Application status and Prospect of the hottest nan

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Application status and Prospect of nano calcium carbonate in coatings

nano materials refer to polycrystalline materials with nano crystal size, which have two important characteristics of small size and high concentration grain boundary. Generally, the continuous energy band of large crystals is divided into energy levels close to molecular orbital, resulting in small-size quantum tunneling effect. At the same time, due to the increase of force imbalance of high concentration grain boundary and interface atoms, the interface effect is produced, These two effects lead to sudden changes in mechanical, magnetic, optical, electrical and thermodynamic properties of materials. When nano materials are applied to coatings, because there are many active points in the molecules of film-forming base materials, pigments, fillers and additives, these active points may have a strong interaction with the active points on the surface of nanoparticles, which may form a dense and stable coating, and significantly improve the physical and chemical properties of the film. Calcium carbonate is a non-toxic, non irritating, odorless white soft filler. In the coating industry, it is easy to be compatible with various polymers and has good thermal stability. It is one of the most commonly used raw materials and plays a skeleton role in film-forming materials. In recent years, with the rise of nanotechnology, the application of nano calcium carbonate in coatings in order to improve the performance of coatings is one of the hot topics in the coating industry. In particular, the completion of many domestic 10000 ton nano calcium carbonate production lines is an urgent need to find applications in a series of fields including coatings. However, the direct application of nano calcium carbonate in coatings has the following defects: high particle surface energy, In a thermodynamically unstable state, it is easy to agglomerate; The surface of calcium carbonate is hydrophilic and oil repellent, with high polarity, which is difficult to disperse in organic media, poor adhesion with the base material, and easy to form interface defects, resulting in the decline of film performance

based on the author's research on nano calcium carbonate composite coatings in recent years, this paper summarizes the research status of nano calcium carbonate composite coatings at home and abroad, hoping to help further deepen the research of nano calcium carbonate composite coatings in China and provide reference for the industrialization research of nano calcium carbonate composite coatings

1 surface modification of nano calcium carbonate particles

the application of nano calcium carbonate particles in coatings involves the compatibility between nano materials and substrates. The film-forming substrates of coatings are significantly different from polymers such as plastics and rubber in terms of the type and number of functional groups, relative molecular weight, etc., resulting in differences in the surface polarity of polymers and the interaction mode with pigments and fillers. In order to successfully use nano calcium carbonate in coatings, the surface of nano calcium carbonate must be specially modified

so far, the surface treatment of nano calcium carbonate mostly adopts the traditional treatment method of inorganic pigments and fillers. The treatment agent used is stearic acid and who can find gold salts in the R & D and processing industry of non-ferrous new materials, as well as various surfactants and coupling agents. Zhang Shengsheng and others used sodium fatty acid instead of fatty acid. Because carbon dioxide was introduced during treatment, the actual coating on the surface of calcium carbonate was still fatty acid, but the diffusion of sodium fatty acid in water was smaller than that of fatty acid, and the coating effect was improved. But according to the electron microscope pictures provided by the author, the dispersion improvement is not significant. Han Yuexin, et al. Directly coated the coated nano calcium carbonate with fatty acid through forced emulsification in the aqueous phase, and studied the influence of changing the amount of fatty acid and adjusting the emulsification conditions on the activation index of the coated nano calcium carbonate. It was found that the activation index of the treated nano calcium carbonate was the highest when the slurry concentration was about 9% and the fatty acid was 2.5%. When studying the surface treatment of nano calcium carbonate with different modifiers, Lu Hougen, et al., found that the smaller the cohesion of the modifier, the better the dispersion effect after modification. When the modifier forms a complete single adsorption layer on the particle surface, the shielded surfactant is the most, and the particle agglomeration phenomenon is the weakest. At this time, the adsorption layer has a regular vertical extended conformation, and the steric hindrance is large. Du Zhenxia, et al. ¨ after coating nano calcium carbonate with organic acid, they found that the dispersion in organic solvents was significantly improved. The modified nano calcium carbonate was used in polyurethane varnish, and the film was improved in gloss, leveling, flexibility, hardness and so on. Erika f believes that this improvement in performance is due to the formation of a ductile continuous film between the particles and the substrate by the nano calcium carbonate surface modifier, which promotes the occurrence of stress between the nano calcium carbonate and the substrate and is discharged into the table 1); Caused by transfer. The coating of acrylic acid maleic acid sulfonic acid copolymer makes the surface of nano calcium carbonate form macromolecular insoluble salt, the coating compactness of the treatment agent is improved, and the stability between particles is increased due to the dual action of charge and steric hindrance

2 nano calcium carbonate composite coating

it is well known that calcium carbonate itself, as a physical filler, is widely used in all kinds of coatings. It can change the rheology, toughness, water resistance and weather resistance of the coating, and reduce the processing cost of the coating. Compared with traditional heavy calcium or light calcium, although the cost of nano calcium carbonate has increased significantly, it is still at a lower price compared with other ordinary pigments and fillers. Especially after the nano calcium carbonate, its changes in coating reinforcement, transparency, thixotropy, leveling and so on are the hot spots of coating manufacturers

2.1 architectural coatings

due to the "blue shift" phenomenon, it can shield ultraviolet light in latex paint, play the effect of heat insulation, and the aging resistance of the coating has been improved. When nano calcium carbonate is applied to exterior wall coating, the coating shows strong "hydrophobicity", and the crack resistance and pollution resistance of the coating are enhanced

general coating formulations contain a certain amount of rigid particles, and some formulations contain a considerable amount. The existence of these rigid particles will lead to excessive concentration of stress in the film, resulting in cracks in the resin. The introduction of nano calcium carbonate will generate more contact probability with the resin, generate more microcracks and cause elastic deformation, convert more impact energy into heat energy and absorb it, so as to improve toughness. By adding nano calcium carbonate with special polymer surface treatment with 2% - 5% pigment and filler to the traditional emulsion paint, it is found that not only the rheology and can opening effect of the paint have been improved, but also the water resistance, scrub resistance and hardness have been greatly improved, and the increase of scrub resistance shows a geometric progression. The surface structure of the coating was observed by means of electron microscope, infrared and thermal analysis. It was found that there was no new chemical bond in the coating, but the crystallinity of the polymer in the coating and the compactness of the film were significantly improved. At present, nano calcium carbonate produced by companies such as Baishi in Japan and sime in Italy are mainly used to modify the performance of waterborne latex coatings

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