
Silica sol coatings are inorganic coatings made of water dispersion of colloidal silica as the film-forming material, mixed with pigments, fillers, and additives. Generally, silica sol SiO2 particles are mostly agglomerated in single or multiple spherical shapes. The diameter of colloidal particles is generally 5-80nm. Compared with general emulsions (particle size 0.1-10μm), the particle size is much smaller, and the permeability is good, and water can penetrate. It can penetrate everywhere, and the dispersion and permeability of silica sol are very good when mixed with other substances. Most of the particle surface is surrounded by silanol groups (Si-OH), and a small part is adsorbed by sodium ions as a stabilizer. When the film is formed, as the water evaporates, the colloidal particles keep close to each other, and the adjacent -OH groups in the Si-OH are dehydrated to form a three-dimensional network coating film crosslinked by -Si-0-Si- bonds. When it does not contain alkali metal ions, the coating film has good water resistance. However, due to the strong rigidity of the Si-O bond, no deformation ability, large volume shrinkage during the film forming process, cracks, micropores and cracks are prone to defects, so generally fiber or fibrous or flake-shaped inorganic coatings are added Pigments, fillers, or modified with organic polymer film-forming substances, so that the organic resin is filled in the gaps of the -Si-O-Si- network structure to shield the remaining hydroxyl groups, reduce the sensitivity of the coating to water, and relax the coating The expansion and contraction of the film in the alternating heat and cold improves the toughness, impact resistance and water resistance of the coating film.